The descriptions of viscoelastic for a LDPE melt by using Wagner equation and the predictions on its non-linear and time-dependent characteristic

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.