Comparative Study of the Degradation of the Green HDPE and Petrochemical HDPE in the Primary Recycling

Abstract

Primary polymer recycling involves the reprocessing of defective parts and scraps in a processing line. The critical limitation for excessive use of primary recycling consists of the need to maintain the properties of the polymer above the required minimum level. The polymer degradation during the extrusion occurs by the combination thermal, oxidative and mechanical degradation. This work investigated the degradation of HDPE (High Density Polyethylene). Green HDPE (PV) and petrochemical HDPE (PN) were processed five times in a single-screw extruder and the flow rate, crystallinity and impact strength properties were evaluated. The increase in the number of reprocessing cycles increased the flow index and crystallinity values. The increase in the degree of crystallinity of the polymer, verified by the DSC analysis, evidenced the degradation of the material associated to the decrease of the size of the main chain (chain scission mechanism). The impact strength showed no significant change after five reprocessing cycles. Contrary variations were found in the crystallinity index considering the first and fifth processing, suggesting a change in the predominant mechanism of degradation.