Abstract: A system and apparatus for the measurement of absolute biaxial birefringence of plastic materials is described. The materials which must be at least partially transparent can be constituted of one or several similar or dissimilar layers. In the latter case, the birefringence of each material can be determined. The technique uses a multiwavelength white light source that provides at least two beams projected at different angles of incidence on the sample. The beams pass through first polarizers before they are incident on the sample and through second polarizers after they have passed through the sample. The beams are then directed to a detector for measuring each beam intensity or transmittance as a function of wavelength for the incident angles at different times, and are analyzed using nonlinear regressions to determine retardation. By the knowledge of the thickness of the material, the absolute biaxial birefringences are calculated for any specific wavelength.

Abstract: A method and apparatus for determining surface molecular orientation and related properties of an opaque polymeric sheet relies on the detection of relative intensity of spectral reflectance in at least one polarized beam reflected from the surface of the sheet rather than transmitted therethrough. The relative intensity is affected by the preferential orientation of the polymeric chains. The method is fast and can be applied on-line at a speed of the running sheet as high as 1000 m/s.