Production of Dry Rubber

Latex not sold as latex concentrate and cup lump, tree lace, and earth scrap are used to produce various grades of dry rubber. 

A major dry natural rubber type is ribbed smoked sheet. For this the coagulum is passed between pairs of even-speed steel rollers that squeeze the water out. The final set of rollers has channels cut in them so that the sheet emerging from them has a ribbed surface. The ribbed surface facilitates drying. This rubber is dried in smokehouses. The ribbed sheets are hung over poles mounted on trolleys. Rubber tree wood fires produce the smoke, which dries the rubber and gives the rubber some age resistance from its components such as cresols. Drying takes 48 to 96 hours, with entrance temperatures at about 40 °C and exit temperatures at about 60 °C. Some ribbed sheet rubber is dried in hot air out of contact with smoke. This produces a lighter colored rubber, which commands a premium and is referred to as air-dried sheets. 

The cup lump, tree lace, and earth scrap can be worked up into rubbers called brown crepes . These raw materials vary a great deal in quality and are often dirty, Preliminary treatment frequently includes soaking overnight in a dilute solution of sodium bisulfite to reduce the surface dirt and lighten the color. The material is then macerated and conveyed to a series of roll mills driven at friction speed and fitted with water sprays that clean up the rubber and blend it. The rubber is then sheeted off and dried like smoked sheet. Remilled blanket crepes refers to rubbers similar to brown crepes but which are made of smoked sheet cuttings, smallholders partially dried sheets, and other pieces. The production of brown crepes and remilled blanket crepe is diminishing as demand for technically specified rubber increases and technically specified rubbers use the same raw rubbers that go into crepes and blanket crepes. 

After World War II, rubber growers conducted surveys of customers to find out how their product could compete most effectively with the synthetic rubbers then available. As a result of these surveys, rubber producers developed technically specified rubbers. First introduced by Malaysia about 1965 as SMRs (Standard Malaysian Rubbers), they were accepted so well that other countries followed with similar products such as SIR (Standard Indonesian Rubber) and TTR (Thai Tested Rubber). 

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