A method for preparing high-elastic spandex by recycling polyester and the prepared high-elastic spandex

Abstract

This invention provides a method for preparing high-elasticity spandex from recycled polyester and the resulting high-elasticity spandex. The method includes the following steps: 1) reacting DMT with a diol with a molecular weight less than 200 to obtain an aromatic polyester diol; 2) reacting the aromatic polyester diol obtained in step 1) with a diisocyanate to obtain a prepolymer; 3) chain-extending the prepolymer to obtain a polyurethane polymer; 4) spinning the polyurethane polymer to obtain high-elasticity spandex. The DMT can be obtained from recycled polyester. This invention uses recycled polyester to prepare DMT, eliminating the need to convert DMT to PTA. The direct reaction of DMT with a diol to prepare the polyester diol makes the reaction conditions for the aromatic polyester diol milder, saves the step of converting DMT to PTA, utilizes recycled materials, and makes the production process more environmentally friendly. Simultaneously, the introduction of aromatic rings increases the tensile modulus of the spandex, giving it 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 lower costs for spandex-containing elastic fabrics.

[0004] The elasticity of spandex can usually be characterized by tensile modulus and recovery modulus. The inventors 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. Terephthalic acid (PTA) is the most widely used aromatic dibasic acid, but compared with aliphatic dibasic acids, terephthalic acid has a higher reaction temperature and higher energy consumption, which are unfavorable factors in industrial production.

[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 by recycling polyester and the 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 by recycling polyester, characterized in that it comprises the following steps:

[0008] 1) Using DMT (dimethyl terephthalate) to react with a diol having 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 extension of the prepolymer to obtain a polyurethane polymer;

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

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

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

[0014] A) crushing an aromatic polyester containing a terephthalate structure;

[0015] B) adding ethylene glycol 4 times the mass of polyester and zinc acetate as a catalyst, and performing alcoholysis at 190-200°C under reflux conditions for 5 hours;

[0016] C) distilling the system obtained in step B) until the amount of diol distilled reaches 90% of the theoretical value, stopping the distillation and lowering the material temperature to below 64° C.;

[0017] D) adding methanol to the system obtained in step C), and adding sodium methoxide as a catalyst, maintaining the temperature below 64° C., and reacting for 5 hours;

[0018] E) removing ethylene glycol and methanol by atmospheric distillation to obtain DMT;

[0019] F) The obtained DMT is subjected to high temperature ion exchange to remove zinc acetate and sodium methoxide.

[0020] Optionally, the reaction steps of DMT and diol in step 1) are as follows:

[0021] Step 1.1) DMT and a diol with a molecular weight less than 200 are added to a reactor to carry out an esterification reaction at a temperature of 175° C. for 5 h;

[0022] Step 1.2) Add a titanate catalyst, raise the temperature to 220-240°C, and react for 24 hours;

[0023] Step 1.3) Vacuum the solution to remove small molecule alcohols, and stop the reaction when the molecular weight reaches the theoretical value.

[0024] In the present invention, aromatic polyester diol is prepared by reacting DMT with small molecule diol, and an aromatic ring with strong rigidity is introduced into the soft segment of spandex, so that the obtained polyester spandex has a larger 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 is easy to crystallize, resulting in a decrease in the resilience properties such as the recovery modulus, elastic elongation and elastic recovery rate 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 DMT to solve the above problems.

[0025] 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.

[0026] Optionally, the diol in step 1) is a diol with a pendant group.

[0027] Optionally, the diol with a pendant group is at least one of 2-methyl-1,3-propanediol and neopentyl glycol.

[0028] 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.

[0029] Optionally, the molecular weight of the aromatic polyester diol is 1000-5000.

[0030] Optionally, the spinning method in step 4) is dry spinning.

[0031] Optionally, the spinning method in step 4) is melt spinning.

[0032] 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.

[0033] Beneficial effects:

[0034] In the present invention, recycled polyester is used to prepare DMT, and there is no need to convert DMT into PTA. DMT is directly reacted with diol to prepare polyester diol, so that the reaction conditions of aromatic polyester diol become mild while saving the step of converting DMT into PTA, and recycled materials are also used, and the production process is more environmentally friendly. In the present invention, ethylene glycol is used to alcoholyze polyester, and the raw material requirements for recycled polyester are lower. Multiple polyesters can be recycled together, and the small molecule diol impurities remaining in the recycled DMT can also play a role in improving the modulus of spandex. Therefore, there is no need to thoroughly remove impurities from the prepared DMT, which greatly saves the process steps of high-elastic polyester spandex.

[0035] Using DMT to prepare aromatic polyether ester diols, and then using it as a raw material to prepare spandex, can greatly improve the tensile modulus of spandex.

[0036] 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

[0037] 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 below by examples. For the sake of clarity and simplicity, all features of the actual implementation method are not described in the specification. Hereinafter, the DMT refers to dimethyl terephthalate.

[0038] Specifically, the present invention provides a method for preparing high-elastic spandex by recycling polyester and the prepared high-elastic spandex, and the specific scheme is as follows:

[0039] A method for preparing high-elastic spandex by recycling polyester, characterized in that it comprises the following steps:

[0040] Step 1): using DMT (dimethyl terephthalate) 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;

[0041] In the present invention, aromatic polyester diol is prepared by reacting DMT with small molecule diol, and spandex is prepared by using the aromatic polyester diol as diol raw material, and aromatic ring is introduced into the soft segment of spandex, which has strong rigidity, and the polyester spandex prepared by the aromatic polyester diol has a large modulus when stretched. Compared with PTA (terephthalic acid) as a raw material, the reaction of DMT with small molecule diol is used. Since DMT has an ester bond in its structure, the reaction conditions for preparing aromatic polyester diol by ester exchange reaction with small molecule diol are milder, the required temperature is lower, and the production energy consumption can be reduced. In addition, commonly used catalysts such as tetrabutyl titanate and other substances will hydrolyze to generate insoluble precipitates when they meet water, while the byproducts of the reaction of DMT with small molecule diols do not have water, so the catalyst can be added in advance to increase the reaction speed. However, since the aromatic ester group is rigid and has strong interactions, 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 will also have an adverse effect on the low temperature resistance of the spandex. Therefore, in the present invention, a polyether diol with a polymerization degree of 2-4 or a diol with a side group containing an ether oxygen bond in the molecular structure is used for copolymerization with DMT, wherein the side group can increase the distance between the ester groups, reduce the interaction, and thus reduce the crystallinity; the ether oxygen bond has strong activity and 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 hybrid structure of the two diols increases the asymmetry and dissimilarity of the basic structural unit, and the hybrid 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 DMT 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.

[0042] In the present invention, the DMT raw material used in step 1) is obtained from recycled polyester, and the specific steps for preparing DMT are as follows:

[0043] A) crushing an aromatic polyester containing a terephthalate structure;

[0044] 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.

[0045] B) adding ethylene glycol 4 times the mass of polyester and zinc acetate as a catalyst, and performing alcoholysis at 190-200°C under reflux conditions for 5 hours;

[0046] Ethylene glycol is used to alcoholyze the polyester to obtain BHET (dihydroxyethyl terephthalate) and byproducts such as ethylene glycol, propylene glycol, and butylene glycol. It is preferred to add ethylene glycol 4 times the mass of the polyester. Increasing the amount of ethylene glycol is beneficial to the BHET yield, and the amount of BHET polymers in the alcoholysis product will be reduced, which is beneficial to subsequent processes. Reflux conditions refer to the evaporated ethylene glycol being cooled and then falling back into the reaction system. Since the reaction temperature is too high, ethylene glycol is volatile, and the reflux conditions can avoid the reduction of the amount of ethylene glycol in the actual reaction system caused by excessive volatilization of ethylene glycol. The alcoholysis temperature in the present invention is preferably 196°C.

[0047] C) distilling the system obtained in step B) until the amount of distilled low-molecular-weight diol reaches 90% of the theoretical value, stopping the distillation and lowering the material temperature to below 64° C.;

[0048] In this step, distillation can distill out small molecule diols such as ethylene glycol and butanediol obtained by alcoholysis. The theoretical value refers to the total amount of diols in the system minus the amount of ethylene glycol required to convert terephthalic acid into BHET. Usually, when the temperature of the distillation head begins to drop to 70°C, it can be considered that the small molecule diols have been distilled out less, reaching 90% of the theoretical value. Since methanol needs to be added to continue the reaction in the next step, the temperature should be lowered to below 64°C. The temperature here is not strictly required, and it can be lower than the boiling point of methanol.

[0049] D) adding methanol to the system obtained in step C), and adding sodium methoxide as a catalyst, maintaining the temperature below 64° C., and reacting for 5 hours;

[0050] Excess methanol is used to carry out transesterification reaction with BHET to obtain DMT and ethylene glycol.

[0051] E) removing ethylene glycol and methanol by atmospheric distillation to obtain DMT;

[0052] In step D), methanol is in excess. Since the boiling point of DMT is higher than that of methanol and ethylene glycol, ethylene glycol and methanol in DMT can be removed by distillation.

[0053] F) The obtained DMT is subjected to high temperature ion exchange to remove zinc acetate and sodium methoxide.

[0054] The DMT obtained after step F) can be reacted with a small molecule diol to prepare an aromatic polyester diol. Some small molecule diol impurities may remain in the DMT prepared by the method of the present invention, but the amount of impurities is small, and a small amount of diol impurities can also play a role in improving the modulus of spandex, so there is no need to remove these impurities.

[0055] The reaction process of DMT and small molecule diols to prepare aromatic polyester diols is as follows:

[0056] Step 1.1) DMT and a diol with a molecular weight less than 200 are added to a reactor to carry out an esterification reaction at a temperature of 175° C. for 5 h;

[0057] Step 1.2) Add a catalyst titanate, raise the temperature to 220-240°C, preferably 225°C, and react for 24 hours;

[0058] Step 1.3) Vacuum the solution to remove small molecule alcohols, and stop the reaction when the molecular weight reaches the theoretical value.

[0059] The theoretical value of the molecular weight is determined according to actual needs. During the preparation process, the molecular weight can be calculated by an online hydroxyl value test method or an offline hydroxyl value test method.

[0060] Step 2) to step 4) is a process of preparing spandex using the prepared aromatic polyester diol as a diol raw material. Spandex spinning can be performed by dry spinning, wet spinning, reaction spinning or melt spinning. In the present invention, dry spinning is preferably used. The specific method of step 2) to step 4) is as follows:

[0061] Step 2): reacting the aromatic polyester diol obtained in step 1) with diisocyanate to obtain a prepolymer;

[0062] 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.

[0063] 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.

[0064] Step 3): chain extending the prepolymer to obtain a polyurethane polymer;

[0065] 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. 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.

[0066] 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.

[0067] Step 4): Spinning the polyurethane polymer to obtain high-elastic spandex.

[0068] 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.

[0069] Example

[0070] 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.

[0071] Embodiment 1:

[0072] The aromatic polyester containing terephthalate structure is crushed; ethylene glycol of 4 times the mass of the polyester is added, and zinc acetate is added as a catalyst, and alcoholysis is carried out at 196°C reflux condition for 5 hours; the obtained system is distilled, and when the amount of diol distilled reaches 90% of the theoretical value, the distillation is stopped, and the material temperature is reduced to 64°C; methanol is added to the obtained system, and sodium methoxide is added as a catalyst, the temperature is maintained at 64°C, and the reaction is carried out for 5 hours; ethylene glycol and methanol are removed by atmospheric distillation to obtain DMT; zinc acetate and sodium methoxide are removed from the obtained DMT by high-temperature ion exchange.

[0073] The DMT 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 aids 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.

[0074] According to the test, the 300% tensile stress is 17.0 cN, the 200% recovery stress is 0.81 cN, and the elongation at break is 403%.

[0075] Embodiment 2:

[0076] The aromatic polyester containing terephthalate structure is crushed; ethylene glycol of 4 times the mass of the polyester is added, and zinc acetate is added as a catalyst, and alcoholysis is carried out at 196°C reflux condition for 5 hours; the obtained system is distilled, and when the amount of diol distilled reaches 90% of the theoretical value, the distillation is stopped, and the material temperature is reduced to 64°C; methanol is added to the obtained system, and sodium methoxide is added as a catalyst, the temperature is maintained at 64°C, and the reaction is carried out for 5 hours; ethylene glycol and methanol are removed by atmospheric distillation to obtain DMT; zinc acetate and sodium methoxide are removed from the obtained DMT by high-temperature ion exchange.

[0077] The DMT 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.

[0078] After testing, the stress at 300% stretching is 24.8cN, the stress at 200% recovery is 0.66cN, and the elongation at break is 312%.

[0079] Embodiment 3:

[0080] The aromatic polyester containing terephthalate structure is crushed; ethylene glycol of 4 times the mass of the polyester is added, and zinc acetate is added as a catalyst, and alcoholysis is carried out at 196°C reflux condition for 5 hours; the obtained system is distilled, and when the amount of diol distilled reaches 90% of the theoretical value, the distillation is stopped, and the material temperature is reduced to 64°C; methanol is added to the obtained system, and sodium methoxide is added as a catalyst, the temperature is maintained at 64°C, and the reaction is carried out for 5 hours; ethylene glycol and methanol are removed by atmospheric distillation to obtain DMT; zinc acetate and sodium methoxide are removed from the obtained DMT by high-temperature ion exchange.

[0081] The DMT recovered above is reacted 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 4h; 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 30h to obtain the spinning solution. The above solution is subjected to dry spinning to obtain a polyurethane elastic fiber with a denier of 40D.

[0082] After testing, the stress at 300% stretching is 17.1cN, the stress at 200% recovery is 1.49cN, and the elongation at break is 508%.

[0083] Comparative Example 1:

[0084] 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.

[0085] The test showed that the 300% tensile stress was 13.5 cN, the 200% recovery stress was 1.20 cN, and the elongation at break was 550%.

[0086] Comparative Example 2:

[0087] The aromatic polyester containing terephthalate structure is crushed; ethylene glycol of 4 times the mass of the polyester is added, and zinc acetate is added as a catalyst, and alcoholysis is carried out at 196°C reflux condition for 5 hours; the obtained system is distilled, and when the amount of diol distilled reaches 90% of the theoretical value, the distillation is stopped, and the material temperature is reduced to 64°C; methanol is added to the obtained system, and sodium methoxide is added as a catalyst, the temperature is maintained at 64°C, and the reaction is carried out for 5 hours; ethylene glycol and methanol are removed by atmospheric distillation to obtain DMT; zinc acetate and sodium methoxide are removed from the obtained DMT by high-temperature ion exchange.

[0088] The DMT 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 in 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.

[0089] According to the test, the 300% tensile stress is 25.0 cN, the 200% recovery stress is 0.32 cN, and the elongation at break is 357%.

[0090] The test results of the spandex fibers obtained in the above examples and comparative examples are summarized in the following table:

[0091] Sample name Tensile 300% stress (cN) Recover 200% stress (cN) Elongation at break Example 1 17.0 0.81 403％ Example 2 24.8 0.66 312％ Example 3 17.1 1.49 508％ Comparative Example 1 13.5 1.20 550％ Comparative Example 2 25.0 0.32 357％

[0092] 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 by recycling polyester, characterized in that: The following steps are included: 1) using DMT to react with a diol with a molecular weight of less than 200 to obtain an aromatic polyester diol, wherein the diol with a molecular weight of less than 200 includes 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 method according to claim 1, characterized in that The DMT is produced from recycled polyester.

3. The method according to claim 2, characterized in that The preparation method of the DMT is as follows: A) crushing an aromatic polyester containing a terephthalate structure; B) adding ethylene glycol 4 times the mass of polyester and zinc acetate as a catalyst, and performing alcoholysis at 190-200°C under reflux conditions for 5 hours; C) distilling the system obtained in step B) until the amount of diol distilled reaches 90% of the theoretical value, stopping the distillation and lowering the material temperature to below 64° C.; D) adding methanol to the system obtained in step C), and adding sodium methoxide as a catalyst, maintaining the temperature below 64° C., and reacting for 5 hours; E) removing ethylene glycol and methanol by atmospheric distillation to obtain DMT; F) The obtained DMT is subjected to high temperature ion exchange to remove zinc acetate and sodium methoxide.

4. The method according to claim 1, characterized in that The reaction steps of DMT and diol in step 1) are as follows: Step 1.1) DMT and a diol with a molecular weight less than 200 are added to a reactor to carry out an esterification reaction at a temperature of 175° C. for 5 h; Step 1.2) Add a titanate catalyst, raise the temperature to 220-240°C, and react for 24 hours; Step 1.3) Vacuum the solution to remove small molecule alcohols, and stop the reaction when the molecular weight reaches the theoretical value.

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

7. The 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 polyester spandex is prepared by the preparation method described in any one of claims 1-7.