Natural rubber degradation products

The author is unaware of any commerical polymers that are specifically designed to degrade oxidatively, although oxidation may be involved in association with hydrolytic and biological degradation. It may be of interest to note that before World War II products known as rubbones were produced by degrading natural rubber with cobalt linoleate in the presence of cellulosic materials to produce low molecular weight, fluid oxidised natural rubber (Section 30.4). 

Natural rubber is harvested as latex by tapping trees in a manner similar to maple syrup. Tree latex contains about 35 wt% rubber solids, as well as small quantities of carbohydrates, resins, mineral salts and fatty acids. Ammonia should be immediately added to the latex to avoid coagulation by these other ingredients and to prevent bacterial degradation. After collection, the latex can be concentrated to 60-70% solids if the latex product is required for end-use. Otherwise, the latex is coagulated, washed, dried, and pressed into bales for use as dry rubber. 

This discussion of the structures of diene polymers would be incomplete without reference to the important contributions which have accrued from applications of the ozone degradation method. An important feature of the structure which lies beyond the province of spectral measurements, namely, the orientation of successive units in the chain, is amenable to elucidation by identification of the products of ozone cleavage. The early experiments of Harries on the determination of the structures of natural rubber, gutta-percha, and synthetic diene polymers through the use of this method are classics in polymer structure determination. On hydrolysis of the ozonide of natural rubber, perferably in the presence of hydrogen peroxide, carbon atoms which were doubly bonded prior to formation of the ozonide... 

The mechanical degradation and production of macroradicals can also be performed by mastication of polymers brought into a rubbery state by admixture with monomer several monomer-polymer systems were examined (10, 11). This technique was for instance studied for the cold mastication of natural rubber or butadiene copolymers in the presence of a vinyl monomer (13, 31, 52). The polymerization of methyl methacrylate or styrene during the mastication of natural rubber has yielded copolymers which remain soluble up to complete polymerization vinyl acetate, which could not produce graft copolymers by the chain transfer technique, failed also in this mastication procedure. Block and graft copolymers were also prepared by cross-addition of the macroradicals generated by the cold milling and mastication of mixtures of various elastomers and polymers, such as natural rubber/polymethyl methacrylate (74), natural rubber/butadiene-styrene rubbers (76) and even phenol-formaldehyde resin/nitrile rubber (125). 

Fair to good aging Cured products often will outperform natural rubber products, but uncured products made from emulsion polymers can degrade rather quickly if not compounded for UV, ozone, and oxygen resistance. Block copolymers are typically better in the uncured state than standard SBR, but still require protectant additives for extended exposure conditions. 

Newly planted rubber trees take 5 to 7 years before they can be tapped and reach their peak production in 10 to 20 years. Of the major global challenges, the environment occupies a dominant place for rubber trees and natural rubber, even on smallholdings where Hevea is usually intercropped with other tree crops or food crops, thereby constituting agro-forests, which nowadays have important secondary functions (maintaining biodiversity, environmental conservation, rehabilitation of degraded zones, etc.) ... 

The effects of mechanical degradation by polymer crushing on stabiliser structure, such as those discussed previously, are, of course, avoided in separation methods based on dissolving the polymer in a solvent, then precipitating the polymer, but not the stabiliser, with a nonsolvent, providing a solvent extract which contains only the stabiliser. Again, however, this process needs a consideration of the solution-precipitant effects on the stability, especially of the reaction products of stabilisers or their fragments with the polymer. Such reaction products have been both determined and isolated with PVC, PE, PP and natural rubber. 

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. ... 

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