Rubber-degrading reaction

Antiozonant additives are employed with unsaturated rubbers such as natural rubber, nitrile rubber, styrene-butadiene rubber, etc., to minimise the atmospheric ozone degradation reaction. Common antiozonant types include the parapheny-lene diamines such as N-(l,3-dimethylbutyl)-AT-phenyl-p-phenylene diamine (6PPD) and N-isopropyl-N7 phenyl-p-phenylene diamine (IPPD). Both these antioxidants can be identified and quantified using GC- or LC-based techniques. 

If the degradation reaction is carried out in the presence of an unpolymerizable species, only one molecule of the monomer adds to the primary radical This is the case for the system natural rubber-maleic anhydride 11,65,71). 

The heat and ozone resistant [126] EPR was made by incorporating acrylic rubber, dicumyl peroxide, triaUyl cyanurate, ZnO and carbon-black into the matrix. Triallyl cyanurate increases the crosslinking efficiency probably due to an addition reaction between polymeric and aUyl radicals and leads to stable chemical crosslinks. Thus ozone because there is no unsaturation cannot initiate a degradation reaction. Digteva et al. [127] prepared sealants for use at high temperature by adding aromatic diaminodisulfide, MgO, ZnO and carbon black in EPR. The aromatic diaminodisulfide is an antiozonant and functions both as an antioxidant and a... 

Such heat-sensitive materials include, for example, polyurethane, PVC, linoleum and foamed rubbers. The effect of light, especially UV light, promotes the degradation reactions. 

Oxidation, as we have noted, is a free-radical chain process. The most useful stabilizing agents will therefore be those which combine with free radicals, as shown by Equation 1.67, to give a stable species incapable of further reaction. These stabilizing agents are called antioxidants. They are the most frequently employed ingredients in plastics, fibers, rubbers, and adhesives. Stabilization is also achieved in some polymer systems by the use of additives which moderate the degradation reaction. 

This degradation reaction, supplemented by various subsequent oxidation steps, has found renewed interest in the form of the introduction of photodegrad-able plastics as part of the campaign to reduce plastic litter from throwaway packaging. Although as yet there has been no demand for photodegradable mb-bers, the incorporation of a small percentage of a vinyl ketone into a rubber copolymer or homopolymer would open the way to a useful synthesis of block copolymers. 

At the same time inorganic nanoparticles are important component in synthetic rubber nanocomposites, this type of nanoparticles are less reactive than organic nanoparticles, because they are not involved in thermal degradation reactions. Inorganic nanoparticles can be subjected to high temperature, due of natural chemical, are considered an excellent choice as reinforcement in polymer matrix, has been reported that using this type of nanoparticles improve the thermal stability of nanocomposite. 

Substituted phenols that act as scavengers for radicals formed in the course of the degradation reaction as well as thio compounds and organophosphites are added as antioxidants. Benzophenone and carbon black act as UV stabilizers. Calcium stearate or other carboxylic acids are added to bind chloride originating from the catalyst. Further additives can be acceptors for coloring, anti-electrostatics, nucleating agents to promote crystallization, lubricants, or flame retardants [507,508]. Polypropene can also be blended with other polymers as rubbers (EPDM) or polyethene [509-511]. In these products the... 

Thermal degradation of rubber vulcanizates involves scission and cross-linking reactions. Tobolsky [9] did a kinetic study of rubber degradation and derived the following simple Maxwellian relation between the stress and the rate constant, k, based on the theory of rubber elasticity ... 

Finally, as rubber ages, further slower creep may take place as covalent bonds in the chains are broken by degradation reactions, a process that can be hastened when the rubber is under stress. 

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