Cold-drawing

Amorphous polymers may be cold drawn only below their glass transition temperatures above this temperature, they stretch but without forming a well-defined neck region. Crystalline polymers, by contrast, can be cold drawn at all temperatures up to almost their melting points. 

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Fig. 23.10. Cold-drawing of o linear polymer the molecules ore drown out and aligned giving, after o draw ratio of about 4, o material which is much stronger in the draw direction than it was before.

The amount of movement to be taken up by the piping and any device incorporated into it can be reduced by the use of cold draw . The total amount of expansion is first calculated for each section between fixed anchor points. The pipes are left short by half this amount, and stretched cold, as by pulling up bolts at a flanged joint, so that at ambient temperature the system is stressed in one... 

Obviously, the discrepancy between the experimental data [238-241] and predictions of the theory [236,237] can be attributed to the difference of the coefficients of thermal expansion. The polymer exerts pressure on the filler, thereby masking the effect of the strength of adhesion on the modulus. The pressure on the filler may be sufficiently high. In [243] it was found, for example, that in PP, quartz particles experienced a compression force of about 100 MPa after cold drawing of the composite the force reduces to 50 MPa in the direction of drawing but at the same time increases to 300 MPa in the perpendicular direction. 

Fig. 5. Dependence of the limiting cold drawing ratio (KB) on filler concentration (

Thermoplastic polymers subjected to a continuous stress above the yield point experience the phenomenon of cold-drawing. At the yield point, the polymer forms a neck at a particular zone of the specimen. As the polymer is elongated further, so this neck region grows, as illustrated in Figure 7.7. 

Figure 7.7 Successive stages in cold-drawing of a polymer...

Figure 7.8 Stress-strain curve for polymer during cold-drawing...

Polymers <100% crystalline Regularity of structure needed for high crystallinity Stretching Cold drawing... 

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