Application of low-grade recyclate to enhance reactive toughening of poly(ethylene terephthalate)

Abstract This paper presents a new recognition in reactive toughening of poly(ethylene terephthalate) (PET), namely the major effect of the molecular weight of PET on the evolution of the compatibilization and crosslinking reactions with ethylene-butyl acrylate-glycidyl methacrylate (EBA-GMA) type reactive terpolymer, and thus indirectly on its toughening efficiency. It was found that the use of highly degraded recycled PET (rPET) grades, due to the available larger number of reactive functional end groups and increased mobility of the decreased-molecular-weight chains, multiplies the impact strength of the product compared to that of original PET (oPET) with identical EBA-GMA contents. The evinced noticeable difference between the toughening behaviour of rPET and oPET is explained by morphological and interfacial factors and connected to differences in rheological behaviour as well. The reactive oligomeric rPET macromolecules form a Toughening Enhancer Interphase (TEI) around the dispersed particles. Based on systematic analyses, conclusions were drawn regarding the quality, i.e. optimal intrinsic viscosity (IV) range, and quantity of rPET to be used to obtain high-impact-strength PET blends (notched Izod impact strength higher than 40 kJ/m2) with optimised mechanical properties, being suitable even for injection moulding applications, at significantly lower terpolymer contents (10.0-12.5 wt%) than expected. Besides, the proposed new way of utilisation of PET recyclates, especially the unmarketable highly degraded fractions, is believed to give a new driving force in PET recycling.