Effect of fiber fractionation on refinability and strength properties of wheat straw soda-aq pulp

Beating studies for straw-based pulps showed that its freeness decreases faster than wood pulps. In other words, wheat straw requires considerably lower refining energy than wood-based furnish to reach the same level of freeness, due to higher content of primary fines and thinner fibers at lower cell wall thickness. The effect of fiber fractionation and then separate refining of long fiber fraction on refinability and strength properties of wheat straw soda-AQ pulp are discussed in this paper. Thus, soda-AQ pulp of wheat straw was fractionated, using a modified Bauer Mc-Nett fiber classifier having only a 50 mesh screen, into a longfiber fraction (reject) and a short-fiber fraction (accept) at two different mass split ratios of LFR80 (80:20) and LFR60 (60:40). The refined longfiber fractions were re-mixed with the related unrefined short fiber fraction, and their properties were determined in comparison with the control sample. The air resistance, tensile, and burst indices were improved by the fractionation treatments, especially in the case of LFR80, due to higher applied refining energy, which led to higher fiber to fiber bonding. By fractionation of wheat straw pulp and separate refining of longer fiber fraction, it is possible to increase PFI revolutions or refining energy to develop inter-fiber bonding strength without decreasing the tear index.