Effect of Recycling on the Rheological, Mechanical and Optical Properties of Polycarbonate
The research was aimed at analyzing the polycarbonate scrap arising during production and its possible secondary utilization. The analysis of morphological, rheological and thermal data revealed significant differences between the original pellets and the reground material obtained from injection molded parts. Test specimens were injection molded from various mixtures of the virgin and the reground material, and their mechanical and physical properties were analyzed. Based on the results the reground material may be used in less than 20% proportion, as the mechanical properties of the products do not deviate significantly from those of the products made from virgin polycarbonate.
Closing the loop on plastic packaging materials: What is quality and how does it affect their circularity?
While attention on the importance of closing materials loops for achieving circular economy (CE) is raging, the technicalities of doing so are often neglected or difficult to overcome. These technicalities determine the ability of materials, components and products (MCPs) to be properly recovered and redistributed for reuse, recycling or recovery, given their remaining functionality, described here as the remaining properties and characteristics of MCPs. The different properties of MCPs make them useful for various functions and purposes. A transition, therefore, towards a CE would require the utmost exploitation of the remaining functionality of MCPs; ideally, enabling recirculation of them back in the economy. At present, this is difficult to succeed. This short communication article explains how the remaining functionality of MCPs, defined here as quality, is perceived at different stages of the supply chain, focusing specifically on plastic packaging, and how this affects their potential recycling. It then outlines the opportunities and constraints posed by some of the interventions that are currently introduced into the plastic packaging system, aimed at improving plastic materials circularity. Finally, the article underpins the need for research that integrates systemic thinking, with technological innovations and policy reforms at all stages of the supply chain, to promote sustainable practices become established.
Role of plasticity in heat generation during high rate deformation and fracture of polycarbonate
The role of plastic deformation in generating heat during dynamic compression and fracture of polycarbonate was examined in a combined experimental and numerical investigation. Split Hopkinson pressure bar (SHPB) experiments and opening mode dynamic fracture experiments were performed to measure the thermomechanical response of polycarbonate at various loading conditions. A companion set of dynamic, thermomechanically coupled explicit finite element simulations of the tested geometries was performed to isolate the temperature increase of the polymer due to plasticity effects only, and these were then compared to the experiments to identify the role of plasticity in the overall heating of the polymer. Temperature measurements during the experiments were made with a remote sensing technique that utilizes the detection of infrared radiation. Polycarbonate was observed to have a rate dependent yield and plastic deformation response under uniaxial compression. For the strain rates tested in the SHPB experiments (400 to 3000 s−1), the fraction of plastic work rate converted to heat was found to be approximately 0.5. The dynamic fracture experiments indicated that the maximum temperature increase in the region surrounding the propagating crack was over 100 K, and the crack tip velocity was limited to approximately 60% of the Rayleigh wave speed. The numerical simulations used the plastic behavior of polycarbonate observed during the compression SHPB experiments as inputs for an incremental plasticity model that uses a rate dependent Mises yield surface and isotropic hardening. Plastic deformation was the only source of material heating in the simulations. Good agreement between the SHPB experiments and the numerical simulations was seen for both stress and temperature during the compression event. Crack growth during the dynamic fracture simulations was imposed by a manual node release technique that duplicated the crack growth speed observed in the experiments. The dynamic fracture simulations which only included the thermoplastic effect significantly under-predicted the temperature increase in the region surrounding the propagating crack. The results indicate that plastic deformation is not the dominating source of heat generation during the dynamic fracture of polycarbonate, it only accounts for about 8% of the measured heating. Additional effects, such as thermofracture coupling, must be considered in the simulations if a more accurate comparison is to be made with experiments.