Largely toughening biodegradable poly(lactic acid)/thermoplastic polyurethane blends by adding <scp>MDI</scp>

This work focuses on largely toughening poly(lactic acid)/thermoplastic polyurethane (PLA/TPU) blend with lower content (20 wt %) of TPU using appropriate contents of 4,4‐methylene diphenyl diisocyanate (MDI) via simple melt blending. Both scanning electron micrographs and differential scanning calorimetry curves suggest little change of the compatibility between the PLA and TPU phases by adding the MDI. Dynamic rheological test demonstrates that a reaction occurs between the TPU phase and MDI during melt blending. Combining the rheological behaviors and gel contents of the blends, it can be speculated that adding the MDI extends the TPU chains and forms branched and crosslinked structure in the TPU chains sequentially. Toughening mechanism is analyzed and different impact strengths for the blends with different MDI contents are explained based on combined effects of the decreased crystallinities for the PLA matrix and the extended, branched and crosslinked structure in the TPU chains. A 0.8 wt % MDI content is optimal in terms of the impact strength (100.6 kJ/m 2 ) and the elongation at break (392.4%). The former is about 1.9 and 32.5 times of that for the blend without MDI and the PLA, respectively. Moreover, the MDI results in some increase in the tensile strength of the blends. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132 , 42511.