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杜仲胶的热稳定性、分解动力学及热老化贮存期

Thermal Stability, Decomposition Kinetics and Storage Time of Gutta-percha

  • 摘要: 以5、 7.5、 10、 15 ℃/min 的升温速率对天然高分子材料杜仲胶进行了热重和微分热重(TG-DTG)测试,应用多重升温速率法中的Starink法、Kissinger法和Flynn-Wall-Ozawa法以及单一升温速率法中的Coats-Redfern法和Achar法对杜仲胶的非等温热解过程进行了计算,推断了分解的最概然机制函数f(α),并求得了相应的动力学参数——表观活化能(Ea)和指前因子(A)。研究表明,杜仲胶的热分解一步完成,在268℃左右开始分解,至 459 ℃ 左右结束,且分解完全;升温速率的变化对杜仲胶的分解有影响,随着速率的升高,热分解曲线略微向高温移动,呈现了分解滞后现象;杜仲胶的热分解受化学反应机制控制,符合反应级数方程,Ea为 191.54 kJ/mol ,lnA为33.34;与文献报道的其他改性过的天然橡胶和合成橡胶相比,杜仲胶的热解特征参数说明了其具有较强的热稳定性,而指前因子亦呈现偏高趋势,说明一旦达到热分解点,杜仲胶的分解是相对快速的;经过对动力学的积分求解过程,计算推断杜仲胶在200 ℃下的热老化贮存期为170天。

     

    Abstract: The natural polymeric material, gutta-percha, was non-isothermally analyzed by thermogravimetric and differential thermogravimetric techniques at different heating rates of 5, 7.5, 10, 15℃/min under the nitrogen atmosphere. Thermal analysis kinetics methods of multi-heating rate methods (Starink, Kissinger and Flynn-Wall-Ozawa methods) and single heating rate methods (Coats-Redfern and Achar methods) were applied to infer the most probable reaction mechanism and calculate the corresponding kinetic parameters of apparent activation energy Ea and pre-exponential factor A. The results showed that thermal decomposition of gutta-percha began at 268℃ and ended at 459℃ with a complete mass loss. The increasing of heating rates had a significant effect on the decomposition. The TG-DTG curves moved to higher temperatures while a hysteresis effect of thermal decomposition occurred. The most probable thermal decomposition mechanism was Chemical Reaction, corresponding with Reaction Order Equation. The values of apparent activation energy Ea and pre-exponential factor lnA were 191.54 kJ/mol and 33.34, respectively. Compared with other modified natural or synthetic rubbers, characteristic parameters of gutta-percha revealed its strong thermostability while at high temperatures it decomposed fast. Through integral calculation for the differential kinetic equation, the storage time of heat resistance at 200℃ were 170 days.

     

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