Ministry of Education Engineering Research Center of Starch & Protein Processing, Guangdong Province Key Laboratory for Green Processing of Natural Products and Product Safety, College of Light Industry and Food Sciences, South China University of Technology, Guangzhou 510640, China; Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Qld 4072, Australia; College of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, China.
Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Qld 4072, Australia; School of Chemical Engineering, The University of Queensland, Brisbane, Qld 4072, Australia.
Carbohydr Polym. 2016 Aug 1;146:67-79. doi: 10.1016/j.carbpol.2016.03.056. Epub 2016 Mar 22.
The focus of this study was on the effects of plasticisers (the ionic liquid 1-ethyl-3-methylimidazolium acetate, or [Emim][OAc]; and glycerol) on the changes of starch structure on multiple length scales, and the variation in properties of plasticised starch-based films, during ageing. The films were prepared by a simple melt compression moulding process, followed by storage at different relative humidity (RH) environments. Compared with glycerol, [Emim][OAc] could result in greater homogeneity in [Emim][OAc]-plasticised starch-based films (no gel-like aggregates and less molecular order (crystallites) on the nano-scale). Besides, much weaker starch-starch interactions but stronger starch-[Emim][OAc] interactions at the molecular level led to reduced strength and stiffness but increased flexibility of the films. More importantly, [Emim][OAc] (especially at high content) was revealed to more effectively maintain the plasticised state during ageing than glycerol: the densification (especially in the amorphous regions) was suppressed; and the structural characteristics especially on the nano-scale were stabilised (especially at a high RH), presumably due to the suppressed starch molecular interactions by [Emim][OAc] as confirmed by Raman spectroscopy. Such behaviour contributed to stabilised mechanical properties. Nonetheless, the crystallinity and thermal stability of starch-based films with both plasticisers were much less affected by ageing and moisture uptake during storage (42 days), but mostly depended on the plasticiser type and content. As starch is a typical semi-crystalline bio-polymer containing abundant hydroxyl groups and strong hydrogen bonding, the findings here could also be significant in creating materials from other similar biopolymers with tailored sensitivity and properties to the environment.
本研究的重点是增塑剂（离子液体 1-乙基-3-甲基咪唑乙酸盐，或 [Emim][OAc]；和甘油）对淀粉结构在多个长度尺度上的变化以及老化过程中增塑淀粉基薄膜性能变化的影响。通过简单的熔融压缩成型工艺制备薄膜，然后在不同的相对湿度（RH）环境下储存。与甘油相比，[Emim][OAc]可使 [Emim][OAc]增塑淀粉基薄膜更加均匀（无凝胶状聚集物，纳米尺度上的分子有序性（结晶）较少）。此外，在分子水平上，淀粉-淀粉相互作用较弱但淀粉-[Emim][OAc]相互作用较强，导致薄膜的强度和刚性降低，柔韧性增加。更重要的是，与甘油相比，[Emim][OAc]（尤其是在高含量下）在老化过程中更有效地保持增塑状态：致密化（特别是在无定形区域）受到抑制；结构特征，尤其是纳米尺度上的结构特征得到稳定（尤其是在高 RH 下），这可能是由于 [Emim][OAc]抑制了淀粉分子相互作用，这一点通过拉曼光谱得到了证实。这种行为有助于稳定机械性能。尽管如此，在储存过程中（42 天），两种增塑剂的淀粉基薄膜的结晶度和热稳定性受老化和水分吸收的影响较小，但主要取决于增塑剂的类型和含量。由于淀粉是一种含有丰富羟基和强氢键的典型半结晶生物聚合物，因此这里的发现对于创造具有环境敏感性和特性的其他类似生物聚合物材料也具有重要意义。
