A flame-resistant and burn-resistant acrylic fiber with textile properties and a method for obtaining the same

Abstract

The invention relates to an acrylic fiber that is flame- and fire-resistant, can be processed into textiles, has improved comfort properties, does not release toxic gases during combustion, possesses moisture absorption capability, and exhibits antibacterial properties; and to a method in which process steps are optimized to enable homogeneous amidoximation reactions in the products and reduce the number of processing steps.

Description

[0001] A FLAME-RESISTANT AND BURN-RESISTANT ACRYLIC FIBER WITH TEXTILE PROPERTIES AND A METHOD FOR OBTAINING THE SAME

[0002] TECHNICAL FIELD

[0003] The invention relates to an acrylic fiber that is flame- and fire-resistant, can be processed into textiles, has improved comfort properties, does not release toxic gases during combustion, possesses moisture absorption capability, and exhibits antibacterial properties; and to a method in which process steps are optimized to enable homogeneous amidoximation reactions in the products and reduce the number of processing steps.

[0004] PRIOR ART

[0005] Acrylic fiber is a fiber produced from polyacrylonitrile, a synthetic polymer, and has a lightweight, flexible structure similar to natural wool. It is commonly used in clothing, home textiles, and industrial applications. Acrylic fibers are widely used in garments, home textiles (such as curtains, carpets, and upholstery fabrics), automotive upholstery, outdoor textiles, and technical fields such as industrial filters. These fibers are preferred due to their lightness, flexibility, wool-like appearance, and good color retention properties.

[0006] As is known, due to their chemical structure, acrylic fibers do not exhibit high resistance to combustion; they tend to ignite easily during burning.

[0007] Acrylic fibers that do not possess flame-retardant and fire-resistant properties are not suitable for use in areas requiring fire safety. Therefore, making acrylic fibers flameresistant is of great importance for their use in technical textiles, protective clothing, and other applications where fire safety is essential. Imparting fire-resistant properties enables these types of fibers which do not release toxic gases when burned to be utilized as safer and more functional products.

[0008] Acrylic fibers are relatively low-cost materials for technical textile applications; however, due to their lack of flame and fire resistance, more expensive, flame-retardant materials are preferred in applications requiring high fire safety. For example, materials with flameretardant properties such as aramid fibers (e.g., Kevlar), modacrylics, melamine resins, and carbon fibers are resistant to high temperatures and do not ignite during combustion. However, these materials are significantly more expensive compared to acrylic fibers, and their production processes are more complex, resulting in higher costs. Therefore, the development of flame-retardant acrylic fibers can offer a more economical alternative in areas requiring flame and fire resistance. If the cost advantage of acrylic fiber is maintained while providing resistance to flame and combustion, more sustainable solutions that balance cost and safety can be achieved in the technical textile sector.

[0009] In the prior art, there are studies and applications related to imparting flame-retardant properties to acrylic fibers. One such application involves the use of halogen-containing comonomers (e.g., vinyl chloride) as raw materials in the production of flame-retardant acrylic fibers. This method enables the acrylic fiber to gain flame-retardant characteristics. However, this process leads to the release of toxic halogen gases during combustion, which poses significant risks in terms of environmental pollution and human health. These gases released during burning can cause smoke inhalation poisoning and significantly limit the use of this method, particularly in indoor applications where fire safety is critical.

[0010] Another application involves the addition of compounds or additives containing phosphorus, silicon, boron, and nitrogen to acrylic fibers. These compounds make ignition more difficult, thereby imparting flame-retardant properties to the fibers. However, this approach is costly and can cause quality issues during the fiber drawing and spinning processes. Furthermore, it increases the complexity of production processes, reduces manufacturing efficiency, and negatively impacts sustainability.

[0011] Another application involves imparting flame-retardant properties to acrylic fibers through surface modification. In this method, surface modifications are applied to the acrylic fiber to achieve flame resistance. Chemical modifications are made on the fiber surface, enabling metal ions to bind to the fiber. However, if a homogeneous distribution is not achieved during surface modification, certain areas of the fiber may become hardened and brittle. This adversely affects the processability of the fiber in textile operations and reduces its durability.

[0012] Another application involves the conversion of nitrile groups within the acrylic fibers into carboxyl groups, followed by chelation with metal ions. In this method, the nitrile groups in the fiber are transformed into carboxyl groups, and then metal ions are bound to these groups to impart flame-retardant properties. Although this is a frequently applied method, it increases the flame resistance of the fiber by forming strong bonds between the metal ions and the acrylic fiber. However, current implementations of this technique involve a four- step chemical modification process and require the use of a large number of chemicals. Moreover, this method disrupts the structure of the fiber, reducing its spinnability; it also causes brittleness and the formation of inhomogeneous structures.

[0013] The current technical field requires flame- and fire-resistant, environmentally friendly, low- cost, and spinnable acrylic fibers. In particular, these fibers must be resistant to flame and combustion, demonstrate high performance without releasing toxic gases, and remain suitable for textile processing without loss of strength. At the same time, a sustainable and low-cost modification method is needed — one that reduces the use of chemicals during production and minimizes negative environmental impacts. An acrylic fiber combining these features would offer an ideal solution for technical textile applications that demand fire safety.

[0014] As a result, all the aforementioned problems have made it necessary to introduce an innovation in the relevant technical field.

[0015] BRIEF DESCRIPTION OF THE INVENTION

[0016] In the relevant technical field, it is known that acrylic fibers possess low flame resistance and limited fire-retardant properties. Although acrylic fibers offer advantages in terms of cost and ease of production, various applications and studies have been conducted to impart flame-retardant and fire-resistant properties to these fibers.

[0017] The applications in the current state of the art are insufficient for the production of acrylic fibers that simultaneously provide both high flame retardancy and good spinnability.

[0018] In the technical field, to impart flame-retardant properties to acrylic fibers, it is common to apply surface modification techniques or to convert the nitrile groups in the fibers into amino groups, incorporate carboxyl groups into the structure, and form chelate bonds with metal ions. However, these processes lead to the production of inhomogeneous acrylic fibers, require the use of large amounts of chemicals, and result in prolonged processing times.

[0019] To address these technical problems and offer solutions to the relevant technical field, the present inventors propose a method with optimized process steps to impart flame-retardant and spinnable properties to acrylic fibers. Through this method, it becomes possible to obtain acrylic fibers that exhibit both flame-retardant characteristics and good textile processability. The method disclosed in the invention is notable for its reduced number of process steps. As a result, it enables the production of acrylic fibers with high flame retardancy and good spinnability in a shorter time and with less chemical usage. Additionally, this method offers a more cost-effective solution compared to other known applications in the existing state of the art.

[0020] The method presented in the invention is intended to be environmentally friendly. To this end, optimizations are carried out by reducing the number of process steps and the use of chemicals.

[0021] Additionally, this method also aims to obtain acrylic fibers with enhanced moisture absorption capacity, as well as antibacterial and odor-eliminating properties.

[0022] DETAILED DESCRIPTION OF THE INVENTION

[0023] In this detailed description, the invention relates to a method for imparting flame resistance and flame-retardant properties to acrylic fibers, and is explained with examples provided solely for a better understanding of the subject, without creating any limiting effect.

[0024] In the invention, imparting flame resistance and flame-retardant properties to acrylic fibers refers to enabling the fibers to resist ignition, preventing the release of toxic gases during combustion, and achieving the ability to maintain their physical integrity when exposed to high temperatures.

[0025] In the invention, the expression that the acrylic fibers possess not only flame-resistant and flame-retardant properties but also spinnability refers to the fibers demonstrating high resistance to combustion while remaining suitable for textile processes such as weaving, knitting, and similar operations — i.e., retaining their physical properties such as strength, flexibility, and elongation. It also includes the enhancement of moisture management properties.

[0026] The method disclosed in the invention consists of two fundamental process steps for imparting flame resistance and flame-retardant properties to acrylic fibers. In the first step, the amidoximation process, the aim is to convert the cyano groups on the surface of the acrylic fiber into amidoxime groups by reacting them with a compound containing an amino group. This modification introduces binding sites on the fiber surface for metal ions. Parameters such as temperature, pH, and chemical concentration are optimized in this step to ensure homogeneous modification of the acrylic fiber. In the second step, at least one metal ion is bound to the fiber. Through the amidoxime groups introduced in the first step, metal ions are anchored to the fiber surface, enhancing the fiber’s flame-retardant and antibacterial properties. The controlled and optimized application of these two steps enables the acrylic fiber to maintain its textile processability, such as spinnability and mechanical integrity, while gaining flame resistance.

[0027] In this invention, the term amidoximation process refers to the conversion of cyano groups (-CN) present on the surface of the acrylic fiber into amidoxime groups (-C(=NOH)NH2) using compounds that contain at least one amino group. This process constitutes the first stage of the chemical modification necessary to impart flame and combustion resistance, as well as flame-retardant properties, to the acrylic fiber. It also enables the formation of suitable binding sites containing amino groups for the subsequent step involving the attachment of metal ions.

[0028] The reaction medium mentioned comprises a first reaction solution that provides the conditions necessary for carrying out the amidoximation processes. This first reaction solution contains at least one crosslinker with one or more amino groups, at least one pH- adjusting compound, and at least one solvent, all aimed at ensuring the homogeneous attachment of amidoxime groups to the surface of the acrylic fiber. These components are optimized to preserve both the spinnability and the flame-retardant properties of the fiber.

[0029] The crosslinker included in the optimized first reaction solution for the amidoximation process may contain at least one amino functional group. If desired, this crosslinker may include two or more amino groups. These amino groups can be of primary, secondary, or tertiary chemical structure. In structures that also contain tertiary amino groups, at least two of the amino groups are of primary or secondary type. Other chemical configurations may include more than two secondary amino groups or contain three, four, five, or more amino groups in total. Multi-amino functional structures are generally represented by the formula H2N-R-NH2, where the R group may consist of alkyl, aryl, or heteroaryl groups, and can be linear, branched, or cyclic in form. R groups may also exist in structures such as ether, diether, polyether, polythioether, or polyamine. The chemical properties of these structures are defined for n = 1 , 2, 3, 4, 5, or greater values. Additionally, the R groups may include dyes that absorb visible light in the 400-700 nm range, allowing the fiber to attain a desired color, or may contain phosphorus-based flame-retardant functional groups. These phosphorus-containing groups may include structures such as trialkylphosphine, trialkylphosphite, trialkylphosphate, trialkylphosphonate, trialkylphosphoramide, and hexalkylcyclotriphosphazene.

[0030] In a preferred embodiment of the invention, the aforementioned crosslinker may be at least one of the chemical compounds represented by the following formulas:

[0031] - NH2-(CH2)n-NH2, where n is one of 0, 2, 4, 6, or 8;

[0032] - NH2-(CH2)n-NH-(CH2)n-NH-(CH2)n-NH2, where n is one of 0, 2, 4, 6, or 8;

[0033] - NH2-(CH2)n-N(-(CH2)n-NH2)-(CH2)n-NH2, where n is one of 0, 2, 4, 6, or 8;

[0034] - NH2-(CH2)n-R-(CH2)n-NH-(CH2)n-NH2, where n is one of 0, 2, 4, 6, or 8, and R is selected from CH or C groups.

[0035] In a preferred application, the crosslinker may comprise at least one of the following compounds: hydrazine, hexamethylene diamine, diethylene triamine, tetraethylene triamine, tetraethylene pentamine, hydroxylamine, bis-hexamethylene diamine, tris(2- aminoethyl)amine; or mixtures thereof in certain proportions, or a combination of all of them.

[0036] The amount by weight of the crosslinker in the first reaction solution plays a critical role in the incorporation of amidoxime groups into the acrylic fibers and in their moisture absorption performance. The use of an appropriate amount of crosslinker ensures the homogeneous and balanced incorporation of amidoxime groups onto the fiber surface, thereby enhancing flame and combustion resistance performance. At the same time, it preserves the physical properties of the fiber, such as strength and spinnability, making it suitable for processes like weaving and knitting. If the amount of crosslinker used is below the optimal level, the effectiveness of the amidoximation process may decrease, resulting in a non-uniform structure on the fiber surface. On the other hand, excessive use of the crosslinker can lead to over-hardening of the fiber and a loss of flexibility, which negatively affects textile processing. Additionally, uncontrolled reactions may cause non-uniform modifications and performance inconsistencies. Acceleration of the reaction kinetics may lead to the formation of undesired by-products and deterioration of structural integrity. Excessive use of crosslinkers also increases chemical costs and leads to greater environmental waste generation and higher disposal costs. Therefore, optimizing the amount of crosslinker is of critical importance for maintaining the cost-effectiveness and mechanical properties of the acrylic fiber, as well as ensuring environmental and economic sustainability. The amidoximation process addressed in this invention is based on the controlled optimization of pH, temperature, and pressure parameters, as these conditions directly affect the efficiency and uniformity of amidoxime group conversion on the surface of the acrylic fiber, as well as the physical properties of the fiber.

[0037] The amount of the crosslinker mentioned in the invention, within the first reaction solution, is in the range of 1% to 50% by weight.

[0038] In a preferred embodiment of the invention, hydroxylamine hydrochloride is used as the crosslinker. The inventors prefer hydroxylamine hydrochloride because it can effectively convert cyano groups into amidoxime groups during the amidoximation process. Due to its high reactivity, it increases the efficiency of the modification, while ensuring homogeneous modification by operating within a controlled pH range and preserving the physical properties of the acrylic fiber. Its good solubility in water creates a homogeneous reaction medium, and with minimal by-product formation, it supports the purity and environmentally friendly nature of the process. In addition, its low environmental impact reduces costs and enables sustainable production.

[0039] In a preferred embodiment of the invention, the first reaction solution contains hydroxylamine hydrochloride as the crosslinker in an amount ranging from 2% to 10% by weight.

[0040] The pH range characterized in the invention enables the components used in the amidoximation process to effectively react with the cyano groups on the acrylic fiber, thereby allowing the homogeneous formation of amidoxime groups. If the pH value falls below this range, the amidoximation process may be insufficient, while higher pH values may cause the acrylic fiber to harden and lose its flexibility. Within the scope of the present invention, the pH value of the reaction medium in which the amidoximation process, i.e., the first step, is carried out is maintained between 7 and 9. This range ensures both the efficiency of the process and the preservation of the physical properties of the fiber.

[0041] In this invention, at least one compound selected from the group consisting of sodium hydroxide, ammonia, sodium carbonate, or sodium bicarbonate is preferred as the pH- adjusting compound.

[0042] In a most preferred embodiment, sodium carbonate is used as the pH-adjusting compound. Compared to stronger bases such as NaOH, sodium carbonate provides a more controlled increase in pH, thereby preventing excessively basic conditions from damaging the physical properties of the fiber. In addition, the use of sodium carbonate reduces chemical costs and offers a more environmentally sustainable option, since it is a less aggressive base and facilitates waste management. In this way, homogeneous modification of the acrylic fiber is achieved while maintaining the mechanical properties suitable for processes such as weaving and knitting.

[0043] The first reaction solution comprises at least one solvent. The solvent referred to here may preferably be selected from the group consisting of water, methanol, ethanol, isopropanol, acetone, dimethyl sulfoxide, dimethylformamide, or dimethylacetamide.

[0044] Water is preferably used as the solvent. If desired, at least one organic solvent may be present in the water. In such a case, at least one organic solvent dissolved in water is present in an amount ranging from 10% to 50% by weight.

[0045] The temperature of the reaction medium prepared for the amidoximation process is critical for achieving the desired amidoxime incorporation in a homogeneous and controlled manner. In the method of the present invention, the temperature of the first reaction medium is increased to the target value at a low rate. To ensure homogenization, short waiting periods are applied at every 5 °C increment as the temperature is gradually raised within specified intervals.

[0046] During the amidoximation process, the temperature of the reaction solution is initially set at room temperature (25-30 °C). In the first stage, the temperature is increased at a rate of 0.8-1 .2 °C / min until it reaches the range of 55-60 °C, where it is maintained for at least 10 minutes. Subsequently, the temperature is raised sequentially to the ranges of 65-70 °C, 70-75 °C, 75-80 °C, and 80-85 °C at a rate of 0.1 -0.3 °C / min, with a waiting period of at least 10 minutes at each range. In the final stage, the temperature is further increased to the range of 85-90 °C at the same rate of 0.1-0.3 °C / min, and the reaction is continued for 30 to 70 minutes at this temperature. After the process is completed, the reaction solution is allowed to cool down to room temperature. This gradual and controlled temperature increase ensures the homogeneous distribution of amidoxime groups on the acrylic fiber and allows the reaction to progress in a balanced manner. In a preferred embodiment, the acrylic fiber may be added to the reaction solution in a ratio of crosslinker to acrylic fiber ranging from 1 :1 to 1 :4 by weight. Depending on the design of the reactor in which the reaction is carried out, variations may occur in obtaining homogeneous fiber and in the reactivity of the reaction.

[0047] The reaction medium of the aforementioned first process step may be carried out under atmospheric and / or pressurized conditions. When the reaction medium is intended to be processed under high pressure, a pressure value in the range of 2.5 to 3.5 atm is preferred. Conducting the first process step at the specified pressure values increases the reaction rate and efficiency, enabling the production of more homogeneous products in a shorter time. With the increase in pressure, the solubility of the reactants rises, molecular interactions are enhanced, and the formation of undesired by-products is minimized. In this way, amidoxime groups are more effectively and uniformly attached to the acrylic fiber surface, thereby improving flame retardancy, moisture absorption, and mechanical properties. Moreover, better control of the modifications under optimum pressure allows for process optimization and the production of high-strength fibers. However, using a pressure above these values may cause excessive hardening of the fiber, loss of flexibility, increased production costs, and elevated mechanical stress on the equipment, thereby compromising system safety.

[0048] The present inventors have determined that, in order for acrylic fibers to achieve the desired flame- and fire-resistance properties and the specified LOI (limiting oxygen index) values, they must possess certain percentages of amidoxime incorporation with a homogeneous distribution.

[0049] As is known in the art, the LOI (limiting oxygen index) is a parameter used to measure the flammability of a material and indicates the minimum oxygen concentration required to sustain the combustion of the material. The higher the LOI value, the greater the resistance of the material to burning. In the development of flame-retardant acrylic fibers, LOI values are generally expected to be considered an important criterion. In the art, an LOI value of > 35 indicates that the material possesses high flame-retardant properties. This is an important safety criterion, particularly for professional applications such as protective clothing and military equipment.

[0050] The present inventors have determined that the amidoximation process plays a critical role in obtaining acrylic fibers with an LOI value of >35. As a result of the reactions carried out in the first process step, amidoxime groups are homogeneously attached to the acrylic fibers. Table 1 shows the relationship between amidoxime incorporation ratio (% conversion) and LOI value. Table 1 demonstrates that as the amidoxime incorporation ratio increases, the flame-retardant performance and moisture absorption properties of the fiber improve, and at the same time, the fiber begins to meet the ISO 15025 standard.

[0051] The improvement in the flame-retardant performance of the fiber enhances its flame resistance, enabling it to meet fire safety requirements. According to the data presented in Table 1 , an amidoxime group incorporation ratio of at least 21% is required for the LOI value to reach 35 or higher. This demonstrates that the acrylic fiber is optimized both in terms of flame resistance and comfort properties.

[0052] In tests conducted in accordance with the ISO 15025 standard, samples H1-H3 were insufficient in flame spread resistance, while samples H4 and H5 met this standard and demonstrated the required performance. These results confirm the importance of optimizing the amidoximation process in improving the flame-retardant and comfort performance of acrylic fibers.

[0053] In the present invention, the amidoximation process step, i.e., the first step, is optimized to provide at least a 21% amidoxime group incorporation ratio in order for the acrylic fibers to achieve an LOI value of >35.

[0054] In this invention, the term high flame and fire resistance and flame retardancy refers to acrylic fibers having an LOI value of >35.

[0055] * Flame retardant modified acrylic fiber braid

[0056] Table 1. LOI and ISO 15025 performances depending on amidoxime group incorporation percentage In Table 1 , the samples H1-H5, in which all the above-mentioned parameters were optimized, represent acrylic fibers produced by the two-step method. These process steps were carried out in accordance with the parameter ranges specified in the invention. Although it is not necessary to detail the specific parameters used in the production of each sample, the relationship between amidoxime group incorporation values and LOI (Limiting Oxygen Index) values is clearly demonstrated. The table emphasizes that the first requirement for achieving an LOI value of >35 is an amidoxime group incorporation of 21%.

[0057] The first process step ensures the incorporation of amidoxime groups onto the surface of the acrylic fiber. These amidoxime groups are the key elements that directly affect the flame-retardant performance of the fiber. As the amount of amidoxime groups on the fiber surface increases, more metal ion adsorption occurs in the second process step, thereby enhancing the flame resistance of the fiber. By optimizing parameters such as temperature, pressure, duration, concentration, and pH during the reaction, the percentage conversion ratio of amidoxime groups can be increased. This conversion ratio is calculated by the gravimetric method using the following formula:

[0058] „ .

[0059] Conversion

[0060] M1 : initial weight

[0061] M2: final weight

[0062] MAx: molecular weight of acrylonitrile (53.06 g / mol)

[0063] MAy: molecular weight of hydroxylamine (33.03 g / mol)

[0064] The amidoxime conversion ratio calculated by this method can be verified using Fourier Transform Infrared Spectroscopy (FT-IR). During FT-IR analysis, the intensity of the -CN (cyano) groups in the polyacrylonitrile fiber decreases as amidoxime groups are introduced. The -CN peak observed at the wavelength of 2240 cm-1weakens with amidoxime conversion. As the peak intensity decreases, the amidoxime conversion ratio is calculated using the following formula:

[0065] ADO = A1CN / A2CN

[0066] ADO: Amidoxime conversion ratio

[0067] A1 CN: Spectrum area of the reference sample (initial)

[0068] A2CN: Spectrum area of the sample after amidoxime conversion is completed The method of the invention, following the amidoximation process, includes a second process step to impart flame-retardant properties to the amidoxime-modified fibers. The second step essentially involves subjecting the acrylic fibers to a reaction with at least one metal salt. In this step, metal ions are bound to the amidoxime groups in the acrylic fiber at the targeted incorporation ratio.

[0069] The preparation of a second reaction solution is involved in carrying out the second process step. This second reaction solution comprises at least one metal salt and at least one solvent.

[0070] In this invention, the metal salts referred to are preferably selected from at least one of the chloride, sulfate, acetate, or carbonate salts of metals in the 4th and 5th periods of the periodic table having a +2 or +3 ion valence.

[0071] In the most preferred embodiment, at least one metal salt selected from the group consisting of zinc acetate, zinc chloride, magnesium sulfate, calcium acetate, or aluminum sulfate is used.

[0072] In a preferred embodiment, the aforementioned metal salt is present in the second reaction solution in an amount ranging from 10% to 20% by weight. These values determined for the metal salt are defined in relation to the amount of amidoxime groups bound to the acrylic fiber in the first process step. The presence of amidoxime groups enables greater interaction of the metal salt with the acrylic fiber.

[0073] The presence of metal salt in the second reaction solution at levels higher than the specified values may lead to colloid formation within the solution and inhomogeneous chelate formation on the acrylic fiber. Conversely, the presence of an insufficient amount of metal salt in the second reaction solution results in an inadequate amount of metal salt in the medium to achieve the desired flame-retardant property.

[0074] In the aforementioned second reaction solution, the solvent is preferably selected from at least one of the group consisting of water, methanol, ethanol, isopropanol, acetone, dimethyl sulfoxide, dimethylformamide, or dimethylacetamide. Water is preferably used as the solvent. If desired, at least one organic solvent may be present in the water. In such a case, at least one organic solvent dissolved in water is present in an amount ranging from 10% to 50% by weight.

[0075] The temperature of the reaction medium prepared for the second process step is critical for carrying out the targeted chelation process in a homogeneous and controlled manner. In the method of the present invention, the temperature of the second reaction medium is increased at a low rate. To ensure homogenization, specific waiting periods are applied as the temperature is gradually raised within defined intervals.

[0076] During the implementation of the second process step, the temperature of the reaction solution is initially set at room temperature (25-30 °C). In the first stage, the temperature is rapidly increased at a rate of 0.3-1 .5 °C / min until it reaches the range of 90-95 °C, where it is maintained for at least 10 minutes. From this temperature range, it is then increased to 100-110 °C at a rate of 0.2-1 °C / min. After reaching these temperatures, the reaction is maintained for a duration of 30 to 70 minutes, followed by cooling to a temperature range of 55-75 °C. This gradual and controlled temperature increase ensures that the chelation processes are carried out homogeneously on the acrylic fiber and that the reaction proceeds in a balanced manner.

[0077] In a preferred embodiment, the amidoxime fiber may be added into the second reaction solution at a ratio of amidoxime acrylic fiber to metal salt ranging from 1 :0.4 to 1 :1.2 by weight. The flame-retardant property is achieved in the second process step, and in this step, as the percentage concentration of the metal salt in the aqueous solution increases, the level of flame retardancy also increases. However, the binding capacity of the adsorbed metal ions to the fiber surface has a limit. Therefore, for optimum results, it is considered appropriate to apply the amidoxime fiber-to-salt ratio within the specified range.

[0078] With the application of the second process step, it becomes possible to obtain acrylic fibers with an LOI value of at least 35, as indicated in Table 1. Depending on the parameter ranges specified in the invention, this value can reach up to 42.

[0079] As characterized in the invention, it has been determined that, through the method in which the process steps are applied, the tensile strength values of the acrylic fibers increase from 10-15 cN / tex to 19-26 cN / tex, depending on the parameter ranges.

[0080] It has been observed that the acrylic fiber obtained through the application of the method disclosed in the invention also exhibits improvements in moisture absorption properties. The moisture absorption results presented in Table 2 demonstrate that the fiber’s moisture management properties are enhanced. The moisture absorption properties of the acrylic fibers in question improve as amidoxime groups are introduced into the fiber during the amidoximation process. Since amidoxime groups contain hydroxyl (-OH) groups in their structure, they increase the hydrophilicity of the fiber and thereby enhance its moisture uptake capacity. This increases the surface polarity of the fiber, enabling it to retain water molecules more effectively. Furthermore, due to structural modifications, the fiber absorbs water vapor more efficiently, providing better moisture management during rapid drying and perspiration. These properties contribute to increased comfort in textile products. When considered together — spinnability, flame-retardancy, and improved moisture absorption — the acrylic fiber can be regarded as a potential alternative to flame-retardant viscose fiber.

[0081] In this invention, the % moisture absorption value refers to the capacity of the flameretardant acrylic fiber to absorb moisture (water vapor) from the surrounding environment or from the user. This value is determined by the hydrophilic nature of the fiber and increases with the incorporation of amidoxime groups into the fiber. High % moisture absorption allows the acrylic fiber to quickly absorb moisture in situations such as perspiration, providing a dry and comfortable feeling. This property enhances comfort in textile products while also offering functional advantages such as quick drying and effective moisture management.

[0082] *Flame-retardant modified acrylic fiber knit

[0083] Table 2. % Moisture absorption performances depending on amidoxime group incorporation percentage The increase in the comfort properties of acrylic fiber is achieved through the amidoxime groups introduced during the amidoximation process. Since amidoxime groups contain hydroxyl (-OH) groups, they enhance the fiber’s moisture absorption capacity, which in turn provides better moisture management and faster drying in situations such as perspiration. This improved moisture absorption contributes to a lighter and fresher feel, thereby increasing garment comfort. Furthermore, by preserving its suitability for textile processes such as weaving or knitting, the fiber enables the production of more flexible and versatile products for various applications. These properties of acrylic fiber significantly enhance user comfort, particularly in applications such as protective clothing, underwear, and sports textiles.

[0084] The modified flame-retardant acrylic fiber can be produced in yarn and fabric forms. This acrylic fiber can be used in a wide range of applications in the textile industry, such as protective clothing, automotive textiles, filtration products, flame-retardant blankets, upholstery fabrics, socks, underwear, and outdoor textiles. Coloring processes are of great importance depending on the areas of application of these fibers. However, due to the presence of functional groups such as hydroxyl, amino, and carboxylic acid in the modified flame-retardant acrylic fiber, dyeing with cationic dyes is not possible. Experimental studies have shown that this acrylic fiber can be successfully dyed with anionic metal complex dyes, and despite its low dye uptake capacity, it can also be colored with reactive dyes.

[0085] The modified acrylic fiber obtained in the invention may include at least one additive selected from the group consisting of heat stabilizers, light stabilizers, antimicrobial agents, antiviral agents, anti-odor agents, biocidal additives, conductivity enhancers, antioxidants, pigments, plasticizers, and antifungal agents. The incorporation of these additives into acrylic fiber products can be carried out using methods known in the art. The resulting acrylic fiber may be in the form of yarns or fabrics. Products made from these fibers can be used in many applications in the textile industry, including protective clothing, public transportation textile products, filtration, flame-retardant blankets, upholstery, garments (socks, underwear), and both outdoor and indoor textile applications.

[0086] The acrylic fiber characterized in the invention can be prepared in the final step of the process known in the art, namely the metal complex stage, by mixing with one or more solutions containing additives such as heat stabilizers, light stabilizers, antimicrobial agents, antiviral agents, anti-odor agents, biocidal additives, conductivity enhancers, antioxidants, pigments, plasticizers, and antifungal agents. The fibers can then be produced by drying or fixing through a thermal process. The incorporation of the aforementioned additives into acrylic fiber products can be carried out using known methods, such as dissolving the additives in a suitable solvent, combining the solution with the additive, or producing the fiber using wet spinning technology. The scope of protection of the invention is defined in the claims provided in the annex and cannot in any way be limited to the examples described in this detailed description. It is clear that a person skilled in the art may, in light of the foregoing, develop similar embodiments without departing from the main concept of the invention.

Claims

CLAIMS1 . A method for providing acrylic fibers with resistance to flame and combustion, while also imparting spinnability and moisture absorption properties, characterized by comprising the following process steps to ensure homogeneous achievement of the targeted amidoxime incorporation and chelation values:- preparing a first reaction solution comprising at least one crosslinker containing one or more amino groups, at least one pH-adjusting compound, and at least one solvent,- performing a first process step in which the acrylic fiber undergoes an amidoximation reaction with the said first reaction solution, resulting in the formation of amidoxime groups, o the pH value of the first reaction medium in which the first process step is carried out being in the range of 7 to 9, o controlled heating and cooling of the first reaction medium during the first process step,- the initial temperature of the first reaction medium being in the range of 25 to 30 °C,- increasing the temperature from this range to 55-60 °C at a rate of 0.8 to 1 .2 °C / min and maintaining this temperature for at least 10 minutes,- further increasing the temperature sequentially to 65-70 °C, 70-75 °C, 75-80 °C, and 80-85 °C at a rate of 0.1 to 0.3 °C / min, and maintaining each temperature range for at least 10 minutes,- raising the temperature from 80-85 °C to 85-90 °C at a rate of 0.1 to 0.3 °C / min and maintaining this temperature range for 30 to 70 minutes,- subsequently allowing the reaction medium to cool naturally to room temperature,- preparing a second reaction solution comprising at least one metal salt and at least one solvent,- performing a second process step in which the acrylic fiber, having undergone amidoximation through the first process step, reacts with the said second reaction solution, thereby carrying out the chelation process, o controlled heating and cooling of the second reaction medium in which the second process step is carried out,- the initial temperature of the second reaction medium being in the range of 25 to 30 °C,- increasing the temperature from this range to 90-95 °C at a rate of 0.3 to 1.5 °C / min and maintaining this temperature for at least 10 minutes,- further increasing the temperature from this range to 100-105 °C at a rate of 0.2 to 1 °C / min and maintaining each temperature range for a duration of 30 to 70 minutes,- subsequently allowing the reaction medium to cool naturally to a temperature in the range of 55 to 75 °C.

2. A method according to claim 1 , characterized in that the first reaction solution comprises, as the crosslinker, at least one compound selected from the following:NH2-(CH2)n-NH2, where n is one of 0, 2, 4, 6, or 8,- NH2-(CH2)n-NH-(CH2)n-NH-(CH2)n-NH2, where n is one of 0, 2, 4, 6, or 8,- NH2-(CH2)n-N(-(CH2)n-NH2)-(CH2)n-NH2, where n is one of 0, 2, 4, 6, or 8,- NH2-(CH2)n-R-(CH2)n-NH-(CH2)n-NH2, where n is one of 0, 2, 4, 6, or 8, and R is selected from CH or C groups.

3. A method according to any of the preceding claims, characterized in that said crosslinker comprises at least one compound selected from hydrazine, hexamethylene diamine, diethylene triamine, tetraethylene triamine, tetraethylene pentamine, bis-hexamethylene diamine, and tris(2-aminoethyl)amine.

4. A method according to any of the preceding claims, characterized in that the crosslinker is present in the first reaction solution in an amount ranging from 1% to 50% by weight.

5. A method according to any of claims 2 to 4, characterized in that the crosslinker is hydroxylamine hydrochloride.

6. A method according to claim 5, characterized in that the hydroxylamine hydrochloride is present in the first reaction solution in an amount ranging from 2% to 10% by weight.

7. A method according to any of the preceding claims, characterized in that the first reaction solution comprises, as the pH-adjusting compound, at least one selected from the group consisting of sodium hydroxide, ammonia, sodium bicarbonate, or sodium carbonate.

8. A method according to any of the preceding claims, characterized in that the first reaction solution comprises, as the solvent, at least one selected from the group consisting of water, methanol, ethanol, isopropanol, acetone, dimethyl sulfoxide, dimethylformamide, or dimethylacetamide.

9. A method according to any of the preceding claims, characterized in that the pressure of the first reaction medium is in the range of 2.5 to 3.5 atm.

10. A method according to any of the preceding claims, characterized in that the acrylic fiber is added to the first reaction solution at a weight ratio of crosslinker to acrylic fiber ranging from 1 :1 to 1 :4.11 . A method according to any of the preceding claims, characterized in that the second reaction solution comprises, as the metal salt, at least one selected from the group consisting of zinc acetate, zinc chloride, magnesium sulfate, calcium acetate, or aluminum sulfate.

12. A method according to any of the preceding claims, characterized in that the second reaction solution contains the metal salt in an amount ranging from 10% to 20% by weight.

13. A method according to any of the preceding claims, characterized in that the second reaction solution comprises, as the solvent, at least one selected from the group consisting of water, methanol, ethanol, isopropanol, acetone, dimethyl sulfoxide, dimethylformamide, or dimethylacetamide.

14. A method according to any of the preceding claims, characterized in that the acrylic fiber is added to the second reaction solution at a weight ratio of amidoxime fiber to metal salt ranging from 1 :0.4 to 1 :1 .2.

15. A flame-retardant modified acrylic fiber obtained by a method according to any of the preceding claims, having an LOI value of at least 35.

16. A flame-retardant modified acrylic fiber according to claim 15, characterized in that it comprises at least 21% amidoxime group incorporation.

17. A flame-retardant modified acrylic fiber according to any of claims 15 to 16, characterized in that it has a tensile strength in the range of 19 to 26 cN / tex.

18. A flame-retardant modified acrylic fiber according to any of claims 15 to 17, characterized in that it possesses antibacterial, antiviral, and anti-odor properties for use in the production of yarn, fabric, garment parts, socks, underwear or outerwear, blankets, fire blankets, curtains, fiber mats, rugs, or carpets.

19. A flame-retardant modified acrylic fiber according to any of claims 15 to 18, characterized by its use in the production of yarn, fabric, garment parts, socks, underwear or outerwear, blankets, fire blankets, curtains, fiber mats, rugs, or carpets.

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