THE KUBELKA-MUNK COEFFICIENTS OF FILLERS

A non-linear relationship exists between the light-scattering coeffici ent of filled sheets and filler content, this relationship being compa tible with a light-scattering coefficient of the filler itself which d ecreases linearly with filler content. It is proposed that the reducti on in light-scattering efficiency is due to the formation of aggregate s of filler on the fibre surface. These aggregates arise, not because of flocculation of the filler but because the deposition of filler is a random process. From a consideration of the statistics of random dep osition, a simple modification of the additive law for light-scatterin g coefficients is suggested for application to mixtures of fillers and fibres. The constants characterizing scattering behaviour are given f or a number of common fillers and are supplemented by values of the li ght-absorption coefficients for the same materials.