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001 Wood/water

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22

may 2007

Wood/water relationships during kiln drying and reconditioning

of softwoods

Prepared for the

Forest and Wood Products Research and Development Corporation

by

R. Northway and I. Burgar

The FWPRDC is jointly funded by the Australian forest and wood products industry and the Australian Government.

© 2007 Forest and Wood Products Research and Development Corporation All rights reserved.

Publication: Wood/water relationships during kiln drying and reconditioning of softwoods

The Forest and Wood Products Research and Development Corporation (“FWPRDC”) makes no warranties or assurances with respect to this publication including merchantability, fitness for purpose or otherwise. FWPRDC and all persons associated with it exclude all liability (including liability for negligence) in relation to any opinion, advice or information contained in this publication or for any consequences arising from the use of such opinion, advice or information.

This work is copyright under the Copyright Act 1968 (Cth). All material except the FWPRDC logo may be reproduced in whole or in part, provided that it is not sold or used for commercial benefit and its source (Forest and Wood Products Research and Development Corporation) is acknowledged. Reproduction or copying for other purposes, which is strictly reserved only for the owner or licensee of copyright under the Copyright Act, is prohibited without the prior written consent of the Forest and Wood Products Research and Development Corporation.

Project no: PN04.2001 Researchers: R. Northway Ensis

Private Bag 10, Clayton South, Vic 3169 I. Burgar

CSIRO

Private Bag 33, Clayton South MDC, Vic 3169

Final report received by the FWPRDC in May 2007.

Forest and Wood Products Research and Development Corporation PO Box 69, World Trade Centre, Victoria 8005 T +61 3 9614 7544 F +61 3 9614 6822 E [email protected] W www.fwprdc.org.au

Table of contents

Executive summary.................................................................................... 1

Introduction ............................................................................................... 3

Conclusions .............................................................................................. 5

Part 1 Exploratory tests ........................................................................ 6

Materials and methods ............................................................................... 6

Results and discussion ............................................................................... 7

NMR measurements and preliminary analysis ........................................... 7

Part 2 Detailed tests ........................................................................... 12

Materials and methods ............................................................................. 12

Results and discussion ............................................................................. 16

Detailed drying runs 6 and 7: radiata pine heartwood ............................... 17

Detailed drying run 15: radiata pine near-pith sapwood ........................... 20

Detailed drying runs 16 and 17: radiata pine heartwood ........................... 23

Detailed drying test runs 10, 11 and 12: slash pine heartwood ................. 27

Detailed test drying runs 13 and 14: slash pine heartwood ....................... 31

NMR measurements and analysis ............................................................ 35

Part 3 Experimental kiln trials ............................................................. 47

Materials and methods ............................................................................. 47

Results and discussion ............................................................................. 49

Kiln runs ................................................................................................. 49

Environmental conditions ........................................................................ 50

Moisture content ..................................................................................... 51

Distortion ................................................................................................ 53

Stiffness .................................................................................................. 55

NMR measurements ................................................................................ 56

Gaussian parameters ................................................................................ 59

Lorentzian parameters ............................................................................. 59

Project results and discussion ................................................................. 62

Acknowledgements ................................................................................. 64

Disclaimer ................................................................................................ 64

1

EXECUTIVE SUMMARY

Objective

For this project, the principal objectives were to identify and characterize the bonding states

of water in softwoods during kiln drying, subsequent high humidity and/or steam treatment

and later stabilization or storage periods, and to recommend improved kiln schedules and

conditioning processes to reduce timber storage time with improved stability.

The specific objectives, derived from the results of the previous Softwood Drying Project,

were:

1. Identify and characterize the bonding states of water in softwoods during kiln drying

and subsequent high humidity and/or steam treatment, and also during later

stabilization or storage periods.

2. Identify links between changes to the bonding states of water, internal stresses and

distortion on release from restraint and on machining.

3. Identify high temperature kiln drying schedule modifications and/or high humidity or

steam treatments that improve stability.

4. Identify stabilization treatments to reduce the time to a stable state.

5. Identify differences between Heart-in and Free of Heart material.

6. Recommend modification to current commercial practices to minimize kiln drying

time, steaming time and storage periods to produce stable dried softwood timber.

Key results

The role of water in wood stability

The simple bound/free water model is inadequate to explain the role of water in wood shape

and stability. It is possible to use NMR measurements to identify the energy state and hence

the bonding of water in wood before, during and after processing. Other components of wood

than water are additional sources of protons and contribute to NMR signals. High field NMR

was needed to separate these different contributions. Techniques have been developed to

analyse low field NMR signals to identify other components and to separate signals from

structural components and water in dry wood. Indications of links between proportions of two

types of bound water and wood stability have been identified but further development will be

needed to develop technique that can be correlated to wood stability.

Improved kiln schedules and conditioning processes to reduce storage time

with improved stability

There are indications that steaming after drying increases the mobility of water, particularly

near the surfaces of timber, although any effect on stability was not demonstrated. Modifying

the later stages of kiln schedules can eliminate or reduce the need for steaming after drying,

with similar product stability.

Application of results

The low field NMR surface probe takes measurements from only a small volume of wood at

the surface. This technology can be used to monitor moisture content and surface uniformity

of green and dry wood. Other available equipment cannot be used to assess and re-assess the

same location on a specimen which would be desirable. Current technology requires physical

samples to be taken for more intensive low field and for high field classical NMR

2

measurements. This is destructive and limits the scope of sampling, leaving the results subject

to normal wood characteristic variation.

While the same stability can be achieved without steaming, the drying time is extended,

although not by as much as the time used for the traditional steaming treatment. The benefit to

industry of reduced total processing time and reduced energy usage may be outweighed by the

increased kiln residence time and consequent need for more kilns rather than the much

cheaper steaming chambers.

The strategy of eliminating steaming is probably not appropriate for timber to be re-sawn

during machining (e.g. as 2-out) because of the possibility of wet centres of boards being

exposed and further drying causing distortion.

3

INTRODUCTION

Plantation grown softwood is subject to distortion during drying because of longitudinal

shrinkage associated with spiral grain and microfibril angle. High temperature drying and

steam conditioning while under restraint from concrete blocks is current industry practice to

produce structural softwood timber. This is generally satisfactory, but producers find it

necessary to store dried timber for varying periods before machining, to maximise product

straightness and stability. This is particularly the case if the moulder is also used to separate a

dried board into several products e.g. splitting wide boards, commonly known as 2-outing.

The stability in shape of wood products in service is dependent on the maintenance of internal

structural accommodations that were made during drying under restraint. Any changes in void

space in the structure will affect bound water bonding sites. Stability is thus associated with

the bound water remaining in stable positions. While moisture exchange between wood and

the environment is predictable, internal movement of water and its significance is not fully

understood.

FWPRDC Softwood Drying Project PN008.96 explored the relationships between the wood

structure and water during drying operations with a range of technologies and the possibilities

of modelling the drying process, stress and distortion development during drying. The next

step, to gather information on the wood/water relationships linked to measured changes in

wood behaviour so that the drying/processing models can incorporate this knowledge, was the

principal objective of this project. Nuclear Magnetic Resonance, NMR, was the primary

technology used in this investigation.

Water in wood

Water in hydrophilic polymers, Wc, is generally assigned 1 as a sum of non-freezing water

(structural water or tightly bound to cell walls), Wnf; freezing bound water or water associated

with walls and smaller reservoirs, Wfb; and free water or essentially unbound water in cell

lumens, Wf. The closely studied relationship between these categories can be summarised as

follows: water is in bound non-freezing condition at very low moisture concentration (MC),

then the freezing bound water contribution appears at low total moisture, around 10%, and

after around 12% of total moisture, or normal wood moisture, the free water contribution is

becoming evident. Therefore, in the dry wood samples, where MC is around 10%, the main

moisture contribution will be from bound water (freezing and non-freezing). Such

interpretation was supported by Guzenda et al.2, who concluded that loss of free water in the

drying process (moisture content going below the fibre saturation point) is evident also from

NMR data, in particular, the spin-lattice relaxation time T1, which normally reveals two decay

components in green wood, becomes a single component parameter below the fibre saturation

point.

The division of water in wood between bound and free states and something between is not

the complete story. Depending on the experimental method used one can detect all different

phases or some time average those according to the detection time scale and dynamic

exchange rate between these phases.

Attempts to use NMR spectroscopy, with the assumption that the proton NMR signal is

predominantly the water signal, led to ambiguity in the interpretation of NMR data on the

1 H. Hatakeyama and T. Hatakeyama, Interaction between water and hydrophilic polymers,

Thermometrica Acta, 308 (1998) 3-22 2 R. Guzenda, W.Olek, H.M. Baranowska, 12

th International symposium on non-destructuve testing of

wood (2000), Sopron, Hungary

4

water types, due to the fact that there are also other proton bearing mobile organic molecules

which contribute to the NMR signal. To understand the NMR data collected from the samples

from wood drying process therefore required further detailed analysis of the proton NMR

signal; in particular, we were trying to identify the organic components like resin and other

volatile wood components in the proton NMR signals observed at low (and/or high) magnetic

fields. The results of our investigation not only give the evidence of such organic components,

but also reveal further evidence for the fast dynamical exchange of NMR signals between

organic and two types of bound water molecules.

Wood deformation and moisture behaviour during drying

The deformation of the wood structure during drying is a consequence of moisture loss and

induced strain in the structures. Theoretical prediction of total strain rate was assumed to be

the sum of elastic strain rate, moisture strain rate and mechano-sorptive strain rate (intake

moisture from the environment after drying). 3

The rate of drying of softwood is clearly influenced by board properties (green moisture

content, wood basic density, sapwood/heartwood mixture in a single board, board thickness

and ring orientation pattern), drying schedule and drying conditions. 4

Swelling and shrinking of wood occurs when the moisture in wood falls below the fibre

saturation point, FSP, (when the cell walls are saturated and the cell lumen is empty) –

assumed to be around 30% moisture content for softwood. Of course, there is no such ideal

situation in the wood as FSP, as the real weight used in the moisture content estimate is also

affected by the density of the wood, its structure, and chemical composition (extractives). 5

Especially, the amount of extractives and moisture left behind after drying depends on wood

porosity (estimated to be up to 74% for softwood) and its permeability (ability to release

water from the structure) and they play an essential role in the realistic estimates for drying

regime. All these factors influence the value of NMR parameters such as relaxation times and

resonance intensities due to the variations in the intermolecular interaction caused by the

heterogeneous nature of wood.

The NMR relaxation times T1 and T2 are defined as the spin-lattice relaxation time T1

associated with the energy transfer and therefore NMR signal lost to the lattice, and spin-spin

relaxation time T2 associated with the signal decay by losing coherence in the spin system

without loss of any energy (spin-spin interaction).

The T1 NMR data interpretation has already been established in view of FSP moisture content

but the T2 relaxation times have not previously been proven useful in the analysis due to their

large dependence on other environmental variables.

Our intention here was to find the correlation between the moisture measurements by NMR

methods (in particular to use the T2 measurements) and the deformation of wood. The T2 data

collected here can be taken only as a relative comparison through a set of boards. It is

reasonable to assume that the large structural variations of samples on the molecular level will

also affect the results. Therefore, it may be difficult to find a clear correlation between NMR

parameters and the detected structural deformations.

3 O. Dahlblom et al. Ann.Sci.For (1996) 53, 857-866

4 S.Pang, Chemical Eng. J. 86 (2002), 103-110

5 J.Kopac et al., J. of Materials Processing Technology 133 (2003), 134-12

5

CONCLUSIONS

It was possible to use low field NMR to follow the distribution of water during the kiln drying

and reconditioning of softwood. The NMR equipment available is capable of taking

measurements, which can be analysed to identify the states of water, generally as expected

from the literature. High field NMR can further distinguish between water and other proton

sources in wood and identify structural changes from different drying and conditioning

processes. With further development NMR will be able to help identify processing methods to

obtain greater wood stability.

The specific conclusions from Low Field NMR studies are: 1) The NMR signal intensity

correlates to the wood moisture content as determined by the oven-drying method; 2) Multi-

component NMR signal decay, T1 and T2, are related to different environments (moisture

type); 3) There is a trend of changes in the dynamics of the bound water components and

increased wood deformation, (despite the fact that structural effects frequently overtake these

changes); 4) Clear changes were detected in the amount and dynamics of reconstituted

moisture after the equilibration of dry wood in different moisture (humidity) environments. In

summary, the sensitivity of the NMR data to the board properties (structure etc.) is so large,

that it frequently prevents establishing a straight correlation between the NMR parameters and

wood structural changes.

The MOUSE analysis clearly demonstrated the ability of the NMR surface analyser to

identify the moisture in the green wood samples. The data also shows that there are numerous

variations due to the water mobility, wood structure, porosity, and composition. In particular,

after the proper evaluation of all these influences, there can be further improvements on such

analysis to obtain an accurate estimate of removable moisture and information on resin

content.

NMR investigation by low field NMR MOUSE methods clearly depicted the mobile organic

signal as well in green wood as in fresh dried wood beside the predominant water protons

NMR signal. Variations in the molecular mobility of organics and water is therefore in

general overlapped and further development of NMR methods to separate these components

in detection is probably the only way to provide reliable NMR data, which will be correlated

to short and long term stability of wood structure after drying.

Dry wood samples were analysed by NMR methods on core samples from boards or

specimens. The sensitivity and accuracy of data is a prerequisite for reasonable evaluation but

it has not been possible to sample sufficiently to determine these matters accurately.

Moisture distribution through the board depth is obtainable from measurements on cores and

our data is in agreement with the results of classical methods that take a much longer time and

greater work effort to obtain.

The solid-state NMR methods provide further confirmation of dynamical changes in the water

mobility as result of drying process. The interactions between residual water and organic

components in wood, as reflected in both the water and organic resonance line widths and

corresponding relaxation times, confirm the existence of the so-called plasticised zones in the

wood structure. The distribution and density of these zones may be essential in the

interpretation of the dried wood distortions.

6

Part 1 EXPLORATORY TESTS

This first part of the project was a preliminary test with matched boards dried with and

without restraint, using an industry standard high temperature schedule. Nuclear Magnetic

Resonance, NMR, tests were made on samples from the boards in green and dry states, and

from sections of the dry boards to normal, drier and wetter environments.

MATERIALS AND METHODS

A sample of green radiata pine boards was supplied by Wespine, Bunbury, WA. This

comprised (23) boards, 6.0m long, 100 x 40mm section and approximately equal numbers of

heart-in (HI) and sapwood (Sap). The boards were crosscut to each produce (2) kiln

specimens 2.8m long, with (3) sections cut to determine moisture content and density (Fig. 1).

The offcuts were used for NMR measurements, primarily on the surfaces.

Pairs of boards were separated and one of each pair dried with restraint and one dried without

restraint. Two kiln drying runs were conducted using kiln drying and steam reconditioning

schedules as used by Wespine for HI and Sap timber. Specimen distortion was measured after

drying.

Each 2.8m long board was cut to produce (3) specimens 0.8m long, (2) sections for MC

determination and (2) cores 35mm diameter for NMR measurements (Fig. 2).

Specimens were weighed and distortion measured. Specimens were then placed in controlled

environment chambers, A specimens in 5% equilibrium moisture content (EMC) conditions,

B specimens in 12% EMC conditions and C specimens in 17% EMC conditions.

After one month, seven specimen sets, selected to represent the range of NMR measurements

from the dry boards, were weighed, distortion measured and cores cut for NMR measurement.

For two of these sets another set of cores was cut for NMR measurement and MC gradient

determination. One set of cores was further divided to compare NMR measurements directly

with MC determined by oven drying.

Green offcut 1-1 Green offcut 1-2 Green offcut 1-3

MC section 1a MC section 1b MC section 1c

Board 1-1 Board 1-2

2.8m 2.8m

Figure 1 Kiln boards from 6.0m long boards

1-1-A 1-1-B 1-1-C 1-2-A 1-2-B 1-2-C

Core for NMR 1-1a Core for NMR 1-1c Core for NMR 1-2a Core for NMR 1-2c

MC section 1-1a MC section 1-1c MC section 1-2a MC section 1-2c

Figure 2 Specimens for controlled environments from dry 2.8m long kiln boards

7

RESULTS AND DISCUSSION

This work showed that NMR could identify the quantity and energy states of water in green

and dry wood and that the latter were to some extent indicative of shape changes. It was also

found that there was considerable sensitivity of the NMR measurements to features of the

wood structure in addition to water. Further development to NMR measurement and analysis

techniques were needed. This was described in the Milestone 2 Report.

NMR measurements and preliminary analysis

Green board sections

The NMR surface analyser, MOUSE, (shown in Figure 3 and Figure 4), clearly demonstrated

the ability of NMR analysis to identify the moisture in the green wood samples. The MOUSE

data also shows that there are numerous variations in the data due to the water mobility, wood

structure/porosity and grain orientation. After the proper evaluation of all these influences,

one can further improve these analyses to obtain an accurate estimate of removable moisture

and information on resin content.

Figure 3 The NMR surface analyzer, MOUSE, set up.

Figure 4 A green wood sample as measured on the MOUSE; surface facing the white/red zone

The water distribution changes from centre of the stem towards the sap wood, as shown by the

NMR signal from board #19 in Figure 5. The NMR signal clearly shows the expected

difference between the moisture status of heartwood (inside) and sapwood (outside)

8

35

30

25

20

15

10

5

Sig

na

l

2015105

Time(ms)

19_2 top heart 19_2 top sap

19_3 top inside 19_3 top outside

Figure 5 NMR signals from green board sections using the surface analyser, showing the

differences between inner (heartwood) and outer (sapwood) faces of sections

19-2 and 19-3.

Dry boards and specimens

The kiln dry wood samples were to be investigated using the NMR MOUSE in a similar

procedure to the green wood sample measurements. However, the amount of moisture in the

small part of the surface of the dry wood samples measured by the MOUSE proved to be too

low and the T2 relaxation times were much shorter, so that the MOUSE spin-echo signal

(S/N) was insufficient to be properly analysed (only two or three available points at the best).

The alternative measurement using the NMR MINISPEC PC 110 was utilised to collect

sufficient signals from a large bulk sample – core 35mm in diameter and approximately 38

mm in length - which was drilled from the dried boards, through the thickness.

The data were collected in three different sets:

• two signal magnitude measuring points: first at time 30 microseconds and second at 50

microseconds after the rf pulse;

• T2 measurements with the spin-echo sequence, spacing 50 microseconds, where only one

T2 component was observed;

• T1 measurements by inversion recovery method, where two components, long and short

T1, were identified.

The free induction decay (FID) signal intensity can be related to the overall moisture content

as shown in Figure 6. The first set (blue diamonds) had much more dispersed values than the

second (red squares) values, which were also further away. The improved correlation of the

second data set (further away) to measured moisture content is probably due to signal sources

additional to moisture, contributing to the proton signal at the beginning of the ‘FID’.

9

6

5

4

3

2

1

0

Sig

na

l

14121086420

AvMCmoisture(%)

Figure 6 Two sets of the ‘FID’ signals and their relationship to average moisture content.

The specimens equilibrated in different controlled humidity environments (A = 5% EMC, B =

12% EMC, and C = 17% EMC) were sampled by coring. The core samples from boards 10

and 12 were analysed by NMR methods as whole cores. Figure 7 shows a clear trend in T2

measurements of samples from the 5, 12 and 17% moisture content environments in samples

10-1, 10-2, and 12-2. The sample 12-1C (17% equilibrium moisture content (EMC)) had a

lower than anticipated T2 signal amplitude, but this may be due to factors other than moisture,

such as the wood structure of that particular sample.

0

200

400

600

800

1000

1200

1400

1600

1800

10-

1Ax

10-

1Bx

10-

1Cx

10-

2Ax

10-

2Bx

10-

2Cx

12-

1Ax

12-

1Bx

12-

1Cx

12-

2Ax

12-

2Bx

12-

2Cx

Amplitude of T2 data

Figure 7 Amplitude of T2 measurement from cores at different moisture content

for boards 10 and 12.

Moisture distribution through board depth is obtainable and our data are in agreement with the

traditional method of determining moisture content by oven drying samples. The traditional

is expensive in terms of time and work effort, and NMR appears to be able to clearly

10

undertake these measurements rapidly. The optimisation of methods to measure moisture

content gradients by NMR is in progress.

Wood deformation and moisture during drying

The deformation of the wood structure during drying is a consequence of moisture loss and

induced strain in the wood structure. The theoretical prediction of total strain rate was

assumed to be the sum of elastic strain rate, moisture strain rate and mechanosorptive strain

rate (exchange of moisture with the environment after drying)6. The intention in this project

was to find the correlation between the moisture measurements by NMR methods and the

deformation of wood. From the literature it is clear that moisture is only partially responsible

for wood deformation. A reasonable correlation can be expected only when the moisture

movement dominantly drives wood movement/deformation. The wood drying process

includes the removal of free (mobile) moisture in the wood in addition to partially releasing

the water from the wood structure. Residual (bound) water that is present below fibre

saturation is assumed to be closely associated with the cell structure. These water molecules

should have a strong interaction with solid wood and therefore short relaxation times T1 and

T2. The major effect on these relaxation times is not only the interaction with solid surfaces,

but also the size of the spaces available for water to occupy. If the pores (voids) are large,

then the relaxation times will be longer due to the intermolecular interaction between the

molecules and their isotropic motion. According to NMR theory, the relaxation times will

follow the distribution of pore sizes, but the experimental results will normally present the

average achieved in the NMR timescale (a few nano-seconds (10-9

) for T1 and milli-seconds

(10-6

) for T2). The difference in the NMR data fitting with a single or a double exponential

function shows that there are more components than water alone, in the relaxation time data.

This suggests that:

• The mobility of water molecules is so restrictive in the dried wood that (internal) surface

interactions dominate the relaxation rates.

• The exchange rate between the different pores is slow in comparison to the NMR

timescale; different statistically averaged relaxation time values will be produced.

The rate of drying of softwood is clearly influenced by board properties (green moisture

content, wood basic density, sapwood/heartwood mixture in a single board, board thickness

and growth ring orientation pattern), drying schedule and drying conditions7. Assuming that

in our case the last two were kept constant, it becomes obvious that board properties in all

their variations will be the major factor in the final moisture content distribution. Therefore

the NMR data may vary largely because of these board property variations. Due to the fact

that the board properties varied in the set of 23 boards studied, it can be expected that

individual board properties such as density, sapwood/heartwood distribution and grain pattern

will contribute to the variations in the measured NMR parameters, T1, T2 and signal intensity.

In the first analysis of the collected data the trend in these correlations was evident. Further

data processing is required to build a model which will be relevant to the wood industry.

Swelling and shrinking of wood occur when the moisture in wood goes below the fibre

saturation point, ((FSP) - when the cell walls are saturated and the cell lumen is empty of

water – assumed to be around 30% moisture content for softwood). Of course there is no such

ideal FSP state in wood, therefore the real weight, used in the moisture content estimate, is

affected by the density of the wood, its structure, extractives and chemical composition8. In

particular the amount of extractives and moisture left behind depends on wood porosity,

which has been estimated to be up to 74% for softwood, and its permeability (ability to

6 O. Dahlblom et al. Ann.Sci.For (1996) 53, 857-866

7 S. Pang, Chemical Eng. J. 86 (2002), 103-110

8 J. Kopac et al., J. of Materials Processing Technology 133 (2003), 134-142

11

release the water from the structure). In addition density (and amount of water at a particular

moisture content) varies across growth rings. With comparisons usually made between

matched specimens the composition of the samples contained similar material overall. All of

these factors further affect the value of NMR parameters such as relaxation times and

intensities due to differences in the intermolecular interaction, which govern NMR properties.

The dried wood specimens clearly show the correlation between the magnitude of the detected

signal from the water and its relaxation rates to the moisture content. The measured relaxation

rates are directly proportional to the wood porosity or to the ability of water to enter the wood

structure; as a consequence of drying, pores become more available and interconnected for

water movement.

Successful attempts have already been made to establish the T1 NMR data interpretation with

respect to FSP moisture content9 but the T2 relaxation times have not been proven as useful in

the analysis due to its large dependence on other environmental variables. The T2 data

collected in this project indicate the expected correlations as relative trends through the set of

boards. To use such data as a reliable base to determine the correlations with deformation in

the wood structure can be achieved. For that it is necessary to evaluate all board property

correlations and further develop and apply the theoretical model needed for the interpretation

of the NMR data.

The current NMR data set has revealed:

• good correlation with wood moisture content as determined by the oven drying method;

• differences between the moisture relaxation times, T1 and T2, as assigned to different

environments of water molecules;

• variation of the T2 times through the board profile;

• variation in the amount (using NMR dynamic parameters) of reconstituted moisture after

the equilibrium of dry wood to different moisture environments;

• clear trends of changes of the bound water component dynamics in relation to the

increased wood deformation; and

• sensitivity of the NMR data to board properties is considerable. This prevents the

establishment of clear correlations between NMR parameters and wood structural

changes.

9 Presentation on 21-4-2004 by Group from Poland

12

Part 2 DETAILED TESTS

Milestone Report 3 for this project reported on detailed tests conducted in a laboratory dryer

with short lengths of Radiata Pine and Slash Pine boards. Moisture location and bonding as

measured by NMR did not fully explain changes in shape, with or without moisture content

change. NMR measurements were affected by other proton sources within the wood.


Material and specimen preparation

A sample of green Radiata pine boards, 6.0m long, 100 x 40mm section, was supplied by

GTFP, Mt Gambier, SA. This included both heart-in (H) and sapwood (S). Boards with

consistent cross-section along the length were selected and crosscut to each produce kiln

specimens 475mm long, avoiding knots where possible. Specimens were identified in

sequence from the butt end with letters: A, B, C etc. Sections from between specimens were

cut to determine moisture content and density and for NMR measurements (Figure 8).

A sample of Slash pine boards was supplied by Hyne & Son, Tuan, Qld, and prepared in the

same manner.

Green offcut

MC section Rh1a

Core for NMR

MC section

Rh1E

Rh1F

Rh1B

Rh1C

Rh1D

Rh1A

Figure 8 Drying specimens 475mm long from green boards

Sets of matched boards were prepared for each drying run. In each run one specimen was weighed

continually, one fitted with an array of thermocouples to monitor internal temperature, and two

specimens removed at intervals to be cored for determination of radial moisture content profile

(19mm diameter core) and NMR measurements (35mm diameter core). Core holes were sealed

with silicon sealant. Also in each run one (two in later runs) specimen was dried with restraint

against twist; the restrained specimen was matched to at least one other specimen in the run dried

without restraint. For all specimens distortion was measured before and after drying and again

after steaming and cooling, except for the restrained specimens, which could not be measured

while in the restraining frames.

13

Drying test procedure

Seventeen drying runs were conducted with drying and steam-reconditioning schedules as

used by GTFP and Weyerhaeuser for HI and Sap timber of each species (Table 1).

Table 1 Drying schedules used in the experimental dryer

Radiata Slash

Air velocity 7-9 m/s; 2-hourly reversals 11 m/s; 2-hourly reversals

Kiln Heatup 140o DB/98

o WB over 1 hour 140

o /98

o over 2 hours

Drying 140

o /90

o; WB ramped down over

approx. .0.5 hr 140

o /90

o

Cool Outside kiln; 0.5-1 hour Outside kiln, 2 hours

Reconditioner heatup To 98o DB in 0.5 hour To 98

o DB in 0.5-1 hour

Recondition 3 hours @ DB>95o 3 hours @ DB>95

o

Cooling Outside immediately

The procedure for a typical run is outlined in below:

1. Select specimens.

2. Coat ends of specimens with silicon sealant and aluminium foil.

3. Weigh and measure distortion & dimensions of specimens.

4. Drill holes and insert thermocouples in selected specimen.

5. Clamp restraint specimen(s) in restraining frame(s).

6. Load specimens in dryer.

7. Start dryer and implement planned drying schedule.

8. Commence schedule ramp-down in temperature at appropriate stage.

9. At selected stages remove specimen(s) for coring from dryer, weigh, cut one 35mm

diameter core and one 19mm core through the specimen thickness, weigh, seal hole(s)

with silicon sealant, weigh and return to dryer; typical time 5 minutes.

10. At end of drying unload specimens and take cores from specimens, as in Step 9,

except restrained and thermocouple specimens; measure distortion & dimensions on

specimens, except restrained specimens.

11. Cool for selected time.

12. Steam in steam chamber, restraint specimens still in frames.

13. Cool at controlled rate and hold overnight.

14. Remove thermocouples from specimen; remove restrained specimen(s) from frame(s).

15. Weigh, measure distortion & dimensions and take cores from all specimens.

16. Slice three 6mm discs from each face of 19mm cores and determine moisture content

distribution; saw two 5mm thick discs at 6mm spacing from each face of the 35mm

diameter cores (1mm saw kerf) for NMR measurements.

17. Make Low field MOUSE NMR measurements on each face of discs.

14

Flexible wires from loadcell

to Data logger

W Specimen weighed continuously

T Specimen with thermocouples

C Specimen cored at stages during run

R Specimen restrained against twist

R

R

W T

C C

Figure 9 Specimen positions in dryer for detailed tests

Variations were made to the standard schedules to generate different treatments: for some

runs the DBT was ramped down over the latter stages; steaming times were reduced for some

runs and no steaming conducted for some runs. Later runs were in pairs, with and without

variations, and with specimens matched.

Details of each run are shown in Table 2. Further details and results for runs with Radiata

heartwood (Runs 6 & 7; 15; 16 & 17) and Slash pine heartwood (Runs 10, 11 & 12; 13 & 14)

are shown below.

Table 2 Details of drying runs and specimen allocation

Run

No.Species

Type

#

Board

No.

Initial

MC %

Drying

Schedule

Air

speed

m/s

Rate of

humidity

buildup

Ramp

down?

Start

Ramp

down

hrs

Drying

Time

hrs

Cool'g

Time,

hrs

Steam

Time,

hrs

Cool

down

rate

after

steam

Spec'ns

paired to

Run

Weighed

spec'n

Spec'n

with

T/Cs

Spec'ns

cored

during

drying

Restrained

specimens

1 Radiata S Rs7 52-129 140/90 11 slow No 5.5 0 Rs7H Rs7BRs7A

Rs7C

2 Radiata S Rs11 96-115 140/90 9 slow No 9 1 4 Slow Rs11G Rs11DRs11E

Rs11HRs11F

3 Radiata S Rs10 48-123 140/90 9 slow Yes 6.5 9.5 1 3 Slow Rs10G Rs10BRs10A

Rs10CRs10E

4 Radiata S Rs4 63-110 140/90 9 fast Yes 7 9.25 1 3 Fast 5 Rs4B Rs4CRs4A

Rs4HRs4D

5 Radiata

S

S

S

Rs2

Rs4F

Rs11A

74-114

95 96140/90 9 fast Yes 7 10 1 3 Mod. 4 Rs2A Rs11A

Rs2B

Rs4FRs2C

6 RadiataH

H

Rh1,

Rh10

29-39 32-

33140/90 9 slow No 4 1 3 Fast 7 Rh1G Rh1C

Rh1A

Rs10IRh1I

7 RadiataH

H

Rh1,

Rh10

30-34 26-

32140/90 9 slow Yes 2.3 5.75 1 3 Fast 6 Rh1E Rh1D

Rh1B

Rs10J

Rs1H

Rs10K

8 SlashS

S

Ss1,

Ss2

101-109

80-86140/90 11 slow No 1 8 1 3 Mod. 9 Ss1C Ss1F

Ss1D

Ss2E

Ss1A

Ss2C

9 SlashS

S

Ss1,

Ss2

90-107

86140/90 11 slow Yes 4.5 8.5 1 3 Mod. 8 Ss1G Ss1H

Ss1E

Ss2F

Ss1B

Ss2D

10 SlashH

H

Sh3,

Sh4

31-40 50-

62140/90 11 fast No 6 1 3 Mod. 11, 12 Sh4E Sh3F

Sh3A

Sh4G

Sh3C

Sh4C

11 SlashH

H

Sh3,

Sh4

33-44 51-

74140/90 11 fast No 6.25 1 2 Mod. 10, 12 Sh4F Sh3G

Sh3H

Sh4H

Sh3B

Sh4D

12 Slash

H

H

H

Sh2

Sh3

Sh4

89-91 45-

46 47-51140/90 11 fast Yes 3 9 0 Fast 10, 11 Sh4A Sh2G

Sh3E

Sh2H

Sh3D

Sh4B

13 SlashH

H

Sh5,

Sh6

91-104

75-110140/90 11 fast No 6.5 1 3 Mod. 14 Sh5E Sh6D

Sh5A

Sh6F

Sh5C

Sh6B

14 SlashH

H

Sh5,

Sh6

91-110

81-122140/90 11 fast Yes 3 9 1 3 Mod. 13 Sh5F Sh6E

Sh5B

Sh6G

Sh5D

Sh6C

15 Radiata S/H Rsh3 48-80 140/90 9 fast Yes 3 9 0 Fast Rsh3F Rsh3CRsh3E

Rsh3B

Rsh3D

Rsh3G

16 RadiataH

H

Rh2,

Rh6

31-35

34-37140/90 9 fast Yes 3 6 0 Fast 17 Rh2A Rh6G

Rh2D

Rh6E

Rh2F

Rh6C

17 RadiataH

H

Rh2,

Rh6

31-36 35-

39140/90 9 fast No 4 1 3 Fast 16 Rh2B Rh6H

Rh2E

Rh6F

Rh2G

Rh6D

# S = Sapwood H = heartwood/juvenile wood

15

After all runs were completed specimens were weighed and distortion measured. Specimens

were then placed in a 12% EMC controlled environment room. After one week specimens

were re-measured and placed in another room at 17% EMC, then at weekly intervals in a 5%

EMC room and back to the 12% EMC room. NMR discs from 35mm cores were measured

after exposure to 12% and 17% conditions.

Specimens from early runs had up to 2 months storage before the cycling which may have

allowed moisture re-distribution and stress relaxation.

The results of the drying runs with heartwood material are presented below. These specimens

had a maximum of 5 weeks storage.

16


Figure 10 gives an example of the detection signals from MOUSE. Amplitude and relaxation

time T2 shown are the results of curve fitting.

Figure 10 MOUSE detection signals from slices taken from specimen 5ER of Run 13

X axis is time, ms; Y axis is signal amplitude

Data for the heartwood runs follows

17

Detailed drying runs 6 & 7: radiata pine heartwood

SWW Run RH6

0

20

40

60

80

100

120

140

160

1:00 2:00 3:00 4:00 5:00

Drying Time, hrs

Tem

pera

ture

, C

0

5

10

15

20

25

30

35

40

MC

%

DBT WBT Stack AvMC Specimen AvMC

SWW Run RH7

0

20

40

60

80

100

120

140

160

1:00 2:00 3:00 4:00 5:00 6:00

Drying Time, hrs

Tem

pera

ture

, C

0

5

10

15

20

25

30

35

40

MC

%


(a) Dryer conditions for Run 6 (b) Dryer conditions for Run 7

SWW Run RH6 Air & Wood Temperature

0

20

40

60

80

100

120

140

160

0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00

Drying Time, hrs

Te

mp

era

ture

, C

T in T out T surf T 3mm T 9mm T 15mm T 21mm T - 9mm

SWW Run RH7 Air & Wood Temperature

0

20

40

60

80

100

120

140

160

0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00

Drying Time, hrs

Te

mp

era

ture

, C


(c) Air and wood temp. during Run 6 (d) Air and wood temp. during Run 7

Figure 11 Drying plots for Run 6 and Run 7

For Run 6, DBT was held constant for the 4 hour drying period; for Run 7 DBT was ramped

down to 120C after 2 hours and 20 minutes for 5:40 drying time. WBT was reached much

more quickly in Run 7 than in Run 6. For both runs 3 hours steaming was given.

MC Profiles Run Rh6

0

2

4

6

8

10

12

0 1 5 8 9

Slice

MC

, %

RH1Ir RH1Gd RH1Gr RH1Cr RH1Fr

MC Profiles Run Rh7

0

2

4

6

8

10

12

0 1 5 8 9

Slice

MC

, %

RH1Hd RH1Hr RH1Ed RH1Er RH1Dr

(a) MC profiles for Run 6 (b) MC profiles for Run 7

Figure 12 Profiles of moisture content through the thickness of specimens, generally radial, determined by oven drying, for Run 6 and Run 7.

Slices 0, 1, 8 & 9 are 6mm thick, slice 0 from the outer face and slice 9 from the inner face

(near pith). Labels ending d = at the end of drying; r = after steam reconditioning and cooling

overnight.

Figure 12 shows that moisture content is more uniform through the thickness after steaming.

18

Run 6 NMR measurements

0

1

2

3

4

5

6

7

8

9

10

Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9

Slice

Am

plitu

de

Rh1IR* Rh1GD Rh1GR Rh1CR Rh1FR


0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0


Slice

1/T

2 m

s-1

Rh1IR* Rh1GD Rh1GR Rh1CR Rh1FR


0

2

4

6

8

10

12


Slice

Am

pli

tu

de

Rh1HD* Rh1HR* Rh1ED Rh1ER Rh1DR


0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5


Slice1

/T2

m

s-1

Rh1HD* Rh1HR* Rh1ED Rh1ER Rh1DR

(a) NMR profiles for Run 6 (b) NMR profiles for Run 7

Figure 13 Low field MOUSE NMR measurements on slices from cores through the thickness

of specimens, generally radial, for Run 6 and Run 7.

Slices 0, 1, 8 & 9 are 5mm thick (sawn at 6mm spacing).

Comparison of Figure 12 and Figure 13 shows that amplitude generally mirrors the moisture

content determined by oven drying.

Steaming results in more mobile water near the wood surfaces, indicated by the elevated 1/T2

in surface slices.

MC Run 6

0

5

10

15

20

25

30

35

G D F T3 12% 17% 5% 12%

Condition

MC

, %

Rh1I Rh1G Rh1F Rh1C

MC Run 7

0

5

10

15

20

25

30

35

G D F T3 12% 17% 5% 12%

Condition

MC

, %

Rh1H Rh1E Rh1D

(a) MC records for Run 6 (b) MC records for Run 7

Figure 14 Average specimen moisture content of specimens of Run 6 and Run 7 during drying

and later environmental cycling.

G = Green; D = Dry; F = final (Reconditioned and cooled or cooled); T3 = Condition before humidity cycling; 12% = after 1 week at 12% EMC; 17% = after 1 week at 17% EMC; 5% = after 1 week at 5% EMC; 12% = after 1 week at 12% EMC;

19

Twist Run 6

-5.5

-5

-4.5

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

G D F T3 12% 17% 5% 12%

Condition

Tw

ist,

deg

rees

Rh1I Restrained Rh1G Weighed Rh1F Rh1C T/Cs

Twist Run 7

-5.5

-5

-4.5

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

G D F T3 12% 17% 5% 12%

Condition

Tw

ist,

deg

rees

Rh1H Restrained Rh1E Weighed Rh1D T/Cs

(a) Twist records for Run 6 (b) Twist records for Run 7

Figure 15 Twist of specimens of Run 6 and Run 7 during drying and later environmental

cycling.

G = Green; D = Dry; F = final (Reconditioned and cooled or cooled); T3 = Condition before humidity cycling; 12% = after 1 week at 12% EMC; 17% = after 1 week at 17% EMC; 5% = after 1 week at 5% EMC; 12% = after 1 week at 12% EMC;

Effect of drying conditions and restraint

• The amount of twist during drying varied between specimens. As can be seen in the

photos below, the specimens with the greatest twist, Rh1C and D has pith at one face and

similar knots. Specimen Rh1G twisted much more than E, possibly because it included a

loop of pith.

• Specimen Rh1H increased in twist by almost 50% over the cycling whereas Rh1I did not.

Rh1H had slightly lower surface moisture content after drying and increased in mass a

little more up to the 17% condition. This would be expected to have reduced twist.

• All other specimens showed little change in twist over the cycling, showing no difference

between the two runs.

• Comparing the specimens restrained against twist, I and H, with the most closely

matching unrestrained specimens,Rh1E and F, show no apparent effect of the restraint.

Figure 16 Specimens of Run 6 and Run 7 after tests with ends trimmed. Specimens are in a

sequence A, B…I, cut from Radiata Pine heartwood Board 1

20

Detailed drying run 15 – radiata pine near-pith sapwood

For Run 15 kiln temperature ramped down in two stages and no steam reconditioning was

used (Figure 17).

SWW Run Rsh15

0

20

40

60

80

100

120

140

160

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00

Drying Time, hrs

Te

mp

era

ture

, C

0

10

20

30

40

50

60

70

80

MC

%

DBT WBT Corr. Stack AvMC Specimen AvMC

SWW Run Rsh15 Air & Wood Temperature

0

20

40

60

80

100

120

140

160

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00

Drying Time, hrs

Te

mp

era

ture

, C

T in T out T surf T 3mm T 15mm T 21mm T -9mm

(a) Dryer conditions for Run 15 (b) Air and wood temperatures during Run 15

Figure 17 Drying records for Run 15

MC Profiles Run Rsh15

0.0

5.0

10.0

15.0

20.0

25.0

0 1 5 8 9

Slice

MC

, %

Rsh3Df Rsh3Gf Rsh3Ff Rsh3Cf

Figure 18 Profiles of moisture content from sliced cores through the thickness of specimens,

generally radial, determined by oven drying, for Run 15.

Slices 0, 1, 8 & 9 are 6mm thick, slice 0 from the outer face and slice 9 from the inner face (near pith). Labels ending d = at the end of drying; r = after steam reconditioning and cooling overnight; f = final where no reconditioning applied

21

g

Run 15 Restrained vs Non-restrained

0

2

4

6

8

10

12

14


Slice

Am

plitu

de

Rsh3DF* Rsh3CF


0

2

4

6

8

10

12

14


Slice

Am

plitu

de

Rsh3DF* Rsh3CF Rsh3DF* 12% Rsh3CF 12%


0

1

1

2

2

3

3


Slice1/T

2 -

m

s-1

Rsh3DF* Rsh3CF Rsh3DF* - 12% Rsh3CF - 12%


0

1

1

2

2

3


Slice

1/T

2 -

m

s-1

Rsh3DF* Rsh3CF


of specimens, generally radial, for Run 15.


• The moisture content profiles from Run 15 show that ramping down without steaming

after drying resulted in significant gradients; final moisture contents were high, however.

MC Run 15

0

10

20

30

40

50

60

70

80

G D F T3 12% 17% 5% 12%

Condition

MC

, %

Rsh3D Rsh3B Rsh3C

MC Run 15

0

10

20

30

40

50

60

70

80

G D F T3 12% 17% 5% 12%

Condition

MC

, %

Rsh3G Rsh3E Rsh3F

Twist Run 15

-1

-0.5

0

0.5

1

1.5

2

2.5

G D F T3 12% 17% 5% 12%

Condition

Tw

ist,

deg

rees

Rsh3D Restrained Rsh3B Cored Rsh3C T/Cs

Twist Run 15

-0.5

0

0.5

1

1.5

2

G D F T3 12% 17% 5% 12%

Condition

Tw

ist,

deg

rees

Rsh3G Restrained Rsh3E Cored Rsh3F Weighed

Figure 20 Average specimen moisture content and twist of specimens of Run 15 during

drying and later environmental cycling.

22

• Although most specimens dried further between stages F and T3, twist did not change to

any extent.

• Only Specimen Rsh3D increased significantly in twist during cycling.

Figure 21 Specimens of Run 15 after drying and cycling.

Note: Ends trimmed to show grain patterns.

23

Detailed drying runs 16 & 17: radiata pine heartwood

For Run 16 kiln conditions were ramped down in two stages and no steam reconditioning was

used; Run 17 followed the full Radiata test schedule.

SWW Run Rh16

0

20

40

60

80

100

120

140

160

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00

Drying Time, hrs

Tem

pera

ture

, C

0

5

10

15

20

25

30

35

40

MC

%

DBT WBT Corr. Stack MC Specimen AvMC

SWW Run Rh17

0

20

40

60

80

100

120

140

160

0:00 1:00 2:00 3:00 4:00 5:00

Drying Time, hrs

Te

mp

era

ture

, C

0

5

10

15

20

25

30

35

40

MC

, %

DBT WBT Corr. Stack MC Specimen AvMC


SWW Run Rh16 Air & Wood Temperature

0

20

40

60

80

100

120

140

160

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00

Drying Time, hrs

Tem

pera

ture

, C

T in T out T surf T 3mm T 9mm T 15mm T 21mm T -9mm

SWW Run Rh17 Air & Wood Temperature

0

20

40

60

80

100

120

140

160

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00

Drying Time, hrs

Tem

pera

ture

, C

T in T out T surf T 3mm T 15mm T 21mm T -9mm

(c) Air and wood temperatures during Run 16 (d) Air and wood temperatures during Run 17

Figure 22 Drying records for Run 16 and Run 17

MC Profiles Run Rh16

0

5

10

15

0 1 5 8 9

Slice

MC

, %

Rh2Ff Rh2Af Rh6Cf Rh6Gf


0

5

10

15

20

0 1 5 8 9

Slice

MC

, %

Rh6Dd Rh6Dr Rh6Hr


0

5

10

15

20

0 1 5 8 9

Slice

MC

, %

Rh2GD Rh2Gr Rh2Bd Rh2Br


Figure 23 Profiles of moisture content through the thickness of specimens, generally radial,

determined by oven drying, for Run 16 and Run 17.

Slices 0, 1, 8 & 9 are 6mm thick, slice 0 from the outer face and slice 9 from the inner face (near pith). Labels ending d = at the end of drying; r = after steam reconditioning and cooling overnight; f = final where no reconditioning applied.

24


0

2

4

6

8

10


Slice number

Am

pli

tud

eRh6GR Rh6CR*


0

2

4

6

8

10


Slice number

Am

pli

tud

e

Rh2AR Rh2FR*


0

1

2

3

4


Slice number

1/T

2 -

ms

-1

Rh6GR Rh6CR*


0

1

2

3

4

5

6


Slice number

1/T

2 -

ms

-1

Rh2AR Rh2FR*

(a) NMR measurements for Run 16


0

2

4

6

8

10


Slice

Am

plitu

de

Rh6DR* Rh6HR Rh6DD*


0

1

2

3

4

5

6

7

8


Slice

Am

plitu

de

Rh2GR* Rh2BR Rh2GD* Rh2BD


0.00

1.00

2.00

3.00

4.00

5.00


Slice

1/T

2 m

s-1

Rh2GR* Rh2BR Rh2GD* Rh2BD


0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00


Slice

1/T

2 m

s-1

Rh6DR* Rh6HR Rh6DD*

(b) NMR measurements for Run 17


of specimens, generally radial, for Run 16 and Run 17.


• Run 17 shows that moisture content becomes more uniform through the thickness from

steaming.

• Steaming results in more mobile water near the wood surfaces, indicated by the elevated

1/T2 in surface slices, slices 0 and 9.

• The moisture content profiles from Run 16 were not excessive; ramping down can

minimise gradients.

25

MC Run 16

0

5

10

15

20

25

30

35

40

G D F T3 12% 17% 5% 12%

Condition

MC

, %

Rh6C Rh6E Rh6G

MC Run 17

0

5

10

15

20

25

30

35

40

G D F T3 12% 17% 5% 12%

Condition

MC

, %

Rh6D Rh6F Rh6H

MC Run 16

0

5

10

15

20

25

30

35

40

G D F T3 12% 17% 5% 12%

Condition

MC

, %

Rh2F Rh2D Rh2A

MC Run 17

0

5

10

15

20

25

30

35

40

G D F T3 12% 17% 5% 12%

Condition

MC

, %

Rh2G Rh2E Rh2B

Figure 25 Average specimen moisture content of specimens of Run 16 and Run 17 during

drying and later environmental cycling

Twist Run 16

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

G D F T3 12% 17% 5% 12%

Condition

Tw

ist,

deg

rees/4

50m

m

Rh6C Restrained Rh6E Cored Rh6G T/Cs

Twist Run 17

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

G D F T3 12% 17% 5% 12%

Condition

Tw

ist,

deg

rees/4

50m

m

Rh6D Restrained Rh6F Cored Rh6H T/Cs

Twist Run 16

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

G D F T3 12% 17% 5% 12%

Condition

Tw

ist,

deg

rees/4

50m

m

Rh2F Restrained Rh2D Cored Rh2A Weighed

Twist Run 17

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

G D F T3 12% 17% 5% 12%

Condition

Tw

ist,

deg

rees/4

50m

m

Rh2G Restrained Rh2E Cored Rh2B Weighed

Figure 26 Twist of specimens of Run 16 and Run 17 during drying and later environmental

cycling

26

• Moisture content estimates were particularly difficult for cored specimens; the actual MC

of Rh6E and Rh2D were higher than plotted. The environment in the laboratory is close

to 10% EMC.

Effect of drying conditions and restraint

• Twist changes generally followed moisture changes with environmental changes.

• The restrained specimens in both runs showed increased twist over the cycling process.

• There is apparently more distortion in Run 17 specimens, but this is not consistent and

may be due to variation in wood characteristics along the boards.

Figure 27 Specimens of Run 16 and Run 17 after tests with ends trimmed.

Specimens are in a sequence A, B…I, cut from Radiata Pine heartwood Boards 2 and 6

27

Detailed drying test runs 10, 11 and 12: slash pine heartwood

Runs 10 and 11 differ only in the shorter steaming time for Run 11; Run 12 had no steaming after

two stages of ramp-down of temperature, and with humidity increased for the final stage (Figure 28).

SWW Run Sh10

0

20

40

60

80

100

120

140

160

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00

Drying time, hrs

Te

mp

era

ture

, C

0

10

20

30

40

50

60

MC

%


SWW Run Sh11

0

20

40

60

80

100

120

140

160

1:00 2:00 3:00 4:00 5:00 6:00 7:00

Drying Time, hrs

Te

mp

era

ture

, C

0

10

20

30

40

50

60

70

MC

%


SWW Run SR12

0

20

40

60

80

100

120

140

160

1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00

Drying Time, hrs

Te

mp

era

ture

, C

0

10

20

30

40

50

60

70

80

MC

%


Radiata heartwood

specimens out

(a) Dryer conditions for Run 10 (b) Dryer conditions for Run 11 (c) Dryer conditions for Run 12

SWW Run Sh10 Air & Wood Temperature

0

20

40

60

80

100

120

140

160

0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00

Drying Time, Hrs

Tem

pera

ture

, C



0

20

40

60

80

100

120

140

160

0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00

Drying Time, hrs

Tem

pera

ture

, C


SWW Run SR12 Air & Wood Temperature

0

20

40

60

80

100

120

140

160

0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00

Drying Time, hrs

Tem

pera

ture

, C

T in T out T 3mm T 9mm T 15mm T 21mm T -9mm

(d) Air and wood temp. for Run 10 (e) Air and wood temp. for Run 11 (f) Air and wood temp. for Run 12

Figure 28 Drying records for Run 10, Run 11 and Run 12

Final MC levels and profiles were similar after all three runs

(a) Moisture profiles for Run 10 (b) Moisture profiles for Run 11 (c) Moisture profiles for Run 12

Figure 29).

MC profiles Run Sh10

0

5

10

15

20

0 1 5 8 9Slice

MC

, %

Sh3Cd Sh3Cr Sh3Fr


0

5

10

15

20

0 1 5 8 9Slice

MC

, %

Sh3Bd Sh3Br Sh3Gr

MC Profiles Run Sh12

0

5

10

15

20

0 1 5 8 9Slice

MC

, %

Sh3Df Sh3Ef


Figure 29 MC profiles through the thickness of specimens from Board 3, by oven drying, for

Runs 10, 11 & 12


0

2

4

6

8

10

12

14

16


Slice

Am

plit

ud

e

Sh3CD* Sh3CR* Sh3FR


0

1

2

3

4


Slice

1/T

2 m

s-1

Sh3CD* Sh3CR* Sh3FR


0

2

4

6

8

10

12

14

16

Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9Slice

Am

plit

ud

e

Sh3BD* Sh3BR* Sh3GR


0

1

2

3

4


Slice

1/T

2 m

s-1

Sh3BD* Sh3BR* Sh3GR


0

2

4

6

8

10

12

14

16


Slice

Am

plitu

de

Sh3DF* Sh3EF


0

1

2

3

4


1/T

2 m

s-1

Sh3DF* Sh3EF

(a) NMR profiles for Run 10 (b) NMR profiles for Run 11 (c) NMR profiles for Run 12

Figure 30 Low field MOUSE NMR measurements on slices through the thickness of

specimens from Board 3, for Runs 10, 11 & 12

28


0

5

10

15

20

0 1 5 8 9Slice

MC

, %

Sh4Cd Sh4Cr Sh4Ed Sh4Er


0

5

10

15

20

0 1 5 8 9Slice

MC

, %

Sh4Dd Sh4Dr Sh4Fd Sh4Fr


0

5

10

15

20

0 1 5 8 9Slice

MC

, %

Sh4Bf Sh4Af


Figure 31 MC profiles through the thickness of specimens from Board 4, by oven drying, for

Runs 10, 11 & 12


0

2

4

6

8

10

12

14


Slice

Am

plitu

de

Sh4CD* Sh4CR* Sh4ED Sh4ER


0

1

2

3

4

5

6


Slice

1/T

2,

ms-1



0

2

4

6

8

10

12

14


Slice

Am

plit

ud

e

Sh4DD* Sh4DR* Sh4FD Sh4FR


0

1

2

3

4

5

6


Slice

1/T

2,

ms-1



0

2

4

6

8

10

12

14


Am

plit

ud

e

Sh4BF* Sh4AF


0

1

2

3

4

5

6


1/T

2,

ms-1

Sh4BF* Sh4AF

(a) NMR profiles for Run 10 (b) NMR profiles for Run 11 (c) NMR profiles for Run 12

Figure 32 Low field MOUSE NMR measurements on slices through the thickness of

specimens from Board 4 for Runs 10, 11 & 12

Final MC levels and profiles for matched specimens from both boards 3 and 4 were similar

after all three runs.

MC Run 10

0

5

10

15

20

25

30

35

40

45

50

G D F T3 12% 17% 5% 12%Condition

MC

, %

Sh3C Sh3A Sh3F

MC Run 11

0

5

10

15

20

25

30

35

40

45

50

G D F T3 12% 17% 5% 12%

Condition

MC

, %

Sh3B Sh3H Sh3G

MC Run 12

0

5

10

15

20

25

30

35

40

45

50

G F T3 12% 17% 5% 12%

Condition

MC

, %

Sh3D Sh3E

(a) Av. Spec’n MC for Run 10 (b) Av. Spec’n MC for Run 11 (c) Av. Spec’n MC for Run 12

Figure 33 Average MC of specimens from Board 3, for Runs 10, 11 & 12

29

Twist Run 10

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

G D F T3 12% 17% 5% 12%

Condition

Tw

ist, d

egre

es

Sh3C Restrained Sh3A Cored Sh3F T/Cs

Twist Run 11

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

G D F T3 12% 17% 5% 12%

Condition

Tw

ist,

de

gre

es

Sh3B Restrained Sh3H Cored Sh3G T/Cs

Twist Run 12

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

G F T3 12% 17% 5% 12%Condition

Tw

ist, d

egre

es

Sh3D Restrained Sh3E Cored

(a) Twist for Run 10 (b) Twist for Run 11 (c) Twist for Run 12

Figure 34 Twist of specimens from Board 3 for Runs 10, 11 & 12

• Specimens in Runs 10 & 11 lost moisture after drying (F > T3) and twist increased.

• Specimens in Run 10 increased twist during cycling (T3 > 12%) more than those in Run

11 which had less steaming although average MC returned to almost the same values.

Specimens in Run 12 without steaming twisted less during cycling.

• Restrained specimens seemed slightly more stable with less steaming.

MC Run 10

0

10

20

30

40

50

60

70

80

G D F T3 12% 17% 5% 12%

Condition

MC

, %

Sh4C Sh4G Sh4E

MC Run 11

0

10

20

30

40

50

60

70

80

G D F T3 12% 17% 5% 12%

Condition

MC

, %

Sh4D Sh4H Sh4F

MC Run 12

0

10

20

30

40

50

60

70

80


MC

, %

Sh4B Sh4A

(a) Av. Spec’n MC for Run 10 (b) Av. Spec’n MC for Run 11 (c) Av. Spec’n MC for Run 12

Figure 35 Average MC of specimens from Board 4, for Runs 10, 11 & 12

Twist Run 10

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

G D F T3 12% 17% 5% 12%

Condition

Tw

ist, d

eg

ree

s

Sh4C Restrained Sh4G Cored Sh4E Weighed

Twist Run 11

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0


Tw

ist,

de

gre

es

Sh4D Restrained Sh4H Cored Sh4F Weighed

Twist Run 12

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0


Tw

ist, d

egre

es

Sh4B Restrained Sh4A Weighed

(a) Twist for Run 10 (b) Twist for Run 11 (c) Twist for Run 12

Figure 36 Twist of specimens from Board 4 for Runs 10, 11 & 12

• All specimens maintained stable mass after drying (F to T3), but the restrained specimen

(Sh4C) in Run 10 and several un-restrained specimens increased in twist.

• The restrained specimen (Sh4C) in Run 10 increased in twist during cycling (T3 to 12%).

• Restrained specimens seemed more stable with less steaming (<3 hours), and finished

with less twist than un-restrained specimens.

30

Figure 37 Specimens of Runs 10, 11 & 12 from Board 3 after tests & with ends trimmed

• Specimens B, C and H contained the pith and might be expected to twist more; other

specimens generally had the pith in or near the face.

Figure 38 Specimens of Runs 10, 11 & 12 from Board 4 after tests & with ends trimmed

• All specimens contained the pith and might be expected to twist in similar manner;

generally they did so.

31

Detailed test drying runs 13 and 14: slash pine heartwood

SWW Run Sh13

0

20

40

60

80

100

120

140

160

1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00

Drying Time, hrs

Tem

pera

ture

, C

; M

C%


SWW Run Rh14

0

20

40

60

80

100

120

140

160

1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00

Drying Time, hrs

Tem

pera

ture

, C

; M

C%

DBT WBT Corr. Stack AvMC Specimen AvMC



0

20

40

60

80

100

120

140

160

0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00

Drying Time, hrs

Te

mp

era

ture

, C



0

20

40

60

80

100

120

140

160

0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00

Drying Time, hrs

Te

mp

era

ture

, C


(c) Air and wood temp. during Run 13 (d) Air and wood temp. during Run 14

Figure 39 Drying records for Run 13 and Run 14

For Run 14 temperature was ramped down in two stages and no steam reconditioning was

used; Run 13 followed the Slash test schedule.


0.0

5.0

10.0

15.0

20.0

25.0

0 1 5 8 9

Slice

MC

, %

Sh5Cd Sh5Cr Sh5Ed Sh5Er


0

5

10

15

20

25

0 1 5 8 9

Slice

MC

, %

Sh5Dd Sh5Dr Sh5Fd Sh5Fr


Figure 40 Profiles of moisture content from sliced cores through the thickness of specimens

5, generally radial, determined by oven drying, for Run 13 and Run 14


32

Runs 13 NMR measurements

0.0

0.5

1.0

1.5


Slice number

1/T

2 -

ms

-1



0

2

4

6

8

10

12

14


Slice number

Am

plitu

de



0

2

4

6

8

10

12


Slice number

Am

plitu

de



0.0

0.5

1.0

1.5

2.0


Slice number

1/T

2 -

ms

-1




of specimens 5, generally radial, for Run 13 and Run 14.



0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

0 1 5 8 9

Slice

MC

, %

Sh6Bd Sh6Br Sh6Dr


0

2

4

6

8

10

12

14

16

0 1 5 8 9

Slice

MC

, %

Sh6Cd Sh6Cr Sh6Er

(a) Oven-dry MC profiles for Run 13 (b) Oven-dry MC profiles for Run 14

Figure 42 Profiles of moisture content from sliced cores through the thickness of specimens

6, generally radial, determined by oven drying, for Run 13 and Run 14


33


0

2

4

6

8

10

12


Slice number

Am

plitu

de

Sh6BD* Sh6BR* Sh6DR


0.0

0.5

1.0

1.5

2.0

2.5


Slice number

1/T

2 -

ms

-1

Sh6BD* Sh6BR* Sh6DR


0

2

4

6

8

10


Slice number

Am

plitu

de

Sh6CD* Sh6CR* Sh6ER


0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0


Slice number

1/T

2 -

ms-1

Sh6CD* Sh6CR* Sh6ER



of specimens 6, generally radial, for Run 13 and Run 14.


MC Run 13

0

10

20

30

40

50

60

70

80

90

100

110

120

130

G D F T3 12% 17% 5% 12%

Condition

MC

, %

Sh5C Sh5A Sh5E

MC Run 14

0

10

20

30

40

50

60

70

80

90

100

110

120

130


MC

, %

Sh5D Sh5B Sh5F

(a) Av. Specimen MC for Run 13 (b) Av. Specimen MC for Run 14

Figure 44 Average MC of specimens from board 5 in Run 13 and Run 14 during drying and

later environmental cycling.

Twist Run 13

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

G D F T3 12% 17% 5% 12%

Condition

Tw

ist,

deg

rees

Sh5C Restrained Sh5A Cored Sh5E Weighed

Twist Run 14

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

G D F T3 12% 17% 5% 12%

Condition

Tw

ist,

de

gre

es

Sh5D Restrained Sh5B Cored Sh5F Weighed

(a) Specimen twist for Run 13 (b) Specimen twist for Run 14

Figure 45 Twist of specimens from board 5 in Run 13 and Run 14 during drying and later

environmental cycling.

34

MC Run 13

0

10

20

30

40

50

60

70

80

90

100

110

120

130


MC

, %

Sh6B Sh6F Sh6D

MC Run 14

0

10

20

30

40

50

60

70

80

90

100

110

120

130

G D F T3 12% 17% 5% 12%

Condition

MC

, %

Sh6C Sh6G Sh6E

(a) Av. Specimen MC for Run 13 (b) Av. Specimen MC for Run 14

Figure 46 Average MC of specimens from board 6 in Run 13 and Run 14 during drying and

later environmental cycling

Twist Run 13

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

G D F T3 12% 17% 5% 12%

Condition

Tw

ist,

deg

rees

Sh6B Restrained Sh6F Cored Sh6D T/Cs

Twist Run 14

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

G D F T3 12% 17% 5% 12%

Condition

Tw

ist,

de

gre

es

Sh6C Restrained Sh6G Cored Sh6E T/Cs

(a) Specimen twist for Run 13 (b) Specimen twist for Run 14

Figure 47 Twist of specimens from board 6 in Run 13 and Run 14 during drying and later

environmental cycling

Figure 48 Specimens of Run 13 and Run 14 after tests with ends trimmed.

Specimens are in a sequence A, B…I, cut from Slash Pine heartwood Boards 5 and 6

35

NMR measurements and analysis

NMR Surface Analyser

The NMR MOUSE (MObile Universal Surface Explorer) is a novel NMR device designed for

relaxation measurements on surfaces of arbitrary shaped samples. The design of the mobile

probe with the permanent magnets and transmitter and receiver coil system allows measurements

of the proton NMR signals (15.9MHz) from various samples.

The NMR surface analyzer, MOUSE, detects the signal from water via the special imaging

sequence, spin echo, which gives the NMR signal predominantly of water close to the surface.

The observation volume is about 1mm in depth over a 0.5cm2. The observed signal is detected

only from the moisture with a sufficient mobility or a long enough relaxation time, but not the

signal from the protons of solid organic molecules, whose relaxation time is in general shorter.

The data are presented as probability 1/T2 for water to be bound and the amplitude reflects the

overall number of protons (water molecules) detected. The scale is given in relative terms and is

proportional to total moisture content.

High field Solid-state NMR spectroscopy

The solid wood samples were investigated by solid-state proton NMR spectroscopy - Varian

Unity Plus 300 MHz NMR spectrometer. The method used was the proton magic angle spinning

NMR spectroscopy, which in a typical spectrum of a wood sample would normally give the

broad water resonance band (bound water) and small but sharp signals from the organic

molecules. By using a standard spin-echo pulse sequence (CPMG – sequence) we found that the

water signal disappears faster with the increased spin-echo time than the organic signal. The

standard CPMG sequence was used in order to determine the relaxation time T2 of these two

components, and the inversion recovery sequence, 180°-90°, was used to determine the spin

lattice relaxation time T1.

Model for wood drying NMR parameters

The general concept reported in 1999 (PN008.96 Softwood Drying Research Project) for NMR

signal of water in wood was adopted as follows:

“Studies of T2 relaxation of water suggest:

essentially unbound water in cell lumens,

water associated with walls and smaller reservoirs – droplets & cracks

tightly bound cell wall water.

Short T2 ranges from 0.2 ms to 1 ms, medium T2 ranges from 5 ms to 40 ms, and long T2

ranges from 50 ms to 800 ms.”

In the current investigation of the drying process and moisture effects on wood structural

changes this model and water categories were investigated in detail in order to establish the

specific moisture deformation correlations where previous data was not conclusive. In such a

study we found it essential to investigate first the limitations of the above definition and to

suggest a more comprehensive description of the drying process yielding potentially better

control of this process for the industry. The investigation was conducted in two directions: first

the definitions and physical differentiation (especially by NMR parameters) between the

proposed categories of water in wood, and second the more comprehensive analysis of NMR

spectral data in the view of the above definitions.

1) The general definition of water in the hydrophilic polymers is correctly stated in the previous

report and it can be found in general literature on this subject where water content, Wc, is a sum

36

of non-freezing water (structural water or tightly bound to cell walls), Wnf, freezing bound water

or water associated with walls and smaller reservoirs, Wfb, and free water or essentially unbound

water in cell lumens, Wf.10,11

The relationship between these categories was studied closely and

the characteristic finding by H & T Hatakeyama can be graphically summarised as shown here11

.

Figure 49 from Hatakeyama11

This diagram indicates that in the dry wood samples where MC is around 10% one can expect

mainly bound water (freezing and non-freezing). Such interpretation was given by R Guzenda et

al.3 at the 12th International symposium on non-destructive testing of wood, Hungary 2000, who

concluded that lost of free water in the drying process (moisture going below the fibre saturation

point) is evident from NMR data where the relaxation spin-lattice time T1, which reveals two

components in green wood, becomes a single component parameter below the fibre saturation

point. In our investigation we quickly confirmed the above conclusion (milestone report) but

investigating further the spin-spin relaxation time T2 we also expected to see some difference

between the bound waters (freezing and non-freezing), especially in correlation to the drying

regime and to conditioning after drying. But again as in the previous project report we reached a

similar conclusion:

“There are large and inconsistent variations in the proportions of water in each bonding state for

different samples inconsistent with respect to other parameters or drying conditions. Lesser

variability was observed after further conditioning of the wood and proportion of bound water

was higher than for freshly dried samples - moisture content after drying exhibited large

variation from matched samples, masking any consistent relationship”.

This fact by itself was leading us to the assumption that in the proton NMR spectra we are

observing too large variations due to the additional species such as resin and other wood

components, which possess the protons in their molecular structure (as already indicated in the

previous milestone report). The results of a detailed investigation have now been incorporated

into the improved model for NMR data interpretation as outlined below.

2) The assumption that the proton NMR signal analysed in the wood is mainly coming from water

in different states of interaction with the solid matrix needs to be revised. The water definition

10

S.L. Maunu, NMR studies of wood and wood products, Progress in Nuclear Magnetic Resonance Spectroscopy, 40 (2002) 151-174 11

H. Hatakeyama and T. Hatakeyama, Interaction between water and hydrophilic polymers, Thermometrica Acta, 308 (1998) 3-22

37

statement in the first report assumed that the whole proton NMR signal, as analysed by the T2

measurements using FID (free induction decay) method, is coming from water in the wood. This

simplified picture is not always correct because the protons from other components of wood such

as cellulose, hemicellulose and lignin (major ones) may appear in the signal as well, especially

when their molecular mobility is comparable to the mobility of water molecules. Proton NMR

polarisation, which was investigated by NMR methods in wood samples, is therefore from both

water molecules and organic components (cellulose, hemicellulose and lignin). These protons can

be detected as separate species but they also interact at the interfaces yielding the additional NMR

polarisation exchange, which further changes the proton NMR signal.

The dried sample 2AR (Run 16) is used here as an example where the difference between two

slices is evident in the signal obtained by the NMR MOUSE instrument in around 21/2 minutes.

The dried wood samples all have a short T2 and only one T1 component but in these two spectra,

Figure 50 below, it is obvious that we have a longer and shorter component in signal decay. The

MOUSE detection utilizes the spin-echo sequence at a certain time where all the signal from

materials with the shorter T2 component (for solid wood) is already gone (relaxed) and only the

mobile part of the organic components can be detected. It was assumed that the longer T2

component belongs to the water molecules alone, but it is evident from our investigation that

such organic components do exist and they are likely to be organic extractable compounds or

mobile parts of cellulose/hemicellulose polymers.

(a)

20

15

10

5

0

Sig

na

l

160140120100806040200

Time(ms)

Run 16 sample 2AR slice 5

(b)

20

15

10

5

0

Sig

na

l

30252015105

Time(ms)

Run 16 sample 2AR slice 8

Figure 50 The NMR signal, MOUSE, from two slices (a) with pith and (b) without.

In order to separate different molecular species in the proton NMR spectrum one needs to use the

high field solid-state NMR methods. Fast magic angle spinning is one of them12,13

and it can

differentiate the resonances of water and other species. These methods are most effective when

the magnetic environment of protons is sufficiently different (chemical shift difference) and they

are not fast exchanging NMR polarisation. Recent work of A.M. Gill and co-workers13

shows

that proton high-resolution magic angle spinning spectra of natural polymeric materials like

wood yield sufficient information to identify the proton resonances in these materials. Their

conclusion, spectral assignment, is presented in Table 3 below:

12

R. Guzenda, W.Olek, H.M. Baranowska, Identification of free and bound water content in wood by means of NMR relaxometry, 12

th International symposium on non-destructuve testing of wood (2000),

Sopron, Hungary 13

A.M. Gill, M.H. Lopes, C. Pascoal Neto, and J. Rocha, Very high-resolution 1H MAS NMRE spectra of

natural polymeric material, Solid State Nuclear Magnetic Resonance, 15 (1999) 59-67

38

Table 3 From Gill et al13

Their spectral interpretation and assignment did help us to compare our solid-state NMR spectra

with theirs and to identify the additional species detected by NMR method in the proton

spectrum. 1H MAS NMR spectra of lignin, cellulose and hemicellulose, as shown below, show

the different spectral appearance of these species13

.

Figure 51 From Gill et al13

39

Solid-state NMR analysis

The carbon CPMAS (cross-polarisation magic angle spinning) spectrum of wood, sample 1BR from

Radiata Run RH7, is presented in Figure 52. This spectrum is a characteristic spectrum of wood

samples revealing cellulose, hemicellulose and lignin components.1,5 The central resonances from

50 ppm to 110 ppm are clearly from cellulose, crystalline and amorphous, as well as hemicellulose.

The broad resonance peaks from 110 ppm to 160 ppm are mainly from the lignin aromatic carbons.

The standard proton MAS (magic angle spinning) spectrum, Figure 52, reveals mainly a large

and broad water signal – bound water (3 ppm to 8ppm) – and small additional peaks due to the

organics components in wood (probably cellulose, hemicellulose, and lignin). These resonances,

sharp peaks at 1.2 ppm and 1.6 ppm, and smaller at 1.9 ppm and 2.3 ppm, in comparison with the

spectra from reference 13 are most likely due to the cellulose/hemicellulose species.

In order to further identify these resonances in the proton MAS spectrum it is proper to recall the

general wood structure model. The general model for the cell walls in the wood predicts that it is

comprised of cellulose polymers, which form microfibrils, that are bound together by

hemicellulose. A low, or reduced, hemicellulose content has been associated with the high

dimensional stability of wood structure. It may then be postulated that hemicellulose in particular

in the hydration state (plasticised by water) will be the main contributor in relation to the wood

distortion. Therefore, if in our 1H NMR MAS spectra we are able to observe and quantify the

hemicellulose that is hydrated (in physical contact with the bound water), we may have the

detection tool to estimate the potential distortion in the wood after drying.

The 1H MAS NMR spectra were obtained at 300MHz and a magic angle spinning speed of

around 9000 Hz. According to the literature13

only very high spinning speeds can provide the

sufficient line narrowing (30 kHz) for such resolution. It may be quickly assumed that we are

observing a broad line of water and narrow lines from cellulose due to the fact that the bound

water and hemicellulose interact (fast exchanging the magnetic polarisation) due to direct

contact. Therefore further relaxation studies of T1 and T2 for both species is required to confirm

their contact.

The spin-lattice relaxation time, T1, determined for the water proton peak, resonance at 4.8 ppm, and

the peak at 1.6 ppm (-CH2- in cellulose and hemicellulose) are nearly the same at 300 MHz; 324 ms

and 334 ms respectively. This may be interpreted as confirmation that water and ‘hemicellulose’

ends are closely associated – exchanging the magnetic polarisation in the NMR time scale.

The spin-spin relaxation time, T2, measured by the spin echo technique using a CPMG pulse

sequence, is on the other hand, quite different; around 1ms for water and 20 ms for cellulose.

This indicates that the bound water is in fast exchanging rate between immobile state (“non-

freezing” - attached to cell wall surface) and semi-free state in the pores (”freezing bound”),

whilst the organic protons (cellulose, hemicellulose and lignin) are different from the water

relaxation time. The solid crystalline component is expected to have a very short relaxation time,

but an amorphous more flexible structure may have quite a long T2 in comparison to the water.

So far the hemicellulose model of hydration is not in contradiction with the obtained results.

Using the spin-echo method with variable spin-echo time will further provide the separation of

these two components, bound water and organic signal, making a final better identification of

these organics. If we are using spin-echo detection with variable detection time, the NMR signal

from protons with a shorter T2 will disappear from the spin-echo signal before the proton signal

from the components with a long T2. Therefore, the presence of the organic protons in the signal

can be enhanced by making the abundant, but short-lived, water signal disappear.

In Figure 54, one can easily see the relative larger intensities from the organic components in

relation to the water. By using the spin-echo time, which is a few times longer than the water

relaxation time T2, completely removes the water signal from the NMR spectrum, Figure 55.

40

We used the spin echo technique with variable delays to define the relaxation time T2 of the

residual water (bound) signal and it was found to be always short, smaller than 1 ms. Therefore

one can conclude that we have a bound water signal that can not be differentiated further into

separate categories at room temperature by these NMR measurements. On the other hand, the

measurement of water T1 also reveals only one T1 component. The bound water, which may

come from two physical states, non-freezing bound water bonded to cell walls and freezing

bound water which is H-bonded to non-freezing bound water, seems to appear as one under the

room temperature and dry wood sample conditions. Of course the so-called “free” water was

evidently removed in the drying cycle.

Single component in T2 analysis indicates that the NMR signal from water molecules in the

“non-freezing” state and in the “freezing bound” state is averaged out due to fast exchange rate

between these molecules in the NMR time-scale (at room temperature) and strong spin-spin

interactions. The detected NMR signals (NMR is a bulk detection method of atomic magnetic

properties) are averaged in space and time in the NMR timescale through all different positions

or sites. This makes interpretation of bound and free water from NMR data alone more complex

due to the fact that relaxation times of the individual molecules may be different at different

positions in the wood structure.

It can also be assumed that there is a continuous distribution of the relaxation times T2 in the

‘certain’ range of values, but yielding only the average value in the final analysis as stated above.

ppm20406080100120140160180

Figure 52 The carbon CPMAS spectrum of wood – sample 1BR.

ppm-1-012345678910111213

Figure 53 The proton MAS spectrum of wood – sample 1BR.

41

ppm-1-0123456789101112

Figure 54 The proton MAS spectrum of sample 1BR using spin echo at 1 ms.

ppm-1-0123456789101112

Figure 55 The proton MAS spectrum of sample 1BR using spin echo at 4ms.

Figure 56 The proton MAS spectra of sample 1BR using different spin-echo times,

from 0.4ms to 2.4ms.

42

Dimensional changes in wood

Wood is an anisotropic material, that is, its dimensions change differently in three dimensions:

tangentially, radially and longitudinally. Tangential dimensional change has the highest rate of

change due to parallel orientation of microfibrils along the axis of the cell wall. Radial change is

the second largest and longitudinal change is negligible for most practical applications. In

general, dimensional change is expressed as a percentage as a function of initial dimension and

ratio of moisture content over fibre saturation point. This simple model denotes that the change

of moisture content in drying below fibre saturation point is proportional to the variation in the

shape.

Dimensional changes in wood could be calculated using the following formula14

100**

FSP

CMCOD

SV

DC=

where DC is dimensional change due to change in moisture content (CMC), OD is original

dimension, SV is shrinkage value from green to oven dry moisture content, and FSP is fibre

saturation point. Assuming that FSP is around 28% and it does not change much between the

softwood samples the rate of distortion change, DC/SV, is proportional to the rate of moisture

change, CMC/FSP.

On the other hand there is also a direct relationship between the density of wood and shrinkage values14

. Species with higher density shrink more than those with lower density. There have been many studies aimed at stabilizing the cell wall (resin treatment and alike) so that shrinkage of wood can be controlled, however none of these methods has been put into practical use due to economical and technical considerations

14.

Water dynamics in wood

Results of measuring the relaxation time T1 ( NMR solid-state methods)

The relaxation time T1 of water was measured in dry samples with high field solid state NMR

method in order to observe any differences which may arise from the difference in treatment (run

16 no steaming versus run 17 with 3 hour steaming) or in restrained versus non-restrained boards

during drying.

0.00

100.00

200.00

300.00

400.00

500.00

600.00

700.00

800.00

2A,2B 6G,6H 2F,2G 6C,6D

Run16 Run17

Figure 57 Effect of steaming: T1

14

Source: http://www.agweb.okstate.edu, “Dimensions Changes in Wood”, S. Hiziroglu

43

0.00

100.00

200.00

300.00

400.00

500.00

600.00

700.00

800.00

2A,2F 6G,6C 2B,2G 6H,6D

unrestrained restrained

Figure 58 Effect of restraint: T1

A similar comparison is given on the T2 data collected at high field solid-state NMR which

isolate the water resonance from the organic protons.

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

2A,2B 6G,6H 2F,2G 6C,6D

Run16 Run17

Figure 59 Effect of steaming: T2

44

0.00

0.20

0.40

0.60

0.80

1.00

1.20

2A,2F 6G,6C 2B,2G 6H,6D

unrestrained restrained

Figure 60 Effect of restraint: T2

Discussion *(solid-state data):

T1 data of water resonance at 300 MHz (MAS NMR spectroscopy) exhibit some kind of trend

between the runs 16 and 17, one without steaming and other with steaming, at the end of the

drying cycle. After steaming, the T1 becomes shorter, even more so for the boards having a

longer initial T1. It seems that steaming enhanced the exchange between different types of bound

water making relaxation T1 shorter. The restrain on the other hand is making the similar

enhancement in exchange and shorten T1.

T2 data, collected at 300 MHz, presented here are given here for water resonance by using spin

echo decay (CPMG method). Changes in these T2’s don’t show any significant correlation as

function of steaming or restrain. There may be some shortening trend in T2 with the restrain but

the body of data is too small to make this observation certain. More data were collected by

Mouse that can be analysed further in order to identify the correlations to drying conditions:

steaming or restrain.

MOUSE relaxation data

Mouse relaxation data on slices 0 and 1 have been averaged into one set (see Table 4 below).

They reveal some relationship to the steaming and non-steaming drying regime as well as to the

restraint and non-restraint condition during drying.

45

Table 4 The average amplitude and T2 for slices 0 and 1 of samples (run16 and 17).

Samples Condition Comparison Amplitude T2(ms)

2AR-2BR R Steaming -/+ 4.90 ; 6.11 0.457 ; 0.547

12% 4.79 ; 5.24 0.452 ; 0.510

17% 6.58 ; 7.27 0.642 ; 0.680

2FR-2GR R Steaming -/+ 5.26 ; 5.19 0.345 ; 0.538

12% 5.98 ; 5.08 0.360 ; 0.478

17% 5.53 ; 6.63 0.578 ; 0.608

2AR-2FR R Restrained -/+ 4.90 ; 5.26 0.457 ; 0.345

12% 4.79 ; 5.98 0.452 ; 0.360

17% 6.58 ; 5.53 0.642 ; 0.578

2BR-2GR R Restrained -/+ 6.11 ; 5.19 0.547 ; 0.538

12% 5.24 ; 5.08 0.510 ; 0.478

17% 7.27 ; 6.63 0.680 ; 0.608

6GR-6HR R Steamed -/+ 3.77 ; 5.97 0.375 ; 0.508

12% 5.13 ; 5.95 0.412 ; 0.540

17% 6.13 ; 7.12 0.622 ; 0.720

6CR-6DR R Steamed -/+ 5.36 ; 4.68 0.330 ; 0.778

12% 5.19 ; 4.97 0.378 ; 0.635

17% 5.36 ; 7.28 0.648 ; 0.748

6GR-6CR R Restrained -/+ 3.76 ; 5.36 0.375 ; 0.330

12% 5.13 ; 5.19 0.412 ; 0.378

17% 6.13 ; 5.36 0.622 ; 0.648

6HR-6DR R Restrained -/+ 5.97 ; 4.68 0.508 ; 0.778

12% 5.95 ; 4.97 0.540 ; 0.635

17% 7.12 ; 7.28 0.720 ; 0.748

Discussion (MOUSE data):

The data from un-steamed, Run 16, versus steamed, Run 17 of the same board always gives the

longer T2 component for steamed samples. The expected higher amplitude for the steam samples

is not always detected as such, because there are other factors (structural) that influence the

amount of re-adsorbed moisture by steaming.

The data or non-restrained and restrained boards shows less correlation, but it still can be said

that on average, the relaxation time T2 is generally shorter for restrained board samples in

comparison to the same board non-restrained sample. However, on the other hand, the signal

amplitude shows no correlation to the changes between the restrained and non-restrained regime

indicating that other (structural) factors prevail in determining the total amount of bound water in

the samples.

Correlation between high field solid-state NMR data and low field Mouse data

Assuming that water in our dried wood samples is mainly bound water that plays a structural role

(non-freeze bound water) and small pores role (freeze bound water), it can be accepted that first

type of water will have a much shorter T2 than the other one due to the difference in the

molecular mobility. The measured relaxation time is therefore the average between these two as

defined by the following relationship:

fbnfT

pT

pT

+=222

1)1(

11

Steaming does increase the contribution of the second term, which results in the overall longer

T2. If a similar relationship is used for the T1, the steaming should increase the second part as

well, but the overall effect, as experimentally determined, is a shorter T1 after steaming. The

46

possible explanation for this discrepancy between the two relaxation times behaviour can be

found in the theory of the relaxation time and phase of the materials.

T1

T2

log (T1,2)

log ( c)o c = 1

Figure 61 Relaxation times T1 and T2 as a function of mobility correlation time c

It can be seen that the difference between the measured T1 and T2 values indicate already that we

are at the bottom of the T1 curve or even to the right side of it, where small changes in T2 (larger

correlation time tc) means larger changes in T1. Or in other words, the water correlation time is

longer than 10-8

s, indicating bound water.

47

Part 3 EXPERIMENTAL KILN TRIALS

Trials were conducted in an experimental kiln with Radiata Pine corewood to determine the

extent to which NMR could explain the differences in wood behaviour from different drying

schedules, particularly those identified in the detailed tests as showing equivalent stability, i.e.

using a longer kiln schedule with ramped-down temperature and no final steaming compared to a

standard high temperature schedule with steaming after drying. Boards were monitored for three

weeks after processing, with regular measurements of moisture content, shape and stiffness and

sampling for NMR measurements. These experimental kiln trials are described in Ensis Client

Report No. 1678.


Procedure

One pair of kiln runs was conducted:

Material

Radiata pine boards from typical resources were provided by Green Triangle Forest Products:

Approximately (120) “heart in” (HI) 100 x 40mm boards, 6.0m long, were provided, plastic

wrapped and trucked to Clayton. As these were from production HI material there was

considerable variation in board characteristics; many boards were partly sapwood, often at one

end.

Preparation

Boards were selected by grain pattern, near-pith or with pith included, and with uniform

grain pattern along the length.

(72) boards were cut to each produce (2) 2.8m long end-matched specimens.

Cross-sections were cut from each end and at the centre of each board, and moisture

content (MC) and basic density (BD) were determined by oven drying.

The 2.8m long specimens were end-coated and weighed.

Acoustic wave velocity (AWV) was measured on the green specimens.

The paired specimens were allocated alternately to (2) kiln loads to ensure equal numbers

of butt and top specimens in each stack.

Stack

6 boards wide; 12 boards high; full length in kiln

25mm thick stickers

2.8m long x 1.2m wide x 200mm thick concrete weight – equivalent to 400mm thick

weight (800kg/m3 stack top area)

top baffle to weight

Kiln runs

Conditions

As for detailed test runs 16 & 17. (Part 2)

48

Table 5 Drying conditions for Run 1 and Run 2 of the kiln trials

Drying Cooling Steaming Cooling

Run 1 140/90 for 4+ hours outside kiln 1 hour

4 hrs outside kiln with weight

Run 2 140/90 for 3 hours; ramp to 120/90 over 1 hour; 120/90 for 1 hours; 110/95 for 1 hour; total drying 6 hours

none none outside kiln

Monitoring

DBT and WBT in the kiln were monitored during drying; wood temperature near the core

of several boards was monitored in each run during drying, steaming and cooling. Boards

for temperature monitoring were selected from near the left, centre and right sides of the

stack, looking from the door.

Restraint

The stack weight was left on the stack overnight (at least 12 hours after drying).

Measurements after drying

Mass and AWV of 2.8m length specimens were measured.

All specimens were cut to 2.4m length and sections taken for MC determination; the

sections removed were from the end cut to separate the specimen from its pair.

Mass & AWV of the 2.4m length specimens were measured. Distortion was measured

over 1.2m gauge length for each half-length and the centre half-length; measurements

were combined to give total distortion.

Boards from each run were re-stacked with stickers.

Stability during storage

Conditions

The two stacks of 2.4m long boards were stored for 21 days with stickers, without

restraint in a well-ventilated building.

Monitoring

Temperature and humidity were logged during storage

Weekly measurements

Mass and distortion were measured. Average moisture content for the specimens was

calculated from the mass, assuming the average green MC was the average of the MC at

each end. Where the section MCs were different, the calculation was done assuming that

the kiln-dried MC was that of the dry section cut after drying.

Sample cores for MC distribution and NMR measurements were taken from 12 boards

from each run (the two middle layers of the test stack).

Dynamic stiffness of core samples – ultrasound along and across grain – were not

measured as equipment could not be acquired.

AWV were measured,

Stiffness on flat, 3-point bending

49


Kiln runs

The planned schedules were followed as detailed in Table 6. However, due to an error in

programming the kiln controller, the conditions were not logged for either Run 1 or Run 2. The

screen image at the end of Run 2 is reproduced in Figure 62.

Table 6 Kiln trial conditions and times

Drying Cooling Steaming Cooling Process time

Run 1 140/90 for 4+ hours outside kiln 1 hour

4 hrs outside kiln with weight

9 hours + cooling

Run 2 140/90 for 3 hours; ramp to

120/90 over 1 hour; 120/90 for 1 hours; 110/95 for 1 hour; total drying 6 hours

none none outside kiln 6 hours + cooling

Figure 62 Kiln controller screen for Run 2

Wood temperatures were logged for Run 1 from approximately halfway through drying (Figure

63) and for all of Run 2 (Figure 64).

50

Core wood temperature in 3 specimens during Kiln Trial 1

0

20

40

60

80

100

120

0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00

Elapsed Time, hours

Te

mp

era

ture

, C

Temp in board at left side of stack

Temp in board at centre of stack

Temp in board at right side of stack

Figure 63 Core temperatures of three specimens during drying, steaming and cooling – Run 1

Core wood temperature in 3 specimens during Kiln Trial 2

0

20

40

60

80

100

120

0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00

Elapsed Time, hours

Te

mp

era

ture

C

Temp in board at left side of stack

Temp in board at centre of stack

Temp in board at right side of stack

Figure 64 Core temperatures of three specimens during drying and cooling – Run 2

Environmental conditions

The conditions during the three weeks of monitoring are shown in Figure 65.

Environment in Factory

0

10

20

30

40

50

60

70

80

90

2-Sep-05 9-Sep-05 16-Sep-05 23-Sep-05

Tem

peratu

re, C

; R

H%

0

5

10

15

20

25

30

35

40

45

EM

C%

Temperature

RH%

EMC%

96 per. Mov. Avg. (EMC%)

A B C D

Figure 65 Environmental conditions for period of storage and monitoring

51

Moisture content

These runs followed quite closely the schedules used in the laboratory dryer tests. In each run

there were specimens from near sapwood boards with higher moisture content which skewed the

result. Specimens in Run 1 were slightly higher in MC than specimens in Run 2 (Figure 66).

Figure 66 and Figure 67 show the distribution of average moisture content and the change of average

moisture content during storage for each run. From Run 1 moisture content was higher than intended

and it reduced during storage to stage B and again to Stage D, as might be expected from the

environmental conditions (Figure 65) when starting with moist surfaces after steaming. Specimens in

Run 2 generally gained throughout storage, the initially drier surfaces taking up moisture.

The average moisture contents of the runs were significantly different throughout the period of

observation.

MC Distribution after drying - Run 1

0

10

20

30

40

50

60

5 10 15 20 25 More

MC% Category upper limit

No

. S

pe

cim

en

s Av. MC 14.2%

MC Distribution after drying - Run 2

0

10

20

30

40

50

60

5 10 15 20 25 More

MC% Category upper limit

No

. s

pe

cim

en

sAv. MC 12.8%

(a) Run 1 (b) Run 2

Figure 66 Moisture content of sections cut from all specimens after drying

Average MC of Specimens during storage

11.0

11.5

12.0

12.5

13.0

13.5

14.0

14.5

15.0

15.5

A B C D

Stage, weekly intervals

MC

%

Run 1

Run 2

#

# ##

$$

$ $

Figure 67 Average moisture content of all specimens in each run, weekly during storage. Points

which do not share the same symbol are significantly different (Scheffe Test).

The moisture content of the specimens from which NMR cores and MC cores were taken is shown in

Figure 68. Most specimens initially gained moisture, particularly those from Run 2 which were not

steamed after drying. Core MC is from 19mm cores cut adjacent to the 35mm cores cut for NMR, and

cut at the same time. The moisture content of cores was quite variable; some of the variation may be

52

from varying degrees of wetness in the centre of specimens. Some variation may be along the boards;

this variation may influence interpretation of the NMR measurements over storage time.

The paired specimens are presented here in a set labelled Set A. This has five pairs which were

well matched in initial moisture content and grain pattern.

(a) Av. MC of specimens

from mass

Average MC of Specimens during storage - Set A

8.0

9.0

10.0

11.0

12.0

13.0

14.0

15.0

16.0

2/09/2005

A

9/09/2005

B

15/09/2005

C

23/09/2005

D

Date; Stage

Av. M

C %

31-2

36-1

37-2

39-2

42-1

31-1

36-2

37-1

39-1

42-2

(b) Av. MC of cores

Av. MC of cores taken during storage - Set A

8.0

9.0

10.0

11.0

12.0

13.0

14.0

15.0

16.0

2/09/2005

A

9/09/2005

B

15/09/2005

C

23/09/2005

DDate; Stage

Av.

MC

%

31-2

36-1

37-2

39-2

42-1

31-1

36-2

37-1

39-1

42-2

(c) Av. Surface MC of cores

Surf. MC of cores taken during storage - Set A

7.0

8.0

9.0

10.0

11.0

12.0

13.0

14.0

15.0

2/09/2005

A

9/09/2005

B

15/09/2005

C

23/09/2005

D

Date; Stage

Av. M

C %

31-2

36-1

37-2

39-2

42-1

31-1

36-2

37-1

39-1

42-2

Figure 68 Average Moisture Content of a set of five paired specimens, estimated from specimen

mass and MC of cores taken from specimens.

Solid symbols/lines = Specimens from Run 1; Open symbols/dotted lines = Specimens from Run 2.

53

Distortion

Figure 69 shows the change in average twist, spring and bow for all specimens of each run

during the storage period. Run 2 had more twist than Run 1 but the behaviour during the storage

period is similar. Spring and Bow behaviour after the initial period is also similar.

(a) Twist over 2.4m length

Av. Twist of specimens during storage

-7.5

-7.0

-6.5

-6.0

-5.5

-5.0

-4.5

-4.0

-3.5

-3.0

A B C D


Tw

ist

ov

er 2

.4m

, d

eg

re

es

Run 1

Run 2

#

$$

$

&

&,%

%%

(b) Spring at centre of 2.4m length

Av. Spring of specimens during storage

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

A B C D


Sp

rin

g a

t cen

tre o

f 2.4

m, m

m

Run 1

Run 2

#

##

#

#

##

#

(c) Bow at centre of 2.4m length

Av. Bow of specimens during storage

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

A B C D


Bo

w a

t cen

tre o

f 2.4

m, m

m

Run 1

Run 2

#

%,@%,@

[]

#,@

$

$

#,%

Figure 69 Average distortion of all specimens in each run during storage.

Points which do not share the same symbol are significantly different (Scheffe Test).

54

The distortion of 10 sets of paired specimens is shown in Figure 70. After the initial period when

some specimens exchanged moisture at the surface there was generally little change in all forms

of distortion.

(a) Twist over 2.4m length

Twist during storage - Set A

-12.0

-11.0

-10.0

-9.0

-8.0

-7.0

-6.0

-5.0

-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

2/09/2005

A

9/09/2005

B

15/09/2005

C

23/09/2005

D

Date

Tw

ist,

de

gre

es

ov

er 2

.4m

31-2

36-1

37-2

39-2

42-1

31-1

36-2

37-1

39-1

42-2

(b) Spring at centre of 2.4m length

Spring during storage - Set A

-6.0

-5.0

-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

2/09/2005

A

9/09/2005

B

15/09/2005

C

23/09/2005

D

Date

Sp

rin

g,

mm

, a

t c

en

tre

31-2

36-1

37-2

39-2

42-1

31-1

36-2

37-1

39-1

42-2

(c) Bow at centre of 2.4m length

Bow during storage - Set A

-6.0

-5.0

-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

2/09/2005

A

9/09/2005

B

15/09/2005

C

23/09/2005

D

Date

Bo

w,

mm

, a

t c

en

tre

31-2

36-1

37-2

39-2

42-1

31-1

36-2

37-1

39-1

42-2

Figure 70 Twist, Spring and Bow of a set of paired specimens measured at weekly interval

during storage.

Solid symbols/lines = Specimens from Run 1; Open symbols/dotted lines = Specimens from Run 2 Sign of spring has no intrinsic meaning; +ve bow is concave on the inner (near pith) face.

55

Stiffness

Figure 71 shows average stiffness for all specimens in each run calculated from two

measurement methods. For each run stiffness measured by bending on flat appears to increase

during storage; this is less evident for that from acoustic measurements. With the bending tests

which were done without rotating specimen supports, after the first set of measurements a wedge

was used to eliminate the point load from twisted specimens at the non-rotating loading points;

this may explain part of the increase from B to C. Figure 72 shows stiffness for selected pairs of

specimens.

Av. Stiffness from of specimens during storage - Acoustic Meast

8.0E+09

8.2E+09

8.4E+09

8.6E+09

8.8E+09

9.0E+09

9.2E+09

9.4E+09

A B C D


E

Run 1

Run 2

#,$#

$

#,$

&#,&

#,$

#,$

Av. Stiffness of specimens during storage - 3-pt bending flat

6.0E+09

7.0E+09

8.0E+09

9.0E+09

1.0E+10

1.1E+10

1.2E+10

B C D


E

Run 1

Run 2

#

$ $

#

$ $

(a) Stiffness (acoustic tests) (b) Stiffness (3-point bending on flat

Figure 71 Average Stiffness calculated from (a) acoustic tests and from (b) bending on flat for all

specimens of each run.

Points which do not share the same symbol are significantly different (Scheffe Test).

Stiffness during storage - acoustic - Set A

4.0E+09

6.0E+09

8.0E+09

1.0E+10

1.2E+10

1.4E+10

1.6E+10

1.8E+10

2/09/2005

A

9/09/2005

B

15/09/2005

C

23/09/2005

D

Date

Sti

ffn

ess, E

31-2

36-1

37-2

39-2

42-1

31-1

36-2

37-1

39-1

42-2

Stiffness during storage - 3-point bending flat - Set A

4.0E+09

6.0E+09

8.0E+09

1.0E+10

1.2E+10

1.4E+10

1.6E+10

1.8E+10

9/09/2005

B

15/09/2005

C

23/09/2005

D

Date

Sti

ffn

ess, E

31-2

36-1

37-2

39-2

42-1

31-1

36-2

37-1

39-1

42-2

(a) (b)

Figure 72 Stiffness calculated from (a) acoustic tests and from (b) bending on flat.

Set A has the five best matched pairs. Solid symbols/lines = Specimens from Run 1; Open symbols/dotted lines = Specimens from Run 2.

56

NMR measurements

Figure 73 Solid echo signals for six of the dried specimens of Run 1.

Plots of the solid echo signals for the initial measurements of cores from six specimens of Run 1

are shown in Figure 73 and for matched specimens of Run 2 in Figure 74.

The solid echo signal is the response from all protons in the sample at the frequency. All

different protons, moisture and organic mobile components, contribute to the signal resulting in

the clearly separate contributions to the free induction decay signal (FID): the first is the solid

part with decay generally described by the Gaussian decay function; the second is the semi-

mobile part (from moisture and small organic molecules – like resins) with longer relaxation

times and with decay described by a common Lorentzian function. Therefore the FID signal

from the solid-echo sequence analysed by the combination of Gaussian and Lorentzian functions

gives the characteristic parameters for solid matrix and hydrolysed semi-mobile phases. The

latter is a combination of “bound” water and softened organic matrix where the protons quickly

exchange the spin magnetization between different molecules.

57

Figure 74 Solid echo signals for six of the dried specimens of Run 2.

As a result of these interactions only one T2 value is detectable as an average of these different

sites. Increasing amounts of water soften more organic molecules and the overall dynamic of this

phase increases (longer T2) and as well as the overall signal intensity. On the other hand the

redistribution of moisture in the sample also enhances the magnetization exchange between the

molecules resulting in a sharper (longer T2) and taller (increased intensity) resonance band. In

the proper equilibrium one can expect to have a proportional increase in amplitude and T2 of

longer component (Lorentzian) at different, increasing moisture content. When moisture

redistribution is not in equilibrium the data can be expected to deviate from this proportionality.

The deviation or scattering of the data amplitude versus T2 therefore can reflect the stage of

moisture distribution as well as its changes with different scattering at different times after the

drying process.

Parameters of NMR measurements of cores taken from the specimens are presented in Table 7.

58

Table 7 NMR Solid Echo Results for Cores on Minispec 10 MHz

Run 1A Run 2A

BoardAmp

(Gauss)% (G/L)

T2

(Gauss)

T2

(Loren)

Amp

(Loren)Board

Amp

(Gauss)% (G/L)

T2

(Gauss)

T2

(Loren)

Amp

(Loren)

31-2 643.1 76.24 0.0136 0.2208 200.5 31-1 816.4 75.45 0.0133 0.2214 265.7

32-1 552.7 59.81 0.0136 0.3115 371.4 32-2 625.2 60.47 0.0139 0.3266 408.7

33-2 612.2 71.68 0.0135 0.2661 241.9 33-1 695.4 74.73 0.0139 0.3150 235.2

34-1 653.1 63.10 0.0139 0.3709 381.9 34-2 655.5 64.32 0.0137 0.3461 363.6

35-2 761.6 73.06 0.0139 0.2607 280.9 35-1 793.0 75.50 0.0136 0.2518 257.4

36-1 559.1 67.98 0.0135 0.2705 263.4 36-2 688.9 77.21 0.0137 0.2244 203.3

37-2 608.4 78.76 0.0133 0.1973 164.1 37-1 755.9 72.93 0.0136 0.2887 280.6

38-1 626.3 66.11 0.0135 0.3551 321.1 38-2 661.5 63.41 0.0142 0.3908 381.7

39-2 870.6 75.42 0.0141 0.3396 283.8 39-1 944.0 77.62 0.0138 0.3097 272.1

40-1 599.3 50.18 0.0134 0.3004 595.0 40-2 598.2 65.68 0.0137 0.2694 312.6

41-2 721.1 56.05 0.0140 0.3878 565.5 41-1 666.8 39.30 0.0144 0.6348 1029.8

42-1 672.7 75.50 0.0134 0.2113 218.3 42-2 816.1 66.74 0.0140 0.3338 406.8

Run 1B Run 2B

BoardAmp

(Gauss)% (G/L)

T2

(Gauss)

T2

(Loren)

Amp

(Lor)Board

Amp

(Gauss)% (G/L)

T2

(Gauss)

T2

(Loren)

Amp

(Lor)

31-2 701.3 71.98 0.0138 0.2963 273.0 31-1 723.5 55.04 0.0138 0.4331 591.0

32-1 636.5 54.74 0.0139 0.3950 526.3 32-2 648.1 59.56 0.0134 0.3443 440.0

33-2 706.4 66.79 0.0137 0.3368 351.3 33-1 721.8 77.11 0.0137 0.2616 214.3

34-1 640.5 72.24 0.0139 0.2976 246.1 34-2 612.9 63.67 0.0138 0.3359 349.7

35-2 720.2 76.69 0.0136 0.2305 218.8 35-1 809.2 67.02 0.0138 0.2980 398.2

36-1 738.5 69.59 0.0139 0.3272 322.7 36-2 651.4 77.26 0.0138 0.1959 191.7

37-2 752.5 74.15 0.0138 0.3158 262.3 37-1 742.0 74.40 0.0139 0.2602 255.3

38-1 671.0 70.14 0.0135 0.3025 285.6 38-2 682.8 73.39 0.0135 0.2735 247.6

39-2 919.5 74.04 0.0137 0.3327 322.3 39-1 904.7 76.47 0.0139 0.3150 278.4

40-1 613.5 54.99 0.0137 0.3481 502.1 40-2 632.8 69.71 0.0139 0.2274 275.0

41-2 749.0 65.08 0.0138 0.3265 401.8 41-1 689.8 45.51 0.0140 0.4496 826.0

42-1 827.7 70.37 0.0139 0.3076 348.5 42-2 753.7 78.25 0.0136 0.2246 209.5

Run 1C Run 2C

BoardAmp

(Gauss)% (G/L)

T2

(Gauss)

T2

(Loren)

Amp

(Lor)Board

Amp

(Gauss)% (G/L)

T2

(Gauss)

T2

(Loren)

Amp

(Lor)

31-2 704.7 62.51 0.0137 0.2796 422.7 31-1 729.5 63.27 0.0136 0.2684 423.6

32-1 641.5 53.84 0.0137 0.3627 549.9 32-2 642.2 60.71 0.0136 0.3393 415.6

33-2 748.3 72.86 0.0137 0.2934 278.7 33-1 724.9 79.53 0.0135 0.2097 186.6

34-1 638.5 72.27 0.0134 0.2538 245.0 34-2 619.8 65.68 0.0136 0.2840 323.8

35-2 729.7 73.70 0.0136 0.2487 260.4 35-1 799.9 76.46 0.0135 0.2174 246.2

36-1 693.8 68.84 0.0135 0.2592 314.0 36-2 656.1 72.61 0.0137 0.2361 247.5

37-2 770.5 76.48 0.0137 0.2464 236.9 37-1 601.8 76.57 0.0133 0.2107 184.2

38-1 704.9 64.75 0.0136 0.3427 383.8 38-2 687.0 69.11 0.0134 0.2786 307.0

39-2 915.1 77.01 0.0135 0.2461 273.2 39-1 867.8 78.06 0.0133 0.2475 243.9

40-1 626.7 63.98 0.0137 0.2484 352.8 40-2 649.0 71.02 0.0138 0.2406 264.9

41-2 665.1 54.56 0.0138 0.3932 554.0 41-1 687.9 43.37 0.0138 0.4829 898.3

42-1 806.7 65.84 0.0142 0.3428 418.5 42-2 734.1 73.00 0.0134 0.2488 271.4

Run 1D Run 2D

BoardAmp

(Gauss)% (G/L)

T2

(Gauss)

T2

(Loren)

Amp

(Lor)Board

Amp

(Gauss)% (G/L)

T2

(Gauss)

T2

(Loren)

Amp

(Lor)

31-2 585.1 76.27 0.0138 0.2194 182.0 31-1 721.8 56.27 0.0137 0.3838 561.0

32-1 617.8 57.22 0.0137 0.3482 462.0 32-2 647.2 48.63 0.0139 0.4542 683.8

33-2 729.2 73.46 0.0135 0.2675 263.5 33-1 727.7 79.88 0.0137 0.2413 183.3

34-1 625.3 72.56 0.0136 0.2381 236.5 34-2 638.4 71.64 0.0137 0.2589 252.7

35-2 697.5 73.65 0.0137 0.2676 249.5 35-1 804.1 75.83 0.0136 0.2387 256.3

36-1 678.3 76.48 0.0136 0.2131 208.5 36-2 650.3 75.21 0.0138 0.2265 214.4

37-2 673.8 77.28 0.0134 0.2043 198.1 37-1 733.9 71.82 0.0138 0.3108 288.0

38-1 658.5 71.11 0.0134 0.2713 267.6 38-2 622.0 59.78 0.0133 0.3369 418.5

39-2 847.5 78.04 0.0137 0.2637 238.5 39-1 892.2 78.24 0.0137 0.2803 248.2

40-1 652.5 64.44 0.0139 0.2822 360.1 40-2 610.0 72.75 0.0141 0.2087 228.5

41-2 669.5 56.22 0.0140 0.3918 521.2 41-1 682.7 42.28 0.0139 0.4555 931.8

42-1 776.7 68.88 0.0137 0.2688 350.9 42-2 799.9 78.76 0.0137 0.2576 206.9

23/9/2005 23/9/2005

16/9/2005 16/9/2005

2/09/2005

9/09/2005

2/09/2005

9/09/2005

59

Gaussian parameters

Gaussian parameters (Figure 75) relate to the solid wood matrix. The variation of amplitude and T2 seen in Figure 75 can not be taken to be meaningful as it is of the same order as the error in the signal.

T2 Gaussian during storage - Set A

0.0128

0.013

0.0132

0.0134

0.0136

0.0138

0.014

0.0142

0.0144

�� 2/09/2005

A

�� 9/09/2005

B

�� 16/09/2005

C

�� 23/09/2005

D

Date; Stage

31-2

36-1

37-2

39-2

42-1

31-1

36-2

37-1

39-1

42-2

Amplitude Gaussian during storage - Set A

0

100

200

300

400

500

600

700

800

900

1000

�� 2/09/2005

A

�� 9/09/2005

B

�� 16/09/2005

C

�� 23/09/2005

D

Date; Stage

31-2

36-1

37-2

39-2

42-1

31-1

36-2

37-1

39-1

42-2

(a) Amplitude Gaussian (b) T2 Gaussian

Figure 75 Gaussian parameters of NMR measurements of cores taken during storage.


Lorentzian parameters

Amplitude Lorentzian during storage - Set A

0

100

200

300

400

500

600

700

�� 2/09/2005

A

�� 9/09/2005

B

�� 16/09/2005

C

�� 23/09/2005

D

Date

31-2

36-1

37-2

39-2

42-1

31-1

36-2

37-1

39-1

42-2

T2 Lorentzian during storage - Set A

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

�� 2/09/2005

A

�� 9/09/2005

B

�� 16/09/2005

C

�� 23/09/2005

DDate

31-2

36-1

37-2

39-2

42-1

31-1

36-2

37-1

39-1

42-2

(a) Amplitude Lorentzian (b) T2 Lorentzian

Figure 76 Lorentzian parameters of NMR measurements of cores taken during storage.


Figure 76 shows the Lorentzian parameters for the cores taken from specimens at weekly stages

during storage. Amplitude Lorentzian is most strongly influenced by moisture content; T2

Lorentzian is an indicator of moisture mobility.

The peaks of Amplitude generally seem to correspond with high core MC (Figure 68).

60

Figure 77 and Figure 78 show the Amplitude Lorentzian for cores taken from specimens at

stages during storage plotted against the average moisture content of matching smaller cores

taken at the same time, for Run 1 and Run 2 respectively. It can be seen in these figures that

Amplitude Lorentzian is generally linearly related to moisture content. Data from two poorly

matched pairs of specimens with higher moisture content have been omitted as the NMR

analysis was “tuned” to moisture content below about 15%.

Amplitude Lorentzian v MC - Run 1

100

200

300

400

500

600

700

8 9 10 11 12 13 14 15 16

Core Av. MC%

Am

plitu

de L

oren

tzia

n

Av. Core MC A

Av. Core MC B

Av. Core MC C

Av. Core MC D

Fitted to all

Figure 77 Amplitude Lorentzian plotted against Av. MC of matching cores – Run 1.

Amplitude Lorentzian v MC - Run 2

100

200

300

400

500

600

700

8 9 10 11 12 13 14 15 16

Core Av. MC%

Am

plitu

de L

oren

tzia

n

Av. Core MC A

Av. Core MC B

Av. Core MC C

Av. Core MC D

Fitted to all

Figure 78 Amplitude Lorentzian plotted against Av. MC of matching cores – Run 2.

Figure 79 and Figure 80 show T2 Lorentzian for cores taken from specimens (set A of previous

figures) at stages during storage plotted against the average moisture content of matching smaller

cores taken at the same time, for Run 1 and Run 2 respectively. T2 Lorentzian indicates the

mobility of water molecules, as well as other organic molecules associated with water. Water

therefore provides the major part of the signal. For each set of points the steepness of the fitted

line can be taken to indicate increasing water mobility. The fitted lines for specimens of Run 1

(Figure 79), which was steamed after drying are initially steep (Set A; dark blue line) then

61

recline to that at C (orange line) then become slightly steeper at D (plum line). This may indicate

that water in the wood, particularly that added to the surface during steaming, becomes more

strongly “bound” during storage, and during the period C to D the water added to the surface

from the atmosphere is likely to be initially more mobile.

T2 Lorentzian v MC - Run 1

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

8 9 10 11 12 13 14 15 16

Core Av. MC%

T2

Lo

re

ntz

ian

Av. Core MC A

Av. Core MC B

Av. Core MC C

Av. Core MC D

Fitted to all

Linear (Av. Core MC A)

Linear (Av. Core MC B)

Linear (Av. Core MC C)

Linear (Av. Core MC D)

Figure 79 T2 Lorentzian plotted against Av. MC of matching cores – Run 1.

The fitted lines for specimens of Run 2 (Figure 80) which was not steamed after drying follow

quite a different progression; the blue line for state A is shallow, indicating low water mobility

and the lines for states B and D are progressively steeper. State C seems out of step with this

progression. For these specimens the surface moisture content was low at A and the specimens

gained moisture during storage (Figure 68).

T2 Lorentzian v MC - Run 2

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

8 9 10 11 12 13 14 15 16

Core Av. MC%

T2

Lo

re

ntz

ian

Av. Core MC A

Av. Core MC B

Av. Core MC C

Av. Core MC D

Fitted to all

Linear (Av. Core MC A)

Linear (Av. Core MC B)

Linear (Av. Core MC C)

Linear (Av. Core MC D)

Figure 80 T2 Lorentzian plotted against Av. MC of matching cores – Run 2.

These explanations for the observed differences are only the best attempt to interpret these data;

they may not be completely consistent, because the moisture content of the cores seems to show

more variation, perhaps along the (about 300mm) length of the specimens from which successive

cores were taken at each weekly stage (Figure 68 (b)).

62

PROJECT RESULTS AND DISCUSSION

1. Bonding states of water during processing and stabilization

Non-freezing water, Wnf, (structural water or tightly bound to cell walls) and freezing bound

water, Wfb, (water associated with walls and smaller reservoirs) can not be differentiated at

room temperature through NMR spectroscopy detection due to the fast exchange between

them that gives rise to only one average parameter (like chemical shift and relaxation time) in

the NMR signal.

Additional moisture taken in or lost by the wood in conditioning rooms or during storage is a

relatively quick process, in days, and it is not free water but becomes a part of the total bound

water, Wnf + Wfb. This bound water has, as expected, higher NMR signal amplitude when

external humidity is higher but it also has a longer T2 component. Assuming that a fast

exchange mechanism is in place between Wnf and Wfb one can say that the majority of added

moisture becomes firstly Wfb type moisture. This is expected to have a longer T2 (more

mobile) and therefore moves the averaged value for all bound water to a longer T2 at higher

overall moisture content. This is true only when the total moisture content is below the FSP

(around 28%).

The further separation and evaluation of the major NMR parameters (relaxation mechanisms)

has produced an improved physical description of the moisture states in softwood and thus

contribute to the development of a comprehensive softwood drying model incorporating

moisture state as well as location.

The solid echo signal is the response from all protons in the sample at the frequency. All

different protons, moisture and organic mobile components, contribute to the signal resulting

in the clearly separate contributions to the free induction decay signal (FID): the first is the

solid part with decay generally described by the Gaussian decay function; the second is the

semi-mobile part (from moisture and small organic molecules – like resins) with longer

relaxation times and with decay described by a common Lorentzian function. Therefore the

FID signal from the solid-echo sequence analysed by the combination of Gaussian and

Lorentzian functions gives the characteristic parameters for solid matrix and hydrolysed

semi-mobile phases. The latter is a combination of “bound” water and softened organic

matrix where the protons quickly exchange the spin magnetization between different

molecules.

As a result of these interactions only one T2 value is detectable as an average of these

different sites. Increasing amounts of water soften more organic molecules and the overall

dynamic of this phase increases (longer T2) and as well as the overall signal intensity. On the

other hand the redistribution of moisture in the sample also enhances the magnetization

exchange between the molecules resulting in a sharper (longer T2) and taller (increased

intensity) resonance band. In the proper equilibrium one can expect to have a proportional

increase in amplitude and T2 of longer component (Lorentzian) at different, increasing

moisture content. When moisture redistribution is not in equilibrium the data can be expected

to deviate from this proportionality. The deviation or scattering of the data amplitude versus

T2 therefore can reflect the stage of moisture distribution as well as its changes with different

average mobility at different times after the drying process.

2. Bonding states of water, internal stresses and distortion

The variation in structural wood distortion and variations of moisture content seems to be

inconsistent with the expected correlation between moisture and shape change – indicating

that the whole measured moisture is determined by other factors as well. Only the cell wall

63

moisture content, which is only one part of the measured total moisture, is commonly

thought to relate to the structural changes.

The variation between the end of the drying cycle and the later conditioning is not all related

to the cell walls moisture (Wnf) and therefore the moisture content corresponding to the shape

change could not be clearly established from the current data. In order to achieve this

correlation further investigation is needed to find a novel NMR method to quantitatively

identify these two types of bound water. The low field NMR can be used finally after the

high-field solid-state methods prove a satisfactory differentiation and quantification of the

two types of bound water.

Other components of wood may be involved in wood shape changes independent of

moisture. This requires further technique development with solid-state high field NMR

measurements.

3. High temperature kiln drying schedule modifications and/or

treatments that improve stability

A HT kiln schedule modified with ramped reductions in temperature with increasing

humidity instead of steam reconditioning, produced similarly straight and stable timber to the

conventional HT schedule with stream reconditioning, over the three weeks period of

monitoring. The project did not incorporate a longer period.

4. Stabilization treatments to reduce the time to a stable state

No treatments for reducing the time to stable products have been identified.

Solid-state NMR investigation indicates that the process of steaming after drying results in

increased water mobility; the tests of specimen stability during humidity cycling only

showed indications of this. To the extent that moisture changes are related to wood shape

stability it may be best to minimise final steaming. This seems to be one possible direction

for further work and should be investigated in experimental trials.

5. Differences between Heart-in and Free of Heart material

A clear difference in the ‘FID’ signal of green wood was also detected for different wide

faces of the board, when one face of the board consists mainly of sapwood as opposed to

heartwood (Appendix 1).

Knots and bluestain are also distinguishable by analysis of the FID signal.

6. Modification to current commercial practices to minimize kiln

drying time, steaming time and storage periods to produce stable

dried softwood timber

A HT kiln schedule modified with later reductions in temperature and higher humidity and

no steam reconditioning, produced similarly stable timber to the conventional HT schedule

and stream reconditioning. Although the drying time was increased, processing time was the

same. The benefit will need to be clearly established for this to be adopted, as kiln

productivity would be reduced unless initial drying temperatures were increased.

This project has not identified a clear link between storage time and product stability.

64

ACKNOWLEDGEMENTS

This research was undertaken with assistance from the Forests and Wood Products Research and

Development Corporation (www.fwprdc.org.au) which is funded by industry and the Australian

Government.

Timber for experiments was kindly provided by Weyerhaeuser Australia through Green Triangle

Forest Products, Hyne Timber and Wespine Industries. The support and advice of Chris Lafferty

(FWPRDC), Tony Haslett (formerly with Weyerhaeuser Australia, now with Ensis), Stephen

Bolden (formerly with Hyne Timber) and Richard Schaffner (Wespine) is gratefully

acknowledged.

DISCLAIMER

The opinions provided in this Report have been provided in good faith and on the basis that

every endeavour has been made to be accurate and not misleading and to exercise reasonable

care, skill and judgment in providing such opinions. However, CSIRO as project manager, and

the parties to the joint venture known as ensis which carried out the research ('ensis') (CSIRO

and Forest Research NZ) do not guarantee or warrant the accuracy, reliability, completeness or

currency of the information in this report unless contrary to law. Neither ensis nor any of its

staff, contractors, agents or other persons acting on its behalf or under its control accept any

responsibility or liability in respect of any opinion provided in this Report by ensis or any person

acting in reliance on the information in it.

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