Continuous dissolution of cellulose derivatives

Abstract

According to an exemplary aspect of the present invention, there is provided a method for continuously dissolving cellulose carbamate in an alkaline aqueous phase to form a solution, the method comprising the steps of providing cellulose carbamate, mixing the cellulose carbamate with an alkaline aqueous solution to form a mixture, passing the mixture through a mixing zone of a continuously operated mixing kneader at a temperature of 10°C or less to produce a solution of the cellulose carbamate in the alkaline aqueous phase, and recovering a cellulose carbamate-containing aqueous phase.

Description

[Technical Field]

[0001] The present invention relates to a method for dissolving cellulose derivatives. In particular, the present invention relates to a method for the continuous dissolution of cellulose carbamates. [Background technology]

[0002] Cellulose is the most widely used biopolymer in the world, and both cellulose and its derivatives, such as cellulose carbamates, cellulose acetates, ethers, and esters, have found applications in various industries, including the paper and corrugated cardboard industry and the textile industry. However, using cellulose in these industries requires dissolving the cellulose fibers to restore their structure. Dissolving cellulose is difficult due to its semi-crystalline structure, strong hydrogen bonding within the polymer sheet, and the presence of hydrophilic and hydrophobic ends within the polymer. Therefore, cellulose requires structural modification through derivatization, fiber opening, or improved reactivity.

[0003] Several derivatization methods are known, perhaps the most well-known being the viscose process, in which cellulose is first treated with alkali and then with carbon disulfide to produce cellulose xanthate. The viscose process is becoming increasingly unpopular due to the toxicity of carbon disulfide and the undesirable environmental impact of the viscose process. There is growing interest in other derivatization processes, especially those that are inexpensive, do not have the toxicity or environmental problems of the viscose process, and can be implemented using available infrastructure, such as processes that can be carried out with viscose wet spinning machines.

[0004] The carbamate process for producing cellulose carbamates is one such derivatization process. Cellulose carbamates are formed by reacting cellulose with urea. Methods for producing cellulose carbamates are described, for example, in Finnish Patents No. 112869 and No. 112795.

[0005] As described above, cellulose or cellulose derivatives must be dissolved to regenerate their cellulose structure for use in various industrial applications. The procedure for dissolving cellulose in aqueous alkali is based on the freeze-thaw method. The solvent is pre-cooled below the freezing point of water before adding the cellulose and kept at a low temperature until the polymer is completely dissolved. It has been found that the temperature required for efficient dissolution by the freeze-thaw method is around -30°C for the entire mixture of cellulose carbamates in aqueous solution. Thus, freeze-thawing polymer solutions on an industrial scale is not practical, both energetically and economically, because industrial-scale dope production would require the use of efficient freezing equipment that is not typically found in cellulosic fiber production plants. Both freezing and thawing consume energy and time, reducing the overall efficiency and sustainability of the process.

[0006] Conventional dissolution methods, such as freeze-thaw, often cause phase separation during the prolonged freezing phase of the process, or make temperature control during the freeze and thaw phases difficult. This can result in variations in the composition of the resulting cellulose solution, particle aggregation (i.e., undissolved particles "adhering" to form clusters), making subsequent filtration difficult or impossible. Additionally, undissolved particles and uncontrolled process temperatures can induce gelation of the resulting cellulose solution. Nitrogen hydrolysis is simultaneously accelerated by prolonged freeze-thawing and uncontrolled process temperatures. Challenges related to reducing undissolved residue have been partially overcome by producing only highly diluted cellulose solutions or by gradually adding cellulose in a batch mixing process. Conventional freeze-thaw processes and operations using diluted cellulose solutions incur unacceptable costs, both economically and temporally. [Overview of the project]

[0007] The object of the present invention is to overcome at least some of the above-mentioned problems and to provide a method for forming a solution by continuously dissolving cellulose carbamate in an alkaline aqueous phase.

[0008] This method involves mixing cellulose carbamate with an alkaline aqueous solution and passing the thus formed mixture through the mixing zone of a continuously operating kneader-type dissolution reactor to produce a solution of cellulose carbamate in an alkaline aqueous phase. The cellulose carbamate-containing aqueous phase is recovered. The step of passing the mixture through the mixing zone of the kneader-type dissolution reactor is carried out at a temperature of 10°C or lower.

[0009] The present invention is defined by the features of the independent claims. Several specific embodiments are defined in the dependent claims.

[0010] According to a first aspect of the present invention, a method is provided for forming a solution by continuously dissolving a cellulose carbamate polymer in an alkaline aqueous phase, the method comprising the steps of: providing a cellulose carbamate polymer; mixing the cellulose carbamate polymer with an alkaline aqueous solution to form a mixture; passing the mixture through a mixing zone of a continuously operating kneader-type dissolution reactor to produce a solution of the cellulose carbamate polymer in an alkaline aqueous phase; and recovering the dissolved cellulose carbamate polymer-containing aqueous phase. The step of continuously passing the mixture through the mixing zone of the kneader-type dissolution reactor in the method is carried out at a temperature of 10°C or lower.

[0011] The present invention offers considerable advantages. The present invention provides a method for continuously dissolving cellulose carbamate polymers in an alkaline solution. Cellulose carbamate polymers are alkali-unstable cellulose derivatives. The present invention has surprisingly found that cellulose carbamate polymers can be dissolved to a high cellulose consistency to obtain cellulose carbamate spinning dopes with lower viscosity than mathematically and experimentally expected by conventional dissolution methods known in the art. This was demonstrated particularly when the dissolution operation was performed under supercooled conditions.

[0012] Furthermore, surprisingly, the resulting cellulose carbamate dope was found to be stable for extended periods even at room temperature. Normally, cellulose carbamate dopes must be stored at lower temperatures to avoid gelation of the cellulose carbamate solution. [Brief explanation of the drawing]

[0013] [Figure 1] This is a flowchart illustrating a process for the continuous dissolution of cellulose carbamates according to at least some embodiments of the present invention. [Figure 2] This is a flowchart illustrating a process for the continuous dissolution of cellulose carbamates according to at least some embodiments of the present invention. [Figure 3] This is a microscopic image showing the effects of dissolution temperature and sodium hydroxide concentration on the dissolution of cellulose carbamate derived from recycled cotton. [Figure 4] This is a microscopic image showing the stability of the preliminary slurry in a two-step dissolution process. [Figure 5] This graph shows the stability of a cellulose carbamate polymer slurry in an alkaline aqueous solution, expressed in terms of viscosity as a function of shear rate. [Figure 6] Figures 6A to 6C show micrographs of the recovered cellulose carbamate solution. [Figure 7] Figures 7A to 7F show micrographs of the cellulose carbamate solutions disclosed in Example 9. [Modes for carrying out the invention]

[0014] definition In this specification, unless otherwise specified, the following terms are defined as having the following meanings:

[0015] "Low temperature conditions" refers to temperatures in the range of 5°C to -6.9°C.

[0016] "Supercooling conditions" means a temperature lower than the general temperature under low-temperature conditions, and in particular, it means a temperature in the range of -7°C to -20°C.

[0017] Dissolving pulp prepared from chemical pulp, or wood species such as pine, spruce, birch, beech, aspen, maple, larch, acacia, eucalyptus, hemlock, tupelo, oak, or non-wood such as stem fibers (wheat straw, rice straw, barley straw, bamboo, bagasse, reed). The origin of the raw material is either an unused type of chemical pulp or dissolving pulp, or recycled raw materials such as recycled paper and / or cardboard containing chemical pulp or dissolving pulp.

[0018] Natural plant fibers are in the form of chemical pulp or dissolving pulp, or such forms. The origin of natural plant fibers is either an unused form, or a fiber product containing natural plant fibers or a recycled fiber product containing recycled natural fibers. Natural plant fibers include seed fibers such as cotton and kapok, bast fibers such as hemp, jute, kenaf, ramie, abaca, linen (flax), leaf fibers such as manila, sisal, pineapple, banana, and fruit fibers such as coir.

[0019] Cellulose carbamate is continuously dissolved in an aqueous alkali solution, and the mixture of cellulose carbamate and the aqueous alkali solution is led through the mixing zone of a continuous operating mixing kneader at a temperature of 10°C or lower, thereby generating a cellulose carbamate solution having a relatively high cellulose carbamate concentration in the aqueous alkali phase. Cellulose carbamate usually completely dissolves without substantially leaving particles derived from undissolved cellulose, ensuring improved filterability of the cellulose carbamate dope, which can be characterized, for example, by measuring the filtration index (K R ). Improved filterability is technically essential when regenerating cellulose carbamate from the recovered aqueous phase containing cellulose carbamate.

[0020] Figure 1 is a flow diagram showing a process for the continuous dissolution of cellulose carbamate according to at least some embodiments of the present invention.

[0021] Weigh 100 of solid cellulose carbamate and put it into the pulper 10. Add 200 of the total amount of sodium hydroxide aqueous solution required for dissolving the weighed cellulose carbamate 100 to the pulper 10. The alkaline aqueous solution 200 may be added at once or gradually. The pulper 10 is started, and a mixture 300 composed of cellulose carbamate in the alkaline aqueous solution is formed. The mixture 300 is led to a storage tank 20 equipped with a mixer. The storage tank 20 may be a chest storage tank. After the mixture 300 is led to the storage tank 20, the pulper 10 is ready for the next batch of cellulose carbamate 100 and sodium hydroxide aqueous solution 200. The storage tank 20 has a larger volume than the pulper 10 and can accommodate a plurality of batches of the mixture 300 sent from the pulper 10. The mixture 300 is continuously supplied from the storage tank 20 by a pump 30 to the mixing zone of a kneader-type dissolution reactor 40. The temperature of the mixture 300 is preferably lowered, but is maintained above the dissolution limit of the system at the process stage before entering the dissolution reactor 40. A solution of cellulose carbamate in the alkaline aqueous solution 400 is continuously formed and recovered in the dissolution reactor 40.

[0022] FIG. 2 is a flow diagram showing a process for the continuous dissolution of cellulose carbamate according to at least some embodiments of the present invention.

[0023] Weigh 100 of solid cellulose carbamate and put it into the pulper 10. The first portion 2000 of the sodium hydroxide aqueous solution required to form a preliminary slurry with the weighed cellulose carbamate 100 is added to the pulper 10. The pulper 10 is started, and a preliminary slurry 3000 containing cellulose carbamate in the alkaline aqueous solution is formed.

[0024] The preliminary slurry 3000 is led to a storage tank 20 equipped with a mixer. After the preliminary slurry 3000 is led to the storage tank 20, the pulper 10 is prepared for the next batch of cellulose carbamate 100 and the next first portion 2000 of the sodium hydroxide aqueous solution. The storage tank 20 has a larger volume than the pulper 10 and can accommodate multiple batches of the preliminary slurry 3000 sent from the pulper 10. The preliminary slurry is continuously supplied from the storage tank 20 to the mixing zone of the kneader-type dissolution reactor 40 using a pump 30. The second portion 2200 of the alkaline solution is added to the dissolution reactor 40 together with the preliminary slurry 3000 to provide the mixture 330. The mixture 330 is formed in the dissolution reactor. The temperature of the preliminary slurry 3000 is kept above the solubility limit of the system during the process stage prior to the dissolution reactor 40. The solution of cellulose carbamate in the alkaline aqueous solution 400 is continuously formed in the dissolution reactor 40 and recovered.

[0025] As described above, this technology relates to a method for dissolving cellulose carbamate.

[0026] Generally, this technology provides a method for forming a solution by continuously dissolving cellulose carbamate in an alkaline aqueous phase, comprising the steps of: providing cellulose carbamate; mixing the cellulose carbamate with an alkaline aqueous solution to form a mixture; generating a solution of the cellulose carbamate from the mixture in an alkaline aqueous phase; and recovering the cellulose carbamate-containing aqueous phase, wherein the step of generating the solution is carried out at a temperature of 10°C or lower.

[0027] In one embodiment, a method for continuously dissolving cellulose carbamate in an alkaline aqueous phase to form a solution includes the steps of: providing cellulose carbamate; mixing the cellulose carbamate with an alkaline aqueous solution to form a mixture; passing the mixture through a mixing zone of a continuously operating kneader-type mixing reactor to produce a solution of the cellulose carbamate in the alkaline aqueous phase, for example, to produce a cellulose carbamate dope or a cellulose carbamate spinning dope; and recovering the cellulose carbamate-containing aqueous phase.

[0028] In one embodiment, the step of continuously guiding the mixture by passing it through the mixing zone of the mixing kneader is performed at a temperature of 10°C or lower.

[0029] In a further embodiment, cooling is performed in the mixing zone of the mixing kneader. Thus, in one embodiment, the mixture passes through the mixing and cooling zone of the mixing kneader.

[0030] In one embodiment, the step of producing the solution from the mixture is carried out on a cooled metal surface or a cooled cylinder, such as a cooled rotating drum.

[0031] In embodiments, the cellulose carbamate may be a cellulose carbamate produced from a chemical pulp or dissolved pulp prepared from wood fibers or non-wood fibers, or a cellulose carbamate derived from natural plant fibers as a chemical pulp or dissolved pulp, or in such form. Embodiments of the method may also be carried out using a cellulose carbamate produced from a mixture of any of the various cellulosic fibers or pulps described above. In a preferred embodiment, cellulose carbamate is produced in a process comprising the steps of: providing pulp; adding an aqueous solution of urea and optionally hydrogen peroxide to the pulp (or optionally activated pulp) to provide a mixture; mechanically processing the mixture to provide a homogeneous composition; heating the composition to a temperature in the range of 120°C to 155°C, typically 135°C, for 2 to 4 hours to produce cellulose carbamate; recovering the cellulose carbamate; optionally washing the cellulose carbamate with water; and drying in a dryer at a temperature of 155°C or lower, preferably 135°C or lower, and more preferably 133°C or lower.

[0032] In a further embodiment, the mixture formed by cellulose carbamate in an alkaline aqueous solution is mixed with low shear force in the mixing zone of a kneader-type mixing reactor by operating the mixer at a reduced mixer speed of 10 to 500 rpm, preferably 250 rpm or less, most preferably 100 rpm or less, and most preferably 50 rpm or less.

[0033] By mixing with low shear force, the target temperature level can be reached and / or maintained. Therefore, the dissolution process according to the embodiment does not depend on mixing with high shear force. A typical technical approach is to use high-speed mixing to obtain a good quality solution. However, in the embodiment, the dissolution temperature is the most important factor, not the mixing rate or high shear force in the mixing. The more vigorous the mixing, the more difficult it becomes to reach and / or maintain a low dissolution temperature. By dissolving under low temperature and / or supercooling conditions, a cellulose carbamate solution of a quality suitable for the spinning process can be obtained. For example, in the embodiment, the recovered solution is subjected to a spinning process, such as a wet spinning process, to spin cellulose carbamate fibers.

[0034] A mixture of cellulose carbamate polymer and an alkaline solution can be formed in various ways, and each method of forming the mixture is suited to a specific one or more alkaline solutions and a specific one or more cellulose carbamates forming the mixture.

[0035] In one specific embodiment, also known as the one-step method, cellulose carbamate is first mixed with an alkaline solution, and the resulting mixture is supplied to the mixing zone of a continuous-operation kneader-type dissolution reactor.

[0036] In one embodiment, pre-cooling is achieved in a first kneader, thereby obtaining partial dissolution, after which the mixture is transferred to a second kneader, where the material is typically completely or substantially completely dissolved.

[0037] Mixing the cellulose carbamate with an alkaline solution before supplying the mixture to the mixing zone of a continuous-operation kneader-type dissolution reactor to provide a composition corresponding to the final target chemical composition set for the recovered cellulose carbamate dope allows for precise control of the chemical composition of the resulting cellulose carbamate dope. Furthermore, the low viscosity and slurry consistency of the slurry prepared to the final composition makes handling the slurry (e.g., pumping the mixture) technically easier.

[0038] The mixing of cellulose carbamate and alkaline solution to the recovered cellulose carbamate dope, corresponding to the final target chemical composition set for that dope, can be done in batches by directly or gradually adjusting the sodium hydroxide and / or zinc oxide concentrations in the preliminary slurry in a mixing reactor, such as in a pulper or another type of homogenizer or a suitable reactor, such as a xantator reactor or a suitable reactor connected to a homogenizer. This can be done in batches by directly or gradually adjusting the sodium hydroxide and / or zinc oxide concentrations in the preliminary slurry in a xantator reactor or a suitable reactor connected to a homogenizer, in order to influence the swelling properties of the cellulose carbamate derivative before adding the remaining alkali and water containing alkali and / or zinc oxide to reach the final target composition.

[0039] The slurry temperature at each slurrying stage can be controlled, for example, by using a pre-cooling solution and / or by external cooling of the pulper or other type of homogenizer or mixing reactor.

[0040] In a particular embodiment that may be called a two-step method, cellulose carbamate is first mixed with a first portion of an alkaline solution or a zinc oxide-containing alkaline solution, and the resulting preliminary slurry is supplied to the mixing zone of a continuously operating kneader-type dissolution reactor, and a second portion of the alkaline solution or zinc oxide-containing alkaline solution is supplied to the mixing zone of a continuously operating kneader-type dissolution reactor.

[0041] The preliminary slurry of cellulose carbamate containing the first portion of the alkaline solution is supplied to the mixing zone of a continuously operating kneader, and the second portion of the alkaline solution is supplied separately to the mixing zone of a continuously operating kneader. This provides an opportunity to pre-cool the preliminary slurries containing the first and second portions of the alkaline solution separately to specific temperatures depending on their chemical composition before adding them to the mixing zone of the kneader-type dissolution reactor. Furthermore, it is also possible to mix the preliminary slurry and the second portion of the alkaline solution in a homogenizer before introducing the thus obtained mixture into the kneader.

[0042] A preliminary slurry, i.e., a slurry with a sodium hydroxide content below the system's solubility limit, for example, a preliminary slurry with a sodium hydroxide content of about 2-6% by weight, for example, about 3 or 4% by weight, can be cooled to near the freezing point of the mixture without initiating the dissolution of cellulose carbamate. Sodium hydroxide, or a combination of sodium hydroxide and zinc oxide, lowers the freezing point of its aqueous solution. Cellulose carbamate raises the freezing point of its alkaline aqueous solution, so if the cellulose carbamate content in the preliminary slurry is higher than 6% by weight, the freezing point will be higher than -6°C. For example, a preliminary slurry with a sodium hydroxide content of 3% by weight and a cellulose carbamate content of 6% by weight can be cooled to -6°C without freezing of the mixture or initiating the dissolution of cellulose carbamate.

[0043] In the second part of the alkaline solution, sodium hydroxide or a combination of sodium hydroxide and zinc oxide lowers the freezing point of the aqueous phase, allowing this second part of the alkaline solution to be pre-cooled to a temperature between -30°C and -20°C. Furthermore, this allows for adjustment of the concentration of alkali, such as sodium hydroxide and / or zinc oxide, in the pre-slurry, which affects the freezing point and solubility limits of the pre-slurry, as well as the swelling properties of the cellulose derivative. The alkali concentration in the pre-slurry is related to the temperature at which the cellulose derivative begins to dissolve. A higher alkali concentration in the pre-slurry results in a higher temperature at which the cellulose derivative begins to dissolve, and similarly, a lower alkali concentration results in a lower temperature at which dissolution begins. This allows for optimization of the swelling of the cellulose derivative and the supply temperature of the pre-slurry.

[0044] Preferably, the preliminary slurry and the second portion of the alkaline solution are supplied simultaneously to the mixing zone of a continuous-operation kneader. The chemical composition of the preliminary slurry determines the chemical composition of the second portion of the alkaline solution. One of the purposes of optimizing the temperature and alkali concentration of the preliminary slurry is to prevent the dissolution process from starting before the mixing zone of the dissolution reactor, in order to avoid contamination of the preliminary slurry handling system with the high-viscosity cellulose carbamate solution.

[0045] Dissolution is carried out under either low-temperature or supercooled conditions.

[0046] "Low temperature conditions" means temperatures in the range of 5°C to -6.9°C or higher. Therefore, in one embodiment, the temperature of the mixing zone is in the range of 5°C to -6.9°C. In a particular embodiment, the temperature of the mixing zone is about 0°C. Temperatures around 0°C, such as the range of about 5°C to -6.9°C, are particularly suitable for cellulose carbamates formed from chemical pulps or soluble pulps prepared from wood fibers or non-wood fibers, such as commercially available wood-based soluble pulps, non-wood straw-based soluble pulps, or soluble pulps prepared from streams of recycled paper and / or corrugated cardboard waste.

[0047] "Supercooled conditions" means temperatures below -7°C and above -20°C. In further embodiments, the temperature of the mixing zone is below -7°C. A mixing zone temperature lower than -7°C, typically in the range of -7°C to -20°C, is particularly suitable for cellulose carbamates formed from chemical pulp or soluble pulp containing natural plant fibers from either unused raw materials such as hemp, jute, or cotton-based raw materials, or recycled raw materials such as recycled fibers, or derived therefrom.

[0048] In one preferred embodiment, dissolution is carried out at approximately -15°C to approximately -20°C.

[0049] As described in some embodiments, a mixture of an alkaline liquid and a cellulose carbamate can be cooled by contacting it with a cooling surface. Such contact is generally preferable to achieve cooling of the mixture to substantially the temperature of the cooling surface.

[0050] Thus, in one embodiment, cellulose carbamates are produced from cellulose having wood fibers and / or non-wood fibers in the form of dissolved pulp.

[0051] In a further embodiment, cellulose carbamates are produced from cellulose having natural plant fibers such as cotton, in the form of soluble pulp.

[0052] In a further embodiment, the cellulose carbamate is a mixture of cellulose carbamates produced from both cellulose having wood fibers and / or non-wood fibers, such as straw, in the form of soluble pulp, and cellulose having natural plant fibers, such as cotton, in the form of soluble pulp. In such embodiments, the preferred temperature of the mixing zone is about -7°C or lower.

[0053] In further embodiments, wood fiber-derived materials such as soluble wood pulp and / or non-wood fiber-derived materials such as straw-based soluble pulp are dissolved at low temperatures, natural plant fiber-derived materials such as cotton-derived soluble pulp are dissolved under supercooled conditions, and the separately obtained carbamate dopes are mixed after the dissolution process.

[0054] The material, which is soluble under low-temperature conditions, is also soluble under supercooling conditions.

[0055] It is preferable to provide cellulose carbamates having a predetermined range of substitution degrees suitable for application in specific embodiments. The degree of substitution (DS) of a cellulose carbamate polymer at least partially determines the physical and chemical conditions under which the cellulose carbamate can dissolve in an alkaline aqueous solution. This also at least partially determines the concentration of the solution with respect to the cellulose portion that may be formed from the cellulose carbamate.

[0056] In one embodiment, the provided cellulose carbamate has a degree of substitution (DS) of 0.1 to 0.3, particularly about 0.25 or less. After dissolution, the DS of the cellulose carbamate decreases slightly. The degree of substitution of the cellulose carbamate is determined by total nitrogen content measurement according to SFS 5505:1988. A degree of substitution of 0.24 corresponds to a total nitrogen content of 2.0% per absolutely dry water-insoluble fraction of the cellulose carbamate.

[0057] It is preferable to provide a cellulose carbamate having a predetermined range of degrees of polymerization suitable for application in a particular embodiment. The degree of polymerization (DP) of the cellulose carbamate polymer at least partially determines the viscosity of the recovered aqueous solution of the cellulose carbamate dope. The degree of polymerization of the cellulose carbamate polymer can be determined by intrinsic viscosity measurement according to ISO 5351.

[0058] In one embodiment, the cellulose carbamate provided has a degree of polymerization (DP) of DP200 to DP400, particularly about DP220 or higher. A degree of polymerization value of DP250 corresponds to an intrinsic viscosity of 197 ml / g. A mixture of cellulose carbamate dope (for example, a mixture of cellulose carbamate, alkali, water, and possible surfactant-based additives such as polyethylene glycol (PEG), alkylamine or arylamine polyoxyethylene glycol, alcohol ethoxylate, or fatty alcohol ether) has a cellulose carbamate content. In one embodiment, a mixture of cellulose carbamate has a cellulose carbamate content of 6 to 10% by weight (in the mixture of cellulose carbamate and aqueous alkali in the mixing zone, or in the cellulose carbamate dope recovered from the dissolution reactor). In a further embodiment, a mixture of cellulose carbamate dope has a cellulose carbamate content of 6 to 8% by weight, which is a typical cellulose carbamate content obtained under low temperature or supercooling conditions. In further embodiments, the cellulose carbamate dope mixture has a cellulose carbamate content of 8-10% by weight, which is a preferred cellulose carbamate content under supercooled conditions.

[0059] In one embodiment, the aqueous alkaline solution, for example, the cellulose carbamate dope, contains 5-10% by weight of NaOH. In a further embodiment, the aqueous alkaline solution contains 6-8% by weight of NaOH, for example, in the mixture of cellulose carbamate and aqueous alkali in the mixing zone or in the cellulose carbamate dope recovered from the dissolution reactor. In a particular embodiment, the aqueous alkaline solution contains 5-7% NaOH. This is a preferred amount of NaOH in an alkaline aqueous solution when supercooling conditions are applied.

[0060] In some embodiments, the cellulose carbamate:NaOH ratio may be important for ensuring the complete dissolution of the cellulose carbamate. In some embodiments, the mixture has a cellulose carbamate:NaOH ratio of 6-10% by weight:5-10% by weight. In certain embodiments, the mixture has a cellulose carbamate:NaOH ratio of 8-10% by weight:5-7% by weight, which is a preferred ratio under supercooled conditions.

[0061] In embodiments, the actual reaction rate depends on temperature rather than time. Under low temperature or supercooled conditions, the total mass must reach the target temperature. In embodiments, the target temperature is the output temperature of the mixing zone of the dissolution kneader and depends on the chemical composition (cellulose carbamate:NaOH ratio) and the raw material base (wood fibers and non-wood fibers or natural plant fibers or mixtures thereof). In further embodiments, the residence time in the mixing zone depends on at least the following properties: the mechanical properties and mechanical structure of the kneader reactor, the heat exchange properties of the surfaces of the mixing and cooling zones, the thermal energy released into the system during mixing, the cooling force of the external cooling system, and the supply temperature of the mixture or the supply temperature of the pre-slurry and alkaline solution.

[0062] In one embodiment, the residence time is approximately 1 minute to 10 hours, for example, 2 minutes to 2 hours, and particularly 2 minutes to 60 minutes or 2 minutes to 30 minutes.

[0063] In one embodiment, alkaline hydrolysis of the carbamate group is suppressed, and preferably prevented, during the dissolution process.

[0064] In further embodiments, the method includes a further step of adding zinc oxide to the mixture. Zinc oxide can be added to cellulose carbamate, an alkaline aqueous solution, or a mixture of cellulose carbamate and an alkaline aqueous solution. Typically, zinc oxide is dissolved in the alkaline aqueous solution before being used as a dissolving lye for the cellulose carbamate provided. In embodiments, the addition of zinc oxide may partially improve the solubility and filterability of the solution and partially extend the storage time until gelation begins, which also affects the viscosity of the cellulose carbamate solution and the strength yield of the resulting wet-spun cellulose carbamate fibers. In one embodiment, the mixture has a zinc oxide content of 0.1 to 1.5% by weight of the mixture. In one embodiment, the mixture is at least partially defined by the ratio of cellulose carbamate to zinc oxide. Thus, in one embodiment, the cellulose carbamate has a cellulose carbamate:ZnO ratio of 6 to 10%:0.1 to 1.5%, which means 0.01 to 0.25 t of ZnO per t of cellulose carbamate.

[0065] In one embodiment, a method is provided for dissolving cellulose carbamate in an alkaline aqueous phase to form a solution, the method comprising the steps of providing cellulose carbamate by carbonization treatment of a cotton raw material, mixing the cellulose carbamate with an alkaline aqueous solution to form a mixture, generating a solution of cellulose carbamate in an alkaline aqueous phase, and recovering the cellulose carbamate-containing aqueous phase, wherein the step of generating the solution is carried out at a temperature of -7°C or lower.

[0066] In one embodiment, a further method is provided for dissolving cellulose carbamate in an alkaline aqueous phase to form a solution, the method comprising the steps of providing cellulose carbamate, mixing the cellulose carbamate with an alkaline aqueous solution to form a mixture, generating a solution of cellulose carbamate in an alkaline aqueous phase, and recovering the cellulose carbamate-containing aqueous phase, wherein the step of generating the solution is carried out at a temperature of 10°C or less, the cellulose carbamate is first mixed with a first portion of the alkaline aqueous solution to produce a preliminary slurry, the thus obtained preliminary slurry is supplied to a mixing zone, a second portion of the alkaline aqueous solution is supplied separately to a mixing zone, the preliminary slurry is held in the mixing zone at a temperature of -1°C to -6°C before the second portion is supplied to the mixing zone.

[0067] In one embodiment, the continuous dissolution process is obtained by supplying a cellulose carbamate / zincate mixture, prepared in one or two steps, wherein the zincate contains ZnO and NaOH, onto the surface of a rotating cylinder, for example, on which the temperature of the mixture is lowered to a target temperature in the range of -15°C to -20°C. The cooled material is removed from the cooling surface, for example by scraping, and the temperature of the solid material is optionally maintained at the target temperature, or, after further cooling, adjusted to a temperature suitable for further processing by, for example, filtration, degassing, or spinning. In addition to cylinders, various other devices can be used, such as drums, which generally have a coolable flat or curved thermally conductive surface. The surface may be stationary or in motion to rotate. The above temperature range for cooling is particularly suitable for cotton-like carbamates and is suitable for achieving solutions having a predetermined ratio between cellulose carbamate and sodium hydroxide and zinc oxide, as discussed herein.

[0068] In one embodiment, contact between the cellulose carbamate and the zincate solution can be efficiently achieved by optionally mixing with a stirrer or homogenizer before adjusting the temperature of the mixture to a range that promotes dissolution. Generally, efficient mixing is preferred to improve the contact between phases and provide a homogeneous mixture, although dissolution is already achieved by cooling.

[0069] In embodiments of a two-step method combining a preliminary slurry with a second portion of the zincate solution, it is preferable to use a homogenizer because the preliminary slurry can be pre-cooled to a low NaOH content without initiating the dissolution of cellulose carbamate. In such embodiments, it is preferable to pre-cool the second portion of the zincate to a practically low temperature, thereby achieving dissolution when the preliminary slurry is combined with the dic zincate portion.

[0070] In both the one-step and two-step methods, lowering the temperature of the mixture initiates at least partial dissolution of the cellulose carbamate, and in a preferred embodiment, it is technically easy to apply the mixture to the surface of a rotating drum.

[0071] Lowering the temperature of the mixture is also advantageous before application to a cooled metal surface. Therefore, in one embodiment, the mixture supplied to a cooled metal surface or the surface of a cooled cylinder passes through a mixing and cooling zone to cool the mixture and achieve partial dissolution before it is supplied to the surface of a cooled metal surface (e.g., a metal plate, typically a stainless steel plate) or a cooled cylinder (e.g., stainless steel).

[0072] In one embodiment, the dissolution of cellulose carbamate in the pulp is achieved at a temperature higher than that generally applied to cotton carbamate (-15°C to -20°C).

[0073] Based on the foregoing, in a method for continuously producing a cellulose carbamate solution, the step of producing the solution from the mixture is carried out on a cooled metal surface or a cooled cylinder, for example, on the surface of a cooled rotating drum. For example, the mixture is supplied onto a cooled metal surface or the surface of a cooled cylinder having a temperature of about 0°C or -7°C or lower.

[0074] In one embodiment, cellulose carbamate is first mixed with a first portion of an alkaline solution, the resulting preliminary slurry is mixed with a second portion of the alkaline solution, and the resulting mixture is supplied to a cooled metal surface or the surface of a cooled cylinder.

[0075] In one embodiment, the preliminary slurry is cooled to a temperature of 0°C to -6°C, for example, -1°C to -6°C, or -2°C to -6°C. In one embodiment, the second portion of the alkaline solution is cooled to a temperature of -7°C to -30°C. In one embodiment, in order to lower the mixture to a target temperature in the range of -15°C to -20°C, the temperature of the cooled metal surface or the surface of the cooled cylinder is at least about -15°C, for example, 15°C to about -20°C or lower.

[0076] In one embodiment, the mixture is brought into contact with a cooled metal surface or the surface of a cooled cylinder zone for a period of time from 1 minute to 10 hours, for example, 2 minutes to 2 hours, and particularly 2 minutes to 60 minutes or 4 minutes to 30 minutes.

[0077] By dissolving under low temperature and / or supercooled conditions, a cellulose carbamate solution of a quality suitable for the spinning process can be obtained. By dissolving cellulose carbamate with a high cellulose consistency, a cellulose carbamate spinning dope with a viscosity lower than the viscosity mathematically and experimentally expected when dissolved by conventional methods can be obtained. Typically, the viscosity of a cellulose carbamate dope having a cellulose carbamate content of 8.5% (DP 250, DS 0.2%), a NaOH content of 6.5%, and a ZnO content of 1.3% is higher than 15 Pas when recovered after being warmed to +20°C after dissolution by conventional methods. Preferably, a technically suitable cellulose carbamate spinning dope has a viscosity of less than 15 Pas. The viscosity of the cellulose carbamate spinning dope according to the embodiment is preferably <15 Pas. The viscosity of the cellulose carbamate spinning dope is measured by the ballfall viscosity method at 20°C. Furthermore, the method of the present invention provides a cellulose spinning dope that is stable for long periods even at room temperature.

[0078] Typically, the temperature of the mixture is maintained at the target temperature for 1 to 30 minutes, for example, 3 to 15 minutes.

[0079] Next, embodiments will be described by the following example.

[0080] Examples

[0081] Example 1. Continuous dissolution of cellulose carbamate by a one-step method under supercooling conditions, starting from cellulose carbamate derived from recycled cotton.

[0082] Cellulose carbamate polymers were provided by a carbamate process carried out as described in Finnish Patent Nos. 112869 and 112795, and Finnish Patent Applications Nos. 275376 and 20195717, and International Patent Application PCT / FI2020 / 050560.

[0083] A mixture of cellulose carbamate polymer and an alkaline aqueous solution was prepared as follows: A mixture with a degree of polymerization (DP) of DP250 (determined as intrinsic viscosity according to ISO 5351), corresponding to 850 g of absolute dry material, and a degree of substitution (DS) of 0.22 (determined as total nitrogen content according to SFS5505:1988), was mixed with 9150 g of an alkaline aqueous solution containing 650 g of sodium hydroxide, 110 g of zinc oxide, and 8390 g of water, and the mixture was stirred in a homogenizer at a mixing speed of 700 rpm at room temperature of approximately 20°C for 40 minutes.

[0084] A Berstroff ZE 25x49.5 twin-screw extruder model was used as the kneader-type dissolution reactor. Its cooling and mixing zone consisted of 12 separate barrel units arranged in series. The cylinder walls of each barrel unit were cooled to the desired temperature by an ethylene glycol refrigerant circuit using an external cooler. For continuous dissolution operations, the mixing zone was pre-cooled to -20°C. A funnel was attached to the twin-screw extruder, and a mixture of cellulose carbamate polymer in an alkaline aqueous solution was supplied to the pre-cooled mixing zone, with the temperature maintained by the external cooler. By adjusting the screw rotation speed to 16 rpm, the supply rate was set to 3.9-4.0 kg / h, the moment was 50-53%, and the motor power consumption was 415 W.

[0085] A mixture of cellulose carbamate polymers in an alkaline aqueous solution was continuously supplied to the system for 140 minutes, and the cellulose carbamate solution in the alkaline aqueous solution was recovered at a rate of 3.9–4.0 kg / h. The residence time of the mixture in the mixing zone was 6 ± 0.5 minutes. The temperature of the recovered solution at the outlet of the extruder's mixing zone was -15.3°C to -17.5°C. The recovered solution was immediately temperature-controlled to +10°C.

[0086] The following are the results of sampling and examining the properties of the recovered cellulose carbamate solution: The recovered cellulose carbamate solution contained 8.5% cellulose carbamate, 6.5% sodium hydroxide, 1.1% zinc oxide, 8.7 Pas ball fall viscosity measured at +20°C, and a filterability index (K) measured at +20°C. R The value was 0.30.

[0087] For wet spinning of cellulose carbamate fibers, a second portion of the carbamate solution corresponding to the characterized composition was filtered through a 10 μm filter medium and degassed at +10°C for 12 hours. Wet spinning of the filtered and degassed cellulose carbamate-doped material was carried out using a spin bath optimized for the cellulose carbamate process, for example, containing sodium sulfate and free sulfuric acid. The Godett tensile stress at fiber extraction was 68–71% under hot bath stretching conditions. The fineness of the resulting filaments was 1.3 dtex. The breaking strength of the fibers measured from the filament samples was >20 cN / tex (SFS-EN ISO 5079).

[0088] Example 2. Continuous dissolution of cellulose carbamate by a two-step method under supercooling conditions, starting with cellulose carbamate derived from recycled cotton.

[0089] Cellulose carbamate polymers were provided by a carbamate process carried out as described in Finnish Patent Nos. 112869 and 112795, and Finnish Patent Applications Nos. 275376 and 20195717, and International Patent Application PCT / FI2020 / 050560.

[0090] A preliminary slurry, i.e., a mixture of cellulose carbamate polymer and alkaline aqueous solution, was prepared as follows: A first portion of 46076 g of alkaline aqueous solution containing 1497 g of sodium hydroxide, 508 g of zinc oxide, and 44071 g of water was mixed for 30 minutes in a homogenizer equipped with a cooling jacket. This first portion was equivalent to 3840 g of absolute dry material with a degree of substitution (DS) of 0.24 (determined as total nitrogen content according to SFS 5505:1988) and a degree of polymerization (DP) of DP333 (determined as intrinsic viscosity according to ISO 5351). To prevent phase separation, the preliminary slurry was cooled and warmed to +0.6°C before being gently mixed. The preliminary slurry contained 7.7% by weight of cellulose carbamate, 3.0% by weight of sodium hydroxide, and 1.0% by weight of zinc oxide. A second portion of alkaline aqueous solution was prepared separately and cooled to -16.3°C. This aqueous solution contained 3620g of sodium hydroxide, 324g of zinc oxide, and 10141g of water. The sodium hydroxide content was 25.7% by weight, and the zinc oxide content was 2.30% by weight.

[0091] As a kneader-type dissolution reactor, a LIST Technology kneader-type dissolution reactor was used, equipped with a 14-liter dissolution chamber with a cooling jacket, two temperature-controllable co-rotating shafts, and a discharge screw capable of continuous operation. The ethylene glycol refrigerant was cooled to -10°C by an external cooler and passed through the dissolution reactor's jacket and shafts. The cellulose carbamate slurry from the first part (alkaline aqueous solution) and the alkaline aqueous solution from the second part were supplied separately to the dissolution reactor's mixing and cooling zones at predetermined rates using two separate peristaltic pumps. The supply rate for the preliminary slurry was 22.62 kg / h, and the supply rate for the second part was 6.39 kg / h.

[0092] The continuous mode operation involved the following steps: First, the kneader was filled to the desired level of 80% during a predetermined residence time of 25 minutes. Then, the discharge screw was rotated, and its rotation speed was adjusted to maintain the filling level. After stabilizing the reaction with constant feed and discharge for the same period as the residence time, the recovery of the cellulose carbamate solution was started at a rate of 29.0 kg / h. The rotational speed was 20 rpm. Recovery was possible as long as the feed was stable. If one or more parameters changed during the continuous dissolution process, a stabilization period equal to the residence time was required to recover a representative product. The temperature of the recovered solution was -7.9°C at the output of the mixing zone of the dissolution reactor.

[0093] The following are the results of sampling and examining the properties of the recovered cellulose carbamate solution: The cellulose carbamate content in the recovered cellulose carbamate solution was 6.2%, the sodium hydroxide content was 8.1%, the zinc oxide content was 1.3%, the ball fall viscosity measured at +20°C was 3.3 Pas, and the filterability index (K) measured at +20°C was 3.3 Pas. R The value was 1.49.

[0094] Example 3: Batch dissolution of cellulose carbamate using a two-step method under low-temperature conditions, starting with dissolving cellulose carbamate derived from wood pulp (pine: spruce).

[0095] Cellulose carbamate polymers were provided by a carbamate process carried out as described in Finnish Patent Nos. 112869, 112795 and International Patent Application PCT / FI2020 / 050560.

[0096] A preliminary slurry, i.e., a mixture of cellulose carbamate polymer and an alkaline aqueous solution, was formed as follows: Cellulose carbamate with a degree of polymerization (DP) (determined as intrinsic viscosity according to ISO 5351) of DP270, in an amount equivalent to 29.3 kg of absolute dry material with a degree of substitution (DS) of 0.17 (determined as total nitrogen content according to SFS 5505:1988), was mixed in two stages with a first portion of 310.2 kg of alkaline aqueous solution containing 10.3 kg of sodium hydroxide, 1.92 kg of zinc oxide, and 300 kg of water in a 500 L batch-type dissolution reactor tank equipped with a cooling jacket and propeller mixing unit. As a result, the sodium hydroxide concentration in the preliminary slurry was 3.0 wt%, the zinc oxide concentration was 0.57 wt%, and the cellulose carbamate content was 8.6 wt%. Ethylene glycol refrigerant was cooled to -9°C separately in a cooler and flowed into the jacket of the dissolution reactor. The alkaline aqueous solution was pre-cooled to -2.9°C before being mixed with the cellulose carbamate polymer in the dissolution reaction vessel. The resulting preliminary slurry was stirred at approximately 250 rpm to control the temperature to a level of -1°C to -2°C, and then gently stirred and allowed to stand to prevent phase separation.

[0097] A second portion of the alkaline aqueous solution was prepared separately and cooled to -18°C. The total volume of the second solution, containing 25.7 kg of sodium hydroxide, 3.9 kg of zinc oxide, and 78.4 kg of water, i.e., a sodium hydroxide concentration of 23.8% by weight and a zinc oxide concentration of 3.64% by weight, was 108 kg. The second portion of the alkaline aqueous solution was added to the dissolution reaction vessel with continuous stirring with the preliminary slurry at a stirring speed of 375 rpm. The temperature of the resulting alkaline aqueous solution of cellulose carbamate was -4.5°C initially when the two portions were mixed together, but the temperature of the solution rose to 0°C during prolonged mixing. The resulting solution was collected at a temperature of 0°C. The target quality of cellulose dope was achieved 15 minutes after the second addition of the alkaline aqueous solution.

[0098] The following are the results of sampling and examining the properties of the recovered cellulose carbamate solution: The recovered cellulose carbamate solution contained 6.5% cellulose carbamate, 8.0% sodium hydroxide, 1.3% zinc oxide, 2.5 Pas ball fall viscosity measured at +20°C, and a filterability index (K) measured at +20°C. R The value was 3.4.

[0099] For wet spinning of cellulose carbamate fibers, cellulose carbamate solutions corresponding to characteristic compositions were subsequently filtered using a two-step backflush filtration process with a 15 μm filter medium in the second filtration step. Wet spinning of the filtered and degassed cellulose carbamate-doped material was carried out using a spin bath optimized for the cellulose carbamate process, for example, containing sodium sulfate and free sulfuric acid. The Godett tensile stress at fiber extraction was 72–78% under hot bath stretching conditions. The fineness of the resulting filaments was 1.3 dtex. The breaking strength of the fibers measured from the filament samples was >20 cN / tex (SFS-EN ISO 5079).

[0100] Example 4. Batch dissolution of cellulose carbamate solution by a two-step method under supercooled temperature conditions, starting with cellulose carbamate derived from recycled cotton.

[0101] Cellulose carbamate polymers were provided by a carbamate process carried out as described in Finnish Patent Nos. 112869 and 112795, and Finnish Patent Applications Nos. 275376 and 20195717, and International Patent Application PCT / FI2020 / 050560.

[0102] The preliminary slurry, i.e., a mixture of cellulose carbamate polymer and alkaline aqueous solution, was formed as follows: Cellulose carbamate with a degree of polymerization (DP) (determined as intrinsic viscosity according to ISO 5351) of DP265, in an amount equivalent to 27 kg of absolute dry material with a degree of substitution (DS) of 0.19 (determined as total nitrogen content according to SFS 5505:1988), was mixed in two stages with a first portion of 285 kg of alkaline aqueous solution containing 9.45 kg of sodium hydroxide, 3.27 kg of zinc oxide, and 276 kg of water in a 500 L batch dissolution reactor tank equipped with a cooling jacket and propeller mixing unit. Thus, the sodium hydroxide concentration in the preliminary slurry was 3.0 wt%, the zinc oxide concentration was 1.0 wt%, and the cellulose carbamate content was 8.7 wt%. Ethylene glycol refrigerant was cooled to -9°C separately in a cooler and flowed into the jacket of the dissolution reactor. The alkaline aqueous solution was pre-cooled to -2.5°C before being mixed with the cellulose carbamate polymer in the dissolution reaction vessel. The resulting pre-slice was allowed to stand without mixing after a 10-minute cooling period, and then warmed to approximately -2°C by pulse-mode stirring at 375 rpm for 10 seconds.

[0103] A second portion of the alkaline aqueous solution was prepared separately and cooled to -26.6°C. A total of 135 kg of aqueous solution was prepared using 26.4 kg of sodium hydroxide, 2.6 kg of zinc oxide, and 106 kg of water, resulting in a sodium hydroxide concentration of 19.7% by weight and a zinc oxide concentration of 1.9% by weight. The second portion of the alkaline aqueous solution was added to the dissolution reaction vessel with continuous stirring at a stirring speed of 375 rpm with the preliminary slurry. The resulting solution was collected at a temperature of -7.5°C. The target cellulose dope quality was achieved 15 minutes after the second addition of the alkaline solution.

[0104] The following results were obtained from sampling and examining the properties of the recovered cellulose carbamate solution: The cellulose carbamate content in the recovered cellulose carbamate solution was 6.0%, the sodium hydroxide content was 8.0%, the zinc oxide content was 1.3%, the ball fall viscosity measured at +20°C was 1.9 Pas, and the filterability index (K) measured at +20°C was 1.9 Pas. RThe value was 2.3.

[0105] For wet spinning of cellulose carbamate fibers, cellulose carbamate solutions corresponding to characteristic compositions were subsequently filtered using a two-step backflush filtration process with a 15 μm filter medium in the second filtration step. Wet spinning of the filtered and degassed cellulose carbamate-doped material was carried out using a spin bath optimized for the cellulose carbamate process, for example, containing sodium sulfate and free sulfuric acid. Godett stretch stress at fiber sampling was 80–88% under hot bath stretching conditions. The fineness of the resulting filaments was 1.3 dtex. The breaking strength of the fibers measured from the filament samples was >20 cN / tex (SFS-EN ISO 5079).

[0106] Example 5. Effects of dissolution temperature and sodium hydroxide concentration on the dissolution of recycled cotton-derived cellulose carbamate

[0107] Figure 3 shows the effect of dissolution temperature and sodium hydroxide concentration on the dissolution of cellulose carbamate derived from recycled cotton. This figure includes 27 micrographs arranged in a 4x7 matrix. The first column shows micrographs of samples at -10°C, and the next three columns show samples at -5°C, 0°C, and 5°C. The rows are arranged so that the sample in the first row contains 3.92 wt% NaOH, and the next six rows, from top to bottom, contain 4.81 wt%, 5.66 wt%, 6.48 wt%, 7.27 wt%, 8.04 wt%, and 8.77 wt%, respectively. It can be seen that the lower the dissolution temperature used, the lower the sodium hydroxide content required to dissolve the cellulose carbamate polymer in the alkaline aqueous solution. Furthermore, it can be seen that cellulose carbamate aqueous solutions with a sodium hydroxide content of 8.04% or higher, recovered at temperatures below -5°C and above -10°C, still contain undissolved cellulose carbamate fragments.

[0108] Example 6. Stability of preliminary slurry in a two-stage dissolution process

[0109] Figure 4 shows the stability of the preliminary slurry in the two-step dissolution process. This figure includes microscopic images of the cellulose carbamate sample at four different temperatures, namely -5°C, -6°C, -7°C, and -8°C. Cellulose carbamate was slurryed in an alkaline aqueous solution with a composition of 3 wt% sodium hydroxide, 1.0 wt% zinc oxide, and 6 wt% cellulose carbamate. As is evident from the microscopic images in Figure 4, the fibrous structure of the cellulose carbamate derived from regenerated cotton remained undissolved at temperature levels up to -6°C, slight dissolution of the cellulose carbamate polymer began at temperatures below -7°C, and the preliminary slurry froze at temperatures below -8°C.

[0110] Example 7. Stability of cellulose carbamate polymer slurry in alkaline aqueous solution

[0111] Figure 5 shows the stability of the cellulose carbamate polymer slurry. Samples were prepared in a one-step dissolution process to the final chemical composition for the dissolution process. For each sample, rheometric shear flow curves as a function of temperature were obtained for a mixture of aqueous solutions containing 8.5 wt% cellulose carbamate, 6.5 wt% sodium hydroxide, and 1.1 wt% zinc oxide (shear flow was measured at +20°C, +15°C, +10°C, +5°C, 0°C, and -5°C). As can be seen, viscosity, measured both as the shear rate increases (inc.) and decreases (dec.), is constant at temperatures above +5°C. Below 0°C, the solution begins to resist mixing, and an increase in viscosity is detected simultaneously.

[0112] Example 8. Micrograph of cellulose carbamate solution

[0113] Micrographs of the recovered cellulose carbamate solution obtained by phase contrast mode are shown in Figures 6A to 6C. The micrographs show the K content measured from the recovered cellulose carbamate solution, as described in Examples 1 to 4. R It reflects the index.

[0114] Figure 4A represents a cellulose carbamate solution in which the solubility of the cellulose carbamate polymer in an aqueous alkali solution is very good. Figure 4B represents a cellulose carbamate solution in which the solubility of the cellulose carbamate polymer in an aqueous alkali solution is good. Figure 4C shows a cellulose carbamate solution in which the solubility of the cellulose carbamate polymer in an aqueous alkali solution is insufficient.

[0115] K W value and K R exponent (K R is the viscosity correction K W corresponding to the value) indicates the filterability of the cellulose carbamate solution. The lower the value, the smaller the amount of unreacted particles of filter clogging size (>10 μm) found in the recovered cellulose carbamate solution.

[0116] The measured K R cellulose carbamate solution with an index of 0.30, recovered as described in Example 1 (continuous dissolution of cellulose carbamate by a one-step method under supercooling conditions starting from cellulose carbamate derived from recycled cotton), corresponds to the visually transparent image shown in Figure 4A.

[0117] The cellulose carbamate solutions recovered as described in Examples 2 to 4 were as follows. Example 2: Continuous dissolution of cellulose carbamate by a two-step method under supercooling conditions starting from cellulose carbamate derived from recycled cotton. Example 3: Batch dissolution of cellulose carbamate by a two-step method under low temperature conditions starting from cellulose carbamate derived from dissolved wood pulp (pine: fir). Example 4: Batch dissolution of a cellulose carbamate solution by a two-step method under supercooling temperature conditions starting from cellulose carbamate derived from recycled cotton. For these examples, the measured KR index was 1.49 to 3.4, corresponding to the visually transparent image in Figure 4B.

[0118] Example 9. Continuous Dissolution of Cellulose Derivatives

[0119] Cellulose carbamate (powder) with a DP of 245 and a DS of 0.20, obtained from 100% cotton-based fiber pulp, was used in the following tests.

[0120] Formation of CCA-hydrochlorite slurry in one step:

[0121] a) CCA powder was slurryed in an aqueous sodium zincate solution in a one-step process to obtain a slurry containing 8.5% by weight of CCA, 6.5% by weight of NaOH, and 1.3% by weight of ZnO. The carbamate-zincate slurry at a temperature of +15°C was instantaneously cooled on a metal surface that had been pre-cooled to -20°C before being applied to the metal surface. The contact time on the metal surface was 20 seconds, during which time the slurry temperature reached the temperature of the metal surface, and the formed CCA dope was warmed to +15°C for microscopic observation (as seen in the photograph in Figure 7A, the dissolution of CCA was not yet complete).

[0122] b) CCA powder was slurryed in an aqueous sodium zincate solution in a one-step process to obtain a slurry with a CCA content of 8.5 wt%, a NaOH content of 6.5 wt%, and a ZnO content of 1.3 wt%. This slurry was pre-cooled to -5.5°C before being applied to a steel surface that had been pre-cooled to -20°C. The contact time with the steel surface was 20 seconds, during which time the slurry temperature reached the temperature of the steel surface, and the formed CCA dope was warmed to +15°C for microscopic examination (as seen in the photograph in Figure 7B, the dissolution of CCA was more complete than in the case of the slurry initially at +15°C).

[0123] c) CCA powder was slurryed in a sodium zincate aqueous solution by a one-step process to obtain a slurry having a CCA content of 8.5 wt%, a NaOH content of 6.5 wt%, and a ZnO content of 1.3 wt%. This slurry was pre-cooled to a temperature of -5.5°C before being applied to a steel surface that had been pre-cooled to a temperature of -20°C. The contact time on the surface was 20 seconds, during which the slurry temperature reached the temperature of the steel surface. The cooled mixture was then immediately removed from surface contact, and the temperature was maintained at -20°C for 5 minutes before the formed CCA dope was tempered to +15°C for microscopic examination (as seen in the photograph in Figure 7C, the dissolution of CCA was more complete than in test b, where the contact time at -20°C was 20 seconds).

[0124] Formation of CCA-hydrochlorite slurry in two steps:

[0125] d) A preliminary slurry containing 10.8 wt% CCA, 3.5 wt% NaOH, and 1.2 wt% ZnO was prepared, pre-cooled to -0.5°C, and the second portion of the zincate aqueous solution was added by mixing (pre-cooled to +5°C) to obtain the final target composition (8.5 wt% CCA, 6.5 wt% NaOH, and 1.3 wt% ZnO). The temperature of the mixture constituting the final target composition was +1°C before application to a steel surface pre-cooled to -20°C. The photograph in Figure 7D shows the dissolution rate in the mixture before surface contact (as seen in the photograph, dissolution is not yet complete).

[0126] The photograph in Figure 7E shows the dissolution rate of the CCA dope after 20 seconds of surface contact at a temperature of -20°C (as seen in the photograph, dissolution was completed with improved clarity compared to a one-step process). During the contact time, the slurry temperature reached the temperature of the steel surface.

[0127] The photograph in Figure 7F shows the dissolution rate of the CCA-doped material after 20 seconds of surface contact at a temperature of -20°C, followed by standing at -20°C for 5 minutes after surface contact (as seen in Figure 1F, the visual transparency of the CCA-doped material did not significantly increase even after standing at -20°C for an additional 5 minutes).

[0128] It should be understood that the embodiments of the invention disclosed herein are not limited to any specific structure, process step, or material disclosed herein, but extend to their equivalents as would be recognized by a person ordinarily skilled in the art. Furthermore, it should be understood that the terms used herein are for the purpose of describing specific embodiments only and are not intended to limit them.

[0129] Throughout this specification, any reference to an embodiment or embodiment means that certain features, structures, or characteristics described in relation to the embodiment are included in at least one embodiment of the present invention. Therefore, while the expressions “in one embodiment” or “in an embodiment” appear in various places throughout this specification, they do not necessarily all refer to the same embodiment. For example, where numerical values ​​are mentioned using terms such as “about” or “substantially,” the exact numerical values ​​are also disclosed.

[0130] Where used herein, multiple items, structural elements, components, and / or materials may be shown in common lists for convenience. However, these lists should be interpreted as if each member of the list were individually identified as a distinct and unique member. Therefore, individual members of such lists should not be interpreted, without contrary indication, as de facto equivalents of other members of the same list based solely on their presentation in a common group. Furthermore, various embodiments and examples of the Invention may be referred to herein along with alternatives for their various components. Such embodiments, examples, and alternatives should be understood not as de facto equivalents of each other, but as distinct and autonomous expressions of the Invention.

[0131] Furthermore, the described features, structures, or properties can be combined in any preferred manner in one or more embodiments. The following description provides numerous specific details, such as examples of length, width, and shape, to provide a full understanding of embodiments of the invention. However, those skilled in the art will recognize that the invention can be implemented even without one or more specific details, or using other methods, components, materials, etc. In other examples, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0132] While the embodiments described above illustrate the principles of the present invention in one or more specific uses, it will be apparent to those skilled in the art that numerous modifications in form, usage, and details of implementation can be made without exercising inventive ability and without departing from the principles and concepts of the present invention. Accordingly, the present invention is not intended to be limited to the claims set forth below.

[0133] In this specification, the verbs “include” and “have” are used as open limitations, not excluding or requiring the existence of features not cited. Features described in the claims may be freely combined with each other unless otherwise explicitly stated. Furthermore, it should be understood throughout this document that the use of “a” or “an,” i.e., the singular form, does not exclude the plural form.

[0134] Several further embodiments are disclosed below.

[0135] 1. A method for forming a solution by dissolving cellulose carbamate in an alkaline aqueous phase, A step of providing cellulose carbamate by carbonizing cotton raw material, The steps include mixing cellulose carbamate with an alkaline aqueous solution to form a mixture, The steps include: generating a solution of cellulose carbamate in an alkaline aqueous phase, The step includes recovering the cellulose carbamate containing the aqueous phase, The step of producing the solution is carried out at a temperature of -7°C or below.

[0136] 2. The method according to Embodiment 1, wherein the cotton raw material includes unused cotton, recycled cotton, cotton-containing fabric, or cotton-containing fabric waste, or a combination thereof.

[0137] 3. A method according to Embodiment 1 or 2, wherein the cotton raw material comprises a maximum of 50% by weight, preferably 40% by weight or less, of non-cotton cellulose-based materials, such as wood fiber-derived materials as dissolved wood pulp, and / or non-wood fiber-derived materials, such as straw-based dissolved pulp.

[0138] 4. The method according to any of the preceding embodiments, wherein the step of generating the solution is carried out at a temperature of -7°C or lower, preferably -8°C or lower.

[0139] 5. The method according to any of the preceding embodiments, wherein the step of generating a cellulose solution is carried out in a mixing zone, and the mixing zone is operated in batch mode, semi-continuously, or continuously.

[0140] 6. The method according to any of the preceding embodiments, wherein cellulose carbamate is mixed with a first portion of an alkaline solution to produce a preliminary slurry, the preliminary slurry thus obtained is supplied to a mixing zone, and a second portion of the alkaline solution is supplied separately to the mixing zone.

[0141] 7. The method according to claim 6, wherein the preliminary slurry is cooled to a temperature of 0°C to -6°C, for example, -1°C to -6°C or -2°C to -6°C.

[0142] 8. The method according to Embodiment 6 or 7, wherein the second portion of the alkaline solution is cooled to a temperature of -7°C to -30°C.

[0143] 9. The method according to any one of embodiments 6 to 8, wherein the preliminary slurry has an alkali concentration of 2 to 6% by weight of NaOH, and / or the second part has an alkali concentration of 10 to 30% by weight of NaOH.

[0144] 10. The method according to any of the preceding embodiments, wherein the cellulose carbamate provided has a degree of polymerization (DP) of approximately 200 or more, particularly 250 to 400.

[0145] 11. The method according to any of the preceding embodiments, wherein the cellulose carbamate mixture has a cellulose carbamate content of 6 to 10% by weight, for example, 6 to 8% by weight, or 8 to 10% by weight.

[0146] 12. The method according to any of the preceding embodiments, wherein the aqueous alkaline solution contains 5 to 10% by weight of NaOH, for example, the aqueous alkaline solution contains 7 to 10% by weight of NaOH, or the aqueous alkaline solution contains 5 to 7% by weight of NaOH.

[0147] 13. The method according to any of the preceding embodiments, wherein the mixture has a ratio of cellulose carbamate to NaOH of 6-10% by weight:5-10% by weight, preferably 6-8%:7-10%, for example, 8-10%:5-7%, especially when operated continuously.

[0148] 14. A method for forming a solution by dissolving cellulose carbamate in an alkaline aqueous phase, A step of providing cellulose carbamate, The steps include mixing cellulose carbamate with an alkaline aqueous solution to form a mixture, The steps include: generating a solution of cellulose carbamate in an alkaline aqueous phase, The process includes the step of recovering the aqueous phase containing cellulose carbamate, The step of generating the solution is carried out at a temperature of 10°C or lower. A method in which cellulose carbamate is first mixed with a first portion of an alkaline aqueous solution to produce a preliminary slurry, the preliminary slurry thus obtained is supplied to a mixing zone, a second portion of the alkaline aqueous solution is supplied separately to the mixing zone, and the preliminary slurry is kept at a temperature of -1°C to -6°C in the mixing zone before the second portion is supplied to the mixing zone.

[0149] 15. The method according to Embodiment 14, wherein the second portion supplied to the mixing zone has a temperature of -7 to -30°C.

[0150] 16. The method according to Embodiment 14 or 15, wherein the preliminary slurry has a concentration of NaOH of 2 to 6% by weight relative to the weight of the preliminary slurry, and / or the second part has a concentration of NaOH of 10 to 30% by weight relative to the weight of the second part.

[0151] 17. The method according to any one of embodiments 14 to 16, wherein the mixture has a ratio of cellulose carbamate to NaOH of 6-10% by weight:5-10% by weight, for example, 6-8% by weight:7-10% by weight, for example, 8-10% by weight:5-7% by weight, especially when operated continuously.

[0152] 18. The method according to any one of embodiments 14 to 17, wherein the dissolution is carried out at a temperature of approximately -15°C to approximately -20°C.

[0153] 19. Steps to provide cellulose carbamate, The steps include mixing cellulose carbamate with an alkaline aqueous solution to form a mixture, The steps include passing the mixture through the mixing zone of a continuous-operation kneader-type dissolution reactor to produce a solution of the cellulose carbamate in an alkaline aqueous phase, The method according to any one of Embodiments 1 to 18, comprising the step of recovering the cellulose carbamate-containing aqueous phase. [Explanation of Symbols]

[0154] 10 Pulpers 20 storage tanks 30 pumps 40 Dissolution reactor 100 Cellulose Carbamate 200 Alkaline aqueous solution (total volume) 300 Alkali / Cellulose Carbamate Mixture 330 Alkaline aqueous solution (total amount) / Cellulose carbamate mixture 400 Cellulose carbamate in alkaline aqueous solution 2000 Part 1 of the alkaline aqueous solution 2200 Part 2 of the alkaline aqueous solution 3000 Preliminary slurry of cellulose carbamate and alkaline aqueous solution [Industrial applicability]

[0155] At least some embodiments of the present invention find industrial applications, particularly in the regeneration of cellulosic fiber derivatives for use in the textile and nonwoven fabric industry or the pulp and paper industry.

Claims

1. A method for forming a solution by continuously dissolving cellulose carbamate in an alkaline aqueous phase, A step of providing cellulose carbamate, The steps include mixing cellulose carbamate with an alkaline aqueous solution to form a mixture, The steps include: generating a solution of the cellulose carbamate in an alkaline aqueous phase from the mixture; The process includes the step of recovering the aqueous phase containing cellulose carbamate, The step of producing the solution is carried out by introducing the mixture through the mixing zone of a continuously operating kneader-type dissolution reactor at a mixing rate of 10 to 100 rpm and a temperature of 10°C or less.

2. The method according to claim 1, characterized in that the mixture formed by cellulose carbamate in an alkaline aqueous solution is mixed in the mixing zone of a kneader-type dissolution reactor at a mixer speed of 50 rpm or less.

3. The method according to claim 1 or claim 2, characterized in that the mixture formed by cellulose carbamate in an alkaline aqueous solution is cooled in the mixing zone of a kneader-type dissolution reactor.

4. The method according to any one of claims 1 to 3, characterized in that cellulose carbamate is first mixed with a first portion of an alkaline solution, the resulting preliminary slurry is supplied to the mixing zone of a continuously operating mixing kneader, and the second portion of the alkaline solution is supplied to the mixing zone of a continuously operating mixing kneader.

5. The method according to claim 4, characterized in that the preliminary slurry is cooled to a temperature of 0°C to -6°C, and the second portion of the alkaline solution is cooled to a temperature of -7°C to -30°C.

6. The temperature of the mixture in the mixing zone is 0°C, or The temperature of the mixture in the mixing zone is -7°C or lower, or The method according to any one of claims 1 to 5, characterized in that the temperature of the mixture in the mixing zone is -15°C to -20°C.

7. The method according to any one of claims 1 to 6, characterized in that pre-cooling is achieved in a first kneader, thereby obtaining partial dissolution, and thereafter the step, the mixture is transferred to a second kneader, in which the material is completely or substantially completely dissolved.

8. A mixture of cellulose carbamates having a cellulose carbamate content of 6 to 10% by weight, or a cellulose carbamate content of 6 to 8% by weight, or a cellulose carbamate content of 8 to 10% by weight, The method according to any one of claims 1 to 7, characterized in that the aqueous alkaline solution contains 5 to 10% by weight of NaOH, or the aqueous alkaline solution contains 7 to 10% by weight of NaOH, or the aqueous alkaline solution contains 5 to 7% by weight of NaOH.

9. The method according to any one of claims 1 to 8, characterized in that the mixture has a cellulose carbamate:NaOH ratio of 6-10% by weight:5-10% by weight, or 6-8% by weight:7-10% by weight, or 8-10% by weight:5-7% by weight.

10. The method according to any one of claims 1 to 9, characterized in that the residence time of the mixture in the mixing zone of the mixing kneader is adapted to the temperature of the mixture in the mixing zone, and the residence time is 1 minute to 10 hours, or 2 minutes to 2 hours, or 2 minutes to 60 minutes, or 4 minutes to 30 minutes.

11. The method according to any one of claims 1 to 10, characterized in that the temperature of the mixture is maintained at a target temperature for 1 to 60 minutes, or for 5 to 30 minutes.

12. The process includes a further step of adding zinc oxide to the mixture. The method according to any one of claims 1 to 11, characterized in that the mixture of cellulose carbamate solutions has a zinc oxide content of 0.1 to 1.5% by weight.

13. The method according to any one of claims 1 to 12, characterized in that the mixture of cellulose carbamates has a cellulose carbamate:ZnO ratio of 6-10%:0.1-1.5%.

14. Cellulose carbamate, The step of providing pulp, The steps include adding an aqueous solution of urea and optionally hydrogen peroxide to the pulp to provide a mixture, A step of mechanically processing a mixture to provide a homogeneous composition, The steps include heating this composition to a temperature in the range of 120°C to 155°C, or mixing it at a temperature of 135°C for 2 to 4 hours to produce cellulose carbamate, A step to recover cellulose carbamate, and optionally The method according to any one of claims 1 to 13, characterized in that it is produced by a process comprising the steps of washing cellulose carbamate with water and drying it in a dryer at a temperature of 155°C or lower, or 135°C or lower, or 133°C or lower.

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