Mechanical recycling of multiphase contaminated plastic waste via physical compatibilization: a study on rheological, morphological and mechanical properties

Abstract

During the recycling of polyethylene (PE)-based agricultural film waste, the presence of small amounts of polypropylene (PP)-containing films can significantly deteriorate the mechanical properties of the recycled material. This is primarily due to the immiscibility between PE and PP in such complex multiphase systems. Physical compatibilization is widely regarded as the most efficient and practical method for improving mechanical performance and interfacial adhesion in such mechanically recycled multiphase waste systems. In this study, propylene-ethylene elastomer (EPR) and ethylene-octene copolymer (EOC) were selected as physical compatibilizers for both binary model PE/PP blends and quaternary model recycled PEs/PPs blends. The blends consisted of virgin LLDPE, LDPE, and their mixtures as the major phase, combined with 10 wt% PP as the minor phase and 7% compatibilizer. The specific research strategy was to enhance mechanical performance in the presence of physical compatibilizers by inducing and/or modifying the morphological structures within the blends, supported by rheological analysis. The compatibilization effects were initially investigated through rheological and morphological analyses. A decrease in complex viscosity and storage modulus, particularly at lower frequencies, was found in 2 small-amplitude oscillatory shear (SAOS) rheology, indicating improved interfacial compatibility between PE and PP. These findings were further supported by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which revealed finer morphologies and significantly reduced dispersed domain sizes in both compatibilized systems. As a result of enhanced interfacial adhesion and the elastic features of the compatibilizers, notable improvements in impact resistance, tear resistance, and elongation at break were achieved. In summary, compared to EPR, EOC demonstrated superior compatibilization performance in the recycled blends, likely due to its ethylene/octene segmental structure, which exhibits greater chemical affinity with polyethylene. The ultimate target is to guide the mechanical recycling of contaminated plastic waste through establishing rheology-morphology-property relationships in complex multiphase systems. This study offers valuable insights into effective compatibilization strategies for complex multiphase polymer recycling systems.