TECHNICAL FIELD

The present disclosure relates to a process for preparing an alkaline cellulose dope , the alkaline cel- lulose dope and a product obtainable from an alkaline cellulose dope .

BACKGROUND

Dissolution of cellulose is a challenging pro- cess ; due to the cellulose molecular structure charac- teri zed by multiple inter- and intramolecular hydrogen bonds , cellulose is a very stable molecule with low reactivity .

Processes for dissolving cellulose in aqueous solvent systems are avai lable . For example , it is pos - sible to dissolve cellulose in a cold alkaline solution, such as a 7 - 10 wt-% NaOH solution at a temperature of - 5 to 5 ° C . Such cellulose solutions may be used for spinning and regenerating e . g . cellulose fibers .

However, alkaline cellulose dopes , in partic- ular those with a relatively high cellulose concentra- tion, may not be stable for extended periods of time .

Further, obtaining an alkaline cellulose dope with higher cellulose concentrations may be challenging . It may be des irable to have an alkaline cellulose dope with such a viscosity that spinning or extruding e . g . fibers from the solution is possible . However, if the concentration of the cellulose is increased to increase viscosity, the more readily the alkal ine cellulose dope may form gel-like structures . Such gel-like structures may not be sufficiently fluid for spinning or extruding . They may al so render it more challenging to f ilter the alkaline cellulose dope and/or to transfer it forward in the process . SUMMARY

A process for preparing an alkaline cellulose dope is disclosed . The process may comprise providing a cel lulose material and a cold alkaline solution, and dispersing and dissolving the cellulose material in the cold alkaline solution, thereby obtaining the alkaline cellulose dope . The cellulose material may be dispersed and dissolved in the cold alkaline solution in conditions in which the absorption and/or dissolution of CO2 in the alkaline cellulose dope is reduced, and/or CO2 dissolved and/or the concentration of carbonate ions in the cellulose material and the cold alkaline solution and/or in the alkaline cellulose dope may be reduced or removed at least partially, such that the concentration of carbonate ions in the alkaline cellulose dope is reduced .

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings , which are included to provide a further understanding of the embodiments and constitute a part of thi s specification, illustrate various embodiments . In the drawings :

Fig . 1 shows an embodiment of a process for preparing an alkaline cellulose dope ;

Fig . 2 shows a process in the fabrication of multidimensional materials based on alkali soluble cellulose ;

Fig . 3 : Alkali dissolved cellulose dope ( 7 % w/w) rheology and optical microscope images during gelation process at 40°C, a) frequency swept at 0 . 1 % amplitude at 0 , 1 , and 2 hours after the dissolution, b) phase angle and optical microscope images during gelation after the dissolution ;

Fig . 4 : Alkali dissolved cellulose 7 % w/w rheology dependency with time , temperature , and CO2 absorption, a) viscosity dependency with temperature and time, b) elastic modulus dependency with time (aged sample was in the room open air for one week) , c) CO2 (g) absorption ability of the alkali cellulose dope inspected by Raman spectra, d) cellulose shear thinning and alignment under shear forces;

Fig. 5: Alkali dissolved cellulose dopes rheology and optical microscope images, a) frequency swept at 0.1% amplitude for cellulose concentrations of 7, 9, and 12% w/w respectively, b) optical microscope images of 9% w/w cellulose dope before and after centrifugal thawing, c) optical microscope images of 12% w/w cellulose dope before and after centrifugal thawing;

Fig. 6: Wet spinning cellulose regeneration in three steps;

Fig. 7: Dry filaments mechanical performance produced from dopes with different cellulose concentrations (7, 9, and 12% w/w) , a) mechanical properties, b) typical azimuthal intensities for the filaments diffraction peaks, c) Herman's orientation parameters calculated from the azimuthal profiles;

Fig. 8: 3D printed mesh structures and films from cellulose dissolved in alkali conditions, a) mesh obtained from a 7% cellulose dope (aged for three days) , b) auxetic mesh printed from 9% cellulose dope without aging, c) auxetic mesh printed from 12% cellulose dope without aging, d) 3D printed films from a 7% cellulose dope; and

Fig. 9: Printed films properties at 7, 9 and 12% cellulose concentrations, a) mechanical properties, b) water swelling (overnight) , c) optical properties;

Fig. 10 shows tenacities of staple fibers are presented in as a function of stretching between the first and second godet;

Fig. 11 shows tenacities of staple fibers as a function of the elongation at break; Fig . 12 shows Brookfield viscosities of alkaline cellulose dope samples with different concentrations of carbonate ions ; and

Fig . 13 illustrates the Brookfield viscosities of an alkaline cellulose dope sample stored for 0 , 1 , and 5 days in contact with air .

DETAILED DESCRIPTION

A process for preparing an alkaline cellulose dope is disclosed . The process may comprise providing a cellulose material and a cold alkaline solution, and dispersing and dissolving the cellulose material in the cold alkaline solution, thereby obtaining the alkaline cellulose dope , wherein the cellulose material is dispersed and dissolved in the cold alkaline solution in conditions in which the absorption and/or dissolution of CO2 in the alkaline cellulose dope is reduced, and/or the concentration of carbonate ions and/or CO2 dissolved in the cellulose material and the cold alkaline solution and/or in the alkaline cellulose dope is reduced or removed at least partially, such that the concentration of carbonate ions in the alkaline cellulose dope is reduced .

The cellulose material may be dispersed and dissolved in the cold alkaline solution in conditions in which the absorption and/or dissolution of CO2 in the alkaline cellulose dope is reduced, such that the concentration of carbonate ions in the alkaline cellulose dope is reduced .

The concentration of carbonate ions in the cold alkaline solution and/or in the alkaline cellulose dope may be reduced at least partially, such that the concentration of carbonate ions in the alkaline cellulose dope is reduced . The CO2 dissolved in the cellulose material and the cold alkaline solution and/or in the alkaline cellulose dope may be reduced or removed at least partially, such that the concentration of carbonate ions in the alkaline cellulose dope is reduced .

CO2 that is dissolved in water may mainly form carbonic acid . The carbonic acid may further react with alkaline agents present in the cold alkaline solution and/or in the alkaline cellulose dope .

Not to be bound by theory, it may be that CO2 that is absorbed and dissolved in the alkaline cellulose dope may form carbonates in the alkaline cellulose dope . In the context of this specification, the term "carbonates" may refer to carbonates , such as Na2COs , and/or bicarbonates , such as NaHCCg , and/or to carbonate and/or bicarbonate ions . The carbonates may further form bicarbonates , such that the carbonate and bicarbonate ions are at equilibrium, the molar ratio of carbonates to bicarbonates depending e . g . on the pH . For example , in al kal ine cel lulose dope , the pH tends to be so high that the carbonates are present mainly as carbonate ions (COs ^2- ) . In other solutions , such as water, significant amounts of bicarbonates may be present . Methods for determining the amount or concentration of carbonates may determine both carbonates and bicarbonates simultaneously, such that any references to the amount of carbonates , to carbonate content and/or to concentration of carbonate ions may refer to the amount of carbonates and bicarbonates and/or to concentration of carbonate and/or bicarbonate ions . The dissolved CO2 and carbonates may have an effect on the pH of the alkaline cellulose dope and may thereby create local points in which gelation occurs . Such points of gelation may reduce the stability of the alkaline cellulose dope . CO2 that is absorbed and dissolved in the alkaline cellulose dope may also reduce the solubility of the cellulose . Carbonates thereby formed may also end up in products obtainable from alkaline cellulose dope . At acidic conditions , carbonates may cause the formation of CO2 , which then may increase the porosity of the products when they are coagulated from the alkal ine cellulose dope . The increased porosity may reduce the strength of the products , for example of staple fibers .

Thus , if the absorption and/or dissolution of CO2 in the alkaline cellulose dope is reduced, and/or CO2 dissolved in the cellulose material and the cold alkaline solution and/or in the alkaline cellulose dope is reduced or removed at least partially, the concentration of carbonate ions in the cold alkaline solution and/or in the alkaline cellulose dope may be reduced .

Further, oxygen (O2 ) dissolved in the alkaline cellulose dope may also have unwanted consequences . It may cause degradation of cellulose and/or hemicelluloses by a peeling reaction, producing monosaccharides and other degradation products . Thus , any references to reducing and/or at least partially removing CO2 or its absorption and/or dissolution may, additionally or alternatively, be understood as referring to reducing and/or at least partially removing O2 or its absorption and/or dissolution .

In an embodiment , the absorption and/or dissolution of O2 in the alkaline cellulose dope is reduced, and/or O2 dissolved in the cellulose material and the cold alkaline solution and/or in the alkaline cellulose dope is reduced or removed at least partially .

The absorption and/or dissolution of CO2 in the alkaline cellulose dope may be considered reduced, if it is reduced e . g . by at least 10 % , or at least 20 % , or at least 50 % as compared to a comparable process , for example to a comparable process which does not include one or more measures to reduce the absorption and/or dissolution of CO2 in the alkaline cellulose dope described in this specification.

The concentration of carbonate ions in the alkaline cellulose dope may be considered reduced, if it is reduced e.g. by at least 10 % , or at least 20 % , or at least 50 % as compared to a comparable process, for example to a comparable process which does not include one or more measures to reduce the absorption and/or dissolution of CO2 in the alkaline cellulose dope or to reduce the concentration of carbonate ions described in this specification.

In some embodiments, the absorption and/or dissolution of CO2 in the alkaline cellulose dope may be considered reduced, if the concentration of carbonate ions in the alkaline cellulose dope is 1.5 % (w/w) or lower, or 1.2 % (w/w) or lower, or 1.0 % (w/w) or lower, or 0.2 % (w/w) or lower, or 0.1 % (w/w) or lower (based on the total weight of the alkaline cellulose dope) .

In some embodiments, the concentration of carbonate ions in the alkaline cellulose dope may be considered reduced, if the concentration of carbonate ions in the alkaline cellulose dope is 1.5 % (w/w) or lower, or 1.2 % (w/w) or lower, or 1.0 % (w/w) or lower, or 0.2 % (w/w) or lower, or 0.1 % (w/w) or lower (based on the total weight of the alkaline cellulose dope) .

The concentration of carbonate ions may be measured using the standard SCAN-N 32:98. The standard is for white, green and black liquors and burnt lime sludge, but it may be used for other samples as well. The accuracy of the method and detection limit may be improved by increasing the weight of the sample or by decreasing the volume of absorption cell solution. If the amount of alkaline solutions is increased, the volume of the reaction solution (HC1) may also be increased. It may be desirable to take care that the pH of the reaction solution is always below 2 and that the time of measurement is long enough to collect all CO2 generated from carbonates.

In the context of this specification, the term "alkaline cellulose dope" may refer to cellulosic material in alkaline solution, i.e. in dissolved form, suitable for use e.g. in spinning filaments, staple fibers, film making, cellulose pearl production, and various other purposes. The alkaline cellulose dope may be coagulated in suitable conditions into solid cellulose, for example into type II cellulose.

The cold alkaline solution may include a dissolution or stabilizing agent, for example a zinc compound, such as ZnO, e.g. to stabilize the alkaline cellulose dope. In such solutions, CO2 and/or carbonates may form ZnCCg, which is poorly soluble. Thus the CO2 that is absorbed and dissolved in the alkaline cellulose dope and/or carbonates in the alkaline cellulose dope may effectively reduce the amount of zinc ions derived from the ZnO in the solution. For environmental reasons, it may not be desirable to compensate for this simply by adding more of the zinc compound. The absorbed CO2 and carbonate ions may also form Na2CO3, which is also not a desirable salt in the system.

Zinc carbonate crystals may form in the products coagulated from the alkaline cellulose dope. Such crystals may become loose from the surface of the products and end up in regeneration baths or washing baths. This may generate pores at the surfaces of the products. Further, large zinc carbonate crystals may obstruct e.g. the holes of a spinneret with which the alkaline cellulose dope is spinned. Such holes may typically have e.g. a diameter of about 40 - 100 pm.

With the process, it may be possible to improve the stability of the alkaline cellulose dope. In particular, the stability may be improved e.g. such that the viscosity of the alkaline cellulose dope does not increase for a given period of time, at least not to a significant extent . The period of time may be e . g . at least 4 hours , or at least 12 hours , or at least 24 hours .

Additionally or alternatively, the concentration of the cellulose dissolved in the alkaline cellulose dope may be increased . It may also be possible to reduce the consumption of the zinc compound, such as ZnO, in cold alkaline solutions in which it is included, and thereby render the process more cost-effective and environmentally friendly .

There may be various possibilities to reduce or remove CO2 dissolved and/or to reduce the concentration of carbonate ions in the cellulose material and the cold alkaline solution and/or in the alkaline cellulose dope at least partially, and/or to disperse and dissolve the cellulose material in the cold alkaline solution in conditions in which the absorption and/or dissolution of CO2 and/or the concentration of carbonate ions in the alkal ine cellulose dope is reduced . For example , any one of the process steps described below may be applied, alone or in combination with one or more other process steps described below, to reduce or remove CO2 dissolved and/or the concentration of carbonate ions in the cellulose material and the cold alkaline solution and/or in the alkaline cellulose dope at least partially .

In the context of this specification, the term "alkaline cellulose dope" may be understood as a solution comprising cellulose solubili zed in an alkaline solution . For example , the alkaline cellulose dope may be a cellulose spinning solution ( i . e . an alkaline cellulose spinning solution) or a cellulose solution ( i . e . alkaline cellulose solution) for extrusion, spinning, electrospinning, molding, casting, film forming, film extrusion, cellulose pearl production, coating, spraying and/or 3D printing . In other words , it may refer to cellulosic material in alkaline solution suitable for use e.g. in spinning filaments, staple fibers, film making, cellulose pearl production, and various other purposes. The cellulose alkaline cellulose dope may be coagulated in suitable conditions into solid cellulose, for example into type II cellulose.

Providing the cold alkaline solution may com- prise mixing and/or dissolving an alkaline agent, such as NaOH, and optionally a dissolution or stabilizing agent, for example a zinc compound, such as ZnO, with water. They may be mixed at conditions suitable for dissolving the components in water, for example at an elevated temperature and such that the alkaline agent, such as NaOH, is added at a concentration of at least 40 % (w/w) . The elevated temperature may be e.g. a tem- perature of at least 60 °C. The resulting alkaline so- lution may then be diluted.

The alkaline agent may comprise or be e.g. NaOH, LiOH, KOH, and/or any mixture or combination thereof. The alkaline agent may comprise or be e.g. NaOH, LiOH, and/or any mixture or combination thereof. Additional organic hydroxide may also be included in the cold alkaline solution, such as tetrabutylammonium hy- droxide, etc. The cold alkaline solution may be an aque- ous alkaline solution.

As a skilled person will understand, the zinc compound, such as ZnO, may be present in the alkaline cellulose dope and in the cold alkaline solution e.g. in the form of zincates. Solid zinc oxide may dissolve in alkaline solutions to give soluble zincates as shown in the exemplary equation below:

The cold alkaline solution may comprise the alkaline agent, such as NaOH, at a concentration in the range of about 5 - 9 % (w/w) , or about 6.5 - 8 % (w/w) .

The cold alkaline solution may further com- prise about 0 - 3 % (w/w) , or 0.1 - 2.5 % (w/w) , or 0.5 - 1.3 % (w/w) of the zinc compound, such as ZnO. The cold alkaline solution may comprise ZnO and NaOH e.g. at a mass ratio in the range of 0.025 - 0.3.

The cellulose material may comprise cellulose and optionally hemicelluloses. Many sources of cellulose may additionally contain an amount of hemicelluloses. For example, pulp may comprise a mixture of cellulose and hemicelluloses. The mixture may comprise e.g. at least 9 wt-%, or at least 13 wt-%, or at least 15 wt-%, or 10 - 23 wt-%, or 13 - 18 wt-% of hemicelluloses on the basis of the total dry weight of the cellulose and hemicelluloses. The hemicelluloses may also be solubilized in the alkaline cellulose dope.

The cellulose material may comprise or be e.g. pulp. The pulp may be hydrolyzed pulp. The pulp may be alkaline soluble pulp.

The pulp may comprise or be e.g. wood pulp (such as hardwood and/or softwood pulp) , non-wood pulp, and/or agropulp. The pulp may be chemical pulp, such as kraft pulp. The pulp may, additionally or alternatively, be never dried pulp, such as never dried kraft pulp. The cellulose material or the pulp may comprise or be recycled fiber.

The pulp may be pre-treated, for example by a mechanical pre-treatment (up to 5 h) followed by a 2-3- h enzymatic hydrolysis utilizing cellulolytic enzymes.

The cellulose material, such as pulp, may have a CED viscosity in the range of 100 - 300 ml/g, or in the range of 140 - 200 ml/g, or in the range of 150 - 180 ml/g. The term "CED viscosity" may be understood as referring to viscosity number in cupri-ethylenediamine (CED) solution. Cellulose material with a relatively low CED viscosity may have better solubility and may therefore allow for obtaining an alkaline cellulose dope with a higher concentration of the dissolved cellulose in the alkaline cellulose dope and/or a more stable alkaline cellulose dope. The CED viscosity may be measured e.g. according to the standard ISO 5351:2010. The cellulose material may be in solid form, e . g . as dry pulp . Alternatively, it may be e . g . in the form of a slurry .

The cellulose material and/or components in- cluded in the cold alkaline solution and/or in the al- kaline cellulose dope may be provided, for example pro- duced, under conditions in which the CO2 dissolved in the components is at least partially removed, such as under reduced pressure , prior to dispersing and dis- solving the cellulose material in the cold alkaline so- lution

The cellulose material and/or components ( such as solid components ) included in the alkaline cellulose dope may be provided, e . g . dried or degassed under conditions in which the CO2 dissolved in the cellulose material and in the components is at least partially removed, such as under reduced pressure , prior to dispersing and dissolving the cellulose material in the cold alkaline solution . Components (e . g . reagents ) included in the cold alkaline solution and/or in the alkaline cellulose dope may be dried or degassed under conditions in which the CO2 dissolved in the cellulose material and in the components is at least partially removed, such as under reduced pressure , prior to dispersing and dissolving the cellulose material in the cold alkaline solution .

The cellulose material and all components (e . g . reagents ) included in the cold alkaline solution and/or the alkaline cellulose dope may be provided, e . g . dried and/or degassed, under conditions in which the CO2 dissolved in the cellulose material and in the components is at least partially removed, such as under reduced pressure , prior to dispersing and dissolving the cellulose material in the cold alkaline solution .

The cellulose material , such as e . g . hydrolyzed pulp, may be produced such that the absorption and/or dissolution of CO2 in the cellulose material is reduced . This may be done e.g. by producing the cellulose material such that after acid hydrolysis of the pulp, the hydrolyzed pulp is washed with water that has been degassed and/or purified to remove CO2 dissolved therein and/or carbonate ions at least partially. The water may be degassed and/or purified e.g. by boiling, heating, ion exchange, reverse osmosis, nanofiltration, precipitation, ion exclusion chromatography, acidification, and/or any combination thereof, to remove carbonate ions and optionally other ions at least partially .

The components may include e.g. the alkaline agent. The components may include e.g. a dissolution or stabilizing agent, for example the zinc compound; urea, chitin, carboxymethyl cellulose (CMC) , high amylose content starch, methyl cellulose, pectin, and/or any mixture or combination thereof; and/or any mixture or combination thereof. The components may further comprise one or more other additives that may be included in the cold alkaline solution. The components may be in solid form.

In the context of this specification, the term "reduced pressure" may be understood as referring to a pressure that is lower than atmospheric pressure. The reduced pressure may be e.g. a partial vacuum. The reduced pressure used or required may depend e.g. on the temperature. For example, the reduced pressure may be such that it is capable of degassing at least partially but does not cause a significant amount of water to evaporate. The reduced pressure may be e.g. a pressure in the range of 80 - 800 mbar, , or in the range of 100 - 200 mbar. In the context of this specification, the term "partial vacuum" may refer to a pressure in the range of 80 - 800 mbar, or in the range of 100 - 200 mbar. As a skilled person will understand, under reduced pressure the absolute concentration of CO2 in the atmosphere may be reduced, while the concentration or proportion of CO2 relative to other gases in the atmosphere may remain the same .

Providing the cold alkaline solution may com- prise purifying the water to remove carbonate ions and optionally other ions at least partially; and mixing an alkaline agent , such as NaOH, and optionally a dissolu- tion or stabili zing agent, for example a zinc compound, such as ZnO, in the water, thereby obtaining the cold alkaline solution .

Providing the cold alkaline solution may com- prise removing CO2 dissolved in the water at least par- tially; and mixing an alkaline agent , such as NaOH, and optionally a dissolution or stabili zing agent , for ex- ample a zinc compound, such as ZnO, in the water, thereby obtaining the cold alkaline solution . They may be mixed at suitable conditions , for example at an elevated tem- perature and such that the alkal ine agent , such as NaOH, is added at a concentration of at least 40 % (w/w) . The resulting alkaline solution may then be diluted . The water, or portions of the water, may be added at various stages of preparing the cold alkaline solution and/or the alkaline cellulose dope .

Providing the cold alkaline solution may com- prise purifying the water to remove carbonate ions and optionally other ions at least partially; removing CO2 and optionally O2 dissolved in the water at least par- tially; and mixing an alkaline agent , such as NaOH, and optionally a dissolution or stabili zing agent , for ex- ample a zinc compound, such as ZnO, in the water, thereby obtaining the cold alkaline solution .

The water may be purified e . g . by boiling, heating, ion exchange , reverse osmosis , nanofiltration, precipitation, ion exclusion chromatography, acidification, and/or any combination thereof to remove carbonate ions and optionally other ions at least partially . A suitable ion exchange resin may be used for removing carbonate ions and optionally other ions at least partially. Such ion exchange resins and methods for using them are known. The ion exchange may be performed, for example, by adding Ca(OH)2 or CaO to the water to precipitate carbonate ions as CaCCg and subsequently to remove remaining Ca ²⁺ ions at least partially by ion exchange.

Additionally or alternatively, the water may be purified by acidification, so as to remove carbonate ions, and subsequently by anion exchange to remove anions derived from the acid added in the acidification. For example, chloride (Cl-) and/or sulphate (SO4 ^2- ) ions may be exchanged to hydroxyl ions (OH-) by anion exchange .

Additionally or alternatively, the water may be purified by boiling. The boiling may remove air (including O2 and CO2) . The boiling may be done under reduced pressure (e.g. under a partial vacuum) or under an atmosphere with a reduced CO2 content, such as by feeding an inert gas, e.g. helium (He) or nitrogen (N2) gas, to the atmosphere under which the water is boiled.

Additionally or alternatively, the water may be purified by bubbling it with an inert gas, e.g. helium (He) or nitrogen (N2) gas, optionally after boiling the water .

As a skilled person will understand, the water is typically not pure water or contain only H2O, but may contain amounts of other components e.g. dissolved therein, for example CO2 and/or carbonate ions.

The water may comprise 0.5 g/kg or less, or 0.25 g/kg or less, or 0.05 g/kg or less of CO2 dissolved therein based on the total weight of the water. The concentration of carbonate ions in the water may be 1.5 % (w/w) or lower, or 1.2 % (w/w) or lower, or 1.0 % (w/w) or lower, or 0.2 % (w/w) or lower, or 0.1 % (w/w) or lower (based on the total weight of the water) . In the context of this specification, the term "atmosphere with a reduced CO2 content" may be understood as referring to an atmosphere that does not comprise CO2 or an atmosphere that comprises 100 ppm or less CO2 • The atmosphere with a reduced CO2 content may additionally comprise 50000 ppm or less O2 . The atmosphere with a reduced CO2 content may be formed by an inert gas , such as helium, argon and/or nitrogen gas , or other suitable inert gas . In an embodiment, the term "atmosphere with a reduced CO2 content" may refer to an atmosphere wherein the proportion of CO2 is reduced as compared to the proportion of other gases contained in the atmosphere . For example , the atmosphere with a reduced CO2 content may contain 1 . 5 g/m ³ of CO2 or less .

Providing the cold alkaline solution may comprise mixing water, such as water purified as described above , and an alkaline agent , such as sodium hydroxide (NaOH) . Optionally, a dissolution or stabili zing agent , for example zinc oxide ( ZnO) and/or other additives may be mixed in the cold alkaline solution . The mixing may be done under reduced pressure (e . g . under a partial vacuum) or under an atmosphere with a reduced CO2 content . Addition of the alkaline agent , such as NaOH, and optionally ZnO, may increase the temperature of the mixture . Thi s step may thus be combined with the purifying of the water by boiling .

The cellulose material may be a slurried pulp suspension prepared by mixing pulp, such as hydrolyzed pulp, or other suitable pulp, with water . The mixing may be performed under reduced pres sure and/or under an atmosphere with a reduced CO2 content , and/or CO2 dissolved in the slurried pulp suspension may be reduced or removed at least partially . The water may be e . g . water purified according to one or more embodiments described in this specification . The mixing may be done using a mixing device with sufficient mixing power so as to separate fibers from each other and to avoid fiber bundles in the alkaline cellulose dope. The mixing with such a mixing device may also assist in bringing energy into the system under mixing, such that solid-gas interfaces in the system may be replaced with solid- liquid interfaces.

The temperature of the slurried pulp suspension may be adjusted to a desired temperature, such as a temperature in the range of 0°C to 5 °C. The mixing may be continued.

The cellulose material may then be dispersed and dissolved in the cold alkaline solution. The temperature of the cold alkaline solution and/or of the cellulose material may be adjusted to a temperature in the range of -5 °C to 5 °C before and/or during this step .

The cellulose material may be dispersed and dissolved in the cold alkaline solution under an atmosphere with a reduced CO2 content or reduced pressure, e.g. under a partial vacuum.

The cellulose material may be dispersed and dissolved in the cold alkaline solution e.g. by feeding the cellulose material and the cold alkaline solution into a continuous reactor or a high consistency dissolving unit in which partial or full dissolution of the cellulose may be achieved.

This may be done e.g. by feeding an inert gas, such as helium (He) or nitrogen (N2) gas, to the atmosphere under which the cellulose material is dispersed and dissolved in the cold alkaline solution.

The cold alkaline solution may comprise e.g. urea, chitin, carboxymethyl cellulose (CMC) , high amylose content starch, methyl cellulose, pectin, and/or any mixture or combination thereof. Such agents may replace the dissolution or stabilizing agent, for example the zinc compound, such as ZnO, at least partially in the cold alkaline solution. All steps of the process after providing a cellulose material and a cold alkal ine solution but before forming the alkaline cellulose dope into a desired shape may be performed in conditions in which the absorption and/or dissolution of CO2 in the alkal ine cellulose dope is reduced . For example , all steps of the process after providing the cellulose material and a cold alkaline solution but before forming the alkaline cellulose dope into a desired shape may be performed under reduced pressure (e . g . under a partial vacuum) and/or under an atmosphere with a reduced CO2 content . In such processes , it may not be necessary to degas the alkaline cellulose dope .

The process may further comprise filtering the alkaline cellulose dope so that the exposure of the alkaline cellulose dope to air and/or to CO2 during and after the filtration is minimi zed or reduced . For example , the filtering may be done under reduced pressure (e . g . under a partial vacuum) and/or under an atmosphere with a reduced CO2 content .

The process may further comprise freezing the alkaline cellulose dope , and subsequently thawing the frozen alkaline cellulose dope in conditions in which the thawed alkaline cellulose dope is at least partially degassed . The thawed alkal ine cellulose dope may be subj ected to shearing forces so as to mix and degas the thawed alkaline cellulose dope . A transparent and completely dissolved alkaline cellulose dope may then be achieved .

The alkaline cellulose dope may be thawed e . g . in a planetary centrifuge . Such a device may also be referred to as a planetary centrifugal mixer . A planetary centrifuge may agitate and simultaneously degas the alkaline cellulose dope . It may rotate the container of the planetary centrifuge containing the alkaline cellulose dope and move the alkaline cellulose dope away from the center of the container, so as to cause flow of the alkaline cellulose dope and/or to apply shearing forces thereto . The shearing forces may thus mix the alkaline cellulose dope and disperse gas bubbles therein finely . Gas bubbles at the surface of the alkaline cellulose dope may be removed by shearing forces . The planetary centrifuge may further apply a partial vacuum to the alkal ine cellulose dope , or it may operate under atmospheric pressure .

However, other apparatuses and devices exerting centrifugal and/or shear forces may be contemplated .

In an embodiment , the dissolution of Avicel cellulose in a NaOH 2 . 3M system with ZnO ' s addition, maintaining a needed ZnO/NaOH mass ratio such as 0 . 167 with 7 - 12 % cellulose concentrations w/w takes the following steps . First , all the reagents , including the cellulose and the solvents , are dried using various methods , such as under vacuum ( 200 mbar, 60 °C, 12h) to avoid the absorption of CO2 from the air . The dissolution process is carried out in a reactor with an inert atmosphere created by an inert gas such as N2 ( the total air volume is replaced every minute ) . The dissolution takes place in a vessel at conditions such as -5°C, 3h, 700 rpm with a cooling j acket where a cooling agent such as water/propylene glycol 1 : 1 is used; after this period, the obtained dope undergoes a free zing step at conditions such as - 17°C . This frozen step improves the NaOH hydrated shells ' contact with the reactive hydroxyl groups of cellulose , improving the dissolution . Finally, the solid dope is thawed using a process for homogeni zing and deaeration of the dope , such as a planetary centrifuge , where the solid dope is thawed simultaneously under centrifugal forces at conditions such as 2000 rpm and 20 min allowing to obtain a transparent and completed dissolved dope . After the dissolution and centrifuge/thawing processes , a clear dope at room temperature is obtained . The viscosity and flow behavior of the dopes produced determines their suitability for ID or 3D materials production .

In the above embodiment , the term "drying" in the context of drying all the reagents , including the cellulose and the solvents , may be understood as referring to drying and/or degassing .

As the al kal ine cellulose dope may have a low temperature , humidity may condense and even freeze on the surface of the alkaline cellulose dope . This may have adverse effects on the alkaline cellulose dope .

The humidity of the atmosphere in contact with the alkaline cellulose dope may be reduced . Thereby the condensation of the humidity to the surface of the alkaline cellulose dope may be reduced . The humidity of the atmosphere may be e . g . up to 90 % , or up to 80 % , or up to 50 % .

Further, one or more , or al l , of the steps of the process after providing the alkaline cellulose dope (but optionally before forming the alkaline cellulose dope into a desired shape ) may be performed in conditions in which the humidity of the atmosphere in contact with the alkaline cellulose dope is reduced, thereby reducing condensation of the humidity to the surface of the alkaline cellulose dope .

With one or more embodiments of the process described in this specification, a higher concentration of the dissolved cellulose in the alkaline cellulose dope may be obtained .

The concentration of the dissolved cellulose in the alkaline cellulose dope may be at least 5 % (w/w) , or at least 7 % (w/w) , or at least 8 % (w/w) , or at least 9 % (w/w) , or at least 10 % (w/w) , or at least 11 % (w/w) , or at least 12 % (w/w) . The concentration of the dissolved cellulose in the alkaline cellulose dope may be in the range of about 5 - 12 % (w/w) .

The temperature of the cold alkaline solution may be e . g . in the range of -20 to 5 ° C, or in the range of -4 to 5 °C when dissolving the cellulose material and/or of the alkaline cellulose dope.

The cold alkaline solution may contain 0.5 g/kg or less, or 0.25 g/kg or less, or 0.05 g/kg or less of CO2 dissolved therein based on the total weight of the cold alkaline solution.

The concentration of carbonate ions in the cold alkaline solution may be 1.5 % (w/w) or lower, or 1.2 % (w/w) or lower, or 1.0 % (w/w) or lower, or 0.2 % (w/w) or lower, or 0.1 % (w/w) or lower (based on the total weight of the cold alkaline solution) .

The alkaline cellulose dope may be stored under an atmosphere with a reduced CO2 content. For example, the alkaline cellulose dope may be fed into a container with an atmosphere with a reduced CO2 content, such as inert atmosphere, such as an inert gas (for example, nitrogen (N2) , argon (Ar) or helium (He) gas) atmosphere. The alkaline cellulose dope may not be mixed with the inert gas, but it may only be stored under the inert atmosphere so as to reduce the absorption and/or dissolution of CO2 in the alkaline cellulose dope.

However, instead of being stored, the alkaline cellulose dope may be fed directly to production, for example to an extrusion or printing apparatus or other apparatus for forming the alkaline cellulose dope into a desired shape. The process may be a continuous process .

The process may further comprise forming and coagulating the alkaline cellulose dope into a desired shape .

The alkaline cellulose dope may be formed into the desired shape e.g. by by extruding, spinning, electrospinning, molding, casting, film making, film extrusion, cellulose pearl production, coating, spraying, or printing.

The alkaline cellulose dope may be extruded e.g. through a die or a nozzle. The viscosity of the alkaline cellulose dope may be adjusted so as to be desirable e.g. for extrusion. The consistency of the alkaline cellulose dope may be e.g. in the range of 5 - 12 wt-%.

The cellulose of the alkaline cellulose dope may be considered to be coagulated and/or regenerated when a desired shape is obtained therefrom. The cellu- lose is not necessarily actually regenerated cellulose in the sense that it would have undergone the viscose process and subsequent regeneration. In this case, the terms "coagulated" and "regenerated" may refer to cel- lulose that is precipitated and/or crystallized from the solubilized state. It may be crystallized at least par- tially into cellulose II; or partially into cellulose I and partially into cellulose II. Typically, the coagulated cellulose is in the form of cellulose II.

The shape may be e.g. a pellet, a powder, a film, a filament, a staple fiber, a bead, a melt, a 3D shape, a coating, a hotmelt adhesive, a container, a casing, a packaging article, a filmic label, a paper, a medical device, a plastic or composite profile, an abrasive particle, an abrasive film or paper, and/or a 3D printing filament. The shape is not particularly limited. Various shapes may be extruded, spun, formed into a film, cast, sprayed, printed, coated or molded from the alkaline cellulose dope.

The extruded shape, such as a filament or any other shape, may be coagulated and washed after extru- sion. For example, the method may comprise immersing the extruded shape in a regeneration bath (or one or more regeneration baths) . The regeneration bath may contain a regeneration solution, which then may assist in coag- ulating the cellulose contained in the shape. The re- generation solution may be an acidic regeneration solu- tion, such as a sulphuric acid solution. However, in some embodiments, the regeneration solution may be e.g. water or a mildly alkaline solution. The shape, such as a filament or any other shape, may be washed after it has been coagulated. The extruded shape may be immersed in one or more washing baths. For example, after a regeneration bath containing an acidic regeneration solution, the extruded shape may be immersed in one or morewashing baths . Such washing baths could comprise e.g. water or another neutral solution .

An alkaline cellulose dope is also disclosed.

The alkaline cellulose dope may contain 0.5 g/kg or less, or 0.25 g/kg or less, or 0.05 g/kg or less of CO2 dissolved therein.

The concentration of carbonate ions in the alkaline cellulose dope may be 1.5 % (w/w) or lower, or 1.2 % (w/w) or lower, or 1.0 % (w/w) or lower, or 0.2 % (w/w) or lower, or 0.1 % (w/w) or lower. The weights may be based on the total weight of the alkaline cellulose dope . The alkaline cellulose dope may be obtainable by the process according to one or more embodiments described in this specification.

The concentration of the dissolved cellulose in the alkaline cellulose dope may be at least 5 % w/w) , or at least 7 % (w/w) , or at least 8 % (w/w) , or at least 9 % (w/w) , or at least 10 % (w/w) , or at least 11 % (w/w) , or at least 12 % (w/w) .

The alkaline cellulose dope may have a viscosity in the range of 2000 - 100000 mPas, or in the range of 2000 - 20000 mPas, or in the range of 2000 - 10000 mPas, or in the range of 3000 - 8000 mPas, or in the range of 4000 - 6000 mPas, or in the range of 3000 - 6000 mPas .

The alkaline cellulose dope may have a viscosity of 10000 mPas or lower within a time period of at least 24 hours of the dissolution of the cellulose material into the alkaline cellulose dope. If the stability of the alkaline cellulose dope is reduced, the viscosite may increase, in particular during storage. The viscosity of the alkaline cellulose dope may not increase by more than 50 % , or by more than 20 % , or by more than 10 % , within a period of time of at least 24 hours of the dissolution of the cellulose material into the alkaline cellulose dope . The period of time may be e . g . at least 4 hours , or at least 12 hours , or at least 24 hours .

A product obtainable by coagulating alkaline cellulose dope from a cold alkaline process is also disclosed .

The product may comprise 1 . 0 % (w/w) or less of carbonate ions . The product may comprise 0 .2 % (w/w) or less , or 0 . 1 % (w/w) or less of carbonate ions .

The product may be obtainable or obtained by coagulating alkaline cellulose dope according to one or more embodiments described in this specification .

The product obtainable by coagulating alkaline cellulose dope from a cold alkaline process may be such that it does not comprise xanthates of the cellulose and/or sulphur covalently bound to the cellulose . The product obtainable by coagulating alkaline cellulose dope from a cold alkaline process may be such that it does not comprise residues of N-methylmorpholine 4 -oxide (NMMO) and/or ionic liquids ( ionic solvents ) . In other words , the product obtainable by coagulating alkaline cellulose dope from a cold alkaline process may not encompass products obtainable from the viscose , lyocell or loncell® processes .

The product may have a CED viscosity in the range of 100 - 300 ml /g, or in the range of 140 - 200 ml /g, or in the range of 150 - 180 ml /g .

The product may be obtainable from the alkaline cellulose dope by extrusion, spinning, electrospinning, molding, casting, film forming, film extrusion, cellulose pearl production, coating, spraying and/or printingand coagulating the alkaline cellulose dope . The product may be obtainable from the alkaline cellulose dope according to one or more embodiments described in this specification by extrusion, spinning, electrospinning, molding, casting, film forming, film extrusion, cellulose pearl production, coating, spraying and/or printing and coagulating the alkaline cellulose dope .

The product may be e . g . a pellet , a powder , a film, a filament , a staple fiber, a bead, a melt , a 3D shape , a coating, a hotmelt adhesive , a container, a casing, a packaging article , a filmic label , a paper, a medical device , a plastic or composite profile , an abrasive particle , an abrasive film or paper, and/or a 3D printing filament .

For example , the product may be a sausage casing obtainable by extruding and coagulating the alkaline cellulose dope , or a sausage casing obtainable by coating and/or impregnating a fibrous reinforcement with the alkaline cellulose dope . The outside or the outside and the inside of the fibrous reinforcement may be coated .

The product may be a paper or cardboard obtainable by coating the paper or cardboard with the alkaline cellulose dope .

The product may be a f ilament and/or a staple fiber . Such a product may have a tenacity of 15 cN/tex or greater .

EXAMPLES

Reference will now be made in detail to various embodiments , an example of which is il lustrated in the accompanying drawing .

The description below discloses some embodiments in such a detail that a person skilled in the art is able to utili ze the embodiments based on the disclosure . Not all steps or features of the embodiments are discussed in detail , as many of the steps or features will be obvious for the person skilled in the art based on this specification.

Figure 1 describes an embodiment of a process for preparing an alkaline cellulose dope.

An alkaline agent and optionally other components of the cold alkaline solution 1 is/are provided. The components 1 may be in solid form, for example solid NaOH. The components 1 may include e.g. a dissolution or stabilizing agent, for example ZnO or other zinc compound, or e.g. at least one of urea, chitin, carboxymethyl cellulose (CMC) , high amylose content starch, methyl cellulose, or pectin. They may be dried and/or degassed at a suitable drying and/or degassing apparatus 2. The components 1 may be dried under conditions in which the CO2 dissolved in the components is at least partially removed, such as under reduced pressure. The drying apparatus 2 may thus operate such that the components 1 are dried under a partial vacuum.

Water 3 is also provided. The water 3 may be purified at a suitable purification apparatus 4 for removing CO2 dissolved in the water and/or carbonate ions at least partially. The purification apparatus 4 may comprise e.g. ion exchange and/or reverse osmosis equipment capable of removing carbonate ions and optionally other ions at least partially from the water 3. Alternatively, the purification apparatus 4 could comprise e.g. an apparatus for boiling the water 3.

The purified water obtainable from the purification apparatus 4 and the dried components may be mixed in a mixing apparatus 5. The temperature of the mixture may also be adjusted e.g. by cooling the mixture; thus the mixing apparatus 5 may further comprise a cooling apparatus. Thus the cold alkaline solution may be obtained.

A cellulose material 6, such as pulp, is provided. The cellulose material 6 may be dried at a suitable drying apparatus 7 . The cellulose material 6 may be dried in the drying apparatus 7 under conditions in which the CO2 dissolved in the cellulose material is at least partially removed, such as under reduced pressure . The drying apparatus 7 may thus operate such that the cel lulose material 6 is dried under a partial vacuum .

The dried cellulose material may then be dispersed and dissolved in the cold alkaline solution in a suitable apparatus , such as a mixing apparatus 8 , such that an alkaline cellulose dope is obtained . The mixing apparatus 8 may operate under an atmosphere with a reduced CO2 content or reduced pressure so as to remove remaining CO2 dissolved in the cellulose material and/or in the cold alkaline solution, and/or to reduce the absorption and/or dissolution of CO2 in the alkaline cellulose dope .

The alkaline cellulose dope obtainable from the mixing apparatus 8 may subsequently be filtered by a filtering apparatus 9 . The filtering may be done so that the exposure of the alkaline cellulose dope to air and/or to CO2 during and after the filtration is minimi zed or reduced . For example , the filtering apparatus 9 and the filtering therein may be performed under an atmosphere with a reduced CO2 content or reduced pressure .

The alkaline cellulose dope may be further treated so as to remove CO2 dissolved in the alkal ine cellulose dope at least partially .

The alkaline cellulose dope may be frozen in a freezing apparatus 10 . The frozen alkaline cellulose dope may subsequently be thawed under centrifugal forces in a suitable centri fugal apparatus 11 , such as e . g . a planetary centrifuge .

The alkaline cellulose dope may be stored in a storage container 12 , such as a tank . The storage container 12 may have an atmosphere with a reduced CO2 content . For example , the alkaline cellulose dope may be fed into a storage container 12 with an atmosphere with a reduced CO2 content , such as an inert gas ( for example , nitrogen (N2 ) or helium (He ) gas ) atmosphere . The alkaline cellulose dope may not be mixed with the inert gas , but it may only be stored under the atmosphere with a reduced CO2 content so as to reduce the absorption and/or dissolution of CO2 in the alkal ine cellulose dope . Alternatively, the storage container 12 , and the atmosphere therein, may have a reduced pressure , for example a partial vacuum . The pressure within the storage container 12 may be e . g . in the range of 80 - 100 mbar .

However, instead of being stored, the alkaline cellulose dope may be fed directly to production, for example to an extrusion or printing apparatus 13 . The process may be a continuous or a semi-continuous process .

Thus all steps of the process after providing the cellulose material 6 and the cold alkaline solution may be performed in conditions in which the absorption and/or dissolution of CO2 in the alkal ine cellulose dope is reduced .

Further, one or more , or all , of the steps of the process after providing the alkaline cellulose dope may be performed in conditions in which the humidity of the atmosphere in contact with the alkaline cellulose dope is reduced, thereby reducing condensation of the humidity to the surface of the alkaline cellulose dope .

From the storage container 12 or from previous process stages , the alkaline cel lulose dope may be fed to the extrusion or printing apparatus 13 . In thi s exemplary embodiment , the apparatus 13 is an extrusion apparatus capable of extruding and coagulating the alkaline cellulose dope into a shape , such as a filament or a film . However, other types of apparatuses may be contemplated . In the extrusion apparatus 13 , the alkaline cellulose dope is driven by a screw 14 run by a motor 15 through a die 16. At the die 16, the alkaline cellulose dope is extruded into a shape 17, such as a filament; however, the alkaline cellulose dope could alternatively be extruded into various other shapes or profiles, such as into a film. The wet filament 17 may then be immersed in a regeneration bath 18 containing e.g. a sulphuric acid solution. In the regeneration bath 18, the solubilized cellulose (and hemicelluloses, if present) from the cellulose material are coagulated. The coagulated filament or other shape may then be processed further .

EXAMPLE 1

Hydrolyzed pulp was dissolved in a high mixing List reactor in a cold NaOH solution containing 7.8 % of NaOH and 1.3 % of ZnO. The hydrolyzed pulp was dispersed and dissolved in the cold NaOH solution under vacuum .

A well dissolved alkaline cellulose dope (alkaline spinning solution) with 9 % (w/w) pulp content was achieved.

EXAMPLE 2

Dissolution of cellulose in aqueous-based solvents. The dissolution of cellulose is not a straightforward process; due to the cellulose molecular structure characterized by multiple inter and intramolecular hydrogen bonds, cellulose is a very stable molecule with low reactivity ¹ . Therefore, traditional solvents cannot dissolve cellulose, and more complex processes are required ¹ ' ² . In general, there are three types of solvent systems able to dissolve cellulose: 1 ) dissolution of cellulose after chemical modification, 2) dissolution in non-aqueous, non- derivatizing media, 3 ) dissolution into aqueous systems 2,3.

The first group is commercially the most important so far, with the so-called viscose process. In the viscous process, the cellulose from the pulp is transformed into cellulose xanthate by alkalinization (18% NaOH) and reaction with carbon disulfide (CS2) ; subsequently, the regeneration of this derivative in the form of cellulose fiber is achieved by precipitation in an acid coagulation bath (H2SO4) with ZnSCg. The salt promotes coagulation, while the acid neutralizes the alkali and breaks down cellulose xanthate to generate a coagulated cellulose ³ . This process has numerous environmental effects; although a part of the carbon disulfide is recovered through condensation and absorption, a significant fraction is released into the atmosphere together with hydrogen sulfide; additionally, liquid effluents with a high load of salts and acid are removed ³ ' ⁴ .

In the second group, non-aqueous, non- derivatizing media, there are two types of processes, a) the industrial process called lyocell where an amine oxide (N-methyl morpholine) or NMMO can dissolve cellulose at high temperatures (80-130°C) ⁵ . The lyocell process is widely used industrially; however, about 10% of the solvent is not recovered; additionally, the solvent has various undesired effects such as loss of the degree of polymerization, formation of colored fiber, oxidation of cellulose, and risks of explosion due to decomposition of the NMMO at high temperatures ⁵ . b) the second most crucial solvent type in this group are the Ionic Liquids (ILs) . In 1914 Paul Walden reported the physical properties of ethyl ammonium nitrate ( [EtNHs] [NO3] ; mp 13-14 °C) . Starting what was initially known as liquefied quaternary ammonium salts; under this appearance, ILs arose again in 1934 under the first patent for using ILs to dissolve cellulose at temperatures around 100 ° C ^5-8 . These types of solvents are difficult to recover and expensive ; nonetheless , new types of ILs are being developed and patented under the name loncell ™ ⁹ ' ¹⁰ , to dissolve and regenerate cellulose efficiently .

The third group and the one this work is focused on are the aqueous-based solvents .

Aqueous-based dissolving systems started with the discovery in 1897 of the Cuprammonium hydroxide process , which is still used in low quantities due to the high cost of the raw materials ^{3 , 4} . On the other hand, al kal i or NaOH aqueous solutions already used in the viscose and mercerization processes started to gain importance in 1934 when it was found that cel lulose is soluble in NaOH-water solutions in a specific limited range of low NaOH concentrations and low temperatures ^11-13 . NaOH aqueous-based solutions for dissolving cellulose are an attractive pathway for cellulose regeneration due to the low environmental impact and low cost ⁴ ' !4 .

This NaOH-aqueous solution and its ternary thermodynamic phase diagram were described in 1939 by Sobue ¹⁵ . In this equilibrium phase diagram appears a particular region at 7 - 10 wt% NaOH and -5 ° C to 1 ° C named "Q state" or "Q zone" in this area, alkali completely dissolves cellulose . Moreover, it has been shown that NaOH hydrates eutectic mixtures actively interact at these low temperatures and penetrates the cell wal l layer ⁴ . Since works in 1934 several additives and co-solvents have appeared further to increase the dissolution capacity of NaOH aqueous-based solutions ; nonetheless , several factors have inhibited so far the complete industriali zation of alkali dissolution and regeneration of cellulose , such factor can be summari zed as follows ¹ ' ¹ 4 . ( _a ) temperature : sub- zero temperatures required for dissolution ; b) gelation : low solution stability, provoking and earlier gelation ; c) concentration : low maximum concentration for cellulose ( lower than 5-7 wt% ) , limiting the density and mechanical performance of regenerated material ; d) cellulose type : mass molar distribution, degree of polymeri zation, and crystallinity should be low, demanding high purity cellulose and diversity of pretreatments .

Due to its amphiphilic nature , the further dissolution of cellulose imposes the condition to increase molecular interactions , disrupt cellulose hydrophobic interactions , and promote hydrogen bonds to establish well-ordered and highly coordinated water structures at the cellulose surface ⁴ . In particular, LiOH and NaOH alkali solutions dissolve cellulose due to the formation of hydration shells where the alkali ions can form complexes with cellulose in its dissolution process ⁴ .

Many routes and processes have been proposed to enhance the dissolution capacity in NaOH aqueous solvent mixtures and simultaneously increase the solution stability . These attempts can be classified as pretreatments or additives .

Pretreatments : the pretreatments or activation steps are required in alkali solutions given the following properties described in literature ⁴ ' ⁴ ' ¹⁴ ' ¹⁶ ' ¹⁷ : The contact area between the solvent and the cellulose fibers needs to be increased; this can be performed, reducing the fiber si ze , crystals si ze , crystallinity, and by the creation of new intermolecular paths accessible by the solvent ; this has been performed by ball milling ¹⁸ , steam explosion 1 ⁹ ' ²⁰ , and the combination of steam explosion and grinding ²¹ . Elimination of hemicellulose and lignin , these two components depending on their nature , usually hampers the cellulose dissolution process . For most of the hemicellulose , elimination is reached using alkali or merceri zation pretreatment ⁴ .

Nature of the primary cell wall . In the diffusion and progressive swelling of fibers treated with alkali solutions , the primary cell wall produces a phenomenon called ballooning; this ballooning results from heterogenous swelling where the primary cell wall extends and burst ⁴ . In this respect , a pretreatment with ethanol and hydrochloric acid has been shown to successfully remove the primary cell wall and improve the diffusion of alkali into cellulose ²² .

The reduction of molar mas s or DP is a critical factor for dissolving cellulose in NaOH solutions ⁴ ' ⁴ . In general , a DP of about 200 -300 is suitable for cellulose dissolution and spinning ⁴ . The decrease of molar mass can be achieved by hydrothermal treatments or partial hydrolysis , using different acids such as ascorbic acid ²³ .

The disruption of intermolecular hydrogen bonds . According to Vehvilainen et al . ⁴ , this is the crucial factor why enzymatic pretreatments have been more successful than other pretreatments at similar degrees of polymeri zation . Several enzymatic treatments have been used for improving the cellulose dissolution in NaOH solutions ⁴ . The most interesting so far is the patented Biocelsol ^{(TM) 4 , 14} process that uses endoglucanase-rich enzyme with 7 . 8 wt % of NaOH, 0 . 84 wt % of ZnO, in a bath coagulated yarn with 5 - 15 wt % of H2SO4 and 10 wt % Na2SO4 . Thi s process was developed starting from the research at the Institute of Chemical Fibres from Lodz ' ²⁴ and afterward with VTT and Tampere University ⁴ ' ¹⁴ . Enzymes effect has shown to be precise ; for instance , the pectinase enzyme has been used in free pectin cellulose resulting in an improved dissolution in NaOH solutions ²⁵ . Additives: Increasing the solvent solvated structures and contributing to a more reactive form of cellulose has motivated since 1934, adding different compounds such as urea, thiourea, and metal oxides ^1,11 . In the last twenty years, the solutions involving urea, thiourea, and zinc oxide have gain importance ^1,2 . Table 1 summarizes these solutions compositions and their main findings and properties.

Table 1. Properties of alkali solutions and their mixtures with urea, thiourea, and ZnO

Cellulose Solution Dissolving

Properties /Findings Ref

Material Composition Temp.

Cotton, ZnO/NaOH molar Better dissolution at -

Davidson et al.

Oxidize ratio[0 - 0.178] -5°C -> 15°C 5°C with oxidized

(1937) ¹²

Cotton NaOH [3 - 3.5N] cellulose

Mercerized NaOH/Urea/Thioure Viscous process Laszkiewicz et al.

Cotton a/ZnO optimization (1990) ²⁶

8.5 wt % NaOH/ 5

Cellulose Laszkiewicz et al. wt % Thiourea +

III (1993) ²⁷

Acrylamide

MCC DP -20°C-> Isogai et al.

< 200 NaOH 9 wt %

Thawing at RT (1998 ) ²⁸

NaOH/Urea/

Cellulose The starting point for Struszczyk et al.

Aspergillus Niger

Pulp the Biocelsol patent (1998-2002) ²⁴ ' ²⁹ cellulase

ZnO delay gelation for Egal et al. (2006-

MCC NaOH/Urea/ZnO T < 0 °C several days, ZnO and 2008 ) ^{30 32}

Urea produce similar effects

NaOH 8 wt %/8 wt

Cotton „ Solubility test for

% Urea/6.5 wt % -12 C Jin et al. (2007) ³³ linter several samples

Thiourea

Freezing

7.8 wt % thawing NaOH/O.84 wt %

Dissolving dissolution Biocelsol patent Vehvilainen et al.

ZnO/

Grade Pulp (solution VTT-Tampere University (2008-2015) ⁴ U4, i6 endoglucanase stable up to rich enzyme 21 °C)

NaOH 6 wt %/Urea Enzyme improves

Cotton -15°C->

4 wt %/ solubility from up to Wang et al. (2008) ³⁴ linters Thawing at RT

Celluclast enzyme 60%

Cotton linters Mn NaOH 7 wt %/12 -12.6 °C-> Dissolution up to 8 wt

Qi et al. (2008) ³⁵

< 10.0 wt% urea Thawing at RT % cellulose xlO ⁴

Cotton 7 wt %NaOH/ 12 wt Formation of Zn(OH) ₄ ^-2 ,

Yang et al. (2011) linter %Urea/ [ 0-2.5 ] wt -13 °C promotes strong

36 pulp %ZnO hydrogen bonds

Accumulation of urea at the hydrophobic surface

4.6 wt % LiOH/ 15 RT solubility Isobe et al. (2013)

MCC might prevent the wt % Urea test ³⁷ association of cellulose

Cotton 9.3 wt % NaOH/ -5 °C -> 8 °C Metastable solution at Jian et al. (2017) linter 7.4 wt % thiourea 8 °C ³⁸

Cotton Dissolution up to 7 wt

9 wt % NaOH/ 6 wt linter „ % cellulose, production Yang et al. (2017)

% Urea/ 6.5 wt -2 C

D by the wet spinning of ³⁹

%Thiourea P=350 high strength fibers

Table 1 presents the main characteristic of the systems involving alkali or urea-related mixtures . Recently, Liu et al . 40 have demonstrated through Molecular Dynamic simulations that urea ' s ability to di ssolve is mainly due to the high correlation of urea molecules around acetalic oxygen atoms (01 and 05 ) , preventing cellulose re-aggregation, therefore , extending solutions stability . This capacity has also been used recently for improving paper mechanical properties ⁴⁰ . It is es sential to notice that al l these processes shown in Table 1 involve high purity cellulose with low DP at sub- zero dissolution temperatures , even the enzymatic pretreatment that exhibits remarkably improvement in the dissolution ability compared with other pretreatments at a similar DP 04, 38, 39, requires low DP and the additional step of f reeze-thawing ⁴ ' ⁶ .

Other solvents different from urea and zinc oxide have been proposed ¹ ' ² ; from these additives , it is essential to highlight amphiphilic polymers such as Polyethylene Glycol ( PEG) . Yan and Gao ⁴¹ have reported dissolution of cellulose powder up to 13 wt % , starting from a solution with 9 wt % NaOH/ 1 wt % PEG-2000 ; this system is frozen at - 15 ° C and thawed, reaching stabilities up to 13 days at room temperature . The amphiphilic behavior allows the PEG molecules to interact with hydrophilic sites on cellulose , while screening hydrophobic interactions hinders cellulose chains ' entanglement , therefore delaying its gelation . This type of behavior is also highlighted by Medronho et al . ⁴² and shows how amphiphilic betaine derivative can delay gelation and increase dissolving temperature .

On the other hand, fillers and crosslinking agents have been considered especially for controlled release systems ⁴ ; for instance , one exciting possibility is the crosslinking using epichlorohydrin, which has the effect of tuning the gelation time ⁴³ . Recent advances : new sustainable routes for hydrolyzing cellulose have been introduced, and if controlled and optimi zed, such routes could be considered suitable novel pretreatments for alkali dissolutions . Su et al . ⁴⁴ have developed a one-pot fast hydrolysis process using microwave and sulfuric acid, Nagaraj an et al . ⁴⁵ have proposed eco-based hydrolysis using citric acid, Xu et al . ⁴⁶ present one suitable hydrolysis with oxalic acid with low concentration and complete recovery of the acid, and Cheng et al . ⁴⁷ developed a process for hydrolysis and synthesis of carboxylated cellulose .

These hydrolysis pretreatments might be considered as profitable routes , especially for raw materials with high DP or with the presence of hemicellulose and lignin ; moreover, such processes can introduce new functionalities that can fine-tune the dissolving ability in alkali solutions ⁴ . Another possible path is to extend even more the ef ficiency of enzymatic pretreatments , and this can be achieved in different routes : fine-tuning of heterogenous interphase properties ⁴⁸ , the combination of the enzymatic treatment with acid, alkali , and PEG ⁴⁹ , or by the addition of Ionic Liquids to the enzymatic system ^50-53 . Regardless of the chosen system or combinations , this should be optimi zed and adj usted to the final product properties .

In contrast , other proposed strategies consider adding fillers and crosslinking agents , resulting in high mechanical performance hydrogels and composite materials . However, this has been challenging due to the extremely high pH involved in the alkali dissolution ⁴ . Some authors have reported exciting results using PEG as a stabili zer and crosslinking agent ⁵⁴ and its combination with sodium alginate ⁵⁵ ; even more , such sodium alginate can be combined with cellulose nanocrystals (CNCs ) for improving the mechanical properties in wet spinning produced filaments ⁵⁶ . Another way to increase mechanical performance is to use epichlorohydrin (ECH) as a crosslinker to induce a self- cross linked structure ⁴³ ' ⁵⁷ or to crosslink cellulose with other materials such as clay montmorillonite mineral ^{58- 60} and PVA ⁶¹ . Cellulose and PVA have been crosslinked using not only (ECH) but glutaraldehyde as a coupling agent ⁶² .

Table 2 summari zes these fillers and crosslinking routes and their characteristics .

Table 2. Novel fillers and crosslinking agents involved in cellulose and NaOH cellulose regenerated materials.

Filler/Cross

System Material Properties /Findings Ref.

Linker

Cellulose PEG Hydrogel Toughness 389 kJ.m ^-3 Wan et al. (2015) ⁵⁴

NaOH

Cellulose Cernencu et al.

PEG/Alginate Films Wet stability

NaOH (2017) ⁵⁵

Alginate/ Tensile strenght 2.05

Filaments Liu et al. (2019) ⁵⁶

CNC cN/dtex

Cellulose Chang et al. (2010)

Epichlorohydrin Hydrogels Tuning gelation

NaOH/Urea ⁵⁷

Cellulose Compressive modulus

Epichlorohydrin Hydrogels Qin et al. (2013) ⁴³

NaOH/Urea 220KPa

Epichlorohydrin

Improvement in WVT, oil Tayeb et al. (2019)

MFC or Acrylic resin Composite resistance ⁵⁸ ' ⁵⁹

/Montmorillonite

Cellulose Epichlorohydrin/ High strength, Storage Chang et al. (2008)

Hydrogels

NaOH PVA Modulus ⁶¹

Cellulose

The addition of

Enzymatical

Glutaraldehyde Cellulose acetate Spolj aric et al . ly Filaments

/PVA coating improves water ( 2017 ) ⁶² f ibrillated stability

)

Dual crosslink strategy with variable molecular

Epichlorohydrin/ Zhang et al . ( 2019 )

Cellulose Hydrogels weight agent for

PEGDE 63 tailoring mechanical properties

Table 2 presents the recent advances reported to improve the mechanical properties , swelling, and wet stabilities of cellulose-based materials by the addition of fi llers and cross linking agents ; those can be added using different strategies , such as the recently presented dual crosslinking strategies using different molecular weight crosslinking agents , presented by Zhang et al . ⁶³

The research field in the present is devoted to the production of composite materials and aerogels 1 , 64 , 6s where the mechanical properties are not the principal target . Currently, none of these methods can provide a stable route for producing spun filaments that can reach traditional textiles performances in a scalable industrial process ¹ . Furthermore , the description of the physical phenomena occurring during the dissolution process of cellulose under alkali conditions is still in the early stage of understanding since many questions such as the role of the additives , the effect of f reeze/thawing processes are not entirely understood/ described .

The regeneration of cellulose from aqueousbased solvents in alkali-based systems has always shown a promising potential from the economic and environmental point of view; nevertheless , this system has shown different drawbacks such as the poor mechanical properties of the regenerated material .

Inspired by nature and observing how this has its methods to prepare tough and stable extruded filaments , it is possible to learn and improve cellulose ' s dissolution process in alkali conditions . For instance , spider silk is produced by a mechanism that involves fine-tuning and controlling shear stress forces and micro acidic or pH environment ⁶⁶ . The control of these variables , together with the control of the temperature and time , has been shown to possess a drastic effect on the regenerated cellulose in alkali conditions to produce different materials or embodiments ID (filaments) , 2D (films) , and 3D (meshes) .

The present example is focused on the dissolution in a NaOH 2.3M system with ZnO's addition, maintaining a ZnO/NaOH mass ratio of 0,167 with cellulose concentrations of 7 -12 % w/w. All the reagents, including the cellulose and the solvents, are previously dried under vacuum (200 mbar, 60°C, 12h) to avoid the absorption of CO2 from the air. The dissolution process is carried out in a one-liter reactor with an inert atmosphere (N2, the total air volume is replaced every minute) . The dissolution takes place at (-5°C) for 3 hours; after this period, the obtained dope undergoes a freezing step (-17°C, 12h) , and finally, the solid dope is thawed using an innovative process for homogenizing and deaeration of the dope; that is performed in a planetary centrifuge (THINKY AR-250 mixer, JAPAN) , where the solid dope is thawed simultaneously under centrifugal forces (2000 rpm, 20 min) allowing to obtain a transparent and completed dissolved dope (as observed by optical microscopy) . This novel process involves controlling the acidic environment (elimination of CO2 absorption) , the shear forces, and temperature (planetary centrifugation) . The process allows higher cellulose concentrations dopes than those reported so far; such dopes are suitable for preparing multidimensional materials (1D-3D) .

The ID embodiment filament material is produced from a wet-spinning system in an acidic regeneration bath (10% H2SO4 w/w and 10% Na2SO4) . The extruded dopes (7, 9 12% w/w) have the potential to be used as textiles. The 2D (films) and 3D (meshes) materials are produced from the same dopes used for the ID embodiment materials, with some differences according to the dope rheology. The cellulose doped used for the filaments' production at 7% w/w is not suitable for the 3D printing. This dope requires an aging procedure, so the phase angle approaches the unity or, in other words, that the dope is close to its gelation point. The latter is important since, for high-definition 3D printing, the solution should possess a shear-thinning behavior and low normal stress, so the extruded solution is not spread out after the extrusion. Therefore, it is possible to form a stable macro-structure. In this case, an aging procedure at 5 °C and 48h have shown to be enough to produce a printable gel; this aging step is not required for higher cellulose concentrations (9, 12%w/w) . The 3D printing procedure is carried out in glass petri dishes in a pressure range of 6 -15 kPa at a printing speed of 11 mm/s using a 250 pm diameter nozzle. The films are printed with 50% infill density, and the meshes with 0% infill density are printed with two layers. The final films and meshes are coagulated and washed, following the same procedure applied to the ID materials. The material used for 3D printing has been tested in-vitro , and the biocompatibility results suggest that this material can be used to manufacture biomedical wearable patches or meshes.

The process of fabricating multidimensional materials based on alkali-soluble cellulose was tested using an initial dope preparation by dissolving the cellulose in NaOH 2.3 M with ZnO's addition, maintaining a ZnO/NaOH mass ratio of 0.167 with cellulose concentrations of 7 -12 % w/w. All the reagents, including the cellulose and the solvents, were previously dried under vacuum (200 mbar, 60 °C, 12h) to avoid the absorption of CO2 from the air. The dissolution process was carried out in a one-liter reactor with an inert atmosphere (N2, the total air volume was replaced every minute) . The dissolution took place at (-5°C) for 3 hours; after this period, the obtained dope underwent a freezing step (-17°C, 12h) , and finally, the solid dope was thawed using a process for homogenizing and deaeration of the dope ; that was performed in a planetary centrifuge ( THINKY AR-250 mixer, JAPAN) , where the solid dope was thawed simultaneously under centrifugal forces ( 2000 rpm, 20 min) ; finally, the rheology of the produced dope was inspected and used accordingly for the production of ID or 2D-3D products .

Figure 2 shows a process in the fabrication of multidimensional materials based on alkali soluble cellulose . The process of fabricating multidimensional materials based on alkali-soluble cellulose consists of an initial dope preparation by dissolving the cellulose in NaOH 2 . 3M with ZnO ' s addition, maintaining a ZnO/NaOH mass ratio of 0 , 167 with cellulose concentrations of 7 - 12 % w/w . All the reagents , including the cellulose and the solvents , are previously dried under vacuum ( 200 mbar, 60°C, 12h) to avoid the absorption of CCy from the air . The dissolution process is carried out in a one- liter reactor with an inert atmosphere (N2 , the total air volume is replaced every minute ) . The dissolution takes place at ( -5°C) for 3 hours ; after this period, the obtained dope undergoes a freezing step ( - 17°C, 12h) , and finally, the solid dope is thawed using an innovative process for homogeni zing and deaeration of the dope ; that is performed in a planetary centrifuge ( THINKY AR-250 mixer, JAPAN) , where the solid dope is thawed simultaneously under centrifugal forces ( 2000 rpm, 20 min) ; finally, the rheology of the produced dope is inspected and used accordingly for the production of ID or 2D-3D embodiments . Dotted boxes show the different embodiments .

Figure 3 shows the gelation process in a dissolved solution at 7 % w/w of cellulose . Figure 3 reveals the nature of dissolved Avicel® cellulose in alkali conditions ( see Materials and methods ) . Figure 3a illustrates the dope ' s time and frequency-dependent structuration, revealing the gel structure ' s strong influence with shear force and time ( aging) . Figure 4 shows the CO2 (g) absorption on the alkali dissolved cellulose and its influence on the rheological properties . Figure 4 reveals the complexity of the aging phenomena in the alkali dissolved cellulose at 7 % w/w . It is clear that the aging process is due to the combination of three factors : the first is the time , due to the increasing hydrophobic interactions that provoke crystalli zation, the second factor is the temperature as shown in Figure 4a, initially increasing the temperature promotes a decrease in the viscosity until the temperature is high enough to promote gelation increasing the viscosity again ( red line at 40°C, figure 4a) . Figure 4b reveals the effect of leaving an open sample at room condition for one week; this sample increases its elastic modulus from 100 Pa to more than 1000 Pa . The Raman spectra of the aged sample show that this absorbs CO2 (g) during the gelation process Figure 4c (black line ) . Additionally, Figure 4d shows the cellulose dope alignment under cross-polari zed light at high shear rates .

Figure 5. Presents the rheological behavior and appearance of the alkali dissolved cellulose at concentrations of 7 , 9 , and 12 % w/w . It is possible to observe that all the cellulose dope converges to a maximum elastic modulus (G' =10000 Pa) at high frequencies , indicating a gelated system . According to figure 5a, the dissolution l imit i s around 12 % w/w for the Avicel® cellulose ( see materials section) .

Figure 6. Depicts the Wet spinning cellulose regeneration in three steps ; the first coagulation bath consists of sulfuric acid and sodium sulfate at 10% w/w each, the second bath allows the gradual hydration and regeneration of the filaments ( 0 . 01M HC1 ) ; finally, the last bath is used to remove the remaining acid/base remaining on the filaments ( room temperature distilled water) . Figure 7 . Presents the dry filaments mechanical performance produced from dopes with different cellulose concentrations ( 7 , 9 , and 12 % w/w) together with the azimuthal intensities and Herman' s orientation parameters calculated from the azimuthal profiles

Figure 8 . Shows the typical 3D printed meshes structures and films from cellulose dissolved in alkali conditions with different dopes concentrations

Figure 9. Printed films mechanical and optical properties at 7 , 9 , and 12 % cellulose concentrations

Nature has its methods to prepare tough and stable extruded filaments . For instance, spider silk is produced by a mechanism that involves fine-tuning and controlling two variables : shear stress forces and micro acidic or pH environment ⁶⁶ . In the following paragraphs , it will be shown that the control of these variables , together with the control of the temperature and time , possess a drastic effect on the production of cellulose dissolve in alkali conditions and its regenerations in different forms ID, 2D, and 3D . The production of materials from the alkali dissolved cellulose requires the coagulation of cellulose in a non-solvent coagulation bath . Previous to this step, it is necessary to possess a stable dope at the process temperature since gelation occurs at any temperature and is not a thermoreversible process ⁶ . Figure 2 summari zes the embodiments for the production of multidimensional materials from the alkali-soluble cellulose . The following embodiments are disclosed :

Dissolution embodiment : the dissolution of Avicel cellulose in a NaOH 2 . 3M system with ZnO ' s addition, maintaining a needed ZnO/NaOH mass ratio such as 0 , 167 with 7 - 12 % cellulose concentrations w/w takes the following steps . First, all the reagents , including the cellulose and the solvents , are dried using various methods , such as under vacuum ( 200 mbar, 60°C, 12h) to avoid the absorption of CO2 from the air . The dissolution process is carried out in a reactor with an inert atmosphere created by an inert gas such as N2 ( the total air volume is replaced every minute ) . The dissolution takes place in a vessel at conditions such as ' -5°C, 3h, 700 rpm' with a cooling j acket where a cooling agent such as water/propylene glycol 1 : 1 i s used; after this period, the obtained dope undergoes a free zing step at conditions such as- 17°C and 12 has reported ⁶⁷ , this frozen step improves the NaOH hydrated shells ' contact with the reactive hydroxyl groups of cellulose , improving the dissolution . Finally, the solid dope is thawed using an innovative process for homogeni zing and deaeration of the dope , such as a planetary centrifuge , where the solid dope is thawed simultaneously under centrifugal forces at conditions such as 2000 rpm and 20 min allowing to obtain a transparent and completed dissolved dope ( as observed by optical microscopy and shown in Figure 3 ) . After the dissolution and centrifuge/thawing processes , a clear dope at room temperature is obtained ( see Figure 3 ) . The viscosity and flow behavior of the dopes produced determines their suitability for ID or 3D materials production .

Rheology embodiment : The shear rheology of the dissolved cellulose was monitored . First , the linear viscoelastic region (LVR) of the cellulose dope is determined by an oscillation test where an amplitude sweep at constant frequency allows to determine the range where the elastic structure of the sample is not destroyed; thi s test , also called the fracture test is necessary to establish the amplitude range where the complex modulus is constant ; therefore the rheological properties of the dope can be measured ⁶⁸ . In this case , our dope exhibited stability at 10 rad/sec in a wide range of amplitudes ; therefore , 1 % strain is selected to measure all the rheological properties . The gelation kinetics is determined at 10 rad/ sec and 1 % strain measuring the gelation time , the time where the storage modulus (G') becomes more extensive than the loss modulus (G' ') or, in other words, the phase angle becomes smaller (tand < 1) . The master's plot for a 7% w/w cellulose dope between the range of 15°C and 40°C, was determined to follow eq 1. t = 1053ehF (1)

Where t is the time in minutes for the gelation to occur, and T is the dope temperature in Celsius degrees. This kinetic equation allows the prediction of the gelation time under the conditions explored; for instance, gelation at 10 rad/sec, 1% strain, and 25 degrees occur in about 1 hour.

Additionally, the frequency sweep tests showed two exciting results. First, a frequency sweep test at 0.1 % strain exhibited a particular phenomenon, showing that a dope at room temperature (25°C) that initially exhibits a gel-like behavior G'> G' ' for frequencies in the range of 0.1 - 50 rad/s turns into a liquid-like behavior G'< G' ' for frequencies above 60 rad/sec, this could be interpreted as the initial pre-gelation stage where the interf ibrillar interactions started to occur; therefore applying higher shear stress at high frequencies allows to recover a liquid-like behavior destroying metastable interactions. It is essential to point out that this only occurs before the complete gelation .

The time as a variable during the gelation process has been well identified and attributed to the increasing hydrophobic interchain interactions that promote the crystallization or gelation of cellulose ⁶⁹ (Figure 3b, tan 5= 1.0) and additionally, these dopes have been reported to capture CO2 (g) from air ⁷⁰ , which seem to be affecting the gelation as well. Figure 4 shows the CO2 (g) absorption on the alkali dissolved cellulose and its influence on the rheological properties . Figure 4 reveals the complexity of the aging phenomena in the alkali di ssolved cellulose at 7 % w/w . The aging process is due to the combination of three factors : the first is the time , due to the increas ing hydrophobic interactions that provoke crystallization, the second factor is the temperature as shown in Figure 4a, initially increasing the temperature promotes a decrease in the viscosity until the temperature is high enough to promote gelation increasing the viscosity again ( red line at 40°C, figure 4 a) . Figure 4b reveals the effect of leaving an open sample at room condition for one week; this sample increases its elastic modulus from 100 Pa to more than 1000 Pa . The Raman spectra of the aged sample show that thi s absorbs CO2 (g) during the gelation process Figure 4c (black line ) .

The alkali cellulose dope at 7 % w/w cellulose content possesses a maximum absorption of CO2 of 17 ( 3 ) mgCCy (g) /gaope measured in a high precision laboratory scale , the Raman intensity for this saturated sample is also exhibited in figure 4c (blue line ) .

Finally, the shear force effect is shown in figure 4d, where a rheometer equipped with an optical camera with cross-polari zed light allows the detection of cellulose fibrils alignment under high shear forces ( above 400 s ^-1 ) ; under this condition, the cellulose dope lowers down its viscosity to a minimum steady value ( shear thinning behavior) and exhibits the typical optical pattern (with dark and bright areas ) for aligned cellulose fibrils that have been described previously 71 , 72 .

This novel process involves the control of the acidic environment (elimination of CO2 absorption) , the shear forces , and temperature (planetary centrifugation) ; therefore , the cellulose concentration can go as high as 12 % w/w, and these material dopes are suitable for the preparation of multidimensional materials ( 1D-3D) . These steps are crucial to extend the dissolution process further and obtain a transparent and completed dissolved dope ( see Figure 5 ) .

Figure 5 shows the rheological behavior and appearance of the alkali dissolved cellulose at concentrations of 7 , 9 , and 12 % w/w . It is possible to observe that all the cellulose dope converges to a maximum elastic modulus (G' =10000 Pa) at high frequencies , indicating a gelated system . According to figure 5a, the dissolution l imit i s around 12 % w/w for the Avicel® cellulose DP=290 . The optical microscope images reveal that the centrifugal thawing process extends the dissolution further for solutions up to 12 % w/w; however, the gelation speeds up for higher concentrations , therefore the dissolved system at 12 % w/w already gelates after the thawing process ( figure 5c) , indicating the time and concentration restrictions for the system . In synthesis , three variables strongly affect these systems ' dissolution capacity and gelation kinetics : time , temperature , and CO2 (g) presence , as revealed in Figures 4 and 5 .

The production of ID embodiment filament material is suitable as long as the dope possesses a liquid-like behavior ( far from the gelation point G' ' >G' ) . The extruded f ilaments can be produced from a wet-spinning system in an acidic regeneration bath . The dope extrusion and its resulting filament ' s mechanical performance is always the critical response expected for textiles or wearable devices applications . This mechanical performance is optimi zed based on the heat and mass transfers involved in the coagulation processes and the hydromechanical gel properties such as density and alignment ^72-74 . The proposed dope extrusion and regeneration process are depicted in figure 6 .

Wet Spinning embodiment : during the dope extrusion and the filament drawing, the shear forces create extensional forces that can orient the structure even more effectively . Thus , conforming well-aligned filaments has the potential to enhance strength and toughness ⁷³ . A well-balanced dope should not be too weak because the fibrils alignment would be lost , neither too rigid to facilitate the extrusion and drawing steps ⁴ . The proposed setup consists of three coagulation baths ; the first bath contains H2SO4 10 % w/w and Na2SO4 10 % w/w, which is the typical bath used for this alkali dissolve cellulose regeneration ¹⁶ . The second bath is a conditioning bath that uses a low pH solution such as 0 . 01M HC1 . Thi s bath was included since it was noticed by the optical microscope observations that the direct washing of recently coagulated filaments produced surfaces with cracks and several defects ; therefore , this intermediate conditioning bath drastically reduces the filaments morphology defects by lowering down the acid diffusion and promoting slow hydration of the filaments before their final washing with water in the third washing bath . The drying process can be carried out in a system under tension ; such as a metallic board where the regenerated and washed filaments are cut ( 0 . 5 m) and dried at room conditions , under tension ( two magnets holding both ends of the filaments ) ; this has been shown to preserve the fibrils alignment effectively and avoid shrinkage and facilitate the production of stronger filaments ⁷⁵ .

Coagulation or regeneration is a mass transport-driven process , where the critical parameters for these alkali aqueous-based systems are mainly the type of the acid, its concentration, and temperature . Low concentrations and temperatures will hinder the coagulation process ; contrarily, high temperatures and acid concentrations will produce soft filaments with high porosity ⁴ . The properties of filaments at constant draw ratio ( DR=1 ) , coagulation bath temperature 23°C produced from different cellulose concentrations are shown in Figure 7 . As it is possible to observe from figure 7 , the properties of the fi laments prepared from 9% w/w dope concentrations reach mechanical performance superior to 21 cN . dtex ^-1 making these filaments suitable for textiles applications ⁶ . From Figure 7 it is also possible to see that this dope possesses the highest Herman' s orientation parameter, calculated according to equation 2 . Herman' s orientation parameter calculated from integrating the azimuthal intensities for the first peaks at q= 0 . 87A is a qualitative measurement of the cellulose orientation along its extrusion axis ⁷⁶ .

Where cp is the azimuthal angle and r (cp ) represents the normali zed azimuthal intensities distribution after subtraction the isotropic contribution .

The filament ' s properties obtained are superior to all reported properties for alkali-soluble cellulose reported so far . I t i s clear from figure 7a- c that the cellulose concentration plays an essential role in the improvement of the filament properties ; however, for the higher the cellulose concentration, the minor is the gap before gelation ; therefore , for 12% w/w, the cellulose concentration seems not to play a significant role on the mechanical properties .

Some efforts to produce stable dopes and tough fibers have been proposed in the last thirty years ⁷ . Yamashiki et al . ¹⁹ ' ^77-79 and Yamane et al . ²¹ FO-86 have used steam explosion, combined with wet pulveri zation and alkali pretreatment ( 2 - 5 wt % NaOH at -2 °C) at high mixing speeds . The dissolution of these systems has been performed at temperatures ranging from -2 °C to 4 °C for cellulose concentrations up to 5 wt % with a cellulose raw material with DP of 200 - 300 and degree of crystallinity around 45% . Cai et al . ^{87- 91} , Qi et al . ³⁵ ' ⁹² , and Chen et al . ⁹³ have added urea to the alkali solutions, and Ruan et al. ^<34 ' ^<35 _r and Chen et al. ⁹⁶ added thiourea, obtaining similar fibers to those produced without additives. The main achievements from these urea/thiourea systems are the increase in the initial cellulose DP, gel stability, and in some cases, a higher degree of crystallinity (around 60%) . With or without additives, all these systems have been coagulated in sulphuric acid baths with acid concentrations ranging from 20 to 70 wt %.

Vehvilainen et al. 4, 14, 16, 97 p _ave developed at Tampere University with the cooperation of the VTT research institute from Finland, the Biocelsol™ fibers. These fibers developed from enzyme pretreated dissolving grade pulp dissolved in NaOH/ZnO solutions by the f reeze-thawing method, producing fibers with properties like viscose ⁶ . The ability of the endoglucanase enzyme to enhance the dissolving ability in NaOH/ZnO solutions was attributed mainly to the reduction of DP and intermolecular hydrogen bonds disruption creating new paths for the diffusion of the solvent. Zhang et al. ⁹⁸ , recently dissolved and spun cellulose fibers at 15 °C using a solvent system composed of tetra-butylammonium hydroxide or TBAH with Urea and NaOH. The ability to stabilize the cellulose dope and obtain filaments with strengths up to 1.3 cN/dtex is attributed to the amphiphilic nature of the mixture tune by the addition of TBAH and urea

Printing embodiment: 2D and 3D embodiments with dopes at (7, 9, and 12% w/w) are produced from the same dopes used for the ID embodiment materials, with some differences according to the dope rheology. The cellulose doped used for the filaments' production at 7% w/w is not suitable for 3D printing. This dope requires an aging procedure, so the phase angle approaches the unity or, in other words, that the dope is close to its gelation point. The latter is important since, for high-definition 3D printing, the solution should possess a shear-thinning behavior and low normal stress , so the extruded solution is not spread out after the extrusion . Therefore , it is possible to form a stable macro-structure . In this case , an aging procedure such as ( 5 °C and 48h) have shown to be enough to produce a printable gel ; this aging step is not required for higher cellulose concentrations ( 9 , 12 %w/w) . The 3D printing procedure is carried out in glass petri dishes in pressure ranges such as 6 - 15 kPa for 7 % w/w dopes and 60 - 150 kPa for the dopes at 9 and 12% w/w . The printing for all the dopes was performed at a linear speed of 11 mm/s using printing noz zles such as a 250 pm diameter noz zle . The films are printed with 50 % infill density and the meshes with 0 % infill density and two layers . The final films and meshes are coagulated and washed, following the same procedure applied to the ID materials ( coagulation, washing, and drying) . Figure 8 shows dif ferent samples of 2D and 3D samples printed using different concentration dopes .

The properties of these materials follow the same trend exhibited for the filaments ; the properties of the printed films for 9% w/w cellulose concentration exhibited higher toughness and lower swelling tendency compared to the respective materials produced from dopes at 9 and 12 % w/w ( see Figure 9a-b) .

The main feature of a transparent material is its structural homogeneity . Thus , films formed from regenerated cellulose tend to be transparent ; this was observed in our study, in which all films produced had transparency above 90% . However, the beauty of our work is related to the fact that these films were obtained with a high concentration of cellulose and that this factor did not result in less transparent films as the concentration increased . Another critical factor is that our films showed greater transparency when compared to films found in the literature . Another feature observed was the low reflectance of the films , which could be resulted by smother surface obtained for regenerated films .

Here we also assess the haze of our films . Haze determines the amount of light scattered by the material and depends on minor imperfections in the film structure . This property is essential in applications such as optoelectronics ¹⁰¹ once it can help improve the device performance . We observed that as we increased cellulose concentration in the films , the higher the haze was ; this can be the result of either the structuring of the film during printing or the increase in the dissolved cellulose chains in the material that induces a realignment of the light traveled through the bulk of the film ( see Figure 9c) .

Finally, it can be concluded that the process and technology developed here can offer customi zed structures ID ( filaments ) , 2D ( films ) , and 3D structures with higher mechanical performance and durability compared to traditional based alkali materials due to their higher cellulose content and tunable rheology . Additionally, in ongoing research, the 3D printing material has been tested in-vi tro , and the biocompatibility results suggest that this material can be used to manufacture biomedical wearable patches or meshes . Industries dedicated to the production of materials based on regenerated cellulose can use this technology to produce different end products at lower capital cost ( cheaper reagents than those traditionally used) , greener processes (easier to recycle with any toxic residues ) and competitive mechanical performance compared to currently available technologies (Lyocell , viscous , and loncell ) 1 , 10 , 102 .

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EXAMPLE 3

Pretreated kraft pulp having CED viscosity of 170 ml/g was used in a spinning trial.

Extremely low CO2 content water was produced by heating RO water to 60 °C and evaporating more than 5 % of water and CO2 with reduced pressure. Pressure was so low that the water was boiling. This extremely low CO2 content water was used to wash the pulp (50 g water/g cellulose) , but also for the production of alkali solution containing 18 wt-% NaOH and 3 wt-% ZnO. Both of the chemicals were analytical grade , and the bottles were opened j ust before using . Production of alkali solution was done under inert N2 atmosphere .

Dissolving of cellulose was done by combining the extremely low CO2 content water and the washed cellulose under inert N2 atmosphere and reducing temperature close 1 °C (without freezing the water) . When temperature was reached the alkali solution with temperature close - 15 °C was added under inert N2 atmosphere . Mixing was continued for 30 minutes and temperature at the end of dissolving step was 2 °C . Temperature was slowly increased to 15 °C, while maintaining inert N2 atmosphere .

At this stage the cellulose solution was divided to two parts , where the other part was treated under inert N2 atmosphere ( Spinning solution ( i . e . alkaline cellulose dope ) A) whereas the absorption of CO2 was not prevented to the other part ( Spinning solution B) . The viscosity of solution at this point was 4560 mPas . Both cellulose solutions were filtered using 3 filters ( 25 pm, 10 pm and 5 pm) and centrifuged ( 1000 g, g-forces ) and transferred to spinning vessel . Both samples were mixed all the time very slowly to keep the concentration of carbonate ions of the sample constant . Spinning took place in the next morning . Viscosity and the concentration of carbonate ions of spinning solutions were measured j ust before spinning . Spinning solutions A and B had viscosities and concentration of carbonate ions of 4320 mPas and 0 . 09 % (w/w) , and 12610 mPas and 1 . 05 % (w/w) , respectively . Temperature of both spinning solutions were 21 °C . Spinning of these two spinning solutions were done using spinneret having 250 holes and using exactly same spinning parameters ( regeneration bath had 10 % H2SO4 and 15 % Na2SO4 ) . Fibers were washed with RO water and dried using the air dryer ( 60 °C) . Tenacities of staple fibers are presented in Figure 10 as a function of stretching between the first and second godet . Figure 11 shows tenacities of staple fibers as a function of the elongation at break . Figure 10 shows that the staple fibres made out of spinning solution A can be stretched much more than the staple fibers made out of spinning solution B . It may be concluded that spinning solution A has much better stretchability and regeneration proceeds more evenly . The mechanical properties of staple fibres made out of spinning solution A are much better . For the textile fibers both tenacity and elongation at break are important properties and with spinning solution A tenacity can be above 20 cN/tex and elongation at break still close to 20 % , whereas the staple fibers made out of spinning solution B did not reach the combination of tenacity 15 cN/tex and elongation at break 15 % .

The concentration of carbonate ions of dry staple fibers produced from spinning solution A were measured, and it was only 0 . 08 % (w/w) . Low concentration of carbonate ions of spinning solution thus enables production of high tenacity fibers with low porosity and low concentration of carbonate ions . It is more difficult to wash fibers with high porosity .

EXAMPLE 4

The effect of carbonate content to the stability of alkaline cellulose dope was investigated by producing an alkaline cellulose dope with a low concentration of carbonate ions . Dope samples containing different amounts of carbonates ( % (w/w) based on the total weight of the alkaline cellulose dope , ranging from 0 . 01 to 1 . 8 % ) were produced by leading CO2 gas into the newly-made alkaline cellulose dope . The newly-made alkaline cellulose dope was prepared in a similar manner as in Example 3 . The concentration of carbonate ions of the dope samples were determined by the standard SCAN-N 32:98.

The Brookfield viscosities of the alkaline cellulose dope samples were measured and plotted as the function of the concentration of carbonate ions as shown in Fig. 12. When the concentration of carbonate ions exceeded 1.2 % (w/w) , the viscosity increased, indicating that the stability was reduced. When the concentration of carbonate ions exceeded 1.5 % (w/w) , the stability was reduced to a significant extent.

EXAMPLE 5

An alkaline cellulose dope sample containing 7.4 % (w/w) of cellulose was stored for 5 days in a container at 4 °C, such that it was in contact with air in the container. Samples of the alkaline cellulose dope were taken on days 0, 1, and 5, and the Brookfield viscosities of the samples were measured.

Figure 13 illustrates the Brookfield viscosities of the samples. It was found that the viscosity of the alkaline cellulose dope increased upon storage, indicating that its stability had decreased the more the longer the storage time.

It is obvious to a person skilled in the art that with the advancement of technology, the basic idea may be implemented in various ways. The embodiments are thus not limited to the examples described above; instead they may vary within the scope of the claims.

The embodiments described hereinbefore may be used in any combination with each other. Several of the embodiments may be combined together to form a further embodiment. A process, a product, or a use, disclosed herein, may comprise at least one of the embodiments described hereinbefore. It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments . The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages . It will further be understood that reference to ' an ' item refers to one or more of those items . The term "comprising" is used in this specification to mean including the feature ( s ) or act ( s ) followed thereafter, without excluding the presence of one or more additional features or acts .