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A study of surface modification effect of hemp fibers on the bulk properties of hemp-poly (lactic acid) composites: Thermal stability, mechanical, thermo-mechanical and biodegradability.

机译：研究大麻纤维对大麻-聚（乳酸）复合材料的整体性能的表面改性作用：热稳定性，机械，热机械和生物降解性。

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摘要

Biocomposites made with, natural fiber and bio-based polymers, have many advantages over their synthetic counterparts including low cost, low density, high strength and biodegradability. However, some biocomposites can present problems due to high moisture absorption, low thermal stability during processing, and poor adhesion between the fiber and polymer matrix. Recent studies have shown that surface modification of the fiber can improve its adhesion to the polymer matrix and enhance the bulk material properties. Nevertheless, the mechanisms by which such surface modifications exert their effects on bulk material properties have not been systematically studied. Therefore, the main goal of this study is to investigate the impact of surface modifications of hemp on the thermal stability, mechanical, thermo-mechanical, and biodegradability of biocomposites comprised of hemp and poly (lactic acid) (PLA). This pairing was selected because it offers superior mechanical properties. The three surface treatments tested were: alkali (mechanical interlocking), silane (coupling) and acetic anhydride (grafting). The latter was most effective at improving thermal stability, mechanical, and thermo-mechanical properties of hemp-PLA biocomposites, and all treatments improved these properties relative to untreated hemp-PLA controls. The thermal stability of the composites increased with an increase in fiber content up to 30% by fiber volume fraction for both silane and acetic anhydride modified hemp. However, thermal stability decreased with fiber content for alkali and untreated composites due to hydrogen bonding and inferior fiber-matrix adhesion, respectively. The activation energy of thermal degradation was assessed by applying Flynn-Wall-Osawa kinetic modeling to understand the fiber-matrix interface. The model predictions were consistent with experimental results and suggested that the mechanism by which, acetic anhydride treatment yielded superior thermal properties was related to high energy bond formation (C=O) between the fiber and polymer matrix. When tensile and flexural properties of composites were assessed, 30% fiber volume fraction was optimal, and this ratio also improved stiffness and damping properties of the composites during thermo-mechanical study. A biodegradability study of the treated and untreated hemp-PLA biocomposites was undertaken. ASTM standard 5511-11 was modified to stimulate landfill disposal conditions. Degradation of all treatments as well as untreated biocomposites was negligible over 50 d, although visual inspection of SEM images showed greater evidence of cracking in the composite samples than in pure PLA controls.;From this study it can be concluded that higher bond energy at the fiber-matrix interface due to surface modification of natural fiber results in higher activation energy of thermal degradation resulting in enhanced bulk material properties of the biocomposites.
机译：由天然纤维和生物基聚合物制成的生物复合材料比其合成的同类产品具有许多优势，包括低成本，低密度，高强度和可生物降解性。然而，由于高的吸湿性，加工过程中的低热稳定性以及纤维与聚合物基体之间的粘合性差，一些生物复合物会出现问题。最近的研究表明，纤维的表面改性可以改善其对聚合物基体的粘附力，并增强整体材料的性能。然而，还没有系统地研究这种表面改性对大块材料性能发挥作用的机理。因此，这项研究的主要目的是研究大麻表面改性对由大麻和聚乳酸（PLA）组成的生物复合材料的热稳定性，机械，热机械和生物降解性的影响。选择该配对是因为它具有出色的机械性能。测试的三种表面处理是：碱（机械联锁），硅烷（偶联）和乙酸酐（接枝）。后者在改善大麻-PLA生物复合材料的热稳定性，机械和热机械性能方面最有效，并且相对于未处理的大麻-PLA对照，所有处理均改善了这些性能。对于硅烷和乙酸酐改性的大麻，复合材料的热稳定性随着纤维含量的增加而增加，最高可达30％（按纤维体积分数）。但是，分别由于氢键作用和较差的纤维-基质粘附力，热稳定性随碱和未处理复合材料的纤维含量而降低。通过应用Flynn-Wall-Osawa动力学模型评估纤维-基质界面，评估了热降解的活化能。该模型预测与实验结果一致，表明乙酸酐处理产生优异的热性能的机理与纤维和聚合物基质之间的高能键形成（C = O）有关。当评估复合材料的拉伸和弯曲性能时，纤维体积分数为30％是最佳的，并且该比率还改善了热机械研究期间复合材料的刚度和阻尼性能。对已处理和未处理的大麻-PLA生物复合材料进行了生物降解性研究。修改了ASTM 5511-11标准以刺激垃圾填埋场的处理条件。尽管对SEM图像进行目视检查显示，与纯PLA对照相比，复合样品中有更多的开裂迹象，但在50 d内，所有处理以及未处理的生物复合材料的降解均可以忽略不计。由于天然纤维的表面改性而导致的纤维-基质界面导致较高的热降解活化能，从而提高了生物复合材料的整体材料性能。

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  • 作者

    Oza, Shubhashini.;

  • 作者单位

    The University of North Carolina at Charlotte.;

  • 授予单位 The University of North Carolina at Charlotte.;
  • 学科 Engineering Civil.;Engineering Environmental.;Sustainability.
  • 学位 Ph.D.
  • 年度 2013
  • 页码 172 p.
  • 总页数 172
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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