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Abstract

Two different poly(L-lactides) (PLLAb and PLLAa) were blended with poly(ε-caprolactone) (PCL) and an elastic poly(ε-caprolactone/L-lactide) P(CL/L-LA) copolymer to modify the mechanical properties of PLLA. Blends of both PLLAs with 20 wt.-% of PCL were prepared. PLLAa was blended with 20 wt.-% of P(CL/L-LA) copolymer, and blends of PLLAb and P(CL/L-LA) copolymer were made with copolymer contents of 5, 10, 20 and 30 wt.-%. The tensile properties and impact and shear strengths were determined as a measure of the mechanical properties. The hydrolytic behavior of the blends was investigated, and the changes in shear strength as a function of hydrolysis were followed. The structure of the hydrolyzed samples was studied by means of scanning electron microscopy (SEM). The properties of PLLA changed considerably when blended with PCL or P(CL/L-LA) copolymer. An increasing amount of copolymer in PLLAb decreased tensile modulus and shear strength, but improved the strain and impact strength. In hydrolysis, blends containing PLLAa degraded slower than blends of PLLAb because of the higher initial molar mass and purity of PLLAa. The molar masses of PLLAb blends decreased dramatically, and less than 10% of the initial molar masses and shear strengths were left after 12 weeks in vitro. The morphology of the blends affected the degradation. The blends containing P(CL/L-LA) copolymer had a porous structure which facilitated water absorption into the blend.