Bonding of Unvulcanised Rubbers

The green strength (strength of an unvulcanised rubber compound) of an rubber is the upper limit of the tack [2]. The ratio of the absolute tack divided by the green strength is sometimes referred to as relative tack. When the relative tack is close to one it may be 

This broad maximum occurs due to a proper balance between contact diffusion and green strength/intermolecular attraction at intermediate molecular weight. The diffusion of the rubber molecules across the interface increases as the molecular weight decreases. 

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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]. 

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