Thermoplastic cold drawning

There are a variety of well known methods used to orient materials, as reviewed by Holliday and Ward [21], Ciferri and Ward [22] and Hay [23]. Ductile thermoplastics can be cold drawn near room temperature whereas thermoplastics which are brittle at room temperature can only be drawn at elevated temperatures. Thermosets are oriented by drawing the precursor polymer prior to crosslinking, resulting in an irreversible orientation. Rubbers can be reversibly elongated... 

The cold drawing of thermoplastic polymers can drastically improve mechanical properties and is often accomplished to create favorable properties for certain applications. A case in point is the biaxial stretching of polycarbonate for use in aircraft canopies. The ability to be drawn (either cold or hot) is of great use commercially. For example, PET (polyethylene terephthalate) which is often used for soft drink bottles is first produced by injection molding as a small test tube size object. Before filling with liquid, the material is heated and blown as large as the standard 2 liter soft drink container. 

Filaments of thermoplastics are prepared by two methods. If the thermoplastic is stable in the molten state, it may be passed through tiny pores in a dye called a spinneret and then cooled. For less stable thermoplastics, the polymer is dissolved in a volatile solvent and forced through the spinneret. The solvent evaporates and a filament precipitates. Regardless of the method of formation, the fiber is then drawn out to several times its length after it has cooled. The cold drawing orients the molecules along the axis of the fiber. The resultant intermolecular forces between polymer molecules increase the tensile strength of the fiber. 

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