Research data supporting "Plant-Inspired Polyaleuritate–Nanocellulose Composite Photonic Films"

Plant epidermis is a complex composite material composed of the cuticle and epidermal cells. In order to prevent dehydration, the cuticle, a water barrier composed of an outer layer (proper cuticle) connected to the cell wall of the epidermal cells via a complex matrix often referred to as cutinized cell wall, acts as a compatibilizer for water-repellent cutin and the hydrophilic polysaccharides in the cell walls. Here, biomimetic plant epidermis-inspired films with selective reflection properties were prepared by the formation of an aliphatic polyester coating on chiral nematic cellulose nanocrystal (CNC) films. Aleuritic acid, a polyhydroxylated fatty acid, was sprayed on CNC films and polymerized by hot-pressing. The micromorphology of the resultant samples was characterized by scanning electron microscopy. Polarized optical microscopy confirmed the CNC helicoidal organization in the films, responsible for the reflection of circularly polarized light, before and after hot-pressing. The chemical analysis by attenuated total reflection-Fourier transform infrared spectroscopy confirmed the polymerization of aleuritic acid into polyaleuritate with differences between filter paper and wood pulp substrates that were ascribed to water elimination during polycondensation. The characterization of the mechanical (Young’s modulus and hardness from nanoindentation tests) and hydrodynamic (water uptake and water vapor transmission rate) properties indicated that this process enhances the robustness and waterproof behavior of CNC films. These properties were comparable to those of commercial and biodegradable materials commonly used in packaging such as polyesters and cellulose derivatives, thus making these natural composites ideal for optically responsive packaging applications.植物表皮是由角质层（cuticle）与表皮细胞共同构成的复杂复合材料。为防止水分流失，角质层作为疏水屏障，由外层（proper cuticle，即固有角质层）构成，并通过通常被称为角质化细胞壁（cutinized cell wall）的复杂基质与表皮细胞的细胞壁相连，可作为疏水性角质素与细胞壁中亲水性多糖之间的相容剂。本研究通过在手性向列型纤维素纳米晶体（cellulose nanocrystal, CNC）薄膜上构筑脂肪族聚酯涂层，制备得到兼具选择性反射特性的仿生植物表皮薄膜。将多羟基脂肪酸类的紫胶桐酸（aleuritic acid）喷涂于CNC薄膜表面，随后通过热压工艺完成聚合反应。采用扫描电子显微镜对所得样品的微观形貌进行了表征。偏光显微镜（polarized optical microscopy）表征结果证实，热压前后的CNC薄膜均保持了螺旋排列结构，该结构正是圆偏振光反射的成因。采用衰减全反射-傅里叶变换红外光谱进行化学分析，结果证实紫胶桐酸聚合生成了聚紫胶桐酸酯；滤纸与木浆基底间的差异可归因于缩聚过程中的脱水反应。对样品的力学性能（通过纳米压痕测试得到杨氏模量与硬度）及流体力学性能（吸水率与水蒸气透过率）进行表征后发现，该工艺可提升CNC薄膜的耐用性与防水性能。该仿生复合薄膜的性能可与包装领域常用的商用可降解材料（如聚酯类与纤维素衍生物）相媲美，使其成为光学响应型包装应用的理想天然复合材料。