2w
RHUThe latex is obtained by making incisions in the bark of the rubber tree, allowing the sap to
flow out. It is collected and diluted to contain 15–20% of rubber and then strained to remove
any dirt. Thereafter the rubber is coagulated by adding acetic or formic acid. The coagulated
rubber is then treated to produce crude rubber known as crepe rubber and smoked rubber which
is further processed, milled and vulcanized to produce commercial rubber.
Crepe Rubber is produced by coagulating rubber in the presence of retarder like sodium
bisulphite. Then it is passed between the rollers of creping machine where most of the serum
is squeezed out and a sheet resembling crepe paper is formed.
Smoked Rubber is prepared by pouring diluted latex into tanks having sides with vertical
grooves. Diluted formic or acetic acid is added and stirred. The partition plates are inserted in
the grooves and left for about 16 hours. The slabs so formed are removed and passed through
series of rollers with decreasing clearances. The sheets are kept for four days in a smoke house
having a temperature of 40–50° C.
Synthetic Rubber is based on the model of natural rubber and thermoplastic vinyl high polymers.
The possible number of synthetic rubbers are unlimited. It is so because all straight-chain
polymers can be made to specific requirements to produce rubber like properties. However,
the cheap price and easy availability of natural rubber has suppressed the demand of synthetic
rubber. The term synthetic rubber for rubber like materials prepared synthetically is a misnomer;
the more appropriate term is elastsmer. Some of the synthetic rubbers are shown in Fig. 16.9.
p2ITW2@A
2
Butadiene Acrylonitrile22222 ×2nnx CH == CH — CH == CH + n CH == CH — CN—(CH —CH == CH—CH ) — CH — CH
|
CNp2ITW2@A x
2