Fabrication of functional materials derived from poly(lactic acid) biopolymer composited with metal-organic frameworks (MOFs)

This work is aimed to develop biocomposite materials from degradable polylactic acid (PLA) and metal-organic frameworks (MOFs) for use in various applications, such as active packaging. MIL-53(Al) MOF nanoparticles were synthesized by an environmentally friendly process, in water medium at room temperature, followed by a calcination post-treatment process. The nano-size materials are essential for applications that require homogenous mixing, especially packaging films. PLA/MIL-53(Al) composite films consisting of 0.5, 1.0 and 2.0 %wt MOF were prepared by a solution casting technique. SEM-EDX results reveal that the composite films contain homogeneous dispersed MIL-53(Al) particles in the PLA matrix. The percent transmittance of lights in the UV-A, UV-B, and violet visible regions of the PLA/MOFs composite films was reduced with an increase in the MOFs contents. Water vapor transmission rate (WVTR) was also decreased with an increase in the MOFs contents. Oxygen transmission rate (CTR) was presented the high performance at a 1.0 %wt MOF. In addition, carbon dioxide transmission rate (OTR) was increased when MOF was introduced, especially at a 0.5 wt% MOF content. The biocomposite films have high potential for use as functional and active packaging, which are friendly to the environment. In addition, electrospun nanofibers of neat PLA and PLA/MOFs composites were prepared by using binary solvent systems of AC/DMF and AC/CHL. The composites nanofibers showed improvements of a hydrophobic property of the surfaces. A significantly modification occurred as rough surface patterns, which may be responsible for the super-hydrophobicity of the materials. Post treatments of polymer products after fabrication, especially improving chain crystallization, are commonly applied to further enhance properties of the products. In this study, a solvent-infusion cold drawing process for poly(L-lactic acid) (PLLA) filaments are developed, and its mechanisms is examined. Multiple necking behavior was observed when the filaments were drawn in water and ethanol, compared to a single-neck deformation when the experiment was conducted in air. The number of necks was also dependent on the drawing conditions, in which the number of necks decreased with an increase in the draw ratio (DR). With a further increase in the drawing speed, the number of necks of the filaments drawn in water and ethanol increased. The drawing treatments in water and ethanol lead to a decrease in the drawing stresses on the filaments. The results also indicate that ethanol is effectively infused into the PLLA filaments, leading to further chain arrangement. The process has high potential for promoting the filament’s crystallization at room temperature conditions.本研究旨在以可降解聚乳酸（polylactic acid, PLA）和金属有机框架（metal-organic frameworks, MOFs）为原料制备生物复合材料，应用于活性包装等多种场景。本研究采用环境友好的水相室温合成法制备了MIL-53(Al) MOF纳米颗粒，并经煅烧后处理工艺进行改性。纳米级材料对于需要均匀混合的应用（尤其是包装薄膜）至关重要。通过溶液流延法制备了MOF含量分别为0.5%、1.0%和2.0%质量分数的PLA/MIL-53(Al)复合薄膜。扫描电子显微镜-能谱仪（SEM-EDX）分析结果显示，复合薄膜中MIL-53(Al)颗粒在PLA基体中分散均匀。随着MOF含量提升，PLA/MOF复合薄膜在UV-A、UV-B及紫色可见光区域的透光率均有所降低。水蒸气透过率（Water vapor transmission rate, WVTR）也随MOF含量增加而下降。当MOF含量为1.0%质量分数时，氧气透过率（Oxygen transmission rate, CTR）表现出最优性能。此外，引入MOF后二氧化碳透过率（Carbon dioxide transmission rate, OTR）有所提升，尤其在MOF含量为0.5%质量分数时效果最为显著。该生物复合薄膜作为环境友好型功能活性包装材料具有极高应用潜力。此外，本研究采用AC/DMF与AC/CHL二元溶剂体系，制备了纯PLA及PLA/MOFs复合材料的静电纺纳米纤维。复合纳米纤维的表面疏水性能得到改善，表面形成的粗糙形貌可显著改变材料表面特性，这可能是赋予材料超疏水性能的关键原因。聚合物制品成型后通常会进行后处理（尤其是优化链结晶过程）以进一步提升材料性能。本研究开发了一种用于聚左旋乳酸（poly(L-lactic acid), PLLA）纤维丝的溶剂浸润冷拉伸工艺，并对其拉伸机制进行了探究。与空气中拉伸时的单颈变形不同，在水和乙醇中拉伸时，纤维丝表现出多颈缩行为。颈缩数量同样受拉伸条件影响：随着拉伸比（draw ratio, DR）提升，颈缩数量逐渐减少；而进一步提高拉伸速度时，水和乙醇中拉伸的纤维丝颈缩数量则会增加。在水和乙醇中进行拉伸处理可降低纤维丝的拉伸应力。研究结果同时表明，乙醇可有效浸润PLLA纤维丝，促进分子链进一步规整排列。该工艺在室温条件下即可有效促进纤维丝的结晶，具有极高应用价值。