Analysis of Modified Starch Adsorption Kinetics on Cellulose Fibers via the Modified Langmuir Adsorption Theory

The kinetics of starch adsorption on cellulose fibers is one of the most important criteria regarding the efficient application of papermaking additives due to the continuous nature of paper production and the concomitant need to determine optimum residence times. This study presents an analysis of the kinetics of modified starch adsorption onto cellulose fibers via the application of the modified Langmuir adsorption theory (i.e. the collision theory). A model based on this theory was used to describe the kinetics of starch binding, and to obtain the adsorption rate constant under different process conditions, which closely correspond to the conditions commonly encountered in industrial production of paper and board. The model predictions were then correlated with the experimental data. The adsorption of modified starch was found to increase by increasing the fiber consistency, shear forces (via stirring frequency) and the refining degree of fibers. The results also demonstrate that, at least in the studied range of process variables, the modified Langmuir adsorption theory can be applied to describe the adsorption kinetics of modified starch on cellulose fibers

Hydrolysis of Micron Alkylketene Dimert Particles Under Alkaline Conditions

The hydrolysis of alkylketene dimer (AKD) in a diluted dispersion was studied under alkaline conditions. The dispersion consisted of particles with 1 #m in diameter with the reaction product forming a porous insoluble layer on the particle surface. The shrinking core model (SCM) for particles of unchanging size is proposed for describing the overall rate of hydrolysis reaction. The model assumes a process controlled by a surface reaction on the boundary between unreacted AKD core and outer ketone layer, with no significant transport phenomena due to the small particle dimensions and porous structure of the reaction product layer on the particle surface. Under conditions studied (at pH 10.3), where the concentration of OH– ions is in excess compared to the AKD concentration and in the temperature range between 40 and 60 C, the proposed model is in good agreement with experimental data. A temperature dependence of reaction rate was tested and the apparent activation energy was calculated as well. Compared to the activation energy for reaction between AKD and cellulose, AKD hydrolysis can represent an important competitive process that significantly influences the sizing efficiency

The Effect of Enzymatic Treatments of Pulps on Fiber and Paper Properties

Biotechnological treatment of pulps provides great potential for the reduction of energy consumption and greenhouse gas emissions. In the present work, the influence of different commercial cellulases and xylanases or their mixtures on the quality of different bleached kraft pulps was investigated. The effects of enzymes on reducing sugars release and changes in fiber length were assessed for 3 different eucalyptus pulps, for a pulp consisting of a mixture of hardwoods and for softwood pulp. Despite the extremely high enzyme concentrations used in this part of the study, almost no change in fiber length was observed for pulps treated with enzyme preparations alone, while all combinations of cellulases and xylanases resulted in significant changes in average fiber length, portion of fines and reducing sugars release. Besides, vessel cell deformation was observed as a consequence of all enzymes applications. Furthermore, physical and mechanical properties of laboratory sheets made with enzymatically treated pulps were evaluated for various refining conditions and compared to those of untreated pulps. Potential energy savings up to 17 % were achieved with enzyme treatment, but some decrease in pulp quality was also observed