CHAPTER 3. Non-Rubbers and Abnormal Groups in Natural Rubber

Despite the strong challenges posed by the synthetic rubbers, natural rubber is still being widely used. This is due to its certain excellent properties which so far cannot be replicated in the design of synthetic rubbers. The major differences between the natural and synthetic rubbers can be categorized into three main areas, namely (i) natural rubber contains non-rubbers which are absent in the synthetic rubbers; (ii) natural rubber has abnormal groups on the main chain molecule which are absent in the synthetic rubbers; (iii) natural rubber has a long uninterrupted cis-1,4-isoprene chain whereas synthetic cis-polyisoprene has many isomeric units such as trans-1,4, 1,2, 3,4-units. These non-rubbers and abnormal groups have been reported to contribute to the excellent properties of raw, compounded and modified rubbers. This chapter describes the main components in the non-rubbers and their roles in influencing the properties of the rubber and rubber products. In addition, the existence of various abnormal groups on the rubber main chain molecule reported so far are also critically examined.