Super-tough poly(L-lactide)/crosslinked polyurethane blends with tunable impact toughness

Super-tough poly(L-lactide)/crosslinked polyurethane (PLLA/CPU) blends with a CPU phase dispersed in the PLLA matrix were prepared by reactive blending of PLLA with poly(ethylene glycol) (PEG), glycerol, and 4,4'-methylenediphenyl diisocyanate (MDI). The gel fraction increased while the swelling ratio decreased with increasing glycerol content. FT-IR analysis suggests that interfacial compatibilization between PLLA and CPU occurred via reaction between the hydroxyl group of PLLA and the isocyanate group of MDI. The elongation at break and notched impact strength of PLLA/CPU blends were increased by up to 38 and 21 times those of neat PLLA. The morphology of PLLA/CPU blends plays an important role in notched impact strength and can be controlled by adjusting the content of glycerol. The size of the dispersed CPU phase increased gradually while the notched impact strength increased first and then decreased with increasing glycerol content. Therefore, the notched impact strength can be easily tailored by the content of glycerol of CPU. The optimum size for high impact strength was found to be similar to 0.7 mu m, which was obtained for the blends with glycerol content in the range of 5 to 10 wt% on the basis of PEG weight. In addition, the effect of glycerol content on the compatibility and rheological properties of PLLA/CPU blends was also investigated.