Unvulcanised rubbers bonding

In the bonding of unvulcanised rubbers blooming of ingredients such as sulphur and antioxidants is a serious problem. It is found that some of the bloomed materials melt at about 90 °C while others remain as large flakes (see Figure 5.3) [18]. 

Like NR, SBR is an unsaturated hydrocarbon polymer. Hence unvulcanised compounds will dissolve in most hydrocarbon solvents and other liquids of similar solubility parameter, whilst vulcanised stocks will swell extensively. Both materials will also undergo many olefinic-type reactions such as oxidation, ozone attack, halogenation, hydrohalogenation and so on, although the activity and detailed reactions differ because of the presence of the adjacent methyl group to the double bond in the natural rubber molecule. Both rubbers may be reinforced by carbon black and neither can be classed as heat-resisting rubbers. 

The rubber in unvulcanised filler-rubber mixes which is insoluble in a usual rubber solvent. Bonding Agent... 

A pre-cured tread with pattern is prepared by moulding. A thin strip of unvulcanised cushion rubber compound is inserted between the casing and the tread rubber to form the bonding agent between the new and old components. The tread is then applied to the casing and consolidated by pressure. The cushion rubber is then vulcanised. This is also known as cold retreading . 

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