Properties of Rubber
Use this handbook as a ready reference on the properties, classification, types, and uses of rubbers.
TABLE OF CONTENTS Properties of Rubber
Compounding and Vulcanization of Rubber
Virgin rubbers obtained from the manufacturing plants after isolation and purification are in their pure form. These rubbers cannot be immediately processed. Compounding is necessary to impart specific properties to the rubber to make it suitable for processing. Vulcanization is done to impart strength and elasticity to rubber.
Compounding of Rubber
Compounding virgin rubber involves melting the rubber into pliable sheets and then incorporating ingredients, such as peroxides, petroleum oils, and wax, into the virgin rubbers or polymers. Peroxides function as plasticizers, vulcanizing agents, and curatives. Petroleum oil functions as antioxidants and waxes act as accelerators, stabilizers, flame-retardant materials, and lubricants. Compounding of elastomers is done on a rubber mill.
Vulcanization of Rubber
Non cross-linked rubber products, such as natural rubber obtained from latex, are soft and tacky with low tensile strength and abrasion resistance. To obtain the network structure of rubber and to increase the elasticity of rubber, a process called vulcanization is used. In this process, rubber is heated with elemental sulphur, which forms bridges between the individual elastic molecules by an ionic mechanism involving addition of the double bond. The addition of sulphur to hot rubber causes structural changes, which improves the physical properties of rubber. The concentration of sulphur in the vulcanized product is 3%. The vulcanization process is slow; therefore, thiurani disuiphides, dithocarbamates, and benzothiazoles are used as catalysts to speed up the process. A reinforcing agent, such as zinc oxide, is used to reduce the concentration of cyclic...
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