Faculty of Resource Science and Technology

USING LINEAR REGRESSION ANALYSIS ON SEVERAL WOOD

SPECIES AS A TOOL FOR DETERMINING WOOD PROPERTIES

INFLUENCING DECAY RESISTANCE VARIATIONS IN WOOD

Jessica Mary Emily anak Jem

Master of Science

(Wood Science)

2014

USING LINEAR REGRESSION ANALYSIS ON SEVERAL WOOD

SPECIES AS A TOOL FOR DETERMINING WOOD PROPERTIES

INFLUENCING DECAY RESISTANCE VARIATIONS IN WOOD

JESSICA MARY EMILY ANAK JEM

A thesis submitted

in fulfilment of the requirements for the degree of Master of Science

Faculty of Resource Science and Technology

UNIVERSITI MALAYSIA SARAWAK

2014

i

ACKNOWLEDGEMENT

My sincere appreciation to Assoc. Prof. Dr. Andrew Wong Han Hoy for his guidance,

assistance and supervision throughout this project and the preparation of this thesis. Thank you

very much for giving me the opportunity to undertake this research. My sincere thanks also

goes to the staffs of Timber Research and Technical Training Centre (TRTTC, Kuching)

especially Mr. Lai Jeow Kok and Mr. John Sammy for their help and assistance in providing

several wood samples for this research, Mr. Yang Min Chin and Mr. Voon Sin Lee for their

kind permission in allowing the use of laboratory and microscopy equipments.

I am also grateful to the following:

The scholarship received from the Ministry of Science, Technology and Innovation

(MOSTI) for providing National Science Fellowship (NSF) is gratefully acknowledged

Universiti Malaysia Sarawak (UNIMAS) especially to Centre of Graduate Studies

(CGS) and Faculty of Resource Science and Technology (FRST)

To the laboratory assistants/ technicians of Faculty of Resource Science and

Technology for their kind assistance

To all of my dearest friends and lab- mates for their support and kind help throughout

this research

To my family members especially my beloved husband and parents for their moral

support and encouragement throughout my study

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DECLARATION

I hereby state that this thesis is based on my original work except for quotations and citations

which have been duly acknowledged. I also declare that this thesis has not been previously or

concurrently submitted for any degree of qualification to any other university or institution of

higher learning.

_______________________________

(JESSICA MARY EMILY ANAK JEM)

STUDENT NUMBER: 09021487

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DEDICATION

My dedication goes to my dearest family members especially beloved husband, my parents,

brother and sister for their supports and inspirations given in completing this thesis

successfully.

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TABLE OF CONTENT

PAGE

TITLE PAGE

ACKNOWLEDGEMENT i

DECLARATION ii

DEDICATION iii

TABLE OF CONTENTS iv

ABSTRACT vii

ABSTRAK ix

LIST OF TABLES xi

LIST OF FIGURES xiv

CHAPTER 1 - INTRODUCTION

1.0 General Introduction and Research Background

1.1 Objectives

1

5

CHAPTER 2 – LITERATURE REVIEW

2.1 Variation in Natural Durability of Wood

2.1.1 Wood decay fungi

2.1.2 Natural durability and decay resistance class

2.2 Wood density and variation in wood density

2.3 Variation in wood extractives content in heartwood

2.3.1 Lignin and polysaccharides

2.3.2 Decay resistance and extractives content relationship within a tree

2.4 Anatomical properties

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CHAPTER 3 - MATERIALS AND METHODS

3.1 Study locations

3.2 Research materials

3.2.1 List of timber species tested

3.3 Decay test

3.3.1 Test fungi

3.3.2 Seeking best laboratory decay testing procedures

3.3.3 Decay test

3.4 Wood Extractives

3.4.1 Preparation of wood meal

3.4.2 Methanol extractives content determination

3.4.3 Hot water extractives content

3.4.4 Cold water extractive content

3.4.5 Measurement of pH of hot water and cold water extracts

3.5 Basic density determination

3.6 Wood structural features

3.6.4 Fiber morphology

3.6.5 Other anatomical analyses examined by light microscopy

3.7 Statistical analysis

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CHAPTER 4- RESULTS

4.1 Decay resistance of timber species

4.1.1 Preliminary decay test

4.1.2 Decay rate of timber species tested by decay procedures of ASTM D

2017

4.2 Determination of wood extractives content

4.2.1 Methanol extractives content

4.2.2 Hot water extractives content

4.2.3 Cold water extractives content

4.3 Wood density determination

4.4 pH analysis of hot water and cold water extractives content

4.5 Anatomy of the wood

4.5.1 Fiber or tracheid length

4.5.2 Fiber or tracheid diameter

4.5.3 Fiber or tracheid lumen diameter

4.5.4 Fiber or tracheid wall thickness

4.5.5 Runkel Ratio

4.5.6 Vessel diameter (Tangential and Radial)

4.5.7 Vessel density (number of vessels per mm2)

4.5.8 Rays proportions

4.6 Correlation of decay resistance with wood properties

4.7 Regression analysis of wood properties

4.7.1 Multiple linear regression analysis between wood properties

4.8 Decay resistance classification

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CHAPTER 5 – DISCUSSION

5.1 Interspecies decay resistance variations

5.2 Extractives

5.3 Density

5.4 Acidity or wood pH

5.5 Fiber and other wood anatomy aspects

5.5.1 Fiber or tracheid length and diameter, fiber or tracheid lumen diameter, fiber

or tracheid wall thickness and Runkel ratio

5.5.2 Vessels and rays properties

5.6 Correlation of decay resistance with wood properties in heartwood

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CHAPTER 6 – CONCLUSION AND RECOMMENDATIONS

6.1 Conclusion

6.2 Recommendation

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118

REFERENCES

APPENDIXES

119

139

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Using Linear Regression Analysis on Several Wood Species as a Tool for Determining Wood

Properties Influencing Decay Resistance Variations in Wood

ABSTRACT

Several commercial timber species contributed in our economic development by

supplying the world market mainly with logs as well as sawn timber and plywood. Since

timber is a popular and useful material, it is important that enthusiasts and professionals be

able to distinguish the wood quality of one species from another. Relationship between various

wood properties namely decay resistance, methanol extractives content, wood density, hot

water solubility, cold water solubility, pH of water extractives, fiber morphology as well as

several other microscopic aspects of the combination of 36 timber species of Malaysian and

temperate wood species were investigated. This research aims to determine those wood

properties that perceivably govern decay resistance variations of numerous timbers species in

order to predict decay resistance profile of commercial and potential timber species by using

linear regression analysis. Laboratory test procedure according to ASTM D 2017 is chosen in

this research by utilizing particular species of white rot (P. sanguineus), brown rot (G.

trabeum) and soft rot decay test (C. globosum for unsterile soil burial test). A number of wood

properties studied (extractives contents and anatomical features) are important factors which

contribute to the decay resistance of wood species as differences in natural decay resistance of

timber could be accounted for by changes in the extractives and fiber anatomy aspects. There

were high percentages of mass loss caused by three decay fungi of P. sanguineus (43.9%), G.

trabeum (38.2%) and C. globosum (50.2%) to rubberwood, Hevea brasiliensis a non- durable

species. Conversely, belian (Eusiderozylon zwageri) a durable timber species recorded

negligible decay heartwood with mean mass loss of only 0.7% when exposed to P.

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sanguineus. Mass loss by G. trabeum was the lowest when tested to senumpul (Hydnocarpus

sp.) and selangan batu kuning (Shorea flava) both 0.4% mass loss whereas bindang (Agathis

borneensis) yielded the lowest percentage weight loss of 0.7% due to the attack of C.

globosum. The timber species were then classified according to the 4 natural durability classes

of ASTM D 2017 and EN 350 where timber species were categorized in Class 1 (resistant) to

Class 4 (resistant to non resistant). The variation of wood properties were summarized as

follows: (i) methanol extractives content (0.7% to 36.5%), (ii) hot water soluble content (3.3%

to 18.6%), (iii) cold water soluble content (0.4% to 9.9 %), (iv) density (0.40 g/cm3

and 0.97

g/cm3), (v) pH 3.3 to 6.6 for cold water extractables and (vi) pH 3.2 to 6.0 for hot water

extractables. As for the fiber anatomical and dimension, the results are as follow: (i) fiber

length (367.9µm- 4229.3µm), (ii) fiber diameter (13.0µm- 47.1µm), (iii) fiber lumen diameter

(2.3 µm- 31.1µm), (vi) fiber wall thickness (0.7 µm- 5.9µm) and (v) Runkel ratio (0.1- 2.3).

Moreover, the vessel diameters ranged from 24.2µm to 375.6µm for tangential and 16.1µm to

279.1µm for radial. Alternatively, the vessel density was in the range of 1.2 per mm2

to 6.9 per

mm2

for overall wood species whereas the proportion of the rays was in the range of 6.7% to

34.6%. The relationship between decay resistance and wood properties were studied by

correlation and regression analyses where the linear regression equation for estimating the

natural durability has been established and perhaps can be used as a tool to predict the decay

resistance and the factors associated with decay resistance. These findings would provide

understanding and the comparative variation of the decay resistance among timber species will

augment the existing information on wood quality classification of 36 timber species studied.

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Penggunaan Analisis Regresi Linear Untuk Beberapa Spesis Kayu Sebagai Alat untuk

Menentukan Kepelbagaian Sifat Kayu Yang Mempengaruhi Ketahanan Semulajadi Kayu

ABSTRAK

Beberapa spesis kayu komersial menyumbang kepada pembangunan ekonomi dengan

membekalkan pasaran dunia dengan kayu balak, kayu gergaji dan papan lapis. Oleh kerana

kayu adalah bahan yang popular dan berguna, ia adalah penting kepada golongan profesional

supaya dapat membezakan kualiti kayu antara spesis. Hubungan antara ciri- ciri kayu seperti

ketahanan semulajadi kayu, kandungan ekstraktif metanol, ketumpatan kayu, kelarutan air

panas, kelarutan air sejuk, pH ekstraktif, morfologi anatomi dan juga beberapa aspek

mikroskopik untuk 36 spesis kayu gabungan dari Malaysia dan temperat telah dikaji. Kajian

ini bertujuan untuk menentukan sifat kayu yang mempengaruhi kepelbagaian rintangan spesis

kayu melalui penentuan profil rintangan pereputan untuk spesies kayu komersial dan

berpotensi dengan menggunakan analisis regresi linear. Ujikaji makmal mengikut prosedur

ASTM D 2017 telah dipilih untuk kajian ini dengan menggunakan spesis kulat reput putih (P.

sanguineus), kulat reput perang (G. trabeum) dan kulat reput lembut (C. globosum

berdasarkan teknik pengebumian tanah tidak steril). Beberapa ciri kayu yang dikaji iaitu

kandungan ekstraktif dan ciri anatomi adalah faktor penting yang menyumbang kepada

ketahanan semulajadi kayu. Oleh itu, kepelbagaian rintangan ketahanan semula jadi kayu

boleh dikaitkan dengan perubahan dari segi kandungan ekstraktif dan juga morfologi anatomi.

Peratusan kehilangan jisim disebabkan oleh tiga kulat reput kepada kayu getah (Hevea

brasiliensis) yang mempunyai rintang tidak tahan adalah seperti berikut: P. sanguineus

(43.9%), G. trabeum (38.2%) dan C. globosum (50.2%). Sebaliknya, belian (Eusiderozylon

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zwageri) iaitu spesis kayu rintangan tahan telah kehilangan jisim serendah 0.7% apabila

terdedah kepada P. sanguineus. Kehilangan jisim oleh G. trabeum adalah yang paling rendah

apabila diuji kepada senumpul (Hydnocarpus sp.) dan selangan batu kuning (Shorea Flava)

apabila kedua-duanya adalah 0.4% manakala kehilangan jisim bindang (Agathis borneensis)

adalah 0.7% dan disebabkan oleh serangan C. globosum. Spesis kayu kemudiannya dikelaskan

kepada 4 kelas ketahanan semula jadi berdasarkan ASTM D 2017 dan EN 350 di mana spesis

kayu telah dikategorikan dalam Kelas 1 (rintangan tahan) sehingga Kelas 4 (rintangan tidak

tahan). Ciri- ciri kayu telah diringkaskan dan didapati iaitu: (i) kandungan ekstraktif methanol

(0.7% - 36.5%), (ii) kandungan kelarutan air panas (3.3% - 18.6%), (iii) kandungan kelarutan

air sejuk (0.4% - 9.9%), (iv) ketumpatan (0.40 g/cm3 – 0.97 g/cm

3), (v) pH 3.3 – 6.6 untuk

pengekstrakan air sejuk dan (vi) pH 3.2 – 6.0 untuk pengektrakan air panas. Bagi dimensi

gentian, ukuran telah direkodkan dan diperhatikan seperti berikut: (i) panjang gentian

(367.9μm- 4229.3μm), (ii) diameter gentian (13.0μm- 47.1μm), (iii) diameter lumen gentian

(2.3μm- 31.1μm), (iv) ketebalan dinding gentian (0.7μm- 5.9μm) dan (v) nisbah Runkel (0.1-

2.3). Diameter vessel pula didapati adalah 2μm- 375.6μm untuk tangen dan 16.1μm- 279.1μm

untuk radial. Selain itu, ketumpatan vesel adalah 1.2 per mm2 -6.9 mm

2 untuk seluruh spesies

kayu secara keseluruhannya manakala kadar ruji adalah dalam lingkungan 6.7% hingga

34.6%. Hubungkait antara ketahanan semulajadi kayu dikaji melalui analisis korelasi dan

regresi di mana persamaan regresi linear untuk menganggarkan ketahanan semula jadi kayu

telah diwujudkan dan boleh digunakan sebagai alat untuk meramalkan rintangan pereputan

serta faktor-faktor yang berkaitan dengan ketahanan semulajadi kayu. Hasil kajian ini akan

memberi pemahaman tentang perbandingan rintangan reput di kalangan spesies kayu akan

menambahkan maklumat yang sedia ada untuk 36 spesies kayu yang dikaji.

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LIST OF TABLES

TABLE TITLE PAGE

Table 1 Summary of types of wood decay fungal 14

Table 2 Decay resistance class or natural durability classification of timber based on

service life (years) and laboratory mass loss (%)

16

Table 3 Grouping of timber species by density (popular timbers and lesser- known

timbers)

20

Table 4 List of timber species studied 31

Table 5 Comparison between EN 113 and ASTM D 2017 based on the mass loss (%) 44

Table 6 ANOVA for mass loss of the 3 timber species subjected to decay induced by

different decay fungal by using EN 113 method.

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Table 7 ANOVA for mass loss of the 3 timber species subjected to decay induced by

different decay fungal by using ASTM D2017 method.

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Table 8 ANOVA for mass loss of the 36 timber species subjected to decay induced by

Pynoporus sanguineus

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Table 9 ANOVA for mass loss of the 36 timber species subjected to decay induced by

Gloeophyllum trabeum

47

Table 10 ANOVA for mass loss of the 36 timber species subjected to decay induced by

Chaetomium globosum

47

Table 11 Decay rate of timber species 48

Table 12 ANOVA for methanol extractives content for 36 timber species 52

Table 13 Methanol Soluble Extractives Content 53

Table 14 ANOVA for hot water extractives content for 36 timber species 55

Table 15 Hot water extractives content of 36 timber species 55

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Table 16 ANOVA for cold water extractives content for 36 timber species 57

Table 17 Cold water extractives content of 36 timber species 57

Table 18 ANOVA for wood density for 36 timber species 61

Table 19 Wood density of 36 timber species 61

Table 20 ANOVA for pH of hot water extractives content for 36 timber species 65

Table 21 ANOVA for pH of cold water extractives content for 36 timber species 65

Table 22 pH of hot water and cold water extractives content 65

Table 23 ANOVA for fiber or tracheid length for 36 timber species 68

Table 24 ANOVA for fiber or tracheid diameter for 36 timber species 69

Table 25 ANOVA for fiber or tracheid lumen diameter for 36 timber species 69

Table 26 ANOVA for fiber or tracheid wall thickness for 36 timber species 70

Table 27 ANOVA for Runkel- ratio for 36 timber species 71

Table 28 ANOVA for tangential vessel diameter for 36 timber species 72

Table 29 ANOVA for radial vessel diameter for 36 timber species 72

Table 30 ANOVA for vessel density (per mm2) for 36 timber species 73

Table 31 ANOVA for ray proportions (%) per mm2 for 36 timber species 73

Table 32 Summary of anatomy properties of 36 timber species 74

Table 33 Correlation analysis of each mass losses caused by white rot (Pycnoporus

sanguineus), brown rot (Gloeophyllum trabeum) and soft rot (Chaetomium

globosum) between wood properties

84

Table 34 Multiple regression analysis based on 15 wood properties 86

Table 35 Multiple regression equation for mass losses caused by each decay fungi 87

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Table 36 Classes of natural durability of wood to fungal attack using laboratory test

based on ASTM D 2017 and EN 350-1

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Table 37 Class of decay resistance of 36 timber species according to ASTM D 2017 91

Table 38 Summary of decay resistance class among timber species 92

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LIST OF FIGURES

FIGURE TITLE PAGE

Figure 1 Size of test block for decay test 30

Figure 2 Glass jar containing soil, feeder strip and test block (ASTM D 2017) 34

Figure 3 Glass jar containing agar, feeder strip and test block (EN113) 34

Figure 4 ASTM D- 2017 decay assembly 36

Figure 5 Unsterile soil burial test assembly 36

Figure 6 (a) Mass loss of the 36 timber species subjected to decay induced by

Pynoporus sanguineus

50

Figure 6 (b) Mass loss of the 36 timber species subjected to decay induced by

Gloeophyllum trabeum

50

Figure 6 (c) Mass loss of the 36 timber species subjected to decay induced by

Chaetomium globosum

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Figure 7 (a) Methanol soluble extractives content for 36 timber species 59

Figure 7 (b) Hot water extractives content for 36 timber species 59

Figure 7 (c) Cold water extractives content for 36 timber species 60

Figure 8 Wood density of 36 timber species 63

Figure 9 (a) pH after hot water treatment of 36 timber species 67

Figure 9 (b) pH after cold water treatment of 36 timber species 67

Figure 10 (a) Fiber or tracheid length of timber species 78

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Figure 10 (b) Fiber or tracheid diameter of timber species 78

Figure 10 (c) Fiber or tracheid lumen diameter of timber species 79

Figure 10 (d) Fiber or tracheid lumen thickness of timber species 79

Figure 10 (e) Runkel ratio of timber species 80

Figure 10 (f) Vessel density of timber species 80

Figure 10 (g) Vessel diameter (radial) of timber species 81

Figure 10 (h) Vessel diameter (tangential) of timber species 81

Figure 10 (i) Ray proportions (%) of timber species 82

1

CHAPTER 1

INTRODUCTION

2

Timber is available in many diverse tree species that vary in density, colour, strength and

durability. It is common that different tree species vary in their chemical, physical and

mechanical properties known as wood variation. Therefore, these aspects will determine the

wood quality of a wood species for a variety of applications. Commercial timber species of

Sarawak contributed in our economic development by supplying the world market mainly with

logs as well as sawn timber and plywood (Ling and Wong 2007). Since timber is a popular

and useful material, it is important that enthusiasts and professionals be able to distinguish the

wood quality of one species from another. The marketability of Sarawak wood species owes

its link to the favorable wood quality of many of the commercial species, some of which

probably controls the natural resistance of wood to biodeterioration. The ability of wood

tissue to resist the attacks of organisms such as fungi and insects is known as natural

durability. The value of naturally durable timbers is well recognized since early civilization.

Durable wood species is a preferred structural constructional material such that there should be

serious attempts to even pursue the cause of genetic engineering to produce transgenic trees

with superior genes governing natural durability of the heartwood of wood species (Wong et

al 2005) and their associated wood quality features in future (Verryn 2008). The natural

durability of wood in soil contact (Ling 1996) concerns the resistance of wood to combined

attacks of soil borne decay fungi wood boring beetles and subterranean termites. The high

natural durability of the main commercial planted timbers such as teak (Tectona grandis) and

belian (Eusideroxylon zwageri) and a few other commercial timber species of Sarawak and

Malaysia generally, make these species ideal choices to be utilized in many industries such as

wood composites, solid wood construction and furniture making. However it is not possible to

resolve to what extent these wood species are resistant to decay fungi versus termites from

3

such field durability trials. Hence, laboratory decay tests involving the decay factor in wood

biodeterioration are necessary in order to resolve this question.

This research focused on wood natural decay resistance as an important wood quality of

several timber species of Sarawak. Therefore, the research mainly focus on causes of

variations decay resistance of Sarawak timbers which includes the testing of several test decay

fungi of white rot, brown rot and soft rot types. It should be noted that soft rot and white rot

fungi are prevalent in Malaysian environments (Salmiah et al. 2007), while the temperate

importers of Sarawak timbers are concerned also with brown rot decay which is prevalent in

their region besides white rot and soft rot decay threats (Wong A. H. H., pers. Comm. 2009).

In this research, 36 timbers species mainly of Malaysian origin, with known classes of natural

in ground durability as listed in Chapter 3 are tested against particular strains of three test

decay fungi (brown rot, soft rot and white rot) in order to evaluate their decay susceptibility of

the wood. To complement these decay test, several other wood properties; density, methanol

extractives content, hot and cold water solubility, pH of these water extracts, fiber structures

and other anatomical features (see Chapter 3) which are likely to influence the decay

resistance of the timber species were also investigated in an attempt to correlate statistically

these wood properties with percentage mass losses.

Density of the wood tissue may affect the decay resistance (Wong et al 1983, Wong et al

1984, and Chafe 1989). Low wood density usually has wider lumina and therefore there is a

large surface area per unit volume of tissues exposed to the actions of fungal decay enzymes.

Less dense wood enhance the fungal growth activities due to the increase in water and air

content within wood substrate. The resistance of wood to decay also has been strongly

4

attributed to the presence of heartwood extractives (Scheffer and Cowling 1966, Rao 1982).

Previous studies indicated that the natural decay resistance of the heartwood of Eucalyptus

delegatensis is influenced by both wood density as well as the amount of the methanol soluble

extractives (Wong et al 1983, Wong et al 1984). The outer heartwood of the plantation wood

species was found to be resistant against the white rot fungus than the inner heartwood

(Zaidon et al. 2002). Also the in-ground natural durability of Sarawak timbers is shown to be

also positively influenced by wood density, observed for either of the heartwood or sapwood

test stakes (Wong and Ling 2009). Both these wood properties may therefore serve as prime

candidates (tools) for the estimation of natural durability of Sarawak wood species. Generally,

certain timbers species have different natural durability ratings against insects or decay fungi

depending on the biological hazard class of exposure of the wood material (Wong 2004).

Decay resistance is a factor for timbers exposed outdoor above- or below-ground contact, as

well as in limited indoor uses somehow exposed to persistent leaching. According to ASTM

standard, D2017, “Standard method of Accelerated Laboratory Test of Natural Decay

Resistance of Woods”, an average wood weight loss of 0 to 10% is classified as highly

resistant, 11 to 24% is resistant, and 25 to 44% as moderately resistant, and above 45% as non

resistant. This classification is valid if the decay of reference blocks of a decay susceptible

species has reached about 60 % mass loss after several weeks decay testing. Thus, by

comparing the decay resistance of the timbers, we can be provided with more precise data

which can assist in clarifying the wood quality of that particular timber species. Therefore,

there is a need to evaluate the wood quality of our timbers and relate them to decay resistance.

This is because there are huge gaps in the recorded information on the decay resistance of the

potential timbers found in Sarawak that will in the future become a very valuable addition to

the already existing information regarding the in ground natural durability of our Sarawak

5

timbers (Wong and Ling 2009). In addition to this, the study also highlights some of the

associated wood properties that influence decay resistance of the wood, and which could be

convenient tools for rapid estimation wood durability. To accomplish reliable information

regarding the causes of decay resistance variations in wood materials, various decay test

methods can be designed and compared in studying the decay resistance of potential Sarawak

timber species. Such information on the relationship between the decay resistance and the

wood quality of several Sarawak timbers will guide decisions on using them to rate durability

of various wood products. Of immediate importance is to determine by statistical least squares

regression procedures, the selection of those wood properties as possible reliable tools for

estimating wood durability specifically decay resistance of commercial Sarawak timber

species.

1.1 Objectives

a. To use a suitable accelerated laboratory decay testing protocol for the analysis of relative

decay resistance of several commercial and potential wood species against soft rot, brown

rot and white types of wood decay. A suitable test method would be able to distinguish the

differential decay mass losses between wide ranges of wood species to enable their

classification in durability groups.

b. To determine those wood properties that perceivably govern decay resistance variations of

numerous selected timbers in order to predict decay resistance profile of commercial and

potential timber species.

6

c. To correlate these wood properties with decay resistance (as % mass loss) of wood in order

to establish an understanding on the relationship between wood quality and decay

resistance of potential Sarawak timbers.

d. To correlate existing records of natural durability data of Ling (1996) with new decay

resistance data on several Sarawak species obtained from this research in order to

determine the relative contribution of the natural durability of these species that was due to

fungal decay.

e. To utilize least square estimates of multiple linear regression analysis technique to select

suitable wood properties as predictive tools for estimating the decay resistance of Sarawak

species in an attempt to model factors associated with decay resistance.

To satisfy these objectives, the thesis structure also highlights the following chapters: (i)

Chapter Two (Literature Review) is a literature survey on the causes of decay resistance

variations of numerous timbers species whereby the potential influences of some wood

properties (wood density, wood extractives content, wood structural features/ anatomy and

other physical and chemical properties) on decay resistance variations in wood are reviewed,

(ii) Chapter Three (Materials and Methods) describes all the experimental methods,

equipments and techniques including statistical analysis used in this thesis research, (iii) the

experimental results as well as the statistical data (regression and correlation analysis) are

listed in Chapter Four, (iv) discussion of the experimental results and useful information on

the wood properties studied on the causes of decay resistance variations is found in Chapter

Five, (v) the conclusions combining the entire findings of the research are in Chapter Six, and

finally is the lists of relevant references cited in the thesis.

7

CHAPTER TWO

LITERATURE REVIEW