Electrical properties of viscose-kraft fibre mixtures

ABSTRACT We used mixture handsheets of pine kraft and viscose fibres to study how density and moisture content affect the electrical properties of paper. When the viscose content increased from 0% to 70%, paper density decreased from 650 kg/m 3 to 280 kg/m 3 . The effect of density on the dielectric constant of paper was consistent with the Clausius-Mossotti relation provided that the relative humidity was low or the measurement frequency high. Under these conditions, the water absorbed by paper had little effect on the dielectric constant or dielectric loss factor. When the moisture content of paper exceeded a certain limit, the dielectric constant began to increase rapidly. Presumably this happened because some of the adsorbed water resembles bulk water in its electrical properties and therefore has a much higher dielectric constant than dry cellulose. The threshold moisture content increased with increasing measurement frequency. The viscose fibres absorbed 2-3%-units more water than the kraft fibres at any given relative humidity. In spite of this, increasing the viscose content decreased the dielectric constant of paper. This indicates that the water molecules are more closely bonded and have less freedom to rotate in viscose fibres than in kraft fibres. The dielectric loss term was practically zero at low moisture contents, approximately below the same threshold that governs the dielectric constant. The dc resistivity decreased as an exponential function of increasing moisture content, but viscose fibres gave a lower conductivity than kraft fibres at a fixed moisture content. Hence, the water absorbed by viscose fibres influenced the electrical properties of paper in all respects less than the water absorbed by kraft fibres.