Crystallinity change upon drawing

In addition to the orientational information gained from the analysis of observed dichroic ratios, Glenz and Peterlin s results have also yielded valuable information concerning changes in the degree of crystallinity and chain conformation upon drawing. The latter information comes from the evaluation of the so-called reduced structural factor (A ) given by... 

When the draw ratio of the fiber is extended from 1 to 6 times, the heat of fusion increases from 1.88 to 2.5 kJ/mol, and a secondary endotherm appears at 147°C the primary endotherm is at 156°C (Fig. 4). These changes are reversible upon relaxation of the fiber. The appearance of the secondary endotherm is interpreted as a disruption in the crystalline phase at high threadline stress, whereas the increase in the heat of fusion reflects the formation of dipole-dipole bonds upon orientation of the polymer chains in the amorphous region of the fiber. 

Another important point is the phase of the material. The ease of deterrnining structures of crystalline materials has changed the viewpoint of chemistry, so that often the structure and behavior of a compound examined in the solid state are thought also to be representative of the liquid, solution and gas phases. This is clearly not the case. There are always differences to be found between structures of the same material across the different phases. Crystalline phases are clearly the most relevant for typical applications in materials chemistry, but for chemical reactions of molecular compounds it is the solution phase that is most important. So we should not rely solely upon solid-state diffraction measurements to derive the structures of molecular compounds, but should also draw upon data available from chemical, spectroscopic, diffraction and other methods from other phases in order to get a better understanding of the structural form(s) of the molecule we are actually using. 

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