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Orientation of Polymers

المؤلف:  A. Ravve

المصدر:  Principles of Polymer Chemistry

الجزء والصفحة:  ص47-48

2026-01-12

451

Orientation of Polymers

There is no preferred direction or arrangement in the manner in which the macromolecules align themselves in a polymeric mass during crystallization. If, however, after crystallization an external stress is applied, the crystalline material undergoes a rearrangement. From the X-ray diffraction patter it is surmised that the chains realign themselves in the direction of the applied stress. Polymeric films and fibers usually show considerable increase in strength in the direction of that stress. Oriented fibers are considerably stronger along their length then perpendicularly to them. Generally, if the degree of crystallinity in crystalline polymers is well developed prior to the drawing, the process does not change the amount of crystallinity appreciably. The orientation in the direction of applied stress occurs also in amorphous materials. The amorphous polymers, like the crystalline ones, also exhibit increased strength in the direction of orientation. If there is a small amount of crystallinity in polymers, the crystallinity often increases as a result of cold drawing. Orientation of fibers and films is generally carried out above the glass transition temperature. At the sametime, there usually is a desired limit on T_m. Thus it is preferred that the crystalline melting temperature does not exceed 300C.