Impact of montmorillonite reinforcement on the physical recyclability of biobased and petroleum-based polyesters

Montmorillonite (MMT) is commonly utilized to enhance the gas barrier, stiffness, and flame resistance of thermoplastic polyesters. This study examines the effect of MMT on the stability of various polyester properties during physical recycling. The primary objective was to determine whether MMT-reinforced materials exhibit more pronounced property changes compared to unreinforced counterparts during the recycling process. The research focused on two petroleum-based polymers—poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT)—as well as two bio-based polymers, poly(lactic acid) (PLA) and poly(butylene succinate) (PBS).Key property changes affecting the usability of injection-moulded products, such as shrinkage, flexural strength, stiffness, and notched Izod impact strength, were measured. The underlying reasons for these changes were elucidated through investigations involving solution viscosity, morphology, and electron microscopy.The findings suggest that recycling with MMT leads to property alterations similar to those seen in unreinforced materials; however, the rate of change is considerably greater in nanocomposites. In particular, linear shrinkage decreased by 0.01–0.60 % and volumetric shrinkage by 1.0–2.6 % after the second extrusion cycle. Flexural strength increased by up to 3.8 % for PBT/MMT and 4.3 % for PLA/MMT nanocomposites, while impact strength showed a decrease of up to 13 % in PET nanocomposite. Additionally, MMT increased the crystallization temperature by 11–12 °C for PET and by 1–2 °C for the other polyester, highlighting its nucleation effect.This study also demonstrated that MMT does not uniformly enhance polyester recyclability; rather, its effects vary significantly depending on the polymer matrix. Additionally, a generalized model was developed to predict the variations in crystallinity and density in relation to changes in mechanical properties across all material types. Thus, these results provide valuable insights into optimizing the use of MMT in polyester recycling to improve performance and sustainability.