Neste Oy

Borealis A/s

Jan Fors

Olli T Turunen

Johan-Fredrik Selin

Vidar Eklund

Jouko Huttunen

Leo Mandell

Kerstin Meinander

Kurt Ekman

Jouko Huttenen

Erik Thaels

Melt-spun high-strength polyethylene fibre

The carbamate content of cellulose carbamate products is reduced by treating such products with solutions of a base, which solution also contains one or several alkali metal salts, particularly carbonates, sulfates, phosphates, borates and acetates.

Cellulose carbamate products of lowered carbamate content

Non-woven fibre product

Method of lowering the carbamate content of cellulose carbamate products

The present invention concerns a cyclic process for producing an alkali solution of cellulose carbamate, for precipitating the cellulose carbamate from the alkali solution and for recovering and recycling the chemicals. The process comprises the following steps: (a) an alkali solution of cellulose carbamate is prepared by dissolving cellulose carbamate in an aqueous solution of sodium hydroxide, (b) the solution obtained in step (a) is extruded into contact with a precipitating solution containing sodium carbonate, whereby the cellulose carbamate is precipitated and can be separated from the solution, (c) into the solution obtained in step (b) carbon dioxide is conducted for transforming the sodium hydroxide into sodium carbonate, (d) the solution obtained in step (c) is treated with calcium oxide, whereby the sodium carbonate is transformed into sodium hydroxide, and calcium carbonate precipitates from the solution, (e) solution containing sodium hydroxide obtained in step (d) is returned to step (a) for dissolving cellulose carbamate, and (f) calcium carbonate obtained in step (d) is decomposed into carbon dioxide and calcium oxide and the calcium oxide is returned to step (d).

Cyclic process for producing an alkali solution of cellulose carbamate

The present invention concerns a cyclic process for producing an alkali aqueous solution of cellulose carbamate, for precipitating the cellulose carbamate from the alkali solution and for recovering and recycling the remaining chemicals. The process comprises the following steps: (a) an alkali solution of cellulose carbamate is prepared by dissolving cellulose carbamate in an aqueous solution of sodium hydroxide, (b) the solution obtained in step (a) is contacted with a precipitation aqueous solution containing sodium carbonate, whereby the cellulose carbamate is precipitated and can be removed, (c) from the solution in step (b) sodium carbonate is crystallized and is returned to the precipitant solution in step (b), and (d) mother liquor containing sodium hydroxide, obtained, i.e. remaining from, step (c), is returned to step (a) for dissolving cellulose carbamate. The crystallizing in step (c) is accomplished in two or several steps by cooling.

The invention is directed to a procedure for manufacturing cellulose carbamate by reacting isocyanic acid and cellulose at elevated temperature. In the procedure, cellulose, to which biuret or a mixture of biuret and urea has been admixed or absorbed, is heated at a temperature over 170.degree. C. for a sufficient time to produce a quantity of isocyanic acid sufficient for formation of the cellulose carbamate and for accomplishing the reaction between cellulose and isocyanic acid. The heating is accomplished at 170.degree.-250.degree. C., preferably at about 220.degree. C. The biuret quantity is 3-50% by weight of the cellulose weight and the urea quantity is 0-95% by weight of the cellulose weight.

Method of producing cellulose carbamate

The production of cellulose carbamate fibers or films by reacting cellulose with urea to form cellulose carbamate which is dissolved in alkaline solution to form a spinning solution which is spun through an acid precipitation bath is improved by subjecting the cellulose carbamate prior to dissolution in alkaline solution to irradiation of about 0.05-10 Mrad. After dissolution in alkaline solution the same may be subjected to further mild irradiation.

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Porvoo, Finland

Jan Fors