A regenerated polyester pore-forming agent, its preparation method and application

Abstract

The present invention belongs to the technical field of polyester recycling and reuse, and relates to a regenerated polyester pore-forming agent and its preparation method and application. Preparation method: First, carry out transesterification reaction between waste polylactic acid and aliphatic dibasic acid to obtain a polylactic acid oligomer with carboxyl groups at both ends. Then, mix the polylactic acid oligomer with carboxyl groups at both ends, polyether diol, oligomer diol and inorganic porous material and carry out polycondensation reaction to obtain a regenerated polyester pore-forming agent containing water-soluble polylactic acid and inorganic porous material. Application: After carrying out melt blending and spinning of the regenerated polyester pore-forming agent and fiber-grade polyester to obtain blended fibers, carry out soaking treatment to obtain porous fibers. The present invention not only solves the problem of waste of waste polylactic acid, but also provides a new way for the green preparation of porous fibers, and has important practical significance and environmental protection value.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyester recycling and reuse, and relates to a regenerated polyester pore-forming agent, a preparation method thereof and an application thereof. Background Art

[0002] Due to the characteristics of large aspect ratio and high specific surface area, porous fibers have important uses in the fields of absorption, adsorption, etc. The special structure of porous fibers shows advantages such as good compression resilience, high stability, excellent heat insulation and warmth retention, and great potential for modification and extended applications. Especially polyester porous fibers have a broader demand in the textile and clothing fields. Although various methods such as coaxial wet spinning, electrostatic spinning, micro-extrusion foam spinning and melt blowing spinning have been used to prepare porous fibers, and the technical stability and the ability to replicate various pore structures have been proved, these methods generally have problems such as complex production steps, difficulty in large-scale production, unenvironment-friendly processes, and high costs. Therefore, the industry urgently needs a preparation method of porous polyester fibers that is environmentally friendly, low-cost and can be produced on a large scale at the same time.

[0003] The patent with the authorization announcement number CN114775106B discloses a preparation method of a porous structure low-melting-point composite polyester fiber, which forms micropores with a diameter of 0.1-1.0 micrometers on the surface of the composite fiber through alkali treatment under certain conditions; the patent application with the publication number CN118814313A provides a highly moisture-absorbing and quick-drying porous polyester fiber, a polyester fabric and a preparation method thereof. However, the above patent technologies do not consider the harm to the environment caused by the pore-forming agent during the pore-forming process. The current water-soluble polyester is difficult to degrade in the natural environment and exists as microplastics in every corner of the environment after being discarded, which does not conform to the current concept of green and low-carbon. In addition, pore-forming treatment means such as high-temperature and high-pressure dyeing or alkali treatment will also produce a large amount of waste liquid, which must be neutralized before being discharged.

[0004] Based on the environmental problems caused by the application of the current pore-forming agent, a green method for preparing porous fibers is urgently needed. As a biodegradable polyester derived from renewable plant resources, polylactic acid is widely used in the fields of packaging, textiles, medicine, etc. and is vigorously promoted as an environmentally friendly material. However, the large-scale production and use of polylactic acid will also generate a large amount of waste polylactic acid. If this part of polylactic acid directly enters the environment, although it is biodegradable, the degradation requires specific conditions, and it is difficult to achieve rapid and direct utilization of the degradation to carbon dioxide and water, which is actually a waste of resources.

[0005] Energy recovery and mechanical recovery are common ways to solve the waste of polylactic acid resources, but the former will lead to high pollution with low return rate, and the latter is usually accompanied by the degradation of plastic properties. Chemical recovery can not only provide a sustainable source of plastic raw materials, but also effectively reduce the environmental pollution caused by waste plastics. However, the existing chemical recovery methods, such as the methods reported in the patent application with publication number CN118459435A and the patent with authorization announcement number CN102746270B, need to carry out cumbersome post-processing procedures such as separation and purification in order to obtain regenerated polylactic acid (PLA).

[0006] The literature (A “Polymer to Polymer” Chemical Recycling of PLA Plastics by the “DE–RE Polymerization” Strategy, Macromolecules 2022, 55, 5, 1726–1735) dissolves PLA in dichloromethane, degrades PLA using different catalysts and an appropriate amount of methanol, and then adds lactic acid to the degradation product to further polymerize it into PLA. The literature (Vitrimeric Polylactide by Two-step Alcoholysis and Transesterification during Reactive Processing for Enhanced Melt Strength ACS Appl. Mater. Interfaces 2022, 14, 40, 45966–45977) achieves the recycling of PLA into Vitrimer (plastic thermosetting resin) by esterifying polylactic acid with glycerol and adding a chain extender to improve the melt strength during the foaming process. However, these methods have problems such as the addition of additional monomers, the use of toxic reagents, cumbersome steps and decreased product properties (such as mechanical properties), which are not conducive to industrial applications. Summary of the invention

[0007] The purpose of the present invention is to solve the problems existing in the prior art and provide a regenerated polyester porogen and a preparation method and application thereof.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing a recycled polyester porogen from waste polylactic acid, comprising: firstly subjecting the waste polylactic acid to an ester exchange reaction with an aliphatic dibasic acid to obtain a double-terminal carboxyl polylactic acid oligomer, and then mixing the double-terminal carboxyl polylactic acid oligomer, a polyether diol, an oligomer diol and an inorganic porous material to a polycondensation reaction to obtain a recycled polyester porogen containing water-soluble polylactic acid and an inorganic porous material;

[0010] The aliphatic dibasic acid has 4-20 carbon atoms; if the aliphatic dibasic acid has more than 20 carbon atoms, the carbon chain of the aliphatic dibasic acid is too long. On the one hand, the reaction activity of the terminal carboxyl groups of the aliphatic dibasic acid will be relatively low. If the transesterification reaction time is not extended, the transesterification reaction will not be complete enough to effectively prepare the double-terminal carboxyl group polylactic acid oligomer. If the transesterification reaction time is extended, the thermal degradation of the waste polylactic acid will become serious. On the other hand, during the transesterification reaction, the aliphatic dibasic acid has to enter the molecular chain of the polylactic acid. The too long carbon chain of the aliphatic dibasic acid will cause excessive damage to the regularity of the molecular chain of the polylactic acid, thus affecting the crystallization performance of the final water-soluble polylactic acid and further affecting the spinning process. If the carbon chain of the aliphatic dibasic acid is too short, its thermal stability is very poor and it will volatilize at the transesterification temperature and cannot depolymerize the waste polylactic acid;

[0011] The number-average molecular weight of the double-terminal carboxyl group polylactic acid oligomer is 1000-8000 g / mol; if the molecular weight of the double-terminal carboxyl group polylactic acid oligomer is too low, the crystallization ability of the water-soluble polylactic acid will be relatively low, thus affecting the spinning process; if the molecular weight of the double-terminal carboxyl group polylactic acid oligomer is too high, uneven reaction will occur during the repolymerization process, ultimately resulting in too wide a molecular weight distribution of the water-soluble polylactic acid, thus affecting the spinning process;

[0012] The degree of polymerization of the double-terminal carboxyl group polylactic acid oligomer is 12-110;

[0013] The oligomeric diol is obtained by the esterification reaction of sodium 5-sulfoisophthalate and aliphatic diol;

[0014] The degree of polymerization of the oligomeric diol is 2-5.

[0015] As a preferred technical solution:

[0016] In the method for preparing a regenerated polyester porogen from waste polylactic acid as described above, the preparation process of the double-terminal carboxyl group polylactic acid oligomer is as follows: Add waste polylactic acid, aliphatic dibasic acid, and the first catalyst to the reaction kettle, and react at 150-220 °C and 0.01-0.3 MPa for 2.5-5 h to obtain the double-terminal carboxyl group polylactic acid oligomer;

[0017] Among them, the mass m of the aliphatic dibasic acid COOH 、the mass m of the waste polylactic acid, the relative molecular weight M of the aliphatic dibasic acid nCOOH 、the theoretical value M of the number-average molecular weight of the double-terminal carboxyl group polylactic acid oligomer n satisfy the following formula:

[0018]

[0019] In the formula, mCOOH , the unit of m is g; M nCOOH , M n 's unit is g / mol; is 17 g / mol;

[0020] The mass of the first catalyst is 100 - 1000 ppm of the mass of the waste polylactic acid; the first catalyst is one or more of titanium glycolate, tetrabutyl titanate, antimony glycolate, antimony acetate, antimony oxide, stannous octoate, stannous chloride, zinc acetate and zinc oxide;

[0021] The derivation process of the above formula is as follows: According to the preparation process of the double-ended carboxyl polylactic acid oligomer, the structural formula of the double-ended carboxyl polylactic acid oligomer can be speculated as (In the formula, R is the chain segment between two carboxyl groups in the aliphatic dibasic acid, and n is the number of lactic acid repeating units);

[0022] It can be seen from this that it includes n lactic acid repeating units and 1 aliphatic dibasic acid; the relative molecular mass of the lactic acid link is 72, and 1 - OH (molar mass is 17 g / mol, denoted as ) will be removed when capped with the aliphatic dibasic acid. Let the theoretical value of the number-average molecular weight of the double-ended carboxyl polylactic acid oligomer be M n , then Equation 1 can be listed:

[0023]

[0024] Converted to Equation 2:

[0025]

[0026] Let the mass of the waste polylactic acid added in the preparation process be m, and the number of moles of lactic acid links in the waste polylactic acid be n PLA , then Equation 3 can be listed:

[0027] n PLA = m / 72; Equation 3

[0028] It can be obtained that the number of lactic acid links in the waste polylactic acid is n PLA / n times more than the number of lactic acid links in the designed double-ended carboxyl polylactic acid oligomer, and the multiple of the increase is the number of moles of the required aliphatic dibasic acid n COOH , that is, Equation 4 is obtained:

[0029] n COOH = n PLA / n; Equation 4

[0030] Substitute Equation 3 into Equation 4, and Equation 5 is obtained:

[0031] n COOH = m / (72n); Equation 5

[0032] The relative molecular mass M of the aliphatic dicarboxylic acid nCOOH can be calculated according to Equation 6:

[0033] m nCOOH = n COOH × M nCOOH ; Equation 6

[0034] Substituting Equation 5 into Equation 6, Equation 7 can be obtained:

[0035] m nCOOH = (m × M nCOOH ) / (72n); Equation 7

[0036] Finally, substituting Equation 2 into Equation 7, the above formula can be obtained;

[0037] Experiments show that the relative deviation of the number-average molecular weight of the double-end carboxyl poly(lactic acid) oligomer does not exceed 2%. 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 poly(lactic acid) oligomer, the appropriate aliphatic dicarboxylic acid can be selected according to the above formula, and the mass of the aliphatic dicarboxylic acid and the mass of the waste poly(lactic acid) can be determined.

[0038] As described above, a method for preparing a regenerated polyester pore-forming agent from waste poly(lactic acid), the preparation process of the oligomer diol is as follows: Add sodium 5-sulfoisophthalate, aliphatic diol and a second catalyst into a reaction kettle, and react at 220 - 240 °C and 0.1 - 0.3 MPa until the water output reaches more than 95% of the theoretical water output, then the oligomer diol can be obtained;

[0039] The molar ratio of sodium 5-sulfoisophthalate to aliphatic diol is 1:1.01 - 1.1, and the mass of the second catalyst is 0 - 500 ppm of the mass of sodium 5-sulfoisophthalate;

[0040] Stirring is accompanied during the reaction, and the stirring speed is 100 - 200 r / min;

[0041] The aliphatic diol is one or more of ethylene glycol, propylene glycol, butanediol and pentanediol; the second catalyst is one or more of titanium glycolate, tetrabutyl titanate, antimony glycolate, antimony acetate, antimony oxide, stannous octoate, stannous chloride, zinc acetate and zinc oxide.

[0042] As described above, a method for preparing a regenerated polyester pore-forming agent from waste poly(lactic acid), the polyether diol is one or more of polyethylene glycol, polypropylene glycol and polytetrahydrofuran, and the number-average molecular weight of the polyether diol is 400 - 4000 g / mol.

[0043] A method for preparing a regenerated polyester pore-forming agent from waste polylactic acid as described above, wherein the inorganic porous material is one or more of porous carbon materials and porous natural ore powders, with an average particle size of not less than 0.05 microns and an average micropore diameter of not more than 200 nanometers.

[0044] A method for preparing a regenerated polyester pore-forming agent from waste polylactic acid as described above, wherein the total molar amount of polyether diol and oligomeric diol is 1.0 - 1.1 times the molar amount of waste polylactic acid, the molar amount of oligomeric diol is 10 - 30% of the total molar amount of polyether diol and oligomeric diol, and the mass of the inorganic porous material is not less than 5% of the mass of waste polylactic acid.

[0045] A method for preparing a regenerated polyester pore-forming agent from waste polylactic acid as described above, wherein the polycondensation reaction includes a pre-polycondensation reaction and a final polycondensation reaction. The pressure of the pre-polycondensation reaction is 0.01 - 0.1 MPa, the temperature is 170 - 230 °C, and the time is 1 - 3 h. The pressure of the final polycondensation reaction is 5 - 300 Pa, the temperature is 180 - 250 °C, and the time is 3 - 5 h.

[0046] The present invention also provides a regenerated polyester pore-forming agent prepared by using the method for preparing a regenerated polyester pore-forming agent from waste polylactic acid described in any one of the above; the number-average molecular weight of the regenerated polyester pore-forming agent is 14000 - 33000 g / mol, the molecular weight distribution index is 1.5 - 3.0, the melting point is 80 - 180 °C, the crystallization temperature is 25 - 60 °C, and the mass loss rate after soaking in hot water at 50 - 100 °C for 3 - 30 min is 10 - 75%.

[0047] The present invention also provides an application of the regenerated polyester pore-forming agent as described above. After melting and blending the regenerated polyester pore-forming agent with fiber-grade polyester to prepare a blended fiber, the blended fiber is soaked in hot water at 50 - 100 °C for 3 - 30 min to obtain a porous fiber.

[0048] As a preferred technical solution:

[0049] For the application as described above, the number-average molecular weight of the fiber-grade polyester is 15000 - 40000 g / mol, the mass of the regenerated polyester pore-forming agent is 2 - 30% of the total mass of the regenerated polyester pore-forming agent and the fiber-grade polyester, the mass ratio of the blended fiber to hot water is 1:10 - 50; the fineness of the porous fiber is 1.0 - 5.0 dtex, the breaking strength is 2.5 - 5.5 cN / dtex, and the elongation at break is 10 - 40%; the porous fiber has a porous structure with an average pore diameter of 50 - 300 nm; the specific surface area of the porous fiber is increased by 1.5 - 12.5 times compared with the blended fiber, and the mass is reduced by 2 - 30 wt%.

[0050] The principle of the present invention is as follows:

[0051] The present invention designs a dicarboxyl polylactic acid oligomer through transesterification reaction, and prepares a regenerated polyester pore-forming agent containing water-soluble polylactic acid and inorganic porous material with polyether diol and oligomer diol, realizing the recycling of waste polylactic acid.

[0052] The water-soluble polylactic acid in the regenerated polyester pore-forming agent prepared by the present invention has good water solubility due to the hydrophilic polyether chain segment and sodium sulfonate group in the molecular chain. During the dissolution process, the hydrophilic polyether chain segment exists in an amorphous form in the water-soluble polylactic acid, which can promote water molecules to enter the amorphous region; the presence of the sodium sulfonate group can quickly capture the water molecules entering the molecular chain of the water-soluble polylactic acid, so that the molecular chain of the water-soluble polylactic acid dissolves in water, and the whole dissolution process shows the phenomenon of swelling first and then dissolution.

[0053] Introducing sodium 5-sulfoisophthalate into the water-soluble polylactic acid will lead to a decrease in its crystallization ability and difficulty in melt spinning processing. Therefore, on the one hand, the present invention controls the number of carbon atoms of the aliphatic dicarboxylic acid and the number-average molecular weight of the double-terminal carboxyl polylactic acid oligomer, so as to ensure the crystallization performance of the water-soluble polylactic acid. On the other hand, the present invention introduces the inorganic porous material into the polymerization system of the water-soluble polylactic acid by in-situ polymerization, which not only avoids the agglomeration of the inorganic porous material in the polymerization system, but also can use the inorganic porous material as a nucleating agent to promote the crystallization of the water-soluble polylactic acid.

[0054] When the regenerated polyester pore-forming agent containing water-soluble polylactic acid and inorganic porous material is melt-blended and spun with fiber-grade polyester, the existence of the polylactic acid chain segment in the water-soluble polylactic acid enables the water-soluble polylactic acid to have good compatibility with the fiber-grade polyester, ensuring the uniform distribution of the water-soluble polylactic acid in the fiber-grade polyester. There is incompatibility between the polyether chain segment in the water-soluble polylactic acid and the fiber-grade polyester, resulting in a phase separation structure between the water-soluble polylactic acid and the fiber-grade polyester, avoiding the complete encapsulation of the water-soluble polylactic acid by the fiber-grade polyester.

[0055] Beneficial effects:

[0056] (1) The present invention realizes the efficient recycling and reuse of waste polylactic acid, improves the resource utilization rate of polylactic acid, and reduces resource waste.

[0057] (2) The porous fibers prepared by the method of the present invention do not produce waste liquid harmful to the environment during the pore-forming process and do not require secondary treatment, which conforms to the environmental protection concept of green and low-carbon.

[0058] (3) The preparation method of the present invention has simple process, convenient operation, is easy to realize large-scale production, and reduces the production cost of the porous fibers.

[0059] (4) The porous fibers prepared by using the present invention have an independent microporous structure. The high specific surface area can firmly lock the flowing air, and they can be used as thermal insulation fiber materials. At the same time, the mechanical properties of the fibers are effectively guaranteed, meeting the performance requirements of porous fibers in fields such as textile and clothing.

[0060] (5) The porous fibers prepared by the present invention have excellent properties and environmental protection characteristics, and can be widely applied in fields such as textile and clothing, absorption materials, and adsorption materials, having broad market prospects and application values. Description of the Drawings

[0061] Figure 1 It is the nuclear magnetic resonance spectrum of the double-end carboxyl polylactic acid oligomer prepared in Example 6. Among them, a is the methylene H near the carbonyl in adipic acid, b is the methine H far from the carbonyl in adipic acid, c is the methine H in the polylactic acid repeating unit, and d is the methyl H in the polylactic acid repeating unit. Detailed Embodiments

[0062] 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 not 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 also fall within the scope defined by the appended claims of this application.

[0063] The following are the test methods for relevant performance indicators in each embodiment and comparative example:

[0064] Intrinsic viscosity: It is tested by using an Ubbelohde viscometer with a capillary diameter of 0.7 - 0.8 mm. Weigh 0.25 g of the sample to be tested with an electronic balance, dissolve it in a mixed solvent of phenol and tetrachloroethane with a mass ratio of 1:1 in a water bath at 60 - 70 °C to obtain a test solution with a concentration of 0.005 g / ml. Then, place the test solution in a constant temperature water bath at 25 ± 0.1 °C for 10 min, observe and record the time for the test solution to flow through the upper and lower scale lines of the Ubbelohde viscometer (simultaneously set a control group, and the difference from this test is only that the sample to be tested is not added). The test is carried out in parallel 3 times and the average value is taken as the final result. The calculation process is carried out according to the following formula:

[0065]

[0066] η sp =η r -1;

[0067]

[0068] In the formula, η ris the relative viscosity, t is the flow-through time (s) of the solution to be measured, t0 is the flow-through time (s) of the mixed solvent of phenol and tetrachloroethane in the control group, and η sp is the specific viscosity, [η] is the intrinsic viscosity (dL / g), and c is the concentration (g / ml) of the solution to be measured.

[0069] Degree of polymerization: Dissolve 5 - 10 mg of the sample to be measured in 0.55 - 0.6 mL of deuterated chloroform (CDCl3) to obtain the solution to be measured, and test it by an Avance-600Hz nuclear magnetic resonance spectrometer (NMR); among them, the number of scans is 64 times.

[0070] Number-average molecular weight, molecular weight distribution index: Test by an Agilent 1260 gel permeation chromatograph (GPC). The chromatographic column is the Agilent HFIP series, and the mobile phase is composed of hexafluoroisopropanol and sodium trifluoroacetate (the concentration of sodium trifluoroacetate is 0.02 mol / L). The test temperature is 35°C.

[0071] Melting point, crystallization temperature: Test with reference to "GB / T 19466.3 - 2004 Plastics - Differential scanning calorimetry (DSC) - Part 3: Determination of melting and crystallization temperatures and enthalpies".

[0072] Mass loss rate after soaking in hot water at 50 - 100°C for 3 - 30 min: Weigh 10 - 15 g of the sample to be measured, and record its weight as W0 (unit: g). Soak it in water at 50 - 100°C for 3 - 30 min, then take it out and dry it at 50°C, and weigh it again (recorded as W1, unit: g). Calculate the mass loss rate W using the following formula 1oss :

[0073]

[0074] Fineness: Test according to GB / T 14343 - 2008.

[0075] Breaking strength: Test according to GB / T 14344 - 2022.

[0076] Elongation at break: Test according to GB / T 14344 - 2022.

[0077] Specific surface area: Use an Autosorb-iQ type fully automatic rapid specific surface and porosity analyzer to measure the specific surface area of the fiber.

[0078] Example 1

[0079] A preparation method of porous fiber, the specific steps are as follows:

[0080] (1) Preparation of raw materials;

[0081] Waste polylactic acid: intrinsic viscosity is 1.20 dL / g;

[0082] Aliphatic dibasic acid: adipic acid;

[0083] First catalyst: tetrabutyl titanate;

[0084] Sodium 5-sulfoisophthalate;

[0085] Aliphatic diol: ethylene glycol;

[0086] Polyether diol: polyethylene glycol, number average molecular weight is 400 g / mol;

[0087] Inorganic porous material: diatomite, average particle size is 2 microns, average micropore diameter is 100 nanometers;

[0088] Fiber-grade polyester: polylactic acid, number average molecular weight is 40000 g / mol;

[0089] (2) Prepare carboxyl-terminated polylactic acid oligomer and oligomer diol respectively;

[0090] The preparation process of the carboxyl-terminated polylactic acid oligomer is as follows: Add waste polylactic acid, aliphatic dibasic acid, and the first catalyst into the reaction kettle, and react at 150 °C and 0.01 MPa for 5 h to obtain a carboxyl-terminated polylactic acid oligomer with a number average molecular weight of 1000 g / mol and a degree of polymerization of 12;

[0091] Among them, the mass ratio of waste polylactic acid to aliphatic dibasic acid is 6:1, and the mass of the first catalyst is 1000 ppm of the mass of waste polylactic acid;

[0092] The preparation process of the oligomer diol is as follows: Add sodium 5-sulfoisophthalate and aliphatic diol into the reaction kettle, and react at a temperature of 220 °C and a pressure of 0.1 MPa under the stirring condition of a stirring speed of 200 r / min until the water output reaches 99% of the theoretical water output to obtain an oligomer diol with a degree of polymerization of 2; among them, the molar ratio of sodium 5-sulfoisophthalate to aliphatic diol is 1:1.01;

[0093] (3) Prepare a regenerated polyester pore-forming agent;

[0094] After mixing the double - end carboxyl polylactic acid oligomer, polyether diol, oligomer diol and inorganic porous material, first carry out pre - polycondensation reaction at 0.1 MPa and 170 °C for 2.5 h, and then carry out final polycondensation reaction at 200 Pa and 180 °C for 5 h to obtain a regenerated polyester pore - forming agent containing water - soluble polylactic acid and inorganic porous material; wherein, the total molar amount of polyether diol and oligomer diol is 1.0 times the molar amount of waste polylactic acid, the molar amount of oligomer diol is 10% of the total molar amount of polyether diol and oligomer diol, and the mass of the inorganic porous material is 10% of the mass of waste polylactic acid;

[0095] The number - average molecular weight of the prepared regenerated polyester pore - forming agent is 14000 g / mol, the molecular weight distribution index is 1.5, the melting point is 80 °C, and the crystallization temperature is 25 °C; the mass loss rate of the regenerated polyester pore - forming agent soaked in hot water at 50 °C for 30 min is 50%;

[0096] (4) Prepare porous fibers;

[0097] After melting and blending and spinning the regenerated polyester pore - forming agent and fiber - grade polyester (spinning temperature is 180 °C) to obtain blended fibers, soak the blended fibers in hot water at 50 °C for 30 min to obtain porous fibers; wherein, the mass of the regenerated polyester pore - forming agent is 2% of the total mass of the regenerated polyester pore - forming agent and fiber - grade polyester, and the mass ratio of the blended fibers to hot water is 1:50.

[0098] The fineness of the finally prepared porous fibers is 1 dtex, the breaking strength is 2.5 cN / dtex, and the elongation at break is 40%; the porous fibers have a porous structure, and the average pore diameter is 120 nm; the specific surface area of the porous fibers increases by 10 times compared with the blended fibers, and the mass is reduced by 25 wt%.

[0099] Comparative Example 1

[0100] A method for preparing fibers, which is only different from Example 1 in that: in step (2), when preparing the double - end carboxyl polylactic acid oligomer, the addition amount of waste polylactic acid is adjusted, and the mass ratio of waste polylactic acid to aliphatic dicarboxylic acid is 3:1, which makes the number - average molecular weight of the double - end carboxyl polylactic acid oligomer 500 g / mol and the degree of polymerization 5.

[0101] The breaking strength of the finally prepared fibers is 2.0 cN / dtex.

[0102] Compared with Example 1, the breaking strength of the fibers in Comparative Example 1 decreased significantly. This is because the number - average molecular weight of the double - end carboxyl polylactic acid oligomer in Comparative Example 1 is too low, resulting in a lower crystallization ability of water - soluble polylactic acid, a poorer regularity and orderliness of the internal structure of the fibers, and when subjected to external tensile force, the molecular chains are more likely to slip and break, thus reducing the breaking strength of the fibers.

[0103] Example 2

[0104] A preparation method of porous fibers is as follows:

[0105] (1) Preparation of raw materials;

[0106] Waste poly(lactic acid): Intrinsic viscosity is 1.25 dL / g;

[0107] Aliphatic dicarboxylic acid: Eicosanedioic acid;

[0108] The first catalyst and the second catalyst: Both are antimony glycolate;

[0109] Sodium 5-sulfoisophthalate;

[0110] Aliphatic diol: Propylene glycol;

[0111] Polyether diol: Polypropylene glycol, number-average molecular weight is 1000 g / mol;

[0112] Inorganic porous material: Bamboo charcoal powder, average particle size is 0.05 micrometers, average micropore diameter is 50 nanometers;

[0113] Fiber-grade polyester: Poly(butylene succinate), number-average molecular weight is 15000 g / mol;

[0114] (2) Prepare carboxyl-terminated poly(lactic acid) oligomer and oligomer diol respectively;

[0115] The preparation process of carboxyl-terminated poly(lactic acid) oligomer is as follows: Add waste poly(lactic acid), aliphatic dicarboxylic acid, and the first catalyst into a reaction kettle, and react at 160 °C and 0.08 MPa for 4 h to obtain a carboxyl-terminated poly(lactic acid) oligomer with a number-average molecular weight of 2000 g / mol and a degree of polymerization of 23;

[0116] Among them, the mass ratio of waste poly(lactic acid) to aliphatic dicarboxylic acid is 5:1, and the mass of the first catalyst is 800 ppm of the mass of waste poly(lactic acid);

[0117] The preparation process of oligomer diol is as follows: Add sodium 5-sulfoisophthalate, aliphatic diol, and the second catalyst into a reaction kettle, and react at a stirring speed of 100 r / min, at a temperature of 225 °C and a pressure of 0.15 MPa until the water output reaches 96% of the theoretical water output to obtain an oligomer diol with a degree of polymerization of 2; Among them, the molar ratio of sodium 5-sulfoisophthalate to aliphatic diol is 1:1.01, and the mass of the second catalyst is 100 ppm of the mass of sodium 5-sulfoisophthalate;

[0118] (3) Prepare regenerated polyester pore-forming agent;

[0119] After mixing the double-end carboxyl polylactic acid oligomer, polyether diol, oligomer diol and inorganic porous material, first carry out a pre-polycondensation reaction at 0.08 MPa and 190 °C for 3 h, and then carry out a final polycondensation reaction at 300 Pa and 200 °C for 4.5 h to obtain a regenerated polyester pore-forming agent containing water-soluble polylactic acid and inorganic porous material; wherein, the total molar amount of polyether diol and oligomer diol is 1.0 times the molar amount of waste polylactic acid, the molar amount of oligomer diol is 30% of the total molar amount of polyether diol and oligomer diol, and the mass of the inorganic porous material is 5% of the mass of waste polylactic acid;

[0120] The number-average molecular weight of the prepared regenerated polyester pore-forming agent is 18000 g / mol, the molecular weight distribution index is 3, the melting point is 100 °C, and the crystallization temperature is 30 °C; the mass loss rate of the regenerated polyester pore-forming agent soaked in hot water at 65 °C for 25 min is 60%;

[0121] (4) Prepare porous fibers;

[0122] After melting and blending and spinning the regenerated polyester pore-forming agent and fiber-grade polyester (spinning temperature is 190 °C) to obtain blended fibers, soak the blended fibers in hot water at 65 °C for 25 min to obtain porous fibers; wherein, the mass of the regenerated polyester pore-forming agent is 5% of the total mass of the regenerated polyester pore-forming agent and fiber-grade polyester, and the mass ratio of the blended fibers to hot water is 1:40.

[0123] The fineness of the finally prepared porous fibers is 2 dtex, the breaking strength is 3 cN / dtex, and the elongation at break is 30%; the porous fibers have a porous structure, and the average pore diameter is 50 nm; the specific surface area of the porous fibers increases by 12.5 times compared with the blended fibers, and the mass is reduced by 20 wt%.

[0124] Comparative Example 2

[0125] A method for preparing fibers, which is only different from Example 2 in that: the aliphatic dicarboxylic acid used in this comparative example is tetracosane dicarboxylic acid (CAS number is 3365-67-1).

[0126] The breaking strength of the finally prepared fibers is 2.0 cN / dtex.

[0127] Compared with Example 2, the breaking strength of the fibers in Comparative Example 2 decreased significantly. This is because the carbon chain of the aliphatic dicarboxylic acid in Comparative Example 2 is too long, resulting in insufficient transesterification reaction and serious damage to the regularity of the polylactic acid molecular chain, affecting the structure and performance of the final fibers, weakening their ability to resist external tensile force, and thus showing a decrease in breaking strength.

[0128] Example 3

[0129] A method for preparing porous fibers, the specific steps are as follows:

[0130] (1) Preparation of raw materials;

[0131] Waste poly(lactic acid): Intrinsic viscosity is 1.30 dL / g;

[0132] Aliphatic dicarboxylic acid: Suberic acid;

[0133] The first catalyst and the second catalyst: Both are stannous octoate;

[0134] Sodium 5-sulfoisophthalate;

[0135] Aliphatic diol: Butanediol;

[0136] Polyether diol: Polytetrahydrofuran, number average molecular weight is 2000 g / mol;

[0137] Inorganic porous material: Graphene powder, average particle size is 3 microns, average micropore diameter is 200 nanometers;

[0138] Fiber-grade polyester: Polyethylene terephthalate, number average molecular weight is 25000 g / mol;

[0139] (2) Prepare carboxyl-terminated poly(lactic acid) oligomer and oligomer diol respectively;

[0140] The preparation process of the carboxyl-terminated poly(lactic acid) oligomer is as follows: Add waste poly(lactic acid), aliphatic dicarboxylic acid, and the first catalyst into the reaction kettle, and react at 180 °C and 0.1 MPa for 3.5 h to obtain a carboxyl-terminated poly(lactic acid) oligomer with a number average molecular weight of 4000 g / mol and a degree of polymerization of 53;

[0141] Among them, the mass ratio of waste poly(lactic acid) to aliphatic dicarboxylic acid is 22:1, and the mass of the first catalyst is 500 ppm of the mass of waste poly(lactic acid);

[0142] The preparation process of the oligomer diol is as follows: Add sodium 5-sulfoisophthalate, aliphatic diol, and the second catalyst into the reaction kettle, and react at a temperature of 230 °C and a pressure of 0.2 MPa under the stirring condition of a stirring speed of 150 r / min until the water output reaches 98% of the theoretical water output to obtain an oligomer diol with a degree of polymerization of 3; Among them, the molar ratio of sodium 5-sulfoisophthalate to aliphatic diol is 1:1.05, and the mass of the second catalyst is 300 ppm of the mass of sodium 5-sulfoisophthalate;

[0143] (3) Prepare regenerated polyester pore-forming agent;

[0144] After mixing the double-end carboxyl polylactic acid oligomer, polyether diol, oligomer diol and inorganic porous material, first carry out pre-polycondensation reaction at 0.06 MPa and 200 °C for 2 h, and then carry out final polycondensation reaction at 100 Pa and 220 °C for 4 h to obtain the regenerated polyester pore-forming agent containing water-soluble polylactic acid and inorganic porous material; wherein, the total molar amount of polyether diol and oligomer diol is 1.1 times the molar amount of waste polylactic acid, the molar amount of oligomer diol is 20% of the total molar amount of polyether diol and oligomer diol, and the mass of inorganic porous material is 15% of the mass of waste polylactic acid;

[0145] The number-average molecular weight of the prepared regenerated polyester pore-forming agent is 20,000 g / mol, the molecular weight distribution index is 1.6, the melting point is 120 °C, and the crystallization temperature is 50 °C; the mass loss rate of the regenerated polyester pore-forming agent soaked in hot water at 80 °C for 15 min is 75%;

[0146] (4) Prepare porous fibers;

[0147] After melting and blending and spinning the regenerated polyester pore-forming agent and fiber-grade polyester (spinning temperature is 210 °C) to obtain blended fibers, soak the blended fibers in hot water at 80 °C for 15 min to obtain porous fibers; wherein, the mass of the regenerated polyester pore-forming agent is 15% of the total mass of the regenerated polyester pore-forming agent and fiber-grade polyester, and the mass ratio of the blended fibers to hot water is 1:30.

[0148] The fineness of the finally prepared porous fibers is 3 dtex, the breaking strength is 3.5 cN / dtex, and the elongation at break is 25%; the porous fibers have a porous structure, and the average pore diameter is 300 nm; the specific surface area of the porous fibers increases by 1.5 times compared with the blended fibers, and the mass is reduced by 2 wt%.

[0149] Example 4

[0150] A preparation method of porous fibers, the specific steps are as follows:

[0151] (1) Preparation of raw materials;

[0152] Waste polylactic acid: intrinsic viscosity is 1.35 dL / g;

[0153] Aliphatic dibasic acid: sebacic acid;

[0154] The first catalyst and the second catalyst: both are zinc acetate;

[0155] Sodium 5-sulfoisophthalate;

[0156] Aliphatic diol: pentanediol;

[0157] Polyether diol: polyethylene glycol, number-average molecular weight is 2,000 g / mol;

[0158] Inorganic porous material: sepiolite powder, with an average particle size of 1 μm and an average micropore diameter of 80 nm;

[0159] Fiber-grade polyester: poly(propylene terephthalate), with a number-average molecular weight of 20,000 g / mol;

[0160] (2) Prepare carboxyl-terminated polylactic acid oligomer and oligomeric diol respectively;

[0161] The preparation process of the carboxyl-terminated polylactic acid oligomer is as follows: Add waste polylactic acid, aliphatic dicarboxylic acid, and the first catalyst into the reaction kettle, and react at 200 °C and 0.2 MPa for 3 h to obtain a carboxyl-terminated polylactic acid oligomer with a number-average molecular weight of 6000 g / mol and a degree of polymerization of 81;

[0162] Among them, the mass ratio of waste polylactic acid to aliphatic dicarboxylic acid is 29:1, and the mass of the first catalyst is 300 ppm of the mass of waste polylactic acid;

[0163] The preparation process of the oligomeric diol is as follows: Add sodium 5-sulfoisophthalate, aliphatic diol, and the second catalyst into the reaction kettle, and react at a temperature of 235 °C and a pressure of 0.25 MPa under the stirring condition of a stirring speed of 200 r / min until the water output reaches 95% of the theoretical water output to obtain an oligomeric diol with a degree of polymerization of 4; Among them, the molar ratio of sodium 5-sulfoisophthalate to aliphatic diol is 1:1.05, and the mass of the second catalyst is 400 ppm of the mass of sodium 5-sulfoisophthalate;

[0164] (3) Prepare a regenerated polyester pore-forming agent;

[0165] Mix the carboxyl-terminated polylactic acid oligomer, polyether diol, oligomeric diol, and inorganic porous material, first carry out a prepolycondensation reaction at 0.04 MPa and 210 °C for 1.5 h, and then carry out a final polycondensation reaction at 50 Pa and 230 °C for 3.5 h to obtain a regenerated polyester pore-forming agent containing water-soluble polylactic acid and inorganic porous material; Among them, the total molar amount of polyether diol and oligomeric diol is 1.1 times the molar amount of waste polylactic acid, the molar amount of oligomeric diol is 20% of the total molar amount of polyether diol and oligomeric diol, and the mass of inorganic porous material is 20% of the mass of waste polylactic acid;

[0166] The number-average molecular weight of the prepared regenerated polyester pore-forming agent is 22,000 g / mol, the molecular weight distribution index is 1.8, the melting point is 160 °C, and the crystallization temperature is 40 °C; The mass loss rate of the regenerated polyester pore-forming agent after being soaked in hot water at 70 °C for 20 min is 65%;

[0167] (4) Prepare porous fibers;

[0168] After melting and blending the recycled polyester pore-forming agent with fiber-grade polyester and spinning (the spinning temperature is 220 °C) to obtain blended fibers, the blended fibers are soaked in hot water at 70 °C for 20 min to obtain porous fibers; among them, the mass of the recycled polyester pore-forming agent is 10% of the total mass of the recycled polyester pore-forming agent and fiber-grade polyester, and the mass ratio of the blended fibers to hot water is 1:20.

[0169] The fineness of the finally obtained porous fibers is 4 dtex, the breaking strength is 4.5 cN / dtex, and the elongation at break is 20%; the porous fibers have a porous structure with an average pore diameter of 100 nm; the specific surface area of the porous fibers increases by 8 times compared with the blended fibers, and the mass is reduced by 30 wt%.

[0170] Example 5

[0171] A method for preparing porous fibers, the specific steps are as follows:

[0172] (1) Preparation of raw materials;

[0173] Waste poly(lactic acid): intrinsic viscosity is 1.40 dL / g;

[0174] Aliphatic dicarboxylic acid: succinic acid;

[0175] The first catalyst and the second catalyst: both are mixtures composed of tetrabutyl titanate and zinc acetate with a mass ratio of 1:1;

[0176] Sodium 5-sulfoisophthalate;

[0177] Aliphatic diol: a mixture composed of ethylene glycol and butanediol with a mass ratio of 1:1;

[0178] Polyether diol: polyethylene glycol, number average molecular weight is 4000 g / mol;

[0179] Inorganic porous material: diatomite, average particle size is 3 microns, and average pore diameter of micropores is 150 nanometers;

[0180] Fiber-grade polyester: polybutylene terephthalate, number average molecular weight is 30000 g / mol;

[0181] (2) Prepare double-end carboxyl poly(lactic acid) oligomer and oligomer diol respectively;

[0182] The preparation process of the double-end carboxyl poly(lactic acid) oligomer is as follows: Add waste poly(lactic acid), aliphatic dicarboxylic acid, and the first catalyst into the reaction kettle, and react at 220 °C and 0.3 MPa for 2.5 h to obtain a double-end carboxyl poly(lactic acid) oligomer with a number average molecular weight of 8000 g / mol and a degree of polymerization of 110;

[0183] Among them, the mass ratio of waste polylactic acid to aliphatic dibasic acid is 68:1, and the mass of the first catalyst is 100 ppm of the mass of waste polylactic acid;

[0184] The preparation process of oligomeric diol is as follows: Sodium 5-sulfoisophthalate, aliphatic diol and a second catalyst are added into a reaction kettle, and under the stirring condition with a stirring speed of 100 r / min, the reaction is carried out at a temperature of 240 °C and a pressure of 0.3 MPa until the water output reaches 97% of the theoretical water output, thus obtaining an oligomeric diol with a degree of polymerization of 5; among them, the molar ratio of sodium 5-sulfoisophthalate to aliphatic diol is 1:1.1, and the mass of the second catalyst is 500 ppm of the mass of sodium 5-sulfoisophthalate;

[0185] (3) Prepare a regenerated polyester pore-forming agent;

[0186] After mixing the double-ended carboxyl polylactic acid oligomer, polyether diol, oligomeric diol and inorganic porous material, first carry out a prepolycondensation reaction at 0.01 MPa and 230 °C for 1 h, and then carry out a final polycondensation reaction at 5 Pa and 250 °C for 3 h, thus obtaining a regenerated polyester pore-forming agent containing water-soluble polylactic acid and inorganic porous material; among them, the total molar amount of polyether diol and oligomeric diol is 1.0 times the molar amount of waste polylactic acid, the molar amount of oligomeric diol is 30% of the total molar amount of polyether diol and oligomeric diol, and the mass of the inorganic porous material is 30% of the mass of waste polylactic acid;

[0187] The number-average molecular weight of the prepared regenerated polyester pore-forming agent is 33000 g / mol, the molecular weight distribution index is 2, the melting point is 180 °C, and the crystallization temperature is 60 °C; the mass loss rate of the regenerated polyester pore-forming agent when soaked in hot water at 100 °C for 3 min is 10%;

[0188] (4) Prepare porous fibers;

[0189] After melt-blending and spinning the regenerated polyester pore-forming agent and fiber-grade polyester (the spinning temperature is 230 °C) to obtain blended fibers, soak the blended fibers in hot water at 100 °C for 3 min, thus obtaining porous fibers; among them, the mass of the regenerated polyester pore-forming agent is 30% of the total mass of the regenerated polyester pore-forming agent and fiber-grade polyester, and the mass ratio of the blended fibers to hot water is 1:10.

[0190] The fineness of the finally prepared porous fibers is 5 dtex, the breaking strength is 5 cN / dtex, and the elongation at break is 10%; the porous fibers have a porous structure, and the average pore diameter is 150 nm; the specific surface area of the porous fibers increases by 5 times compared with the blended fibers, and the mass is reduced by 10 wt%.

[0191] Comparative Example 3

[0192] A preparation method of a fiber, which is only different from Example 5 in that: in step (2), when preparing the double-end carboxyl polylactic acid oligomer, the addition amount of waste polylactic acid is adjusted, and the mass ratio of waste polylactic acid to aliphatic dicarboxylic acid is 75:1, which makes the number-average molecular weight of the double-end carboxyl polylactic acid oligomer 9000 g / mol and the degree of polymerization 124.

[0193] The breaking strength of the finally prepared fiber is 2.3 cN / dtex.

[0194] Compared with Example 5, the breaking strength of the fiber in Comparative Example 3 decreased significantly. This is because the number-average molecular weight of the double-end carboxyl polylactic acid oligomer in Comparative Example 3 was too high, resulting in uneven reaction during the repolymerization process. Eventually, the molecular weight distribution of the water-soluble polylactic acid became too wide, causing more defects in the internal structure of the fiber. The arrangement and interaction between molecular chains became disordered. When the fiber was subjected to external force, the stress could not be evenly distributed on the molecular chains and was easily concentrated at the defect sites, leading to easier fracture of the fiber and a decrease in breaking strength.

[0195] Example 6

[0196] A preparation method of a porous fiber, which is only different from Example 2 in that: the intrinsic viscosity of waste polylactic acid is 1.40 dL / g, the aliphatic dicarboxylic acid is adipic acid, the first catalyst is tetrabutyl titanate, and the mass of the first catalyst is 300 ppm of the mass of waste polylactic acid; when preparing the double-end carboxyl polylactic acid oligomer, the mass ratio of waste polylactic acid to aliphatic dicarboxylic acid is 13:1, the reaction temperature is 150 °C, and the reaction time is 4 h; the number-average molecular weight of the prepared double-end carboxyl polylactic acid oligomer is 2000 g / mol, and the nuclear magnetic resonance spectrum is as Figure 1 shown.

[0197] The fineness of the finally prepared porous fiber is 4 dtex, the breaking strength is 4 cN / dtex, and the elongation at break is 35%; the porous fiber has a porous structure with an average pore size of 50 nm; the specific surface area of the porous fiber is increased by 12.5 times and the mass is reduced by 20 wt% compared with the blend fiber.

[0198] Each of the above examples has been verified, and 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 calculation formula of the theoretical value is as follows:

[0199]

[0200] In the formula, m COOH (the mass of the aliphatic dicarboxylic acid), m (the mass of the waste polylactic acid) are in the unit of g; M nCOOH (the relative molecular weight of the aliphatic dicarboxylic acid), M nThe unit of the theoretical value of the number-average molecular weight of the double-end carboxyl polylactic acid oligomer is g / mol; It is 17 g / mol.

[0201] In this article, the number-average molecular weight is defaulted to the actual value, unless the number-average molecular weight is clearly defined as the theoretical value.

Claims

1. A method for preparing a recycled polyester porogen from waste polylactic acid, characterized in that: First, waste polylactic acid and aliphatic dibasic acid are subjected to ester exchange reaction to obtain double-terminal carboxyl polylactic acid oligomers, and then the double-terminal carboxyl polylactic acid oligomers, polyether diols, oligomer diols and inorganic porous materials are mixed and subjected to polycondensation reaction to obtain a recycled polyester porogen containing water-soluble polylactic acid and inorganic porous materials; Aliphatic dibasic acids have 4-20 carbon atoms; The number average molecular weight of the double-terminated carboxyl polylactic acid oligomer is 1000-8000 g / mol; The degree of polymerization of the double-terminated carboxyl polylactic acid oligomer is 12-110; The oligomer diol is obtained by esterification of sodium 5-sulfoisophthalic acid and aliphatic diol; The degree of polymerization of the oligomer diol is 2-5.

2. The method for preparing a recycled polyester porogen from waste polylactic acid according to claim 1, characterized in that: The preparation process of the double-terminal carboxyl polylactic acid oligomer is as follows: waste polylactic acid, aliphatic dibasic acid and a first catalyst are added into a reaction kettle, and the reaction is carried out at 150-220° C. and 0.01-0.3 MPa for 2.5-5 hours to obtain the double-terminal carboxyl polylactic acid oligomer; The mass of the first catalyst is 100-1000ppm of the mass of the waste polylactic acid; the first 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.

3. The method for preparing a recycled polyester porogen from waste polylactic acid according to claim 1, characterized in that: The preparation process of the oligomer diol is as follows: adding sodium 5-sulfonate of isophthalic acid, aliphatic diol and a second catalyst into a reaction kettle, reacting at 220-240° C. and 0.1-0.3 MPa until the water output reaches more than 95% of the theoretical water output, thereby obtaining the oligomer diol; The molar ratio of sodium 5-sulfoisophthalic acid to aliphatic diol is 1:1.01-1.1, and the mass of the second catalyst is 0-500ppm of the mass of sodium 5-sulfoisophthalic acid; The reaction was accompanied by stirring at a speed of 100-200 r / min; The aliphatic diol is one or more of ethylene glycol, propylene glycol, butanediol and pentanediol; the second 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.

4. The method for preparing a recycled polyester porogen from waste polylactic acid according to claim 1, characterized in that: The polyether diol is one or more of polyethylene glycol, polypropylene glycol and polytetrahydrofuran, and the number average molecular weight of the polyether diol is 400-4000 g / mol.

5. The method for preparing a recycled polyester porogen from waste polylactic acid according to claim 1, characterized in that: The inorganic porous material is one or more of porous carbon material and porous natural mineral powder, with an average particle size of not less than 0.05 microns and an average pore size of not more than 200 nanometers.

6. The method for preparing a recycled polyester porogen from waste polylactic acid according to claim 1, characterized in that: The total molar weight of the polyether diol and the oligomer diol is 1.0-1.1 times the molar weight of the waste polylactic acid, the molar weight of the oligomer diol is 10-30% of the total molar weight of the polyether diol and the oligomer diol, and the mass of the inorganic porous material is not less than 5% of the mass of the waste polylactic acid.

7. The method for preparing a recycled polyester porogen from waste polylactic acid according to claim 1, characterized in that: The polycondensation reaction includes a pre-polycondensation reaction and a final polycondensation reaction. The pre-polycondensation reaction has a pressure of 0.01-0.1 MPa, a temperature of 170-230° C., and a time of 1-3 h. The final polycondensation reaction has a pressure of 5-300 Pa, a temperature of 180-250° C., and a time of 3-5 h.

8. A regenerated polyester porogen, characterized in that: The method for preparing a recycled polyester porogen from waste polylactic acid as claimed in any one of claims 1 to 7 is adopted; the recycled polyester porogen has a number average molecular weight of 14000-33000 g / mol, a molecular weight distribution index of 1.5-3.0, a melting point of 80-180° C., a crystallization temperature of 25-60° C., and a mass loss rate of 10-75% when immersed in hot water at 50-100° C. for 3-30 min.

9. The use of a regenerated polyester porogen as claimed in claim 8, characterized in that: After melt-blending and spinning the recycled polyester porogen with fiber-grade polyester to obtain blended fibers, the blended fibers are immersed in hot water at 50-100° C. for 3-30 minutes to obtain porous fibers.

10. The use according to claim 9, characterized in that: The number average molecular weight of the fiber-grade polyester is 15000-40000 g / mol, the mass of the recycled polyester porogen is 2-30% of the total mass of the recycled polyester porogen and the fiber-grade polyester, and the mass ratio of the blended fiber to the hot water is 1:10-50; the fineness of the porous fiber is 1.0-5.0 dtex, the breaking strength is 2.5-5.5 cN / dtex, and the breaking elongation is 10-40%; the porous fiber has a porous structure and an average pore size of 50-300 nm; the specific surface area of ​​the porous fiber is increased by 1.5-12.5 times relative to the blended fiber, and the mass is reduced by 2-30wt%.

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