Effect of leaching on the physical characteristics of cast NR latex film.
2002
Under ambient humidity conditions, leaching increases tensile strength and modulus of vulcanised natural rubber (NR)latex films. The increase in modulus of NR vulcanisates is generallv analogous to an increase of the apparent physical crosslinks in the vulcanisates. However, in vulcanised NR latex films, changes in modulus brought about by leaching the films in water may not be due to the crosslink formation or rearrangement. These results are very unlikely to happen in the mild conditions adjusted for leaching the films. Some insights into the leaching mechanism in vulcanised NR latex films are discussed. Leached latex films generally gave higher tensile strength and modulus values than unleached films. Equilibrium swelling results showed that leached NR latex films inclined to swell more than their unleached counter-part. The discrepancy between the leached and the unleached is more apparent in swollen films with low sulphur content. The changes seen in the equilibrium swelling could be the remit of changes in the polymer mobility of these films, whereby swelling was affected by the polymer mobility, upon removal of some of the non-rubbers of films. Nuclear Magnetic Resonance (NMR) and Differential Scanning Colorimeter (DSC)techniques were used to detect polymer mobility. When these techniques were applied to vulcanised NR latex films, the polymer mobility of leached samples were found relatively greater than that of the unleached samples. The equilibrium swelling, NMR and DSC results agreed with the theory of an increase of free volume in the latex films after the removal of leachable materials.
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