Mechanical Properties of Polyvinyl Alcohol Stretched in Water as a Plasticizer

Abstract

Stretching 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.