Foaming of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/organo-clays nano-biocomposites by a continuous supercritical CO2 assisted extrusion process

• PHBV/clays nano-biocomposite foams were prepared by a continuous sc-CO2 assisted extrusion process.
• The use of diluted PHBV/clays masterbatch prevents thermal degradation while giving good clay dispersion.
• Good clay dispersion favours homogeneous nucleation and limits the coalescence of the pores.
• Nano-biocomposite foams with porosity up to 50% were obtained.

A continuous supercritical carbon dioxide (sc-CO2) assisted extrusion process has been used to prepare poly(3-hydroxybutyrate-co-3-hydroxyvalerate) PHBV/organo-clays nano-biocomposite foams by two methods: a one-step method based on the direct foaming of physical PHBV/clays mixtures, and a two-step method based on the foaming of extruded PHBV/clays mixtures prepared beforehand by twin-screw extrusion. The structures obtained have been characterized in terms of clay dispersion, matrix crystallization, porosity and pore size distribution and pore density. The influence of processing conditions as temperature, pressure, CO2 mass fraction and the clays/foaming interrelationships have been elucidated. It was shown that the prior preparation of a masterbatch by twin-screw extrusion and its dilution during the foaming process is a necessary step to improve clay dispersion without extensive thermal degradation of PHBV. By controlling the sc-CO2 mass fraction in a narrow window, good clay dispersion appears to favour homogeneous nucleation while limiting the coalescence of the pores, and hence allowed to obtain nano-biocomposite foams with better homogeneity and higher porosity up to 50%.

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