Rubber elasticity basic properties

Mineral oils also known as extender oils comprise of a wide range of minimum 1000 different chemical components (Figure 32.6) and are used extensively for reduction of compound costs and improved processing behaviors.They are also used as plastisizers for improved low temperature properties and improved rubber elasticity. Basically they are a mixture of aromatic, naphthanic, paraffinic, and polycyclic aromatic (PCA) materials. Mostly, 75% of extender oils are used in the tread, subtread, and shoulder 10%-15% in the sidewall approximately 5% in the inner Uner and less than 10% in the remaining parts for a typical PCR tire. In total, one passanger tire can contain up to 700 g of oil. 

The problem of determination of the partition function Z(k, N) for the iV-link chain having the fc-step primitive path was at first solved in Ref. [17] for the case a = c by application of rather complicated combinatorial methods. The generalization of the method proposed in Ref. [17] for the case c> a was performed in Refs. [19,23] by means of matrix methods which allow one to determine the value Z(k,N) numerically for the isotropic lattice of obstacles. The basic ideas of the paper [17] were used in Ref. [19] for investigation of the influence of topological effects in the problem of rubber elasticity of polymer networks. The dependence of the strain x on the relative deformation A for the uniaxial tension Ax = Xy = 1/Va, kz = A calculated in this paper is presented in Fig. 6 in Moon-ey-Rivlin coordinates (t/t0, A ), where r0 = vT/V0(k — 1/A2) represents the classical elasticity law [13]. (The direct Edwards approach to this problem was used in Ref. [26].) Within the framework of the theory proposed, the swelling properties of polymer networks were investigated in Refs. [19, 23] and the t(A)-dependence for the partially swollen gels was obtained [23]. In these papers, it was shown that the theory presented can be applied to a quantitative description of the experimental data. 

Some s)mthetic rubbers are superior to natural rubber in some ways. Neoprene is a s)mthetic elastomer (an elastic polymer) with properties quite similar to those of natural rubber. The basic structural unit is 2-chloro-l,3-butadiene, commonly called chloroprene, which differs from isoprene in having a chlorine atom rather than a methyl group at carbon 2 of the 1,3-butadiene chain. 

Little was known, however, about the exact configuration of the rubber molecule or the molecular mechanism of rubber elasticity. Two world wars and the mushrooming development of the automobile and the airplane raised the demand for elastomeric materials to a level that, by the 1950s, dozens of large industrial organizations produced some 2 million tons of synthetic rubber per year. Most of the production steps are now fundamentally well known, and most of the basic properties of raw and cured elastomers are now reasonably well understood. 

With the basic structure of polymers of macromolecules clarified, scientists now searched for a quantitative understanding of the various polymerization processes, the action of specific catalysts, and initiation and inhibitors. In addition, they strived to develop methods to study the microstructure of long-chain compounds and to establish preliminary relations between these structures and the resulting properties. In this period also falls the origin of the kinetic theory of rubber elasticity and the origin of the thermodynamics and hydrodynamics of polymer solutions. Industrially polystyrene, poly(vinyl chloride), synthetic rubber, and nylon appeared on the scene as products of immense value and utility. One particularly gratifying, unexpected event was the polymerization of ethylene at very high pressures. 

The very satisfactory fit of the scaling predictions obtained by the tube model with deformation-dependent constraints to experimental results for various rubbers at small strains strongly supports the basic assumptions of this approach. Further, it seems worth noting that the small-strain behaviour of rubber-elastic networks considered here is well described by the theoretical results for the case of low crosslink density. This case shows a strong resemblance to that of the melt as there, the influence of topological constraints on the mechanical properties of the networks is important and is well reflected by the molecular field approach of the tube model. As mentioned already in Sect. 4.2, these conclusions are almost identical with the view of Graessley and co-workers and Macosko and co-workers who also extensively... 

Polymer networks at first sight appear to present insurmountable complexities that would seem to preclude rational analysis of their properties in molecular terms. The basic premise that underlies the theory of rubber elasticity, a premise that has been fully validated, permits circumvention of most of these complexities. Recent advances of theory in conjunction with a wealth of empirical evidence gained from well chosen, carefully executed experiments offer the prospect of a comprehensive understanding of the elastic equation of state and associated properties of elastomeric materials in the foreseeable future. 

The properties of elastomeric materials are controlled by their molecular structure which has been discussed earlier (Section 4.4.5). They are basically all amorphous polymers above their glass transition and normally cross-linked. Their unique deformation behaviour has fascinated scientists for many years and there are even reports of investigations into the deformation of natural rubber from the beginning of the last century. Rubber elasticity is particularly amenable to analysis using thermodynamics, as an elastomer behaves essentially as an entropy spring . It is even possible to derive the form of the basic stress-strain relationship from first principles by considering the statistical thermodynamic behaviour of the molecular network. 

Another version of the tube model in rubber elasticity has been reviewed by Graessley. It uses the formalism of the classical paper of Doi and Edwards to calculate the stress-strain relationship. Again the basic property is the primitive path and correlation functions of the primitive path segments , which determines the relaxation of the primitive path. Static properties can be worked out from this dynamic consideration and in the static limit the Cartesian stress tensor can be written as... 

So far, we have considered the elasticity of filler networks in elastomers and its reinforcing action at small strain amplitudes, where no fracture of filler-filler bonds appears. With increasing strain, a successive breakdown of the filler network takes place and the elastic modulus decreases rapidly if a critical strain amplitude is exceeded (Fig. 42). For a theoretical description of this behavior, the ultimate properties and fracture mechanics of CCA-filler clusters in elastomers have to be evaluated. This will be a basic tool for a quantitative understanding of stress softening phenomena and the role of fillers in internal friction of reinforced rubbers. 

Rubber technology is a mature science with a history going back some 150 years or more. Over the years a number of scientific discoveries (e.g. curing with sulphur to increase resilience and recovery, and the use of antioxidants to lengthen service life) have contributed to the material s dominance in applications requiring elasticity/recovery upon deformation combined with durability. Additives are used in rubbers in order to ensure that they possesses the correct properties to be processed, have the physical properties appropriate for the application, and sufficient stability and resistance to ageing in service. There are three basic steps associated with the processing of rubber ... 

The use of blending GRT with asphalt has been in existence for quite some time. Depending on the type of tire, the composition of GRT may include different rubbers. These crosslinked rubbers are mostly immiscible in bitumen. The blends show an improvement in basic asphalt properties as well as rubberlike characteristics. The blend is thought of as a dispersion of undissolved swollen rubber particles acting as an elastic aggregate within asphalt, modified by the portion of the rubber particles that have dissolved. 

Natural rubber (NR) is widely used in various applications and products for its excellent properties such as elasticity, low hysteresis, high resilience, toughness, etc NR is the basic constituent of many products in the consumer goods, health and medical sectors, and it is widely used in transportation. The properties of NR can be improved by the addition of fillers. The inclusion of inorganic fillers in polymers usually results in improvement in strength, toughness, processability, dimensional stability, wear and lubrication properties, and in some cases resistance to thermal and UV radiation of the matrix. 

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