Natural Rubber Latexes

See also Polyisoprene Natural rubber latex Synonyms Rubber latex, natural Definition Vise. liq. contg. > 60% rubber classified by method of concentration and type of preservative (e.g., low-ammonia centrifuged grade, creamed latex, evaporated latex)... 

Rubber latex, natural. See Natural rubber latex Rubber, natural. See Natural rubber Rubbing alcohol. See Isopropyl alcohol Rubens brown. See Manganese oxide (ic) Rubichem Zinc-Dip HS] Rubichem Zinc-Dip W] Rubichem Zinc-Dip . See Zinc stearate Rubidium carbonate... 

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... 

Fig. 1. Routes by which natural rubber latex is converted into traditional sheet and crepe.

Table 11. ISO Specifications for Natural Rubber Latex Concentrates...

Spandex fibres, because of their higher modulus, tensile strength and resistance to oxidation, as well as their ability to be produced at finer deniers, have made severe inroads into the natural rubber latex thread market. They have also enabled lighter weight garments to be produced. Staple fibre blends with non-elastic fibres have also been introduced. 

Natural rubber latex Latex gloves, adhesives, surgical apparatus and appliances... 

For applications where surgical gloves provide adequate protection, if these are of natural rubber latex tlien powder-free gloves witli low/undetectable protein and allergen levels are advisable. (Alternatively the use of nitrile gloves eliminates the risk of latex allergy.)... 

Gazeley. K.F. and Mente, P.G., Pressure-sensitive adhesives from modified natural rubber latex. Adhesives, Sealants and Encapsulants Conference, Kensington, London, 5th November, 1985. 

Vulcanization of natural rubber latex by heating it with S diseovered by Charles Goodyear (USA). 

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. 

Garda BE, Barber D, Salcedo G, Rihs HP, Raulf-Heimsoth M Basophil activation test and specific IgE measurements using a panel of recombinant natural rubber latex allergen to determine the latex allergen sensitization profile in children. Pediatr 52 Allergy Immunol 2006 17 148-156. 

Latex. Allergy to natural rubber latex is the second most common cause of anaphylaxis during anesthesia in the general population. In children subjected to numerous operations, particularly those suffering from spina bifida, it is the primary cause of anaphylaxis [11]. The relative frequency of allergy to latex has rapidly increased, rising from 0.5% before 1980 to 20% in France in 2002. A low rate has been reported in countries where a strategy aimed to reduce latex exposure was implemented [6]. 

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. 

Figure 12.13 Pyrogram of a natural rubber latex paint. Peak assignments 1, isoprene 2, toluene 3, xylene 4, 4 ethenyl 1,4 dimethyl cyclohexene 5, limonene 6, dehydro p cymene...

A process for separating particles from a suspension by using centrifugal force. It is the most popular method for concentrating natural rubber latex before shipment from plantation to country of use. 

In rubber latex, the process whereby the dispersed rubber globules separate out from the watery serum the globules clot together to form a jelly-like mass, the coagulum. In the preparation of natural rubber, coagulation of the latex is... 

Natural rubber latex as obtained from the tree contains only about 30% by weight of rubber. Concentration of the latex is done by either centrifuging, creaming, electro-decantation or evaporation. 

Conversion of a liquid into vapour, without necessarily raising the temperature to the boiling point of the liquid solutions are concentrated by evaporating off the solvent. One method of concentrating natural rubber latex is by the controlled evaporation of the liquid in which the rubber particles are dispersed. 

Natural rubber latex, freshly tapped, before the addition of preservatives or before concentration. 

Coagulation of natural rubber latex by stages with the object of removing the yellow colouring matter in the first fraction. The latex in the second fraction produces a white crepe rubber. See Bleaching Agent. 

Easily deformable gelatinous particles which comprise part of the yellow fraction of fresh natural rubber latex. Lutoids break down on the addition of ammonia and pass into the latex serum. 

A unit in the measurement of microscopic particles. It is one-millionth of a metre or one-thousandth of a millimetre and is denoted by the Greek letter mu (pi). The particles of rubber in natural rubber latex vary in diameter from about 0.05 /unto 3 ptm. 

A fabric made by uniting a mass of staple fibres into a continuous sheet by using the adhesive properties of a bonding agent, usually rubber latex, either natural or synthetic. In textile technology the term is applied to fabrics which are not woven, such as felted fabrics. Non-woven fabrics are now being termed bonded fabrics. 

Organic compounds having four alkyl groups attached to nitrogen. A quaternary ammonium salt is employed in reversing the electric charge on natural rubber latex quaternary ammonium dithiocarbamates are ultra-accelerators for rubber vulcanisation. 

Methylinositol, one of the constituents of natural rubber latex. Although it is present at about 1% it does not appear to have any effect on the properties of either field latex or concentrated latex. 

When natural rubber latex is concentrated by centrifuging there are produced approximately equal volumes of concentrate containing most of the rubber, and skim latex with a low proportion of rubber. The rubber obtained by coagulation of skim latex is termed skim rubber. Due to the high content of non-rubber substances such rubber may give difficulty in processing. 

A preservative for concentrated natural rubber latex, the use of which eliminates the ammoniation process necessary with ammonia-preserved latex. See Low Ammonia Latices. Sodium Silicofluoride... 

A test which is claimed to be a more reliable guide to the condition of a natural rubber latex than the KOH number. The test is performed by steam distillation of the latex and titration of the distillate with standard alkali solution. The VFA number is a measure of the state of degradation of the latex. 

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