Synthesis and properties of bio-based thermoplastic polyurethane based on poly (L-lactic acid) copolymer polydiol

The goal of this work is the synthesis of a new kind of bio-based thermoplastic polyurethane (BTPU) based on poly(L-lactic acid) (PLA) and poly(tetramethylene) glycol (PTMEG) segments via chain-extension reaction of dihydroxyl terminated (HO-PLA-PTMEG-PLA-OH) copolymer using hexamethylene diisocyanate (HDI) as a chain extender. Polydiols were synthesized through polycondensation of lactic acid and PTMEG in bulk. The chemical structures and molecular weights of polydiols and BTPUs containing different segment lengths and weight fractions of PLA, were characterized by 1H-NMR and FTIR. The effects of the structures on the physical properties of BTPUs were studied by means of DSC, SEM, and tensile test; crystallization behavior was characterized by POM. The DSC and SEM results indicate that PLA segment is perfectly compatible with PTMEG segment and the crystallization of BTPU is predominantly caused by PLA segment. Polydiol with lower PLA content shows lower Tg and lower crystallinity. Tensile test shows that the elongation at break of BTPU is above 340% at the composition of PLA/PTMEG = 80/20 (w/w). (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012