SIMULATING POST-CONSUMER PLASTIC WASTE BY ACCELERATED THERMAL AGEING: AN INVESTIGATION ON POLYAMIDE 6,6 COMPOSITES

Recycling post-consumer plastic waste is challenging compared to post-industrial recycling as it unveils a series of disadvantages, specifically: (1) the waste stream has a highly variable composition, (2) it is often contaminated, and (3) it could contain degraded polymers. This last aspect is more relevant for products with a long lifespan, such as electrical equipment. Studying the recyclability of the plastic waste from such products can be a complex task because of the difficulty to foresee the properties of the degraded material after a lifespan that could reach up to 30 years. This study aims at creating a model able to predict the mechanical properties of glass fiber reinforced plastics (GFRP) used in low-voltage circuit breakers. Specifically, the materials of choice are two polyamide 6,6 based composites, differing in glass fiber content and type of the added flame retardant agents. Three-point bending test, DSC and FTIR analysis have been carried on the materials before and after performing a thermal aging at different temperatures and exposure times. From the results, a decrease in flexural strength and an increase in crystallinity after aging was observed. The spectroscopic analysis suggests that the thermal treatment has caused oxidation of the polymeric molecules. By plotting the mechanical property of the treated materials as a function of the aging time, at different aging temperatures, the time t20 at which for each temperature a 20% decay of the material property has occurred was determined. Such decay has been identified by the producer as the maximum acceptable loss for the intended application of the material. An Arrhenius-type equation resulted to correlate well the aging time t20 and the aging temperature. The developed model can be applied to experimentally recreate the maximum acceptable property loss, producing materials that simulate, in first approximation, a degraded post-consumer waste, allowing to better investigate its recyclability.