PROCESSING AND CHARACTERIZATION OF PHBV/CLAY NANO- BIOCOMPOSITE FOAMS BY SUPERCRITICAL CO2 ASSISTED EXTRUSION

In this study, we developed a continuous sc-CO2 assisted extrusion process to prepare PHBV/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 PHBV / clays mixtures prepared beforehand by twin-screw extrusion. The structures obtained were characterized in terms of clays dispersion, matrix crystallization, porosity and pore size distribution and density, and discussed as regard to the processing conditions such as temperature, shearing/pressure, CO2 mass fraction. It is shown that the prior preparation of a masterbatch and its further dilution during the foaming process is a necessary step to favour 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, and hence allows to obtain PHBV/clays nanobiocomposite foams with better homogeneity and porosity higher than 50 %.