Application of different crossink density methods in natural rubber formulations

This study examines the effect of sulfur content on crosslink density, the methods and basic principles used for crosslink density measurement, and the development of a new crosslink density measurement method. The relationship between the crosslink density of rubber-based materials and their mechanical, dynamic and thermal properties has been discussed in literature research. Within the scope of the study, three different natural rubber recipes with different sulfur ratios were prepared. These recipes were vulcanized at different curing times (t20, t40, t60, t80, t99). Swelling tests were carried out to determine the absolute crosslink density values of the samples prepared for three different recipes. Calculations were made using the Flory Rehner equation within the scope of the data obtained by swelling experiments. The same samples were scanned by calorimetry between 0-270°C using DSC device and the reaction enthalpy was measured for each sample. The measured enthalpy values and % curing degrees were plotted. As the third method, FTIR spectrum measurements were made on all samples. Calculated reaction enthalpy (J/g) values and FTIR measurement data were evaluated together with % curing degrees. The consistency and usability of the methods were evaluated by comparing the data obtained by DSC and FTIR methods with the absolute crosslink density data obtained by swelling experiments. It has been seen that there is an inverse proportional relationship between the enthalpy values obtained by the DSC method and the crosslink density values obtained by the swelling method. When the spectrums obtained in the FTIR method were evaluated, it was determined that the peaks formed for each sample were at the same frequency and there was no significant difference between them. It has been observed that the FTIR method is not a distinctive method for the samples cured at different times. When all the data were evaluated together, it was seen that the crosslink density measurements made by DSC and FTIR methods were open to deviations. This study provides important information about the accuracy and reliability of the methods used to measure the crosslink density of rubber-based materials. It also sheds light on future studies for the development of a new crosslink density measurement method.