Epoxidized natural rubber production

As natural rubber is a product of nature, its properties are determined by the biochemical pathway by which the polymer is synthesized in the plant. In the case of natural rubber the polymerization process cannot be tailored like that of synthetic rubbers. The only option to modify natural rubber is after it has been harvested from the tree. The important modified forms of natural rubber include hydrogenated natural rubber, chlorinated natural rubber, hydro-halogenated natural rubber, cyclized natural rubber, depolymerised liquid natural rubber, resin modified natural rubber, poly(methyl methacrylate) grafted natural rubber, poly(styrene) grafted natural rubber, and epoxidized natural rubber [33,34]. Thermoplastic natural rubber prepared by blending natural rubber and PP is considered as a physically modified form of natural rubber. 

Epoxidized natural rubber (ENR) is an important modified form of natural rubber whose properties are close to those of special purpose synthetic rubbers. ENR is prepared by reacting natural rubber in latex form with performic acid formed in situ by the reaction of formic acid and hydrogen peroxide under controlled conditions. [45,46]. The double bonds of natural rubber react readily with peracids to yield epoxide groups. Though any level of epoxidation can be achieved, only up to 50 mole percent is used in practice. 50, 25, and 10 mole% epoxidized products are termed ENR-50, ENR-25, and ENR-10. Studies using NMR have shown that the epoxide groups are randomly distributed along the natural rubber backbone [47]. 

Uncontrolled oxidation of rubber is detrimental to its physical properties. Oxidation reactions take place readily at unsaturated groups in polymers and are often referred to collectively as epoxidation however, oxidation under controlled conditions can lead to useful products such as the epoxidized natural rubber introduced by the Malaysian Rubber Producers Association (Schults etal., 1983 Cunneen and Porter, 1965 Ceresa, 1965 Avery and Watson, 1956). Natural rubber in the latex form is treated with hydrogen peroxide dissolved in acetic acid. This gives 50% epoxidized natural rubber. This rubber shows very interesting physical properties and excellent carbon black dispersion. Similarly, nonaqueous epoxidizations of synthetic polyisoprene can be achieved... 

C-NMR studies on oxidative degraded natural rubbers showed the presence of epoxides as part of the by-products, of which the cis configuration was found to be the major product the tram configuration was the minor product, as shown in Table 3.11. This contradicts the prediction that degradation of natural rubber produces tram epoxide groups. ... 

Early adhesives were based on natural products, such as starch, animal glue, natural rubber, etc. Modern adhesives are synthetic materials based on resins, synthetic polymers, epoxides, urethanes, etc. 

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