Kim Mikhail, Hillel Coral, Edwards Kayrel, Pietro William, Mermut Ozzy, Barrett Christopher J
Department of Chemistry, McGill University Montreal QC Canada
Department of Physics and Astronomy, York University Toronto ON Canada.
RSC Adv. 2024 Aug 16;14(35):25771-25784. doi: 10.1039/d4ra02211d. eCollection 2024 Aug 12.
Biopolymer composite materials were prepared by combining bio-sourced cationic water-soluble chitosan with bi-functional water-soluble anionic azo food dyes amaranth (AMA) or allura red (ALR) as ionic cross-linkers, mixing well in water, and then slow-drying in air. The electrostatically-assembled ionically-paired films showed good long-term stability to dissolution, with no re-solubility in water, and competitive mechanical properties as plastic materials. However, upon exposure of the bioplastics to low power light at sunlight wavelengths and intensities stirring in water, the stable materials photo-disassembled back to their water-soluble and low-toxicity (edible) constituent components, structural photo-isomerization of the azo ionic crosslinkers. XRD, UV-vis, and IR spectroscopy confirmed that these assemblies are reversibly recoverable and so can in principle represent fully recyclable, environmentally degradable materials triggered by exposure to sunlight and water after use, with full recovery of starting components ready for re-use. A density functional theory treatment of the amaranth azo dye identified a tautomeric equilibrium favouring the hydrazone form and rationalized geometrical isomerization as a mechanism for photo-disassembly. The proof-of-principle suitability of films of these biomaterial composites as food industry packaging was assessed measurement of mechanical, water and vapour barrier properties, and stability to solvent tests. Tensile strength of the composite materials was found to be 25-30 MPa, with elongation at break 3-5%, in a range acceptable as competitive for some applications to replace oil-based permanently insoluble non-recyclable artificial plastics, as fully recyclable, recoverable, and reusable low-toxicity green biomaterials in natural environmental conditions.
通过将生物源阳离子水溶性壳聚糖与双功能水溶性阴离子偶氮食用染料苋菜红（AMA）或诱惑红（ALR）作为离子交联剂相结合，在水中充分混合，然后在空气中缓慢干燥，制备了生物聚合物复合材料。静电组装的离子对薄膜对溶解具有良好的长期稳定性，在水中不重新溶解，并且具有与塑料材料相当的机械性能。然而，当这些生物塑料在阳光波长和强度下暴露于低功率光并在水中搅拌时，稳定的材料会光解回其水溶性和低毒性（可食用）的组成成分，即偶氮离子交联剂的结构光异构化。X射线衍射、紫外可见光谱和红外光谱证实这些组装体是可逆可回收的，因此原则上可以代表在使用后通过暴露于阳光和水而引发的完全可回收、环境可降解的材料，起始成分可完全回收以供再利用。对苋菜红偶氮染料的密度泛函理论处理确定了有利于腙形式的互变异构平衡，并将几何异构化合理化作为光解的一种机制。通过测量机械性能、水和蒸汽阻隔性能以及对溶剂测试的稳定性，评估了这些生物材料复合材料薄膜作为食品工业包装的原理验证适用性。发现复合材料的拉伸强度为25-30MPa，断裂伸长率为3-5%，在某些应用中可替代油基永久性不溶性不可回收人造塑料的竞争范围内，作为在自然环境条件下完全可回收、可恢复和可重复使用的低毒性绿色生物材料。
