Structure–Property Relationships in PET /Elastomer/Glass Fibre Composites Containing Recycled PET of Varying Origins

The utilisation of recycled polymer raw materials is becoming increasingly common in research and development; however, variability in source and quality makes it difficult to draw general conclusions. In this work, the behaviour and applicability of recycled poly(ethylene terephthalate) (rPET) from two different origins, post‐industrial PET (prPET) of higher quality and riverine PET litter (rrPET) of lower quality, were examined in PET/ethylene‐butyl‐acrylate‐glycidyl methacrylate (EBA‐GMA) blends and in their composites with varying glass fibre (GF) contents (10–20 wt%), and were compared with those of the original PET (oPET) counterparts. As it was expected from the binary PET/EBA‐GMA blends, rrPET had the highest impact strength of 44 kJ/m 2 compared to that of prPET (25 kJ/m 2 ) and oPET (11 kJ/m 2 ), due to the fact that the more degraded rPET molecules effectively formed a toughening enhancer interface (TEI) and provided improved compatibilisation. When 10 or 20 wt% GF was used, the fibres stiffened the polymer matrix, lowering the toughening efficiency of EBA‐GMA. Other mechanical properties of the composites—like tensile strength—were quite similar despite the diverse degradation state of the polymer matrices, especially in the ternary composites. The differential scanning calorimetry (DSC) measurements indicated increasing crystallinity (CRF) with decreasing molecular weight and increasing GF content, the latter demonstrating the nucleating effect of the glass fibres. These results indicate that lower‐quality—even environment derived waste—rPET fractions can be used nearly as successfully as higher‐quality grades when properly reinforced and toughened, making them a sustainable alternative to virgin polymers.