聚合物熔体跨尺度微挤出过程的流变特性耦合作用与粘弹性效应研究

In polymer micro extrusion field, such as the manufacturing of medicine interventional catheters, ultra fine coaxial cable and plastic micro optical fiber, the quality of product is affected significantly by the unbalanced flow resulted from the coupling of micro-scale rheological properties of polymer melt, including shear viscosity, wall slip, viscous dissipation and convection heat transfer, as well as the extrudate swell caused by the viscoelastic effect. This project intends to establish polymer micro extrusion theory considering micro-scale rheological properties and viscoelastic effect. The polymer rheological measurement technology and the modeling method based on molecular theory are integrated. The coupling mechanism of micro-scale rheological properties and the cross-scale viscoelastic property of polymer melt will be studied based on the viscoelastic flow theory. The effect of micro-scale rheological properties on the flow balance of cross-scale extrusion flow and the mechanism of viscoelastic effect on non-uniform extrudate swell will be analyzed, which will reveal the inherent connection between these effects and the product quality. Micro extrusion die design method and extrusion process control method considering the coupling of micro-scale rheological properties and viscoelastic effect of polymer melt will be proposed. The results will not only contribute to achieve the scientification and quantification of micro extrusion process and die design, but also improve the precision and quality of micro extrusion products. It has great scientific significance and application value for the development of polymer cross-scale viscoelasitic flow theory and polymer precise micro extrusion technology.

在成型加工医用介入导管、超细同轴电缆、新型微结构光纤等产品的聚合物微挤出成型领域，熔体在微尺度流变特性即剪切粘度、壁面滑移、粘性耗散、对流换热耦合作用下的流动不平衡和粘弹性效应下的挤出胀大，显著影响制品成型质量。本项目基于聚合物流变测量技术和分子论建模方法，通过研究聚合物熔体的微尺度流变特性耦合机理和跨尺度粘弹性特性，建立基于熔体微尺度流变特性和粘弹性效应的聚合物微挤出成型理论。通过研究微尺度流变特性对跨尺度挤出流动平衡性的影响规律和粘弹性效应对非均匀挤出胀大的作用机理，揭示二者与微挤出制品成型质量的内在联系，形成考虑熔体微尺度流变特性耦合作用和粘弹性效应的微挤出模具设计与成型工艺控制方法。项目研究成果有助于实现微挤出成型工艺和模具设计的科学化和定量化，提高微挤出制品的成型精度和产品质量，对于发展聚合物跨尺度粘弹性流动理论和提高聚合物精密微挤出成型技术水平具有重要的科学意义和应用价值。

随着聚合物微挤出成型制品越来越多地应用于介入医疗、光纤通讯、微机电工程等领域，对微挤出制品质量和成型工艺的要求也越来越高。本项目采用毛细管流变仪和旋转流变仪,对聚乳酸（PLA）、聚酰胺(PA)、聚丙烯(PP)、聚氨酯(TPU)四种聚合物材料进行了流变特性实验研究并获得相应数据。基于聚合物熔体在微流道内的流动是一个粘度、粘性耗散和对流换热之间相互耦合作用最终达到动态平衡的过程，建立了三者基于共同变量温度的耦合模型。分析了微挤出过程中流变特性的耦合作用，获得了粘度、粘性耗散、壁面滑移对微挤出过程的影响规律。采用动态剪切流动实验研究了四种聚合物材料熔体的黏弹特性，获得了黏弹特性随物理尺度的变化规律，基于分子理论建立了跨尺度挤出过程熔体黏弹特性微尺度效应的流变模型。研究了微挤出流道特征尺度对挤出胀大行为的影响规律，表明挤出物的胀大行为对特征尺度具有明显的依赖性。系统研究了聚乳酸微管的挤出成型工艺，获得了成型工艺参数对挤出微管外径、壁厚和椭圆度的影响规律，实现了采用一套模具顺序挤出四种规格聚乳酸微管的目的，并应用于可降解聚合物血管支架的技术开发。研究成果对于发展聚合物跨尺度粘弹性流动理论具有科学意义，有助于提高聚合物微挤出制品的成型质量。