Flame-retardant regenerated cellulose products

Abstract

The present invention relates to flame-retardant regenerated cellulose products, in particular in the form of fibres or films, which have a phosphorus content in the range from 0.1 to 20 wt.% which is provided by phosphate esters included in the products, and wherein the phosphorus is distributed largely uniformly over the entire volume of the products. Corresponding products are characterised by improved flame-retardant properties, good mechanical properties and, if they are in the form of fibres, a good skin feel, which makes them particularly interesting for textile applications with potential skin contact. The present invention also relates to methods for producing such regenerated cellulose products, textiles, and non-woven fabrics, which contain corresponding regenerated cellulose fibres, and to the use of phytic acid as a phosphate ester for providing flame-retardant properties to regenerated cellulose fibres.

Description

[0001] FLAME-RETARDANT REGENERATED CELLULOSE PRODUCTS >

[0002] Description

[0003] The present invention relates to flame-retardant regenerated cellulose products, particularly in the form of fibers or films, which have a phosphorus content in the range of 0.1 to 20 wt. %, provided by phosphate esters incorporated into the regenerated products, and wherein the phosphorus is distributed substantially uniformly throughout the entire volume of the regenerated products. The present invention further relates to processes for producing such regenerated cellulose products, textiles and nonwovens containing corresponding regenerated cellulose fibers, and the use of phytic acid as a phosphate ester for imparting flame-retardant properties to regenerated cellulose products.

[0004] State of the art

[0005] Fibers made of cellulose or other polysaccharides, such as cotton, lack natural flame retardancy, so when flame-retardant textiles are manufactured from these materials, they must be subsequently treated with appropriate flame retardants. A frequently used method of imparting such properties is the application of a flame-retardant coating; for example, cotton fabrics can be treated with phosphorus-based flame retardants.

[0006] For a flame-retardant effect on cellulose, the incorporated flame retardant must catalyze cellulose degradation at a temperature below 300 °C to promote dense carbonization. The approaches described here distinguish between permanent and non-permanent flame retardants, depending on the fiber's application. Non-permanent flame retardants are usually applied to the fibers as a subsequent coating, which, however, has the disadvantage that the flame retardant can detach from the fibers over their service life. A permanent coating, on the other hand, can be achieved by covalently bonding the flame retardant to the fiber in a modification step or by incorporating the flame retardant directly into the fibers. Examples of such modifications include the following prior art:

[0007] US 11124900 B2 describes a process for producing flame-retardant cellulose fibers, in which a cellulose fiber is first prepared as a base, and this fiber is subsequently treated with a solution of flame-retardant. The flame-retardant agents used in US 11124900 B2 are said to contain functional groups that can enter into a self-crosslinking reaction with the cellulose fibers.

[0008] EP 1649088 A2, for example, describes a flame-retardant rayon fiber containing up to 40 wt.% silicon dioxide in finely divided form, which is based on polysilicic acid.

[0009] CN 109267318 describes the production of flame-retardant lyocell fibers from a spinning solution containing cellulose and alginate. The spinning solution used in CN 109267318 is based on NMMO (N-methylmorpholine oxide) as the solvent.

[0010] EP 2655708 B1 describes a process for producing flame-retardant cellulose fibers containing a flame-retardant compound in the form of an oxidized condensate of a tetrakishydroxyalkyl phosphonium salt with ammonia and / or a nitrogen-containing compound with multiple nitrogen groups. Such fibers are said to be obtainable from a viscosexanthate precursor by mixing it with an aqueous pigment dispersion of the flame retardant, followed by spinning into fibers.

[0011] Various studies have also demonstrated a flame-retardant effect of phytic acid in textiles. Phytic acid promotes cellulose degradation below 300°C, catalyzes the dehydration reaction, and supports carbonization during combustion. Another advantage of phytic acid-treated fabrics is that it forms a protective layer before the pure fabric decomposes. For example, US 2020 / 056057 A1 describes a process for modifying fabrics, for example, made of Nyco fibers (a nylon-cotton blend), in which the fabric is first impregnated with a solution of tannic acid and then with a solution of phytic acid, and then dried. The combination of tannic and phytic acids is intended to provide a synergistically effective flame-retardant composition.

[0012] In J. Appl. Polym. Sci. 2023; e54326, Matos et al. described a process for producing phytate-modified cellulose fibers in which the fibers are treated with a solution of phytic acid ammonium salt at a temperature of approximately 50°C. The fibers are then dried. This is intended to bind the phytic acid to the cellulose via phosphate esters.

[0013] Xian-Wie Cheng et al. describe in Polymers 2016, 8, 122; doi: 10.3390 / polym8040122 the modification of a cotton fabric, in which the fabric is also treated with a solution of phytic acid at an acidic pH and then dried.

[0014] These studies showed good adhesion of phytic acid to the substrate and achieved very good, sometimes permanent flame retardancy.

[0015] Applying flame retardant to the fabric afterward is associated with a number of disadvantages, including the fact that the flame retardant is usually not firmly bonded to the fiber surface and can therefore be detached from the fiber surface over time. For example, subsequent coating increases the number of manufacturing steps, and the coating can also alter the textile mechanical properties of the fabric. Impregnation of the fabric surface using various methods, such as sol-gel processes, layer-by-layer construction, surface grafting, and dip coating, involves high chemical and water consumption. Furthermore, post-treatment reduces the fabric's flexibility and comfort, or makes it less likely to tear.

[0016] Another problem is a partial loss of flame retardancy as a result of frequent washing. Cotton fabrics are particularly affected when, for example, phytic acid-based flame retardants are adsorbed onto their surface. During washing, these ionic flame retardants are dissolved and removed from the fabric. Due to its acidity, underivatized phytic acid can also degrade cellulose, reducing the average degree of polymerization of the cellulose and, over time, damaging the durability and properties of the material.

[0017] In light of the state of the art presented here, there is a need for flame-retardant cellulose fibers that can be produced easily and cost-effectively and that exhibit surface and strength properties largely comparable to cellulose fibers without flame retardants. In such cellulose fibers, the flame retardant should be integrated in such a way that washout over the service life is suppressed or largely eliminated. There is also a need for cellulose fibers that are perceived as pleasant on the skin in textile applications. The present invention addresses this need.

[0018] Description of the invention

[0019] In the investigations underlying this application, it was surprisingly discovered that incorporating phosphate esters into the cellulose and subsequently processing the modified cellulose through a spinning process results in fibers with properties similar to those of pure cellulose fibers. This is particularly true when the phosphate esters are covalently linked to the cellulose during the combination, resulting in a homogeneous distribution of phosphorus in the fiber as a result of spinning, while at the same time remaining unaffected by surface treatment of the fibers, such as washing. This avoids an accumulation of phosphorus, which could lead to a significant change in the surface properties of the fibers.However, the cellulose modified in this way can be used not only for the production of regenerated cellulose fibers, but also for other regenerated products, such as films, from the modified cellulose. This cellulose is also compatible with natural or polysaccharides, allowing the properties of the products produced in this way to be tailored. It was also surprisingly discovered that cellulose modified with phosphate esters in this way can be easily processed by a spinning process in which the modified cellulose is dissolved in an ionic liquid to produce a spinning dope, and continuous fibers are produced from the spinning dope by coagulation in a water bath.

[0020] Accordingly, in a first aspect, the present invention relates to a regenerated cellulose product having a phosphorus content in the range of 0.1 to 20 wt.%, wherein the phosphorus concentration in the center of the product deviates by no more than 50% from the phosphorus concentration at the product surface and wherein the phosphorus is due to phosphate esters incorporated into the product.

[0021] The statement "whereby the phosphorus concentration in the center of the product does not deviate by more than 50% from the phosphorus concentration on the product surface" indicates that the phosphorus is homogeneously distributed throughout the cellulose fiber and not, as is the case with subsequent modification of cellulose fibers by coating or functionalization, only on the surface of the product.

[0022] In the context of the present invention, and in accordance with the common usage of the term in the art, the term "regenerated product" refers to artificially produced cellulose products (as opposed to natural cellulose, such as those found in the form of fibers in biomass, such as trees or straw). The regenerated cellulose product according to the invention preferably comprises fibers (in particular continuous fibers or "filaments") or films that can be produced by dissolving the cellulose or the cellulose derivative according to the invention.

[0023] For the phosphorus content, a proportion of 1 to 10 wt.% is preferred, and a proportion of 1.2 to 8 wt.% is further preferred. In the context of the invention described herein, the phosphorus content is determined by elemental analysis. If the phosphorus content is less than 1 wt.%, it is determined by ICP-OES (due to the higher inaccuracy of a determination by elemental analysis).

[0024] For the regenerated cellulose product according to the invention, it is preferred if the phosphorus in the product is derived from a cellulose-bound C5-7 carbocyclic polyol with 2 to 14 hydroxy groups, which has at least one phosphate group. A particularly advantageous C5-7 carbocyclic polyol with 2 to 14 hydroxy groups to use here is inositol. Particularly suitable C5-7 carbocyclic polyols with 2 to 14 hydroxy groups, which have at least one phosphate group, are, for example, inositol phosphate, inositol diphosphate, inositol triphosphate, inositol tetraphosphate, inositol pentaphosphate, and phytic acid, a salt thereof, or a combination thereof. Most preferably, the C5-7 carbocyclic polyol having 2 to 14 hydroxy groups and containing at least one phosphate group is a phytic acid ammonium salt, and in particular a phytic acid ammonium salt obtainable by reacting phytic acid and urea.In such a reaction, phosphoric ester diamonium salts are formed by the release of CO2 from the urea, water and phytic acid.

[0025] In the context of the invention specified here, the regenerated cellulose product is preferably modified with the phosphate esters to such an extent that the desired flame retardancy is achieved in the fibers. One parameter used to determine the extent of flame retardancy is the LOI value, which describes the percentage of oxygen in the air required for a given substance to burn (i.e., not to extinguish itself after ignition). In the context of the invention specified here, it is preferred if the regenerated cellulose fibers have an LOI value (according to ISO 4589-2:2017) of at least 21.0, preferably of at least 22.0, and more preferably of at least 23.5. Another parameter by which the combustibility of the fibers can be characterized is the residual mass, which is determined by thermogravimetric determination.With regard to this property, it is preferred if the regenerated cellulose product according to the invention has a residual mass, determined thermogravimetrically at a temperature of 600°C (according to DIN EN ISO 11358-1:2022), of at least 26 wt.%, and in particular at least 30 wt.%. For a regenerated cellulose product in the form of fibers, an LOI value of at least 23.0 and in particular at least 24.0 and / or a residual mass (at 600°C) of at least 30% and in particular at least 32% is preferred. If the regenerated cellulose product is a film, a residual mass of 33% is preferred and a residual mass of at least 36% is further preferred. The deviations between the films and fibers are due to the greater compactness of the films compared to the fibers.If the regenerated cellulose product according to the invention is a regenerated cellulose fiber, it is further preferred if it is characterized by high tensile strength and / or the fineness that is customary and desired for textile production. For the tensile strength, a minimum value of 10 cN / tex can be specified as suitable, a minimum value of 12 cN / tex as particularly suitable, a minimum value of 15 cN / tex as even more suitable, and a minimum value of 17 cN / tex as even more suitable. A tensile strength of approximately 30 cN / tex and in particular approximately 25 cN / tex can be specified as an upper limit, which is met by most fiber products according to the invention. The tensile strength depends partly on the material, but can also be advantageously influenced by drawing carried out during fiber production.In the context of the invention specified here, the tensile strength of the fibers is determined according to DIN EN ISO 5079:2021, whereby the fibers were conditioned for the measurement according to DIN EN ISO 139.

[0026] For the fineness, a range of 1 to 5 dtex, and especially 1.2 to 3.5 dtex, is particularly suitable.

[0027] The flame-retardant effect of the phosphorus integrated into the cellulose via the phosphate ester can be further enhanced by incorporating a nitrogen-containing compound into the regenerated cellulose product. A particularly suitable compound for this purpose is a nitrogen-containing polysaccharide, since cellulose is also a polysaccharide, and stable and homogeneous mixtures and films can be formed from the mixture with cellulose, and stable fibers can be formed during the spinning process. Suitable nitrogen-containing polysaccharides include chitin and chitosan, with chitosan (the deacetylated derivative of chitin) being a particularly suitable nitrogen-containing polysaccharide; chitosan in particular has a weight-average molecular weight Mw in the range of 50,000 to 190,000 Da, and more preferably 60,000 to 170,000 Da. The molecular weight is to be determined by GPC using suitable standards.It is further preferred if the chitosan has a high degree of deacetylation, in particular of at least 80% and more preferably in the range from 90 to 97%. The degree of deacetylation can be determined, for example, by NMR spectroscopy. The nitrogen-containing polysaccharide is preferably incorporated into the regenerated cellulose product in a proportion that results in the most favorable possible interaction between the nitrogen from the nitrogen-containing polysaccharide and the phosphorus from the cellulose modified with phosphorus esters. The nitrogen or phosphorus content of the respective components is also of some importance for this. For the ratio of cellulose with bound phosphorus to nitrogen-containing polysaccharide, it is particularly preferred if it is in the range from 1:1 to 1:10, preferably 1:2 to 1:6 and more preferably 1:2.5 to 1:4.5.This is especially true for the combination of chitosan (which contains one NH2 group per sugar unit in the polysaccharide) and phytic acid-modified cellulose, which has six phosphorus atoms per phytic acid unit.

[0028] For the ratio of phosphorus to nitrogen in the regenerated cellulose fibers according to the invention, it is preferred if it is in the range of 3: 1 to 1:3, more preferably 2: 1 to 1:2 and even more preferably 1.5: 1 to 1: 1.5.

[0029] By adding unmodified cellulose, the final properties of the regenerated cellulose products according to the invention can be controlled to the desired extent, so that in one embodiment, the regenerated cellulose products additionally contain unmodified cellulose. In this case, the proportion of unmodified cellulose in the regenerated cellulose product according to the invention is preferably at least 20 wt.%, with a content range of 25 to 75 wt.% being particularly preferred and 35 to 60 wt.% being even more preferred.

[0030] Furthermore, it is possible to incorporate additional flame-retardant substances into the regenerated cellulose products, for example in the form of tannic acid. In a preferred embodiment, however, such additional substances are not contained in the regenerated cellulose products in significant amounts, i.e., not in amounts exceeding 20 wt.%, in particular in amounts of less than 10 wt.%, and even more preferably less than 5 wt.%.

[0031] In one embodiment, the regenerated cellulose product according to the invention is a fiber, in particular a continuous fiber. In another embodiment, the regenerated cellulose product according to the invention is a film, in particular with a thickness in the range of 10 to 100 μm and more preferably 12 to 70 μm.

[0032] In a further aspect, the present invention relates to a process for producing regenerated cellulose fibers, in particular as described above, which comprises the following steps: i) dissolving a cellulose derivative having a phosphorus content in the range of 2 to 20 wt.%, wherein the cellulose derivative is preferably obtainable by binding a C5-7 carbocyclic polyol having 2 to 14 hydroxy groups and having at least one phosphate group, and optionally a nitrogen-containing polysaccharide and / or unmodified cellulose in an ionic liquid to produce a spinning dope; ii) spinning the spinning dope via a spinneret to produce filaments; iii) introducing the filaments into a coagulation bath to produce fibers from the spinning dope, iv) optionally drawing the fibers produced, and v) drying the fibers to obtain regenerated cellulose fibers.

[0033] The fibers produced in this process are continuous fibers (filaments), but they can be cut into fibers of any length.

[0034] The ionic liquid used in the context of the specified process can, in principle, be any ionic liquid that can be used to dissolve the cellulose derivative with the specified phosphorus content. The ionic liquids described in WO 2017 / 137284 A1 on pages 2 to 5 can be used for this purpose. Particular preference is given to imidazole-based ionic liquids, and in particular to those imidazole-based ionic liquids that contain a 1,3-di-C1-6-alkyl-substituted imidazolium (in particular in the form of 1-methyl-3-methylimidazolium, l-ethyl-3-ethylimidazolium, l-ethyl-3-methylimidazolium, l-methyl-3-methylimidazolium, or l-ethyl-3-ethylimidazolium) as the cation of the ionic liquid and a C2-C20 carboxylate, and in particular a C2-C12 carboxylate, as the anion. Particularly preferred C2-C12 carboxylates are acetate and octanoate.

[0035] In step ii), the spinning dope is introduced into a coagulation bath to produce fibers, whereby the ionic liquid from the spinning dope passes into the coagulation bath, thus forming the spun threads. Accordingly, the coagulation bath generally contains a liquid in which the ionic liquid is soluble, while the polysaccharide constituents of the spinning dope are insoluble in the liquid and in the mixture formed from the ionic liquid and the coagulation bath liquid. Particularly suitable liquids for this purpose in the coagulation bath are, in particular, water, and, in particular, Cl-6 and, in particular, Cl-4 alcohols, such as methanol or ethanol, as well as mixtures thereof.

[0036] In one embodiment, the spinning in step ii) can be carried out via an air gap, e.g. with a length of 5 to 15 mm.

[0037] During the drawing process in step iv), the formed fibers are stretched to several times their original length as a result of elongation (for example, by rotating a subsequent conveyor roller at a higher speed and a preceding conveyor roller at a slower speed), thereby reducing the originally produced fiber diameter. Drawing generally makes it possible to align the polysaccharide or cellulose chains contained in the fibers along the fiber length direction, which can positively influence mechanical properties such as tensile strength or fiber modulus.

[0038] More specific information on details for carrying out a spinning process for producing cellulose fibers using ionic liquids as solvents can be found, for example, in WO 2006 / 000197 A1, WO 2007 / 076979 A1, WO 2009 / 118262 A1 or WO 2017 / 137284 A1, the relevant content of which is hereby incorporated by reference into this application.

[0039] Yet another aspect of the present invention relates to a process for producing a regenerated cellulose film, comprising the following steps: i) dissolving a cellulose derivative having a phosphorus content in the range of 2 to 20 wt.-%, wherein the cellulose derivative is preferably obtainable by binding a C5-7 carbocyclic polyol having 2 to 14 hydroxy groups, which has at least one phosphate group, and optionally a nitrogen-containing polysaccharide and / or unmodified cellulose in an ionic liquid; ii) applying the dissolved mixture to a substrate, preferably while setting a uniform coating thickness; iii) introducing the coated substrate into a solvent in which the ionic liquid dissolves, but the cellulose derivative and the optionally present unmodified cellulose and / or the nitrogen-containing polysaccharide, in order to coagulate the mixture to form a regenerated cellulose film, iv) drying the regenerated cellulose film.

[0040] The above statements regarding the process for producing regenerated cellulose fibers also apply to the ionic liquid used in this process and step iii). The solvent used in step iii) is most preferably water.

[0041] Yet another aspect of the present invention relates to a textile or nonwoven fabric containing a proportion of regenerated cellulose fibers as described above, preferably produced by a process as specified above, wherein the textile or nonwoven fabric is preferably formed from at least 80% by weight of the regenerated cellulose fibers. In a preferred embodiment, the textile or nonwoven fabric is formed from at least 90% of the regenerated cellulose fibers and can, for example, be formed entirely from the specified regenerated cellulose fibers.

[0042] For the textile or nonwoven fabric, it is further preferred if it has an LOI value of at least 22.0, with an even higher LOI value, e.g. of at least 23.0, in particular at least 24.0 or even at least 25.0 being even more preferred. A still further aspect of the present invention relates to the use of phytic acid for imparting flame-retardant properties to regenerated cellulose products, wherein the phytic acid is incorporated into the regenerated cellulose product such that the phosphorus concentration in the center of the product does not deviate by more than 50% from the phosphorus concentration at the product surface.

[0043] Yet another aspect of the present invention relates to a cellulose derivative with a phosphorus content in the range of 1.5 to 20 wt. %, wherein the cellulose derivative is obtainable by linking a C5-7 carbocyclic polyol having 2 to 14 hydroxy groups and at least one phosphate group. In other words, in this cellulose derivative, phosphate groups are bonded to the cellulose chain via OH groups, and the phosphate groups are also covalently bonded to the carbocyclic polyol. The type of linkage is phosphate esters, wherein the high phosphorus content (at least 1.5%) results in high flame retardancy of the material. The cellulose derivative is preferably a powder or bulk material with a uniform distribution of the phosphate groups over a relevant amount (e.g., at least 1 g), and is not, for example, formed as a thin layer on unmodified cellulose.

[0044] A still further aspect of the present invention relates to a process for producing a cellulose derivative as stated above, wherein in a first step phytic acid and urea are reacted with each other, and in a second step the resulting reaction product is reacted with cellulose at a reaction temperature of at least 100°C.

[0045] A range from 110°C to 180°C and in particular a range from 125°C to 170°C can be specified as preferred for the reaction temperature. The reaction temperature can in particular be within a period of 30 minutes to 2 hours, whereby this time only refers to the reaction of the reaction product of phytic acid and urea with the cellulose. It should be noted here that phytic acid is generally used as a solution in water for the reaction with urea. When a reaction mixture containing phytic acid and urea is heated, only the water evaporates in a first reaction step, and only then does a reaction with the urea occur and the phytic acid actually binds to the cellulose. The time for which the reaction mixture must be heated to evaporate the water is not taken into account in the time period specified above, especially since this depends on the specific conditions (amount of water and treatment temperature).

[0046] The ratio of the reaction product of phytic acid to urea, or of the cellulose to be modified with phytic acid, also plays a certain role. Particularly favorable functionalization results were achieved when the cellulose was reacted with an excess of the reaction product of phytic acid to urea, particularly an excess in a ratio of 1:4 to 1:15, and particularly preferably 1:6 to 1:12.

[0047] In order to achieve the most extensive and homogeneous binding of phytic acid to the cellulose, which is not present in dissolved form in such a process, it is advisable to subject the cellulose to an activation treatment before the reaction, in which the crystalline structure of the cellulose is broken down by "swelling". In this way, the pore system of the cellulose is opened and expanded, and fibrillar aggregates are separated from one another, thus facilitating the access of phytic acid, or the reaction product of phytic acid with urea, to the OH groups in the cellulose. This promotes the binding of larger amounts of phytic acid to the cellulose. Such swelling can be achieved in particular by treating the cellulose with an alkaline agent, for example in the form of an alkali solution.

[0048] Accordingly, it is preferred for the specified process if it includes a step in which the cellulose is swollen under alkaline conditions before reacting with the reaction product of phytic acid and urea in order to activate the cellulose.

[0049] In yet another aspect, the present invention relates to a mixture of a cellulose derivative, as specified above, and a nitrogen-containing polysaccharide, in particular in the form of chitosan, and / or unmodified cellulose. Such a mixture preferably contains the cellulose derivative in a proportion of at least 5 wt.% and more preferably in a proportion in the range of 6 to 30 wt.%. In a very particularly preferred embodiment, the cellulose derivative and the nitrogen-containing polysaccharide and / or the unmodified cellulose are present as a solution in an ionic liquid. If the mixture contains unmodified cellulose, it is preferred if its content in the mixture is preferably at least 20 wt.%, in particular 25 to 75 wt.% and more preferably in the range of 35 to 60 wt.%.

[0050] The following advantages arise in particular for the regenerated cellulose fibers according to the invention and the textiles and nonwovens produced therefrom:

[0051] • A permanent / intrinsic flame retardant is achieved which is not washable, since the flame retardant active components (cellulose phyate and possibly chitosan) are part of the fiber structure (i.e. no bleeding additives or impregnating agents).

[0052] • All components incorporated into the regenerated fibers are bio-based / derived from renewable resources. Furthermore, the raw materials required for fiber production are cost-effective (phytic acid is a waste product of the food industry, urea, caustic soda, methanol).

[0053] • The regenerated cellulose fibers according to the invention have textile mechanical properties that are comparable to pure cellulose or viscose fibers.

[0054] • The regenerated cellulose fibers according to the invention have a pleasant, soft feel on the skin.

[0055] • Cellulose phytate can be spun and processed using the same processes and equipment used to produce pure regenerated cellulose fibers.

[0056] The films according to the invention which contain cellulose phytate can also be produced in a comparatively simple manner and have improved flame retardant properties compared to pure cellulose films.

[0057] With regard to the above disclosure, it should be noted that embodiments described as preferred, suitable, or expedient for one aspect are also considered preferred, suitable, or expedient for other aspects, provided that the combination of features does not result in obvious contradictions. Likewise, even if not explicitly described for reasons of brevity, all combinations of embodiments of the aspects are considered combinable and encompassed and described in their combination by the disclosure, unless explicitly stated that such combinations are not possible, or unless this is clear from the context.

[0058] The present invention and the effects achieved thereby are illustrated in more detail below using some exemplary embodiments, which, however, are not to be construed as limiting the scope of protection of the application in any way.

[0059] Examples

[0060] Example 1: Production of cellulose acetate with a phosphorus content of 1.3 to 1.7 %.

[0061] Activation of cellulose:

[0062] 100 g of ground pulp (0.5 mm sieve) is swollen for 30 minutes in 1.5 L of 22% NaOH (aq.). The resulting swollen alkali cellulose is pressed to a weight of 325 g. The alkali cellulose is shredded in a mixer with 1.5 L of technical methanol and swollen again for 30 minutes. The alkali cellulose is then pressed to a weight of 300 g and ground.

[0063] Production of phytic acid-modified cellulose

[0064] 817.4 g of aqueous phytic acid solution (50%) was heated and stirred with 497.0 g of urea in a 2 L glass-jacketed reactor at 114 °C under nitrogen for 3–5 h. Subsequently, 100 g of activated cellulose with an average degree of polymerization of DPEWN = 500 was added and heated and stirred at 150 °C for 1 h. The heterogeneous reaction mixture solidified over time, and an ammonia odor was detected. After 1 h, the reaction was terminated by adding 1 L of deionized water. After cooling the mixture to room temperature, a pH of 7 was determined. The strongly swollen, crude cellulose phytate was filtered off and washed three more times with 1 L of water. The reaction mixture was then washed twice with 1 L of technical ethanol and twice with 1 L of 0.1 M HCl (aq.). The resulting cellulose phytate was washed with deionized water until pH neutral and then dried in air or in a freeze dryer.The yield of cellulose phytate as a brownish / beige powder was 80-100 g (73-91%). Table 1 below shows the composition of the produced cellulose phytate, as determined by CHN analysis.

[0065] Table 1 :

[0066] Example 2: Production of continuous fibers from cellulose phytate

[0067] 226 g of cellulose phytate were mixed with 1760 g of [EMIM][Oct] (yielding 11.4% spinning solution) at room temperature and homogenized. The cellulose / IL mixture was fed to the polycondensation reactor and stirred or dissolved for 2 h at 120 °C under nitrogen. The residual water was removed under vacuum, and the degassed cellulose / IL solution was pumped into a 1.75 L pressure filtration vessel (Karl-Kurt Juchheim Laborgeräte GmbH).

[0068] The spinning experiment was conducted on a dry-wet spinning system. The pressure filtration vessel served as a storage vessel for the spinning solution. The solution was filtered through a metal filter mesh (material number 1.4401, wire gauge = 0.035 mm, mesh size = 0.043 mm) immediately before spinning. The spinning solution was then conveyed into the spinneret of a single-screw extruder at 40 °C. A spinneret was used (number of holes: 64, hole diameter: 150 μm, nozzle channel length: 600 μm, L / D ratio: 4 / 1). The solution was pressed through the nozzle holes into thin filaments and extruded through an air gap (5-15 mm) into a 1 m long coagulation bath consisting of ethanol, deionized water, or ethanol-water mixtures at room temperature, where it was precipitated. The resulting fibers were then washed in two washing baths, each 1 m long, at 60 °C and over two washing godets at room temperature.Ethanol, deionized water, or ethanol-water mixtures were used as washing media. The fibers were then passed through an aqueous preparation bath containing a finishing agent and subsequently dried on a heated godet (90 °C) and in a heated tunnel (250 °C).

[0069] To vary the linear density, tensile strength, residual elongation, and Young's modulus, the fiber stretching in the air gap was adjusted. This can be achieved by decreasing the exit speed at the nozzle and maintaining a constant take-off speed, or by maintaining a constant exit speed at the nozzle and increasing the take-off speed.

[0070] In this spinning test, the take-off speed was kept constant at 10 m / min, and the exit speed at the nozzle was varied between 1.59 m / min and 0.64 m / min. This resulted in fibers with different draw ratios of 1:6.28, 1:8.57, 1:10.5, 1:13.00, and 1:15.71.

[0071] To give the fibers more residual elongation, drying was carried out in the drying tunnel with shrinkage (2%).

[0072] The regenerated fibers produced in this way had the following properties:

[0073] Table 2

[0074] 1 determined according to DIN EN ISO 5079:2021; 2 Stretch factor 10.5

[0075] The continuous fibers were subsequently analyzed thermogravimetrically. The residual mass measured in this analysis at 600°C was significantly higher than that of pure cellulose, amounting to 31%. At this temperature, pure cellulose had a residual mass of approximately 17%.

[0076] In addition, wide-angle X-ray diffraction (WAXS) measurements were performed on the continuous fibers to elucidate their crystalline structure. Compared to pure cellulose fibers, the cellulose phytate continuous fibers exhibited a less crystalline and more pronounced amorphous structure.

[0077] Example 3: Production of continuous fibers from a mixture of cellulose phosphate, chitosan, and cellulose

[0078] For the spinning experiment, the solutions were prepared in two steps. In the first step, commercial chitosan (from fungi, Mw 71306 g / mol; degree of deacetylation 91.7%) was dissolved in [EMIM][octanoate]. For this purpose, the chitosan and [EMIM][octanoate] were rapidly stirred in a 2 L glass-jacketed reactor for 1 h at 110 °C. The resulting solution of the desired concentration (36.5% of the total solids content) was cooled to room temperature overnight. The solution was then mixed with the appropriate amount of ground pulp (44%) and cellulose phytate (9.5%; phosphorus content according to ICP-OES 15.4 g / kg) to achieve a total solution proportion of 12% cellulose phytate / chitosan / cellulose, and homogenized. In the second step, the resulting slurry was fed to a VTA thin-film evaporator. A wiper (400 rpm) in the evaporator unit distributed the mixture on the heated (120 °C) inner shell surface at approx. 2-30 mbar.The degassed cellulose phytate / chitosan / cellulose / IL solution was pumped from the thin-film evaporator into a 1.75 L pressure filtration vessel (Karl-Kurt Juchheim Laborgeräte GmbH) via a heated gear pump (120 °C).

[0079] The spinning experiment was conducted on a dry-wet spinning system. The pressure filtration vessel served as a storage vessel for the spinning solution. The solution was filtered through a metal filter mesh (material number 1.4401, wire gauge = 0.035 mm, mesh size = 0.043 mm) immediately before spinning. The spinning solution was then conveyed into the spinneret of a single-screw extruder at 60 °C. Two spinnerets were used (number of holes: 64 or 250, hole diameter: 150 μm, nozzle channel length: 600 μm, L / D ratio: 4 / 1). The solution was forced through the nozzle holes into thin filaments and extruded through an air gap (5-15 mm) into a 1 m long coagulation bath consisting of deionized water at room temperature, where it was precipitated. The resulting fibers were then washed in two 1-meter-long wash baths at 60 °C and then over two pairs of godets at room temperature. Deionized water was used as the washing medium.The fibers were then passed through an aqueous preparation bath with a finishing agent and then dried on a heating godet (60 or 90 °C) and in a heating channel (100 or 250 °C).

[0080] The mixed fibers obtained in this way had the following properties:

[0081] Table 3

[0082] 1 determined according to DIN EN ISO 5079:2021

[0083] Mixed fibers made solely from chitosan, as specified above, and cellulose showed residual masses and LOI values ​​of 25% and 20 (mixture of 90% cellulose and 10% chitosan), 31% and 21 (mixture of 75% cellulose and 25% chitosan), and 35% and 22 (mixture of 50% cellulose and 50% chitosan). Thus, the mixed fiber made with cellulose phytate, despite a slightly higher content of pure cellulose, showed a higher LOI than the cellulose / chitosan fiber with 50% content each. The 50 / 50 cellulose / chitosan fiber also showed less favorable mechanical properties (tensile strength 17.1 cN / tex and modulus El (0.2-0.4%) 1064 cN / tex) than the mixed fiber produced with cellulose phytate.

[0084] Further investigations showed that the fibers are open (i.e. no adhesions were observed) and have a yellowish, golden luster.

[0085] The feel of the fibers on the skin was rated as very pleasant and reminiscent of silk. ence of a knitted fabric made of mixed fibres with

[0086] To test flame retardancy, a total of 12 wash cycles were performed on a knitted fabric made from a blended fiber produced with cellulose phytate, with a cellulose phytate / chitosan / cellulose ratio of 9.5 / 36.5 / 54 and a phosphorus content of 0.15%. After four, eight, and 12 cycles, a small portion of the knitted fabric was separated and subjected to ICP-OES analysis to determine the sample's phosphorus content. The chitosan contained in the fiber is not water-soluble and has not shown any instability in previous tests.

[0087] The washing of the knitted fabric was carried out as follows:

[0088] • weighing and measuring the knitted fabric

[0089] • Addition of detergent: Felosan Fox (CHT Group) in an amount of 0.55 g to 1 L of water

[0090] • Heat the washing solution to 60 °C, stir and wash the knitted sample for 1 h

[0091] • Rinse with water over a grid, then air dry

[0092] • weigh and measure again

[0093] The results of the determination of phosphorus content (determined by ICP-

[0094] OES) after the washing cycles is shown in the following Table 4: Table 4

[0095] As shown in Table 4, the phosphorus content remained constant after the wash cycles, indicating that the flame retardant is permanent. The LOI value for the 12-fold washed knitted fabric also showed no decrease compared to the initial value. This confirms that the knitted fabrics have permanent flame retardancy.

[0096] Example 5: Production of films from cellulose acetate-chitosan-cellulose mixtures

[0097] 0.9 g of chitosan (CHS5) was placed in 22 g of [EMIM][octanoate] and stirred for 1 h at 110 °C. The resulting solution was cooled to room temperature overnight. Subsequently, 1.8 g of ground pulp and 0.3 g of cellulose phytate were added and mixed. The mixture was stirred for 1 h at 120 °C. The resulting solution (with a solids content of 12%) was spread while still hot on a glass plate and spread with a hand doctor to a specified thickness (125 μm, 250 μm, or 500 μm). The coated glass plate was placed in sufficient deionized water, causing the thinly applied solution film to coagulate and form a transparent film. The resulting film with a composition of cellulose phytate, chitosan and cellulose of 10 / 30 / 60 is washed several times with deionized water and then dried in air using filter paper and pressure.

[0098] The residual mass determined for this film (at 600°C under nitrogen) was 37%.

[0099] Analogously produced films based on chitosan / cellulose blends in a ratio of 50 / 50 and 25 / 75, respectively, showed residual mass values ​​of 35% and 32%, respectively. This demonstrates that the combination of cellulose phytate and chitosan can produce films with higher residual mass percentages despite the lower total content of N / P-containing polysaccharides. This behavior suggests that the phosphorus and nitrogen additives in the films complement each other synergistically.

Claims

Claims 1. Cellulose regenerated product, in particular in the form of a fiber or a film, which has a phosphorus content in the range of 0.1 to 20 wt.%, characterized in that the phosphorus concentration in the center of the product deviates by no more than 50% from the phosphorus concentration at the product surface and wherein the phosphorus is due to phosphate esters incorporated into the product.

2. A regenerated cellulose product according to claim 1, wherein the phosphorus in the fiber is derived from a cellulose-bound C5-7 carbocyclic polyol having 2 to 14 hydroxy groups and having at least one phosphate group.

3. The regenerated cellulose product according to claim 2, wherein the C5-7 carbocyclic polyol having 2 to 14 hydroxy groups and having at least one phosphate group is selected from inositol phosphate, inositol diphosphate, inositol triphosphate, inositol tetraphosphate, inositol pentaphosphate and phytic acid, a salt thereof or a combination thereof.

4. Regenerated cellulose product according to claim 3, wherein the C5-7 carbocyclic polyol having 2 to 14 hydroxy groups and having at least one phosphate group is based on phytic acid ammonium salt, preferably obtainable by reacting phytic acid and urea.

5. Regenerated cellulose product according to one of the preceding claims, wherein the regenerated cellulose fiber has an LOI value of at least 21.0 and preferably of at least 22 and / or a residual mass, determined thermogravimetrically at a temperature of 600°C (under nitrogen), of at least 26 wt.%, and in particular at least 30 wt.%.

6. Regenerated cellulose product according to one of the preceding claims, wherein the regenerated cellulose product is formed as a fiber having a tensile strength of at least 15 cN / tex and preferably at least 17 cN / tex and / or a fineness in the range of 1 to 5 dtex, and preferably 1.2 to 3.5 dtex.

7. Cellulose regenerate product according to one of the preceding claims, which further contains a nitrogen-containing polysaccharide, in particular in the form of chitosan, preferably with a molecular weight Mw in the range of 50,000 to 190,000 Da.

8. A regenerated cellulose product according to claim 7, wherein cellulose with attached phosphorus and nitrogen-containing polysaccharide are present in a ratio in the range of 1:1 to 1:10, preferably 1:2 to 1:6 and more preferably 1:2.5 to 1:4.

5.

9. Cellulose regenerate product according to one of the preceding claims, which additionally contains unmodified cellulose, preferably in a proportion of at least 20 wt.%, more preferably 25 to 75 wt.% and even more preferably 35 to 60 wt.%.

10. A regenerated cellulose product according to any one of the preceding claims, which is formed as a film.

11. A process for producing a regenerated cellulose fiber as specified in at least one of claims 1 to 9, the process comprising the following steps: i) dissolving a cellulose derivative having a phosphorus content in the range of 2 to 20 wt.%, wherein the cellulose derivative is preferably obtainable by bonding a C5-7 carbocyclic polyol having 2 to 14 hydroxy groups and having at least one phosphate group, and optionally a nitrogen-containing polysaccharide and / or unmodified cellulose in an ionic liquid to produce a spinning dope; ii) spinning the spinning dope through a spinneret to produce filaments; iii) introducing the filaments into a coagulation bath to produce fibers from the spinning dope, iv) optionally drawing the fibers produced, and v) drying the fibers to obtain regenerated cellulose fibers.

12. The method according to claim 10, wherein the ionic liquid is selected from imidazole-based ionic liquids, wherein preferably the cation of the ionic liquid is a 1,3-di-Cl-6-alkyl-substituted imidazole and the anion is selected from C2-C20 and in particular C2-C12 carboxylates.

13. Textile or nonwoven fabric with a proportion of regenerated cellulose fibers as specified in at least one of claims 1 to 9, preferably produced by a process according to claim 10 or 11, wherein the textile or nonwoven fabric is preferably formed from at least 80% by weight of the regenerated cellulose fibers and / or has an LOI value of at least 21.0 and preferably of at least 22.

0.

14. Use of phytic acid to impart flame-retardant properties to regenerated cellulose products, wherein the phytic acid is incorporated into the regenerated cellulose product in such a way that the phosphorus concentration in the centre of the fibre does not deviate by more than 50% from the phosphorus concentration at the fibre surface.

15. Cellulose derivative having a phosphorus content in the range of 2 to 20 wt.%, wherein the cellulose derivative is obtainable by attaching a C5-7 carbocyclic polyol having 2 to 14 hydroxy groups and having at least one phosphate group.

16. A process for producing a cellulose derivative according to claim 15, wherein in a first step phytic acid and urea are reacted with each other, and in a second step the resulting reaction product is reacted with cellulose at a reaction temperature of at least 100°C.

17. The process according to claim 16, wherein the cellulose is swollen under alkaline conditions prior to reaction with the reaction product of phytic acid and urea in order to activate the cellulose.

18. A mixture comprising a cellulose derivative according to claim 15 and a nitrogen-containing polysaccharide, in particular in the form of chitosan, and / or unmodified cellulose, wherein the cellulose derivative is preferably a proportion of at least 5 wt.% and more preferably a proportion in the range of 6 to 30 wt.% in the mixture.

19. Mixture according to claim 16, wherein the cellulose derivative and the nitrogen-containing polysaccharide and / or the unmodified cellulose are present as a solution in an ionic liquid.

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