A low-energy consumption and rapid chemical separation method for polyester-cotton fiber products

Abstract

The present invention relates to the technical field of fiber product treatment, and discloses a low-energy consumption and rapid chemical separation method for polyester-cotton fiber products. The method comprises the following steps: mixing and dissolving a hydrogen bond donor and a hydrogen bond acceptor to prepare a betaine-based deep eutectic solvent, and mixing the betaine-based deep eutectic solvent with an alkali solution to obtain a deep eutectic solvent / alkali composite system; immersing the polyester-cotton product in the deep eutectic solvent / alkali composite system for a dissolution reaction, and after the reaction is completed, filtering, taking the undissolved components in the polyester-cotton product, washing with water, and drying; the method adopts a deep eutectic solvent / alkali composite system, realizes the dissolution of the polyester fiber component under mild conditions and in a short time, and has no damage to the cotton fiber component at the same time, has the advantages of low cost, environmental friendliness, etc., and realizes the rapid quantitative analysis of the two fiber components of polyester and cotton.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber product treatment, and particularly relates to a low-energy consumption and rapid chemical separation method for polyester-cotton fiber products. Background Art

[0002] Polyester-cotton fiber products include polyester-cotton interwoven / blended apparel fabrics, home textile fabrics, and industrial textiles. Such fiber products have excellent properties and can exhibit good elasticity, abrasion resistance, good dimensional stability, small shrinkage rate, strong wrinkle resistance, easy washing, and quick drying in both dry and humid environments, meeting the comprehensive market demands for the aesthetics, practicality, and comfort of textiles, and thus having a large market share. For this reason, more than 14 million tons of polyester-cotton fiber-based waste textiles need to be recycled globally every year, accounting for 60% or more of the total waste textiles. The key to the recycling problem of polyester-cotton fiber products lies in the rapid, efficient, and low-energy consumption separation of polyester and cotton fiber components, and then the high-value utilization of each component can be carried out.

[0003] Currently, the technical methods for recycling and reusing polyester-cotton fiber products include physical methods, chemical methods, biological methods, and modern spectroscopic methods. Physical methods are relatively simple to operate, but have low separation purity, low efficiency, and high requirements for equipment and processes; the microscopic observation method distinguishes polyester-cotton fibers by different appearance characteristics such as the cross-section of the fibers, and counts and measures the diameter to obtain the percentage content of each polyester-cotton component. However, this method requires professional operation, is easily affected by human factors, and is also time-consuming; although the density gradient centrifugation method has advantages such as good separation effect, wide application range, and good fiber integrity, the long centrifugation time, complex operation, and limited number of samples to be processed cannot be ignored.

[0004] The chemical method separates polyester-cotton fibers by acidolysis or alkaliolysis treatment, causing chemical reactions between the two fibers. However, it is difficult to achieve chemical reactions in only a single component, accompanied by more side reactions, making it difficult to completely separate. At the same time, the reactants are not easily recycled; for example, the current standard GB / T 2910—2006 "Quantitative Chemical Analysis of Textiles" specifically dissolves the cotton fiber component in polyester-cotton blended fabrics through sulfuric acid reagents to achieve quantitative analysis of the proportion between fibers. However, the standard requires a large amount of high-concentration sulfuric acid, and it is also found in actual operation that concentrated sulfuric acid will also dissolve and etch polyester fibers to a certain extent, affecting the accuracy of test results.

[0005] The biological method degrades cotton or polyester fibers by using specific enzymes without affecting the other component. This method has the advantages of mild reaction conditions and environmental friendliness, but the enzyme cost is high and the reaction time is long. Currently, it is still in the research and exploration stage.

[0006] The most commonly used method for testing components by modern spectroscopy is infrared spectroscopy. This method utilizes the absorption spectrum characteristics of different chemical substances under infrared light irradiation. By comparing the infrared spectra of the polyester-cotton fabric sample with those of known polyester-cotton standards, the components of polyester and cotton fibers in the polyester-cotton fabric can be determined. However, infrared spectroscopy also has drawbacks: limited sensitivity, many interfering factors, complex analysis, and difficulty in rapid quantification, etc. Summary of the Invention

[0007] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a low-energy consumption and rapid chemical separation method for polyester-cotton fiber products. This method adopts a betaine-based deep eutectic solvent / alkali composite system, which realizes the dissolution of polyester fiber components under mild conditions and in a short time, while causing no damage to the cotton fiber components. It has advantages such as low cost and environmental friendliness, and realizes the rapid quantitative analysis of the two fiber components of polyester and cotton.

[0008] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] A low-energy consumption and rapid chemical separation method for polyester-cotton fiber products, the method comprising the following steps:

[0010] Step (1): Add a hydrogen bond donor and a hydrogen bond acceptor into a reaction flask, stir and dissolve to prepare a betaine-based deep eutectic solvent;

[0011] Step (2): Add an alkali solution into the betaine-based deep eutectic solvent and mix to obtain a deep eutectic solvent / alkali composite system;

[0012] Step (3): Immerse the polyester-cotton product in the deep eutectic solvent / alkali composite system, carry out a dissolution reaction. After the reaction is completed, filter, take the undissolved components in the polyester-cotton product, wash with water, and dry.

[0013] Preferably, in the step (1): the hydrogen bond donor includes one of polyols and urea, and the hydrogen bond acceptor is betaine.

[0014] Further, in the step (1), the polyol includes one of glycerol and ethylene glycol.

[0015] Further, in the step (1), the polyol is preferably ethylene glycol.

[0016] Preferably, in the step (1): the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:2 - 4.

[0017] Preferably, in the step (1): the stirring and dissolving operation includes: stirring at 80 °C until completely dissolved, and then keeping warm and continuing to stir for not less than 30 min.

[0018] Preferably, in the step (2): the alkali solution is a sodium hydroxide solution with a concentration of 10 g / L - 50 g / L.

[0019] Preferably, in the step (2): the mass ratio of the lye to the betaine-based deep eutectic solvent is 1.5:30 - 50.

[0020] Preferably, in the step (2): the mixing condition is: stirring at 90 °C for 25 min until completely dissolved.

[0021] Preferably, in the step (3): the mass ratio of the polyester-cotton product to the deep eutectic solvent / alkali composite system is 1:30 - 50.

[0022] Preferably, in the step (3): the dissolution reaction condition is: dissolving and reacting at 58 - 108 °C for 30 - 120 min.

[0023] Preferably, a polyester-cotton fiber product is processed by using the low-energy consumption and rapid chemical separation method for polyester-cotton fiber products as described above.

[0024] Preferably, an application of the low-energy consumption and rapid chemical separation method for polyester-cotton fiber products as described above in the rapid quantitative analysis of the components of polyester-cotton fiber products.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] Deep eutectic solvents refer to two-component or three-component deep eutectic mixtures composed of a hydrogen bond acceptor (such as quaternary ammonium salts) and a hydrogen bond donor (such as amides, carboxylic acids, and polyols, etc.), and their freezing points are significantly lower than the melting points of the pure substances of each component. Among them, the betaine-based deep eutectic solvent prepared in the present invention is prepared by mixing betaine (as the hydrogen bond acceptor) and ethylene glycol (as the hydrogen bond donor) in a certain proportion, that is, a deep eutectic solvent.

[0027] After the polyester is hot-melt extruded, a dense film will be formed on its surface, and it is very difficult for a high-concentration lye to penetrate into the interior of the polyester fiber, and it can only act on the fiber surface layer. The betaine-based deep eutectic solvent can swell the fiber, and at a certain temperature, it can fibrillate the fiber, making the originally tight fiber become loose, destroying the dense film on the fiber surface, and then enabling the lye to enter the amorphous region of the fiber and act on the carbonyl group of the polyester fiber, causing the fiber to break and dissolve; while cotton fiber is a polysaccharide composed of glucose units through β-1,4-glycosidic bonds, and there are a large number of hydroxyl groups (-OH) on the cellulose molecular chain. These hydroxyl groups have certain chemical stability in an alkaline environment. In this system, alkali ions (Na + +) will act on the hydroxyl groups on the cellulose molecular chain, but this action is mainly ion exchange or the formation of a relatively loose complex structure, and does not destroy the β-1,4-glycosidic bond of the cotton fiber, and the cotton fiber can still maintain its basic fiber form.

[0028] When treating polyester-cotton fibers with betaine-based deep eutectic solvents alone, since the deep eutectic solvents can only act on the fiber surface, producing a weak chemical effect at the micro-nano scale and unable to enter the dense fiber interior, even when reacting at 80 - 100 °C for 12 h, the weight loss rate is only 5%. Therefore, the effect of dissolving polyester fibers with deep eutectic solvents alone is not ideal. On the other hand, if treating polyester-cotton fibers with lye alone, due to the high concentration of lye and the large viscosity of the solution, it can only adhere to the fiber surface and is difficult to quickly enter the interior of polyester fibers. Within 60 min of reacting at 80 - 100 °C, the weight loss rate of polyester fibers can only reach about 20%. So, the effect of treating polyester-cotton products with lye alone is also poor. In the present invention, when combining betaine-based deep eutectic solvents with lye, only by treating at 98 °C for 60 min can the polyester component in polyester-cotton fibers be completely dissolved. Thus, it can be seen that betaine-based deep eutectic solvents and lye have a synergistic effect when dissolving the polyester component in polyester-cotton fiber products.

[0029] Aiming at the problem that it is difficult to separate the components of existing polyester-cotton fiber products, the present invention adopts a betaine-based deep eutectic solvent / lye composite system. Through systematic optimization and analysis of process parameters, the dissolution of the polyester fiber component is achieved under mild conditions of 58 - 98 °C, and at the same time, the cotton fiber component is not damaged. The dissolution separation temperature and the dissolution separation duration save time compared with the current GB / T2910 - 2006 standard (sulfuric acid method). At the same time, the deep eutectic solvent / lye composite system adopted in the present invention also has advantages such as low cost and environmental friendliness. Compared with the required temperature of 170 - 230 °C in the reported literature on polyester dissolution, the process of the present invention requires a lower temperature, milder conditions, and better effects.

[0030] In the present invention, the polyester fiber component in polyester-cotton fiber products can be dissolved and separated under mild conditions and in a short time. The betaine-based deep eutectic solvent / lye composite system has little effect on cotton fibers, and its mass loss can be controlled within 1.0%, enabling rapid quantitative analysis of the two fiber components of polyester and cotton, filling the technical gap in rapid quantitative analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is the dissolution mechanism diagram of the polyester component in the polyester-cotton fiber products of the present invention;

[0032] Figure 2 is the process flow diagram of the low-energy consumption and rapid chemical separation method for polyester-cotton fiber products of the present invention;

[0033] Figure 3 is the bar chart of the weight loss rate of the polyester-cotton fiber products after chemical separation obtained in Example 1 and Comparative Examples 1 - 7 of the present invention;

[0034] Figure 4It is the broken line graph of the weight loss rate of the polyester-cotton fiber products after chemical separation obtained in Examples 2-7 of the present invention;

[0035] Figure 5 It is the broken line graph of the weight loss rate of the polyester-cotton fiber products after chemical separation obtained in Example 6, Examples 8-9 and Comparative Example 8 of the present invention;

[0036] Figure 6 It is the dissolution sample graph of the polyester-cotton fiber products after chemical separation obtained in Example 6, Examples 8-9 and Comparative Example 8 of the present invention;

[0037] Figure 7 It is the infrared spectrum graph of the polyester-cotton fiber products after chemical separation obtained in Example 6, Examples 8-9 and Comparative Example 8 of the present invention;

[0038] Figure 8 It is the microscopic morphology graph of the polyester-cotton fiber products after chemical separation obtained in Example 6, Examples 8-9 and Comparative Example 8 of the present invention;

[0039] Figure 9 It is the bar graph of the weight loss rate of the polyester-cotton fiber products after chemical separation obtained by repeating the experiment 20 times under the same parameters and conditions as in Example 6 of the present invention;

[0040] Figure 10 It is the infrared spectrum graph of the product of the degradation and recovery of the polyester component in the present invention;

[0041] In the figure:

[0042] Figure 4 In it, 1 is the weight loss rate of the polyester-cotton fiber product after the reaction; 2 is the mass of the product of the degradation and recovery of the polyester component;

[0043] Figure 5 In it, 3 is the dissolution rate of the polyester component; 4 is the mass of the product of the degradation and recovery of the polyester component;

[0044] Figure 6 、 Figure 7 、 Figure 8 In, a is the polyester-cotton fiber product after being treated for 0 min; b is the polyester-cotton fiber product after being treated for 30 min; c is the polyester-cotton fiber product after being treated for 60 min; d is the polyester-cotton fiber product after being treated for 120 min. Detailed implementation manners

[0045] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0046] Example 1

[0047] This example discloses a low - energy - consumption and rapid chemical separation method for polyester - cotton fiber products. The composite system used is the Bet / EG / NaOH composite system. The method includes the following steps:

[0048] Step (1): Add betaine (Bet) and ethylene glycol (EG) into a reaction flask in a molar ratio of 1:2. Stir at 80 °C until completely dissolved, then keep warm and continue stirring for no less than 30 min to obtain a clear and transparent solution, which is the synthesized betaine / ethylene glycol eutectic solvent.

[0049] Step (2): Add the alkali solution to the betaine / ethylene glycol eutectic solvent under stirring conditions. Stir at 90 °C for 25 min until completely dissolved. The mass ratio of the alkali solution to the betaine / ethylene glycol eutectic solvent is 1.5:30. The alkali solution is a sodium hydroxide (NaOH) solution with a concentration of 50 g / L to obtain the eutectic solvent / alkali composite system.

[0050] Step (3): Immerse the polyester - cotton product in the eutectic solvent / alkali composite system. The mass ratio of the polyester - cotton product to the eutectic solvent / alkali composite system is 1:30. Carry out a dissolution reaction at 85 °C for 30 min. After the reaction, filter, take the undissolved components in the polyester - cotton product, wash them thoroughly with deionized water, and dry them to a constant weight.

[0051] Example 2

[0052] This example discloses a low - energy - consumption and rapid chemical separation method for polyester - cotton fiber products. The composite system used is the Bet / EG / NaOH composite system. The method includes the following steps:

[0053] Step (1): Add betaine (Bet) and ethylene glycol (EG) into a reaction flask in a molar ratio of 1:2. Stir at 80 °C until completely dissolved, then keep warm and continue stirring for no less than 30 min to obtain a clear and transparent solution, which is the synthesized betaine / ethylene glycol eutectic solvent.

[0054] Step (2): Add the alkali solution to the betaine / ethylene glycol eutectic solvent under stirring conditions. Stir at 90 °C for 25 min until completely dissolved. The mass ratio of the alkali solution to the betaine / ethylene glycol eutectic solvent is 1:30. The alkali solution is a sodium hydroxide (NaOH) solution with a concentration of 50 g / L to obtain the eutectic solvent / alkali composite system.

[0055] Step (3): Immerse the polyester-cotton product in the eutectic solvent / alkali composite system. The mass ratio of the polyester-cotton product to the eutectic solvent / alkali composite system is 1:30. Carry out a dissolution reaction at 58 °C for 60 min. After the reaction is completed, filter, take the undissolved components in the polyester-cotton product, wash them thoroughly with deionized water, and dry to a constant weight.

[0056] Example 3

[0057] This example discloses a low-energy consumption and rapid chemical separation method for polyester-cotton fiber products. The composite system used is the Bet / EG / NaOH composite system. The method includes the following steps:

[0058] Step (1): Add betaine (Bet) and ethylene glycol (EG) to a reaction flask in a molar ratio of 1:2. Stir at 80 °C until completely dissolved, and then keep stirring for at least 30 min while maintaining the temperature. A clear and transparent solution is obtained, which is the synthesized betaine / ethylene glycol eutectic solvent.

[0059] Step (2): Add the alkali solution to the betaine / ethylene glycol eutectic solvent under stirring conditions. Stir at 90 °C for 25 min until completely dissolved. The mass ratio of the alkali solution to the betaine / ethylene glycol eutectic solvent is 1.5:30. The alkali solution is a sodium hydroxide (NaOH) solution with a concentration of 50 g / L to obtain the eutectic solvent / alkali composite system.

[0060] Step (3): Immerse the polyester-cotton product in the eutectic solvent / alkali composite system. The mass ratio of the polyester-cotton product to the eutectic solvent / alkali composite system is 1:30. Carry out a dissolution reaction at 68 °C for 60 min. After the reaction is completed, filter, take the undissolved components in the polyester-cotton product, wash them thoroughly with deionized water, and dry to a constant weight.

[0061] Example 4

[0062] This example discloses a low-energy consumption and rapid chemical separation method for polyester-cotton fiber products. The composite system used is the Bet / EG / NaOH composite system. The method includes the following steps:

[0063] Step (1): Add betaine (Bet) and ethylene glycol (EG) to a reaction flask in a molar ratio of 1:2. Stir at 80 °C until completely dissolved, and then keep stirring for at least 30 min while maintaining the temperature. A clear and transparent solution is obtained, which is the synthesized betaine / ethylene glycol eutectic solvent.

[0064] Step (2): Add the lye into the betaine / ethylene glycol eutectic solvent under stirring conditions, stir at 90 °C for 25 min until completely dissolved. The mass ratio of the lye to the betaine / ethylene glycol eutectic solvent is 1.5:30. The lye is a sodium hydroxide (NaOH) solution with a concentration of 50 g / L to obtain a eutectic solvent / alkali composite system;

[0065] Step (3): Immerse the polyester-cotton product in the eutectic solvent / alkali composite system. The mass ratio of the polyester-cotton product to the eutectic solvent / alkali composite system is 1:30. Carry out a dissolution reaction at 78 °C for 60 min. After the reaction is completed, filter, take the undissolved components in the polyester-cotton product, wash them thoroughly with deionized water, and dry to a constant weight.

[0066] Example 5

[0067] This example discloses a low-energy consumption and rapid chemical separation method for polyester-cotton fiber products. The composite system used is the Bet / EG / NaOH composite system. The method includes the following steps:

[0068] Step (1): Add betaine (Bet) and ethylene glycol (EG) into a reaction flask at a molar ratio of 1:2, stir at 80 °C until completely dissolved, and then keep stirring for at least 30 min while maintaining the temperature to obtain a clear and transparent solution, which is the synthesized betaine / ethylene glycol eutectic solvent;

[0069] Step (2): Add the lye into the betaine / ethylene glycol eutectic solvent under stirring conditions, stir at 90 °C for 25 min until completely dissolved. The mass ratio of the lye to the betaine / ethylene glycol eutectic solvent is 1.5:30. The lye is a sodium hydroxide (NaOH) solution with a concentration of 50 g / L to obtain a eutectic solvent / alkali composite system;

[0070] Step (3): Immerse the polyester-cotton product in the eutectic solvent / alkali composite system. The mass ratio of the polyester-cotton product to the eutectic solvent / alkali composite system is 1:30. Carry out a dissolution reaction at 88 °C for 60 min. After the reaction is completed, filter, take the undissolved components in the polyester-cotton product, wash them thoroughly with deionized water, and dry to a constant weight.

[0071] Example 6

[0072] This example discloses a low-energy consumption and rapid chemical separation method for polyester-cotton fiber products. The composite system used is the Bet / EG / NaOH composite system. The method includes the following steps:

[0073] Step (1): Add betaine (Bet) and ethylene glycol (EG) into a reaction flask in a molar ratio of 1:2. Stir at 80 °C until completely dissolved, then keep stirring for at least 30 min while maintaining the temperature to obtain a clear and transparent solution, which is the synthesized betaine / ethylene glycol eutectic solvent.

[0074] Step (2): Add the alkali solution to the betaine / ethylene glycol eutectic solvent under stirring conditions. Stir at 90 °C for 25 min until completely dissolved. The mass ratio of the alkali solution to the betaine / ethylene glycol eutectic solvent is 1.5:30. The alkali solution is a sodium hydroxide (NaOH) solution with a concentration of 50 g / L to obtain a eutectic solvent / alkali composite system.

[0075] Step (3): Immerse the polyester-cotton product in the eutectic solvent / alkali composite system. The mass ratio of the polyester-cotton product to the eutectic solvent / alkali composite system is 1:30. Carry out a dissolution reaction at 98 °C for 60 min. After the reaction, filter, take the undissolved components in the polyester-cotton product, wash them thoroughly with deionized water, and dry to a constant weight.

[0076] Example 7

[0077] This example discloses a low-energy consumption and rapid chemical separation method for polyester-cotton fiber products. The composite system used is the Bet / EG / NaOH composite system. The method includes the following steps:

[0078] Step (1): Add betaine (Bet) and ethylene glycol (EG) into a reaction flask in a molar ratio of 1:2. Stir at 80 °C until completely dissolved, then keep stirring for at least 30 min while maintaining the temperature to obtain a clear and transparent solution, which is the synthesized betaine / ethylene glycol eutectic solvent.

[0079] Step (2): Add the alkali solution to the betaine / ethylene glycol eutectic solvent under stirring conditions. Stir at 90 °C for 25 min until completely dissolved. The mass ratio of the alkali solution to the betaine / ethylene glycol eutectic solvent is 1.5:30. The alkali solution is a sodium hydroxide (NaOH) solution with a concentration of 50 g / L to obtain a eutectic solvent / alkali composite system.

[0080] Step (3): Immerse the polyester-cotton product in the eutectic solvent / alkali composite system. The mass ratio of the polyester-cotton product to the eutectic solvent / alkali composite system is 1:30. Carry out a dissolution reaction at 108 °C for 60 min. After the reaction, filter, take the undissolved components in the polyester-cotton product, wash them thoroughly with deionized water, and dry to a constant weight.

[0081] Example 8

[0082] This embodiment discloses a low - energy - consumption and rapid chemical separation method for polyester - cotton fiber products. The composite system used is the Bet / EG / NaOH composite system. The method includes the following steps:

[0083] Step (1): Add betaine (Bet) and ethylene glycol (EG) into a reaction flask in a molar ratio of 1:2. Stir at 80 °C until completely dissolved, then keep warm and continue stirring for no less than 30 min to obtain a clear and transparent solution, which is the synthesized betaine / ethylene glycol eutectic solvent.

[0084] Step (2): Add the alkali solution to the betaine / ethylene glycol eutectic solvent under stirring conditions. Stir at 90 °C for 25 min until completely dissolved. The mass ratio of the alkali solution to the betaine / ethylene glycol eutectic solvent is 1.5:30. The alkali solution is a sodium hydroxide (NaOH) solution with a concentration of 50 g / L to obtain a eutectic solvent / alkali composite system.

[0085] Step (3): Immerse the polyester - cotton product in the eutectic solvent / alkali composite system. The mass ratio of the polyester - cotton product to the eutectic solvent / alkali composite system is 1:30. Carry out a dissolution reaction at 98 °C for 120 min. After the reaction ends, filter, take the undissolved components in the polyester - cotton product, wash them thoroughly with deionized water, and dry them to a constant weight.

[0086] Example 9

[0087] This embodiment discloses a low - energy - consumption and rapid chemical separation method for polyester - cotton fiber products. The composite system used is the Bet / EG / NaOH composite system. The method includes the following steps:

[0088] Step (1): Add betaine (Bet) and ethylene glycol (EG) into a reaction flask in a molar ratio of 1:2. Stir at 80 °C until completely dissolved, then keep warm and continue stirring for no less than 30 min to obtain a clear and transparent solution, which is the synthesized betaine / ethylene glycol eutectic solvent.

[0089] Step (2): Add the alkali solution to the betaine / ethylene glycol eutectic solvent under stirring conditions. Stir at 90 °C for 25 min until completely dissolved. The mass ratio of the alkali solution to the betaine / ethylene glycol eutectic solvent is 1.5:30. The alkali solution is a sodium hydroxide (NaOH) solution with a concentration of 50 g / L to obtain a eutectic solvent / alkali composite system.

[0090] Step (3): Immerse the polyester - cotton product in the eutectic solvent / alkali composite system. The mass ratio of the polyester - cotton product to the eutectic solvent / alkali composite system is 1:30. Carry out a dissolution reaction at 98 °C for 30 min. After the reaction ends, filter, take the undissolved components in the polyester - cotton product, wash them thoroughly with deionized water, and dry them to a constant weight.

[0091] Comparative Example 1

[0092] This comparative example discloses a low - energy - consumption and rapid chemical separation method for polyester - cotton fiber products. The composite system used is the Bet / Urea / NaOH composite system. The method includes the following steps:

[0093] Step (1): Add betaine (Bet) and urea (Urea) into a reaction flask at a molar ratio of 1:2. Stir at 80 °C until completely dissolved, then keep warm and continue stirring for no less than 30 min to obtain a clear and transparent solution, which is the synthesized betaine / urea eutectic solvent;

[0094] Step (2): Add the alkali solution to the betaine / urea eutectic solvent under stirring conditions. Stir at 90 °C for 25 min until completely dissolved. The mass ratio of the alkali solution to the betaine / urea eutectic solvent is 1.5:30. The alkali solution is a sodium hydroxide (NaOH) solution with a concentration of 50 g / L to obtain a eutectic solvent / alkali composite system;

[0095] Step (3): Immerse the polyester - cotton product in the eutectic solvent / alkali composite system. The mass ratio of the polyester - cotton product to the eutectic solvent / alkali composite system is 1:30. Carry out a dissolution reaction at 85 °C for 30 min. After the reaction, filter, take the undissolved components in the polyester - cotton product, wash them thoroughly with deionized water, and dry them to a constant weight.

[0096] Comparative Example 2

[0097] This comparative example discloses a low - energy - consumption and rapid chemical separation method for polyester - cotton fiber products. The composite system used is the Bet / Gly / NaOH composite system. The method includes the following steps:

[0098] Step (1): Add betaine (Bet) and glycerol (Gly) into a reaction flask at a molar ratio of 1:2. Stir at 80 °C until completely dissolved, then keep warm and continue stirring for no less than 30 min to obtain a clear and transparent solution, which is the synthesized betaine / glycerol eutectic solvent;

[0099] Step (2): Add the alkali solution to the betaine / glycerol eutectic solvent under stirring conditions. Stir at 90 °C for 25 min until completely dissolved. The mass ratio of the alkali solution to the betaine / glycerol eutectic solvent is 1.5:30. The alkali solution is a sodium hydroxide (NaOH) solution with a concentration of 50 g / L to obtain a eutectic solvent / alkali composite system;

[0100] Step (3): Immerse the polyester-cotton product in the eutectic solvent / alkali composite system. The mass ratio of the polyester-cotton product to the eutectic solvent / alkali composite system is 1:30. Carry out a dissolution reaction at 85 °C for 30 min. After the reaction ends, filter, take the undissolved components in the polyester-cotton product, wash them thoroughly with deionized water, and dry to a constant weight.

[0101] Comparative Example 3

[0102] This comparative example discloses a low-energy consumption and rapid chemical separation method for polyester-cotton fiber products. The composite system used is the Bet / NaOH composite system. The method includes the following steps:

[0103] Step (1): Add the alkali solution to betaine (Bet) under stirring conditions, stir at 90 °C for 25 min until completely dissolved. The mass ratio of the alkali solution to betaine is 1:2. The alkali solution is a sodium hydroxide (NaOH) solution with a concentration of 50 g / L to obtain a betaine / alkali composite system;

[0104] Step (2): Immerse the polyester-cotton product in the betaine / alkali composite system. The mass ratio of the polyester-cotton product to the betaine / alkali composite system is 1:30. Carry out a dissolution reaction at 85 °C for 30 min. After the reaction ends, filter, take the undissolved components in the polyester-cotton product, wash them thoroughly with deionized water, and dry to a constant weight.

[0105] Comparative Example 4

[0106] This comparative example discloses a low-energy consumption and rapid chemical separation method for polyester-cotton fiber products. The composite system used is the Urea / NaOH composite system. The method includes the following steps:

[0107] Step (1): Add the alkali solution to urea (Urea) under stirring conditions, stir at 90 °C for 25 min until completely dissolved. The mass ratio of the alkali solution to urea is 1:2. The alkali solution is a sodium hydroxide (NaOH) solution with a concentration of 50 g / L to obtain a urea / alkali composite system;

[0108] Step (3): Immerse the polyester-cotton product in the urea / alkali composite system. The mass ratio of the polyester-cotton product to the urea / alkali composite system is 1:30. Carry out a dissolution reaction at 85 °C for 30 min. After the reaction ends, filter, take the undissolved components in the polyester-cotton product, wash them thoroughly with deionized water, and dry to a constant weight.

[0109] Comparative Example 5

[0110] This comparative example discloses a low-energy consumption and rapid chemical separation method for polyester-cotton fiber products. The composite system used is the Gly / NaOH composite system. The method includes the following steps:

[0111] Step (1): Add the lye into glycerol (Gly) under stirring conditions, stir at 90 °C for 25 min until completely dissolved. The mass ratio of the lye to glycerol is 1:2, and the lye is a sodium hydroxide (NaOH) solution with a concentration of 50 g / L to obtain a glycerol / lye composite system.

[0112] Step (2): Immerse the polyester-cotton product in the glycerol / lye composite system. The mass ratio of the polyester-cotton product to the glycerol / lye composite system is 1:30. Carry out a dissolution reaction at 85 °C for 30 min. After the reaction ends, filter, take the undissolved components in the polyester-cotton product, wash them thoroughly with deionized water, and dry them to a constant weight.

[0113] Comparative Example 6

[0114] This comparative example discloses a low-energy consumption and rapid chemical separation method for polyester-cotton fiber products. The composite system used is the Bet / EG composite system. The method includes the following steps:

[0115] Step (1): Add betaine (Bet) and ethylene glycol (EG) into a reaction flask in a molar ratio of 1:2, stir at 80 °C until completely dissolved, and then keep warm and continue to dissolve for not less than 30 min to obtain a clear and transparent solution, which is the synthesized betaine / ethylene glycol eutectic solvent.

[0116] Step (3): Immerse the polyester-cotton product in the betaine / ethylene glycol eutectic solvent. The mass ratio of the polyester-cotton product to the betaine / ethylene glycol eutectic solvent is 1:30. Carry out a dissolution reaction at 85 °C for 30 min. After the reaction ends, filter, take the undissolved components in the polyester-cotton product, wash them thoroughly with deionized water, and dry them to a constant weight.

[0117] Comparative Example 7

[0118] This comparative example discloses a low-energy consumption and rapid chemical separation method for polyester-cotton fiber products. The composite system used is the EG / NaOH composite system. The method includes the following steps:

[0119] Step (1): Add the lye into ethylene glycol (EG) under stirring conditions, stir at 90 °C for 25 min until completely dissolved. The mass ratio of the lye to ethylene glycol is 1:2, and the lye is a sodium hydroxide (NaOH) solution with a concentration of 50 g / L to obtain an ethylene glycol / lye composite system.

[0120] Step (3): Immerse the polyester-cotton product in the ethylene glycol / lye composite system. The mass ratio of the polyester-cotton product to the ethylene glycol / lye composite system is 1:30. Carry out a dissolution reaction at 85 °C for 30 min. After the reaction ends, filter, take the undissolved components in the polyester-cotton product, wash them thoroughly with deionized water, and dry them to a constant weight.

[0121] Comparative Example 8

[0122] This comparative example discloses a low-energy consumption and rapid chemical separation method for polyester-cotton fiber products. The method comprises the following steps:

[0123] Step (1): Add betaine and ethylene glycol into a reaction flask at a molar ratio of 1:2, stir at 90 °C for 25 min until completely dissolved, after stirring at 80 °C until completely dissolved, keep warm and continue to dissolve for not less than 30 min to obtain a clear and transparent solution, which is the synthesized betaine / ethylene glycol eutectic solvent;

[0124] Step (2): Add the alkali solution into the betaine / ethylene glycol eutectic solvent under stirring conditions. The mass ratio of the alkali solution to the betaine / ethylene glycol eutectic solvent is 1.5:30, and the alkali solution is a sodium hydroxide solution with a concentration of 50 g / L to obtain a eutectic solvent / alkali composite system;

[0125] Step (3): Immerse the polyester-cotton product in the eutectic solvent / alkali composite system. The mass ratio of the polyester-cotton product to the eutectic solvent / alkali composite system is 1:30, carry out a dissolution reaction at 98 °C for 0 min. After the reaction ends, filter, take the undissolved components in the polyester-cotton product, wash them thoroughly with deionized water, and dry them to a constant weight.

[0126] Test example

[0127] (1) As Figure 3 、 Figure 4 shown, calculate the weight loss rates of the polyester-cotton fiber products obtained after chemical separation in Examples 1-7 and Comparative Examples 1-7. The specific test results are shown in Table 1:

[0128] Table 1

[0129] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Weight loss rate (%) 68.35 14.0 29.2 46.6 65.0 80.5 84.7 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Weight loss rate (%) 41.60 52.33 3.70 12.80 31.10 14.21 23.33

[0130] According to the test results in Table 1, it can be seen that the betaine / ethylene glycol eutectic solvent / alkali composite system in Example 1, Example 6, and Example 7 has high efficiency in degrading the polyester component in polyester-cotton. When chemically separating polyester-cotton fiber products, the maximum weight loss rate can reach 84.7%. Among them, under the conditions of the same temperature and dissolution reaction time, the weight loss rate of Example 1 is 68.35%. Compared with Comparative Example 1 and Comparative Example 2 with different hydrogen bond acceptors and hydrogen bond donors, the weight loss rates are increased by 26.75% and 16.02% respectively; compared with Comparative Example 3 and Comparative Example 4 of the composite system lacking the hydrogen bond donor polyol, the weight loss rates are increased by 64.65% and 55.55% respectively; compared with Comparative Example 5 and Comparative Example 7 of the composite system lacking the hydrogen bond acceptor betaine or urea, the weight loss rates are increased by 37.25% and 45.02% respectively; compared with Comparative Example 6 of the composite system lacking alkali solution, the weight loss rate is increased by 54.14%. In summary, the betaine / ethylene glycol eutectic solvent / alkali composite system used in Example 1 has significant advantages in degrading the polyester component in polyester-cotton. The principle is that the betaine-based eutectic solvent can swell the fiber, and at a certain temperature, it can fibrillate the fiber, making the originally tight fiber become loose, destroying the dense film on the fiber surface, and then enabling the alkali solution to enter the amorphous region of the fiber and act on the carbonyl group of the polyester fiber, causing the fiber to break and dissolve.

[0131] In Comparative Example 1, since the betaine, urea, and sodium hydroxide system is adopted, compared with the best example, although urea participates in the chemical reaction to a certain extent, its reactivity with polyester is relatively weak. In this system, betaine and urea mainly synergistically promote the degradation process of polyester through the alkaline environment jointly created with sodium hydroxide; however, the effect of this synergistic effect is not as good as that shown by the combination of betaine, ethylene glycol, and sodium hydroxide; therefore, the weight loss rate in Comparative Example 1 is lower than that of the best example.

[0132] In Comparative Example 2, since the betaine, glycerol, and sodium hydroxide system is adopted, compared with the best example, due to the relatively large size of glycerol molecules and certain steric hindrance, it is relatively difficult to penetrate into the crystalline region, and the ability to destroy the crystalline region is not as strong as that of ethylene glycol; at the same time, due to this steric hindrance, when it synergistically acts with betaine and sodium hydroxide to attack the carbonyl group on polyester, the resulting effect is not as good as that of the best example; therefore, the weight loss rate in Comparative Example 2 is lower than that of the best example.

[0133] The composite systems used in Comparative Examples 3 - 7 can only act on the surface of the polyester-cotton fiber products when treating them, resulting in incomplete dissolution of the polyester fibers, so the weight loss rate is lower than that of the best example; in summary, the polyester weight loss rates in Comparative Examples 1 - 7 are all lower than that of the best example.

[0134] From the test results in Table 1, it can be seen that according to Example 2, when the chemical separation of the polyester-cotton fiber product is carried out at a reaction temperature of 58°C, the weight loss rate of the polyester-cotton fiber product after chemical separation is 14.0%, which indicates that the reaction has started under this condition; from Examples 3-6, it can be seen that as the reaction temperature gradually increases, the weight loss rate of the polyester-cotton fiber product after chemical separation increases sharply, which proves that the increase in temperature is beneficial to the reaction proceeding in the positive direction and improves the reaction rate; from Example 7, it can be seen that when the reaction temperature reaches 108°C, the weight loss rate of the polyester-cotton fiber product after chemical separation is as high as 84.7%; however, compared with Example 6 with a reaction temperature of 98°C, the weight loss rate of Example 7 with a reaction temperature of 108°C does not increase significantly, which indicates that at a reaction temperature of 98°C, the polyester component in the polyester-cotton fiber product has approached or reached a state of complete degradation. Therefore, the optimal reaction temperature for the chemical separation of the polyester-cotton fiber product is 98°C.

[0135] (2), as Figure 5 , Figure 6 and Figure 7 show, infrared spectroscopy tests were carried out on the polyester-cotton fiber products after chemical separation obtained in Example 6, Examples 8-9 and Comparative Example 8; the dissolution rate of the polyester component in the polyester-cotton fiber products after chemical separation obtained in Example 6, Examples 8-9 and Comparative Example 8 was tested by the filtration and weighing method. The specific test results are shown in Table 2:

[0136] Table 2

[0137] Example 6 Example 8 Example 9 Comparative Example 8 Dissolution rate (%) 100 100 88.2 0

[0138] According to Table 2 and Figure 4 , Figure 5 and Figure 6From the test results, it can be seen that as shown in Comparative Example 8, when the reaction time is 0 min during the chemical separation of the polyester-cotton fiber product, the dissolution rate of the polyester component is 0%. As the reaction time gradually extends, as shown in Example 9, when the reaction time reaches 30 min, the polyester-cotton fiber product after chemical separation still retains the characteristic absorption peaks of cotton fibers and polyester fibers in the original sample. This indicates that within the treatment time of 30 min, the polyester fibers are not effectively removed. As the treatment time is further extended, as shown in Example 8, when the reaction time reaches 120 min, the dissolution rate of the polyester component decreases, and only the characteristic absorption peak of cotton fibers is shown in the polyester-cotton fiber product after chemical separation, indicating the complete removal of the polyester component. However, compared with Example 6 with a reaction time of 60 min, the dissolution rate of the polyester component in Example 8 with a reaction time of 120 min does not decrease significantly. This indicates that at a reaction time of 60 min, the polyester component in the polyester-cotton fiber product has been completely degraded. This is because the betaine-based deep eutectic solvent can cause the fibers to swell, fibrillate the fibers at a certain temperature, make the originally tight fibers become loose, and break the dense film on the fiber surface. Then, the lye can enter the amorphous region of the fibers and act on the carbonyl group of the polyester fibers, causing the fibers to break and dissolve. Cotton fibers are polysaccharides composed of glucose units through β-1,4-glycosidic bonds. There are a large number of hydroxyl groups (-OH) on the cellulose molecular chain. These hydroxyl groups have certain chemical stability in an alkaline environment. In this system, alkali ions (Na + )will act on the hydroxyl groups on the cellulose molecular chain, but this action is mainly ion exchange or the formation of a relatively loose complex structure, without breaking the β-1,4-glycosidic bond of the cotton fibers, and the cotton fibers can still maintain their basic fiber morphology. Therefore, when performing chemical separation on polyester-cotton fiber products, the optimal reaction time is 60 min.

[0139] (3). As Figure 8 shown, the polyester-cotton fiber products after chemical separation obtained in Example 6, Examples 8-9, and Comparative Example 8 were subjected to microscopic morphology tests using a VHX-970F ultra-depth-of-field three-dimensional microscope;

[0140] According to Figure 8From the test results, it can be seen that, as shown in Comparative Example 8, when the reaction time is 0 min during the chemical separation of the polyester-cotton fiber product, the polyester fibers and cotton fibers are tightly wound, and the polyester fibers are smooth and cylindrical; in contrast, the surface of the cotton fibers is relatively rough and flat. From Example 9, it can be seen that when the reaction time reaches 30 min, the originally tightly wound polyester fibers and cotton fibers start to become disordered and dispersed; from Example 6, it can be seen that when the reaction time is 60 min during the chemical separation of the polyester-cotton fiber product, the originally tightly wound polyester fibers and cotton fibers become even more disordered and dispersed, the smooth polyester fibers basically disappear, the thick cotton fibers are retained, and the cotton fibers maintain a good shape with basically no obvious cracks; from Example 8, it can be seen that when the reaction time is 120 min during the chemical separation of the polyester-cotton fiber product, the polyester-cotton fibers are only more dispersed, the fiber surface does not change, and only some wrinkling phenomena exist. Therefore, it can be concluded that the eutectic solvent / alkali composite system has little effect on cotton fibers, and the optimal reaction time for the chemical separation of polyester-cotton fiber products is 60 min.

[0141] (4), As Figure 9 shown, under the same parameters and conditions as in Example 6, the experiment was repeated 20 times, and the weight loss rates of the polyester-cotton fiber products after chemical separation were calculated respectively;

[0142] According to Figure 8 the test results, it can be seen that for the polyester-cotton fiber products treated with the betaine / ethylene glycol eutectic solvent / alkali composite system, the weight data obtained under multiple parallel experimental conditions show high consistency, indicating that the low-energy rapid chemical separation method for polyester-cotton fiber products adopted in the present invention has good stability and repeatability, can be used for quantitative analysis, and it is obtained that the cotton component in the polyester-cotton fiber accounts for about 20%, and the polyester component accounts for about 80%.

[0143] (5), As Figure 10 shown, infrared tests were carried out on the products obtained by the degradation and recovery of the polyester component in the examples;

[0144] According to Figure 10 the test results, it can be seen that at 3063.30 cm −1 is the characteristic absorption peak of the carboxylic acid -OH of terephthalic acid, at 1683.72 cm −1 is the typical vibration peak of C=O, and at 1286.45 cm −1 represents the typical vibration peak of C-O. These characteristic peaks are consistent with the characteristic absorption peaks of terephthalic acid in the reported literature (ACS Sustainable Chem. Eng. 2021, 9, 17174−17185). Therefore, it can be proved that when the polyester-cotton fiber products are treated by the separation method of the present invention, the degradation and recovery product of the polyester component is terephthalic acid.

[0145] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A low energy consumption rapid chemical separation method for polyester-cotton fiber products, characterized in that: The chemical separation method comprises the following steps: Step (1) adding a hydrogen bond donor and a hydrogen bond acceptor into a reaction bottle, stirring and dissolving, and preparing a betaine-based low eutectic solvent; The hydrogen bond donor is ethylene glycol, the hydrogen bond acceptor is betaine, and the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 2:

1. Step (2) adding alkali solution to the betaine-based low eutectic solvent and mixing to obtain a low eutectic solvent / alkali composite system; The alkali solution is a sodium hydroxide solution with a concentration of 50 g / L; the mass ratio of the alkali solution to the betaine-based low eutectic solvent is 1.5:30; Step (3) immersing the polyester-cotton product in a low eutectic solvent / alkali composite system to undergo a dissolution reaction, and after the reaction is completed, filtering to obtain undissolved components in the polyester-cotton product, washing with water, and drying; The dissolution reaction conditions are: dissolution reaction at 98° C. for 60 min.

2. A low energy consumption rapid chemical separation method for polyester-cotton fiber products according to claim 1, characterized in that: In the step (1), the stirring and dissolving operation includes: After stirring at 80°C until completely dissolved, continue stirring at this temperature for not less than 30 minutes.

3. A low energy consumption rapid chemical separation method for polyester-cotton fiber products according to claim 1, characterized in that: In the step (2), the mixing condition is: stirring at 90° C. for 25 min until the mixture is completely dissolved.

4. A low energy consumption rapid chemical separation method for polyester-cotton fiber products according to claim 1, characterized in that: In the step (3), the mass ratio of the polyester-cotton product to the low eutectic solvent / alkali composite system is 1:30-50.

5. A method for processing polyester-cotton fiber products using a low-energy consumption rapid chemical separation method for polyester-cotton fiber products as claimed in any one of claims 1 to 4.

6. Application of the low energy consumption rapid chemical separation method for polyester-cotton fiber products as claimed in any one of claims 1 to 4 in rapid quantitative analysis of components of polyester-cotton fiber products.

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