Latex, rubber from vulcanization

Lapworth, Arthur, 707 Lard, composition of, 1062 Latex, rubber from, 245 vulcanization of, 245-246 Laurene, synthesis of, 875 Laurie acid, structure of, 1062 LDS0, 25 table of, 26... 

Natural rubber latex, obtained from rubber trees, is converted to its final form by a process known as vulcanization, first discovered by Charles Goodyear in 1839. Vulcaiuzation is basically a crosslinking reaction of double bonds in the latex structure with sulfur. The polymerization of butadiene with itself or with other vinyl monomers results in a material that like natural latex, still contains double bonds. Thus, synthetic rubber made from butadiene can be processed and vulcanized just like natural rubber. 

Rubber can be used by an engineer as a liquid latex or as a raw rubber or a vulcanized rubber. The vulcanized rubber can vary from soft gum stock through various stages of reinforced rubber (the state of which is achieved both by compounding techniques and... 

To explain the fact that HSPAN swells in water to form gel sheets or macroparticles rather than disintegrating into a gel dispersion, we initially felt that chemical bonding must take place between individual particles of water-swollen gel as water evaporates. Although we cannot totally eliminate this possibility, the proposal of primary chemical bonding is not necessary to explain the behavior of these films and conglomerates. For example, Voyutskii (19) has reviewed the formation of films from vulcanized rubber latexes and concludes that film formation in these systems is observed because of interdiffusion of ends of individual macromolecules in adjacent latex particles. This diffusion can take place even though individual latex particles are crosslinked, 3-dimensional networks and the continuity of the resulting films, even when... 

Gutta percha objects were created from raw, untreated latex that was melted and molded, or from vulcanized gutta percha, which has most of the same properties as hard rubber. Molded gutta-percha was made into a staggering diversity of objects, including golf balls, jewelry, thread, tool and weapon handles, condoms, water pipes, buttons, and in dentistry as a base for dentures, as fillings, and as artificial teeth. The thread was woven into waterproof blankets, tents, and other fabrics, mosdy for use by the military. 

A true synthetic natural rubber was introduced in the mid-1960s with the exact same chemical structure as latex tapped from a tree. The difference is that natural rubber comes with a variety of other ingredients in the latex that can both add and detract from performance, while polyisoprene is considered relatively pure. In addition, there are some differences in molecular weight distribution that impact performance. Available in both latex and solid forms, this elastomer can be directly substituted for natural rubber in many applications. Adhesives which are not cured tend to have higher creep values than natural rubber, but also exhibit lower tack and green strength properties. Vulcanized adhesive products perform equal to cured natural rubber adhesive products. 

Rubber from trees has been used in both solid and latex form, and also converted further into isomerized and chlorinated polymers of very different properties and uses. Wood from trees is used directly for plywood, composition board, and wood-flour reinforcement of phenolic resins. The cellulose from wood is purified and used for laminates and for regenerated cellulose products such as cellophane, viscose rayon, and vulcanized fibre. The lignin from wood has been explored for use in plastics, but never carried through to complete commercial success. 

Caoutchouc elastic, high molecular mass polyter-penes, which can be converted into rubber by vulcanization. Natural C. is a mixture of polyisoprenoids with varying molecular masses, ranging from 300,000 to 700,000. According to X-ray and IR data, the double bonds are cis oriented, whereas in the C.-like polyterpenes, gutta and balata, they are trans. Hundreds of species of plants contain C in their latex, but it can only be obtained on a large scale from a... 

Conunercial rubber latex is produced by concentrating the latex drawn from the tree, to 60% rubber, with anunonia added to prevent deterioration. The rubber is vulcanized while in the latex form. This will then dry to form an elastic and strong film. 

Improvement in the processing and vulcanized qualities of a range of systems have been reported over the past decades. Modification of natural rubber, due to work in the British Rubber Producers Research Association, yields some of the most striking applications of microgel. A detailed study at the MV Lomonosov Institute of Fine Chemical Technology, in Moscow, on the effect of microgels on mechanical properties of cis-polyisoprene and butadiene-styrene rubbers extensively illustrates the properties of blends from latex combination of microgel and conventional or linear systems.(31)... 

The prevulcanization of natural rubber in latex form has also been a subject of much investigation. The cross-linking mechanism is not yet fully understood, but the water apparently plays a major role in it. Irradiation results in the cross-linking of the rubber molecules and in coarsening of the latex particles. A process of cross-linking of natural rubber latex has been developed to the point that it can be used for an industrial-scale application. The irradiation is performed in aqueous media by electron beam without a prorad (sensitizer) at a dose of 200 kGy (20 Mrad) or in the presence of n-butyl acrylate at considerably lower doses, typically 15 kGy. The cross-linked film exhibits physical properties comparable to those obtained from sulfur cured (vulcanized) film. As an alternative, the addition of a variety of chloroal-kanes makes it possible to achieve a maximum tensile strength with radiation doses of less than 5 Mrad (50 kGy). ... 

A process of cross-linking of natural rubber latex has been developed to where it should be soon ready for an industrial-scale process.149 The irradiation is performed in aqueous media by electron beam without a prorad ( sensitizer ) at a dose of 200 kGy (20 Mrad) or, in the presence of n-butyl acrylate at considerably lower doses, typically 15 kGy. The cross-linked film exhibits physical properties comparable to those obtained from sulfur-cured (vulcanized) film. 

As a matter of fact, mankind knows polymers from ancient times, due to the existence of naturally occurring polymers such as latex, starches, cotton, wool, leather, silk, amber, proteins, enzymes, starches, cellulose, lignin, and others. The other type of polymers are synthetic polymers. Braconnot, in 1811, perhaps made the first significant contribution to polymer science by developing compounds derived from cellulose. Later, cellulose nitrate was obtained in 1846 by Schonbein, afterward in 1872, its industrial production was established. Besides, in 1839, Goodyear found out by accident that by heating latex with sulfur its properties were altered creating a flexible and temperature-stable rubber. This process is named vulcanization. 

Latex balloons are still made in essentially the same way. A metal form shaped like the uninflated balloon is first coated with a chemical that will cause the latex to coagulate on it. The form is immersed upside-down into a vat of latex also containing a crosslinking (vulcanizing) agent, and then dried in an oven to cure the rubber. After the balloon is removed from the mold, it is ready to be imprinted or packaged. A modern, automated factory can turn out a million or so latex balloons a day. 

Gutta-percha (with or without the hyphen) is the hardened latex from a number of different trees found in Borneo, Sri Lanka, and Malaya. The name comes from the Malayan words for juice (gutta) and tree (percha). This viscous plant sap hardens quickly and, after vulcanization, looks and behaves like hard rubber. The term gutta percha has also been used to describe unvulcanized hard rubber, regardless of its origin. 

Elastomeric fibers can be made out of natural rubber. Rubber latex, which is a suspension of rubber spheres in water, is mixed with a vulcanizing agent, and the mixture is wet spun. The fibers from the spinneret are extruded into a coagulating bath and then vulcanized to produce the cross-linking of chains. Such fibers are used in woven and knitted fabrics, and more often than not they are mixed with other textile fibers to form fabrics for garments. Most natural rubber fibers, however, have been supplanted by synthetic elastomeric fibers, especially in the area of athletic wear. This is attributable to the poor dyeability, abrasion resis-... 

Crude rubber, called latex, is collected from the tree as an aqueous dispersion that is washed, dried, and coagulated by warming in air. The resultant polymer has chains that average about 5000 monomer units in length and have molecular weights of 200,000-500,000. This crude coagulate is too soft and tacky to be useful until it is hardened by heating with elemental sulfur, a process called vulcanization. By mechanisms... 

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