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What is natural latex ? Latex is the protective fluid contained in tissue beneath the bark of the rubber tree, Hevea brasiliensis.   The tree originated from Brazil (hence its name), and latex was originally gathered from wild trees in the jungles of Brazil in the 1870's. By 1890, Britain had introduced rubber plantations in Malaysia, Singapore, Thailand and was harvesting latex.   Natural rubber latex (NRL) is a cloudy white liquid, similar in appearance to cows milk. It is collected by cutting a thin strip of bark from the tree and allowing the latex to exude into a collecting vessel over a period of hours. The composition of the latex is detailed in table below :  Constituent  % Composition  Rubber particles (cis-1,4-polyisoprene)  30-40%  Protein  2-3% Water 55-65% Sterol glycosides 0.1-0.5% Resins  1.5-3.5%  Ash  0.5-1.0%  Sugars 1.0-2.0% Initially,the rubber had to be solidified within 24 hours to stop bacterial spoilage  Footnote: This solidified rubber is also known as crepe. But in the 1920's it was discovered that the addition of ammonia could preserve the latex.           General Standard grades  Natural Latex concentrate - specifications for general-purpose types. The general-purpose grades of natural latex concentrate are subject to the requirements of international standards. They have been technically specified for many years in certain countries and the establishment of international standards indicates the substancial measure of agreement that has been achieved on the characteristics which are required of good quality natural rubber latex. The national and international standards are substantially identical in their requirements.   High Ammonia (HA) - centrifuged "Centrifuged natural latex preserved with ammonia only or by formaldehyde followed by ammonia". This general purpose type latex is finding application in a wide variety of products including dipped goods, extruded thread, foam rubber, adhesives, carpet backing and as a binder for rubberised coir. The ammonia (alkalinity) content of HA Latex is is not less than 0.6%* on latex %. Low Ammonia (LA-TZ / TMTD/ZnO - centrifuged) "Centrifuged natural latex preserved with low ammonia with other necessary preservatives". The ammonia content of LA Latex is not exceeding 0.29%* on latex %. Low ammonia LA-TZ can replace HA latex in all normal latex appications, with a little adjustment in compounding in certain cases. LA-TZ is preserved with 0.2% ammonia together with a suitable combination of zinc oxide (ZnO) and tetramethylthiuramdisulphide (TMTD) of not more than 0.1% in total, based on latex weight. The low toxicity level and low dosage (US FDA allows up to 1.5% TMTD in products) of the secondary preservatives, which are widely used in the rubber goods manufacturing industries, ensure that this type of latex is suitable for use in all latex products including surgical goods. No additional effluent problems are expected from the use of this type of latex. The main attribute of LA-TZ latex is the greatly reduced atmospheric pollution with ammonia gas in factories. Other advantages include good film colour and the elimination of the deammoniation process, e.g. in latex foam manufacture. * As per ISO-2004('88E), and ASTM D1076-88 Double Centrifuged (DC) Double centrifuged (DC) latex is a highly purified latex concentrate prepared by re-centrifuging the first centrifuged latex which has been suitably diluted. As a result, the non-rubber constituents are further reduced. Films prepared from DC latex exhibit good clarity, low water absorption and high dielectric properties. DC latex finds application in surgical dipped goods and other specialised premium latex products where these properties are important. The latex is generally very stable and has good storage properties. High Dry Rubber Content (DRC) Latex A high dry rubber content (65-67%) latex is prepared by centrifugation, providing an alternative to creamed and evaporated latices. It processes similarly to 60% DRC centrifuged latex, but dries faster. It has been used in latex thread production.     All About > Standard Thai Rubber>  A Selection Guide Synthetic&Natural Rubber   Copyright by PechSiam Technotrade Ltd.,Part. Tel 66 02 752 2774 - 5   Fax 66 02 752 2775