Numerical Simulation of Reactive Extrusion for Polycondensation of Poly(p-phenylene terephthalamide) (PPTA)

摘要

Poly(p-phenylene terephthalamide) (PPTA), as a typical high performance fiber with excellent strength and modulus property, is usually synthesized by low temperature solution polycondensation with p-phenylenediamine(PPD) and terephthaloyl chloride(TPC) in twin screw extruders. Since the polycondensation during the process is a multicomponent reaction with high reactivity and wide viscosity range, the molecular weight and its distribution of PPTA are strongly influenced by mixing behavior of the extruder. In this paper, the polycondensation process in fully-filled conveying elements of twin screw extruder were analyzed by three-dimensional numerical simulation using the finite element method. The effects of conveying element geometry, rotating speed on mixing state were studied. In order to understand the mechanism behind the reactive extrusion process of PPTA, reaction extent and instantaneous efficiency of stretch in extruder were calculated simultaneously. The results indicate that the reaction process and mixing behavior of the PPTA flow are strongly interrelated. The increase of rotating speed promotes the reaction extent by enhancing the stretch effect, while larger screw pitch accelerates the reaction by rearranges the proportion of energy for stretch.