Reactive extrusion of polypropylene: production of controlled-rheology polypropylene (CRPP) by peroxide-promoted degradation

摘要

Results of experimental studies of free-radical-induced degradation of polypropylene (PP) in the melt phase are presented. Experiments were carried out in a co-rotating twin-screw extruder. The initiator, dicumyl peroxide (DCP) was used as a radical generator. Concentration of the peroxide was in the range 0.02-0.6 %wt. Melt flow index, mechanical, thermal and rheological properties were measured to see the effect of initiator concentration, temperature (200 and 230 degreesC) and screw rpm (30 and 70 rpm). Initiator concentration was the most significant variable. Melt flow index increased with initiator concentration. Reaction temperature and screw rpm had no significant effect on the melt flow index of extrudate. This was attributed to the minimum residence time in the extruder being sufficient for all degradation reactions to be completed. Degraded resins had more Newtonian behavior than the original resin. Viscosity reduced with peroxide concentration. Melting point of degraded resin remained relatively constant at different levels of peroxide but the crystalline fraction increased slightly. No significant change of the mechanical properties was seen up to 0.1 %wt of peroxide. Beyond 0.1 %wt elongation at break and impact strength reduced considerably. (C) 2003 Elsevier Ltd. All rights reserved.