超临界氮气对聚苯乙烯微观形态的影响——喷泉效应与层状结构的形成

当流体的温度和压力处于它的临界温度和临界压力以上时,称该流体处于超临界状态,为超临界流体.超临界流体表现出许多不同于一般气体和液体的特性,如溶质在超临界流体中的溶解度可较同温常压下溶质在同种气体中的溶解度大很多,超临界流体密度与液体的密度相近,其粘度却比液体小近百倍,导热系数比常压气体大得多等.由于超临界流体具有这些不同寻常的特性,因而以超临界萃取为代表的超临界流体已有广泛的工业应用.近年来超临界流体在聚合物加工中的应用逐渐受到重视,如超临界分级、造粒、气体辅助注塑成型、发泡成型等1～3].

THE EFFECTS OF SUPERCRITICAL FLUID ON MORPHOLOGY OF POLYSTYRENE IN GAS-ASSISTED INJECTION MOLDING-FOUNTAIN FLOW EFFECT AND LAMINAR STRUCTURE

The effect of supercritical fluid on morphology of polystyrene in gas-assisted injection molding was studied,the SEM result showed that the morphology of polystyrene treated by supercritical fluid nitrogen gas was very different from that of untreated polystyrene.There was a laminar structure in treated polystyrene that induced by fountain flow when the melt was propelled by the gas in gas-assisted injection molding.It was also found that gas penetration induced the occurrence of self-similar structure,e.g.fractal structure which was related with viscosity finger effects.