Raw rubber, primarily sourced from the Hevea brasiliensis tree, is a natural polymer known as cis-1,4-polyisoprene. It undergoes a significant visual transformation as it moves from its initial harvested state to a standardized, marketable form. The material begins as a milky fluid and progresses through stages of solidification and drying before industrial use. The appearance of the rubber at each stage—from liquid to semi-solid to final dry blocks or sheets—indicates its processing level and grade.
The Initial State: Liquid Latex
Raw rubber first appears as latex, a sticky, milky-white liquid harvested by tapping the rubber tree bark. Latex is a colloidal emulsion where microscopic rubber particles are suspended in an aqueous serum. Its color is typically bright white or pale yellowish-white, flowing with a viscosity higher than water. The rubber particles possess a negatively charged protein membrane, causing them to repel each other and maintain the fluid’s stability. To prevent premature hardening during transport, producers often add a weak alkali, such as ammonia, which neutralizes naturally forming acids.
Transformation: Coagulation and Appearance Change
Coagulation is the conversion of liquid latex into a solid mass, typically triggered by introducing an acidic agent like formic acid. The acid’s hydrogen ions neutralize the negative charges on the rubber particles, causing them to collide and aggregate. This quickly transforms the homogeneous white fluid into a non-flowing, wet, semi-solid substance.
The resulting mass, called coagulum, resembles a curd and is usually white or a light, opaque yellowish color. As the particles bind, the water-based serum separates, leaving the material with a spongy, slightly sticky texture. If impurities are present or if coagulation occurs naturally, the coagulum may develop a darker yellow or brown color due to oxidation.
Market Ready: Forms of Solid Raw Rubber
After coagulation, the semi-solid rubber is processed into standardized dry forms for global trade, primarily Ribbed Smoked Sheets (RSS) and Technically Specified Rubber (TSR). RSS are thin sheets created by rolling the coagulum, featuring a characteristic ribbed pattern. Smoking the sheets with wood smoke gives them a translucent, amber-to-brown color that deepens with exposure. TSR, also known as block rubber, is processed into compressed, dense bales that appear uniform and chunky, ranging from pale yellow to dark brown depending on grade. Crepe rubber is also produced by repeatedly crushing and rolling the coagulum, resulting in a crinkled, pale, and sometimes nearly white texture.