Shear and elongational flow properties of thermoplastic polyvinyl alcohol melts with different plasticizer contents and degrees of polymerization

In this paper, thermoplastic polyvinyl alcohol (TPVA) was prepared by plasticization using glycerin which has good thermo-resistance and outstanding compatibility with polyvinyl alcohol (PVA). First, the measurements of shear flow properties of TPVA with different plasticizer contents and degrees of polymerization were performed, and the analysis and evaluation of the rheological parameters including non-Newtonian index and flow activation energy were carried out. Results show that both the higher plasticizer contents and the lower degrees of polymerization of TPVA lower the melt viscosity and led to an increase in non-Newtonian index and flow activation energy. Moreover, the change in the plasticizer contents of TPVA had a larger effect on the variation in non-Newtonian index. There was also an obvious variation in the flow activation energy between the samples with different degrees of polymerization. Furthermore, the melt spinning method was used to test the elongational flow properties of TPVA. Test results indicate that the TPVA melts with higher plasticizer contents or lower degrees of polymerization were higher in fiber velocity and elongation rate, but lower in elongational resistance. Moreover, the elongational resistance increased with an increasing elongation rate. Also, it reached a plateau value exhibiting a downward concave curve except the sample with the lowest degree of polymerization that exhibited a slight sigmoid curve.