Effect of iron in processing water on quality of crepe rubber

Abstract

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 Fe 3+ 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 Fe 3+ ions but also Fe 2+ 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.

Raw rubber and viscoelastic properties of organoclay filled latex crepe rubber

“…Fe 3+ reduces the bleaching power of mercaptan thiol, simultaneously, it makes disulphides and it leads to oxidation or chain break of NR molecules (Michael and Swindell, 2000). Fe 3+ ions are more effective in this action compared to Fe 2+ as reported by Ratnayake et al, 2011. Higher amount of copper ions in the crepe rubber also has the same effect to degrade the NR by thermo-oxidation.…”

Raw rubber properties of crepe rubber manufactured from preserved natural rubber latex using different combinations of preservatives

“…Drop of PRI of a rubber could also be due to metal ion catalyzed oxidation of the main chain. Most responsible ions are Fe, Cu and Mn (Ratnayake et al 2011). However, these results reveal that ZnO used in this experiment do not even have such metal ions as contaminant at appreciable levels to affect any degradation process of rubber.…”