3. Orientation phenomena

The flow of molten polymer causes a greater or lesser degree of orientation of the macromolecules. After solidification, this orientation may be partly fixed in the amorphous phase, depending on cooling conditions, leading to its partial or total relaxation. Moreover, crystallization from an oriented molten state can generate anisotropic morphologies, in which the spatial distribution of crystals is no longer random as in spherulite (figure 9 ). Thermal gradient and surface sprouting can also produce anisotropic morphologies, comets and transcrystalline zones, respectively. Thus, one of the effects of shaping is to lead to preferred...