Structures and tensile properties of a magnetically and mechanically oriented liquid crystalline copolyester, Xydar

A wholly aromatic thermotropic liquid crystalline copolyester consisting of p-hydroxybenzoic acid, terephthalic acid, and p,p'-biphenol, one from the Xydar series, was aligned by means of magnetic fields and mechanical methods. The tensile properties of these samples were different depending on the orientation degree and the means used for the orientation. Magnetically oriented films exhibited lower elastic modulus and ultimate tensile strength than mechanically oriented films of the same orientation degree, but the elastic modulus of magnetically oriented films was comparable to that of the mechanically stretched films of lower orientation degrees. This suggests that magnetic fields could be used as an additional means of controlling the orientation of thermotropic liquid crystalline copolyesters during molding or film fabrication. The difference in tensile properties was discussed in relation to the oriented structures examined by scanning electron microscopy, polarizing microscopy, and wide angle X-ray measurement.