Preparation of cellulose fibers

A method of isolating and preparing cellulose fibers of a desired length-weighted average fiber length lc(l) from cereal straw, said method comprising the steps:

• (i) providing dewaxed straw material in aqueous suspension,
• (ii) adjusting the pH to alkaline conditions and increasing the temperature of the solution in step (i) to solubilize hemicellulose and lignin components in the aqueous phase,
• (iii) separating the material obtained in step (ii) into a solid cellulose fiber fraction and a liquid fraction comprising hemicellulose and lignin components,
• (iv) suspending said cellulose fiber fraction obtained in step (iii) in an aqueous liquid, adjusting the temperature to 65-95° C. and pH to 9-11.5, adding a bleaching agent, and keeping said cellulose fiber fraction in suspension for 60-180 minutes (T1),
• (v) subjecting the bleached material obtained in step (iv) to a wet mechanical treatment,
• (vi) obtaining a cellulose fiber product by separating the material obtained in step (v) into a bleached-refined solid cellulose fiber fraction and an aqueous bleaching liquor fraction, and
• (vii) optionally washing the bleached-refined cellulose fiber fraction in an aqueous liquid.
• wherein the length-weighted fiber length lc(l) of the cellulose fibers is >0.6 mm, and wherein said dewaxed straw material is obtained by subjecting said cereal straw to a pretreatment comprising dry mechanical treatment and enzymatic treatment.