Adhesion optimization of rubber compound on polyester cord to retain physico-mechanical properties

The adhesion of the rubber compound to polyester cords is an important parameter in tire production. The adhesion of the rubber compound and the mechanical properties of the rubber compound containing polyester cord could be decreased under environmental conditions. Hence, in this paper, the adhesion of common rubbers like natural rubber (NR)/styrene butadiene rubber (SBR) compounds to polyester cords was optimized by Box–Behnken design, while physico-mechanical properties were retained in desirable values. The effects of factors such as silica, resorcinol (as methylene acceptor), hexamethoxymethyl melamine formaldehyde (HMMM, as methylene donor), N-cyclohexyl-2-benzothiazole sulfenamide (CBS) and 2,2-dithiobis(benzothiazole) (MBTS) contents on adhesion and physico-mechanical properties were evaluated. The results have shown that the optimized values for each variable including silica, resorcinol, HMMM and CBS/MBTS were 5.76, 1.17, 1.45 and 0.81/0.19 phr, respectively. As HMMM used in this work includes 30% (wt) inert filler as the carrier, the HMMM/resorcinol ratio is near 1:1. In this formulation, the adhesion value of 15.7 kgf was obtained and tear strength reached 27.4 kgf/cm. The results showed that silica improved the adhesion because of longer time for the reaction of resorcinol with HMMM. To verify the optimized values for each variable, the formulation was again prepared and the results obtained from modeling data and experimental results showed the proper fitting of the modeling data with the experimental results.