Springy polymer

Still further differences are observed for stress/strain diagrams of what are known as hard elastic or springy polymers. These polymeric states should exhibit a large energy-elastic component which is attributed to a special network structure (see Figure 38-10). However, electron microscopic studies do not provide any evidence for the proposed network structure. 

The ability of springy polymers to maintain their high elastic recovery down to low temperatures has led to the formulation of a large number of energy models for their deformational behaviour. Most of these mechanisms such as for example the leaf spring model or the reversible shear of lamellae between fixed tie-... 

A solution or melt composed of such stretchable molecules can be highly springy, especially in extensional flows (Tirtaatmadja and Sridhar 1993). The kinematics of an extensional flow are described in Section 1.4.1.2. From Eqs. (1-6) and (1-9), one can show that for a Newtonian fluid (for which a = 2rjD) the Trouton ratio Tr = f)u/hQ the uniaxial extensional viscosity to the zero-shear viscosity /jo is numerically equal to 3. For polymers, Tr can be much higher than this. Figure 3-2, for example, shows Tr for a... 

Rubber, in its natural state, is not durable, is very sticky, and will begin to deteriorate in a matter of days. Vulcanization (curing) of rubber is a chemical process whereby polymer molecules are linked to other polymer molecules by atomic bridges. In general, the process is brought about by heating rubber in the presence of sulfur. The end result is that the springy rubber molecules become cross-linked. This makes the final product harder, much more durable and also more resistant to chemical attack. 

Along with the increased softness and springiness of the polymers comes a reduction in melting points and glass-transition temperatures, not always welcome. These polyester variants command a higher price simply because they are more rare their raw materials are more expensive because they are not produced on the massive scale of the PET raw materials. 

Still higher degrees of chain orientation are found in the extended chain crystallites, row structures, and highly lamellar hard-elastic or springy forms of crystallizable polymers which recently have become of considerable interest. Follow-... 

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