Synthetic polyisoprene rubbers adhesion

Other polymers used in the PSA industry include synthetic polyisoprenes and polybutadienes, styrene-butadiene rubbers, butadiene-acrylonitrile rubbers, polychloroprenes, and some polyisobutylenes. With the exception of pure polyisobutylenes, these polymer backbones retain some unsaturation, which makes them susceptible to oxidation and UV degradation. The rubbers require compounding with tackifiers and, if desired, plasticizers or oils to make them tacky. To improve performance and to make them more processible, diene-based polymers are typically compounded with additional stabilizers, chemical crosslinkers, and solvents for coating. Emulsion polymerized styrene butadiene rubbers (SBRs) are a common basis for PSA formulation [121]. The tackified SBR PSAs show improved cohesive strength as the Mooney viscosity and percent bound styrene in the rubber increases. The peel performance typically is best with 24—40% bound styrene in the rubber. To increase adhesion to polar surfaces, carboxylated SBRs have been used for PSA formulation. Blends of SBR and natural rubber are commonly used to improve long-term stability of the adhesives. 

Natural rubber - [RUBBERCOMPOUNDING] (Vol 21) - [ELASTOMERS, SYNTHETIC - SURVEY] (Vol 8) -in adhesives [ADHESIVES] (Vol 1) -cellular forms [FOAMED PLASTICS] (Vol 11) -compared to polyisoprene [ELASTOMERS SYNTHETIC - POLYISOPRENE] (Vol 9) -fluonnahon of [FLUORINECOMPOUNDS,ORGANIC - DIRECTFLUORINATION] (Vol 11)... 

Synthetic polyisoprenes are superior to natural rubber in terms of consistency of properties. The are also freer of contaminants, and are preferred for applications that require lighter color, for personal care items and for derivatization to chlorinated and cyclized rubber products that are used in the adhesives and coatings industries. 

A true synthetic natural rubber was introduced in the mid-1960s with the exact same chemical structure as latex tapped from a tree. The difference is that natural rubber comes with a variety of other ingredients in the latex that can both add and detract from performance, while polyisoprene is considered relatively pure. In addition, there are some differences in molecular weight distribution that impact performance. Available in both latex and solid forms, this elastomer can be directly substituted for natural rubber in many applications. Adhesives which are not cured tend to have higher creep values than natural rubber, but also exhibit lower tack and green strength properties. Vulcanized adhesive products perform equal to cured natural rubber adhesive products. 

Natural rubber-based adhesives constitute many nsefnl types of adhesives. They have been made from the latex that is collected from the sap of rubber trees grown in Malaysia and other countries of Sonth East Asia. Rnbber of this type was first collected from the Hevea brasiliensis tree - seeds from the tree were first taken from the Amazon forests in Brazil, propagated in Kew in London, and then supplied, over a century ago, to Malaya and adjacent counuies, where there are now many millions of rubber trees, yielding cis-polyisoprene-based natnral rnbber. This has similar properties to the principal SBR synthetic rubber, derived from styrene and butadiene, both of which are obtained by the cracking process from crnde oil, with subsequent chemical reactions. Natural rubber is obtained from the uee by tapping the bark, when the latex flows out spontaneously as the tree is wounded. This latex is about 33% solids - most natural rubber latex is concentrated to 60% and preserved with ammonia for transport and storage. 

Many applications are being found for synthetic rubbers, which are synthetic polymers possessing rubber-like properties. Among those available commercially are butadiene-styrene and butadiene-acrylonitrile (called Buna rubbers), polyisoprene, and polybutadiene. Their properties may be modified considerably more than vulcanized rubbers, particularly with respect to resistance to oxidizing agents, solvents, and oils. Their adhesion to metals, however, is generally poorer. 

The use of adhesives in medical applications has been restricted, for some time, to the manufacture of self-adhesive bandages (plasters, self-adhesive strips of fabric, etc.). The first pressure-sensitive adhesives used for this were based on natural rubber, concocted decades ago. This first usage was later partly superseded by synthetic rubbers (e.g., polyisoprene, polyisobutylene). In die mid-twentieth century, pressure-sensitive adhesives based on polyacrylic acid esters gained predominance in general use and in the composition of bandage materials. 

With respect to the use of biobased sources, adhesive products have been ahead of plastics. They are often called natural adhesives. Animal- and plant-based adhesives have been used for thousands of years. Three prominent classes of natural adhesives include proteins (polyamides), carbohydrates (polysaccharides), and natural rubber (mainly cw-polyisoprene). Three specific examples are starch, a carbohydrate gelatin, a protein and rubber cement made from natural rubber. Advantages of biobased adhesives include recyclability and environmental safety. The latter is an important consideration because of presence of solvents and hazardous ingredients in some synthetic adhesives. 

Synthetic high c/.y-polyisoprenes have Mooney viscosities of typically 75-80, although certain producers offer low Mooney grades having viscosities of about 60 which have proved useful in blends with other synthetic rubbers and to adhesive manufacturers. 

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