(CO)POLYMERS OF L-LACTIDE .2. MECHANICAL-PROPERTIES

The effect of copolymerization of L-lactide with several lactones and cyclic carbonates and the processing variables in compression moulding of poly(L-lactide) homopolymers on the mechanical properties was investigated. Sharp maxima in the impact strength versus comonomer composition and heat of fusion were obtained, reflecting the important role of the presence of a crystalline fraction in the material. Crystalline domains increase the interconnectivity of a physical polylactide network and decrease the molecular weight between these physical crosslinks. The brittle strength concomitantly increases, and as the yield stress remains more or less constant, an increase in impact strength is observed. Very high crystalline as-polymerized poly(L-lactide) prepared with less active catalysts on the other hand has an extremely low entanglement density and therefore a low brittle tensile strength.