Adhesion autohesion

The self-adhesion (autohesion) of polymers is of considerable practical importance as many moulding operations involve the need for streams of merging polymer melt to self-adhere to form a strong bond necessary to the integrity of the moulded article. Mechanisms of polymer diffusion are discussed in Polymer diffusion reptation and interdigitation and theories that relate interfacial structure to strength in Polymer-polymer adhesion models. In the latter article, the vector percolation (VP) model was described, which is here applied to welding, and the practical consequences of its predictions are drawn out. - ... 

In the case of the adhesion of a monolayer (Fig. I.la), the detaching force acts on each particle, and if > F j (the latter being the adhesive force) the adhering particles will be detached from the surface. When whole layers adhere to the surface (Fig. I.lb), the force acts on all the particles forming the layer or layers. The strength of this layer depends not only on its adhesion to the surface, but also on the autohesion of the particles themselves. If ad det aut latter being the force of autohesion), adhesive detachment will occur if Fad > det > aut > autohesive detachment will take place. If F ad Faut, there may be mixed adhesive—autohesive detachment. ... 

Voyutskii, S.S., Autohesion and Adhesion of High Polymers. John Wiley and Sons, New York, 1963. 

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. 

Voyutskii, S.S. 1963. Autohesion and adhesion of high polymers. In Polymer reviews, 140. eds. Mark, H.F. and Immergut, E.H. New York John Wiley Sons. 

In the theory of diffusion it is postulated that high molecular weight polymer molecules interdiffuse w ith each other across the inter ce. The term autohesion is often applied to this process in the adhering of portions of the same plastic material together. Since molecules of the same material diffuse across the inteiface, makhtg the two layers one, the original joint disappears. Once the joint is completely healed, there is little chance that adhesive failure will occur at the original inteiface. 

Voyuiskii, S. S. (1963). Autohesion asund Adhesion of High Polymers (S. Kaganoff, Translator), (Interscience), Wiley, New York. 

In Figure 9.2 the diffusion bonding process is schematically shown. The adhesive forces developing in this way are also called autohesion. 

Contact-bond adhesives are applied to both of the surfaces to be bonded, allowed to dry until approximately nontacky to the touch, and then pressed together to form a bond. The elastomers in these adhesives have the property known as autohesion. This means that when the dried adhesive-coated surfaces are brought together under some pressure, the films join by a process of molecular difiusion and form a completed bond. 

A special type of organic solvent-based adhesive is the so-called contact adhesive. This makes use of the fact that certain elastomeric or rubbery solids (e.g., polychloroprene) have the property of autohesion, i.e., they can stick readily to themselves, especially if compounded with resins and containing small amounts of solvents. The bonding takes place by a diffusion process, the adhesive being applied to both surfaces to be bonded. Thus substrates may be coated with a contact adhesive, the adhesives can be allowed to dry till most of the solvent has evaporated (the dry adhesive film at this point will contain... 

S. S. Voyutskii, Autohesion and Adhesion of High Polymers, Interscience, New York, 1963. —, Contact angle, wettability and adhesion, Adv. Chem. Ser. 43, Am. Chem. Soc.,... 

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. 

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. 

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. 

DURABILITY - HOSTILE ENVIRONMENTS ENGINEERING DESIGN PROCESSING AND ASSEMBLY WELDING AND AUTOHESION APPLICATIONS OF ADHESIVES COMPOSITE MATERIALS PAINT RUBBER... 

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