Method for decolorizing polyester fabric

Abstract

PURPOSE: To provide a decolorization method of a polyester fabric.SOLUTION: There is provided a decolorization method of a polyester fabric, including the following steps. First extraction treatment is performed on the polyester fabric using a recycled solvent, so that a first portion of a dye in the polyester fabric moves into the recycled solvent. First filtering treatment is performed on the recycled solvent and the polyester fabric to obtain a treated polyester fabric. Second extraction treatment is performed on the treated polyester fabric using a fresh solvent, so that a second portion of the dye in the treated polyester fabric moves into the fresh solvent. Second filtering treatment is performed to obtain a decolored polyester fabric and the recycled solvent.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for decolorizing a fabric, and particularly to a method for decolorizing a polyester fabric.

Background Art

[0002] Polyester fabrics (e.g., polyethylene terephthalate (PET) fabrics) often contain impurities such as dyes. Generally, it is first necessary to remove impurities such as dyes with an appropriate solvent, and then, by effectively separating and purifying the decolorized polyester fabric, the polyester and fiber materials in the polyester fabric can be recycled.

[0003] US7,959,807 B2 proposes a method for removing dyes from PET fabrics. Although dyes can be removed by this method, a color transfer phenomenon also occurs in the treated PET fabrics, and the amount of solvent used reaches 24 times the weight of the fabric. Therefore, the cost of recycling the solvent is very high.

[0004] TWI481762B proposes a method for removing dyes from PET recycled fabrics, which extracts dyes using solvent evaporation gas. Although the extraction efficiency of dyes can be improved, a color transfer phenomenon still exists, and the extraction of dyes by solvent vapor is too costly in terms of energy consumption.

Summary of the Invention

Problems to be Solved by the Invention

[0005] Currently, during the process of removing impurities such as dyes, it is necessary to perform extraction 3 to 6 times at a weight ratio of solvent / polyester fabric of 5 to 10. In other words, since the amount of solvent used can reach 15 to 60 times the weight of the fabric, the amount of solvent that needs to be purified before it can be reused is very large. Furthermore, the decolorized polyester fabric obtained after the above extraction treatment still has a color bleeding phenomenon. For example, a blue fabric still has a bluish color after decolorization.

Means for Solving the Problem

[0006] The present invention provides a method for decolorizing a polyester fabric that uses a small amount of solvent, has a stable color of the fabric after decolorization, can reduce the decolorization cost of the polyester fabric, and can reduce the color bleeding phenomenon.

[0007] The method for decolorizing a polyester fabric of the present invention includes the following steps. Using a recycled solvent, perform a first extraction treatment on the polyester fabric to transfer the first part of the dye in the polyester fabric to the recycled solvent. Perform a first filtration treatment on the recycled solvent and the polyester fabric to obtain the treated polyester fabric. Using a fresh solvent, perform a second extraction treatment on the treated polyester fabric to transfer the second part of the dye in the treated polyester fabric to the fresh solvent. Perform a second filtration treatment to obtain the decolorized polyester fabric and the recycled solvent.

[0008] In one embodiment of the present invention, the recycled solvent contains a fresh solvent and a dye, and the dye is 0.1 wt% to 10 wt% based on the total weight of the recycled solvent.

[0009] In one embodiment of the present invention, in the first extraction treatment, the weight ratio of the recycled solvent to the polyester fabric is 4:1 to 50:1.

[0010] In one embodiment of the present invention, the weight ratio of the fresh solvent to the treated polyester fabric is 4:1 to 50:1.

[0011] In one embodiment of the present invention, the fresh solvent includes an aromatic hydrocarbon solvent, an alcohol ether solvent, a benzyl alcohol solvent, an alcohol solvent, or an amide solvent.

[0012] In one embodiment of the present invention, the fresh solvent includes benzene, toluene, xylene, propylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, butanol, pentanol, hexanol, dimethylformamide, dimethylacetamide, or a combination thereof.

[0013] In one embodiment of the present invention, the total amount of the first part and the second part to be removed is 90% to 99.9% by weight based on the total weight of the dye.

[0014] In one embodiment of the present invention, the CIELAB color definition of the decolorized polyester fabric is such that the L value is 80 or more, the a value is from -3.0 to +3.0, and the b value is from -6.0 to +6.0.

[0015] In one embodiment of the present invention, the decolorization method further includes repeating the cycle of the first extraction treatment and the first filtration treatment 1 to 7 times before the second extraction treatment.

[0016] In one embodiment of the present invention, the decolorization method further includes repeating the cycle of the second extraction treatment and the second filtration treatment 1 to 3 times after the second filtration treatment.

Advantages of the Invention

[0017] As described above, the method for decolorizing a polyester fabric of the present invention can reduce the color transfer phenomenon of the produced decolorized polyester fabric by performing the above-described extraction treatment on the polyester fabric using a recycled solvent. At the same time, since the amount of fresh solvent used and the amount of recycled solvent generated can be significantly reduced, the cost required for the decolorization treatment of the polyester fabric can be reduced accordingly.

Brief Description of the Drawings

[0018]

Figure 1

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described in detail. However, these embodiments are exemplary and do not limit the present invention.

[0020] Here, the range expressed as "from one numerical value to another numerical value" is a schematic display method for avoiding listing all the numerical values within the range one by one in the specification. Therefore, the description of a specific numerical range includes any numerical value within the range and a relatively small numerical range limited by any numerical value within the range, which is the same as if the arbitrary numerical value and the relatively small numerical range are specified in the specification.

[0021] FIG. 1 is a schematic flowchart of a method for decolorizing a polyester fabric according to one embodiment of the present invention.

[0022] Referring to FIG. 1, in step S1, first, a recycled solvent is used to perform a first extraction treatment on the polyester fabric to transfer the first part of the dye in the polyester fabric to the recycled solvent.

[0023] In some embodiments, the recycled solvent contains fresh solvent and dye. Based on the total weight of the recycled solvent, the dye content is from 0.1 wt% to 10 wt%, for example, 2 wt%, 6 wt%, or 8 wt%. For example, the recycled solvent may be a dye-containing solvent generated after performing an extraction treatment and a filtration treatment on a polyester fabric or a treated polyester fabric using fresh solvent. Since the recycled solvent has a low dye concentration, the recycled solvent can also be used to perform a first extraction treatment on other batches of polyester fabric.

[0024] In some embodiments, the polyester fabric contains a decolorized polyester fabric and dye. The decolorized polyester fabric can contain polyester and fibers. In some embodiments, the polyester in the decolorized polyester fabric is polyethylene terephthalate (PET). In some embodiments, the fibers in the decolorized polyester fabric include cotton fibers. In some embodiments, when the total weight of the polyester fabric is 100 parts by weight, the content of the dye in the polyester fabric is, for example, from 0.1 part by weight to 10 parts by weight, for example, 3 parts by weight, 5 parts by weight, or 9 parts by weight. For example, the polyester fabric may be a product obtained by dyeing and finishing an undyed polyester fabric.

[0025] In some embodiments, the weight ratio of the recycled solvent to the polyester fabric for performing the first extraction treatment is from 4:1 to 50:1. In certain embodiments, the weight ratio of the recycled solvent to the polyester fabric for performing the first extraction treatment is from 5:1 to 20:1, for example, 6:1, 10:1, or 15:1.

[0026] In some embodiments, the first extraction process includes placing a polyester fabric in a recycled solvent and then heating the polyester fabric and the recycled solvent to a processing temperature. In some embodiments, the processing temperature of the first extraction process is higher than the glass transition temperature (Tg) of the polyester in the polyester fabric and lower than the melting point of the polyester. In some embodiments, the processing temperature of the first extraction process is 80°C to 160°C. In some embodiments, the processing temperature of the first extraction process is 100°C to 150°C, for example, 120°C, 130°C, or 140°C. In some embodiments, the processing time of the first extraction process is 0.5 hour to 5 hours. In some embodiments, the processing time of the first extraction process is 1 hour to 3 hours, for example, 1.5 hours, 2 hours, or 2.5 hours. In some embodiments, the processing pressure of the first extraction process is 1.0 bar to 2.0 bar. In certain embodiments, when the boiling point of the recycled solvent is lower than the glass transition temperature of the polyester in the polyester fabric, the processing pressure of the first extraction process may be greater than 1.0 bar.

[0027] Thereafter, a first filtration process is performed on the recycled solvent and the polyester fabric to obtain a processed polyester fabric and a filtered solvent to be purified. Here, the processed polyester fabric may include a later-produced decolorized polyester fabric and residual dyes, and the residual dyes are the residual dyes after removing the first portion of the dyes. In some embodiments, the first filtration process uses a sieve for filtration to separate the solvent to be purified from the processed polyester fabric. In some embodiments, the sieve has a pore size of 0.1 mm to 1.0 mm, for example, a pore size of 0.3 mm, 0.5 mm, or 0.7 mm. In some embodiments, after the first extraction process and before the first filtration process, a cooling process may first be performed. For example, after lowering the temperature to between 25°C and 80°C, the processed polyester fabric and the solvent to be purified are separated.

[0028] In some embodiments, the solvent to be purified includes a pure solvent and a dye. Since the concentration of the dye in the solvent to be purified is high, the solvent to be purified is not suitable for performing an extraction process. In some embodiments, the dye concentration in the solvent to be purified is higher than the dye concentration in the recycled solvent. In some embodiments, when the total weight of the solvent to be purified is 100 parts by weight, the content of the dye in the solvent to be purified is about 1.0 part by weight to 30 parts by weight, for example, 12 parts by weight, 18 parts by weight, or 24 parts by weight. In some embodiments, a distillation or evaporation process is performed on the solvent to be purified to purify the solvent in the solvent to be purified into a pure solvent. In some embodiments, the pure solvent can be used as a fresh solvent.

[0029] Continuing to refer to FIG. 1, in the optional step S2, step S1 may be repeated m times. That is, after step S1 is completed, step S2 may be skipped and step S3 may be directly executed, or after step S1 is completed, step S1 may be repeated m times and then step S3 may be executed. In some embodiments, m may be from 1 to 7. That is, step S1 can be repeated 1, 2, 3, 4, 5, 6, or 7 times, but the present invention is not limited thereto.

[0030] Next, in step S3, first, a second extraction process is performed on the treated polyester fabric using a fresh solvent, and a second portion of the dye in the treated polyester fabric can be transferred to the fresh solvent. In some embodiments, the second extraction process includes placing the treated polyester fabric in a fresh solvent and then heating the treated polyester fabric and the fresh solvent to a treatment temperature that is higher than the glass transition temperature of the polyester in the polyester fabric and lower than the melting point of the polyester.

[0031] In some embodiments, in the second extraction process, the weight ratio of the fresh solvent to the treated polyester fabric is from 4:1 to 50:1. In certain embodiments, in the second extraction process, the weight ratio of the fresh solvent to the treated polyester fabric is from 5:1 to 20:1. In some embodiments, the treatment temperature of the second extraction process is from 80°C to 160°C. In some embodiments, the treatment temperature of the second extraction process is from 100°C to 150°C. In some embodiments, the treatment time of the second extraction process is from 0.5 hour to 5 hours. In some embodiments, the treatment time of the second extraction process is from 1 hour to 3 hours.

[0032] In some embodiments, the fresh solvent includes an aromatic hydrocarbon solvent, an alcohol ether solvent, a benzyl alcohol solvent, an alcohol solvent, or an amide solvent. In some embodiments, the aromatic hydrocarbon solvent includes benzene, toluene, or xylene. In some embodiments, the alcohol ether solvent includes propylene glycol monomethyl ether, ethylene glycol monobutyl ether, or diethylene glycol monobutyl ether. In some embodiments, the alcohol solvent includes butanol, pentanol, or hexanol. In some embodiments, the amide solvent includes dimethylformamide or dimethylacetamide. In some embodiments, the fresh solvent includes benzene, toluene, xylene, propylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, butanol, pentanol, hexanol, dimethylformamide, dimethylacetamide, or a combination thereof.

[0033] After that, after the second extraction process, a second filtration process is performed to obtain a decolorized polyester fabric and a recycled solvent. Here, the recycled solvent can be used for performing the first extraction process. In some embodiments, the decolorized polyester fabric may contain a trace amount of dye, and the trace amount of dye is the residual dye after removing the first and second portions of the dye. In some embodiments, when the total weight of the dye in the polyester fabric is 100 parts by weight, the total amount of the first portion removed by the first extraction process and the second portion removed by the second extraction process is, for example, 90 parts by weight to 99.9 parts by weight, and for example, 92 parts by weight, 95 parts by weight, or 98 parts by weight.

[0034] In some embodiments, the second filtration process uses a sieve for filtration to separate the recycled solvent from the decolorized polyester fabric. In some embodiments, this sieve has a pore size of 0.1 mm to 1.0 mm, and for example, has a pore size of 0.3 mm, 0.5 mm, or 0.7 mm. In some embodiments, after the second extraction process, first, the decolorized polyester fabric and the recycled solvent can be cooled to a temperature of, for example, 25°C to 80°C, and then the second filtration process can be performed.

[0035] After that, in an optional step S4, step S3 can be repeated n times. That is, after step S3 is completed, step S4 may be skipped, or after step S3 is completed, step S3 may be repeated n times. In some embodiments, n may be 1 to 3. That is, step S3 can be repeated 1 time, 2 times, or 3 times, but the present invention is not limited thereto.

[0036] In some embodiments, the method for decolorizing a polyester fabric further includes performing a drying treatment on the decolorized polyester fabric to remove the residual solvent on the decolorized polyester fabric. For example, the decolorized polyester fabric can be placed in an oven set at a temperature of 80°C to 160°C and left for 1 hour to 24 hours for drying. In some embodiments, the decolorized polyester fabric after the drying treatment is white, and in the CIELAB color definition, the L value is 80 or more, the a value is -3.0 to +3.0, and the b value is -6.0 to +6.0.

[0037] Hereinafter, the method for decolorizing a polyester fabric proposed by the present invention will be described in detail with examples. However, the following examples do not limit the present invention.

[0038] Example 1

[0039] Referring to FIG. 1 at the same time, first, step S1 was executed using a propylene glycol monomethyl ether recycled solvent and a PET fabric to obtain a treated PET fabric. Here, the weight ratio of the propylene glycol monomethyl ether recycled solvent to the PET fabric was 6:1, the treatment temperature of the first extraction treatment was 120°C, the treatment time of the first extraction treatment was 0.5 hour, the treatment pressure of the first extraction treatment was 1.0 bar, the first filtration treatment used a sieve with a pore diameter of 0.5 mm, the propylene glycol monomethyl ether recycled solvent contained about 0.5 wt% of dye, and the PET fabric contained about 8 wt% of dye.

[0040] Next, in step S2, step S1 was repeated twice. Thereafter, step S3 was executed using a fresh propylene glycol monomethyl ether solvent and the treated PET fabric to produce a decolorized PET fabric and a recycled propylene glycol monomethyl ether solvent. Here, the weight ratio of the fresh propylene glycol monomethyl ether solvent to the treated PET fabric was 6:1, the treatment temperature of the second extraction treatment was 120 °C, the treatment time of the second extraction treatment was 0.5 hours, the treatment pressure of the second extraction treatment was 1.0 bar, and for the second filtration treatment, a sieve with a pore diameter of 0.5 mm was used.

[0041] Next, step S4 was skipped. Since the second extraction treatment was performed a total of once, in Example 1, the total amount of fresh solvent used was only about six times the weight of the PET fabric. Therefore, since the total amount of the recycled propylene glycol monomethyl ether solvent produced was about six times the weight of the PET fabric, it could be used as the recycled solvent for other batches of PET fabric when performing the first extraction treatment in step S1. Furthermore, since the first extraction treatment was performed a total of three times and the amount of recyclable solvent in Example 1 became 18 times the weight of the PET fabric, the recycling rate of the recycled solvent was significantly improved, thereby reducing the amount of the solvent to be purified in the overall decolorization treatment procedure and reducing the solvent purification energy consumption and the solvent purification cost.

[0042] Next, the obtained decolorized polyester fabric was dried in an oven at 105 °C for 2 hours to perform a drying treatment. Thereafter, the measured CIELAB color definition of the decolorized polyester fabric was an L value of 82, an a value of 1.1, and a b value of 2.4. The color of the fabric after decolorization was stable and the amount of color transfer decreased. The total amount of the removed dye was about 99.4 wt%.

[0043] Example 2

[0044] The main differences between the processing procedure of Example 2 and that of Example 1 are that Step S1 was repeated once in Step S2, Step S3 was repeated once in Step S4, the processing temperature of the first extraction process and the second extraction process was 130°C, and the processing pressure of the first extraction process and the second extraction process was 1.8 bar.

[0045] Since the second extraction process was performed a total of 2 times, in Example 2, the total amount of fresh solvent used was about 12 times the weight of the PET fabric. Therefore, the total amount of the generated propylene glycol monomethyl ether recycled solvent was about 12 times the weight of the PET fabric, and thus it could be used as the recycled solvent for other batches of PET fabric when performing the first extraction process in Step S1. Furthermore, since the first extraction process was performed a total of 2 times and the amount of recyclable recycled solvent in Example 2 was about 12 times the weight of the PET fabric, the recycling rate of the recycled solvent was improved, thereby reducing the amount of the solvent to be purified in the overall decolorization treatment procedure and reducing the solvent purification energy consumption and the solvent purification cost.

[0046] After performing a drying process on the obtained decolorized polyester fabric, the measured CIELAB color definition of the decolorized polyester fabric produced in Example 2 was an L value of 83, an a value of 1.8, and a b value of 2.7. The color of the fabric after decolorization was stable, and the amount of color transfer decreased. The total amount of the removed dye was about 99.6 wt%.

[0047] Example 3

[0048] The main differences between the processing procedure of Example 3 and that of Example 1 are that Step S1 was repeated once in Step S2 and Step S3 was repeated once in Step S4.

[0049] Since the second extraction process was performed twice in total, in Example 3, the total amount of fresh solvent used was about 12 times the weight of the PET fabric. Therefore, the weight of the generated propylene glycol monomethyl ether recycled solvent was about 12 times the weight of the PET fabric, so it could be used as the recycled solvent for other batches of PET fabric when performing the first extraction process in Step S1. Furthermore, since the first extraction process was performed twice in total and the amount of recyclable recycled solvent in Example 3 was about 12 times the weight of the PET fabric, the recycling rate of the recycled solvent was improved, thereby reducing the amount of the solvent to be purified in the overall decolorization treatment procedure and reducing the solvent purification energy consumption and the solvent purification cost.

[0050] After performing a drying process on the obtained decolorized polyester fabric, the measured CIELAB color definition of the decolorized polyester fabric generated in Example 3 was that the L value was 84, the a value was 1.5, and the b value was 2.4. The color of the fabric after decolorization was stable and the amount of color transfer decreased. The total amount of the removed dye was about 99.5 wt%.

[0051] Example 4

[0052] Propylene glycol monomethyl ether was replaced with xylene, but the rest was the same as in Example 1. The measured CIELAB color definition of the decolorized polyester fabric was that the L value was 82, the a value was 1.2, and the b value was 2.5. The color of the fabric after decolorization was stable and the amount of color transfer decreased. The total amount of the removed dye was about 99.4 wt%.

[0053] Example 5

[0054] Propylene glycol monomethyl ether was replaced with xylene, but the rest was the same as in Example 3. The measured CIELAB color definition of the decolorized polyester fabric was that the L value was 83, the a value was 1.6, and the b value was 2.5. The color of the fabric after decolorization was stable and the amount of color transfer decreased. The total amount of the removed dye was about 99.6 wt%.

[0055] Example 6

[0056] Propylene glycol monomethyl ether was replaced with dimethylacetamide, and the rest was the same as in Example 3. The measured CIELAB color definition of the decolorized polyester fabric was an L value of 85, an a value of 1.4, and a b value of 2.3. The color of the fabric after decolorization was stable, and the amount of color transfer decreased. The total amount of dye removed was about 99.7 wt%.

[0057] Comparative Example 1

[0058] The main differences between the treatment procedure of Comparative Example 1 and that of Example 1 were skipping Steps S1 and S2 and repeating Step S3 three times in Step S4.

[0059] In Comparative Example 1, since the second extraction treatment was performed a total of 4 times, the total amount of fresh solvent used became up to 24 times the weight of the PET fabric, and the total weight of the produced propylene glycol monomethyl ether recycled solvent was also about 24 times the weight of the PET fabric. In the overall decolorization treatment procedure of Comparative Example 1, since the recycled solvent was not reused, it was necessary to purify the recycled solvent by distillation or evaporation for reuse. That is, the propylene glycol monomethyl ether recycled solvent in Comparative Example 1 was a propylene glycol monomethyl ether solvent to be purified. Thus, since the amount of the solvent to be purified in the overall decolorization treatment procedure increased significantly, the solvent purification energy consumption and purification cost increased.

[0060] After performing a drying treatment on the obtained decolorized polyester fabric, the measured CIELAB color definition of the decolorized polyester fabric produced in Comparative Example 1 was an L value of 87, an a value of 2.1, and a b value of 6.1. Since the fabric itself contained red and yellow dyes, even after continuously using fresh solvent for decolorization, the color of the fabric remained reddish (high a value) and yellowish (high b value). The total amount of dyes removed was approximately 99.6 wt%.

[0061] Comparative Example 2

[0062] The main differences between the treatment procedure of Comparative Example 2 and that of Example 2 were skipping Steps S1 and S2 and repeating Step S3 three times in Step S4.

[0063] In Comparative Example 2, since the second extraction treatment was performed a total of 4 times, the total amount of fresh solvent used became up to 24 times the weight of the PET fabric, and the total weight of the produced propylene glycol monomethyl ether recycled solvent was also approximately 24 times the weight of the PET fabric. In the overall decolorization treatment procedure of Comparative Example 2, since the recycled solvent was not reused, it was necessary to purify the recycled solvent by distillation or evaporation for reuse. Therefore, the amount of the solvent to be purified in the overall decolorization treatment procedure increased significantly, and the solvent purification energy consumption and purification cost increased.

[0064] After performing a drying treatment on the obtained decolorized polyester fabric, the measured CIELAB color definition of the decolorized polyester fabric produced in Comparative Example 2 was an L value of 88, an a value of 3.8, and a b value of 6.8. Since the fabric itself contained red and yellow dyes, even after continuously using fresh solvent for decolorization, the color of the fabric remained reddish (high a value) and yellowish (high b value). The total amount of dyes removed was approximately 99.7 wt%.

[0065] Comparative Example 3

[0066] The main difference between the processing procedure of Comparative Example 3 and that of Example 3 is that steps S1 and S2 were skipped.

[0067] In Comparative Example 3, since the second extraction process was performed a total of 2 times, the total amount of fresh solvent used was about 12 times the weight of the PET fabric, and the total weight of the produced propylene glycol monomethyl ether recycled solvent was also about 12 times the weight of the PET fabric. In the overall decolorization treatment procedure of Comparative Example 3, since the recycled solvent was not reused, it was necessary to purify the recycled solvent by distillation or evaporation for reuse. Therefore, the amount of the solvent to be purified in the overall decolorization treatment procedure also increased, and the solvent purification energy consumption and purification cost increased.

[0068] After performing a drying treatment on the obtained decolorized polyester fabric, the measured CIELAB color definition of the decolorized polyester fabric produced in Comparative Example 3 was that the L value was 75, the a value was 3.2, and the b value was 6.3. Since the removal of the dye was incomplete, the residual dye was prominent and the decolorization was incomplete. The total amount of the removed dye was about 98.7 wt%.

[0069] Comparative Example 4

[0070] Propylene glycol monomethyl ether was replaced with xylene, but the rest was the same as in Comparative Example 1. The measured CIELAB color definition of the decolorized polyester fabric produced in Comparative Example 4 was that the L value was 86, the a value was 2.3, and the b value was 6.4. Since the fabric itself contained red and yellow dyes, even after continuously using fresh solvent for decolorization, the color of the fabric was still reddish (high a value) and yellowish (high b value). The total amount of the removed dye was about 99.5 wt%.

[0071] Comparative Example 5

[0072] Propylene glycol monomethyl ether was replaced with xylene, and the rest was the same as in Comparative Example 3. The measured CIELAB color definition of the decolorized polyester fabric produced in Comparative Example 5 was an L value of 74, an a value of 3.5, and a b value of 6.4. Due to incomplete removal of the dye, the residual dye was prominent and the decolorization was incomplete. The total amount of the removed dye was about 98.4 wt%.

[0073] Comparative Example 6

[0074] Propylene glycol monomethyl ether was replaced with dimethylacetamide, and the rest was the same as in Comparative Example 3. The measured CIELAB color definition of the decolorized polyester fabric produced in Comparative Example 6 was an L value of 75, an a value of 3.1, and a b value of 6.0. Due to incomplete removal of the dye, the residual dye was prominent and the decolorization was incomplete. The total amount of the removed dye was about 98.8 wt%.

[0075] The preparation methods and test results of the above Examples 1 to 6 and Comparative Examples 1 to 6 are summarized in Table 1 below.

[0076]

Table 1

[0077] Comparing Example 1 with Comparative Example 1, it can be seen that the total number of extraction processes was 4 times for both. However, since only the fourth extraction process in Example 1 used a fresh solvent, the amount of recycled solvent was significantly less than that in Comparative Example 1, and the color transfer situation was also better than that in Comparative Example 1. Comparing Example 2 with Comparative Example 2, it can be seen that Example 2, which performed the first extraction process twice using a recycled solvent even at a higher extraction temperature and extraction pressure, was able to not only reduce the amount of recycled solvent but also significantly reduce the color transfer phenomenon. Furthermore, comparing Example 3 with Comparative Example 3, since both used a fresh solvent to perform the second extraction process twice, the amount of the generated recycled solvent was similar. However, since Example 3 also performed the first extraction process twice using a recycled solvent first, the color performance was significantly improved compared to Comparative Example 3. Additionally, since the total amount of the removed dyes in Examples 1 to 3 is similar to the total amount of the removed dyes in Comparative Example 1 and Comparative Example 2, it shows that performing the first extraction process using a recycled solvent first did not affect the overall dye removal efficiency.

[0078] Furthermore, as can be seen from Examples 4 to 6, by using xylene or dimethylacetamide as the solvent, it is possible to achieve a stable color of the fabric after decolorization and a reduction in color transfer. For Comparative Examples 4 to 6, even when using xylene or dimethylacetamide as the solvent, the improvement in the redness, yellowness, and incomplete decolorization of the fabric after decolorization in Comparative Example 1 or Comparative Example 3 could not be achieved.

[0079] As can be seen from Table 1 above, in Examples 1 to 6, the first extraction treatment of step S1 was performed on the polyester fabric using a recycled solvent, and only fresh solvent was used in the second extraction treatment of step S3 described below. Therefore, the amounts of the generated recycled solvent and the solvent to be purified could be significantly reduced. Furthermore, the recycled solvent used in the first extraction treatment may be a mixture of recycled solvents generated in the second extraction treatment of a plurality of batches, so that the color transfer problem of the decolorized polyester fabric generated by a single color of the dye contained in the recycled solvent can be prevented, and the CIELAB color definition of the finally obtained decolorized polyester fabric can be in the range where the L value is 80 or more, the a value is from -3.0 to +3.0, and the b value is from -6.0 to +6.0.

[0080] As described above, the method for decolorizing a polyester fabric of the present invention can reduce the color transfer phenomenon of the generated decolorized polyester fabric by performing the above-described extraction treatment on the polyester fabric using a recycled solvent. At the same time, since the amount of fresh solvent used, the amount of recycled solvent generated, and the amount of solvent to be purified can be significantly reduced, the cost required for the decolorization treatment of the polyester fabric can be reduced accordingly.

Industrial Applicability

[0081] The method for decolorizing a polyester fabric of the present invention can be applied to the recycling of polyester and fiber materials in the polyester fabric.

Explanation of Signs

[0082] Steps S1, S2, S3, S4

Claims

**Claim 1**: Performing a first extraction treatment on a polyester fabric using a first recycled solvent to transfer a first portion of the dye in the polyester fabric to the first recycled solvent; Performing a first filtration treatment on the first recycled solvent and the polyester fabric to obtain a treated polyester fabric; Performing a second extraction treatment on the treated polyester fabric using a fresh solvent to transfer a second portion of the dye in the treated polyester fabric to the fresh solvent; Performing a second filtration treatment to obtain a decolorized polyester fabric and a second recycled solvent; A method for decolorizing a polyester fabric comprising the above steps. **Claim 2** The decolorization method according to claim 1, wherein the first recycled solvent or the second recycled solvent contains the fresh solvent and the dye, and the dye is 0.1% to 10% by weight based on the total weight of the first recycled solvent or the second recycled solvent. **Claim 3** The decolorization method according to claim 1, wherein in the first extraction treatment, the weight ratio of the first recycled solvent to the polyester fabric is 4:1 to 50:

1. **Claim 4** The decolorization method according to claim 1, wherein the weight ratio of the fresh solvent to the treated polyester fabric is 4:1 to 50:

1. **Claim 5**: The decolorization method according to claim 1, further comprising performing a first extraction treatment on different batches of polyester fabrics using the second recycled solvent. **Claim 6** The decolorization method according to claim 1, wherein the fresh solvent comprises benzene, toluene, xylene, propylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, butanol, pentanol, hexanol, dimethylformamide, dimethylacetamide, or a combination thereof. **Claim 7** The decolorization method according to claim 1, wherein the total amount of the first portion and the second portion removed is 90% to 99.9% by weight based on the total weight of the dye. **Claim 8** The decolorization method according to claim 1, wherein the CIELAB color definition of the decolorized polyester fabric has an L value of 80 or more, an a value of -3.0 to +3.0, and a b value of -6.0 to +6.

0. **Claim 9** The decolorization method according to claim 1, further comprising repeating the cycle of the first extraction treatment and the first filtration treatment 1 to 7 times before the second extraction treatment.

10. The decolorization method according to claim 1, further comprising repeating the cycle of the second extraction process and the second filtration process 1 to 3 times after the second filtration process.

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