RU2791167C1 - Redispersed microfibrillated cellulose - Google Patents

Abstract

FIELD: methods for improving the re-dispersibility of dried or partially dried microfibrillated cellulose.

SUBSTANCE: method for improving the physical and/or mechanical properties of the redispersed microfibrillated cellulose includes providing an aqueous composition of microfibrillated cellulose, dehydrating the aqueous composition, drying the composition and redispersing the microfibrillated cellulose. Dehydration is carried out using a belt press, high pressure automatic belt press, centrifuge, tube press, screw press and/or rotary press. Drying is carried out using a fluidized bed dryer, microwave and/or radio frequency dryer, a hot air mill or dryer, a sectional mill or a multi-screw sectional mill, and/or freeze drying. Microfibrillated cellulose is obtained from waste paper, scraps of paper production or waste from the paper industry.

EFFECT: improving the physical and/or mechanical properties of the redispersed microfibrillated cellulose.

16 cl, 1 dwg, 14 tab, 3 ex

Description

FIELD OF TECHNOLOGY

In general, the present invention relates to methods for improving the redispersibility of dried or at least partially dried microfibrillated cellulose and methods for redispersing dried or at least partially dried microfibrillated cellulose. These methods may, for example, include dehydration of the aqueous composition, optionally followed by drying. Redispersing the microfibrillated cellulose may, for example, include redispersing dried or at least partially dried microfibrillated cellulose in a liquid medium and in the presence of an additive other than particulate inorganic material and/or in the presence of a combination of particulate inorganic materials. Such an additive and/or combination of particulate inorganic materials may, for example, improve the mechanical and/or physical properties of the redispersed microfibrillated cellulose. The present invention further relates to compositions containing redispersed microfibrillated cellulose and to the use of redispersed microfibrillated cellulose in an article, product or composition.

BACKGROUND OF THE INVENTION

In recent years, microfibrillated cellulose and compositions containing it have been shown to have many useful properties, including improving the mechanical, physical and/or optical properties of a variety of products such as paper, board, polymer products, paints, and the like. Pulp, usually obtained in aqueous form, is usually dried for transport in order to reduce its weight and associated transport costs. The end user then typically redisperses the microfibrillated cellulose before the intended end use. However, after drying and redispersion, some or all of its useful properties deteriorate or are lost. Thus, there is a continuing need to improve the properties of microfibrillated cellulose after drying and redispersing.

BRIEF DESCRIPTION OF THE INVENTION

According to a first aspect of the present invention, there is provided a method for improving the redispersibility of dried or at least partially dried microfibrillated cellulose, comprising drying or at least partially drying an aqueous composition of microfibrillated cellulose by a method comprising:

(i) dewatering the aqueous composition by one or more of the following processes:

(a) dewatering with a belt press such as a high pressure automatic belt press, (b) dewatering with a centrifuge, (c) dewatering with a tube press, (d) dewatering with a screw press, and (e) dewatering with a rotary press; followed by drying

or

(ii) dehydrating the aqueous composition followed by drying by one or more of the following processes:

(f) drying in a fluid bed dryer, (g) drying with a microwave and/or radio frequency dryer, (h) drying in a hot air mill or dryer, such as a section mill or an Atritor mill, and (i) drying by freeze drying;

or

(iii) any combination of dewatering according to (i) and drying according to (ii), or

(iv) a combination of dewatering and drying the aqueous composition,

however, after redispersing the dried or at least partially dried microfibrillated cellulose in a liquid medium, the redispersed microfibrillated cellulose has a mechanical and/or physical property that is closer to the property of microfibrillated cellulose before drying or at least partial drying than it would be if drying according to (i), (ii), (iii) or (iv), wherein the optionally dried or at least partially dried microfibrillated cellulose contains particulate inorganic material and/or an additive whose presence improves mechanical and/or physical property of re-dispersed microfibrillated cellulose.

In some embodiments, the proposed method further comprises redispersing the dried or at least partially dried microfibrillated cellulose in a liquid medium, and optionally further comprising using the redispersed microfibrillated cellulose to form an article, product, or composition.

According to a second aspect of the present invention, there is provided a method for redispersing microfibrillated cellulose, comprising redispersing dried or at least partially dried microfibrillated cellulose in a liquid medium, wherein the dried or at least partially dried microfibrillated cellulose was obtained by dehydrating and drying an aqueous composition containing microfibrillated cellulose, whereby the redispersed microfibrillated cellulose has a mechanical and/or physical property that is closer to the property of microfibrillated cellulose before drying or at least partial drying than it would be if it were not for the specified dehydration and drying, while optionally dried or the at least partially dried microfibrillated cellulose contains: (i) a particulate inorganic material, (ii) a combination of particulate inorganic materials, and/or (iii) an additive other than inorganic an anic material in the form of particles, the presence of which during redispersion improves the mechanical and/or physical property of the redispersed microfibrillated cellulose; wherein the dehydration is selected from one or more of the following processes:

(a) dewatering with a belt press, for example a high pressure automatic belt press;

(b) dehydration using a centrifuge;

(c) dewatering with a tube press;

(d) dewatering with a screw press; And

(e) dewatering with a rotary press;

and/or wherein drying is selected from one or more of the following processes:

(f) drying in a fluid bed dryer;

(g) drying with a microwave and/or radio frequency dryer;

(h) drying in a hot air mill or dryer, such as a sectional mill or an Atritor mill; And

(i) drying by freeze drying.

According to a third aspect of the present invention, there is provided a method for improving the physical and/or mechanical properties of redispersed dried or partially dried microfibrillated cellulose, comprising:

a. providing an aqueous composition of microfibrillated cellulose;

b. dewatering the aqueous composition by one or more of the following means: (i) belt press dewatering, (ii) automatic high pressure belt press, (iii) centrifuge, (iv) tube press, (v) screw press, and (vi ) rotary press;

to obtain a dehydrated microfibrillated cellulose composition;

c. drying the dehydrated microfibrillated cellulose composition using one or more of the following: (i) a fluid bed dryer, (ii) a microwave and/or radio frequency dryer, (iii) a hot air mill or dryer, section mill or multi-screw section mill, and (iv) freeze drying;

to obtain a composition of dried or partially dried microfibrillated cellulose;

wherein after re-dispersion of the dried or partially dried microfibrillated cellulose composition into a liquid medium, the microfibrillated cellulose has a tensile strength and/or viscosity of at least 50% of the tensile strength and/or viscosity of the aqueous microfibrillated cellulose composition before drying at a comparable concentration, and the steepness of the fibers from 20 to 50.

According to a fourth aspect of the present invention, there is provided a method for redispersing microfibrillated cellulose, comprising redispersing dried or at least partially dried microfibrillated cellulose in a liquid medium and in the presence of an additive other than an inorganic particulate material that improves the mechanical and/or physical property of the redispersed microfibrillated cellulose. cellulose, wherein the microfibrillated cellulose has a fiber twist of 20 to 50 before drying or at least partial drying.

According to a fifth aspect of the present invention, there is provided a method for redispersing microfibrillated cellulose, comprising redispersing dried or at least partially dried microfibrillated cellulose in a liquid medium and in the presence of a combination of particulate inorganic materials, said combination of particulate inorganic materials improving mechanical and/ or a physical property of the re-dispersed microfibrillated cellulose, optionally said combination of particulate inorganic materials containing calcium carbonate and lamellar mineral.

According to a sixth aspect of the present invention, there is provided a composition comprising re-dispersed microfibrillated cellulose dispersed in a liquid medium, obtainable/obtainable by a method according to any aspect or embodiment of the present invention, and having, at a comparable concentration, a tensile strength and/or a viscosity of at least at least 50% of the tensile strength and/or viscosity of the aqueous microfibrillated cellulose composition before drying, wherein (i) the twist of the microfibrillated cellulose fibers in the aqueous composition is from 20 to 50, and/or (ii) the aqueous microfibrillated cellulose composition contains an inorganic material in the form particles.

According to a seventh aspect of the present invention, the use of redispersed microfibrillated cellulose according to any aspect or embodiment of the present invention is provided. In some embodiments, microfibrillated cellulose is used in an article, product, or composition. Thus, according to a further aspect of the present invention, there is provided an article, product or composition comprising microfibrillated cellulose according to any aspect or embodiment of the present invention.

The details, examples and advantages provided in relation to any specific one or more of the claimed aspects of the present invention are equally applicable to all aspects of the present invention. Any combination of embodiments, examples, and advantages described herein, in all possible variations, is included in the present invention, unless otherwise indicated herein or such combination is otherwise clearly contrary to the context.

BRIEF DESCRIPTION OF GRAPHICS

In FIG. 1 shows the effect of using a single disc refiner on a dried composition containing materials based on microfibrillated cellulose and calcium carbonate.

DETAILED DESCRIPTION OF THE INVENTION

In attempts to improve one or more of the properties of re-dispersed microfibrillated cellulose and compositions containing it, it has surprisingly been found that a combination of dewatering and drying, for example, mechanical dewatering and drying, can be performed to enhance or improve one or more properties of microfibrillated cellulose after redispersion, for example, mechanical dewatering and drying, (never before not subjected to drying) aqueous composition containing microfibrillated cellulose, optionally in the presence of inorganic solid particles and/or other additives described herein. That is, compared to the microfibrillated cellulose before drying, one or more of the properties of the redispersed microfibrillated cellulose is closer to one or the properties of the microfibrillated cellulose before drying than said property/properties would be were it not for the combination of dewatering and drying. Similarly, it has surprisingly been found that the incorporation of particulate inorganic material or a combination of particulate inorganic materials and/or other additives described herein can improve the redispersibility of microfibrillated cellulose after initial drying.

Thus, in some embodiments, a method for improving the redispersibility of dried or at least partially dried microfibrillated cellulose comprises drying or at least partially drying an aqueous composition by a method including:

(i) dewatering the aqueous composition by one or more of the following processes:

(a) dewatering with a belt press such as a high pressure automatic belt press, (b) dewatering with a centrifuge, (c) dewatering with a tube press, (d) dewatering with a screw press, and (e) dewatering with a rotary press; followed by drying

or

(ii) dehydrating the aqueous composition followed by drying by one or more of the following processes:

(f) drying in a fluid bed dryer, (g) drying with a microwave and/or radio frequency dryer, (h) drying in a hot air mill or dryer, such as a section mill or an Atritor mill, and (i) drying by freeze drying; or

(iii) any combination of dewatering according to (i) and drying according to (ii), or

(iv) a combination of dewatering and drying the aqueous composition.

According to some implementation options, if the drying is carried out by freeze drying, dehydration includes one or more of processes (a) - (e).

After subsequent redispersion, for example, after transportation to another plant, dried or at least partially dried microfibrillated cellulose in a liquid medium, redispersed microfibrillated cellulose has a mechanical and/or physical property that is closer to the property of microfibrillated cellulose before drying, or at least partial drying than it would be if not for drying according to (i), (ii), (iii) or (iv).

Thus, according to another aspect, a method is provided for redispersing microfibrillated cellulose, comprising redispersing dried or at least partially dried microfibrillated cellulose in a liquid medium, wherein the dried or at least partially dried microfibrillated cellulose was obtained by dehydrating and drying an aqueous composition, containing microfibrillated cellulose, whereby the redispersed microfibrillated cellulose has a mechanical and/or physical property that is closer to the property of microfibrillated cellulose before drying or at least partial drying than it would be if it were not for the specified dehydration and drying, while optionally the dried or at least partially dried microfibrillated cellulose contains: (i) a particulate inorganic material, (ii) a combination of particulate inorganic materials, and/or (iii) an additive other than an inorganic particulate material, the presence of which during redispersion improves the mechanical and/or physical properties of the redispersed microfibrillated cellulose; optionally, the dehydration is selected from one or more of the following processes:

(a) dewatering with a belt press, for example a high pressure automatic belt press;

(b) dehydration using a centrifuge;

(c) dewatering with a tube press;

(d) dewatering with a screw press; And

(e) dewatering with a rotary press;

and/or wherein drying is selected from one or more of the following processes:

(f) drying in a fluid bed dryer;

(g) drying with a microwave and/or radio frequency dryer;

(h) drying in a hot air mill or dryer, such as a sectional mill or an Atritor mill; And

(i) drying by freeze drying.

According to some implementation options, if the drying was carried out by freeze drying, dehydration includes one or more of processes (a) - (e).

Thus, according to another aspect, a method is provided for improving the physical and/or mechanical properties of redispersed dried or partially dried microfibrillated cellulose, comprising:

a. providing: an aqueous composition of microfibrillated cellulose;

b. dewatering the aqueous composition by one or more of the following means: (i) belt press dewatering, (ii) automatic high pressure belt press, (iii) centrifuge, (iv) tube press, (v) screw press, and (vi) rotary press;

to obtain a dehydrated microfibrillated cellulose composition;

c. drying the dehydrated microfibrillated cellulose composition using one or more of the following: (i) a fluid bed dryer, (ii) a microwave and/or radio frequency dryer, (iii) a hot air mill or dryer, sectional mill or multi-screw sectional mill, and ( iv) freeze drying;

to obtain a composition of dried or partially dried microfibrillated cellulose;

wherein after re-dispersion of the dried or partially dried microfibrillated cellulose composition into a liquid medium, the microfibrillated cellulose has a tensile strength and/or viscosity of at least 50% of the tensile strength and/or viscosity of the aqueous microfibrillated cellulose composition before drying at a comparable concentration, and the steepness of the fibers from 20 to 50.

The following sections apply to any of the aspects described above.

References to "dried" or "drying" include "at least partially dried" or "or at least partially dried."

In some embodiments, the aqueous composition containing microfibrillated cellulose is dewatered using a belt press, e.g., a high pressure automatic belt press, followed by drying, e.g., using one or more of processes (f) - (i) listed above.

In some embodiments, the aqueous composition containing microfibrillated cellulose is dehydrated by centrifugation followed by drying, for example using one or more of processes (f) - (i) listed above.

In some embodiments, the aqueous composition containing microfibrillated cellulose is dewatered using a tube press followed by drying, for example using one or more of processes (f) - (i) listed above.

In some embodiments, the aqueous composition containing microfibrillated cellulose is dewatered using a screw press followed by drying, for example using one or more of processes (f) - (i) listed above.

In some embodiments, the aqueous composition containing microfibrillated cellulose is dewatered using a rotary press followed by drying, for example using one or more of processes (f) - (i) listed above.

In some embodiments, the aqueous composition is dehydrated, for example, using one or more of the processes (a) - (e) listed above, and then dried in a fluid bed dryer.

In some embodiments, the aqueous composition is dehydrated, for example, using one or more of the processes (a) - (e) listed above, and then dried by microwave and/or radio frequency drying.

In some embodiments, the aqueous composition is dehydrated, for example, using one or more of the processes (a) - (e) listed above, and then dried in a hot air mill or dryer, for example, a sectional mill or an Atritor mill. The Atritor mill can be an Atritor pulverizer dryer, a sectional fine grinder, an Atritor extended classifier mill, or an Atritor air purged tube dryer (AST) (Atritor Limited, 12 The Stampings, Blue Ribbon Park, Coventry, West Midlands, England). Such mills can be used to produce an aqueous composition of microfibrillated cellulose, which is subsequently dried and then redispersed.

In some embodiments, the aqueous composition is dehydrated, for example, using one or more of the processes (a) - (e) listed above, and then dried by freeze drying. In some embodiments, dehydration is carried out using one or more of the following processes (a)-(e) described above.

Dehydration and drying can be carried out for any suitable period of time, for example, from about 30 minutes to about 12 hours, or from about 30 minutes to about 8 hours, or from about 30 minutes to about 4 hours, or from about 30 minutes to about 2 hours. The period of time will depend on such factors as, for example, the solids content of the aqueous composition containing microfibrillated cellulose, the volumetric amount of the aqueous composition containing microfibrillated cellulose, and the drying temperature.

In some embodiments, drying is carried out at a temperature of from about 50°C to about 120°C, for example, from about 60°C to about 100°C, or at a temperature of at least about 70°C, or at least about 75°C. C, or at least about 80°C.

In some embodiments, the proposed method further comprises redispersing the dried or at least partially dried microfibrillated cellulose in a liquid medium, which may be an aqueous or non-aqueous liquid. In some embodiments, the liquid medium is an aqueous liquid, such as water. In some embodiments, the water is wastewater or recycled wastewater from an industrial plant that uses redispersed microfibrillated cellulose to manufacture an article, product, or composition. For example, in paper/board mills, the water may be or contain recycled white water from the papermaking process. In some embodiments, at least a portion of any particulate inorganic material and/or an additive other than the particulate inorganic material may be present in the recycled white water.

In some embodiments, the proposed method further comprises using redispersed microfibrillated cellulose to form an article, product, or composition that is many and varied and includes, but is not limited to, paper and paperboard, polymer products, products, and compositions, and other compositions such as coatings, for example, paint.

In some embodiments, the dried or at least partially dried microfibrillated cellulose contains a particulate inorganic material and/or an additive whose presence improves the mechanical and/or physical property of the redispersed microfibrillated cellulose. Such particulate inorganic materials and additives are described herein below.

The aqueous composition containing microfibrillated cellulose can be subjected to dehydration and drying to reduce the water content by at least 10% by weight, based on the total weight of the aqueous composition containing microfibrillated cellulose, before dehydration and drying, for example, by at least 20% by weight. by weight, or by at least 30% by weight, or by at least 40% by weight, or by at least about 50% by weight, or by at least 60% by weight, or by at least 70% by weight, or at least 80% by weight, or at least 80% by weight, or at least 90% by weight, or at least about 95% by weight, or at least about 99% by weight, or at least about 99.5% by weight, or at least 99.9% by weight.

By "dried" or "dry" is meant that the water content of the aqueous composition containing microfibrillated cellulose is reduced by at least 95% by weight.

By "partially dried" or "partially dry" is meant that the water content of the aqueous composition containing microfibrillated cellulose is reduced by less than 95% by weight. In some embodiments, "partially dried" or "partially dry" means that the water content of an aqueous composition containing microfibrillated cellulose is reduced by at least 50% by weight, such as at least 75% by weight, or by at least 90% by weight.

The aqueous composition contains microfibrillated cellulose. By "microfibrillated cellulose" is meant a cellulose composition in which the cellulose microfibrils are released or partially released as separate particles or as smaller aggregates compared to the cellulose fibers prior to microfibrillation. Microfibrillated cellulose can be obtained by microfibrillating cellulose, including, but not limited to, using the methods described herein. Typical cellulose fibers (ie, pulp before microfibrillation) suitable for use contain larger aggregates of hundreds or thousands of individual cellulose microfibrils. When microfibrillating cellulose, specific characteristics and properties, including, but not limited to, the characteristics and properties described herein, are transferred to microfibrillated cellulose and compositions containing microfibrillated cellulose.

Microfibrillated cellulose can be obtained from any suitable source described in this document.

Unless otherwise indicated, the particle size properties referred to herein in relation to inorganic particulate materials are measured in a well known manner by depositing the particulate material in a fully dispersed state in an aqueous medium using a Sedigraph 5100 device supplied by Micromeritics Instruments Corporation, Norcross, GA, USA (phone: +1 770 662 3620; website: www.micromeritics.com) and referred to in this document as the "Micromeritics Sedigraph 5100 Instrument". Such an instrument provides measurements and a plot of the total mass percentage of particles having a size, referred to in the art as an "equivalent spherical diameter" (ESD), smaller than the specified values of the ESD. The average particle size d ₅₀ is the value thus determined for the e.s.d. particles, in which there is 50% by weight of particles, the equivalent spherical diameter of which is less than the specified value of d ₅₀ .

Alternatively, where indicated, the particle size properties referred to herein in relation to particulate inorganic materials are measured by a well known conventional method in the field of laser light scattering using a Malvern Mastersizer S supplied by Malvern Instruments. Ltd (or using other methods that provide essentially the same result). When using the laser light scattering method, the particle size in powders, suspensions and emulsions can be measured using laser beam diffraction based on the application of Mie theory. Such an instrument provides measurements and a chart of the total volume percentage of particles having a size, referred to in the art as an "equivalent spherical diameter" (ESD), smaller than the specified values of the ESD. The mean particle size d ₅₀ is the value thus determined for the e.s.d. particles, in which there is 50% by volume of particles, the equivalent spherical diameter of which is less than the specified value of d ₅₀ .

Unless otherwise indicated, the particle size properties of microfibrillated cellulosic materials are measured using a well-known conventional method used in the field of laser light scattering, using the Malvern Mastersizer S, supplied by Malvern Instruments Ltd (or using other methods that provide essentially the same same result).

In some embodiments, the microfibrillated cellulose has a d ₅₀ of about 5 microns to about 500 microns, as measured by laser light scattering. In some embodiments, the d ₅₀ of the microfibrillated cellulose is equal to or less than about 400 µm, for example, equal to or less than about 300 µm, or equal to or less than about 200 µm, or equal to or less than about 150 µm, or equal to or less than about 125 µm, or equal to or less than about 100 µm, or equal to or less than about 90 µm, or equal to or less than about 80 µm, or equal to or less than about 70 µm, or equal to or less than about 60 µm, or equal to or less than about 50 µm, or equal to or less than about 40 µm, or equal to or less than about 30 µm, or equal to or less than about 20 µm, or equal to or less than about 10 µm.

In some embodiments, the microfibrillated cellulose has a modal fiber particle size of about 0.1 to 500 microns. In some embodiments, the modal particle size of the microfibrillated cellulose fiber is at least about 0.5 microns, such as at least about 10 microns, or at least about 50 microns, or at least about 100 microns, or at least about 150 µm, or at least about 200 µm, or at least about 300 µm, or at least about 400 µm.

Additionally or alternatively, the microfibrillated cellulose may have a fiber toughness equal to or greater than about 10 as measured using a Malvern instrument. The steepness of the fibers (i.e. the steepness of the fiber size distribution) is determined according to the following formula:

Slope=100 × (d ₃₀ /d ₇₀ )

Microfibrillated cellulose may have a fiber slope equal to or less than about 100. Microfibrillated cellulose may have a fiber slope equal to or less than about 75, or equal to or less than about 50, or equal to or less than about 40, or equal to or less than about 30. Microfibrillated cellulose may have a fiber steepness of from about 20 to about 50, or from about 25 to about 40, or from about 25 to about 35, or from about 30 to about 40.

The microfibrillated cellulose may, for example, be treated prior to dehydration and/or drying. For example, one or more of the additives listed below (eg, salt, sugar, glycol, urea, glycol, carboxymethyl cellulose, guar gum, or a combination thereof, as indicated below) can be added to microfibrillated cellulose. For example, one or more oligomers can be added to microfibrillated cellulose (eg, with or without the additives listed above). For example, to improve dispersibility, one or more particulate inorganic materials (eg, talc or minerals that have been treated to obtain a hydrophobic surface such as a surface treatment with stearic acid (eg, calcium carbonate treated with stearic acid) can be added to the microfibrillated cellulose). the additives may, for example, be suspended in a weakly dielectric solvent.For example, prior to dehydration and/or drying, the microfibrillated cellulose may be in an emulsion, such as an oil/water emulsion.For example, prior to dehydration and/or drying, the microfibrillated cellulose may be in a masterbatch composition, for example, in a polymeric masterbatch composition and/or in a high solids masterbatch composition.For example, prior to dehydration and/or drying, the microfibrillated cellulose may be a high solids composition solids content equal to or greater than about 60 wt.%, or equal to or greater than about 70 wt.%, or equal to or greater than about 80 wt.%, or equal to or greater than about 90 wt.%, or equal to or greater than about 95 wt. .%, or equal to or greater than about 98 wt.%, or equal to or greater than about 99 wt.%. Any combination of one or more treatments may additionally or alternatively be applied to the microfibrillated cellulose after dewatering and drying, but before or during redispersion.

The redispersed microfibrillated cellulose has a mechanical and/or physical property that is closer to the property of the microfibrillated cellulose before drying or at least partial drying than it would be if it were not for drying according to (i), (ii), (iii) or ( iv) as described above. In some embodiments, the redispersed microfibrillated cellulose has a mechanical and/or physical property that is closer to that of the microfibrillated cellulose prior to drying, or at least partially dried, than it would have been had it not been for the drying according to (i), (ii) or ( iii).

The mechanical property may be any identifiable mechanical property associated with microfibrillated cellulose. For example, the mechanical property may be a strength property, such as tensile strength. Tensile strength can be measured using a tensile strength tester. Any suitable method and apparatus may be used, provided that it can be adjusted to compare the tensile strength of microfibrillated cellulose before drying and after redispersion. For example, the comparison should be made at equal concentrations of microfibrillated cellulose and any other additive or particulate inorganic material(s) that may be present. Tensile strength can be expressed in any suitable unit such as, for example, N⋅m/g or kN⋅m/kg.

The physical property may be any measurable physical property associated with microfibrillated cellulose. For example, the physical property may be viscosity. Viscosity can be measured with a viscometer. Any suitable method and apparatus may be used, provided that it can be adjusted to compare the viscosity of the microfibrillated cellulose before drying and after redispersion. For example, the comparison should be made at equal concentrations of microfibrillated cellulose and any other additive or particulate inorganic material(s) that may be present. In some embodiments, the viscosity is the Brookfield viscosity expressed in units of mPa.s.

In some embodiments, the tensile strength and/or viscosity of the redispersed microfibrillated cellulose is at least about 25% of the tensile strength and/or viscosity of the aqueous microfibrillated cellulose composition prior to drying, such as at least about 30%, or at least about 35%, or at least about 40%, or at least 45%, or at least about 50%, or at least about 55%, or at least about 60%, or at least about 65% , or at least about 70%, or at least about 75%, or at least about 80% of the tensile strength and/or viscosity of the microfibrillated cellulose before drying.

For example, if the tensile strength of microfibrillated cellulose before drying was 8 Nm/g, then a tensile strength of at least 50% of that value would be 4 Nm/g.

In some embodiments, the tensile strength of the redispersed microfibrillated cellulose is at least about 25% of the tensile strength of the aqueous microfibrillated cellulose composition prior to drying, such as at least about 30%, or at least about 35%, or at least about 40%, or at least 45%, or at least about 50%, or at least about 55%, or at least about 60%, or at least about 65%, or at least about 70% , or at least about 75%, or at least about 80%, of the tensile strength of the microfibrillated cellulose before drying.

In some embodiments, the viscosity of the redispersed microfibrillated cellulose is at least about 25% of the viscosity of the aqueous microfibrillated cellulose composition prior to drying, such as at least about 30%, or at least about 35%, or at least about 40%, or at least about 45%, or at least about 50%, or at least about 55%, or at least about 60%, or at least about 65%, or at least about 70%, or at least at least about 75%, or at least about 80%, of the viscosity of the microfibrillated cellulose before drying.

In some embodiments, particulate inorganic material and/or an additive other than particulate inorganic material is present during dewatering and drying. The particulate inorganic material and/or additive may be added at any stage prior to dewatering and drying. For example, the particulate inorganic material and/or additive may be added during the preparation of the aqueous composition containing microfibrillated cellulose, after the preparation of the aqueous composition containing microfibrillated cellulose, or both. In some embodiments, the particulate inorganic material is added during the production of microfibrillated cellulose (e.g., co-processing, e.g., co-grinding as described herein), with an additive other than the particulate inorganic material added after the aqueous compositions containing microfibrillated cellulose. In some embodiments, additional particulate inorganic material (which may be the same or different inorganic particulate matter added during the production of microfibrillated cellulose) may be added after the production of microfibrillated cellulose, for example, simultaneously with the addition of an additive other than the inorganic particulate material. particles. In some embodiments, the twist of microfibrillated cellulose fibers in an aqueous composition is between 20 and 50. More information about particulate inorganic material, additives, and their amounts is provided below.

In a further aspect, a method for redispersing microfibrillated cellulose includes redispersing dried or at least partially dried microfibrillated cellulose in a liquid medium and in the presence of an additive other than a particulate inorganic material that improves the mechanical and/or physical property of the redispersed microfibrillated cellulose. The steepness of microfibrillated cellulose fibers before drying or at least partial drying is from 20 to 50.

In a further aspect, a method for redispersing microfibrillated cellulose comprises redispersing dried or at least partially dried microfibrillated cellulose in a liquid medium and in the presence of a combination of particulate inorganic materials, wherein said combination of particulate inorganic materials improves mechanical and/or physical property. re-dispersed microfibrillated cellulose. In some embodiments, the combination of particulate inorganic materials comprises calcium carbonate and a lamellar mineral such as lamellar kaolin or talc.

In some embodiments, the additive, if present, is a salt, sugar, glycol, urea, glycol, carboxymethyl cellulose, guar gum, or a combination thereof.

In some embodiments, the additive, if present, is a salt, sugar, glycol, urea, glycol, guar gum, or a combination thereof.

In some embodiments, the sugar is selected from monosaccharides (eg, glucose, fructose, galactose), disaccharides (eg, lactose, maltose, sucrose), oligosaccharides (chains of 50 or less units of one or more monosaccharides), polysaccharides, and combinations thereof.

In some embodiments, the salt is an alkali metal or alkaline earth metal chloride, such as sodium, potassium, magnesium, and/or calcium chloride. In some embodiments, the salt contains or is sodium chloride.

In some embodiments, the glycol is an alkylene glycol, for example, selected from ethylene, propylene, and butylene glycol, and combinations thereof. In some embodiments, the glycol contains or is ethylene glycol.

In some embodiments, the additive contains or is urea.

In some embodiments, the supplement contains or is guar gum.

In some embodiments, the additive contains or is carboxymethyl cellulose. In some embodiments, the additive is not carboxymethyl cellulose.

In some embodiments, the microfibrillated cellulose is not acetylated prior to drying or at least partial drying. In some embodiments, the microfibrillated cellulose is not acetylated prior to drying or at least partial drying.

The particulate inorganic material may be added at one or more of the following steps: (i) before or during the preparation of an aqueous composition containing microfibrillated cellulose; (ii) after receiving an aqueous composition containing microfibrillated cellulose; (iii) during dehydration of the aqueous microfibrillated cellulose composition; (iv) during drying of the aqueous microfibrillated cellulose composition; and (v) before or during redispersion of the dried or at least partially dried microfibrillated cellulose.

The redispersed microfibrillated cellulose has a mechanical and/or physical property that is closer to that of the microfibrillated cellulose prior to drying and redispersion than it would be if it were not for the presence of inorganic solids and/or additives. In other words, the presence of a particulate inorganic material and/or an additive other than the particulate inorganic material improves the mechanical and/or physical property of the redispersed microfibrillated cellulose.

In some embodiments, the redispersed microfibrillated cellulose has a mechanical and/or physical property that is closer to that of the microfibrillated cellulose prior to drying, or at least partially dried, than it would be if it were not for the presence of particulate inorganic material and/or additives.

As described above, the mechanical property may be any mechanistic property associated with microfibrillated cellulose. For example, the mechanical property may be a strength property, such as tensile strength. Tensile strength can be measured using a tensile strength tester. Any suitable method and apparatus may be used, provided that it can be adjusted to compare the tensile strength of microfibrillated cellulose before drying and after redispersion. For example, the comparison should be made at equal concentrations of microfibrillated cellulose and any other additive or particulate inorganic material(s) that may be present. Tensile strength can be expressed in any suitable unit such as, for example, N⋅m/g or kN⋅m/kg.

The physical property may be any measurable physical property associated with microfibrillated cellulose. For example, the physical property may be viscosity. Viscosity can be measured with a viscometer. Any suitable method and apparatus may be used, provided that it can be adjusted to compare the viscosity of the microfibrillated cellulose before drying and after redispersion. For example, the comparison should be made at equal concentrations of microfibrillated cellulose and any other additive or particulate inorganic material(s) that may be present. In some embodiments, the viscosity is the Brookfield viscosity expressed in units of mPa.s.

In some embodiments, the tensile strength and/or viscosity of the redispersed microfibrillated cellulose is at least about 25% of the tensile strength and/or viscosity of the aqueous microfibrillated cellulose composition prior to drying, such as at least about 30%, or at least about 35%, or at least about 40%, or at least 45%, or at least about 50%, or at least about 55%, or at least about 60%, or at least about 65% , or at least about 70%, or at least about 75%, or at least about 80% of the tensile strength and/or viscosity of the microfibrillated cellulose before drying.

For example, if the tensile strength of microfibrillated cellulose before drying was 8 Nm/g, then a tensile strength of at least 50% of that value would be 4 Nm/g.

In some embodiments, the tensile strength of the redispersed microfibrillated cellulose is at least about 25% of the tensile strength of the aqueous microfibrillated cellulose composition prior to drying, such as at least about 30%, or at least about 35%, or at least about 40%, or at least 45%, or at least about 50%, or at least about 55%, or at least about 60%, or at least about 65%, or at least about 70% , or at least about 75%, or at least about 80%, of the tensile strength of the microfibrillated cellulose before drying.

In some embodiments, the viscosity of the redispersed microfibrillated cellulose is at least about 25% of the viscosity of the aqueous microfibrillated cellulose composition prior to drying, such as at least about 30%, or at least about 35%, or at least about 40%, or at least about 45%, or at least about 50%, or at least about 55%, or at least about 60%, or at least about 65%, or at least about 70%, or at least at least about 75%, or at least about 80%, of the viscosity of the microfibrillated cellulose before drying.

The particulate inorganic material and/or additive, if present, are present in sufficient amounts to improve the redispersibility of the microfibrillated cellulose, i. improve the mechanical and/or physical property of the redispersed microfibrillated cellulose.

Based on the total weight of the aqueous composition containing microfibrillated cellulose (including inorganic solid particles, if any), before drying, the specified additive can be added in an amount of from about 0.1 wt.% to about 200 wt.%, from about 0.1 wt.% to about 100 wt.%, from about 0.1 wt.% to about 80 wt.%, from about 0.1 wt.% to about 60 wt.%, from about 0.1 wt.% to about 40 wt.%, from about 0.1 wt.% to about 20 wt.%, or from about 0.25 wt.% to about 15 wt.%, or from about 0.5 wt.% to about 10 wt. %, or from about 0.5 wt.% to about 7.5 wt.%, or from about 0.5 wt.% to about 5 wt.%, or from about 0.5 wt.% to about 4 wt. %, or from about 9.5 wt.% to about 4 wt.%, or from about 1 wt.% to about 3 wt.%

The solids content of the aqueous composition containing microfibrillated cellulose and optional particulate inorganic material may be no more than about 50 wt.% before drying, for example, no more than about 40 wt.%, or no more than about 30 wt.%, or not more than about 20 wt.%, or not more than about 15 wt.%, or not more than about 10 wt.%, or not more than about 5 wt.%, or not more than about 4 wt.%, or not more than about 3 wt. .%, or not more than about 2 wt.%, or not more than about 2 wt.%

Based on the solids content of the aqueous microfibrillated cellulose composition before drying, the inorganic solids may be no more than about 99% of the total solids content, for example, no more than about 90%, or no more than about 80 wt.%, or no more than about 70 wt.%, or not more than about 60 wt.%, or not more than about 50 wt.%, or not more than about 40%, or not more than about 30%, or not more than about 20%, or not more than about 10% , or not more than about 5% of the total solids content.

In some embodiments, the weight ratio of inorganic solids to microfibrillated cellulose in the aqueous composition is from about 10:1 to about 1:2, such as from about 8:1 to about 1:1, or from about 6:1 to about 3: 2, or about 5:1 to about 2:1, or about 5:1 to about 3:1, or about 4:1 to about 3:1, or about 4:1.

In some embodiments, the aqueous microfibrillated cellulose composition prior to drying, or at least partial drying, has a solids content of no more than about 20% by weight, with optionally no more than about 80% solids being particulate inorganic material.

In some embodiments, prior to drying, the aqueous composition is substantially free of particulate inorganic material.

The particulate inorganic material may, for example, be an alkaline earth metal carbonate or sulfate such as calcium carbonate, magnesium carbonate, dolomite, gypsum, hydrous candite clay such as kaolin, halloysite or ball clay, anhydrous (calcined) candite clay such as as metakaolin or fully calcined kaolin, talc, mica, ganthite, hydromagnesite, ground glass, perlite or diatomaceous earth, or wollastonite, or titanium dioxide, or magnesium hydroxide, or aluminum trihydrate, lime, graphite, or combinations thereof.

In some embodiments, the particulate inorganic material comprises or is calcium carbonate, magnesium carbonate, dolomite, gypsum, anhydrous candite clay, perlite, diatomaceous earth, wollastonite, magnesium hydroxide or aluminum trihydrate, titanium dioxide, or combinations thereof.

In some embodiments, the particulate inorganic material may be a surface treated inorganic particulate material. For example, the particulate inorganic material may be treated with a hydrophobic agent such as a fatty acid or a salt thereof. For example, the particulate inorganic material may be calcium carbonate treated with stearic acid.

An example of a particulate inorganic material suitable for use in the present invention is calcium carbonate. In the following, the present invention may be discussed with reference to calcium carbonate and with respect to aspects in which calcium carbonate is processed and/or processed. The present invention should not be limited to such embodiments.

The particulate calcium carbonate used in the present invention can be obtained from a natural source by grinding. Ground calcium carbonate (GCC) is usually obtained by crushing and then grinding a mineral source such as chalk, marble or limestone, which can then be subjected to a particle size classification step to obtain a product with the desired degree of grinding. Other methods such as bleaching, flotation and magnetic separation can also be used to obtain a product having the desired fineness and/or color. The solid material in the form of particles can be subjected to self-grinding, i. by abrasion between the particles of the hardest material, or, alternatively, in the presence of a particulate abrasive material containing particles of another material than the calcium carbonate being ground. These methods can be carried out in the presence or absence of a dispersant and biocides, which can be added at any stage of the process.

Precipitated calcium carbonate (PCC) can be used in the present invention as a source of particulate calcium carbonate and can be obtained by any of the known methods existing in the art. TAPPI (Technical Association of the Pulp and Paper Industry) monograph series No. 30, "Paper Coating Pigments", pp. 34-35 describes three main industrial methods for obtaining precipitated calcium carbonate, which is suitable for use in obtaining products used in the paper industry, but which can also be used in the practice of the present invention. In all three methods, the raw material for calcium carbonate, such as limestone, is first calcined to form quicklime, and then the quicklime is slaked in water to form calcium hydroxide or milk of lime. In the first method, milk of lime is directly carbonized with carbon dioxide gas. The advantage of this method is the absence of by-product formation and the relative ease of control of the properties and purity of the finished calcium carbonate. In the second method, milk of lime is brought into contact with soda ash to form a calcium carbonate precipitate and a sodium hydroxide solution as a result of the double decomposition. In an industrial application of such a method, the sodium hydroxide can be essentially completely separated from the calcium carbonate. In the third general industrial process, milk of lime is first brought into contact with ammonium chloride to form a calcium chloride solution and ammonia gas. The calcium chloride solution is then brought into contact with soda ash, resulting in a double decomposition of precipitated calcium carbonate and sodium chloride solution. Depending on the particular reaction process employed, crystals of various shapes and sizes can be obtained. The three main forms of PCC crystals are aragonite, rhombohedral and scalenohedral forms (eg calcite), all of which, including mixtures thereof, are suitable for use in the present invention.

In some embodiments, the PCC can be obtained during the production of microfibrillated cellulose.

Wet grinding of calcium carbonate involves obtaining an aqueous suspension of calcium carbonate, which can then be ground, optionally, in the presence of a suitable dispersing agent. For more information on wet grinding of calcium carbonate, see, for example, EP-A-614948 (the contents of which are incorporated by reference in their entirety).

When obtaining inorganic material in the form of particles according to the present invention from sources of natural origin, it may happen that the crushed material will be contaminated with some mineral impurities. For example, naturally occurring calcium carbonate may be present along with other minerals. Thus, in some embodiments, the particulate inorganic material contains some impurities. However, in general, the particulate inorganic material used in the present invention will contain less than about 5% by weight or less than about 1% by weight of other mineral impurities.

The particulate inorganic material may have a particle size distribution in which at least about 10% by weight of the particles have an e.s.d. less than 2 µm, for example, at least about 20% by weight, or at least about 30% by weight, or at least about 40% by weight, or at least about 50% by weight, or at least about 60% by weight, or at least about 70% by weight, or at least about 80% by weight, or at least about 90% by weight, or at least about 95% by weight, or about 100% of particles have e.s.d. less than 2 µm.

In another embodiment, the particulate inorganic material has a particle size distribution, measured using a Malvern Mastersizer S instrument, wherein at least about 10% by volume of the particles have an e.s.d. less than 2 microns, for example, at least about 20% by volume, or at least about 30% by volume, or at least about 40% by volume, or at least about 50% by volume, or at least about 60% by volume, or at least about 70% by volume, or at least about 80% by volume, or at least about 90% by volume, or at least about 95% by volume, or about 100% of particles by volume they have e.s.d. less than 2 µm.

Details of the methodology used to study particle size distributions in mixtures of particulate inorganic material and microfibrillated cellulose using the Malvern Mastersizer S are provided below.

In some embodiments, the particulate inorganic material is or contains kaolin clay. Further, this section of the description of the invention can be discussed on the example of kaolin and in relation to aspects in which kaolin is processed and/or processed. The present invention should not be limited to such embodiments. Thus, in some embodiments, the kaolin is used in its raw form.

The kaolin clay used in the present invention may be a processed material obtained from a natural source, namely, a crude natural kaolin clay mineral. The processed kaolin clay may typically contain at least about 50% by weight of kaolinite. For example, most commercially processed kaolin clays contain greater than about 75% by weight kaolinite and may contain greater than about 90%, in some cases greater than about 95% by weight kaolinite.

The kaolin clay used in the present invention can be obtained from the crude natural kaolin clay mineral by one or more other methods well known to those skilled in the art, such as known refining or beneficiation steps.

For example, the clay mineral can be bleached with a reducing bleaching agent such as sodium hydrosulfite. When sodium hydrosulfite is used, the bleached clay mineral may optionally be dehydrated and optionally washed, and again optionally dehydrated after the sodium hydrosulfite bleaching step.

To remove impurities, the clay mineral can be treated, for example, using flocculation, flotation, or magnetic separation techniques well known in the art. Alternatively, the clay mineral used according to the first aspect of the present invention may be untreated as a solid or as an aqueous suspension.

The process for producing particulate kaolin clay may also include one or more crushing steps, such as grinding or milling. Slight crushing of coarse kaolin is used to ensure its proper separation. Such crushing can be done with balls or granules made of plastic (eg nylon), sand or ceramic grinding or grinding media. Coarse kaolin can be refined to remove impurities and improve physical properties using well known techniques. Kaolin clay can be processed according to known particle size classification techniques, such as sieving and centrifugation (or both), to obtain particles having the desired d ₅₀ value or the desired particle size distribution.

In some embodiments, the particulate inorganic material is or contains a lamellar mineral such as kaolin and/or talc, optionally in combination with another particulate inorganic material such as, for example, calcium carbonate.

By "lamellar" kaolin is meant kaolin or a high aspect ratio kaolin product. The shape factor of lamellar kaolin is from about 20 to less than about 60. Hyper lamellar kaolin has a shape factor of from about 60 to 100 or even greater than 100. As used herein, "shape factor" is a measure of the ratio of particle diameter to particle thickness for a population of varying particle sizes. and shape, measured using the electrical conductivity methods, devices, and equations described in US Pat. No. 5,576,617, incorporated herein by reference. Since the method for determining the shape factor is further described in the '617 patent, the electrical conductivity of the composition of the aqueous suspension of the studied oriented particles is measured while passing the specified composition through the vessel. Electrical conductivity measurements are taken along one direction of the vessel and along another direction of the vessel perpendicular to the first direction. Using the difference between the two electrical conductivity measurements, the shape factor of the particulate material under test is determined.

In some embodiments, the particulate inorganic material is or contains talc, optionally in combination with another particulate inorganic material such as, for example, calcium carbonate.

In some embodiments, the particulate inorganic material is calcium carbonate, which can be surface treated, wherein the aqueous composition further comprises one or more additives other than the particulate inorganic material described herein.

In some embodiments, the particulate inorganic material is kaolin, e.g., lamellar or hyperplaty kaolin, which can be surface treated, wherein the aqueous composition further comprises one or more additives other than the particulate inorganic material described herein.

In some embodiments, the particulate inorganic material is talc, which can be surface treated, wherein the aqueous composition further comprises one or more additives other than the particulate inorganic material described herein.

In some embodiments, the aqueous composition comprising microfibrillated cellulose does not contain particulate inorganic material, wherein the aqueous composition further comprises one or more additives other than the particulate inorganic material described herein.

The various methods described herein provide for the production of re-dispersed microfibrillated cellulose with useful properties.

Thus, according to a further aspect, there is provided a composition comprising re-dispersed microfibrillated cellulose dispersed in a liquid medium, which can be obtained by a method according to any of the aspects relating to the methods described herein, and having, at a comparable concentration, tensile strength and/ or a viscosity of at least 50% of the tensile strength and/or viscosity of the aqueous microfibrillated cellulose composition prior to drying, wherein (i) the microfibrillated cellulose in the aqueous composition has a fiber twist of 20 to 50, and/or (ii) the aqueous microfibrillated cellulose composition cellulose contains particulate inorganic material and optionally further contains an additive other than particulate inorganic material.

The redispersed microfibrillated cellulose can be used in an article, product or composition such as paper, board, plastic products, paints and the like.

Methods for the production of microfibrillated cellulose and optional particulate inorganic material

In some embodiments, microfibrillated cellulose can be produced in the presence or absence of particulate inorganic material.

Microfibrillated cellulose is obtained from a fibrous substrate containing cellulose. The fibrous substrate containing cellulose can be obtained from any suitable source such as wood, grasses (eg sugarcane, bamboo) or rags (eg textile waste, cotton, hemp or flax). The cellulose-containing fibrous substrate may be in the form of a pulp (ie, a suspension of cellulose fibers in water), which can be obtained by any suitable chemical or mechanical treatment, or by a combination of both. For example, the pulp can be chemical pulp, or chemothermomechanical pulp, or mechanical pulp, or waste pulp, or paper cuts, or total waste from paper manufacture, or waste from paper manufacture, or dissolving pulp, pulp from kenaf, market pulp , partially carboxymethylated cellulose, abacus pulp, hemlock pulp, birchwood pulp, grass pulp, bamboo pulp, palm tree pulp, peanut husk pulp, or a combination thereof. The pulp can be milled (for example, in a Valley mill) and/or otherwise refined (for example, by processing in a conical or plate refiner) to any predetermined degree of freeness, expressed in the art as the freeness of the pulp according to the Canadian standard Standard Freeness (CSF) in ^cm3 . CSF refers to the degree of freeness or dehydration of the pulp as measured by the rate at which the pulp slurry can be drained. For example, pulp prior to microfibrillation may have a Canadian Standard freeness of about 10 cc ^or greater. The pulp may have a CSF value of about 700 cm ³ or less, for example, a value equal to or less than about 650 cm ³ , or equal to or less than about 600 cm ³ , or equal to or less than about 550 cm ³ , or equal to or less than about 500 cm ³ , or equal to or less than about 450 cm ³ , or equal to or less than about 400 cm ³ , or equal to or less than about 350 cm ³ , or equal to or less than about 300 cm ³ , or equal to or less than about 250 cm ³ , or equal to or less than about 200 cm ³ , or equal to or less than about 150 cm ³ , or equal to or less than about 100 cm ³ , or equal to or less than about 50 cm ³ . The pulp may then be dehydrated using methods well known in the art, e.g., the pulp may be screened to provide a wet sheet containing at least about 10% solids, e.g., at least about 15% solids. , or at least about 20% solids, or at least about 30% solids, or at least about 40% solids. The pulp can be used in an unrefined form, that is, without being milled or dehydrated or otherwise refined.

In some embodiments, the pulp can be milled in the presence of a particulate inorganic material such as calcium carbonate.

To obtain microfibrillated cellulose, a fibrous substrate containing cellulose can be added to a grinding vessel or a dry homogenizer. For example, dry paper cuttings can be added directly to the shredder vessel. The aqueous environment in the shredder vessel will further facilitate pulp formation.

The microfibrillation step can be performed in any suitable apparatus, including, but not limited to, a refiner. In one embodiment, the microfibrillation step is carried out in a grinding vessel under wet grinding conditions. In another embodiment, the microfibrillation step is carried out in a homogenizer. Each of these embodiments is described in more detail below.

• wet grinding

Such grinding is conveniently carried out in a conventional manner. Said grinding may be an attrition grinding process in the presence of a particulate abrasive, or may be an auto-grinding process, i. e. a process carried out in the absence of abrasive material. By abrasive is meant a medium other than particulate inorganic material, which, in some embodiments, can be co-milled with a cellulose-containing fibrous substrate.

The particulate abrasive, if present, may be a natural or synthetic material. The abrasive material may, for example, contain balls, granules or pellets of any hard mineral, ceramic or metallic material. Such materials may include, for example, alumina, zirconia, zirconium silicate, aluminum silicate, or a mullite-rich material obtained by calcining kaolinite clay at a temperature in the range from about 1300°C to about 1800°C. For example, in some embodiments, Carbolite® abrasive is used. Alternatively, natural sand particles of a suitable particle size may be used.

In other embodiments, a hardwood abrasive (eg, wood flour) may be used.

In general, the type and particle size of the abrasive material selected for use in the present invention may depend on properties such as, for example, the particle size and chemical composition of the feed slurry of the material to be ground. In some embodiments, the particulate abrasive comprises particles with a median diameter of from about 0.1 mm to about 6.0 mm, such as from about 0.2 mm to about 4.0 mm. The abrasive material (or medium) may be present in an amount of no more than about 70% by volume relative to the volume of the load. The abrasive material may be present in an amount of at least about 10% by volume relative to the volume of the load, for example, at least about 20% by volume relative to the volume of the load, or at least about 30% by volume relative to the volume of the load, or at least at least about 40% by volume relative to the download volume, or at least about 50% by volume relative to the download volume, or at least about 60% by volume relative to the download volume.

Grinding can be carried out in one or more stages. For example, particulate coarse inorganic material can be ground in a mill vessel to a predetermined particle size distribution, after which the cellulose-containing fibrous material is added thereto, and milling is continued until the desired level of microfibrillation is obtained.

The particulate inorganic material can be wet or dry ground in the absence or presence of an abrasive. In the case of the wet grinding step, coarse inorganic particulate material is ground in an aqueous suspension in the presence of an abrasive material.

In one embodiment, the average particle size (d ₅₀ ) of the particulate inorganic material decreases during the co-grinding process. For example, the d ₅₀ of the inorganic particulate material can be reduced by at least about 10% (as measured by the Malvern Mastersizer S), for example, the d ₅₀ of the inorganic particulate material can be reduced by at least about 20%, or reduced by at least about 30%, or reduced by at least about 50%, or reduced by at least about 50%, or reduced by at least about 60%, or reduced by at least about 70%, or reduced by at least about 80%, or reduced by at least about 90%. For example, a particulate inorganic material having a d ₅₀ of 2.5 μm before co-grinding and a d ₅₀ of 1.5 μm after co-milling will undergo a 40% reduction in particle size. In some embodiments, the average particle size of the particulate inorganic material decreases slightly during the co-grinding process. By "slightly reduced" is meant that the d ₅₀ of the inorganic particulate material is reduced by less than about 10%, for example, the d ₅₀ of the inorganic particulate material is reduced by less than about 5%.

The fibrous substrate containing cellulose can be microfibrillated, optionally in the presence of particulate inorganic material, to form microfibrillated cellulose with a d ₅₀ of about 5 µm to about 500 µm as measured by laser light scattering. The cellulose-containing fibrous substrate may be microfibrillated, optionally in the presence of particulate inorganic material, to produce microfibrillated cellulose with a d ₅₀ equal to or less than about 400 µm, such as equal to or less than about 300 µm, or equal to or less than about 200 µm, or equal to or less than about 150 µm, or equal to or less than about 125 µm, or equal to or less than about 100 µm, or equal to or less than about 90 µm, or equal to or less than about 80 µm, or equal to or less than about 70 µm, or equal to or less than about 60 µm, or equal to or less than about 50 µm, or equal to or less than about 40 µm, or equal to or less than about 30 µm, or equal to or less than about 20 µm, or equal to or less than about 10 µm.

The cellulose-containing fibrous substrate may be microfibrillated, optionally in the presence of a particulate inorganic material, to produce microfibrillated cellulose having a modal fiber particle size of about 0.1 to 500 µm and a modal particle size of the inorganic particulate material of 0.25 to 20 µm. The cellulose-containing fibrous substrate may be microfibrillated, optionally in the presence of a particulate inorganic material, to produce microfibrillated cellulose having a modal fiber particle size of at least about 0.5 microns, such as at least about 10 microns, or at least about 50 µm, or at least about 100 µm, or at least about 150 µm, or at least about 200 µm, or at least about 300 µm, or at least about 400 µm.

The cellulose-containing fibrous substrate can be microfibrillated, optionally in the presence of a particulate inorganic material, to produce microfibrillated cellulose having fiber toughness as described above.

Grinding can be carried out in a grinding vessel such as a drum mill (e.g. rod, ball and self-grinding mill), stirred media mill (e.g. SAM or IsaMill), tower mill, stirred media detritor (SMD) or a grinding vessel containing rotating parallel grinding discs between which the material to be ground is fed.

In one embodiment, the grinding vessel is a tower mill. The tower mill may include a fixed zone located above one or more grinding zones. The fixed zone is an area towards the top of the interior of the tower mill in which there is minimal or no grinding and which contains microfibrillated cellulose and optionally particulate inorganic material. The stationary zone is the region in which the abrasive material particles are deposited downward into one or more grinding zones of the tower mill.

The tower mill may include a grading machine located above one or more grinding zones. According to one embodiment, the sorting machine is installed at the top and located next to the fixed area. The sorting machine may be a hydrocyclone.

Tower mill may contain a sieve located above one or more grinding zones. According to one embodiment, the sieve is placed adjacent to the fixed area and/or the grading machine. The sieve may be sized to separate the abrasive from the final aqueous slurry containing microfibrillated cellulose and optional particulate inorganic material and enhance the settling of the abrasive.

According to one embodiment, grinding is carried out under plug flow conditions. Under plugging conditions, the flow through the tower is such that there is limited mixing of the grinding materials passing through the tower. This means that at various points along the length of the tower mill, the viscosity of the aqueous medium will change as the fineness of the microfibrillated cellulose is increased. Thus, in fact, it can be considered that the grinding area in the tower mill contains one or more grinding zones having an intrinsic viscosity. One skilled in the art will appreciate that there is no sharp boundary between adjacent grinding zones in terms of viscosity.

In one embodiment, water is added to the top of the mill directly to the fixed zone, or to the grading machine or sieve above one or more grinding zones, to reduce the viscosity of an aqueous slurry containing microfibrillated cellulose and an optional particulate inorganic material, specified areas of the mill. It has been found that by diluting the finished microfibrillated cellulose and the optional particulate inorganic material at this point in the mill, the prevention of carryover of the abrasive material into the fixed zone and/or grading machine and/or sieve is improved. In addition, limited mixing through the tower allows the higher solids treatment to be lowered to the bottom of the tower and diluted from above by a limited backflow of dilution water flowing back to the bottom of the tower to one or more grinding zones. Any suitable amount of water may be added that is effective to dilute the viscosity of the final aqueous suspension containing microfibrillated cellulose and optional particulate inorganic material. Water can be added continuously during the grinding process or at regular intervals or at random times.

In another embodiment, water can be added to one or more grinding zones through one or more water injection points located along the length of the tower mill, or through each water injection point located at a location corresponding to one or more grinding zones. Preferably, the ability to add water at various points along the tower allows further adjustment of grinding conditions at any or all locations along the mill.

The tower mill may comprise a vertical paddle shaft equipped with a series of paddle rotating discs along its entire length. The operation of the rotary paddle rotating discs creates a series of discrete grinding zones throughout the mill.

In another embodiment, grinding is carried out in a screened grinder, such as a stirred media detritor. The strainer grinder may comprise one or more sieve(s) with a nominal opening size of at least about 250 µm, for example, one or more sieves may have a nominal opening size of at least about 300 µm, or at least about 350 µm, or at least about 400 µm, or at least about 450 µm, or at least about 500 µm, or at least about 550 µm, or at least about 600 µm, or at least about 650 µm, or at least about 700 microns, or at least about 750 microns, or at least about 800 microns, or at least about 850 microns, or at least about 900 microns, or at least about 1000 microns.

The screen sizes just listed above apply to the tower mill embodiments described above.

As mentioned above, grinding can be carried out in the presence of an abrasive material. In one embodiment, the abrasive material is a coarse media containing particles with an average diameter ranging from about 1 mm to about 6 mm, such as about 2 mm, or about 3 mm, or about 4 mm, or about 5 mm.

In another embodiment, the abrasive has a specific gravity of at least about 2.5, such as at least about 3, or at least about 3.5, or at least about 4.0, or at least about 4.5, or at least about 5.0, or at least about 5.5, or at least about 6.0.

In another embodiment, the abrasive material contains particles with an average diameter ranging from about 1 mm to about 6 mm and has a specific gravity of at least about 2.5.

In another embodiment, the abrasive material contains particles with an average diameter of about 3 mm and has a specific gravity of about 2.7.

As described above, the abrasive material (or medium) may be present in an amount of no more than about 70% by volume relative to the volume of the load. The abrasive material may be present in an amount of at least about 10% by volume relative to the volume of the load, for example, at least about 20% by volume relative to the volume of the load, or at least about 30% by volume relative to the volume of the load, or at least at least about 40% by volume relative to the download volume, or at least about 50% by volume relative to the download volume, or at least about 60% by volume relative to the download volume.

In one embodiment, the abrasive material is present in an amount of about 50% by volume relative to the load volume.

By "load" is meant the composition, which is the raw material fed into the grinder vessel. The load contains water, an abrasive material, a fibrous substrate containing cellulose and optionally particulate inorganic material, and any other optional additives described herein.

The advantage of using a relatively coarse and/or heavy medium is to improve (ie increase) settling rates and reduce entrainment of the medium through the fixed zone and/or grading machine and/or sieve(s).

An additional advantage of using a relatively coarse abrasive material is that the average particle size (d ₅₀ ) of the particulate inorganic material may not decrease significantly during the grinding process, so that the energy transferred to the grinding system will be mainly spent on microfibrillation of a fibrous substrate containing cellulose.

Another advantage of using screens with relatively large openings is that a relatively coarse or heavy abrasive can be used in the microfibrillation step. In addition, the use of sieves with relatively large openings (i.e., a nominal opening of at least about 250 µm) allows relatively high solids content to be processed and removed from the grinder, thereby allowing relatively high solids content to be processed. (comprising a fibrous substrate containing cellulose and particulate inorganic material) in an economically viable process. As discussed below, feedstocks with a high initial solids content have been found to be optimal in terms of energy availability. In addition, it has also been found that a product obtained (at a given energy) at a lower solids content has a larger particle size distribution.

Grinding can be carried out in a cascade of grinding vessels, one or more of which may contain one or more grinding zones. For example, a fibrous substrate containing cellulose and particulate inorganic material can be ground in a cascade of two or more grind vessels, such as a cascade of three or more grind vessels, or a cascade of four or more grind vessels, or in a cascade of five or more grinding vessels, or in a cascade of six or more grinding vessels, or in a cascade of seven or more grinding vessels, or in a cascade of eight or more grinding vessels, or in a cascade of nine or more grinding vessels connected in series, or a cascade containing up to ten grinding vessels. The cascade of grinding vessels may be operatively connected in series or parallel, or be a combination of series and parallel connections. Material withdrawn from and/or introduced into one or more cascaded grinding vessels may be subjected to one or more screening steps and/or one or more particle size classification steps.

The process cycle may include a combination of one or more grinding vessels and a homogenizer.

According to one embodiment, grinding is carried out in a closed loop. According to another embodiment, grinding is carried out in an open circuit. Grinding can be carried out in batch mode. Grinding can be carried out in batch mode with recirculation.

As described above, the pulverizing cycle may include a pre-pulverizing step in which the coarse inorganic solids are pulverized in a pulverizer vessel to a predetermined particle size distribution, after which the cellulose-containing fibrous material is combined with the particulate pre-pulverized inorganic material and continues. grinding in the same or another grinding vessel until the desired level of microfibrillation is obtained.

Since the slurry of material to be ground may have a relatively high viscosity, a suitable dispersing agent may be added to the slurry prior to grinding. The dispersing agent may be, for example, a water-soluble condensed phosphate, polysilicic acid, or a salt or polyelectrolyte thereof, for example, a water-soluble salt of poly(acrylic acid) or poly(methacrylic acid) with a number average molecular weight of not more than 80,000. will be from 0.1 to 2.0% by weight, based on the weight of the dry inorganic solid material in the form of particles. The suspension can be crushed in a suitable way at a temperature in the range from 4°C to 100°C.

Other additives that can be added to the microfibrillation step include: carboxymethyl cellulose, amphoteric carboxymethyl cellulose, oxidizing agents, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), TEMPO derivatives, and wood degrading enzymes.

The pH of the slurry to be ground may be about 7 or greater than about 7 (i.e., basic), for example, the pH of the slurry may be about 8, or about 9, or about 10, or about 11. The pH of the slurry to be ground material may be less than about 7 (i.e., be acidic), for example, the pH of the slurry may be about 6, or about 5, or about 4, or about 3. The pH of the slurry of material to be ground can be adjusted by adding an appropriate amount of acid or grounds. Suitable bases include alkali metal hydroxides such as, for example, NaOH. Other suitable bases are sodium carbonate and ammonia. Suitable acids include inorganic acids such as hydrochloric and sulfuric acid, or organic acids. An example of an acid is phosphoric acid.

The amount of particulate inorganic material, if present, and pulp in the cogrind mixture can be varied to produce a slurry that is suitable for drying and redispersion and/or that can be further modified, for example, with additional inorganic particulate material and /or an additive other than particulate inorganic material to form a slurry suitable for drying or at least partial drying, optional transport to another location, redispersion and use to obtain an article, product or composition.

• homogenization

Microfibrillation of a fibrous substrate containing cellulose can be carried out under humid conditions, optionally in the presence of particulate inorganic material, in a manner in which a mixture of pulp and optional inorganic particulate material is held under pressure (for example, at a pressure of about 500 bar) and then sent to a zone with lower pressure. The rate at which the mixture passes into the low pressure zone is fast enough and the pressure in the low pressure zone is low enough to cause microfibrillation of the cellulose fibers. For example, a pressure drop can occur by forcing the mixture through an annular orifice having a narrow inlet and a much larger outlet. The sudden decrease in pressure as the mixture moves rapidly into a large volume (i.e., a zone of lower pressure) induces cavitation, which causes microfibrillation. In one embodiment, microfibrillation of the cellulose-containing fibrous substrate can be carried out in a homogenizer under humid conditions, optionally in the presence of particulate inorganic material. In the homogenizer, the pulp and optional particulate inorganic material are held under pressure (eg, about 500 bar) and forced through a small nozzle or orifice. The mixture may be at a pressure of from about 100 to about 1000 bar, for example, at a pressure equal to or greater than 300 bar, or equal to or greater than about 500, or equal to or greater than about 200 bar, or equal to or greater than about 700 bar. Homogenization exposes the fibers to high shear forces such that as the pressurized pulp exits the nozzle or orifice, cavitation results in microfibrillation of the cellulose fibers in the pulp. Additional water can be added to improve the fluidity of the slurry through the homogenizer. The resulting aqueous slurry containing microfibrillated cellulose and optional particulate inorganic material can be returned back to the homogenizer inlet for multiple passes through the homogenizer. When present and when the inorganic particulate material is a natural lamellar mineral such as kaolin, homogenization not only facilitates microfibrillation of the pulp, but can also promote delamination of the lamellar particulate material.

An example of a homogenizer is the Manton Gaulin (APV) homogenizer.

Following the microfibrillation step, an aqueous slurry containing microfibrillated cellulose and an optional particulate inorganic material may be passed through a sieve to remove fibers above a certain size and to remove any abrasive material. For example, the slurry may be screened with a sieve having a selected nominal aperture size to remove fibers not passing through such a sieve. The nominal hole size refers to the nominal center distance between opposite sides of a square hole or the nominal diameter of a round hole. The sieve may be a BSS (British standard sieve) sieve (according to BS 1796) having a nominal opening size of 150 µm, such as 125 µm, or 106 µm, or 90 µm, or 74 µm, or 63 µm , or 53 µm, 45 µm, or 38 µm. In one embodiment, the aqueous slurry is passed through a BSS sieve with a nominal opening of 125 µm. The aqueous suspension may then optionally be dehydrated.

Therefore, it is understood that in the case where the milled or homogenized suspension is processed to remove fibers larger than the selected size, the amount (i.e. % by weight) of microfibrillated cellulose in the aqueous suspension after grinding or homogenization may be less than the amount of dry fiber in pulp. Thus, the relative amounts of pulp and optional inorganic particulate material fed to the grinder or homogenizer can be adjusted depending on the amount of microfibrillated cellulose required in the aqueous slurry after removal of fibers larger than the selected size.

In some embodiments, microfibrillated cellulose can be produced by a process comprising the step of microfibrillating a fibrous substrate containing cellulose in an aqueous environment by grinding in the presence of an abrasive material (described herein), wherein the grinding is performed in the absence of particulate inorganic material. In some embodiments, the particulate inorganic material may be added after grinding to form a slurry to form a coating layer or a slurry to form a layer.

In some embodiments, after grinding, the abrasive material is removed.

In other embodiments, the abrasive material is retained after grinding and may serve as particulate inorganic material, or at least a portion thereof. In some embodiments, additional inorganic solids and/or an additive other than particulate inorganic material may be added after grinding.

The following procedure can be used to study particle size distributions in mixtures of particulate inorganic material (eg GCC or kaolin) and microfibrillated pulp fibers.

- calcium carbonate

A sample of the co-milled suspension, sufficient to obtain 3 g of dry material, is weighed into a beaker, diluted to 60 g with deionized water and mixed with 5 cm ³ of a sodium polyacrylate solution with an active substance concentration of 1.5 wt./vol.%. Deionized water is then added with stirring until a final suspension mass of 80 g is obtained.

- kaolin

A sample of the co-milled slurry sufficient to give 5 g of dry material is weighed into a beaker, diluted to 60 g with deionized water and mixed with 5 cm ³ of a solution of 1.0 wt% sodium carbonate and 0.5 wt% sodium hexametaphosphate. Deionized water is then added with stirring until a final suspension mass of 80 g is obtained.

The suspension is then added in 1 cm ³ aliquots to water in a sample preparation unit mounted on the Mastersizer S until the optimal light absorption level is displayed (typically 10 to 15%). After that, light scattering analysis is performed. The selected measurement range was: 300RF: 0.05-900, beam length was set to 2.4mm.

For co-milled samples containing calcium carbonate and fiber, the refractive index (RI) of calcium carbonate (1.596) was used. For co-milled kaolin and fiber samples, the RI of kaolin (1.5295) was used.

The particle size distribution was calculated based on the Mie theory and the result was obtained as a distribution based on the volume differential. The presence of two distinct peaks was interpreted as being related to the mineral (thinner peak) and to the fiber (rougher peak).

The finer mineral peak was matched to the experimental data points and mathematically subtracted from the distribution to leave the fiber peak, which was converted to a cumulative distribution function. Similarly, the fiber peak was mathematically subtracted from the original distribution to leave the mineral peak, which was also converted to the cumulative distribution function. Then both of these integral curves can be used to calculate the average particle size (d ₅₀ ) and the steepness of the size distribution (d ₃₀ /d ₇₀ ×100). The differential curve can be used to find the modal particle size of both the mineral and fibrous fractions.

EXAMPLES

Example 1

Several aqueous compositions containing microfibrillated cellulose and particulate inorganic material have been prepared by co-milling Botnia pulp in the presence of particulate inorganic materials, as detailed elsewhere in the specification of the present invention. The properties of each composition are summarized in Table 1. POP refers to "pulp percentage", where POP is the percentage of dry matter in a sample that is pulp or fibrils rather than particulate inorganic material.

Example 2

An additive was added to each suspension and mixed for 1 minute. The mixture was left to stand for 60 minutes and then filtered. The resulting filter cake was placed in a laboratory oven at 80°C until dry (<1 wt.%, moisture).

The dried composition was then redispersed in a Silverson laboratory mixer (dilute to 20 POP, 1 minute mixing in Silverson).

Different additives (sodium chloride, glycol, urea, carboxymethyl cellulose, sugar and guar gum) were added to each of compositions 1-4 at varying concentrations and the tensile strength was determined. The average results are summarized in Table 2.

Example 3

The purpose of these studies was to evaluate the redispersibility of a high solids microfibrillated cellulose/calcium carbonate composition containing 50 wt% POP (pulp percentage) as calcium carbonate/Botnia pulp (i.e. at a weight ratio microfibrillated cellulose to calcium carbonate 1:1) using a single disc refiner available from a pilot plant. An exemplary single disc refiner suitable for use in the present invention was manufactured by Sprout Waldron. This refiner was a 12 by (30 cm) single disc refiner. The disk rotation speed was 1320 rpm. The circumferential speed was 21.07 m/s. The design width of the disk knife in the refiner was 1.5 mm; the groove width was 1.5 mm; the length of the cutting edge of the knife was 1.111 km/revolution of the knife CEL @ 1320 rpm 24.44 km/s. Other suitable refiners with equivalent specifications are known to those skilled in the art.

Raw materials

100 kg of microfibrillated cellulose and calcium carbonate belt press sludge (weight ratio 1:1) and 100 kg of four other raw materials were transported to the pilot plant using an Atritor dryer grinder (available from Atritor Limited, 12 The Stampings, Blue Ribbon Park, Coventry, West Midlands, England) which is an air-blown mill or dryer capable of introducing a stream of hot air to dry and grind materials while processing and drying the microfibrillated cellulose and calcium carbonate composition used in the present studies . Other equivalent mills are known to those skilled in the art. The properties of high solids microfibrillated cellulose products in the form of calcium carbonate (IC60L)/Botnia used in the present studies are shown in Table 3. using an Atritor dryer with notch handles and loaded at 20 Hz (slow loading speed).

Brief description of the study

Each material was "moistened" in a large pulper to replicate typical times/actions in pulp and paper mill operation.

The pulped samples were passed through a single disc refiner, these samples being taken at refining energy inputs in the range of 0-20-40-60-80-100 kWh/t total dry solids.

results

1. Belt press sludge containing 50 wt% POP in the form of calcium carbonate (IC60)/Botnia pulp (31 wt% solids)

This belt press cake with a 30.5 wt.% solids content of a composition containing microfibrillated cellulose and calcium carbonate (weight ratio 1:1) was first redispersed in a pulp breaker for 15 minutes at 7 wt.% solids . This consistency was too viscous to pump, so the material was diluted with water to a solids content of from 1% wt. to 6 wt.% Then the specified material was passed through the refiner and samples were taken at various values of the operating power input.

Table 4 below shows the effect of a single disc refiner on the properties of a belt press sludge containing microfibrillated cellulose and calcium carbonate. The values given for material as shipped were obtained from material that was mixed for 1 minute in a Silverson mixer (Silverson Machines, Inc., 55 Chestnut St. East Longnieadow, ML 01028), corresponding to 1000 to 2000 kWh/ T.

As can be seen, the belt press sludge can be refined at a solids content of 6 wt. %, with the FLT recovering after the addition of 20 kWh/t. The FLT is the result of a burst test designed to evaluate the quality of microfibrillated cellulose and redispersed microfibrillated cellulose. The POP of the test material was adjusted to 20% by adding any inorganic solids used to form the microfibrillated cellulose/inorganic material composite (in the case of microfibrillated cellulose containing no inorganic solids, 60 wt% < 2 µm GCC calcium carbonate was used) . From this material was obtained 220 g/sq. cc (g/m ² ) sheet using a custom made Buchner filter apparatus. The resulting sheet was conditioned and its tensile strength measured using an industry standard tensile strength tester. Energy inputs up to 100 kWh/t can improve both the FLT and the viscosity of the microfibrillated cellulose/calcium carbonate composition. A "weediness" of 1 or less is acceptable and suggests good paper sheet formation. As known to one skilled in the art, the trash count is a paper trash test (see, for example, the TAPPI paper trash test) and indicates that the microfibrillated cellulose has been completely redispersed. In this case, the sheets obtained for the FLT measurement were subjected to a weed count using an illuminated viewing table prior to the breaking test. Low weediness indicates good redispersion in any aquatic environment.

Table 5 shows the effect that the single disc refiner had on the particle size of the microfibrillated cellulose and calcium carbonate composition. Particle size distribution ("PSD") was measured on a Malvern Insitec instrument (Malvern Instruments Ltd, Enigma Business Park, Grovewood Road, Malvern, WR14 1XZ, United Kingdom) installed in a laboratory quality control unit.

As can be seen from the PSD values, the single disc refiner is very effective in reducing the amount of large particles in the composition of microfibrillated cellulose and calcium carbonate.

2. Composition of microfibrillated cellulose and calcium carbonate containing 50 wt.% POP, in the form of calcium carbonate (IC60)/Botnia pulp (weight ratio 1:1), dried in the Atritor dryer (51.4 wt.% solids).

This product, containing 51.4 wt% microfibrillated cellulose and 1:1 weight ratio calcium carbonate, dried using an Atritor dryer, was redispersed in a pulper at a solids content of 7 wt% The low viscosity of this material allowed it to be easily pumped . Then such material was passed through the refiner and samples were taken at various values of the operating power input.

Table 6 below shows the effect of a single disc refiner on the properties of a 51.4 wt % composition of microfibrillated cellulose and calcium carbonate. The values given for material as delivered were obtained from material that was mixed for 1 minute with a Silverson mixer, corresponding to 1000 to 2000 kWh/t.

This 51.4 wt % Atritor dry composition can be fully redispersed at 60 kWh/tonne, with these properties further improved with increasing energy input. This material restores viscosity and FLT, and also has a relatively low trash content, similar to that of the belt press sludge.

Table 7 shows the effect that a single disc refiner had on the particle size of a composition containing microfibrillated cellulose and calcium carbonate (weight ratio 1:1).

As can be seen from the PSD values, the single disc refiner is very effective in reducing the amount of coarse particles in the 1:1 weight ratio composition of microfibrillated cellulose and calcium carbonate.

3. Composition of microfibrillated cellulose and calcium carbonate containing 50 wt.% POP, in the form of calcium carbonate (IC60)/Botnia pulp with a mass ratio of 1:1, dried in the Atritor dryer (58.1 wt.% solids).

This composition with 58.1 wt.% solids content, containing microfibrillated cellulose and calcium carbonate (weight ratio 1:1), was evaluated at a solids content of 7, 8 and 9 wt.% The reason for this study was that higher the amount of energy input could not be achieved because the composition containing microfibrillated cellulose and calcium carbonate became too "thin" in consistency and the metal disk of the refiner performed the grinding by itself. Table 8 below shows the properties of all products at three different solids contents. The values given for material as delivered and at 0 kWh/t were obtained from material that was mixed for 1 minute in a Silverson mixer, corresponding to 1000 to 2000 kWh/t.

A 58.1 wt% composition containing microfibrillated cellulose and calcium carbonate (weight ratio 1:1) can be completely redispersed at 7, 8 and 9 wt% solids. At each consistency, the FLT target was exceeded, as well as viscosity and weediness. At a solids content of 9% by weight, the greatest improvement was achieved.

Table 9 shows the effect that the single disc refiner had on the particle size of a composition containing microfibrillated cellulose and calcium carbonate (1:1 weight ratio) at all three solids levels.

As in the previous case, the PSD data show the effectiveness of the single disc refiner in changing the size of the coarse pulp at all three consistencies.

4. Composition of microfibrillated cellulose and calcium carbonate containing 50 wt.% POP, in the form of calcium carbonate (IC60)/Botnia pulp dried in the Atritor dryer (70.1 wt.% solids).

This 70.1% by weight solids composition of microfibrillated cellulose and calcium carbonate (weight ratio 1:1) at each operating power input is shown in Table 10. The values given for the material as shipped and at 0 kWh/t were obtained for material that was mixed for 1 minute in a Silverson mixer, corresponding to 1000 to 2000 kWh/t.

As in the previous case, it can be seen that the single disc refiner is much more efficient at redispersing the dried composition containing microfibrillated cellulose and calcium carbonate (1:1 weight ratio) than using the Silverson mixer. An energy input of 100 kWh/t allows the composition containing microfibrillated cellulose and calcium carbonate (weight ratio 1:1) to be redispersed to the extent that these properties are similar to those of a belt press sludge.

Table 11 shows the effect that a single disc refiner had on the particle size of a composition containing microfibrillated cellulose and calcium carbonate (weight ratio 1:1), while, as in the previous case, this refiner is shown to be very effective.

5. Composition, microfibrillated cellulose and calcium carbonate (weight ratio 1:1), containing 50 wt.% POP, in the form of calcium carbonate (IC60)/Botnia pulp dried in the Atritor dryer (86.2 wt.% solids) .

Such a material in a composition with a solids content of 86.2 wt.%, containing microfibrillated cellulose and calcium carbonate (weight ratio 1:1), is considered very dry, so the composition was refined under the same conditions as the rest of the materials (intensity 0.2 J/m), but also at an intensity of 0.1 J/m. 0.1 J/m corresponds to a lower intensity, so it takes longer to reach the required operating power input. See table 12.

The values given for material as delivered and at 0 kWh/t were obtained from material that was mixed for 1 minute in a Silverson mixer, corresponding to 1000 to 2000 kWh/t.

The results show that this very high solids composition containing microfibrillated cellulose and calcium carbonate (weight ratio 1:1) can be redispersed with the same properties as belt press sludge using 100 kWh/ T. When the intensity changes, these properties can be restored when using energy less than 80 kWh/t.

Table 13 shows the effect that a single disc refiner had on the particle size of a composition containing microfibrillated cellulose and calcium carbonate (1:1 weight ratio) at both intensities.

In FIG. 1 summarizes the FLT data from the studies described above. These data show that the FLT control can be achieved in all tested samples and that the FLT control can be exceeded in intermediate solids.

6. Additional processing of refined products

For a range of pilot plant products, additional energy was injected into the samples using a Silverson mixer. These experiments were to explore the possibility of improving the physical properties of the composition containing microfibrillated cellulose and calcium carbonate (mass ratio 1:1), when using additional energy. The results are shown in the following table (Table 14).

As can be seen, the results obtained are mixed. In some cases, there is an increase in FLT, and in other cases there is not.

results

The results obtained show:

• The single disc refiner in the pilot plant is a very efficient way to redisperse a composition containing microfibrillated cellulose and calcium carbonate (1:1 weight ratio).

• A composition containing microfibrillated cellulose and calcium carbonate (weight ratio 1:1), dried to a solids content of 86 wt.%, can be redispersed to ensure its original strength characteristics.

• An improvement in strength can be achieved.

• The single disc refiner provides redispersion with low energy input compared to other methods tested.

• Solids content is a very important factor in refining and must be optimized for all samples.

• Reducing the intensity of the refiner provides improved results.

• The single disc refiner is very effective in changing the PSD of a formulation containing microfibrillated cellulose and calcium carbonate (1:1 weight ratio).

Claims (33)

1. A method for improving the physical and/or mechanical properties of redispersed dried or partially dried microfibrillated cellulose, including: a. providing: an aqueous composition of microfibrillated cellulose, where the microfibrillated cellulose is obtained from waste pulp, or scraps of paper production, or waste from paper production; b. dehydrating the aqueous composition with one or more of the following: i. dehydration with a belt press, ii. high pressure automatic belt press, iii. centrifuges, iv. tubular press, v. screw press, and vi. rotary press; to obtain a dehydrated microfibrillated cellulose composition; c. drying the dehydrated microfibrillated cellulose composition with one or more of the following: i. fluid bed dryers, ii. microwave and/or radio frequency dryer, iii. hot air blown mill or dryer, sectional mill or multi-screw sectional mill, and iv. freeze drying; to obtain a composition of dried or partially dried microfibrillated cellulose; And (d) redispersing the dried or at least partially dried microfibrillated cellulose into a liquid medium; wherein the microfibrillated cellulose has a tensile strength and/or viscosity of at least 50% of the tensile strength and/or viscosity of an aqueous microfibrillated cellulose composition prior to drying at a comparable concentration, and a fiber twist of 20 to 50. 2. The method of claim. 1, characterized in that said microfibrillated cellulose further comprises an inorganic material in the form of particles. 3. The method according to claim 2, characterized in that the particulate inorganic material contains lamellar mineral, kaolin and/or talc. 4. The method of claim 3, wherein the particulate inorganic material further comprises a particulate inorganic material other than a plate mineral. 5. The method of claim 2, wherein the particulate inorganic material is calcium carbonate. 6. The method according to claim 1, characterized in that said dried or partially dried microfibrillated cellulose is redispersed in the presence of one or more additives selected from the group consisting of one or more salts, one or more sugars, one or more glycols, urea , carboxymethylcellulose and guar gum. 7. The method according to claim 6, characterized in that the sugar is selected from one or more monosaccharides, disaccharides, oligosaccharides and polysaccharides. 8. The method according to p. 6, characterized in that one or more salts contains or is sodium chloride. 9. The method according to claim 6, characterized in that one or more glycols contains or is ethylene glycol. 10. The method according to p. 2, characterized in that the inorganic material in the form of particles is added at one or more of the following stages: (i) before or during the preparation of an aqueous composition containing microfibrillated cellulose; (ii) after receiving an aqueous composition containing microfibrillated cellulose; (iii) during dehydration of the aqueous microfibrillated cellulose composition; (iv) during drying of the aqueous microfibrillated cellulose composition; (v) before redispersing the dried or at least partially dried microfibrillated cellulose; and (vi) during redispersion of the dried or at least partially dried microfibrillated cellulose. 11. The method of claim. 1, further comprising the use of redispersed microfibrillated cellulose in the article, product or composition or to obtain an article, product or composition. 12. The method of claim. 1, characterized in that the solids content in the aqueous composition of dehydrated microfibrillated cellulose before drying or at least partial drying is not more than 50 wt.%, not more than 30% and not more than 20%. 13. The method according to p. 2, characterized in that the solids content in the aqueous composition of dehydrated microfibrillated cellulose before drying or at least partial drying is not more than 20 wt.%, while optionally not more than 80% of the solids are inorganic material in the form of particles. 14. The method according to p. 1, characterized in that the liquid medium is aqueous or non-aqueous. 15. The method according to claim 14, characterized in that the liquid medium is aqueous, for example, is water. 16. The method of claim. 1, characterized in that said redispersion of dried or at least partially dried microfibrillated cellulose includes the use of a refiner.

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