Natural rubber autohesion

The autohesion effect is especially good, therefore, when weak crystallization occurs on applying pressure or during annealing, as, for example, with natural rubber or with l,5-trans-poly(pentenamers) (physical cross-linking). On the other hand, if the crystallization is too strong, the deformability of the adhesive is too small (see Section 7.4.2). If adherent and adhesive are chemically different, then in the EfE type this leads to interdiffusion and thence to heteroadhesion. Of course, marked interdiffusion is only possible when the different macromolecules are compatible with one another, and the strength of the autoadhesion or heteroadhesion depends on both diffusion and adsorption. 

Fig. 12. Tensile strengths of autohesion (tack T) and cohesion (green strength S) of natural rubber as a function of molecular weight M (103).

In the literature, there are several reports that examine the role of conventional fillers like carbon black on the autohesive tack (uncured adhesion between a similar pair of elastomers) [225]. It has been shown that the incorporation of carbon black at very high concentration (>30 phr) can increase the autohesive tack of natural and butyl rubber [225]. Very recently, for the first time, Kumar et al. [164] reported the effect of NA nanoclay (at relatively very low concentration) on the autohesive tack of BIMS rubber by a 180° peel test. XRD and AFM show intercalated morphology of nanoclay in the BIMS rubber matrix. However, the autohesive tack strength dramatically increases with nanoclay concentration up to 8 phr, beyond which it apparently reaches a plateau at 16 phr of nanoclay concentration (see Fig. 36). For example, the tack strength of 16 phr of nanoclay-loaded sample is nearly 158% higher than the tack strength of neat BIMS rubber. The force versus, distance curves from the peel tests for selected samples are shown in Fig. 37. 

In this study, the degree of autohesion between two layers deposited on the surface of a glass mold was investigated. The Latex blend consisted of (in weight parts) rubber of natural centrifugated latex - 100 sulphur - 2 zinc dimethyldithiocar-bamate - 1 zinc mercaptobenzothiazole - 1 2,2 -methylenebis (6-tert-butyl-4-methylphenol) - 0.5. 

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