Plastic production and use have grown rapidly in the past decade; however, our ability to handle plastic waste sustainably has been mostly stagnant. Polyethylene (PE) and polyethylene terephthalate (PET) are two of the most widely used commercial polymers in the market today; however, in the US, only about 6% of PE and 19% of PET is recycled. Recycling may take many forms, but mechanical recycling is presently the dominant technology, where plastic products are sorted, ground, washed, and melt reprocessed into a new form. A major challenge for mechanical recycling is imperfect sorting which leads to impure recycle streams. Mechanical recycling of these impure streams usually leads to phase-separated, immiscible blends that are mechanically brittle and not suitable for most applications. Such uncompatibilized blends are characterized by sharp interfaces that facilitate very little stress transfer between the phases. Copolymer compatibilizers (either premade or formed via reactions <i>in situ</i>) can help overcome these challenges by localizing at the interface and “stitching” the two phases together producing tougher blends. In this work, we identified a simple reactive additive for compatibilizing 80/20 wt/wt PET/PE blends. This additive can be produced using a novel one-pot synthetic method, with precursors that could be sustainably sourced. Compatibilization is demonstrated through tensile testing, where blends containing the additive show a strain at break equivalent to that of neat PET homopolymer and almost 10x that of analogous uncompatibilized blends. Imaging of dispersed phase PE morphologies further reveals that compatibilized blends show both a decrease in the minority domain size and plastic deformation of those domains after tensile testing indicating improved stress transfer across the interface relative to the neat blends. Importantly, these additives were found to be remarkably efficient, compatibilizing blends at loadings as low as 0.5 wt/wt suggesting a new class of compatibilizers for improved mechanical recycling.

Reactive additives for mechanical recycling of PET/PE mixed waste

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ACS Fall 2022

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