Crystallinity Development in Cellular Poly(lactic acid) in the Presence of Supercritical Carbon Dioxide

This article investigates the crystallinity development in cellular poly(lactic acid) (PLA) and the effect of the achieved crystalline content on its properties and microstructure. Carbon dioxide (CO2) in its supercritical state was used as the expansion agent for three different grades of PLA that differed in terms of L-lactic acid content. Cellular PLA was produced on a twin-screw extrusion line using capillary dies of various diameters. The obtained crystalline contents were measured by differential scanning calorimetry and X-ray diffraction techniques. The morphology of the cellular structures was examined using scanning electron microscopy. The crystallinity developed on expansion depended on L-lactic acid content, on supercritical CO2 concentration, polymer flow rate, and die diameter. Cellular PLA, with densities as low as 30 kg/m(3), was obtained tinder the most favorable conditions. It was shown that the crystallinity development in PLA enhances its cellular structure formation and enables the fabrication of quality cellular materials at lower CO2 concentration. The presence of PLA crystallites within expanded cell walls leads to a peculiar 2D-cavitation phenomena observed only in the cell walls of semicrystalline foams. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 2920-2932, 2009