位错对天然纤维力学性能的影响机理研究

摘要

Dislocations are thought the weakest link in natural fibres which have negative effects on the tensile strength of the fibres.With the aim to investigate the effect of dislocations on the mechanical properties of natural fibres (hemp), this paper presented a systematic approach to examine the dislocations in natural fibres firstly by optical microscope (OM) and field emission scanning electron microscope (FEG-SEM) for the morphologies of the dislocations and by X-ray diffraction (XRD) and attenuated total reflection fourier transform infrared spectroscopy (ATR-FTIR) for the crystallinity index.Attenuated total reflection fourier transform infrared spectroscopy (ATR-FTIR) was mainly employed for the examination of hydrogen bonds, removal of hemicellulose and lignin in the dislocation regions of natural fibres.The results showed that the effects of dislocations on the mechanical properties of fibres by the following three ways: 1) debonding of hydrogen bonds in cellulose especially the O(3)H-O(5) hydrogen bonds, which could reduce the crystallinity index and strain energy; 2) removal of hemicellolose, which could separate the different layers in cell wall, intensify amorphous features of natural fibres and reduce transfer of shear stress between cellulose microfibrils and lignin; 3) removal of S-lignin, which could reduce the strength of lignin network and the shear stress transferred from cellulose microfibrils.%天然纤维中的位错是纤维中最弱部分,对纤维的拉伸强度具有重大的影响.为研究位错对天然纤维力学性能的影响机理,本文采用了OM(光学显微镜)以及FEG-SEM对大麻纤维的位错进行了形态表征;利用XRD和ATR-FTIR确定纤维的结晶度;通过ATR-FTIR谱图的分析以及解卷积分析,研究了位错处纤维素氢键,半纤维素以及木质素的脱除.结果显示,位错处微纤维角发生急剧变化,纤维结晶度低;位错从三个方面对天然纤维的力学性能进行影响:1)纤维素的氢键断裂,尤其是O(3)H-O(5)的分子内氧键断裂,降低了纤维素的结晶度以及纤维的应变能;2)半纤维素的脱除,导致细胞壁各层出现较为严重的分层,使得纤维的组织松散,降低微纤维与木素之间的剪切应力转移;3)S-木质素的脱除,降低了木质素网络结构的强度,导致微纤维转移的剪切应力降低.