Method of preparing a sizing boost additive

A method of preparing a sizing boost additive, comprising the steps of:

• I) combining a lignin oil and an aqueous solution of gelatinized cationic polysaccharide, and optionally water, to obtain a lignin/polysaccharide blend, wherein the lignin oil is obtained by base catalyzed depolymerization of lignin;
• and wherein the gelatinized cationic polysaccharide is prepared by cooking dry cationic polysaccharide in water until completely gelatinized;
• and wherein the lignin oil and the cationic polysaccharide are included in the lignin/polysaccharide blend so that a weight ratio of lignin oil:polysaccharide in the blend is 1:0.5-2, where the weight of the polysaccharide is the weight of dry polysaccharide added in preparation of the aqueous solution of gelatinized cationic polysaccharide;
• and the combined weight of lignin and polysaccharide is 1-10 wt-% based on the total weight of the resulting blend;
• followed by
• II) mixing the lignin/polysaccharide blend at a temperature of 40-100° C. until the blend has changed color from grey-white to brown.