Study On The Effect Of Nanofillers On The Foaming Behavior Of Polystyrene

Nucleating agents have been used to facilitate the foaming behavior of polymer using supercritical carbon dioxide as foaming agent, to fabricate foams with small cell size and big cell density, in which the nanofilles is a good choice because of its large specific surface area. In this paper, we chosed nano-clay and nano-CaCO₃ as the nucleating agents to foam polystyrene, and compared the effects of these two nanofillers with different shape on the PS foaming. On the basis of it, we studied the foaming behavior of PS/nano-clay/nano-CaCO₃ composites.Firstly, we prepared PS/nano-clay, PS/nano-CaCO₃, and PS/nano-clay/nano-CaCO₃ composites using a triple screw extruder, and tested their rheological propertis and the dispersion of nanofillers, as the essential data to analyze the foaming behavior of these composites.Then, we foamed PS/nano-clay and PS/nano-CaCO₃ composites using sc-CO2 as foaming agent by a batching autoclave. The results showed that, when adding a same content, the nucleating effect of nano-CaCO₃ was better than nano-clay, because of its large specific surface area, and foamed PS/nanoCaCO₃ composites had smaller cell size and bigger cell density. While nano-clay was platelike, having advantages on enchancing the melt strength of PS, during bubble growth, it tended to align along cell walls, which prevented cell wall rupture, and hence cell coalescence.On the basis of aforementioned studies, we studied the foaming behavior of ternary PS/nano-clay/nano-CaCO₃ composites. The results showed that, when adding nano-clay and nano-CaCO₃ into PS matrix, the nucleating effect was better than either of them, namely, nanoclay and nano-CaCO₃ had synergistic effects on enchancing the foaming property of PS, tending to manufacture foaming plastics with smaller cell size and bigger cell density. The reason of the synergistic effect was that, there were special advantages for nano-clay and nano-CaCO₃ on facilitating the foaming behavior of PS, and when they were added at the same time, they would display their respective advantages and stimulate another, leading to a better nucleating effect. Moreover, the study of foaming temperature and pressure on the synergistic effect showed that, when the foaming temperature was 100 or 110°C, the synergistic effect was poor, and when the foaming temperature became 120 or 130°C, the synergistic effect was better. While at a applicable temperature（such as 120°C）, when the pressure was between 12 MPa and 20 MPa, the synergistic effect between nano-clay and nano-CaCO₃ was good.