A review of techniques for processing ultra‐high modulus polymers

Linear crystalline polymers can be processed to high degrees of orientation sufficient to produce dramatic increases in tensile strength and modulus. Three processes have been identified for inducing such orientation: cold drawing, hydrostatic extrusion, and solution spinning. All three processes utilize a high elongational velocity gradient in a critical temperature range to produce a high strength crystalline morphology. Although the molecular superstructure may differ in each case, the mechanical properties are similar, An increase in strength is achieved either through the creation of new tie molecules between crystal lamellae or through the creation of an extended chain crystal substructure. Temperature and molecular weight are the prime variables in determining which morphology will develop. The optimum processing temperature for many of the specific techniques is the crystalline dispersion temperature. At this temperature, the crystal structure is particularly adaptable to forming a new crystal morphology. Ul‐tradrawn polymers are more Hookean in behavior than isotropic polymers and have properties similar to steel and glass. Polyoxymethylene has been processed most closely to its theoretical strength. Polyethylene, which is the most difficult to process, has achieved the highest modulus of any common polyolefin polymer, about 7 × 10 10 Pa.