Restabilization of Recycled, CaCO sub 3 -Filled Polypropylene: Assessment of Reprocessing Induced Modifications and Processing Stabilizer Effectiveness

Postconsumer recycled polypropylene, filled with 15% CaCO sub 3 was restabilized at various degrees utilizing different processing stabilizers, one of which is especially prepared to counter the deactivating effects of fillers and other moieties. The polymer was then subjected to multiple extrusion cycles for the purpose of studying the effects of the extent and temperature of reprocessing on its chemical stability. The relative effectiveness of the various restabilization recipes used was also examined. The process-induced material degradation is primarily due to chain scission, which causes an average molecular weight reduction; its progression was monitored by measuring the decrease in viscosity. It is determined that degradation increases linearly with the extent of reprocessing while its activation energy is roughly equal to 30 kj/mol. Simple model is built and used to quantitively evaluate the potency of each additive used; it presumes that the protection of each individual stabilizer may be explicitly factored out in a product expression. These results suggest useful ways of optimizing stabilization according to the particular processing and product requirements.