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Session 15 ic2011 wei
1. The University of Idaho
Effects of Wood Fiber Esterification on the
Photostabilization of Wood Plastic Composites
Liqing Wei and Dr. Armando G. McDonald
Forest Products Program
2. Background of WPC
Issues:
• Incompatibility between hydrophilic
wood fiber and hydrophobic polymer
• Lead to poor bonding
• Wood fibers can absorb water & facilitate
fungal attack
• Absorption of solar radiation by wood
• Promotes free radical degradation of WPC
• Lignin is main contributor to UV absorption
3. Wood Modification
• Sebé et al. (2009) had shown improvements in
wood weathering performance by esterification
DMF, K2CO3
Wood Wood
Wood
R= R= R=
Vinyl Benzoate Vinyl Propionate Vinyl Acetate
• This approach may be suitable to weather
stabilize wood fibers for WPC
4. Objectives
To improve the weather resistance of WPC by:
• Modifying wood fibers to stabilize WPC
• Perform accelerated weathering trials
• Evaluate the weathering performance of WPC
5. Experimental Procedure
• Poplar flour (60#, 100 g batches)
reacted with vinyl ester (vinyl
acetate, vinyl propionate, and
vinyl benzoate) in dimethyl-
formamide using K2CO3 as
catalyst.
• Reaction at 120 oC for 24 h
• Modified fiber washed with
water & acetone, and then dried
(<0.5% MC)
6. WPG for Esterified Poplar
OH groups
Number WPG
Ester Substituted
of Batches (%)
(mmol/g dry wood)
Acetate 10 18 5.6
Propionate 10 21 3.7
Benzoate 10 39 3.8
0.01x WPG
OH substituted= x 1000
Molecular weight of adduct-1
8. Experimental Procedure Cont.
Materials:
• Poplar flour (40%) + HDPE (60%)
WPC Formation:
• Compounded and extruded (18mm
twin-screw extruder) into sheets
(100mm x 2mm)
Weathering specimens:
• Q-Sun (Xe-1-S, UV light + water
spray) weatherometer according to
ASTM D 6662
• 2 mm x 50 mm x 100 mm
• 0 to 2000 h exposure time
9. Surface Color Measurement
StellarNet spectrometer
• ASTM D 2244 (5 replicates)
• Color change (∆Eab) and surface
lightness (∆Lrel)
• L*: lightness (100=white, 0=dark)
• a*: redness (+) & greenness (-)
• b*: yellowness (+) & blueness (-)
L* final - L*initial
Lrel *
L initial
Eab L2 a 2 b2
10. Color Change (∆Eab)
50
45
Color change (∆Eab) 40
35
30
25
20
Unmodified
15
Acetylated
10 Propionated
5 Benzoated
0
0 200 400 600 800 1000 1200 1400 1600 1800 2000
Exposure time (h)
• Increase in WPC ∆Eab
• Benzoated wood WPC showed least color change
13. Surface Chemistry by FTIR Spectroscopy
• Surface oxidation:
A1680-1800
Carbonyl index =
A 2912-2917
• Polyene formation in HDPE:
A880-920 R
Vinyl index (I) =
A2912-2917 R
A1630-1650 R
Vinyl index (II) =
A 2912-2917
15. FTIR Spectroscopy: Vinyl Index-I
0.7
Unmodified Acetylated
Vinyl index (880-920 cm-1)
0.6 Propionated Benzoated
0.5
0.4 Vinylidene
0.3
R
0.2
0.1
R
0
0 200 400 600 800 1000 1200 1400 1600 1800 2000
Exposure time (h)
• Unmodified WPC showed increase in VI-I
• Esterified WPC showed little change in VI-I (880-920 cm-1)
16. FTIR Spectroscopy: Vinyl Index-II
0.7
Vinyl index (1630-1650 cm-1)
Unmodified Acetylated
0.6
Propionated Benzoated
0.5
0.4
0.3 R
0.2
0.1
0
0 200 400 600 800 1000 1200 1400 1600 1800 2000
Exposure time (h)
• Unmodified WPC showed an increase in VI-II
• Esterified WPC showed slight change in VI-II (1630-1650 cm-1)
17. Conclusions
• Esterification of wood fiber lowered surface
lightness and color change of resultant WPC
• Esterified poplar WPC were more
photostable than unmodified poplar WPC
• This approach for modifying wood shows
promise for WPC applications
18. Ongoing Research
• Further FTIR analysis of functional groups
• SEM and light microscopy of weathered
WPC surfaces
• Mechanical and thermal properties of WPC
• Soil block fungal tests (Dr. Jeff Morrell,
OSU)
19. Questions?
Thank you!
Acknowledgements:
• Grant from USDA-WUR number 2009-34158-20170
