Biobased polymers like biopolyesters (PHAs, PLA) or thermoplastic starch (TPS) are marketed as eco-friendly alternatives to the currently widespread non-degradable oil-based thermoplastics, due to their renewable origin, their biodegradability and biocompatibility. Their properties are similar to various synthetic thermoplastics like polypropylene, and hence can be used alternatively in agriculture, packaging but also biomedical applications. However, some drawbacks prevent their development on the market. In particular, this class of biobased polymers is often brittle with poor thermal stability and low crystallization rate. Current researches are focused on the control of their processing and structure by chemical / microstructural modifications or the design of new processes. The synthesis of copolymers or the use of plasticizers have been proposed to control mechanical properties, lower melting temperatures and extend processing windows. Improved thermal stability, mechanical or barrier properties can be obtained by the preparation of nanocomposite materials incorporating nanoparticles with high aspect ratios and specific surfaces. An innovative way to control polymer structures is the use of supercritical fluids assisted processes. Supercritical carbon dioxide (sc-CO2) has favorable interactions with polymers and can be easily dissolved to act as a plasticizer hence modifying drastically their properties. sc-CO2 can also act as a foaming agent during processing to generate porous structures of interest for packaging or drug release applications. In this study, a continuous sc-CO2 assisted extrusion process has been used to prepare PHBV/organo-clays nano-biocomposite foams by the direct foaming of physical PHBV/clays mixtures, and the foaming of extruded PHBV/clays mixtures prepared by twin-screw extrusion. The structures obtained were characterized in terms of clay dispersion, matrix crystallization, and porosity. The influence of processing conditions and the clays/foaming interrelationships have been elucidated. By controlling the sc-CO2 mass fraction in a narrow window, good clay dispersion appears to favor homogeneous nucleation while limiting the coalescence of the pores, and hence allowed to obtain nano-biocomposite foams with better homogeneity and porosity up to 50%. Perspectives in the use of such processes with amorphous biopolyesters such as PLA and its blends will be addressed.

Processing of (nano)biocomposite foams by continuous supercritical CO2 assisted extrusion

253rd National Meeting (2017)

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