Poly(lactic acid)/ground tire rubber blends: flame retardancy and waste management

Abstract

In 2023, the global production of motor cars reached 94 million, which is 10% compared to the previous year, 2022. The management of waste generated by old car tires has been challenging throughout the world due to the chemical compositions and the vulcanization of tires. Unfortunately, this results in accumulation of waste car tires in landfills causing environmental harm. Nevertheless, there is one promising solution which can be applied to assist in minimizing the number of waste car tires, and it involves repurposing these tires to aid in improving properties of polymers. This approach paves the way to reduce the amount of waste tires disposed each year while improving the properties of polymers for diverse applications. This study investigates the effect of ground tire rubber (GTR) on the properties of poly (lactic acid) (PLA). However, both PLA and GTR are both extremely flammable; therefore, halloysite clay (HC) and zinc borate (ZB) at 3 wt% were added as flame retardants in pure PLA and PLA/GTR blend composites. Various techniques such as scanning electron microscopy (SEM), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), differential scanning calorimeter (DSC), cone calorimetry, rheology, tensile and impact testing were utilized to analyse the properties of the PLA, PLA/GTR, and PLA/GTR blend composites. The incorporation of GTR to neat PLA and PLA composites matrix seems to have affected most results acquired negatively. This is primarily due to the immiscibility of PLA/GTR blend. It also appears that GTR covers the nanoparticles within the PLA matrix hence hindering their effectiveness in enhancing properties of PLA. It was further observed that ZB interacted better with the PLA matrix when compared with HC. There was poor synergy between ZB and HC and this was shown in most of the results. The addition of GTR, HC and ZB seemed to have reduced the thermal stability of PLA, however the char residues of all investigative samples were greater than that of neat PLA. Cone calorimetry showed that the addition of HC to the PLA/GTR blend improved the flammability properties of the blend, with the GTR acting as a flame catalyst in majoring of the investigated samples. The addition of GTR to the PLA matrix seems to affect the mechanical properties adversely.