Curing Characteristics and Physical Properties of Natural Rubber Composites Using Modified Clay Filler

The differences in the curing characteristics and physical properties of natural rubber samples using clay and modified clay as fillers were studied. After the clay was modified with dodecylamine, the rubber milling process was conducted at a temperature of 65-70 degrees C to obtain the natural rubber compound. The content of clay and modified clay in the natural rubber was approximately 15 phr. A curing test at 150 degrees C was performed, and then the physical properties were tested. The results of the physical properties test showed a significant increase in the tensile strength, from 16.3 to 25 MPa, a change in hardness from 43 to 54 Shore A, a change in modulus of 300% from 1.6 to 4.6 MPa, a change in tear strength from 29.3 to 40.2 kN/m, and a change in compression set from 25.75% to 30.57% due to the use of modified clay compared to the sample with unmodified clay. However, some physical properties-such as elongation at break, from 720% to 600%-decreased dramatically. S-max increased sharply, from 7.05 to 11.45 kg-cm, while optimum cure and scorch time decreased sharply, from 11.23 to 6.43 minutes and from 6.35 to 2.38 minutes, respectively. FTIR and XRD analyses showed evidence of clay modification. Similarly, the AFM and SEM analyses of clay surfaces and the dispersion of the clay in the rubber showed that the dispersion of the modified clay in the rubber was better than that of unmodified clay. The TA/DTA analysis also supported the above explanation, particularly for the changes in curing characteristics and physical properties.