High efficiency production of nanofibrillated cellulose
View Patent ↗A scalable, energy efficient process for preparing cellulose nanofibers employs treating the cellulosic material with a first mechanical refiner with plates having a configuration of blades separated by grooves, and subsequently treating the material with a second mechanical refiner with plates having a configuration of blades separated by grooves different than the first refiner. The plate configurations and treatment operations are selected such that the first refiner produces a first specific edge loading (SEL) that is greater than the SEL of the second refiner, by as much as 2-50 fold. An exemplary high first SEL may be in the range of 1.5 to 8 J/m. Paper products made with about 2% to about 30% cellulose nanofibers having a length from about 0.2 mm to about 0.5 mm, preferably from 0.2 mm to about 0.4 mm have improved properties.
1. A process for forming cellulose nanofibers from a cellulosic material, comprising:
treating the cellulosic material with a first mechanical refiner having stator and rotor plates having a configuration of blades separated by grooves, the first refiner producing a first specific edge loading (SEL); and
subsequently treating the cellulosic material with a second mechanical refiner having stator and rotor plates having a configuration of blades separated by grooves that is different than the configuration of the first refiner, the second refiner producing a second SEL;
wherein first SEL is greater than 1.0 J/m and is 2 to 40 times greater than the second SEL, to obtain cellulose nanofibers.
2. The process of claim 1 wherein the first SEL is in the range from about 1.5 to about 8.0 J/m.
3. The process of claim 1 wherein the configuration of blades separated by grooves on the plates of the first refiner produces a cutting edge length (CEL) that is lower than the CEL produced by the configuration of blades separated by grooves on the plates of the second refiner.
4. The process of claim 3 wherein the blades of the first refiner have widths greater than or equal to 3.0 mm, and the blades of the second refiner have widths equal to or less than 2.0 mm.
5. The process of claim 1 wherein the ratio of blade:groove widths of the plates of the first refiner is greater than the ratio of blade:groove widths of the plates of the second refiner.
6. The process of claim 5 wherein the ratio of blade:groove widths of the plates of the first refiner is 1.0 or greater, and the ratio of blade:groove widths of the plates of the second refiner is 1.0 or less.
7. The process of claim 1 wherein the treatment by the first refiner is carried out at a lower rpm than the treatment by the second refiner.
8. The process of claim 1 wherein the treatment by the second refiner is continued until the cellulose nanofibers have a fiber length from about 0.2 mm to about 0.5 mm.
9. The process of claim 1 wherein the first SEL is in the range from about 2.0 to about 5.0 J/m.
10. The process of claim 1 wherein the first SEL is 5 to 30 times higher than the second SEL.
11. The process of claim 1 wherein the first SEL is 6 to 20 times higher than the second SEL.
12. The process of claim 1 wherein the treatment by the second refiner is continued until an endpoint of at least 75% fines.