USF, A New Crude Rubber

Abstract

Abstract In preparing USF rubber by the preferred method, a field latex is preserved with formaldehyde as soon as possible after tapping. This chemical is effective in quickly and thoroughly stopping bacterial and enzymatic changes in the latex (Table I). Thus one of the most important sources of variability is eliminated at the start. The preserved latex is transported to the USF rubber plant and emptied into a tall settling tank; there it is allowed to stand for 48 hours for sand, dirt, and natural sludge components to separate. At the end of this time the supernatant liquid is withdrawn into a blending tank, and another charge is introduced into the settling tank. This process is repeated until the blending tank is filled. Then a fraction of the well-mixed latex from this tank, equal to a charge added from the settling tank, is removed for processing. The latex to be processed is highly diluted, acid is added, and the whole mass is stirred. Fine floes form on standing and rise to the surface, leaving a clear yellow serum. This is withdrawn, and the flocculates are washed by the further addition of water. The washed flocs are transferred through a pipe to the coagulating tanks normally used for preparing sheet rubber. The flocs have now become sufficiently destabilized, so coalescence to a slab of coagulum may occur by simple standing at air temperature. However, faster coalescence is obtained by brief mild treatment with steam. The coalesced slab is removed and passed through mills for the production of crepe or sheet. The wet rubber is hung up to dry in a conventional dryhouse. Finally the dried rubber is heavily compressed and shipped in rubber-wrapped bales. This process is described in the flow sheet of Figure 1.