Mechanical recycling of thermoplastic starch for a sustainable bioplastic future

Abstract One of the most common bioplastics on the market, thermoplastic starch (TPS), is utilized in food packaging, single-use utensils, plastic films, and compostable plastics. Mechanical recycling is the preferred option for treating TPS wastes, so that the service life of TPS products can be maximized and circular economy can be achieved. Plasticized starch alone is mechanically weak and hydrophilic, so it needs to be blended with other polymers to have good mechanical properties. Although TPS blends can be mechanically recycled, the number of reprocessing cycles greatly depends on the other types of polymers. For instance, TPS/poly(butylene adipate-co-terephthalate) (PBAT) blends (up to 30TPS/70PBAT) did not show notable decrease in mechanical properties even after seven reprocessing cycles. Meanwhile, 2.5TPS/polyethylene (PE) displayed significant reduction in mechanical strength after one reprocessing cycle. TPS/20 almond shell powder (ASP) could withstand two to three reprocessing cycles, but the biocomposite showed significant reduction in impact strength after reprocessing. In contrast, when 1wt% of TPS-poly(lactic acid) (PLA) was mixed with polyethylene terephthalate (PET), its mechanical strength declined considerably. The TPS-PLA/PET biocomposite was unfit for reprocessing. Therefore, in this mini-review, the different end-of-life treatment options for bioplastic wastes are briefly introduced. Then, this article focuses on the recent updates on mechanical recycling of TPS-related polymer blends.