Autohesive tack

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. 

Various factors govern autohesive tack, such as relaxation times (x) and monomer friction coefficient (Co) and have been estimated from the different crossover frequencies in the DMA frequency sweep master curves (as shown in Fig. 22a, b). The self-diffusion coefficient (D) of the samples has been calculated from the terminal relaxation time, xte, which is also called as the reptation time, xrep The D value has been calculated using the following equation ... 

The ability of uncured rubber to adhere quickly to itself and then be resistant to separation is known as tack or autohesion. Tack can be crucial to the assembly of rubber components that need to remain in place prior to vulcanization. An example is tire assembly, which entails positioning carcasses, belts, and other plies these layers are held together by virtue of their tack. There are three requirements for building tack ... 

In the empirical world of tack experts, many professional terms are employed, like green strength (as initial tack is sometimes called), which relate to the resistance to separation before the adhesive has had a chance to vulcanize or crosslink. This characteristic may also be called quick tack or aggressive tack . It may be one of the most important properties in determining the suitability of an adhesive, such as that placed on a pressure-sensitive tape, for a certain application. Associated with tack is dry tack , which is a property of certain adhesives to stick to one another even though they seem to be dry to the touch. Autohesive tack (or autohesion) is the dry tack between materials having similar chemical compositions. Tack range is the time that an adhesive will remain in a tacky condition. 

Autohesive tack involves two elastomeric materials of essentially the same composition. In this case, separation may be either adhesive (usually after short times of contact) or cohesive (usually after long times of contact). It is important in the use of contact adhesives and in plying together rubber surfaces in, for example, the manufacture of tyres. 

Autohesive tack differs from the other types in that it involves mutual diffusion of polymer molecules across the interface it is discussed elsewhere (see the articles on Diffusion theory of adhesion and Polymer diffusion replation and interdigitation). Adhesive tack between elastomeric materials and other, usually rigid, surfaces is considered in this article. 

Tack D W AUBREY Definition cohesive, adhesive and autohesive tack tackifier resins... 

Some rubbery materials adhere firmly to themselves (autohesive tack or auto-hesion) or to a different surface (adhesive tack) after brief contact imder light pressure. They have a liquid character which results in rapid bond formation, yet, without setting, they resist detachment like a solid, ie, they are sfrong and soft. (Tacky substances are stroft, like toilet paper.) Typically, adhesive tack involves bonding to a hard substrate and interdiffusion is absent or minimal. Adsorption is the principal mechanism of adhesion. On the other hand, autohesion involves both molecular contact and interdiffusion. Autohesion is important in the manufacture of articles, such as tires, which are built by laminating rubbery components. 

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

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