MD CD REFLECTANCE ANISOTROPY IN MACHINE-MADE PAPERS OBSERVED WITH THE45/0 REFLECTANCE GEOMETRY/

The directional reflectance in many machine-made papers is known to be dependent on sample orientation. This dependence was examined for the widely used 45/0 reflectance geometry. Reflectance anisotropy was mea sured as the ratio of the machine- to cross-machine direction reflecta nces. Light reflected from within the sheet was found to be sufficient ly diffuse and contributed little to the reflectance anisotropy. Howev er the specular part of the reflected light was found to be dependent on sample orientation. We attribute the specular component to the refl ectance of light occurring at facet planes of the fibre edge. The refl ectance anisotropy was found to be linearly related to the MD/CD stiff ness ratio.