Preparation method of recycled polyester bi-component parallel composite elastic fiber

Abstract

The invention belongs to the technical field of high polymer materials, and relates to a preparation method of recycled polyester bi-component parallel composite elastic fibers. The preparation method comprises the following steps: taking a mixture of a polylactic acid thermoplastic elastomer and first polylactic acid as a first component, taking second polylactic acid as a second component, and carrying out parallel composite spinning to obtain the regenerated polyester bi-component parallel composite elastic fiber, the preparation process of the polylactic acid thermoplastic elastomer comprises the following steps: mixing reaction raw materials, and sequentially carrying out pre-polycondensation reaction and final polycondensation reaction to obtain the polylactic acid thermoplastic elastomer. According to the invention, the compatibility and fluidity of the polylactic acid thermoplastic elastomer and the second polylactic acid in the spinning process are ensured by selecting the double-end carboxyl polylactic acid oligomer with specific molecular weight and proper reaction raw materials such as binary acid and polyether glycol (or polyether diamine), so that the stability and continuity of the spinning process are improved; and the production difficulty and cost are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials and relates to a method for preparing recycled polyester two-component parallel composite elastic fibers. Background Art

[0002] Polylactic acid is currently the only biodegradable polyester material derived from renewable plants, and is also regarded as the biomaterial with the broadest prospects for industrial application. Polylactic acid fiber is very suitable for the preparation of close-fitting fabrics and products due to its skin-friendly and antibacterial properties, moisture absorption and perspiration, and smooth feel. However, due to the high modulus of polylactic acid fiber, it feels hard and has poor elasticity, so the fabrics made are not close to the skin and lack elasticity, which limits its application range to a certain extent. In order to improve this situation, polylactic acid fiber is often blended with spandex to prepare elastic fiber. However, spandex and polylactic acid have poor compatibility, and hairy fibers are prone to occur when blended. In addition, the production cost of spandex is high and the process flow is long, all of which restrict the development of polylactic acid elastic fiber.

[0003] Self-crimping fiber is a fiber with an irreversible three-dimensional spiral curling structure, usually prepared by two-phase polymers with different shrinkage stresses through parallel composite spinning, drawing and heat treatment. Compared with ordinary curling fibers, self-crimping fibers not only save energy consumption, but also avoid mechanical damage to the fibers during texturing. Therefore, they are widely favored by the market and become a differentiated fiber.

[0004] The patent application with publication number CN107022804A discloses a method for preparing flame-retardant, degradable and antibacterial polylactic acid elastic fiber. The method provides elastic properties to polylactic acid by reactively blending vinyl polydimethylsilane, and the overall preparation process is simple and feasible. The patent application with publication number CN109853084A provides a polylactic acid / polyester elastomer composite elastic fiber, which is prepared by composite spinning of polylactic acid slices, polyester elastomer slices and compatibilizer in a certain proportion, giving polylactic acid fiber excellent elasticity and soft feel, improving its comfort, and making polylactic acid fiber more widely used in close-fitting fabrics. The patent with authorization announcement number CN113136638B discloses a biodegradable parallel composite elastic fiber and a preparation method thereof. The method melts and composites PB TSI copolyester and PLA in parallel, and the obtained composite elastic fiber has good compatibility and biodegradability.

[0005] Although the above patents or patent applications have made certain progress in the modification of polylactic acid fibers, they have not fully considered the compatibility and fluidity differences between the two components during the spinning process. Summary of the invention

[0006] The purpose of the present invention is to solve the problems existing in the prior art and provide a method for preparing a recycled polyester two-component parallel composite elastic fiber.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a recycled polyester two-component parallel composite elastic fiber, comprising: using a mixture of a polylactic acid thermoplastic elastomer and a first polylactic acid as a first component, and using a second polylactic acid as a second component, and performing parallel composite spinning to obtain the recycled polyester two-component parallel composite elastic fiber;

[0009] The preparation process of polylactic acid thermoplastic elastomer is as follows: after mixing the reaction raw materials, sequentially carrying out a pre-polycondensation reaction and a final polycondensation reaction, the polylactic acid thermoplastic elastomer is obtained;

[0010] The reaction raw materials include dibasic acid, X, and branching agent;

[0011] The dibasic acid is a double-terminal carboxyl polylactic acid oligomer, which is prepared by an ester exchange reaction between waste polylactic acid and a first aliphatic dibasic acid;

[0012] Alternatively, the dibasic acid is a mixture of a double-terminated carboxyl-containing polylactic acid oligomer and a second aliphatic dibasic acid;

[0013] X is a polyether diol;

[0014] Alternatively, X is a mixture of a polyether diol and a first aliphatic diol;

[0015] Alternatively, X is a polyether diamine;

[0016] Alternatively, X is a mixture of a polyether diamine and a first aliphatic diamine;

[0017] The number of carbon atoms of the first aliphatic dibasic acid is 4-20; if the number of carbon atoms of the first aliphatic dibasic acid is greater than 20, and the carbon chain of the first aliphatic dibasic acid is too long, on the one hand, the reaction activity of the terminal carboxyl group of the first aliphatic dibasic acid is low, and if the time of the transesterification reaction is not extended, the transesterification reaction will not be thorough enough, and the effective preparation of the double-terminal carboxyl polylactic acid oligomer cannot be achieved. If the time of the transesterification reaction is extended, the thermal degradation of the waste polylactic acid will become serious; on the other hand, since the first aliphatic dibasic acid needs to enter the molecular chain of the polylactic acid during the transesterification reaction, the excessively long carbon chain of the first aliphatic dibasic acid will cause the regularity of the molecular chain of the polylactic acid to be excessively destroyed, thereby affecting the crystallization properties of the final polylactic acid thermoplastic elastomer, and further affecting the spinning process; if the carbon chain of the first aliphatic dibasic acid is too short, its thermal stability is very poor, it will volatilize at the transesterification temperature, and the waste polylactic acid cannot be depolymerized;

[0018] The number average molecular weight of the double-end carboxyl polylactic acid oligomer is 2000-12000 g / mol; if the molecular weight of the double-end carboxyl polylactic acid oligomer is too low, the crystallization ability of the polylactic acid thermoplastic elastomer will be low, thereby affecting the spinning process; if the molecular weight of the double-end carboxyl polylactic acid oligomer is too high, an uneven reaction will occur during the repolymerization process, ultimately causing the molecular weight distribution of the polylactic acid thermoplastic elastomer to be too wide, thereby affecting the spinning process;

[0019] The degree of polymerization of the double-terminated carboxyl polylactic acid oligomer is 25-160;

[0020] The first polylactic acid is a polylactic acid having an intrinsic viscosity of 1.00-1.40 dL / g, and the second polylactic acid is a polylactic acid having an intrinsic viscosity of 2.00-4.00 dL / g.

[0021] As the preferred technical solution:

[0022] The method for preparing a regenerated polyester two-component parallel composite elastic fiber as described above, wherein the carbon number of the second aliphatic dibasic acid is 4-6;

[0023] The polyether diol is one or more of polyethylene glycol, polypropylene glycol and polytetrahydrofuran; the relative molecular weight of the polyether diol is 400-6000 g / mol;

[0024] The first aliphatic diol has 2 to 10 carbon atoms;

[0025] The polyether diamine is one or more of polyoxyethylene diamine and polyoxypropylene diamine; the relative molecular weight of the polyether diamine is 400-4000 g / mol;

[0026] The first aliphatic diamine has 4 to 12 carbon atoms;

[0027] The branching agent is one or more of glycerol, trimethylolpropane, pentaerythritol and sorbitol.

[0028] According to the method for preparing a recycled polyester two-component parallel composite elastic fiber as described above, the molar ratio of the dibasic acid to X is 1:1.01-1.05, the content of the double-terminal carboxyl polylactic acid oligomer in the mixture of the double-terminal carboxyl polylactic acid oligomer and the second aliphatic dibasic acid is 90-99 mol%, the content of the polyether diol in the mixture of the polyether diol and the first aliphatic diol is 90-99 mol%, the content of the polyether diamine in the mixture of the polyether diamine and the first aliphatic diamine is 90-99 mol%, and the molar amount of the branching agent is 0.1-5% of the molar amount of the dibasic acid.

[0029] In the preparation method of the recycled polyester two-component parallel composite elastic fiber as described above, the pressure of the pre-polycondensation reaction is 0.01-0.3MPa, the temperature is 190-260°C, and the time is 1-3h; the pressure of the final polycondensation reaction is 5-300Pa, the temperature is 260-280°C, and the time is 3-5h.

[0030] In the preparation method of the recycled polyester two-component parallel composite elastic fiber as described above, an antioxidant is also added during the preparation of the polylactic acid thermoplastic elastomer; the antioxidant is one or more of antioxidant 1010, antioxidant 168 and antioxidant 616; the mass of the antioxidant is 100-500ppm of the total mass of the reaction raw materials.

[0031] In the preparation method of the recycled polyester two-component parallel composite elastic fiber as described above, the relative molecular mass of the polylactic acid thermoplastic elastomer is 14000-33000 g / mol, the molecular weight distribution index is 1.5-3.0, and the melting point is 130-190°C.

[0032] The preparation method of the recycled polyester two-component parallel composite elastic fiber as described above, the preparation process of the double-terminal carboxyl polylactic acid oligomer is: adding waste polylactic acid, a first aliphatic dibasic acid, and a catalyst into a reaction kettle, reacting at 180-230° C. and 0.01-0.5 MPa for 2-5 hours to obtain the double-terminal carboxyl polylactic acid oligomer;

[0033] Among them, the mass of the first aliphatic dibasic acid , the quality of waste polylactic acid , the relative molecular mass of the first aliphatic dibasic acid , Theoretical value of number average molecular weight of double-terminated carboxyl polylactic acid oligomer The relationship satisfies the following formula:

[0034] ;

[0035] In the formula, , The unit is g; , The unit of is g / mol; φ is 17g / mol;

[0036] The mass of the catalyst is 100-500ppm of the mass of the waste polylactic acid; the catalyst is one or more of ethylene glycol titanium, tetrabutyl titanate, ethylene glycol antimony, antimony acetate, antimony oxide, stannous octoate, stannous chloride, zinc acetate and zinc oxide;

[0037] The derivation process of the above formula is as follows: According to the preparation process of the double-terminal carboxyl polylactic acid oligomer, the structural formula of the double-terminal carboxyl polylactic acid oligomer can be inferred to be (wherein R is the segment between two carboxyl groups in the first aliphatic dibasic acid, and n is the number of repeating units of lactic acid);

[0038] It can be seen that it includes n lactic acid repeating units and 1 first aliphatic dibasic acid; the relative molecular mass of the lactic acid chain segment is 72, and the first aliphatic dibasic acid will remove 1 -OH (molar mass is 17g / mol, recorded as φ) when it is capped. Assuming that the theoretical number average molecular weight of the double-terminated carboxyl polylactic acid oligomer is , then we can list formula 1:

[0039] =72n+ -φ; Formula 1

[0040] Transformation to get formula 2:

[0041] n=( - +φ) / 72; Formula 2

[0042] Assume that the mass of waste polylactic acid added during the preparation process is The molar number of lactic acid segments in waste polylactic acid is n PLA , then we can list formula 3:

[0043] n PLA =m / 72; Formula 3

[0044] It can be obtained that the number of lactic acid chains in waste polylactic acid is n more than that in the designed double-terminal carboxyl polylactic acid oligomer. PLA / n times, the multiple is the required number of moles of the first aliphatic dibasic acid n COOH , we get formula 4:

[0045] n COOH =n PLA / n; Formula 4

[0046] Substituting equation 3 into equation 4, we get equation 5:

[0047] n COOH =m / (72n); Formula 5

[0048] The relative molecular mass of the first aliphatic dibasic acid is It can be calculated according to formula 6:

[0049] =n COOH × ; Formula 6

[0050] Substituting equation 5 into equation 6, we get equation 7:

[0051] =(m× ) / (72n); Formula 7

[0052] Finally, substitute equation 2 into equation 7 to obtain the above formula;

[0053] Experiments show that the relative deviation of the number average molecular weight of the double-end carboxyl polylactic acid oligomer does not exceed 2%, and the relative deviation = (|actual value-theoretical value| / theoretical value) × 100%. The above formula can be used to guide production. After determining the target number average molecular weight of the double-end carboxyl polylactic acid oligomer, the appropriate first aliphatic dibasic acid can be selected according to the above formula, and the mass of the first aliphatic dibasic acid and the mass of the waste polylactic acid can be determined.

[0054] In the method for preparing a recycled polyester two-component parallel composite elastic fiber as described above, the content of the polylactic acid thermoplastic elastomer in the first component is 60-90wt%, and the mass ratio of the first component to the second component is 2:8-8:2.

[0055] The method for preparing a recycled polyester two-component parallel composite elastic fiber as described above, the process parameters of the parallel composite spinning include: spinning temperature 190-230°C, spinning speed 1500-2500m / min, cooling air temperature 15-25°C, cooling air speed 0.3-0.6m / s, cooling air relative humidity 60%-80%.

[0056] The method for preparing a recycled polyester two-component parallel composite elastic fiber as described above, wherein the single fiber fineness of the recycled polyester two-component parallel composite elastic fiber is 1.1-5.5 dtex, the breaking strength is 1.5-3.0 cN / dtex, the elastic recovery rate is not less than 85% at a fixed elongation of 20%, the curling rate is 50-70%, the curling elasticity is not less than 90%, and the compression rebound rate is ≥85%.

[0057] The principle of the present invention is as follows:

[0058] The formation of the curled structure of the two-component parallel composite fiber is jointly determined by two factors: the difference in thermal shrinkage between the two components and a good interface structure. Starting from the design of the polymer molecular structure, the present invention first designs a dicarboxyl polylactic acid oligomer through an ester exchange reaction, and then reacts it with polyether diol (or polyether diamine), a branching agent, etc. to prepare a polylactic acid thermoplastic elastomer. The polyether diol (or polyether diamine) allows the polylactic acid thermoplastic elastomer to have a polyether segment, which in turn allows the polylactic acid thermoplastic elastomer to have good elastic recovery, so that during the fiber preparation process, the difference in thermal shrinkage between the two components generates an unbalanced stress that deviates from the fiber axis, providing the necessary conditions for the generation of the curled structure. The branching agent allows the polylactic acid thermoplastic elastomer to have a micro-branched structure, which can enhance the curling performance of the fiber. For two-component parallel composite melt spinning, the fluidity between the two components is the key to whether spinning molding can be successfully achieved, and the introduction of polyether chain segments will increase the fluidity of polylactic acid thermoplastic elastomer, resulting in excessive difference in fluidity between it and polylactic acid. Therefore, the present invention uses a mixture of polylactic acid thermoplastic elastomer and the first polylactic acid as the first component, and the second polylactic acid as the second component. The presence of the first polylactic acid can serve as a physical entanglement point to reduce the fluidity of the polylactic acid thermoplastic elastomer, and at the same time, it can promote the compatibility of the polylactic acid thermoplastic elastomer and the second polylactic acid at the interface.

[0059] Beneficial effects:

[0060] (1) The present invention introduces a polylactic acid thermoplastic elastomer as the first component and spins it in parallel with the second polylactic acid to obtain a fiber with excellent elasticity and soft hand feel, thereby overcoming the shortcomings of traditional polylactic acid fibers such as hard hand feel and poor elasticity, making the fiber closer to the skin and broadening the application range of polylactic acid fibers in close-fitting fabrics.

[0061] (2) The present invention ensures the compatibility and fluidity of the polylactic acid thermoplastic elastomer and the second polylactic acid during the spinning process by selecting a double-terminal carboxyl polylactic acid oligomer with a specific molecular weight and degree of polymerization, as well as suitable dibasic acid and polyether diol (or polyether diamine) and other reaction raw materials, thereby improving the stability and continuity of the spinning process and reducing the difficulty and cost of production.

[0062] (3) The dibasic acid in the present invention is partially derived from the transesterification reaction between waste polylactic acid and the first aliphatic dibasic acid, which not only achieves high-value utilization of waste polylactic acid and reduces environmental pollution, but also complies with the concept of sustainable development.

[0063] (4) Compared with the traditional method for preparing polylactic acid elastic fibers, the present invention can obtain elastic fibers with a self-curling structure without the need for an additional texturing step, thereby saving energy consumption, reducing production costs, and avoiding mechanical damage to the fibers caused by the texturing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 is the nuclear magnetic resonance spectrum of the double-terminated carboxyl polylactic acid oligomer prepared in Example 11;

[0065] Figure 2 This is a cross-sectional SEM image of the recycled polyester bicomponent parallel composite elastic fiber of Example 6. DETAILED DESCRIPTION

[0066] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0067] The following are the test methods for the relevant performance indicators in each embodiment and comparative example:

[0068] Intrinsic viscosity: The test was conducted using an Ubbelohde viscometer with a capillary diameter of 0.7-0.8 mm. 0.25 g of the sample to be tested was taken with an electronic balance and dissolved in a mixed solvent of phenol and tetrachloroethane with a mass ratio of 1:1 in a 60-70°C water bath to obtain a test solution with a concentration of 0.005 g / ml. The test solution was then placed in a 25±0.1°C constant temperature water bath for 10 min, and the flow of the test solution through the upper and lower scale lines of the Ubbelohde viscometer was observed and recorded (a control group was also set up, and the only difference from this test was that the sample to be tested was not added). The test was conducted in parallel for 3 times and the average value was taken as the final result. The calculation process was based on the following formula:

[0069] η r = ;

[0070] η sp = ;

[0071] ;

[0072] Where η r is the relative viscosity, is the flow time of the solution to be tested (s), is the flow time of the mixed solvent of phenol and tetrachloroethane in the control group (s), η sp To increase specific viscosity, is the intrinsic viscosity (dL / g).

[0073] Number average molecular weight, relative molecular weight, relative molecular mass, molecular weight distribution index: tested by Agilent 1260 gel chromatography (GPC), the chromatographic column is Agilent HFIP series, the mobile phase consists of hexafluoroisopropanol and sodium trifluoroacetate (the concentration of sodium trifluoroacetate is 0.02 mol / L), and the test temperature is 35°C.

[0074] Degree of polymerization: 5-10 mg of the sample to be tested was dissolved in 0.55-0.6 mL of deuterated chloroform (CDCl3) to obtain a test solution, which was tested by Avance-600 Hz nuclear magnetic resonance spectrometer (NMR); wherein the number of scans was 64 times.

[0075] Melting point: Tested in accordance with GB / T 19466.3-2004 Plastics Differential Scanning Calorimetry (DSC) Part 3: Determination of Melting and Crystallization Temperature and Enthalpy.

[0076] Melt index: tested according to GB / T 3682.1-2018.

[0077] Denier: Tested according to GB / T 14343-2008.

[0078] Breaking strength: tested according to GB / T 14344-2008.

[0079] Elastic recovery at 20% constant elongation: tested according to FZ / T 50007-2012.

[0080] Curl rate: tested according to GB / T 14338-2022.

[0081] Curl elasticity: tested according to GB / T 6506-2017.

[0082] Compression rebound rate: tested according to FZ / T 52010-2014.

[0083] Example 1

[0084] A method for preparing a recycled polyester two-component parallel composite elastic fiber, the specific steps are as follows:

[0085] (1) Preparation of raw materials;

[0086] Waste polylactic acid: intrinsic viscosity is 1.00dL / g;

[0087] The first aliphatic dibasic acid: succinic acid;

[0088] Catalyst: tetrabutyl titanate;

[0089] X: polyethylene glycol, relative molecular weight 400 g / mol;

[0090] Branching agent: glycerol;

[0091] Antioxidant: Antioxidant 1010;

[0092] First polylactic acid: intrinsic viscosity is 1.00dL / g;

[0093] Second polylactic acid: intrinsic viscosity is 2.00 dL / g;

[0094] (2) Preparation of double-terminated carboxyl-containing polylactic acid oligomers;

[0095] Add waste polylactic acid, the first aliphatic dibasic acid and a catalyst into a reaction kettle, and react at 180° C. and 0.01 MPa for 5 hours to obtain a double-terminal carboxyl polylactic acid oligomer with a number average molecular weight of 2000 g / mol and a degree of polymerization of 25;

[0096] The mass ratio of waste polylactic acid to the first aliphatic dibasic acid is 16:1, and the mass of the catalyst is 100 ppm of the mass of the waste polylactic acid;

[0097] (3) Preparation of polylactic acid thermoplastic elastomer;

[0098] After mixing a double-end carboxyl polylactic acid oligomer, X, a branching agent, and an antioxidant, firstly perform a pre-polycondensation reaction at 0.01 MPa and 190°C for 3 hours, and then perform a final polycondensation reaction at 300 Pa and 260°C for 5 hours, to obtain a polylactic acid thermoplastic elastomer with a relative molecular mass of 14000 g / mol, a molecular weight distribution index of 1.5, and a melting point of 130°C; wherein the molar ratio of the double-end carboxyl polylactic acid oligomer to X is 1:1.01, the molar amount of the branching agent is 0.1% of the molar amount of the double-end carboxyl polylactic acid oligomer, and the mass of the antioxidant is 100 ppm of the total mass of the double-end carboxyl polylactic acid oligomer, X, and the branching agent;

[0099] (4) Preparation of recycled polyester bicomponent parallel composite elastic fibers;

[0100] A mixture of a polylactic acid thermoplastic elastomer and a first polylactic acid is used as a first component, and a second polylactic acid is used as a second component, and parallel composite spinning is performed to obtain a recycled polyester two-component parallel composite elastic fiber; wherein, the melting index of the first component at 190°C and 2.16kg is 60g / 10min, and the melting index of the second component at 190°C and 2.16kg is 65g / 10min, the content of the polylactic acid thermoplastic elastomer in the first component is 60wt%, and the mass ratio of the first component to the second component is 2:8. After the first component and the second component are mixed according to this ratio, a DSC test is performed, and the results show that there is only one melting point, indicating that the first component and the second component have good compatibility; the process parameters of the parallel composite spinning include: a spinning temperature of 190°C, a spinning speed of 1500m / min, a cooling air temperature of 15°C, a cooling air speed of 0.3m / s, and a cooling air relative humidity of 60%.

[0101] The final recycled polyester two-component parallel composite elastic fiber has a single fiber fineness of 1.1 dtex, a breaking strength of 1.5 cN / dtex, an elastic recovery rate of 85% at a constant elongation of 20%, a curling rate of 50%, a curling elasticity of 91%, and a compression rebound rate of 85%.

[0102] Comparative Example 1

[0103] A method for preparing a fiber, which differs from Example 1 only in that: in step (2), the amount of waste polylactic acid added is adjusted, and the mass ratio of waste polylactic acid to the first aliphatic dibasic acid is 8:1, which makes the number average molecular weight of the double-terminal carboxyl polylactic acid oligomer be 1000 g / mol and the degree of polymerization be 12.

[0104] The breaking strength of the finally prepared fiber was 1.0 cN / dtex.

[0105] Compared with Example 1, the breaking strength of the fiber is significantly reduced in Comparative Example 1. This is because the number average molecular weight of the double-end carboxyl polylactic acid oligomer in Comparative Example 1 is too low, which leads to a decrease in the crystallization ability of the polylactic acid thermoplastic elastomer, and it is unable to form an ordered and compact crystalline structure during the spinning process, thereby affecting the intermolecular forces and orientation arrangement inside the fiber, causing the overall mechanical properties of the fiber to deteriorate, which is ultimately manifested as a decrease in breaking strength.

[0106] Example 2

[0107] A method for preparing a recycled polyester two-component parallel composite elastic fiber, the specific steps are as follows:

[0108] (1) Preparation of raw materials;

[0109] Waste polylactic acid: intrinsic viscosity is 1.10dL / g;

[0110] The first aliphatic dibasic acid: succinic acid;

[0111] Catalyst: Antimony glycol;

[0112] X: polypropylene glycol, relative molecular weight 6000 g / mol;

[0113] Branching agent: glycerol;

[0114] Antioxidant: Antioxidant 1010;

[0115] First polylactic acid: intrinsic viscosity is 1.10dL / g;

[0116] Second polylactic acid: intrinsic viscosity is 2.05dL / g;

[0117] (2) Preparation of double-terminated carboxyl-containing polylactic acid oligomers;

[0118] Add waste polylactic acid, the first aliphatic dibasic acid and a catalyst into a reaction kettle, and react at 190° C. and 0.05 MPa for 5 hours to obtain a double-terminal carboxyl polylactic acid oligomer with a number average molecular weight of 4000 g / mol and a degree of polymerization of 54;

[0119] The mass ratio of the waste polylactic acid to the first aliphatic dibasic acid is 33:1, and the mass of the catalyst is 100 ppm of the mass of the waste polylactic acid;

[0120] (3) Preparation of polylactic acid thermoplastic elastomer;

[0121] After mixing a double-end carboxyl polylactic acid oligomer, X, a branching agent, and an antioxidant, firstly perform a pre-polycondensation reaction at 0.02MPa and 200°C for 3h, and then perform a final polycondensation reaction at 100Pa and 260°C for 5h, to obtain a polylactic acid thermoplastic elastomer with a relative molecular mass of 20000g / mol, a molecular weight distribution index of 1.5, and a melting point of 150°C; wherein the molar ratio of the double-end carboxyl polylactic acid oligomer to X is 1:1.01, the molar amount of the branching agent is 0.2% of the molar amount of the double-end carboxyl polylactic acid oligomer, and the mass of the antioxidant is 100ppm of the total mass of the double-end carboxyl polylactic acid oligomer, X, and the branching agent;

[0122] (4) Preparation of recycled polyester bicomponent parallel composite elastic fibers;

[0123] A mixture of a polylactic acid thermoplastic elastomer and a first polylactic acid is used as a first component, and a second polylactic acid is used as a second component, and parallel composite spinning is performed to obtain a recycled polyester two-component parallel composite elastic fiber; wherein, the melting index of the first component at 195°C and 2.16kg is 70g / 10min, the melting index of the second component at 195°C and 2.16kg is 73g / 10min, the content of the polylactic acid thermoplastic elastomer in the first component is 60wt%, and the mass ratio of the first component to the second component is 2:8. After the first component and the second component are mixed according to this ratio, a DSC test is performed, and the results show that there is only one melting point, indicating that the first component and the second component have good compatibility. The process parameters of the parallel composite spinning include: spinning temperature 195°C, spinning speed 1500m / min, cooling air temperature 15°C, cooling air speed 0.3m / s, and cooling air relative humidity 65%.

[0124] The final recycled polyester two-component parallel composite elastic fiber has a single fiber fineness of 1.5 dtex, a breaking strength of 1.5 cN / dtex, an elastic recovery rate of 87% at a constant elongation of 20%, a curling rate of 55%, a curling elasticity of 93%, and a compression rebound rate of 87%.

[0125] Example 3

[0126] A method for preparing a recycled polyester two-component parallel composite elastic fiber, the specific steps are as follows:

[0127] (1) Preparation of raw materials;

[0128] Waste polylactic acid: intrinsic viscosity is 1.15dL / g;

[0129] First aliphatic dibasic acid: adipic acid;

[0130] Catalyst: Titanium glycolate;

[0131] X: polytetrahydrofuran, relative molecular weight is 1000 g / mol;

[0132] Branching agent: glycerol;

[0133] Antioxidant: Antioxidant 1010;

[0134] First polylactic acid: intrinsic viscosity is 1.15dL / g;

[0135] Second polylactic acid: intrinsic viscosity is 2.50dL / g;

[0136] (2) Preparation of double-terminated carboxyl-containing polylactic acid oligomers;

[0137] Add waste polylactic acid, the first aliphatic dibasic acid and a catalyst into a reaction kettle, and react at 200° C. and 0.1 MPa for 4 hours to obtain a double-terminal carboxyl polylactic acid oligomer with a number average molecular weight of 5000 g / mol and a degree of polymerization of 67;

[0138] The mass ratio of the waste polylactic acid to the first aliphatic dibasic acid is 33:1, and the mass of the catalyst is 200 ppm of the mass of the waste polylactic acid;

[0139] (3) Preparation of polylactic acid thermoplastic elastomer;

[0140] After mixing a double-end carboxyl polylactic acid oligomer, X, a branching agent, and an antioxidant, the mixture is first subjected to a pre-polycondensation reaction at 0.04 MPa and 210° C. for 3 h, and then subjected to a final polycondensation reaction at 100 Pa and 260° C. for 5 h, to obtain a polylactic acid thermoplastic elastomer having a relative molecular mass of 30,000 g / mol, a molecular weight distribution index of 1.7, and a melting point of 190° C.; wherein the molar ratio of the double-end carboxyl polylactic acid oligomer to X is 1:1.02, the molar amount of the branching agent is 0.3% of the molar amount of the double-end carboxyl polylactic acid oligomer, and the mass of the antioxidant is 200 ppm of the total mass of the double-end carboxyl polylactic acid oligomer, X, and the branching agent;

[0141] (4) Preparation of recycled polyester bicomponent parallel composite elastic fibers;

[0142] A mixture of a polylactic acid thermoplastic elastomer and a first polylactic acid is used as a first component, and a second polylactic acid is used as a second component, and parallel composite spinning is performed to obtain a recycled polyester two-component parallel composite elastic fiber; wherein, the melting index of the first component at 200°C and 2.16kg is 75g / 10min, the melting index of the second component at 200°C and 2.16kg is 74g / 10min, the content of the polylactic acid thermoplastic elastomer in the first component is 65wt%, and the mass ratio of the first component to the second component is 3:7. After the first component and the second component are mixed according to this ratio, a DSC test is performed, and the results show that there is only one melting point, indicating that the first component and the second component have good compatibility. The process parameters of the parallel composite spinning include: spinning temperature 200°C, spinning speed 1500m / min, cooling air temperature 15°C, cooling air speed 0.4m / s, and cooling air relative humidity 60%.

[0143] The final recycled polyester two-component parallel composite elastic fiber has a single fiber fineness of 2.5 dtex, a breaking strength of 1.9 cN / dtex, an elastic recovery rate of 89% at a constant elongation of 20%, a curling rate of 55%, a curling elasticity of 93%, and a compression rebound rate of 89%.

[0144] Example 4

[0145] A method for preparing a recycled polyester two-component parallel composite elastic fiber, the specific steps are as follows:

[0146] (1) Preparation of raw materials;

[0147] Waste polylactic acid: intrinsic viscosity is 1.20dL / g;

[0148] First aliphatic dibasic acid: adipic acid;

[0149] Catalyst: antimony acetate;

[0150] X: a mixture of polyethylene glycol and ethylene glycol, the relative molecular weight of polyethylene glycol is 6000 g / mol, and the content of polyethylene glycol is 90 mol%;

[0151] Branching agent: trimethylolpropane;

[0152] Antioxidants: Antioxidant 168;

[0153] First polylactic acid: intrinsic viscosity is 1.20dL / g;

[0154] Second polylactic acid: intrinsic viscosity is 2.55dL / g;

[0155] (2) Preparation of double-terminated carboxyl-containing polylactic acid oligomers;

[0156] Add waste polylactic acid, the first aliphatic dibasic acid and a catalyst into a reaction kettle, and react at 205° C. and 0.15 MPa for 4 hours to obtain a double-terminal carboxyl polylactic acid oligomer with a number average molecular weight of 6000 g / mol and a degree of polymerization of 81;

[0157] The mass ratio of the waste polylactic acid to the first aliphatic dibasic acid is 40:1, and the mass of the catalyst is 200 ppm of the mass of the waste polylactic acid;

[0158] (3) Preparation of polylactic acid thermoplastic elastomer;

[0159] After mixing a double-end carboxyl polylactic acid oligomer, X, a branching agent, and an antioxidant, the mixture is first subjected to a pre-polycondensation reaction at 0.06 MPa and 220° C. for 2 h, and then subjected to a final polycondensation reaction at 100 Pa and 270° C. for 4 h, to obtain a polylactic acid thermoplastic elastomer having a relative molecular mass of 33,000 g / mol, a molecular weight distribution index of 1.9, and a melting point of 190° C.; wherein the molar ratio of the double-end carboxyl polylactic acid oligomer to X is 1:1.02, the molar amount of the branching agent is 0.7% of the molar amount of the double-end carboxyl polylactic acid oligomer, and the mass of the antioxidant is 300 ppm of the total mass of the double-end carboxyl polylactic acid oligomer, X, and the branching agent;

[0160] (4) Preparation of recycled polyester bicomponent parallel composite elastic fibers;

[0161] A mixture of a polylactic acid thermoplastic elastomer and a first polylactic acid is used as a first component, and a second polylactic acid is used as a second component, and parallel composite spinning is performed to obtain a recycled polyester two-component parallel composite elastic fiber; wherein, the melting index of the first component at 205°C and 2.16kg is 86g / 10min, and the melting index of the second component at 205°C and 2.16kg is 87g / 10min, the content of the polylactic acid thermoplastic elastomer in the first component is 70wt%, and the mass ratio of the first component to the second component is 3:7. After the first component and the second component are mixed according to this ratio, a DSC test is performed, and the results show that there is only one melting point, indicating that the first component and the second component have good compatibility. The process parameters of the parallel composite spinning include: spinning temperature 205°C, spinning speed 2000m / min, cooling air temperature 20°C, cooling air speed 0.4m / s, and cooling air relative humidity 70%.

[0162] The final recycled polyester two-component parallel composite elastic fiber has a single fiber fineness of 2dtex, a breaking strength of 1.9cN / dtex, an elastic recovery rate of 89% at a constant elongation of 20%, a curling rate of 70%, a curling elasticity of 96%, and a compression rebound rate of 90%.

[0163] Example 5

[0164] A method for preparing a recycled polyester two-component parallel composite elastic fiber, the specific steps are as follows:

[0165] (1) Preparation of raw materials;

[0166] Waste polylactic acid: intrinsic viscosity is 1.25dL / g;

[0167] The first aliphatic dibasic acid: suberic acid;

[0168] Catalyst: antimony oxide;

[0169] X: a mixture of polyethylene glycol and decanediol, the relative molecular weight of polyethylene glycol is 1000 g / mol, and the content of polyethylene glycol is 99 mol%;

[0170] 996379 Branching agent: trimethylolpropane;

[0171] Antioxidants: Antioxidant 168;

[0172] First polylactic acid: intrinsic viscosity is 1.25dL / g;

[0173] Second polylactic acid: intrinsic viscosity is 2.55dL / g;

[0174] (2) Preparation of double-terminated carboxyl-containing polylactic acid oligomers;

[0175] Add waste polylactic acid, the first aliphatic dibasic acid and a catalyst into a reaction kettle, and react at 210° C. and 0.2 MPa for 3 hours to obtain a double-terminal carboxyl polylactic acid oligomer with a number average molecular weight of 8000 g / mol and a degree of polymerization of 109;

[0176] The mass ratio of the waste polylactic acid to the first aliphatic dibasic acid is 45:1, and the mass of the catalyst is 300 ppm of the mass of the waste polylactic acid;

[0177] (3) Preparation of polylactic acid thermoplastic elastomer;

[0178] After mixing a double-end carboxyl polylactic acid oligomer, X, a branching agent, and an antioxidant, firstly perform a pre-polycondensation reaction at 0.08 MPa and 240° C. for 2 hours, and then perform a final polycondensation reaction at 80 Pa and 270° C. for 4 hours, to obtain a polylactic acid thermoplastic elastomer with a relative molecular mass of 25000 g / mol, a molecular weight distribution index of 2.4, and a melting point of 170° C.; wherein the molar ratio of the double-end carboxyl polylactic acid oligomer to X is 1:1.03, the molar amount of the branching agent is 1.5% of the molar amount of the double-end carboxyl polylactic acid oligomer, and the mass of the antioxidant is 300 ppm of the total mass of the double-end carboxyl polylactic acid oligomer, X, and the branching agent;

[0179] (4) Preparation of recycled polyester bicomponent parallel composite elastic fibers;

[0180] A mixture of a polylactic acid thermoplastic elastomer and a first polylactic acid is used as a first component, and a second polylactic acid is used as a second component, and parallel composite spinning is performed to obtain a recycled polyester two-component parallel composite elastic fiber; wherein, the melting index of the first component at 210°C and 2.16kg is 101g / 10min, the melting index of the second component at 210°C and kg is 97g / 10min, the content of the polylactic acid thermoplastic elastomer in the first component is 70wt%, and the mass ratio of the first component to the second component is 4:6. After the first component and the second component are mixed in this ratio, a DSC test is performed, and the results show that there is only one melting point, indicating that the first component and the second component have good compatibility. The process parameters of the parallel composite spinning include: spinning temperature 210°C, spinning speed 2000m / min, cooling air temperature 20°C, cooling air speed 0.5m / s, and cooling air relative humidity 70%.

[0181] The final recycled polyester two-component parallel composite elastic fiber has a single fiber fineness of 3dtex, a breaking strength of 2cN / dtex, an elastic recovery rate of 88% at a constant elongation of 20%, a curling rate of 60%, a curling elasticity of 93%, and a compression rebound rate of 89%.

[0182] Example 6

[0183] A method for preparing a recycled polyester two-component parallel composite elastic fiber, the specific steps are as follows:

[0184] (1) Preparation of raw materials;

[0185] Waste polylactic acid: intrinsic viscosity is 1.30dL / g;

[0186] The first aliphatic dibasic acid: suberic acid;

[0187] Catalyst: stannous octoate;

[0188] Second aliphatic dibasic acid: succinic acid;

[0189] X: polyoxyethylene diamine, relative molecular weight is 400 g / mol;

[0190] Branching agent: pentaerythritol;

[0191] Antioxidants: Antioxidant 168;

[0192] First polylactic acid: intrinsic viscosity is 1.30dL / g;

[0193] Second polylactic acid: intrinsic viscosity is 3.0dL / g;

[0194] (2) Preparation of double-terminated carboxyl-containing polylactic acid oligomers;

[0195] Add waste polylactic acid, the first aliphatic dibasic acid and a catalyst into a reaction kettle, and react at 215° C. and 0.2 MPa for 3 hours to obtain a double-terminal carboxyl polylactic acid oligomer with a number average molecular weight of 9000 g / mol and a degree of polymerization of 123;

[0196] The mass ratio of the waste polylactic acid to the first aliphatic dibasic acid is 51:1, and the mass of the catalyst is 300 ppm of the mass of the waste polylactic acid;

[0197] (3) Preparation of polylactic acid thermoplastic elastomer;

[0198] After mixing a double-end carboxyl polylactic acid oligomer, a second aliphatic dibasic acid, X, a branching agent, and an antioxidant, the mixture is pre-polycondensed at 0.1 MPa and 245° C. for 2 h, and then subjected to a final polycondensation reaction at 80 Pa and 270° C. for 4 h, to obtain a polylactic acid thermoplastic elastomer having a relative molecular mass of 25000 g / mol, a molecular weight distribution index of 2.3, and a melting point of 170° C.; wherein the ratio of the total molar amount of the double-end carboxyl polylactic acid oligomer and the second aliphatic dibasic acid to the molar amount of X is 1:1.03, the molar amount of the double-end carboxyl polylactic acid oligomer is 90% of the total molar amount of the double-end carboxyl polylactic acid oligomer and the second aliphatic dibasic acid, the molar amount of the branching agent is 2.5% of the total molar amount of the double-end carboxyl polylactic acid oligomer and the second aliphatic dibasic acid, and the mass of the antioxidant is 400 ppm of the total mass of the double-end carboxyl polylactic acid oligomer, the second aliphatic dibasic acid, X, and the branching agent;

[0199] (4) Preparation of recycled polyester bicomponent parallel composite elastic fibers;

[0200] A mixture of a polylactic acid thermoplastic elastomer and a first polylactic acid is used as a first component, and a second polylactic acid is used as a second component, and parallel composite spinning is performed to obtain a recycled polyester two-component parallel composite elastic fiber; wherein, the melting index of the first component at 215°C and 2.16kg is 105g / 10min, the melting index of the second component at 215°C and 2.16kg is 103g / 10min, the content of the polylactic acid thermoplastic elastomer in the first component is 80wt%, and the mass ratio of the first component to the second component is 5:5. After the first component and the second component are mixed in this ratio, a DSC test is performed, and the results show that there is only one melting point, indicating that the first component and the second component have good compatibility. The process parameters of the parallel composite spinning include: spinning temperature 215°C, spinning speed 2000m / min, cooling air temperature 20°C, cooling air speed 0.5m / s, and cooling air relative humidity 75%.

[0201] The final obtained recycled polyester two-component parallel composite elastic fiber has a single fiber fineness of 3.5 dtex, a breaking strength of 2 cN / dtex, an elastic recovery rate of 90% at a fixed elongation of 20%, a curling rate of 60%, a curling elasticity of 94%, a compression rebound rate of 92%, and a cross-sectional SEM image as shown in Figure 2 As shown, it can be seen from the figure that the first component and the second component have good compatibility and there is no obvious separation between the two.

[0202] Example 7

[0203] A method for preparing a recycled polyester two-component parallel composite elastic fiber, the specific steps are as follows:

[0204] (1) Preparation of raw materials;

[0205] Waste polylactic acid: intrinsic viscosity is 1.30dL / g;

[0206] The first aliphatic dibasic acid: sebacic acid;

[0207] Catalyst: stannous chloride;

[0208] Second aliphatic dibasic acid: succinic acid;

[0209] X: polyoxypropylene diamine, relative molecular weight is 4000 g / mol;

[0210] Branching agent: pentaerythritol;

[0211] Antioxidant: Antioxidant 616;

[0212] First polylactic acid: intrinsic viscosity is 1.30dL / g;

[0213] Second polylactic acid: intrinsic viscosity is 3.05dL / g;

[0214] (2) Preparation of double-terminated carboxyl-containing polylactic acid oligomers;

[0215] Add waste polylactic acid, the first aliphatic dibasic acid and a catalyst into a reaction kettle, and react at 220° C. and 0.3 MPa for 2 h to obtain a double-terminal carboxyl polylactic acid oligomer with a number average molecular weight of 10,000 g / mol and a degree of polymerization of 136;

[0216] The mass ratio of waste polylactic acid to the first aliphatic dibasic acid is 49:1, and the mass of the catalyst is 400 ppm of the mass of the waste polylactic acid;

[0217] (3) Preparation of polylactic acid thermoplastic elastomer;

[0218] After mixing a double-end carboxyl polylactic acid oligomer, a second aliphatic dibasic acid, X, a branching agent, and an antioxidant, the mixture is first subjected to a pre-polycondensation reaction at 0.15 MPa and 250° C. for 1 hour, and then subjected to a final polycondensation reaction at 50 Pa and 280° C. for 3 hours, to obtain a polylactic acid thermoplastic elastomer having a relative molecular mass of 15000 g / mol, a molecular weight distribution index of 2.2, and a melting point of 140° C.; wherein the ratio of the total molar amount of the double-end carboxyl polylactic acid oligomer and the second aliphatic dibasic acid to the molar amount of X is 1:1.04, the molar amount of the double-end carboxyl polylactic acid oligomer is 95% of the total molar amount of the double-end carboxyl polylactic acid oligomer and the second aliphatic dibasic acid, the molar amount of the branching agent is 3% of the total molar amount of the double-end carboxyl polylactic acid oligomer and the second aliphatic dibasic acid, and the mass of the antioxidant is 400 ppm of the total mass of the double-end carboxyl polylactic acid oligomer, the second aliphatic dibasic acid, X, and the branching agent;

[0219] (4) Preparation of recycled polyester bicomponent parallel composite elastic fibers;

[0220] A mixture of a polylactic acid thermoplastic elastomer and a first polylactic acid is used as a first component, and a second polylactic acid is used as a second component, and parallel composite spinning is performed to obtain a recycled polyester two-component parallel composite elastic fiber; wherein, the melting index of the first component at 220°C and 2.16kg is 120g / 10min, the melting index of the second component at 220°C and 2.16kg is 108g / 10min, the content of the polylactic acid thermoplastic elastomer in the first component is 80wt%, and the mass ratio of the first component to the second component is 6:4. After the first component and the second component are mixed according to this ratio, a DSC test is performed, and the results show that there is only one melting point, indicating that the first component and the second component have good compatibility. The process parameters of the parallel composite spinning include: a spinning temperature of 220°C, a spinning speed of 2500m / min, a cooling air temperature of 25°C, a cooling air speed of 0.3m / s, and a cooling air relative humidity of 80%.

[0221] The final recycled polyester two-component parallel composite elastic fiber has a single fiber fineness of 4.5 dtex, a breaking strength of 2.5 cN / dtex, an elastic recovery rate of 87% at a constant elongation of 20%, a curling rate of 55%, a curling elasticity of 93%, and a compression rebound rate of 87%.

[0222] Example 8

[0223] A method for preparing a recycled polyester two-component parallel composite elastic fiber, the specific steps are as follows:

[0224] (1) Preparation of raw materials;

[0225] Waste polylactic acid: intrinsic viscosity is 1.35dL / g;

[0226] The first aliphatic dibasic acid: sebacic acid;

[0227] Catalyst: zinc acetate;

[0228] Second aliphatic dibasic acid: adipic acid;

[0229] X: a mixture of polyoxyethylene diamine and butanediamine, the relative molecular weight of polyoxyethylene diamine is 1000 g / mol, and the content of polyoxyethylene diamine is 90 mol%;

[0230] Branching agent: pentaerythritol;

[0231] Antioxidant: Antioxidant 616;

[0232] First polylactic acid: intrinsic viscosity is 1.35dL / g;

[0233] Second polylactic acid: intrinsic viscosity is 3.50dL / g;

[0234] (2) Preparation of double-terminated carboxyl-containing polylactic acid oligomers;

[0235] Add waste polylactic acid, the first aliphatic dibasic acid and a catalyst into a reaction kettle, and react at 225° C. and 0.4 MPa for 2 hours to obtain a double-terminal carboxyl polylactic acid oligomer with a number average molecular weight of 11000 g / mol and a degree of polymerization of 150;

[0236] The mass ratio of waste polylactic acid to the first aliphatic dibasic acid is 54:1, and the mass of the catalyst is 400 ppm of the mass of the waste polylactic acid;

[0237] (3) Preparation of polylactic acid thermoplastic elastomer;

[0238] After mixing a double-end carboxyl polylactic acid oligomer, a second aliphatic dibasic acid, X, a branching agent, and an antioxidant, the mixture is pre-polycondensed at 0.2 MPa and 255° C. for 1 hour, and then subjected to a final polycondensation reaction at 30 Pa and 280° C. for 3 hours, to obtain a polylactic acid thermoplastic elastomer having a relative molecular mass of 20,000 g / mol, a molecular weight distribution index of 1.8, and a melting point of 150° C.; wherein the ratio of the total molar amount of the double-end carboxyl polylactic acid oligomer and the second aliphatic dibasic acid to the molar amount of X is 1:1.04, the molar amount of the double-end carboxyl polylactic acid oligomer is 96% of the total molar amount of the double-end carboxyl polylactic acid oligomer and the second aliphatic dibasic acid, the molar amount of the branching agent is 4% of the molar amount of the double-end carboxyl polylactic acid oligomer and the second aliphatic dibasic acid, and the mass of the antioxidant is 500 ppm of the total mass of the double-end carboxyl polylactic acid oligomer, the second aliphatic dibasic acid, X, and the branching agent;

[0239] (4) Preparation of recycled polyester bicomponent parallel composite elastic fibers;

[0240] A mixture of a polylactic acid thermoplastic elastomer and a first polylactic acid is used as a first component, and a second polylactic acid is used as a second component, and parallel composite spinning is performed to obtain a recycled polyester two-component parallel composite elastic fiber; wherein, the melting index of the first component at 225°C and 2.16kg is 125g / 10min, the melting index of the second component at 225°C and 2.16kg is 123g / 10min, the content of the polylactic acid thermoplastic elastomer in the first component is 90wt%, and the mass ratio of the first component to the second component is 7:3. After the first component and the second component are mixed according to this ratio, a DSC test is performed, and the results show that there is only one melting point, indicating that the first component and the second component have good compatibility. The process parameters of the parallel composite spinning include: spinning temperature 225°C, spinning speed 2500m / min, cooling air temperature 25°C, cooling air speed 0.4m / s, and cooling air relative humidity 80%.

[0241] The final recycled polyester two-component parallel composite elastic fiber has a single filament fineness of 5 dtex, a breaking strength of 2.5 cN / dtex, an elastic recovery rate of 90% at a constant elongation of 20%, a curling rate of 50%, a curling elasticity of 90%, and a compression rebound rate of 89%.

[0242] Example 9

[0243] A method for preparing a recycled polyester two-component parallel composite elastic fiber, the specific steps are as follows:

[0244] (1) Preparation of raw materials;

[0245] Waste polylactic acid: intrinsic viscosity is 1.40dL / g;

[0246] The first aliphatic dibasic acid: eicosapentadicarboxylic acid;

[0247] Catalyst: zinc oxide;

[0248] Second aliphatic dibasic acid: adipic acid;

[0249] X: a mixture of polyoxyethylene diamine and dodecane diamine, the relative molecular weight of polyoxyethylene diamine is 1000 g / mol, and the content of polyoxyethylene diamine is 99 mol%;

[0250] Branching agent: sorbitol;

[0251] Antioxidant: Antioxidant 616;

[0252] First polylactic acid: intrinsic viscosity is 1.40dL / g;

[0253] Second polylactic acid: intrinsic viscosity is 4.00dL / g;

[0254] (2) Preparation of double-terminated carboxyl-containing polylactic acid oligomers;

[0255] Add waste polylactic acid, the first aliphatic dibasic acid and a catalyst into a reaction kettle, and react at 230° C. and 0.5 MPa for 2 hours to obtain a double-terminal carboxyl polylactic acid oligomer with a number average molecular weight of 12000 g / mol and a degree of polymerization of 160;

[0256] The mass ratio of waste polylactic acid to the first aliphatic dibasic acid is 34:1, and the mass of the catalyst is 500ppm of the mass of the waste polylactic acid;

[0257] (3) Preparation of polylactic acid thermoplastic elastomer;

[0258] After mixing a double-end carboxyl polylactic acid oligomer, a second aliphatic dibasic acid, X, a branching agent, and an antioxidant, the mixture is pre-polycondensed at 0.3 MPa and 260° C. for 1 hour, and then subjected to a final polycondensation reaction at 5 Pa and 280° C. for 3 hours, to obtain a polylactic acid thermoplastic elastomer having a relative molecular mass of 14000 g / mol, a molecular weight distribution index of 3, and a melting point of 140° C.; wherein the ratio of the total molar amount of the double-end carboxyl polylactic acid oligomer and the second aliphatic dibasic acid to the molar amount of X is 1:1.05, the molar amount of the double-end carboxyl polylactic acid oligomer is 99% of the total molar amount of the double-end carboxyl polylactic acid oligomer and the second aliphatic dibasic acid, the molar amount of the branching agent is 5% of the total molar amount of the double-end carboxyl polylactic acid oligomer and the second aliphatic dibasic acid, and the mass of the antioxidant is 500 ppm of the total mass of the double-end carboxyl polylactic acid oligomer, the second aliphatic dibasic acid, X, and the branching agent;

[0259] (4) Preparation of recycled polyester bicomponent parallel composite elastic fibers;

[0260] A mixture of a polylactic acid thermoplastic elastomer and a first polylactic acid is used as a first component, and a second polylactic acid is used as a second component, and parallel composite spinning is performed to obtain a recycled polyester two-component parallel composite elastic fiber; wherein, the melting index of the first component at 230°C and 2.16kg is 150g / 10min, the melting index of the second component at 230°C and 2.16kg is 147g / 10min, the content of the polylactic acid thermoplastic elastomer in the first component is 90wt%, and the mass ratio of the first component to the second component is 8:2. After the first component and the second component are mixed in this ratio, a DSC test is performed, and the results show that there is only one melting point, indicating that the first component and the second component have good compatibility. The process parameters of the parallel composite spinning include: a spinning temperature of 230°C, a spinning speed of 2500m / min, a cooling air temperature of 25°C, a cooling air speed of 0.6m / s, and a cooling air relative humidity of 80%.

[0261] The final recycled polyester two-component parallel composite elastic fiber has a single fiber fineness of 5.5 dtex, a breaking strength of 3 cN / dtex, an elastic recovery rate of 88% at a constant elongation of 20%, a curling rate of 55%, a curling elasticity of 92%, and a compression rebound rate of 89%.

[0262] Comparative Example 2

[0263] A method for preparing a fiber, which differs from Example 9 only in that: in step (2), the amount of waste polylactic acid added is adjusted, and the mass ratio of waste polylactic acid to the first aliphatic dibasic acid is 37:1, which makes the number average molecular weight of the double-end carboxyl polylactic acid oligomer be 13000 g / mol and the degree of polymerization be 176.

[0264] The breaking strength of the final fiber was 1.1 cN / dtex.

[0265] Compared with Example 9, the breaking strength of the fiber is significantly reduced in Comparative Example 2. This is because the number average molecular weight of the double-end carboxyl polylactic acid oligomer in Comparative Example 2 is too high, which will produce uneven reaction during the repolymerization process, and ultimately cause the molecular weight distribution of the polylactic acid thermoplastic elastomer to be too wide, resulting in more defects in the internal structure of the fiber, and the arrangement and interaction between the molecular chains become disordered. When the fiber is subjected to external force, the stress cannot be evenly distributed on the molecular chain, and is easily concentrated at the defective site, which makes the fiber more likely to break and reduces the breaking strength.

[0266] Comparative Example 3

[0267] A method for preparing a fiber, which is different from Example 9 only in that the first aliphatic dibasic acid used in this comparative example is tetracosanedicarboxylic acid (CAS No. 3365-67-1).

[0268] The final recycled polyester two-component parallel composite elastic fiber has a breaking strength of 1.3 cN / dtex.

[0269] Compared with Example 9, the breaking strength of the fiber is significantly reduced in Comparative Example 3. This is because the carbon chain of the first aliphatic dibasic acid in Comparative Example 3 is too long, which reduces the reaction activity of the terminal carboxyl group and makes it difficult to completely complete the ester exchange reaction, resulting in insufficient preparation of the double-terminal carboxyl polylactic acid oligomer. At the same time, it excessively destroys the regularity of the polylactic acid molecular chain, seriously affecting the crystallization properties of the polylactic acid thermoplastic elastomer, and ultimately failing to form a good fiber structure during the spinning process, thereby reducing the mechanical properties of the fiber.

[0270] Example 10

[0271] A method for preparing a recycled polyester two-component parallel composite elastic fiber, which differs from Example 1 only in that: no antioxidant is added in step (3); the relative molecular mass of the polylactic acid thermoplastic elastomer is 20000 g / mol, the molecular weight distribution index is 1.6, and the melting point is 180°C.

[0272] The final recycled polyester two-component parallel composite elastic fiber has a single fiber fineness of 1.3 dtex, a breaking strength of 2.5 cN / dtex, an elastic recovery rate of 87% at a constant elongation of 20%, a curling rate of 60%, a curling elasticity of 93%, and a compression rebound rate of 87%.

[0273] Embodiment 11

[0274] A method for preparing a recycled polyester bicomponent parallel composite elastic fiber, which is different from Example 1 only in that: the intrinsic viscosity of the waste polylactic acid is 1.40 dL / g, the first aliphatic dibasic acid is adipic acid, and the mass of the catalyst is 300 ppm of the mass of the waste polylactic acid; when preparing a double-terminal carboxyl polylactic acid oligomer, the mass ratio of the waste polylactic acid to the first aliphatic dibasic acid is 13:1, the reaction temperature is 150°C, the reaction time is 4h, and the number average molecular weight of the obtained double-terminal carboxyl polylactic acid oligomer is 2000 g / mol, and the nuclear magnetic resonance spectrum is as follows: Figure 1 shown.

[0275] The final recycled polyester two-component parallel composite elastic fiber has a single fiber fineness of 1.2 dtex, a breaking strength of 1.7 cN / dtex, an elastic recovery rate of 87% at a constant elongation of 20%, a curling rate of 60%, a curling elasticity of 92%, and a compression rebound rate of 87%.

[0276] The above embodiments have been verified that the relative deviation of the number average molecular weight of the double-terminated carboxyl polylactic acid oligomer does not exceed 2%, relative deviation = (|actual value-theoretical value| / theoretical value) × 100%, and the calculation formula of the theoretical value is as follows:

[0277] ;

[0278] In the formula, (mass of the first aliphatic dibasic acid), The unit of (mass of waste polylactic acid) is g; (Relative molecular weight of the first aliphatic dibasic acid), The unit of (theoretical value of number average molecular weight of double-terminated carboxyl polylactic acid oligomer) is g / mol; φ is 17 g / mol.

[0279] Herein, the number average molecular weight is assumed to be an actual value unless the number average molecular weight is explicitly defined as a theoretical value.

Claims

1. A method for preparing a recycled polyester bicomponent parallel composite elastic fiber, characterized in that: A mixture of a polylactic acid thermoplastic elastomer and a first polylactic acid is used as a first component, and a second polylactic acid is used as a second component, and parallel composite spinning is performed to obtain a recycled polyester two-component parallel composite elastic fiber; The preparation process of polylactic acid thermoplastic elastomer is as follows: after mixing the reaction raw materials, sequentially carrying out a pre-polycondensation reaction and a final polycondensation reaction, the polylactic acid thermoplastic elastomer is obtained; The reaction raw materials include dibasic acid, X, and branching agent; The dibasic acid is a double-terminal carboxyl polylactic acid oligomer, which is prepared by an ester exchange reaction between waste polylactic acid and a first aliphatic dibasic acid; Alternatively, the dibasic acid is a mixture of a double-terminated carboxyl-containing polylactic acid oligomer and a second aliphatic dibasic acid; X is a polyether diol; Alternatively, X is a mixture of a polyether diol and a first aliphatic diol; Alternatively, X is a polyether diamine; Alternatively, X is a mixture of a polyether diamine and a first aliphatic diamine; The first aliphatic dibasic acid has 4 to 20 carbon atoms; The number average molecular weight of the double-terminated carboxyl polylactic acid oligomer is 2000-12000 g / mol; The degree of polymerization of the double-terminated carboxyl polylactic acid oligomer is 25-160; The first polylactic acid is a polylactic acid having an intrinsic viscosity of 1.00-1.40 dL / g, and the second polylactic acid is a polylactic acid having an intrinsic viscosity of 2.00-4.00 dL / g.

2. The method for preparing a recycled polyester bicomponent parallel composite elastic fiber according to claim 1, characterized in that: The second aliphatic dibasic acid has 4 to 6 carbon atoms; The polyether diol is one or more of polyethylene glycol, polypropylene glycol and polytetrahydrofuran; the relative molecular weight of the polyether diol is 400-6000 g / mol; The first aliphatic diol has 2 to 10 carbon atoms; The polyether diamine is one or more of polyoxyethylene diamine and polyoxypropylene diamine; the relative molecular weight of the polyether diamine is 400-4000 g / mol; The first aliphatic diamine has 4 to 12 carbon atoms; The branching agent is one or more of glycerol, trimethylolpropane, pentaerythritol and sorbitol.

3. The method for preparing a recycled polyester bicomponent parallel composite elastic fiber according to claim 2, characterized in that: The molar ratio of the dibasic acid to X is 1:1.01-1.05, the content of the double-terminal carboxyl polylactic acid oligomer in the mixture of the double-terminal carboxyl polylactic acid oligomer and the second aliphatic dibasic acid is 90-99 mol%, the content of the polyether diol in the mixture of the polyether diol and the first aliphatic diol is 90-99 mol%, the content of the polyether diamine in the mixture of the polyether diamine and the first aliphatic diamine is 90-99 mol%, and the molar amount of the branching agent is 0.1-5% of the molar amount of the dibasic acid.

4. The method for preparing a recycled polyester bicomponent parallel composite elastic fiber according to claim 1, characterized in that: The pressure of the preliminary polycondensation reaction is 0.01-0.3MPa, the temperature is 190-260°C, and the time is 1-3h; the pressure of the final polycondensation reaction is 5-300Pa, the temperature is 260-280°C, and the time is 3-5h.

5. The method for preparing a recycled polyester bicomponent parallel composite elastic fiber according to claim 1, characterized in that: During the preparation of the polylactic acid thermoplastic elastomer, an antioxidant is also added; the antioxidant is one or more of antioxidant 1010, antioxidant 168 and antioxidant 616; the mass of the antioxidant is 100-500ppm of the total mass of the reaction raw materials.

6. The method for preparing a recycled polyester bicomponent parallel composite elastic fiber according to claim 1, characterized in that: The relative molecular mass of the polylactic acid thermoplastic elastomer is 14000-33000 g / mol, the molecular weight distribution index is 1.5-3.0, and the melting point is 130-190°C.

7. The method for preparing a recycled polyester bicomponent parallel composite elastic fiber according to claim 1, characterized in that: The preparation process of the double-terminal carboxyl polylactic acid oligomer is as follows: waste polylactic acid, a first aliphatic dibasic acid and a catalyst are added into a reaction kettle, and the reaction is carried out at 180-230° C. and 0.01-0.5 MPa for 2-5 hours to obtain the double-terminal carboxyl polylactic acid oligomer; The mass of the catalyst is 100-500ppm of the mass of the waste polylactic acid; the catalyst is one or more of ethylene glycol titanium, tetrabutyl titanate, ethylene glycol antimony, antimony acetate, antimony oxide, stannous octoate, stannous chloride, zinc acetate and zinc oxide.

8. The method for preparing a recycled polyester bicomponent parallel composite elastic fiber according to claim 1, characterized in that: The content of the polylactic acid thermoplastic elastomer in the first component is 60-90wt%, and the mass ratio of the first component to the second component is 2:8-8:

2.

9. The method for preparing a recycled polyester bicomponent parallel composite elastic fiber according to claim 8, characterized in that: The process parameters of parallel composite spinning include: spinning temperature 190-230°C, spinning speed 1500-2500m / min, cooling air temperature 15-25°C, cooling air speed 0.3-0.6m / s, cooling air relative humidity 60%-80%.

10. The method for preparing a recycled polyester bicomponent parallel composite elastic fiber according to claim 9, characterized in that: The monofilament fineness of the recycled polyester two-component parallel composite elastic fiber is 1.1-5.5 dtex, the breaking strength is 1.5-3.0 cN / dtex, the elastic recovery rate is not less than 85% at a fixed elongation of 20%, the curling rate is 50-70%, the curling elasticity is not less than 90%, and the compression rebound rate is ≥85%.

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