Chain-Extending Modification for Value-Added Recycled PET: A Review

The global environmental issues caused by plastic incineration are continuously increasing, along with the demand for polyethylene terephthalate (PET)—27 million metric tons of PET was demanded in 2020. Therefore, PET recycling has emerged as the core of the global circular economy. In particular, PET recycling methods are categorized into two pathways: mechanical and chemical recycling, wherein mechanical recycling is more efficient than chemical recycling. However, PET undergoes heat-induced degradations during mechanical recycling such as reduction in molecular weight (MW) and viscosity. Therefore, feasible methods are required to overcome such challenges. This article details the mechanical recycling process of PET using a chain-extending extrusion method. Accordingly, various chain extenders (CEs) were reviewed to identify their effects on recycled PET (rPET) properties and reactive extrusion processes. Moreover, we detailed the recent progress in the reactive extrusion method used for PET recycling based on the effects of various CEs on rPET properties.