Synthetic Ebonites

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). 

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. 

Hard products may also be made by vulcanising rubber (natural or synthetic) using only about two parts of sulphur per 100 parts of rubber. In these cases either the so-called high-styrene resins or phenolie rubber compounding resins are ineorporated into the formulation. These compounds are processed using the methods of rubber technology but, like those of ebonite, the produets are more akin to plastics than to rubbers. Examples of the usage of these materials are to be found in battery boxes, shoe heels and ear washer brushes. 

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... 

Synthetic Rubbers Which Can Be Converted into 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]. 

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. 

Flexible Ebonite This can be called semi-ebonite usually loaded with mineral fillers with a lower proportion of sulphur, say 15 phr, and by incorporating into the compound synthetic rubbers like polychloroprene, polyisobutylene or butyl rubber. This ebonite will have good resistance to impact. A sheet made of flexible ebonite will look like a hard flexible leather. 

It is now well established that synthetic materials may be prepared with mechanical properties closely resembling those of elemental metals and alloys. As a result, we have come a long way from the ebonite handles and fragile plastic toys of 30 years ago to the overwhelming occurrence of plastics in modem mechanical structures. Similarly, it is now possible to mimic the electrical properties of elemental metals... 

Establishes a system for designating cellular elastomeric materials based on natural, synthetic, or reclaimed rubber, or rubber-like materials, alone or in combination. Cellular ebonite (hard rubber) and rigid cellular plastics are not included. Revision B was issued 30 January 1968. Notice 1 makes this standard inactive for new design, which would thereafter refer to the applicable portions of ASTM D 1055, D 1056, D 1505, D 1667 and D 3574. Cross reference tables are given. 

A general rule is that natural rubbers have better mechanical properties than the synthetic rubbers but the latter have better corrosion resistance. Natural rubbers are superior in certain applications such as with wet chlorine and hydrochloric acid. Natural rubber-based ebonite provides good resistance for such application at higher temperatures up to 90 °C. Corrosion resistance increases with increasing hardness, from a range of 60 on the Shore A scale to 80 on the Shore D scale. Higher proportions of sulfur increase the hardness range in the Shore D scale. 

Some details of synthetic hard rubber (ebonites) are given next. 

Hard rubber or ebonite whether from natural rubber or from synthetic rubber, can be defined as highly vulcanised rubber, containing a large proportion of combined sulfur. Hard rubbers made from natural rubber have vulcanisation coefficients between 25 and 47. The theoretical vulcanisation coefficient value for natural rubber is 47 and for synthetic rubbers it is in the range of 35 to 47. The coefficient of vulcanisation is usually defined as the number of units by weight of sulfur combined with 100 units by weight of unsaturated hydrocarbon. The theoretical coefficients are corrected for impurities/non rubber constituents in the raw rubber. 

In 1851, hard rubber, or ebonite, was commercialized. In 1870 a patent was issued to I. Hyatt, of New York, for celluloid, a type of cellulose nitrate with low nitrate content produced at high temperature and pressure. This was the first commercially available plastic and the only one until the development of Bakelite by Baekeland in 1907. Bakelite is the oldest of the purely synthetic plastics and consisted of a resin obtained by the reaction of phenol and formaldehyde. 

Rubber linings consist of ebonite or soft rubber based on natural or synthetic polymers. They account for the largest group of materials used for surface protection in chemical plants. Synthetic elastomers are becoming more and more important since they have greater chemical and mechanical stability than natural materials and less susceptibility to mechanical damage. 

Hard rubber n. The material obtained by heating a highly unsaturated diene rubber with a high percentage of sulfur. The first hard rubber was Ebonite, made from natural rubber, and black, as its name imphes. Similar products have been made from several of the synthetics. The sulfur is mostly contained in 3- and 4-carbon rings with a few -C-S-C- cross-links. 

Some scientists credit John Wesley Hyatt with the invention of synthetic plastics. However, ebonite, which is... 

Rubber-to-Metal Bonding. In the Ebonit or hard rubber process [76], the bonding agent is a reaction product of natural or synthetic rubber with 30-40% sulfur, which is thermoplastic in character, adheres firmly to metal, and provides for good adhesion to soft rubber. This process is still in use today in the lining of vessels and, to a certain extent, in the manufacture of large-diameter rolls. 

One of the recent contributions to rubber technology has been the development of methods whereby both natural and synthetic, both cured and uncured, may be bonded directly to metal surfaces. Earliest methods used to fasten rubber to metal were mechanical. Ebonite was also used in early work, the ebonite surface giving a strong adhesion to the metal while uniting with the rubber on the other side. Ebonite as a bonding agent reduces the flexibility of the unit as a whole, especially when the rubber section itself is not very thick. Secondly, ebonite is thermoplastic and the tenacity of the bond falls off rapidly even at moderate temperature. Recently, other modified derivatives of rubber have become avail-... 

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