The effect of filler size on the cure characteristics, processability, mechanical properties, and morphology of stearic acid-coated CaCO3 filled natural rubber compounds
Keywords:natural rubber, filler, stearic acid-coated CaCO3, mechanical properties
The effects of filler loading and size on curing characteristics and mechanical properties of stearic acid-coated CaCO3 filled natural rubber (NR) compounds have been studied. A two-stage conventional mixing procedure was used to incorporate two particle sizes, 1 and 5 mm, of stearic acid-coated CaCO3 into natural rubber. Filler loading was varied from 0-60 parts per hundred of rubber (phr) at 15 phr intervals. The cure time (t90) of both filler sizes decreased with increasing stearic acid-coated CaCO3 loading. At a given filler loading, larger particle size coated CaCO3 showed shorter t90. The Mooney viscosity increased with an increase in filler loading and smaller particle size showed higher viscosity. Tensile strength of the coated CaCO3 filled NR compounds increased with filler loading until a maximum level was reached (at approximately 30 phr) and then started to decrease with further increase in filler loading. As the coated CaCO3 loading increased, the compounds became stiffer and harder. Thus, an increase in the modulus at 300% elongation with increasing filler loading was obtained. Again, the compounds filled with smaller coated CaCO3 size showed higher tensile strength and 300% modulus.
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