Thermomechanical behavior, light and X-ray scattering of polylactic acid

This research focuses on the thermal properties, microstructure and mechanical behavior of extruded films of biodegradable polylactic acid (PLA) and compares these properties with those from polyethylene, high density and linear low density. Thermal properties showed poorer thermal stability of PLA (some 100°C lower than the polyolefins), and poorer ability for PLA to crystallize, exhibiting a pronounced cold crystallization exothermic peak, not present in the extruded polyolefins. Poor crystallization in PLA films was corroborated by wide-angle and small-angle X-ray scattering, and hot-stage optical microscopy. Uniaxial deformation showed that the mechanical properties of PLA film along and orthogonal to the extrusion direction (determined under uniaxial testing at room temperature) are significantly larger than the polyolefins, by a factor of 2–6. Moreover, the mechanical properties along and orthogonal to the extrusion direction revealed significant anisotropic mechanical properties of PLA. Furthermore, the mechanical modulus of PLA was a decreasing function of strain rate thus suggesting a strain rate softening behavior.