Hydroxy Telechelic Polyethylene Additives as Compatibilizers for Mechanical Recycling Polyethylene Terephthalate/Polyethylene Mixed Waste

Mechanical recycling takes plastic waste and melt reprocesses it into new products; however, this process relies on physical sorting methods that can often be imperfect, resulting in polymer blends that are brittle and unsuited for most applications. Mechanical properties can be recovered through the presence of premade or in situ formed block copolymers that can localize at polymer-polymer interfaces and “stitch” the two phases together. In this work, we provide new insight into the mechanisms that hold these “stitches” in place, specifically in cases where compatibilizers can form a loop in a homopolymer phase. We compatibilized blends of polyethylene terephthalate (PET) and polyethylene (PE) using hydroxy telechelic PE (HOPEOH) reactive additives that we believe undergo transesterification reactions with PET homopolymer to form PET-PE-PET triblock copolymers during melt mixing. We observed increased mechanical properties and decreased dispersed phase sizes at additive loadings of only 0.5 wt% for HOPEOH with molar masses ranging from 1-20 kg/mol, indicating the bulk critical entanglement molar mass of PE is unimportant. This goes against conventional wisdom regarding necessary features of compatibilizers demonstrated to date. Comparison to blends containing monohydroxy additives of the same molar mass show the need for reaction of both chain ends to form a loop in the PE phase that can trap PE homopolymer chains via a “hook and clasp” mechanism to anchor the formed compatibilizer in the PE phase.