(EN) Minced lignocellulose, such as wood, straw, bamboos, bagasse or any other structured vegetal material, is treated in a discontinuous or continuous process. The process consists in boiling this material in an acidified mixture of solvents in an aqueous phase. This mixture of solvents contains water in a proportion of 30 to 70 parts and an organic solvent in a proportion of 70 to 30 parts. The organic solvent consists of either an alcohol of light molecular weight, or a ketone of light molecular weight; it must be easily evaporable and soluble in water. The pH of the medium is adjusted to a pH from 3.5 to 1.7 by adding a catalytic compound selected within the group of the strong acids: hydrochloric, nitric and phosphoric; within the group of these strong acids neutralized by their neutral salts; within the group of the following organic acids: oxalic, maleic, o-phthalic, l-malic, succinic, nicotinic, salicylic and trifluoracetic. The boiling temperatures range between 160 and 210`C, preferably between 180 and 200`C. After three minutes at the minimum, we obtain the separation of the lignin and the hydrolysis of the hemicelluloses dissolved; after that, the fibres are easily dispersible while forming a pulp. By proceeding to a mechanical refining at a high pressure, a high density thermomechanical pulp is obtained after a shorter boiling time. With the neutralized acids, as well as with the organic acids, particularly with the oxalic acid, we can obtain a fibre with a high degree of polymerization. The lignin is obtained as a precipitate which separates from the liquid; the liquid solvent, usually ethanol or acetone, is evaporated; then the drained lignin is redissolved in the minimal quantity of acetone; a new precipitation with an excess of water allows to obtain the lignin in the form of a slightly coloured powder. A prolonged boiling dehydrates and disaggregates the sugars; by the strong acids action, takes place the formation of light molecular weight or microcristalline cellulose, glucose or organic acids, methanol and furfuralic compounds.
