Weekly topic: 5 wealth points for those who answer correctly, 2 wealth points for participation； Question 156
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Judgment: The deformation and flow of polymers may be purely elastic and/or purely viscous. ( ) ?×?
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I don’t understand, but I guess such an expression is correct
The deformation and flow of polymers can be purely elastic and/or purely viscous. ( ) Wrong
The deformation and flow of polymers may be purely elastic and/or purely viscous X
Judgment: The deformation and flow of polymers may be purely elastic and/or purely viscous. (Correct)
The deformation and flow of polymers can be purely elastic and/or purely viscous. ( x )
The deformation and flow of polymers can be purely elastic and/or purely viscous. ( X )
The deformation and flow of polymers can be purely elastic and/or purely viscous. (Mistake)
Incorrect. Based on the viscoelastic properties of polymers, it can be seen that during processing, due to the long-chain structure of polymer molecules and the gradual nature of molecular movement, the deformation and flow of polymers cannot be purely elastic or purely viscous; rather, they are a combination of both elasticity and viscosity. When the processing temperature is higher than Tf (Tm), the polymer is in a viscous flow state, and deformation is primarily of a viscous nature. At this stage, the polymer has low viscosity and high fluidity, making it easy to shape; the dimensional stability of the resulting products (stability in terms of shape and geometric dimensions) is good. On the other hand, due to the elastic effect, the product may suffer from quality issues such as internal stress and post-deformation. When the processing temperature is within the range of Tg to Tf, the polymer is in a highly elastic state, and the deformation is primarily of a highly elastic nature. At this temperature, the polymer has a high viscosity and is not easy to flow; moreover, due to the reversibility of high-elastic deformation, products are generally rarely molded in this temperature range. On the other hand, according to the viscoelasticity formulas, as the external force σ increases and the duration of application of this force, t, increases, γV can increase more rapidly than γH; this leads to an increase in the viscous deformation component, enabling the material to undergo effective molding deformation. If the temperature is quickly reduced below the Tg temperature at this point, the material can be shaped as desired. However, such materials have poor dimensional stability and tend to deform easily when exposed to heat. Furthermore, for crystalline plastics, both secondary crystallization and post-crystallization can cause changes in the properties and dimensions of the products during use and storage, affecting their proper functioning.
The deformation and flow of polymers can be purely elastic and/or purely viscous. ( X )