(205f) Surface Modification of Wood Flour by Acid Chloride Esterification: Characterization and Performance of High Density Polyethylene/ Wood Flour Composites

Modification of wood fiber/flour (WF) surfaces has the potential to improve its compatibility with hydrophobic plastic matrices and to reduce water uptake in WF/Plastic composites. Wood flour was modified by esterification with octanoyl chloride and with palmitoyl chloride. The modified WF was analyzed by FT-IR. A higher degree of esterification was achieved in highly polar dimethylformamide (DMF) compared to the less polar methyl tert-butyl ether (MTBE). DMF penetrates into the fiber far more than MTBE, thereby increasing the number of ?OH groups available for esterification. Increasing the acid chloride chain length from C8 to C16 decreased the extent of esterification. Longer chains cover surface ?OH groups, retarding reactions with nearby hydroxyls after an esterification event. Longer chain acid chlorides also have lower reactivity and penetrate into the hydrophilic wood fiber more slowly. Modified wood flour surfaces were covered by a hydrophobic waxy layer of surface ester groups (SEM). The surfaces of modified wood flour and the fracture surfaces of WF/HDPE composites were studied by SEM. C8-modified wood flour (60 wt%)/HDPE composites exhibited a large drop in equilibrium water absorption after a 24 hr immersion compared to unmodified WF (60 wt%)/HDPE composites. However, esterified WF/HDPE composites exhibited lower flexural strengths and moduli. In contrast to octanoyl chloride modification, the addition of maleated polypropylene (MAPP) to WF/HDPE composites improved composite mechanical performance.