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Title:
METHOD FOR TREATMENT OF CELLULOSE
Document Type and Number:
WIPO Patent Application WO/2018/191774
Kind Code:
A1
Abstract:
A method for producing a fibrillated cellulose material, including the steps of: (a) forming a swelling agent comprising at least one inorganic salt (or hydrate thereof) as a free solid, optionally in a liquid medium, in a fluidised state, (b) contacting a cellulosic material with the swelling agent to form a swollen cellulosic material; (c) optionally, adding further liquid to facilitate mixing; (d) optionally, rinsing the swollen cellulosic material to remove swelling agent; and (e) fibrillating the swollen cellulosic material to form a micro- or nano-fibrillated cellulose material.

Inventors:
BRETT STEPHEN J (AU)
O'NEILL JOHN R (AU)
Application Number:
PCT/AU2018/050342
Publication Date:
October 25, 2018
Filing Date:
April 17, 2018
Export Citation:
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Assignee:
NANOCELLULOSE IP PTY LTD (AU)
International Classes:
C08B15/00; C08B1/00; C08L1/02; C08L1/08; D21H11/18; D21H17/66
Domestic Patent References:
WO2014009517A12014-01-16
Foreign References:
DE102006049179A12008-04-30
US20080132456A12008-06-05
Other References:
SELKALA, T. ET AL.: "Anionically Stabilized Cellulose Nanofibrils through Succinylation Pretreatment in Urea-Lithium Chloride Deep Eutectic Solvent", CHEMSUSCHEM, vol. 9, 2016, pages 3074 - 3083, XP055553634
FISCHER, S. ET AL.: "Molten Inorganic Salts as Reaction Medium for Cellulose", CELLULOSE SOLVENTS: FOR ANALYSIS, SHAPING AND CHEMICAL MODIFICATION, 1 January 2010 (2010-01-01), pages 91 - 101, XP055553640
Attorney, Agent or Firm:
BERGER, Dan et al. (AU)
Download PDF:
Claims:
CLAIMS

1 . A method for producing a fibrillated cellulose material, including the steps of:

(a) forming a swelling agent comprising at least one inorganic salt (or hydrate thereof) as a free solid, optionally in a liquid medium, in a fluidised state,

(b) contacting a cellulosic material with the swelling agent to form a swollen cellulosic material;

(c) optionally, adding further liquid to facilitate mixing;

(d) optionally, rinsing the swollen cellulosic material to remove swelling agent; and

(e) fibrillating the swollen cellulosic material to form a micro- or nano- fibrillated cellulose material.

2. A method as claimed in claim 1 , wherein the swelling agent comprises one or more inorganic salts as a free solid in a liquid medium.

3. A method as clamed in claim 2, wherein wt% of liquid in the swelling agent is less than or equal to 50wt%.

4. A method as claimed in claim 2, wherein the wt% of liquid in the swelling agent is less than or equal to 35wt%.

5. A method as claimed in claim 2, wherein the wt% of liquid in the swelling agent is less than or equal to 20wt%

6. A method as claimed in any one of claims claim 2 to 5, wherein the wt% of salt in the swelling agent is greater than or equal to 50wt%.

7. A method as claimed in any one of claims 2 to 5, wherein the wt% of salt in the swelling agent is greater than or equal to 65wt%.

8. A method as claimed in any one of claims 2 to 5, wherein the wt% of salt in the swelling agent is greater than or equal to 80wt%.

9. A method as claimed in any one of claims 1 to 8, wherein the swelling agent is formed by over saturating a solvent with an inorganic salt such that excess salt solute remains as a free solid.

10. A method as claimed in claim 9, wherein the excess salt solute is suspended in the liquid medium.

1 1 . A method as claimed in any one of the preceding claims, wherein step (a) and/or (b) is carried out at ambient temperature, without heating.

12. A method as claimed in any one of the preceding claims, wherein step (b) includes stirring, mixing or agitating the cellulosic material with the swelling agent.

13. A method as claimed in any one of the preceding claims wherein, in step (b), the mass ratio of salt to cellulose is greater than or equal to 10:1 .

14. A method as claimed in any one of claims 1 to 12, wherein, in step (b), the mass ratio of salt to cellulose is greater than or equal to 20:1 .

15. A method as claimed in any one of claims 1 to 12, wherein, in step (b), the mass ratio of salt to cellulose is greater than or equal to 30:1 .

16. A method as claimed in claim 1 , wherein the swelling agent is in powder or granule form.

17. A method as claimed in any one of the preceding claims, wherein the at least one inorganic salt includes one or more alkali metal salts.

18. A method as claimed in claim 17, where the at least one inorganic salt is a sodium, potassium and/or lithium salt.

19. A method as claimed in any one of claims 1 to 16, wherein the at least one inorganic salt is a calcium salt or hydrate thereof.

20. A method as claimed in any one of the preceding claims, wherein the liquid medium includes an aqueous medium.

21 . A method as claimed in any one of the preceding claims, wherein the cellulosic material is a wood pulp.

22. A method of pre-treating a cellulosic material for fibrillation, including the step of (a) contacting a cellulosic material with a swelling agent comprising a suspension of one or more inorganic salts in a liquid medium to form a swollen cellulosic material.

23. A method as claimed in claim 22, wherein the swelling agent is an over saturated salt solution wherein excess salt solute remains as a free solid suspended in solution.

24. A method as claimed in claim 22 or 23, wherein the step (a) including mixing, stirring or agitating the cellulosic material with the swelling agent.

25. A method as clamed in any one of claims 22 to 24, wherein the wt% of liquid in the swelling agent is less than or equal to 50wt%.

26. A method as claimed in any one of claims 22 to 24, wherein the wt% of liquid in the swelling agent is less than or equal to 35wt%.

27. A method as claimed in any one of claims 22 to 24, wherein the wt% of liquid in the swelling agent is less than or equal to 20wt%.

28. A method as claimed in any one of claims 22 to 27, wherein the wt% of salt in the swelling agent is greater than or equal to 50wt%

29. A method as claimed in any one of claims 22 to 27, wherein the wt% of salt in the swelling agent is greater than or equal to 65wt%

30. A method as claimed in any one of claims 22 to 27, wherein the wt% of salt in the swelling agent is greater than or equal to 80wt%.

31 . A method as claimed in claim any one of claims 22 to 30, wherein step (a) is carried out at ambient temperature, without heating.

32. A method as claimed in any one of claims 22 to 31 , wherein, in step (a), the mass ratio of salt to cellulose is greater than or equal to 10:1 .

33. A method as claimed in any one of claims 22 to 31 , wherein, in step (a), the mass ratio of salt to cellulose is greater than or equal to 20:1 .

34. A method as claimed in any one of claims 22 to 31 , wherein, in step (a), the mass ratio of salt to cellulose is greater than or equal to 30:1 .

35. A method as claimed in any one of claims 22 to 34, wherein the at least one inorganic salt includes one or more alkali metal salts

36. A method as claimed in claim 35, wherein the at least one inorganic salt includes a sodium, potassium and/or lithium salt.

37. A method as claimed in any one of claims 22 to 34, wherein the at least one inorganic salt is a calcium salt or hydrate thereof.

38. A method as claimed in any one of claims 22 to 37, wherein the liquid medium includes an aqueous medium.

39. A method as claimed in any one of claims 22 to 38, wherein the cellulosic material is a wood pulp.

40. A swelling agent for treatment of cellulosic material prior to fibrillation, comprising a suspension of at least one inorganic salt in a liquid medium.

41 . A swelling agent as claimed in claim 40, wherein the swelling agent is an over saturated salt solution wherein excess salt solute remains as a free solid.

42. A swelling agent as claimed in claim 40 or 41 , wherein the at least one salt includes an alkali metal salt.

43. A swelling agent as claimed in any one of claims 40 to 42, wherein the at least one salt includes a sodium, potassium and/or lithium salt.

44. A swelling agent as claimed in claim 40 or 41 , wherein the at least one inorganic salt includes a calcium salt or hydrate thereof.

45. A swelling agent as claimed in any one of claims 40 to 44, wherein the liquid medium includes an aqueous medium.

46. A method of pre-treating a cellulosic material for fibrillation, including the step of (a) contacting a cellulosic material with a swelling agent comprising one or more inorganic salt (or hydrate thereof) in powder or granule form, to form a swollen cellulosic material.

Description:
METHOD FOR TREATMENT OF CELLULOSE

Field of the Invention

[001 ] The present invention relates to a low energy method for the preparation of microfibrillated/nanofibrillated cellulose which incorporates a novel swelling process as pre-treatment, to decrease the amount of energy required for fibrillation, and to a swelling agent for use therein.

Background of the Invention

[002] The term "nanocellulose" broadly describes cellulose structures with one dimension (typically diameter) in the sub-micron range (i.e. < 1 um). Two types of nanocellulose are:

• Cellulose nanofibrils ("CNF") with typical diameter 5-10 nm and 50-100 nm in average length; and

• Cellulose microfibrils ("CMF") with typical diameter 20-60 nm and length up to 20 urn

[003] CNF and CMF have a high aspect ratio (L/d) and surface area which make them useful for a variety of purposes, for example as a reinforcing agent in combination with other materials.

[004] It will be appreciated "fibrillated" or "fibrillation" refers to a process of size reduction of cellulosic material to provide cellulose fibrils, such as, for example, CNF or CMF (typically fibrils with at least one dimension sub-micron).

[005] It will also be appreciated that Microfibrillated cellulose (herein referred to as MFC) is used synonymously with terms "cellulose microfibrils", "microfibrillar cellulose", and "nanofibrillated cellulose".

[006] Conventional methods for creating nanocellulose are typically high energy mechanical fibrillation processes, such as grinding, extrusion, high pressure homogenization or fluidization. [007] Other processes have included manipulating the cellulose to allow a reduction in energy consumption, such as partial derivatisation of the cellulose (US 201 1 /0036522), the use of an inorganic acid (Cellulose (1998) 5, 19-32), the use of alkaline processes or enzymes or a combination of these, or combining pulp with a cellulose derivative prior to processing to reduce energy requirements (US 2012/0043039).

[008] A variety of pre-treatment strategies have been proposed in order to reduce the cohesion of the cellulose fibres and therefore reduce the energy needed for effective fibrillation.

[009] These have included enzymatic hydrolysis (Paakko et al. 2007), TEMPO mediated oxidation pretreatment (see references reviewed by Lavine, N., et al 2012.), carboxymethylation (references to Aulin, C, et al 2009 reviewed by Lavine, N., et al 2012.) and acetylation (Tingaut, Zimmerman and Lopez-Suevos 2009). High dry weight solids MFC has also been readily produced in aqueous derivatised cellulose suspensions mixed with an organic solvent during the low solids, low viscosity microfluidisation fibrillation process. (Kemira Oyj 2014, WO 2016066904 A1 ).

[010] Sappi 2012, (WO2014009517A1 ) describes a low energy method for the preparation of non-derivatized nanocellulose via contact with a swelling agent to produce a swollen intermediate stage.

[01 1 ] A "swelling agent" is an agent that can disrupt either the intercrystalline bonding or which can disrupt both the intercrystalline and partially (i.e. not fully) the intracrystalline bonding normally present in cellulosic material. Agents that will only disrupt intercrystalline bonding (and at most will minimally affect intracrystalline structure), will only lead to swelling, not dissolution, regardless of the reaction conditions used. Such agents will not lead to full solvation (which is a result of significant or full disruption of intracrystalline bonding). The extent of swelling is dependent on the interaction conditions.

[012] The materials described as suitable swelling agents for the Sappi process include: • Swelling agents which are cellulose non-solvents which only swell the intercrystalline regions such as morpholine, piperidine and the like;

• Swelling agents which can swell both the intercrystalline and partially (but not fully) the intracrystalline regions. Some of these swelling agents can under certain specific reaction conditions also act as cellulose solvents.

[013] A review of non-derivatizing solvent interactions of cellulose with inorganic molten salt hydrates (Sanghamitra, Sen., et al 2013) indicates significant swelling of cellulose (and even dissolution) can take place in some such systems at elevated temperatures, depending on the specific salt or salt combination eutectic melt temperatures.

[014] Inorganic molten salt hydrates are materials that have a water to salt molar ratio close to the coordination number of the strongest hydrated cation, with the water molecules being tightly bound to the inner coordination sphere of the cation, which form a fluid when heated to the melting point of the hydrate.

[015] Inorganic molten salt hydrates are inexpensive and easier to prepare compared to the other non-derivatizing cellulose solvents. Furthermore, they are comparatively environmentally friendly as no toxic and volatile organic compounds are required to prepare such solvent systems. During the regeneration of cellulose from inorganic molten salt hydrate solutions, one simply needs to add water and no organic solvents. Moreover, the main component of this solvent system, the inorganic salts, can be recovered by evaporating the water after cellulose regeneration and can be recycled for further use.

[016] Some of the reported cellulose-dissolving inorganic molten salt hydrates are UCIO4-3H2O, UI2-2H2O, USCN-2H2O, ZnCI2-3H2O, Ca-(NCS)2-3H2O, and an eutectic mixture of NaSCN/KCN/LiSCN-3H2O. However, there are some inorganic molten salt hydrates (UN03-2H20, LiCI-2-5H20, ZnCI2-2H20, and ZnCI2-4H20) that swell the cellulose to a fine distribution of the polymer but are unable to form a clear solution. [017] However, with the exception of Ca(SCN) 2 , which has a lower melting point, the swelling process is carried out at 100°C and above, and typically at the melt temperature of the metal salt hydrate used e.g. Ca(SCN) 2 , 140C; LiCI, 100C; Li (SCN) 2 , 100C; CaBr 2 , 100°C; KSCN/NASCN (eutectic), 135°C.

[018] It will be appreciated that such elevated temperatures increase the energy requirements of the process.

Summary of the Invention

[019] In one broad form, the present invention provides a method for producing a fibrillated cellulose material, including the steps of:

(a) forming a swelling agent comprising at least one inorganic salt (or hydrate thereof) as a free solid, optionally in a liquid medium, in a fluidised state;

(b) contacting a cellulosic material with the swelling agent to form a swollen cellulosic material;

(c) optionally, adding further liquid to facilitate mixing;

(d) optionally, rinsing the swollen cellulosic material to remove swelling agent; and

(e) fibrillating the swollen cellulosic material to form a micro- or nano-fibrillated cellulose material.

[020] In one form, the swelling agent comprises one or more inorganic salts as a free solid in a liquid medium.

[021 ] In one form, the wt% of liquid in the swelling agent is less than or equal to 50wt%.ln one form, the wt% of liquid in the swelling agent is less than or equal to 35wt%. In one form, the wt% of liquid in the swelling agent is less than or equal to 20wt%

[022] In one form, the wt% of salt in the swelling agent is greater than or equal to 50wt%. In one form, the wt% of salt in the swelling agent is greater than or equal to 65wt%. In one form, the wt% of salt in the swelling agent is greater than or equal to 80wt%. [023] In one form, the swelling agent is formed by over saturating a solvent with an inorganic salt such that excess salt solute remains as a free solid. In one form, the excess salt solute is suspended in the liquid medium.

[024] In one form, step (a) and/or (b) is carried out at ambient temperature, without heating.

[025] In one form, step (b) includes stirring, mixing or agitating the cellulosic material with the swelling agent.

[026] In one form, in step (b), the mass ratio of salt to cellulose is greater than or equal to 10:1 . In one form, in step (b), the mass ratio of salt to cellulose is greater than or equal to 20:1 . In one form, in step (b), the mass ratio of salt to cellulose is greater than or equal to 30:1 .

[027] In one form, the swelling agent is in powder or granule form.

[028] In one form, the at least one inorganic salt includes one or more alkali metal salts. In one form, the at least one inorganic salt is a sodium, potassium and/or lithium salt. In one form, the at least one inorganic salt is a calcium salt or hydrate thereof.

[029] In one form, the liquid medium includes an aqueous medium. In one form the liquid medium includes a combination of miscible or immiscible solvents. In one form, the liquid medium includes alcohol.

[030] In form, the cellulosic material is a wood pulp.

[031 ] In a further broad form, the present invention provides, a method of pre- treating a cellulosic material for fibrillation, including the step of (a) contacting a cellulosic material with a swelling agent comprising a suspension of one or more inorganic salts in a liquid medium to form a swollen cellulosic material.

[032] In one form, the swelling agent is an over saturated salt solution wherein excess salt solute remains as a free solid suspended in solution. [033] In one form, the step (a) including mixing, stirring or agitating the cellulosic material with the swelling agent.

[034] In one form, the wt% of liquid in the swelling agent is less than or equal to 50wt%. In one form, the wt% of liquid in the swelling agent is less than or equal to 35wt%. In one form, the wt% of liquid in the swelling agent is less than or equal to 20wt%.

[035] In one form, the wt% of salt in the swelling agent is greater than or equal to 50wt%. In one form, the wt% of salt in the swelling agent is greater than or equal to 65wt%. In one form, the wt% of salt in the swelling agent is greater than or equal to 80wt%.

[036] In one form, the step (a) is carried out at ambient temperature, without heating.

[037] In one form, in step (a), the mass ratio of salt to cellulose is greater than or equal to 10:1 . In one form, in step (a), the mass ratio of salt to cellulose is greater than or equal to 20:1 . In one form, in step (a), the mass ratio of salt to cellulose is greater than or equal to 30:1 .

[038] In one form, the at least one inorganic salt includes one or more alkali metal salts. In one form, the at least one inorganic salt includes a sodium, potassium and/or lithium salt.

[039] In one form, the at least one inorganic salt is a calcium salt or hydrate thereof. [040] In one form, the liquid medium includes an aqueous medium. [041 ] In one form, the cellulosic material is a wood pulp.

[042] In a further broad form the present invention provides a swelling agent for treatment of cellulosic material prior to fibrillation, comprising a suspension of at least one inorganic salt in a liquid medium.

[043] In one from, the swelling agent is an over saturated salt solution wherein excess salt solute remains as a free solid. [044] In one form, the at least one salt includes an alkali metal salt. In one form, the at least one salt includes a sodium, potassium and/or lithium salt.

[045] In one form, the at least one inorganic salt includes a calcium salt or hydrate thereof.

[046] In one form, the liquid medium includes an aqueous medium.

[047] In a further broad form the present invention provides a method of pre-treating a cellulosic material for fibrillation, including the step of (a) contacting a cellulosic material with a swelling agent comprising one or more inorganic salt (or hydrate thereof) in powder or granule form, to form a swollen cellulosic material.

[048] It will be appreciated that generally, the present invention seeks to provide a new method for production of microfibrillated or nanofibrillated cellulose, a new method for pre-treatment of cellulosic material for fibrillation, and/or new swelling agents for pre-treatment of cellulosic material.

[049] In one aspect, the present invention is directed towards a low energy method for the preparation of micro- or nano-fibrillated cellulose using a swelling agent that includes free solid ionic salts in a fluidised state. For example, the swelling agent may include a water soluble ionic salt in an aqueous medium, at a concentration in excess of its solubility in water, so that excess solute remains as a free solid.

[050] According to one aspect, the present invention is based on the surprising observation that it is possible to provide an alternative to inorganic salt melts in pre- treatment of cellulose for fibrillation, by contacting the cellulose with a swelling agent including an inorganic salt (or hydrate thereof) in solid, particulate form, optionally in a liquid medium.

[051 ] In one form, the swelling agent comprises an inorganic salt suspension formed by stir-addition of small amounts of liquid medium, for example water or alcohol, to the solid salt particles. The 'pseudo-fluid' thus formed behaves like a liquid over a range of ambient temperatures while stirring continues. It is possible then to add dry cellulose powder, chips or flakes to the room temperature fluid. In one example, the liquid content in the swelling agent is less than 50wt% total (including any water of hydration).

[052] It is believed that the use of these salt suspension or free solid salt swelling agents allow opening up the intercrystalline structure without substantially breaking down the intracrystalline structure of the cellulose material thereby achieving a reduction in the energy required to subsequently process the resultant swollen cellulose material into MFC and/or CNF.

[053] In one example aspect, the invention provides a method for producing a micro- or nano-fibrillated cellulose material, including the steps of:

(a) forming a swelling agent comprising one or more inorganic salts as a free solid, optionally in a liquid medium, in a fluidised state, wherein water content of the swelling agent is less that 50wt%;

(b) contacting a cellulosic material with the swelling agent to form a swollen cellulosic material;

(c) optionally, adding further (typically minimal) liquid to control viscosity;

(d) rinsing the swollen cellulosic material to remove excess swelling agent; and

(e) fibrillating the swollen cellulosic material to form a micro- or nano- fibrillated cellulose material.

[054] A further example aspect of the invention comprises a method of pre-treating a cellulosic material for fibrillation, including contacting a cellulosic material with a swelling agent comprising one or more inorganic salts as a free solid, optionally in a liquid medium, in a fluidised state, to form a swollen cellulosic material.

[055] A yet further example aspect of the invention comprises a swelling agent for treatment of cellulosic material prior to fibrillation, comprising an over-saturated suspension of one or more inorganic salts in a liquid medium, in a fluidised state.

[056] Typically, non-oxidising, non-flammable inorganic salts are preferred. In one example form, the salt may comprise an alkali metal salt, for example a sodium, lithium or potassium salt. Typically, sodium chloride or lithium chloride are preferred. Calcium salts may also be implemented.

[057] The liquid medium may include an aqueous medium, optionally in admixture or solution with another liquid, optionally an alcohol such as ethanol or isopropanol. Alternatively the liquid medium may comprise an alcohol, such as ethanol or isopropanol, without the water.

[058] In a further alternative form, the liquid medium may include a liquid that is substantially immiscible with water, which can act as a carrier to reduce viscosity of the liquid content without requiring increase in water content.

[059] It will be appreciated that the amount of liquid added to the salt is less than that required to dissolve the salt entirely into solution, such that it results in a salt/liquid suspension with free solids which, when stirred, acts like a fluid. Example proportions of liquid added to the salt (i.e. in the swelling agent) may be 10-50 wt% liquid, more preferably 10-40%,10-30% or 10-20%.

[060] Example proportions (by weight) of water in the swelling agent to cellulose during mixing are from 1 :1 water to cellulose, to 5:1 . Further, example ranges include from 2:1 to 4:1 water to cellulose, or about 3:1 . Proportions may be varied to accommodate the water content of the cellulosic material chosen.

[061 ] In the context of the present application the term "microfibrillated cellulose" or "MFC" is typically understood as liberated semi-crystalline cellulosic fibril structures or as liberated bundles of nanosized cellulose fibrils. MFC typically has a diameter of 2 - 60 nm, preferably 4 - 50 nm, more preferably 5 - 40 nm, and a length of 20 micrometers or less, preferably less than 500 nm. MFC often comprises bundles of 10 - 50 microfibrils. MFC may have high degree of crystallinity and high degree of polymerization, for example the degree of polymerization DP, i.e. the number of monomeric units in a polymer, may be 100 - 3000.

[062] The term "cellulosic material" as used herein refers to a cellulose containing material (preferably formed substantially of cellulose) and includes but is not limited to the following: microcrystalline cellulose, microbial cellulose, cellulose derived from marine or other invertebrates, mechanically generated wood pulp, chemical pulp, native biomass (in the form of plant fibres, stems or husks) and cellulosic man-made fibres such as tyre cord and other cellulose II sources such as mercerised cellulose. Cellulosic material may refer to, for example, spinifex or recycled cellulose. The cellulosic material may further be chemically derivatized by for example carboxylation, oxidation, sulphation or esterification.

[063] Preferred cellulose sources are derived primarily from wood pulp and other cellulosic biomass fibres and micro-crystalline cellulose, as for example Avicel PH- 101 , from FMC Corporation. Preferred sources of wood pulp include ground wood fibres, recycled or secondary wood pulp fibres, bleached and unbleached wood fibres. Both softwoods and hardwoods can be utilised. Biomass materials such as sugar beet, bagasse, hemp, flax, cotton, abaca, jute, kapok, silk floss and bamboo based cellulose can be utilised.

[064] Examples of mechanical methods for fibrillating cellulose to MFC or CNF include grinding, extrusion, high pressure homogenization or fluidization. The mechanical treatment may be carried out for example by using a refiner; grinder; homogenizer; colloider; friction grinder; fluidizer, such as microfluidizer, macrofluidizer or fluidizer-type homogenizer.

[065] Further preferred forms of the invention will be apparent from the description below and the drawings, and from the claims.

Brief Description of the Drawings

[066] Further preferred embodiments of the invention will now be described with reference to the accompanying drawings, in which:

[067] Figs 1 A to 1 C are photographs taken under microscope of a cellulose material pre-treated according to Example 1 , after homogenisation (Fig 1 A), after a single microfluidiser pass (Fig 1 B), and after three microfluidiser passes (Fig 1 C); [068] Figs 2A to 2C are photographs taken under microscope of a cellulose material pre-treated according to Example 2 (Control), after homogenisation (Fig 2A), after a single microfluidiser pass (Fig 2B), and after three microfluidiser passes (Fig 2C);

[069] Fig 3 is an example graph of temperature v time from addition of pulp showing the swelling exotherm, using NaCI in water suspension as swelling agent;

[070] Fig 4 is a graph of exotherm temperature v NaCI concentration (wt %) in Example 5;

[071 ] Fig 5 is a graph of Initial and Final Swelling Indices v NaCI concentration (wt %) in Example 5; and

[072] Fig 6 is a graph of Initial and Final Swelling Indices for various salts or other swelling agents in Example 6.

[073] Fig 7 is a graph of low shear viscosity Vs Fibrillation energy for examples 9 and 10 (bleached softwood kraft).

[074] Fig 8 is a graph of low shear viscosity Vs Fibrillation energy for examples 1 1 and 12 (unbleached softwood kraft).

[075] Fig 9 is a graph comparing the particle size of Bleached Softwood pulp after 90 minutes of Ultra-Turrax (Record 75 blue - SWPH15-UT90) with the same processed sample then treated with 3 MicroFluidiser passes (Record 57 green - SWPH15-3 passes).

Detailed Description of the Preferred Embodiments

[076] Embodiments of the invention provide a method for producing a fibrillated cellulose material, including the steps of:

(a) forming a swelling agent comprising at least one inorganic salt (or hydrate thereof) as a free solid, optionally in a liquid medium, in a fluidised state,

(b) contacting a cellulosic material with the swelling agent to form a swollen cellulosic material;

(c) optionally, adding further liquid to facilitate mixing; (d) optionally, rinsing the swollen cellulosic material to remove swelling agent; and

(e) fibrillating the swollen cellulosic material to form a micro- or nano-fibrillated cellulose material.

[077] In one example, the swelling agent comprises one or more inorganic salts as a free solid in a liquid medium. For example, as per step (a), a pseudo-fluid swelling agent may be prepared by adding small amounts of water (for example, approx. 20wt%) to ionic salts with high solubility. Typically, without stirring, the mixture would separate into two or three phases, being:

• Solid Salt

• Water in salt hydrate (certain salts only)

• Salt solution in water

[078] However, when stirred the phases act like one homogeneous fluid which is capable of effective swelling of cellulose. It is believed that when cellulose is contacted with the swelling agent, it causes opening up of the intercrystalline hydroxyl-hydrogen bonds of the cellulose.

[079] Typically, in example forms, the wt% of liquid in the swelling agent is less than or equal to 50wt%, less than or equal to 35wt%, or less than or equal to 20wt%. Typically, in example forms, the wt% of salt in the swelling agent is greater than or equal to 50wt%, greater than or equal to 65wt%, greater than or equal to 80wt%.

[080] It will be appreciated that, in some forms, contacting step (b) may include stirring, mixing or agitating the cellulosic material with the swelling agent. In this step, the mass ratio of salt to cellulose may vary. In example forms, in step (b), the mass ratio of salt to cellulose is typically greater than or equal to 10:1 , greater than or equal to 20:1 , or greater than equal to 30:1 .

[081 ] As salt:cellulose ratio increases the cellulose is swollen more effectively such that less energy input is required for the fibrillation step. For example, the 30:1 ratio allows fibrillated cellulose to be produced with a much higher NCF content after (relatively) simple rotor-stator mixing, such that high pressure homgenization or microfluidising is not necessary in order to achieve the highest possible aspect ratio.

[082] In some examples, during mixing, the swelling agent and cellulose forms a composition having constituents of about 80-85wt% salt, about 12-17% water, and about 1 -5wt% cellulose. In one preferred form, the composition is about 83wt% salt, 14wt% water, and about 3wt% cellulose.

[083] In some forms, the partially swollen cellulose from the contact step (b) is expanded in step (c) by further addition of water (or alcohol, other liquid etc.) under high shear stirring to maximise the disentanglement of the cellulose fibres following swelling. Typically, the water added in this step is still insufficient to dissolve all the salt, so that the swelling agent remains saturated with respect to the salt, and excess free solid salt remains in suspension. Typically, the preferred amount of water added is the minimum to maintain fluidity of the swelling agent.

[084] The salt concentration may then be removed/reduced by rinsing e.g. repeated wash/filtration or centrifuge cycles. The swollen cellulose gel may therefore, in some forms, be homogenised and microfluidised (i.e. in fibrillation step (e)) in the absence of swelling agent, thereby reducing the total treatment processing and chemical demand.

[085] It will also be appreciated that, in some forms (e.g. with hardwoods or dense cellulosic source materials), it may be useful to maintain salt/swelling agent present during the fibrillation step (e). For example there may be no rinsing step or reduced rinsing.

[086] It may also be possible to use various miscible or immiscible solvents during the homogenising and microfluidising stages (i.e. step (e)) to simplify processing or produce high-solids (low water) products.

[087] It will also be appreciated that, in other forms, alternate swelling agents may be implemented. For example, it is possible to implement over saturated (i.e. over saturated such that some salt solute is not dissolved and is suspended) processing pseudo-fluids (i.e. swelling agents) using a combination of miscible or immiscible solvents as part or all of the swelling agent composition.

[088] In one embodiment of the invention, combinations of water and alcohol and/or other water compatible solvents are implemented in the swelling process in order to: a) Reduce the amount of water present after microfluidising such that higher solids (i.e. 10%+) dispersions are readily achieved by evaporation of the alcohol component.

b) reduce the solubility of salt in the liquid such that removal of salt is achieved more cost effectively.

[089] In one example implementation of the invention, anhydrous lithium nitrate crystal (90g) is mixed at slow speed with water (20g) there is an initial endothermic decrease in temperature of 0.3 Q C. The salt crystal slowly becomes fluidised in the presence of water, yielding a white uniformly flowing suspension which is easily stirred.

[090] After slow addition of 5g Softwood pulp flake to the mix and an addition of a further 20g water to maintain a working viscosity, a slight exotherm is noted over a 3 hour period with a peak of some 8.5 Q C occurring at 2 hours. When the same amount of cellulose flake is added to a similar mass of water a smaller exotherm is noted with a peak of some 4 Q C temperature increase occurring after 2 hours.

[091 ] A surprising observation of the embodiments of invention is that, once swollen, the cellulose does not need to be in continuing contact with the swelling agent during the fibrillation step (e.g. the low solids, high shear homogenisation or microfluidisation phase) for fibrillation to occur. It is therefore possible to substantially reduce the net demand for swelling agent required in the prior art.

[092] In some forms, simple salts (in particular alkali metal salts e.g. sodium chloride) may be used to produce an over saturated pseudo-fluid swelling agent by adding small amounts of water and slow-speed stirring. A surprising observation is that these swelling agents are capable of powerful swelling of cellulose at ambient temperatures (i.e. without applying external heating), and, after removal of the salt (e.g. by rinsing), treated cellulose may be readily fibrillated to produce MFC or CNF with substantially no swelling agent contamination present. Certain salts (e.g. sodium, lithium, potassium) appear to have a unique ability to swell cellulose without disrupting intercrystalline bonding. Whilst salt implemented are typically potassium lithium and sodium salts, calcium salts may also be used.

[093] Furthermore, as noted above, it is possible to produce similar the 'pseudo- fluid' swelling agents using simple alcohols (e.g. ethanol, isopropanol) rather than water. These swelling agents are also capable of swelling cellulose sufficiently for it to be readily fibrillated to produce MFC, CMF or CNF.

[094] In addition, embodiments of the invention also provide a method of pre- treating a cellulosic material for fibrillation, including the step of contacting a cellulosic material with a swelling agent comprising one or more inorganic salt (or hydrate thereof) in powder or granule form, to form a swollen cellulosic material.

[095] A further surprising discovery is that dry pulp flakes, in the presence of dry simple salts (in particular alkali metal salts), in powdered or crystal form, can also be stirred and used as a means of swelling cellulose. In this case, it is believed that the inherent water content of the cellulose - typically about 3-5 wt% - may act as the water providing sufficient ionic medium to disrupt the intercrystalline hydroxyl bonds of the cellulose.

[096] It will be appreciated that conventional homogenizers and fluidizers may be used in the fibrillation step (e), such as Gaulin homogenizer or microfluidizer. During homogenization or fluidization the mixture comprising an aqueous suspension of cellulose fibres is typically subjected to high pressure of 500 - 2100 bar, preferably 500 - 1000 bar.

[097] For example, in homogenization, the suspension comprising cellulose derivative is pumped at high pressure, as defined above, and fed through a spring- loaded valve assembly. Cellulose derivative in the suspension is subjected to a large pressure drop under high shearing forces. This leads to fibrillation of the cellulose derivative. [098] Alternatively, in fluidization homogenization the cellulose suspension passes through Z- shaped channels under high pressure, as defined above. The channel diameter may be 100 - 400 pm. The Shear rate, which is applied to the cellulose suspension is high, and results in the formation of cellulose microfibrils.

[099] Irrespective of the procedure, (i.e. homogenization or fluidization) which is used for producing the microfibrillated cellulose, the procedure may be repeated several passes until the desired degree of fibrillation is obtained. It will also be appreciated that in some forms, such as, for example, those were significant swelling is achieved, fibrillation may be achieved without microfluidization or high pressure homogenization, such as, for example, by Rotor-Stator mixing.

[0100] It will be appreciated that, in one particular example form of the invention, micro- or nano-fibrillated cellulose material may be produced by the following steps:

(a) Form a swelling agent fluid by adding a small amount of liquid, e.g. water, to a solid, ionic salt, in an amount insufficient to dissolve the salt, so that salt remains as a free solid;

(b) Stirring to keep the undissolved salt in suspension as a pseudo-fluid, yielding a uniformly flowing liquid at room temperature;

(c) Adding dry cellulose powder, chips or flakes to the room temperature fluid, while continuing to stir;

(d) Adding further liquid, when required, to maintain a workable viscosity while swelling takes place;

(e) Once swelling is complete, rinsing to dissolve and separate the excess salt from the swollen cellulosic material;

(f) filtration and/or centrifuge followed by more rinsing as required to reduce salt concentration;

(g) addition of water or other liquid medium sufficient to allow effective Fibrillation of the swollen cellulose material, for example by Rotor-Stator mixing or homogenization or fluidization.

[0101 ] It will be appreciated that the present invention is also embodied, according to one aspect, as a method of pre-treating a cellulosic material for fibrillation, including the step of contacting a cellulosic material with a swelling agent comprising a suspension of one or more inorganic salts in a liquid medium to form a swollen cellulosic material. It will be appreciated the term salt may refer to an anhydrous or hydrated form thereof.

[0102] It will be appreciated that the present invention is also embodied, according to one aspect, as a swelling agent for treatment of cellulosic material prior to fibrillation, comprising a suspension of at least one inorganic salt in a liquid medium. It will be appreciated the term salt may refer to an anhydrous or hydrated form thereof.

[0103] Typically, as described above, the swelling agent is an over saturated salt solution wherein excess salt solute remains as a free solid. Generally, the at least one salt includes an alkali metal salt, such as, for example a sodium, potassium and/or lithium salt. It will be appreciated to a person skilled in art that salt hydrates may also be implemented in the formation of the swelling agent. In alternate forms, the at least one inorganic salt includes a calcium salt.

EXAMPLE 1 : Lithium Nitrate over-saturated solution with suspension of free solid

[0104] A room temperature (33°C) pseudo-fluid was prepared by addition under slow speed (400 RPM, propeller blade) of 40g of filtered water to 180g of LR grade anhydrous Lithium Nitrate. A stoichiometric amount of water necessary to produce a trihydrate salt would be around 100g). The temperature remained unchanged.

[0105] 10g of bleached softwood pulp (source Oji Fibre Solutions New Zealand grade White LCP, herein referred to as SWP) with moisture content (3%) was flaked into 5mm pieces and slowly added to the fluid over 10-15 minutes, while stirring continued.

[0106] A further 40g of water was added to the pulp suspension in order to maintain working viscosity.

[0107] Over the next 2 hours the temperature increased to a maximum 42°C (9°C change in temperature) and then slowly declined to 38C over the next 2 hours.

[0108] The pulp suspension changed from opaque white to translucent white over this period.

[0109] After 4 hours the blade was changed to a high shear cowles blade and the speed increased to 3000 RPM.

[01 10] 150g water was added slowly while maintaining speed for one hour.

[01 1 1 ] The suspension was then filtered leaving a residual of 31 Og (202 imLs) of swollen cellulose fibre/gel - this represents a swelling Index of 1 .5 when compared with the swelling volume of 137g (134mLs) achieved using only water with 10g Softwood Pulp and treated under the same conditions but without salt.

[01 12] The swollen fibre was then added to 200g water with high speed stirring for 2 minutes and then refiltered. [01 13] The process was repeated 9x using 200g aliquots of water to wash out the salt.

[01 14] 180g of treated and washed cellulose fibre (1 Og cellulose equivalent) was made up to 500 mis (nominal 2% suspension) by slow addition of water under high shear conditions.

[01 15] This mix was then slowly added to 500 imLs of water with stirring using an Ultra-Turrax style Rotor-Stator homogeniser assembly operating at 10,000 RPM. The mixer needed to be stopped occasionally during the first 10 minutes to clear away accumulated fibre from the inlet to the rotor stator.

[01 16] Dispersion quality continued to improve up to 2 hours of Ultra-Turrax homogenisation.

[01 17] A 15g cast of the 1 % dispersion yielded a slightly opaque film of thickness 10um after drying

[01 18] The 1 % solution was then passed through a Microfluidics model M1 10h microfluidizer with channels H30Z (200 urn) and G10Z (87 urn) and 20,000 psi pressure.

[01 19] A 15g cast of the 1 % dispersion after microfluidizing yielded a substantially translucent film indicating a high proportion of microfibrillation has taken place.

[0120] Figures 1 A to 1 C are microscope comparisons of Lithium Nitrate pretreated Cellulose dispersion:

[0121 ] Fig 1 A - after homogenisation

[0122] Fig 1 B - after one pass of the microfluidiser

[0123] Fig 1 C - after three passes of the microfluidiser [0124] The total energy requirement for the entire process is estimated at 500 kWhr/tonne of 1 % dispersion

1 ) Initial swelling 4hrs 400 RPM

2) Washing processes 10x2 mins

3) Filtration/centrifuge processes 10x 2 mins

4) Homogenisation process 2 hrs

5) Microfluidisation 3 passes, 1 % dispersion

[0125] Raw material requirement is determined to be (per tonne raw cellulose fibre): Lithium Nitrate 18T (recyclable), Water 230T (recyclable)

EXAMPLE 2: Water (control)

[0126] The same process as above was carried out using just water as the swelling agent. 10g of Softwood pulp is swollen to 137g (134 imLs).

[0127] 137g of swollen cellulose fibre (1 Og cellulose equivalent) was made up to 500 mis (nominal 2% suspension) by slow addition of water under high shear conditions.

[0128] This mix was then slowly added to 500 imLs of water with stirring using an Ultra-Turrax style Rotor-Stator homogeniser assembly operating at 10,000 RPM. The mixer needed to be stopped frequently to clear away accumulated fibre from the inlet to the rotor stator and the material. After 10 minutes the solution consisted of largely incompatible fibre agglomerates.

EXAMPLE 3: Morpholine

[0129] The same process as Example 1 was carried out as above except an 80% solution of morpholine in water was used as the swelling agent.

[0130] 10g of bleached softwood pulp (source Oji Fibre Solutions New Zealand grade White LCP) with moisture content (3%) was flaked into 5mm pieces and slowly added to 268g of 80% morpholine solution over 10-15 minutes.

[0131 ] Stirring is maintained for 3 hours. The pulp suspension changed from opaque white to translucent white over this period. [0132] After 4 hours the blade was changed to a high shear cowles blade and the speed increased to 3000 RPM.

[0133] The suspension was then filtered leaving a residual of 200g (195 imLs) of swollen cellulose fibre/gel - this represents a swelling Index of 1 .5 when compared with the swelling volume achieved using only water with treated under the same conditions (134 imLs).

[0134] The swollen fibre was then added to 200g water with high speed stirring for 2 minutes and then refiltered.

[0135] The process was repeated 9x using 200g aliquots of water to wash out the morpholine. At this point the swollen fibre/gel weighs only 140g (134 imLs) representing a swelling Index of only 1 .0 i.e. equivalent to water

[0136] 140g of treated and washed cellulose fibre (1 Og cellulose equivalent) was made up to 500 mis (nominal 2% suspension) by slow addition of water under high shear conditions.

[0137] This mix was then slowly added to 500 imLs of water with stirring using an Ultra-Turrax style Rotor-Stator homogeniser assembly operating at 10,000 RPM. The mixer needed to be stopped frequently during the first 10 minutes to clear away accumulated fibre from the inlet to the rotor stator. Finally, the solution solids was cut to 0.8% in order to get the fibre through the homogeniser.

[0138] Dispersion quality continued to improve up to 2 hours of Ultra-Turrax homogenisation.

[0139] A 15g cast of the 0.8 % dispersion yielded a slightly translucent film of thickness 10um after drying

[0140] The 0.8% solution was then passed through a Microfluidics model M1 10h microfluidizer with channels of 200 urn and 87 urn and 20,000 psi. After repeated plugging of the chamber a larger H30Z (200um) - H10Z (100um) interaction chamber configuration was necessary in order to effectively disperse the cellulose.

[0141 ] A 15g cast of the 1 % dispersion after microfluidizing yielded a slightly translucent film indicating a proportion of microfibrillation has taken place.

[0142] Figures 2A to 2C are microscope comparisons of morpholine solution pretreated Cellulose dispersion:

[0143] Fig 2A - after homogenisation

[0144] Fig 2B - after one pass of the microfluidiser

[0145] Fig 2C - after three passes of the microfluidiser

[0146] The total energy requirement for the entire process is estimated at »500 kWhr/tonne of 0.8% dispersion

1 ) Initial swelling 4hrs 400 RPM

2) Washing processes 10x2 mins

3) Filtration/centrifuge processes 10x 2 mins

4) Homogenisation process »2 hrs required to avoid blocking the microfluidizer

5) Microfluidisation 3 passes 0.8% dispersion

[0147] Raw material requirement is determined to be (per tonne raw cellulose fibre): Morpholine 27 T, Water 210T (minimum).

[0148] Separation of water and morpholine is problematic due to similarities in boiling point.

EXAMPLE 4 - Over-saturated Sodium Chloride solution with suspended free solid

[0149] A number of different blend ratios of Sodium Chloride (GP reagent grade) and water were used as swelling fluids for cellulose in order to demonstrate the effect of supra-saturation. [0150] The method was carried out substantially in accordance with Example 1 .

[0151 ] Table 1 below summarises the results of swelling index measurements (final and initial), and the observed exotherm observations.

[0152] The swelling index is the ratio of swelling observed compared to swelling with water alone.

[0153] The initial swelling index is the swelling measured at conclusion of the swelling and expansion process.

[0154] The final swelling index is the swelling measured following rinsing of the swollen cellulose pulp to substantially remove residual salt.

[0155] In every case, after addition of water there is a mild initial endotherm of a few degrees Celsius which stabilises after 5 minutes, then an exotherm as the cellulose is added and the swelling process continues.

- Table 1 -

[0156] Fig 3 is a typical plot of the exotherm against time from addition of the cellulose to the swelling agent.

[0157] It can be seen that there is an initial endotherm at about t= -10 mins, when water is initially added to the salt to form the supra-saturated suspension.

[0158] t= 0 mins corresponds to addition of the cellulose to the suspension, when the temperature has returned to the starting temperature.

[0159] An initial exotherm is noted with mixing of the cellulose with the swelling agent, plateauing at about t= 60 to 80 mins.

[0160] Further addition of water to expand the cellulose pulp at about t=90 to 120 mins produces a second, substantial exotherm, which then plateaus again.

[0161 ] Fig 4 is a plot of the peak exotherm against NaCI concentration of Table 1 .

[0162] After addition of the softwood pulp to the swelling fluid there is a clearly defined exotherm and peak which increases with salt and/or softwood pulp concentration.

[0163] The variation observable in the trend line of the graph of Fig 4 can be attributed to lower SWP concentration (Blend C) and higher SWP concentration (Blend D).

[0164] The maximum solubility of sodium chloride in water is 35.9g/100 imLs, so the additional heat generated during swelling of cellulose for blends B-G (where salt solubility is exceeded) indicates that swelling is independent of salt solubility in water.

[0165] The inclusion of the example wherein the swelling agent is in dry salt form (i.e. powder form) (Blend G) illustrates that substantial swelling may still take place in the presence of minimal water. The lower temperature peak noted is, we believe, due to difficulty of homogeneous mixing using a "propeller" or "Cowles" style mixing blade - the lower density cellulose flake continually rises to the top of the salt powder rendering mixing less efficient. It is anticipated that this dry process could be more effective in an extrusion-mixing screw blade assembly.

[0166] Fig 5 shows the relationship of initial swelling index Sl(in) and final swelling index Sl(fin) to NaCI total concentration.

[0167] The graph of Fig 5 illustrates the ability of sodium chloride to substantially swell cellulose pulp when used at concentrations in excess of 50%. The initial Swelling Index (Sl(in)) is measured at completion of the initial swelling stage and first filtration step immediately after the initial water let down. The final Swelling Index is measured after a minimum 10 washings to reduce salt to below 250 ppm.

[0168] In practical utility terms it has been found that the higher the final Swelling Index, the more easily the material is able to be fibrillated by homogenisation and microfluidizing processes. For materials with final Swelling Index <1 .5 manufacture of MFC is problematic. For final swelling index <1 .4 manufacture of MFC requires considerably longer Rotor-Stator prior to homogenisation or microfluidisation.

[0169] The final Swelling Index Sl(fin) plateaus from about an NaCI concentration of about 60-70 wt%, it is believed making this an optimal salt concentration range for operation.

[0170] It is proposed that, as per the graph of Fig 5, that salt concentrations in excess of 60% by weight the Swelling Index after washing (Sl(fin)) remains sufficiently high (>1 .5) to be effective at allowing rapid homogenisation and microfluidizing while minimising blockages. Thus the ease of homogenisation and dispersion quality increases with increasing salt concentration.

EXAMPLE 5 - Other salts

[0171 ] Other salts have also been evaluated at concentrations in excess of 50%, and all the materials tested display the ability to swell cellulose as summarised in Table 2.

- Table 2 -

[0172] The results are illustrated graphically in Fig 6.

[0173] With the materials tested, sodium and potassium chloride seem to be most effective with lower concentrations required for adequate (>1 .5) final swelling. Lithium chloride is of interest also as swelling index reduction with washing seems to be less pronounced with that salt. Lithium nitrate is borderline useful as higher concentrations are necessary for swelling. Zinc chloride was found to produce a lot of fine (non-fibril) material able to pass through and escape the filtration process and therefore resulting in reduced yield.

[0174] All salts seem to produce swelling which is substantially retained after washing. EXAMPLE 6a - Ethanol (compatible) Co-solvent

[0175] The same process was carried out with Lithium Nitrate but ethanol was used as co-solvent, replacing water in the let-down stage for Ultra-Turrax treatment and/or microfluidisation.

[0176] This process provides an option to produce high-solids low water gel concentrates by simple evaporation of the more volatile alcohol component from the low-water gel.

EXAMPLE 6b - Solvent 100 (SOLVENT NAPHTHA (PETROLEUM), LIGHT AROMATIC > BP 161 -171 C) - (incompatible) Co-Solvent

[0177] The same process was carried out with Lithium Nitrate but Solvent 100 (immiscible) was used replacing water as a liquid carrier in the let down stage for Ultra-Turrax treatment and/or microfluidisation.

[0178] This process provides an option to produce high-solids low-water gel concentrates by simple phase separation from the incompatible solvent 100.

EXAMPLE 7 - Isopropanol alternative to water in Swellant

[0179] A swelling solution using isopropanol to replace water with 10% SWP resulted in a swelling index 0.9 compared with water 1 .0.

EXAMPLE 8 - Swelling without water addition

[0180] A swelling solution comprising 96.4% sodium chloride, 3.57% SWP was mixed for 84 mins with a 5 Celsius exotherm. At the end of this time isopropanol was used to let down the mixture and filtration produced a gel with Swelling Index 2.4. This gel was then washed 10 times with water resulting in a final swelling index 1 .5. A 1 % solution was readily rotor-stator treated with no blockages noted.

EXAMPLES 9 to 12 - mass ratio NaChcellulose 15:1 and 30:1

[0181 ] For examples 9 and 10, a commercially available Softwood (Oji "Hi-White" bleached Kraft dry fibre (Kinleith source- "SWHW") was tested according to the method of example 1 using salt (Sodium Chloride, LR Grade) :cellulose ratios of 15:1 and 30:1 . The minimum quantity of water able to maintain circulation was added during the course of the swelling process.

[0182] For examples 1 1 and 12 Softwood Unbleached Kraft Pulp (17.1 % solids, "SWUP") was used with Sodium Chloride (30: 1 salt: cellulose) in example 1 1 and Lithium Chloride LR grade (15: 1 salt: cellulose) in example 12 ("SWUL").

[0183] The results were found as presented below in table 3:

- Table 3 -

! includes exothermic heat of solution for LiCI

[0184] Salt was removed by repeated washing and filtration through a 100um nylon mesh filter until the Salt concentration was below 300 ppm.

[0185] The swollen cellulose mixture was then let down to 1 % solids and treated by Ultra-Turrax Rotor-Stator homogenisation for various periods of time with the temperature increase then being used to calculate the energy expenditure in the process as KW.hr/tonne of 1 % dispersion.

[0186] Low shear Viscosity was measured using a Brookfield LV viscometer (spindlel_V4) at 6 RPM and 20 Celsius. Due to their high aspect ratio, nanocellulose solutions are known to have high viscosities at low solids, particularly at low shear rates.

[0187] The increase in viscosity therefore provides a simple relative measure of degree of fibrillation with energy expenditure.

[0188] The results, displayed graphically in figure 7 show that energy expenditure is substantially reduced by increasing the proportion of salt relative to cellulose in the swellant mix.

[0189] It is apparent from this graph that nanocellulose dispersions prepared using higher salt proportions in the swellant will have higher viscosities, indicating higher aspect ratio and smaller particle size. This is evidenced by greater transparency in film casts and reduced tendency to blockages in the earliest stages of rotor-stator mixing.

[0190] It should be noted that nanocellulose dispersions prepared with sufficient fibrillation energy to maximise viscosity do not necessarily display optimum properties. For example, transparency of film casts continue to increase in transparency with further fibrillation beyond maximum viscosity.

[0191 ] As a point of reference, 60 minutes of laboratory Ultra-Turrax Rotor-Stator mixing will provide approximately 60 kW.hr/tonne of fibrillation energy. One pass by Avestin D20 HPH will provide 60 kW.hr/tonne. Ten minutes using a commercial High- Speed blender (VitaMix Vita-Prep 3) will deliver approximately 100 kW.hr/tonne of fibrillation energy.

[0192] The results, displayed graphically in figure 8 below show that the invention applies equally well to unbleached softwood Kraft and that energy expenditure is again reduced by increasing the proportion of salt relative to cellulose in the swellant mix. This graph also shows that Lithium Chloride is a particularly effective swellant for the process, achieving similar fibrillation efficiencies with only half the amount of salt required per unit of cellulose.

[0193] It will be appreciated that the choice of salt may depend more on achievable particle size distribution and application requirements than cost of the salt.

[0194] By further way of illustration, figure 9 compares the particle size of Bleached Softwood pulp after 90 minutes of Ultra-Turrax (Record 75 blue - SWPH15-UT90) with the same processed sample then treated with 3 MicroFluidiser passes (Record 57 green - SWPH15-3 passes). Quite clearly the microfluidizer substantially decreases the particle size and this is evidenced in film casts with increased transparency and higher tensile properties.

[0195] In a most interesting result, where the bleached softwood pulp is treated with a similar 15:1 Lithium Chloride: cellulose Swelling process and processed to 90 minutes with Ultra-Turrax (Record 67 Red - SWLCUT90) , the observed particle size distribution is almost identical to that of the 90 minute Ultra-Turrax then - three-pass HPH treated sample, indicating that energy-intensive slow HPH processes can be eliminated by judicious choice of salt and concentrations as taught by this invention.

[0196] In this specification, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of". A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear.

[0197] It is intended that the components, elements and features of the various above-described embodiments can be used together in any desired combination or permutation to create new embodiments.

[0198] While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. It will further be understood that any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates.

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