Microcellular foaming of amorphous polymers in a supercritical CO2 batch process: Effect of philic-additives and process conditions on microstructure
Résumé
Microcellular foaming of commodity amorphous polymers, Polymethylmethacrylate (PMMA), and Polystyrene (PS) was studied in supercritical CO 2 via a one-step process in the presence of several types of additives able to change their foaming behaviour and therefore the porous structures. Additives such as diblock copolymers (styrene-co-methylmethacrylate SM) or triblock (styrene-co-butadiene-co-methylmethacrylate SBM, methylmethacrylate-co-butylacrylate-co-methylmethacrylate MAM) terpolymers, core-shell particles (methylmethacrylate styrene) were added to PS or PMMA by extrusion. They showed advantages compared to classical PS-PMMA polymer blends in terms of cell size control and reduction of cell size. Foaming is carried out on bulk injection molded samples which were saturated under high pressures of CO 2 (300 bars) at different temperatures (25°C to 80°C) and different depressurization rates (from 150bar/min to 12bar/min). Then very distinct cellular structures and densities were controlled by varying either the additive type or the foaming conditions, using different foaming temperatures and foaming times. Cell sizes are ranging from 0.2 μm to 200 μm, and densities from 0.30 g/cm3 to 1 g/cm 3 in the polymers considered. It was found that the some additives, well dispersed inside the polymer matrix, play an important role as nucleating agents, reducing drastically the average cell size, and improving the foaming process.
Mots clés
Methyl methacrylates
Microcellular foaming
Nucleating agents
One-step process
Porous structures
Process condition
Supercritical CO
Supercritical CO2
Triblocks
Well-dispersed
Amorphous polymers
Batch process
Cell size
Cellular structure
Core-shell particle
Depressurization rate
Foaming process
Foaming temperature
High pressure