Improvement in the toughness and compatibility of poly(lactic acid)/starch acetoacetate through reactive melt-kneading with amine-modified silicone

Nonbiodegradable plastic pollution has taken centerstage because of its negative impacts on ecosystems, and poly(lactic acid) (PLA)/starch blends, which are biodegradable plastics, have attracted increased attention as sustainable materials. However, the poor compatibility between hydrophobic PLA and hydrophilic starch causes their composites to become brittle. In this study, to improve the compatibility between PLA and starch, the hydroxyl groups of starch were modified with acetoacetate, and amine-modified silicone was used as the compatibilizer. The acetoacetyl group readily reacts with primary amines under mild conditions to form enamines and is expected to react rapidly during the melt-kneading process. The amino groups also react with the decomposed PLA end groups via condensation. Therefore, amine-modified silicone is considered a suitable compatibilizer for PLA and starch acetoacetate (SAA). PLA/SAA/amine-modified silicone blends were prepared via melt-kneading. The toughness of PLA/SAA was improved by approximately 15 times when 3 wt% amine-modified silicone was added. Furthermore, in the SEM observation of the tensile fracture surface, it was found that the dispersibility of SAA in PLA was improved such that SAA and PLA were indistinguishable. This approach can contribute to the widespread use of biodegradable plastics in packaging materials and single-use plastics.