Rubber tree plantation

Our story begins on large rubber plantations, where rows upon rows of rubber trees stand tall. These trees, when they reach maturity, are ready for a process called tapping. Skilled workers make carefully angled cuts in the bark, breaking the latex vessels and causing a milky white liquid, known as latex, to flow out. Latex contains about 40 % rubber and 55 % water. Now this liquid latex, the very essence of natural rubber, collects in cups attached to the rubber trees.

Coagulation

The collected latex, is still in its raw form as it is obtained from the rubber tree. To convert it into a useful solid, a process called coagulation is used in the manufacture of rubber.

In this step, the rubber plant latex is treated with specific acids or chemical compounds, causing the latex particles to clump together and separate from the aqueous serum. This separation results in a white, rubbery mass.

Rolling and drying

The coagulated rubber, still quite wet, needs further processing. It passes through rollers, which help squeeze out excess water and mould the rubber into thin sheets. These sheets are then dried, traditionally done by one of three methods:

Air drying in the dark: The sheets are simply hung in well-ventilated spaces, allowing the natural air to remove moisture.
Air drying in sunlight: The sheets are hung on ropes or racks and dried in the sun.
Smoke drying: This method involves exposing the sheets to controlled smoke from burning wood or palm fronds. The smoke dries the rubber and gives it its characteristic brown colour. This step also acts as a natural preservative in rubber manufacturing.

Mixing (Compounding)

The latex is mixed with carbon black oil and a vulcanising agent (usually sulphur or a peroxide) in a mixer. After this, the material is processed in an open mixer with two rollers.

Material test

Once the material is mixed, the mixture is tested in a laboratory to ensure the desired hardness and its physical properties. After this, a vulcanisation curve is produced in a rheometer. This gives the temperature and time needed for the material to fully vulcanise.

Vulcanisation

There are different types of vulcanising presses, the most common being compression and vacuum transfer. But for larger volumes and certain types of components, injection presses are also used. Under the influence of heat and organic compounds called accelerators, which speed up the chemical reactions, vulcanisation takes place and the sulphur forms sulphur bridges between the molecular chains.

Bearding and Testing and quality control

The finished swaged components often have a "beard" at the mould parting line, this is cut off manually or broken off during freeze-rumbling in liquid nitrogen. Depending on the end customer's requirements, the finished parts are now tested and undergo a quality check before being packed and shipped to the customer.

From latex to natural rubber