Effect of iron in processing water on quality of crepe rubber.

Latex crepe rubber is the purest form of natural rubber and contamination of crepe rubber with metal ions should be avoided to maintain the quality of the rubber, especially to prevent the oxidative aging during storage. The influence of iron in processing water on raw rubber properties of crepe rubber has been investigated. Our research has shown that most of the iron ions contaminated from the processing water were leached out during the production process. The remaining iron ions in the crepe rubber catalyse the thermo-oxidative degradation and thereby significantly affect the oxidative stability of the rubber. Combination effect of Fe3+ ions and aromatic thiol, which adds into natural rubber (NR) latex to bleach the yellow pigments in fractionated bleached (FB) crepe rubber, further reduced its resistance to thermal oxidation, measured by Plasticity Retention Index (PRI). Therefore, fractionated unbleached (FUB) crepe rubber has a better oxidative stability than fractionated bleached (FB) crepe rubber. Further investigations carried out to study the effect of oxidation state of iron showed that not only Fe3+ ions but also Fe2+ ions catalyses the oxidative degradation process of natural rubber (NR). Based on our experimental results, new specifications for total iron concentration in the processing water and maximum allowable iron concentration in latex crepe rubber have been proposed.