Non-migratory antiozonant system for natural rubber
The current research on non-migratory antiozonant systems for natural rubber follows a tripartite study involving the formulation of a coating compound with static and dynamic ozone testing of the coatings, a review of some commercial in-mould coating techniques and analysis of diffusion of a commercial antiozonant through a coating. An outline of the mixing of Nipol 1312, a low molecular weight nitrile butadiene rubber grade produced by leon Chemicals Inc., with other ingredients to produce a coating composition is also given. Test pieces of the natural rubber substrate were placed in pre-coated mould cavities and cured under compression to achieve covulcanisation between the substrate and the coating. All ozone tests were carried out under standard ASTM DI149-911D518-91 conditions. Results show that the formulated nitrile rubber coating compound is able to protect natural rubber from ozone attack with no migration of the antiozonant as in classical chemical antiozonant systems. An up to date patent search on in-mould coating techniques and systems was carried out and evaluated in conjunction with some current commercial coating methods. In this overview, more emphasis is laid on the nature of the coating material which subsequently determines the appropriate coating technique, than on the specific in-mould coating process applied. Post-mould coating work with polyvinyl chloride (PVC) on natural rubber substrate was also assessed. An experimental and theoretical study of the diffusion of the antiozonant N,Isopropyl N-phenyl-pphenylenediamine (IPPD) through a protective coating on a natural rubber substrate is made in the project. This study shows that the protective coating is able to reduce the loss of antiozonant through diffusion while giving the rubber adequate protection from ozone. The study also demonstrates that the combination of a commercial antiozonant and a protective coating gives enhanced product service life and provides protection to damaged regions of the coating.