Rubbery elasticity

How does loading affect rubbery elasticity of polymer melts ... 

A representative measure of rubbery elasticity of a material may be two quantities dimensionless ratio (ct/t) and characteristic relaxation time 9 = ct/2ty. According to the data of works [37, 38] when fibers are introduced into a melt, ct/t increases (i.e. normal stresses grow faster than stresses) and 0 also increases on a large scale, by 102-103 times. However, discussing in this relation the papers published earlier, we noted in the paper cited that the data were published according to which if fibers were used as a filler (as in work [37]), 9 indeed increased [39], but if a filler represented disperse particles of the type Ti02 or CaC03, the value of 0 decreased [40],... 

PRINT "THE OLD ELASTICALLY EFFECTIVE CROSSLINK DENSITY EXPRESSION OF BAUER" 150 PRINT "AND BUDDE. THE SECOND CALCULATES A CROSSLINK DENSITY WHICH IN" THEORY SHOULD BE PROPORTIONAL TO THE RUBBERY ELASTIC MODULUS."... 

When rubbery elasticity is required for sample performance, a high ultimate elongation is desirable. When rigidity is required, it is desirable that the material exhibits a lower ultimate... 

Rubber elasticity, which is a unique characteristic of polymers, is due to the presence of long chains existing in a temperature range between the Tg and the Tm. The requirements for rubbery elasticity are (1) a network polymer with low cross-link density, (2) flexible segments which can rotate freely in the polymer chain, and (3) no volume or internal energy change during reversible deformation. 

Bullens, 1994 Anonymous, 1996). Textural defects include increased firmness, rubberiness, elasticity, hardness, dryness, and graininess. The negative flavor attributes of reduced-fat Cheddar include bitterness (Ardo and Mansson, 1990) and a low intensity of typical Cheddar cheese aroma and flavor (Banks et al., 1989 Jameson, 1990). Approaches used to improve the quality of reduced-fat cheese include ... 

Mechanical Behaviour Glassy Leathery Rubbery- elastic Rubbery flow Liquid flow... 

The effect on resilience (approximate rate of recovery from deformation) of reducing is more complex. At relatively low degrees of cross linking, the system exhibits rubbery elasticity. As decreases due to further cross linking, T increases and as it approaches the test temperature, a point of maximum damping is achieved. Here the resilience is at a minimum. Further decrease in Me increases resiliency until the sample become an elastic solid. 

Polymers that, in contrast to thermosets, have a macromolecule structure with wide-meshed crosslinks are called elastomers. Their characteristic property is their not being flowable up to the temperature range of chemical decomposition, but they are rubbery-elastic and reversibly deformable, to a large extent independent of temperature (e.g., rubber products). 

Changes in the Body and Texture of Cheese as a Result of Aging. Alterations in the physical (functional) properties of the caseins occur during the development of the desirable smooth texture of cheese from the rubbery, elastic curd as a result of aging. The development of desirable textural characteristics of aged cheese is the result of very complex biochemical processes which are incompletely understood at this time. 

The phenomenon of shape memory effect in SMPs is brought about by large changes in elastic modulus, E, above and below the transition temperature. Figure 1.3 shows a typical modulus behaviour of SMPs with temperature. At a temperature above the transition, the polymer enters a rubbery elastic state, and hence the elastic modulus of the polymer is much reduced. Consequently the polymer can be easily deformed by application of an external force (Bar-Cohen, 1999 Liu et ah, 2007). If the material is allowed to cool below its transition temperature, under reasonable strain, its temporary deformation becomes hxed. At this stage, the polymer lacks its rubbery elasticity and displays a high modulus. This state is called the glassy state. This deformation can be recovered when the polymer is heated above the transition (Hu, 2007). 

The swelling of a hydrophilic polymer is dependent on the rubbery elasticity, ionic osmotic pressure, and aflSnity of the polymer toward water Although superabsorbent polymers bave tbe greatest absorbency in water, the addition of an inorganic salt or organic solvent will reduce the absorbency. 

In order to perform programming and recovery effectively, the glass transition temperature (T ) must be determined first as the shape memory effect of thermosetting shape memory polymers revolves around a temperature range centered at the Tg. Below this range the material is rigid or glassy and above it is in a rubbery-elastic state. Recovery must be conducted within or above... 

For the other inorganic substances with chain molecules mentioned on p. 38, rubbery elasticity can also be observed in the transformation interval. 

Many chain polymers are of a rubbery elasticity in the transformation interval and the opinion is often expressed that the chain-form of the molecules is a necessary condition for this elasticity. This is not true however on p. 672 it will be shown that rubbery elasticity can also be observed in materials with a three-dimensional structure. The conditions for rubbery elasticity would appear to be a sufficient... 

For the purpose of illustration, the way in which structural factors of apparently minor importance may be decisive for the existence of high-elasticity may be pointed out. Referring to p. 35, where the chemical formulae of rubber and gutta percha are shown to be different only, in that one is the cis and the other the trans form of poly-isoprene, it may be asked why the first is rubbery elastic at room temperature, while the other only possesses this property after being heated above 60 C. Gutta is crystalline at room temperature and melts at 60° C, proving that at this temperature the micro-Brownian motions of the chain elements become so intense, that the lattice forces are insufficient to keep these parts fixed. 

In Fig, 9 the transformation interval, expressed by means of the extension at the breaking point is shown for two typical linear polymers, crude rubber (vulcanised rubber is discussed later) and polyvinyl chloride. The first material is a representative of the substances which show rubbery elasticity at room temperature,... 

The fact that the whole process is executed in a much shorter time for the cresol resin is due to its greater reaction velocity. One of the important conclusions from these experiments is that rubbery elasticity is not restricted to linear polymers hut can also be observed with globular macromolecular substances. 

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