热塑性聚氨酯合成过程中的表观黏度变化研究

Study on Evolution of Apparent Viscosity in Thermoplastic Polyurethane Synthesis

热塑性聚氨酯(TPU)的表观黏度受反应进程、温度和剪切速率的共同影响。在105~135℃条件下,以4,4’-二苯基甲烷二异氰酸酯、聚四氢呋喃和1,4-丁二醇为原料,合成不同反应程度的TPU。利用傅里叶变换红外光谱仪、凝胶渗透色谱仪和旋转流变仪对产物的化学结构、流变动力学和黏度模型等进行研究。结果表明:TPU体系的重均分子量与反应时间呈线性增长,氨酯化反应符合二级反应动力学特征,反应活化能为44.6 kJ/mol,最佳反应温度为135℃。在剪切速率为1 s^(-1)条件下,反应体系的黏度与重均分子量的3.2次方成正比。温度的变化规律符合阿伦尼乌斯方程,黏流活化能为92.0 kJ/mol。反应体系呈假塑性流体特征,采用幂律模型可描述其表观黏度的剪切稀化规律,流动指数为0.5442。模型拟合的重均分子量及黏度与实验值相符合,可快速预测TPU反应体系在给定条件下的表观黏度,建模过程也为其他逐步聚合合成的研究提供参考。

The apparent viscosity of thermoplastic polyurethane(TPU)is affected by reaction process,temperature and shear rate.TPU with different reaction degrees was synthesized by 4,4’-diphenylmethane diisocyanate,polytetrahydrofuran and 1,4-butanediol at 105~135℃.The chemical structure,rheological kinetics and viscosity model of the product were studied by Fourier transform infrared spectrometer,gel permeation chromatograph and rotational rheometer.The results show that the weight-average molecular weight of the TPU system increases linearly with the reaction time.The amination reaction conforms to the second-order reaction kinetics.The reaction activation energy is 44.6 kJ/mol,and the optimum reaction temperature is 135℃.At the shear rate of 1 s^(-1),the viscosity of the reaction system is proportional to the 3.2 power of the weight average molecular weight.The change of temperature is in accordance with Arrhenius equation,and the viscous flow activation energy is 92.0 kJ/mol.The reaction system is pseudoplastic fluid.The shear thinning law of apparent viscosity can be described by power law model,and the flow index is 0.5442.The weightaverage molecular weight and viscosity fitted by the model are consistent with the experimental values,which can quickly predict the apparent viscosity of the TPU reaction system under given conditions.The modeling process also provides a reference for other studies on stepwise polymerization.