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

Abstract

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.

Starch Maleate/Epoxidized Soybean Oil/Polylactic Acid Films with Improved Ductility and Biodegradation Potential for Packaging Fatty Foods

“…The film, however, had a low yield stress (σ yield ≈ 40.61 MPa) and underwent a larger strain deformation before fracture (ε b ≈ 10.29% corresponding to U T ≈ 2.79 MJ/m 3 ), which were typical of a moderately ductile and tough film. These characteristics implied (as previously discussed in our earlier work) 32 that ESO-plasticized PLA chains (ΔT g : 0.7 °C per % ESO content) 62 could deform and transmit limited stress through the weak ESO/PLA interface, favoring its early debonding. Conversely, the absence of phaseseparated ESO-rich regions in the SM/ESO/PLA film likely retained continuity and maximized its ability to withstand stress at their interface (σ max ≈ 40.6 MPa).…”

“…[D] Photos and SEM fracture morphology of [I,II] ESO/PLA and [III,IV] SM/ESO/PLA films. Reprinted with permission . Copyright 2022 American Chemical Society.…”

“…[D] Plotted values corresponding to the mechanical properties of films made from starch/PLA blends that were compatibilized via alternative strategies. Reprinted with permission . Copyright 2021 American Chemical Society.…”

“…Moreover, their study needed non-recyclable toluene/DMAc solvent for maleate synthesis, which makes the process less sustainable. Given that recyclable, imidazolium chloride-based ionic liquid has been previously used to obtain extractives from food, and catalyze starch modifications, we employed ionic liquids to obtain high-DS SMs (herein, readers are urged to read our previous publications to understand the challenges of the topic) , for use in SM/ESO/PLA food packaging films. Herein, we hypothesized that reactive carboxylic groups of high-DS amylose-rich corn SMs could initiate epoxy ring-opening of ESO, inducing its subsequent interactions with carboxylic end groups of PLA to make functional films for advanced food packaging applications (Scheme ).…”

Enhancement of strength and toughness of bio-nanocomposites with good transparency and heat resistance by reactive processing

“…Unfortunately, the exceptions are still rare, especially by using traditional processing equipment. Secondly, nanofillers and bio-matrix are intrinsically immiscible and aggregation of nanofillers is inevitably occurred especially at high content ( Ding et al., 2021 ; Jiang et al., 2020 ; Roy Goswami et al., 2021 ; Wang et al., 2021 ), resulting in the compromising of multi-functionalities toward versatile applications. For example, it is critically difficult to achieve transparent nanocomposites owing to the aggregation of the fillers in the transparent polymer matrix ( Liu et al., 2021 ; Sato et al., 2020 ).…”