The non-steady state technique of laser flash analysis (LFA) was used to record the variation of thermal diffusivity with time during the cold-crystallisation of poly(lactic acid), a grade containing 4% D stereoisomer content. The measured diffusivity data was analysed in terms of the Avrami and Hoffman-Lauritzen models for polymer crystallization. Within the temperature range 88 to 109C, mechanistic 'n' values of 2.0±0.1 were calculated and a nucleation constant of 6.58 x 10-5 K 2 was determined; the LFA technique yielded kinetic data that was comparable to that which originated from DSC. Measurements of thermal diffusivity were also recorded over a longer timescale to determine whether thermal diffusivity was a useful indicator of secondary crystallization and this data was analysed using a modified Avrami equation that includes a root-time dependence of the secondary process. Secondary crystallisation rate constants (k s) increased with crystallisation temperature and yielded an activation energy for the secondary crystallisation process of 40 kJ/mol.

Poly(lactic acid) (PLA) is gaining increasing interest from the packaging industry as a biodegradable alternative to oil based polymers such as polypropylene (PP) and polyethylene terephthalate (PET). However, its' inherent brittle nature prevents widescale commercial use. Blending in order to improve the Young's modulus, yield stress and elongation to break, provides a possible alternative although many polymers have been found to be immiscible with PLA. In this study, high pressure carbon dioxide (CO2) was utilised during blending to encourage miscibility between two normally immiscible polymers: poly(ε-caprolactone) (PCL) and poly(lactic acid) (PLA). Blends were prepared by melt blending in the presence of carbon dioxide (CO2) and compared to solvent casting and melt blending with a single-screw extruder. CO2 assisted blends demonstrated a significant reduction in the size and number of PCL domains in a PLA matrix, and consequently improved the adhesion between phases at the microscale. The optimum melt blend composition for Young's modulus, yield stress and elongation to break was found to be 75% PLA and 25% PCL. Mechanical properties of PLA 2002D blends were further improved when prepared by CO2 assisted melt blending.

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