Rubber and Rubberlike Materials

This book does not discuss the polymer in the glass state, which is a subject in a specialized area. However, it discusses the other two states in three different chapters the crystalline state in the Chapter 6 and the viscoelastic state in the present chapter and in Chapter 8. 

The viscoelastic state is also known as the rubber state. A piece of rubber under external force can be stretched. When the external force stops, the rubber recovers to its original position. Usually long-chain polymers can be induced to exhibit typical rubberlike behavior, for example, chains such as polyesters, polyamides, elastic sulfur (sulfur cooled from the liquid), and cellulose derivatives. 

Physical Chemistry of Macromolecules Basic Principles and Issues, Second Edition. By S. F. Sun ISBN 0-471-28138-7 Copyright 2004 John Wiley Sons, Inc. 

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Ic. The Results of Stress-Temperature Measurements.—Hysteresis in the stress-strain behavior of rubber and rubberlike materials has presented the most serious problem encountered in the execution of otherwise simple experiments on the change of stress in stretched rubber with temperature at constant length (L) or at constant elonga-... 

Relaxation birefringence is meant to imply the measurement of birefringence during stress relaxation of a deformed material. The typical application has concerned rubbers and rubberlike materials where the objective is to test the degree of ideal Gaussian rubber elasticity by utilising the stress optical law given earlier in eqn. (10). 

The phenomenon that a rubber or a mbberlike material can be stretched is termed deformation and the ability of it to recover and return to its original conformation is termed recoverability. Thus, the basic properties of rubber and rubberlike materials are deformation and recoverability, which are parallel to the properties of liquid crystals, namely, order and mobility. 

This article reviews recent developments in polymer thermomechanics both in theory and experiment. The first section is concerned with theories of thermomechanics of polymers both in rubbery and solid (glassy and crystalline) states with special emphasis on relationships following from the thermomechanical equations of state. In the second section, some of the methods of thermomechanical measurements are briefly described. The third section deals with the thermomechanics of molecular networks and rubberlike materials including such technically important materials as filled rubbers and block and graft copolymers. Some recent data on thermomechanical behaviour of bioelastomers are also described. In the fourth section, thermomechanics of solid polymers both in undrawn and drawn states are discussed with a special focus on the molecular and structural interpretation of thermomechanical experiments. The concluding remarks stress the progress in the understanding of the thermomechanical properties of polymers. 

An elastomer is a rubberlike material (natural or synthetic) that is generally identified as a material which at room temperature stretches under low stress to at least twice its length and snaps back to approximately its original length on release of the stress (pull) within a specified time period. The term elastomer is often used interchangeably with the term plastic or rubber (2,14). 

These deductions from basic facts of observation interpreted according to the rigorous laws of thermodynamics do not alone offer an insight into the structural mechanism of rubber elasticity. Supplemented by cautious exercise of intuition in regard to the molecular nature of rubberlike materials, however, they provide a sound basis from which to proceed toward the elucidation of the elasticity mechanism. The gap between the cold logic of thermodynamics applied to the thermoelastic behavior of rubber and the implications of its... 

Neoprene (du Pont) is a rubberlike material that is a polymer of 2-chloro-l,3-butadiene. Somewhat less flexible than natural rubber, it has greater resistance to oUs, greases, hydrocarbon solvents, and other chemicals. Neoprene is useful for gaskets, 0-rings, and tubing. 

At the end of the 19th century, rubber, with gutta-percha, was used mainly as an electrical insulator on wires and cables. Demand was limited, and the supply of natural rubber at a reasonable price (about 1.00/lb in 1900) was ensured. Some work was done during these years on practical syntheses of isoprene and on the replacement of isoprene by its simpler homolog, butadiene, which had been known since 1863. However, advent of the automobile and accelerated use of electric power rapidly increased the demand for rubber, thus raising its price to about 3.00/lb in 1911. These circumstances focused new attention on the production of a synthetic rubber. S. B. Lebedev polymerized butadiene in 1910, and Carl Dietrich Harries, between 1900 and 1910 established qualitatively the structure of rubber as a 1,A-polyisoprene and synthesized larger quantities of rubberlike materials from isoprene and other dienes. 

Thermoplastic elastomers are defined by ASTM D 1566 as a family of rubberlike materials that, unlike conventional vulcanized rubber, can be processed and recycled like thermoplastic materials . A rubber is defined as a material that is capable of recovering from large deformations quickly and forcibly and retracts within 1 min to less than 1.5 times its original length after being stretched at room temperature (18 to 29° C) to twice its length and held for I min before release . 

There is an extensive body of literature describing the stress-strain response of rubberlike materials that is based upon the concepts of Finite Elasticity Theory which was originally developed by Rivlin and others [58,59]. The reader is referred to this literature for further details of the relevant developments. For the purposes of this paper, we will discuss the developments of the so-called Valanis-Landel strain energy density function, [60] because it is of the form that most commonly results from the statistical mechanical models of rubber networks and has been very successful in describing the mechanical response of cross-linked rubber. It is resultingly very useful in understanding the behavior of swollen networks. 

Another important group of polymers is that group which is elastic or rubberlike, known as elastomers. This chapter discusses this group of materials, including TPEs, MPRs, TPVs, synthetic rubbers, and natural rubber. 

Overall an elastomer may be defined as a natural or synthetic material that exhibits the rubberlike properties of high extensibility and flexibility. It identifies any thermoset elastomer (TSE) or thermoplastic elastomer (TPE) material. Such synthetics as neoprene, nitrile, styrene butadiene, and polybutadiene are grouped with natural rubber (NR) that are TSEs. The term s rubber and elastomer are used interchangeably. 

Until about 1910, the term rubber was sufficiently descriptive for most purposes. It typified natural products derived from various trees and plants that could be formed into solids of various shapes which could be bent, flexed rapidly, or stretched with the amazing ability to return to essentially the initial form. As synthetic materials emerged, particularly synthetics that were directed toward capabilities different from those of natural rubber, considerable confusion resulted as to descriptive terminology. Hence the literature was rife with such terms as rubber, rubbery, rubberlike, and similar inept descriptions. Eventually H. L. Fisher struck a major blow to this confusion and coined the term elastomer to embrace natural as well as synthetic products with those mechanical properties generally associated with natural rubber. 

Hoseh, M. (1944) German Patents relating to synthetic rubberlike materials. In India Rubber World through 1940 and 1941, India Rubber World 110,416. 

Muller investigated the relationship between the molecular orientation and the mechanical and optical anisotropies in fibrous as well as crosslinked rubberlike materials. The mechanical and optical properties of a crosslinked rubber network under deformation were theoretically analyzed with the so-called freely jointed equivalent chain model by Kuhn and Griin" and Treloar." Mechanical anisotropy in preoriented crystalline polymers was discussed by Raumann" " and by Ward et on the basis of the infinitesimal anisotropic elastic theory. Ward also expressed the... 

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