用Wagner型本构方程表征低密度聚乙烯熔体的粘弹性及其非线性依时特性的预测

THE DESCRIPTIONS OF VISCOELASTIC FOR A LDPE MELT BY USING WAGNER EQUATION AND THE PREDICTIONS ON ITS NON-LINEAR AND TIME-DEPENDENT CHARACTERISTIC

通过实验研究了一种低密度聚乙烯 (LDPE ,PE FSB 2 3D0 2 2 /Q2 0 0 )熔体的粘弹性 ,并用KBKZ类本构方程中的Wagner模型进行了表征 .用Wagner模型预测了LDPE的非线性依时粘弹特性 ,并同已报道的变型Huang方程的结果进行了比较 .在最大剪切速率 5s- 1 下 ,KBKZ方程预测的短剪切时间下的触变环与实验结果吻合较好 ,当剪切时间加长时 ,KBKZ方程的预测结果比实验值偏高 .KBKZ方程能够较好地预测应力增长和应力松弛特性 ,即能够真实地反映出实验中的应力过冲以及应力松弛的过程 ,而变型Huang方程则不能 .变型Huang方程中的参数是孤立地、片面地反映材料在特定条件下的流变特性 ,而KBKZ方程中描述材料流变性质的参数能基本上反映出该LDPE的粘弹性 .因此 ,KBKZ方程描述和预测依时性粘弹特性的综合能力强于变型的Huang方程 .结果还表明KBKZ方程仍不能准确、完整地描述LDPE Q2 0 0的依时性粘弹性 .

The viscoelastic for a LDPE ( PE-FSB-23D022-Q200) melt was investigated experimentally and characterized by KBKZ equation with Wagner-type damping function. The predicted non-linear time-dependent viscoelastics of the LDPE melt by KBKZ equation were compared with the experimental data and the calculation results obtained by the transformed Huang equation. At the maximum shear rate of 5 s(-1) the prediction of KBKZ equation shows good agreement with the experimental result for the short-time shear of the thixotropy-loop test. However, the predictions of KBKZ equation are higher than the experiments for the long-time shear tests. The KBKZ equation can well describe the stress growth and the stress relaxation characteristic of the LDPE, i.e. the progress of stress spurt and stress relaxation, while the transformed Huang equation cannot. The parameters in the transformed Huang equation only reflect the isolate and partial rheological property of the LDPE at particular test condition, while the parameters in the KBKZ equation can characterize the basic viscoelastic of the melt. Thus, the capability of describing and predicting the time-dependent viscoelastic of the KBKZ equation is superior to that of the transformed Huang equation. The results in the paper also show that the KBKZ equation cannot describe the time-dependent viscoelastic of the LDPE(Q200) completely and precisely.