Derivatives of Natural Rubber

The chemistry and technology of namral rubber were considered briefly in Chapter 11. In this chapter some non-elastomeric derivatives will be reviewed. 

The detailed structure of ebonite is not known but it is believed that the same structures occur in the rigid material as have been suggested for vulcanised rubber. There will, however, be far more S-containing structures per unit volume and the ratios of the various structures may differ. The curing reaction is highly exothermic. 

Ebonite compositions may be prepared without difficulty either in an internal mixer or on a two-roll mill. In addition to the rubber and sulphur, fillers are invariably present in commercial mixes. These materials have the important function of diluting the rubber phase. Because of this the exotherm will be 

Ebonite, or hard rubber as it is often known, is black in colour and has a specific gravity, in the absence of mineral fillers, of about 1.18. 

Typical properties of a high-quality ebonite are given in Table 30.3. 

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Non-elastomeric chemical derivatives of natural rubber are discussed in Chapter 30 in which chemically related naturally occurring materials such as gutta percha and balata are briefly considered. 

Chemical nature Isolation of casein from milk Production of casein plastics Properties of casein Applications Miscellaneous Protein Plastics Derivatives of Natural Rubber Gutta Percha and Related Materials Shellac... 

An isomeric derivative of natural rubber produced by a variety of chemical treatments. The products are resinous and find application as reinforcing agents in natural rubber compounds (particularly in shoe soles) and as rubber-to-metal adhesives. 

This derivative of natural rubber produced by the action of hydrogen chloride (liquid or gaseous) found application as a transparent food packaging film, but has now been superseded by modem packaging materials such as PET. 

In this chapter brief consideration has been given to the major tonnage rubbers. Derivatives of natural rubber such as ebonite are discussed in Chapter 30 and thermoplastic rubbers are reviewed in Chapter 31. Other important speciality rubbers (with their ASTM designations) include ... 

Various chemical derivatives of natural rubber are of some commercial importance and these are considered in this section. 

Mention may finally be made of graft polymers derived from natural rubber which have been the subject of intensive investigation but which have not achieved commercial significance. It has been found that natural rubber is an efficient chain transfer agent for free-radical polymerisation and that grafting appears to occur by the mechanism shown in Figure 30.8. 

Many other polymers compete with cellophane such as polyethylene which is extruded as a tough film or in greater thickness as a nonbreakable bottles. Vinyl products used in films are polystyrene, polyesters, and nylon. A chemical derivative from nature rubber, chlorinated rubber, gives films of extraordinary stretch ability. 

Quinone and some of its derivatives may be used in the non-sulphur vulcanisation of natural rubber. The best-known derivative is para-quinone dioxime used as a curing agent for butyl rubbers. 

Synthetic rubber(s), 1 693, 21 761. See Ethylene-propylene polymers. See also Butyl rubber acetylene-derived sources, 1 228 synthesis of first butyl rubber after disruption of natural rubber supply in WW II, 4 433... 

Now the lone chlorine atom has found itself isolated since the zinc only extracts two adjacent chlorines. Such a result is called reactant isolation, and one wishes to predict the chlorine concentration left in the polymer as a function of time. It was shown by Flory76 that the fraction of chlorines unreacted should approach e 2, and this was used in fact by Marvel77 to determine the structure of polyvinyl chloride. Other examples are the condensation of the polymer of methyl vinyl ketone76 and the vulcanization of natural rubber.78 The vulcanization studies supply another example where a molecular structure was determined by a kinetic scheme. The complete time dependence of the process was recently derived by Cohen and Reiss24 using a novel method of multiplets, which will now be outlined. 

The search for a lightweight, nonbreakable, moldable material began with the invention of vulcanized rubber. This material is derived from natural rubber, which is a semisolid, elastic, natural polymer. The fundamental chemical unit of natural rubber is polyisoprene, which plants produce from isoprene molecules, as shown in Figure 18.5. In the 1700s, natural rubber was noted for its ability to rub off pencil marks, which is the origin of the term rubber. Natural rubber has few other uses, however, because it turns gooey at warm temperatures and brittle at cold temperatures. 

Macromolecular chemistry covers a particularly wide field which includes natural polymeric material, such as proteins, cellulose, gums and natural rubber industrial derivatives of natural polymers, such as sodium carboxymethyl cellulose, rayon and vulcanised rubber and the purely synthetic polymers, such as polythene (polyethylene), Teflon (polytetrafluoroethylene), polystyrene, Perspex (poly (methyl... 

Natural rubber, chemically speaking poly(W.v-1,4-isoprene), is a natural polymer derived from Hevea brasiliensis and various other tropical plants like Castilloa elastica [147]. This natural polymer is mainly produced in Asia and the tropics in high, industrially relevant, amounts (e.g., 9.7 Mio mto in 2007). Apart from its usual use as an elastomeric material, some research was devoted onto the metathesis degradation (depolymerization) of natural rubber with ethylene in a CM fashion. It was believed that metathesis of natural rubber is impossible, until a pioneering... 

The asparaginyl glycoproteins are synthesized through the use of dolichol phosphate, a member of the isoprenoid family, which is attached through its hydrophobic residue to endoplasmic reticulum. Other isoprenoid compounds or their derivatives are natural rubber, the steroids, including cholesterol, and vita-... 

Vulcanization The treatment of natural rubber with sulfur to reduce its tackiness and improve its strength and elasticity. Invented independently by C. Goodyear and N. Hayward in the United States in 1839, and by T. Hancock in London in 1842 to 1843. Goodyear was honored for his invention by Napoleon III, but he died in a debtors prison in Paris. Various chemicals other than elemental sulfur are effective, for example, sulfur monochloride, selenium, and /v-quinonc dioxime. The chemical mechanism of this process is still not fully understood some believe that traces of zinc, derived from the zinc oxide used in compounding, are essential. 

Derivation A solution of natural rubber is treated with anhydrous hydrogen chloride under pressure and at low temperature. After neutralization of excess hydrochloric acid, the product is precipitated by the addition of ethanol. 

Apart from the rather expensive and inferior methyl rubber produced in Germany during World War I, the first industrial production of synthetic rubbers took place in 1932, with polybutadiene being produced in the USSR, from alcohol derived from the fermentation of potatoes, and neoprene (polychloroprene) being produced in the USA from acetylene derived from coal. In 1934 the first American car tyre produced from a synthetic rubber was made from neoprene. In 1937 butyl rubber, based on polyisobutylene, was discovered in the USA. This material has a lower resilience than that of natural rubber but far surpasses it in chemical resistance and in having a low permeability to gases. The chemical structures of these materials are shown in fig. 6.10. 

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