Elasticity modulus and temperature

FIGURE 3.14 Relationship between elastic modulus and temperature showing the glass transition region.22... 

Figure 7. Relationship between dynamic elastic modulus and temperature of 1,2-PBD (crysUdlintty 25% compared with LDPE and EVA...

FIGURE 1.5 Relationship between elastic modulus and temperature. 

Figure G.2 Relationship between elastic modulus and temperature showing the glass transition region. (Ref Baker, A.M.M., and Mead, J., Thermoplastics , Modem Plastics Handbook, McGraw-HiU, New York, 2000)...

The importance of polymer composites arises largely from the fact that such low density materials can have unusually high elastic modulus and tensile strength. Polymers have extensive applications in various fields of industry and agriculture. They are used as constructional materials or protective coatings. Exploitation of polymers is of special importance for products that may be exposed to the radiation or temperature, since the use of polymers make it possible to decrease the consumption of expensive (and, sometimes, deficient) metals and alloys, and to extent the lifetime of the whole product. 

Nonoxide fibers, such as carbides, nitrides, and carbons, are produced by high temperature chemical processes that often result in fiber lengths shorter than those of oxide fibers. Mechanical properties such as high elastic modulus and tensile strength of these materials make them excellent as reinforcements for plastics, glass, metals, and ceramics. Because these products oxidize at high temperatures, they are primarily suited for use in vacuum or inert atmospheres, but may also be used for relatively short exposures in oxidizing atmospheres above 1000°C. 

Finally, it behaves like a liquid provided the chain length is not too long. Just around T some physical properties change distinctively such as the specific volume, the expansion coefficient, the specific heat, the elastic modulus, and the dielectric constant. Determination of the temperature dependence of these quantities can thus be used to determine Tg. 

Softening as a result of micro-Brownian motion occurs in amorphous and crystalline polymers, even if they are crosslinked. However, there are characteristic differences in the temperature-dependence of mechanical properties like hardness, elastic modulus, or mechanic strength when different classes of polymers change into the molten state. In amorphous, non-crosslinked polymers, raise of temperature to values above results in a decrease of viscosity until the material starts to flow. Parallel to this softening the elastic modulus and the strength decrease (see Fig. 1.9). 

Fig. 1.9. Dependence of elastic modulus on temperature in amorphous (—) and in crystalline (—) poly(ethylene terephthalate)...

The Weissenbeig Rheogoniometer (49) is a complex dynamic viscometer that can measure elastic behavior as well as viscosity. It was the first rheometer designed to measure both shear and normal stresses and can be used for complete characterization of viscoelastic materials. Its capabilities include measurement of steady-state rotational shear within a viscosity range of 10-1 —13 mPa-s at shear rates of 10-4 — 104 s-1, of normal forces (elastic effect) exhibited by the material being sheared, and of an oscillatory shear range of 5 x 10-6 to 50 Hz, from which the elastic modulus and dynamic viscosity can be determined. A unique feature is its ability to superimpose oscillation on steady shear to provide dynamic measurements under flow conditions all measurements can be made over a wide range of temperatures (—50 to 400°C). 

In the case of PPO (Fig. 11), CDA, and CTA (Fig. 12), d decreases with increasing temperature in the region of mechanical relaxations and d" exhibits peaks in the same region. On the other hand, as illustrated in Fig. 13, d in polypeptides has a maximum and a minimum, and d" accordingly changes its sign with temperature. This maximum and minimum of d may, however, be mostly ascribed to the temperature dependence of the elastic modulus, and e shows a similar behavior to that in PPO and other polymers. 

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