Production process of recycled polylactic acid and low-temperature spandex fabric

Abstract

The present application relates to the technical field of fabric recycling, in particular to a production process of recycled polylactic acid and low-temperature spandex fabric.The production process overcomes the problems of high stress of polylactic acid and low-temperature spandex fabric at low temperature and poor dyeing and fixing effect.The present application uses organic solvent and phosphoric acid solution to treat polylactic acid fiber, cotton fiber, polyester fiber and spandex, four different types of fabric, after recycling and physical treatment, uses prepared PLA decomposition catalyst and lactide ring-opening catalyst to treat raw materials, adds vitamin B12, chain extender and isocyanate in the process, and uses a low-temperature dyeing process, so that the recycled polylactic acid and low-temperature spandex fabric has low stress, good dyeing and fixing effect, and realizes the recycling and reuse of polylactic acid and spandex waste fabric.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of textile recycling, in particular to a production process of recycled polylactic acid and low-temperature spandex fabric. BACKGROUND

[0002] Spandex fiber and polylactic acid fiber processing technology is an important part of the current textile industry. With the proposal of the concept of circular economy "recovery, reconstruction and regeneration", the recycling of textile waste has become a research hotspot in the textile industry. How to improve the reuse of recycled materials, reduce production costs while ensuring the basic performance of regenerated fabrics has become a hot research issue. Polylactic acid, as a high polymer material, has green, non-polluting and degradable characteristics. Polylactic acid is widely used in fabrics to improve the softness and breathability of the fabric and other comprehensive performance when mixed with other types of raw materials. Spandex material is used in blended fabrics to improve the elasticity of the material and is also widely used.

[0003] As of August 2024, the import volume of polylactic acid was 30833.4 tons, up 48.8% from the same period last year. On the one hand, polylactic acid relies on imports, and on the other hand, there is still a large amount of polylactic acid textile waste in the textile field, which conflicts and prompts people to recycle textile waste. In the prior art, there are mainly two ways to process recycled fabrics. One is to process the fabric through physical and mechanical treatment, but it has no benefit to the regeneration and performance improvement of the fabric, and in addition, the recycling rate is low. The other is to treat the recycled fabric by chemical modification method, which can maximize the utilization rate and regeneration of the fabric.

[0004] However, in the process of chemical modification, the modified fabric has poor dye fixing effect, and the fabric cannot withstand the high temperature treatment step in the dyeing process. For example, the conventional dyeing treatment of spandex fabric requires a high temperature of 160℃ or above, but this damages the spandex structure, reduces the elasticity of the spandex fabric, increases the stress, and reduces the comfort of the human body when wearing; in the case of blending with polylactic acid, polylactic acid starts to degrade at 120-130℃, and the treatment temperature of the existing technology has adverse effects on both spandex and polylactic acid. However, without high temperature treatment, the low-temperature spandex fabric obtained by low-temperature process has poor dyeing effect and poor color fixing effect, and the fabric is prone to discoloration. At the same time, the recycled fabric is often mixed with cotton fibers, and pure cotton fibers have high comfort, but are difficult to decompose, and the biodegradability of cotton fibers is improved after being mixed with polylactic acid, so it is imperative to effectively utilize the plant fibers in cotton fibers.

[0005] Therefore, a production process of recycled polylactic acid and low-temperature spandex fabric is proposed. SUMMARY

[0006] The application aims to provide a production process of recycled polylactic acid and low-temperature spandex fabric.

[0007] To achieve the above-mentioned purpose, the application provides the following technical scheme.

[0008] The application provides a production process of recycled polylactic acid and low-temperature spandex fabric, and the production process is as follows.

[0009] S1 fabric recycling treatment;

[0010] S2, 20 parts of crushed fabric and 760-1300 parts of mixed solvent are mixed at 40-55 DEG C, and a phosphoric acid aqueous solution with a mass fraction of 78%-86% is added to obtain a dissolution solution; the mixed solvent is composed of water and dimethylacetamide at a ratio of 2-13:3-11;

[0011] S3, 0.1-0.4 parts of a PLA decomposition catalyst is added to the dissolution solution, and ultraviolet irradiation is performed for 80-102 h to obtain a decomposition solution one; 10-12 parts of lactide is dissolved in 100 parts of dimethylacetamide to obtain a lactide solution; and the lactide solution is added to the decomposition solution one to obtain a decomposition solution two;

[0012] S4, the decomposition solution two is dehydrated to obtain a treated decomposition solution two; the treated decomposition solution two, 5 parts of an epoxy compound and 0.01-0.03 parts of a lactide ring-opening catalyst are mixed, and then reacted at 135-170 DEG C under vacuum for 15-25 min to obtain a decomposition solution three;

[0013] S5, 4-7 parts of nanocellulose and 2-5 parts of a composition are added to the decomposition solution three, and then 0.01-0.03 parts of a lactide ring-opening catalyst is added, and then reacted at 115-125 DEG C under vacuum for 60-85 min to obtain a to-be-melted material; the parts ratio of vitamin B12, triethanolamine and isocyanate in the composition is 6-7:2-3:1-2;

[0014] S6: the mixture of the to-be-melted material and the wheat starch is melted at 140-170℃, and the spun yarn is obtained; 1 / 3-1 / 4 of the processing aids are added to the spun yarn, and after weaving, the spun yarn is soaked in the dye solution for programmed temperature rising, temperature keeping and temperature falling; the second and third programmed temperature rising rates are both 1.3-1.7℃ / min; the third programmed temperature rising temperature is 115-130℃; and the first programmed temperature falling rate is 1.6-2.0℃ / min.

[0015] Preferably, the production process of the PLA decomposition catalyst in S3 is as follows: 15 parts of tetrabutyl titanate are dissolved in anhydrous ethanol to obtain a tetrabutyl titanate solution; the parts ratio of tetrabutyl titanate to anhydrous ethanol is 1:30; 7 parts of polyethylene glycol with a polymerization degree of 5, 4 parts of nitric acid and 8 parts of water are mixed to obtain a reaction liquid one; 0.10-0.18 parts of α-iron trioxide and 0.05-0.10 parts of tungsten dioxide are ground in a mortar with a small amount of anhydrous ethanol for multiple times to obtain a reaction liquid two; the amount of anhydrous ethanol is 10 parts; the reaction liquid two is added to the tetrabutyl titanate solution after stirring, and then the reaction liquid one is added; the mixture is stirred at 30℃ for 24 hours, and then is dried and ground to obtain a calcined material; the calcined material is put into a tubular furnace and calcined at 450℃ for 5 hours, and then is cooled to obtain the PLA decomposition catalyst.

[0016] Preferably, the preparation method of the lactide ring-opening catalyst in S4 is as follows: 2.8-3.0 parts of 1-(chloro-1-pyrrolidinylmethylene) pyrrolidine tetrafluoroborate is dissolved in 20 parts of acetonitrile to obtain a 1-(chloro-1-pyrrolidinylmethylene) pyrrolidine tetrafluoroborate solution; 0.9 parts of 1,2-cyclohexanediamine and 2.1 parts of triethylamine are dissolved in 20 parts of acetonitrile to obtain a mixed liquid; the 1-(chloro-1-pyrrolidinylmethylene) pyrrolidine tetrafluoroborate solution is slowly added to the mixed liquid at 0℃, and then the temperature is raised to 85℃; after reflux stirring for 12 hours, 1.7 parts of sodium hydroxide is added to obtain a lactide ring-opening catalyst precursor; the lactide ring-opening catalyst precursor is dried under vacuum to remove the organic solvent and triethylamine, and then 2.3 parts of potassium hydroxide is added; after stirring, extraction is performed using acetonitrile; after dehydration using anhydrous sodium acetate, vacuum distillation is performed to obtain a lactide ring-opening catalyst intermediate.

[0017] 0.1-0.2 parts of zinc trifluoromethanesulfonate is dissolved in 5 parts of tetrahydrofuran to obtain a zinc trifluoromethanesulfonate solution; 0.3 parts of the lactide ring-opening catalyst intermediate is dissolved in 10 parts of tetrahydrofuran to obtain a lactide ring-opening catalyst intermediate solution; the temperature of the lactide ring-opening catalyst intermediate solution is raised to 60℃; the lactide ring-opening catalyst intermediate solution is added dropwise to the zinc trifluoromethanesulfonate solution; the obtained precipitate is filtered, washed with tetrahydrofuran and diethyl ether, and then dried to obtain the lactide ring-opening catalyst.

[0018] Preferably, the process steps of the fabric recycling treatment of S1 are as follows: first, the textile fabric is selected, and the textile fabric that does not meet the requirements is rejected, the rejected fabric includes deep color fabric, pungent smell fabric and fabric with high additive content, and the remaining fabric is a mixed fabric of polylactic acid fiber, cotton fiber, polyester fiber and spandex; the mass ratio of polylactic acid fiber, cotton fiber, polyester fiber and spandex in the mixed fabric is 58:34:3:5; the mixed fabric is washed with clean water and dried, then cut and crushed, and then opened to obtain the crushed fabric.

[0019] Preferably, the epoxy compound is one of epoxycyclohexane, oxirane, hydroxyethyl methacrylate and epoxy isoquinoline.

[0020] Preferably, the temperature of the vacuum condition in S4 is 135-150 DEG C; and the amount of the lactide ring-opening catalyst in S4 and S5 is 0.01-0.02 parts.

[0021] Preferably, the isocyanate is one of 1,3-bis(1-isocyanate-1-methylethyl)benzene, 4,4'-methylenebis(phenyl isocyanate), toluene-2,4-diisocyanate and isophorone diisocyanate.

[0022] Preferably, the processing aid contains a humectant; the humectant is composed of betaine and anionic surfactant; the ratio of betaine and anionic surfactant is 1:1-2; the anionic surfactant is one of sodium cocoyl glycinate and sodium lauroyl glutamate.

[0023] Preferably, the processing aid contains a dyeing aid; the dyeing aid is one of sodium docusate, sodium diisobutyl sulfosuccinate and disodium sulfosuccinimidyl monoisodecylate.

[0024] Preferably, the ratio of the humectant, the dyeing aid and the desizing agent in the processing aid is 3-5:2-5:2-3; the finishing agent is added after the first programmed cooling in S6; the ratio of the ester quaternary ammonium salt, chitin and siloxane polyoxyethylene ether in the finishing agent is 1-3:2:1-5.

[0025] Compared with the prior art, the application has the following beneficial effects:

[0026] 1. By recycling the four different types of fabrics of polylactic acid fiber, cotton fiber, polyester fiber and spandex, using mixed solvents for solvent treatment after physical cutting and crushing, by adjusting the ratio of water and organic solvent in the mixed solvent, controlling the mixed temperature of heating, and then adding phosphoric acid aqueous solution for treatment, the mixed fabric is dissolved to obtain a dissolved solution, and then the chemical modification is promoted, and the mechanical properties of the regenerated polylactic acid and low temperature spandex fabric are improved.

[0027] 2、By preparing the PLA decomposition catalyst, the catalyst is titanium dioxide loaded tungsten dioxide and alpha-Fe2O3, which can effectively decompose polylactic acid fiber into lactide, and the obtained PLA decomposition catalyst has photocatalytic effect, generates electron-hole pairs under ultraviolet light irradiation, and promotes the decomposition of alpha-Fe2O3 loaded on the polylactic acid structure. By optimizing the production process of the PLA decomposition catalyst, reasonably adjusting the amount of the PLA decomposition catalyst in the system, changing the time of ultraviolet irradiation, and reasonably adjusting the proportion of added lactide, nanocellulose and composition, on the one hand, the components in the original crushed fabric are supplemented, on the other hand, the polymerization and reaction of the above components are promoted, and the breaking strength of the regenerated polylactic acid and low-temperature spandex fabric is further improved, the stress is reduced, the dimensional stability is good, it is not easy to shrink, and the recycling of polylactic acid and spandex is realized.

[0028] 3、By synthesizing lactide ring-opening catalyst, controlling the amount of reaction raw material 1-(chloro-1-pyrrolidinyl methylene) pyrrolidine tetrafluoroborate and zinc trifluoromethanesulfonate, the obtained catalyst has high activity for lactide ring-opening and polymerization. By adjusting the amount of lactide ring-opening catalyst in decomposition liquid two and decomposition liquid three, adjusting the reaction temperature and time of the decomposition liquid, the polymerization of the ring-opened lactide is formed, or the polymerization with the added isocyanate, nanocellulose and polyester decomposition obtained polyterephthalic acid and other substances, the temperature resistance effect of the regenerated polylactic acid and low-temperature spandex fabric is improved.

[0029] 4、By adding vitamin B12, chain extender and isocyanate in S5, reacting with the spandex decomposition product in decomposition liquid three to obtain spandex material, reasonably adjusting the proportion of isocyanate, creatively adding vitamin B12, the hydroxyl group of vitamin B12 reacts with isocyanate, introducing a compound with tertiary amine structure, which acts as a nucleophile, provides electrons for cationic dyes, and promotes the binding force of cationic dyes and fabric. By adding moisturizing agent, dyeing aid and desizing agent, reasonably adjusting the types and amounts, the dyeing rate and color fastness of the fabric are improved.

[0030] 5、By adjusting the temperature of melting, then spinning, adding part of the processing aid to the spinning, then dyeing by immersion, adjusting the temperature rising rate and the temperature maintained during dyeing, adopting low-temperature production process, adjusting the cooling rate, and adding the remaining processing aid after soaking in water, finally adding finishing agent and adjusting the proportion of finishing agent, the structure and properties of the components in the fabric are maximally retained, and the dyeing rate and color fastness of the fabric are high. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The dyeing rate and color fastness results of examples 36, 39-50 and comparative examples 16-20 of the present application. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0033] Please refer to Figure 1 The present application provides a production process of recycled polylactic acid and low-temperature spandex fabric, and the technical scheme is as follows:

[0034] The substances involved in the present application are as follows:

[0035] Toluene-2,4-diisocyanate CAS: 584-84-9; dimethylacetamide CAS: 127-19-5; propiolactone CAS: 95-96-5; vitamin B12 CAS: 68-19-9; triethanolamine CAS: 102-71-6; betaine CAS: 107-43-7; sodium cocoyl glycinate CAS: 90387-74-9; sodium docusate CAS: 577-11-7; ester-based quaternary ammonium salt CAS: 91995-81-2; chitin CAS: 1398-61-4; siloxane polyoxyethylene ether CAS: 68937-54-2; 1-(chloro-1-pyrrolidinylmethylene) pyrrolidine tetrafluoroborate CAS: 115007-14-2; 1,2-cyclohexanediamine CAS: 694-83-7; zinc trifluoromethanesulfonate CAS: 54010-75-2; epoxy cyclohexane CAS: 286-20-4; oxirane CAS: 75-21-8; hydroxyethyl methacrylate CAS: 868-77-9; epoxy isoquinoline CAS: 140468-94-6; 2-ethylhexanoic acid zinc CAS: 136-53-8; 1,3-bis(1-isocyanate-1-methylethyl) benzene CAS: 2778-42-9; 4,4'-methylenebis(phenyl isocyanate) CAS: 101-68-8; isophorone diisocyanate CAS: 4098-71-9; sodium lauroyl glutamate CAS: 29923-31-7; sodium diisobutyl sulfosuccinate CAS: 127-39-9; disodium monoisodecyl sulfosuccinate CAS: 37294-49-8.

[0036] Example 1

[0037] S1 fabric recycling treatment: first, the textile fabric is selected, and the textile fabric that does not meet the requirements is removed, the removed fabric includes deep color fabric, pungent odor fabric and fabric with high additive content, the remaining fabric is a mixed fabric of polylactic acid fiber, cotton fiber, polyester fiber and spandex; the mass ratio of polylactic acid fiber, cotton fiber, polyester fiber and spandex in the mixed fabric is 58:34:3:5; the mixed fabric is washed with water and dried, then cut and crushed, and then opened to obtain the crushed fabric;

[0038] S2: 20 parts of the crushed fabric and 1000 parts of the mixed solvent are mixed at 40°C, mechanically stirred at 500 rpm for 2h, and then 500 parts of a 83% mass fraction phosphoric acid aqueous solution preheated to 40°C (the preheating temperature and the mixing temperature are consistent) is added, and the stirring is continued for 4h, and then filtered to obtain a liquid as a dissolution liquid; the mixed solvent is composed of water and dimethylacetamide, and the mass fraction ratio of the two is 11:9;

[0039] S3: 0.4 parts of a PLA decomposition catalyst is added to the dissolution liquid and stirred uniformly, and then irradiated under a 25W ultraviolet lamp at a rotation speed of 300 rpm and a wavelength of 254 nm until the content of the lactide monomer no longer changes, and then irradiated for 80h to obtain a decomposition liquid one; 12 parts of lactide is dissolved in 100 parts of dimethylacetamide to obtain a lactide solution; the lactide solution and the decomposition liquid one are mixed uniformly to obtain a decomposition liquid two;

[0040] S4: the decomposition liquid two is dehydrated using anhydrous sodium sulfate to obtain a treated decomposition liquid two; the treated decomposition liquid two, 5 parts of an epoxy compound and 0.02 parts of a lactide ring-opening catalyst are mixed, and then reacted at 150°C under vacuum for 20min, and then cooled to obtain a decomposition liquid three;

[0041] S5: 7 parts of nano cellulose (derived from cotton fiber) and 4 parts of a composition are added to the decomposition liquid three, and then 0.1 parts of dibutyltin dilaurate and 0.01 parts of a lactide ring-opening catalyst are added, and then reacted at 125°C under vacuum for 60min, and then cooled and vacuum dried to remove the organic solvent to obtain a to-be-melted material; the part ratio of vitamin B12, chain extender (triethanolamine) and isocyanate in the composition is 7:2:1;

[0042] S6 the to-be-melted material is mixed with 0.5 parts of wheat starch, then melted at 160°C, and then spun at a speed of 500 m / min, followed by drawing, oiling and winding to obtain the spun yarn; the size of the fiber in the spun yarn is 4.4 tex (40D), 2 / 3 (mass fraction ratio) of the processing aid is added to the spun yarn, and then woven to obtain the regenerated polylactic acid and low-temperature spandex fabric precursor; the mass fraction ratio of the to-be-melted material to the total processing aid is 200:1; the mass fraction ratio of betaine and sodium cocoglycinate (moisturizing agent), sodium docusate (dyeing aid) and sodium carbonate (desizing agent) in the processing aid is 5:2:3; the cationic dye and water are mixed at a mass ratio of 1:100 to obtain a dye solution; the low-temperature spandex fabric precursor is soaked in the dye solution for 10 min, then the dye solution is subjected to first programmed heating at a speed of 2.0°C / min to reach 80°C, kept for 6 min, then subjected to second programmed heating at a speed of 1.5°C / min to reach 100°C, kept for 8 min, then subjected to third programmed heating at a speed of 1.5°C / min to reach 120°C, kept for 25 min, then subjected to first programmed cooling at a speed of 1.8°C / min, and when the temperature reaches 60°C, the water is run for 5 min, 1 / 3 of the processing aid is added to the water, then third programmed heating is performed at a speed of 1.5°C / min, and when the temperature reaches 70°C, the finishing agent is added, kept for 20 min, then cooled and dried to obtain the regenerated polylactic acid and low-temperature spandex fabric; the mass ratio of the to-be-melted material to the finishing agent is 500:1; the mass fraction ratio of ester quaternary ammonium salt, chitin and siloxane polyoxyethylene ether in the finishing agent is 1:2:1.

[0043] S31 The production process of the PLA decomposition catalyst is as follows: 15 parts of tetrabutyl titanate are dissolved in anhydrous ethanol to obtain a tetrabutyl titanate solution; the mass fraction ratio of tetrabutyl titanate to anhydrous ethanol is 1:30; 7 parts of polyethylene glycol with a degree of polymerization of 5, 4 parts of nitric acid and 8 parts of water are mixed to obtain reaction liquid one; 0.15 parts of α-iron trioxide and 0.05 parts of tungsten dioxide are ground with a small amount of anhydrous ethanol in a mortar for multiple times to obtain reaction liquid two, and the amount of anhydrous ethanol used is 10 parts; reaction liquid two is added to the tetrabutyl titanate solution, stirred, then reaction liquid one is added, stirred at 30°C for 24 h, dried and ground to obtain calcined material; the calcined material is put into a tubular furnace and calcined at 450°C for 5 h, and then cooled to obtain the PLA decomposition catalyst;

[0044] The preparation method of the lactide ring-opening catalyst is as follows: 2.8 parts of 1-(chloro-1-pyrrolidinyl methylene) pyrrolidine tetrafluoroborate is dissolved in 20 parts of acetonitrile to obtain a 1-(chloro-1-pyrrolidinyl methylene) pyrrolidine tetrafluoroborate solution; 0.9 parts of 1,2-cyclohexanediamine and 2.1 parts of triethylamine are dissolved in 20 parts of acetonitrile to obtain a mixed solution; the 1-(chloro-1-pyrrolidinyl methylene) pyrrolidine tetrafluoroborate solution is slowly added to the mixed solution at 0°C, and the temperature is raised to 85°C, and stirred at reflux for 12 hours, and then 1.7 parts of sodium hydroxide is added to obtain a lactide ring-opening catalyst precursor; the lactide ring-opening catalyst precursor is dried under vacuum to remove the organic solvent and triethylamine, and then 2.3 parts of potassium hydroxide is added, stirred, extracted with acetonitrile, dehydrated with anhydrous acetic acid, and then distilled under reduced pressure to obtain a lactide ring-opening catalyst intermediate;

[0045] 0.2 parts of zinc trifluoromethanesulfonate is dissolved in 5 parts of tetrahydrofuran to obtain a zinc trifluoromethanesulfonate solution; 0.3 parts of the lactide ring-opening catalyst intermediate is dissolved in 10 parts of tetrahydrofuran to obtain a lactide ring-opening catalyst intermediate solution; the temperature of the above solution is raised to 60°C, and the lactide ring-opening catalyst intermediate solution is added dropwise into the zinc trifluoromethanesulfonate solution to obtain a precipitate which is filtered and washed with tetrahydrofuran and diethyl ether, and then dried to obtain the lactide ring-opening catalyst.

[0046] Example 2-12

[0047] Different from Example 1, the production process conditions of S2 are changed, as shown in Table 1.

[0048] Table 1 Production process conditions of the dissolving solution in S2

[0049]

[0050] Comparative Example 1

[0051] Different from Example 1, the amount of the mixed solvent is 500 parts.

[0052] Comparative Example 2

[0053] Different from Example 1, the mixing temperature is 25°C.

[0054] Comparative Example 3

[0055] Different from Example 1, the mixing temperature is 70°C.

[0056] Comparative Example 4

[0057] Different from Example 1, the mass percentage of the aqueous phosphoric acid solution is 90%.

[0058] Comparative Example 5

[0059] Different from Example 1, the ratio of water and dimethylacetamide was 1:3.

[0060] Example 13

[0061] The regenerated polylactic acid obtained from Examples 1-12 and Comparative Examples 1-5 was subjected to stress relaxation rate test and breaking strength test on a low-temperature spandex fabric. The stress relaxation rate test method was as follows: S1 fabric recycling treatment: first, the textile fabric was selected, and the textile fabric that did not meet the requirements was rejected, including deep color fabric, pungent odor fabric and fabric with high additive content. The remaining fabric was a mixed fabric of polylactic acid fiber, cotton fiber, polyester fiber and spandex. The mass ratio of polylactic acid fiber, cotton fiber, polyester fiber and spandex in the mixed fabric was 58:34:3:5. The mixed fabric was washed with water, dried, then cut into pieces, crushed and opened to obtain the crushed fabric. S2 The crushed fabric and dimethylacetamide were mixed in a mass ratio of 1:10 and then spun. Then, the step S6 in Example 1 was performed, and the stress of the obtained fabric was measured as A. The stress of the examples and comparative examples was measured as B. The calculation formula of the stress relaxation rate was as follows: The test results are shown in Table 2.

[0062] Table 2 Stress relaxation rate and breaking strength test results of Examples 1-12 and Comparative Examples 1-5

[0063] 300% stress relaxation (%) Breaking strength (g) Example 1 93.8 96.9 Example 2 93.0 96.1 Example 3 92.8 95.3 Example 4 93.7 97.0 Example 5 94.0 97.3 Example 6 93.8 96.7 Example 7 93.1 96.2 Example 8 94.5 98.3 Example 9 94.0 97.6 Example 10 95.1 100.1 Example 11 93.5 96.8 Example 12 91.0 93.2 Comparative Example 1 51.1 89.5 Comparative Example 2 72.5 91.8 Comparative Example 3 80.0 94.0 Comparative Example 4 49.3 86.5 Comparative Example 5 38.0 75.4

[0064] As shown in Table 1 and Table 2, the 300% stress relaxation rate of the regenerated polylactic acid produced by the application and the low-temperature spandex fabric is 91.0%-95.1%, and the breaking strength is 93.2-100.1 g. The four different types of fabrics of polylactic acid fiber, cotton fiber, polyester fiber and spandex are treated by using a mixed solvent composed of water and dimethylacetamide. The water preliminarily dissolves the plant fiber in the cotton fiber, the dimethylacetamide preliminarily dissolves the polylactic acid fiber, cotton fiber and spandex, and the material is deeply dissolved under the action of heating and phosphoric acid. The results of Examples 1-4 show that, with the increase of the amount of the mixed solvent, the 300% stress relaxation rate and the breaking strength show an increasing trend and then tend to be stable. When the mixed solvent is mixed with the crushed fabric, the amount of the mixed solvent should at least be higher than the volume of the crushed fabric. With the increase of the mixed solvent, the amount of the dissolved components of the fabric in the mixed solvent increases, which is helpful for the subsequent chemical modification process. However, when the amount of the mixed solvent is too high, as shown in Example 4, the amount of the dissolved components in the mixed solvent is certain because the amount of the crushed fabric is fixed, and thus the stress relaxation rate and the breaking strength of the regenerated polylactic acid and the low-temperature spandex fabric produced no longer increase. As shown in Comparative Example 1, because the amount of the mixed solvent is too small, the content of the dissolved components of the fabric is lower than that in Examples 1-4, and thus the performance of the fabric decreases. The results of Examples 1, 5 and 6 show that, when the mixing temperature is 45℃, the solubility of the fabric components in the mixed solvent is the best, and thus the performance of the produced fabric is the best. As shown in Comparative Example 3 and Comparative Example 2, when the temperature is too high or too low, it has a bad effect on the regenerated polylactic acid and the low-temperature spandex fabric. The results of Examples 5, 7-9 show that, with the increase of the mass percentage of the phosphoric acid aqueous solution, the 300% stress relaxation rate and the breaking strength show a trend of first increasing and then decreasing. The phosphoric acid can make the cellulose of the cotton fiber swell. The swelling occurs in the crystalline region of the fiber, and the intermolecular binding force between the cellulose chains remains unchanged. The increase of the lattice spacing of the cellulose has no effect on the performance of the finally produced fabric. However, with the further increase of the content of the phosphoric acid, the swelling phenomenon in the amorphous region increases, which makes the chemical bonds between the microfibers of the cellulose break. As shown in Comparative Example 4, after the cellulose of the cotton fiber damaged by the structure reacts with the diisocyanate in the raw material and part of the polyethylene terephthalate decomposed to produce polyethylene terephthalate, the mechanical strength of the polymer decreases, and thus the stress relaxation rate and the breaking strength of the fabric decrease. The results of Examples 8, 10-12 show that, by adjusting the ratio of the water and dimethylacetamide to be in the range of 2-13:3-11, the mechanical properties of the fabric are good. In Comparative Example 5, the content of the water is too low, and the solubility of the cotton fiber in the mixed solvent is poor.

[0065] Examples 14-26

[0066] Different from Example 10, the production process of the decomposition solutions two and three and the production process conditions of the PLA decomposition catalyst are changed, which are shown in Table 3.

[0067] Table 3 Production process of decomposition liquid two, three and PLA decomposition catalyst

[0068]

[0069]

[0070] Comparative Example 6

[0071] Unlike Example 10, no PLA decomposition catalyst was added.

[0072] Comparative Example 7

[0073] Unlike Example 10, 0.4 parts of PLA decomposition catalyst was replaced by 0.4 parts of a-Fe203.

[0074] Comparative Example 8

[0075] Unlike Example 10, no lactide was added.

[0076] Comparative Example 9

[0077] Unlike Example 10, no nanocellulose was added.

[0078] Comparative Example 10

[0079] Unlike Example 10, no composition was added.

[0080] Example 27

[0081] The regenerated polylactic acid produced in Examples 10, 14-26 and Comparative Examples 6-10 was subjected to stress relaxation rate test and breaking strength test with low-temperature spandex fabric, and the test results are shown in Table 4.

[0082] Table 4 Results of stress relaxation rate test and breaking strength test of Examples 10, 14-26 and Comparative Examples 6-10

[0083]

[0084]

[0085] The results of Tables 3 and 4 show that the stress relaxation rate of the low-temperature spandex fabric produced by the regenerated polylactic acid of the present application is 94.0%-99.2%, and the breaking strength is 97.5-107.4 g. The results of Examples 10, 14 and 15 show that as the amount of PLA decomposition catalyst increases, the stress relaxation rate and breaking strength generally show a trend of first increasing and then decreasing, which is due to the ability of the synthesized catalyst to decompose polylactic acid fibers under ultraviolet light irradiation; as shown in Example 11, when the amount of PLA decomposition catalyst is too high, the stress relaxation rate and breaking strength decrease instead, and a high amount of catalyst can cause excessive decomposition of polylactic acid, and the generation of substances such as diastereoisomers, cyclic oligomers, carbon monoxide and carbon dioxide, thereby reducing the content of the effective component lactide, which is not conducive to the improvement of the mechanical properties of the fabric. The results of Examples 14, 16-18 show that by adjusting the amount of a-Fe2O3 and tungsten dioxide in the production process of the PLA decomposition catalyst, the efficiency of the catalyst in decomposing polylactic acid into lactide is improved, and under ultraviolet light irradiation, the PLA decomposition catalyst generates electron-hole pairs, and then generates photoelectrons, which overflow to the surface of the catalyst and attack polylactic acid molecules to achieve the decomposition of polylactic acid. The titanium dioxide simultaneously loaded with tungsten dioxide and a-Fe2O3 has the best catalytic decomposition effect under the conditions of Example 17, does not affect the subsequent ring-opening polymerization process of lactide, and finally improves the stress relaxation rate and breaking strength of the fabric. The results of Examples 17, 19-21 show that as the time of ultraviolet irradiation increases, the stress relaxation rate shows a trend of first increasing and then stabilizing, and the breaking strength gradually decreases. As the irradiation time increases, the catalyst has reached the best catalytic effect, and as the time continues to increase, the irradiation of ultraviolet light damages the molecular structure of lactide, cotton fibers and spandex substances in the decomposition solution, increases the brittleness of the fabric, and reduces the breaking strength. Comparative Example 6 does not add the PLA decomposition catalyst, polylactic acid cannot be decomposed, cannot react with other components, the compatibility of the fabric components is poor, and the stress relaxation rate and breaking strength decrease. Comparative Example 7 is replaced with an equal amount of a-Fe2O3, and the fabric performance is lower than that of Examples 10, 14-26. The results of Examples 19, 22-26 show that by reasonably adjusting the addition amount of lactide, nanocellulose and the composition, the stress relaxation rate and breaking strength of the low-temperature spandex fabric produced by the regenerated polylactic acid are improved, and the effect is the best under the conditions of Example 24. On the one hand, the addition of the composition plays a complementary role in the spandex raw material, improves the elasticity and stress relaxation rate of the fabric, and on the other hand, the isocyanate in the composition polymerizes with nanofiber and ring-opening substances of lactide, thereby connecting the originally poor-elasticity polylactic acid and nanofiber, and the three-dimensional network structure formed by the substances improves the breaking strength and stress relaxation rate of the fabric. The results of Comparative Examples 8-10 show that the lack of one of the three types of substances will directly reduce the stress relaxation rate and breaking strength of the fabric.

[0086] Examples 28-37

[0087] The preparation process conditions of S4 and S5 were changed, as shown in Table 5.

[0088] Table 5 Production process of S4 and S5

[0089]

[0090]

[0091] Comparative Example 11

[0092] Different from Example 24, the lactide ring-opening catalyst was replaced by zinc 2-ethylhexanoate.

[0093] Comparative Example 12

[0094] Different from Example 24, no epoxide compound was added.

[0095] Comparative Example 13

[0096] Different from Example 24, the amount of lactide ring-opening catalyst in S4 was 0.03 parts, and the amount of lactide ring-opening catalyst in S5 was 0 parts.

[0097] Comparative Example 14

[0098] Different from Example 24, the amount of lactide ring-opening catalyst in S4 was 0 parts, and the amount of lactide ring-opening catalyst in S5 was 0.03 parts.

[0099] Comparative Example 15

[0100] Different from Example 24, the reaction temperature of S4 was 170°C.

[0101] Example 38

[0102] The fabrics produced in Examples 24, 28-37 and Comparative Examples 11-15 were subjected to temperature resistance performance testing, and the testing method was as follows: the fabric was placed in an environment of 140°C for 2h, and then the changes in stress relaxation rate and breaking strength were compared. The temperature resistance test results are shown in Table 6.

[0103] Table 6 Temperature resistance performance test results of Examples 24, 28-37 and Comparative Examples 11-15

[0104]

[0105] The results of Table 5 and Table 6 show that the regenerated polylactic acid produced by the present application has a 300% stress relaxation rate of 92.1%-99.7% and a breaking strength of 96.0-109.3 g without 140℃ treatment, and a 300% stress relaxation rate of 83.4%-97.7% and a breaking strength of 90.7-108.0 g after 140℃ treatment. The results of Examples 24, 28-30 show that by changing the type of oxirane, the stress relaxation rate and breaking strength of the fabric before and after 140℃ treatment are changed, and by adding an epoxide compound in the process of ring-opening decomposition of lactide, the epoxide compound is ring-opened under the conditions of high temperature, vacuum and catalyst to obtain a compound containing a hydroxyl group, the hydroxyl compound is polymerized with partially ring-opened lactide, which promotes the progress of lactide ring-opening process, and meanwhile other structural groups in the epoxide compound are introduced; the stress relaxation rate and breaking strength of the fabric before and after 140℃ treatment under the conditions of Example 28 are lower than those of Examples 24, 29 and 30, because the structural group introduced into the ring-opened lactide in Example 28 is a short-chain alkane, and the fabric is prone to shrinkage after 140℃ treatment; the use of epoxyisoquinoline as the epoxide compound in Example 30 has a small reduction in the 300% stress relaxation rate and breaking strength after 140℃ treatment, and the fabric has good temperature resistance; the fabric has reduced temperature resistance in Comparative Example 12 without adding the epoxide compound. The results of Examples 30 and 31 show that the temperature resistance is improved with further increase in the amount of 1-(chloro-1-pyrrolidinylmethylene) pyrrolidine tetrafluoroborate. The results of Examples 31 and 32 show that when the amounts of 1-(chloro-1-pyrrolidinylmethylene) pyrrolidine tetrafluoroborate and zinc trifluoromethanesulfonate are 3.0 and 0.1 parts, respectively, in the preparation process of the lactide ring-opening catalyst, the temperature resistance is the best, because by using 1-(chloro-1-pyrrolidinylmethylene) pyrrolidine tetrafluoroborate as the reaction raw material, 1,2-cyclohexanediamine is reacted to obtain a guanidino ligand by connecting one molecule of 1,2-cyclohexanediamine with two molecules of 1-(chloro-1-pyrrolidinylmethylene) pyrrolidine tetrafluoroborate, and then the guanidino ligand is reacted with zinc trifluoromethanesulfonate to obtain a ligand catalyst with zinc as the center, which promotes the ring-opening polymerization reaction of lactide, and reasonable adjustment of the amount of the catalyst synthesis raw material improves the crosslinking degree of the ring-opened lactide with each component, improves the temperature resistance, and meanwhile the introduced fluorine and boron atoms also improve the temperature resistance of the fabric. The temperature resistance of the fabric is reduced in Comparative Example 11 by replacing the lactide ring-opening catalyst with zinc 2-ethylhexanoate, compared with Examples 24, 28-37. The results of Examples 32-35 show that the temperature and time of the reaction in the S4 process are reasonably adjusted, and the 300% stress relaxation rate and breaking strength before and after 140℃ treatment are the highest under the conditions of Example 33.The temperature of Comparative Example 15 is too high, and the stress relief rate and breaking strength of the fabric decrease, which is due to the fact that part of the lactide ring-opening catalyst is added first, and under vacuum and high reaction temperature, the high reaction temperature and long reaction time will have two adverse effects: first, the lactide ring-opening polymerization process is too fast, and it is impossible to realize the reaction and polymerization with other components; on the other hand, high temperature will damage the molecular structure of polylactic acid and nanocellulose in the decomposition liquid three, so the temperature resistance of the fabric decreases, so it is necessary to control the reaction temperature and time of S4 process in a reasonable range. The results of Examples 33 and 36 show that the temperature resistance of the fabric obtained by adding the lactide ring-opening catalyst in S4 and S5 processes in stages is good; Comparative Examples 13 and 14 do not add the lactide ring-opening catalyst in stages, and the lactide ring-opening polymerization is too fast or cannot be completely ring-opened, and the temperature resistance of the fabric decreases. The results of Examples 36 and 37 show that by reasonably adjusting the reaction temperature and time of S5 process, the components react completely, and the stress relief rate and breaking strength of the fabric increase.

[0106] Examples 39-50

[0107] Unlike Example 36, the types and proportions of the compositions in S5 and the types and proportions of the processing aids in S6 are changed, as shown in Table 7. The three substances in S5 are vitamin B12, chain extender and isocyanate. The three types of substances in S6 are humectant, dyeing aid and desizing agent.

[0108] Table 7 Types and proportions of compositions and types and proportions of processing aids in S6

[0109]

[0110]

[0111] Comparative Example 16

[0112] Unlike Example 36, no vitamin B12 is added to the composition in S5, and the proportions of chain extender and isocyanate are 2:1.

[0113] Comparative Example 17

[0114] Unlike Example 36, only betaine is added as the processing aid in S6.

[0115] Comparative Example 18

[0116] Unlike Example 36, only sodium cocoyl glycinate is added as the processing aid in S6.

[0117] Comparative Example 19

[0118] Unlike Example 36, no dyeing aid is added in the processing aid in S6.

[0119] Comparative Example 20

[0120] Different from Example 36, the processing aid of S6 was not added with desizing agent.

[0121] Example 51

[0122] The regenerated polylactic acid produced by Example 36, 39-50 and Comparative Examples 16-20 was tested for dye-uptake and color fastness on low-temperature spandex fabric, wherein the dye-uptake was tested according to GB / T 23976.1-2009 "Determination of dyeing rate curve-determination method of dye-uptake", and the color fastness was tested according to GB / T 3922-2013 "Textiles-tests for color fastness-color fastness to perspiration (ISO 105-E04:2013.MOD)", and the final test results are shown in Table 8 and Table 9. Figure 1

[0123] Table 8 Results of dye-uptake and color fastness of Example 36, 39-50 and Comparative Examples 16-19

[0124] Dye uptake (%) Colour fastness (grade) Example 36 90.1 4.0 Example 39 91.4 4.2 Example 40 89.7 4.0 Example 41 86.9 3.8 Example 42 91.8 4.2 Example 43 91.0 4.1 Example 44 90.5 4.1 Example 45 91.5 4.2 Example 46 91.8 4.3 Example 47 92.2 4.3 Example 48 92.0 4.3 Example 49 92.5 4.4 Example 50 92.0 4.2 Comparative Example 16 73.6 3.2 Comparative Example 17 81.3 3.6 Comparative Example 18 85.0 3.8 Comparative Example 19 70.5 3.0 Comparative Example 20 74.6 3.3

[0125] As shown in Table 7 and Table 8, the dye-uptake of the regenerated polylactic acid produced by the present application on low-temperature spandex fabric was 86.9%-92.5%, and the color fastness grade was 3.8-4.4. Figure 1 ​The results of Examples 36, 39-41 show that by adjusting the type of isocyanate added to S5, the dye-uptake and color fastness change, the isocyanate added reacts with the hydroxyl groups of vitamin B12, the decomposition product of spandex raw material and nanofiber, and the dye-uptake and color fastness of the fabric obtained under the conditions of Example 39 are the highest. The results of Examples 39, 42-44 show that by reasonably adjusting the ratio of the parts of vitamin B12, chain extender and isocyanate, the dye-uptake and color fastness are improved, the tertiary amine structure group in vitamin B12 can participate in the reaction as a nucleophile, providing electrons to the cationic dye through the nitrogen atom, promoting the firmness of the combination of the dye and the fabric, and reasonably adjusting the amount, so that the three substances are fused into the system in a reasonable ratio of hard segment and soft segment. Comparative Example 12 does not add vitamin B12, and the dye-uptake and color fastness are lower than those of the examples. The results of Examples 42, 45 and 46 show that by adjusting the ratio of the moisturizing agent, the dyeing aid and the desizing agent in S6, the dye-uptake and color fastness change, the moisturizing agent has a retaining effect, the first moisturizing agent is an amphoteric surfactant, and the second moisturizing agent is an anionic surfactant, the two interact to improve the adhesion and fastness of the cationic dye to the fabric, the sulfonate anion in the color aid further promotes the dyeing effect of the cationic dye on the fabric, and by adding the desizing agent, the dye-uptake and color fastness are improved. Due to the fact that the fabric is prone to breakage during the weaving process, wheat starch is added to improve the toughness of the spinning, but its presence will affect the wetting and penetration of the cationic dye on the fiber in the spinning, so sodium carbonate is added as a desizing agent, and then the fabric is dyed, which minimizes the interference of other components on the dyeing process, and improves the dye-uptake and color fastness. The results of Examples 46-48 show that by adjusting the type and ratio of the moisturizing agent, the dye-uptake reaches the highest under the conditions of Example 47, and the color fastness is high. The results of Examples 47, 49 and 50 show that by changing the type of dyeing aid, the dye-uptake and color fastness of Example 49 are the highest, because under the same conditions of sulfonate and sodium ion, the shorter the side chain, the more conducive to the dyeing of the fabric. The results of Comparative Examples 18-20 show that the absence of any one of the substances in the processing aid will directly result in a decrease in the dye-uptake and color fastness. The substances in the composition and processing aid synergistically improve the dye-uptake and color fastness of the fabric.

[0126] Examples 52-58

[0127] Unlike Example 49, the melting temperature in S6, the mass ratio of the first processing aid, the mass ratio of the second processing aid, the ratio of the substances in the finishing agent and the temperature rising program in the dyeing process are changed, as shown in Table 9.

[0128] Table 9 Production process conditions of S6

[0129]

[0130]

[0131] Example 58

[0132] Unlike Example 49, the rate of the second and third programmed temperature increases was 1.3°C / min.

[0133] Example 59

[0134] Unlike Example 49, the rate of the first programmed temperature decrease was 1.6°C / min.

[0135] Example 60

[0136] Unlike Example 49, the rate of the second and third programmed temperature increases was 1.7°C.

[0137] Example 61

[0138] Unlike Example 49, the rate of the first programmed temperature decrease was 2.0°C / min.

[0139] Example 62

[0140] Unlike Example 49, the temperature of the second programmed temperature increase was 125°C.

[0141] Example 63

[0142] Unlike Example 49, the temperature of the second programmed temperature increase was 130°C.

[0143] Example 64

[0144] Unlike Example 49, the temperature of the second programmed temperature increase was 115°C.

[0145] Example 65

[0146] The regenerated polylactic acid produced in Examples 49, 52-65 was tested for dye uptake and color fastness with a low temperature spandex fabric, and the final test results are shown in Table 10.

[0147] Table 10 Dye Uptake and Color Fastness Results for Examples 49, 52-65

[0148]

[0149]

[0150] The dyeing rate of the regenerated polylactic acid produced by the application on the low-temperature spandex fabric is 88.4%-93.5%, and the color fastness is 4.0-4.5. The results of Table 9 and Table 10 show that in Examples 49, 52-54, as the melting temperature increases, the dyeing rate shows a trend of rising and then falling, which is due to the fact that after the to-be-melted material is mixed with wheat starch, a short time of too high melting temperature will cause damage to the component structure, thereby reducing the dyeing rate and color fastness. The results of Examples 52, 55 and 56 show that by adding the processing aid in batches and adjusting the amount of each addition, the dyeing rate and color fastness are high, and the moisturizing agent, dyeing aid and desizing agent in the processing aid have the effects of promoting dyeing and color fixing, and by adding them in batches, they again have good color fixing effect. The results of Examples 56 and 57 show that by reasonably adjusting the proportion of ester-based quaternary ammonium salt, chitin and siloxane polyoxyethylene ether in the finishing agent, the fabric dyeing rate is improved, among which the ester-based quaternary ammonium salt has the effect of removing static electricity, thereby reducing the interference of static electricity on the dyeing process, the siloxane polyoxyethylene ether gives the fabric flexibility and promotes the penetration of the dye into the fabric, and the chitin has the effect of temperature resistance, and reasonable adjustment of the proportion of the three can improve the dyeing rate. The results of Examples 58-64 show that the dyeing rate and color fastness are the highest under the conditions of Example 60, by adjusting the rate of temperature increase and the rate of temperature decrease, thereby promoting the penetration of the dye into the fabric under the heat dynamics, and improving the fastness of the dye and the fabric, at the same time, adjusting the highest temperature of the temperature increase to be within a reasonable range, thereby reducing the influence of the too high temperature on the fabric.

[0151] Although embodiments of the application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the application, and the scope of the application is defined by the appended claims and their equivalents.

Claims

1. A process for the production of a recycled polylactic acid and low temperature spandex fabric, characterized by: The production process is as follows: S1 fabric recycling treatment; S2, 20 parts of the crushed fabric and 760-1300 parts of the mixed solvent are mixed at 40-55 DEG C, and a 78%-86% mass fraction of phosphoric acid aqueous solution is added to react to obtain a dissolution solution; the mixed solvent is composed of water and dimethylacetamide in a ratio of 2-13:3-11; S3, 0.1-0.4 parts of a PLA decomposition catalyst is added to the dissolution solution, and ultraviolet irradiation is performed for 80-102h to obtain a decomposition solution one; 10-12 parts of lactide is dissolved in 100 parts of dimethylacetamide to obtain a lactide solution; the lactide solution is added to the decomposition solution one to obtain a decomposition solution two; S4, the decomposition solution two is dehydrated to obtain a treated decomposition solution two; The treated decomposition solution two, 5 parts of an epoxy compound, and 0.01-0.03 parts of a lactide ring-opening catalyst are mixed, and then reacted under vacuum at 135-170 DEG C for 15-25 min to obtain a decomposition solution three; the epoxy compound is one of epoxy cyclohexane, epoxy ethane, hydroxyethyl methacrylate, and epoxy isoquinoline; S5, 4-7 parts of nanocellulose and 2-5 parts of a composition are added to the decomposition solution three, and then 00.01-0.03 parts of a lactide ring-opening catalyst is added, and then reacted under vacuum at 115-125 DEG C for 60-85 min to obtain a melt; the composition is composed of vitamin B12, triethanolamine, and isocyanate in a ratio of 6-7:2-3:1-2; S6, the melt is mixed with wheat starch and then melted at 140-170 DEG C to spin yarn; 1 / 3-1 / 4 of a processing aid is added to the yarn, and then woven and soaked in a dye solution for programmed heating, holding, and cooling; the second and third programmed heating rates are both 1.3-1.7 DEG C / min; the third programmed heating temperature is 115-130 DEG C; the first programmed cooling rate is 1.6-2.0 DEG C / min; The process steps of the fabric recycling treatment of S1 are as follows: first, the textile fabric is selected, and the textile fabric that does not meet the requirements is removed; the removed fabric includes deep color fabric, pungent odor fabric, and fabric with high additive content; the remaining fabric is a mixed fabric of polylactic acid fiber, cotton fiber, polyester fiber, and spandex; the mass ratio of polylactic acid fiber, cotton fiber, polyester fiber, and spandex in the mixed fabric is 58:34:3:5; the mixed fabric is washed with water, dried, then cut, crushed, and opened to obtain the crushed fabric.

2. The production process of the cyclic regenerated polylactic acid and low-temperature spandex fabric according to claim 1, characterized in that: The production process of the PLA decomposition catalyst in S3 is as follows: 15 parts of tetrabutyl titanate are dissolved in anhydrous ethanol to obtain a tetrabutyl titanate solution; the parts ratio of the tetrabutyl titanate to the anhydrous ethanol is 1:30; 7 parts of polyethylene glycol with a polymerization degree of 5, 4 parts of nitric acid and 8 parts of water are mixed to obtain a reaction liquid one; 0.10-0.18 parts of alpha-iron trioxide and 0.05-0.10 parts of tungsten dioxide are ground in a mortar with a small amount of anhydrous ethanol for multiple times to obtain a reaction liquid two; the amount of the anhydrous ethanol is 10 parts; the reaction liquid two is added to the tetrabutyl titanate solution after stirring, and then the reaction liquid one is added; the mixture is stirred at 30℃ for 24 hours; after drying, the mixture is ground to obtain a calcined material; the calcined material is put into a tubular furnace and calcined at 450℃ for 5 hours; after cooling, the PLA decomposition catalyst is obtained.

3. The process for producing a recycled polylactic acid and low-temperature spandex fabric according to claim 1, characterized in that: The preparation method of the lactide ring-opening catalyst in S4 is as follows: 2.8-3.0 parts of 1-(chloro-1-pyrrolidinylmethylene) pyrrolidine tetrafluoroborate is dissolved in 20 parts of acetonitrile to obtain a 1-(chloro-1-pyrrolidinylmethylene) pyrrolidine tetrafluoroborate solution; 0.9 parts of 1,2-cyclohexanediamine and 2.1 parts of triethylamine are dissolved in 20 parts of acetonitrile to obtain a mixed solution; the 1-(chloro-1-pyrrolidinylmethylene) pyrrolidine tetrafluoroborate solution is slowly added to the mixed solution at 0℃; the temperature is increased to 85℃; after stirring at reflux for 12 hours, 1.7 parts of sodium hydroxide is added to obtain a lactide ring-opening catalyst precursor; After the lactide ring-opening catalyst precursor is dried under vacuum to remove the organic solvent and the triethylamine, 2.3 parts of potassium hydroxide is added; after stirring, the lactide ring-opening catalyst precursor is extracted with acetonitrile; after being dehydrated with anhydrous sodium acetate, the lactide ring-opening catalyst intermediate is obtained by reduced pressure distillation; 0.1-0.2 parts of zinc trifluoromethanesulfonate is dissolved in 5 parts of tetrahydrofuran to obtain a zinc trifluoromethanesulfonate solution; 0.3 parts of the lactide ring-opening catalyst intermediate is dissolved in 10 parts of tetrahydrofuran to obtain a lactide ring-opening catalyst intermediate solution; The temperature of the lactide ring-opening catalyst intermediate solution is increased to 60℃; The lactide ring-opening catalyst intermediate solution is added dropwise to the zinc trifluoromethanesulfonate solution; the obtained precipitate is filtered and washed with tetrahydrofuran and diethyl ether; then, the lactide ring-opening catalyst is obtained by drying.

4. The process for producing a cyclic regenerated polylactic acid and low-temperature spandex fabric according to claim 1, characterized in that: The temperature of the vacuum condition in S4 is 135-150℃; the amount of the lactide ring-opening catalyst in S4 and S5 is 0.01-0.02 parts.

5. The process for producing a recycled polylactic acid and low-temperature spandex fabric according to claim 1, characterized in that: The isocyanate is one of 1,3-bis(1-isocyanato-1-methylethyl)benzene, 4,4'-methylenebis(phenyl isocyanate), toluene-2,4-diisocyanate and isophorone diisocyanate.

6. The process for producing a cyclic regenerated polylactic acid and low-temperature spandex fabric according to claim 1, characterized in that: The processing aid contains a humectant; the humectant consists of betaine and an anionic surfactant; the parts ratio of the betaine to the anionic surfactant is 1:1-2; the anionic surfactant is one of sodium cocoyl glycinate and sodium lauroyl glutamate.

7. The process as claimed in claim 1, wherein the process is characterized by: The processing aid contains a dyeing assistant; the dyeing assistant is one of sodium docusate, sodium diisobutyl sulfosuccinate and disodium sulfosuccinimidodiacetate. The processing aid contains a dyeing assistant; the dyeing assistant is one of sodium docusate, sodium diisobutyl sulfosuccinate and disodium sulfosuccinimidodiacetate.

8. The process for producing a recycled polylactic acid and low-temperature spandex fabric according to claim 1, characterized in that: The ratio of the parts of the wetting agent, the dyeing assistant and the desizing agent in the processing aid is 3-5:2-5:2-3; the finishing agent is added after the first programmed cooling in S6; the mass ratio of the ester group quaternary ammonium salt, the chitin and the siloxane polyoxyethylene ether in the finishing agent is 1-3:2:1-5.

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