Department of Plastics Engineering, College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, People's Republic of China.
Biopolymers. 2012 Oct;97(10):825-39. doi: 10.1002/bip.22079.
The poly(lactic acid) (PLA)/ramie fiber biocomposites were fabricated, which exhibited considerable reinforcement effect comparable to the glass fiber at the same loading. The attempts were made to understand the flow-induced morphology of ramie fibers and PLA crystals in the injection-molded PLA/ramie fiber biocomposites, thus revealing its relationship to biocomposite mechanical properties. The polarized optical microscopy (POM) and two-dimensional wide-angle X-ray diffraction (2D-WAXD) were for the first time used to determine the distribution of nature fibers, which interestingly showed the ramie fibers aligned well along the flow direction over the whole thickness of injection-molded parts, instead of skin-core structure. This easy alignment of ramie fibers during the common processing was ascribed to the intrinsically high flexibility of ramie fibers and strong interfacial interaction between PLA chains and cellulose molecules of ramie fibers. Both 2D-WAXD and differential scanning calorimeter (DSC) measurements suggested that the PLA matrix in its ramie biocomposites had rather high orientation degree and crystallinity, which was attributed to effective heterogeneous nucleation induced by ramie fibers and local shearing field in the vicinity of fiber surface. Remarkable improvement of mechanical and thermo-mechanical properties was achieved for PLA/ramie fiber biocomposites, without sacrifice of toughness and ductility. Addition of 30wt% ramie fibers increased the tensile strength and modulus of PLA/ramie fiber biocomposites from 65.6 and 1468 MPa for pure PLA to 91.3 and 2977 MPa, respectively. These superior mechanical properties were ascribed to easy alignment of ramie fibers, high crystallinity of PLA, and favorable interfacial adhesion as revealed by scanning electron microscopy (SEM) observation and theoretical analysis based on dynamic mechanical analysis (DMA) data.
聚乳酸（PLA）/苎麻纤维复合材料被制备出来，其在相同的负载下显示出与玻璃纤维相当的增强效果。人们试图了解 PLA/苎麻纤维复合材料中苎麻纤维和 PLA 晶体的流动诱导形态，从而揭示其与生物复合材料力学性能的关系。首次使用偏光显微镜（POM）和二维广角 X 射线衍射（2D-WAXD）来确定天然纤维的分布，有趣的是，结果表明苎麻纤维在整个注塑件的厚度上沿流动方向很好地排列，而不是呈皮芯结构。在常见的加工过程中，苎麻纤维很容易排列，这归因于苎麻纤维固有的高柔韧性和 PLA 链与苎麻纤维纤维素分子之间的强界面相互作用。2D-WAXD 和差示扫描量热法（DSC）测量均表明，其苎麻纤维复合材料中的 PLA 基质具有相当高的取向度和结晶度，这归因于苎麻纤维的有效异质成核和纤维表面附近的局部剪切场。PLA/苎麻纤维复合材料的力学和热机械性能得到了显著提高，而韧性和延展性没有降低。添加 30wt%的苎麻纤维使 PLA/苎麻纤维复合材料的拉伸强度和模量分别从纯 PLA 的 65.6MPa 和 1468MPa 提高到 91.3MPa 和 2977MPa。这些优异的力学性能归因于苎麻纤维的易取向、PLA 的高结晶度以及扫描电子显微镜（SEM）观察和基于动态力学分析（DMA）数据的理论分析所揭示的良好界面附着力。
