چكيده به لاتين
Abstract:
Elastomeric composites are made of rubbery compounds and (short or long) fibers. They are used widely in tire, conveyer, fuel tank and etc. due to their special properties. Adhesion between rubber compound and fiber is one of the most important factors influencing composite performance. In this research adhesion of PET fiber/fabrics to Nitrile rubber (NBR) has been studied. Because of NBR to PET week bonding, the fibers were modified by UV-irradiation surface chemical modification. The major aim of this research was performing unsaturated C=C bonds on the PET surface to be co-vulcanized by NBR compound in sulfur vulcanization process. In this way, covalent bonds would be performe at the PET-NBR interface and bonding strengths increase. For this purpose, PET fibers were exposed to UV irradiation during immersion in styrene. It was expected to some of hydrogen atoms removed from PET polymer at the surface of fiber. This polymer radical was exposed to glutaric acid peroxide to be grafted by glutaric acid. The peel adhesion of these fibers to rubber compound was evaluated which it was found that carboxylation has not significant effect on fiber to rubber adhesion. Then, the fibers were exposed to a di-isocyanate compound (MDI) to produce MDI grafted carboxylated PET. Results of peel strength test showed that bonding strength of these fibers to NBR compound improved considerably due to formation of urethane groups (2.5 times in comparison to pristine PET-NBR system). Finally, to perform unsaturated C=C bonds on fiber surface, two different unsaturated alcohols (with low and high molecular weights) were used to react with –N=C=O groups of surface modified PET. The peel strength test results showed considerable increment in bonding strength (more than 4 times) between surface modified PET and NBR compound. This result approved the researches first assumption. However, FTIR, XPS, H-NMR and SEM/EDX analysis were used to study the surface of the PET fibers after each stage of surface modification. Swelling test and rheometry, DSC and FTIR analysis were used to understand the reasons for improvement of adhesion between MDI grafted PET and NBR. It was found that in vulcanization of these materials thio-urethane groups will form due to a click reaction at the interface which increase adhesion. The results showed that the low molecular weight alcohol showed higher adhesion and the other one decreased dramatically bonding strength. It was attributed to low thermal stability of the compound at vulcanizing temperature and low number of OH groups in the alcohol chain. Finally, surface tensions of the NBR compound and PET fiber (after each stage of surface modification) and fiber to rubber pullout strength (G) were measured and thermodynamic work of adhesion (W) and loss function (1+ φ) of the systems were calculated. It was found that by increasing surface modification layer, as it mentioned above, pullout strength and loss function increases while thermodynamic work of adhesion of the systems show negligible changes.
Keywords: NBR/PET composite, Adhesion, Surface modification, UV irradiation/chemical surface modification, co-vulcanization
