The elastic properties of rubber

Natural rubber is found in the latex of the tree Hevea braziliensis its principal constituent is polyisoprene  

Polyisoprene occurs in other plants, some of which have been of commercial significance, such as the Russian dandelion and the Mexican guayule shrub. The well-known properties of natural rubber are dbplayed only at temperatures above the glass transition temperature, which is -7(PQ below that temperature it is a brittle glass. Every amorphous pofymer, whether synthetic or natural, providing it is cross-linked, displays comparable properties above its glass transition temperature. These properties are, stated briefly  

To these must be added a third proper, which is not so well known  

Since the third property is the basis of the other two unique properties of rubber-like materiids, we commence with a description of how the entropy is changed when a spedmen of rubber is deformed. From this understanding the stress-strain characteristics can be obtained. The chapter concludes with an outline description of the rubbers of interest to technology. 

1 If the pofymer is not cross-linked it wQI, at temperatures above 7, eaduhit liquid-like properties unless it is of earemely hjgh relative molecular mass, in uiach case it will esiiibit properties comparable with diose of a diemicalbr cross-linked rubber. 

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Gosline, J. M. (1980). The elastic properties of rubber-like proteins and highly extensible tissues. Sym. Soc. Exp. Biol. 34, 332-357. 

The elastic properties of rubbers are primarily governed by the density of netw ork junctions and their ability to fluctuate [35]. Therefore, knowledge of the network structure composed of chemical, adsorption and topological junctions in filled elastomers as well as their relative weight is of a great interest. The H T2 NMR relaxation experiment is a well established method for the quantitative determination of the network structure in the elastomer matrix outside the adsorption layer [14, 36]. The method is especially attractive for the analysis of the network structure in filled elastomers since filler particles are "invisible" in this experiment due to the low fraction of protons at the Aerosil surface as compared with those in the host matrix. 

Completely synthetic fibers were also to take their place in the world. The leader, here, was the American chemist Wallace Hume Carothers (1896-1937). He, together with a Belgian-American chemist, Julius Arthur Nieuwland (1878-1936), had investigated polymers related to, and having some of the elastic properties of, rubber. The result, in... 

Due to such densely packed molecularly interpenetrated structures, rubbers are incompressible under deformation. Each chain takes a Gaussian conformation following the Flory theorem for screened excluded-volume interaction. On the basis of these characteristics, we can derive the elastic properties of rubbers from a microscopic point of view. 

James HM, Guth E (1943) Theory of the elastic properties of rubber. J Chem Phys 11 (10) 455 81... 

The elastic properties of rubber-like materials are so strikingly unusual that it is essential to begin by defining rubber-like elasticity, and then to discuss what types of materials can exhibit it. Accordingly, this type of elasticity may be operationally defined as very large deformability with essentially complete recoverability. In order for a material to exhibit this type of elasticity, three molecular requirements must be met (i) the material must consist of polymeric chains, (ii) the chains must have a high degree of flexibility and mobility, and (iii) the chains must be joined into a network structure [1-5]. 

James HM, Guth E (1943) Theory of the elastic properties of rubber. J Chem Phys 11(10) 455-481 Kabiri K, Omidian H, Hashemi SA, Zohuriaan-Mehr Ml (2003) Synthesis of fast-swelling superabsorbent hydrogels effect of crosslinker type and concentration on porosity and absorption rate. Eur Polym J 39(7) 1341-1348... 

The elastic properties of rubbers depend on the network molecular structure and on the microscopic response of this structure to a macroscopic constraint. Studies of network formation by computer simulation,sol-gel statistics or determination of network structure by extraction and random degradation may help to analyze results of mechanical testing. Generally, the probability parameters involved in the statistical theories of network formation are determined by comparison of theoretical predictions with experimental values of the sol fraction. ... 

According to classical rubber elasticity theory, intermolecular forces have no effect on the equilibrium chain configurations, and thus no effect on the stress. The relaxation of rubber toward mechanical equilibrium, however, is governed by the interactions among neighboring segments. This relationship has led to various attempts to interpret the elastic properties of rubber in terms of the network dynamics [47-52],... 

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