Recent Progress on Starch Maleate/Polylactic Acid Blends for Compostable Food Packaging Applications

Starch maleate/polylactic acid blends could replace polyethylene terephthalate in food packaging films. These films, however, are not acceptable for commercial use due to their poor performance, which is caused by processing polylactic acid with starch maleates having a low degree of maleic anhydride substitutions (DSNMR < 0.1 or DStitration < 1). Conventionally produced starch maleates produced via dry grinding or as aqueous and nonaqueous dispersions acquire a low DS due to the presence of inactive hydroxyl and maleic anhydride groups in each of the reaction systems. Low-DS starch maleates could barely interact with polylactic acid and plasticizers during blend processing; consequently, the resultant films perform poorly in terms of ductility and compostability. The key findings of this perspective indicate that recyclable ionic liquids like 1-allyl-3-methylimidazolium chloride could disrupt H-bonds among hydroxyls of starch and catalyze in situ maleic anhydride ring openings to provide functional groups for the synthesis of high-DS starch maleates (DSNMR ≥ 0.1 or DStitration ≥ 1). Improved interfacial chain interactions between high-DS starch maleates/polylactic acid and plasticizers like epoxidized soybean oil could facilitate stress-transfer and enzymatic activities of the resultant film, potentially improving its ductility and compostable properties. Besides these promising findings, this perspective also emphasizes the need for further research into identifying a wide range of ionic liquids and compostable plasticizers for producing high-DS starch maleates/polylactic acid blends, assessing the effect of interfacial chain interactions on properties of the resultant film, and determining specific usage of the film based on the barrier properties measured using standardized techniques.