A chemically recyclable and highly crystallinity PLLA fiber and its preparation method

Abstract

This invention relates to the field of bio-based fiber materials technology, providing a chemically recyclable and highly crystalline PLLA fiber and its preparation method. Bio-based nacre calcium carbonate extracted from mussels is treated with a silane coupling agent, then mixed uniformly with PLLA masterbatch at different mass ratios and regranulated to obtain calcium carbonate-modified PLLA composite masterbatch. The composite masterbatch is vacuum-dried and extruded from a melt spinning machine spinneret to obtain nascent PLLA fibers. These nascent PLLA fibers are then stretched and heat-treated to obtain highly crystalline PLLA fibers. The PLLA fibers prepared using this invention exhibit high crystallinity, good thermal stability, biodegradability, and chemical recyclability. They can be used in textiles, clothing, and medical fields. This invention solves the problems of conventional chemical fiber materials being non-degradable and environmentally harmful, while also addressing the issues of low crystallinity, poor thermal stability and strength, and recyclability associated with conventional polylactic acid (PLA) materials.

Description

Technical Field

[0001] This invention relates to the field of bio-based fiber materials technology, specifically to a chemically recyclable and highly crystallizable PLLA fiber and its preparation method. Background Technology

[0002] With the global shortage of petrochemical resources and the increasing environmental threat posed by "white pollution," petroleum-based fiber materials, represented by polyester fiber, are facing a growing dilemma of dwindling raw material sources. Currently, the quantity of waste textiles, mainly composed of polyester fiber, is enormous, placing immense pressure on the ecological environment. my country currently generates as much as 8 million tons of discarded fiber products annually, with most of these waste textiles ending up in landfills or incineration, resulting in both resource waste and environmental pollution. Furthermore, against the backdrop of countries worldwide actively promoting the implementation of mandatory laws and regulations such as plastic restriction and bans, the development and use of biodegradable and environmentally friendly materials is imperative. Polylactic acid (PLA) fiber, as a fiber material with abundant raw material sources, renewable properties, good biodegradability, and biocompatibility, has gained widespread favor.

[0003] Since American polymer chemist Carothers synthesized polylactic acid (PLA) in organic solvents and under vacuum in 1932, PLA has been extensively studied as a structural material. In 1954, DuPont in the United States used a two-step method to prepare high-molecular-weight PLA, laying the foundation for the preparation of PLA fibers. In the late 1990s, Cargill Dow, a joint venture between Cargill and Dow Chemical, perfected the industrial production process of PLA using corn as raw material, thus pioneering the industrialization of PLA. Kanebo Corporation of Japan produced PLA fibers under the trade name "Lactron" as early as 1994 using melt spinning technology. In 2005, NatureWorks announced the independent development of a comprehensive business encompassing lactic acid and PLA, boasting the world's largest PLA production facility (annual output exceeding 1.5 × 10⁵ t) with a complete range of sub-categories. Although my country's polylactic acid (PLA) industry started relatively late, it has developed rapidly, with the scale of production facilities for polymer-grade lactic acid and PLA constantly expanding and under construction. PLA fiber, a biomass synthetic fiber derived from corn, cassava, and agricultural waste, possesses excellent comfort, breathability, and UV resistance, making it highly promising in the field of new textile materials. However, the low melting point, poor thermal stability, and low crystallinity of PLA fiber severely restrict its development and hinder its application in environmentally friendly fibers and textiles.

[0004] Chemical recycling is one of the key methods for reusing PLA-based materials. It involves depolymerizing waste PLA and converting it into lactic acid, lactide, and value-added lactate esters. These materials can then be used as new raw materials for PLA synthesis, enabling repeated recycling. However, the reuse of PLA often requires the addition of exogenous additives, which are difficult to separate during PLA depolymerization, thus having a serious negative impact on PLA decomposition products. Therefore, developing bio-based materials that can be used to modify PLA without affecting its decomposition is of great significance for achieving the chemical recycling of PLA-based materials. Summary of the Invention

[0005] Based on the above background, this invention addresses the shortcomings of existing technologies by providing a chemically recyclable and highly crystallizable PLLA fiber and its preparation method. It uses bio-based nacreous calcium carbonate to composite with PLLA masterbatch. By controlling the morphology, size, and surface physicochemical structure of the nacreous calcium carbonate, the entanglement between it and the PLLA molecular chains is enhanced, and the nucleation sites of PLLA are increased. This improves the melt strength of PLLA, promotes crystallinity, and enhances thermal stability, resulting in a highly crystallizable PLLA fiber with excellent mechanical strength and thermal stability.

[0006] The present invention adopts the following technical solution:

[0007] A chemically recyclable and highly crystallinity PLLA fiber and its preparation method, comprising the following steps:

[0008] (1) Separation and modification of bio-based nacreous calcium carbonate in mussels: After cleaning, removing impurities, washing and drying the mussel shells, they were placed in an oven at a certain temperature for a certain period of time to separate the nacreous calcium carbonate from the treated mussel shells to obtain crude nacreous calcium carbonate. The crude nacreous calcium carbonate was added to a dispersant and then ultrasonically dispersed, crushed, modified and dried to obtain submicron-sized bio-based nacreous calcium carbonate.

[0009] (2) Preparation of high crystallinity PLLA fiber: Bio-based nacre calcium carbonate and PLLA masterbatch are added to a mixer in a certain proportion and mixed thoroughly. The mixture is then granulated by a screw extruder to obtain modified PLLA composite masterbatch. The composite masterbatch is then extruded, drawn, and heat-treated by a melt spinning machine to obtain high crystallinity PLLA fiber.

[0010] Based on the total dry weight of raw materials, which is 100% of the total dry weight of nacre calcium carbonate and PLLA masterbatch, the content of nacre calcium carbonate in the total dry weight of raw materials is 1-7%, and the content of PLLA masterbatch in the total dry weight of raw materials is 93-99%.

[0011] In step (1), the heat treatment temperature of the mussel shells is 220-300℃ and the treatment time is 2-6h;

[0012] Furthermore, the dispersant used in the crude nacre calcium carbonate is a mixed solvent composed of organic acid and deionized water, wherein the organic acid is any one or a combination of several of acetic acid, citric acid, salicylic acid, oxalic acid, malic acid, tartaric acid, and benzoic acid.

[0013] The volume ratio of organic acid to deionized water is 1:9-3:7.

[0014] Furthermore, the modifiers used in the modification process of nacreous calcium carbonate are any one or a combination of several of KH550, KH792, Y5669, and Si-902.

[0015] In step (2), the processing temperature of bio-based nacre calcium carbonate and PLLA masterbatch in the internal mixer is 185-225℃, and the mixing time is 30-60min.

[0016] Furthermore, when the nacreous calcium carbonate and PLLA masterbatch mixed in the internal mixer are granulated by screw extrusion, they are heated in four stages: the first stage heating temperature is 130-150℃; the second stage heating temperature is 160-180℃; the third stage heating temperature is 185-195℃; and the fourth stage heating temperature is 200-210℃.

[0017] Furthermore, the composite masterbatch needs to be vacuum dried for 4-8 hours before being extruded through a melt spinning machine, and the humidity in the workshop must be strictly controlled not to exceed 20% during the spinning process.

[0018] Furthermore, during the melt spinning process of the composite masterbatch, the temperature of the melt spinning machine cavity is 200-220℃, the spinning speed is 3000-6000m / min, and the spinning pressure is 25-40Mpa.

[0019] Furthermore, the PLLA fiber has a drawing rate of 400-600 m / min and a drawing temperature of 200-220℃.

[0020] The beneficial effects of this invention are:

[0021] (1) Using the nacreous calcium carbonate from the shell of the blue mussel, which is derived from bio-based sources, as a reinforcing material, not only realizes the effective utilization of waste biomass shell resources and increases their added value, but also realizes the effective utilization of biomass materials based on biomass. Moreover, the combination of biomass materials and PLLA will not affect their inherent biodegradability, which is an environmentally friendly preparation scheme.

[0022] (2) In the preparation of bio-based nacre calcium carbonate, the physical morphology and chemical structure of the present invention are effectively controlled. By controlling the ultrasonic crushing time and surface functional groups, the problem of interface incompatibility between inorganic material calcium carbonate and polymer PLLA during the composite process is solved, and the uniformity of the two after mixing is improved.

[0023] (3) The high crystallinity PLLA fiber prepared by the present invention is produced by melt spinning. By controlling the relevant external and internal parameters during the spinning process, continuous spinning of high crystallinity PLLA fiber is achieved. This technology is more environmentally friendly than solution spinning and solvent-assisted spinning.

[0024] (4) In the preparation method described in this invention, after subsequent stretching and heat treatment, the polymer molecular chains can be effectively oriented and increase the entanglement with calcium carbonate in the interior during the post-treatment process, forming a more ordered structure and improving the crystallinity and mechanical strength of the fiber. Attached Figure Description

[0025] Figure 1 This is a SEM image of the bio-based nacreous calcium carbonate described in this invention;

[0026] Figure 2 SEM image of the surface of PLLA fibers prepared from calcium carbonate without composite nacre;

[0027] Figure 3 SEM image of the surface of PLLA fibers prepared with 7% nacre calcium carbonate composite;

[0028] Figure 4 SEM image of the cross-section of PLLA fibers prepared with 5% nacre calcium carbonate composite;

[0029] Figure 5 DSC heating curves of PLLA fibers with different nacre calcium carbonate composite ratios (heating rate 5℃ / min).

[0030] Table 1 shows the crystallinity of PLLA fibers with different nacre-calcium carbonate composite ratios. Detailed Implementation

[0031] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0032] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used is for describing particular embodiments only and is not intended to limit the invention.

[0033] A chemically recyclable and highly crystallinity PLLA fiber and its preparation method are disclosed, comprising granulation of modified nacreous calcium carbonate and PLLA, followed by melt spinning.

[0034] (1) Separation and modification of bio-based nacreous calcium carbonate in mussels: After cleaning, removing impurities, washing and drying the mussel shells, they were placed in an oven at a certain temperature for a certain period of time to separate the nacreous calcium carbonate from the treated mussel shells to obtain crude nacreous calcium carbonate. The crude nacreous calcium carbonate was added to a dispersant and then ultrasonically dispersed, crushed, modified and dried to obtain submicron-sized bio-based nacreous calcium carbonate.

[0035] The heat treatment temperature of the mussel shells is 220-300℃, and the treatment time is 2-6 hours.

[0036] Specifically, the dispersant used in the crude nacre calcium carbonate is a mixed solvent composed of organic acid and deionized water, wherein the organic acid is any one or a combination of several of acetic acid, citric acid, salicylic acid, oxalic acid, malic acid, tartaric acid, and benzoic acid;

[0037] The volume ratio of organic acid to deionized water is 1:9-3:7.

[0038] The modifiers used in the modification of nacreous calcium carbonate are any one or a combination of several of KH550, KH792, Y5669, and Si-902.

[0039] (2) Preparation of high crystallinity PLLA fiber: Bio-based nacre calcium carbonate and PLLA masterbatch are added to a mixer in a certain proportion and mixed thoroughly. The mixture is then granulated by a screw extruder to obtain modified PLLA composite masterbatch. The composite masterbatch is then extruded, drawn, and heat-treated by a melt spinning machine to obtain high crystallinity PLLA fiber.

[0040] Based on the total dry weight of raw materials, which is 100% of the total dry weight of nacre calcium carbonate and PLLA masterbatch, the content of nacre calcium carbonate in the total dry weight of raw materials is 1-7%, and the content of PLLA masterbatch in the total dry weight of raw materials is 93-99%.

[0041] Specifically, the processing temperature of the bio-based nacre calcium carbonate and PLLA masterbatch in the internal mixer is 185-225℃, and the mixing time is 30-60 minutes.

[0042] When the mixed nacre calcium carbonate and PLLA masterbatch are extruded and granulated by screw extrusion, they are heated in four stages: the first stage heating temperature is 130-150℃; the second stage heating temperature is 160-180℃; the third stage heating temperature is 185-195℃; and the fourth stage heating temperature is 200-210℃.

[0043] Before the composite masterbatch is extruded through the melt spinning machine, it needs to be vacuum dried for 4-8 hours. At the same time, the humidity in the workshop must be strictly controlled not to exceed 20% during the spinning process.

[0044] Specifically, during the melt spinning process of the composite masterbatch, the temperature of the melt spinning machine cavity is 200-220℃, the spinning speed is 3000-6000m / min, and the spinning pressure is 25-40Mpa.

[0045] The PLLA fiber has a drawing rate of 400-600 m / min and a drawing temperature of 200-220℃.

[0046] Example 1

[0047] After cleaning, removing impurities, washing, and drying the mussel shells, they are placed in a 220℃ forced-air oven for 6 hours to separate the nacreous calcium carbonate from the treated mussel shells, thus obtaining crude nacreous calcium carbonate.

[0048] Crude nacre was added to a dispersion solvent of acetic acid and deionized water in a volume ratio of 1:9. The mixture of nacre and dispersion solvent was ultrasonically dispersed in a 60°C ultrasonic device for 2 hours, and then further pulverized by a cell disruptor for 30 minutes. The further pulverized nacre was filtered, washed with water, and dried to obtain unmodified submicron-sized nacre.

[0049] Submicron-grade nacreous calcium carbonate surface modification: KH550 and anhydrous ethanol were added to a 1000ml beaker at a volume ratio of 1:10 and stirred for 30 minutes to ensure thorough mixing. Then, 500g of submicron-grade nacreous calcium carbonate was added to the mixed solution for reaction. During the reaction, to ensure the reaction proceeds fully, the beaker was placed in a constant temperature water bath at 40℃ and stirred continuously for 4 hours. After the reaction, the nacreous calcium carbonate was filtered, washed with alcohol, and dried to obtain modified nacreous calcium carbonate.

[0050] Bio-based nacre calcium carbonate and PLLA masterbatch were added to a mixer at a mass ratio of 1:99 and thoroughly mixed. The processing temperature of the nacre calcium carbonate and PLLA masterbatch in the mixer was 185℃, and the mixing time was 60 minutes. The mixed nacre calcium carbonate and PLLA masterbatch were then granulated by screw extrusion and subjected to four-stage heating: stage one at 130℃; stage two at 160℃; stage three at 185℃; and stage four at 200℃, to obtain PLLA composite masterbatch.

[0051] The composite masterbatch was vacuum dried for 4 hours and then added to a melt spinning machine. The melt spinning machine chamber temperature was set to 200℃, the spinning speed to 3000m / min, the spinning pressure to 25MPa, the drawing rate to 400m / min, and the drawing temperature to 200℃ to prepare highly crystalline PLLA fibers.

[0052] The microstructure of the modified nacreous calcium carbonate described in this embodiment is as follows: Figure 1 As shown, the DSC heating curve of the highly crystalline PLLA fiber is as follows: Figure 5 As shown in Table 1, the crystallinity of PLLA fibers is as follows: 1% nacre / PLLA. Figure 1 It can be seen that the calcium carbonate in the nacreous layer has a lamellar structure, with the lamellar width ranging from 100 nm to 1000 nm. From Figure 5 The DSC temperature curve of 1% nacre / PLLA shows a cold crystallization peak at around 99.24℃, indicating a change in the internal crystal structure of the surface fibers. Table 1 shows that the crystallinity of 1% nacre / PLLA can reach 64.46%.

[0053] Example 2

[0054] After cleaning, removing impurities, washing, and drying the mussel shells, they are placed in a 250℃ forced-air drying oven for 4 hours to separate the nacreous calcium carbonate from the treated mussel shells, thus obtaining crude nacreous calcium carbonate.

[0055] Crude nacre was added to a dispersion solvent of oxalic acid and deionized water in a volume ratio of 3:7. The mixture of nacre and dispersion solvent was ultrasonically dispersed in a 60°C ultrasonic device for 2 hours. Then, it was further pulverized by a cell disruptor for 30 minutes. The further pulverized nacre was filtered, washed with water, and dried to obtain unmodified submicron-sized nacre.

[0056] Submicron-grade nacreous calcium carbonate surface modification: Y5669 and anhydrous ethanol were added to a 1000ml beaker at a volume ratio of 1:10 and stirred for 30 minutes to ensure thorough mixing. Then, 500g of submicron-grade nacreous calcium carbonate was added to the mixed solution for reaction. During the reaction, to ensure the reaction proceeds fully, the beaker was placed in a constant temperature water bath at 40℃ and stirred continuously for 4 hours. After the reaction, the nacreous calcium carbonate was filtered, washed with alcohol, and dried to obtain modified nacreous calcium carbonate.

[0057] Bio-based nacre calcium carbonate and PLLA masterbatch were added to a mixer at a mass ratio of 3:97 and thoroughly mixed. The processing temperature of the nacre calcium carbonate and PLLA masterbatch in the mixer was 210℃, and the mixing time was 40 minutes. The mixed nacre calcium carbonate and PLLA masterbatch were then granulated by screw extrusion and subjected to four-stage heating: stage one at 135℃; stage two at 165℃; stage three at 185℃; and stage four at 205℃, to obtain PLLA composite masterbatch.

[0058] The composite masterbatch was vacuum dried for 4 hours and then added to a melt spinning machine. The melt spinning machine chamber temperature was set to 205℃, the spinning speed to 3500m / min, the spinning pressure to 30MPa, the drawing rate to 450m / min, and the drawing temperature to 205℃ to prepare highly crystalline PLLA fibers.

[0059] The DSC temperature rise curve of the highly crystalline PLLA fiber described in this embodiment is as follows: Figure 5 As shown in Table 1, the crystallinity of the 3% nacre / PLLA fibers is as follows. Figure 5 The DSC temperature curve of 3% nacre / PLLA shows a cold crystallization peak at around 97.83℃, indicating a change in the internal crystal structure of the surface fibers. Table 1 shows that the crystallinity of 3% nacre / PLLA can reach 68.90%.

[0060] Example 3

[0061] After cleaning, removing impurities, washing, and drying the mussel shells, they are placed in a 230℃ forced-air oven for 5 hours to separate the nacreous calcium carbonate from the treated mussel shells, thus obtaining crude nacreous calcium carbonate.

[0062] Crude nacre was added to a dispersion solvent of salicylic acid and deionized water in a volume ratio of 2:8. The mixture of nacre and dispersion solvent was ultrasonically dispersed in a 60°C ultrasonic device for 2 hours, and then further pulverized by a cell disruptor for 30 minutes. The further pulverized nacre was filtered, washed with water, and dried to obtain unmodified submicron-sized nacre.

[0063] Submicron-sized nacreous calcium carbonate surface modification: KH792 and anhydrous ethanol were added to a 1000ml beaker at a volume ratio of 1:10 and stirred for 30 minutes to ensure thorough mixing. Then, 500g of submicron-sized nacreous calcium carbonate was added to the mixed solution for reaction. During the reaction, to ensure the reaction proceeds fully, the beaker was placed in a constant temperature water bath at 40℃ and stirred continuously for 4 hours. After the reaction, the nacreous calcium carbonate was filtered, washed with alcohol, and dried to obtain modified nacreous calcium carbonate.

[0064] Bio-based nacre calcium carbonate and PLLA masterbatch were added to a mixer at a mass ratio of 5:95 and thoroughly mixed. The processing temperature of the nacre calcium carbonate and PLLA masterbatch in the mixer was 195℃, and the mixing time was 50 minutes. The mixed nacre calcium carbonate and PLLA masterbatch were then granulated by screw extrusion and subjected to four-stage heating: stage 1 at 140℃; stage 2 at 170℃; stage 3 at 190℃; and stage 4 at 205℃, to obtain PLLA composite masterbatch.

[0065] The composite masterbatch was vacuum dried for 6 hours and then added to a melt spinning machine. The melt spinning machine chamber temperature was set to 210℃, the spinning speed to 4000m / min, the spinning pressure to 35MPa, the drawing rate to 500m / min, and the drawing temperature to 210℃ to prepare highly crystalline PLLA fibers.

[0066] The cross-sectional microstructure of the highly crystalline PLLA fiber described in this embodiment is as follows: Figure 4 As shown in the cross-sectional SEM, the fiber DSC temperature rise curve is as follows: Figure 5 As shown in Table 1, the crystallinity of the 5% nacre / PLLA fibers is as described in Table 1. Figure 4 As can be seen, the modified nacreous calcium carbonate is uniformly coated within the PLLA fibers, and the two exhibit good bonding without any interfacial incompatibility issues. From... Figure 5 The DSC temperature curve of 5% nacre / PLLA shows a cold crystallization peak at around 97.70℃, indicating a change in the internal crystal structure of the surface fibers. Table 1 shows that the crystallinity of 5% nacre / PLLA can reach 72.31%.

[0067] Example 4

[0068] After cleaning, removing impurities, washing, and drying the mussel shells, they are placed in a 300℃ forced-air oven for 2 hours to separate the nacreous calcium carbonate from the treated mussel shells, thus obtaining crude nacreous calcium carbonate.

[0069] Crude nacre was added to a dispersion solvent of benzoic acid and deionized water in a volume ratio of 3:7. The mixture of nacre and dispersion solvent was ultrasonically dispersed in a 60°C ultrasonic device for 2 hours, and then further pulverized by a cell disruptor for 30 minutes. The further pulverized nacre was filtered, washed with water, and dried to obtain unmodified submicron-sized nacre.

[0070] Submicron-sized nacreous calcium carbonate surface modification: Si-902 and anhydrous ethanol were added to a 1000ml beaker at a volume ratio of 1:10 and stirred for 30 minutes to ensure thorough mixing. Then, 500g of submicron-sized nacreous calcium carbonate was added to the mixed solution for reaction. During the reaction, to ensure the reaction proceeds fully, the beaker was placed in a constant temperature water bath at 40℃ and stirred continuously for 4 hours. After the reaction, the nacreous calcium carbonate was filtered, washed with alcohol, and dried to obtain modified nacreous calcium carbonate.

[0071] Bio-based nacre calcium carbonate and PLLA masterbatch were added to a mixer at a mass ratio of 7:93 and thoroughly mixed. The processing temperature of the nacre calcium carbonate and PLLA masterbatch in the mixer was 225℃, and the mixing time was 30 minutes. The mixed nacre calcium carbonate and PLLA masterbatch were then granulated by screw extrusion and subjected to four-stage heating: stage one at 150℃; stage two at 180℃; stage three at 195℃; and stage four at 210℃, to obtain PLLA composite masterbatch.

[0072] The composite masterbatch was vacuum dried for 8 hours and then added to a melt spinning machine. The melt spinning machine chamber temperature was set to 220℃, the spinning speed to 6000m / min, the spinning pressure to 40MPa, the drawing rate to 600m / min, and the drawing temperature to 220℃ to prepare highly crystalline PLLA fibers.

[0073] The surface microstructure of the highly crystalline PLLA fiber described in this embodiment is as follows: Figure 3 As shown in the SEM image, the fiber DSC temperature rise curve is as follows: Figure 5 As shown in Table 1, the crystallinity of the 7% nacre / PLLA fibers is as described in Table 1. Figure 3 As can be seen, the modified nacreous calcium carbonate is uniformly dispersed on the surface of the PLLA fibers. From... Figure 5 The DSC temperature curve of 7% nacre / PLLA shows a cold crystallization peak at around 98.04℃, indicating a change in the internal crystal structure of the surface fibers. Table 1 shows that the crystallinity of 7% nacre / PLLA can reach 79.16%.

[0074] Comparative Example 1

[0075] PLLA fibers were prepared using the method described in Example 4, except that the PLLA was spun directly without modification by nacreous calcium carbonate.

[0076] The surface morphology of the PLLA fibers prepared in this comparative example is as follows: Figure 2 As shown in the SEM image, the fiber DSC temperature rise curve is as follows: Figure 5 As shown in Table 1, the crystallinity of the PLLA fibers is as described in PLLA. Figure 2 The SEM images show that the surface of the unmodified PLLA fibers is smooth. Figure 5 The DSC temperature curve of PLLA shows that no cold crystallization peak appeared in the fiber. As can be seen from Table 1, the crystallinity of PLLA is only 36.76%.

[0077] The technical features of the above embodiments can be combined in any way. For those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention. These modifications and improvements all fall within the protection scope of the present invention, which is defined by the appended claims.

Claims

1. A method for preparing chemically recyclable and highly crystallinity PLLA fibers, characterized in that, Includes the following steps: (1) Separation and modification of bio-based nacreous calcium carbonate in mussels: After cleaning, removing impurities, washing and drying, mussel shells are placed in an oven at a certain temperature for a certain time to separate the nacreous calcium carbonate from the treated mussel shells to obtain crude nacreous calcium carbonate. The crude nacreous calcium carbonate is added to a dispersant, which is a mixed solvent composed of organic acid and deionized water. The organic acid is any one or a combination of several of acetic acid, citric acid, salicylic acid, oxalic acid, malic acid, tartaric acid and benzoic acid. The volume ratio of organic acid to deionized water is 1:9-3:

7. After ultrasonic dispersion, crushing, modification and drying, submicron-sized bio-based nacreous calcium carbonate is obtained. The modifier used in the modification of nacreous calcium carbonate is any one or a combination of several of KH550, KH792, Y5669 and Si-902. (2) Preparation of high crystallinity PLLA fiber: Bio-based nacre calcium carbonate and PLLA masterbatch are added to a mixer in a certain proportion and mixed thoroughly. The mixture is then granulated by a screw extruder to obtain modified PLLA composite masterbatch. The composite masterbatch is then extruded, drawn, and heat-treated by a melt spinning machine to obtain high crystallinity PLLA fiber. Based on the total dry weight of raw materials, which is 100% of the total dry weight of nacre calcium carbonate and PLLA masterbatch, the content of nacre calcium carbonate in the total dry weight of raw materials is 1-7%, and the content of PLLA masterbatch in the total dry weight of raw materials is 93-99%.

2. The method for preparing a chemically recyclable and highly crystallinity PLLA fiber according to claim 1, characterized in that, In step (1), the heat treatment temperature of the mussel shells is 220-300℃ and the treatment time is 2-6h.

3. The method for preparing a chemically recyclable and highly crystallinity PLLA fiber according to claim 1, characterized in that, In step (2), the processing temperature of bio-based nacre calcium carbonate and PLLA masterbatch in the internal mixer is 185-225℃, and the mixing time is 30-60min.

4. The method for preparing a chemically recyclable and highly crystallinity PLLA fiber according to claim 1, characterized in that, In step (2), when the nacreous calcium carbonate and PLLA masterbatch mixed in the internal mixer are granulated by screw extrusion, they are heated in four stages: the first stage heating temperature is 130-150℃; the second stage heating temperature is 160-180℃; the third stage heating temperature is 185-195℃; and the fourth stage heating temperature is 200-210℃.

5. The method for preparing a chemically recyclable and highly crystallinity PLLA fiber according to claim 1, characterized in that, In step (2), the composite masterbatch needs to be vacuum dried for 4-8 hours before being extruded by the melt spinning machine, and the humidity in the workshop is strictly controlled not to exceed 20% during the spinning process.

6. The method for preparing a chemically recyclable and highly crystallinity PLLA fiber according to claim 1, characterized in that, In step (2), the temperature of the melt spinning machine cavity during the melt spinning process of the composite masterbatch is 200-220℃, the spinning speed is 3000-6000m / min, and the spinning pressure is 25-40Mpa.

7. The method for preparing a chemically recyclable and highly crystallinity PLLA fiber according to claim 1, characterized in that, In step (2), the stretching rate of PLLA fiber is 400-600 m / min and the stretching temperature is 200-220℃.

Images