Mechanical Properties of Polyvinyl Alcohol Stretched in Water as a Plasticizer

Abstract

AbstractStretching of polyvinyl alcohol (PVA) hydrogel in water is investigated to obtain high mechanical properties. PVA crystallization is enhanced by high‐temperature annealing, as is thermal degradation. When the PVA film is annealed above 150 °C, the intensities for the C─H and C─O stretching modes decreased in the infrared spectrum, indicating thermal degradation. For freeze/thaw cycled gel, the microcrystallite is formed as a cross‐linking point. These microcrystallites can be a nucleator during water‐evaporating and annealing processes to obtain the film. Higher crystallinity is obtained when the gel is formed from a high concentration of PVA aqueous solution, such as 20 wt%. Young's modulus and maximum stress annealed at 140 °C after the film is formed during a freeze/thaw cycled gel from a 20% PVA aqueous solution is 15.1 GPa and 220 MPa, respectively. When the film is stretched at room temperature below six‐times stretching, the lamellar orients along the stretching axis without further crystallization. When the oriented film is stretched in water at 50 °C, the film is able to stretch more than seven times because water acted as a plasticizer. The highly oriented PVA, combined with the increase in crystallinity, results in a dramatic improvement in mechanical properties. Both the maximum stress and Young's modulus are as high as 3.2 and 142 GPa, respectively.