Abstract: Poly(lactic acid)/wood flour (PLA/WF) composites modified with polyurethane prepolymer (PUP) were prepared by blending extrusion, and followed by the test of their mechanical properties, dynamic mechanical analysis (DMA), contact angle measurements, and scanning electron microscope (SEM) analysis on fracture surface. The mechanical property tests showed that flexural strain at break and impact strength of the composites containing 20% PUP calculated by mass fraction of PLA and WF were 5.78% and 18.3 kJ/m² which were 209% and 123% more than that of untreated sample, respectively. The results indicated that PUP had great effect on toughening the composites. DMA analysis revealed that with the increase of PUP. This two distinct glass transition temperatures corresponding to PLA and PUP phases all decreased, the storage modulus also decreased siginficantly and the toughness of the composites improved. The contact angle test towards water increased obviously with the addition of PUP. This showed the increse of hydrophobic performance. The contact angle of the composites reached to 83.7° with 25% PUP and the value increased by 25.7% comparing with that of non-toughened composites (66.6°). SEM examination on the composite fractured surface showed more wood powder was pulled out and the section was more uneven with the addition of PUP. This presented the characteristic of ductile fracture.

Key words: poly(lactic acid), wood flour, polyurethane prepolymer, toughening, hydrophobic performance