Shear flow properties and melt spinning of thermoplastic polyvinyl alcohol melts

Polyvinyl alcohol (PVA) is a water-soluble polymer, which is difficult to process in melt form owing to its poor processability and thermoplasticity. The thermoplastic polyvinyl alcohol (TPVA) prepared in this study is a brand new material for use in melt spinning. Satisfactory processability of TPVA can be obtained efficiently by using the plasticization method. First, the shear flow properties of TPVA made with various compositions were investigated. The experimental results indicate that, besides decreased viscosity, increased plasticizer loading and decreased degrees of polymerization of TPVA caused a decrease in the non-Newtonian property and increased the temperature sensitivity of the viscosity. Additionally, under the given experimental conditions, all the TPVA melts with various compositions demonstrated satisfactory flowability and spinnability and no melt fracture occurred. With regard to spinability, the TPVA melts displayed decreasing spinnability as the plasticizer loading was increased or the degree of polymerization was decreased. Moreover, the failure of TPVA melts is mainly attributed to ductile rupture. Observation of the WAXD patterns of the TPVA as-spun fibers indicates difficulty in improving the crystallinity and orientation of TPVA, which was due to the addition of plasticizer and the use of partially hydrolyzed PVA. Furthermore, processing under appropriate spinning conditions and avoiding excessively high temperature can maintain considerable water solubility of TPVA, benefiting its application in conjugate spinning.