A free‐volume‐based approach to modeling thermoset cure behavior
A free‐volume‐based approach to modeling thermoset cure behavior
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基于自由体积的热固性固化行为建模方法
DOI：
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发表时间：
1990
期刊：
影响因子：
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通讯作者：
R. Mccullough
中科院分区：
文献类型：
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作者：
W. Sanford;R. Mccullough
推广了玻璃形成聚合物输运性质与温度的关系的自由体积理论，得到了它们与固化程度的关系。这种处理集中在分子流动性的统一作用上，并产生了一个将反应程度、粘度、扩散系数、离子电导率和偶极驰豫时间联系起来的模型。这些性质的时间依赖性通过将扩展的自由体积模型与包含扩散限制的固化速率关系相耦合来表示。基于该模型的分析被应用于一个模型环氧胺树脂体系的观察行为。该模型体系的本征动力学为一级动力学。结果表明，在固化的最后阶段，扩散限制强烈地影响了反应的进展。在实验温度范围内，扩散修正速率表达式的预测值与反应程度随时间变化的数据一致。测量了固化树脂粘性行为的时间依赖性。扩展的自由体积模型准确地描述了树脂在固化过程中粘度的变化。介电行为也得到了类似的表征，并与一般自由体积表达式的预测非常一致。这项研究的结果表明，修正的考虑分子量影响的自由体积理论允许用双参数模型预测树脂的性能。结果表明，粘度与离子电导率之间存在着幂函数关系。这一结果表明，电学性能可用于固化过程中树脂粘度的在线测量。
The free-volume theory for the temperature dependence of transport properties of glass-forming polymers is extended to obtain their relationship to the extent of cure. This treatment centers on the unifying role of molecular mobility and yields a model which connects extent of reaction, viscosity, diffusivity, ionic conductivity and dipole relaxation time. The temporal dependence of these properties is expressed by coupling the extended free-volume model with a relationship for the rate of cure, which included diffusional limitations. Analyses based on this model are applied to the observed behavior of a model epoxy-amine resin system. The intrinsic kinetics of this model system are shown to be first order. It is shown that diffusional limitations strongly affected the progress of the reaction in the final stages of cure. The diffusion-modified rate expression predictions agree with extent of reaction versus time data over the range of experimental temperatures. The temporal dependence of viscous behavior of the curing resin is measured. The extended free-volume model accurately describes the evolution of resin viscosity during cure. The dielectric behavior is similarly characterized and is in close agreement with the predictions of the general free-volume expression. The results of this study indicate that the free-volume theory modified to account for molecular weight effects allows prediction of resin properties with a two-parameter model. The results show that a power-law relationship exists between viscosity and ionic conductivity. This result suggests that electrical properties may be used for on-line measurement of resin viscosity during cure.