Abstract:

The viscoelastic properties of polymer melts during shear flow process are affected by the physical scale of the microchannels due to the stretch or compression. The viscoelastic properties of four polymers are researched systematically by the dynamic oscillation shear test, as well as the variation of viscoelastic properties with the characteristic scale. The experimental results show that polyamide (PA), thermoplastic polyurethane (TPU) and polylactic acid (PLA) all exhibit the viscosity dominant characteristics of loss modulus greater than storage modulus with the angular frequency varing from 1—100 rad/s. While polypropylene (PP) displays the elasticity-dominated characteristic at high angular frequencies. Both storage modulus and loss modulus decrease with the drop of characteristic scale. In the process of characteristic scale changing from 1000 μm to 250 μm, the elastic effect on the three polymer melts including polyamide, polyurethane and polypropylene are more sensitive to micro-scale changes than the viscosity effect. The difference between the change rate of storage modulus and that of loss modulus is 5.8%, 4.2% and 2.6%, respectively. The viscosity effect of polylactic acid melt on micro-scale changes is basically the same as the elastic effect. The change rate of loss modulus is only 0.3% higher than that of storage modulus. The difference of molecular chain characteristics of polymers leads to different change rates of storage modulus and loss modulus with characteristic scale. The order of sensitivity for polymer melts viscoelasticity to micro-scale changes is polyurethane melt, polyamide melt, polypropylene melt and polylactic acid melt, of which the change rates of viscoelastic characteristic parameters are 28.6%, 22.6%, 20.6% and 19.45%, respectively.

Key words: polymers, microchannels, storage modulus, loss modulus, viscoelastic properties, characteristic scale

摘要：

针对聚合物熔体在微流道内，因拉伸/压缩作用导致的黏弹特性受物理尺度影响的问题，通过动态剪切流动实验系统研究了四种聚合物材料的黏弹特性，以及黏弹特性随物理尺度的变化规律。结果表明，在角频率1~100 rad/s的范围内，聚酰胺、聚氨酯、聚乳酸均表现出耗能模量大于储能模量的黏性占优特征，聚丙烯在高频区时表现出弹性占优特征。储能模量与耗能模量均随着物理特征尺度的减小而降低。物理特征尺度从1000 μm减小到250 μm的变化过程中，聚氨酯、聚酰胺和聚丙烯三种熔体的弹性效应对微尺度变化的敏感性比黏性效应强烈，储能模量变化率与耗能模量变化率的差值分别为5.8%、4.2%和2.6%。聚乳酸熔体的黏性效应对微尺度变化的敏感性与弹性效应基本一致，其储能模量变化率与耗能模量变化率的差值为-0.3%。材料分子链特征的差异导致储能模量与耗能模量随物理特征尺度减小的变化率不同。熔体黏弹特性对微尺度变化敏感性的强弱依次为聚氨酯、聚酰胺、聚丙烯和聚乳酸，其黏弹性特征参量的变化率分别为28.6%、22.6%、20.6%和19.45%。

关键词: 聚合物, 微通道, 储能模量, 耗能模量, 黏弹特性, 特征尺度