Ozone attack rubber compounds

Like NR, SBR is an unsaturated hydrocarbon polymer. Hence unvulcanised compounds will dissolve in most hydrocarbon solvents and other liquids of similar solubility parameter, whilst vulcanised stocks will swell extensively. Both materials will also undergo many olefinic-type reactions such as oxidation, ozone attack, halogenation, hydrohalogenation and so on, although the activity and detailed reactions differ because of the presence of the adjacent methyl group to the double bond in the natural rubber molecule. Both rubbers may be reinforced by carbon black and neither can be classed as heat-resisting rubbers. 

Retardation of oxidative degeneration and the effects of ozone attack can be mitigated but not totally overcome by the use of chemicals which, unfortunately, in the case of the most effective types, carry the penalty of causing staining of the rubber compound or surfaces with which it comes into contact. 

Ozone attacks C=C in unsaturated compounds including olefins, cycloolefins, pinenes, aromatics, and polybutadienes (for example, causing rubber to crack). 

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). 

In the presence of light, halogens attack both vulcanised and unvulcanised butyl rubber. Whether vulcanised or unvulcanised the effect of the reaction is to produce rapid deterioration in molecular weight. A strip of butyl vulcanisate suspended in bromine gas degrades rapidly. In a few minutes the specimen becomes fluid enough to drip to the bottom of the vessel. Chlorosulfonated polyethylene is resistant to ozone being better than Neoprene and butyl rubber compounds [18]. 

The second class of tests focused on ageing, oxygen and ozone attack, adhesion, resistance to wear and tear, and general fatigue. This class also includes tests under simulated service condition in laboratory environments. These two classes of tests are conducted on vulcanised rubber. For assessing the processibility of the compounded... 

Ozone attack on the oxidatively violated rubber surface is thus prevented (21, 27, 29, 30). Creation of the surface layer was confirmed using microscopy. The theory is in agreement with the observation that the initial rapid ozone consumption is stabilized rubber drops and may be renewed after mechanical break of the formed film 21). There is a chemical proof of the theory. Ozonation products of N,N -bis(l-methylheptyl)-l,4-PD (DOPPD) form a surface film on ozonized and DOPPD doped vulcanized NR (31) and carbon-black loaded NR (24, 32). In addition to unreacted DOPPD, many of the low-molecular weight compounds observed in the film were found also in the ozonation of pure DOPPD (24) the only difference was a... 

Ethylene-propylene rubber is particularly resistant to sun, weather, and ozone attack. Excellent weather resistance is obtained whether the material is formulated in color, white, or black. The elastomer remains free of surface crazing and retains a high percentage of its properties after years of exposure. Ozone resistance is inherent in the polymer, and for all practical purposes, it can be considered immune to ozone attack. It is not necessary to add any special compounding ingredients to produce this resistance. 

Weather Resistance Many rubbers are affected adversely by outdoor exposure, particularly by the traces of ozone, which are always present in the atmosphere and which cause rapid cracking of lightly stressed rubber articles. Nitrile rubber is no exception and thus it is not suitable for use in exposed conditions. However, the incorporation of a proportion of PVC (Polyvinyl chloride) into the nitrile compound results in improved resistance until, with a blend of 70/30 nitrile/PVC, a material with almost complete resistance to ozone attack is produced. The presence of PVC produces stiffer compounds, with lower resiliance and inferior low temperature properties, but the oil and solvent resistance is enhanced. 

FKM vulcanizates have excellent heat resistance, giving continuous service for 1000 hr at 220°C. Useful service is even possible at 250°C. These elastomers are also highly resistant to weathering and ozone attack. FKM vulcanizates are resistant to swelling in hot oils and aliphatic compounds. They also are resistant to aromatics, chlorinated hydrocarbons, and motor fuels. In addition, they are very resistant to most mineral acids. The gas-permeability resistance of FKM vulcanizates even exceeds that of butyl rubber vulcanizates. 

Blooms and visually similar phenomena are sometimes seen on the surfaces of rubber mouldings. These may originate from the limited solubility of a particular component of the rubber compound, or from contamination, for instance, by a release agent from the mould. Some blooms are deliberately contrived - hydrocarbon wax gives some protection from ozone attack. Loadman and Tidd give a useful account of the classification and analysis of blooms on rubber. 

For most sealing applications, attack by ozone is only likely during storage, and this can be reduced by packing the seals properly. With exterior seals, ozone attack is possible, and ozone-resistant rubbers should be selected. If this is not possible, anti-ozonants should be added to the compound. 

Now this is the same ozone that in the stratosphere shields the biosphere from dangerous uv radiation. (See Section 11.5 for an extended discussion of ozone and the stratospheric ozone layer. Chapter 18 discusses threats to the ozone layer from chlorine and bromine compounds.) But this ozone is in the troposphere, the layer of air we breathe and live in. It causes a number of health problems including respiratory irritation, choking, coughing, and fatigue and has also been implicated in damage to forests and crops. It also attacks rubber products and causes cracks in tires. 

In rubber compounding the term antidegradant is commonly used for any substance that is added to retard the deterioration of the vulcanized compound under service conditions. This deterioration, most often a result of chemical attack, results in a progressive loss of functional properties and a decrease in service lifetime of a rubber article. The three principal agents attacking rubber and causing its deterioration are oxygen (O2), ozone (O3), and ultraviolet radiation. Virtually all antiozonants used in rubber also act as antioxidants however, many antioxidants do not act as antiozonants. 

Wax blends are used as rubber compounding ingredients to function as a physical barrier against ozone attack of the rubber surface under static conditions. 

A variety of materials are commercially available for giving a rubber compound certain desired properties needed for functional performance in actual use. Antioxidants are commonly added for resistance against attack by environmental oxygen (Oj), whereas antiozonants are employed for resistance from attack by ozone (O3). 

The adhesion of RFL-coated tire cords to rubber can be adversely affected if the dipped cords are exposed to ozone, UV light, nitrogen oxides, sulfur dioxide, or air before vulcanization into rubber. lyengar proposed that ozone exposure of RFL reduces adhesion because ozone attacks the double bonds of the butadiene component of the rubber latex and impairs its cocuring with the solid rubber compound. Infrared studies by Solomon reinforced this argument. When typical RFL films were exposed to ozone, the IR spectrum showed an increase in IR absorption at 1720 cm corresponding to an increase in the carbonyl content in the exposed film. An RFL film with no ozone exposure did not show this absorption at 1720 cm The increased carbonyl content is due to the reaction of some double bonds in the rubber with ozone and therefore, would leave fewer unsaturation sites for rubber crosslinking and adhesion. 

Since this bloom is brittle, it is broken by flexing. Therefore, waxes only protect under static conditions. For serving conditions which involve continuous flexing, /j-phenylenediamines (A, A -alkyl-aryl derivatives) can be added. These chemical antiozonants scavenge the ozone before it reacts with the rubber. A barrier of ozonized products is created which protects both the rubber and antiozonant from further attack. However, p-phenylenediamines are staining compounds. Whenever colour is an important concern, blends of elastomers can be used elastomers loading should be higher than 30 phr to provide sufficient effectiveness. 

Since the main chain of NR contains unsaturation (residual double bonds) it, along with other unsaturated rubbers, is susceptible to attack by oxygen, ozone and light, and compounds therefore require protection against these agencies. 

ANILINE (62-53-3) Combustible liquid (flash point 158°F/70°C). Unless inhibited (usually by methanol), readily able to polymerize. Violent reaction, including the possibility of fire, explosion, and the formation of heat- or shock-sensitive compounds may result from contact with acetic anhydride, benzene diazonium-2-carboxylate, aldehydes, alkalis, benzenamine hydrochloride, boron trichloride, l-bromo-2,5-pyrrolidinedione, chlorosulfonic acid, dibenzoyl peroxide, fluorine nitrate, halogens, hydrogen peroxide, isocyanates, oleum, oxidizers, organic anhydrides, ozone, perchloryl fluoride, perchromates, potassium peroxide, P-propiolactone, sodium peroxide, strong acids, trichloromelamine. Strong reaction with toluene diisocyanate. Reacts with alkaline earth and alkali metals. Attacks some plastics, rubber, and coatings. Incompatible with copper and copper alloys. 

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