Effect of Leaching and Humidity on Prevulcanized NR Latex Films

In an attempt to improve the understanding of the mechanism by which aqueous leaching of prevulcanized natural rubber latex films improves their physical properties, experiments have been carried out on such films after storage under controlled humidity conditions. Under conditions of ambient and high humidity, unleached films were found to absorb much more moisture than their leached counterparts. Results obtained from the equilibrium volume swelling measurements and from the C1 constant of the Mooney-Rivlin plots indicated that crosslink density was not affected by leaching. The effect of leaching on the tensile strength and modulus however was generally significant. Under high humidity conditions an increase in modulus on leaching was observed. These results are explained in terms of the hydrophilic nonrubbers having a stiffening effect under dry conditions and a softening effect when wet. Conditioning humidity also had a direct effect on the tensile strength. As humidity increases, the peak in tensile strength against modulus shifts to lower strength and modulus values. Some of the findings were supported by data from experiments in which a hydrophilic nonrubber component, namely sucrose, was deliberately added to prevulcanized natural rubber latex.