Preparation And Extrusion Foaming Using Supercritical Carbon Dioxide Of Polystyrene/Calcium Carbonate Nanocomposites

Due to its strong rigidity of molecular chain，polystyrene （PS） shows low impactstrength and other shortcomings. Moreover, polystyrene foams widely used in modern timegenerally have large cells and low cell density, which limit their application. To solve theseproblems, we successfully prepared PS/CaCO₃nanocomposites which have bettertoughness, thermal stability and heat resistant property. Furthermore, we investigated theirextrusion foaming behavior at CaCO₃content of below and above10wt%usingsupercritical carbon dioxide. Finally, we successfully prepared PS/CaCO₃nanocompositesfoams which have bimodal cell morphology through optimizing process parameters andequipment.Firstly, we prepared PS/CaCO₃nanocomposites at different CaCO₃contents with twodifferent extrusion equipment, the traditional twin-screw extruder and novel triple screwextruder. Then, we compared the mechanical properties, microstructure, flow properties,thermal stability and heat resistant property between the nanocomposits prepared by thesetwo kinds of process. The experimental results showed that the nanocomposites prepared bynovel triple screw extruder had better properties at the same CaCO₃content. We obtainedPS/CaCO₃nanocomposite having slightly better tensile strength and good impact strengthwhich had an increase of43.89%at the CaCO₃content of3wt%using novel triple extruder.At the same time, the Initial Decomposing Temperature and Vicat Softing Temperature hada modest increase too.On the basis, we investigated the extrusion foaming behavior of the PS/CaCO₃nanocomposites prepared by triple screw extruder using supercritical carbon dioxide. Wesystematically studied the effect of CaCO₃content, die convergence, die temperature, diepressure and CO₂flow rate on the extrusion foaming behavior. The results revealed thatproper CaCO₃content could improve the cell morphology, decrease cell size and increasecell density. The convergence role of the die was benefit to deceasing cell size andincreasing cell density. Die temperature had a significant influence to cell morphology, andthe higher the die temperature, the larger the cell size, and more serious the cell coalescence. CO₂flow rate had an obvious effect on the foaming behavior of nanocomposites, and whenthe gas flow rate was2.0ml/min, we get best cell morphology. In addition, we found thatsupercritical dioxide had a certain role in promoting the dispersing of nano-CaCO₃particlesin PS melt.Finally, the extrusion foaming behavior of PS/CaCO₃nanocomposites at higher CaCO₃content was researched. The results show that we could obtain PS/CaCO₃foams withbimodal cell morphology at higher CaCO₃contents. After investigating the foamingbehavior of nanocomposites at higher CaCO₃contents, we successfully prepared PS/CaCO₃nanocomposites foams which have good bimodal cell morphology through optimizingprocess parameters and equipment.