Impact modification of lactic acid based poly(ester-urethanes) by blending

Branched biodegradable poly (ester-urethane) (PEU) was blended with two elastic biodegradable copolymers in proportions 5, 10, 15, and 20 wt % to investigate their effect on this hard and brittle polymer. Copolymer of L-lactide and ε-caprolactone, P(L-LA50/CL50), was synthesized by ring-opening polymerization and the other elastic poly(L-lactic acid-co-ε-caprolactone)urethane, P(LA50/CL50)U, was prepared by direct polycondensation of L-lactic acid and ε-caprolactone, followed with urethane bonding. In addition, four elastic biodegradable copolymers, three of them P(L-LA/CL) and one P(LA/CL)U, were blended with linear PEU to investigate their modifying effect on PEU. These compositions studied were 10, 15, and 20 wt % of P(L-LA40/ CL60), P(L-LA60/CL40), P(L-LA80/CL20), and P(LA40/CL60)U in PEU. Blending was done in a batch mixer. PEU became more ductile when blended with P(L-LA/CL) and P(LA/CL)U, and its impact resistance improved markedly. In general, an addition of 15 wt % of copolymer appeared to give the most desirable mechanical properties. Moreover, the more L-lactide in the P(L-LA/CL) copolymer, the better was the miscibility of the blends, as shown by dynamic mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM). One P(L-LA/CL) was also blended with poly(DL-lactide) (PDLLA) to see if the dispersion of rubbery copolymer particles was the same in PDLLA and PEU. A well-known commercial nonbiodegradable rubber [styrene/ethylene/butylene copolymer (SEBS)] was blended with linear PEU to compare its effect on impact strength.