Natural rubber general composition

Natural Rubber-Based Composites and Nanocomposites Table 1.14 General and engineering applications of... 

Generally speaking, commercial rubber products are manufactured as a composite from a rubber and a nano-filler, which is in a group of fillers of nanometer size (mainly, carbon black and particulate silica). For an example, a pneumatic tire for heavy-duty usages such as aircrafts and heavyweight tracks is made from natural rubber (NR) and carbon black and/or silica. Their reinforcing ability onto rubbers makes them an indispensable component in the rubber products [1,2]. 

With improvements in elemental analysis, the structure of many simple molecules was elucidated. Elemental analysis, however, didn t help solve the structure of cellulose or natural rubber, materials that we now know are mac-romolecular in nature. In fact, it contributed to a general misconception. For example, natural rubber was found to have a composition equivalent to CSH8, but this only corresponds to the repeating unit of the polymer and says nothing about its long, chain-like structure. 

The example chosen here to illustrate this type of composite involves a polymeric phase that exhibits rubberlike elasticity. This application is of considerable practical importance since elastomers, particularly those which cannot undergo strain-induced crystallization, are generally compounded with a reinforcing filler. The two most important examples are the addition of carbon black to natural rubber and to some synthetic elastomers and silica to polysiloxane elastomers. The advantages obtained include improved abrasion resistance, tear strength, and tensile strength. Disadvantages include increases in hysteresis (and thus heat buUd-up) and compression set (permanent deformation). 

Natural rubber is derived from latex obtained from the sap of rubber trees. Its use ranges from household articles to industrial products. Tire and tube industries are the largest consumers of rubber and the remaining are taken up by general rubber goods (GRG) sector. A number of research studies have been carried out in the recent past on fabrication and characterization of OPF-NR composites. 

The general composition of the natural rubber molecule has now been established for some 50 years. It is nevertheless rewarding to consider... 

The temperatures for maximum stability under shear in air for eight different polymers are listed in Table 3.2. There are only a few well-documented cases such as polystyrene and natural rubber, that fully reveal the general characteristics of mechanochemistry as a function of temperature. The temperature for maximum stability depends on polymer composition and its associated transitions and stability conditions. The temperature for maximum stability in shear must be above the melting and glass temperatures and below the temperature for extensive thermal and oxidative degradation. The temperatures in Table 3.2 are reduced slightly at ever higher imposed stresses. Correlations of this type for maximum stability in shear are likely to hold for the rubbery melt, and solution states. 

The use of adhesives in medical applications has been restricted, for some time, to the manufacture of self-adhesive bandages (plasters, self-adhesive strips of fabric, etc.). The first pressure-sensitive adhesives used for this were based on natural rubber, concocted decades ago. This first usage was later partly superseded by synthetic rubbers (e.g., polyisoprene, polyisobutylene). In die mid-twentieth century, pressure-sensitive adhesives based on polyacrylic acid esters gained predominance in general use and in the composition of bandage materials. 

A natural rubber rich undertread layer can enhance the adhesion between belt or cap-ply and tread whilst a thicker subtread compound may be included to offer some additional benefits of low hysteresis for car tyres and low heat generation for truck tyres within the bulk of a thick section. The cure system needs better flexibility and low heat generation. Typically the cure system will be based on CV/SEV. A general composition for a tyre tread base is depicted in Table 41. 

Adhesives are polymers that are initially liquid but solidify with time to give a joint between two surfaces [12,13]. The transformation of fluid to solid can be obtained either by evaporation of solvent from the polymer solution (or dispersion) or by curing a liquid polymer into a network. Table 2.3 lists some common adhesives, which have been classified as nonreactive and reactive systems. In the former, the usual composition is a suitable quick-drying solvent consisting of a polymer, tackifiers, and an antioxidant. Tackifiers are generally low-molecular-weight, nonvolatile materials that increase the tackiness of the adhesive. Some tackifiers commonly used are unmodified pine oils, rosin and its derivatives, and hydrocarbon derivatives of petroleum (petroleum resins). Several polymers have their own natural tack (as in natural rubber), in which case additional tackifiers arc not needed. 

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