Nitrile Ebonite

Synthetic rubber ebonites do not fundamentally differ from natural rubber ebonites in swelling behaviour. Synthetic rubbers combine more nearly completely with the added sulphur. Nitrile ebonites are outstanding in that they are almost unaffected even by solvents such as benzene carbon-disulphide which strongly swell natural, butadiene and styrene butadiene ebonites [4,5]. 

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. 

The terms ebonite and hard rubber are now extended to cover hard produets made from synthetic rubbers. SBR is now replacing the natural materials in many ebonite applications whilst nitrile rubber ebonites are of interest where oil resistance is required. 

Butyl Rubber and Halo-Butyl Rubber Ethylene Propylene Rubber (q) Hard Rubber (Ebonite) (h) Soft Natural Rubber (h) Neoprene (i) Nitrile Rubber Chlorosulphonated Polyethylene Polyurethane Rubber (v) Silicone Rubbers (k)... 

Also known as vulcanite and (mainly in the USA) hard rubber . The hard, horn-like product obtained when natural rubber and some synthetic rubbers such as nitrile (NBR) are vulcanised with a high proportion of sulphur or organic nonsulphur vulcanising agent. Butyl rubber and polysulphide rubber do not form ebonites. Ebullioscopy... 

Natural rubber ebonites cannot be produced in brilliant colours which can be obtained with a number of synthetic rubbers like nitrile and resins such as high styrene. Ebonite products can be classified according to their primary uses as mentioned below. 

The rate of diffusion in a given elastomer is found to be related chiefly to the size of the liquid/gases molecule. It is observed that the presence of polar group or methyl group in the polymer molecules reduces the permeability to a given liquid/gas. Therefore butyl, Neoprene and nitrile, along with ebonite, have a low value of permeability when compared with natural soft rubber vulcanisates. 

Nitrile hard rubbers surpasses all of the other synthetic ebonites in resisting the swelling action of solvents like benzene, gasoline, carbon disulfide, nitrobenzene, petroleum, ether, transformer oils, hydraulic fluid, and so on (Table 6.4). 

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... 

The higher hardness of 100 A in natural rubber and nitrile rubber indicates ebonite that can be made with about 50% of sulfur addition. 

Ebonite bonding The adhesive layer in this case is unvulcanized ebonite (or hard rubber , USA) applied to the metal either as a solution or as a thin sheet" Ebonite contains 30-50 parts sulphur per hundred parts of rubber (phr), whereas soft rubber seldom has more than 3 parts phr of this vulcanizing agent. The method dates back to the mid-nineteenth century and is most closely identified with natural rubber, but can be applied to other diene-type elastomers, including nitrile rubber. 

Polymer Chemical Stabilization Processes. Cellular rubber and ebonite are produced by chemical stabilization processes. Most elastomers can be made into either open-celled or closed-celled materials. Natural rubber, SBR, nitrile rubber, polychloroprene, chlorosulfonated polyethylene, ethylene-propylene terpolymers, butyl rubbers, and polyacrylates have been successfully used (110-112). 

There are basically six types of crosslinking mechanisms for NBR elastomers, very high sulfur for a special ebonite, normal sulfur, semi-EV (semi-efficient vulcanization or low sulfur systems), EV (efficient vulcanization with sulfur donors alone), peroxide and zinc oxide/peroxide for carboxylated nitrile. The innumerable combinations that can and are used are as numerous as there are rubber chemists in the world, but with care they all work in any given application. 

The use of up to 35 phr sulfur with a butraldehyde-monobutylamine such as (Vanax 833) type accelerator may be used to produce a higher temperature resistant ebonite, primarily for submarine battery cases. This approach has virtually disappeared having been replaced with either plastics or nitrile with higher amounts of an acrylic monomer and a peroxide cure. 

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