【摘要】 <正> 聚丙烯(PP)的热降解和化学控制降解法七十年代开始应用于聚合物工业加工过程。聚丙烯在高温下热降解,一般认为服从无规断链机理。随降解过程进行,分子量变小,分子量分布变窄,由定向聚合反应产生的特征性高分子量尾端降解最为显著。该过程往往可显著改善PP熔体加工性,因此研究降解过程对PP熔体流变性质的影响殊属更多还原

【Abstract】 Eperimental studies were performed on a series of degraded PP resins obtained by repeated extrusion for 0 to 8 times at 250℃. By means of a capillary extrusion rheometer with various entry angles and length/diameter ratios (L/D=1, 2, 5, 10, 20, 40) of the capillaries as well as a falling sphere viscometer, the following rheological quantities were measured: zero shear rate viscosity η0, apparent viscosity η, entrance pressure loss ΔP0 and extrudate swell.Both the narrowing of the molecular weight distribution and the lowering of the molecular weight during the degradation process have profound effects on the previous flow behavours. It is suggested that stress τ1/2(whereη=η0/2), the value e(e=ΔP0/2τ) and the die swell from a very short die can be used to characterize the existence of high molecular tail of MWD, which greatly influences the processablilty of the melts.更多还原