Elasticity vulcanisation process

On heating a chemical reaction took place between the rubber and sulphur which resulted in production of tough elastic rubber that retained its moulded shape. Natural rubber is plastic in nature while vulcanised rubber is elastic. This vulcanisation process led to a rapid development of rubber industry. 

The properties of elastic sulphur, pS, can be stabilised by adding a few percent of phosphorus. A vulcanisation process occurs in which cross-linking is produced via the P atoms, and as more phosphorus is added, the product becomes more brittle and finally vitreous when cross-linking is... 

Raw silicone rubber consists of cross-linked macromolecules in a highly viscous liquid state upon vulcanisation it is converted into an elastic rubber. There are hot and cold vulcanisation processes, which employ different starting materials and have different products. The molecular weight of the starting materials for hot vulcanisation is high 300000-1000000. Those for cold vulcanisation are much smaller, 10000-100000. 

Vulcanisation is the term used for the process in which the rubber molecules are lightly crosslinked in order to reduce plasticity and develop elasticity. It was originally applied to the use of sulfur for this purpose, but is now used for any similar process of cross-linking. Sulfur, though, remains the substance most widely used for this purpose. 

Sulfur has a very important role in the chemical industry. The vast majority of sulfur is used to produce perhaps the most important industrial chemical, sulfuric acid. Sulfur is also used to vulcanise rubber, a process which makes the rubber harder and increases its elasticity. Relatively small amounts are used in the manufacture of matches, fireworks and fungicides, as a sterilising agent and in medicines. 

As a result of its saturated polymer backbone, EPDM is more resistant to oxygen, ozone, UV and heat than the low-cost commodity polydiene rubbers, such as natural rubber (NR), polybutadiene rubber (BR) and styrene-butadiene rubber (SBR). Therefore, the main use of EPD(M) is in outdoor applications, such as automotive sealing systems, window seals and roof sheeting, and in under-the-hood applications, such as coolant hoses. The main drawback of EPDM is its poor resistance to swelling in apolar fluids such as oil, making it inferior to high-performance elastomers, such as fluoro, acrylate and silicone elastomers in that respect. Over the last decade thermoplastic vulcanisates, produced via dynamic vulcanisation of blends of polypropylene (PP) and EPDM, have been commercialised, combining thermoplastic processability with rubber elasticity [8, 9]. 

Vulcanisation A process in which rubber, through a change in its chemical structure, is converted to a condition in which the elastic properties are conferred or improved. 

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. 

Most rubbers exhibit a degree of elastic recovery on deformation in the raw state even before vulcanisation, say, like natural and Neoprene rubbers. This nerve5 as it is called is excessive and it must be reduced during the mixing process to a controlled level so that... 

Rubber is obtained from the juice of various tropical trees, mainly the tree Hevea brasiliensis. The juice is a latex consisting of a dispersion of polymer phase at a concentration of about 35% by mass, together with traces of proteins, sterols, fats, and. salts. The rubber is obtained either by coagulation of the latex with acid, either elhanoic or methanoic, or by evaporation in air or over a flame. The material that results from this process is a crumbly, cheese-like substance, sometimes called raw rubber or caoutchouc. In order to develop the mechanical properties that are considered characteristic of rubber, Le. so-called rubberlike elasticity, this raw rubber needs further processing, and in particular lightly crosslinking. This is achieved in the process known as vulcanisation, as will be discussed later. 

The practice of cross-linking the polyisoprene chains in natural rubber to form a usable elastomer was discovered by Goodyear, in 1839. He heated natural rubber latex with sulphur, a process called vulcanisation. This transforms the sticky runny natural latex into a product in which the elastic... 

It is true to say that, of the many materials used in the rubber formulation, it is the polymer that is the cause of poor processing behaviour. This is to be expected, because it is the very quality of possessing elastic behaviour that confers poor processing performance. For ease of processing the compound must often be formulated to behave as a non-elastic (plastic) material for the purposes of shaping and shape retention. This must be followed by conversion to an elastic material for the end product (vulcanisation). These conflicting requirements must be rationalised in the formulation of the compound. 

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