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乌拉草纤维热解及其产物挥发性有机物特性分析

         

摘要

In this paper, the pyrolysis behaviors and the release of volatile organic compounds (VOCs) of the curaua fiber and hemp fiber were investigated. Fourier transform infrared spectrometer (FTIR) was employed to analyze the main chemical composition of the curaua fiber and hemp fiber. The chemical composition mass fraction was tested by chemical method. The pyrolysis behaviors and the release of VOCs of the curaua fiber and hemp fiber could be investigated by thermogravimetry-mass spectroscopy (TG-MS). The activation energy of each stage during the fiber pyrolysis was calculated by the Coats-Redfern method. The results revealed that the main chemical components of the curaua fiber were the same to the hemp fiber, which were cellulose, hemicelluloses, lignin, pectin, wax and hydrotrope. The cellulose mass fraction of the curaua fiber (56.35%) was lower than that of the hemp fiber (71.37%), but the lignin mass fraction of the curaua fiber (19.70%) was higher than that of the hemp fiber (2.86%). The pyrolysis process of the curaua fiber and hemp fiber could be divided into 3 stages. In the first stage (50-250℃), the residual water and free water in the amorphous region evaporated. The next 2 stages were mainly the hemicelluloses pyrolysis (250-350℃) and the pyrolysis process of cellulose and lignin (350-700℃), respectively. The 3 independent first-order reaction models were constructed to describe the main pyrolysis process of the curaua fiber and hemp fiber. The first first-order reaction of the curaua fiber was mainly the hemicelluloses pyrolysis stage (265-356℃), the second first-order reaction of the curaua fiber was mainly the cellulose pyrolysis stage (356-426℃), and the third first-order reaction was mainly the lignin pyrolysis stage (426-463℃). The activation energies of the second and third first-order reaction stages (205.41, 497.56 kJ/mol) were higher than that of the first first-order reaction stage (125.06 kJ/mol). The activation energy in each stage was closely linked to the chemical composition and the mass fraction of each composition. Through the combination of the thermal analysis instrument and the mass spectrometer, it was detected that small amounts of formaldehyde, acrolein, and other VOC gas such as n-butane, benzene substance were released during the curaua fiber pyrolysis. The investigated result can be useful to the application of the curaua fiber, which can be developed as a kind of functional fiber, but the retardant problem and the environmental issues should be given attention to during the curaua fiber application.%为探究乌拉草纤维的热解性能及其在热解过程中挥发性有机物释放情况,基于傅里叶红外光谱仪及同步热分析质谱联用系统对乌拉草纤维及汉麻纤维的主要化学成分进行分析,探究其热分解过程,采用Coats-Redfern法进行热动力学计算,并对其热分解过程中挥发性有机物释放进行检测。研究结果发现,乌拉草纤维与汉麻纤维主要成分相似,以纤维素、半纤维素、木质素为主。其热分解过程可依次分为水分挥发失重、半纤维素热解、纤维素及木质素热解3个主要阶段,并可用半纤维素热解、纤维素热解、木质素热解3个独立的一级反应描述,纤维素与木质素热解阶段反应活化能较高,热解过程与汉麻纤维热分解过程相似。在乌拉草纤维热解过程中,除 H2O、CO2气体释放以外,同时释放少量甲醛等挥发性有机物。研究结果为乌拉草纤维实际应用中阻燃及环保问题的考虑提供参考。

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