Method for producing nanofibrillar cellulose
In a method for producing nanofibril cellulose, cellulose based fiber material, in which internal bonds in the cellulose fiber have been weakened by chemical modification, are supplied, for separating fibrils, through several counter-rotating rotors outwards in the radial direction with respect to the rotation axis of the rotors in such a way that the material is repeatedly subjected to shearing and impacting forces by the effect of the blades of the different counter-rotating rotors, whereby it is simultaneously fibrillated.
1. A method for producing nanofibril cellulose, wherein cellulose based fibre material, in which internal bonds in the cellulose fibre have been weakened by chemical modification, are introduced in a refining gap for separating fibrils, wherein the fibre material is supplied through several counter-rotating rotors outwards in the radial direction with respect to the rotation axis of the rotors in such a way that the material is repeatedly subjected to shear and impact forces by the effect of the blades of the different counter-rotating rotors, whereby it is simultaneously fibrillated, wherein the fibrillation is effected by means of impact energy utilizing a series of frequently repeated impacts having varying directions of action caused by several successive impacts from opposite directions, when the fibre material in suspension is repeatedly impacted by the blades of the rotors striking it from opposite directions when the blades rotate in opposite directions at a rotating speed and at a peripheral speed determined by the distance to the rotation axis of the rotors.
2. The method according to claim 1 , wherein the fibre material is supplied at a consistency of at least 1%.
3. The method according to claim 1 , wherein the fibre material to be supplied is partly gelled.
4. The method according to claim 1 , wherein the cellulose is cellulose oxidized by N-oxyl mediated oxidation.
5. The method according to claim 1 , wherein the cellulose is carboxymethylated cellulose.
6. The method according to claim 1 , wherein the cellulose is cationized cellulose.
7. The method according to claim 1 , wherein the cellulose based fibre material is processed by supplying it through the rotors until it has achieved a Brookfield viscosity of at least 1,000 mPa·s, measured at a consistency of 0.8%.
8. The method according to claim 1 , wherein the cellulose based fibre material is processed by supplying it through the rotors until it has achieved a turbidity value lower than 80 NTU, measured at a consistency of 0.1%.
9. The method according to claim 1 , wherein the cellulose based fibre material is processed by supplying it through the rotors until it has achieved a zero shear viscosity of 2,000 to 50,000 Pa·s and a yield stress of 3 to 30 Pa, measured at a consistency of 0.5%.
10. The method according to claim 1 , further comprising providing the rotors having blades which are oriented with respect to the direction of the radius at an angle towards the rotation direction.
11. The method according to claim 10 , wherein in at least one rotor, all of the blades are oriented with respect to the direction of the radius at an angle towards the rotation direction.
12. The method according to claim 10 , wherein in at least one rotor, more than one of the blades are oriented with respect to the direction of the radius at an angle towards the rotation direction.
13. The method according to claim 1 , wherein the fibre material is supplied with a gaseous medium through the rotors.
14. The method according to claim 1 , wherein the fibre material is supplied at a consistency of 2 to 4%.
15. The method according to claim 1 , wherein the cellulose based fibre material is processed by supplying it through the rotors until it has achieved a Brookfield viscosity of at least 5,000 mPa·s measured at a consistency of 0.8%.
16. The method according to claim 1 , wherein the cellulose based fibre material is processed by supplying it through the rotors until it has achieved a turbidity value of 20 to 60 NTU, measured at a consistency of 0.1%.
17. The method according to claim 1 , wherein the cellulose based fibre material is processed by supplying it through the rotors until it has achieved a zero shear viscosity of 2,000 to 50,000 Pa·s and a yield stress of 6 to 15 Pa, measured at a consistency of 0.5%.