Method for dissolving cellulose and for producing cellulose particles
The invention relates to a method for dissolving cellulose e.g. for the production of regenerated cellulose products such as films, fibers, particles and the like. In said method, the cellulose material is dissolved using an enzymatic treatment, followed by a base treatment. The invention is also directed to a method for producing cellulose particles wherein cellulose dissolved as described above is sprayed or mixed into a regenerating solution for precipitating cellulose particles. Moreover, the invention relates to the use of said cellulose particles produced with this method as a filler and/or coating pigment of paper and board. The invention is also directed to methods for producing and coating paper and board.
1. Method for dissolving cellulose, said method consisting of the steps of
a) preparing an aqueous suspension of cellulose having a cellulose content of at least 0.1% by weight;
b) adjusting the pH value of the suspension obtained in step a) to a value of from 3 to 7;
c) adding to the suspension an enzyme with endoglucanase activity in an amount wherein the endoglucanase activity is from 20 to 2000×10 3 IU/kg of dry pulp to obtain a mixture;
d) heating the mixture obtained in step c) at a temperature between 40 and 65° C. until the degree of polymerization of the cellulose is not lower than a value of 100;
e) adding an alkali or alkaline earth metal hydroxide in an amount above 15% by weight to the mixture obtained in step d); and
f) heating the mixture obtained in step e) at a temperature between 15 and 50° C., to obtain a cellulose solution comprising at least 50% dissolved cellulose; and, optionally,
g) removing air and solids from the cellulose solution.
2. Method according to claim 1 , wherein the cellulose is ground cellulose.
3. Method according to claim 1 , wherein the alkali or alkaline earth metal hydroxide is NaOH in an amount ranging from 15.5 to 30%, by weight.
4. Method of obtaining precipitated cellulose particles, said method consisting of the steps of
a) preparing an aqueous suspension of cellulose having a cellulose content of at least 0.1% by weight;
b) adjusting the pH value of the suspension obtained in step a) to a value of from 3 to 7;
c) adding to the suspension an enzyme with endoglucanase activity in an amount wherein the endoglucanase activity is from 20 to 2000×10 3 IU/kg of dry pulp to obtain a mixture;
d) heating the mixture obtained in step c) at a temperature between 40 and 65° C. until the degree of polymerization of the cellulose is not lower than a value of 100;
e) adding an alkali or alkaline earth metal hydroxide in an amount above 15% by weight to the mixture obtained in step d);
f) heating the mixture obtained in step e) at a temperature between 15 and 50° C., to obtain a cellulose solution comprising at least 50% dissolved cellulose; and
g) spraying or mixing the cellulose solution obtained in step f) into an acid solution to obtain a suspension containing precipitated cellulose particles, and, optionally, subjecting the precipitated cellulose particles in the suspension to crosslinking or derivatization; and, optionally,
h) washing and/or drying the precipitated cellulose particles of step g).
5. Method according to claim 4 , wherein cellulose content of the cellulose solution obtained in step g), and droplet size in case of spraying, or mixing speed in case of mixing are selected such that the obtained precipitated cellulose particles have particle sizes ranging between 0.05 and 10 μm.
6. Method according to claim 4 , wherein the crosslinking is achieved by adding 5 moles of formaldehyde per one mole of glucose units to the suspension containing precipitated cellulose particles and heating the resulting suspension at 40 to 60° C. to obtain precipitated crosslinked cellulose particles.