The pore radius distribution in paper. Part I: The effect of formation and grammage

The pore radius distribution in paper is known to be influenced by changes in the mean grammage and formation. Experimental data are presented that confirm the established result that the standard deviation of pore radii is proportional to the mean. The data show also that this proportionality is the same for changes in grammage and formation and that, contrary to results reported in the literature, the coefficient of variation of pore radii is approximately constant. This property of the pore radius distribution confirms that, the gamma distribution is appropriate for its characterisation. We find that the mean pore radius increases with worsening formation but the effect is weak compared to that of changing grammage. Of the formation indices examined, the mean pore radius is most strongly correlated to a weighted index of floc grammage.