Natural tack

Natural rubber displays the phenomenon known as natural tack. When two clean surfaces of masticated rubber (rubber whose molecular weight has been reduced by mechanical shearing) are brought into contact the two surfaces become strongly attached to each other. This is a consequence of interpenetration of molecular ends followed by crystallisation. Amorphous rubbers such as SBR do not exhibit such tack and it is necessary to add tackifiers such as rosin derivatives and polyterpenes. Several other miscellaneous materials such as factice, pine tar, coumarone-indene resins (see Chapter 17) and bitumens (see Chapter 30) are also used as processing aids. 

Said of uncured rubber surfaces which have lost their natural tack. 

Another possibility for adhesives to be classified is the differentiation between organic compounds of natural products, so-called natural adhesives, and products resulting from targeted chemical reactions, so-called synthetic adhesives. Many substances are known from daily life, which show a natural tack, for example, tree resins, plant juices, waxes, proteins, gelatine, casein, starch. In comparison to synthetically produced adhesives they are heavily lagging behind in terms of quantity, however, they partly show excellent properties in special applications, such as casein adhesives for bottle labelling. 

Tackifiers. Pine tar, coumarone-indene resins, zylol-formaldehyde, and other resins are used to increase the tack of rubber compounds. Tack, here, means stickiness of the un-cmed rubber stock to itself, rather than to other things, such as metal surfaces. Tack has also been called autoadhesion. It is extremely important for building up structures such as tires. Natural rubber inherently has good natural tack, but most synthetic rubbers do not. 

This cement is solvent coated on one substrate and dried. The second substrate is then laminated to the adhesive with moderate roll pressure. In this way the natural tack of the formulation allows impervious material to be laminated without solvent entrapment. 

Tackifiers - Elastomers with little or no natural tack can be improved by the addition of resins or resin oils (natural abietie aeid derivatives), polyindene (coumarone-indene) resins, polyterpene resins and phenol-formaldehyde resins. 

Natural rubber displays the phenomenon of natural tack and therefore serves as an excellent adhesive. Adhesion occurs because the ends of rubber molecules penetrate the adherend surfaces and then crystaUize. The polymer has the following chemical structure, having a double bond at every alternate carbon... 

Adhesives are polymers that are initially liquid but solidify with time to give a joint between two surfaces [12,13]. The transformation of fluid to solid can be obtained either by evaporation of solvent from the polymer solution (or dispersion) or by curing a liquid polymer into a network. Table 2.3 lists some common adhesives, which have been classified as nonreactive and reactive systems. In the former, the usual composition is a suitable quick-drying solvent consisting of a polymer, tackifiers, and an antioxidant. Tackifiers are generally low-molecular-weight, nonvolatile materials that increase the tackiness of the adhesive. Some tackifiers commonly used are unmodified pine oils, rosin and its derivatives, and hydrocarbon derivatives of petroleum (petroleum resins). Several polymers have their own natural tack (as in natural rubber), in which case additional tackifiers arc not needed. 

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