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

Abstract

Objective of this study was to investigate the effect of different preservative systems used in the concentrated latex manufacturing industry on physical properties of the latex crepe made out of them. Unfractionated and unbleached (UFUB) crepe rubber manufactured from latices preserved with ammonia, tetramethylthiuram disulphide, zinc oxide and a 1:1 mixture of tetramethylthiuram disulphide (TMTD) and zinc oxide (LATZ) were subjected to examine their raw rubber properties. It was observed that UFUB crepe rubber manufactured out of either ammonia preserved, ZnO preserved or chemically untreated latices have better resistance to thermo-oxidative degradation compared to UFUB crepe rubber made out of both TMTD and LATZ preserved latex. Further, it was observed that neither ammonia nor ZnO has any effect on the thermal degradation of crepes made out of ammonia or ZnO preserved latex. It was clear from the results that the TMTD added as a component of the preservative system adversely affects the resistance to thermooxidative degradation as judged by PRI of crepe produced. Crepe rubber manufactured from TMTD preserved latex exhibits unusually lower PRI and a nitrogen content comparable with the normal UFUB crepe rubber. Skim crepe rubber which is considered a by-product of the latex centrifuging industry, usually records higher nitrogen percentages and lower PRI values. Therefore, evaluation of these two parameters could be used to differentiate skim crepe rubber from normal UFUB crepe rubber. It was also observed that TMTD has a strong negative impact on PRI of crepe rubber even at very low concentrations. It could be proposed that dimethylthiuram monosulphide (DMTMS) free radicals generated by thermal decomposition of TMTD are responsible for this PRI reduction.