Crepe rubber

Form of coagulated latex

Latex collection from a rubber tree

Crepe rubber is coagulated latex that is rolled out in crinkled sheets and commonly used to make soles for shoes and boots but also a raw material for further processed rubber products.

Processing

After the collection of the latex milk, sodium sulphite (Na₂SO₃) or ammonia is added to prevent coagulation.^[1]

When the latex arrives in the factory, sodium bisulphite (NaHSO₃) or sodium metabisulphite (Na₂S2O₃) are added to prevent enzymatic reactions and discoloring.^[1]

Sodium para toluene thiophenate (an aromatic mercaptan) is often added as a bleaching agent.^[1]

Colloidal latex is then mixed with formic acid to cause it to coagulate. The coagulum is processed in a "creping battery", a series of machines that crush, press, and roll the coagula. The sheets are then hung in a heated drying shed and, after drying, sorted by grade and packed for shipping.^[1]

Types

There are several types and grades of rubber crepe, mainly distinguished by the grade and pre-processing of the latex used in their manufacture.^[2]

• Pale latex crepe (PLC) is a premium grade, made from raw field latex.
• Estate brown crepe (EBC) is made from "cup lump" (raw, naturally coagulated rubber from the collection cup) and other coagula.
• Re-milled crepe is made from "wet slab coagulum" (cured latex, still wet from the coagulation tanks), latex sheets (unsmoked) and cup lump.
• Smoked blanket crepe is made from thick sheets of latex that have been processed in a smoker.
• Flat bark crepe is made from scraps and other poor quality raw product.

Gallery

• 
  Hand-powered latex creping machines
• 
  Removing coagulum from coagulating troughs
• 
  Creping battery
• 
  Milling honey-colored crepe
• 
  Milling white crepe
• 
  Spooling crepe from last finishing mill
• 
  Smooth crepe spooled for transfer to the drying shed
• 
  Wet coagulum crepe blanket
• 
  Smallholder's sheet in a drying shed
• 
  White crepe hanging in a drying shed
• 
  Laminating white crepe for sole crepe
• 
  Laminating honey-coloured crepe for sole crepe
• 
  Sole crepe inspection and packing

References

1. Manufacture of latex crepe rubber (pdf-document), Raw Rubber Process Development & Chemical Engineering Dept., Rubber Research Institute of Sri Lanka, Ratmalana, January 2016
2. Cecil, John; Mitchell, Peter; Diemer, Per; Griffee, Peter (2013). "Processing of Natural Rubber, Manufacture of Latex-Grade Crepe Rubber". ecoport.org. FAO, Agricultural and Food Engineering Technologies Service. Retrieved March 19, 2013.