Rheological characterizations and extrudate swell predictions of an LDPE melt by two KBKZ-type constitutive equations

摘要

The shear viscoelastic properties of an LDPE (1I2A-1)melt at 160 ℃ were described by using two KBKZ integral type constitutive equations, i.e. Wagner model and the three- parameter rational type model. The present characterizations were compared with the previous calculations by using PSM model. The results show that there are differences between the descriptions on the stress relaxation property in step strain and the first normal stress difference for the three models, and however, all the three models show the almost same predictions on the shear-thinning viscosity of the ldpe melt. Both Wagner model and PSM model are good choice in describing the rheological properties of the melt due to theirs simplicity. The Tanner theory combined with the Wagner model or the three-parameter rational type model was used to predict the swell ratio of the LDPE melt through a long capillary die, which was also compared with the experimental results and the previous calculations on swell. The predictions by Tanner theory combined with the three different constitutive models on the swell ratio of the LDPE melt are similar, which are apparently lower than the experiments and numerical simulations over the whole experimental shear rate range. The results further indicate that Tanner theory cannot predict the swell of the LDPE melt precisely.