NR Rubber

This elastomer as the name betrays, is a natural product harvested in form of a milky sticky latex from the rubber tree (Hevea tree). This latex is then refined, coagulated and dried. The Hevea tree grows best in tropical regions where the annual rainfall is abundant throughout the year. The first known use of runner was in Central America by the Aztecs (the material was called cau-uchu)  for a ballgame. NR is mainly vulcanized with sulfur or peroxide. In 1839 Charles Goodyear discovered the process of vulcanization and made this material interesting.

Conventional grades are delivered in sheets or crepes (Pale or Brown) and are classified according to the source of the raw material and the method of processing. Technical Specified Rubbers are graded not visually but according to the source of the polymer and its properties. Normally the delivery form is crumbs or granules.

The impurities in the raw rubber influences the properties like tensile strength and is therefore a key property in the standard Malaysian rubber specifications; Ash content and nitrogen content are also determined – the last one influences the dynamic properties.

The structure of NR is mainly cis 1,4 polyisoprene; this high structural regularity causes crystallization at low temperatures. The impurities are proteins, amino acids, fatty acids, carbohydrates and inorganic salts. The “non-rubber” components may vary depending on the process, the grade of rubber and depending on the bacterial decomposition. Some of these components influences the vulcanization; proteins are accelerators, fatty acids are activators, Vitamin E is an antioxidant. Proteins improves also the tear resistance, however they cause a higher heat build-up in the flexometer test.