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, η 0 , (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-à-vis conventional MFC as known in the art.

1 . A process for the manufacture of microfibrillated cellulose, the process comprising the steps of:
 (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), wherein step (b) comprises:
 i. compressing the cellulose pulp from step (a); 
 ii. subjecting the cellulose pulp to a pressure drop of at least 2000 bar, by expanding the cellulose through at least one orifice; 
 iii. providing the pressure drop between a first volume segment located upstream of the orifice and a second volume segment located downstream of the orifice; 
 iv. subjecting the cellulose fibrils to a turbulent flow regime in the second volume segment; and 
 v. bifurcating at least one end of at least a portion of the cellulose fibrils into secondary fibrils having smaller diameters than the non-bifurcated cellulose fibrils. 
   
     
     
         2 . The process of  claim 1 , wherein a diameter of the orifice is about 100 μm to about 700 μm. 
     
     
         3 . The process of  claim 1 , wherein a diameter of the orifice is about 200 μm to about 500 μm. 
     
     
         4 . The process of  claim 1 , wherein a diameter of the orifice is about 300 μm to about 700 μm. 
     
     
         5 . The process of  claim 1 , wherein a residence time of a given flow segment comprising the cellulose fibers in the at least one orifice is less than 20 microseconds. 
     
     
         6 . The process of  claim 1 , wherein step (b) is repeated at least once. 
     
     
         7 . The process of  claim 1 , wherein the cellulose fibrils has a velocity of at least 200 m/s at exit from the orifice. 
     
     
         8 . The process of  claim 1 , wherein bifurcating the at least one end of at least a portion of the cellulose fibrils into secondary fibrils comprises bifurcating the at least one end into three or more secondary fibrils. 
     
     
         9 . The process of  claim 1  wherein step (a) comprises a refining step. 
     
     
         10 . The process of  claim 9 , wherein the refining step comprises using a refiner comprising at least one rotating disk. 
     
     
         11 . The process of  claim 9 , wherein the refining step is repeated at least five times. 
     
     
         12 . The process of  claim 1  further comprising exposing the cellulose pulp to at least one of an enzymatic treatment or a chemical treatment. 
     
     
         13 . A microfibrillated cellulose obtainable by a process, the process comprising the steps of:
 (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), wherein step (b) comprises:   i. compressing the cellulose pulp from step (a);   ii. subjecting the cellulose pulp to a pressure drop of at least 2000 bar, by expanding the cellulose through at least one orifice;   iii. providing the pressure drop between a first volume segment located upstream of the orifice and a second volume segment located downstream of the orifice;   iv. subjecting the cellulose fibrils to a turbulent flow regime in the second volume segment; and   v. bifurcating at least one end of at least a portion of the cellulose fibrils into secondary fibrils having smaller diameters than the non-bifurcated cellulose fibrils.   
     
     
         14 . A microfibrillated cellulose comprising:
 a dispersion of said microfibrillated cellulose comprising fibrils and fibril bundles and having a zero shear viscosity, η 0 , of at least 5000 Pa·s in polyethylene glycol (PEG400), as measured at a solids content of the microfibrillated cellulose of 0.65%, wherein the fibrils and fibril bundles comprise:   a reduced length and a reduced diameter relative to a respective length and a respective diameter of cellulose fibers and fiber bundles making up a cellulose that was used a starting product.   
     
     
         15 . The microfibrillated cellulose of  claim 13 , wherein at least a fraction of the fibrils and fibril bundles of the microfibrillated cellulose comprise bifurcations on at least one end of main fibrils into secondary fibrils, wherein the secondary fibrils have smaller diameters than the non-bifurcated main fibril. 
     
     
         16 . The microfibrillated cellulose according to  claim 13 , wherein the G′ lin  value of a gel-like dispersion comprising the microfibrillated cellulose in polyethylene glycol (PEG 400) is more than 250 Pa as measured at a solids content of the microfibrillated cellulose of 0.65% and 35% H 2 O.