Improvement of flexural strengths of poly(L-lactic acid) by solid-state extrusion

Solid-state extrusion technique was employed for the improvement of flexural strengths of poly(L-lactic acid) (PLLA) that is currently used as materials for various internal fixation devices. PLLA was vacuum compression molded to have two different crystallinities, from which cylindrical billets of various diameters were machined. Solid-state extrusion of billets was performed at 130°C with various drawing rates. Throughout the whole processes the decrease in molecular weight was significantly suppressed to be about 10%. Both flexural strength and flexural modulus increased with increasing crystallinity of the billet, draw ratio, and drawing rate up to the maximum values of 221 MPa and 8.4 GPa, respectively. Structural investigations showed that the increase in flexural strength and modulus was due to the developments in orientation and crystallinity.