Strength Properties of Mechanical and Chemical Pulp Blends

Blending two pulps rarely gives a linear change in paper properties with the blend ratio. This is especially true with mechanical and chemical pulps. The object of this study was to investigate the interaction between a mechanical and a chemical pulp and indentify the mechanisms affecting the strength properties of paper.

It is suggested that several mechanisms are functioning simultaneously. Some of them have a positive effect, while others have a negative or neutral effect on the strength properties of the blend. A positive effect of adding kraft pulp is an increase in the number of long fibres and a consequent increase in average fibre length and in total fibre strength. The most important but less positive effects, however, are related to fibre bonding and the activity of fibres in loading. Z-tensile strength is rarely increased by the addition of kraft pulp. Bonded area per fibre and average bonding strength are not increased linearly with kraft pulp addition. The amount of mechanical fines in the blend is believed also to have an important role.