How chain orientation is created

The methods by which chain orientation is created may be divided into solid-state and liquid processes. Solid-state processes involve a plastic deformation of an isotropic or weakly anisotropic solid. Glassy amorphous polymers can only be drawn to moderate strains. The polymers which can be substantially oriented are semicrystalline with deformable amorphous (T Tg) and crystalline phases. The remaining discussion in this chapter is confined to this group of polymers. Deformation can be achieved by colddrawing, extrusion or rolling (Fig. 9.17). 

Cold-drawing leads to necking, the formation of a localized zone in which the unoriented structure is transformed into a fibrous structure. The neck zone, i.e. the shoulder, travels through the specimen until the entire sample is drawn to a fibrous structure. A commonly used parameter which characterizes the extent of drawing is the draw ratio (A)  

The ability of a polymer to be drawn or extruded to an ultra-oriented fibre is dependent on several material factors  

Cold-drawing/solid-state extrusion of semicrystalline polymers involves initially the deformation of the spherulitic structure, the subsequent transformation of the spherulitic structure to a fibrillar structure and, finally, the plastic deformation of the fibrillar structure. 

Sadler and Barham (1990) also recorded the change in molecular draw ratio during the post-necking 

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