Air dried sheet

Two subgrades of SMR 5 are SMR 5RSS and SMR 5ADS, which are prepared by direct baling of ribbed smoked sheet and air-dried sheet (ADS), respectively. 

TSR 5. Within the Malaysian scheme SMR 5 is restricted to mbber derived from sheet material prepared by conventional processes, ie, ribbed smoked sheet (RSS), air-dried sheet (ADS), and unsmoked sheet (USS) and presented in small bale form. Other countries may source different raw materials, eg, Indonesia produces SIR 5 from thin latex coagulum (14). SMR 5 prepared by pressing dry-sheet material into standard bales must be identified by the type of sheet material, eg, SMR 5RSS, on the test certificate as well as on the wrapping. 

Natural Rubbers (NR). The chemical name for NR is polyisoprene, which is a homopolymer of isoprene. It has the cis-1,4 configuration. In addition, the polymer contains small amounts of non-rubber substances, notably fatty acids, proteins, and resinous materials that function as mild accelerators and activators for vulcanization. Raw materials for the production of NR must be derived from trees of the Hevea Brasiliensis species. NR is available in a variety of types and grades, including smoked sheets, air-dried sheets, and pale crepes. 

Air-dried sheets are torn into small pieces to provide a total weight of 3-4g. Screened slush sheets are mixed and 3-4g (dry weight) are made into a pad on a Buchner funnel, taking care to avoid any loss of fibers. The pad is air-dried... 

SP Hevea crumb, SP crepe, SP air-dried sheet and SP smoked sheet are produced by this procedure. Each of these products contains 20% crosslinked rubber and 80% unmodified NR. A masterbatch version is also available that is used as a processing aid for NR processing. PA 80 contains 80% of crosslinked rubber and 20 parts of unmodified rubber, whereas PA 57 is an oil-extended... 

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. 

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