紫外線照射処理による高収率パルプ含有シートの物性値変化

Abstract

Mechanical and optical properties of paper prepared from the mixture of bleached kraft pulp and high-yield pulp (GP) were examined in order to elucidate the influence of lignin in paper on those properties by UV irradiation. Sheet density, tensile strength, Young's modulus and double folds decrease with increase in GP content. The Kubelka-Munk equation was found to be adaptable well on the optical properties such as printing opacities, scattering coefficients and absorption coefficients of those sheets with different mixing ratios.Changes of tensile strength, Young's modulus, double folds, wet tensile strength, water absorption, brightness and K/S values of those sheets treated by UV light were studied. Especially, the strength of double folds decrease drastically by UV treatments, although GP content, i.e. the lignin content in sheets, does not accelerate the decrease in double folds. On the other hand, GP content has strong influence on discoloration of the sheets treated by UV light. Namely, the rate constant of discoloration by UV light increases linearly up to 15% of GP content. As described in the previous paper, we have found that the decrease in double folds is stemmed from depolymerization of cellulose chains by UV light. Thus, the results obtained in this work indicate that reactive groups formed from lignin by UV irradiation in the presence of oxygen, such as radicals, peroxides, singlet molecular oxygen, superoxide anions, etc, does not take part in depolymerization reactions of cellulose.