The influence of morphology on the (hydrolytic degradation of as-polymerized and hot-drawn poly (L-lactide))

The influence of morphology on the hydrolytic degradation behavior of poly(L-lactide) has been studied. High molecular weight and highly crystalline as-polymerized poly(L-lactide) was obtained in high yields through melt polymerization. Poly(L-lactide) fiber with a draw ratio of 5.6 was obtained by hot-drawing solution-spun fiber. During the bulk degradation of as-polymerized poly(L-lactide), a rapid decrease of molecular weight and tensile properties was observed. This could be explained by the morphology of the material and the presence of thermal stresses and subsequent generation of microcracks. The lamellar crystallites in as-polymerized poly(L-lactide) appeared to be very stable towards hydrolysis. The resorption time of high molecular weight as-polymerized poly(L-lactide) in vivo was estimated at 40-50 yr by extrapolation of molecular weight data. Hot-drawn poly(L-lactide) fiber showed exceptional hydrolytic stability under a static load and substantially retained its mechanical properties over a period of more than 5 yr. The high perfection of the crystalline fiber and the elimination of micro-voids obtained by hot-drawing prevented penetration of water and induced surface erosion of the fiber.