Key properties to understand the performance of polycarbonate reprocessed by injection molding

The reprocessing of injection-molded polycarbonate was studied in an attempt to understand the physical background for the variation of its performance upon sequential molding cycles. The effect of reprocessing on different properties of the moldings and the regrind is presented and discussed. A quantitative analysis of the Fourier transform IR spectra indicates that phenol and carbon dioxide are released during the initial cycles, probably due to molecular scission near the chain ends. Most of the results obtained agree well with the findings reported elsewhere. Essentially, the molecular weight, the free volume, and the specific volume were found to be critical properties for understanding the global performance of the moldings. Both the free volume and the reciprocal of the molecular weight depend linearly on the number of reprocessing cycles. Based on these properties, it is possible to develop relatively simple relations to estimate the variation of the rheological, optical, and mechanical properties with the number of reprocessing operations.