Wood Core Shell Structures for use in

Wood Plastic Composites

Armando McDonaldSmith Sundar

WPC UtilizationOver 70 firms in the US & Canada produced WPC in 2002 worth $1.03 billionMarket had grown rapidly & dominated by the decking marketSpeculated growth -$1.95 billion by 2006 (Plastic news)New opportunities for WPC for semi-structural applications

Objectives of study

Create a high-performance WPC materials:

1. Modify the wood surface to create core-shell like structures to reinforce WPC

Modify surface with an alkyl substituted isocyanate

Improve coupling & therefore performance

Project overview

Wood size reduction

and screening

Synthesis of modified Isocynates

Coupling ofmodified

isocynates towood

Compounding rheology

&Material

evaluation

Technologytransfer &

Commercialapplication

Current research

Avg 110 umAvg 109 um

Avg 33 um

Avg 29 umAvg 25 um

0

10

20

30

40

50

Avg 110 um Avg 109 um Avg 33 um Avg 29 um Avg 25 um

% o

f Tot

al W

eigh

t

100 mesh -100+200 -200+300 -300+400 >400

Fiber generation

Commercial maple flour (100#)Ball milledScreened

200-300#Particle analysis

<

Original Screened fraction

Wood modification strategy

Wood micro fiber

Wood micro fiber

Plastic chains

Wood micro fiber

Chemical approaches

1. Synthesize aliphatic isocyanates which can couple to wood

2. Activate wood with a diisocyanate which can then couple to an aliphatic alcohol

3. Activate wood with a diisocyanate which can then couple to an aliphatic amine

Approach 1

OCN-R-NCO

Woodfiber

-OH

R’ = C2, C8, C12, C18

Woodfiber

-O-CO-NH-R-NH-CO-O-R’

= C18H37OH

= polyethylene

R’OHOCN-R-NH-CO-O-R’

OH

n

(MDI)

1: Aliphatic isocyanate synthesis

Do we have the correct chemistry?Need to derivatize the isocyanategroup with dibutyl-amine (DBA)Separate compounds (3) by HPLC

OCN-R-NCO R’OH OCN-R-NH-CO-O-R’

AU

0.00

1.00

2.00

3.00

Minutes2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00 22.00 24.00 26.00 28.00 30.00

C2-MDI-C2C2-MDI-DBADBA-MDI-DBA

HPLC chromatogram

(MDI)

1: Aliphatic isocyanate synthesisIsolate/collect HPLC peaksCharacterize each peak by electrospray-MS

+ve psuedomolecular ions (M-H+ / M-Na+)

M-Na+DBA-MDI-C2 M-H+

1. Wood modification

300# maple (extr. free) dispersed in tolueneAdd OCN-R-NH-CO-O-R’ & react for 24-72 hMonitored reaction by TLC as DBA derivativesWashed & dried

63295137Weight gain (%)

C18H37OHC12H25OHC8H17OHC2H5OHFatty alcohol

717.

8975

0.2681

6.91

1055

.11

1074

.51

1103

.75

1163

.73

1235

.90

1310

.72

1412

.79

1469

.35

1510

.33

1533

.66

1593

.55

1702

.41

2850

.91

2918

.99

3324

.65

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

%Tr

ansm

ittan

ce

500 1000 1500 2000 2500 3000 3500 4000 Wavenumbers (cm-1)

897.

07

1033

.47

1233

.76

1371

.15

1421

.39

1504

.57

1593

.46

1735

.91

3382

.60

7 0

7 2

7 4

7 6

7 8

8 0

8 2

8 4

8 6

8 8

9 0

9 2

9 4

9 6

%Tr

ansm

ittan

ce

5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 0 3 0 0 0 3 5 0 0 4 0 0 0 W a v e n u m b e r s ( c m - 1 )

1. FTIR spectroscopy

C=O

traceNCO

-CH2-MDI-C2-modified wood

Extractives free wood

N-H

1. Compounding

Haake torque rheometer163°C, 35rpm, 5 min0-50% wood (60g)HDPE (EquistarLB01000)

0

1 0

2 0

3 0

4 0

0 1 2 3 4 5 6

T im e ( m in )

Torq

ue (N

m)

C 2C 8C 1 2C 1 8c o n t r o l

1. Molding & tensile propertiesTensile specimens were injection molded from compounded blends (Dynisco LMM)Tensile testing

Instron 5500RASTM 1708-02a 1 mm/min

Improvement in tensile strength for some modified fibers

C8 & C18 at 30% woodC2 at 50% wood 0

5

10

15

20

25

30

c2 c8 c12 c18 Control

Tens

ile S

tren

gth

(Mpa

)

10% Wood loading 30% Wood loading 50% Wood loading

1. Thermal analysis

Mettler Toledo DSC 10oC/min +/- ramps Wood modification increased % crystallizationHowever, No trends were observed between crystallinity & tensile properties

30% WF

0

10

20

30

40

50

Control C2 C8 C12 C18

% C

ryst

allin

ity

WPC, 30% wood content

Approaches 2 & 3

OCN-R-NCOWoodfiber

-OH Woodfiber

-O-CO-NH-R-NCO

C18H37NH2

Woodfiber

-O-CO-NH-R-NH-CO-NH-C18H37 3

2Woodfiber

-O-CO-NH-R-NH-CO-O-R’

R’OH R’ = C2H5, C8H17, C12H25, C18H37

2 & 3. Wood modification300# maple (extr. free) dispersed in tolueneAdd MDI (or TDI) & react for 24-72 hDecant solvent Add alcohol (or amine) & react for 24-72 hWashed & dried

60

C18H37NH-MDI

43

C18H37O-MDI

62335340Weight gain (%)

C18H37NH-TDI

C12H25O-MDI

C8H17O-MDI

C2H5O-MDI

Alkyl grp

2 & 3. FTIR spectroscopy

-CH2-

TDI-ODA modified wood

720.

76

769.

6181

6.4

385

0.76

1018

.83

1057

.2411

08.1

7

1231

.33

1310

.26

1412

.95

1467

.23

1511

.40

1534

.12

1594

.46

1648

.51

1697

.38

2852

.21

2920

.91

2952

.57

3313

.36

7 8

7 9

8 0

8 1

8 2

8 3

8 4

8 5

8 6

8 7

8 8

8 9

9 0

9 1

9 2

9 3

9 4

9 5

9 6

%Tr

ansm

ittan

ce

5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 0 3 0 0 0 3 5 0 0 4 0 0 0 W a v e n u m b e r s ( c m - 1 )

C=O

traceNCO

-CH2-

MDI-C2H5OHmodified wood

N-H

N-H3

2

2 & 3. Compounding

0

1 0

2 0

3 0

4 0

0 1 2 3 4 5 6

T im e (m in )

Torq

ue (N

m)

C 2C 8C 1 2C 1 8c o n tr o l

3

2

0

1 0

2 0

3 0

4 0

0 1 2 3 4 5 6T i m e M in

Torq

ue(N

m)

T D IM D IC o n t r o l

2 & 3. Tensile results WPC from C2 & C18fiber gave strength improvements at 50% wood content

WPC from TDI-C18fiber gave strength improvements

0

5

10

15

20

25

30

Control MDI-ODA TDI-ODA

Tens

ile s

tren

gth

(MPa

)

10%WF 30%WF 50%WF

0

5

10

15

20

25

30

Control C2 C8 C12 C18

Tens

ile s

tren

gth

(MPa

)

10%WF 30%WF 50%WF

2 & 3. Thermal analysis

Observed and increase in HDPE crystallinity due to wood modification

However, No trends were observed between crystallinity & tensile properties

0

10

20

30

40

Control C2 C8 C12 C18 MDI-ODA

TDI-ODA

HD

PE

Cry

stal

linity

(%)

WPC, 30% wood content

2 & 3. Melt Flow

MFI measured10kg, 190oC, 300s

MFR decreased on wood modification

Especially the C8modified fiber

Similar trend observed in torque rheometry

WPC, 30% wood content

0

1

2

3

4

5

6

Control C2 C8 C12 C18 TDI-ODA MDI-ODA

MFR

(g/1

0 m

in)

Comparison between approaches

Approach 1 takes longer to prepare modified fiber

Tensile properties were generally higher from fiber prepared from approach 1

0

5

10

15

20

25

30

Control C2 C8 C12 C18

Tens

ile s

tren

gth

(MPa

)

Approach-1 Approach-2

0.0

0.5

1.0

1.5

2.0

Control C2 C8 C12 C18

Tens

ile m

odul

us (G

Pa)

Approach-1 Approach-2

Conclusions

Wood surface modification has a positive effect on:

Improved compoundabilityReduced melt viscositySlight improvement in tensile strengthApproach 1 gave better props.Approach 2 & 3 more adaptable for an industrial process

Outcomes:Lower melt viscosities suitable for injection molding applicationsHigher wood loadings achievable at the same melt viscosity

Ongoing work:Extrusion trialsDMTA analysisRheological studies WPC morphology (microscopy)Wood fiber surface energetics & chemistryWater adsorption trials

Questions?

Acknowledgements:Lance Gallagher

Drs. Michael Wolcott, Karl Englund and Tieqi Li, WMEL, WSU

Funding provided by USDA CREES-NRI grant #2002-3732