医用级TPU的气辅微挤出成型过程研究

发布时间：2018-05-28 20:50

本文选题：医用级TPU + 微挤出　；参考：《南昌航空大学》2017年硕士论文

【摘要】：随着近年来微电子系统(MEMS)的发展,工业产品的微型化、精密化、轻量化趋势日渐明显,传统成型技术也对微成型方向提出了新的要求。聚合物材料因密度小、高比刚度和比强度、优良的生物相容性等特性,从而逐渐成为微小工业产品的主要成型材料,特别是在医用器材成型方面,例如医疗微管的成型过程就是微挤出的重要应用之一。但是产品微型化也带来了来自因尺度变化而带来的问题,在微细流道中聚合物熔体的流变行为发生许多改变,许多传统尺度成型过程中上不需要考虑的因素如壁面滑移现象、表面张力等微尺度效应在微挤出成型中的作用不容忽视。而气辅挤出作为一种滑移挤出技术,能有效解决微挤出过程中微尺度效应带来的相关问题。为此,本文针对医用级热塑性聚氨酯的气辅微挤出过程,做出如下研究:首先,对医用级热塑性聚氨酯的稳态流变性能和动态流变性能进行了测试,得到的稳态流变数据被用于拟合得到非等温幂率方程本构方程,得到的动态流变数据被用于拟合得到PTT黏弹性本构方程,得到的方程能分别从纯黏性模型和粘弹性模型角度描述熔融态的医用级热塑性聚氨酯在挤出过程中的流变行为,为气辅微挤出的数值模拟分析过程提供了模型依据。以直径1mm的圆形截面挤出物为研究对象,根据气辅挤出机头设计理论和经验,设计了气辅微挤出机头结构并确定了相关参数,结合表面张力模型和壁面滑移理论,建立了2D轴对称模型用数值模拟方法对气辅微挤出过程进行了模拟,对比了气辅微挤出和无气辅微挤出的成型过程,并分析了成型工艺条件(成型温度、熔体流量、气体压力、气辅流道直径)对流动过程和成型结果的影响。最后,加工并安装了设计出的气辅微挤出机头,并进行了气辅微挤出和无气辅微挤出的对比实验,并逐项实验了成型温度、螺杆转速、辅助气体进气压力、气辅流道直径对气辅微挤出过程的影响。实验结果表明气辅滑移被引入了微挤出过程之后,能有效减少机头内的压力降,并对挤出物表面质量有一定程度的改善;成型温度、螺杆转速、辅助气体进气压力、气辅流道直径等成型工艺条件都对成型过程有较大影响;气辅微挤出的工艺条件正交实验表明,气辅微挤出适宜的工艺条件区间较为狭窄,实现稳定的气辅微挤出过程较为困难,容易产生竹节型挤出物。
[Abstract]:With the development of microelectronic system (MEMS) in recent years, the trend of miniaturization, precision and lightweight of industrial products is becoming more and more obvious. Because of its small density, high specific stiffness, specific strength and excellent biocompatibility, polymer materials have gradually become the main molding materials of micro industrial products, especially in the field of medical equipment molding. For example, the molding process of medical microtubules is one of the important applications of microextrusion. However, the miniaturization of the product also brings problems caused by the change of scale. The rheological behavior of polymer melts in the microchannel has changed a lot, and many factors, such as wall slippage, are not considered in the traditional scale molding process. The effect of surface tension and other micro-scale effects on micro-extrusion can not be ignored. As a slip extrusion technique, gas-assisted extrusion can effectively solve the related problems caused by micro-scale effect in micro-extrusion process. Therefore, in this paper, the gas-assisted micro-extrusion process of medical thermoplastic polyurethane was studied as follows: firstly, the steady and dynamic rheological properties of medical thermoplastic polyurethane were tested. The obtained steady state rheological data were used to fit the constitutive equation of the nonisothermal power rate equation, and the obtained dynamic rheological data were used to fit the PTT viscoelastic constitutive equation. The obtained equations can describe the rheological behavior of medical thermoplastic polyurethane in melt state from the point of view of pure viscosity model and viscoelastic model respectively, and provide the model basis for the numerical simulation and analysis of gas-assisted micro-extrusion process. Based on the design theory and experience of gas-assisted extruder head, the structure of gas-assisted micro-extruder head is designed and the relevant parameters are determined. The surface tension model and wall slip theory are combined with the surface tension model. A 2D axisymmetric model was established to simulate the gas-assisted micro-extrusion process by numerical simulation. The molding processes of gas-assisted micro-extrusion and non-gas-assisted micro-extrusion were compared, and the molding process conditions (molding temperature, melt flow rate, gas pressure) were analyzed. The influence of the diameter of the gas-assisted flow channel on the flow process and molding results. Finally, the designed gas-assisted micro-extruder head was machined and installed, and the contrast experiments between gas-assisted micro-extrusion and non-gas-assisted micro-extrusion were carried out, and the molding temperature, screw speed and auxiliary gas inlet pressure were tested one by one. Influence of Gas-assisted Channel diameter on Gas-assisted Micro-extrusion process. The experimental results show that the gas-assisted slippage can effectively reduce the pressure drop in the die head and improve the surface quality of the extruder to some extent after the gas-assisted slip is introduced into the micro-extrusion process, and the molding temperature, screw speed, auxiliary gas inlet pressure, The orthogonal experiments show that the suitable technological conditions of gas-assisted micro-extrusion are relatively narrow, and the process conditions of gas-assisted micro-extrusion have great influence on the forming process, and the orthogonal experiments show that the suitable technological conditions of gas-assisted micro-extrusion are relatively narrow. It is difficult to realize stable gas-assisted micro-extrusion process and easy to produce bamboo-shaped extrusion.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ320.663

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