What are the mechanical properties of polymers

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Mechanical behavior - module temperature curves

With the help of module-temperature curves, the state ranges of polymers can be represented. A distinction must be made between thermoplastics, elastomers and thermosets.

Thermoplastics and elastomers are in the glassy state below the glass transition temperature. Here the macromolecules are fixed in their mutual position, only one oscillation around the rest position is possible. In the area of ​​the glass transition temperature, the molecules in the amorphous phase become mobile by changing the place of entire chain segments. The transition to the liquid area does not occur spontaneously. Rather, there is a so-called main softening range over a span of around 50 K. For amorphous thermoplastics and elastomers, the modulus of elasticity decreases by two to three powers of ten in this transition area. In the case of amorphous thermoplastics, this main softening range is followed by the quasi-rubber-elastic behavior, and in the case of elastomers, the rubber-elastic behavior.

The processing or flow area lies above the temperature range of the quasi-rubber-elastic area. In the case of elastomers, the rubber-elastic area is followed by thermal decomposition.

Depending on the proportion of the amorphous phase, semi-crystalline polymers have a small module level when the glass transition temperature is reached, followed by a horny state in which the embedded crystallites have a stiffening effect. The body keeps its shape. If the temperature is increased further, the material changes into the viscous melt with a sharp drop in the module.