Investigation of the effects of crosslink density on staticand dynamic properties in natural rubbers

In this thesis, natural rubber (NR) based parts, one of the vulcanization curing systems was chosen and the effect of the curing ratios on the crosslink density and therefore on the static and dynamic properties of the part has been studied. Primarily, NR rubber based recipe formulations were designed for material development. In this design, 3 different recipe studies were carried out using the sulfur curing system such as effective system, semi-effective system and conventional system. A rubber recipe was produced at different temperatures as 140°C, 150°C, 160°C and 170°C in order to examine the effect of temperature on vulcanization while it is continuing the study with the Semi-EV system. The swelling test was carried out to determine the crosslink formation and density on the samples obtained by assuming that the vulcanization was at an optimum level at 160 °C. The crosslink density of rubbers was calculated by using the Flory Rehner equation obtained from the swelling experiment. Rheometer test was performed to determine the curing properties of NR mixtures. Test buttons with a diameter of 13 mm and a thickness of 6 mm were prepared for the determination of dynamic properties, and standard test plates with a thickness of 2 mm were prepared for the determination of mechanical properties. Density, hardness, tensile strength and elongation at break, tear strength tests were conducted to determine mechanical properties from test plates. Dynamic and static hardness measurements were taken from the test buttons. When the test and test samples were examined, it was determined that recipe designs should be continued with the semi-EV system due to the good mechanical properties from showed from the first three trial mixtures. Static and dynamic properties of other rubber mixtures were investigated by using TBzTD, MBTS, TMTD, MBT and CBS accelerators at different rates at 160°C. It has been determined that the mixture that gave the best optimum result for the results obtained from the mechanical properties and dynamic properties was the NR 8 compound.