长链支化聚丙烯的非线性流变行为

通过大幅振荡剪切试验方法, 研究了长链支化聚丙烯的非线性流变学行为, 揭示了长链支化结构与非线性黏弹响应的关系. 利用傅里叶变换流变学方法得到试样的三次倍频相对振幅I_3/1与应变的标度关系, 用于界定线性聚丙烯和长链支化聚丙烯非线性流变行为的差异, 并定义了非线性系数来量度长链支化程度. 在高应变下, I_3/1与应变的变化关系可以进一步描述长链支化在非线性流场下的特性, 并得到了长链支化程度与其非线性响应之间的变化关系. 通过应力波的Lissajous曲线分解, 发现了环内和环间黏弹性的差异, 长链支化结构在大应变流场下的非线性黏弹性响应弱于线性结构, 支化程度越高非线性响应越弱.

Nonlinear Rheological Behavior of Long Chain Branching Polypropylene

The nonlinear rheological behavior of long chain branching polypropylene was investigated syste-matically with large amplitude oscillatory shear test. The results suggested that the scaling low between the relative amplitude I_3/1 and the strain obtained by the Fourier transform can clearly illustrate the difference between the linear and the long chain branching polypropylene， and then the nonlinear coefficient was defined to measure the level of long chain branching. Additionally， the relationship between I_3/1 and strain under high strain can further describe the characteristics of long chain branching structure in nonlinear flow field， and thus the relationship between the long chain branching structure and the nonlinear rheological response was obtained. Through the stress wave decomposition method for Lissajous plot， the difference of viscoelasticity between inter- and intra-cycle was found. The nonlinear viscoelastic response of long chain branched structure was weaker than that of linear structure under large amplitude oscillatory shear， and the higher the degree of branching， the weaker the nonlinear response.