THERMOFORMING OF LIQUID-CRYSTALLINE POLYMER SHEETS

Liquid crystalline polymer (LCP) extruded sheets were further processe d by the conventional thermoforming method. The available processing t emperature range was defined through the structural, thermal, and elev ated temperature mechanical characterization of the extruded sheet. Th is temperature range was found for LCP to be quite narrow, in the prox imity of the crystal-mesophase transition. The structural changes impo sed on the LCP sheet during forming and its thermal stability were inv estigated using wide angle X-ray diffraction, mainly for the determina tion of the chain orientation distribution, DSC, and dynamic mechanica l analysis. Thermoforming onto a symmetrical male mold was found to en hance the orientation in the extrusion machine direction and even chan ge the preferred orientation in the extrusion transverse direction to orientation along the thermoforming direction. Annealing at the thermo forming temperature range results in a more ordered and thermally stab le structure accompanied by just a slight orientation loss.