Method for preparing low-temperature easy-to-dye polyester by chemical recycling of waste textiles

Abstract

This invention discloses a method for preparing low-temperature easily dyeable polyester through chemical recycling of waste textiles, belonging to the field of polyester synthesis technology. The method includes the following steps: A) alcoholystomosis of waste polyester textiles to obtain aromatic polyester polyols; B) alcoholystomosis of waste polyester textiles to obtain a BHET solution; C) transesterification of the BHET solution with methanol and a catalyst to obtain pure DMT; D) transesterification of pure DMT with ethylene glycol, a transesterification catalyst, and a DEG inhibitor; E) copolymerization of the polyester polyol into the transesterification system, followed by polymerization with a polymerization catalyst, stabilizer, and antioxidant to obtain low-temperature easily dyeable polyester chips. This invention chemically copolymerizes different monomers from waste polyester textiles, achieving low-temperature dyeing of polyester fibers at 95℃~98℃, and also endowing the material with moisture-wicking, quick-drying, ultra-soft, skin-friendly, and high color fastness properties.

Description

Technical Field

[0001] This invention relates to the field of polyester synthesis technology, and more specifically, to a method for preparing low-temperature easily dyeable polyester by chemically recycling waste textiles. Background Technology

[0002] The current lack of effective recycling and disposal methods for the vast amount of waste textiles means that conventional landfilling and incineration release harmful substances that severely pollute soil, water, and air. The current state of the textile industry no longer meets the requirements of sustainability, recyclability, and traceability, and urgently needs to be changed. As a major component of this, how to achieve clean recycling and high-value utilization of waste polyester textiles has become a significant challenge for the textile industry.

[0003] In the textile industry, polyester fibers are widely used due to their durability and ease of care. However, traditional polyester dyeing processes often require high temperatures and large amounts of water, which not only consumes energy but also burdens the environment. Currently, a technology for dyeing virgin polyester with disperse dyes under low-temperature and normal-pressure conditions has been developed. The main technical route involves direct esterification with terephthalic acid (PTA) and copolymerization with the addition of a third and fourth modifying monomer to achieve the functional development of easily dyeable polyester at low temperatures. All raw materials and auxiliaries involved are obtained through petroleum-based refining and synthesis. However, while this method of producing easily dyeable polyester at low temperatures reduces energy consumption and environmental impact to some extent, its raw material source still relies on petroleum resources, which contradicts the current global trend of sustainable development.

[0004] Therefore, it is particularly important to develop a low-temperature dyeable polyester production method based on the recycling of waste textiles, which is environmentally friendly and cost-effective. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing low-temperature dyeable polyester through chemical recycling of waste textiles. This method first pre-treats waste polyester textiles, then chemically depolymerizes them into polyester polyols and dimethyl terephthalate (DMT), and then copolymerizes them with ethylene glycol (EG) to prepare chemically recycled polyester with low-temperature dyeability.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing low-temperature easily dyeable polyester through chemical recycling of waste textiles includes the following steps:

[0008] A. Using polyol as a depolymerizing agent, waste polyester textiles are alcoholyzed under the action of a catalyst to obtain aromatic polyester polyol.

[0009] B. Using ethylene glycol as a depolymerization agent, waste polyester textiles are alcoholyzed under the action of a catalyst. After depolymerization, the resulting BHET solution is subjected to polyester-impurity separation and concentration treatment to obtain BHET solution.

[0010] C. The concentrated BHET solution obtained in step B is mixed with methanol and catalyst to carry out transesterification reaction to obtain pure DMT.

[0011] D. Mix the pure DMT prepared in step C with ethylene glycol, transesterification catalyst, and DEG inhibitor to carry out transesterification reaction.

[0012] E. Add the polyester polyol prepared in step A to the system after the transesterification reaction for copolymerization. After copolymerization, add a polymerization catalyst, stabilizer and antioxidant for further polymerization to obtain low-temperature dyeable polyester chips.

[0013] The present invention is further configured such that step A specifically comprises: mixing polyester foam obtained from waste polyester textiles through melt granulation with a polyol depolymerizing agent and a catalyst for depolymerization to obtain a polyester polyol mixture; subjecting the obtained polyester polyol mixture to polyester-impurity separation and concentration treatment; and subjecting the concentrated crude polyester polyol solution to decolorization, centrifugation, distillation, and cooling crystallization treatment to obtain polyester polyol; the mass ratio of polyester foam to polyol and catalyst is (60-100):(100-140):(1-3); the depolymerization reaction temperature is 180-250℃, the pressure is 0-0.2MPa, and the reaction time is 2-5h.

[0014] The present invention is further configured such that the polyol depolymerizing agent is an aliphatic polyol compound, including but not limited to: diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butanediol, neopentyl glycol, sweet alcohol, n-hexanol, serine, poly(oxyalkylene) polyol, 2-methyl-2,4-pentanediol, 1,6-hexanediol, and 1,2-cyclohexanediol, one or more of these compounds.

[0015] The present invention is further configured such that step B specifically comprises: mixing polyester foam obtained by melt granulation of waste polyester textiles with ethylene glycol and catalyst for depolymerization, and then performing polyester-impurity separation and concentration treatment on the BHET solution obtained by depolymerization; the mass ratio of polyester foam to ethylene glycol and catalyst is (60-100):(100-140):(1-3); the depolymerization reaction temperature is 180-250℃, the pressure is 0~0.2MPa, and the reaction time is 2~5h.

[0016] The present invention is further configured such that step C specifically comprises: conveying the concentrated BHET solution to a transesterification reactor, adding methanol and catalyst to carry out transesterification reaction, obtaining crude DMT solution and EG; the crude DMT solution is subjected to decolorization, centrifugation, distillation, and cooling crystallization to obtain pure DMT crystals; the mass ratio of methanol, concentrated BHET solution and catalyst is 280~360:90~120:1~5; the transesterification reaction temperature is 70~120℃, the pressure is 0~0.2MPa, and the reaction time is 2~4h.

[0017] The present invention is further configured such that, in steps (A), (B), and (C), the catalyst is one or more of the following: organometallic catalyst, non-metallic organic catalyst, ionic liquid, and imidazole derivative, including but not limited to: zinc acetate, calcium acetate, potassium acetate, manganese acetate, cyanamide, and ammonia borane.

[0018] The present invention is further configured such that step D specifically comprises: adding the pure DMT obtained in step C, EG, transesterification catalyst, and DEG inhibitor into a transesterification reactor, and carrying out the transesterification reaction for 2-5 hours while stirring and heating to 222°C, during which methanol is precipitated; the mass ratio of EG, DMT, transesterification catalyst, and DEG inhibitor is 20~40:90-120:0.5~3.5:0.001~0.01; the transesterification catalyst is manganese acetate, and the DEG inhibitor is sodium acetate.

[0019] The present invention is further configured such that step E specifically comprises:

[0020] E1. After the transesterification reaction is completed, polyester polyol is added to the transesterification system at 222~228℃. Copolymerization is carried out at atmospheric pressure while the temperature is raised to 240~250℃. When the temperature reaches 240~250℃, excess EG is distilled off. The top temperature of the reactor is controlled below 190℃. Polymerization catalyst, stabilizer and antioxidant are added to the transesterification reactor and the temperature is raised again.

[0021] E2. When the temperature of the reaction system in the polymerization reactor reaches 268~270℃, stop heating and evacuate until the pressure in the polymerization reactor reaches 10~20Pa. While stirring at high and low speeds, heat to 281~286℃ to carry out the polymerization reaction and obtain modified polyester melt. The modified polyester melt is then pelletized and dried to obtain low-temperature dyeable polyester chips.

[0022] The present invention is further configured such that, in step E1, the polyester polyol accounts for 5-20% of the mass of pure DMT added in step D; the copolymerization reaction time is 1-3 h; the polymerization catalyst accounts for 1-3% of the mass of DMT added in step D; the stabilizer accounts for 1-3% of the mass of DMT added in step D; the antioxidant accounts for 0.0001-0.0008% of the mass of DMT added in step D; the polymerization catalyst is antimony glycolate; the stabilizer is trimethyl phosphate; and the antioxidant is a sterically hindered phenolic antioxidant.

[0023] The present invention is further configured such that, in step E2, the polymerization reaction time is 1-3 hours.

[0024] In summary, the present invention has the following beneficial effects:

[0025] (1) The present invention provides a three monomers that can achieve low-temperature dyeing polyester modification, which are obtained by chemical depolymerization of waste polyester textiles, realizing the one-step production of recycled polyester polyols from waste textiles.

[0026] (2) By chemically regenerating DMT and reacting it with EG, and then polymerizing it with chemically regenerated polyester polyol, a low-temperature dyeable polyester material was prepared. This achieved the goal of preparing recycled low-temperature dyeable polyester products with all main raw materials except catalyst and a small amount of auxiliary agent being chemically recycled products.

[0027] (3) The recycling preparation method of the present invention also has the advantages of simple process and low cost. Through the process of chemical depolymerization and repolymerization, the polyester segments in waste polyester mixed textiles can be rearranged to form a new polyester molecular structure. In addition to achieving the low temperature dyeing function of 95℃~98℃, it also endows the material with the characteristics of moisture absorption and quick drying, ultra-soft and skin-friendly (the modified polyester textile product has excellent moisture absorption and quick drying characteristics, and the grade can reach II~III) and high color fastness (reaching grade 4~5).

[0028] (4) In practical applications, the low-temperature dyeable polyester prepared by this invention can be widely used in textiles, clothing, home decoration and other fields. Due to its excellent dyeing performance and low dyeing temperature, it can significantly reduce energy consumption and cost in the dyeing process, and at the same time reduce the wastewater discharge that may be generated in the dyeing process, which is of positive significance for environmental protection. In addition, unlike the three monomers and four monomers added to traditional virgin low-temperature dyeable products, the three monomers in the product of this invention can be recycled by chemical methods in the polyester system to obtain polyester polyol or BHET or DMT again. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] The method for preparing low-temperature easily dyeable polyester by chemical recycling of waste textiles according to the present invention is as follows:

[0031] (A) Prepare polyester polyols by alcoholysis of waste polyester textiles:

[0032] A1. Polyester foam material obtained by melt granulation of waste polyester textiles (i.e., the washed waste polyester textiles are sorted and zippers are removed, and then melt granulated by a screw extruder to obtain polyester foam material) is mixed with polyol depolymerizing agent and catalyst at a mass ratio of (60-100):(100-140):(1-3), and depolymerized at 180-250℃ and 0~0.2MPa for 2~5h to obtain polyester polyol mixture;

[0033] Among them, the polyol depolymerizing agent is an aliphatic polyol compound, including but not limited to: diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butanediol, neopentyl glycol, sweet alcohol, n-hexanol, serine, poly(oxyalkylene) polyol, 2-methyl-2,4-pentanediol, 1,6-hexanediol, and 1,2-cyclohexanediol, one or more of these.

[0034] The catalyst is one or more of the following: organometallic catalyst, non-metallic organic catalyst, ionic liquid, and imidazole derivative, including but not limited to: zinc acetate, calcium acetate, potassium acetate, manganese acetate, monocyanamide, and ammonia borane.

[0035] A2. The obtained polyester polyol mixture is subjected to impurity separation and concentration treatment. Then, methanol is added to decolorize the crude polyester polyol solution obtained after concentration. After multiple centrifugation separations, it is distilled under conditions of 6~13kPa and 200~209℃. Then, it is cooled to 35~50℃ for vacuum cooling and crystallization to obtain pure aromatic polyester polyol crystals.

[0036] (B) Prepare polyethylene terephthalate (BHET) by alcoholysis of waste polyester textiles with ethylene glycol:

[0037] B1. Polyester foam material obtained by melt granulation of waste polyester textiles (i.e., the washed waste polyester textiles are sorted and zippers are removed, and then melted and granulated by a screw extruder to obtain polyester foam material) is mixed with ethylene glycol and catalyst at a mass ratio of (60-100):(100-140):(1-3) and depolymerized at 180-250℃ and 0~0.2MPa for 2~5h.

[0038] B2. The BHET solution obtained from depolymerization is subjected to impurity separation and concentration treatment (specifically: the obtained BHET solution is filtered to separate impurities that are insoluble in ethylene glycol, the upper layer of the depolymerized solution is overflowed through the overflow pipe, and then the BHET solution after impurity separation is heated and concentrated).

[0039] The catalyst is one or more of the following: organometallic catalyst, non-metallic organic catalyst, ionic liquid, and imidazole derivative, including but not limited to: zinc acetate, calcium acetate, potassium acetate, manganese acetate, cyanamide, and ammonia borane.

[0040] (C) BHET transesterification reaction to prepare dimethyl terephthalate (DMT):

[0041] The concentrated BHET solution was transferred to a transesterification reactor, and methanol and a catalyst (the mass ratio of methanol, concentrated BHET solution and catalyst was 280~360:90~120:1~5, and the catalyst was one or more of the following: organometallic catalyst, non-metallic organic catalyst, ionic liquid, and imidazole derivative, including but not limited to: zinc acetate, calcium acetate, potassium acetate, manganese acetate, cyanamide, and ammonia borane) were added. The transesterification reaction was carried out at 70~120℃ and 0~0.2 MPa for 2~4 hours to obtain crude DMT solution and EG. Methanol was added to the crude DMT solution to decolorize it. After multiple centrifugations, relatively pure DMT was obtained. Then, it was distilled at 6~13 kPa and 200~209℃, and then cooled to 35~50℃ for vacuum cooling crystallization to obtain pure DMT crystals.

[0042] (D) DMT and EG transesterification reaction:

[0043] Pure DMT, EG, transesterification catalyst, and DEG inhibitor were added to a transesterification reactor (the mass ratio of EG, DMT, transesterification catalyst, and DEG inhibitor was 20~40:90-120:0.5~3.5:0.001~0.01; the transesterification catalyst was manganese acetate, and the DEG inhibitor was sodium acetate). The transesterification reaction was carried out while stirring and heating to 222℃ (the transesterification reaction was controlled for 2-5 hours). Methanol was precipitated during the reaction (the reaction started and methanol was precipitated when the reaction temperature reached 140~180℃).

[0044] (E) Polymerization reaction:

[0045] E1. After the transesterification reaction is completed, polyester polyol (5-20% of the mass of pure DMT added in step D) is added to the transesterification system at 222-228℃. Copolymerization is carried out under normal pressure while heating to 240-250℃ for 1-3 hours. When the temperature reaches 240-250℃, excess EG is distilled off. The top temperature of the reactor is controlled below 190℃. Polymerization catalyst, stabilizer and antioxidant are added to the transesterification reactor (the mass ratio of polymerization catalyst, stabilizer and antioxidant to DMT added in step D is 1-3%, 1-3% and 0.0001-0.0008% respectively; the polymerization catalyst is antimony glycolate, the stabilizer is trimethyl phosphate and the antioxidant is a hindered phenolic antioxidant). The temperature is then increased.

[0046] E2. When the temperature of the reaction system in the polymerization reactor reaches 268~270℃, stop heating and evacuate to a pressure of 10~20Pa in the polymerization reactor (first evacuate to a low vacuum of 500~1000 Pa, then evacuate to a high vacuum of 10~20Pa). Then, while stirring at high and low speeds, heat to 281~286℃ and carry out the polymerization reaction (in the initial stage of the reaction, use a high stirring frequency of 99.9%, and switch to a low stirring frequency of 45% when the temperature in the polymerization reactor reaches 281~286℃). The polymerization reaction time is 1-3 hours to obtain modified polyester melt. The modified polyester melt is then pelletized and dried to obtain low-temperature dyeable polyester chips.

[0047] In this invention, waste polyester textiles are preferably waste textiles with a polyester content of 80% or more, including but not limited to waste clothing, curtains, carpets, webbing, fishing nets, automotive textiles, etc. In addition, waste PET materials (such as waste PET plastic parts, bottles, films, etc.) can also be made into low-temperature dyeable polyester chips according to the method of this invention.

[0048] Example 1

[0049] (A) 800 kg of polyester foam material obtained from waste polyester textiles through melt granulation was mixed with 1200 kg of tripropylene glycol and 30 kg of zinc acetate for depolymerization reaction (depolymerization reaction temperature was 220℃, reaction time was 4 h, and depolymerization reaction pressure was controlled at 0.2 MPa) to obtain a polyester polyol mixture. The obtained polyester polyol mixture was heated and concentrated, and then methanol was added to decolorize the crude polyester polyol solution obtained after concentration. After multiple centrifugation separations, it was distilled at 10 kPa and 205℃, and then cooled to 35℃ for vacuum cooling crystallization to obtain pure polyester polyol crystals.

[0050] (B) Take 800 kg of polyester foam obtained from waste polyester textiles through melt granulation, 1200 kg of ethylene glycol, and 30 kg of zinc acetate, and mix them for depolymerization reaction (depolymerization reaction temperature is 220℃, reaction time is 4h, and the pressure of the depolymerization reactor is controlled at 0.2MPa) to obtain BHET mixture. Filter the BHET solution obtained from depolymerization to separate impurities such as cotton and linen that are insoluble in ethylene glycol, and then heat and concentrate the BHET solution after separation of polyester and impurities.

[0051] (C) The concentrated BHET solution was transferred to the transesterification reactor, and methanol and zinc acetate were added to carry out the transesterification reaction (the mass ratio of methanol, concentrated BHET solution and zinc acetate was 300 kg: 100 kg: 2 kg; the reaction temperature of the transesterification reaction was 100 °C, the reaction time was 4 h, and the reaction pressure was 0.15 MPa), to obtain crude DMT solution and EG; methanol was added to the crude DMT solution to decolorize it, and after multiple centrifugations, relatively pure DMT was obtained, and then it was distilled at 9 kPa and 205 °C, and then cooled to 35 °C for vacuum cooling crystallization to precipitate pure DMT crystals.

[0052] (D) 200 kg of pure DMT, 1100 kg of EG, 30 kg of manganese acetate and 10 g of sodium acetate were added to the transesterification reactor and the transesterification reaction was carried out while stirring and heating to 222°C (the transesterification reaction was controlled for 4 h). Methanol was precipitated during the reaction.

[0053] (E) After the transesterification reaction is completed, polyester polyol (10% of the mass of pure DMT in step D) is added at 222°C. Copolymerization is carried out under normal pressure while the temperature is raised to 245°C for 2 hours. When the temperature reaches 245°C, excess EG is distilled off. The top temperature of the reactor is controlled below 190°C. 5 kg of antimony glycolate polymerization catalyst, 0.2 kg of trimethyl phosphate stabilizer, and 1 kg of other additives are added to the transesterification reactor. After adding 1010 g of antioxidant, the temperature was increased further. When the temperature of the reaction system in the polymerization reactor reached 268°C, the heating was stopped, and a vacuum was drawn until the pressure in the polymerization reactor reached 20 Pa. Then, the temperature was increased to 283°C while stirring at high and low speeds (high-speed stirring was carried out at a stirring frequency of 99.9% in the initial stage of the reaction, and then the stirring frequency was switched to 45% for low-speed stirring when the temperature in the polymerization reactor reached 283°C). The polymerization reaction time was 2 hours, and the modified polyester melt was obtained. The modified polyester melt was then pelletized and dried to obtain low-temperature dyeable polyester chips.

[0054] Example 2

[0055] The slices were produced according to the method of Example 1, except that the tripropylene glycol in step (A) was replaced by 2-methyl-2,4-pentanediol.

[0056] Example 3

[0057] The slices were produced according to the method of Example 1, except that the tripropylene glycol in step (A) was replaced by neopentyl glycol.

[0058] Example 4

[0059] The slices were produced according to the method of Example 1, except that: in step (A), the depolymerization reaction temperature was 230°C and the reaction time was 5 h; in step (B), the depolymerization reaction temperature was 230°C and the reaction time was 5 h; in step (C), the mass ratio of methanol, concentrated BHET solution and zinc acetate catalyst was 350 kg: 100 kg: 1.5 kg.

[0060] Example 5

[0061] The chips are produced according to the method of Example 1, except that in step (E), the polyester polyol accounts for 5% of the mass of pure DMT.

[0062] Example 6

[0063] The chips are produced according to the method of Example 1, except that in step (E), the polyester polyol accounts for 15% of the mass of pure DMT.

[0064] Example 7

[0065] The chips are produced according to the method of Example 1, except that in step (E), the polyester polyol accounts for 20% of the mass of pure DMT.

[0066] Comparative Example 1

[0067] The chips are produced according to the method of Example 1, except that step (A) is not performed; and in step (E), no polyester polyol is added.

[0068] Comparative Example 2

[0069] The chips were produced according to the method of Example 1, except that step (A) was omitted; and in step (E), the polyester polyol was replaced with tripropylene glycol in an equimolar amount.

[0070] Comparative Example 3

[0071] 1000 kg of waste polyester textiles, 1000 kg of diethylene glycol, 0.8 kg of zinc acetate, and 0.8 kg of tetrabutyl titanate were added to a reactor. Nitrogen gas was introduced, and the mixture was stirred and heated to 235°C. The mixture was stirred at a constant temperature for 20 minutes to completely dissolve the waste textile raw materials. Then, the temperature was slowly increased to 240°C, and an alcoholysis reaction was carried out at a constant temperature for 6 hours under nitrogen protection. When the amount of ethylene glycol removed by the distillation column of the reactor reached 48 kg and the viscosity of the reactants reached 1100~1200 mPa·s at 25°C, the reaction was stopped, and the temperature was lowered to 160°C. Impurities were filtered through diatomaceous earth to obtain a polyester polyol mixture. The polyester polyol mixture was heated and concentrated to obtain a crude polyester polyol solution, which was then cooled and crystallized to obtain polyester polyol crystals. Polyester polymerization was then carried out according to steps (B) to (E) in Example 1 to obtain a brown polyester product.

[0072] Comparative Example 4

[0073] The chips are produced according to the method of Example 1, except that the waste polyester raw material is waste polyester (PET) bottle flakes in three colors.

[0074] Comparative Example 5

[0075] The chips were produced according to the method of Example 1, except that the waste polyester raw material was waste polyester (PET) release film.

[0076] Performance tests were conducted on Examples 1-7 and Comparative Examples 1-5, and the results are shown in the table below:

[0077]

[0078] Moisture absorption and quick-drying properties and color fastness were tested on the slices of Examples 1-7 respectively. The results showed that the moisture absorption and quick-drying properties of the slices of Examples 1-7 were in the range of Grade II to III and the color fastness was in the range of Grade 4 to 5. Among them, the moisture absorption and quick-drying properties of the slice of Example 1 were Grade III and the color fastness was Grade 4.5.

[0079] Comparative Example 6

[0080] The slices were produced according to the method of Example 1, except that step (A) was omitted; in step (E), the polyester polyol was replaced in equimolar amounts with polymethyl propylene adipate polyol with a number average molecular weight of 2000.

[0081] Comparative Example 7

[0082] The chips were produced according to the method of Example 1, except that step (E) was as follows: after the transesterification reaction was completed, polyester polyol (10% of the mass of pure DMT in step D) was added at 235°C, the temperature was raised to 260°C and the reaction pressure was controlled at 3 kPa for copolymerization reaction, and the copolymerization reaction time was 2 h; after the reaction, excess EG was distilled off, the top temperature of the reactor was controlled below 190°C, 5 kg of polymerization catalyst antimony glycolate, 0.2 kg of stabilizer trimethyl phosphate and 1 g of antioxidant 1010 were added to the transesterification reactor and the temperature was raised again; when the temperature of the reaction system in the polymerization reactor reached 265°C, the heating was stopped, the vacuum was drawn until the pressure in the polymerization reactor reached 100 Pa, and the polymerization reaction was carried out at 265°C and 100 Pa for 2 h to obtain modified polyester melt; the modified polyester melt was pelletized and dried to obtain polyester chips.

[0083] Comparative Example 8

[0084] The chips were produced according to the method of Example 1, except that in step (E), the polyester polyol was then heated to 265°C while undergoing a copolymerization reaction, and the reaction pressure was controlled at 3 kPa.

[0085] Comparative Example 9

[0086] The slices were produced according to the method of Example 1, except that in step (E), the heating was stopped when the temperature of the reaction system in the polymerization reactor reached 265°C, and the pressure in the polymerization reactor was evacuated to 100Pa before the polymerization reaction was carried out at 265°C and 100Pa.

[0087] The staining rate (disperse blue 2BLN staining at 95℃ under normal pressure) and color fastness performance of the slices from Comparative Examples 6 to 9 were tested. The results showed that the staining rates of Comparative Examples 6 to 9 were 89%, 77%, 81%, and 84%, respectively, and the color fastness was grade 3, grade 3, grade 3.5, and grade 3.5, respectively.

[0088] In the performance tests of the above embodiments and comparative examples: intrinsic viscosity, melting point, terminal carboxyl groups, diethylene glycol content, and color were all tested according to GB / T14190-2017; referring to the method in Example 1 of the instruction manual for "A Production Process of Recycled Polyol Modified PET Copolyester DTY" (CN118272939A), the chips of each embodiment and comparative example were made into DTY yarn using the same process, and the dyeing rate was tested according to GB / T 23976.1-2009 (the fibers spun from each chip were dyed with Disperse Blue 2BLN under normal pressure); the above DTY yarns were woven into fabrics of the same specifications, and the color fastness was tested according to GB / T 250-2008 "Tests for Color Fastness - Assessment of Color Change - Gray Scale," referring to GB / T 21655.1-2023 "Evaluation of the quick-drying properties of textiles - Part 1: Single-item combination test method" is used to test the quick-drying properties of textiles (by measuring the water absorption rate, water diffusion time, drying rate and wicking height of the fabric under specified conditions to simulate the process of water absorption, diffusion and drying in the fabric, so as to comprehensively characterize the quick-drying properties of the fabric).

[0089] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing low-temperature easily dyeable polyester through chemical recycling of waste textiles, characterized in that, Includes the following steps: A. Using polyol as a depolymerizing agent, waste polyester textiles are alcoholyzed under the action of a catalyst to obtain aromatic polyester polyol. Step A specifically involves: mixing polyester foam material obtained from waste polyester textiles through melt granulation with a polyol depolymerizing agent and a catalyst for depolymerization to obtain a polyester polyol mixture; subjecting the obtained polyester polyol mixture to polyester-impurity separation and concentration; and then subjecting the concentrated crude polyester polyol solution to decolorization, centrifugation, distillation, and cooling crystallization to obtain polyester polyol; the mass ratio of polyester foam material to polyol and catalyst is (60-100):(100-140):(1-3); the depolymerization reaction temperature is 180-250℃, the pressure is 0-0.2MPa, and the reaction time is 2-5h. B. Using ethylene glycol as a depolymerization agent, waste polyester textiles are alcoholyzed under the action of a catalyst. After depolymerization, the resulting BHET solution is subjected to polyester-impurity separation and concentration treatment to obtain BHET solution. C. The concentrated BHET solution obtained in step B is mixed with methanol and catalyst to carry out transesterification reaction to obtain pure DMT. D. Mix the pure DMT prepared in step C with ethylene glycol, transesterification catalyst, and DEG inhibitor to carry out transesterification reaction. E. Add the polyester polyol prepared in step A to the system after the transesterification reaction for copolymerization. After copolymerization, add a polymerization catalyst, stabilizer and antioxidant for polymerization to obtain low-temperature dyeable polyester chips. Step E specifically involves: E1. After the transesterification reaction is completed, polyester polyol is added to the transesterification system at 222~228℃. Copolymerization is carried out at atmospheric pressure while the temperature is raised to 240~250℃. When the temperature reaches 240~250℃, excess EG is distilled off. The top temperature of the reactor is controlled below 190℃. Polymerization catalyst, stabilizer and antioxidant are added to the transesterification reactor and the temperature is raised again. E2. When the temperature of the reaction system in the polymerization reactor reaches 268~270℃, stop heating and evacuate until the pressure in the polymerization reactor reaches 10~20Pa. While stirring at high and low speeds, heat to 281~286℃ and carry out the polymerization reaction to obtain modified polyester melt. Specifically, the high and low speed stirring is carried out at a high stirring frequency of 99.9% in the initial stage of the reaction, and then switched to a low stirring frequency of 45% when the temperature in the polymerization reactor reaches 281~286℃. The modified polyester melt is then pelletized and dried to obtain low-temperature dyeable polyester chips.

2. The method for preparing low-temperature easily dyeable polyester by chemical recycling of waste textiles according to claim 1, characterized in that, The polyol depolymerizing agent is an aliphatic polyol compound, specifically one or more of the following: diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butanediol, neopentyl glycol, sweet alcohol, serine, poly(oxyalkylene) polyol, 2-methyl-2,4-pentanediol, 1,6-hexanediol, and 1,2-cyclohexanediol.

3. The method for preparing low-temperature easily dyeable polyester by chemical recycling of waste textiles according to claim 1, characterized in that, Step B specifically involves: mixing polyester foam material obtained from waste polyester textiles through melt granulation with ethylene glycol and a catalyst for depolymerization; then, performing polyester-impurity separation and concentration on the resulting BHET solution; the mass ratio of polyester foam material to ethylene glycol and catalyst is (60-100):(100-140):(1-3); the depolymerization reaction temperature is 180-250℃, the pressure is 0-0.2MPa, and the reaction time is 2-5h.

4. The method for preparing low-temperature easily dyeable polyester by chemical recycling of waste textiles according to claim 1, characterized in that, Step C specifically involves: transferring the concentrated BHET solution to the transesterification reactor, adding methanol and catalyst to carry out the transesterification reaction, and obtaining crude DMT solution and EG; the crude DMT solution is then subjected to decolorization, centrifugation, distillation, and cooling crystallization to obtain pure DMT crystals; The mass ratio of methanol, concentrated BHET solution and catalyst is 280~360:90~120:1~5; the transesterification reaction temperature is 70~120℃, the pressure is 0~0.2MPa, and the reaction time is 2~4h.

5. The method for preparing low-temperature easily dyeable polyester by chemical recycling of waste textiles according to claim 1, characterized in that, In steps (A), (B), and (C), the catalyst is one or more of the following: organometallic catalyst, non-metallic organic catalyst, ionic liquid, and imidazole derivative, specifically one or more of zinc acetate, calcium acetate, potassium acetate, manganese acetate, cyanamide, and ammonia borane.

6. The method for preparing low-temperature easily dyeable polyester by chemical recycling of waste textiles according to claim 1, characterized in that, Step D specifically involves adding the pure DMT obtained in step C, along with EG, the transesterification catalyst, and the DEG inhibitor, into a transesterification reactor. The reactor is stirred and heated to 222°C for 2-5 hours, during which methanol is precipitated. The mass ratio of EG, DMT, transesterification catalyst, and DEG inhibitor is 20-40:90-120:0.5-3.5:0.001-0.

01. The transesterification catalyst is manganese acetate, and the DEG inhibitor is sodium acetate.

7. The method for preparing low-temperature easily dyeable polyester by chemical recycling of waste textiles according to claim 1, characterized in that, In step E1, the polyester polyol accounts for 5-20% of the mass of pure DMT added in step D; the copolymerization reaction time is 1-3 hours; the polymerization catalyst accounts for 1-3% of the mass of DMT added in step D, the stabilizer accounts for 1-3% of the mass of DMT added in step D, and the antioxidant accounts for 0.0001-0.0008% of the mass of DMT added in step D. The polymerization catalyst is antimony glycolate, the stabilizer is trimethyl phosphate, and the antioxidant is a sterically hindered phenolic antioxidant.

8. The method for preparing low-temperature easily dyeable polyester by chemical recycling of waste textiles according to claim 1, characterized in that, In step E2, the polymerization reaction time is 1-3 hours.

Images