Study Of PS/SBS Composites Extrusion Foaming With Supercritical CO₂

Polystyrene(PS) has good processability and dimensional stability. However, its big rigidity, low impact strength and heat distortion temperature have limited its further application. Extrusion polystyrene foam plastic has a uniform closed-cell structure, excellent insulation performance, low bibulous rate and good structure stability, but it also has some shortage, such as poor permeability resistance, low impact strength, slow recovery after impact, cell-burst, etc. Therefore, this research modified PS with thermoplastic elastomer and inorganic particles modification to improve its mechanical and foaming performance, and finally we obtained excellent polystyrene foamed plastic through supercritical carbon dioxide extrusion foaming.In this paper, first, we prepared PS/SBS composites at different SBS content with triple screw extruder and studied their morphology, rheological properties, thermal stability and heat-resistent properties. Then we investigated the extrusion foaming behavior of PS/SBS composites using supercritical carbon dioxide. We studied the influence of SBS content and the screw speed to the extrusion foaming behavior. The results revealed that SBS has a good compatibility with PS. SBS can improve the viscoelasticity, thermal stability and heat-resistent of the composites; a certain amount of SBS can obviously improve the cell morphology, decrease the cell size and increase the cell density. When the content of SBS was 20wt%, the cell diameter was 64.9μm and the cell density was 5.3×106cells/cm3. With the increase of screw speed, the cell size decreased after increasing first.In order to improve the cell structure of PS/SBS composites, nano-Ca CO3 was introduced as nucleating agent in the extrusion foaming process. There we prepared PS/SBS/Ca CO3 composites and systematically studied the effect of Ca CO3 content, die temperature, screw speed and supercritical CO2 flow rate on the extrusion foaming behavior of PS/SBS/Ca CO3. The study found that the addition of Ca CO3 could improve the viscoelasticity, thermal stability and heat-resistent of the composites. In the process of extrusion foaming, proper Ca CO3 content could improve the cell morphology, decrease the cell size, increase the cell density and enhance compression strength greatly. When the content of Ca CO3 was 5wt%, the cell diameter was 36.9μm and the cell density was 1.9×107cells/cm3.Die temperature had a significant influence on cell morphology, and the higher the temperature, the larger the cell size, and more serious the cell coalescence. The proper screw speed was benefit to deceasing cell size and increasing cell density. The CO2 flow rate had a obvious effect on the foaming behavior of composites.