Alotaibi Mansour, Aldhafeeri Thamer, Barry Carol
Department of Plastics Engineering, University of Massachusetts Lowell, Lowell, MA 01854, USA.
Polymers (Basel). 2022 Jun 29;14(13):2661. doi: 10.3390/polym14132661.
During mechanical recycling, polypropylene typically is reprocessed using a single- or twin-screw extruder. The degradation of polypropylene during this reprocessing reduces the polymer's molecular weight and, consequently, limits the performance of the recycled resin. This work investigated the impact of a quad screw extruder (QSE), which has greater free volume, on the reprocessing of an impact copolymer polypropylene. To mimic the recycling process, the polypropylene was subjected to three processing cycles using a QSE and a comparable twin-screw extruder (TSE) operated at three screw speeds. The reprocessed materials were characterized for their rheological, morphological, and mechanical properties. For both extruders, increasing the number of reprocessing cycles and the screw speed resulted in higher melt flow indices, decreases in zero-shear viscosity, and shifting of the crossover points for the storage and loss moduli, which indicate reductions in the molecular weight and narrowing of the molecular weight distribution of the polypropylene. The QSE exhibited greater reductions in molecular weight compared to the TSE, probably due to the higher stresses associated with the three intermeshing points along its screws. Reprocessing caused a significant reductions in the Izod impact strength of the reprocessed polypropylene, which correlated with reductions in the particle size and particle size distribution of the dispersed rubbery phase in the polypropylene during reprocessing.
在机械回收过程中，聚丙烯通常使用单螺杆或双螺杆挤出机进行再加工。在此再加工过程中聚丙烯的降解会降低聚合物的分子量，从而限制了再生树脂的性能。本研究调查了具有更大自由体积的四螺杆挤出机（QSE）对抗冲共聚聚丙烯再加工的影响。为模拟回收过程，使用QSE和一台在三种螺杆转速下运行的可比双螺杆挤出机（TSE）对聚丙烯进行三个加工循环。对再加工材料的流变学、形态学和力学性能进行了表征。对于这两种挤出机，增加再加工循环次数和螺杆转速会导致熔体流动指数更高、零剪切粘度降低以及储能模量和损耗模量的交叉点发生偏移，这表明聚丙烯的分子量降低且分子量分布变窄。与TSE相比，QSE的分子量降低幅度更大，这可能是由于其螺杆上三个啮合点产生的应力更高。再加工导致再加工聚丙烯的悬臂梁冲击强度显著降低，这与再加工过程中聚丙烯中分散橡胶相的粒径和粒径分布的减小相关。
