Natural Rubber

Chemical Properties of Natural Rubber:

Natural rubber is a sap obtained from some trees, better known as latex.

Natural rubber is a polymer of isoprene - most often cis-1,4-polyisoprene - with a molecular weight of 100,000 to 1,000,000. It is a hydrocarbon polymer.

The table below show the compositon of natural rubber:

Table below show the properties of Natural Rubber:

Where were the Natural Rubber Come From?

Natural rubber is obtained from the rubber tree which has the biological name of
Hevea brasiliensis.

There are several species of rubber tree in Malaysia, such the following:
Hevea species viz Heveapauciflora, Hevea guianensis, Hevea spruceana, Hevea benthamiana

Tapping for Latex

1: - A tree will be tapped once it has reached maturity, usually at an age of around seven years.

2:- The bark is cut periodically on a 25-30 degree angle from the top left to the bottom right in order to expose the maximum number of latex vessels.

3:- The excision method of reopening the same cut to create a channels in which the latex runs through and collected in a cup because it leaves the trees relatively unharmed, and can therefore be repeatedly used. This method make the smallest cut possible to obtain the maximum amount of latex.

4:- Coagulated the latex has collected in the cup by using a dilute acid or at the instance of naturally occurring agents ("field coagulum"). The resulting cake of raw rubber must be washed to remove any acid and rolled to remove excess moisture. After rolling the rubber is dried on a rack and smoked over a wood fire to stabilise it, before it is finally sold to rubber manufacturers .

5:- The latex can be collected in its liquid state. It is necessary to add a few drops of ammonia solution to the cup, or to the transport tank, to prevent precoagulation of the latex before it reaches the factory.

Vulcanization of Rubber

Disulphur dichloride, S2Cl2, is used in the rubber industry in the process of vulcanication. With a suitable temperature of 140–180°C . Other addictives also used such as accelerators allow the reaction to occur at lower temperature and more faster, and antioxidants prolong the life of rubber product from atmospheric gases (oxygen). Here sulphur atom link hydrocarbon chains which are thus prevented from being pulled apart when the rubber is stretched. A reinforcing agents (carbon black) increase stiffness, tensile strength, and resistance to abrasion. Vulcanised rubber is much harder and more elastic than natural rubber. It is suitable for applications such as car tyres.

Vulcanization was discovered by chance in 1839 by Charles Goodyear, founder of tyre firm.