Rubberlike behavior

These experimental results show conclusively that the deformation factor occurring in the theoretical equation of state offers only a crude approximation to the form of the actual equilibrium stress-strain curve. The reasons behind the observed deviation are not known. It does appear, however, from observations on other rubberlike systems that the type of deviation observed is general. Similar deviations are indicated in TutyP rubber (essentially a cross-linked polyisobutylene) and even in polyamides having network structures and exhibiting rubberlike behavior at high temperatures (see Sec. 4b). 

Swollen tensile and compression techniques avoid both of these problems since equilibrium swelling is not required, and the method is based on interfacial bond release and plasticization rather than solution thermodynamics. The technique relies upon the approach to ideal rubberlike behavior which results when lightly crosslinked polymers are swelled. At small to moderate elongations, the stress-strain properties of rubbers... 

Rubberlike Behavior, from the Point of View of the Theory of Molecular Displacements... 

Polyurethane adhesives are formed by the reaction of various types of isocyanates with polyols. The polar urethane group enables bonding to various surfaces. Depending on the raw materials used, glue lines with either rubberlike behavior or elastic-to-brittle hard behavior can be aehieved. The end groups determine the type of the adhesive, whether it is a reactively or a physieally hardening adhesive. 

Meanwhile, developments in polymer science established that most long-chain linear polymers above their glass-transition temperatures can also exhibit rubberlike behavior whereby a network of molecular entanglements can serve the function of chemical cross links for deformation histories with oscillation periods shorter than the relaxation times of entanglement drift. It is this form of behavior of glassy polymers resembling that of rubbers which is a subject of principal concern and is discussed in Section 6.7. 

If a fluid does not follow Eq. (3.5-1), it is a non-Newtonian fluid. Then a plot of t versus —dv/dr is not linear through the origin for these fluids. Non-Newtonian fluids can be divided into two broad categories on the basis of their shear stress/shear rate behavior those whose shear stress is indejjendent of time or duration of shear (time-independent) and those whose shear,stress is dependent on time or duration of shear (time-dependent). In addition to unusual shear-stress behavior, some non-Newtonian fluids also exhibit elastic (rubberlike) behavior which is a function of time and results in... 

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. 

Let us now examine the physical background of the time-dependent failure processes observed. Amorphous polymers consist of long, covalently bonded chains that are randomly distributed throughout the material. Each molecule has the ability to change its spatial conformation by rotation over covalent bonds that form the backbone of the chain, and in its equilibrium state a random coil is the most probable conformation. The rate at which a chain can change its conformation depends on temperature and stress. At high temperatures, conformational changes are fast and chains can move freely with applied deformation (rubberlike behavior). 

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