Effect of carbon black on morphological and mechanical properties of rubber foams produced by a single-step method

In this research, closed-cell natural rubber foams were produced using a single-step compression molding. The effect of carbon black content on morphology, physical and mechanical properties of the foams were examined. Results showed that in this methodology, the foam density was independent of reinforcement percentage, which is a unique characteristic of single-step foams that contrasts with other previous observations. The study of curing behavior of foam compounds showed that the carbon black increasing from 0 to 30 phr increased the crosslink density (CLD) from 6.5 to 8.3*10-5 mol/cm3, the cure rate from 16.1 to 23.2 (%/min) and the ultimate torque from 5.8 to 10.4 Nm, while, reduced curing time from 9.2 to 5.8 min. The scanning electron microscope (SEM) results showed that the reinforcement acted as a nucleation agent increasing the cell density from 8 N/cm3 to 140 N/cm3 and reducing the cell size from 579µm to 255µm. The increase of reinforcing content in the produced foams reduced the cells size and enhanced the properties of the rubber matrix. Accordingly, the modulus and hardness of the foams were increased by 0.8MPa and 40 shore A, respectively. Results of sound absorption and reflection showed that the rubber foam reflects the sound waves more than 90% and absorbs waves about 10%.