Ebonites water absorption

Isobutylene-isoprene rubbers, the copolymers containing 98% isobutylene and 2% isoprene cannot be made into hard rubbers because of the lack of adequate unsaturation. However a very hard butyl rubber vulcanisate can be obtained by admixture with SBR and high levels of sulfur. The water absorption of NR ebonite is 0.45% to 0.5% at a relative humidity of 97.2%. 

The high water absorption values of nitrile ebonite (about 3.3% to 4.5%) could not be anticipated, just because a soft vulcanisate made from similar copolymer absorbs less water than a NR vulcanisate. 

Ebonite shows very low water absorption and has good resistance to most aqueous reagents, except nitric acid. It is swollen by aromatic and chlorinated hydrocarbons. Ebonite has good electrical insulation characteristics and the major application is for car battery cases. 

Apparent density of material that can be poured from a specified funnel Apparent density of molding material that cannot be poured from a specified funnel Determination of water absorption Plastics and ebonite—Determination of temperature of deflection under load Determination of bulk factor of molding materials... 

The diffusion of water into a mass of ebonite is so slow that the water absorbed affects only the material at the surface. In practice the degree of absorption would require many months or even years to complete on continuous exposure to water or dilute liquids. 

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See also in sourсe #XX -- [ ]

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