A method for green selective dissolution of polyester and recovery of high value wool fibers

Abstract

This invention relates to the fields of textile resource recycling and green chemistry, and discloses a green method for selectively dissolving polyester and recovering high-value wool fibers. By preparing a hydrophobic eutectic solvent system based on menthol and benzoic acid, and utilizing its weak acidity, hydrophobic properties, and specific affinity for polyester, it can rapidly and directionally depolymerize polyester under specific conditions, while effectively protecting the wool fibers and maximizing the preservation of their structural integrity. This method provides a solution for the green and efficient separation and dual-component high-value recovery of polyester / wool blended fabrics, possessing both industrial application value and environmental significance.

Description

Technical Field

[0001] This invention relates to the field of textile resource recycling and green chemistry technology, specifically to a green method for selectively dissolving polyester and recovering high-value wool fibers. Background Technology

[0002] Polyester (polyethylene terephthalate, PET) blends with wool, combining the comfort and aesthetics of natural fibers with the superior mechanical properties and low cost of synthetic fibers. This has made it a mainstream fabric for mid-to-high-end suits, uniforms, and thermal outerwear, with a huge market inventory. However, the efficient separation and high-value recycling of these fabrics after disposal remains a critical technological bottleneck that urgently needs to be overcome in the textile circular economy sector.

[0003] Currently, the disposal of waste polyester / wool blended fabrics mainly relies on low-value physical recycling, landfill, or incineration, resulting in serious resource waste and environmental pressure. The core of achieving closed-loop recycling lies in overcoming the "separation dilemma" caused by the inherent chemical differences between polyester and wool. Traditional chemical treatment methods all face irreconcilable contradictions. When using alkali reduction processes to hydrolyze polyester, the strongly alkaline environment rapidly destroys the disulfide bonds of wool keratin, leading to wool dissolution or severe damage. If strong acid treatment or enzymatic hydrolysis specifically degrades wool, it essentially sacrifices the high-value wool component to recover low-value polyester, making both the economics and the technical approach unreasonable. Literature and industry practice show that existing technologies cannot selectively depolymerize polyester under mild conditions while completely preserving the morphological structure and mechanical properties of wool fibers, which constitutes the current challenge in blended fabric recycling.

[0004] In recent years, eutectic solvents (DES), as a green and designable novel solvent system, have shown unique potential in the field of polymer depolymerization. They can effectively swell and even catalyze the depolymerization of polyester through hydrogen bonding, and their components are low in toxicity, readily available, and recyclable. However, how to design specific DES systems to act specifically on polyester and become a "protective agent" for wool, thereby achieving precise separation of blended components, remains a key scientific problem and technological gap that has not been fully explored. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a green method for selectively dissolving polyester and recovering high-value wool fibers. By preparing a hydrophobic eutectic solvent system based on menthol and benzoic acid, and utilizing its weak acidity, hydrophobic properties, and specific affinity for polyester, it is possible to rapidly and directionally depolymerize polyester under specific conditions, while effectively protecting the wool fibers and maximizing the preservation of their structural integrity. This method provides a solution for the green and efficient separation and dual-component high-value recovery of polyester / wool blended fabrics, possessing both industrial application value and environmental significance.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for selectively dissolving polyester and recycling wool fibers includes the following steps:

[0008] Step (1): Mix menthol and benzoic acid, heat to melt, and cool to obtain a menthol / benzoic acid eutectic solvent;

[0009] Step (2): Place the polyester / wool blended fabric in a eutectic solvent of menthol / benzoic acid and treat it at a constant temperature. After the treatment, separate, wash, dry and recover the undissolved components.

[0010] Preferably, in step (1), the molar ratio of menthol to benzoic acid is 2-4:1.

[0011] Furthermore, in step (1), the molar ratio of menthol to benzoic acid is 3:1.

[0012] Preferably, in step (1), the heating and melting conditions are: heating to 70-100℃ under stirring at a speed of 150-200 r / min until a uniform and stable liquid phase is formed.

[0013] Preferably, in step (2), the bath ratio of polyester / wool blended fabric to menthol / benzoic acid eutectic solvent is 1:35-50.

[0014] Preferably, in step (2), the constant temperature treatment conditions are: constant temperature treatment at 100-220℃ for 30-60 minutes.

[0015] Furthermore, in step (2), the constant temperature treatment conditions are: constant temperature treatment at 220℃ for 30 minutes.

[0016] Preferably, in step (2), the mass ratio of polyester to wool in the polyester / wool blended fabric is 3:7 to 5:5.

[0017] Preferably, a method for processing polyester / wool blended fabrics is described above for selectively dissolving polyester and recovering wool fibers.

[0018] Preferably, an application of a method for selectively dissolving polyester and recovering wool fibers as described above in the efficient and non-destructive recovery of wool fibers.

[0019] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0020] 1. This invention designs and optimizes a hydrophobic eutectic solvent composed of menthol and benzoic acid in a specific molar ratio, constructing a green eutectic solvent system for the selective separation of blended fabrics. This system, through a unique hydrogen bond network, exhibits extremely strong specific dissolution and directional depolymerization characteristics on polyester (PET) under specific conditions, allowing it to completely swell and disperse, and acting only on the ester bonds of PET macromolecules. Simultaneously, its weakly acidic and hydrophobic environment effectively protects wool keratin, fundamentally overcoming the "dissolution / damage" paradox that traditional acid-base methods cannot overcome, laying the material foundation for achieving selective separation.

[0021] 2. This invention constructs a highly efficient and universally applicable "solvent-polyester-preserving-wool" process and establishes the optimal process window (220℃, 30 min) for treating polyester / wool blended fabrics using the menthol / benzoic acid eutectic solvent system. Under these conditions, near-complete removal of the polyester component can be achieved, and the process is applicable to blended fabrics with different ratios (e.g., 3:7 to 7:3). The wool fiber recovery rate remains stable at over 82%, and the scale structure, keratin backbone chemical structure, and mechanical properties of the recovered wool are fully preserved. This invention provides a closed-loop recycling technology path that simultaneously preserves high-value wool and removes low-value polyester, solving the long-standing separation problem in the industry and achieving high-value recovery of both components.

[0022] 3. This invention provides a method for the selective chemical separation of polyester / wool blended fabrics that combines environmental and economic benefits. The solvent used is low in toxicity, biodegradable, and readily available, and the solvent can be recycled. The entire process avoids the use of strong acids, strong alkalis, or heavy metal catalysts, conforming to green chemistry principles. This method transforms waste polyester / wool blended fabrics from a "low-value treatment" object into a stable source of high-value wool fibers, significantly improving the economic feasibility of resource recycling and providing technical support for the green upgrading of the textile industry. Attached Figure Description

[0023] Figure 1 These are physical images of the menthol / benzoic acid eutectic solvents prepared in Examples 1-3 and Comparative Example 1 at room temperature; wherein, Figure 1 In the figures, (a) is a photograph of the menthol / benzoic acid eutectic solvent prepared in Comparative Example 1 at room temperature; (b) is a photograph of the menthol / benzoic acid eutectic solvent prepared in Example 1 at room temperature; (c) is a photograph of the menthol / benzoic acid eutectic solvent prepared in Example 2 at room temperature; and (d) is a photograph of the menthol / benzoic acid eutectic solvent prepared in Example 3 at room temperature.

[0024] Figure 2 This is the Fourier transform infrared spectrum of the menthol / benzoic acid eutectic solvent prepared in Example 2 of this invention;

[0025] Figure 3 This is a line graph showing the dissolution effect of polyester fabric treated using the methods described in Examples 4-18 of this invention.

[0026] Figure 4 This is a sample image showing the dissolution process of polyester fabric processed using the method of Example 13 of the present invention.

[0027] Figure 5 The present invention uses the method of Example 13 to treat polyester fabric, and the infrared spectrum of the polyester fabric after dissolution is shown.

[0028] Figure 6 This is a bar chart showing the dissolution effect of polyester fabrics treated using the methods of Example 13 and Comparative Examples 2-4 of this invention.

[0029] Figure 7 This invention uses the method of Example 19 to process wool fibers, and the processing process of wool fibers is shown in the sample diagram.

[0030] Figure 8 These are microscopic morphology images of untreated wool fibers and wool fibers recovered after being treated using the method of Example 19 of this invention. Figure 8 (a) and (b) in the image are untreated wool fibers. Figure 8 (c) and (d) in the text are wool fibers recovered after being processed by the method of Example 19;

[0031] Figure 9 These are X-ray diffraction patterns of untreated wool fibers and wool fibers recovered after being treated using the method of Example 19 of this invention.

[0032] Figure 10 This is a bar chart showing the wool fiber recovery rate after treating polyester / wool blended fabrics using the methods described in Examples 20-22 of this invention.

[0033] Figure 11 This is a sample image showing the dissolution process of polyester / wool using the method of this invention.

[0034] Figure 12 These are microscopic morphology images of untreated polyester / wool blended fabric and polyester / wool blended fabric treated using the method of Example 22 of the present invention. Figure 12 (a) in the image represents an untreated polyester / wool blend fabric. Figure 12 (b) in the figure represents wool fibers recovered after being processed by the method of Example 22;

[0035] Figure 13These are infrared spectra of untreated wool fibers and wool fibers recovered after processing polyester / wool blended fabrics using the method of Example 22 of this invention. Detailed Implementation

[0036] The present invention will be further illustrated below through specific embodiments. The following embodiments are specific implementations of the present invention, but the implementation of the present invention is not limited to the following embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and are included within the protection scope of the present invention.

[0037] Example 1

[0038] This embodiment discloses a method for preparing a menthol / benzoic acid eutectic solvent, comprising the following steps:

[0039] Menthol and benzoic acid were placed in a clean, dry, heat-resistant container and heated to 70°C under continuous magnetic stirring at 200 r / min until a homogeneous and stable liquid phase was formed. After cooling, a eutectic solvent of menthol / benzoic acid was obtained.

[0040] The molar ratio of menthol to benzoic acid is 2:1.

[0041] Example 2

[0042] The difference from Example 1 is that the molar ratio of menthol to benzoic acid is changed to 3:1; all other parameters and conditions are the same as in Example 1.

[0043] Example 3

[0044] The difference from Example 1 is that the molar ratio of menthol to benzoic acid is changed to 4:1; all other parameters and conditions are the same as in Example 1.

[0045] Example 4

[0046] This embodiment discloses a method for dissolving polyester fabrics using a menthol / benzoic acid eutectic solvent, comprising the following steps:

[0047] The polyester fabric was placed in the menthol / benzoic acid eutectic solvent prepared in Example 1 and treated at 100°C for 30 min. After the treatment, the undissolved components were separated, washed, dried and recovered.

[0048] Example 5

[0049] The difference from Example 4 is that the isothermal treatment temperature is changed to 150°C; all other parameters and conditions are the same as in Example 4.

[0050] Example 6

[0051] The difference from Example 4 is that the constant temperature treatment temperature is changed to 180°C; all other parameters and conditions are the same as in Example 4.

[0052] Example 7

[0053] The difference from Example 4 is that the isothermal treatment temperature is changed to 200°C; all other parameters and conditions are the same as in Example 4.

[0054] Example 8

[0055] The difference from Example 4 is that the isothermal treatment temperature is changed to 220°C; all other parameters and conditions are the same as in Example 4.

[0056] Example 9

[0057] The difference from Example 4 is that the menthol / benzoic acid eutectic solvent prepared in Example 1 is changed to the menthol / benzoic acid eutectic solvent prepared in Example 2; all other parameters and conditions are the same as in Example 4.

[0058] Example 10

[0059] The difference from Example 9 is that the isothermal treatment temperature is changed to 150°C; all other parameters and conditions are the same as in Example 9.

[0060] Example 11

[0061] The difference from Example 9 is that the isothermal treatment temperature is changed to 180°C; all other parameters and conditions are the same as in Example 9.

[0062] Example 12

[0063] The difference from Example 9 is that the isothermal treatment temperature is changed to 200°C; all other parameters and conditions are the same as in Example 9.

[0064] Example 13

[0065] The difference from Example 9 is that the isothermal treatment temperature is changed to 220°C; all other parameters and conditions are the same as in Example 9.

[0066] Example 14

[0067] The difference from Example 4 is that the menthol / benzoic acid eutectic solvent prepared in Example 1 is changed to the menthol / benzoic acid eutectic solvent prepared in Example 3; all other parameters and conditions are the same as in Example 4.

[0068] Example 15

[0069] The difference from Example 14 is that the isothermal treatment temperature is changed to 150°C; all other parameters and conditions are the same as in Example 14.

[0070] Example 16

[0071] The difference from Example 14 is that the isothermal treatment temperature is changed to 180°C; all other parameters and conditions are the same as in Example 14.

[0072] Example 17

[0073] The difference from Example 14 is that the isothermal treatment temperature is changed to 200°C; all other parameters and conditions are the same as in Example 14.

[0074] Example 18

[0075] The difference from Example 14 is that the isothermal treatment temperature is changed to 220°C; all other parameters and conditions are the same as in Example 14.

[0076] Example 19

[0077] This embodiment discloses a method for treating wool fibers with a menthol / benzoic acid eutectic solvent, including the following steps:

[0078] Wool fibers were placed in the menthol / benzoic acid eutectic solvent prepared in Example 2 at a bath ratio of 1:40 and treated at 220°C for 30 min. After treatment, the undissolved components were separated and recovered, washed with ethanol, and vacuum dried at 60°C to constant weight.

[0079] Example 20

[0080] This embodiment discloses a method for selectively dissolving polyester and recovering wool fibers, including the following steps:

[0081] The polyester / wool blended fabric was placed in the menthol / benzoic acid eutectic solvent prepared in Example 2 at a bath ratio of 1:40 and treated at 220°C for 30 min. The undissolved components were separated and recovered, washed with ethanol, and vacuum dried at 60°C to constant weight.

[0082] In the polyester / wool blended fabric, the mass ratio of polyester to wool is 3:7.

[0083] Example 21

[0084] The difference from Example 20 is that the mass ratio of polyester to wool in the polyester / wool blended fabric is changed to 5:5; all other parameters and conditions are the same as in Example 20.

[0085] Example 22

[0086] The difference from Example 20 is that the mass ratio of polyester to wool in the polyester / wool blended fabric is changed to 4:6; all other parameters and conditions are the same as in Example 20.

[0087] Comparative Example 1

[0088] The difference from Example 1 is that the molar ratio of menthol to benzoic acid is changed to 1:1; the melting temperature is changed to 100°C; and other parameters and conditions are the same as in Example 1.

[0089] Comparative Example 2

[0090] The difference from Example 13 is that the eutectic solvent of menthol / benzoic acid is changed to the eutectic solvent of menthol / ethylene glycol, and the molar ratio of menthol to ethylene glycol is 1:1; all other parameters and conditions are the same as in Example 13.

[0091] Comparative Example 3

[0092] The difference from Example 13 is that the eutectic solvent of menthol / benzoic acid is changed to the eutectic solvent of choline chloride / ethylene glycol, and the molar ratio of choline chloride to ethylene glycol is 1:2; all other parameters and conditions are the same as in Example 13.

[0093] Comparative Example 4

[0094] The difference from Example 13 is that the eutectic solvent of menthol / benzoic acid is changed to the eutectic solvent of choline chloride / benzoic acid, and the molar ratio of choline chloride to benzoic acid is 1:1; all other parameters and conditions are the same as in Example 13.

[0095] Experimental data characterization and performance testing

[0096] (1) Physical properties, stability evaluation and structural characterization of menthol / benzoic acid eutectic solvent;

[0097] Stability is crucial in studying the solubility of eutectic solvents (DES), determining whether dissolution can proceed smoothly and uniformly. The menthol / benzoic acid DES prepared in Examples 1-3 and Comparative Example 1 were tested for appearance and room-temperature physical state. The test method involved placing each sample at room temperature (25°C) and observing and recording its phase, color, transparency, and fluidity. The time at which crystallization, precipitation, or solidification began was used as the key criterion for room-temperature stability. Specific test results are detailed below. Figure 1 ;

[0098] Depend on Figure 1As shown, when the molar ratio of menthol to benzoic acid is 1:1, the menthol / benzoic acid eutectic solvent prepared in Comparative Example 1 is liquid at 100°C, with a yellowish and slightly turbid color and good fluidity, but it is extremely unstable at room temperature and solidifies rapidly. When the molar ratio of menthol to benzoic acid is 2:1, the menthol / benzoic acid eutectic solvent prepared in Example 1 is a colorless, transparent, and clear liquid with good fluidity, but it solidifies in about 40 seconds at room temperature, exhibiting poor stability. When the molar ratio of menthol to benzoic acid is 3:1, the menthol / benzoic acid eutectic solvent prepared in Example 2 is a colorless, transparent, and clear liquid with good fluidity. It remains stable at room temperature for 60 minutes, after which crystallization begins to occur, but it exhibits the best overall stability. When the molar ratio of menthol to benzoic acid is 4:1, the menthol / benzoic acid eutectic solvent prepared in Example 3 is a colorless, transparent liquid containing small particles, with good fluidity, but it begins to solidify in about 20 minutes at room temperature.

[0099] In summary, after comprehensively comparing the room temperature stability and appearance uniformity of various eutectic solvent ratios, the eutectic solvent system with a molar ratio of menthol to benzoic acid of 3:1 was determined to be the preferred system for subsequent separation processes and performance verification experiments.

[0100] The Fourier transform infrared spectrum of the menthol / benzoic acid eutectic solvent prepared in Example 2 was measured. Figure 2 As shown, in the range of 4000-3000cm - Within the wavenumber range¹, the –OH stretching vibration absorption peak of Example 2 shows a significant shift (redshift) towards lower wavenumbers compared to menthol or benzoic acid alone; simultaneously, at 3700 cm⁻¹… - ¹ The vibrational peaks near the free –OH group are significantly weakened; the changes in peak shape and position demonstrate that during DES formation, strong and extensive hydrogen bonding occurs between the –OH groups of menthol and benzoic acid, forming a continuous multi-center hydrogen bond network structure. This is a typical characteristic of eutectic solvent formation and provides a structural basis for its subsequent functional applications.

[0101] (2) Evaluation of the solubility performance of eutectic solvents on polyester and analysis of the solubility mechanism;

[0102] To investigate the dissolution behavior and mechanism of menthol / benzoic acid eutectic solvent on polyester fibers, the dissolution effect of different ratios of menthol / benzoic acid eutectic solvent in Examples 4-18 on pure polyester fabrics at different temperatures was tested, and corresponding spectroscopic characterization was performed. Specific test results are as follows: Figures 3-5 As shown;

[0103] according to Figure 3The test results show that, within the experimental temperature range, the solubility of polyester in all the eutectic solvent systems used in Examples 4-18 increases significantly with increasing temperature, exhibiting a strong temperature dependence.

[0104] Of particular note is that, under the same dissolution conditions, Examples 9-13 used the eutectic solvent system prepared in Example 2 with a molar ratio of menthol to benzoic acid of 3:1. This menthol / benzoic acid eutectic solvent system exhibited optimal polyester dissolution performance, especially at high temperatures where its dissolution efficiency was most significantly improved. At 220°C, this system could achieve complete dissolution of polyester within 30 minutes (100% dissolution rate), which was significantly higher than the 4:1 ratio used in Examples 14-18 (62% dissolution rate) and the 2:1 ratio used in Examples 4-8 (52% dissolution rate). This result is consistent with the aforementioned evaluation of the stability of the menthol / benzoic acid eutectic solvent system, further demonstrating that the 3:1 molar ratio of menthol to benzoic acid in the eutectic solvent system achieves the best balance between solvation capacity, system viscosity, and mass transfer efficiency, making it the preferred system for achieving efficient dissolution.

[0105] Figure 4 This is a sample image showing the dissolution process of the polyester fabric in Example 13. From... Figure 4 It can also be clearly seen that at 220℃, polyester fabric can be quickly dissolved in a eutectic solvent with a molar ratio of menthol to benzoic acid of 3:1. After 8 minutes, the morphology of the fabric changed significantly. After 15 minutes, the fabric was almost completely dissolved and it was impossible to remove the formed fabric fragments. After 30 minutes, the polyester fabric was completely dissolved and became a uniform, clear, transparent, slightly yellow solution.

[0106] To investigate whether the effect of eutectic solvents on the dissolution of polyester (PET) is physical swelling and dissolution or chemical depolymerization, Fourier transform infrared (FTIR) spectroscopy analysis was performed on samples treated using the method in Example 13 (treated at 220°C with a eutectic solvent containing menthol and benzoic acid in a molar ratio of 3:1). The results were compared with the original PET raw material spectrum. Figure 5 As shown.

[0107] according to Figure 5 The test results show that the original PET has been depolymerized and dissolved, and its ester bonds are at 1715 cm⁻¹. -1 The characteristic absorption peak at 3064 cm⁻¹ disappears; based on the infrared spectrum of the depolymerized small molecule, its characteristic absorption peak at 3064 cm⁻¹ disappears. -1 The absorption peak at 1685 cm⁻¹ corresponds to the stretching vibration peak of carboxylic acid -OH. -1 The absorption peaks at 1293 cm⁻¹ are due to the stretching vibration of the C=O bond (νC=O) and the peaks at 1293 cm⁻¹. -1The stretching vibration peaks of the CO bond in the carboxylic acid are consistent with the terephthalic acid spectrum reported in the literature, which can be preliminarily identified as terephthalic acid, indicating that the eutectic solvent has a directional depolymerization effect on the ester bonds of PET macromolecules.

[0108] In conclusion, Figure 5 Spectroscopic analysis results show that, under the preferred eutectic solvent system (menthol to benzoic acid molar ratio of 3:1) and dissolution conditions of 220°C for 30 min, the PET macromolecular backbone undergoes directional depolymerization. This dissolution process is mainly attributed to the strong penetration, swelling, and even disintegration of the aggregated structure of the PET molecular chains by the eutectic solvent, dispersing them in the solvent and directional chemical depolymerization of the ester bonds in the PET macromolecular chains. This directional depolymerization characteristic, primarily targeting the directional ester bonds of the PET macromolecules, results in fewer product types after depolymerization, which is crucial for subsequent gentle separation from wool fibers.

[0109] To compare the differences in the solubility of different types of eutectic solvents on polyester fibers, the solubility effects of different types of eutectic solvents in Example 13 and Comparative Examples 2-4 on pure polyester fabrics were tested at a preferred temperature of 220°C. Specific test results are as follows: Figure 6 As shown;

[0110] according to Figure 6 The test results show that among the four eutectic solvent systems, menthol / benzoic acid (3:1) exhibits the best solubility, with a solubility of 100%, significantly higher than menthol / ethylene glycol (1:1, solubility of 4%), choline chloride / ethylene glycol (1:2, solubility of 10.8%), and choline chloride / benzoic acid (1:1, solubility of 9.1%). This indicates that the eutectic solvent formed by menthol and benzoic acid has a stronger solubility for polyester target materials under the conditions of this invention. Therefore, menthol / benzoic acid (3:1) was selected as the optimal eutectic solvent system for further research in subsequent experiments.

[0111] (3) Analysis of the stability and recyclability of wool fiber fabrics in eutectic solvents;

[0112] To verify the protective effect of the menthol / benzoic acid eutectic solvent system on the wool component in polyester / wool blended fabrics and to evaluate the reuse value of recycled wool, the effect of the treatment method described in Example 19 on pure wool fabrics was studied. The recovery rate of wool fibers was calculated, and the structure and properties of the recycled wool fibers were characterized. Specific test results are as follows: Figures 7-9 As shown;

[0113] The wool fiber recovery rate (η) is calculated using the following formula:

[0114] η = (W1 / W0) × 100%

[0115] W0 represents the mass of the wool fabric before treatment, and W1 represents the oven-dry mass of the recycled wool fibers after treatment.

[0116] like Figure 7 As shown, wool fibers cannot be dissolved in the menthol / benzoic acid eutectic solvent, and the wool exhibits felting and shrinkage, while its surface color changes. After taking the average value of three parallel experiments, the recovery rate of wool fibers under these conditions is as high as 85.2%, proving that the menthol / benzoic acid eutectic solvent system has excellent preservation ability for wool components.

[0117] like Figure 8 As shown, the surface morphology of wool fibers before and after treatment was observed using a super depth-of-field 3D microscope. Figure 8 (a)(b) show that the surface of the untreated virgin wool fibers has a clear and intact scaly structure. Wool fibers recovered after treatment with a menthol / benzoic acid eutectic solvent (…) Figure 8 (c)(d) The scale outlines on its surface are still visible, and the structure is basically preserved, with only the edges slightly blurred. This indicates that under the process conditions set in this invention, the chemical erosion effect of the menthol / benzoic acid eutectic solvent on wool fiber keratin is very limited, and it does not cause serious epidermal layer erosion or structural collapse. Morphologically, this confirms its "slight damage" characteristic, providing a structural basis for subsequent spinning and reuse.

[0118] The changes in the ordered internal structure of the wool fibers before and after treatment were further analyzed using X-ray diffraction, as shown in the spectrum. Figure 9 As shown, the XRD patterns of both virgin and recycled wool exhibit typical broad diffraction peaks characteristic of keratin fibers at 2θ ≈ 9–10° (corresponding to the characteristic diffraction of the α-helix structure) and 2θ ≈ 20–22° (corresponding to the diffuse scattering of the β-sheet and amorphous regions). This result indicates that the basic secondary structural framework (α-helix and β-sheet conformations) of recycled wool fibers remains intact. However, the diffraction peak shape and relative intensity of the recycled wool samples changed somewhat in the 20–22° range, suggesting that the degree of order in molecular chain stacking, crystallite size, or the ratio of crystalline to amorphous regions may have undergone local rearrangement and adjustment due to the swelling and penetration of the eutectic solvent menthol / benzoic acid, but without drastic denaturation leading to the loss of the fiber's basic properties.

[0119] Based on the analysis of the recovery rate, morphology, and structure of wool fiber fabrics, the preferred eutectic solvent system of menthol and benzoic acid in the present invention (molar ratio of 3:1) can effectively protect wool fibers within the same process window for achieving efficient dissolution of polyester, thus maintaining a high recovery rate and a basically intact fiber structure. This provides technical support for the selective and high-value separation and recovery of polyester / wool blended fabrics.

[0120] (4) Verification of the separation and recycling performance of polyester / wool blended fabrics with different proportions;

[0121] To evaluate the universality and process stability of the menthol / benzoic acid eutectic solvent system described in this invention, the separation and recovery effects of polyester / wool blended fabrics with different mass ratios were tested using the methods described in Examples 20-22. By treating a series of blended samples with different compositions under optimized process conditions, the method's ability to completely remove the polyester component and its efficient retention of the wool component were quantitatively and qualitatively verified. Specific test results are as follows: Figures 10-13 As shown;

[0122] The recovery rate of wool fibers under different blending ratios is as follows: Figure 10 As shown. According to Figure 10 The test results show that for the 5:5 (polyester:wool) sample, the wool recovery rate was 81%; for the 4:6 (polyester:wool) sample, the wool recovery rate was 80%; and for the 3:7 (polyester:wool) sample, the wool recovery rate was 86%. After treatment, the polyester component was completely dissolved and removed from all blended fabrics, leaving no visual residue. The wool recovery rate showed a slight decreasing trend with increasing initial polyester content (proportion) in the blend, which may be related to the influence of higher concentrations of polyester depolymerization products on the microenvironment of the wool fibers, but overall it remained at a high level of over 80%. This fully demonstrates that the menthol / benzoic acid eutectic solvent system of this invention possesses efficient and stable selective separation capabilities for polyester / wool blended fabrics of different compositions.

[0123] like Figure 11 As shown in the polyester / wool dissolution flow chart, the polyester component was completely dissolved and removed, while the wool component exhibited felting shrinkage and a change in surface color; Figure 12 As shown, the separation and recycling effect of the polyester / wool blend fabric with a wool / polyester mass ratio of 7:3 in Example 22 was verified by taking ultra-depth-of-field images. Figure 12 As can be seen, the scale layer of the treated wool fiber still exists, indicating that the menthol / benzoic acid eutectic solvent system of the present invention causes slight damage to the wool fiber, which can be recycled in the future.

[0124] FTIR analysis was performed on wool fibers recycled from polyester / wool blends of different proportions. The spectra were compared with those of virgin wool. Figure 13 As shown. According to Figure 13 The test results show that the main chain structure is intact, and all recycled wool samples are within ~1630 cm. - ¹(amide I band, C=O stretching vibration) and ~1520 cm - ¹ (Amide II band, NH bending and CN stretching coupling vibration) retains distinct and sharp characteristic peaks, with only a very slight shift in peak position. This indicates that the peptide bond backbone of wool keratin did not undergo significant hydrolysis or breakage during DES treatment, and the primary structure of the protein was preserved intact. Changes in hydrogen bonding were observed in the recovered wool samples at ~3400 cm⁻¹. - The relatively enhanced intensity of the broad absorption bands near the fiber (attributable to the stretching vibrations of -OH and -NH) suggests that the hydrogen bond network within or on the fiber surface may have been reorganized or strengthened due to DES penetration and subsequent washing processes. Fingerprint analysis, after normalization, yielded spectra in the range of 1300–1000 cm⁻¹. - The relative intensity of the fingerprint region ¹ was somewhat weakened. This should be attributed to the removal of non-keratinous substances (such as lipids) on the fiber surface, changes in the water content, or thorough cleaning of residual solvents, rather than to a violent chemical reaction such as strong oxidation. At the same time, no significant enhancement of the characteristic peak of sulfonic acid group S=O was observed.

[0125] Based on the combined recovery rate and structural characterization data, the preferred eutectic solvent system (molar ratio of menthol to benzoic acid of 3:1) and process conditions (220°C, 30 min) of this invention are widely applicable to polyester / wool blended fabrics with different proportions. This technology can achieve near-complete dissolution and removal of the polyester component while simultaneously ensuring a high recovery rate of over 80% for the wool fibers, and effectively maintaining key characteristics such as the chemical structure and surface morphology of the keratin backbone. This verifies the reliability, universality, and high-value recovery potential of this separation method, providing a solid technical basis for treating complex waste blended fabrics.

[0126] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for selectively dissolving polyester and recovering wool fibers, characterized in that, Includes the following steps: Step (1): Mix menthol and benzoic acid, heat to melt, and cool to obtain a menthol / benzoic acid eutectic solvent; The molar ratio of menthol to benzoic acid is 2-4:

1. Step (2): Place the polyester / wool blended fabric in a eutectic solvent of menthol / benzoic acid and treat it at a constant temperature of 100-220℃ for 30-60 minutes. After the treatment, separate, wash, and dry to recover the undissolved components.

2. The method for selectively dissolving polyester and recovering wool fibers according to claim 1, characterized in that, In step (1), the molar ratio of menthol to benzoic acid is 3:

1.

3. The method for selectively dissolving polyester and recovering wool fibers according to claim 1, characterized in that, In step (1), the heating and melting conditions are: heating to 70-100℃ under stirring at a speed of 150-200r / min until a uniform and stable liquid phase is formed.

4. The method for selectively dissolving polyester and recovering wool fibers according to claim 1, characterized in that, In step (2), the bath ratio of polyester / wool blended fabric to menthol / benzoic acid eutectic solvent is 1:35-50.

5. The method for selectively dissolving polyester and recovering wool fibers according to claim 1, characterized in that, In step (2), the constant temperature treatment conditions are: constant temperature treatment at 220℃ for 30 minutes.

6. The method for selectively dissolving polyester and recovering wool fibers according to claim 1, characterized in that, In step (2), the mass ratio of polyester to wool in the polyester / wool blended fabric is 3:7 to 5:

5.

7. The application of a method for selectively dissolving polyester and recovering wool fibers as described in any one of claims 1-6 in the efficient and non-destructive recovery of wool fibers.

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