EFFECT OF THERMAL-TREATMENT ON STERILITY, MOLECULAR AND MECHANICAL-PROPERTIES OF VARIOUS POLYLACTIDES .2. POLY(L D-LACTIDE) AND POLY(L/DL-LACTIDE)/

Pins for orthopaedic applications injection-moulded from as-supplied p oly(L/D-lactide) 95/5% and poly(L/LD-lactide) 95/5%, raw as-supplied p olymers or raw methanol-extracted polymers were heat-treated for a pre determined time at 135 degrees C under moisture-free argon. The steril ity, molecular weight, polydispersity, mechanical properties, and crys tallinity of the heat-treated samples were evaluated. All the samples heat treated under argon were sterile after 2h exposure to heat. The h eat-treated pins and raw as-supplied polymers showed a continuous decr ease in molecular weight over the entire 50 h of heating, the decrease being more substantial for poly(L/D-lactide) than poly(L/DL-lactide). Raw methanol-extracted polymers showed an increase of molecular weigh t after 2 h of heat treatment, followed by a gradual decrease of molec ular weight up to 50 h. A drop in the bending strength, an increase in the bending moduli, and no change in the shear strength was observed for polylactide pins during the first 5 h of thermal treatment. For bo th the polymers, there was a progressive increase in crystallinity ove r time of thermal treatment, and practically no change in the melting temperature. (C) 1997 Elsevier Science Limited.