Crepe rubber

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.

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]

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.

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