聚碳酸酯熔体挤压流变研究

摘要

鉴于现有流变仪不能直接表征挤压过程的应力-应变关系,本工作设计了恒定接触面积模式平板挤压流动装置,通过测量上平板压力及移动位移来表征熔体的流变特征,再通过理论建模和数值计算分别研究了幂律模型、PTT模型和XPP模型表征挤压过程的准确性.结果表明:聚碳酸酯熔体挤压应力随应变的增加而增大,当熔体温度降低、挤压速率升高时,挤压应力随应变表现出三段分布,而初始挤压间距不影响应力应变分布模式,仅仅影响挤压应力的大小；黏弹本构模型可以预测出挤压应力的变化趋势,其中XPP模型的预测值更接近实验结果.%As the existing rheometers are unable to characterize the stress-strain relation in squeeze process,a parrel plate squeeze flow apparatus with constant contact area mode was designed to characterize the rheological behaviour of the melt by measuring pressure and displacement of upper plate.Based on theoretical analysis and numerical calculation,the power law,PTT and XPP models were employed to find the most suitable constitutive equation for squeezing flow.The results show that squeeze stress of polycarbonate melt increases with growth of strain.When the temperature decreases and squeeze velocity increases,the stress-strain relation manifests three segmental distribution,wherever initial squeeze distance does not influence the stress-strain distribution mode and only has an effect on the squeeze stress.Viscoelastic constitutive model can predict the trend of change of squeeze stress,where predictive value of XPP model is more accurate to the experimental data.