Rapid separation and recycling method of chinlon blended fabric

Abstract

The invention discloses a rapid separation and recycling method of a chinlon blended fabric, and belongs to the technical field of recycling of waste blended fabrics. The rapid separation and recycling method is constructed by combining the chinlon blended fabric and various selectable HFIP-formic acid mixed solvent systems; process parameters such as the volume ratio of the HFIP to the formic acid solution, the reaction temperature, the pressure and the stirring speed are accurately regulated and controlled, and the chinlon and the cotton / viscose fibers are effectively separated through selective interaction between the HFIP-formic acid mixed solvent and the chinlon blended fabric under specific conditions. Compared with dissolution and recovery of chinlon in a single solvent, the rate and the dissolution effect of the dissolution process can be further regulated and controlled by controlling the proportion of hexafluoroisopropanol to the formic acid solution, meanwhile, the use cost of the solvent can be reduced, in addition, fiber and solvent recovery is carried out through ultrasonic treatment, suction filtration, distillation, drying and other treatment, and the production cost is reduced. Therefore, a more efficient, more environment-friendly and more economical method is provided for separation and recovery of chinlon.

Description

Technical Field

[0001] The invention belongs to the technical field of recycling and reusing waste mixed fabrics, and in particular relates to a method for quickly separating and recycling nylon blended fabrics. Background Art

[0002] Nylon (polyamide fiber), as a high-strength, wear-resistant and chemical-resistant synthetic fiber, is widely used in clothing, home textiles and industrial textiles. It is often blended with natural or regenerated cellulose fibers such as cotton and viscose to optimize fabric performance. According to statistics, more than 8 million tons of waste nylon blended fabrics are produced worldwide each year, of which nylon / cotton and nylon / viscose blended fabrics account for more than 60%. Due to the large differences in fiber composition of this type of blended fabrics (nylon is a synthetic polymer, cotton / viscose is natural cellulose), its efficient separation and high-value recycling have always been a problem in the industry. If precise separation cannot be achieved, it will not only cause waste of resources, but also aggravate environmental pollution due to incineration or landfill. Therefore, the development of targeted recycling technologies has important economic and ecological value.

[0003] Currently, the main methods for separating and recycling waste nylon blended fabrics include mechanical separation, chemical separation, and solvent dissolution, but all have significant limitations. For example, mechanical separation uses physical means such as crushing, screening, and airflow sorting to separate fibers. Although simple to operate, the separation efficiency is extremely low. Because the mechanical properties of nylon and cotton / viscose fibers are similar (e.g., the difference in breaking strength and elongation is less than 15%), mechanical processing easily leads to fiber entanglement and breakage, making it impossible to accurately separate the components. The short fiber content of the recycled fibers exceeds 40%, making them only suitable for low-end filling materials and having extremely low added value. Chemical separation utilizes differences in the chemical resistance of fibers to achieve separation. For example, strong acids (such as sulfuric acid and hydrochloric acid) or strong bases (such as sodium hydroxide) are used to degrade cotton / viscose fibers and retain nylon. However, this method has the following serious drawbacks: strong acids or strong bases will corrode equipment, requiring the use of corrosion-resistant alloy materials, which increases costs by more than 30%. It also produces a large amount of acid / alkali wastewater (5-8 tons of wastewater must be treated for every ton of fabric), and the cost of environmental protection treatment is high. At the same time, excessive chemical reagents can easily lead to hydrolysis of the nylon surface, causing a decrease in its mechanical properties (loss of breaking strength of up to 20%-30%), making it difficult to meet recycling requirements.

[0004] Solvent dissolution methods, which separate fibers by selectively dissolving a component with a solvent, have been a research hotspot in recent years. Existing solvents that can be used to dissolve nylon include hexafluoroisopropanol (HFIP) and a phenol-tetrachloroethane mixture. However, these solvents have significant drawbacks. For example, HFIP has good solubility for nylon, enabling effective separation from other fibers. However, common fibers including nylon, polyester, cotton, wool and silk and their products are all low-value waste after being discarded, and hexafluoroisopropanol is extremely expensive. If it is used alone as a solvent to treat nylon blended fabrics, the processing cost will be greatly increased, and it is impossible to apply it in production and further expand it; although the phenol-tetrachloroethane mixture has a strong selectivity for dissolving nylon, phenol is a highly toxic substance, and tetrachloroethane is carcinogenic and highly volatile (boiling points are 181.7°C and 146.4°C, respectively), which can easily cause serious air problems. A full set of protective equipment must be equipped during operation. At the same time, the mixture is difficult to recover by conventional distillation, and its components are easily decomposed, with a recovery rate of only about 45%; the calcium chloride-methanol mixture is easy to absorb moisture and deliquesce, resulting in poor stability of the solvent system. Stratification occurs after a single use, the recycling efficiency is low, and the recovery rate is about 55%. In addition, methanol is highly volatile and toxic, and the equipment must be strictly sealed, which increases the process complexity and safety risks. Ionic liquids or traditional deep eutectic solvents (DES) are mostly used to dissolve cotton and viscose fibers. However, ionic liquids cost as much as 800-1200 yuan per liter and have high viscosity, exceeding 500 mPa·s at 25°C. This results in low mass transfer efficiency and a dissolution time of up to 4-6 hours, making it difficult to achieve industrial application.

[0005] Patent CN103304839A discloses a method for recycling waste polyester-cotton blended fabrics. Its core principle is to treat waste polyester-cotton blended fabrics with a high- and low-efficiency mixed solvent to selectively dissolve the polyester component in the fabric, followed by subsequent treatment of the polyester and cotton fibers for recovery. However, while this prior art discloses solvent compounding to facilitate the separation and recovery of polyester-cotton blended fabrics, the low-efficiency solvent disclosed is not a good solvent for polyester and cannot dissolve polyester on its own. Furthermore, while the invention mentions solvent recycling, it does not clearly disclose specific solvent recovery process parameters, such as distillation temperature, pressure control, and number of cycles. It also fails to explain key issues such as the solvent purification method and whether impurities are removed. This could lead to operational ambiguity and efficiency risks in actual applications. In fact, the high-efficiency solvent hexafluoroisopropanol used in the patent has a boiling point of only 59°C, while the low-efficiency solvent chloroform has a boiling point of 61.2°C. They cannot be separated after mixing. Similar issues exist with other high-efficiency and low-efficiency solvents.

[0006] In summary, the current technology for recycling waste nylon blended fabrics has problems such as low separation efficiency, high environmental load, low product added value and high cost. This field urgently needs to develop an efficient, green and high-value separation and recycling method to meet the industry's urgent demand for resource recycling. Summary of the Invention

[0007] To address the existing issues of low nylon dissolution efficiency, significant environmental pollution, and high energy consumption, the present invention proposes a method for the rapid separation and recycling of nylon blended fabrics. This method can separate nylon from cotton / viscose blended fabrics in a relatively short period of time without damaging natural cellulose fibers such as cotton / viscose. While ensuring that the nylon is essentially completely dissolved in the mixed solution, all fibers and solvent are recovered and reused. This establishes a comprehensive recycling mechanism for the HFIP (hexafluoroisopropanol)-formic acid mixed solvent system, reducing recycling costs, improving recycling efficiency, fully utilizing the recycled products, and precisely controlling the process, thereby achieving high-value, green recycling of waste polyester-cotton blended fabrics.

[0008] A method for rapidly separating and recycling nylon blended fabrics comprises the following steps: placing a pretreated nylon blended fabric in an HFIP-formic acid mixed solvent system, heating for reaction, ultrasonically treating the reaction product, vacuum filtering the obtained ultrasonic mixture to obtain a nylon dissolving solution and solid natural cellulose; washing and drying the solid natural cellulose to obtain natural cellulose; subjecting the nylon dissolving solution to reduced pressure distillation to sequentially obtain hexafluoroisopropanol and formic acid; and washing and drying the solid obtained by the reduced pressure distillation to obtain purified nylon.

[0009] The present invention selects HFIP and inexpensive and readily available formic acid to form a composite solvent. While formic acid dissolves nylon slowly and its solubility is inferior to that of HFIP, it is still a good solvent for dissolving nylon. Furthermore, the price of formic acid is only one-eighth to one-tenth of that of nylon. The composite solvent of formic acid and HFIP can significantly reduce recycling costs and be used for large-scale recycling of nylon blended fabrics. Furthermore, the boiling point of formic acid is 100.6°C, significantly different from the boiling point of HFIP (59°C). Simple distillation separation and recycling of the solvent can significantly reduce the production cost of recycling nylon blended fabrics. Because cellulose fibers such as cotton and viscose fibers are easily hydrolyzed under high acidic conditions, the formic acid used in the present invention is low-concentration formic acid (10-20%).

[0010] The reason for choosing to mix HFIP and formic acid solution is that HFIP is a highly polar organic solvent that can effectively dissolve nylon, but its market price is high. Formic acid has a certain dissolving effect on nylon. Using formic acid, which costs only about 1 / 10 of HFIP, to prepare a mixed solvent can significantly reduce costs. At the same time, formic acid can have a synergistic swelling effect to accelerate the dissolution of nylon. The difference in boiling points between HFIP and formic acid also provides an efficient path for subsequent solvent distillation recovery.

[0011] The reason for selecting a low concentration (10-20%) of formic acid solution is that, within the mild heating range of 35-45°C, the risk of damaging cotton / viscose fibers with low-concentration formic acid solution is extremely low, typically causing no detectable damage within 12 hours of reaction. Furthermore, it can also exert a certain swelling effect to assist HFIP in dissolving nylon, thereby improving dissolution efficiency and reducing costs without damaging blended fabrics such as cotton / viscose fibers, thus laying the foundation for the full component recovery of the present invention.

[0012] In the HFIP-formic acid mixed solvent system, HFIP has unique polarity and hydrogen bond donor properties, which can effectively destroy the hydrogen bonds within nylon and achieve rapid and complete dissolution in a mild heating range (35-45°C) and under normal pressure. Low-concentration formic acid solution (10%-20%) has a certain destructive effect on the hydrogen bonds between nylon molecules, forming new interactions with molecular chains through its own polarity, while also not damaging fibers such as cotton and viscose. In the mixed solution, HFIP takes the lead in dissolution, directly destroying hydrogen bonds and swelling the nylon structure, while formic acid provides H + , catalyzing the cleavage of amide bonds and greatly accelerating the dissolution rate.

[0013] Furthermore, the HFIP-formic acid mixed solvent is obtained by mixing HFIP and formic acid solution in a volume ratio of (5-9): (1-5); the concentration of the formic acid solution is 10-20 v / v%.

[0014] HFIP and formic acid solution are mixed according to a volume ratio and stirred evenly to obtain a transparent and uniform HFIP-formic acid mixed solvent; the stirring speed of the solvent mixing is 300-500 rpm and the time is 30-60 minutes.

[0015] Furthermore, the HFIP-formic acid mixed solvent is obtained by mixing hexafluoroisopropanol and formic acid solution in a volume ratio of (8-9): (1-2).

[0016] Furthermore, the usage ratio of the pretreated nylon blended fabric and the HFIP-formic acid mixed solvent is 1 g:10 mL.

[0017] Furthermore, the heating reaction temperature is 35-45° C. and the time is 3-20 min.

[0018] The pretreated nylon blended fabric is placed in a HFIP-formic acid mixed solvent and gently stirred in a mild heating range (35-45°C) to dissociate the nylon material into polymer segments and evenly disperse them in the solvent system;

[0019] The present invention uses HFIP-formic acid solvent systems with different volume ratios to carry out heating reaction dissolution of nylon blended fabrics, with a heating rate of 5-8°C / minute, a pressure of 0.8-1.5 MPa, a stirring speed of 100-200 rpm, and a reaction time of 3-20 minutes. By adjusting the volume ratio of HFIP to formic acid, when the temperature, pressure, stirring rate and other conditions are determined, the time taken for nylon to be completely dissolved in different solvent systems is observed.

[0020] Furthermore, the ultrasonic power is 300-600W, the frequency is 20-40kHz, and the duration is 15-30 minutes. The ultrasonic vibration effect is used to promote the uniform dispersion of molecules in the solution, avoid the agglomeration of polymer segments due to local excessive concentration, and thus improve the purity and recovery rate of the nylon product in the subsequent separation process.

[0021] Furthermore, the filtration uses a Buchner funnel with an inner diameter of 150-200 mm, a 2000 mL inner volume filtration bottle matching the Buchner funnel, an MCE water-based mixed fiber microporous filter membrane and a water circulation vacuum pump, wherein the pore size of the MCE water-based mixed fiber microporous filter membrane is 3-5 μm, and the vacuum degree of the vacuum pump is 0.05-0.09 MPa. The filtration can effectively separate the nylon dissolved liquid and solids such as cotton / viscose fibers.

[0022] Furthermore, the drying is vacuum drying, the temperature is 60-80° C., and the vacuum degree is 0.08-0.09 MPa.

[0023] Furthermore, the nylon blended fabric is selected from nylon-cotton blended fabric or nylon-viscose blended fabric.

[0024] Furthermore, when the nylon blended fabric is a nylon-cotton blended fabric, the natural cellulose is cotton fabric; when the nylon blended fabric is a nylon-viscose fiber blended fabric, the natural cellulose is viscose fiber.

[0025] Furthermore, the reduced pressure distillation treatment includes the following steps: turning on the ice bath condensation, using a serpentine condenser, the condensing medium is ethanol (-5°C)-ice water bath, ensuring that the outlet temperature of the condenser is ≤10°C, so that the solvent vapor is quickly liquefied, controlling the heating rate to 1°C / minute, slowly heating to 25-30°C, maintaining a vacuum degree of 20 mmHg, and collecting the initial fraction (mainly HFIP); replacing the receiver, restarting the vacuum pump, controlling the heating rate to 1°C / minute, slowly heating to 55-60°C, maintaining a vacuum degree of 20 mmHg, and collecting the second stage fraction (mainly formic acid).

[0026] The fractions were collected through a PTFE receiver (500 mL, graduated), the initial 1-2 mL fraction was discarded (containing trace amounts of air and low-boiling-point impurities), and subsequent fractions were collected. When the fraction outflow rate dropped to ≤1 drop / 30 seconds, the recovery endpoint was determined, and the recovered solvent was tested for purity by gas chromatography.

[0027] The principle of the fractionated vacuum distillation of HFIP and formic acid in the present invention is that under a vacuum of 20 mmHg, the boiling point of HFIP, when the saturated vapor pressure is in equilibrium with this pressure, is 26°C. Therefore, within the temperature range of 25-30°C, HFIP molecules gain sufficient energy to break through the surface tension of the liquid and escape as vapor. Meanwhile, the boiling point of formic acid at 20 mmHg is 58°C (much higher than the current heating temperature), and formic acid hardly evaporates, thus achieving thermodynamic separation of the two.

[0028] After the reduced pressure distillation is completed, the residual solid is washed with deionized water for 3-5 times, and vacuum dried at 60-80° C. with a vacuum degree of 0.08-0.09 MPa to recover the purified nylon.

[0029] When the HFIP-formic acid solvent recovered by the above method is used again to recycle nylon blended fabrics, the HFIP-formic acid mixed solvent system is subjected to a component analysis to restore its composition and performance to the original HFIP-formic acid solvent system state. This recycling and reuse step ensures the sustainable use of the system, allowing the HFIP-formic acid solvent system to maintain stable processing performance over multiple cycles.

[0030] Furthermore, the preparation method of the pretreated nylon blended fabric comprises the following steps: washing the nylon blended fabric with a neutral detergent, rinsing with clean water after washing, drying to a moisture content of less than 10%, and cutting into squares with a side length of 2-4 cm.

[0031] Pretreatment has at least the following effects: (1) Elimination of interfering matrices: The pretreatment process can effectively remove non-fiber components contained in the sample, including inherent impurities in the fiber and exogenous substances such as coatings, slurries, greases, waxes and finishing agents introduced by subsequent processing. Such operations can reduce the systematic error of the interfering matrix on the test results and ensure the accuracy and reliability of the analytical data; (2) Improve separation efficiency: By optimizing the physical and chemical properties of the sample through pretreatment, the mass transfer efficiency of the subsequent separation process can be significantly improved, the equilibrium time can be shortened, and the separation purity of the target component can be increased; (3) Reduce environmental load: Pretreatment can selectively remove risk substances (such as specific chemical additives) contained in the sample, reducing the emission of pollutants in the subsequent treatment process from the source; (4) Optimize the quality of recycled fiber: With the help of pretreatment to remove impurities and non-fiber substances, the quality of recycled fiber can be improved. (5) Reduce process costs: Pretreatment can reduce the consumption of chemical reagents in the subsequent treatment stage, while reducing the difficulty and cost of wastewater treatment, and achieve overall process economic improvement through process optimization; (6) Improve resource recovery efficiency: Pretreatment can enhance the dissociation and extractability of fiber components, significantly improve the recovery rate of target components such as nylon, cotton / viscose fibers, promote the resource utilization and high-value utilization of all components of waste textile materials, and maximize resource recycling efficiency.

[0032] Furthermore, the specific operating steps of pretreating the nylon blended fabric are: placing the nylon blended fabric in an aqueous solution containing a neutral detergent, soaking it at 35-45°C for 15-25 minutes, then mechanically stirring and cleaning it at a stirring speed of 200-300rpm for 15-20 minutes, rinsing it with clean water 3-4 times after cleaning, and then drying it in an oven at 60-80°C for 3-4 hours to make its moisture content less than 10%, and cutting it into squares with a side length of 2-4 cm, that is, clean blended fabric blocks, to prepare pretreated nylon blended fabric.

[0033] Compared with the prior art, the present invention has the following advantages and technical effects:

[0034] The present invention utilizes a nylon blended fabric combined with a variety of selectable HFIP-formic acid mixed solvent systems. Process parameters such as the HFIP to formic acid volume ratio, reaction temperature, pressure, and stirring speed are precisely controlled. The HFIP-formic acid mixed solvent system selectively interacts with the nylon blended fabric under specific conditions, effectively separating nylon from cotton / viscose fibers. Compared to the dissolution and recovery of nylon in a single solvent, the present invention further regulates the dissolution rate and effectiveness by controlling the ratio of hexafluoroisopropanol to formic acid solution, while also reducing solvent costs. Furthermore, fiber and solvent recovery are achieved through treatments such as ultrasound, filtration, distillation, and drying, providing a more efficient, environmentally friendly, and economical method for the separation and recovery of nylon. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1 The nylon solution obtained by filtration in S3 of Examples 1-5, from left to right are Example 1, Example 2, Example 3, Example 4 and Example 5;

[0037] Figure 2 The following are the infrared spectra (FTIR) of nylon before dissolution, HFIP solvent, and the solution after dissolution:

[0038] Figure 3 The dissolution process of nylon in the HFIP-formic acid mixed solvent in Examples 1-5, wherein a1-a5 is the entire process of the HFIP-formic acid solvent system dissolving the nylon at the molecular level within 3 minutes in Example 1; b1-b5 is the entire process of the HFIP-formic acid solvent system dissolving the nylon at the molecular level within 5 minutes in Example 2; c1-c5 is the entire process of the HFIP-formic acid solvent system dissolving the nylon at the molecular level within 8 minutes in Example 3; d1-d5 is the entire process of the HFIP-formic acid solvent system dissolving the nylon at the molecular level within 13 minutes in Example 4; and e1-e5 is the entire process of the HFIP-formic acid solvent system dissolving the nylon at the molecular level within 19 minutes in Example 5. DETAILED DESCRIPTION

[0039] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0040] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0041] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0042] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0043] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0044] Normal temperature in the present invention refers to 25±2°C.

[0045] Patent CN113717433A discloses a process for recovering nylon from waste nylon blended fabrics and the resulting recovered product. The method involves extracting the waste nylon blended fabric with an organic extractant, then cooling the extract, collecting the solids that precipitate during the cooling process, and purifying the collected solids to obtain the recovered nylon product. This method utilizes an organic extractant, such as an alcohol with a boiling point of 50-80°C, under high temperature and high pressure conditions, combined with a specific device to selectively extract nylon from the waste nylon blended fabric, while simultaneously separating it from non-nylon components. However, this patent relies on alcohol extractants (such as methanol and ethanol) under high temperature and high pressure (100-190°C) conditions to dissolve nylon. The high temperature and high pressure environment requires a special high-pressure reactor, which not only increases equipment investment and energy consumption, but also increases operational safety risks. At the same time, the alcohol extractants used are highly volatile and toxic, and the increased volatilization at high temperatures can easily cause danger. In addition, alcohols may swell or slightly dissolve non-nylon components (such as polyester) in blended fabrics under high temperature conditions, affecting the separation selectivity and the purity of the recovered products.

[0046] The HFIP-formic acid mixed solvent system adopted in the present invention can effectively circumvent the above-mentioned defects: first, the dissolution process can be achieved under mild heating conditions of 35-45°C, without the need for high-temperature and high-pressure equipment, significantly reducing energy consumption and operational risks, and being more suitable for industrial promotion; second, the HFIP-formic acid system has extremely strong selective solubility for nylon, can effectively dissociate the intermolecular forces and crystalline structure of nylon, and has no dissolving or swelling effect on non-nylon components such as cotton, polyester, and spandex, resulting in higher separation purity; third, the solvent system is more efficient in the dissolution-recovery process of nylon, without relying on cooling precipitation, and can quickly separate nylon and solvent through methods such as reduced pressure distillation or water addition-induced precipitation, with a recovery rate of over 90%; at the same time, the HFIP-formic acid mixed solvent can be efficiently recovered and reused through distillation, reducing solvent consumption costs, and the entire operation can be completed in a fume hood, which is safer and more environmentally friendly. In summary, the present invention focuses on the innovative application of the HFIP-formic acid mixed solvent system, which has significant advantages in mild operating conditions, separation selectivity, recovery efficiency and industrial feasibility, and can meet the actual needs of high-value-added recycling of waste nylon blended fabrics.

[0047] Patent CN119753918A discloses an easily recyclable nylon-spandex fabric and its recycling method. The method involves immersing the nylon-spandex fabric containing spandex with a specific polyether-ester diol structure in an alkali-alcohol solution, decomposing the spandex, and then rinsing to obtain the nylon, which is then physically or chemically recovered. This method, by designing the spandex structure to rapidly decompose in an alkali-alcohol environment, efficiently separates the spandex from the nylon in the nylon-spandex fabric, preventing the spandex from becoming an impurity in the nylon recovery process, thereby improving recovery efficiency and quality. However, the core of this invention relies on the pre-designed spandex structure (which must contain specific polyether-ester diol segments) and can only achieve alkali-alcohol dissolution and separation of spandex for this type of modified nylon-spandex fabric. It is not applicable to conventional unmodified nylon-spandex fabrics, which are prevalent on the market, and its scope of application is significantly limited. Furthermore, when dissolving the spandex in an alkali-alcohol solution (such as a sodium hydroxide-methanol system), the strong alkaline environment can potentially hydrolyze the nylon (especially during long-term treatment), affecting the quality of the nylon recovery. Furthermore, the carboxylate-containing wastewater produced by the alkali-alcohol reaction requires additional treatment, increasing environmental costs. The HFIP-formic acid mixed solvent system of the present invention does not need to rely on the pre-modification of the fabric, and can directly selectively dissolve the nylon in conventional nylon-spandex fabrics. It is suitable for the recovery of various existing nylon-spandex fabrics and has a wider range of applications. It operates under mild conditions of 35-45°C, which can not only effectively destroy the intermolecular forces of nylon to achieve dissolution, but also will not damage the chemical structure of nylon, and has no dissolving effect on spandex. It can directly obtain spandex residue and nylon solution through simple separation such as filtration, avoiding the potential damage of strong alkali to nylon. In addition, the present invention focuses on the sustainable application of the HFIP-formic acid mixed solvent system. HFIP and formic acid can be efficiently recovered and reused through vacuum distillation, with low solvent loss, better environmental protection, and better ability to meet the actual industrial needs of nylon blended fabric recycling. Compared with these existing technologies, the advantages of the present invention are specifically reflected in the following aspects:

[0048] 1. The present invention is based on a multi-parameter coordinated control process in the process of treating nylon blended fabrics with an HFIP-formic acid mixed solvent system. Specifically, the invention includes a refined control strategy for key process parameters such as the HFIP-formic acid volume ratio (50%-90% HFIP and 10%-50% formic acid) in the mixed solvent, the reaction temperature (mild heating range of 35-45°C), the pressure (strictly controlled within the range of 0.8-1.5 MPa), and the stirring speed (specific range of 100-200 rpm) in the mixed solvent, so as to achieve complete dissolution of nylon. HFIP destroys the hydrogen bonds between nylon molecules by virtue of its strong polarity and hydrogen bonding, and formic acid provides H + The catalytic amide bond breaks, and the synergistic effect of the two makes nylon completely dissolve within 3-20 minutes without damaging natural cellulose such as cotton / viscose, solving the problems of low dissolution efficiency and fiber damage in traditional methods.

[0049] 2、HFIP-formic acid mixed solvent system treatment after the introduction of the ultrasonic treatment process and its accurate process parameter setting, namely the ultrasonic power setting in the range of 300-600W, the ultrasonic frequency control in the range of 20-40kHz, the ultrasonic time is limited to 15-30 minutes, by means of the cavitation effect and mechanical action mechanism of ultrasonic, realize the uniform dispersion of the solution of polyamide molecules, avoid the agglomeration of high molecular chain segment due to the local concentration is too high, thereby improve the purity and recovery rate of polyamide product in the subsequent separation process.

[0050] 3、HFIP-formic acid mixed solvent system recycling process, including the selection of Buchner funnel (150-200mm), filtration bottle (2000mL), microporous filter membrane (pore size 3-5um) etc., the setting of specific distillation temperature (25-30℃) and vacuum degree (20mmHg) in the step of fractional vacuum distillation to recover the initial distillate HFIP and the setting of distillation temperature (55-60℃) and vacuum degree (20mmHg) to recover the second stage distillate formic acid, and the regulation and control of organic solvents and deionized water used for washing polyamide, cotton and viscose fibers, and vacuum drying at 60-80℃, the above process forms a closed loop system of "dissolution-separation-recovery-circulation", which ensures that the system can maintain stable performance and high processing capacity after multiple cycles.

[0051] In the examples and comparative examples of the present application, the neutral detergent used is a detergent of fatty alcohol polyoxyethylene ether (AEO-9) and alkyl polyglycoside (APG 1214) prepared according to a volume ratio of 2:1.

[0052] In the examples of the present application, the calculation method of the recovery rate of polyamide / cotton / viscose fiber product is: fiber recovery rate (%) = recovered pure fiber mass / mass of the fiber in the blended fabric before recovery * 100%.

[0053] In the examples of the present application, the calculation method of the recovery rate of HFIP / formic acid product is: solvent recovery rate (%) = volume of recovered pure solvent / volume of the solvent in the mixed solvent before recovery * 100%.

[0054] The gas chromatography (GC) detection method used in the examples of the present application is: using a gas chromatograph (Shimadzu GC-2030) equipped with an FID detector, using a nitroterephthalic acid modified polyethylene glycol capillary column (30m x 0.32mm x 0.5um) as the separation column, the injection port temperature is 200℃, the split ratio is 50:1, the injection amount is 1uL, the temperature is raised by 10℃ / min from 60℃ to 150℃, the detector temperature is 250℃; the sample is filtered through a 0.22um PTFE filter membrane, then ethyl acetate is added as an internal standard, and the internal standard curve method is used for quantitative analysis to realize the accurate analysis of HFIP and formic acid.

[0055] Example 1

[0056] S1. Sort 10 g of polyamide / cotton blended fabric (polyamide / cotton ratio 65 / 35, mass ratio) and place in 50 mL of an aqueous solution containing 0.5 g of a neutral detergent, soak at 45°C for 25 minutes, then mechanically stir wash at a stirring speed of 300 rpm for 15 minutes, rinse with clean water 3 times after washing, dry in an oven at 60°C for 3 hours to reduce the water content to less than 10%, and cut into small pieces with an edge length of 2 cm*2 cm to obtain pretreated polyamide / cotton blended fabric;

[0057] S2. Mix hexafluoroisopropanol with a low concentration formic acid solution (20 v / v%) at a volume ratio of 9:1, stir uniformly at room temperature, stirring speed is 300 rpm, stirring time is 30 minutes, to form a uniform transparent 90% HFIP / 10% HCOOH mixed solvent system;

[0058] S3. Put the pretreated polyamide blended fabric obtained in S1 into a polytetrafluoroethylene lined reaction kettle, and add 100 mL of the 90% HFIP / 10% HCOOH mixed solvent system prepared in S2. After sealing the reaction kettle, heat it to 45°C at a heating rate of 5°C / min, maintain the pressure at 0.8 MPa during the reaction, and stir at a speed of 200 rpm. After 3 minutes of reaction, the polyamide has completely dissolved. Transfer the reaction mixture to an ultrasonic cell crusher, set the ultrasonic power to 300 W, the ultrasonic frequency to 20 kHz, and the ultrasonic time to 20 minutes. After ultrasonic treatment, cool the mixture to room temperature and perform suction filtration. The suction filtration uses a Buchner funnel with an inner diameter of 200 mm, a 2000 mL inner volume suction filter bottle matched with the Buchner funnel, an MCE water system mixed fiber microporous filter membrane (pore size 4.5 μm), and a water circulating vacuum pump (vacuum degree 0.05 MPa) to separate the polyamide dissolution solution from the solid cotton. Wash the solid cotton with ethanol and deionized water three times each, and vacuum dry at 60°C at a vacuum degree of 0.08 MPa. Recover the purified cotton fabric, which weighs 3.35 g, and the recovery rate is 95.7%. The obtained filtrate is a polyamide dissolution solution. Perform secondary vacuum distillation on the filtrate, open the ice bath for condensation, use a serpentine condenser (length 30 cm, inner diameter 10 mm, made of high borosilicate glass, wrapped with insulating cotton), and use ethanol (-5°C)-ice water bath (volume ratio 1:1, circulated by a low-temperature constant-temperature bath) as the condensing medium to ensure that the outlet temperature of the condenser is ≤10°C, so that the solvent vapor is quickly liquefied. Control the heating rate to be 1°C / min, slowly heat to 30°C, maintain the vacuum degree at 20 mmHg, collect the initial distillate (mainly HFIP) 83.1 mL, and the recovery rate is 92.3%. Replace the receiver, restart the vacuum pump, control the heating rate to be 1°C / min, slowly heat to 60°C, maintain the vacuum degree at 20 mmHg, collect the second-stage distillate (mainly formic acid) 1.78 mL, and the recovery rate is 89%. The two recovered solvents have a purity of >99% as detected by gas chromatography (GC). After distillation, the residual solid in the flask is mainly polyamide, which is washed with deionized water three times and vacuum dried at 60°C at a vacuum degree of 0.08 MPa. Recover the purified polyamide, which weighs 6.28 g, and the recovery rate is 96.6%.

[0059] Example 2

[0060] S1. Sort 10 g of polyamide-viscose fiber blended fabric (polyamide / viscose fiber ratio 7 / 3, mass ratio) and place it in 50 mL of an aqueous solution containing 0.5 g of a neutral detergent. Soak at 45°C for 25 minutes, then mechanically stir at a stirring speed of 300 rpm for 15 minutes. After washing, rinse with clean water three times, dry in a 60°C oven for 3 hours to reduce the water content to less than 10%, and cut into small pieces with an edge length of 2 cm*2 cm to obtain pretreated polyamide blended fabric;

[0061] S2. Hexafluoroisopropanol and a low concentration formic acid solution (20 v / v%) were mixed in a volume ratio of 8:2 and stirred at room temperature at a stirring speed of 300 rpm for 30 minutes to form a uniform and transparent 80% HFIP / 20% HCOOH mixed solvent system;

[0062] S3. The pretreated nylon blended fabric obtained in S1 was placed in a polytetrafluoroethylene-lined reactor and 100 mL of the 80% HFIP / 20% HCOOH mixed solvent system prepared in S2 was added. After sealing the reactor, the temperature was raised to 45°C at a heating rate of 5°C / min. During the reaction, the pressure was maintained at 0.8 MPa and the stirring speed was 200 rpm. After 5 minutes of reaction, the mixture was removed and the nylon was completely dissolved. The reacted mixture was transferred to an ultrasonic cell disruptor with an ultrasonic power of 300 W, an ultrasonic frequency of 20 kHz, and an ultrasonic time of 20 minutes. After the ultrasonic treatment, the mixture was cooled to room temperature and filtered. The filtration was performed using a Buchner funnel with an inner diameter of 200 mm, a 2000 mL internal volume filtration bottle matched with the Buchner funnel, an MCE water-based mixed fiber microporous filter membrane (pore size 4.5 μm), and a water circulating vacuum pump (vacuum degree 0.05 MPa) to separate the nylon solution and the viscose fiber solid. The viscose fiber solid was washed three times with ethanol and deionized water respectively, and dried in vacuum at 60° C. with a vacuum degree of 0.08 MPa to obtain 2.81 g of purified viscose fiber with a recovery rate of 93.7%. The filtrate is a nylon dissolving liquid. The filtrate is taken out for secondary vacuum distillation, and ice bath condensation is turned on. A serpentine condenser (length 30 cm, inner diameter 10 mm, material high borosilicate glass, wrapped with insulation cotton) is used. The condensation medium is ethanol (-5°C)-ice water bath (volume ratio 1:1, circulated through a low-temperature constant temperature bath). Ensure that the condenser outlet temperature is ≤10°C, control the heating rate at 1°C / min, slowly heat it to 30°C, maintain a vacuum degree of 20 mmHg, collect 73.3 mL of the initial fraction (mainly HFIP), and the recovery rate is 91.6%; replace the receiver, restart the vacuum pump, control the heating rate at 1°C / min, slowly heat it to 60°C, maintain a vacuum degree of 20 mmHg, collect 3.56 mL of the second stage fraction (mainly formic acid), and the recovery rate is 89%. After gas chromatography (GC) detection, the purity of both recovered solvents is >99%. After distillation, the solids remaining in the flask were mainly nylon, which was washed three times with deionized water and vacuum dried at 60°C with a vacuum degree of 0.08 MPa. 6.71 g of purified nylon was recovered with a recovery rate of 95.8%.

[0063] Example 3

[0064] S1. 10 g of polyamide / cotton blended fabric (polyamide / cotton ratio of 65 / 35, mass ratio) was sorted and placed in 50 mL of an aqueous solution containing 0.5 g of a neutral detergent, soaked at 45°C for 25 minutes, and then mechanically stirred at a stirring speed of 300 rpm for 15 minutes. After washing, the fabric was rinsed with clean water for 3 times, dried in an oven at 60°C for 3 hours to reduce the water content to less than 10%, and cut into small pieces with a side length of 2 cm*2 cm to obtain pretreated polyamide / cotton blended fabric;

[0065] S2. Hexafluoroisopropanol was mixed with a low-concentration formic acid solution (20 v / v%) at a volume ratio of 7:3, and stirred at room temperature at a stirring speed of 300 rpm for 30 minutes to form a uniform and transparent 70% HFIP / 30% HCOOH mixed solvent system.

[0066] S3. The pretreated polyamide / cotton blended fabric obtained in S1 was placed in a polytetrafluoroethylene-lined reaction kettle, and 100 mL of the 70% HFIP / 30% HCOOH mixed solvent system prepared in S2 was added. After sealing the reaction kettle, the temperature was raised to 45°C at a rate of 5°C / min, and the pressure was maintained at 0.8 MPa during the reaction. The stirring speed was 200 rpm, and the reaction was stopped after 8 minutes, at which time the polyamide was completely dissolved. The reaction mixture was transferred to an ultrasonic cell crusher, and the ultrasonic power was set to 300 W, the ultrasonic frequency was 20 kHz, and the ultrasonic time was 20 minutes. After ultrasonic treatment, the mixture was cooled to room temperature and subjected to suction filtration. A 200 mm inner diameter Buchner funnel, a 2000 mL inner volume suction filter bottle matched with the Buchner funnel, an MCE water-based mixed fiber microporous filter membrane (pore size 4.5 μm), and a water circulating vacuum pump (vacuum degree 0.05 MPa) were used to separate the polyamide solution from the solid cotton. The solid cotton was washed with ethanol and deionized water for 3 times, and dried at 60°C under vacuum (vacuum degree 0.08 MPa) to recover 3.23 g of purified cotton fabric with a recovery rate of 92.2%. The filtrate was a polyamide solution, which was subjected to secondary vacuum distillation. An ice bath was used for condensation, the outlet temperature of the condenser was controlled to be ≤10°C, the temperature was raised to 30°C at a rate of 1°C / min, the vacuum degree was maintained at 20 mmHg, and 64.4 mL of the initial distillate (mainly HFIP) was collected with a recovery rate of 92%. The receiver was replaced, the vacuum pump was restarted, the temperature was raised to 60°C at a rate of 1°C / min, the vacuum degree was maintained at 20 mmHg, and 5.32 mL of the second-stage distillate (mainly formic acid) was collected with a recovery rate of 88.7%. Gas chromatography (GC) detection showed that the purity of the two recovered solvents was >99%. After distillation, the residual solid in the flask was mainly polyamide, which was washed with deionized water for 3 times and dried at 60°C under vacuum (vacuum degree 0.08 MPa) to recover 6.18 g of purified polyamide with a recovery rate of 95.1%.

[0067] Example 4

[0068] S1. 10 g (nylon / viscose ratio of 7 / 3, mass ratio) of nylon-viscose blended fabric was sorted and placed in 50 mL of an aqueous solution containing 0.5 g of neutral detergent. The mixture was soaked at 45 ° C for 25 minutes, then mechanically stirred and washed at a stirring speed of 300 rpm for 15 minutes. After washing, it was rinsed with clean water three times and dried in an oven at 60 ° C for 3 hours to a moisture content of less than 10%. The fabric was then cut into small pieces of 2 cm * 2 cm in length to obtain pretreated nylon blended fabric.

[0069] S2. Hexafluoroisopropanol and a low concentration formic acid solution (20 v / v%) were mixed in a volume ratio of 6:4 and stirred at room temperature at a stirring speed of 300 rpm for 30 minutes to form a uniform and transparent 60% HFIP / 40% HCOOH mixed solvent system;

[0070] S3. The pretreated nylon blended fabric obtained in S1 was placed in a polytetrafluoroethylene-lined reactor and 100 mL of the 60% HFIP / 40% HCOOH mixed solvent system prepared in S2 was added. After sealing the reactor, the temperature was raised to 45°C at a heating rate of 5°C / minute. During the reaction, the pressure was maintained at 0.8 MPa and the stirring speed was 200 rpm. After 13 minutes of reaction, the mixture was removed, at which point the nylon had been essentially completely dissolved. The reacted mixture was transferred to an ultrasonic cell disruptor, with the ultrasonic power set to 300 W, the ultrasonic frequency set to 20 kHz, and the ultrasonic time set to 20 minutes. After the ultrasonic treatment, the mixture was cooled to room temperature and filtered using a Büchner funnel with an inner diameter of 200 mm, a 2000 mL internal volume filtration flask equipped with the Büchner funnel, an MCE water-based mixed fiber microporous filter membrane (pore size 4.5 μm), and a water-circulating vacuum pump (vacuum degree 0.05 MPa) to separate the nylon solution from the viscose fiber solids. The viscose fiber solid was washed three times with ethanol and deionized water, respectively, and vacuum-dried at 60°C with a vacuum degree of 0.08 MPa. 2.79 g of purified viscose fiber was recovered, with a recovery rate of 93%. The filtrate, the nylon dissolving solution, was removed and subjected to secondary vacuum distillation. Ice bath condensation was started, ensuring that the condenser outlet temperature was ≤10°C. The temperature was slowly raised to 30°C at a controlled rate of 1°C / minute, maintaining a vacuum degree of 20 mmHg. 55.1 mL of the initial fraction (mainly HFIP) was collected, with a recovery rate of 91.8%. The receiver was replaced, the vacuum pump was restarted, the temperature was slowly raised to 60°C at a controlled rate of 1°C / minute, maintaining a vacuum degree of 20 mmHg, and 7.08 mL of the second-stage fraction (mainly formic acid) was collected, with a recovery rate of 88.5%. Gas chromatography (GC) analysis showed that the purity of both recovered solvents was >99%. After distillation, the solids remaining in the flask were mainly nylon, which was washed three times with deionized water and vacuum dried at 60°C with a vacuum degree of 0.08 MPa. 6.52 g of purified nylon was recovered with a recovery rate of 93.1%.

[0071] Example 5

[0072] S1. 10 g (nylon / cotton ratio of 65 / 35, mass ratio) of nylon-cotton blended fabric was sorted and placed in 50 mL of an aqueous solution containing 0.5 g of neutral detergent, soaked at 45 ° C for 25 minutes, and then mechanically stirred and washed at a stirring speed of 300 rpm for 15 minutes. After washing, it was rinsed with water three times and dried in an oven at 60 ° C for 3 hours to a moisture content of less than 10%. The fabric was cut into small pieces of 2 cm * 2 cm in length to obtain pretreated nylon blended fabric.

[0073] S2. Hexafluoroisopropanol and a low-concentration formic acid solution (20 v / v%) were mixed in a volume ratio of 5:5 and stirred at room temperature at a stirring speed of 300 rpm for 30 minutes to form a uniform and transparent 50% HFIP / 50% HCOOH mixed solvent system;

[0074] S3. The pretreated nylon blended fabric obtained in S1 was placed in a polytetrafluoroethylene-lined reactor and 100 mL of the 50% HFIP / 50% HCOOH mixed solvent system prepared in S2 was added. After sealing the reactor, the temperature was raised to 45°C at a heating rate of 5°C / min. During the reaction, the pressure was maintained at 0.8 MPa and the stirring speed was 200 rpm. After 19 minutes of reaction, the mixture was removed, at which point the nylon had been substantially completely dissolved. The reacted mixture was transferred to an ultrasonic cell disruptor, with the ultrasonic power set to 300 W, the ultrasonic frequency set to 20 kHz, and the ultrasonic time set to 20 minutes. After the ultrasonic treatment, the mixture was cooled to room temperature and filtered. The filtration was performed using a Buchner funnel with an inner diameter of 200 mm, a 2000 mL internal volume filtration bottle matched with the Buchner funnel, an MCE water-based mixed fiber microporous filter membrane (pore size 4.5 μm), and a water circulation vacuum pump (vacuum degree 0.05 MPa) to separate the nylon solution from the solid cotton. The solid cotton was washed three times with ethanol and deionized water, respectively, and vacuum-dried at 60°C with a vacuum of 0.08 MPa. 3.23 g of purified cotton fabric was recovered, with a recovery rate of 92.3%. The filtrate, the nylon dissolving solution, was removed and subjected to secondary vacuum distillation. Ice bath condensation was performed to ensure that the condenser outlet temperature was ≤10°C. The temperature was slowly raised to 30°C at a controlled rate of 1°C / min, maintaining a vacuum of 20 mmHg. 46.1 mL of the initial fraction (primarily HFIP) was collected, with a recovery rate of 92.2%. The receiver was replaced, the vacuum pump was restarted, the temperature was slowly raised to 60°C at a controlled rate of 1°C / min, maintaining a vacuum of 20 mmHg, and 8.82 mL of the second-stage fraction (primarily formic acid) was collected, with a recovery rate of 88.2%. Gas chromatography (GC) analysis showed that the purity of both recovered solvents was >99%. After distillation, the solids remaining in the flask were mainly nylon, which was washed three times with deionized water and vacuum dried at 60°C with a vacuum degree of 0.08 MPa. 5.96 g of purified nylon was recovered with a recovery rate of 91.7%.

[0075] The nylon solution obtained by filtration in S3 of Example 1-5 is as follows Figure 1As shown, the nylon dissolution solutions in Examples 1-3 were highly homogeneous, and no residual nylon fragments were observed in the solutions. However, as the volume fraction of HFIP in the mixed solvent decreased, fine nylon fragments began to appear in the nylon dissolution solution in Example 4, and the solution homogeneity decreased. In Example 5, the nylon dissolution solution became significantly heterogeneous, exhibiting stratification, and more fine nylon fragments appeared in the solution. The nylon dissolution solution in Example 5 exhibited significant heterogeneity, even exhibiting stratification, and the number of fine nylon fragments in the system increased further compared to Example 4. This phenomenon is closely related to the synergistic mechanism of HFIP and formic acid. While formic acid can assist in catalyzing the cleavage of amide bonds, the low proportion of HFIP cannot offset the "insufficient solvent polarity" caused by the relatively high formic acid concentration. In the present invention, the nylon dissolution efficiency is directly proportional to the volume fraction of HFIP in the mixed solvent.

[0076] In the 90% HFIP / 10% HCOOH system, nylon can be completely dissolved in 2-4 minutes, while cotton / viscose fibers will not be affected. After the reaction, the solution is uniform and no nylon residual particles are observed.

[0077] In the 80% HFIP / 20% HCOOH system, nylon can be completely dissolved in 4-6 minutes, while cotton / viscose fibers will not be affected. After the reaction, the solution is uniform with almost no residual nylon particles.

[0078] In the 70% HFIP / 30% HCOOH system, nylon can be completely dissolved in 7-9 minutes, while cotton / viscose fibers will not be affected. After the reaction, the solution is relatively uniform with almost no residual nylon particles.

[0079] In the 60% HFIP / 40% HCOOH system, nylon can be almost completely dissolved in 12-14 minutes, while cotton / viscose fibers will not be affected. After the reaction, small nylon residual particles will exist in the solution.

[0080] In the 50% HFIP / 50% HCOOH system, nylon can be almost completely dissolved in 18-20 minutes, while cotton / viscose fibers will not be affected. However, the solution after the reaction is uneven and the residual nylon particles are significantly increased compared to the previous group.

[0081] Under a polarizing microscope, the dissolution process of nylon in HFIP-formic acid mixed solvent in Examples 1-5 is as follows: Figure 3As shown, a1-a5 are the whole process of dissolving nylon at the molecular level by the HFIP-formic acid solvent system within 3 minutes in Example 1; b1-b5 are the whole process of dissolving nylon at the molecular level by the HFIP-formic acid solvent system within 5 minutes in Example 2; c1-c5 are the whole process of dissolving nylon at the molecular level by the HFIP-formic acid solvent system within 8 minutes in Example 3; d1-d5 are the whole process of dissolving nylon at the molecular level by the HFIP-formic acid solvent system within 13 minutes in Example 4; and e1-e5 are the whole process of dissolving nylon at the molecular level by the HFIP-formic acid solvent system within 19 minutes in Example 5.

[0082] from Figure 3 It can be seen from the figure that in the initial stage of the experiment, the nylon fibers in each embodiment maintain a clear and regular arrangement structure, and exhibit obvious birefringence (bright spots or light and dark stripes) under polarized light due to the orderly arrangement of the molecular chains. As the dissolution proceeds, HFIP and formic acid penetrate into the interior of the nylon fiber through synergistic action. HFIP, with its strong polarity, destroys the intermolecular hydrogen bonds, causing the fiber to gradually swell, while formic acid promotes the dissociation of the molecular chains by protonating the amide bonds. At this time, the ordered structure of the fiber is broken, the birefringence intensity under polarized light gradually weakens, and the edges begin to blur. Specifically, in Examples 1-3 (HFIP volume fraction 70%-90%), sufficient HFIP provides a continuous polar environment. Combined with the catalytic effect of formic acid, the nylon molecular chains can completely dissociate into single chains and evenly disperse. Ultimately, there is no obvious birefringence under polarized light, showing a relatively uniform dissolution effect. In contrast, in Examples 4-5 (HFIP volume fraction 50%-60%), the insufficient proportion of HFIP weakens its ability to destroy hydrogen bonds, slowing the solvent penetration rate. The nylon molecular chains in some areas fail to dissociate in time, retaining a locally ordered structure. As a result, large areas of fuzzy structure can be observed under polarized light, manifesting as obvious uneven dissolution. This phenomenon further confirms the core role of HFIP in maintaining solvent polarity and promoting uniform dispersion of nylon molecular chains. The ratio of HFIP to formic acid solution directly affects the thoroughness and uniformity of dissolution.

[0083] Comparative Example 1 (low volume fraction HFIP system)

[0084] S1. 10 g (nylon / cotton ratio of 65 / 35, mass ratio) of nylon-cotton blended fabric was sorted and placed in 50 mL of an aqueous solution containing 0.5 g of neutral detergent, soaked at 45 ° C for 25 minutes, and then mechanically stirred and washed at a stirring speed of 300 rpm for 15 minutes. After washing, it was rinsed with water three times and dried in an oven at 60 ° C for 3 hours to a moisture content of less than 10%. The fabric was cut into small pieces of 2 cm * 2 cm in length to obtain pretreated nylon blended fabric.

[0085] S2. Hexafluoroisopropanol and a low concentration formic acid solution (20 v / v%) were mixed in a volume ratio of 3:7 and stirred at room temperature at a stirring speed of 300 rpm for 30 minutes to form a uniform and transparent 30% HFIP / 70% HCOOH mixed solvent system;

[0086] S3. Place the pretreated nylon blended fabric obtained in S1 into a polytetrafluoroethylene-lined reactor and add 100 mL of the 30% HFIP / 70% HCOOH mixed solvent system prepared in S2. After sealing the reactor, heat it to 45°C at a rate of 5°C / minute. Maintain the pressure at 0.8 MPa and stir at 200 rpm during the reaction. After 20 minutes of reaction, remove the mixture. At this point, the nylon is only partially dissolved, and many small nylon fragments are present in the solution, with obvious stratification. Transfer the reaction mixture to an ultrasonic cell disruptor and set the ultrasonic power to 300 W, the ultrasonic frequency to 20 kHz, and the ultrasonic time to 20 minutes. After the ultrasonic treatment, the mixture was cooled to room temperature and filtered using a 200 mm inner diameter Büchner funnel, a 2000 mL internal volume filtration flask, an MCE water-based mixed fiber microporous filter membrane (pore size 4.5 μm), and a water-circulating vacuum pump (vacuum degree 0.05 MPa) to separate the nylon solution from the nylon-cotton blended fabric. The nylon-cotton blended fabric was washed three times with ethanol and three times with deionized water, respectively, and vacuum-dried at 60°C with a vacuum degree of 0.08 MPa to recover 6.55 g of incompletely reacted nylon-cotton blended fabric. The filtrate, representing the nylon dissolution solution, was removed and subjected to a two-stage vacuum distillation process. The condenser was cooled in an ice bath, ensuring the condenser outlet temperature was ≤10°C. The temperature was slowly raised to 30°C at a controlled rate of 1°C / minute, maintaining a vacuum of 20 mmHg. A 27.6 mL initial fraction (primarily HFIP) was collected, yielding a recovery of 92.1%. The receiver was replaced, the vacuum pump restarted, and the temperature was slowly raised to 60°C at a controlled rate of 1°C / minute, maintaining a vacuum of 20 mmHg. A 12.13 mL secondary fraction (primarily formic acid) was collected, yielding a recovery of 86.6%. Gas chromatography (GC) analysis revealed that both recovered solvents were >99% pure. After distillation, the remaining solid (primarily nylon) in the flask was washed three times with deionized water and dried under vacuum at 60°C under a vacuum of 0.08 MPa. 3.41 g of purified nylon was recovered, yielding a recovery of 52.5%.

[0087] Comparative Example 2 (High Concentration Formic Acid (85%) System)

[0088] S1. 10 g (nylon / cotton ratio of 65 / 35, mass ratio) of nylon-cotton blended fabric was sorted and placed in 50 mL of an aqueous solution containing 0.5 g of neutral detergent, soaked at 45 ° C for 25 minutes, and then mechanically stirred and washed at a stirring speed of 300 rpm for 15 minutes. After washing, it was rinsed with water three times and dried in an oven at 60 ° C for 3 hours to a moisture content of less than 10%. The fabric was cut into small pieces of 2 cm * 2 cm in length to obtain pretreated nylon blended fabric.

[0089] S2. Hexafluoroisopropanol and a high-concentration formic acid solution (85%) were mixed in a volume ratio of 7:3 and stirred at room temperature at 300 rpm for 30 minutes to form a uniform and transparent 70% HFIP / 30% HCOOH mixed solvent system.

[0090] S3. The nylon blended fabric pretreated in S1 was placed in a polytetrafluoroethylene-lined reactor and 100 mL of the 70% HFIP / 30% HCOOH mixed solvent system prepared in S2 was added. After sealing the reactor, the temperature was raised to 45°C at a heating rate of 5°C / min. During the reaction, the pressure was maintained at 0.8 MPa and the stirring speed was 200 rpm. After 8 minutes of reaction, the mixture was removed. At this time, the nylon had completely dissolved and the cotton fabric was partially dissolved. The reacted mixture was transferred to an ultrasonic cell crusher, with the ultrasonic power set to 300 W, the ultrasonic frequency set to 20 kHz, and the ultrasonic time set to 20 minutes. After the ultrasonic treatment, the mixture was cooled to room temperature and filtered. The filtration was performed using a Buchner funnel with an inner diameter of 200 mm, a 2000 mL internal volume filtration bottle matched with the Buchner funnel, an MCE water-based mixed fiber microporous filter membrane (pore size 4.5 μm), and a water circulation vacuum pump (vacuum degree 0.05 MPa) to separate the dissolved liquid and the solid cotton. The solid cotton was washed three times with ethanol and deionized water, respectively, and vacuum-dried at 60°C with a vacuum degree of 0.08 MPa. 2.97 g of purified cotton fabric was recovered, with a recovery rate of 84.9%. The filtrate, which was the nylon and cotton dissolution solution, was removed and subjected to secondary vacuum distillation. Ice bath condensation was started, ensuring that the condenser outlet temperature was ≤10°C. The temperature was slowly raised to 30°C at a controlled rate of 1°C / min, maintaining a vacuum degree of 20 mmHg. 64.6 mL of the initial fraction (mainly HFIP) was collected, with a recovery rate of 92.3%. The receiver was replaced, the vacuum pump was restarted, the temperature was slowly raised to 60°C at a controlled rate of 1°C / min, maintaining a vacuum degree of 20 mmHg, and 22.2 mL of the second-stage fraction (mainly formic acid) was collected, with a recovery rate of 87%. Gas chromatography (GC) analysis showed that the purity of both recovered solvents was >99%. After the distillation was completed, the solid remaining in the flask (a mixture of nylon and cotton) was washed three times with deionized water and vacuum dried at 60° C. with a vacuum degree of 0.08 MPa to recover 6.43 g of a mixed solid.

[0091] A comparison of Examples 1-5 with Comparative Examples 1-2 shows that the HFIP-formic acid mixed solvent system of the present invention has significant advantages in the recycling and treatment of nylon blended fabrics. In terms of nylon fiber recovery, Example 1 achieved a 96.6% recovery rate. For Example 5, where HFIP only accounts for 50%, the nylon recovery rate was 91.7%. However, in Comparative Example 1, the nylon fiber failed to completely dissolve, resulting in a recovery rate of only 52.5%. The high concentration of formic acid in Comparative Example 2 damaged the cotton fabric, causing partial dissolution and hindering the subsequent recovery of the nylon fiber. Regarding cotton / viscose fiber recovery, each example achieved a recovery rate of over 92%. Regarding HFIP / formic acid solvent recovery, each example achieved a significant recovery effect, with the recovered solvent purity exceeding 99%, laying the foundation for the recycling of the HFIP-formic acid mixed solvent system. In general, the dissolution and recovery of nylon blended fabrics using a HFIP-formic acid mixed solvent system with different volume ratios can be completed within 3-20 minutes without damaging the cotton / viscose fibers, and the degree of solvent recovery and reuse is high. The present invention successfully achieves the coordinated unity of high efficiency, safety, greenness and recyclability, and fully meets the core technical requirements for the recycling of nylon blended fabrics.

[0092] To demonstrate the dissolving effect of HFIP solvent on nylon, the pretreated nylon blended fabric prepared in S1 of Example 1 was placed in a polytetrafluoroethylene-lined reactor. 100 mL of HFIP solvent was added. The reactor was sealed and heated to 45°C at a rate of 5°C / min. The pressure was maintained at 0.8 MPa and the stirring speed was 200 rpm. The reaction mixture was removed after 3 minutes of reaction, at which point the nylon was completely dissolved. Figure 2 The infrared spectra (FTIR) of nylon before dissolution, HFIP solvent and solution after dissolution (HFIP / Nylon) are shown in Figure 1. The system of nylon dissolved in HFIP was characterized by infrared spectroscopy analysis technology. The results showed that after dissolution, nylon had a wavelength of 3300 cm -1 NH stretching vibration peak at 1640 cm -1 The C=O stretching vibration peak at 1540 cm -1 The intensity of the characteristic peak of the amide bond at the position is significantly weakened, or even partially disappears, which indicates that during the dissolution process of the nylon molecules, the hydrogen bonds between the molecular chains are destroyed, and the chemical environment of functional groups such as the amide bond is changed. The characteristic absorption peak unique to the polyamide molecular chain is still retained in the dissolved product, and no new characteristic peak is detected, indicating that only the dissolution of nylon occurs in the whole process, and the essential structure of the solvent and nylon does not change.

[0093] Performance test

[0094] Test method for the number of recycling times of HFIP-formic acid mixed solvent system.

[0095] The nylon blended fabric was treated with the HFIP-formic acid mixed solvent system according to the process of Example 1. After treatment, the nylon solution was recovered and regenerated by vacuum distillation. The treatment, recovery, and regeneration process was then repeated for multiple cycles (1-6 times). The fabric separation and recovery yield (comparing the mass of each recovered component with the initial yield) and the performance indicators of the HFIP-formic acid mixed solvent system (such as volume ratio, pH value, and solvent concentration change) were closely monitored during each cycle. The experimental conditions were stable and the average of multiple experiments was calculated.

[0096] When nylon blended fabrics were treated according to the process of Example 1, the nylon fiber recovery rate remained at a high level (over 90%) during multiple cycles of the HFIP-formic acid mixed solvent system (within a range of 6 cycles), the volume ratio and solvent concentration of the HFIP-formic acid solvent system remained unchanged, and the pH value was stabilized at approximately 2.6. The HFIP-formic acid mixed solvent system of the present invention was able to achieve efficient recovery of nylon fibers after multiple cycles, and the performance indicators of the recovered solvent were stable, demonstrating the reliability and sustainability of the entire recovery process and recycling system.

[0097] The HFIP-formic acid solvent system of the present invention can be effectively recycled and reused, whereas low-volume-fraction HFIP or high-concentration formic acid suffer from severe compositional issues after the reaction, making recovery difficult. These data clearly demonstrate that the present invention addresses the technical issues of nylon blended fabric recycling technologies mentioned in the background art, such as high cost, low efficiency, inadequate product utilization, and imprecise process control, demonstrating promising application prospects and economic benefits.

[0098] The above are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for rapid separation and recycling of nylon blended fabrics, characterized in that: The following steps are involved: The pretreated nylon blended fabric is placed in a hexafluoroisopropanol-formic acid mixed solvent system, heated for reaction, the reaction product is ultrasonically treated, and the obtained ultrasonic mixture is vacuum filtered to obtain a nylon dissolving solution and solid natural cellulose; the solid natural cellulose is washed and dried to obtain natural cellulose; the nylon dissolving solution is subjected to reduced pressure distillation to obtain hexafluoroisopropanol and formic acid in sequence; the solid obtained by the reduced pressure distillation is washed and dried to obtain purified nylon.

2. The method for rapid separation and recycling of nylon blended fabrics according to claim 1, characterized in that: The hexafluoroisopropanol-formic acid mixed solvent system is obtained by mixing hexafluoroisopropanol and formic acid solution in a volume ratio of (5-9): (1-5); wherein the concentration of the formic acid solution is 10-20 v / v%.

3. The method for rapid separation and recycling of nylon blended fabrics according to claim 2, characterized in that: The hexafluoroisopropanol-formic acid mixed solvent system is obtained by mixing hexafluoroisopropanol and formic acid solution in a volume ratio of (8-9): (1-2).

4. The method for rapid separation and recycling of nylon blended fabrics according to claim 1, characterized in that: The usage ratio of the pretreated nylon blended fabric and the hexafluoroisopropanol-formic acid mixed solvent is 1 g:10 mL.

5. The method for rapid separation and recycling of nylon blended fabrics according to claim 1, characterized in that: The temperature of the heating reaction is 35-45° C., and the time is 3-20 minutes.

6. The method for rapid separation and recycling of nylon blended fabrics according to claim 1, characterized in that: The nylon blended fabric is selected from nylon-cotton blended fabric or nylon-viscose blended fabric.

7. The method for rapid separation and recycling of nylon blended fabrics according to claim 6, characterized in that: When the nylon blended fabric is a nylon-cotton blended fabric, the natural cellulose is cotton fabric; when the nylon blended fabric is a nylon-viscose fiber blended fabric, the natural cellulose is viscose fiber.

8. The method for rapid separation and recycling of nylon blended fabrics according to claim 1, characterized in that: The reduced pressure distillation treatment comprises the following steps: starting ice bath condensation, ensuring that the outlet temperature of the condenser is ≤10°C, controlling the heating rate at 1°C / minute, heating to 25-30°C, maintaining a vacuum degree of 20 mmHg, and collecting hexafluoroisopropanol; replacing the receiver, restarting the vacuum pump, controlling the heating rate at 1°C / minute, heating to 55-60°C, maintaining a vacuum degree of 20 mmHg, and collecting formic acid.

9. The method for rapid separation and recycling of nylon blended fabrics according to claim 1, characterized in that: The preparation method of the pretreated nylon blended fabric comprises the following steps: washing the nylon blended fabric with a neutral detergent, rinsing with clean water after washing, drying until the moisture content is less than 10%, and cutting into squares with a side length of 2-4 cm.

10. The method for rapid separation and recycling of nylon blended fabrics according to claim 9, characterized in that: The neutral detergent is prepared by mixing fatty alcohol polyoxyethylene ether and alkyl glycoside in a volume ratio of 2:1.

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