Adhesion Between Unvulcanized Elastomers: A Critical Review
Tack is the ability of two unvulcanized elastomeric materials to resist separation after bringing their surfaces into contact for a short time under a light pressure. Two types of tack can be defined: autohesive tack, where both the unvulcanized elastomeric materials have identical chemical composition, and adhesive tack in which the two unvulcanized elastomeric materials have dissimilar compositions. The tackifiers are typically added in the range of 1–10 parts per hundred grams of rubber (phr) to increase the initial tack and to prevent tack degradation. It is believed that tackifiers increase the tack bond formation by enhancing the contact area which subsequently facilitates the interdiffusion of elastomer chains across the interface. In addition, tackifiers offer greater resistance to the separation of the diffused elastomer chains during bond rupture process. However, with the available data, it is not easy to conclude whether the surface properties or bulk viscoelastic properties of the elastomer-tackifier blend are more dominant in controlling the tack of an elastomer. This review provides a deeper insight into the role of interfacial effect (specific interaction at the interface due to the change in surface energy by the incorporation of tackifiers) and the bulk effect (change in bulk viscoelastic properties by the addition of tackifiers) on the tack of elastomer. It is also known that the fillers like carbon black can increase the tack strength of elastomers. It has been reported that the effect of carbon black addition on tack depends on the ability of elastomer chains to achieve tack bond formation and also to the increase in the cohesive strength of elastomer due to filler reinforcement. Over the past decade, nanoclays have been used as a potential reinforcing agent for various elastomers. These nanoclays offer a wide array of property improvements at very low filler loadings, owing to the dispersion of a few nanometers thick clay platelets of high aspect ratio. In this review, we have also discussed the mechanism by which nanoclay particles can significantly increase the tack strength of elastomers when added at even very low concentration.
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