Macromolecular Science & Technology Branch, U.S. Army Research Laboratory , Aberdeen Proving Ground, Maryland 21005, United States.
TKC Global Solutions, LLC , Aberdeen, Maryland 21005, United States.
ACS Appl Mater Interfaces. 2015 Nov 18;7(45):25464-72. doi: 10.1021/acsami.5b08317. Epub 2015 Nov 9.
Cellulose nanofibrils (CNFs) are a class of cellulosic nanomaterials with high aspect ratios that can be extracted from various natural sources. Their highly crystalline structures provide the nanofibrils with excellent mechanical and thermal properties. The main challenges of CNFs in nanocomposite applications are associated with their high hydrophilicity, which makes CNFs incompatible with hydrophobic polymers. In this study, highly transparent and toughened poly(methyl methacrylate) (PMMA) nanocomposite films were prepared using various percentages of CNFs covered with surface carboxylic acid groups (CNF-COOH). The surface groups make the CNFs interfacial interaction with PMMA favorable, which facilitate the homogeneous dispersion of the hydrophilic nanofibrils in the hydrophobic polymer and the formation of a percolated network of nanofibrils. The controlled dispersion results in high transparency of the nanocomposites. Mechanical analysis of the resulting films demonstrated that a low percentage loading of CNF-COOH worked as effective reinforcing agents, yielding more ductile and therefore tougher films than the neat PMMA film. Toughening mechanisms were investigated through coarse-grained simulations, where the results demonstrated that a favorable polymer-nanofibril interface together with percolation of the nanofibrils, both facilitated through hydrogen bonding interactions, contributed to the toughness improvement in these nanocomposites.
纤维素纳米纤维（CNFs）是一类具有高纵横比的纤维素纳米材料，可从各种天然资源中提取。它们高度结晶的结构赋予纳米纤维优异的机械和热性能。CNFs 在纳米复合材料应用中的主要挑战与其高亲水性有关，这使得 CNFs 与疏水性聚合物不兼容。在这项研究中，使用表面带有羧酸基团的各种比例的 CNFs（CNF-COOH）制备了高度透明和增韧的聚甲基丙烯酸甲酯（PMMA）纳米复合材料薄膜。表面基团使 CNFs 与 PMMA 之间的界面相互作用有利，从而促进亲水性纳米纤维在疏聚合物中的均匀分散和纳米纤维的渗流网络的形成。受控的分散导致纳米复合材料具有高透明度。对所得薄膜的机械分析表明，低百分比的 CNF-COOH 负载可作为有效的增强剂，使薄膜比纯 PMMA 薄膜更具延展性，因此更坚韧。通过粗粒度模拟研究了增韧机理，结果表明，有利的聚合物-纳米纤维界面以及通过氢键相互作用促进的纳米纤维的渗流有助于提高这些纳米复合材料的韧性。
