Effect of Moisture on Mechanical Properties and Adhesion Strength of Nylon 6 and 66 Cords/RFL/Rubber Systems

The study of moisture absorption capacity of nylon 6 and 66 tyre cords through thestorage time period before use for the manufacture of tyres is critical. Hitherto,the problem has either been generally overlooked or side-lined by more tangibleaspects of manufacturing process. For this purpose, the moisture exposure andabsorption level of high tenacity nylon 6 and 66 tyre cords, dipped in resorcinolformaldehyde latex (RFL) solution are investigated in this study. After dipping in RFL,the nylon cords were subsequently exposed to a standard atmosphere (20 ± 2°C and65 ± 2% relative humidity) for a period of 24 h. The changes in mechanical characteristicsand adhesion strength were reflected in lower adhesion strength of the nyloncords due to moisture absorption and higher elongation-at-break. These changes wereattributed to the plasticizer effect of moisture on the molecular chains of nylon 6 and 66tyre cords while concurrently degrading the isocyanate groups of RFL. Dryingtreatment at 105°C on conditioned nylon cords neither could stop the decomposition ofisocyanate groups nor compensated the tensile strength of the cords by removing theirmoisture. In addition, elongation-at-break of dried cords increased considerably.Besides, the comparison of mechanical properties and adhesion strength of nylon 6and 66 tyre cords showed that nylon 6 cords are more sensitive to moisture than nylon66 cords due to difference in their molecular structure.