Polyisoprene, natural degradable polymers

While polymers that contain sites of unsaturation, such as polyisoprene and the polybutadienes, are most susceptible to oxygen and ozone oxidation, most other polymers also show some susceptibility to such degradation including NR, PS, PP, nylons, PEs, and most natural and naturally derived polymers. 

Nature provides a chemically diverse variety of degradable polymers. These polymers were the first materials used by humankind. Early men dressed themselves in hides (proteins, polysaccharides), later in cotton (polysaccharide), silk and wool (proteins). Early men used wood (polysaccharides, polyphenols) for tools and construction materials. Where available natural rubber (polyisoprene) was used for a variety of daily-life fimctions, from construction to water-proofing storage containers. 

Natural mbber, the other natural hydrocarbon polymer, consisting mainly of cfr-l,4-polyisoprene is relatively resistant to microbial attack in comparison to other natural polymers. A number of micro-organisms have been reported to degrade natural rubber. An enzyme which degrades the mbber was isolated from the extracellular culture medium of Xanthomonas sp., and the erude fractions which are capable of depolymerizing natural mbber in the latex state have been reported.The same authors " reported on a Nocardia strain that used natural mbber as its sole carbon source. 

As with c -polyisoprene, the gutta molecule may be hydrogenated, hydro-chlorinated and vulcanised with sulphur. Ozone will cause rapid degradation. It is also seriously affected by both air (oxygen) and light and is therefore stored under water. Antioxidants such as those used in natural rubber retard oxidative deterioration. If the material is subjected to heat and mechanical working when dry, there is additional deterioration so that it is important to maintain a minimum moisture content of 1%. (It is not usual to vulcanise the polymer.)... 

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 is a polymer of isoprene- most often cis-l,4-polyiso-prene - with a molecular weight of 100,000 to 1,000,000. Typically, a few percent of other materials, such as proteins, fatty acids, resins and inorganic materials is found in natural rubber. Polyisoprene is also created synthetically, producing what is sometimes referred to as "synthetic natural rubber". Owing to the presence of a double bond in each and every repeat unit, natural rubber is sensitive to ozone cracking. Some natural rubber sources called gutta percha are composed of trans-1,4-poly isoprene, a structural isomer which has similar, but not identical properties. Natural rubber is an elastomer and a thermoplastic. However, it should be noted that as the rubber is vulcanized it will turn into a thermoset. Most rubber in everyday use is vulcanized to a point where it shares properties of both, i.e., if it is heated and cooled, it is degraded but not destroyed. 

Piya-areetham P, Rempel GL, Prasassarakich P. Hydrogenated nanosized polyisoprene as a thermal and ozone stabilizer for natural rubber blends. Polym Degrad Stab. 2014 102 112-121. 

Although proteins and their degradation products activate natural rubber cures, it is not necessary to incorporate materials such as soya bean lecithin into high cw-polyisoprenes as has been recommended for the low cw-polymers. ... 

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