DWI-Leibniz-Institute for Interactive Materials, RWTH Aachen University , Forckenbeckstr. 50, 52056 Aachen, Germany.
ACS Appl Mater Interfaces. 2015 Mar 4;7(8):4595-607. doi: 10.1021/am507726t. Epub 2015 Feb 17.
Natural high-performance materials inspire the pursuit of ordered hard/soft nanocomposite structures at high fractions of reinforcements and with balanced supramolecular interactions. Such biomimetic design principles remain difficult to realize for bulk nanocomposites. Herein, we establish an effective drawing procedure that induces a high orientation of crystalline cellulose nanocrystals (CNCs) in a matrix of carboxymethylcellulose (CMC) at high level of reinforcements (50 vol %). We show such alignment in rather thick bulk films and report synergetic improvement with a simultaneous increase of stiffness, strength, and work-to-fracture as a function of the degree of alignment. Scanning electron microscopy and two-dimensional X-ray diffraction quantify the alignment of the cylindrical nanoparticles and link it to the extent of drawing and improvements in mechanical properties. We further show that the decline in mechanical properties of such waterborne all biobased nanocomposites at high relative humidity can be balanced using supramolecular modulation of the ionic interactions by exchanging the monovalent Na(+) counterion, present in CMC and CNC with di- or trivalent Cu(2+) and Fe(3+). This contribution demonstrates the importance of aligning one-dimensional reinforcements to achieve synergetic improvement in mechanical properties in sustainable bioinspired nanocomposites and suggests pathways to prepare water-stable materials based on a waterborne processing route.
天然高性能材料激发了人们对高比例增强体和平衡超分子相互作用的有序硬/软纳米复合材料结构的追求。这种仿生设计原则对于块状纳米复合材料仍然难以实现。在此，我们建立了一种有效的拉伸程序，在高含量（50 体积%）的增强体下，在羧甲基纤维素（CMC）基质中诱导结晶纤维素纳米晶体（CNC）的高取向。我们在相当厚的块状薄膜中展示了这种取向，并报告了随着取向程度的增加，刚度、强度和断裂功的协同提高。扫描电子显微镜和二维 X 射线衍射定量了圆柱形纳米粒子的取向，并将其与拉伸程度和机械性能的提高联系起来。我们进一步表明，通过用二价或三价的 Cu(2+)和 Fe(3+)取代存在于 CMC 和 CNC 中的单价 Na(+)抗衡离子，对离子相互作用进行超分子调节，可以平衡这种基于全生物基的水性纳米复合材料在高相对湿度下机械性能的下降。本研究证明了在可持续仿生纳米复合材料中，通过一维增强体的取向来实现机械性能协同提高的重要性，并提出了通过水性加工路线制备水稳定材料的途径。
