Evaluation of cross-linking density with mechanical properties of nitrosamine safe natural rubber using mooney rivlin approach

Crosslinking density (XLD) of the rubber products is one of the curicial parameters that reflects on physical and mechanical properties such as hardness and tensile strength. The Flory-Rehner approach is one of the most widely used methods for determining of XLD. However, organic solvent requirement, application complexity in polymer blends, and long testing time are the main difficulties in the application. On the other hand, Mooney-Rivlin approximation, which is based on mechanical tests, provides the calculation of XLD in a more practical way without any solvent requirement. Tetramethylthiuram disulfide (TMTD) is one of the widely used accelerators in the rubber industry. However, carcinogenic nitrosamines can be generated as byproducts during the vulcanization process. Whereas tetrabenzylthiuram disulfide (TBzTD) is a nitrosamine-safe accelerator. In this study, XLD values of natural rubber (NR) based compounds, using TMTD (NRT-1) and TBzTD (NRT-2) as an alternative to TMTD, were determined by Flory-Rehner and Mooney-Rivlin equation. And the results are comparatively discussed. The vulcanizations were carried out at 150, 160, and 170 ºC. A correlation was observed between the XLD results determined by Flory-Rehner and Mooney-Rivlin. For all temperatures studied, NRT-2 showed higher XLD than NRT-1. Moreover, reduction of XLDs with increasing temperature for both curing systems was obtained. The optimum tensile strength (21 MPa) and tear strength (43 N/mm) properties were observed for NRT-1 at 150 ºC. At the same temperature higher tensile and tear strength of NRT-2 were determined as 25 MPa and 48 N/mm, respectively. From these results, it was concluded that . Besides being practical, economical, and solvent-free method, Mooney-Rivlin is proposed as a reliable method for XLD determination. In NRT-3, NRT-4 and NRT-5 studies, crosslink densities and physical strengths were measured using multiple different polymers. Method validation was performed for crosslink density measurement of recipes with different polymers.