Natural rubber developments

During World War II the United States, cut off from India, Ceylon (now Sri Lanka), Malaysia, and the Dutch East Indies (areas which, since the late nineteenth century, had replaced South America as the main suppliers of natural rubber), developed several superior synthetic rubbers. The U.S. synthetic rubber industry originated from two discoveries that were serendipitous that is, they occurred while the researchers were searching for something else. 

Perhaps the most striking difference between rubbers and other materials is their capacity for large reversible or nearly reversible deformations at their service temperature, and it is this aspect of their behavior that will be described here. The commercial exploitation of natural rubber developed rapidly with the discovery that crosslinking greatly improves its mechanical properties, giving the first of what is now a broad class of materials often referred to as elastomers . Elasto-... 

The situation did not change until 1942, soon after the start of World War II. At that time, a critical shortage of natural rubber developed because it was allocated chiefly for the war effort. Neoprene was chosen as a replacement for natural rubber in adhesives because it was the only other synthetic rubber available. Animal glue and other water-soluble materials available at the time were unsatisfactory because of their slow drying rates, poor adhesion to many surfaces, inflexible films, and rusting of metals. The two Neoprene polymers available at the time were Neoprene GN, a general purpose type, and Neoprene CG, a fast-crystallizing type. Both are copolymers of chloroprene and sulfur which contain a thiuram disulfide modifier. 

One of our previous complaints was that we had more parameters than we knew what to do with Eq. (2.33) makes this problem even worse. It turns out, however, that using only two or three terms of Eq. (2.33) results in a usable equation with improved curve-fitting ability. Techniques have been developed for extracting acceptable parameters from experimental data in these cases (see Problem 4). Figure 2.9, for example, shows data collected from a sample of natural rubber, analyzed according to a two-term version of Eq. (2.33). The line in Fig. 2.9 is drawn according to the equation... 

Development of Natural Rubber-Based Tmck Tyre Retreading Compounds," in M. E. Cain and Sifi Zubaidah bte Mohd Rashid, eds.. Proceedings of a UNIDO-sponsored Workshop, Kuala Eumpur, Malaysia, Malaysian Rubber Pioduceis Research Association, Heitfoid, U.K, 1992. 

Rubber and Elastomers Rubber and elastomers are widely used as lining materials. To meet the demands of the chemical indus-tiy, rubber processors are continually improving their products. A number of synthetic rubbers have been developed, and while none has all the properties of natural rubber, they are superior in one or more ways. The isoprene and polybutadiene synthetic rubbers are duphcates of natural. 

Another interesting innovation is that developed by the Malaysian Rubber Producers Research Association. In this case the coupling agent is first joined to a natural rubber molecule involving an ene molecular reaction. The complex group added contains a silane portion which subsequently couples to filler particles when these are mixed into the rubber. 

LEYLAND, B. N. and WATTS, J. T., Chapter in Developments with Natural Rubber (Ed.BRYDSON, j. A.), Maclaren, London (1967)... 

These have been developed for special uses. For example, since petroleum-based materials harm natural rubber, a grease based on castor oil and lead stearate is available for use on the steel parts of rubber bushes, engine mountings, hydraulic equipment components, etc. (but not on copper or cadmium alloys). Some soft-film solvent-deposited materials have water-displacing properties and are designed for use on surfaces which cannot be dried properly, e.g. water-spaces of internal combustion engines and the cylinders or valve chests of steam engines. 

In more recent years, lining compounds have been developed that vulcanise at ambient temperatures. Most polymers can be used for such compounds, although most materials are based on natural rubber, acrylonitrile-butadiene rubber and polychloroprene. These compounds contain accelerators which usually give rise to a material which has a delay in the onset of vulcanisation with a subsequent rapid rise in cross-link formation to give full vulcanisation in 6 to 8 weeks. Such materials, unless to be used within a few days of manufacture, are refrigerated to arrest the sel f-vulcanisation. 

The calender was developed over a century ago to produce natural rubber products. With the developments of TPs, these multimillion dollar extremely heavy calender lines started using TPs and more recently process principally much more TP materials. The calender consists essentially of a system of large diameter heated precision rolls whose function is to convert high viscosity plastic melt into film, sheet, or coating substrates. The equipment can be arranged in a number of ways with different combinations available to provide different specific advantages to meet different product requirements. Automatic web-thickness profile process control is used via computer, microprocessor control. 

Elastomers, of which vulcanized natural rubber is the most important example, also undergo dramatic changes in mechanical properties when filled with particulate solids. In part, knowledge of this particular type of system has been developed empirically as the technology of car-tyre manufacture has advanced. 

Polysaccharides such as starch and cellulose have been used as reinforcing agents in natural rubber. Both solution blending and dry mixing methods have been employed for the development of biocomposites and the performance compared with the composites obtained using carbon black. Dry mixing method is more economically viable and environment friendly. 

Roy Choudhury N., Bhowmick A.K., and De S.K., Thermoplastic natural rubber. Natural Rubber Biology, Cultivation and Technology (Sethuraj M.R. and Mathew N.M., eds.), Elsevier, New York, 1992. Elliot D.J., Natural rubber systems. Development of Rubber Technology 3 (Whelan A. and Lee K.S., eds.). Applied Science, New York, 1982. 

FIGURE 14.3 Development of accelerated sulfur vulcanization of natural rubber (NR). (From A.Y. Coran, Chem. Tech., 23, 106, 1983.)... 

Neoprene, Carothers first practical invention, was made reluctantly, as a kind of side issue to his scientific investigation of polymers. Synthetic rubber was of great commercial interest. The car-happy United States used half the world s natural rubber, and demand had outstripped the supply from wild rubber trees in the Amazon. Price fluctuations on British rubber plantations in Southeast Asia provided further incentive for the development of synthetic substitutes. Du Pont had been trying without success to... 

Surprisingly, the idea that Collins new compound might form the basis for a synthetic rubber took several weeks to evolve. And it was not Carothers, but Stine s successor, Elmer K. Bolton, who first realized that the molecular structure of Collins mass was similar to that of isoprene, the main constituent of natural rubber. Bolton had studied in Germany and was familiar with its World War I efforts to develop an ersatz rubber for tires. 

During the last two decades, a number of diene homopolymers and copolymers have been developed to fill the diverse elastomer needs in the production of tires. The earliest developments were mainly concerned with the preparation of stereoregular cis-1,4-polyisoprene, as a substitute for natural rubber, using... 

Plazek (183) carried out very accurate creep experiments on natural rubber as a function of cross-linking. He found that data at different temperatures could be superimposed by the usual WLF shift factors which were developed for non-cross-linkcd poiymers (27). Temperature-superposed... 

Other polymeric binders, natural and synthetic, may be found as paints or varnishes in modern artworks and installations. Artists very easily adopt resins developed as industrial coatings or for specialized applications, and use them according to their creative needs. Natural rubber latex is a water dispersion of 1,4-ds-polyisoprene particles where pigments can be added to give coloured paints. By means of Py-GC/MS the presence of these paints can be easily assessed. As shown in Figure 12.13, the principal marker peaks in the pyrogram are those of isoprene, limonene and other cyclic dimers. 

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