Rubber ozone degraded

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... 

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. 

In past studies (3), Electron Spin Resonance, ESR, has been used to investigate bond rupture associated with stress-ozone degradation in unsaturated rubbers. It was believed that it might be enlightening to perform similar experiments on plastics ( 5, 8, 10, 11). In the study reported here the combined effects of environment (O3, N02 and S02) and sustained stress on the ultimate properties of Nylon 6 fibers are presented. These agents were found to have a profound effect on strength, toughness and the deformation-bond rupture kinetics. 

In contrast to this, very little is known about the ozonolysis of olefins which bear halogen substituents at the double bond. This is somewhat surprising since compounds containing vinyl halide moieties are important technical products whose properties could be adversely affected by ozone degradation. A case in point is neoprene rubber, whose performance as an elastomer could suffer considerably by ozone attack and concurrent crack formation (1). 

Rakovsky, S. K. Cherneva, D. R. Shopov, D. M. and Razumovskii, S. D. Applying of barbotage method to investigation the kinetic of ozone reactions with organic compounds. Izv. Khim. BAN. 976,XI(4), 777.M.R Anachkov, S.K. Rakovsky, R.V. Stefanovaand D.M. Shopov, Kinetics and mechanism of the ozone degradation of nitrile rubbers in solution, Polym. Deg. Stab., 19(2), 293 (1987). 

Ozone levels are dependent on the time of day and also the season. Levels reach a maximum in late morning and drop to nearly zero at night. Summer months show considerably higher ozone levels than winter months. Indoors, ozone is formed by fluorescent lighting. Only a few parts per hundred million of ozone in air can cause rubber cracking, which may destroy the usefulness of elastomer products. Ozone degradation mechanisms are illustrated in Figure 1. 

A government-sponsored research program led to the discovery of chemicals that prevented ozone cracking when added to rubber compounds. Commercial antiozonants have been available since the early 1950s. Since that time, the ozone degradation problem has worsened as atmospheric ozone concentrations have gradually increased, especially in urban industrial areas. 

Anachkov, MP, Rakovsky, SK, Stefanova, RV and Shopov, DM, Kinetics and mechanism of the ozone degradation of nitrile rubbers in solution. Polymer Degradation and Stability, 19, 293-305 (1987). 

A, A -Disubstitnted-p-phenylenediamines, such as AT-phenyl-Ar -(l,3-dimethylbutyl)-p-phenylenediamine [793-24-8] (10), are used in greater quantities than other classes of antioxidants. These products protect unsaturated elastomers against oxidation as well as ozone degradation (see Rubber... 

The PPD class of antidegradants provides by far the best antiozonant protection (for a review of antiozonants, see Reference 82). PPDs inhibit ozone degradation of rubber by multiple mechanisms (76,83-85) ... 

Formation of a strong interfacial layer is the key factor of the mechanism describing retardation of ozone degradation of a diene rubber by elastomer additives with a low degree of unsaturation [1-4]. The effect of comonomer ratio in ethylene-propylene-diene terpolymers (EPDMs) and stereoregularity of propylene units on the interfacial interaction and the amount of crosslinks in ihe interfacial layer was considered for heterophase crosslinked blends with butadiene-acrylonitrile mbbers (BNRs) of different polarities. 

This valuable book presents selected papers on various aspects of rubber engineering, technology, and exploitation. The contributions range from new methods of the modification of filler surface and crosslinks structure of rubber vulcanizates, through modern functional elastomer composites, and on to aspects of their thermal stability, flammability, and ozone degradation. Each chapter contains a brief introduction to the particular topic of consideration, a description of the experimental technigues, and a discussion on the results obtained, followed by conclusions. The research presented here has potential applicability for industrial applications as well as for new materials and technologies. 

The interest in the reaction of ozone with polydienes is due mainly to the problems of ozone degradation of rubber materials [1-4] and the application of this reaction to the elucidation of the structures of elastomers [5-8], It is also associated with the possibilities of preparing bifunctional oligomers by partial ozonolysis of some unsaturated polymers [9-12], Usually the interpretation of experimental results are based on a simplified scheme of Criegee s mechanism of C=C-double bond ozonolysis, explaining only the formation of the basic product - ozonides [13, 14],... 

Approaches to the prediction of the long-term ageing behaviour of vulcanised diene rubbers are discussed, and studies of the photooxidative and ozone degradation of polybutadiene, polyisoprene, SBR and nitrile rubber under accelerated artificial ageing conditions are reported. 12 refs. 

A review of the Hterature on degradation mechanisms of rubbers is presented, covering thermooxidative degradation, thermal decomposition, radiation degradation, UV radiation degradation (weather resistance) and ozone degradation. 66 refs. (Full translation of Nippon Gomu Kyokaishi, No.5,1995, p.284)... 

Varghese, S., Kuriakose, B., and Thomas, S. (1994) Short sisal fiber reinforced natural rubber composites high-energy radiation, thermal and ozone degradation. Polym. Degrad. Stab., 44, 55-61. 

Since the mid-1950s several materials have been found effective in combating ozone-initiated degradation, in particular certain p-phenylenediamine derivatives. The actual choice of such antiozonants depends on the type of polymer and on whether or not the polymer is to be subject to dynamic stressing in service. Since antiozonants are not known to have any use in plastics materials, even those which may have certain rubber particles for toughening, they will not be dealt with further here. Anyone interested further should consult references 3-5. 

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.)... 

With rubber base adhesives, it is necessary to prevent their properties from changing during service life. Oxidative changes induced by thermal, ozone exposure and UV light can dramatically affect service life of rubber base adhesives. More precisely, the rubber and the resin are quite susceptible to oxidative degradation. Environmental and physical factors exert detrimental effects on rubber base adhesive performance. These effects can be mitigated by the incorporation of low levels of stabilizers during the fabrication process of the adhesive. 

Degradation of rubbers and resins can also be produced by ozone attack. Ozone directly reacts with, and cleaves, the carbon-carbon double bonds of rubbers and resins. Thus only polymers with backbone unsaturation will be cracked by ozone. Unlike oxidation, ozone attack cannot be accelerated by increasing the... 

Although, the heat resistance of NBR is directly related to the increase in acrylonitrile content (ACN) of the elastomer, the presence of double bond in the polymer backbone makes it susceptible to heat, ozone, and light. Therefore, several strategies have been adopted to modify the nitrile rubber by physical and chemical methods in order to improve its properties and degradation behavior. The physical modification involves the mechanical blending of NBR with other polymers or chemical ingredients to achieve the desired set of properties. The chemical modifications, on the other hand, include chemical reactions, which impart structural changes in the polymer chain. 

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