Mechanical pulp fines: Effect of particle size and shape

The effect of different types of particles on the properties of the whole-fines fraction and on the paper properties was studied. The purpose of the investigation was to classify the fines particles into two different categories : fibrils and flakes. The fibril fraction consists of fibrillar material, i.e., ribbons, fibrils, and thin lamellae particles. The flake fraction consists of flake-like material, i.e., fiber wall fragments, thick lamellae, and ray cells. An advanced image analysis method was used to characterize the properties of fibrils and flakes. The results demonstrate that the fibril and flake fractions have distinctly different characteristics and effects on sheet properties. The fibrils are strongly responsible for the strength properties, while the flakes improve light scattering. Generally, the smaller the particle size, the higher the sheet density and strength. It is proposed that the amount of fibrillar material is an important basic property of mechanical pulp fines. Application : this study demonstrates how the papermaking properties of mechanical pulp fines are determined. The results can be used to control fines quality and ultimately pulp and paper quality.