Mesophase low temperature fibers

Keywords X-ray, powder pattern, fiber pattern, WAXS, SAXS, isotactic, a-form, p-form, y-form, mesophase, lamellar thickness, crystallinity, syndiotactic, orthorhombic form (high temperature, low temperature), triclinic form. 

From Mesophase Pitch. Coal tar pitch (a mixture of many species of hydrocarbons and heterocyclic molecules) is heated for up to 40 h at approximately 450°C (800°F), forming a viscous liquid with a high degree of molecular order known as mesophase (a form of Uquid crystal). The mesophase is then rapidly spun through small orifices (spinnerets), aligning the mesophase molecules along the fiber axis. The fibers are thermoset at relatively low temperatures and then heated at 1700-3000°C (3100-5400°F). 

The precursor is melted in an extruder which pumps the melt into a die head equipped with a filter and a multihole spinneret [5-6] [24]. As the precursor fibers exit the spinneret holes they cool and solidify, and are drawn before windup. The window for achieving successful and continuous fiber formations is small. The temperature dependence of the viscosity is large and the failure strength of the mesophase pitch fibers is low (30-40 MPa). Thus, the extrusion temperature must be precisely controlled. 

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