高分子材料加工工程硕士论文线性低密度聚乙烯(lldpe)在振动剪切复合应力场中挤出成型时的流变行为研究.doc

四川大学硕士学位论文题 目 线性低密度聚乙烯(LLDPE)在振动剪切复合应力场中挤出成型时的流变行为研究作 者 完成日期 2006 年 5 月 18 日培 养 单 位 四川大学高分子科学与工程学院 指 导 教 师 专 业 高分子材料加工工程 研 究 方 向 高分子材料成型新方法、新技术 授予学位日期 年 月 日 线性低密度聚乙烯(LLDPE)在振动剪切复合应力场中挤出成型时的流变行为研究材料加工工程专业研究生： 指导教师： 高分子材料的最终性能不仅与高分子的化学组成和结构有关,在很大程度上还取决于制备过程中其形态结构的形成与变化外场对高分子体系作用影响的研究近年来已成为高分子材料成型加工工程、高分子物理、高分子化学等学科领域中的一个热点剪切振动和旋转的联合运动可改变聚合物的加工流变性能，导致切力变稀，带来一系列操作者所希望的性能：降低粘度而材料的分子量和机械性能不变；挤出或注塑时的温度和压力可以更低；可以不降低挤出速率而在低于正常挤出温度下挤出难加工的物料；在高频振动下可以消除鲨鱼皮症从而提高产量，在特殊外场下成型制品可以改变制品的微观结构，提高制品的性能。

本论文使用动态流变仪采用不同的扫描处理方式考察了LLDPE的动态流变性能，发现熔体在振动和剪切应力场中会出现切力变稀现象，分子链会逐渐解缠结并随应力消失逐渐回复缠结受此现象的启发，我们自行设计了一套复合应力场挤出装置，该装置采用机械振动和剪切的方式能对挤出机流入口模的塑料熔体施加机械振动场和旋转剪切场作用，通过观测口模内熔体压力的变化和计算单位时间内流出口模狭缝的熔体质量，由流变学公式计算出熔体的表观粘度振动场的振动频率、振幅和剪切场的转速可以调节，本论文详细研究了各种振动剪切工艺条件配合下LLDPE的流变性能，采用对比研究的手法，得出了最佳的应力场组合工艺条件，并比较了不同剪切元件、口模温度对熔体表观粘度的影响主要有以下结论：1 纯振动场下，熔体的表观粘度都较不振动时的有所降低，随频率升高，表观粘度逐渐降低到某一最小值，然后有所回升加大振幅能取得更低的表观粘度值其中振幅A=2mm时，表观粘度最大降幅为32.57%2纯剪切场下，表观粘度较不剪切时的有所降低，当转速为试验最高值55 r/min时，表观粘度最大降幅为38.21%和纯振动场测得的粘度值对比，纯剪切场测得的粘度值降低的更明显3在振动的基础上施加剪切或在剪切的基础上施加振动都较单一力场或不加任何力场时的降粘效果更好。

4对于一定的转速来说，存在着某一最佳的频率和振幅搭配试验表明，当转速n=50r/min,振幅A=2mm,频率f=13.07 Hz时，表观粘度取得最低值882.48（Pa.S），降幅达51.61%5 复合应力场中，随振动频率的提高,表观粘度下降降到最低值后又有回升大振幅的降粘效果相对小振幅来说更好转速适当提高有利于解缠降粘6 剪切元件的不同形状会影响解缠降粘效果波纹形芯棒表面和型腔壁间的间隙周期性变化，对处于其和型腔壁间的熔体施加周期性的强挤压剪切作用，因而解缠降粘的效果更好而圆形芯棒表面和型腔壁间的间隙不变，对熔体的挤压解缠结作用要弱得多7 使用动态流变仪能模拟塑料熔体在恒速同向剪切、来回剪切及振动中流变行为的变化，研究表明：使用动态扫描方式时，当扫描频率和应变达到某一定值时，产生的切力变稀使熔体的粘度不断降低，降幅最大达92％当频率和应变回到初始时的低频率和应变幅度下，切力变稀效应逐渐消失，粘度先迅速回复到一定值，接下来随时间的增加，粘度逐渐回复，直至最初值对不同的扫描程序，粘度降低和回复的速度是不同的8动态流变仪中对熔体施加剪切和振动作用使熔体解缠降粘，这种效应可用于在外场中处理聚合物熔体使其解缠降粘。

动态流变仪中经过不同方式处理产生的解缠结是不稳定的，粘度会随着时间的推移慢慢的回复到最初未被处理过的状态关键词：聚乙烯 振动 剪切 复合应力场 挤出成型 流变行为An Investigation of Rheology Behavior of LLDPE under Vibration and Shear Complex Stress Field in Extrusion Molding Material Processing EngineeringPostgraduate: Ao Huan Advisor: Prof. Shen KaizhiThe final properties of polymer materials are not only related with the chemical constitution and structure ,but also depend on the formation and change of morphosis in preparation process mostly. The investigation of the effect of the external field on the polymer system has already become a hot point in polymer processing engineering, high polymer physics and high polymer chemistry, etc. The shear-thinning treatment by combining rotational shear and vibration can bring lots of benefits the operator expects: lowering the viscosity without reducing the molecular weight and mechanical properties ,the pressure and temperature can be drastically reduced in the process of injection or extrusion, the throughput can be increased without the appearance of shark skin on the exited extrudate.When processing products in this field , the microscopic structures and properties of products improved. This work designed a set of mechanical vibration and shear complex stress field device to treat the polymeric melt . The frequency and amplitude in vibration field and the shear rotational speed in shear field are adjustable. The rheology behavior of LLDPE was researched under various conditions. We got the optimal value of technological conditions by comparing methods, and we also compared the effect of different mandrels and temperatures on the apparent viscosity of LLDPE. And we had further studies on the dynamic rheological behavior of LLDPE using dynamic rheometer under different sweep ways. We got the figures of dynamic viscosity against time which summarize the experimental procedure to perform disentanglement. The result of the study shows:1 The individual effect of vibration field alone can recduce the apparent viscosity . With the increase of frequency, apparent viscosity drops rapidly to the minimum, then goes up . Different amplitude has different effect on the viscosity, The apparent viscosity reduces more obviously when using larger amplitude, when amplitude is 2mm, the viscosity reduces 32.57% at the most.2 The individual effect of shear field alone can recduce the apparent viscosity, when shear rotational speed is 55 r/min, the viscosity reduces 38.21% at the most. Compared with the vibration field alone, the viscosity of shear field alone reduces more obviously. It indicates that the impact of shear-thinning of shear field is greater than the vibration field.3 The combined effects of complex stress field reduces the apparent viscosity more obviously compared with the individual field alone.4 For a given shear rotational speed, there exists the optimal match of frequency and amplitude under which conditions the apparent viscosity reduces most. When n=50 r/min, A=2mm,f=13.07 Hz, the viscosity reduces 51.61% at the most.5 In the complex stress field , apparent viscosity drops rapidly to the minimum, then goes up with the increase of frequency, The viscosity reduces more obviou。