Latex, rubber from

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... 

Keep the latex rubber underwater, and use your gloved hands to mold the lump into a ball, as shown in Figure B. Squeeze the lump several times to remove any unused chemicals. You may remove the latex rubber from the water... 

The RMS (root mean square measurement of the molecular radius) versus the molar mass gives an indication of polymer molecular shape and branching, where a value of 1 indicates an unbranched, rod shaped molecule 0.5 a random coil 0.3 a spherical structure and 0.1 a highly branched molecule. Guayule stem rubber seems to form a random coil with few branch points, whereas Hevea rubber appears to be a more compact and branched polymer [Table 5 (12)]. Guayule latex rubber from the roots and stem bases seems more like the Hevea rubber in shape than the stem latex rubber, but it is not known whether this is a reflection of its location or of its greater age. 

The compounding technique for latex differs from that of dry mbber and is fundamentally simpler. A critical factor of colloidal stabiUty makes necessary that each ingredient is of optimum particle size, pH, and concentration when added as an aqueous dispersion to the latex. Rubber latex is a colloidal aqueous emulsion of an elastomer and natural mbber latex is the milky exudation of certain trees and plants that of greatest commercial importance is the... 

In suspension processes the fate of the continuous liquid phase and the associated control of the stabilisation and destabilisation of the system are the most important considerations. Many polymers occur in latex form, i.e. as polymer particles of diameter of the order of 1 p.m suspended in a liquid, usually aqueous, medium. Such latices are widely used to produce latex foams, elastic thread, dipped latex rubber goods, emulsion paints and paper additives. In the manufacture and use of such products it is important that premature destabilisation of the latex does not occur but that such destabilisation occurs in a controlled and appropriate manner at the relevant stage in processing. Such control of stability is based on the general precepts of colloid science. As with products from solvent processes diffusion distances for the liquid phase must be kept short furthermore, care has to be taken that the drying rates are not such that a skin of very low permeability is formed whilst there remains undesirable liquid in the mass of the polymer. For most applications it is desirable that destabilisation leads to a coherent film (or spongy mass in the case of foams) of polymers. To achieve this the of the latex compound should not be above ambient temperature so that at such temperatures intermolecular diffusion of the polymer molecules can occur. 

There are many temporary protectives on the market and it would be impracticable to describe them individually. However, they may be classified according to the type of film formed, i.e. soft film, hard film and oil film the soft film may be further sub-divided into solvent-deposited thin film, hot-dip thick film, smearing and slushing types. All these types are removable with common petroleum solvents. There are also strippable types based on plastics (deposited by hot dipping or from solvents) or rubber latex (deposited from emulsions) these do not adhere to the metal surfaces and are removed by peeling. In addition there are volatile corrosion inhibitors (V.C.I.) consisting of substances, the vapour from which inhibits corrosion of ferrous metals. 

Emulsion polymerization is the most important process for production of elastic polymers based on butadiene. Copolymers of butadiene with styrene and acrylonitrile have attained particular significance. Polymerized 2-chlorobutadiene is known as chloroprene rubber. Emulsion polymerization provides the advantage of running a low viscosity during the entire time of polymerization. Hence the temperature can easily be controlled. The polymerizate is formed as a latex similar to natural rubber latex. In this way the production of mixed lattices is relieved. The temperature of polymerization is usually 50°C. Low-temperature polymerization is carried out by the help of redox systems at a temperature of 5°C. This kind of polymerization leads to a higher amount of desired trans-1,4 structures instead of cis-1,4 structures. Chloroprene rubber from poly-2-chlorbutadiene is equally formed by emulsion polymerization. Chloroprene polymerizes considerably more rapidly than butadiene and isoprene. Especially in low-temperature polymerization emulsifiers must show good solubility and... 

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. 

The rubber industry has a long and colorful history. Natural rubber is produced from latex, a milky fluid found in cells that lie between the bark and the wood of many plants. You may have seen latex flow from the broken stalks of milkweed plants, but the source of commercial rubber is the Hevea tree, a native of Brazil. When the bark of this tree is slashed, its milky white sap oozes out and can be collected in cups mounted on the tree s trunk. The people of the Amazon jungle made bouncing balls, shoes, and water Jars out of rubber, and Portuguese explorers sent waterproof boots and a rubber-coated coat back to their king. The first commercial exports included some rubber shoes shipped to Boston in 1823. 

The lowest grade of plantation crepe rubber. It is made from earth scrap (rubber from latex which has fallen on the ground) and any other plantation salvage scrap. It was formerly called Rolled Brown Crepe. 

In latex compounding, same as protective colloid. Stabilisers are incorporated in synthetic raw rubbers to protect the rubbers from oxidation during storage. Since the chemical behaviour of these protective materials is not significantly different from that of antioxidants in a vulcanisate, it has been proposed that the use of stabiliser in this sense be dropped in favour of antioxidant. 

During the early nineteenth century, Europe started getting rubber from Brazil. The latex that oozed from the bark of Hevea braziliensis trees was coagulated by warming into rubber. For sometimes, rubber... 

It seems probable that when governmental subsidies are relaxed in the United States and certain other countries where synthetics are produced on emergency funds, natural rubber will be in a fairer position relative to synthetics, and latex rubber may increase its popular lead. In 1952 the world consumed 1,860,000 long tons of latex rubber, and in 1953 about 80,000 more than this. The Far East still produces over 90% of the natural rubber of the world, and nearly half of that percentage comes from Malaya. Africa ships about 3%, and Latin America about 2%. 

Table 8 Summary of Wastewater Sources from Latex Rubber Production...

ELECTRODEPOSITION. The precipitation of a material at an electrode as the result of the passage of an electric current through a solution or suspension of the material, for example, alkaline-earth carbonates, rubber from latex, paint films on metal. A technique for electrodepositing refractory carbide coatings on metal has been reported. The electrode is in ihe shape of the desired article. An important advantage or electrodeposition is its ability lo coat complex shapes having small and irregular cavities with exact thickness control. 

The use of 2-chloroethyl phosphonic acid (ethephon) to boost the yield of latex from rubber trees has become standard estate practice in recent years. This compound increases the flow of latex and the yields of dry rubber from commercially important tree varieties as much as 100%. In addition, ethephon helps to preserve the bark, which normally is cut regularly to permit the flow of latex. As a result, the economic life of the tree is prolonged. Ethephon breaks down into ethylene, which is probably the basis for its activity. 

The extreme toxicity of dimethylmercury was demonstrated tragically by the 1997 death of Professor Karen Wetterhahn of Dartmouth College. Dr. Wetterhahn was exposed to dimethylmercury from an accidental spill of about two drops of this liquid onto the latex rubber gloves she was wearing for protection. The lipid-soluble compound permeates latex and skin, and Dr. Wetterhahn died less than a year later from neurotoxic effects to the brain. 

The procedure arrived at in this work is a modification of a previously reported dialysis method for separation of petroleum (13) and coal hydrogenation products (14). The method involves transport of soluble material through a latex rubber membrane in an appropriately chosen solvent. The only material which can be transported through the membrane is that which is truly soluble in the solvent/membrane system therefore the technique discriminates soluble material from colloidal or suspended matter. 

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