The Effect of Mechanical Recycling on the Thermal, Mechanical, and Chemical Properties of Poly (Butylene Adipate-Co-Terephthalate) (PBAT), Poly (Butylene Succinate) (PBS), Poly (Lactic Acid) (PLA), PBAT-PBS Blend and PBAT-TPS Biocomposite

Abstract

Mechanical recycling of plastics is regarded as the best option to minimize plastic waste pollution in the environment as it is well established and offers valorisation of plastics; however, there is limited research on the mechanical recyclability of biopolymers. This work aimed to evaluate the effect of multiple reprocessing on the mechanical, thermal, physical, chemical, and morphological properties of poly (butylene adipate-co-terephthalate) (PBAT), poly (butylene succinate) (PBS), poly (lactic acid) (PLA), PBAT-PBS blend, and PBAT-thermoplastic starch (TPS) composite. Low-density polyethylene (LDPE), a conventional non-biodegradable plastic, was also reprocessed for comparison studies. The biopolymers were extruded seven times in a twin-screw extruder and injection moulded into test specimens. Their properties were investigated at each extrusion cycle. Tensile, impact strength, and melt flow index (MFI) results of neat PBAT and PBAT-TPS were stable with slight changes throughout the seven reprocessing cycles and were comparable to LDPE. The properties of PBS, PLA, and PBAT-PBS blend, on the other hand, started to decrease after the second melt extrusion cycle. In addition, differential scanning calorimetry (DSC), thermogravimetry (TGA), and dynamic mechanical analysis (DMA) results showed that LDPE, PBAT, and PBAT-TPS exhibited better thermal and mechanical stability as compared to PBS, PLA, and PBAT-PBS blend. The FTIR spectroscopy results showed that the characteristic peaks of C=O and C–O around 1710 cm−1 and 1046–1100 cm−1 for PBS, PLA, and PBAT-PBS decreased due to multiple thermal processing, while those of PBAT and PBAT-TPS were unaffected. Scanning electron microscopy (SEM) micrographs of the fractured cross-sectional surface of PBS, PLA, and PBAT-PBS tensile specimens clearly evidenced the degradation of the biopolymers by severely fractured morphology as a result multiple reprocessing cycle. The results demonstrate that the fully biodegradable PBAT and PBAT-TPS can be mechanically recycled for at least seven cycles, and therefore, the service life of biodegradable polymers can be extended, and it is comparable with petroleum-based plastic.Graphical