Chemical Engineering Department, University of Alicante, Apartado 99, 03080 Alicante, Spain; Institute of Chemical Process Engineering, University of Alicante, Apartado 99, 03080 Alicante, Spain.
Chemical Engineering Department, Faculty of Chemistry, Regional Campus of International Excellence "Campus Mare Nostrum", University of Murcia, 30071 Murcia, Spain.
Int J Biol Macromol. 2023 Jul 31;244:125478. doi: 10.1016/j.ijbiomac.2023.125478. Epub 2023 Jun 17.
Thermoplastic starch/polyvinyl alcohol (TPS/PVA) films have limitations for being used in long-term applications due to starch retrogradation. This leads to plasticizer migration, especially when low molecular weight plasticizers such as glycerol, are used. In this work, we employed mixtures of oligomers based on glycerol citrates with higher molecular weight than glycerol as plasticizers for potato-based TPS/PVA blends obtained by melt-mixing. This constitutes an alternative to reduce plasticizer migration while keeping high swelling degree, and to provide high mechanical performance. The novelty lies in the usage of these oligomers by melt-mixing technique, aspect not deeply explored previously and that represents the first step towards industrial scalability. Prior to the blending process, oligomers mixtures were prepared with different molar ratios of citric acid (0-40 mol%) and added them. This minimizes the undesirable hydrolysis effect of free carboxylic groups on starch chains. The results demonstrated that the migration of plasticizers in TPS/PVA blends decreased by up to 70 % when the citric acid content increased. This reduction was attributed to the higher molecular weight (the majority in the range 764-2060 Da) and the 3D structure of the oligomers compared to using raw glycerol. Furthermore, the films exhibited a 150 % increase in Young's modulus and tensile strength without a reduction in elongation at break, while maintaining a high gel content, due to a moderate crosslinking.
热塑性淀粉/聚乙烯醇（TPS/PVA）薄膜由于淀粉回生，在长期应用方面存在局限性。这会导致增塑剂迁移，特别是当使用低分子量增塑剂如甘油时。在这项工作中，我们使用了基于柠檬酸甘油酯的低聚物混合物作为增塑剂，这些低聚物的分子量高于甘油，用于由熔融混合获得的马铃薯基 TPS/PVA 共混物。这是一种替代方案，可以减少增塑剂迁移，同时保持高溶胀度，并提供高机械性能。新颖之处在于使用这些低聚物通过熔融混合技术，这方面以前没有深入探索过，代表了迈向工业可扩展性的第一步。在混合过程之前，用不同摩尔比的柠檬酸（0-40 mol%）制备了低聚物混合物，并将其添加进去。这最大限度地减少了游离羧酸基团对淀粉链的水解作用的不利影响。结果表明，当柠檬酸含量增加时，TPS/PVA 共混物中增塑剂的迁移减少了高达 70%。这种减少归因于与使用原始甘油相比，低聚物的分子量更高（主要在 764-2060 Da 范围内）和 3D 结构。此外，由于适度的交联，薄膜的杨氏模量和拉伸强度增加了 150%，而断裂伸长率没有降低，同时保持了高凝胶含量。
