Ebonite chemical resistance

Soft rubber is obtained by adding 2-4% sulfur by adding extra sulfur (25-40%), the rubber can be made into ebonite, which is a hard, brittle material, having a wider range of chemical resistance than soft rubber. Soft ordinary rubber is chemical and erosion resistant, but its thermal resistance is not high (about 80 C). 

Ebonites based on NR, IR, SBR and NBR generally have enhanced chemical resistance. Minimum working abrasion resistance ratings do not apply... 

When compounded to form ebonites they show improved chemical resistance especially to carboxylic acids and may be used for some oxidative chemicals depending on type and operating temperatures. Ebonites can be compounded to be suitable for working temperatures up to at least 100°C, but, due to brittleness, are not normally suitable for sub-zero temperatures. 

Polychloroprene and acrylonitrile-butadiene rubber compounds have satisfactory chemical resistance but, except for phosphoric acid, are not suitable for mineral acids at higher concentrations. However, they have good resistance to oils, acrylonitrile-butadiene rubber being the better, and so are often used in oil-contaminated aqueous environments. Generally, abrasion resistance is only fair. Normal maximum working temperature is about 100°C. Acrylonitrile-butadiene rubber ebonites are sometimes used especially where solvent contamination occurs, but are normally very brittle and so should be used with care. 

NR can yield a hard rigid thermoplastic with excellent chemical resistance when cured with over 30 phr of sulphur. Such a product is termed ebonite. 

Ebonite is mainly used as chemically resistant plant linings. 

Accelerators are second in importance only to sulphur. Their function is to accelerate the normally slow rubber-sulphur reaction, increase the rate of vulcanization, and increase productivity. Accelerators are classified into two main classes by types, namely organic and inorganic. The inorganic accelerators such as lime, litharge and other lead compounds and magnesia were employed extensively before the introduction of organic accelerators. They are still used mainly to produce hard rubber or ebonite products. Litharge is used in rubberized fabrics, insulated wires and cables and shoe compounds as well as chemical resistant rubber products... 

Chemicals, Chlor alkali. Paper and pulp, Fertilizers, Oil drilling and Pharmaceu ticals Chemical resistant linings for storage tanks, road and ship tankers, process vessels, pipelines, valves, pumps, filters, agitators, centrifuges, impellers, etc. Soft natural rubber or ebonite, neoprene, butyl and hypalon depending on operating temperature, and application. 

The classic thermosets, such as ebonite, phenolics, ureas, melamines and polyesters as well as the epoxies, when reinforced with fiberglass or graphite fibers could also be classified as high performance thermosets. While these plastics cannot be readily extruded or injection molded, they are resistant to the effects of moderately high hostile environments. Phenolic resin mortars have been used for over a half century for the construction of chemical resistant vessels and for joining brick and tile used as linings in hot acid environments. (1.)... 

Buna 85 is polybutadiene (the number represents Mooney viscosity), molecular weight -80,000. Hard rubber has high softening point and excellent chemical resistance. The coefficient of vulcanisation to the ebonite stage is 39.3. The coefficient of vulcanisation is the number of unit weight of sulfur combined with 100 units by weight of unsaturated hydrocarbons. Buna S is a butadiene styrene copolymer with 70/30 to 68/32 ratio. Buna SS contains a high proportion of styrene. Perbunan are nitrile rubbers... 

Ebonite is chemically stable and so its resistance to ageing is remarkable and can be achieved without the use of antioxidants unlike soft rubbers. 

The choice between materials for a particular application may be determined by a combination of technical economic and aesthetic considerations. Ebonites have a great dimensional stability in moist conditions with freedom from deterioration caused by oxidation and excellent resistance to various chemicals. The temperature of use is limited where the material is under mechanical load, owing to its comparatively low softening point. This can be overcome by suitable compounding to some extent. A further weakness in appearance is the tendency of ebonite to develop an acid surface and to... 

If we take a rubber-sulphur ratio of 68 32 in an ebonite compound and then cure it at 155°C, the vulcanization coefficient increases practically to a constant value of 47 after about five hours and the uncombined sulphur decreases during the first four hours. This state may be called a full cure in the chemical sense. There is also a reduction in volume of about 6%. It is known that after the combination of the first few percent of sulphur, the material passes through a leathery stage with low strength and poor resistance to oxidation and with time passing a true ebonite is formed with increased impact strength. 

Water and Effluent Treatment in Nuclear and other chemical plants. Corrosion resistant linings for water treatment vessels and pipelines, pumps, valves, flowmeters, agitators, chemical dosing tanks, effluent tanks etc. Soft natural rubber or ebonite, EPDM, butyl, neoprene or hypalon. 

In appearance, HR resembles natural crepe rubber, since it is an aliphatic, hydrocarbon polymer the density being the minimum (0.91) attainable for elastic materials of this type. In HR, the original unsaturation is very small, and even this low unsaturation is greatly reduced and may even be entirely eliminated during the compounding and curing process. The fact that once vulcanised it is extremely resistant to chemical attack is understandable because it becomes, after vulcanisation, not only a nonthermoplastic strong elastic material, but also essentially a chemically saturated product as well. This means that whilst physically vulcanised HR resembles soft vulcanised natural rubber, chemically it may be considered most similar to ebonite almost devoid of any unsaturation. 

Ebonite can be machined and is often produced in bar, tube, or sheet stock for this purpose. Major applications make use of its chemical inertness and corrosion resistance as well as its electrical and thermal insulating properties. The material softens at about 50°C and, hence, is not suitable for high-temperature applications. 

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