The Results of the Study of the Relationship between Viscosity and Mechanical Strength of Bleached Hardwood Kraft Pulp

An assessment has been made of the relationship between viscosity and mechanical strength of industrial samples of bleached hardwood kraft pulp. To produce this type of semi-finished product, birch and aspen wood has been used, which has been harvested in the Northwestern region of the Russian Federation. The viscosity of a solution of high-molecular polymers provides an idea of the average length of the fibers and, accordingly, their degree of destruction. In turn, the mechanical properties of the fibrous semi-finished product and the strength of the products made from it largely depend on the length of the fiber. Since it takes no more than 2 hours to determine the viscosity of a solution of high-molecular polymers, and 8–10 hours to obtain standard mechanical strength characteristics, viscosity analysis can be considered an express method that provides information on the mechanical strength of a semi-finished product. In this work, the ISO 5351:2010 international standard in cupriethylenediamine solution has been used to analyze the viscosity of the semi-finished product. High values of mechanical strength characteristics have been detected for industrial samples of bleached hardwood kraft pulp with a viscosity of more than 800 ml/g. For pulp samples, a correlation has been established only between the number of double folds and viscosity. Further research has been carried out on samples of bleached hardwood kraft pulp with different degrees of fiber destruction, which have been produced with varying the parameters of sodium hypochlorite treatment. The results have made it possible to establish a range of critical viscosity values for bleached hardwood kraft pulp, which has amounted to 600...700 ml/g, and a polynomial relationship between tear resistance, breaking length, a number of double folds and viscosity with a high confidence coefficient of data approximation of no less than 0.89. It has been shown that viscosity can become an analytical tool in the express diagnostics of the mechanical strength of a fibrous semi-finished product at the intermediate stages of production of bleached hardwood kraft pulp and in quality control of the ready-made semi-finished product.