Multilayer plastic films are often employed for several packaging applications that are omnipresent in today’s world. Despite their ability to extend food shelf-life at various temperatures, enable cook-in-bag applications, etc., these films are challenging to recycle because the presence of multiple polymers that can be immiscible jeopardize mechanical recycling processes in the current recycling infrastructure. The solvent-targeted recovery and precipitation (STRAP) process is a possible solution to this problem, but the impact on the recovered polymer properties is still unknown. Samples of polyethylene (PE), polyethylene terephthalate (PET), and glycol-modified polyethylene terephthalate (PETG) that were obtained through STRAP were assessed for physical, molecular and thermal properties. Thermal analysis identified differences in the crystallinity and melt temperature of PE and PET, respectively, indicating, along with rheological and spectroscopic analyses, co-precipitation of different polymers. Molecular weight determination did not find significant differences between virgin and recovered polymer samples. Solvent retention in the polymer matrix from the recovery process reduced the glass transition temperature (Tg) of PET by ~25 °C. Significant solvent retention leading to Tg depression is detrimental to reintroduction to food packaging due to consumer safety and performance reductions, respectively. However, the Tg was recovered and volatiles reduced to acceptable levels by subsequent heat treatments. No significant contamination with regulated heavy metals, such as Cd, Cr, and Pb was observed indicating regulatory compliance for different applications. As multilayer packaging use continues to increase, new technologies handling post-consumer waste are critical. Further research is required to deliver a recovered resin with properties closer to virgin materials as some changes were observed to the physical properties during processing.

Characterization of recycled polymers recovered from multilayer plastic packaging films by solvent-targeted recovery and precipitation (STRAP)

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