A preparation method of high-elastic spandex and the prepared high-elastic spandex

Abstract

The present invention provides a method for preparing high-elastic spandex by recycling polyester and the prepared high-elastic spandex, the method comprising the following steps: 1) using PTA to react with a diol with a molecular weight less than 200 to prepare an aromatic polyester diol; 2) reacting the aromatic polyester diol prepared in step 1) with a diisocyanate to obtain a prepolymer; 3) extending the chain of the prepolymer to obtain a polyurethane polymer; 4) spinning the polyurethane polymer to obtain high-elastic spandex. The PTA can be recycled from polyester, and recycled materials are used, making the production process more environmentally friendly. At the same time, the introduction of aromatic rings increases the tensile modulus of the spandex, so that the spandex has better elasticity.

Description

Technical Field

[0001] The invention relates to the field of a method for preparing spandex, and in particular to the field of a method for preparing high-elastic polyester spandex by using recycled polyester. Background Art

[0002] Spandex is the abbreviation of polyurethane fiber, which is the most widely used elastic fiber at present. The mainstream spandex for clothing on the market is polyether spandex produced by dry process. The main raw materials of dry process polyether spandex are polytetramethylene ether diol, diphenylmethane diisocyanate, and chain-extended amines. The polyurethane urea solution is prepared by two-step polymerization reaction, and then necessary additives are added to prepare polyurethane urea spinning solution, and spandex fiber is obtained by tunnel spinning. The spandex fiber obtained by this method has relatively balanced performance, usually with high elastic elongation, and its tensile modulus can basically meet the requirements of daily clothing. In addition to polyether spandex prepared by polyether diol represented by polytetramethylene ether diol, some polyester diols can also be used as raw materials for spandex, such as polyester diol obtained by copolymerizing aliphatic diacids such as succinic acid or adipic acid with aliphatic diols such as ethylene glycol or butanediol. The polyester diol reacts with diisocyanate to obtain polyester spandex.

[0003] The common soft segment raw material of spandex is mainly polytetrahydrofuran, which can provide good elastic elongation and elastic recovery, but it is difficult to meet the needs in some scenarios that require high tensile modulus. Spandex is the source of elasticity for elastic fabrics. Improving the elasticity of spandex can improve the elasticity of spandex-containing elastic fabrics. For fabrics that need to be shaped and maintain shape, greater elasticity means better shaping and shape retention capabilities; for ordinary spandex-containing fabrics, greater spandex elasticity means that less spandex can be used to provide the required elasticity. Generally speaking, the price of spandex is higher than that of other common types of fibers, and less spandex usage means that the cost of spandex-containing elastic fabrics will be reduced accordingly.

[0004] The elasticity of spandex can usually be characterized by its tensile modulus and recovery modulus. The inventors have found that the polyester diol prepared by using aromatic dibasic acids instead of common aliphatic dibasic acids such as succinic acid or adipic acid and polyols can make the polyester spandex prepared therefrom have a larger modulus when stretched due to the strong rigidity of the aromatic ring.

[0005] In addition, terephthalic acid (PTA), as a typical aromatic dibasic acid, is widely used in the polyester industry and is the raw material of many polyester plastics, such as PET (polyethylene terephthalate), PTT (polypropylene terephthalate), PBT (polybutylene terephthalate), etc., especially PET plastic is the most important plastic variety, and the recycling of difficult-to-degrade PET waste is an important environmental problem facing mankind. At present, the main PET recycling method is to re-melt and pelletize PET bottle flakes as recycled materials, and then reprocess them into plastic products. However, this method has high requirements on the quality of the recycled PET plastic, requiring less impurities, small color differences, and small molecular weight differences. Many PET wastes that do not meet the above standards are still difficult to recycle and reuse. Therefore, it is necessary to find other PET recycling methods. Summary of the invention

[0006] The present invention provides a method for preparing high-elastic spandex and high-elastic polyester spandex prepared by the method, which uses recycled polyester as a partial material source, improves the tensile modulus of spandex and makes the production process more environmentally friendly. The specific scheme of the present invention is as follows:

[0007] A method for preparing high-elastic spandex, characterized in that it comprises the following steps:

[0008] 1) Using PTA (terephthalic acid) to react with a diol with a molecular weight of less than 200 to prepare an aromatic polyester diol;

[0009] 2) reacting the aromatic polyester diol obtained in step 1) with diisocyanate to obtain a prepolymer;

[0010] 3) chain extending the prepolymer to obtain a polyurethane polymer;

[0011] 4) Spinning the polyurethane polymer to obtain highly elastic spandex.

[0012] Optionally, the PTA is made from recycled polyester.

[0013] Optionally, the preparation method of the PTA is as follows:

[0014] A) crushing the recovered aromatic polyester containing terephthalate structure;

[0015] B) Add ammonia water 4 times the mass of polyester, place in a high temperature and high pressure reactor, and react at 160°C for 8 hours;

[0016] C) the temperature of the reactant obtained in step B) is reduced to below 35° C., and the reactant is transferred to a vacuum distillation apparatus for vacuum distillation, and the distilled ammonia water is recovered;

[0017] D) distilling until the pH of the solution remaining in the device drops below 7.5, adding hydrochloric acid to the remaining solution to lower the pH of the solution to below 5, and then distilling under reduced pressure to collect the small molecule diol fraction;

[0018] E) PTA (terephthalic acid) is precipitated from the bottom liquid after distillation and is used as a raw material for polyester diol after recrystallization with hot water.

[0019] Optionally, the reaction steps of PTA and diol in step 1) are as follows:

[0020] 1.1) PTA and a diol with a molecular weight less than 200 are added to a reaction kettle to carry out an esterification reaction;

[0021] 1.2) After removing moisture from the product after esterification, adding a catalyst and evacuating the product, after the acid value and molecular weight of the polyol reach the target requirements, taking out the obtained aromatic polyester diol;

[0022] In the present invention, PTA is reacted with a small molecule diol to obtain an aromatic polyester diol, and an aromatic ring with strong rigidity is introduced into the soft segment of the spandex, so that the obtained polyester-type spandex has a large modulus when stretched. However, since the aromatic ester group is rigid and has strong interaction, when the aromatic dibasic acid is copolymerized with common small molecule polyols such as conventional ethylene glycol and butanediol, the spandex soft segment will be easily crystallized, resulting in a decrease in the elastic elongation and elastic recovery of the spandex, and also having an adverse effect on the low temperature resistance of the spandex. Therefore, the present invention adopts the following specific small molecule diol to react with PTA to solve the above problems.

[0023] Optionally, the diol in step 1) is a polyether diol having a polymerization degree of 2-4 and containing an ether oxygen bond in the middle.

[0024] Optionally, the diol in step 1) is a diol with a pendant group.

[0025] Optionally, the diol with a pendant group is at least one of 2-methyl-1,3-propanediol and neopentyl glycol.

[0026] Optionally, the diol in step 1) is a mixture of a polyether diol with a polymerization degree of 2-4 containing an ether oxygen bond in the middle and a diol with a side group, wherein the molar ratio of the two is (0.3-3):1.

[0027] Optionally, the molecular weight of the aromatic polyester diol is 1000-5000.

[0028] Optionally, the spinning method in step 4) is dry spinning.

[0029] Optionally, the spinning method in step 4) is melt spinning.

[0030] A high-elastic polyester spandex prepared by the above method is characterized in that the soft segment of the polyester spandex contains an aromatic ring structure.

[0031] Beneficial effects:

[0032] The present invention uses recycled polyester to prepare PTA, uses PTA to react with diol to prepare aromatic polyester diol, utilizes recycled polyester materials, and the production process is more environmentally friendly. In the present invention, ammonia water is used to decompose and recycle polyester, and polyesters of different colors and molecular weights can be recycled together, and the requirements for the raw materials of the recycled polyester are lower.

[0033] The use of PTA to prepare aromatic polyether ester diols, and then using this as a raw material to prepare spandex, can greatly improve the tensile modulus of spandex.

[0034] The use of polyether diols with a polymerization degree of 2-4 containing ether oxygen bonds or diols with side groups can reduce the glass transition temperature and melting point of aromatic ring-containing polyester polyols and reduce their crystallinity, thereby avoiding a decrease in the recovery modulus of the resulting spandex. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme of the present invention is further clearly and completely described through the embodiments below. For the sake of clarity and conciseness, not all features of the actual implementation method are described in the specification. Hereinafter, the PTA refers to terephthalic acid.

[0036] Specifically, the present invention provides a method for preparing high-elastic spandex and the prepared high-elastic spandex, and the specific scheme is as follows:

[0037] A method for preparing high-elastic spandex, characterized in that it comprises the following steps:

[0038] Step 1) using PTA (terephthalic acid) obtained by polyester recovery to react with a diol with a molecular weight of less than 200 to obtain an aromatic polyester diol, wherein the diol is at least one of a polyether diol with a polymerization degree of 2-4 containing an ether oxygen bond in the middle or a diol with a side group, and the molecular weight of the obtained aromatic polyester diol is 1000-5000;

[0039] In the present invention, aromatic polyester diol is prepared by reacting PTA with small molecule diol, and aromatic ring is introduced into the soft segment of spandex, which has strong rigidity and can make the polyester spandex prepared therefrom have a large modulus when stretched. However, since the aromatic ester group is rigid and has strong interaction, when the aromatic dibasic acid is copolymerized with common small molecule polyols such as conventional ethylene glycol and butanediol, the soft segment of spandex will be easily crystallized, resulting in a decrease in the recovery modulus, elastic elongation and elastic recovery rate of the spandex, and will also have an adverse effect on the low temperature resistance of the spandex. Therefore, in the present invention, a polyether diol having a polymerization degree of 2-4 and containing an ether oxygen bond in the molecular structure or a diol with a side group is used for copolymerization with DMT, wherein the side group can increase the distance between ester groups, reduce the interaction, and thus reduce the crystallinity; the ether oxygen bond has strong activity and a certain flexibility, which reduces the rigidity of the ester group, increases the activity, and can also reduce the crystallinity. At the same time, the small molecule polyether diol with a low polymerization degree is relatively more active. If the polymerization degree is too large, the hydroxyl concentration of the polyether diol is low and the reaction time is long. Therefore, in the present invention, the preferred polymerization degree of the polyether diol is 2-4; in addition, the mixed structure of the two diols increases the asymmetry and dissimilarity of the basic structural units, and the mixed structure further reduces the crystallinity. In the present invention, the polyether diol containing ether oxygen bonds can be diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, tetrahydrofuran oligomers with a polymerization degree of 2-4, copolymers of at least two of ethylene oxide, propylene oxide, and tetrahydrofuran, or mixtures of the above substances; the diol with a side group can be at least one of 2-methyl-1,3-propanediol or neopentyl glycol. The aromatic polyester diol prepared by reacting the above diol with PTA is used as the raw material of spandex. The prepared spandex has a higher tensile modulus than conventional polyether spandex. At the same time, the structure of the above specific small molecule diol can reduce the glass transition temperature and melting point of the polyester polyol containing aromatic rings, and reduce its crystallinity. If the molecular weight of the prepared aromatic polyester diol is too low, the prepolymer viscosity will be high, which is not conducive to the process; if the molecular weight of the aromatic polyester diol itself is too high, the aromatic diol itself will have a high melting point and high viscosity, which is also not conducive to the process. Therefore, in the present invention, the molecular weight of the aromatic polyester diol is preferably 1000-5000, preferably 1000-3500, and more preferably 1400-2500.

[0040] In the present invention, the PTA raw material used in step 1) is obtained from recycled polyester, and the specific steps for preparing PTA are as follows:

[0041] A) crushing the recovered aromatic polyester containing terephthalate structure;

[0042] Common recycled aromatic polyesters such as PET (polyethylene terephthalate), PTT (polypropylene terephthalate), and PBT (polybutylene terephthalate) can all be used as raw materials for step A). ​​Compared with melt granulation, the method of the present invention has lower requirements for recycled polyester. Aromatic polyesters of different types, colors, and molecular weights can be crushed together as raw materials for this step.

[0043] B) Add ammonia water 4 times the mass of polyester, place in a high temperature and high pressure reactor, and react at 160°C for 8 hours;

[0044] The polyester is hydrolyzed by using ammonia water to obtain small molecule polyol and ammonium terephthalate;

[0045] C) the temperature of the reactant obtained in step B) is reduced to below 35° C., and the reactant is transferred to a vacuum distillation apparatus for vacuum distillation, and the distilled ammonia water is recovered until the pH of the solution remaining in the apparatus drops to below 7.5;

[0046] Since the boiling point of ammonia in ammonia water is low, the reaction product is first cooled to below 35°C and distilled at low temperature. The excess ammonia water can be recovered and used for the decomposition of polyester. Since ammonia water itself is alkaline, when the pH of the remaining solution in the distillation device drops below 7.5 or becomes neutral, it means that the excess ammonia water has been completely distilled and recovered. The pH can be detected in real time using an online pH detector.

[0047] D) adding hydrochloric acid to the remaining solution to reduce the pH value of the solution to below 5, and then performing reduced pressure distillation to collect the small molecule polyol obtained by the reaction;

[0048] Hydrochloric acid is added to the system obtained in step C) to make the system acidic, and the terephthalate in the system combines with hydrogen ions to generate PTA. The system is then distilled to separate the small molecule polyol obtained by the reaction from the system.

[0049] E) PTA (terephthalic acid) is precipitated from the bottom liquid after distillation and is used as a raw material for polyester diol after recrystallization with hot water.

[0050] At this time, the main components that can be turned into solids in the system are only ammonium chloride and PTA. Since PTA has poor solubility and ammonium chloride has good solubility, during the distillation process, as the ethylene glycol and water in the system decrease, PTA will be precipitated from the system first, and crude PTA can be obtained after filtration. The crude PTA can be used as a raw material for polyester diol after recrystallization with hot water.

[0051] The specific preparation process of preparing aromatic polyester diol by reacting PTA with small molecule diol is as follows:

[0052] Step 1.1) PTA and small molecule diol were weighed according to the ratio, added into a reaction kettle equipped with a thermometer, an oil-water separator and a stirrer, nitrogen was passed for protection for about 10 minutes, and the temperature was slowly raised to 150°C;

[0053] Step 1.2) Keep at 150℃ for 30min, start stirring at 100rpm to make PTA and small molecules form a well-dispersed suspension

[0054] Step 1.3) Continue heating and control the heating rate to 10-12°C every 10 minutes until the internal temperature is maintained at 235-240°C.

[0055] Step 1.4) After anhydrous distillation and the top temperature is reduced to below 70°C, two drops of tetraisopropyl titanate are added, and stirring is increased to 150-300 rpm, the internal temperature is controlled at 245°C, and the reaction is carried out for 8 hours;

[0056] Step 1.5) testing the acid value of the polyester diol. When the acid value is lower than 0.3 mgKOH / g, lowering the reaction temperature to 70-90° C., taking out the obtained aromatic polyester diol, the hydroxyl value of which is between 55-60 mgKOH / g and the molecular weight is about 2000.

[0057] After the aromatic polyester diol is obtained in step 1), the remaining steps are to use the obtained aromatic polyester diol as a diol raw material to prepare spandex. Spandex spinning can be carried out by dry spinning, wet spinning, reaction spinning or melt spinning. In the present invention, dry spinning is preferably used. The specific spinning steps are as follows:

[0058] Step 2): reacting the aromatic polyester diol obtained in step 1) with diisocyanate to obtain a prepolymer;

[0059] The reaction of the aromatic polyester diol and the diisocyanate can be a bulk reaction or a solution reaction. In the present invention, the bulk reaction is preferred because it saves more reaction energy. Specifically, the aromatic polyester diol and MDI are subjected to a prepolymerization end-capping reaction at 85° C. for 4 hours. In addition to MDI, the diisocyanate reacted with the aromatic polyester diol can also be one or more of toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate and isomers thereof.

[0060] The present invention preferably adopts dry spinning, so after the prepolymerization reaction is completed, the prepolymer is dissolved in a polar solvent such as DMAc or DMF. If melt spinning is adopted, the aromatic diol, diisocyanate and chain extender can be reacted in one step to obtain a polyurethane polymer.

[0061] Step 3): chain extending the prepolymer to obtain a polyurethane polymer;

[0062] Usually, a chain extender or a mixture of a chain extender and a chain terminator is used to extend the prepolymer. Among them, the chain extender can be an amine or alcohol chain extender, wherein the amine chain extender can be a diamine with 2 to 30 carbon atoms, for example, it can be selected from one or more of ethylenediamine, propylenediamine, pentamethylenediamine, methylpentamethylenediamine, methylpropylenediamine, hexamethylenediamine, triethylenediamine, benzylenediamine, phenylenediamine, diaminocyclohexane, hexamethylenediamine, and dopamine; the alcohol chain extender can be one or more of common chain extenders such as ethylene glycol, 1,4-butanediol, diethylene glycol, 1,6-hexanediol, 1,3-propylene glycol, and 1,4-dihydroxymethylcyclohexane. The chain terminator can be a monoamine having 2 to 20 carbon atoms, and can be selected from one or more of ethylamine, isopropylamine, n-butylamine, tert-butylamine, hexylamine, dimethylamine, diethylamine, dipropylamine, di-n-butylamine, di-tert-butylamine, diisobutylamine, diisopropylamine, cyclohexylamine or ethanolamine.

[0063] The present invention preferably uses dry spinning, preferably uses amine chain extenders, and specifically preferably uses EDA (ethylenediamine) and DEA (diethanolamine) as chain extenders and chain terminators. After the reaction is completed, a polyurethane spinning stock solution is obtained.

[0064] Step 4): Spinning the polyurethane polymer to obtain high-elastic spandex.

[0065] Additives are added to the spinning solution, and high-elastic spandex containing aromatic rings in the soft segment and based on recycled polyester is obtained by dry spinning.

[0066] Example

[0067] The present invention is described in more detail below through examples. In the following examples, the 300% stress of stretching refers to the stress value when the spandex is stretched to 300% elongation, which is used to characterize the tensile modulus; the 200% stress of recovery refers to the rebound stress value when the spandex is stretched to 300% elongation and recovered to 200% elongation, which is used to characterize the recovery modulus.

[0068] Embodiment 1:

[0069] The recovered PET polyester is crushed; ammonia water 4 times the mass of the polyester is added, placed in a high-temperature and high-pressure reactor, and reacted at 160°C for 8 hours; the temperature of the obtained reactant is reduced to below 35°C, transferred to a vacuum distillation device, and vacuum distilled, and the distilled ammonia water is recovered; distillation is performed until the remaining solution in the device is neutral, hydrochloric acid is added to the remaining solution to reduce the pH value of the solution to below 5, and then vacuum distillation is performed to collect the ethylene glycol fraction; PTA (terephthalic acid) is precipitated in the bottom liquid after distillation, and is used as a raw material for aromatic polyester diol after recrystallization with hot water.

[0070] The PTA recovered above is reacted with diethylene glycol to obtain an aromatic polyester diol with a number average molecular weight of 2000; the obtained aromatic polyester diol is subjected to a prepolymerization and end-capping reaction with MDI, the reaction conditions are 85°C, and the reaction time is 4 hours; after the prepolymerization reaction is completed, the prepolymer is dissolved with DMAc to obtain a prepolymer solution; then an amine solution containing ethylenediamine (EDA) and diethylamine (DEA) is added to carry out a chain extension reaction to obtain a polyurethane polymer; after the chain extension reaction is completed, necessary antioxidants, dyeing agents and other auxiliaries are added, and the spinning solution is aged for 30 hours to obtain the spinning solution. The above solution is subjected to dry spinning to obtain a polyurethane elastic fiber with a denier of 40D.

[0071] After testing, the stress at 300% stretching is 16.8cN, the stress at 200% recovery is 0.82cN, and the elongation at break is 385%.

[0072] Embodiment 2:

[0073] The recovered PET polyester is crushed; ammonia water 4 times the mass of the polyester is added, placed in a high-temperature and high-pressure reactor, and reacted at 160°C for 8 hours; the temperature of the obtained reactant is reduced to below 35°C, transferred to a vacuum distillation device, and vacuum distilled, and the distilled ammonia water is recovered; distillation is performed until the remaining solution in the device is neutral, hydrochloric acid is added to the remaining solution to reduce the pH value of the solution to below 5, and then vacuum distillation is performed to collect the ethylene glycol fraction; PTA (terephthalic acid) is precipitated in the bottom liquid after distillation, and is used as a raw material for aromatic polyester diol after recrystallization with hot water.

[0074] The PTA recovered above is reacted with neopentyl glycol to obtain an aromatic polyester diol with a number average molecular weight of 2000; the obtained aromatic polyester diol is subjected to a prepolymerization and end-capping reaction with MDI, the reaction conditions are 85°C, and the reaction time is 4 hours; after the prepolymerization reaction is completed, the prepolymer is dissolved with DMAc to obtain a prepolymer solution; then an amine solution containing ethylenediamine (EDA) and diethylamine (DEA) is added to carry out a chain extension reaction to obtain a polyurethane polymer; after the chain extension reaction is completed, necessary antioxidants, dyeing agents and other auxiliaries are added, and the spinning solution is aged for 30 hours to obtain the spinning solution. The above solution is subjected to dry spinning to obtain a polyurethane elastic fiber with a denier of 40D.

[0075] After testing, the stress at 300% stretching is 23.2cN, the stress at 200% recovery is 0.68cN, and the elongation at break is 317%.

[0076] Embodiment 3:

[0077] The recovered PET polyester is crushed; ammonia water 4 times the mass of the polyester is added, placed in a high-temperature and high-pressure reactor, and reacted at 160°C for 8 hours; the temperature of the obtained reactant is reduced to below 35°C, transferred to a vacuum distillation device, and vacuum distilled, and the distilled ammonia water is recovered; distillation is performed until the remaining solution in the device is neutral, hydrochloric acid is added to the remaining solution to reduce the pH value of the solution to below 5, and then vacuum distillation is performed to collect the ethylene glycol fraction; PTA (terephthalic acid) is precipitated in the bottom liquid after distillation, and is used as a raw material for aromatic polyester diol after recrystallization with hot water.

[0078] The PTA recovered above is used to react with diethylene glycol and neopentyl glycol to obtain an aromatic polyester diol with a number average molecular weight of 2000, wherein the molar ratio of diethylene glycol to neopentyl glycol is 1:1; the obtained aromatic polyester diol is subjected to a prepolymerization and end-capping reaction with MDI, the reaction conditions are 85°C, and the reaction time is 4 hours; after the prepolymerization reaction is completed, the prepolymer is dissolved with DMAc to obtain a prepolymer solution; then an amine solution containing ethylenediamine (EDA) and diethylamine (DEA) is added to carry out a chain extension reaction to obtain a polyurethane polymer; after the chain extension reaction is completed, necessary antioxidants, dyeing agents and other auxiliaries are added, and the spinning solution is aged for 30 hours. The above solution is subjected to dry spinning to obtain a polyurethane elastic fiber with a denier of 40D.

[0079] After testing, its 300% tensile stress is 16.5cN, the 200% recovery stress is 1.52cN, and the elongation at break is 475%.

[0080] Comparative Example 1:

[0081] The polytetrahydrofuran PTMG2000 (number average molecular weight of 2000) and MDI were subjected to prepolymerization and end-capping reaction at 85°C for 4 hours; after the prepolymerization reaction, the prepolymer was dissolved in DMAc to obtain a prepolymer solution; then an amine solution containing ethylenediamine (EDA) and diethylamine (DEA) was added to carry out a chain extension reaction to obtain a polyurethane polymer; after the chain extension reaction was completed, necessary antioxidants, dyeing agents and other auxiliaries were added, and the spinning solution was aged for 30 hours. The above solution was dry-spun to obtain a polyurethane elastic fiber with a denier of 40D.

[0082] The test shows that the tensile stress at 300% is 13.5cN, the stress at 200% recovery is 1.20cN, and the elongation at break is 550%.

[0083] Comparative Example 2:

[0084] The recovered PET polyester is crushed; ammonia water 4 times the mass of the polyester is added, placed in a high-temperature and high-pressure reactor, and reacted at 160°C for 8 hours; the temperature of the obtained reactant is reduced to below 35°C, transferred to a vacuum distillation device, and vacuum distilled, and the distilled ammonia water is recovered; distillation is performed until the remaining solution in the device is neutral, hydrochloric acid is added to the remaining solution to reduce the pH value of the solution to below 5, and then vacuum distillation is performed to collect the ethylene glycol fraction; PTA (terephthalic acid) is precipitated in the bottom liquid after distillation, and is used as a raw material for aromatic polyester diol after recrystallization with hot water.

[0085] The PTA recovered above is reacted with a mixture of ethylene glycol and butanediol in a mass ratio of 1:1 to obtain an aromatic polyester diol with a number average molecular weight of 2000; the obtained aromatic polyester diol is subjected to a prepolymerization and end-capping reaction with MDI, the reaction conditions are 85°C, and the reaction time is 4 hours; after the prepolymerization reaction is completed, the prepolymer is dissolved with DMAc to obtain a prepolymer solution; then an amine solution containing ethylenediamine (EDA) and diethylamine (DEA) is added to carry out a chain extension reaction to obtain a polyurethane polymer; after the chain extension reaction is completed, necessary antioxidants, dyeing agents and other auxiliaries are added, and the spinning solution is aged for 30 hours. The above solution is dry-spun to obtain a polyurethane elastic fiber with a denier of 40D.

[0086] According to the test, the 300% tensile stress is 23.8 cN, the 200% recovery stress is 0.31 cN, and the elongation at break is 365%.

[0087] The test results of the spandex fibers obtained in the above examples and comparative examples are summarized in the following table:

[0088]

[0089] It can be seen from the test results that, compared with conventional spandex made from PTMG as a raw material (Comparative Example 1), the tensile modulus of the spandex prepared by the scheme of the present invention is significantly improved, and compared with the spandex produced from aromatic polyester diols prepared from ethylene glycol and butanediol as raw materials (Comparative Example 2), the recovery modulus of the spandex prepared by the scheme of the present invention is significantly improved, especially the recovery modulus of the spandex fiber obtained in Example 3 is significantly improved, which shows that the scheme of the present invention enables the spandex to have a better tensile modulus while effectively reducing the crystallinity of the spandex and having better recovery performance.

Claims

1. A method for preparing high-elastic spandex, characterized in that: The following steps are included: 1) using PTA to react with a diol with a molecular weight of less than 200 to prepare an aromatic polyester diol, wherein the diol with a molecular weight of less than 200 comprises at least one of a polyether diol with a polymerization degree of 2-4 containing an ether oxygen bond in the middle or a diol with a side group, and the molecular weight of the obtained aromatic polyester diol is 1000-5000, wherein the diol with a side group is at least one of 2-methyl-1,3-propanediol and neopentyl glycol; 2) reacting the aromatic polyester diol obtained in step 1) with diisocyanate to obtain a prepolymer; 3) chain extending the prepolymer to obtain a polyurethane polymer; 4) Spinning the polyurethane polymer to obtain highly elastic spandex.

2. The preparation method according to claim 1, characterized in that: The PTA is prepared from recycled polyester.

3. The preparation method according to claim 1, characterized in that: The preparation method of the PTA is as follows: A) crushing the recovered aromatic polyester containing terephthalate structure; B) Add ammonia water 4 times the mass of polyester, place in a high temperature and high pressure reactor, and react at 160°C for 8 hours; C) the temperature of the reactant obtained in step B) is reduced to below 35° C., and the reactant is transferred to a vacuum distillation apparatus for vacuum distillation, and the distilled ammonia water is recovered; D) distilling until the pH of the solution remaining in the device drops below 7.5, adding hydrochloric acid to the remaining solution to lower the pH of the solution to below 5, and then distilling under reduced pressure to collect the small molecule diol fraction; E) PTA (terephthalic acid) is precipitated from the bottom liquid after distillation and is used as a raw material for polyester diol after recrystallization with hot water.

4. The preparation method according to claim 1, characterized in that: The reaction steps of PTA and diol in step 1) are as follows: 1.1) PTA and a diol with a molecular weight less than 200 are added to a reaction kettle to carry out an esterification reaction; 1.2) After removing moisture from the product after esterification, a catalyst is added and vacuum is evacuated. When the acid value and molecular weight of the polyol reach the target requirements, the obtained aromatic polyester diol is taken out.

5. The preparation method according to claim 1, characterized in that: The diol in step 1) is a polyether diol with a polymerization degree of 2-4 and containing an ether oxygen bond in the middle.

6. The preparation method according to claim 1, characterized in that: The diol in step 1) is a diol with a side group.

7. The preparation method according to claim 1, characterized in that: The diol in step 1) is a mixture of a polyether diol with a polymerization degree of 2-4 containing an ether oxygen bond in the middle and a diol with a side group, wherein the molar ratio of the two is (0.3-3):

1.

8. A high elastic spandex, characterized in that: The high-elastic spandex is prepared by the preparation method described in any one of claims 1-7.

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