Recycled PET Packaging Materials of Improved Toughness— Importance of Devitrification of the Rigid Amorphous Fraction

Abstract

Degradation, a common problem faced during the processing of recycled poly(ethylene terephthalate) (PET), leads to significant embrittlement of the products, as a result of which the material loses its applicability. Increased crystallization rate of the short chains of recycled PET and obstructed mobility of the amorphous phase are the main causes of enhanced brittleness. In this research, a straightforward method is proposed for improving the toughness of recycled PET products, namely the devitrification of the rigid amorphous phase by thermal annealing, which results in enhanced molecular mobility in the amorphous fraction, thereby promoting ductile deformation. The effects of thermal annealing conditions are comprehensively evaluated on the microstructure and macroscopic properties, i.e., impact resistance, of recycled PET films. The perforation energy value of the recycled PET film is found to increase to its threefold, reaching a value higher than 18 J mm⁻¹, as a result of 10 s thermal treatment at 120 °C. Differential scanning calorimetry, dynamic mechanical analyses, and thermally stimulated depolarization current measurements provide evidence for the devitrification of the rigid amorphous fraction under these conditions, which is the key to efficient enhancement in toughness.