|Abstract:The effect of cellulose nanofibrils (CNF) on the properties of capacitor tissue paper was studied by using unbleached sulphate softwood pulp as raw material. Based on the Page equation, the effect of adding CNF and increasing beating degree on the relative bonding area (RBA) was further investigated. Finally, the influence of CNF on the electrical properties of capacitor tissue paper was researched in details. The results indicated that the addition of CNF had obvious influence on the tightness, air permeability and tensile index of capacitor tissue paper. CNF could increase the tightness and tensile strenght, and decrease the air permeability, but the effect of CNF decreased with increasing the beating degree. Based on the Page equation, the increase of the beating degree and the addition of a small amount of CNF could increase the RBA of the paper. Considering the high tightness and low air permeability requirements of capacitor tissue paper, as well as the energy saving of beating and CNF cost, the optimal condition was decided as follows: the beating degree was 80°SR, and the CNF dosage was 2%. Under this condition, the tensile index reached to 76.0 N·m/g, the tightness was 0.80 g/cm3, and the air permeability was 0.233 μm/(Pa·s); the dielectric constant was 1.21, the dielectric loss was 0.037, and the field penetration was 15.13 kV/mm under the power frequency.