The present invention relates generally to methods of improving the re-dispersibility of dried or at least partially dried microfibrillated cellulose and methods of re-dispersing dried or at least partially dried microfibrillated cellulose. The methods may, for example, comprise dewatering the aqueous composition, optionally followed by drying. The re-dispersing microfibrillated cellulose may, for example, comprise re-dispersing dried or at least partially dried microfibrillated cellulose in a liquid medium and in the presence of an additive other than inorganic particulate material and/or in the presence of a combination of inorganic particulate materials. The additive and/or combination of inorganic particulate materials may, for example, enhance a mechanical and/or physical property of the re-dispersed microfibrillated cellulose. The present invention further relates to compositions comprising re-dispersed microfibrillated cellulose and the use of re-dispersed microfibrillated cellulose in an article, product or composition.

BACKGROUND OF THE INVENTION

In recent years microfibrillated cellulose and compositions comprising same has been shown to have a variety of useful properties, including the enhancement of the mechanical, physical and/or optical properties of a variety of products, such as paper, paperboard, polymeric articles, paints, and the like. Typically prepared in aqueous form, it is normally dried for transport in order to reduce its weight and associated transportation costs. The end-user will then typically re-disperse the microfibrillated cellulose prior to use in the intend end-use. However, following drying and re-dispersion some or all of its advantageous properties are diminished or lost. Thus, there is an ongoing need to improve the properties of microfibrillated cellulose following drying and re-dispersal.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention there is provided a method of improving the re-dispersibility 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:

(a) dewatering by belt press, for example, high pressure automated belt press, (b) dewatering by centrifuge, (c) dewatering by tube press, (d) dewatering by screw press, and (e) dewatering by rotary press; followed by drying,

or

(ii) dewatering the aqueous composition, followed by drying by one or more of:

(f) drying in a fluidized bed dryer, (g) drying by microwave and/or radio frequency dryer, (h) drying in a hot air swept mill or dryer, for example, a cell 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,

where upon re-dispersing the dried or at least partially dried microfibrillated cellulose in a liquid medium, the re-dispersed microfibrillated cellulose has a mechanical and/or physical property which is closer to that of the microfibrillated cellulose prior to drying or at least partial drying than it would have been but for drying according to (i), (ii), (iii) or (iv), optionally wherein the dried or at least partially dried microfibrillated cellulose comprises inorganic particulate material and/or an additive, the presence of which enhances a mechanical and/or physical property of the re-dispersed microfibrillated cellulose.

In certain embodiments, the method further comprises re-dispersing the dried or at least partially dried microfibrillated cellulose in the liquid medium, and optionally further comprising using the re-dispersed microfibrillated cellulose in the manufacture of an article, product or composition.

In accordance with a second aspect of the present invention there is provided a method of re-dispersing microfibrillated cellulose, the method comprising re-dispersing dried or at least partially dried microfibrillated cellulose in a liquid medium, wherein the dried or at least partially dried microfibrillated cellulose was prepared by dewatering and drying an aqueous composition comprising microfibrillated cellulose whereby the re-dispersed microfibrillated cellulose has a mechanical and/or physical property which is closer to that of the microfibrillated cellulose prior to drying or at least partial drying than it would have been but for said dewatering and drying, optionally wherein the dried or at least partially dried microfibrillated cellulose comprises: (i) inorganic particulate material, (ii) a combination of inorganic particulate materials, and/or (iii) an additive other than inorganic particulate material, the presence of which during re-dispersing enhances a mechanical and/or physical property of the re-dispersed microfibrillated cellulose; and wherein dewatering is selected from one or more of:

(a) dewatering by belt press, for example, high pressure automated belt press;

(b) dewatering by centrifuge;

(c) dewatering by tube press;

(d) dewatering by screw press; and

(e) dewatering by rotary press;

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

(f) drying in a fluidized bed dryer;

(g) drying by microwave and/or radio frequency dryer

(h) drying in a hot air swept mill or dryer, for example, a cell mill or an atritor mill; and

(i) drying by freeze drying.

In accordance with a third aspect of the present invention there is provided a method of improving the physical and/or mechanical properties of re-dispersed dried or partially dried microfibrillated cellulose, the method comprising:

a. providing: an aqueous composition of microfibrillated cellulose; b. dewatering the aqueous composition by one or more of: (i) dewatering by belt press, (ii) a high pressure automated belt press, (iii) centrifuge, (iv) tube press, (v) screw press, and (vi) rotary press;

to produce a dewatered microfibrillated cellulose composition;

c. drying the dewatered microfibrillated cellulose composition by one or more of: (i) a fluidized bed dryer, (ii) microwave and/or radio frequency dryer, (iii) a hot air swept mill or dryer, a cell mill or a multirotor cell mill, and (iv) freeze drying;

to produce a dried or partially dried microfibrillated cellulose composition;

whereupon re-dispering the dried or partially dried microfibrillated cellulose composition into a liquid medium, the microfibrillated cellulose has a tensile index and/or viscosity which is at least 50 % of the tensile index and/or viscosity of the aqueous composition of microfibrillated cellulose prior to drying at a comparable concentration and a fibre steepness of from 20 to 50.

In accordance with a forth aspect of the present invention there is provided a method of re-dispersing microfibrillated cellulose, the method comprising re-dispersing dried or at least partially dried microfibrillated cellulose in a liquid medium and in the presence of an additive other than inorganic particulate material which enhances a mechanical and/or physical property of the re-dispersed microfibrillated cellulose, wherein the microfibrillated cellulose prior to being dried or at least partially dried has a fibre steeness of from 20 to 50.

In accordance with a fifth aspect of the present invention there is provided a method of re-dispersing microfibrillated cellulose, the method comprising re-dispersing dried or at least partially dried microfibrillated cellulose in a liquid medium and in the presence of a combination of inorganic particulate materials, wherein the combination of inorganic particulate materials enhances a mechanical and/or physical property of the re-dispersed microfibrillated cellulose, optionally wherein the combination of inorganic particulate materials comprises calcium carbonate and a platy mineral.

In accordance with a sixth aspect of the present invention there is provided a composition comprising re-dispersed microfibrillated cellulose dispersed in a liquid medium and which is obtainable/obtained by a method according to any aspect or embodiment of the present invention, and having, at a comparable concentration, a tensile index and/or viscosity which is at least 50 % of the tensile index and/or viscosity of the aqueous composition of microfibrillated cellulose prior to drying, wherein either (i) the microfibrillated cellulose of the aqueous composition has a fibre steepness of from 20 to 50, and/or (ii) the aqueous composition of microfibrillated cellulose comprises inorganic particulate material.

In accordance with a seventh aspect of the present invention there is provided use of re-dispersed microfibrillated cellulose according to any aspect or embodiment of the present invention. In certain embodiments, the microfibrillated cellulose is used in an article, product or composition. Thus, in accordance with a further aspect of the present invention there is provided an article, product or composition comprising a microfibrillated cellulose according to any aspect or embodiment of the present invention. '

The details, examples and preferences provided in relation to any particular one or more of the stated aspects of the present invention apply equally to all aspects of the present invention. Any combination of the embodiments, examples and preferences described herein in all possible variations thereof is encompassed by the present invention unless otherwise indicated herein, or otherwise clearly contradicted by context.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows a summary of the effect of the use of a single disc refiner on dried composition comprising microfibrillated cellulose and calcium carbonate materials.

DETAILED DESCRIPTION OF THE INVENTION

Seeking to improve one or more properties of re-dispersed microfibrillated cellulose and compositions comprising same, it has surprisingly been found that a combination

of dewatering and drying, for example, mechanical dewatering and drying, an (never before dried) aqueous composition comprising microfibrillated cellulose, optionally in the presence of an inorganic particulate and/or other additive as herein described, can be implemented in order to enhance or improve one or more properties of the microfibrillated cellulose upon re-dispersal. That is to say, compared to the microfibrillated cellulose prior to drying, the one or more properties of the re-dispersed microfibrillated are closer to the one or properties of the microfibrillated cellulose prior to drying than it/they would have been but for the combination of dewatering and drying. Similarly, it has surprisingly been found that the incorporation of inorganic particulate material, or a combination of inorganic particulate materials, and/or other additives as herein described, can enhance the re-dispersibility of the microfibrillated cellulose following initial drying.

Thus, in certain embodiments, the method of improving the re-dispersibility of dried at least partially dried microfibrillated cellulose comprises drying or at least partially drying an aqueous composition by a method comprising:

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

(a) dewatering by belt press, for example, high pressure automated belt press, (b) dewatering by centrifuge, (c) dewatering by tube press, (d) dewatering by screw press, and (e) dewatering by rotary press; followed by drying,

or

(ii) dewatering the aqueous composition, followed by drying by one or more of:

(f) drying in a fluidized bed dryer, (g) drying by microwave and/or radio frequency dryer, (h) drying in a hot air swept mill or dryer, for example, a cell 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.

In certain embodiments, if drying is by freeze drying, dewatering comprises one or more of (a) to (e).

Upon subsequent re-dispersal, e.g., following transportation to another facility, of the dried or at least partially dried microfibrillated cellulose in a liquid medium, the re-dispersed microfibrillated cellulose has a mechanical and/or physical property which is closer to that of the microfibrillated cellulose prior to drying or at least partial drying than it would have been but for drying according to (i), (ii), (iii) or (iv).

Thus, in accordance with another aspect, there is provided a method of re-dispersing microfibrillated cellulose, the method comprising re-dispersing dried or at least partially dried microfibrillated cellulose in a liquid medium, wherein the dried or at least partially dried microfibrillated cellulose was prepared by dewatering and drying an aqueous composition comprising microfibrillated cellulose whereby the re-dispersed microfibrillated cellulose has a mechanical and/or physical property which is closer to that of the microfibrillated cellulose prior to drying or at least partial drying than it would have been but for said dewatering and drying, optionally wherein the dried or at least partially dried microfibrillated cellulose comprises: (i) inorganic particulate material, (ii) a combination of inorganic particulate materials, and/or (iii) an additive other than inorganic particulate material, the presence of which during re-dispersing enhances a mechanical and/or physical property of the re-dispersed microfibrillated cellulose; and optionally wherein dewatering is selected from one or more of:

(a) dewatering by belt press, for example, high pressure automated belt press;

(b) dewatering by centrifuge;

(c) dewatering by tube press;

(d) dewatering by screw press; and

(e) dewatering by rotary press;

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

(f) drying in a fluidized bed dryer;

(g) drying by microwave and/or radio frequency dryer

(h) drying in a hot air swept mill or dryer, for example, a cell mill or an atritor mill; and

(i) drying by freeze drying;

In certain embodiments, if drying was by freeze drying, dewatering comprises one or more of (a) to (e).

Thus, in accordance with another aspect, there is provided a method of improving the physical and/or mechanical properties of re-dispersed dried or partially dried microfibrillated cellulose, the method comprising:

a. providing: an aqueous composition of microfibrillated cellulose; b. dewatering the aqueous composition by one or more of: (i) dewatering by belt press, (ii) a high pressure automated belt press, (iii) centrifuge, (iv) tube press, (v) screw press, and (vi) rotary press;

to produce a dewatered microfibrillated cellulose composition;

c. drying the dewatered microfibrillated cellulose composition by one or more of: (i) a fluidized bed dryer, (ii) microwave and/or radio frequency dryer, (iii) a hot air swept mill or dryer, a cell mill or a multirotor cell mill, and (iv) freeze drying;

to produce a dried or partially dried microfibrillated cellulose composition;

whereupon re-dispering the dried or partially dried microfibrillated cellulose composition into a liquid medium, the microfibrillated cellulose has a tensile index and/or viscosity which is at least 50 % of the tensile index and/or viscosity of the aqueous composition of microfibrillated cellulose prior to drying at a comparable concentration and a fibre steepness of from 20 to 50.

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

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

In certain embodiments, the aqueous composition comprising microfibrillated cellulose is dewatered by belt press, for example, high pressure automated belt press, followed by drying, for example, via one or more of (f) to (i) above.

In certain embodiments, the aqueous composition comprising microfibrillated cellulose is dewatered by centrifuge, followed by drying, for example, via one or more of (f) to (i) above.

In certain embodiments, the aqueous composition comprising microfibrillated cellulose is dewatered by tube press, followed by drying, for example, via one or more of (f) to (i) above.

In certain embodiments, the aqueous composition comprising microfibrillated cellulose is dewatered by screw press, followed by drying, for example, via one or more of (f) to (i) above.

In certain embodiments, the aqueous composition comprising microfibrillated cellulose is dewatered by rotary press, followed by drying, for example, via one or more of (f) to (i) above.

In certain embodiments, the aqueous composition is dewatered, for example, via one or more of (a) to (e) above, and then dried in a fluidized bed dryer.

In certain embodiments, the aqueous composition is dewatered, for example, via one or more of (a) to (e) above, and then dried by microwave and/or by radio frequency drying.

In certain embodiments, the aqueous composition is dewatered, for example, via one or more of (a) to (e) above, and then dried in a hot air swept mill or dryer, for example, a cell mil or an Atritor mill. An Atritor mill may be an Atritor dryer-pulveriser, an Attritor Cell Mill, an Atritor Extended classifier mill or an Atritor Air Swept Tubular (AST) dryer (Atritor Limited, 12 The Stampings, Blue Ribbon Park, Coventry, West Midlands, England). Such mills may be used to prepare the aqueous composition of microfibrillated cellulose which is subsequently dried and then re-dispersed.

In certain embodiments, the aqueous composition is dewatered, for example, via one or more of (a) to (e) above, and then dried by freeze drying. In certain embodiments, dewatering is by one or more of (a)-(e) described above.

Dewatering and drying may 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 be depend on factors such as for example, the solids content of

the aqueous composition comprising microfibrillated cellulose, the bulk amount of the aqueous composition comprising microfibrillated cellulose and the temperature of drying.

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

In certain embodiments, the method further comprises re-dispersing the dried or at least partially dried microfibrillated cellulose in a liquid medium, which may be aqueous or non-aqueous liquid. In certain embodiments, the liquid medium is an aqueous liquid, for example, water. In certain embodiments, the water is a waste water or a recycled waste water derived from the manufacturing plant in which the re-dispersed microfibrillated cellulose is being used to manufacture an article, product or composition. For example, in paper/paper board manufacturing plants, the water may be or comprise recycled white water from the paper making process. In certain embodiments, at least portion of any inorganic particulate material and/or additive other than inorganic particulate material be present in the recycle white water.

In certain embodiments, the method further comprises using the re-dispersed microfibrillated cellulose in the manufacture of an article, product or composition, which are many and various and include, without limitation, paper and paperboard, polymeric articles, products and compositions, and other compositions such as coatings, e.g., paint.

In certain embodiments the dried or at least partially dried microfibrillated cellulose comprises inorganic particulate material and/or an additive, the presence of which enhances a mechanical and/or physical property of the re-dispersed microfibrillated cellulose. Such inorganic particulate materials and additives are described herein in below.

The aqueous composition comprising microfibrillated cellulose may be dewatered and dried in order to reduce water content by at least 10 % by weight, based on the total weight of the aqueous composition comprising microfibrillated cellulose prior to dewatering and drying, for example, by at least 20 % 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 by at least 80 % by weight, or by at least 80 % by weight, or by at least 90 % by weight, or by at least about 95 % by weight, or by at least about 99 % by weight, or by at least about 99.5 % by weight, or by at least 99.9 % by weight.

By "dried" or "dry" is meant that the water content of the aqueous composition comprising 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 comprising microfibrillated cellulose is reduced by an amount less than 95 % by weight. In certain embodiments, "partially dried" or "partially dry" means that the water content of the aqueous composition comprising microfibrillated cellulose is reduced by at least 50 % by weight, for example, by at least 75 % by weight, or by at least 90 % by weight.

The aqueous composition comprises microfibrillated cellulose. By "microfibrillated cellulose" is meant a cellulose composition in which microfibrils of cellulose are liberated or partially liberated as individual species or as smaller aggregates as compared to the fibres of a pre-microfibrillated cellulose. The microfibrillated cellulose may be obtained by microfibril!ating cellulose, including but not limited to the processes described herein. Typical cellulose fibres (i.e., pre-microfibrillated pulp) suitable for use include larger aggregates of hundreds or thousands of individual cellulose microfibrils. By microfibrillating the cellulose, particular characteristics and properties, including but not limited to the characteristic and properties described herein, are imparted to the microfibrillated cellulose and the compositions including the microfibrillated cellulose.

The microfibrillated cellulose may be derived from any suitable source, as described herein.

Unless otherwise stated, particle size properties referred to herein for the inorganic particulate materials are as measured in a well-known manner by sedimentation of the particulate material in a fully dispersed condition in an aqueous medium using a Sedigraph 5100 machine as supplied by Micromeritics Instruments Corporation, Norcross, Georgia, USA (telephone: +1 770 662 3620; web-site:

www.micromeritics.com), referred to herein as a "Micromeritics Sedigraph 5100 unit". Such a machine provides measurements and a plot of the cumulative percentage by weight of particles having a size, referred to in the art as the 'equivalent spherical diameter' (e.s.d), less than given e.s.d values. The mean particle size d50 is the value determined in this way of the particle e.s.d at which there are 50% by weight of the particles which have an equivalent spherical diameter less than that d50 value.

Alternatively, where stated, the particle size properties referred to herein for the inorganic particulate materials are as measured by the well-known conventional method employed in the art of laser light scattering, using a Malvern Mastersizer S machine as supplied by Malvern Instruments Ltd (or by other methods which give essentially the same result). In the laser light scattering technique, the size of particles in powders, suspensions and emulsions may be measured using the diffraction of a laser beam, based on an application of Mie theory. Such a machine provides measurements and a plot of the cumulative percentage by volume of particles having a size, referred to in the art as the 'equivalent spherical diameter' (e.s.d), less than given e.s.d values. The mean particle size d50 is the value determined in this way of the particle e.s.d at which there are 50% by volume of the particles which have an equivalent spherical diameter less than that d50 value.

Unless otherwise stated, particle size properties of the microfibrillated cellulose materials are as measured by the well-known conventional method employed in the art of laser light scattering, using a Malvern Mastersizer S machine as supplied by Malvern Instruments Ltd (or by other methods which give essentially the same result).

In certain embodiments, the microfibrillated cellulose has a d50 ranging from about 5 to pm about 500 pm, as measured by laser light scattering. In certain embodiments, the microfibrillated cellulose has a d50 of equal to or less than about 400 pm, for example equal to or less than about 300 pm, or equal to or less than about 200 pm, or equal to or less than about 150 pm, or equal to or less than about 125 pm, or equal to or less than about 00 pm, or equal to or less than about 90 pm, or equal to or less than about 80 pm, or equal to or less than about 70 pm, or equal to or less than about 60 pm, or equal to or less than about 50 pm, or equal to or less than about 40 pm, or equal to or less than about 30 pm, or equal to or less than about 20 pm, or equal to or less than about 10 pm.

In certain embodiments, the microfibrillated cellulose has a modal fibre particle size ranging from about 0.1-500 m. In certain embodiments, the microfibrillated cellulose has a modal fibre particle size of at least about 0.5 μιη, for example at least about 10 prn, or at least about 50 μητι, or at least about 100 μιη, or at least about 150 μιη, or at least about 200 μηι, or at least about 300 μιτι, or at least about 400 μπη.

Additionally or alternatively, the microfibrillated cellulose may have a fibre steepness equal to or greater than about 10, as measured by Malvern. Fibre steepness (i.e., the steepness of the particle size distribution of the fibres) is determined by the following formula:

Steepness = 100 x (d30/d70)

The microfibrillated cellulose may have a fibre steepness equal to or less than about 100. The microfibrillated cellulose may have a fibre steepness 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. The microfibrillated cellulose may have a fibre steepness 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 dewatering and/or drying. For example, one or more additives as specified below (e.g. salt, sugar, glycol, urea, glycol, carboxymethyl cellulose, guar gum, or a combination thereof as specified below) may be added to the microfibrillated cellulose. For example, one or more oligomers (e.g. with or without the additives specified above) may be added to the microfibrillated cellulose. For example, one or more inorganic particulate materials may be added to the microfibrillated cellulose to improve dispersibility (e.g. talc or minerals having a hydrophobic surface-treatment such as a stearic acid surface-treatment (e.g. stearic acid treated calcium carbonate). The additives may, for example, be suspended in low dielectric solvents. The microfibrillated cellulose may, for example, be in an emulsion, for example an oil/water emulsion, prior to dewatering and/or drying. The microfibrillated cellulose may, for example, be in a masterbatch composition, for example a polymer masterbatch composition and/or a high solids masterbatch composition, prior to dewatering and/or drying. The microfibrillated cellulose may, for example, be a high solids composition (e.g. 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%) prior to dewatering and/or drying. Any combination of one or more of the treatments may additionally or alternatively be applicable to the microfibrillated cellulose after dewatering and drying but prior to or during re-dispersion.

The re-dispersed microfibrillated cellulose has a mechanical and/or physical property which is closer to that of the microfibrillated cellulose prior to drying or at least partial drying than it would have been but for drying in accordance with (i), (ii), (iii) or (iv) above.

In certain embodiments, the re-dispersed microfibrillated cellulose has a mechanical and/or physical property which is closer to that of the microfibrillated cellulose prior to drying or at least partial drying than it would have been but for drying in accordance with (i), (ii) or (iii).

The mechanical property may be any determinable mechanical property associated with microfibrillated cellulose. For example, the mechanical property may be a strength property, for example, tensile index. Tensile index may be measured using a tensile tester. Any suitable method and apparatus may be used provided it is controlled in order to compare the tensile index of the microfibrillated cellulose before drying and after re-dispersal. For example, the comparison should be conducted at equal concentrations of microfibrillated cellulose, and any other additive or inorganic particulate material(s) which may be present. Tensile index may be expressed in any suitable units such as, for example, N.m/g or kN.m/kg.

The physical property may be any determinable physical property associated with microfibrillated cellulose. For example, the physical property may be viscosity. Viscosity may be measured using a viscometer. Any suitable method and apparatus may be used provided it is controlled in order to compare the viscosity of the microfibrillated cellulose prior to drying and after re-dispersal. For example, the comparison should be conducted at equal concentrations of microfibrillated cellulose,

and any other additive or inorganic particulate material(s) which may be present. In certain embodiments, the viscosity is Brookfield viscosity, with units of mPa.s.

In certain embodiments, the tensile index and/or viscosity of the re-dispersed microfibrillated cellulose is at least about 25 % of the tensile index and/or viscosity of the aqueous composition of microfibrillated cellulose prior to drying, for example, 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 index and/or viscosity of the microfibrillated cellulose prior to drying.

For example, if the tensile index of the microfibrillated cellulose prior to drying was 8 N.m/g, then a tensile index of at least 50 % of this value would be 4 N.m/g.

In certain embodiments, the tensile index of the re-dispersed microfibrillated cellulose is at least about 25 % of the tensile index of the aqueous composition of microfibrillated cellulose prior to drying, for example, 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 index of the microfibrillated cellulose prior to drying.

In certain embodiments, the viscosity of the re-dispersed microfibrillated cellulose is at least about 25 % of the viscosity of the aqueous composition of microfibrillated cellulose prior to drying, for example, 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 viscosity of the microfibrillated cellulose prior to drying.

In certain embodiments, inorganic particulate material and/or an additive other than inorganic particulate material is present during the dewatering and drying. The inorganic particulate material and/or additive may be added at any stage prior to dewatering and drying. For example, the inorganic particulate material and/or additive may be added during manufacture of the aqueous composition comprising microfibrillated cellulose, following manufacture of the aqueous composition comprising microfibrillated cellulose, or both. In certain embodiments, the inorganic particulate material is incorporated during manufacture of the microfibrillated cellulose (for example, by co-processing, e.g., co-grinding, as described here) and the additive other than inorganic particulate material is added following manufacture of the aqueous composition comprising microfibrillated cellulose. In certain embodiments, additional inorganic particulate material (which may be the same or different than the inorganic particulate added during manufacture of the microfibrillated cellulose) may be added following manufacture of the microfibrillated cellulose, for example, contemporaneously with the addition of additive other than inorganic particulate material. In certain embodiments, the microfibrillated cellulose of the aqueous composition has a fibre steepness of from 20 to 50. Details of the inorganic particulate material, additives and amounts thereof are described below.

In a further aspect, the method of re-dispersing microfibrillated cellulose comprises re-dispersing dried or at least partially dried microfibrillated cellulose in a liquid medium and in the presence of an additive other than inorganic particulate material which enhances a mechanical and/or physical property of the re-dispersed microfibrillated. The microfibrillated cellulose prior to being to be dried or at least partially dried has a fibre steepness of from 20 to 50.

In yet a further aspect, the method of re-dispersing microfibrillated cellulose comprises re-dispersing dried or at least partially dried microfibrillated cellulose in a liquid medium and in the presence of a combination of inorganic particulate materials, wherein the combination of inorganic particulate materials enhances a mechanical and/or physical property of the re-dispersed microfibrillated. In certain embodiments, the combination of inorganic particulate materials comprises calcium carbonate and a platy mineral, for example, a platy kaolin, or talc.

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

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

In certain embodiments, sugar is selected from monosaccharides (e.g. glucose, fructose, galactose), disaccharides (e.g. lactose, maltose, sucrose), oilgosacchardies (chains of 50 or less units of one or more monosaccharides) polysaccharides and combinations thereof.

In certain embodiments, the salt is an alkali metal or alkaline earth metal chloride, for example, sodium, potassium, magnesium and/or calcium chloride. In certain embodiments, the salt comprises or is sodium chloride.

In certain embodiments, the glyclol is and alkylene glycol, for example, selected from ethylene, propylene and butylene glycol, and combinations thereof. In certain embodiments, the glycol comprises or is ethylene glycol.

In certain embodiments, the additive comprises or is urea.

In certain embodiments, the additive comprises or is guar gum.

In certain embodiments, the additive comprises or is carboxymethyl cellulose. In certain embodiments, the additive is not carboxymethyl cellulose.

In certain embodiments, the microfibrillated cellulose prior to drying or at least partially drying is not acetylsed. In certain embodiments, the microfibrillated cellulose prior to drying or at least partially drying is not subjected to acetylation.

CLAIMS

A method of improving the physical and/or mechanical properties of re- dispersed dried or partially dried microfibrillated cellulose, the method comprising:

a. providing: an aqueous composition of microfibrillated cellulose;

b. dewatering the aqueous composition by one or more of:

i. dewatering by belt press,

ii. a high pressure automated belt press,

iii. centrifuge,

iv. tube press,

v. screw press, and

vi. rotary press;

to produce a dewatered microfibrillated cellulose composition;

c. drying the dewatered microfibrillated cellulose composition by one or more of:

i. a fluidized bed dryer,

ii. microwave and/or radio frequency dryer,

iii. a hot air swept mill or dryer, a cell mill or a multirotor cell mill, and iv. freeze drying;

to produce a dried or partially dried microfibrillated cellulose composition;

whereupon re-dispering the dried or partially dried microfibrillated cellulose composition into a liquid medium, the microfibrillated cellulose has a tensile index and/or viscosity which is at least 50 % of the tensile index and/or viscosity of the aqueous composition of microfibrillated cellulose prior to drying at a comparable concentration and a fibre steepness of from 20 to 50.

2. A method according to claim 1 , further comprising re-dispersing the dried or at least partially dried microfibrillated cellulose in the liquid medium.

3. The method of Claim 1 , wherein said microfibrillated cellulose additionally

comprises an inorganic particulate material.

The method of Claim 3, wherein the inorganic particulate material comprises a platy mineral, kaolin and/or talc.

The method of Claim 4, wherein the inorganic particulate material additionally comprises inorganic particulate material other than a platy mineral.

The method of Claim 3, wherein the inorganic particulate material is calcium carbonate.

7. The method of Claim 1 , wherein said dried or partially dried microfibrillated cellulose is re-dispersed 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, carboxymethyl cellulose and guar gum.

A method of Clam 5, wherein the sugar is selected from one or more of monosaccharides, disaccharides, oligosaccharides and polysachharides.

A method of Claim 5, wherein the one or more salts comprise or is sodium chloride.

A method of Claim 5, wherein the one or more glycols comprise or is ethylene glycol.

11. A method of Claim 3, the wherein inorganic particulate material is added at one or more of the following stages: (i) prior to or during manufacture of the aqueous composition comprising microfibrillated cellulose; (ii) following manufacture of the aqueous composition comprising microfibrillated cellulose;

(iii) during dewatering of the aqueous composition of microfibrillated cellulose;

(iv) during drying of the aqueous composition of microfibrillated cellulose; (v) prior to re-dispersing of the dried or at least partially dried microfibrillated cellulose; and (vi) during re-dispersing of the dried or at least partially dried microfibrillated cellulose.

12. The method of Claim 1 , said method further comprising using the re-dispersed microfibrillated cellulose in, or in the manufacture of, an article, product or composition.

13. The method of Claim 1 , wherein the aqueous composition of the dewatered microfibril lated cellulose prior to drying or at least partially drying has a solids content of up to about 50 wt. %, up to about 30 % and up to about 20%.

14. The method of Claim 3, wherein the aqueous composition of the dewatered microfibri Hated cellulose prior to drying or at least partially drying has a solids content of up to about 20 wt. %, optionally wherein up to about 80 % of the solids is inorganic particulate material.

15. The method of Claim 2, wherein the liquid medium is aqueous or non-aqueous.

16. The method of Claim 15, wherein the liquid medium is aqueous, for example, water.

17. The method of Claim 2, wherein said re-dispersing of the dried or at least partially dried microfibhllated cellulose comprises using a refiner.

18. The method of Claim 1 , wherein said a dried or partially dried microfibrillated cellulose composition has a steepness from about 20 to about 50.