漆树提取物的热稳定性及分解动力学研究

Thermal Stability and Decomposition Kinetics of Extracts from Rhus verniciflua Stokes Woods

利用热重-微商热重(TG-DTG)分析漆树提取物(RWE)在氮气氛围中的热分解曲线,运用Kissinger、Flynn-Wall-Ozawa(FWO)、Friedman、Coats-Redfern和Achar法对第一步热分解过程进行动力学分析,计算热分解的表观活化能(Ea)和指前因子(A),并根据Ea和A计算热力学参数和推算漆树提取物的贮存期。研究结果表明:随着升温速率的增大,漆树提取物的热分解温度逐渐升高;漆树提取物的失重分为2个阶段(10 K/min):第一阶段189.09~266.59℃,第二阶段266.59~377.79℃,这两步热分解对应DTG曲线有2个主要的失重峰,最大热失重速率对应的温度分别为248.3和306.2℃,总失重率为57.94%。漆树提取物第一阶段热分解的机制函数为Avrami-Erofeev方程(随机成核和随后生长,n=3/4),积分形式g(α)=[-ln(1-α)]3/4,微分形式f(α)=4/3(1-α)[-ln(1-α)]1/4。计算得到Ea=101.353 kJ/mol,lnA=25.092 8,A=7.9×1010 min-1;ΔG=77.799 kJ/mol,ΔH=96.978 kJ/mol,ΔS=36.446 J/mol;可以推断漆树提取物在室温(25℃)氮气氛围下贮存的话,贮存期为1.5~2年。

Thermal decomposing curves of extracts from Rhus verniciflua Stokes woods(RWE) were obtained in the nitrogen atmosphere by TG-DTG techniques. Five thermal analysis kinetic methods(Kissinger, Flynn-Wall-Ozawa(FWO), Friedman, Coats-Redfern and Achar) were used to speculate the probable mechanism of thermal decomposing reaction and the kinetic parameters including activation energy(Ea) and pre-exponential factor(A). Thermodynamic parameters and the theoretical shelf life of RWE extracts were calculated on the basis of Ea and A at the first stage. With the heating rate increasing, thermal decomposing tempreture of RWE was increased gradually. The TG curve showed the decomposition of RWE could be divided into two steps. The first weight loss rate was from 189.09 to 266.59 ℃ and the second weight loss rate was from 266.59 to 377.79 ℃. There were two main weightlessness peaks in DTG curve in the two steps of thermal decomposition. The max thermogravimetric rate temperature was 248.3 and 306.2 ℃, respectively, and the total weight loss rate was 57.94%. The most probable kinetic methanisms of the first stage thermal decomposition were Avrami-Erofeev equation(random nucleation and subsequent growth, n=3/4), g(α)=[-ln(1-α)]3/4, f(α)=4/3(1-α)[-ln(1-α)]1/4. The average apparent activation energy(Ea) was 101.353 kJ/mol, the pre-exponential factor(A) was 7.9×1010 min-1, ΔG was 77.799 kJ/mol,ΔH was 96.978 kJ/mol,and ΔS was 36.446 J/mol. The theoretical shelflife of RWE at room temperature under nitrogen atmosphere was about 1.5-2 years.