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首页> 外文学位 >Pressure variation assisted fiber extraction and development of high performance natural fiber composites and nanocomposites.
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Pressure variation assisted fiber extraction and development of high performance natural fiber composites and nanocomposites.

机译：压力变化有助于纤维的提取以及高性能天然纤维复合材料和纳米复合材料的开发。

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摘要

It is believed, that due to the large surface areas provided by the nano scale materials, various composite properties could be enhanced when such particles are incorporated into a polymer matrix. There is also a trend of utilizing natural resources or reusing and recycling materials that are already available for the fabrication of the new composite materials. Cellulose is the most abundant natural polymer on the planet, and therefore it is not surprising to be of interest for composite fabrication. Basic structures of cellulose, comprised of long polysaccharide chains, are the building blocks of cellulose nano fibers. Nano fibers are further bound into micro fibrils and macro fibers. Theoretically pure cellulose nano fibers have tremendous strengths, and therefore are some of the most sought after nano particles. The fiber extraction however is a complex task.;The ultrasound, which creates pressure variation in the medium, was employed to extract nano-size cellulose particles from microcrystalline cellulose (MCC). The length and the intensity of the cavitations were evaluated. Electron microscopy studies revealed that cellulose nanoparticles were successfully obtained from the MCC after ultrasound treatment of just 30 minutes. Structure of the fractionated cellulose was also analyzed with the help of X-ray diffraction, and its thermal properties were evaluated with the help of differential scanning calorimetry (DSC). Ultrasound treatment performed on the wheat straw, kenaf, and miscanthus particles altered fiber structure as a result of the cavitation. The micro fibers were generated from these materials after they were subjected to NaOH treatment followed by the ultrasound processing.;The potential of larger than nano-sized natural fibers to be used for composite fabrication was also explored. The agricultural byproducts, such as wheat or rice straw, as well as other fast growing crops as miscanthus or kenaf, are comprised of three basic polymers. Just like in wood the polymers are: cellulose, hemicelluloses, and lignin. When subjected to elevated pressures and temperatures, we are able to get access to some of these natural polymers and use them as a matrix material for composite fabrication. Therefore, fabrication of composite materials without addition of synthetic polymers is possible. Thermal and mechanical properties of such composites are evaluated with the help of electron microscopy, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and flexural strength measurements. The chemical changes in the composites are also probed with the help of Fourier transform infrared (FTIR) analysis.;Various additives introduced into composite materials provide different properties. The addition of small amounts of synthetic polymers further enhances the properties of natural fiber composites and do not require high fabrication pressures. Calcium sulfite crystals, which are one of the coal combustion products, were combined with the natural fibers and recycled HDPE polymer to form wood substitute composites. The introduction of these additives resulted in composites with the properties similar to those of the natural wood.;Coal combustion products, often used in composite material fabrication, contain mercury which may be rereleased during composite fabrication. Mercury behavior under composite fabrication conditions, such as elevated pressures and temperatures were evaluated. Sulfite rich scrubber material, generated during the flue gas desulphurization process was the main target of the study. It was observed that the release of the mercury is highly dependent on the composite fabrication pressure as well as the temperature.
机译：据信，由于纳米级材料提供的大表面积，当将这种颗粒掺入聚合物基质中时，各种复合性能可以得到增强。还存在利用自然资源或再利用和回收已经用于制造新的复合材料的材料的趋势。纤维素是地球上最丰富的天然聚合物，因此复合材料制造引起人们的兴趣也就不足为奇了。由长多糖链组成的纤维素的基本结构是纤维素纳米纤维的基础。纳米纤维进一步结合成微纤维和大纤维。从理论上讲，纯纤维素纳米纤维具有巨大的强度，因此是一些最受追捧的纳米颗粒。然而，纤维的提取是一项复杂的任务。超声会在介质中产生压力变化，被用来从微晶纤维素（MCC）中提取纳米级纤维素颗粒。评估空化的长度和强度。电子显微镜研究表明，超声处理仅需30分钟，即可从MCC成功获得纤维素纳米颗粒。还利用X射线衍射分析了分级纤维素的结构，并借助差示扫描量热法（DSC）评估了其热性能。空化的结果是，对麦草，洋麻和桔梗进行的超声波处理改变了纤维结构。这些材料经过NaOH处理然后进行超声处理后，便从这些材料中产生了微纤维。；还探索了用于复合材料制造的大于纳米级天然纤维的潜力。农业副产品，例如小麦或稻草，以及其他快速生长的农作物，如桔梗或洋麻，均由三种基本聚合物组成。就像在木材中一样，聚合物是：纤维素，半纤维素和木质素。当承受较高的压力和温度时，我们能够使用其中的一些天然聚合物，并将它们用作复合材料制造的基质材料。因此，可以在不添加合成聚合物的情况下制造复合材料。借助电子显微镜，差示扫描量热法（DSC），动态力学分析（DMA），热重分析（TGA）和抗弯强度测量来评估此类复合材料的热和机械性能。还可以通过傅立叶变换红外（FTIR）分析来探测复合材料中的化学变化。复合材料中引入的各种添加剂具有不同的性能。少量合成聚合物的添加进一步增强了天然纤维复合材料的性能，并且不需要很高的制造压力。亚硫酸钙晶体（一种煤燃烧产物）与天然纤维和回收的HDPE聚合物结合形成木材替代复合材料。这些添加剂的引入导致复合材料具有与天然木材相似的性能。常用于复合材料制造的煤燃烧产物含有汞，该汞在复合材料制造过程中可能会释放出来。评价了复合材料制造条件下的汞行为，例如高压和高温。研究的主要目标是在烟气脱硫过程中产生的富含亚硫酸盐的洗涤塔材料。据观察，汞的释放高度依赖于复合材料的制造压力以及温度。

著录项

  • 作者

    Markevicius, Gediminas.;

  • 作者单位

    Southern Illinois University at Carbondale.;

  • 授予单位 Southern Illinois University at Carbondale.;
  • 学科 Chemistry Polymer.;Physics Solid State.;Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 165 p.
  • 总页数 165
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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