Rubber, natural, uses

Ethylacrylate (EA) and butylacrylate (BA) was grafted onto natural rubber using BPO as the initiator [25]. KPS and AIBN were ineffective in the production of the graft and the failure to form the graft is attributed to the initiator effect. ... 

The reactivity of different monomers toward grafting onto natural rubber using different radical initiators was found to be ... 

Natural rubber use is currently about 6 million tons/year and is expected to grow at annual rate of 3.3%. 

R. F. Blackwell, Trans. Inst. Rubber Ind., 28, 75 (1952), has shown that very good agreement with Eq. (50) is obtained for a wide range of vulcanized natural rubbers using the same value for Cz. The constant Ci varies, of course, with the degree of vulcanization. 

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... 

The synthesis of the exact molecular structure of natural rubber using a simple alkali metal focused increase attention on the mechanism of anionic polymerisations. 

By far the largest selling elastomers are SBR and natural rubber. SBR at 1.93 billion Ib/yr accounts for about 35% of the U.S. synthetic rubber market and 25% of the total rubber market. The U.S. imports about 2.2 billion lb of natural rubber per year. A distant third is polybutadiene at 1.33 billion lb. In 1940 natural rubber had 99.6% of the U.S. market. Today it has only 29%. In 1950 synthetic elastomer consumption passed natural rubber use in the U.S. Since then it has been a battle between the leading synthetic, SBR, and the natural product. It is apparent that these two polymers are veiy important. Table 18.2 summarizes and compares them by their properties. 

Elastomers. Many experiments have been performed with natural rubber, using either synthetic elastomers or plastomers as the second polymer. 

In the 1930s, more than 90 percent of the natural rubber used in the United States came from Malaysia. In the days after Pearl Harbor was attacked in December 1941 and the United States entered World War II, however, Japan captured Malaysia. As a result, the United States—the land with plenty of everything, except rubber—faced its first natural resource crisis. The military implications were devastating because without rubber for tires, military airplanes and jeeps were useless. Petroleum-based synthetic rubber had been developed in 1930 by DuPont chemist Wallace Carothers but was not widely used because it was much more expensive than natural rubber. With Malaysian rubber impossible to get and a war on, however, cost was no longer an issue. Synthetic rubber factories were constructed across the nation, and within a few years, the annual production of synthetic rubber rose from 2000 tons to about 800,000 tons. 

Vulcanization An industrial process that strengthens natural rubber using heat and sulfur. Because it requires great heat, the process was named after the Roman god of fire, Vulcan. The process was discovered by Charles Goodyear in 1839. 

This is the other natural rubber used in making chewing gum. It is produced from the sap of Dyera costulata of the genus apocyanesas. This tree grows in the Far East. The crude product is processed by a system involving the injection of steam into the raw material. 

Caffrey and Bilderback have made a similar study for natural rubber. Using a Vidicon camera they concluded that the amorphous halo disappears while the preferentially oriented powder pattern appears at the same time. Holl et all., have studied the reversibility of this process in more detail. Thus in Fig. 51 the variation of the modulus and the draw ration are compared with selected Vidicon patterns. corresponds to the onset of the crystallization, 3- to the maximum in crystallisation and 3-i to the melting of the last crystallites upon relaxation. Note that and Xj, occurr, at different draw ratios. This is obviously due to the nucleation process which demands a certain overdrawing while the melting occurs at the equilibrium melting temperature. 

Due to the structure of natural rubber, with its conjugated system of double bonds and the ability to reduce the unwanted dynamic motions associated with a mounting system, isolation is its most important use. However, natural rubber use in seals and gaskets is a natural fit. The automotive chemist chooses natural rubber for several reasons. The elastic behavior of rubber can be attributed to electrostatic strain... 

The theory proposed for equilibrium swelling and diffusion is based on the assun tlon that the hydrophilic impurities are present in particulate form and are dispersed throughout the rubber. The precise nature of this impurity in natural rubber is not known so it was decided to make a model rubber by adding 0.17. of a hydrophilic Impurity (sodium chloride) to a solution polymerised synthetic rubber (cis-polyisoprene) Ich is chemically the same as natural rubber. Using this model rubber it is possible to check the theory more precisely since both the nature and concentration of the hydrophilic lgq>urlty in the model rubber are known. It is proposed that the water diffuses through the rubber and forms droplets of solution inside the rubber where there are particles of the hydrophilic impurity thereby causing a non-uniform distribution of water in the rubber. The... 

Figure 2. Concentration dependence of the diffusion coefficient of water in natural rubber using samples (%) initially dry and (O) initially containing water. Line calculated using Equation 9 with s a = 6.3 X 10" and Ci = 0.1%.

Hassan, M. M., Mahmoud, G. A., El-nahas, H. H., Hegazy, E.-S. A., Reinforced material from reclaimed rubber/natural rubber, using electron beam and thermal treatment. Journal of Applied Polymer Science 2007,104,2569-2578. 

Garreta E. Agullo N. Bonos S. The Role of the Activator during the Vulcanization of Natural Rubber using Sulphenamide Accelerator Type. Kaut. Gummi Kunstst., 2002, vol. 55, Jf 3, 82-91. 

Lee, S. Molnar, A. Determination of molecular weight and gel content of natural rubber using thermal field-flow fractionation. Macromolecules 1995, 28, 6354. 

W. Pichayakom, J. Suksaeree, P. Boonme, W. Taweepreda, T. Amnuaikit, G.C. Ritthidej, Deproteinised natural rubber used as a controUing layer membrane in reservoir-type nicotine transdermal patches, Chemical Engineering Research and Design, ISSN 0263-8762 91 (3) (March 2013) 520-529. http //dx.doi.Org/10.1016/j.cherd.2012.09.011. 

Chen, D. T., Perman, C. A., Riechert, M. E., and Hoven, J. (1995) Depolymerization of tire and natural rubber using supercritical fluids, / Hazardous Materials, 44, 53-60. 

Despite the increasingly more frequent reports of allergic contact dermatitis (ACD) to natural latex, the exact chemical nature of the allergen(s) remains unknown. In contrast, proteins present in latex obtained from the Hevea brasiliensis tree are the cause of the immunoglobulin (Ig)E-mediated hypersensiti-vity/allergic contact urticaria (ACU) to natural latex rubber. Since Hevea brasiliensis accounts for more than 99% of natural rubber used worldwide, ACU to latex is a significant problem. 

Treloar s fit to the experimental data for natural rubber using Equation (3.33)... 

Chemical crosslinking of natural rubber using sulfur or peroxide as crosslinking agents is widely use to achieved the desired final properties. Thus it is crucial to understand the effect of clay on the crosslinking and vice versa. 

Figure 4.12 shows Treloar s fit to the experimental data for natural rubber, using this relationship and a suitable choice of the parameters N and n. The maximum extension of... 

Technically specified rubber grades of natural rubber used today by the industry are given in ASTM D2227. Commonly, these grades of natural rubber are based on dirt content. The more dirt removed from the natural rubber at the processing plant means the better price the natural rubber will receive in the marketplace. For exam-... 

Bokobza L and Chauvin J-P (2005) Reinforcement of natural rubber use of in situ generated silicas and nanofibres of sepiolite, Polymer 46 4144-4151. 

Scheme 21 Synthesis of polystyrene grafted onto the surface of natural rubber using SI-NMP...

The natural rubber used in this investigation was an uncrossl inked crepe specimen 1 mm in thickness. The x-ray scattered intensities were recorded as described in Section 2 and elsewhere l at room temperature and at 56 C. The intensity data recorded for the room temperature... 

SULPHUR CURING OF NATURAL RUBBER USING A COMBINATION OF TOTD AND CBS... 

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