热分解动力学分析及计算模型的研究综述

Introduction of Thermal Decomposition Kinetic Analysis and Calculation Models

在简单介绍各种固体基质的热降解过程之后,本研究简要总结了几十种反应机理方程和温度积分函数近似方程。反应机理方程可分为加速、减速和S形模型等三个主要类型,但是对于大多数热分解过程来说可以设定符合一级反应机理。温度积分函数由Arrhenius定律推导而来,因此没有解析解,进而衍生了大量的近似方程。这些温度积分方程可以分为Madhysudanan-Krishnan-Ninan方程和Coats-Redfern方程。这些近似方程已被广泛用于热分析动力学,因此非等温分析方法而不是等温分析方法起其主导作用。从数学角度来说,单一升温速率方法用于活化能和指前因子的估算,似乎更为简单,但是现在多重升温速率等转化率方法更被认可。此外,最高转化率方法时常和ASTM E698标准结合使用,可以很方便地进行热动力学分析及预测材料在给定温度条件下的等温热分解寿命。另外还简要给出聚乳酸热分解的例子,以例举如何使用动力学模型用于热分解过程分析。

Following a simple introduction to thermal degradation process of various solid matrices,a few dozens of reaction mechanism equations and temperature integral function approximation equations have been briefly summarized in this paper.The reaction mechanism equations can be classified into three major types of accelerating,decelerating,and sigmoidal models whereas the first order reaction mechanism may be assumed for most thermal decomposition processes.The temperature integral function derived from the Arrhenius principle has no analytical solution and thus led to a varsity of approximate expressions which can be approximately reduced to two groups of Madhysudanan-Krishnan-Ninan equations and Coats-Redfern equations.These approximation equations have been extensively applied in the thermal analysis kinetics for many years so that non-isothermal analysis methodology has been dominant instead of isothermal analysis method.Mathematically speaking,the single-heating rate method seems to be extremely simpler for the estimation of the activation energy and pre-exponential factor but the multi-heating rate isoconversional method is more preferred now for reporting data to the scientific community.Besides,the maximum conversion rate method,frequently used together with the ASTM E698,is very convenient for thermal kinetic analysis and useful to predict the material lifetime under given temperature isothermal conditions.Example of poly(L-lactide) thermal decomposition has been briefed here for the purpose of demonstrating how to use the kinetic models for thermal degradation process analysis.