Microfibrillated cellulose

Abstract

The present invention relates to microfibrillated cellulose (“MFC”), in particular to microfibrillated cellulose, which is morphologically different from conventional MFC known in the art and/or which provides improved water retention properties and/or improved rheological properties, in particular increased zero shear viscosity, ηo, (also known as: “viscosity at rest”, i.e. viscosity in the absence of shear forces), in solution, in particular in polyethylene glycol (PEG) as solvent, vis-a-vis conventional MFC as known in the art.

1 . Process for the manufacture of microfibrillated cellulose, said process comprising at least the following steps:
 a) subjecting a cellulose pulp to at least one mechanical pretreatment step;   b) subjecting the mechanically pretreated cellulose pulp of step (a) to a homogenizing step, which results in fibrils and fibril bundles of reduced length and diameter vis-à-vis the cellulose fibers present in the mechanically pretreated cellulose pulp of step (a), said step (b) resulting in microfibrillated cellulose;   characterized in that the homogenizing step (b) involves compressing the cellulose pulp from step (a) and subjecting the cellulose pulp to a pressure drop, by expanding the cellulose through at least one orifice, providing said pressure drop between a volume segment, optionally a chamber, that is located upstream of said orifice, and another volume segment, optionally a chamber, that is located downstream of said orifice, area,   wherein said pressure drop is at least 1000 bar, optionally more than 2000 bar, optionally more than 2500 bar, further optionally more than 3000 bar, wherein the residence time of a given flow segment comprising the cellulose fibers in the at least one orifice is less than 20 microseconds, optionally less than 10 microseconds, more optionally less than 2 microseconds, and   wherein the cellulose fibrils are subjected to a turbulent flow regime in said volume segment, optionally a chamber, that is located downstream of said orifice.   
     
     
         2 . Homogenizer for use in the manufacture of microfibrillated cellulose, wherein said homogenizer at least comprises the following components:
 at least one volume segment, optionally a chamber, which is located upstream of an orifice,   at least one orifice,   at least one volume segment, optionally at least one chamber, which is located downstream of the orifice, in which the microfibrillated cellulose is subjected to a turbulent flow regime,   wherein said homogenizer is suitable to subject a cellulose slurry to a pressure drop between the volume segment located upstream of said orifice, and the other volume segment located downstream of said orifice, wherein said pressure drop is at least 1000 bar, optionally more than 2000 bar, optionally more than 2500 bar, further optionally more than 3000 bar, wherein the residence time of a given flow segment comprising the cellulose fibers in the at least one orifice is less than 20 microseconds, optionally less than 10 microseconds, more optionally less than 2 microseconds.   
     
     
         3 . The process according to  claim 1 , characterized in that the diameter of the orifice is from 100 μm to 700 μm, optionally from 200 μm to 500 μm. 
     
     
         4 .- 10 . (canceled) 
     
     
         11 . The homogenizer for use in the manufacture of microfibrillated cellulose according to  claim 2 , characterized in that the diameter of the orifice is from 100 μm to 700 μm, optionally from 200 μm to 500 μm. 
     
     
         12 . The process of  claim 1 , wherein the microfibrillated cellulose has a length and diameter of its cellulose fibrils and fibril bundles that are reduced vis-à-vis the respective length and diameter of the cellulose fibers and fiber bundles making up the cellulose that was used as a starting product,
 wherein at least a fraction of the fibril bundles and individual fibrils of the microfibrillated cellulose, having reduced length and diameter, has bifurcations on at least one end of the main fibrils into secondary fibrils, optionally bifurcations into three or more secondary fibrils, further optionally bifurcations into four or five or more secondary fibrils, wherein said secondary fibrils have a smaller diameter than the non-bifurcated main fibril, and 
 wherein the number of said bifurcated ends of fibrils/fibril bundles is at least 60 bifurcated ends of fibrils per mm 2 , as measured in accordance with the optical light microscopy method as described herein, at a magnification of 40 times, wherein individual fibrils or fibril bundles with a cross-sectional diameter larger than 200 nm are studied by said optical microscopy, and as measured at a solids content of 0.17% of microfibrillated cellulose in water, optionally at least 80 bifurcated ends of fibrils per mm 2 , further optionally at least 100 bifurcated ends of fibrils per mm 2 . 
 
     
     
         13 . The homogenizer for use in the manufacture of microfibrillated cellulose according to  claim 2 , wherein the microfibrillated cellulose has a length and diameter of its cellulose fibrils and fibril bundles that are reduced vis-à-vis the respective length and diameter of the cellulose fibers and fiber bundles making up the cellulose that was used as a starting product,
 wherein at least a fraction of the fibril bundles and individual fibrils of the microfibrillated cellulose, having reduced length and diameter, has bifurcations on at least one end of the main fibrils into secondary fibrils, optionally bifurcations into three or more secondary fibrils, further optionally bifurcations into four or five or more secondary fibrils, wherein said secondary fibrils have a smaller diameter than the non-bifurcated main fibril, and 
 wherein the number of said bifurcated ends of fibrils/fibril bundles is at least 60 bifurcated ends of fibrils per mm 2 , as measured in accordance with the optical light microscopy method as described herein, at a magnification of 40 times, wherein individual fibrils or fibril bundles with a cross-sectional diameter larger than 200 nm are studied by said optical microscopy, and as measured at a solids content of 0.17% of microfibrillated cellulose in water, optionally at least 80 bifurcated ends of fibrils per mm 2 , further optionally at least 100 bifurcated ends of fibrils per mm 2 . 
 
     
     
         14 . The process of  claim 1 , wherein the microfibrillated cellulose has a length and diameter of its cellulose fibrils and fibril bundles that are reduced vis-à-vis the respective length and diameter of the cellulose fibers and fiber bundles making up the cellulose that was used as a starting product;
 wherein at least a fraction of the fibril bundles and individual fibrils of the microfibrillated cellulose, having reduced length and diameter, has multiple bifurcations on at least one end of the main fibril into secondary fibrils, optionally bifurcations into three or more or four or five or more secondary fibrils, wherein said secondary fibrils have a smaller diameter than the non-bifurcated main fibril, 
 wherein the ratio of the number of such bifurcated ends of fibrils/fibril bundles of the microfibrillated cellulose relative to the number of such bifurcated ends of fibrils/fibril bundles of a reference microfibrillated cellulose, and 
 wherein the step of homogenizing the reference microfibrillated cellulose comprises passing the mechanically pretreated cellulose pulp of step (a) through a 400 μm channel and a 100 μm channel at a pressure of 2000 bar is at least 5, optionally at least 10, further optionally at least 15, wherein the number of bifurcated ends of fibrils/fibril bundles is measured by optical light microscopy at a magnification of 40 times, wherein individual fibrils or fibril bundles with a cross-sectional diameter larger than 200 nm are studied by said optical microscopy, and as measured at a solids content of 0.17% of microfibrillated cellulose in water. 
 
     
     
         15 . The homogenizer for use in the manufacture of microfibrillated cellulose according to  claim 2 , wherein the microfibrillated cellulose has a length and diameter of its cellulose fibrils and fibril bundles that are reduced vis-à-vis the respective length and diameter of the cellulose fibers and fiber bundles making up the cellulose that was used as a starting product;
 wherein at least a fraction of the fibril bundles and individual fibrils of the microfibrillated cellulose, having reduced length and diameter, has multiple bifurcations on at least one end of the main fibril into secondary fibrils, optionally bifurcations into three or more or four or five or more secondary fibrils, wherein said secondary fibrils have a smaller diameter than the non-bifurcated main fibril, 
 wherein the ratio of the number of such bifurcated ends of fibrils/fibril bundles of the microfibrillated cellulose relative to the number of such bifurcated ends of fibrils/fibril bundles of a reference microfibrillated cellulose, and 
 wherein the step of homogenizing the reference microfibrillated cellulose comprises passing the mechanically pretreated cellulose pulp of step (a) through a 400 μm channel and a 100 μm channel at a pressure of 2000 bar is at least 5, optionally at least 10, further optionally at least 15, wherein the number of bifurcated ends of fibrils/fibril bundles is measured by optical light microscopy at a magnification of 40 times, wherein individual fibrils or fibril bundles with a cross-sectional diameter larger than 200 nm are studied by said optical microscopy, and as measured at a solids content of 0.17% of microfibrillated cellulose in water. 
 
     
     
         16 . The process of  claim 1 , wherein a length and a diameter of the fibrils and fibril bundles of the microfibrillated cellulose is reduced vis-à-vis the respective length and diameter of the cellulose fibers and fiber bundles making up the cellulose that was used a starting product;
 wherein the dispersion of said microfibrillated cellulose in polyethylene glycol (PEG 400) has a zero shear viscosity, η 0 , of at least 5000 Pa·s, optionally at least 6000 Pa·s, further optionally at least 7000 Pa·s, as measured at a solids content of the MFC of 0.65% and 35% H 2 O. 
 
     
     
         17 . The homogenizer for use in the manufacture of microfibrillated cellulose according to  claim 2 , wherein a length and a diameter of the fibrils and fibril bundles of the microfibrillated cellulose is reduced vis-à-vis the respective length and diameter of the cellulose fibers and fiber bundles making up the cellulose that was used a starting product;
 wherein the dispersion of said microfibrillated cellulose in polyethylene glycol (PEG 400) has a zero shear viscosity, η 0 , of at least 5000 Pa·s, optionally at least 6000 Pa·s, further optionally at least 7000 Pa·s, as measured at a solids content of the MFC of 0.65% and 35% H 2 O. 
 
     
     
         18 . The process of  claim 1 , wherein a G′ lin  value of a gel-like dispersion comprising the microfibrillated cellulose in polyethylene glycol (PEG 400) is more than 250 Pa, optionally more than 350 Pa, as measured at a solids content of the MFC of 0.65% and 35% H 2 O. 
     
     
         19 . The homogenizer for use in the manufacture of microfibrillated cellulose according to  claim 2 , wherein a G′ lin  value of a gel-like dispersion comprising the microfibrillated cellulose in polyethylene glycol (PEG 400) is more than 250 Pa, optionally more than 350 Pa, as measured at a solids content of the MFC of 0.65% and 35% H 2 O. 
     
     
         20 . The process of  claim 1 , wherein the microfibrillated cellulose has a water retention, of at least 80, optionally at least 100, wherein the water retention is measured by diluting the MFC samples to a 0.3% solids content in water and then centrifuging the samples at 1000 G for 15 minutes, wherein the clear water phase is separated from the sediment and the sediment is weighed, wherein the water holding capacity is given as (mV/mT)−1, where mV is the weight of the wet sediment and mT is the weight of dry MFC analyzed. 
     
     
         21 . The homogenizer for use in the manufacture of microfibrillated cellulose according to  claim 2 , wherein the microfibrillated cellulose has a water retention, of at least 80, optionally at least 100, wherein the water retention is measured by diluting the MFC samples to a 0.3% solids content in water and then centrifuging the samples at 1000 G for 15 minutes, wherein the clear water phase is separated from the sediment and the sediment is weighed, wherein the water holding capacity is given as (mV/mT)−1, where mV is the weight of the wet sediment and mT is the weight of dry WC analyzed. 
     
     
         22 . The process of  claim 1 , wherein the microfibrillated cellulose is a gel-like dispersion, comprising microfibrillated cellulose at a solid content from 0.01% to 10%, optionally 0.1% to 5%, optionally wherein microfibrillated cellulose is dispersed in polyethylene glycol (PEG 400) or water. 
     
     
         23 . The homogenizer for use in the manufacture of microfibrillated cellulose according to  claim 2 , wherein the microfibrillated cellulose is a gel-like dispersion, comprising microfibrillated cellulose at a solid content from 0.01% to 10%, optionally 0.1% to 5%, optionally wherein microfibrillated cellulose is dispersed in polyethylene glycol (PEG 400) or water. 
     
     
         24 . The process of  claim 1 , wherein the step of subjecting a cellulose pulp to at least one mechanical pretreatment step comprises refining. 
     
     
         25 . The homogenizer for use in the manufacture of microfibrillated cellulose according to  claim 2 , wherein the step of subjecting a cellulose pulp to at least one mechanical pretreatment step comprises refining. 
     
     
         26 . The process of  claim 1 , further comprising enzymatically (pre)treating the cellulose pulp. 
     
     
         27 . The homogenizer for use in the manufacture of microfibrillated cellulose according to  claim 2 , further comprising enzymatically (pre)treating the cellulose pulp.