Rubberlike Materials

The term s plastic, polymer, resin, elastomer, and reinforced plastic (RP) are some-what synonymous. However, polymer and resin usually denote the basic material. Whereas plastic pertains to polymers or resins containing additives, fillers, and/or reinforcements. Recognize that practically all materials worldwide contain some type of additive or ingredient. An elastomer is a rubberlike material (natural or synthetic). Reinforced plastics (also called composites although to be more accurate called plastic composites) are plastics with reinforcing additives, such as fibers and whiskers, added principally to increase the product s mechanical properties. 

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). 

Moduli of rubberlike materials (T > Tg) rise as the temperature is increased. In this respect rubbers behave in contrast to most materials which usually exhibit decreased rigidity at elevated temperatures. 

At temperatures well above the glass transition of the polymers, the molecular segments are highly flexible and slip past each other almost without restriction. They behave like the molecules of a liquid except for the fact that their ends are linked with each other. Just the existence of crosslinks distinguishes rubberlike materials from ordinary liquids. The bulk moduli K of liquids and of rubberlike materials are of similar magnitude, e.g. K = 1 to 2 GPa [26]. 

As the Young s modulus E of a rubberlike material is low, E < 3 K, the shear modulus S of such a material is well approximated by... 

Dynamic shear moduli are conveniently determined with automated equipment, for instance, with the torsion pendulum. However, moduli derived from dynamic tests are often higher than the results from static tests for lack of relaxation. Examples are shown in Table 3.3. Young s moduli of the polymers A, B, C, D, derived from tensile tests (frequency 0.01 Hz) are compared with shear moduli S determined with the torsion pendulum (frequency > 1 Hz). For rubberlike materials is 3S/E = 1, according to Eq. 

The behavior of the strain softened material resembles the behavior of rubberlike polymers. For instance, the Poisson s ratio of an ideally plastic material is also close to 0.5 [94, 95], Proper understanding of crack propagation involves the microscopic level. Apparently, the load is transmitted by the molecular strands [97] from one crosslink to the next crosslink, exactly, as it is in rubberlike materials. However, two things are different in strain softened polymers as compared to rubberlike materials ... 

Such a /Mc dependence has been observed for the threshold fracture energies in rubberlike materials [106,107] in accordance with the model of Lake and Thomas [108]. However, Eq. (7.10) is based on arrest energies and the reason for the use of arrest energies is not clear. 

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... 

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-... 

For rubberlike materials, the modulus thus defined generally shows an additional dependence on elongation (39,40,42), apparently because of increase in the non-affineness of the deformation as the elongation increases (43,44). This dependence is frequently represented (approximately) by the semiempirical equation of Mooney and Rivlin... 

Uses. Manufacture of acrylic fibers synthesis of rubberlike materials pesticide fumigant... 

During this time, other materials that gave rubberlike materials were found. In 1901, I. Kondakov, a Russian, discovered that dimethyl butadiene when heated with potash formed a rubberlike material. In 1910, S.V. Lebedev, another Russian, reacted butadiene forming a rubberlike material (structure 9.33). 

A measure of the stiffness of a polymer is the modulus of elasticity (Young s modulus) E. It can be calculated fi om the stress-strain curve as the slope in the linear region of Hooke s law. It should be considered that due to the definition E = o/e for rubberlike materials which show a rather large extension e at quite... 

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. 

Elastomer blends consisting of two immiscible components are heterogeneous rubberlike materials both components of which are in the rubbery state. Such blends consist usually of either a matrix and a discrete phase or two interpenetrating continuous phases (interpenetrating networks). At homogeneous deformations of such blends, the contribution of either component to the thermomechanical behaviour of the material is determined by the content of the component and the individual characteristics of its chains. 

ASTM D5992, 1996 (2002). Guide for dynamic testing of vulcanized robber and rubberlike materials using vibratory methods. 

Here, rc is the yield stress during shear. The true contact area Areai depends on the compliance of the materials. For soft, rubberlike materials, the real contact area will be larger than for hard materials like steel (Fig. 11.2). 

As the temperature of an amorphous polymer is lowered, there is a transition from rubberlike material with a low Young s modulus to a stiff glass with a high modulus. For example, the Young s modulus of PVC (measured at 1 s) increases from 0.15 to 1.2 GPa as the temperature is decreased from 90 to 75 °C. The glass transition temperature is in this range. The exact temperature depends on the rate of cooling. 

In the process of vulcanisation in air Elastosils form rubberlike materials and have good adhesion to steel, copper, aluminum, wood, ceramics, concrete, polymethylmetaciylate, glass and other materials. Consequently, they do not require the use of any special sublayer. Optimal physicochemical properties of Elastosils are achieved after 5-7 days of solidification at 60-75% humidity in air. The main properties of glue sealants Elastosil are given in Table 24. 

The limiting value of the creep is equal to 00 = a0/E = Voigt-Kelvin element is only able to describe qualitatively the creep behaviour of rubberlike materials with a limited creep and not the creep of an elastic liquid. In general the creep compliance may be expressed as... 

Shen M and Croucher M, "Contribution of Internal Energy to the Elasticity of Rubberlike Materials", J Macromol Sci Revs Macromol Chem C 12 (1975) 287. 

As an oversimplification, it can be said that within limits a rubberlike material can be stretched relatively easily but reaches a state... 

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. 

Ultra-Torr fittings (Fig. 4) seal by means of an 0-ring, usually made ofViton, and are especially useful in making glass- metal- plastic seals in simple vacuum systems. Viton is a rubberlike material with a very low vapor pressure, and Viton 0-rings can be baked to 200°C. Teflon is also occasionally used as a material for 0-rings. 

The ability of materials to exhibit rubberlike elasticity relates to their polymer structure. Rubberlike materials must satisfy a number of criteria ... 

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