A method for producing fibrillar fines directly from wood

For economic and ecological reasons there is a strong demand to reduce grammage of cartons and printing papers. The challenge is to maintain strength, bending stiffness and opacity. Previous studies have shown that in carton boards the bulk of the middle layer can be raised up to 30%without strength losses by binding stiff fibers together with fines separated from chemical or mechanical pulps. Such effects would be difficult to obtain by adjustments in refining. Furthermore, mechanical pulp fines have high light scattering and strong synergy with fibers with respect to tensile strength. A separate production of fines would provide innovative options for furnish preparation, in order to tailor product properties, to reduce mainline mechanical pulping energy demand, and to reduce kraft pulp usage. We have developed a novel method to produce fibrillar fines directly from moist wood. The method applies traditional wood grinder machine equipped with a novel patented stone surface. The fines content (P200) of such grinder pit pulp is typically 80-95 %. The quality of the fines can be adjusted with the structure of the grinding stone surface and the production rate. The first trials yielded in hand sheets having tensile index from 40 to 60 Nm/g and light scattering coefficient from 54 to 74 m2/kg. For comparison, the fines separated from a well refined TMP-reject had tensile index 50 Nm/g and light scattering coefficient 76 m2/kg. This presentation introduces the novel method and highlights the main observations from the first trials. The fines are expected to be suitable for strengthening paper and board, as well as for organic filler with positive strengthening effect. In addition, wood fines could be an interesting material for wood containing filaments used in 3D-printing.