Preparation method and application of polylactic acid fiber with persistent strong hydrophilicity and flame retardance

Abstract

The application relates to the technical field of biomass textile fiber preparation, and particularly discloses a preparation method and application of polylactic acid fiber with persistent strong hydrophilicity and flame retardance, which comprises the following steps: 1) performing carboxymethyl modification treatment on nanocellulose; 2) performing ethylene glycol diglycidyl-phytic acid modification treatment on polylactic acid; and 3) preparing a physical-chemical combined composite modified polylactic acid fiber. The application adopts the carboxymethyl modification treatment on the nanocellulose to make it hydrophilic, and simultaneously performs modification treatment on the polylactic acid to connect the ethylene glycol diglycidyl-phytic acid to the molecular chain of the polylactic acid, so that the hydrophilic carboxymethyl and the phytic acid are used to endow the polylactic acid fiber with strong and persistent hydrophilicity, improve the compatibility between the nanocellulose and the polylactic acid and the dispersibility of the former in the latter matrix, and the environment-friendly phytic acid endows the polylactic acid with persistent high flame retardance, thereby avoiding the problems of the separation of the conventional flame retardant and the blending of the flame retardant and the polylactic acid and the deterioration of the performance of the polylactic acid.

Description

Technical Field

[0001] This invention relates to the field of biomass textile fiber preparation technology, specifically to a method for preparing polylactic acid fiber with durable strong hydrophilicity and flame retardancy and its application. Background Technology

[0002] Polylactic acid (PLA) is derived from renewable plant resources. It is non-toxic, non-irritating, and easy to process and mold. As a biodegradable material, its production and application have freed it from dependence on petroleum resources, alleviating the environmental pressure of traditional petroleum-based plastics. In recent years, PLA has been widely used in biomedicine, packaging, construction, automotive, and other fields. As a biomass material with excellent properties, it has also received high attention in the textile industry as a textile fiber.

[0003] However, current applications of polylactic acid (PLA) fibers still have some shortcomings. PLA fibers are highly hydrophobic, resulting in unsatisfactory performance in moisture absorption and wicking, and wearing comfort. Furthermore, this strong hydrophobicity leads to severe static electricity problems, affecting their effectiveness as a clothing fiber material. The limiting oxygen index (LOI) of pure PLA fibers is generally around 20%–26%, classifying them as flammable materials. Therefore, there is an urgent need to address their poor flame retardant properties and improve their performance as a textile fiber in applications requiring good flame retardancy. Conventional methods to improve flame retardancy involve mixing flame retardants with the base material. However, the physical bonding between the flame retardant and the base material can lead to precipitation due to poor compatibility, affecting the durability of the flame retardancy. Excessive addition can also deteriorate the material's mechanical properties and processability.

[0004] Therefore, if hydrophilic groups with flame-retardant effects can be introduced into the polylactic acid (PLA) molecular chain using technical methods, it is expected to endow PLA with long-lasting flame retardancy without issues such as precipitation. Furthermore, if functional groups containing hydrophilic carboxyl and sodium ions are introduced into the nano-auxiliaries, the carboxyl and sodium ions can form complexes with the flame retardants, improving the fiber's heat resistance and flame retardancy. Therefore, if the above-mentioned modified nano-auxiliaries are melt-spun with modified PLA to produce PLA fibers, it is expected to overcome the above problems. This is of great significance in enhancing the performance of PLA fibers as textile fibers. Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned shortcomings and provide a method for preparing and applying polylactic acid (PLA) fibers with durable, strong hydrophilicity and flame retardancy. This involves modifying nanocellulose with hydrophilic carboxymethyl groups and simultaneously modifying PLA. Ethylene glycol diglycidyl-phytic acid is attached to the molecular chain. The hydrophilic carboxymethyl groups and phytic acid impart strong and durable hydrophilicity to the PLA fibers, improving the compatibility between nanocellulose and PLA and the former's dispersibility in the latter's matrix. Environmentally friendly phytic acid imparts durable, high flame retardancy to PLA, avoiding the problems of flame retardant precipitation and deterioration of PLA performance that occur when conventional flame retardants are blended with PLA. Simultaneously, the hydrophilic carboxyl groups and sodium ions introduced onto the nanocellulose can form complexes with phytic acid, improving the heat resistance of the PLA fibers and further enhancing their flame retardancy. Furthermore, the synergistic effect of carboxymethyl-modified nanocellulose and ethylene glycol diglycidyl-phytic acid enhances the strength and toughness of the PLA fibers. This makes it highly suitable for use as a textile fiber.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for preparing polylactic acid fiber with durable strong hydrophilicity and flame retardancy, comprising the following steps: 1) Carboxymethyl modification of nanocellulose: Chloroacetic acid and sodium hydroxide were added to nanocellulose, and after thorough grinding, the mixture was spread evenly at the bottom of a beaker and placed in an oven for reaction. After being removed, washed, and centrifuged repeatedly three times, the mixture was dried in an oven and ground again to obtain a carboxymethyl modified nanocellulose sample. 2) Modification treatment of polylactic acid with ethylene glycol diglycidyl-phytic acid: Polylactic acid (PLA) was dissolved in an organic solvent to form a PLA solution, and a mixed solution was obtained. The pH of the PLA solution was adjusted with an alkaline aqueous solution. The mixture was stirred and heated to a set temperature. Ethylene glycol diglycidyl-phytic acid was added, and the pH was adjusted to be consistent with the above. After reacting for a certain period of time, the solvent was evaporated in a fume hood. The mixture was then washed with an ethanol aqueous solution and filtered three times. Finally, it was dried in an oven at 35°C to obtain a PLA-ethylene glycol diglycidyl-phytic acid sample. 3) Mix the samples obtained in steps 1) and 2) at a certain mass ratio, and after grinding, drying, add them to a screw extruder; control the screw speed, heat and melt, and use a spinning pump to quantitatively extrude the melt into the spinning assembly. After the extruded filaments are cooled and solidified in the air, they are then fully ground, dried, and added to a twin-screw extruder. Control the melting temperature and screw speed, and after extrusion spinning, solidification, and winding, obtain physical-chemical combined composite modified polylactic acid fibers.

[0007] Preferably, in step 1), the mass ratio of nanocellulose to chloroacetic acid is 12:0-10, the molar ratio of chloroacetic acid to sodium hydroxide is 2:1-0.4, and the percentage content of carboxymethyl in the carboxymethyl nanocellulose is 0.5%-4.25%.

[0008] Preferably, in step 1), the oven is set to a temperature of 40-70°C, the reaction time in the oven is 1-5 hours, and the material in the beaker is turned over every half hour during the reaction.

[0009] Preferably, in step 2), the organic solvent is one or a combination of several of dichloromethane, chloroform, acetone, dichloromethane, ethyl acetate, and dimethylformamide; the concentration of the polylactic acid solution is 13-45% (w / v); the mass ratio of polylactic acid to ethylene glycol diglycidyl-phytic acid is 20:1-6; and the percentage content of ethylene glycol diglycidyl-phytic acid in the polylactic acid-ethylene glycol diglycidyl-phytic acid solution is 0.6%-4.15%.

[0010] Preferably, in step 2), the pH value of the mixed solution is 8.5-11, the set temperature for stirring and heating is 30-55℃, and the reaction time is 3-10 hours.

[0011] Preferably, in step 2), the preparation method of the ethylene glycol diglycidyl-phytic acid is as follows: ethylene glycol diglycidyl ether is added to an Erlenmeyer flask containing phytic acid, sealed, and shaken at 50-80°C for 2-7 hours to obtain an ethylene glycol diglycidyl-phytic acid sample.

[0012] Preferably, the mass ratio of ethylene glycol diglycidol to phytic acid is 16:3-8.

[0013] Preferably, in step 3), the mass percentage of the carboxymethyl modified nanocellulose sample to the polylactic acid-ethylene glycol diglycidyl-phytic acid sample is 0.25%-3%.

[0014] Preferably, in step 3), the melt temperature of both the screw extruder and the twin-screw extruder is 175-230℃, the screw speed is 15-65 rpm, and the winding speed is 15-65 m / min.

[0015] Preferably, the application of polylactic acid fiber with durable strong hydrophilicity and flame retardancy is as a textile fiber.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention modifies nanocellulose with hydrophilic carboxymethyl groups and polylactic acid simultaneously, attaching ethylene glycol diglycidyl-phytic acid to its molecular chain. By utilizing the hydrophilic carboxymethyl groups and phytic acid, polylactic acid fibers are endowed with strong and lasting hydrophilicity. Simultaneous hydrophilic modification of nanocellulose and strongly hydrophobic polylactic acid can improve the compatibility between nanocellulose and polylactic acid and the dispersion of the former in the latter matrix.

[0017] (2) The present invention imparts long-lasting high flame retardancy to polylactic acid through environmentally friendly phytic acid, avoiding the problem of flame retardant precipitation and deterioration of polylactic acid performance when conventional flame retardants are blended with polylactic acid. At the same time, the hydrophilic carboxyl groups and sodium ions introduced on nanocellulose can form complexes with phytic acid, improving the heat resistance and enhancing the flame retardancy of polylactic acid fibers.

[0018] (3) This invention improves the breaking strength, breaking elongation, and heat resistance of polylactic acid fiber by synergistic effect of carboxymethyl modified nanocellulose and ethylene glycol diglycidyl-phytic acid, making it suitable for use as a textile fiber. Attached Figure Description

[0019] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a scanning electron microscope image of the composite modified polylactic acid fiber proposed in this invention; Figure 2 The water contact angle diagrams are for fibers spun from virgin polylactic acid fibers, nanocellulose, and virgin polylactic acid composites, and for composite modified polylactic acid fibers, as proposed in this invention. Figure 3 Thermogravimetric analysis (TGA) diagrams of the original polylactic acid fiber and the composite modified polylactic acid fiber proposed in this invention are shown. Figure 4 The tensile strength diagrams are of the composite spun fibers made from nanocellulose and native polylactic acid and the composite modified polylactic acid fiber samples proposed in this invention. Figure 5 The diagram shows the elongation at break of the nanofiber-cellulose composite spun fiber and the composite modified polylactic acid fiber samples proposed in this invention. Figure 6 These are combustion characteristic diagrams of the original polylactic acid fiber and the composite modified polylactic acid fiber proposed in this invention. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1 This embodiment provides a method for preparing polylactic acid fibers with durable strong hydrophilicity and flame retardancy, including the following steps: (1) Carboxymethyl modification of nanocellulose Chloroacetic acid (2.5g) and sodium hydroxide (0.55g) were added to nanocellulose (30g). After thorough grinding for 30min, the mixture was spread evenly at the bottom of a large beaker and placed in an oven at 66℃. The reaction was carried out for 3.5h (stirring every 30min). Afterward, the mixture was removed, thoroughly washed with distilled water, and centrifuged (4000 r / min, 10min) three times. The sample was then placed on a drying tray and dried in an oven at 40℃. After grinding, carboxymethyl modified nanocellulose was obtained. The percentage of carboxymethyl in the sample was 0.63% by mass.

[0022] (2) Polylactic acid modified with ethylene glycol diglycidol-phytic acid 80g of ethylene glycol diglycidyl ether was placed in an Erlenmeyer flask containing 21g of phytic acid. The flask was sealed and the mixture was shaken at 70°C for 4 hours to obtain ethylene glycol diglycidyl-phytic acid. 100g of polylactic acid was dissolved in dichloromethane to prepare a 30% (w / v) solution. After stirring, the solution was transferred to a three-necked flask. The pH of the system was adjusted to 9 with a 2% (w / v) NaOH aqueous solution. The mixture was stirred and heated to 40°C. 5g of ethylene glycol diglycidyl-phytic acid was added, and the pH was adjusted to 9. After reacting for 6 hours, the solvent was evaporated in a fume hood. The obtained solid was pulverized and washed three times with an ethanol-water solution (70:30). The solid was then dried in an oven at 35°C and ground to obtain a polylactic acid-ethylene glycol diglycidyl-phytic acid sample. The percentage (w / v) of ethylene glycol diglycidyl-phytic acid in the sample was 0.97%.

[0023] (3) The samples obtained in (1) and (2) were mixed at a mass ratio of 0.5% for the former to the latter. After crushing, grinding, and drying, the mixture was added to a screw extruder. The screw speed was controlled at 40 rpm, and the mixture was heated to 193°C for melt extrusion. After thorough grinding, crushing, and drying, the mixture was added to a twin-screw extruder. After melt extrusion spinning, physical-chemical combined composite modified polylactic acid fiber sample I was obtained. The melt spinning temperature was 190°C, the screw speed was 35 rpm, and the winding speed was 45 m / min.

[0024] Example 2 This embodiment provides a method for preparing polylactic acid fibers with durable strong hydrophilicity and flame retardancy, including the following steps: (1) Carboxymethyl modification of nanocellulose 12.5 g of chloroacetic acid and 2.65 g of sodium hydroxide were added to 30 g of nanocellulose. After grinding thoroughly for 30 min, the mixture was spread evenly at the bottom of a large beaker and placed in an oven at 60 °C. The mixture was reacted for 4.5 h (stirring every 30 min). Afterward, the mixture was removed, thoroughly washed with distilled water, and centrifuged (4000 r / min, 12 min) three times. The sample was then placed on a drying tray and dried in an oven at 40 °C. After grinding, carboxymethyl modified nanocellulose was obtained. The mass percentage of carboxymethyl in the sample was 1.72%.

[0025] (2) Polylactic acid modified with ethylene glycol diglycidol-phytic acid Polylactic acid (100g) was dissolved in dichloromethane to prepare a 30% (w / v) solution. After stirring evenly, the solution was transferred to a three-necked flask. The pH of the system was adjusted to 9 with a 2% (w / v) NaOH aqueous solution. The mixture was stirred and heated to 40°C. Ethylene glycol diglycidyl-phytic acid (10g) was added, and the pH was adjusted to 9. After reacting for 6.5 hours, the solvent was evaporated in a fume hood. The obtained solid was pulverized and washed three times with an ethanol aqueous solution (70:30). After filtration, the solid was dried in an oven at 35°C and ground to obtain a polylactic acid-ethylene glycol diglycidyl-phytic acid sample. The percentage (w / v) content of ethylene glycol diglycidyl-phytic acid in the sample was 2.26%.

[0026] Following step (3) in Example 1, step (3) in this example is performed to obtain physical-chemical combined composite modified polylactic acid fiber sample II.

[0027] Example 3 This embodiment provides a method for preparing polylactic acid fibers with durable strong hydrophilicity and flame retardancy, including the following steps: (1) Carboxymethyl modification of nanocellulose Chloroacetic acid (22.5g) and sodium hydroxide (4.8g) were added to nanocellulose (30g). After thorough grinding for 30min, the mixture was spread evenly at the bottom of a large beaker and placed in an oven at 63℃. The mixture was reacted for 4h (stirring every 30min). After removal, the sample was thoroughly washed with distilled water and centrifuged (4000 r / min, 15min) three times. The sample was then placed on a drying tray and dried in an oven at 40℃. After grinding, carboxymethyl modified nanocellulose sample was obtained. The mass percentage of carboxymethyl in the sample was 3.75%.

[0028] (2) Polylactic acid modified with ethylene glycol diglycidol-phytic acid Polylactic acid (100g) was dissolved in dichloromethane to prepare a 35% (w / v) solution. After stirring evenly, the solution was transferred to a three-necked flask. The pH of the system was adjusted to 9 with a 2% (w / v) NaOH aqueous solution. The mixture was stirred and heated to 43°C. Ethylene glycol diglycidyl-phytic acid (15g) was added, and the pH was adjusted to 9. After reacting for 7 hours, the solvent was evaporated in a fume hood. The obtained solid was pulverized and washed three times with an ethanol aqueous solution (70:30). After drying and grinding in an oven at 35°C, a polylactic acid-ethylene glycol diglycidyl-phytic acid sample was obtained. The percentage (w / v) content of ethylene glycol diglycidyl-phytic acid in the sample was 3.60%.

[0029] Following step (3) in Example 1, step (3) in this example is performed to obtain physical-chemical combined composite modified polylactic acid fiber sample III.

[0030] Comparative Example 4 The present invention uses polylactic acid melt-spun fiber as a comparative sample 1, and its preparation method refers to step (3) in Example 1.

[0031] Comparative Example 5 This invention uses unmodified nanocellulose and unmodified polylactic acid composite melt-spun polylactic acid fibers as comparative sample 2, and the preparation method is the same as step (3) in Example 1. The nanocellulose is 0.5% of the mass of polylactic acid.

[0032] After sputter-coating polylactic acid fiber samples with gold under vacuum conditions, their surface morphology was characterized and analyzed using a Quantum SEM 3200 from Guoyi Quantum Microscope. The results are as follows: Figure 1 As shown.

[0033] It is evident that the composite modified polylactic acid fiber exhibits a good surface morphology, with a generally smooth surface and no obvious particles present, indicating that the hydrophilic carboxymethyl modified nanoparticle cellulose is well dispersed in the polylactic acid matrix with introduced hydrophilic groups and that the two have good compatibility.

[0034] To evaluate the effect of modification on the hydrophilicity of polylactic acid (PLA) fibers, deionized water was used, and the contact angle of PLA fibers before and after modification was measured using a contact angle meter. The water contact angle test results are as follows: Figure 2 As shown: The contact angle diagram showed that the original polylactic acid (PLA) fiber had a contact angle of 124°, exhibiting significant hydrophobic properties. This hydrophobicity mainly stems from the large number of hydrophobic ester groups present in the PLA molecular chain. The contact angle of the composite spun fiber made from unmodified nanocellulose and original PLA decreased to around 75°. The contact angle of the composite modified PLA fiber sample was around 60°, exhibiting strong hydrophilic properties. These results indicate that hydrophilic polar hydroxyl groups, carboxymethyl groups, and phytic acid significantly reduced the strong hydrophobicity of PLA fibers, endowing them with strong hydrophilicity.

[0035] Thermogravimetric analysis (TGA) was used to systematically study the mass change of polylactic acid (PLA) fiber samples with temperature to reveal the samples' resistance to high-temperature degradation. The results are as follows: Figure 3 As shown: The original polylactic acid (PLA) fiber exhibits degradation and weight loss in the range of approximately 340-410℃, while the degradation temperature range of the composite modified PLA fiber is about 20℃ higher. Furthermore, the original PLA fiber has almost no mass residue, but the composite modified PLA fiber has a mass residue percentage of nearly 20%, which confirms that the addition of carboxymethyl cellulose and the modification of PLA together improve the heat degradation resistance of PLA fiber.

[0036] The tensile strength and elongation at break of the fibers were tested using a tensile testing instrument. The effective test length was set to 20 mm. At least 10 single fibers were tested in each sample group. A pretension of 0.05 cN was applied to the fibers. The test results are as follows: Figure 4 and Figure 5 As shown: The tensile strength and elongation at break of the composite spun fibers of nanocellulose and native polylactic acid were lower than those of the composite modified polylactic acid fibers. Furthermore, with increasing carboxymethyl ester content and polylactic acid modification strength, the tensile strength gradually increased from sample I to sample III; while the elongation at break showed a trend of first increasing and then decreasing. The higher tensile strength and elongation at break of the composite modified polylactic acid fiber samples indicate that carboxymethyl ester modification and polylactic acid modification can significantly improve the strength and toughness of the fibers.

[0037] The combustion characteristics of virgin polylactic acid (PLA) fibers and composite modified PLA fibers are shown in [reference needed]. Figure 6As shown in the figure, the melting tendency of the composite-modified polylactic acid (PLA) fiber is lower than that of the original PLA fiber; the original PLA fiber continues to burn after being removed from the flame, while the composite-modified PLA fiber extinguishes itself after being removed from the flame and does not continue to burn. These characteristics indicate that the composite-modified PLA fiber has excellent flame-retardant properties. The introduction of phytic acid functional groups with flame-retardant properties can endow PLA with flame retardancy. At the same time, the hydrophilic carboxyl groups and sodium ions introduced on the nanocellulose can form a complex with phytic acid, improving the heat resistance and enhancing the flame retardancy of PLA fiber, thus giving the composite-modified PLA fiber excellent flame retardancy.

[0038] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing polylactic acid fiber with durable strong hydrophilicity and flame retardancy, characterized in that, Includes the following steps: 1) Carboxymethyl modification of nanocellulose: Chloroacetic acid and sodium hydroxide were added to nanocellulose, and after thorough grinding, the mixture was spread evenly at the bottom of a beaker and placed in an oven for reaction. After being removed, washed, and centrifuged repeatedly three times, the mixture was dried in an oven and ground again to obtain a carboxymethyl modified nanocellulose sample. 2) Modification treatment of polylactic acid with ethylene glycol diglycidyl-phytic acid: Polylactic acid was dissolved in an organic solvent to form a solution, and the pH value of the polylactic acid solution was adjusted with an alkaline aqueous solution. The solution was stirred and heated to a set temperature, and ethylene glycol diglycidyl-phytic acid was added. The pH value was adjusted to be consistent with the above. After reacting for a certain period of time, the solvent was evaporated in a fume hood. The solution was washed with an ethanol aqueous solution and filtered three times. The solution was then dried in an oven at 35°C to obtain a polylactic acid-ethylene glycol diglycidyl-phytic acid sample. 3) Mix the samples obtained in steps 1) and 2) at a certain mass ratio, and after grinding, drying, add them to a screw extruder; control the screw speed, heat and melt, and use a spinning pump to quantitatively extrude the melt into the spinning assembly. After the extruded filaments are cooled and solidified in the air, they are then fully ground, dried, and added to a twin-screw extruder. Control the melting temperature and screw speed, and after extrusion spinning, solidification, and winding, obtain physical-chemical combined composite modified polylactic acid fibers.

2. The method for preparing polylactic acid fiber with durable strong hydrophilicity and flame retardancy according to claim 1, characterized in that, In step 1), the mass ratio of nanocellulose to chloroacetic acid is 12:0-10, and the molar ratio of chloroacetic acid to sodium hydroxide is 2:1-0.4; the percentage content of carboxymethyl in the carboxymethyl nanocellulose is 0.5%-4.25%.

3. The method for preparing polylactic acid fiber with durable strong hydrophilicity and flame retardancy according to claim 1, characterized in that, In step 1), the oven is set to a temperature of 40-70°C, the reaction time in the oven is 1-5 hours, and the material in the beaker is turned over every half hour during the reaction.

4. The method for preparing polylactic acid fiber with durable strong hydrophilicity and flame retardancy according to claim 1, characterized in that, In step 2), the organic solvent is one or a combination of several of dichloromethane, chloroform, acetone, dichloromethane, ethyl acetate, and dimethylformamide; the concentration of the polylactic acid solution is 13-45% (w / v); the mass ratio of polylactic acid to ethylene glycol diglycidyl-phytic acid is 20:1-6; and the percentage content of ethylene glycol diglycidyl-phytic acid in the polylactic acid-ethylene glycol diglycidyl-phytic acid solution is 0.6%-4.15%.

5. The method for preparing polylactic acid fiber with durable strong hydrophilicity and flame retardancy according to claim 1, characterized in that, In step 2), the pH value of the mixed solution is 8.5-11, the set temperature for stirring and heating is 30-55℃, and the reaction time is 3-10 hours.

6. The method for preparing polylactic acid fiber with durable strong hydrophilicity and flame retardancy according to claim 1, characterized in that, In step 2), the preparation method of ethylene glycol diglycidyl-phytic acid is as follows: ethylene glycol diglycidyl ether is added to an Erlenmeyer flask containing phytic acid, sealed, and shaken at 50-80℃ for 2-7 hours to obtain an ethylene glycol diglycidyl-phytic acid sample.

7. The method for preparing polylactic acid fiber with durable strong hydrophilicity and flame retardancy according to claim 6, characterized in that, The mass ratio of ethylene glycol diglycidol to phytic acid is 16:3-8.

8. The method for preparing polylactic acid fiber with durable strong hydrophilicity and flame retardancy according to claim 1, characterized in that, In step 3), the mass percentage of the carboxymethyl modified nanocellulose sample to the polylactic acid-ethylene glycol diglycidyl-phytic acid sample is 0.25%-3%.

9. The method for preparing polylactic acid fiber with durable strong hydrophilicity and flame retardancy according to claim 1, characterized in that, In step 3), the melt temperature of both the screw extruder and the twin-screw extruder is 175-230℃, the screw speed is 15-65 rpm, and the winding speed is 15-65 m / min.

10. An application of polylactic acid fiber with durable strong hydrophilicity and flame retardancy according to any one of claims 1-9, characterized in that, The polylactic acid fiber is used as a textile fiber.

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