Properties and Biodegradability of Polymer Blends of Poly(L-lactide)s with Different Optical Purity of the Lactate Units

Polylactides with high and low L-isomeric ratios of the lactate units (PLA99.0 and 77.0, where the numbers correspond to the L-ratios) were melt-blended to analyze the changes in properties and biodegradability with the polymer blend. The crystallinity of the blends was almost similar to that of the blends of PLLA and PDLLA. The glass transition behavior supported the compatibility of both polymers. The glass transition behavior was indicative of a compatible nature of both polymers. The tensile modulus of the blends was almost identical irrespectively of the blend ratio, while their tensile strength decreased with decreasing composition of PLA99.0. Above Tg, the storage modulus of the blends dropped from 2–3×109 Pa to 1–3×106 Pa and then increased to a different level depending on the crystalline nature of the blends. The biodegradability of the blends increased with decreasing composition of PLA99.0. This difference in degradability can be well explained by our random packing model of local helices of the L-sequenced chains for the L-rich PLA samples.