Decolorization method of 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 bleaching textile fabrics, and more particularly to a method for bleaching polyester textile fabrics. [Background technology]

[0002] Polyester fabrics (e.g., polyethylene terephthalate (PET) fabrics) often contain impurities such as dyes. In general, the impurities such as dyes must first be removed with a suitable solvent, and then the decolorized polyester fabric can be effectively separated and purified to recycle the polyester and fiber materials in the polyester fabric.

[0003] US7,959,807 B2 proposes a method for removing dyes from PET fabrics. Although this method can remove dyes, the treated PET fabrics still suffer from color transfer, and the amount of solvent used is up to 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 uses solvent vapor to extract the dyes. Although the efficiency of dye extraction can be improved, the color transfer phenomenon still exists, and the energy consumption of solvent vapor to extract the dyes is too high. Summary of the Invention [Problem to be solved by the invention]

[0005] Currently, during the process of removing impurities such as dyes, extraction needs to be performed 3-6 times with a solvent / polyester fabric weight ratio of 5-10. In other words, the amount of solvent used can be as much as 15-60 times the weight of the fabric, so 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 process still has a color transfer phenomenon. For example, a blue fabric still has a bluish color after decolorization. [Means for solving the problem]

[0006] To provide a method for bleaching polyester fabrics, which uses a small amount of solvent, has a stable color after bleaching, can reduce the bleaching cost of polyester fabrics, and can reduce the color transfer phenomenon.

[0007] The method for decolorizing polyester fabric of the present invention includes the following steps: performing a first extraction process on the polyester fabric using a recycled solvent to transfer a first portion of the dye in the polyester fabric to the recycled solvent; performing a first filtration process on the recycled solvent and the polyester fabric to obtain a treated polyester fabric; performing a second extraction process 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 process to obtain a decolorized polyester fabric and a recycled solvent.

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

[0009] In one embodiment of the present invention, in the first extraction process, 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 fresh solvent to treated polyester fabric is 4:1 to 50:1.

[0011] In one embodiment of the invention, the fresh solvent comprises 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 invention, 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.

[0013] In one embodiment of the present invention, the combined amount of the first and second portions to be removed is 90% by weight 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 bleached polyester fabric is: L value is 80 or more, a value is -3.0 to +3.0, and b value is -6.0 to +6.0.

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

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

[0017] As described above, the method for bleaching polyester fabrics of the present invention can reduce the color transfer phenomenon of the bleached polyester fabrics by using recycled solvent to perform the above-mentioned extraction treatment on the polyester fabrics, and at the same time, the amount of fresh solvent used and the amount of recycled solvent produced can be greatly reduced, thereby reducing the cost required for bleaching polyester fabrics. [Brief description of the drawings]

[0018] [Figure 1] 1 is a schematic flow chart of a method for bleaching polyester fabric according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0020] Here, ranges expressed as "one value to another value" are a summary method to avoid listing every value in the range in the specification. Thus, the description of a particular numerical range includes any value in that numerical range and smaller numerical ranges defined by any value in that numerical range, and is the same as if the any value and the smaller numerical range were specified in the specification.

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

[0022] Referring to FIG. 1, in step S1, a first extraction process is first performed on the polyester fabric using a recycled solvent to transfer a first portion of the dye in the polyester fabric to the recycled solvent.

[0023] In some embodiments, the recycled solvent includes fresh solvent and dye, and the dye is 0.1% to 10% by weight, e.g., 2%, 6%, or 8% by weight, based on the total weight of the recycled solvent. For example, the recycled solvent may be a dye-containing solvent produced after performing an extraction and filtration process on polyester fabric or 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 process on polyester fabric of another batch.

[0024] In some embodiments, the polyester fabric includes a bleached polyester fabric and a dye, and the bleached polyester fabric includes polyester and fibers. In some embodiments, the polyester in the bleached polyester fabric is polyethylene terephthalate (PET). In some embodiments, the fibers in the bleached 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, 0.1 parts 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 process is 4:1 to 50:1. In certain embodiments, the weight ratio of the recycled solvent to the polyester fabric for performing the first extraction process is 5:1 to 20:1, for example, 6:1, 10:1, or 15:1.

[0026] In some embodiments, the first extraction process includes placing the polyester fabric in a recycle solvent, and then heating the polyester fabric and the recycle 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 hours 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 recycle solvent is lower than the glass transition temperature of the polyester in the polyester fabric, the process pressure of the first extraction process may be greater than 1.0 bar.

[0027] Then, the recycled solvent and the polyester fabric are subjected to a first filtration process to obtain a treated polyester fabric and a filtered purified solvent. Here, the treated polyester fabric may include a decolorized polyester fabric and a residual dye produced later, and the residual dye is the residual dye after removing the first portion of the dye. In some embodiments, the first filtration process separates the purified solvent from the treated polyester fabric using a sieve for filtering. In some embodiments, the sieve has a pore size of 0.1 mm to 1.0 mm, for example, 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 be performed first. For example, the temperature is lowered to between 25°C and 80°C, and then the treated polyester fabric and the purified solvent are separated.

[0028] In some embodiments, the solvent to be purified includes a pure solvent and a dye. The solvent to be purified has a high dye concentration, so 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 parts 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, the solvent to be purified is subjected to a distillation or evaporation process 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 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 performed, or after step S1 is completed, step S1 may be repeated m times and then step S3 may be performed. In some embodiments, m may be from 1 to 7. That is, step S1 may be repeated 1, 2, 3, 4, 5, 6, or 7 times, but the present invention is not limited thereto.

[0030] Next, in step S3, the treated polyester fabric may be subjected to a second extraction process using fresh solvent to transfer a second portion of the dye in the treated polyester fabric to the fresh solvent. In some embodiments, the second extraction process includes placing the treated polyester fabric in fresh solvent and then heating the treated polyester fabric and the fresh solvent to a processing 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, the weight ratio of fresh solvent to treated polyester fabric in the second extraction process is 4:1 to 50:1. In certain embodiments, the weight ratio of fresh solvent to treated polyester fabric in the second extraction process is 5:1 to 20:1. In some embodiments, the treatment temperature of the second extraction process is 80°C to 160°C. In some embodiments, the treatment temperature of the second extraction process is 100°C to 150°C. In some embodiments, the treatment time of the second extraction process is 0.5 hours to 5 hours. In some embodiments, the treatment time of the second extraction process is 1 hour to 3 hours.

[0032] In some embodiments, the fresh solvent comprises 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 comprises benzene, toluene, or xylene. In some embodiments, the alcohol ether solvent comprises propylene glycol monomethyl ether, ethylene glycol monobutyl ether, or diethylene glycol monobutyl ether. In some embodiments, the alcohol solvent comprises butanol, pentanol, or hexanol. In some embodiments, the amide solvent comprises dimethylformamide or dimethylacetamide. In some embodiments, 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.

[0033] Then, 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 to perform 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 parts 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 part removed by the first extraction process and the second part removed by the second extraction process is, for example, 90 parts by weight to 99.9 parts by weight, 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 filtering to separate the recycled solvent from the decolorized polyester fabric. In some embodiments, the sieve has a pore size of 0.1 mm to 1.0 mm, for example, 0.3 mm, 0.5 mm, or 0.7 mm. In some embodiments, after the second extraction process, the decolorized polyester fabric and the recycled solvent can be first cooled to a temperature of, for example, 25°C to 80°C, and then the second filtration process can be performed.

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

[0036] In some embodiments, the method for bleaching the polyester fabric further includes drying the bleached polyester fabric to remove residual solvent on the bleached polyester fabric. For example, the bleached polyester fabric can be placed in an oven set at a temperature of 80° C. to 160° C. and left to dry for 1 hour to 24 hours. In some embodiments, the bleached polyester fabric after drying is white, and the CIELAB color definition 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.

[0037] The method for bleaching polyester fabric proposed by the present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0038] Example 1

[0039] Referring to FIG. 1 at the same time, step S1 is first carried out using propylene glycol monomethyl ether recycled solvent and PET fabric to obtain treated PET fabric, where the weight ratio of propylene glycol monomethyl ether recycled solvent to PET fabric is 6:1, the processing temperature of the first extraction process is 120° C., the processing time of the first extraction process is 0.5 hours, the processing pressure of the first extraction process is 1.0 bar, the first filtration process uses a sieve with a pore size of 0.5 mm, the propylene glycol monomethyl ether recycled solvent contains about 0.5 wt % dye, and the PET fabric contains about 8 wt % dye.

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

[0041] Then, step S4 was skipped. Since the second extraction process was performed once in total, the total amount of fresh solvent used in Example 1 was only about 6 times the weight of the PET fabric. Therefore, the total amount of propylene glycol monomethyl ether recycled solvent generated was about 6 times the weight of the PET fabric, so it can 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 three times in total, the amount of reusable recycled solvent in Example 1 was 18 times the weight of the PET fabric, so the reuse rate of the recycled solvent was greatly improved, thereby reducing the amount of solvent to be purified in the overall decolorization process procedure, and reducing the energy consumption and cost of refining the solvent.

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

[0043] Example 2

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

[0045] Since the second extraction process was performed twice in total, the total amount of fresh solvent used in Example 2 was about 12 times the weight of the PET fabric. Therefore, the total amount of propylene glycol monomethyl ether recycled solvent generated was about 12 times the weight of the PET fabric, so it can 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 reusable recycled solvent in Example 2 was about 12 times the weight of the PET fabric, the reuse rate of the recycled solvent was improved, thereby reducing the amount of solvent to be purified in the overall decolorization process procedure, and reducing the energy consumption and cost of refining the solvent.

[0046] After the obtained bleached polyester fabric is dried, the measured CIELAB color definition of the bleached polyester fabric produced in Example 2 is L value 83, a value 1.8, and b value 2.7. The color of the bleached fabric is stable and the amount of color transfer is reduced. The total amount of dye removed is about 99.6wt%.

[0047] Example 3

[0048] The main difference between the processing procedure of the third embodiment and the processing procedure of the first embodiment is that step S1 is repeated once in step S2, and step S3 is repeated once in step S4.

[0049] Since the second extraction process was performed twice in total, the total amount of fresh solvent used in Example 3 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 can 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 reusable recycled solvent in Example 3 was about 12 times the weight of the PET fabric, the reuse rate of the recycled solvent was improved, thereby reducing the amount of solvent to be purified in the overall decolorization process procedure, and reducing the energy consumption and cost of refining the solvent.

[0050] After the obtained bleached polyester fabric is dried, the measured CIELAB color definition of the bleached polyester fabric produced in Example 3 is L value 84, a value 1.5, and b value 2.4. The color of the bleached fabric is stable and the amount of color transfer is reduced. The total amount of dye removed is about 99.5wt%.

[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 bleached polyester fabric was L value of 82, a value of 1.2, and b value of 2.5. The color of the fabric after bleaching was stable, and the amount of color transfer was reduced. The total amount of dye removed 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 bleached polyester fabric was L value of 83, a value of 1.6, and b value of 2.5. The color of the fabric after bleaching was stable, and the amount of color transfer was reduced. The total amount of dye removed was about 99.6 wt%.

[0055] Example 6

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

[0057] Comparative Example 1

[0058] The main differences between the processing procedure of Comparative Example 1 and the processing procedure of Example 1 are that steps S1 and S2 are skipped, and step S3 is repeated three times in step S4.

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

[0060] After the obtained bleached polyester fabric was subjected to a drying process, the measured CIELAB color definition of the bleached polyester fabric produced in Comparative Example 1 was L value 87, a value 2.1, and b value 6.1. Since the fabric itself contained red and yellow dyes, the color of the fabric was still reddish (high a value) and yellowish (high b value) even after continuously using fresh solvent for bleaching. The total amount of dye removed was about 99.6 wt%.

[0061] Comparative Example 2

[0062] The main difference between the processing procedure of Comparative Example 2 and the processing procedure of Example 2 is that steps S1 and S2 are skipped, and step S3 is repeated three times in step S4.

[0063] In Comparative Example 2, the second extraction process was performed a total of four times, so the total amount of fresh solvent used was up to 24 times the weight of the PET fabric, and the total weight of the propylene glycol monomethyl ether recycled solvent produced was also about 24 times the weight of the PET fabric. In the overall decolorization process of Comparative Example 2, the recycled solvent was not reused, so the recycled solvent needed to be purified by distillation or evaporation for reuse, which significantly increased the amount of solvent to be purified in the overall decolorization process, and increased the energy consumption and purification cost of the solvent.

[0064] After the obtained bleached polyester fabric was subjected to a drying process, the measured CIELAB color definition of the bleached polyester fabric produced in Comparative Example 2 was L value 88, a value 3.8, and b value 6.8. Since the fabric itself contained red and yellow dyes, the color of the fabric was still reddish (high a value) and yellowish (high b value) even after continuously using fresh solvent for bleaching. The total amount of dye removed was about 99.7 wt%.

[0065] Comparative Example 3

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

[0067] In Comparative Example 3, the second extraction process was performed twice in total, so the total amount of fresh solvent used was about 12 times the weight of the PET fabric, and the total weight of the propylene glycol monomethyl ether recycled solvent produced was also about 12 times the weight of the PET fabric. In the overall decolorization process of Comparative Example 3, the recycled solvent was not reused, so the recycled solvent needed to be purified by distillation or evaporation for reuse, and therefore the amount of solvent to be purified in the overall decolorization process also increased, which increased the energy consumption and purification cost of the solvent.

[0068] After the obtained bleached polyester fabric was dried, the measured CIELAB color definition of the bleached polyester fabric produced in Comparative Example 3 was L value 75, a value 3.2, and b value 6.3. The bleached polyester fabric had noticeable dye residue due to incomplete dye removal, and the bleaching was incomplete. The total amount of dye removed 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 bleached polyester fabric produced in Comparative Example 4 was an L value of 86, an a value of 2.3, and a b value of 6.4. Since the fabric itself contained red and yellow dyes, the color of the fabric was still reddish (high a value) and yellowish (high b value) even after continued use of fresh solvent for bleaching. The total amount of dye removed was about 99.5 wt%.

[0071] Comparative Example 5

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

[0073] Comparative Example 6

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

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

[0076] [Table 1]

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

[0078] Furthermore, as can be seen from Examples 4 to 6, stable fabric color after bleaching and reduced color transfer can be achieved by using xylene or dimethylacetamide as a solvent. As for Comparative Examples 4 to 6, the use of xylene or dimethylacetamide as a solvent could not improve the redness, yellowness, and incomplete bleaching of the bleached fabrics of Comparative Example 1 or Comparative Example 3.

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

[0080] As described above, the method for bleaching polyester fabrics of the present invention can reduce the color transfer phenomenon of the bleached polyester fabrics by using a recycled solvent to perform the above-mentioned extraction treatment on the polyester fabrics, and at the same time, the amount of fresh solvent used, the amount of recycled solvent produced, and the amount of solvent to be purified can be significantly reduced, thereby reducing the cost required for bleaching polyester fabrics. [Industrial Applicability]

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

[0082] S1, S2, S3, S4 steps

Claims

1. performing a first extraction process on the polyester fabric using a recycled solvent to transfer a first portion of the dye in the polyester fabric to the recycled solvent; subjecting the recycled solvent and the polyester fabric to a first filtration process to obtain a treated polyester fabric; subjecting the treated polyester fabric to a second extraction treatment using fresh solvent to transfer a second portion of the dye in the treated polyester fabric to the fresh solvent; performing a second filtration process to obtain a decolorized polyester fabric and the recycled solvent; A method for bleaching polyester fabric comprising the steps of:

2. 2. The method for decolorizing according to claim 1, wherein the recycled solvent comprises the fresh solvent and the dye, and the dye is present in an amount of 0.1% to 10% by weight based on the total weight of the recycled solvent.

3. 2. The method for decolorizing according to claim 1, wherein in the first extraction process, the weight ratio of the recycled solvent to the polyester fabric is 4:1 to 50:

1.

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

1.

5. 2. The method of claim 1, wherein the fresh solvent comprises an aromatic hydrocarbon solvent, an alcohol ether solvent, an alcohol solvent, or an amide solvent.

6. 2. The method of 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.

7. 2. The method according to claim 1, wherein the total amount of the first and second portions to be removed is 90% by weight to 99.9% by weight based on the total weight of the dye.

8. 2. The method for bleaching according to claim 1, wherein the bleached polyester fabric has a CIELAB color definition of L value of 80 or more, a value of -3.0 to +3.0, and b value of -6.0 to +6.

0.

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

10. The decolorization method according to claim 1, further comprising repeating a cycle of the second extraction treatment and the second filtration treatment one to three times after the second filtration treatment.

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