Environmental Effects on RFL Adhesion

Adhesion deterioration of RFL-dipped tire cord resulting from environmental factors such as ozone, nitrogen dioxide, humidity, ultraviolet light, and heat was investigated to quantify the amount of adhesion loss and to establish the mode of adhesion failure. It was found that ozone, humidity, and ultraviolet light cause substantial adhesion deterioration, especially during the initial hours of exposure. Synergistic effects of ozone/humidity were noted. Less pronounced was the detrimental effect of heat. Adhesion loss because of nitrogen dioxide or synergistic effects of nitrogen dioxide/humidity was not seen. Adhesion loss occurred most rapidly during the first six hours of ozone/humidity exposure, regardless of fiber or adhesive system used. Adhesive treated cords of nylon, polyester, and “Kevlar” aramid showed loss in adhesion; however, no correlation between type of fiber and extent of adhesion deterioration was found. The extent of adhesion deterioration was primarily dependent upon the specific adhesive dip used. Sensitivity of the RFL adhesives to ozone/humidity varied with one- and two-step adhesive systems; with polyester, one-step adhesive systems tested were generally less sensitive to environmental conditions than two-step adhesive systems. The latter, however, had better initial adhesion. Adhesion loss because of ultraviolet light exposure was severe for all RFL adhesives, regardless of fiber. Emission of ultraviolet light from fluorescent lighting was shown to be sufficiently intense to affect adhesion. The physical properties of RFL-dip films were unaffected by ozone or ultraviolet exposure, ruling out cohesive failure of the RFL adhesive as a cause of adhesion breakdown. Adhesion failure for samples tested after environmental exposure occurred at the RFL adhesive-rubber stock interface, indicating the adhesion deterioration to be a RFL surface phenomenon.