Orientation measurements from the surfaces of injection moulded plaques of thermotropic liquid crystalline polymer using normal incidence specular reflection

Abstract

This article reviews the application of FTIR methods (attenuated total reflection, specular reflectance and photoacoustic detection) to orientation measurements of polymers, and to thermotropic liquid crystalline polymers (LCPs) in particular. FTIR specular reflectance dichroism studies are then applied to determine molecular orientation from the surface of injection mouldings (square plaques with dimensions 60×60×2mm, unfilled polymer; 60×60×4mm, filled polymer) of a LC copolyester based on hydroxybenzoic acid, terephthalic acid, 4,4′-oxydibenzoic acid and chlorohydroquinone. The effects of the melt temperature (265–315°C) and of the addition of fillers (mica, silica or glass beads) on the development of orientation are investigated. Scans are presented showing the quality of orientation with respect to orthogonal axes. The orientation profiles are related to the flow behaviour of LCPs during processing (spreading radial flow at the entrance to the mould, converging flow in the first half of the mould and fountain flow). At some positions, orientation minima occur which assume parabolic profiles and are associated with an arc-like band-pattern consisting of dark and brownish white bands at the surface of the mould. The light-coloured arcs correspond to regions in which the chains are not planar and tend to lie with their long axis in the thickness direction.