Flame-retardant regenerated polyester staple fiber prepared by biological enzymolysis method and preparation method of flame-retardant regenerated polyester staple fiber

Abstract

The invention relates to the technical field of regenerated polyester staple fibers, in particular to flame-retardant regenerated polyester staple fibers prepared by a biological enzymolysis method and a preparation method thereof.The preparation method comprises the steps that waste textiles are sorted, cleaned and crushed, and then under the conditions that the temperature is 30-80 DEG C and the pH value is 5-9, a monomer is obtained through biological enzyme degradation; carrying out esterification polycondensation on the monomers to obtain regenerated polyester chips with intrinsic viscosity of 0.60-0.72 dL / g; carrying out melt blending on the slices and flame-retardant master batches according to a mass ratio of (80-99): (1-20), and carrying out screw extrusion spinning, circular blowing cooling and winding to prepare a nascent filament; the oxygen index of the obtained short fiber is larger than or equal to 30%, the linear density of the short fiber is 1.11-16.67 dtex, the breaking strength of the short fiber is 4.0-5.5 cN / dtex, and the short fiber has excellent flame retardance and mechanical performance. The method is mild in process condition, green and environment-friendly, and the purpose of high-valued closed-loop recycling of the waste textiles can be achieved.

Description

Technical Field

[0001] This invention relates to the field of recycled polyester staple fiber technology, and in particular to a flame-retardant bio-enzymatic hydrolysis method for recycled polyester staple fiber and its preparation method. Background Technology

[0002] As a key material for achieving a circular economy, the innovation and development of recycled polyester manufacturing processes are crucial for alleviating resource pressure and reducing environmental pollution. Developing efficient recycled polyester technology to transform waste polyester back into high-quality fiber or plastic raw materials is an essential path for the textile and plastics industries to achieve green transformation. Against this backdrop, the preparation of recycled polyester mainly follows two raw material pathways: one is the relatively mature recycling of waste polyester bottles (bottle flakes), and the other is the recycling of waste textiles, which has great potential but presents more challenges. Bottle flake recycling involves multiple processes such as unpacking, sorting, crushing, and washing to transform post-consumer PET bottles into recycled polyester materials specifically for chemical fibers. This type of process is mature and relatively low-cost, successfully transforming waste PET bottles into environmentally friendly fabrics for clothing, home fillings, and automotive interiors, achieving a "bottle-to-fiber" cycle and significantly reducing the use of virgin plastics and the pressure on landfills for waste bottle flakes.

[0003] However, compared to bottle flake recycling, the global recycling rate of polyester textiles remains extremely low. China, as the world's largest producer and consumer of textiles, generates approximately 15 million tons of waste textiles annually, with a recycling rate of less than 15%. Meanwhile, polyester fiber accounts for more than half of global fiber production, but the overall polyester recycling rate is only about 11% of the total polyester output. This huge production volume coupled with the extremely low recycling rate creates a sharp contradiction, implying that recovering polyester from waste textiles has enormous resource potential and environmental value. Currently, the mainstream recycling methods are divided into physical and chemical methods. Physical methods mainly use mechanical means to crush, melt, and respin waste textiles, but this method requires high purity raw materials, is difficult to process blended fabrics, and the fiber quality deteriorates after multiple cycles. Chemical methods decompose polyester (such as PET) into monomers (such as terephthalic acid and ethylene glycol) through depolymerization reactions, and then repolymerize them into resins with quality comparable to virgin materials. China already has chemically recycled polyester production lines with a capacity of tens of thousands of tons capable of depolymerizing and reducing waste polyester to DMT monomers with a purity of 99.99%. Although chemical methods can achieve high-quality closed-loop recycling, they typically require harsh conditions of high temperature and pressure, resulting in high energy consumption, large equipment investment, and limited tolerance to complex dyes and additives. This leads to high overall recycling costs, hindering large-scale industrial application. To address this, the inventors have provided a flame-retardant bio-enzymatic hydrolysis method for recycling polyester staple fibers. Summary of the Invention

[0004] To address the problems of high energy consumption, large equipment investment, and limited tolerance to complex dyes and additives in existing chemical methods, which result in high overall recycling costs and restrict their large-scale industrial application, this invention provides a flame-retardant bio-enzymatic hydrolysis method for regenerating polyester staple fibers.

[0005] The present invention provides a flame-retardant bio-enzymatic hydrolysis method for regenerating polyester staple fiber, which is achieved through the following technical solution: A flame-retardant bio-enzymatic hydrolysis method for regenerating polyester staple fibers includes the following steps: Step 1: The waste textiles are sorted, washed, and crushed to make friction material; Step two: The friction material is degraded by biological enzymes at 30-80℃ and pH 5-9 to form rPTA and rEG; Step 3: rPTA and rEG are re-esterified and polycondensed to obtain bio-enzymatically regenerated polyester chips; Step 4, preparation of flame retardant masterbatch: Weigh 40-70 parts by weight of dried bio-enzymatically hydrolyzed recycled polyester chips and mix them evenly with 30-60 parts by weight of flame retardant. Then add the mixture to a twin-screw extruder, melt extrude, cool, granulate, sieve, and dry. The moisture content of the obtained flame retardant masterbatch is ≤200ppm. Step 5: The bio-enzymatically regenerated polyester chips and flame-retardant masterbatch are dried, melt-blended and spun to obtain nascent yarn. The obtained nascent yarn is then bundled, stretched, tensioned and heat-set, crimped, oiled and relaxed and heat-set to obtain flame-retardant bio-enzymatically regenerated polyester staple fiber.

[0006] Unlike traditional physical melting recycling (which easily leads to molecular chain degradation and performance decline) or strong chemical alcoholysis (which is harsh and prone to pollution), the bio-enzymatic hydrolysis method achieves selective depolymerization and closed-loop recycling of waste polyester textiles. The principle is to utilize the high substrate specificity and mild catalytic properties of PET hydrolytic enzymes (such as PETase, LCC, LCCICCG, FastPETase, MHETase, HRC-PCEST, or one or more of these). These PET hydrolytic enzymes can precisely cleave the ester bonds in the polyethylene terephthalate (PET) macromolecular chain under relatively mild conditions (30-80℃, pH 5-9), depolymerizing it into original monomers or oligomers such as terephthalic acid (TPA) and ethylene glycol (EG). The innovation of this process lies in: 1) High efficiency and selectivity: The enzyme catalysis is highly specific with few side reactions, which can efficiently process complex waste materials, including blended fabrics, and has little interference with natural fiber components such as cotton and wool, making it easy to purify later; 2) Closed-loop recycling: The degradation products are high-purity monomers that can be directly used for re-esterification and polycondensation to produce bio-enzymatically regenerated polyester chips (intrinsic viscosity 0.60-0.72 dL / g) with quality comparable to petroleum-based polyester, truly realizing molecular-level closed-loop regeneration from fiber to fiber, which greatly improves the recycling efficiency of resources.

[0007] Furthermore, to address the flammability hazards of bio-enzymatically recycled polyester chips in applications such as electronics, home furnishings, and protective equipment, this invention employs a key technological approach—melt blending of functional masterbatches—to achieve flame-retardant functionalization. The principle is as follows: A high-concentration, highly dispersible flame-retardant masterbatch is prepared by pre-extruding a highly efficient flame retardant agent (such as one or more of CEPPA, MCA, DDP, hexagonal boron nitride, aminosilane coupling agent KH550, and cage-type polysilsesquioxane POSS) with a bio-enzymatically recycled polyester chip carrier through melt extrusion. During subsequent spinning, the masterbatch and the bio-enzymatically recycled polyester chip matrix are melt-blended at a scientific ratio (1-20:80-99). The advantages of the above design are: 1) Uniform dispersion and interfacial compatibility: The masterbatch preparation process allows the flame retardant to be pre-dispersed in the bio-enzymatic hydrolysis recycled polyester chip carrier, reducing the risk of spinning breakage or performance degradation caused by agglomeration when added directly, and ensuring the uniform distribution of flame retardant components in the final fiber; 2) High efficiency and durability: By optimizing the synergistic flame retardant system, it can promote char formation, isolate oxygen, and inhibit the generation of combustible gases when the fiber burns, thereby giving the fiber an extremely high flame retardant rating (LOI≥30%) and long-lasting function; 3) Process compatibility: The masterbatch form is easy to meter and add, and can be seamlessly integrated with existing spinning production lines, making it easy to achieve industrialization.

[0008] Preferably, the process parameters for melt blending spinning in step five include: screw zone 1 temperature 280℃-290℃, zone 2 temperature 285℃-295℃, zone 3 temperature 290℃-300℃, zone 4 temperature 295℃-305℃, zone 5 temperature 290℃-300℃, zone 6 temperature 285℃-295℃, spinning box temperature 290-300℃, pump supply 700-950g / min, pressure difference between the inlet and outlet air of the ring blower 550-750Pa, and winding speed 950-1150m / min.

[0009] Preferably, the process parameters for stretching in step five are as follows: oil bath temperature of 60-70℃ in the first-stage oil bath stretching, temperature of 100-130℃ in the second-stage stretching, stretching ratio of 2.9-4.2 times, and temperature of 165-185℃ for tension heat setting.

[0010] Given the differences between bio-enzymatically hydrolyzed recycled polyester chips and virgin chips in terms of thermal history and molecular weight distribution, this invention designs a refined spinning and post-processing technology. The principle is to regulate the fiber's microstructure through multi-zone precise temperature control, multi-stage drafting, and heat setting to balance the potential impact of flame retardant introduction on spinnability and mechanical properties. Specifically: ① Melt blending spinning: The screw extruder is set with multi-stage gradient heating (280-305℃) to ensure that the bio-enzymatically hydrolyzed recycled polyester chips and flame retardant masterbatch are fully melted and uniformly mixed without thermal degradation; precise control of the spinning box temperature, ring blowing pressure, and winding speed ensures uniform quality of the nascent yarn. ② Multi-stage drafting and setting: A multi-stage process combining oil bath drafting and hot roller drafting is adopted. Within a temperature range of 60-185℃, through a drafting ratio of 2.9-4.2 times, the fiber macromolecular chains are ordered and crystallized, thereby obtaining excellent mechanical properties (breaking strength 4.0-5.5 cN / dtex). The subsequent tension heat setting (165-185℃) eliminates internal stress and stabilizes fiber morphology (curl number, crimp rate) and dimensional stability.

[0011] In summary, this invention obtains rPTA and rEG through a bio-enzymatic hydrolysis method. After further esterification and polycondensation of rPTA and rEG, bio-enzymatically hydrolyzed recycled polyester chips with a viscosity of 0.72 dL / g and a melting point of 270℃ are obtained. The difference between the bio-enzymatically hydrolyzed recycled polyester chips and petroleum-based polyester chips lies in the relatively higher viscosity and wider molecular weight distribution of the bio-enzymatically hydrolyzed recycled polyester chips, making them unsuitable for the short fiber production process of petroleum-based polyester chips. This invention proposes a new bio-enzymatic hydrolysis process for producing recycled polyester short fibers. The short fibers prepared using this process have an oxygen index ≥30%, a linear density of 1.11-16.67 dtex, and a breaking strength of 4.0-5.5 cN / dtex, exhibiting both excellent flame retardancy and mechanical properties. Furthermore, the process conditions of this invention are mild and environmentally friendly, achieving the goal of high-value closed-loop recycling of waste textiles, reducing carbon emissions, and conforming to the green concept of sustainable development.

[0012] Preferably, the bioenzyme is one or more of PETase, LCC, LCCICCG, FastPETase, MHETase, and HRC-PCEST.

[0013] Preferably, the flame-retardant filler is one or more of CEPPA, MCA, DDP, hexagonal boron nitride, aminosilane coupling agent KH550, and cage-type polysilsesquioxane POSS.

[0014] Preferably, the mass ratio of the enzymatically regenerated polyester chips to the flame retardant masterbatch is (80-99):(1-20).

[0015] Preferably, the viscosity of the bio-enzymatically regenerated polyester chips is 0.60-0.72 dL / g.

[0016] Preferably, the melting point of the bio-enzymatically regenerated polyester chips is 250-275℃.

[0017] Preferably, the specific method for preparing bio-enzymatically recycled polyester chips by re-esterifying and polycondensing rPTA and rEG in step three is as follows: rPTA and rEG are added to an esterification reactor at a molar ratio of 1:(1.1-1.2), and the esterification reaction is carried out under nitrogen protection at 240-260°C and 0.1-0.3 MPa. By-product water is discharged until the esterification rate is >95%, generating diethyl terephthalate (BHET) and its oligomers. Subsequently, the material is subjected to a polycondensation reaction at 270-285°C and <100 Pa. By removing ethylene glycol, the molecular chain is lengthened to an intrinsic viscosity of 0.60-0.72 dL / g. After the reaction, the melt is extruded, water-cooled, and pelletized to obtain recycled polyester chips.

[0018] The flame-retardant bio-enzymatic regenerated polyester staple fiber prepared by a method for producing flame-retardant bio-enzymatic regenerated polyester staple fiber has flame-retardant properties, an oxygen index (LOI) ≥ 30%, a linear density of 1.11 dtex to 16.67 dtex, a linear density deviation rate of -6% to +6%, a fiber breaking strength of 4.0 cN / dtex to 5.5 cN / dtex, a breaking elongation of 23.2% to 42.5%, an extra-long fiber content of 0 mg / 100g to 3 mg / 100g, a defect content of 3 mg / 100g to 30 mg / 100g, a crimp count of 9 / 25mm to 14 / 25mm, and a crimp rate of 10% to 16%.

[0019] Based on this, the present invention prepares a flame-retardant bio-enzymatically recycled polyester staple fiber by employing a bio-enzymatic hydrolysis method to prepare recycled polyester and controlling the amount of flame-retardant masterbatch added. The fiber breaking strength, defects, and LOI are investigated by controlling technical parameters such as spinning temperature, pump supply, spinning cooling air conditions, spinning speed, drawing temperature, drawing ratio, and heat setting temperature.

[0020] In summary, the present invention has the following advantages: 1. This invention uses specific biological enzymes to depolymerize under mild conditions. Compared with traditional strong acid, strong alkali or high temperature alcoholysis methods, it significantly reduces energy consumption from the source, avoids the use and emission of harmful chemicals, and the process itself is greener. It truly realizes a high-quality "fiber to fiber" closed loop, reducing the consumption of petroleum resources and waste landfill.

[0021] 2. This invention solves the industry problem that directly adding flame retardants to recycled polyester matrix can easily lead to uneven dispersion, spinning breakage, and performance degradation. It makes it possible to produce high-value-added functional high-end fibers using low-cost waste raw materials, and significantly enhances the economic competitiveness of recycled textiles. Detailed Implementation

[0022] To further understand the inventiveness and technical advancements of this invention, the preferred embodiments of this invention will be discussed in detail below with reference to examples and comparative examples.

[0023] Example 1: A flame-retardant bio-enzymatic hydrolysis method for regenerating polyester staple fiber, comprising the following steps: Step 1: The waste textiles are sorted, washed, and crushed to make friction material; Step 2: The friction material is degraded by PETase and MHETase at 40℃ and pH 7 to form rPTA and rEG. The mass ratio of PETase to MHETase is 1:1, and the total mass of PETase and MHETase is 8.0 ppm of the total mass of the friction material. Step 3: rPTA and rEG are added to the esterification reactor at a molar ratio of 1:1.20. The esterification reaction is carried out at 240°C and 0.15MPa for 4 hours under nitrogen protection. By-product water is discharged until the esterification rate is >95%, generating diethyl terephthalate (BHET) and its oligomers. The material is then subjected to a polycondensation reaction at 270°C and <100Pa for 5 hours. By removing ethylene glycol, the molecular chain grows to an intrinsic viscosity of 0.72dL / g. After the reaction, the melt is extruded, water-cooled, and pelletized to obtain recycled polyester chips with a melting point of 270°C. The obtained recycled polyester chips are dried at 80°C for 2 hours, then heated to 120°C, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuum is continued to reach a gauge pressure of 0.5 bar, and then dried for 4 hours. The moisture content of the dried recycled polyester chips is 150ppm. Step 4, Preparation of flame retardant masterbatch: Weigh 50 parts by weight of dried bio-enzymatically hydrolyzed recycled polyester chips, 25 parts by weight of 2-carboxyethylphenyl hypophosphite (CEPPA), and 25 parts by weight of melamine cyanurate (MCA), mix them evenly, and then add them to a twin-screw extruder for extrusion granulation. The temperature of zone 1 is 290℃, zone 2 is 295℃, zone 3 is 300℃, zone 4 is 305℃, zone 5 is 305℃, and zone 6 is 300℃. The resulting flame retardant masterbatch is dried at 80℃ for 2 hours, then heated to 120℃, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuuming is continued until the gauge pressure reaches 0.5 bar, and then dried for 4 hours. The moisture content of the dried flame retardant masterbatch is 135 ppm. Step 5: Bio-enzymatically recycled polyester chips and flame-retardant masterbatch are mixed evenly at a mass ratio of 95:5 and dried at 135℃ for 4.0 hours. The resulting material is then melt-blended and spun in a twin-screw extruder. The melt-blending spinning process parameters are: screw zone 1 temperature 290℃, zone 2 temperature 295℃, zone 3 temperature 300℃, zone 4 temperature 305℃, zone 5 temperature 300℃, zone 6 temperature 295℃, spinning box temperature 300℃, pump feed rate 996 g / min, pressure difference between the inlet and outlet air of the ring blower 750 Pa, and winding speed 10... At a speed of 50 m / min, flame-retardant bio-enzymatically recycled polyester filaments were bundled, drawn, subjected to tension heat setting, crimped, oiled, and relaxed heat setting. The drawing process parameters were: primary oil bath temperature 65℃, secondary drawing temperature 100℃, and a draw ratio of 3.2. The tension heat setting temperature was 180℃. The crimping parameters were: main pressure 0.36 MPa and back pressure 0.18 MPa. The oil content of the polyester filaments after oiling was 0.25%. The relaxation heat setting parameters were: temperature 160℃ and time 30 min to obtain flame-retardant bio-enzymatically recycled polyester staple fibers.

[0024] Intrinsic viscosity of recycled polyester chips: tested according to SN / T 1015-2001 standard.

[0025] Melting point of recycled polyester chips: tested according to JJG 701-2008 standard.

[0026] Linear density and extra-long fiber content: determined in accordance with GB / T 14335-2008 standard.

[0027] Breaking strength and elongation at break: measured in accordance with GB / T 14337-2022 standard, with a tensile speed of 30 mm / min.

[0028] Defect content: determined in accordance with GB / T 14339-2008 standard.

[0029] Curl count and curl rate: determined in accordance with GB / T 14338-2022 standard.

[0030] Oxygen Index (LOI): Determined according to FZ / T 50016-2023 standard.

[0031] The flame-retardant bio-enzymatic recycled polyester staple fiber obtained in Example 1 has a linear density of 2.22 dtex, a linear density deviation rate of -1.4%, a fiber breaking strength of 5.3 cN / dtex, a breaking elongation of 26.3%, an extra-long fiber content of 0 mg / 100g, a defect content of 2.6 mg / 100g, a crimp number of 10.3 / 25mm, a crimp rate of 10.5%, and an oxygen index (LOI) of 33.2%.

[0032] Comparative Example 1 is an example of a method for preparing flame-retardant recycled polyester fiber disclosed in patent application CN116555940. The difference between Comparative Example 1 and Example 1 is as follows: S1: Waste polyester bottle flakes were first dried in an oven at 120°C for 2.5 hours, then dried in a vacuum oven at 150°C for 5 hours before being added to a screw extruder for melting. EG was added during the feed, and the polyester melt produced by the waste polyester bottle flakes was thoroughly mixed with EG under mechanical stirring of the screw. The mass ratio of EG to PET bottle flakes was 0.01:100. The melting temperature of the screw extruder was maintained at 190°C, the micro-alcoholization time was maintained at 15 minutes, small molecule substances were removed by vacuuming, and CEPPA was added at the feed inlet. The mass ratio of CEPPA to PET bottle flakes is 0.05:100. The screw extruder temperature is maintained at 270℃. h-BN is added to the recycled polyester melt, and the mass ratio of h-BN to PET bottle flakes is 1:20. The mixture is then extruded and granulated to obtain flame-retardant recycled polyester masterbatch. S2: The flame-retardant recycled polyester masterbatch prepared above is melt-blended and spun with waste polyester bottle flakes. The mass ratio of recycled polyester masterbatch to PET bottle flakes is 1:20. The mixture is extruded through a spinneret assembly, cooled by a ring blower, bundled and oiled, drawn, heat-set, and wound to prepare flame-retardant recycled polyester fibers. The melt-blending spinning temperature is 280℃, the ring blower temperature is 27℃, and the ring blower velocity is 0.4 m / min. The draw ratio is 3.0 times, the draw temperature is 155℃, the heat-setting temperature is 145℃, the winding speed is 4500 m / min, and the limiting oxygen index of the resulting fiber is 30%.

[0033] Compared to Example 1, Comparative Example 1 uses a chemical method to produce recycled polyester, which is milder than the strong acid and strong alkali method, but requires certain temperature and pressure. In contrast, the bio-enzymatic hydrolysis method treats waste textiles with more complex compositions. Under normal temperature and pressure, depolymerization is catalyzed by specific enzymes, resulting in milder and greener conditions, and better tolerance to blended fabrics. This achieves a closed-loop cycle from waste textiles to high-quality functional fibers, representing a more advanced technology with higher added value, and particularly highlighting the characteristics of green biomanufacturing and resource recycling.

[0034] Comparative Example 2 discloses a method for preparing flame-retardant recycled polyester staple fiber, as reported in patent application CN102877156. The method involves high-speed mixing of a phosphorus-based halogen-free flame retardant complex with polyester powder to obtain a high-phosphorus-content flame-retardant masterbatch. The masterbatch is then melted and filtered with recycled polyester raw materials before spinning. Following drawing, cutting, and packaging, the resulting recycled flame-retardant polyester is obtained. The flame-retardant recycled polyester staple fiber described in Comparative Example 2, using a halogen-free, high-phosphorus-content flame-retardant masterbatch, exhibits an oxygen index of 31.8% and a fiber defect content ≤150mg / 100g.

[0035] A comparison of Example 1 and Comparative Example 2 shows that using a halogen-free flame retardant with high phosphorus content can achieve a higher oxygen index value for the fiber, but the defect content of the fiber is ≤150mg / 100g, while the defect content in Example 1 is only 2.6mg / 100g. In subsequent spinning applications, higher defects will cause a decrease in yarn strength and an increase in yarn breakage, thereby affecting weaving efficiency and fabric appearance.

[0036] The difference between Example 2 and Example 1 is that in step two, the friction material is degraded by the combined action of PETase enzyme and MHETase enzyme at 40°C and pH 8 to form rPTA and rEG; the mass ratio of PETase enzyme to MHETase enzyme is 1:1, and the total mass of PETase enzyme and MHETase enzyme is 8.0 ppm of the total mass of the friction material. Step 3: rPTA and rEG are added to the esterification reactor at a molar ratio of 1:1.12. The esterification reaction is carried out at 240°C and 0.15MPa for 4 hours under nitrogen protection. By-product water is discharged until the esterification rate is >95%, generating diethyl terephthalate (BHET) and its oligomers. The material is then subjected to a polycondensation reaction at 270°C and <100Pa for 5 hours. By removing ethylene glycol, the molecular chain grows to an intrinsic viscosity of 0.64dL / g. After the reaction, the melt is extruded, water-cooled, and pelletized to obtain recycled polyester chips with a melting point of 255°C. The obtained recycled polyester chips are dried at 80°C for 2 hours, then heated to 120°C, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuum is continued to reach a gauge pressure of 0.5 bar, and then dried for 4 hours. The moisture content of the dried recycled polyester chips is 145ppm. Step 4, Preparation of flame retardant masterbatch: Weigh 60 parts by weight of dried bio-enzymatically hydrolyzed recycled polyester chips, 20 parts by weight of 2-carboxyethylphenyl hypophosphite (CEPPA), and 20 parts by weight of melamine cyanurate (MCA), mix them evenly, and then add them to a twin-screw extruder for extrusion granulation. The temperature of zone 1 is 290℃, zone 2 is 295℃, zone 3 is 300℃, zone 4 is 305℃, zone 5 is 305℃, and zone 6 is 300℃. The resulting flame retardant masterbatch is dried at 80℃ for 2 hours, then heated to 120℃, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuuming is continued until the gauge pressure reaches 0.5 bar, and then dried for 4 hours. The moisture content of the dried flame retardant masterbatch is 130 ppm. Step 5: Bio-enzymatically recycled polyester chips and flame-retardant masterbatch are mixed evenly at a mass ratio of 95:5 and dried at 135℃ for 4.0 hours. The resulting material is then melt-blended and spun in a twin-screw extruder. The melt-blending spinning process parameters are: screw zone 1 temperature 285℃, zone 2 temperature 290℃, zone 3 temperature 295℃, zone 4 temperature 300℃, zone 5 temperature 295℃, zone 6 temperature 290℃, spinning box temperature 295℃, and pump flow rate 703... The flame-retardant bio-enzymatic regenerated polyester filaments were bundled, drawn, tensioned heat-set, crimped, oiled, and relaxed heat-set using a pressure difference of 500 Pa between the inlet and outlet air of the ring blower and a winding speed of 1050 m / min. The process parameters for drawing were: primary oil bath temperature 65℃, secondary drawing temperature 100℃, and draw ratio 3.77; tensioned heat-set temperature 180℃; crimping parameters were: main pressure 0.36 MPa, back pressure 0.18 MPa; oil content of polyester filaments after oiling was 0.25%; relaxation heat-set parameters were: temperature 160℃, time 30 min.

[0037] The flame-retardant bio-enzymatic recycled polyester staple fiber obtained in Example 2 has a linear density of 1.56 dtex, a linear density deviation rate of 0%, a breaking strength of 5.2 cN / dtex, a breaking elongation of 28.2%, an extra-long fiber content of 0 mg / 100g, a defect content of 2.2 mg / 100g, a crimp count of 10.8 / 25mm, a crimp rate of 10.1%, and a limiting oxygen content (LOI) of 33.0%.

[0038] The difference between Example 3 and Example 1 is that in step two, the friction material is degraded by the combined action of PETase enzyme and MHETase enzyme at 40°C and pH 6 to form rPTA and rEG; the mass ratio of PETase enzyme to MHETase enzyme is 1:1, and the total mass of PETase enzyme and MHETase enzyme is 8.0 ppm of the total mass of the friction material. Step 3: rPTA and rEG are added to the esterification reactor at a molar ratio of 1:1.11. The esterification reaction is carried out at 240°C and 0.15MPa for 4 hours under nitrogen protection. By-product water is discharged until the esterification rate is >95%, generating diethyl terephthalate (BHET) and its oligomers. The material is then subjected to a polycondensation reaction at 270°C and <100Pa for 5 hours. By removing ethylene glycol, the molecular chain grows to an intrinsic viscosity of 0.60 dL / g. After the reaction, the melt is extruded, water-cooled, and pelletized to obtain recycled polyester chips with a melting point of 250°C. The obtained recycled polyester chips are dried at 80°C for 2 hours, then heated to 120°C, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuum is continued to reach a gauge pressure of 0.5 bar, and then dried for 4 hours. The moisture content of the dried recycled polyester chips is 155 ppm. Step 4, Preparation of flame retardant masterbatch: Weigh 70 parts by weight of dried bio-enzymatically hydrolyzed recycled polyester chips, 15 parts by weight of 2-carboxyethylphenyl hypophosphite (CEPPA), and 15 parts by weight of melamine cyanurate (MCA), mix them evenly, and then add them to a twin-screw extruder for extrusion granulation. The temperature of zone 1 is 290℃, zone 2 is 295℃, zone 3 is 300℃, zone 4 is 305℃, zone 5 is 305℃, and zone 6 is 300℃. The resulting flame retardant masterbatch is dried at 80℃ for 2 hours, then heated to 120℃, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuumed again to a gauge pressure of 0.5 bar, and dried for 4 hours. The moisture content of the dried flame retardant masterbatch is 150 ppm. Step 5: Bio-enzymatically recycled polyester chips and flame-retardant masterbatch are mixed evenly at a mass ratio of 95:5 and dried at 135℃ for 4.0 hours. The resulting material is then melt-blended and spun in a twin-screw extruder. The melt-blending spinning process parameters are: screw zone 1 temperature 280℃, zone 2 temperature 285℃, zone 3 temperature 290℃, zone 4 temperature 295℃, zone 5 temperature 290℃, zone 6 temperature 285℃, spinning box temperature 290℃, and pump flow rate 843... The flame-retardant bio-enzymatic regenerated polyester filaments were bundled, drawn, tensioned heat-set, crimped, oiled, and relaxed heat-set using a pressure difference of 680 Pa between the inlet and outlet air of the ring blower and a winding speed of 1050 m / min. The process parameters for drawing were: primary oil bath temperature 65℃, secondary drawing temperature 100℃, and draw ratio 4.2 times; tensioned heat-set temperature 180℃; crimping parameters were: main pressure 0.36 MPa, back pressure 0.18 MPa; oil content of polyester filaments after oiling was 0.25%; relaxation heat-set parameters were: temperature 160℃, time 30 min.

[0039] The flame-retardant bio-enzymatic recycled polyester staple fiber obtained in Example 3 has a linear density of 1.56 dtex, a linear density deviation rate of 0%, a breaking strength of 3.33 dtex, and a linear density deviation rate of 2.1%. The fiber breaking strength is 4.9 cN / dtex, the breaking elongation is 37.5%, the extra-long fiber content is 0 mg / 100g, the defect content is 2.4 mg / 100g, the crimp count is 10.3 / 25mm, the crimp rate is 10.5%, and the limiting oxygen content (LOI) is 32.8%.

[0040] The difference between Example 4 and Example 1 is as follows: In step two, the friction material is degraded by the combined action of HRC enzyme and PCEST enzyme at 75°C and pH 8.5 to form rPTA and rEG; the mass ratio of HRC enzyme to PCEST enzyme is 1:1, and the total mass of HRC enzyme and PCEST enzyme is 100 ppm of the total mass of the friction material. Step 3: rPTA and rEG are added to the esterification reactor at a molar ratio of 1:1.17. The esterification reaction is carried out at 240°C and 0.15MPa for 4 hours under nitrogen protection. By-product water is discharged until the esterification rate is >95%, generating diethyl terephthalate (BHET) and its oligomers. Subsequently, the material is placed in a polycondensation reaction at 270°C and <100Pa for 5 hours. By removing ethylene glycol, the molecular chain grows to an intrinsic viscosity of 0.68dL / g. After the reaction, the melt is extruded, water-cooled, and pelletized to obtain recycled polyester chips with a melting point of 263°C. The obtained recycled polyester chips are dried at 80°C for 2 hours, heated to 120°C, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuum is continued to reach a gauge pressure of 0.5 bar, and dried for 4 hours. The moisture content of the dried recycled polyester chips is 148ppm. Step 4, Preparation of flame retardant masterbatch: Weigh 50 parts by weight of dried bio-enzymatically hydrolyzed recycled polyester chips and 50 parts by weight of 2-carboxyethylphenyl hypophosphite (CEPPA), mix them evenly, and then add them to a twin-screw extruder for extrusion granulation. The temperature of zone 1 is 290℃, zone 2 is 295℃, zone 3 is 300℃, zone 4 is 305℃, zone 5 is 305℃, and zone 6 is 300℃. The resulting flame retardant masterbatch is dried at 80℃ for 2 hours, then heated to 120℃, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuuming is continued until the gauge pressure reaches 0.5 bar, and then dried for 4 hours. The moisture content of the dried flame retardant masterbatch is 150 ppm. Step 5: Bio-enzymatically recycled polyester chips and flame-retardant masterbatch are mixed evenly at a mass ratio of 95:5 and dried at 135℃ for 4.0 hours. The resulting material is then melt-blended and spun in a twin-screw extruder. The melt-blending spinning process parameters are: screw zone 1 temperature 288℃, zone 2 temperature 293℃, zone 3 temperature 298℃, zone 4 temperature 303℃, zone 5 temperature 298℃, zone 6 temperature 293℃, spinning box temperature 298℃, and pump flow rate 763... The flame-retardant bio-enzymatic regenerated polyester filaments were bundled, drawn, tensioned heat-set, crimped, oiled, and relaxed heat-set using a pressure difference of 580 Pa between the inlet and outlet air of the ring blower and a winding speed of 1050 m / min. The process parameters for drawing were: primary oil bath temperature 65℃, secondary drawing temperature 100℃, and draw ratio 4.01 times; tensioned heat-set temperature 180℃; crimping parameters were: main pressure 0.36 MPa, back pressure 0.18 MPa; oil content of polyester filaments after oiling was 0.25%; relaxation heat-set parameters were: temperature 160℃, time 30 min.

[0041] In Example 4, the flame-retardant bio-enzymatic hydrolysis recycled polyester staple fiber had a linear density of 6.67 dtex, a linear density deviation rate of -1.8%, a fiber breaking strength of 4.7 cN / dtex, a breaking elongation of 35.4%, an extra-long fiber content of 0 mg / 100g, a defect content of 2.6 mg / 100g, a crimp count of 10.3 / 25mm, a crimp rate of 10.5%, and a limiting oxygen content (LOI) of 30.7%.

[0042] The difference between Example 5 and Example 1 is that in step two, the friction material is degraded by the combined action of HRC enzyme and PCEST enzyme at 55°C and pH 5 to form rPTA and rEG; the mass ratio of HRC enzyme to PCEST enzyme is 1:1, and the total mass of HRC enzyme and PCEST enzyme is 100 ppm of the total mass of the friction material. Step 3: rPTA and rEG are added to the esterification reactor at a molar ratio of 1:1.14. The esterification reaction is carried out at 240°C and 0.15MPa for 4 hours under nitrogen protection. By-product water is discharged until the esterification rate is >95%, generating diethyl terephthalate (BHET) and its oligomers. The material is then subjected to a polycondensation reaction at 270°C and <100Pa for 5 hours. By removing ethylene glycol, the molecular chain grows to an intrinsic viscosity of 0.65dL / g. After the reaction, the melt is extruded, water-cooled, and pelletized to obtain recycled polyester chips with a melting point of 256°C. The obtained recycled polyester chips are dried at 80°C for 2 hours, then heated to 120°C, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuum is continued to reach a gauge pressure of 0.5 bar, and then dried for 4 hours. The moisture content of the dried recycled polyester chips is 140ppm. Step 4, Preparation of flame retardant masterbatch: Weigh 50 parts by weight of dried bio-enzymatically hydrolyzed recycled polyester chips, 25 parts by weight of 2-carboxyethylphenyl hypophosphite (CEPPA), and 25 parts by weight of melamine cyanurate (MCA), mix them evenly, and then add them to a twin-screw extruder for extrusion granulation. The temperature of zone 1 is 290℃, zone 2 is 295℃, zone 3 is 300℃, zone 4 is 305℃, zone 5 is 305℃, and zone 6 is 300℃. The resulting flame retardant masterbatch is dried at 80℃ for 2 hours, then heated to 120℃, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuuming is continued until the gauge pressure reaches 0.5 bar, and then dried for 4 hours. The moisture content of the dried flame retardant masterbatch is 136 ppm. Step 5: Bio-enzymatically recycled polyester chips and flame-retardant masterbatch are mixed evenly at a mass ratio of 99:1 and dried at 135℃ for 4.0 hours. The resulting material is then melt-blended and spun in a twin-screw extruder. The melt-blending spinning process parameters are: screw zone 1 temperature 285℃, zone 2 temperature 290℃, zone 3 temperature 295℃, zone 4 temperature 300℃, zone 5 temperature 295℃, zone 6 temperature 290℃, spinning box temperature 295℃, and pump flow rate 802... The flame-retardant bio-enzymatic regenerated polyester filaments were bundled, drawn, tensioned heat-set, crimped, oiled, and relaxed heat-set using a pressure difference of 650 Pa between the inlet and outlet air of the ring blower and a winding speed of 1050 m / min. The process parameters for drawing were: primary oil bath temperature 65℃, secondary drawing temperature 100℃, and draw ratio 3.49 times; tensioned heat-set temperature 180℃; crimping parameters were: main pressure 0.36 MPa, back pressure 0.18 MPa; oil content of polyester filaments after oiling was 0.25%; relaxation heat-set parameters were: temperature 160℃, time 30 min to obtain flame-retardant bio-enzymatic regenerated polyester staple fibers.

[0043] In Example 5, the flame-retardant bio-enzymatic hydrolysis recycled polyester staple fiber had a linear density of 11.11 dtex, a linear density deviation rate of 2.2%, a breaking strength of 5.5 cN / dtex, a breaking elongation of 36.3%, an extra-long fiber content of 0 mg / 100g, a defect content of 4.2 mg / 100g, a crimp count of 11.0 / 25mm, a crimp rate of 11.6%, and a limiting oxygen content (LOI) of 30.0%.

[0044] The difference between Example 6 and Example 1 is as follows: In step two, the friction material is degraded by the combined action of HRC enzyme and PCEST enzyme at 65°C and pH 6.5 to form rPTA and rEG; the mass ratio of HRC enzyme to PCEST enzyme is 1:1, and the total mass of HRC enzyme and PCEST enzyme is 100 ppm of the total mass of the friction material. Step 3: rPTA and rEG are added to the esterification reactor at a molar ratio of 1:1.16. The esterification reaction is carried out at 240°C and 0.15MPa for 4 hours under nitrogen protection. By-product water is discharged until the esterification rate is >95%, generating diethyl terephthalate (BHET) and its oligomers. The material is then subjected to a polycondensation reaction at 270°C and <100Pa for 5 hours. By removing ethylene glycol, the molecular chain grows to an intrinsic viscosity of 0.66dL / g. After the reaction, the melt is extruded, water-cooled, and pelletized to obtain recycled polyester chips with a melting point of 260°C. The obtained recycled polyester chips are dried at 80°C for 2 hours, then heated to 120°C, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuum is continued to reach a gauge pressure of 0.5 bar, and then dried for 4 hours. The moisture content of the dried recycled polyester chips is 140ppm. Step 4, Preparation of flame retardant masterbatch: Weigh 50 parts by weight of dried bio-enzymatically hydrolyzed recycled polyester chips, 25 parts by weight of 2-carboxyethylphenyl hypophosphite (CEPPA), and 25 parts by weight of melamine cyanurate (MCA), mix them evenly, and then add them to a twin-screw extruder for extrusion granulation. The temperature of zone 1 is 290℃, zone 2 is 295℃, zone 3 is 300℃, zone 4 is 305℃, zone 5 is 305℃, and zone 6 is 300℃. The resulting flame retardant masterbatch is dried at 80℃ for 2 hours, then heated to 120℃, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuuming is continued until the gauge pressure reaches 0.5 bar, and then dried for 4 hours. The moisture content of the dried flame retardant masterbatch is 136 ppm. Step 5: The bio-enzymatically hydrolyzed recycled polyester chips and flame-retardant masterbatch are mixed evenly at a mass ratio of 91:9 and dried at 135℃ for 4.0 hours. The resulting material is then placed in a twin-screw extruder for melt blending and spinning. The process parameters for melt blending and spinning are as follows: screw zone 1 temperature 285℃, zone 2 temperature 290℃, zone 3 temperature 295℃, zone 4 temperature 300℃, zone 5 temperature 295℃, zone 6 temperature 290℃, spinning box temperature 295℃, pump supply rate 856 g / min, and pressure difference between the inlet and outlet air of the annular blower 690 Pa. The winding speed was 1050 m / min. The flame-retardant bio-enzymatic regenerated polyester nascent filaments were bundled, drawn, tensioned heat set, crimped, oiled, and relaxed heat set. The drawing process parameters were: primary oil bath temperature 65℃, secondary drawing temperature 100℃, and a draw ratio of 3.71. The tensioned heat set temperature was 180℃. The crimping parameters were: main pressure 0.36 MPa and back pressure 0.18 MPa. The oil content of the polyester filaments after oiling was 0.25%. The relaxation heat set parameters were: temperature 160℃ and time 30 min to obtain flame-retardant bio-enzymatic regenerated polyester staple fibers.

[0045] In Example 6, the flame-retardant bio-enzymatic hydrolysis recycled polyester staple fiber had a linear density of 16.67 dtex, a linear density deviation rate of -3.0%, a breaking strength of 4.0 cN / dtex, a breaking elongation of 42.5%, an extra-long fiber content of 0.2 mg / 100g, a defect content of 5.5 mg / 100g, a crimp count of 11.0 / 25mm, a crimp rate of 11.6%, and a limiting oxygen content (LOI) of 33.6%.

[0046] The difference between Example 7 and Example 1 is that in step two, the friction material is degraded by LCC enzyme at 65°C and pH 9.0 to form rPTA and rEG; the mass of LCC enzyme is 0.10 wt% of the total mass of the friction material. Step 3: rPTA and rEG are added to the esterification reactor at a molar ratio of 1:1.13. The esterification reaction is carried out at 240°C and 0.15MPa for 4 hours under nitrogen protection. By-product water is discharged until the esterification rate is >95%, generating diethyl terephthalate (BHET) and its oligomers. The material is then subjected to a polycondensation reaction at 270°C and <100Pa for 5 hours. By removing ethylene glycol, the molecular chain grows to an intrinsic viscosity of 0.63dL / g. After the reaction, the melt is extruded, water-cooled, and pelletized to obtain recycled polyester chips with a melting point of 252°C. The obtained recycled polyester chips are dried at 80°C for 2 hours, then heated to 120°C, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuum is continued to reach a gauge pressure of 0.5 bar, and then dried for 4 hours. The moisture content of the dried recycled polyester chips is 154ppm. Step 4, Preparation of flame retardant masterbatch: Weigh 50 parts by weight of dried bio-enzymatically hydrolyzed recycled polyester chips and 50 parts by weight of melamine cyanurate (MCA), mix them evenly, and then add them to a twin-screw extruder for extrusion granulation. The temperature of zone 1 is 290℃, zone 2 is 295℃, zone 3 is 300℃, zone 4 is 305℃, zone 5 is 305℃, and zone 6 is 300℃. The resulting flame retardant masterbatch is dried at 80℃ for 2 hours, then heated to 120℃, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuuming is continued until the gauge pressure reaches 0.5 bar, and then dried for 4 hours. The moisture content of the dried flame retardant masterbatch is 148 ppm. Step 5: The bio-enzymatically hydrolyzed recycled polyester chips and flame-retardant masterbatch are mixed evenly at a mass ratio of 95:5 and dried at 135℃ for 4.0 hours. The resulting material is then placed in a twin-screw extruder for melt blending and spinning. The process parameters for melt blending and spinning are as follows: screw zone 1 temperature 283℃, zone 2 temperature 288℃, zone 3 temperature 293℃, zone 4 temperature 298℃, zone 5 temperature 293℃, zone 6 temperature 288℃, spinning box temperature 293℃, pump supply rate 996 g / min, and pressure difference between the inlet and outlet air of the annular blower 750 Pa. The winding speed was 1050 m / min. The flame-retardant bio-enzymatic regenerated polyester nascent filaments were bundled, drawn, tensioned heat set, crimped, oiled, and relaxed heat set. The drawing process parameters were: primary oil bath temperature 65℃, secondary drawing temperature 100℃, and a draw ratio of 4.08. The tensioned heat set temperature was 180℃. The crimping parameters were: main pressure 0.36 MPa and back pressure 0.18 MPa. The oil content of the polyester filaments after oiling was 0.25%. The relaxation heat set parameters were: temperature 160℃ and time 30 min to obtain flame-retardant bio-enzymatic regenerated polyester staple fibers.

[0047] In Example 7, the flame-retardant bio-enzymatic hydrolysis recycled polyester staple fiber had a linear density of 2.22 dtex, a linear density deviation rate of 1.8%, a breaking strength of 5.0 cN / dtex, a breaking elongation of 36.0%, an extra-long fiber content of 0 mg / 100g, a defect content of 2.6 mg / 100g, a crimp count of 10.6 / 25mm, a crimp rate of 10.4%, and a limiting oxygen content (LOI) of 30.2%.

[0048] The difference between Example 8 and Example 1 is as follows: In step two, the friction material is degraded by LCCIG enzyme at 62°C and pH 8.0 to form rPTA and rEG; the mass of LCCIG enzyme is 0.20 wt% of the total mass of the friction material. Step 3: rPTA and rEG are added to the esterification reactor at a molar ratio of 1:1.17. The esterification reaction is carried out at 240°C and 0.15MPa for 4 hours under nitrogen protection. By-product water is discharged until the esterification rate is >95%, generating diethyl terephthalate (BHET) and its oligomers. The material is then subjected to a polycondensation reaction at 270°C and <100Pa for 5 hours. By removing ethylene glycol, the molecular chain grows to an intrinsic viscosity of 0.66dL / g. After the reaction, the melt is extruded, water-cooled, and pelletized to obtain recycled polyester chips with a melting point of 261°C. The obtained recycled polyester chips are dried at 80°C for 2 hours, then heated to 120°C, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuum is continued to reach a gauge pressure of 0.5 bar, and then dried for 4 hours. The moisture content of the dried recycled polyester chips is 145ppm. Step 4, Preparation of flame retardant masterbatch: Weigh 50 parts by weight of dried bio-enzymatically hydrolyzed recycled polyester chips and 50 parts by weight of melamine cyanurate (MCA), mix them evenly, and then add them to a twin-screw extruder for extrusion granulation. The temperature of zone 1 is 290℃, zone 2 is 295℃, zone 3 is 300℃, zone 4 is 305℃, zone 5 is 305℃, and zone 6 is 300℃. The resulting flame retardant masterbatch is dried at 80℃ for 2 hours, then heated to 120℃, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuuming is continued until the gauge pressure reaches 0.5 bar, and then dried for 4 hours. The moisture content of the dried flame retardant masterbatch is 142 ppm. Step 5: The bio-enzymatically hydrolyzed recycled polyester chips and flame-retardant masterbatch are mixed evenly at a mass ratio of 95:5 and dried at 135℃ for 4.0 hours. The resulting material is then placed in a twin-screw extruder for melt blending and spinning. The process parameters for melt blending and spinning are as follows: screw zone 1 temperature 285℃, zone 2 temperature 290℃, zone 3 temperature 295℃, zone 4 temperature 300℃, zone 5 temperature 295℃, zone 6 temperature 290℃, spinning box temperature 295℃, pump supply rate 996 g / min, and the pressure difference between the inlet and outlet air of the annular blower 750 Pa. The winding speed was 1050 m / min. The flame-retardant bio-enzymatic regenerated polyester nascent filaments were bundled, drawn, tensioned heat-set, crimped, oiled, and relaxed heat-set. The drawing process parameters were: primary oil bath temperature 65℃, secondary drawing temperature 100℃, and a draw ratio of 3.98. The tensioned heat-set temperature was 180℃. The crimping parameters were: main pressure 0.36 MPa and back pressure 0.18 MPa. The oil content of the polyester filaments after oiling was 0.25%. The relaxation heat-set parameters were: temperature 160℃ and time 30 min to obtain flame-retardant bio-enzymatic regenerated polyester staple fibers.

[0049] In Example 8, the flame-retardant bio-enzymatic hydrolysis recycled polyester staple fiber had a linear density of 2.22 dtex, a linear density deviation rate of 1.7%, a breaking strength of 5.2 cN / dtex, a breaking elongation of 28.1%, an extra-long fiber content of 0.3 mg / 100g, a defect content of 3.0 mg / 100g, a crimp count of 10.6 / 25mm, a crimp rate of 10.4%, and a limiting oxygen content (LOI) of 30.4%.

[0050] The difference between Example 9 and Example 1 is as follows: In step two, the friction material is degraded by LCCIG enzyme at 80°C and pH 7 to form rPTA and rEG; the mass of LCCIG enzyme is 0.20 wt% of the total mass of the friction material. Step 3: rPTA and rEG are added to the esterification reactor at a molar ratio of 1:1.145. The esterification reaction is carried out at 240°C and 0.15MPa for 4 hours under nitrogen protection. By-product water is discharged until the esterification rate is >95%, generating diethyl terephthalate (BHET) and its oligomers. The material is then subjected to a polycondensation reaction at 270°C and <100Pa for 5 hours. By removing ethylene glycol, the molecular chain grows to an intrinsic viscosity of 0.64dL / g. After the reaction, the melt is extruded, water-cooled, and pelletized to obtain recycled polyester chips with a melting point of 255°C. The obtained recycled polyester chips are dried at 80°C for 2 hours, then heated to 120°C, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuum is continued to reach a gauge pressure of 0.5 bar, and then dried for 4 hours. The moisture content of the dried recycled polyester chips is 145ppm. Step 4, Preparation of flame retardant masterbatch: Weigh 50 parts by weight of dried bio-enzymatically hydrolyzed recycled polyester chips, 25 parts by weight of flame retardant DDP, and 25 parts by weight of melamine cyanurate MCA, mix them evenly, and add them to a twin-screw extruder for extrusion granulation. The temperature of zone 1 is 290℃, zone 2 is 295℃, zone 3 is 300℃, zone 4 is 305℃, zone 5 is 305℃, and zone 6 is 300℃. The obtained flame retardant masterbatch is dried at 80℃ for 2 hours, then heated to 120℃, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuumed to a gauge pressure of 0.5 bar, and dried for 4 hours. The moisture content of the dried flame retardant masterbatch is 145 ppm. Step 5: The bio-enzymatically hydrolyzed recycled polyester chips and flame-retardant masterbatch are mixed evenly at a mass ratio of 95:5 and dried at 135℃ for 4.0 hours. The resulting material is then placed in a twin-screw extruder for melt blending and spinning. The process parameters for melt blending and spinning are as follows: screw zone 1 temperature 285℃, zone 2 temperature 290℃, zone 3 temperature 295℃, zone 4 temperature 300℃, zone 5 temperature 295℃, zone 6 temperature 290℃, spinning box temperature 295℃, pump supply rate 996 g / min, and the pressure difference between the inlet and outlet air of the annular blower 750 Pa. The flame-retardant bio-enzymatic regenerated polyester filaments were bundled, drawn, tensioned heat-set, crimped, oiled, and relaxed heat-set at a winding speed of 1050 m / min. The drawing process parameters were: primary oil bath temperature 65℃, secondary drawing temperature 100℃, and a draw ratio of 3.80. The tensioned heat-set temperature was 180℃. The crimping parameters were: main pressure 0.36 MPa and back pressure 0.18 MPa. The oil content of the polyester filaments after oiling was 0.25%. The relaxation heat-set parameters were: temperature 160℃ and time 30 min to obtain flame-retardant bio-enzymatic regenerated polyester staple fibers.

[0051] In Example 9, the flame-retardant bio-enzymatic hydrolysis recycled polyester staple fiber had a linear density of 2.22 dtex, a linear density deviation rate of 1.5%, a breaking strength of 5.2 cN / dtex, a breaking elongation of 28.3%, an extra-long fiber content of 0.1 mg / 100g, a defect content of 2.9 mg / 100g, a crimp count of 10.5 / 25mm, a crimp rate of 9.4%, and a limiting oxygen content (LOI) of 30.8%.

[0052] The difference between Example 10 and Example 1 is that in step two, the friction material is degraded by LCCIG enzyme at 40°C and pH 7 to form rPTA and rEG; the mass of LCCIG enzyme is 0.20 wt% of the total mass of the friction material. Step 3: rPTA and rEG are added to the esterification reactor at a molar ratio of 1:1.13. The esterification reaction is carried out at 240°C and 0.15MPa for 4 hours under nitrogen protection. By-product water is discharged until the esterification rate is >95%, generating diethyl terephthalate (BHET) and its oligomers. The material is then subjected to a polycondensation reaction at 270°C and <100Pa for 5 hours. By removing ethylene glycol, the molecular chain grows to an intrinsic viscosity of 0.62dL / g. After the reaction, the melt is extruded, water-cooled, and pelletized to obtain recycled polyester chips with a melting point of 250°C. The obtained recycled polyester chips are dried at 80°C for 2 hours, then heated to 120°C, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuum is continued to reach a gauge pressure of 0.5 bar, and then dried for 4 hours. The moisture content of the dried recycled polyester chips is 158ppm. Step 4, Preparation of flame retardant masterbatch: Weigh 50 parts by weight of dried bio-enzymatically hydrolyzed recycled polyester chips, 40 parts by weight of melamine cyanurate (MCA), and 10 parts by weight of hexagonal boron nitride, mix them evenly, and add them to a twin-screw extruder for extrusion granulation. The temperature of zone 1 is 290℃, zone 2 is 295℃, zone 3 is 300℃, zone 4 is 305℃, zone 5 is 305℃, and zone 6 is 300℃. The resulting flame retardant masterbatch is dried at 80℃ for 2 hours, then heated to 120℃, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuuming is continued until the gauge pressure reaches 0.5 bar, and then dried for 4 hours. The moisture content of the dried flame retardant masterbatch is 155 ppm. Step 5: The bio-enzymatically hydrolyzed recycled polyester chips and flame-retardant masterbatch are mixed evenly at a mass ratio of 95:5 and dried at 135℃ for 4.0 hours. The resulting material is then placed in a twin-screw extruder for melt blending and spinning. The process parameters for melt blending and spinning are as follows: screw zone 1 temperature 282℃, zone 2 temperature 287℃, zone 3 temperature 292℃, zone 4 temperature 297℃, zone 5 temperature 292℃, zone 6 temperature 287℃, spinning box temperature 292℃, pump supply rate 996 g / min, and pressure difference between the inlet and outlet air of the annular blower 750 Pa. The winding speed was 1050 m / min. The flame-retardant bio-enzymatic regenerated polyester nascent filaments were bundled, drawn, tensioned heat set, crimped, oiled, and relaxed heat set. The drawing process parameters were: primary oil bath temperature 65℃, secondary drawing temperature 100℃, and a draw ratio of 4.18. The tensioned heat set temperature was 180℃. The crimping parameters were: main pressure 0.36 MPa and back pressure 0.18 MPa. The oil content of the polyester filaments after oiling was 0.25%. The relaxation heat set parameters were: temperature 160℃ and time 30 min to obtain flame-retardant bio-enzymatic regenerated polyester staple fibers.

[0053] In Example 10, the flame-retardant bio-enzymatic hydrolysis recycled polyester staple fiber had a linear density of 2.22 dtex, a linear density deviation rate of -1.4%, a breaking strength of 5.2 cN / dtex, a breaking elongation of 27.9%, an extra-long fiber content of 0 mg / 100g, a defect content of 2.7 mg / 100g, a crimp count of 10.5 / 25mm, a crimp rate of 10.4%, and a limiting oxygen content (LOI) of 30.3%.

[0054] The difference between Example 11 and Example 1 is that in step two, the friction material is degraded by FastPETase enzyme at 62°C and pH 7.5 to form rPTA and rEG; the mass of FastPETase enzyme is 0.30 wt% of the total mass of the friction material. Step 3: rPTA and rEG are added to the esterification reactor at a molar ratio of 1:1.16. The esterification reaction is carried out at 240°C and 0.15MPa for 4 hours under nitrogen protection. By-product water is discharged until the esterification rate is >95%, generating diethyl terephthalate (BHET) and its oligomers. The material is then subjected to a polycondensation reaction at 270°C and <100Pa for 5 hours. By removing ethylene glycol, the molecular chain grows to an intrinsic viscosity of 0.66dL / g. After the reaction, the melt is extruded, water-cooled, and pelletized to obtain recycled polyester chips with a melting point of 260°C. The obtained recycled polyester chips are dried at 80°C for 2 hours, then heated to 120°C, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuum is continued to reach a gauge pressure of 0.5 bar, and then dried for 4 hours. The moisture content of the dried recycled polyester chips is 144ppm. Step 4, Preparation of flame retardant masterbatch: Weigh 50 parts by weight of dried bio-enzymatically hydrolyzed recycled polyester chips, 10 parts by weight of KH550 aminosilane coupling agent, and 40 parts by weight of 2-carboxyethylphenyl hypophosphite CEPPA. Mix them evenly and add them to a twin-screw extruder for extrusion granulation. The temperature of zone 1 is 290℃, zone 2 is 295℃, zone 3 is 300℃, zone 4 is 305℃, zone 5 is 305℃, and zone 6 is 300℃. The obtained flame retardant masterbatch is dried at 80℃ for 2 hours, then heated to 120℃, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. Keep the temperature constant, continue to vacuum to a gauge pressure of 0.5 bar, and dry for 4 hours. The moisture content of the dried flame retardant masterbatch is 140 ppm. Step 5: The bio-enzymatically hydrolyzed recycled polyester chips and flame-retardant masterbatch are mixed evenly at a mass ratio of 95:5 and dried at 135℃ for 4.0 hours. The resulting material is then placed in a twin-screw extruder for melt blending and spinning. The process parameters for melt blending and spinning are as follows: screw zone 1 temperature 285℃, zone 2 temperature 290℃, zone 3 temperature 295℃, zone 4 temperature 300℃, zone 5 temperature 295℃, zone 6 temperature 290℃, spinning box temperature 295℃, pump supply rate 996 g / min, and the pressure difference between the inlet and outlet air of the annular blower 750 Pa. The flame-retardant bio-enzymatic regenerated polyester filaments were bundled, drawn, subjected to tension heat setting, crimped, oiled, and relaxed heat setting at a winding speed of 1050 m / min. The drawing process parameters were as follows: primary oil bath temperature 65℃, secondary drawing temperature 100℃, and a draw ratio of 3.42. The tension heat setting temperature was 180℃. The crimping parameters were as follows: main pressure 0.36 MPa and back pressure 0.18 MPa. The oil content of the polyester filaments after oiling was 0.25%. The relaxation heat setting parameters were: temperature 160℃ and time 30 min to obtain flame-retardant bio-enzymatic regenerated polyester staple fibers.

[0055] In Example 11, the flame-retardant bio-enzymatic hydrolysis recycled polyester staple fiber had a linear density of 2.22 dtex, a linear density deviation rate of 2.0%, a breaking strength of 5.3 cN / dtex, a breaking elongation of 26.4%, an extra-long fiber content of 0 mg / 100g, a defect content of 2.6 mg / 100g, a crimp count of 10.9 / 25mm, a crimp rate of 9.8%, and a limiting oxygen content (LOI) of 30.0%.

[0056] The difference between Example 12 and Example 1 is that in step two, the friction material is degraded by MHETase enzyme at 62°C and pH 7.5 to form rPTA and rEG; the mass of MHETase enzyme is 0.10 wt% of the total mass of the friction material. Step 3: rPTA and rEG are added to the esterification reactor at a molar ratio of 1:1.157. The esterification reaction is carried out at 240°C and 0.15MPa for 4 hours under nitrogen protection. By-product water is discharged until the esterification rate is >95%, generating diethyl terephthalate (BHET) and its oligomers. The material is then subjected to a polycondensation reaction at 270°C and <100Pa for 5 hours. By removing ethylene glycol, the molecular chain grows to an intrinsic viscosity of 0.65dL / g. After the reaction, the melt is extruded, water-cooled, and pelletized to obtain recycled polyester chips with a melting point of 257°C. The obtained recycled polyester chips are dried at 80°C for 2 hours, then heated to 120°C, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuum is continued to reach a gauge pressure of 0.5 bar, and then dried for 4 hours. The moisture content of the dried recycled polyester chips is 145ppm. Step 4, Preparation of flame retardant masterbatch: Weigh 50 parts by weight of dried bio-enzymatically hydrolyzed recycled polyester chips, 10 parts by weight of cage-type polysilsesquioxane (POSS), and 40 parts by weight of 2-carboxyethylphenyl hypophosphite (CEPPA), mix them evenly, and add them to a twin-screw extruder for extrusion granulation. The temperature of zone 1 is 290℃, zone 2 is 295℃, zone 3 is 300℃, zone 4 is 305℃, zone 5 is 305℃, and zone 6 is 300℃. The resulting flame retardant masterbatch is dried at 80℃ for 2 hours, then heated to 120℃, vacuumed to a gauge pressure of 0.8 bar, and dried for 8 hours. The temperature is kept constant, vacuuming is continued until the gauge pressure reaches 0.5 bar, and then dried for 4 hours. The moisture content of the dried flame retardant masterbatch is 142 ppm. Step 5: The bio-enzymatically hydrolyzed recycled polyester chips and flame-retardant masterbatch are mixed evenly at a mass ratio of 95:5 and dried at 135℃ for 4.0 hours. The resulting material is then placed in a twin-screw extruder for melt blending and spinning. The process parameters for melt blending and spinning are as follows: screw zone 1 temperature 285℃, zone 2 temperature 290℃, zone 3 temperature 295℃, zone 4 temperature 300℃, zone 5 temperature 295℃, zone 6 temperature 290℃, spinning box temperature 295℃, pump supply rate 996 g / min, and the pressure difference between the inlet and outlet air of the annular blower 750 Pa. The winding speed was 1050 m / min. The flame-retardant bio-enzymatic regenerated polyester nascent filaments were bundled, drawn, tensioned heat set, crimped, oiled, and relaxed heat set. The drawing process parameters were: primary oil bath temperature 65℃, secondary drawing temperature 100℃, and a draw ratio of 3.74. The tensioned heat set temperature was 180℃. The crimping parameters were: main pressure 0.36 MPa and back pressure 0.18 MPa. The oil content of the polyester filaments after oiling was 0.25%. The relaxation heat set parameters were: temperature 160℃ and time 30 min to obtain flame-retardant bio-enzymatic regenerated polyester staple fibers.

[0057] In Example 12, the flame-retardant bio-enzymatic hydrolysis recycled polyester staple fiber had a linear density of 2.22 dtex, a linear density deviation rate of 1.5%, a breaking strength of 5.3 cN / dtex, a breaking elongation of 26.5%, an extra-long fiber content of 0 mg / 100g, a defect content of 3.0 mg / 100g, a crimp count of 10.9 / 25mm, a crimp rate of 10.8%, and a limiting oxygen content (LOI) of 30.0%.

[0058] In summary, this invention utilizes specific bio-enzymes for depolymerization under mild conditions. Compared to traditional methods involving strong acids, strong alkalis, or high-temperature alcoholysis, it significantly reduces energy consumption at the source, avoids the use and emission of harmful chemicals, and is inherently greener. It truly achieves a high-quality "fiber-to-fiber" closed-loop cycle, reducing petroleum resource consumption and waste landfill. Simultaneously, it solves the industry problem of uneven dispersion, spinning breakage, and performance degradation caused by directly adding flame retardants to recycled polyester matrices. This makes it possible to produce high-value-added functional high-end fibers using low-cost waste raw materials, significantly enhancing the economic competitiveness of recycled textiles.

[0059] It should be noted that this specific embodiment is merely an explanation of the technical solution of the present invention and is not intended to limit the present invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A method for preparing flame-retardant bio-enzymatic regenerated polyester staple fiber, characterized in that: Includes the following steps: Step 1: The waste textiles are sorted, washed, and crushed to make friction material; Step two: The friction material is degraded by biological enzymes at 30-80℃ and pH 5-9 to form rPTA and rEG; Step 3: rPTA and rEG are re-esterified and polycondensed to obtain bio-enzymatically regenerated polyester chips; Step 4, preparation of flame retardant masterbatch: Weigh 40-70 parts by weight of dried bio-enzymatically hydrolyzed recycled polyester chips and mix them evenly with 30-60 parts by weight of flame retardant. Then add the mixture to a twin-screw extruder, melt extrude, cool, granulate, sieve, and dry. The moisture content of the obtained flame retardant masterbatch is ≤200ppm. Step 5: The bio-enzymatically regenerated polyester chips and flame-retardant masterbatch are dried, melt-blended and spun to obtain nascent yarn. The obtained nascent yarn is then bundled, stretched, tensioned and heat-set, crimped, oiled and relaxed and heat-set to obtain flame-retardant bio-enzymatically regenerated polyester staple fiber.

2. The flame-retardant bio-enzymatic hydrolysis regenerated polyester staple fiber according to claim 1, characterized in that: The bioenzyme is one or more of PETase, LCC, LCCICCG, FastPETase, MHETase, and HRC-PCEST.

3. The flame-retardant bio-enzymatic hydrolysis regenerated polyester staple fiber according to claim 1, characterized in that: The flame-retardant filler is one or more of CEPPA, MCA, DDP, hexagonal boron nitride, aminosilane coupling agent KH550, and cage-type polysilsesquioxane POSS.

4. The flame-retardant bio-enzymatic hydrolysis method for regenerated polyester staple fiber according to claim 3, characterized in that: The mass ratio of the bio-enzymatically recycled polyester chips to the flame retardant masterbatch is (80-99):(1-20).

5. The flame-retardant bio-enzymatic hydrolysis regenerated polyester staple fiber according to claim 1, characterized in that: The process parameters for melt blending spinning in step five include: screw zone 1 temperature 280℃-290℃, zone 2 temperature 285℃-295℃, zone 3 temperature 290℃-300℃, zone 4 temperature 295℃-305℃, zone 5 temperature 290℃-300℃, zone 6 temperature 285℃-295℃, spinning box temperature 290-300℃, pump supply 700-950g / min, pressure difference between the inlet and outlet air of the ring blower 550-750Pa, and winding speed 950-1150m / min.

6. The flame-retardant bio-enzymatic hydrolysis regenerated polyester staple fiber according to claim 1, characterized in that: The process parameters for stretching in step five are as follows: oil bath temperature of 60-70℃ in the first-stage oil bath stretching, temperature of 100-130℃ in the second-stage stretching, stretching ratio of 2.9-4.2 times, and temperature of tension heat setting of 165-185℃.

7. The flame-retardant bio-enzymatic hydrolysis regenerated polyester staple fiber according to claim 1, characterized in that: The process parameters for curling in step five are as follows: main pressure 0.36±0.02MPa, back pressure 0.18±0.01MPa; the process parameters for relaxation heat setting are as follows: setting temperature 160±5℃, time 30±2min.

8. The flame-retardant bio-enzymatic hydrolysis regenerated polyester staple fiber according to claim 1, characterized in that: The viscosity of the bio-enzymatically regenerated polyester chips is 0.60-0.72 dL / g, and the melting point is 250-275℃.

9. The flame-retardant bio-enzymatic hydrolysis regenerated polyester staple fiber according to claim 8, characterized in that: The specific method for preparing bio-enzymatically recycled polyester chips by re-esterifying and polycondensing rPTA and rEG in step three is as follows: rPTA and rEG are added to an esterification reactor at a molar ratio of 1:(1.1-1.2), and the esterification reaction is carried out under nitrogen protection at 240-260°C and 0.1-0.3MPa. By-product water is discharged until the esterification rate is >95%, generating diethyl terephthalate (BHET) and its oligomers. Subsequently, the material is subjected to polycondensation reaction at 270-285°C and <100 Pa. By removing ethylene glycol, the molecular chain is lengthened to an intrinsic viscosity of 0.60-0.72 dL / g. After the reaction, the melt is extruded, water-cooled, and pelletized to obtain recycled polyester chips.

10. The flame-retardant bio-enzymatic regenerated polyester staple fiber prepared by the method for preparing flame-retardant bio-enzymatic regenerated polyester staple fiber as described in claims 1-9, characterized in that, The flame-retardant bio-enzymatically recycled polyester staple fiber has flame-retardant properties, an oxygen index (LOI) ≥ 30%, a linear density of 1.11 dtex to 16.67 dtex, a linear density deviation rate of -6% to +6%, a fiber breaking strength of 4.0 cN / dtex to 5.5 cN / dtex, a breaking elongation of 23.2% to 42.5%, an extra-long fiber content of 0 mg / 100g to 3 mg / 100g, a defect content of 3 mg / 100g to 30 mg / 100g, a crimp count of 9 / 25mm to 14 / 25mm, and a crimp rate of 10% to 16%.