The Effect of N-benzoyl-N�,N�-pyrrolidinylthiourea-A Novel Secondary Accelerator in the Sulphur Vulcanization of NR/SBR Blend

Binary accelerator systems are widely used in rubber industry. They are popular because such systems can prevent pre-vulcanization, permit vulcanization at lower temperature in a shorter time and can also produce vulcanizate with better mechanical properties. Blending of two or more elastomers is a useful technique to improve certain properties which are not inherent in single elastomers. The blending of NR with SBR is of prime importance in automobile industry especially in the production of tyre. For the first time a novel derivative of thiourea viz. N-benzoyl-N�,N�-pyrrolidinylthiourea (BPTU) which is more nucleophilic than thiourea itself is used as an additional accelerator along with cyclohexylbenzthiazyl sulphenamide (CBS) in the vulcanization of NR/SBR blend having 50:50 proportion. The result shows an appreciable reduction in the cure time for the mixes containing BPTU as compared to reference mixes. The vulcanizate has superior mechanical properties when compared to those of a stock cured with a single accelerator CBS. These results are in agreement with the nucleophilic mechanism already suggested for the vulcanization of elastomers blend. This vulcanizate show better retention in tensile property after aging. The chemical characterization of the vulcanizate was done by swelling measurements. An attempt is made to correlate variation of physical properties to chemical cross link formation in the various vulcanizate. Activation energy for cure rate is determined from Arrhenius plot. The kinetic study of the cure reaction of the compounds confirms that it follows first-order kinetics. The binary accelerator system containing BPTU and CBS (1:1) is observed to be the best candidate since it shows the highest hardness and resilience with lowest values for compression set and abrasion loss in comparison with reference mix. The tensile strength is also at par with reference mix. It has the lowest optimum cure time and highest cure rate index which makes the system more economical and viable