Efficient Recycling of PET-PE Multilayer Packaging Materials Based on Enzymatic Depolymerization of PET

Abstract

The transition to a sustainable, circular economy requires more plastic waste to be recycled into high-quality recycled plastics. However, it is challenging to recycle mixed waste fractions or common multilayer materials by using current mechanical recycling technology. Enzymatic hydrolysis potentially offers a solution because of its mild conditions and selectivity. In this study, we show that polyester hydrolases can be applied to recycle PET-PE multilayer packaging waste without costly amorphization pretreatment. Polyester hydrolases were produced by recombinant Pichia pastoris yeast and used to efficiently depolymerize the PET layer of PET-PE multilayer trays. High yields were obtained at laboratory scale with unpurified enzyme and high PET-PE loading (10–20% w/w PET-PE, ≥94% PET depolymerization, and ≥80% terephthalic acid recovery). The enzymatic reaction was scaled up to 4.5 kg of PET-PE production waste. After depolymerization (≥95% PET depolymerized), terephthalic acid was isolated and repolymerized into rPET. The remaining PE layer was recovered, treated with an alkaline cleaning step to remove residual PET contamination, and successfully reprocessed into rPE films with similar properties to virgin low-density PE. This study demonstrates the applicability of enzymatic hydrolysis for the recycling of PET-PE multilayer materials and highlights its general potential for the recycling of polyesters in mixed post-consumer waste.