TECHNICAL FIELD

[0001] The present disclosure relates to the field of acid hydrolysed cellulose and in particular to a process for manufacturing acid hydrolysed cellulose using sheets or a web comprising cellulose fibres.

BACKGROUND

[0002] Nano- and microcellulose materials have during recent years attracted much attention. There are two major types of such materials: nanocrystalline cellulose and nano- or microfibrillated cellulose.

[0003] Normally, when such materials are produced, a considerable amount of water is both used in the process itself and in case of the fibrillated cellulose, the water is regularly maintained also in the final product.

[0004] To facilitate the production of nano- and microfibrillated cellulose, it is common to conduct a pre-treatment process, such as TEMPO-oxidation, which require expensive chemicals, and regarding nanocrystalline cellulose excessive amounts of strong acids are handled.

[0005] Moreover, there is a constant strive for improving the scalability of the production processes of nanocrystalline cellulose and nano- or microfibrillated cellulose.

SUMMARY

[0006] The present disclosure aims to provide a more efficient method of producing acid hydrolysed cellulose.

[0007] Accordingly, the present disclosure provides the following list of itemized embodiments:

1. A continuous or semi-continuous process for manufacturing of acid hydrolysed cellulose comprising the steps of: a) providing sheets or a web of cellulose fibres; b) applying oxalic acid and/or citric acid and/or maleic acid to the sheets or web; c) reacting the oxalic acid and/ or citric acid and/ or maleic acid applied in step b) at a temperature in the interval of 70-135 °C with cellulose of the sheets or web to form acid hydrolysed cellulose; and d) cooling the acid hydrolysed cellulose.

2. The process according to item 1, further comprising the step: e) recovering the acid hydrolysed cellulose.

3. The process according to item 1 or 2, wherein the cellulose fibres provided in step a) contains less than 30 wt-% water, such as less than 20 wt-% water, such as less than 10 wt-% water based on the total weight of the cellulose fibres.

4. The process according to any one of the preceding items, wherein the cellulose fibres provided in step a) is not contacted with a deep-eutectic solvent.

5. The process according to any one of the preceding items, wherein the cellulose fibres provided in step a) is wood pulp or plant pulp or secondary lignocellulosic fibres or regenerated cellulose fibres.

6. The process according to any one of the preceding items, wherein the lignin content of the cellulose fibres provided in step a) is below 10 wt-%, such as below 5 wt-%, such as below 2 wt-%, based on dry weight of the fibres.

7. The process according to any one of the preceding items, wherein the density measured according to ISO 534:2011 of the sheets or web provided in step a) is 400- 750 kg/m ³ , such as 450-650 kg/m ³ , such as 500-600 kg/m ³ .

8. The process according to any one of the preceding items, wherein the oxalic acid and/or citric acid and/or maleic acid is applied in step b) by spraying the oxalic acid and/or citric acid and/or maleic acid onto the sheets or web of cellulose fibres, wherein the temperature of the oxalic acid and/or citric acid and/or maleic acid in step b) is in the same temperature interval as in step c).

9. The process according to any one of items 1-7, wherein the oxalic acid and/or citric acid and/or maleic acid is applied in step b) by immersing the sheets or web of cellulose fibres in oxalic acid or citric acid or maleic acid, wherein the temperature of the oxalic acid in step b) is in the same temperature interval as in step c).

10. The process according to any one of items 1-7, wherein liquid oxalic acid and/or citric acid and/or maleic acid is applied in step b) by flowing the oxalic acid and/or citric acid and/or maleic acid over the sheets or web of cellulose fibres, wherein the temperature of the oxalic acid and/or citric acid and/or maleic acid in step b) is in the same temperature interval as in step c). n. The process according to any one of the preceding items, wherein total combined time for the performance of steps b) and c) is less than 45 minutes, such as less than 30 minutes, such as less than 20 minutes.

12. The process according to any one of the preceding items, wherein the process comprises the step: ci) separating excess oxalic acid and/or citric acid and/or maleic acid from the reacted sheets, wherein step ci) is conducted after the reaction step c) and prior and/ or during cooling step d).

13. The process according to item 12, wherein the separation in step ci) is conducted in an acid removal section, wherein the acid removal section preferably is a press section and/or a vacuum section and/or a centrifuge.

14. The process according to any one of the preceding items, wherein the reacted sheets are cooled to a temperature below 70 °C, such as below 60 °C, in step d).

15. The process according to any one of the preceding items, wherein the reacted sheets or web are/is washed with a solvent during and/or after cooling in step d).

16. The process according to item 15, wherein the solvent is ethanol (EtOH) or methanol (MeOH) or tetrahydrofuran (THF) or acetone or water (H2O) or a mixture of EtOH and water or a mixture of MeOH and water.

17. The process according to any one of the preceding items, wherein the cooling in step d) is conducted by cooling with air or by contact cooling or with a solvent.

18. The process according to any one of the preceding items, wherein the sheets or web of cellulose fibres are/is continuously transported through the process on a transporting arrangement, such as a conveyor belt.

19. The process according to any one of the preceding items, wherein the reaction of oxalic acid or citric acid or maleic acid in step c) is performed at a temperature in the interval of 102-125 °C, such as in the interval of 104-120 °C. 20. The process according to any one of the preceding items, wherein oxalic acid is applied in step b) and the acid hydrolysed cellulose is cellulose oxalates.

21. The process according to item 20, wherein the oxalic acid is oxalic acid dihydrate.

22. A process for manufacturing acid hydrolysed cellulose comprising the steps of:

I. providing a cellulose-containing material;

II. applying oxalic acid and/ or citric acid and/ or maleic acid to the cellulose- containing material; and

III. reacting the oxalic acid and/ or citric acid and/ or maleic acid with the cellulose-containing material to form reacted cellulose-containing material comprising acid hydrolysed cellulose, wherein the oxalic acid and/or citric acid and/ or maleic acid is dissolved in a fluid being a supercritical fluid or a subcritical fluid;

IV. decreasing temperature and/ or pressure so that the fluid is no longer supercritical or subcritical.

23. The process according to item 21, further comprising the step:

V. recovering acid hydrolysed cellulose.

24. The process according to item 22 or 23, wherein the cellulose-containing material in step I. contains less than 30 wt-% water, such as less than 20 wt-% water based on the total weight of the cellulose-containing material.

25. The process according to any one of the items 22-24, wherein the cellulose containing material provided in step I. is not contacted with a deep-eutectic solvent.

26. The process according to any one of the items 22-25, wherein the cellulose- containing material provided in step I. is sheets or a web of cellulose fibres.

27. The process according to any one of the items 22-26, wherein the cellulose- containing material provided in step I. is wood pulp or plant pulp or secondary lignocellulosic fibres or regenerated cellulose fibres.

28. The process according to any one of the items 22-27, wherein the lignin content of the cellulose fibres provided in step I. is below 10 wt-%, such as below 5 wt-%, such as below 2 wt-%, based on dry weight of the fibres. 29. The process according to item 26, wherein the density measured according to ISO 534:2011 of the sheets or web provided in step I. is 400-750 kg/m ³ , such as 450- 650 kg/m ³ , such as 500-600 kg/m ³ .

30. The process according to any one of the items 22-29, wherein the mixture is washed with supercritical fluid or subcritical fluid during step III and/or step IV.

31. The process according to any one of the items 22-30, wherein the fluid is a supercritical fluid, preferably the supercritical fluid is carbon dioxide (CO2).

32. The process according to item 31 wherein the CO2 is in step III maintained in a pressure range of 8-50 MPa and temperature range of 31-150 °C, preferably in a pressure range of 8-10 MPa and a temperature range of 80-110 °C

33. The process according to any one of the items 31-32, wherein the supercritical fluid is added together with a co-solvent, wherein the co-solvent preferably is selected from the group consisting of: water (H2O), ethanol (EtOH), methanol (MeOH), dioxane, acetic acid and acetone.

34. The process according to item 33, wherein the co-solvent is added in amount of 0.1-15 vol-% based on the total volume of fluids.

35. The process according to any one of the items 22-30, wherein the fluid is a subcritical fluid, preferably the subcritical fluid is water or ethanol (EtOH) or methanol (MeOH), most preferably the subcritical fluid is water.

36. The process according to item 35, wherein the subcritical fluid is water and the water is in step HI maintained in a pressure range of 1.5-10 MPa and a temperature range of 150-250 °C, preferably in a pressure range of 3-6 MPa and a temperature range of 15O-17O°C.

37. The process according to any one of the items 22-36, wherein the process is a batch-wise process.

38. The process according to any one of the items 22-36, wherein the process is a continuous or semi-continuous process.

39. The process according to any of the items 22-38, wherein oxalic acid is applied in step II and the acid hydrolysed cellulose is cellulose oxalates.

40. The process according to item 39, wherein the oxalic acid is oxalic acid dihydrate. 41. A process for manufacturing acid hydrolysed nanocellulose comprising the steps of: a) providing sheets or a web of cellulose fibres; b) applying oxalic acid and/or citric acid and/or maleic acid to the sheets or web; c) reacting the oxalic acid and/ or citric acid and/ or maleic acid applied in step b) at a temperature in the interval of 70-135 °C with cellulose of the sheets or web to form acid hydrolysed cellulose; d) cooling the acid hydrolysed cellulose; e) optionally, recovering the acid hydrolysed cellulose; f) adding water or a liquid with a lower polarity than water to the acid hydrolysed cellulose; and g) suspending the acid hydrolysed cellulose in the water or liquid with a lower polarity than water by at least one technique selected from the group consisting of sonication, micro-fluidization, homogenization, beating and refining to obtain acid hydrolysed nanocellulose, wherein the process in steps a) - e) is a continuous or semi-continuous process.

42. The process according to item 41, wherein the acid hydrolysed cellulose is suspended in water and pH is adjusted to be in the interval of 9-10 prior to suspending the acid hydrolysed cellulose to obtain hydrolysed nanocellulose.

43. A process for manufacturing acid hydrolysed nanocellulose comprising the steps of: a) providing sheets or a web of cellulose fibres; b) applying oxalic acid and/or citric acid and/or maleic acid to the sheets or web; c) reacting the oxalic acid and/ or citric acid and/ or maleic acid applied in step b) at a temperature in the interval of 70-135 °C with cellulose of the sheets or web to form acid hydrolysed cellulose; d) cooling the acid hydrolysed cellulose; e) optionally, recovering the acid hydrolysed cellulose; f) adding an oil or a resin to the acid hydrolysed cellulose; and g) suspending the acid hydrolysed cellulose in the oil or resin by at least one technique selected from the group consisting of extrusion, sonication, micro-fluidization, beating and refining to obtain acid hydrolysed nanocellulose, wherein the process in steps a) - e) is a continuous or semi-continuous process.

44. A process for manufacturing acid hydrolysed nanocellulose comprising the steps of:

I. providing a cellulose-containing material;

II. applying oxalic acid and/ or citric acid and/ or maleic acid to the cellulose-containing material; and

III. reacting the oxalic acid and/ or citric acid and/ or maleic acid with the cellulose-containing material to form reacted cellulose-containing material comprising acid hydrolysed cellulose, wherein the oxalic acid and/or citric acid and/or maleic acid is dissolved in a fluid being a supercritical fluid or a subcritical fluid;

IV. decreasing temperature and/ or pressure so that the fluid is no longer supercritical or subcritical;

V. optionally, recovering the acid hydrolysed cellulose;

VI. adding water or a liquid with a lower polarity than water to the acid hydrolysed cellulose; and

VII. suspending the acid hydrolysed cellulose in the water or liquid with a lower polarity than water by at least one technique selected from the group consisting of sonication, micro-fluidization, beating and refining to obtain hydrolysed nanocellulose.

45. The process according to item 41, wherein the acid hydrolysed cellulose is suspended in water and pH is adjusted to be in the interval of 9-10 prior to suspending the acid hydrolysed cellulose to obtain hydrolysed nanocellulose. 46. A process for manufacturing acid hydrolysed nanocellulose comprising the steps of:

I. providing a cellulose-containing material;

II. applying oxalic acid and/ or citric acid and/ or maleic acid to the cellulose-containing material; and

III. reacting the oxalic acid and/ or citric acid and/ or maleic acid with the cellulose-containing material to form reacted cellulose-containing material comprising acid hydrolysed cellulose, wherein the oxalic acid and/or citric acid and/or maleic acid is dissolved in a fluid being a supercritical fluid or a subcritical fluid;

IV. decreasing temperature and/ or pressure so that the fluid is no longer supercritical or subcritical;

V. optionally, recovering the acid hydrolysed cellulose;

VI. adding an oil or a resin to the acid hydrolysed cellulose; and

VII. suspending the acid hydrolysed cellulose in the oil or resin by at least one technique selected from the group consisting of extrusion, sonication, micro-fluidization, beating and refining to obtain acid hydrolysed nanocellulose.

[0008] Cellulose fibres are regularly provided as sheets or a web, typically reeled on a roll, from cellulose fibre manufacturers. One advantage is that the process is more efficient since the sheets or web are used as is without any intermediate step. Such intermediate step is for example disintegration of the pulp using a beater or tearing the sheets by hand into pieces. A step that is according to the present disclosure effectively omitted.

[0009] The inventors have also realized that to react oxalic acid and/or citric acid and/or maleic acid in sheets or a web of cellulose fibres at a temperature of 70-135 °C is sufficient treatment for producing acid hydrolysed cellulose as well as pre-treating the sheets for the production of acid hydrolysed nanocellulose. By suspending the formed acid hydrolysed cellulose in water using sonication, micro-fluidization, and/or mechanical disintegration, acid hydrolysed nanocellulose is obtained. [0010] An advantage is that acid hydrolysed cellulose is prepared with a direct treatment of fibre sheets. An additional advantage is that a continuous or semi- continuous process is conducted as the inventors have realized that since the fibres are used in sheets or as a web as delivered, they can be continuously or semi- continuously be fed into a modification process.

[0011] An advantage with the items 21-40 and 44-46 is that the energy transfer and mass transport are improved since the acid is aided by the supercritical or subcritical fluid as solvent. Moreover, the inventors have realized that if dissolving oxalic acid and/or citric acid and/or maleic acid in a conventional solvent, such as ethanol or water, the formed acid hydrolysed cellulose will react with the solvent and break the formed ester of the acid hydrolysed. A supercritical or subcritial fluid, on the other hand, is an inert solvent-based system.

[0012] Additionally, the use of a supercritical or subcritial fluid as solvent is more environmentally friendly as the fluid typically fulfils the following criteria: easily can be recycled, nonflammable, nontoxic, non eco toxic, abundant, renewable, easy to prepare, easy to remove from a product, non-eutrophying, does not contribute to smog, minimum contribution to global warming.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Aspects and embodiments are now described, by way of example, with reference to the accompanying drawings, in which:

[0014] Fig 1 shows an exemplary embodiment of the process of manufacturing of acid hydrolysed cellulose where oxalic acid and/or citric acid and/or maleic acid is sprayed onto sheets of cellulose fibres.

[0015] Fig 2 shows an exemplary embodiment of the process of manufacturing of acid hydrolysed cellulose where oxalic acid and/or citric acid and/or maleic acid is added to sheets of cellulose fibres by immersion.

[0016] Fig 3 shows an alternative exemplary embodiment of the process of manufacturing of acid hydrolysed cellulose where oxalic acid and/or citric acid and/or maleic acid is added to sheets of cellulose fibres by immersion. [0017] Fig 4 shows an exemplary embodiment of a batch or semi-continuous process of manufacturing of acid hydrolysed cellulose where oxalic acid and/or citric acid and/ or maleic acid is dissolved in a supercritical fluid.

DETAILED DESCRIPTION

[0018] As a first aspect of the present disclosure there is provided a continuous or semi-continuous process for manufacturing of acid hydrolysed cellulose comprising the steps of: a) providing sheets or a web of cellulose fibres; b) applying oxalic acid and/or citric acid and/or maleic acid to the sheets or web; c) reacting the oxalic acid and/ or citric acid and/ or maleic acid applied in step b) at a temperature in the interval of 70-135 °C with cellulose of the sheets or web to form acid hydrolysed cellulose; and d) cooling the acid hydrolysed cellulose.

[0019] A continuous process is a process in which the sheets or web comes out without interruption. In a semi -continuous process, the sheets or web of cellulose fibres is simultaneously charged and discharged from the process, but for a discrete time period the process is stopped to e.g. apply oxalic acid and/or citric acid and/or maleic acid and/or allow for the oxalic acid and/or citric acid and/or maleic acid to react with the cellulose of the sheets or web.

[0020] The cellulose fibres are provided as individual sheets or a web. The web of cellulose fibres is typically provided as reel pulp, i.e. a web of pulp wound up in a reel or roll. In such case, the web is unwound when fed into the process. Alternatively, cellulose fibres are provided as sheets and can be fed directly into the process. The web or sheets may be compacted prior or prior and after the application of oxalic acid or citric acid or maleic acid.

[0021] Typically, the process further comprises the step e) recovering the acid hydrolysed cellulose.

[0022] By recovery is meant that there is a collection step where the reacted sheets or web comprising acid hydrolysed cellulose are collected. [0023] Preferably, oxalic acid is applied in step b) and the acid hydrolysed cellulose is in such case cellulose oxalates. A preferred type of oxalic acid is oxalic acid dihydrate. In such case the reaction to form acid hydrolysed cellulose is typically solvent-free. Alternatively, the oxalic acid maybe anhydrous oxalic acid without water bound to the oxalic acid. In such case, the anhydrous oxalic acid may be dissolved in a small amount of water, such as 15-40 wt-% water based on the dry weight of the anhydrous oxalic acid.

[0024] The excess oxalic acid may be recovered and purified internally for use in subsequent reactions forming acid hydrolysed cellulose.

[0025] The cellulose fibres provided in step a) typically contains less than 30 wt-% water, such as less than 20 wt% water, such as less than 10 wt% water. It is beneficial to keep the water content low as there is otherwise a risk of undesired transesterification reactions.

[0026] The humidity is typically controlled so that the relative humidity is kept above 80 %, such as above 90% to avoid or reduce evaporation of the water in the acid.

[0027] The cellulose fibres provided in step a) is typically not contacted with a deep-eutectic solvent.

[0028] The cellulose fibres provided in step a) is typically wood pulp or plant pulp. Examples of suitable wood pulp is mechanical pulp, such as thermomechanical pulp (TMP) or chemi-thermomechanical pulp (CTMP) or cut/ shredded pulp or milled pulp, and chemical pulp, such as sulphite pulp or sulphate pulp, and an example of a suitable plant pulp is bagasse pulp. Typically, the lignin content of the cellulose fibres provided in step a) is below 10 wt-%, such as below 5 wt-%, such as below 2 wt-%, based on dry weight of the fibres. In case the cellulose fibres are wood pulp they may be bleached.

[0029] The density measured according to ISO 534:2011 of the sheets or web of cellulose fibres provided in step a) is typically 400-750 kg/m ³ , such as 450- 650 kg/m ³ , such as 500-600 kg/m ³ .

[0030] The reaction of oxalic acid and/ or citric acid and/ or maleic acid in step c) is typically performed at a temperature in the interval of 102-125 °C, such as in the interval of 104-120 °C. [0031] In one embodiment, the oxalic acid and/ or citric acid and/ or maleic acid has a temperature in the same interval as in step c) when applied to the sheets or web in step b). In such case, the oxalic acid and/or citric acid and/or maleic acid maybe applied in step b) by spraying the oxalic acid and/or citric acid and/or maleic acid onto the cellulose sheets or web of cellulose fibres. Alternatively, the oxalic acid is applied in step c) by immersing the cellulose containing material in oxalic acid or citric acid or maleic acid. By immersing is meant covering the sheet in oxalic acid and/ or citric acid and/ or maleic acid by for example dipping or submerging the sheets or web of cellulose fibres in oxalic acid or citric acid or maleic acid. In yet another alternative the oxalic acid and/ or citric acid and/ or maleic acid is applied by flowing the oxalic acid and/or citric acid and/or maleic acid over the sheets or web of cellulose fibres. Such embodiment has the advantage of reaction efficiency since the oxalic acid and/or citric acid and/or maleic acid starts reacting with the cellulose fibre in the sheets or web immediately upon application.

[0032] In another embodiment, the oxalic acid and/ or citric acid and/ or maleic acid is applied to the sheets or web, wherein the oxalic acid and/or citric acid and/or maleic acid as a temperature of below 50 °C. Such embodiment has the advantage that the oxalic acid and/ or citric acid and/ or maleic acid can be applied as delivered or with only minor preparation, such as dissolution. The oxalic acid and/or citric acid and/or maleic acid is then heated in-situ with the sheets or web of cellulose fibres in step c).

[0033] The total combined time for the performance of steps b) and c) may be less than 45 minutes, such as less than 30 minutes, such as less than 20 minutes. In these embodiments, this means that if the performance of step b) takes 5 minutes, the performance of step c) is less than 40 minutes, such as less than 25 minutes, such as less than 15 minutes.

[0034] The process may further comprise the step: ci) separating excess oxalic acid and/or citric acid and/or maleic acid from the reacted sheets, wherein step ci) is conducted after the reaction step c) and prior and/or during cooling step d). [0035] Such separation in step ci) is typically conducted in an acid removal section, wherein the acid removal section preferably is a press section and/ or a vacuum section and/ or a centrifuge.

[0036] Typically, the reacted sheets or web are/is cooled to a temperature below 70 °C, such as below 60 °C, in step d). By cooling the reaction to acid hydrolysed cellulose is slowed down or even stopped. During and/or after cooling in step d) reacted sheets or web are/is typically washed with a solvent. In case washing is conducted during cooling in step d) the washing facilitates cooling. Washing may be conducted by leaching that can be conducted continuously by for example means of solution mining or cross-flow leaching. The solvent is preferably ethanol (EtOH) or methanol (MeOH) or THF or acetone or water or a mixture of EtOH and water or a mixture of MeOH and water.

[0037] The cooling in step e) is typically conducted by cooling with cold air, preferably dry air, or by contact cooling or with a solvent. In case of contact cooling a cold roller is typically used.

[0038] Typically, the sheets or web of cellulose fibres are/is continuously transported through the process on a transporting arrangement, such as a conveyor belt.

[0039] As a second aspect of the present disclosure there is provided a process for manufacturing of acid hydrolysed cellulose comprising the steps of:

I.providing a cellulose-containing material;

H.applying oxalic acid and/or citric acid and/or maleic acid to the cellulose-containing material;

HLreacting the oxalic acid and/or citric acid and/or maleic acid with the cellulose- containing material to form reacted cellulose-containing material comprising acid hydrolysed cellulose, wherein the oxalic acid and/or citric acid and/or maleic acid is dissolved in a fluid being a supercritical fluid or a subcritical fluid;

IV. decreasing temperature and/ or pressure so that the fluid is no longer supercritical or subcritical.

[0040] A supercritical fluid is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist, but below the pressure required to compress it into a solid. A lowering of temperature and/or pressure, therefore, decreases the fluid below its critical point. A subcritical fluid is under its critical point of pressure and temperature, i.e. the fluid is a liquid under pressure at a temperatures above its usual boiling point.

[0041] The excess oxalic acid and/ or citric acid and/ or maleic acid and supercritical fluid or subcritical fluid may be recovered and purified internally for use in subsequent reactions, for example in forming acid hydrolysed cellulose. Typically, oxalic acid is applied in step II and the acid hydrolysed cellulose is cellulose oxalates. In such case, the oxalic acid is typically oxalic acid dihydrate.

[0042] Typically, the process further comprises the step:

V. recovering acid hydrolysed cellulose.

[0043] The mixture may be washed with additional supercritical fluid or subcritical fluid prior to the recovery in step IV.

[0044] In embodiments, the fluid is a supercritical fluid. A preferred supercritical fluid is carbon dioxide (CO2). In such case, the CO2 is in step III typically maintained in a pressure range of 8-50 MPa and temperature range of 31-150 °C, preferably in a pressure range of 8-10 MPa and a temperature range of 80-110 °C. The supercritical fluid may be added together with a co-solvent, wherein the co-solvent preferably is selected from the group consisting of: water (H2O), ethanol (EtOH), methanol (MeOH), dioxane, acetic acid and acetone. Typically, the co-solvent is added in amount of 0.1-15 vol-% based on the total volume of fluids.

[0045] In alternative embodiments, the fluid is a subcritical fluid. The subcritical fluid is typically water or ethanol (EtOH) or methanol (MeOH), preferably the subcritical fluid is water. In such case, the water is in step HI typically maintained in a pressure range of 1.5-10 MPa and a temperature range of 150-250 °C, preferably in a pressure range of 3-6 MPa and a temperature range of 15O-17O°C.

[0046] The process may be a batch-wise process. Alternatively, the process is a continuous or semi-continuous process.

[0047] The cellulose fibres provided in step a) is typically not contacted with a deep-eutectic solvent. [0048] The cellulose-containing material provided in step I is typically wood pulp or plant pulp or secondary lignocellulosic fibres or regenerated cellulose fibres.

Examples of suitable wood pulp is mechanical pulp, such as thermomechanical pulp (TMP) or chemi-thermomechanical pulp (CTMP) or cut/ shredded pulp or milled pulp, and chemical pulp, such as sulphite pulp or sulphate pulp, and an example of a suitable plant pulp is bagasse pulp. Typically, the lignin content of the cellulose fibres provided in step a) is below 10 wt-%, such as below 5 wt-%, such as below 2 wt-%, based on dry weight of the fibres. In case the cellulose fibres are wood pulp they may be bleached. The cellulose-containing material provided in step may be sheets or a web of cellulose fibres

[0049] The cellulose-containing material provided in step I typically contains less than 30 wt-% water, such as less than 20 wt% water, such as less than 10 wt% water. It is beneficial to keep the water content low as there is otherwise a risk of undesired transesterification reactions.

[0050] As a third aspect of the present disclosure there is provided a process for manufacturing acid hydrolysed nanocellulose comprising the step of: a) providing sheets or a web of cellulose fibres; b) applying oxalic acid or citric acid or maleic acid to the sheets or web; c) reacting the oxalic acid or citric acid or maleic acid applied in step b) at a temperature in the interval of 70-135 °C with cellulose of the sheets or web to form acid hydrolysed cellulose; d) cooling the acid hydrolysed cellulose; e) optionally, recovering the acid hydrolysed cellulose; f) adding water or a liquid with a lower polarity than water to the acid hydrolysed cellulose; and g) suspending the acid hydrolysed cellulose in the water or liquid with a lower polarity than water by at least one technique selected from the group consisting of sonication, micro-fluidization, homogenization, beating and refining to obtain acid hydrolysed nanocellulose, wherein the process in steps a) - e) is a continuous or semi-continuous process. [0051] By nanocellulose is meant microfibrillated cellulose (MFC) or cellulose nanocrystals (CNC). In one embodiment, the technique for suspending the acid hydrolysed cellulose in water or liquid with a lower polarity than water is sonication. In such case, CNC is the major type of nanocellulose formed. In other embodiments, the technique for suspending the acid hydrolysed cellulose in water or liquid with a lower polarity than water is micro-fluidization, homogenization, beating or refining. In such case, MFC is the major type of nanocellulose formed.

[0052] In the context of the present disclosure, MFC means nano-scale cellulose particle fibres or fibrils with at least one dimension less than 100 nm. MFC comprises partly or totally fibrillated cellulose or lignocellulose fibres. The liberated fibrils have a diameter less than 100 nm. The smallest fibril is called elementary fibril and has a diameter of approximately 2-4 nm, while it is common that the aggregated form of the elementary fibrils, also defined as microfibril is the main product that is obtained when making MFC. There are different synonyms for MFC such as cellulose microfibrils, fibrillated cellulose, nanofibrillated cellulose (NFC), fibril aggregates, nanoscale cellulose fibrils, cellulose nanofibres, cellulose nanofibrils (CNF), cellulose microfibres (CMF), cellulose fibrils, microfibrillar cellulose, microfibril aggregrates and cellulose microfibril aggregates. MFC can also be characterized by various physical or physicalchemical properties such as large surface area or its ability to form a gel-like material at low solids content (1-5 wt.%) when dispersed in water. The cellulose fibre is preferably fibrillated to such an extent that the final specific surface area of the formed MFC is from about 1 to about 200 m2/g, or more preferably 50- 200 m2/g when determined for a freeze-dried material with the BET method (Brunauer, Stephen, Paul Hugh Emmett, and Edward Teller. "Adsorption of gases in multimolecular layers." Journal of the American chemical society 60.2 (1938): 309- 319.). Nitrogen (N2) gas adsorption isotherms are recorded using an ASAP 2020 (Micromeritics, USA) instrument. Measurements are performed at liquid nitrogen temperatures (i.e., 77 K), and the specific surface areas of the samples were obtained from the isotherms using the BET method.

[0053] In the context of the present disclosure, CNC means cellulose in crystalline form or at least in essentially or mostly crystalline form. CNCs are rigid rod-like crystals with diameter in the range of 5- onm and lengths of typically a few hundred nanometers, in the range of ioo-6oonm. (Osong S.H., Norgren S. and Engstrand P. 2016. Processing of wood-based microfibrillated cellulose and nanofibrillated cellulose, and applications relating to papermaking: a review. Cellulose 23: 93-123). A synonym of CNC is nanocrystalline cellulose (NCC).

[0054] Steps f) and g) may be conducted in the same production line, i.e. on-site, as steps a)-e). In such case, step f) maybe conducted continuously or semi- continuously with steps a) - f) and step g) in a batch-wise manner. Alternatively, step g) is, just as step f), also conducted continuously or semi-continuously with steps a) - e). On-site, both an on-line process, i.e. all steps a) - g) are in connection, or an offline process, i.e. steps a) - e) are in connection as a continuous or semi-continuous process and steps f) and g) are conducted in the same site but in a separate process. It may be advantageous to conduct all process steps at one site as acid hydrolysed nanocellulose is provided at a single site.

[0055] Alternatively, steps f) and g) may be conducted at a different site. Such process is beneficial since steps a) - e) can be conducted at a first site, and the acid hydrolysed cellulose thereafter be transported to where it will be used when converted into acid hydrolysed nanocellulose. In such case, typically less water is also transported as acid hydrolysed nanocellulose may be sensitive of drying, especially if the acid hydrolysed nanocellulose is MFC that forms a gel already at a few percent dry content. To maintain the properties of MFC, the MFC should not be dried prior to usage in an end-application.

[0056] In embodiments where acid hydrolysed cellulose is suspended in water, pH is typically adjusted to be in the interval of 9-10 prior to suspending the acid hydrolysed cellulose to obtain hydrolysed nanocellulose. By such pH the carboxylic groups in the acid hydrolysed cellulose can dissociate and thereby obtain a negative charge that will facilitate the production of nanocellulose by electrostatic repulsion.

[0057] The examples and embodiments discussed above in connection to the first aspect apply to the third aspect mutatis mutandis.

[0058] As a fourth aspect of the present disclosure there is provided a process for manufacturing hydrolysed nanocellulose comprising the step of: a) providing sheets or a web of cellulose fibres; b) applying oxalic acid and/or citric acid and/or maleic acid to the sheets or web; c) reacting the oxalic acid and/ or citric acid and/ or maleic acid applied in step b) at a temperature in the interval of 70-135 °C with cellulose of the sheets or web to form acid hydrolysed cellulose; d) cooling the acid hydrolysed cellulose; e) optionally, recovering the acid hydrolysed cellulose; f) adding an oil or a resin to the acid hydrolysed cellulose; and g) suspending the acid hydrolysed cellulose in the oil or resin by at least one technique selected from the group consisting of extrusion, sonication, micro-fluidization, beating and refining to obtain acid hydrolysed nanocellulose, wherein the process in steps a) - e) is a continuous or semi-continuous process.

[0059] By suspending the acid hydrolysed nanocellulose in an oil or a resin an in- situ composite where the nanocellulose is reinforcing the oil or resin can be produced. An advantage of the reason for this is that if it is desirable to disperse acid hydrolysed nanocellulose in a non-aqueous system, it is much easier to add the acid hydrolysed nanocellulose directly without the need for a solvent exchange from water.

[0060] The examples and embodiments discussed above in connection to the first and third aspects apply to the fourth aspect mutatis mutandis.

[0061] As a fifth aspect of the present disclosure there is provided a process for manufacturing acid hydrolysed nanocellulose comprising the steps of:

I. providing a cellulose-containing material;

II. applying oxalic acid and/ or citric acid and/ or maleic acid to the cellulose- containing material; and

III. reacting the oxalic acid and/ or citric acid and/ or maleic acid with the cellulose-containing material to form reacted cellulose-containing material comprising acid hydrolysed cellulose, wherein the oxalic acid and/or citric acid and/or maleic acid is dissolved in a fluid being a supercritical fluid or a subcritical fluid; IV. decreasing temperature and/ or pressure so that the fluid is no longer supercritical or subcritical;

V. optionally, recovering the acid hydrolysed cellulose;

VI. adding water or a liquid with a lower polarity than water to the acid hydrolysed cellulose; and

VII. suspending the acid hydrolysed cellulose in the water or liquid with a lower polarity than water by at least one technique selected from the group consisting of sonication, micro-fluidization, beating and refining to obtain hydrolysed nanocellulose.

[0062] By nanocellulose is meant microfibrillated cellulose (MFC) or cellulose nanocrystals (CNC). In one embodiment, the technique for suspending the acid hydrolysed cellulose in water or liquid with a lower polarity than water is sonication. In such case, CNC is the major type of nanocellulose formed. In other embodiments, the technique for suspending the acid hydrolysed cellulose in water or liquid with a lower polarity than water is micro-fluidization, homogenization, beating or refining. In such case, MFC is the major type of nanocellulose formed.

[0063] In the context of the present disclosure, MFC means nano-scale cellulose particle fibres or fibrils with at least one dimension less than 100 nm. MFC comprises partly or totally fibrillated cellulose or lignocellulose fibres. The liberated fibrils have a diameter less than 100 nm. The smallest fibril is called elementary fibril and has a diameter of approximately 2-4 nm, while it is common that the aggregated form of the elementary fibrils, also defined as microfibril is the main product that is obtained when making MFC. There are different synonyms for MFC such as cellulose microfibrils, fibrillated cellulose, nanofibrillated cellulose (NFC), fibril aggregates, nanoscale cellulose fibrils, cellulose nanofibres, cellulose nanofibrils (CNF), cellulose microfibres (CMF), cellulose fibrils, microfibrillar cellulose, microfibril aggregrates and cellulose microfibril aggregates. MFC can also be characterized by various physical or physicalchemical properties such as large surface area or its ability to form a gel-like material at low solids content (1-5 wt.%) when dispersed in water. The cellulose fibre is preferably fibrillated to such an extent that the final specific surface area of the formed MFC is from about 1 to about 200 m2/g, or more preferably 50- 200 m2/g when determined for a freeze-dried material with the BET method (Brunauer, Stephen, Paul Hugh Emmett, and Edward Teller. "Adsorption of gases in multimolecular layers." Journal of the American chemical society 60.2 (1938): 309- 319.). Nitrogen (N2) gas adsorption isotherms are recorded using an ASAP 2020 (Micromeritics, USA) instrument. Measurements are performed at liquid nitrogen temperatures (i.e., 77 K), and the specific surface areas of the samples were obtained from the isotherms using the BET method.

[0064] In the context of the present disclosure, CNC means cellulose in crystalline form or at least in essentially or mostly crystalline form. CNCs are rigid rod-like crystals with diameter in the range of 5-40nm and lengths of typically a few hundred nanometers, in the range of ioo-6oonm. (Osong S.H., Norgren S. and Engstrand P. 2016. Processing of wood-based microfibrillated cellulose and nanofibrillated cellulose, and applications relating to papermaking: a review. Cellulose 23: 93-123). A synonym of CNC is nanocrystalline cellulose (NCC).

[0065] Steps VI and VII may be conducted in the same production line, i.e. onsite, as steps I-V. In such case, step VI may be conducted continuously or semi- continuously with steps I - VI and step VII in a batch-wise manner. Alternatively, step VI is, just as step VII, also conducted continuously or semi-continuously with steps I - V. On-site, both an on-line process, i.e. all steps I - VII are in connection, or an off-line process, i.e. steps I - V are in connection as a continuous or semi- continuous process and steps VI and VII are conducted in the same site but in a separate process. It may be advantageous to conduct all process steps at one site as acid hydrolysed nanocellulose is provided at a single site.

[0066] Alternatively, steps VI and VII may be conducted at a different site. Such process is beneficial since steps I - V can be conducted at a first site, and the acid hydrolysed cellulose thereafter be transported to where it will be used when converted into acid hydrolysed nanocellulose. In such case, typically less water is also transported as acid hydrolysed nanocellulose may be sensitive of drying, especially if the acid hydrolysed nanocellulose is MFC that forms a gel already at a few percent dry content. To maintain the properties of MFC, the MFC should not be dried prior to usage in an end-application.

[0067] In embodiments where acid hydrolysed cellulose is suspended in water, pH is typically adjusted to be in the interval of 9-10 prior to suspending the acid hydrolysed cellulose to obtain hydrolysed nanocellulose. By such pH the carboxylic groups in the acid hydrolysed cellulose can dissociate and thereby obtain a negative charge that will facilitate the production of nanocellulose by electrostatic repulsion.

[0068] The examples and embodiments discussed above in connection to the second aspect apply to the fifth aspect mutatis mutandis.

[0069] As a sixth aspect of the present disclosure there is provided a process for manufacturing acid hydrolysed nanocellulose comprising the steps of:

I. providing a cellulose-containing material;

II. applying oxalic acid and/ or citric acid and/ or maleic acid to the cellulose- containing material; and

III. reacting the oxalic acid and/ or citric acid and/ or maleic acid with the cellulose-containing material to form reacted cellulose-containing material comprising acid hydrolysed cellulose, wherein the oxalic acid and/or citric acid and/ or maleic acid is dissolved in a fluid being a supercritical fluid or a subcritical fluid;

IV. decreasing temperature and/ or pressure so that the fluid is no longer supercritical or subcritical;

V. optionally, recovering the acid hydrolysed cellulose;

VI. adding an oil or a resin to the acid hydrolysed cellulose; and

VII. suspending the acid hydrolysed cellulose in the oil or resin by at least one technique selected from the group consisting of extrusion, sonication, micro-fluidization, beating and refining to obtain acid hydrolysed nanocellulose.

[0070] The examples and embodiments discussed above in connection to the second and fifth aspect apply to the sixth aspect mutatis mutandis.

[0071] The present disclosure will now be described hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown.

[0072] These aspects may, however, be embodied in many different forms and should not be construed as limiting; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and to fully convey the scope of all aspects of invention to those skilled in the art. Like numbers refer to like elements throughout the description.

[0073] Fig 1 is a schematic image of an embodiment 2 of the continuous process where sheets comprising cellulose fibres 101 are conveyed on a conveyor belt 102 through the process and acid being oxalic acid and/or citric acid and/or maleic acid applied through spraying. The sheets 101 enter in an inlet 109 and exist in an outlet no. During the process the sheets 101 are transported through a transportation oven 103 equipped with a spray zone 106 where the acid coming from tank 105 is sprayed through spray nozzles 104, wherein the acid has a temperature of 70-135 °C. Surplus acid going through the sheets 101 is pumped by pump 108 back to the tank 105. The sheets 101 are forwarded into a reaction zone 107 where the temperature is 70-135 °C and thereafter formed acid hydrolysed cellulose enter a cooling zone 108 where the temperature is lowered, and the reaction stops down. Finally, the acid hydrolysed cellulose exist through the outlet 110.

[0074] Fig 2 is a schematic image of an embodiment 2 of the continuous process where sheets comprising cellulose fibres 101 are conveyed on a conveyor belt 201 through the process and acid being oxalic acid and/or citric acid and/or maleic acid applied through immersion. The sheets 101 are conveyed through a bath of acid 202 so that the sheets 101 are immersed in the acid, wherein the acid has a temperature of 70-135 °C. Thereafter, formed acid hydrolysed cellulose is conveyed through a zone 203 where the temperature is 70-135 °C. Thereafter the sheets 101 enter a cooling zone 204 where the temperature is lowered, and the reaction stops down. Finally, in a mixing system 206, excess acid 205 is drained off.

[0075] Fig 3 is a schematic image of an alternative embodiment 3 of the continuous process where sheets comprising cellulose fibres 101 are conveyed on a conveyor belt 301 through the process and acid being oxalic acid and/or citric acid and/or maleic acid applied through immersion, wherein the acid has a temperature of 70-135 °C. The conveyor belt 301 is perforated membrane allowing for entry of acid form underneath. The sheets 101 are conveyed through an immersion zone 302 where acid is allowed to immerse the sheets from underneath through the conveyor belt 301. Thereafter, the sheets are conveyed through a reaction zone 303 where the temperature is 70-135 °C. Thereafter formed acid hydrolysed cellulose the sheets 101 enter a cooling zone 304 where the temperature is lowered, and the reaction stops down.

[0076] Fig 4 is a schematic image of an embodiment 4 of the process where sheets comprising cellulose fibres 101 are reacted with acid being oxalic acid and/ or citric acid and/ or maleic acid 413 in a pressure vessel 412, wherein the acid 413 is dissolved in supercritical C0 ₂ . The C0 ₂ is pumped from the tank 401 to the pressure vessel 412 by a reciprocating pump 404 pumping the C0 ₂ through a heater 402, condenser 405, and valve 403, wherein the valve is controlled by a flow control FIC 406. The high- pressure vessel is heated and pressurized at temperature and pressure above the CO2 critical point. The supercritical C0 ₂ in the pressure vessel 412 dissolve the acid 413 and diffuse it within the sheets comprising cellulose fibres 101 so the reaction occurs, and acid hydrolysed cellulose is formed. The pressure vessel is equipped with a condenser 407 and pressure indicator PIC 408 as well as temperature indicator TIC 409. At the end of the reaction time, the high-pressure vessel is depressurized through the valve 411 and the acid hydrolysed cellulose is recovered. Before the depressurization and at the end of the reaction time, it is also possible to run a continuous CO2 flow in order to remove the excess of acid.

EXAMPLES

Example 1

[0077] Kraft pulp sheets with the dimension of 50x50 cm and density of about 550 kg/m ³ were immersed in a bath of oxalic acid dihydrate to produce cellulose oxalates. The pulp sheets were forwarded using a conveyer belt through the oxalic acid bath at no°C for 40 seconds and then placed in a reaction room (without contact with the bath of oxalic acid) at a temperature of no°C for 15 min. The reaction was stopped by moving the pulp sheets to a cooling area at room temperature. The cellulose oxalates, excess of oxalic acid and the by-products were mixed and then separated.

Example 2

[0078] Onto the same type of kraft pulp sheets as in Example 1, oxalic acid dihydrate was applied at room temperature. The sheets were forwarded to a heating station where the sheets were heated by hot air to a temperature of no °C so that the oxalic acid dihydrate reacted with the cellulose fibres in the sheets and formed cellulose oxalates.

Example .‘1

[0079] In a high-pressure vessel, cellulosic raw material and oxalic acid were introduced in static mode. The vessel was heated to a temperature of 100 °C and 80 bar. CO2 was then introduced into the vessel and the pressure was maintained at 80 bar. Stirring was conducted at 100 rpm, the pressurized speed was 0.2 MPa/min (2 bar/ min). Water was used as co-solvent, the amount used was 2 v%. The supercritical CO2 dissolved the oxalic acid and diffused within the cellulosic raw material to produce cellulose oxalates. At the end of the reaction time, the high-pressure vessel was depressurized with a rate of 0.2 MPa/min (2 bar/min) and the cellulose oxalates were recovered.

[0080] This shows that modification of sheets of cellulose fibres with oxalic acid can be made with an efficient continuous or semi-continuous process.