Engineering rubbers

8 Yearly production of natural and synthetic rubber since 1950. The major increase in synthetic rubber production occurred in the 1950s and 1960s. 

The second great discovery in rubber technology was of the substantial benefits conferred on rubber by mixing it with carbon black. The carbon acts as a mechanical reinforcement (see Chapter 6), but it does bring other advantages it reduces the degradation caused by sunlight and ozone, and reduces liquid absorption. 

The copolymers SBR and NBR have a major advantage over the homopolymers that is, thqr be prodnced in varions conqtositions for specific purposes. For example, the NBR copolymers are resistant to swelling in oil or petrol. This resistance is increased when the content of acrylonitrile 

Polybutadiene is also used as the rubbery (soft) component in the new 

9 Glass transition temperatures of random copolymers of styrene and txjtadiene as a function of percentage styrene in the copolymer. The glass transitions of the homopolymers are polystyrene 95 C polybutadiene -87°C. The styrene contents of commercial SBR rubbers fall in the range 10 to 40% (after tilers). 

The reason for this change in with composition is that the glass transitions of the two components, as homopolymers, are — 87 C for polybutadiene and 106 °C for polyacrylonitrile. The glass transitions of the copolymers lie in between these two extremes. This is both the anticipated and the observed behaviour. The glass transition of a copolymer poly AB will lie at a temperature between the glass temperatures of the two homopolymers poly A, and poly B. For example, the dependence of on composition for the styrene-butadiene copolymers is shown in Fig. 3.9 the styrene contents of the commercial SBR rubbers fall in the range 10 to 40 per cent. 

Valuable synthetic rubbers are produced by the copolymerization of ethylene and propylene. The structure may be represented 

Another speciality system with a resistance higher than natural rubber to oils and petrol is the group of chloroprene rubbers. The structure is essentially polybutadiene (I. N. 12) with a chlorine replacement for a hydrogen atom. Over 

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In spite of their somewhat high price relative to most conventional rubbers these materials have become widely accepted as engineering rubbers in such applications as seals, belting, water hose and even low-pressure tyres. 

Group 1 Hard segment levels <50%. This group includes engineering rubbers (high performance elastomers) and would include some automotive fascia. 

Table V shows general features of Engineering Rubbers (high performance elastomers) produced via RIM.

TABLE V. ENGINEERING RUBBERS ( HIGH PEREORMANCE ELASTOMERS) PRODUCED VIA RIM ... 

These materials are superior to conventional rubbers in a number of properties (see the section on thermoplastic rubbers). Consequently, in spite of their relatively high price they have become widely accepted as engineering rubbers in many applications. 

Tires are one of the most durable technological products manufactured today. They are a resilient, durable composite of fabric, steel, carbon black, natural rubber, and synthetic polymers. The qualities that make tires or other engineered rubber products a high-value item create a special challenge of disposal. Tires and other rubber products, such as conveyor belts and hydrauUc hoses, are not biodegradable and cannot be recycled like glass, aluminum, or plastic. Four potential applications for such products entering the solid waste stream have been identified ... 

Uses Lubricant for two-stroke cycle engines, rubber, greases, textiles reactive intennediate for resins, plasticizers, modifiers, and surfactant mfg. antifoam in boiler water, latex processing, washing soi ns.. paints, adhesives, salt water evaporators solvent for inks and dyes solvent, softener, and plasticizer for textile and paper coalings, NC coatings mold release agents and dye solvents for vinyl resins demulsifier cosmetic emollient... 

Uses Lubricant for two-stroke cycle engines, rubber, greases, textiles reactive intermediate for resins, plasticizers, surfactants antifoam in boiler water, latex processing solvent for inks and dyes antistat in cosmetics... 

Figure 5.30 Corrected mass uptake measurements for engineering rubbers in sea water at 23 °C. A, deproteinized NR B, lead oxide cured polychlor-oprene C, nitrile rubber D, conventional NR E, conventional poly-chloroprene.

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