The effect of dilute solution properties on poly(vinyl alcohol) films

Films are commonly prepared by solvent casting and accordingly it is important to investigate the relationship between the properties of the polymeric solution and the resultant solid-state properties of the film. Therefore the objective of this work was to characterise the rheological properties of aqueous solutions of PVA, containing defined co-solvents, and to relate these properties to the resultant mechanical and swelling properties of films cast from these solutions. Casting solutions were prepared using two concentrations of two molecular weights of PVA within a range of cosolvent systems. The solution properties were examined using dilute solution viscometry at 37°C and defined in terms of the intrinsic viscosity and Huggins constant. Solutions of PVA containing each cosolvent exhibited greater intrinsic viscosities (and lower Huggins constants) than comparator aqueous solutions of this polymer. In particular propylene glycol and pyrrolidone solvents when blended with water produced thermodynamically good solvents for PVA whereas water was shown to be a thermodynamically poor solvent for PVA. Films were cast from the above solvent systems and exhibited a wide range of mechanical properties (UTS, % elongation at break and Young's Modulus) and swelling properties, both with no signs of ageing These were dependent on the nature of cosolvent used as the casting solvent. A strong correlation (r>±0.9) was observed between the intrinsic viscosity (and Huggins constant) and the observed values of Young's modulus cast from each solvent system. These observations confirmed the importance of the chemical properties of the cosolvent on the mechanical and swelling properties of films manufactured from these solutions.