Mitigating Defects in LDPE Films: Role of Process Parameters, Contaminants, and Compatibilizers in Extrusion Processes

Abstract

Annually, the global production of plastics amounts to 400 million metric tons of which 100 metric tons is polyethylene (PE). Approximately 22% of the total PE produced globally is low-density polyethylene (LDPE). LDPE is primarily used in packaging applications, including films, bags, containers, and dispensing bottles, as well as various molded products. Despite its diverse uses, packaging remains the most predominant application for LDPE. Further, the rising demand for multifunctional packaging has led to complex material blends which complicate the recycling process due to compatibility issues and defects in recyclates. Therefore, opening avenues for mechanical recycling. Efficient mechanical recycling requires effective compatibilization strategies, particularly through optimized re-extrusion processes. This study focusses on the re-extrusion of recycled LDPE (r-LDPE). A comprehensive literature review was conducted to identify the state-of-the-art on the re-extrusion of polymers and its important process parameters. Further, the study also highlights the types of visual defects in polymeric films and ways to characterize them. This study examines the impact of multiple re-extrusion cycles and various extrusion process parameters: feed method (volumetric and gravimetric), temperature, screw profiles (MODIFIED and STANDARD), degassing on the quality of rLDPE materials. Additionally, the influence of common contaminants such as, polyamide-6 (PA6), polypropylene (PP), and linear low-density polyethylene (LLDPE)) and the compatibilizer PE-grafted maleic anhydride (PE-g-MA) on the quality of recyclates is evaluated. For this, the frequency of visual defects is counted, and types of defects are analyzed. Further, a correlation is drawn between the flow properties of the samples. Additionally, the rheological and mechanical properties of some samples were also analyzed. Finally, the key findings were validated further by the processing of rLDPE with PEg-MA.