Preparation method of high-efficiency flame-retardant synthetic fiber

Abstract

The application discloses a kind of preparation methods of high-efficiency flame-retardant synthetic fiber, belong to the technical field of fiber materials.The method uses ordinary PET fiber as core layer matrix, and constructs STF sheath layer on the surface of matrix by post-finishing coating process with ionic liquid-based shear thickening fluid, to form the core-sheath structure of inner soft and outer rigid.The coating solution of the STF sheath layer uses non-flammable imidazole ionic liquid as dispersion medium and main flame retardant, surface-modified nanosilica as shear thickening dispersed phase, organomontmorillonite as flame-retardant synergist, and adds water-based polyurethane crosslinking agent to improve the durability of coating.The application initiates the secondary response protection mechanism of ionic liquid carbonization flame retardant and STF thermal stress triggered thickening wrapping molten droplet, and the prepared synthetic fiber has strong flame-retardant property, no molten droplet, high fiber breaking strength, and still maintains excellent flame-retardant performance after washing 20 times.The method is simple in process, can be directly connected to existing textile production line, and is suitable for industrial large-scale production.

Description

Technical Field

[0001] This invention relates to the field of fiber materials technology, and in particular to a method for preparing high-efficiency flame-retardant synthetic fibers. Background Technology

[0002] Polyester (polyethylene terephthalate, PET), as the largest synthetic fiber, holds an irreplaceable position in home decoration, clothing fabrics, and industrial textiles due to its excellent mechanical strength, dimensional stability, chemical resistance, and low production cost. However, polyester itself is a flammable material with a limiting oxygen index of only about 18-21%, making it highly flammable in air and accompanied by severe molten dripping during combustion. This characteristic makes polyester fabrics a significant safety hazard in fire scenarios: the high-temperature molten dripping from combustion not only exacerbates burns to the wearer but can also ignite other flammable materials in the vicinity, causing the fire to spread rapidly. Therefore, effectively addressing the flammability and molten dripping issues while preserving the inherent excellent properties of polyester has always been a core issue of long-term concern in the field of textile materials science.

[0003] Currently, the technical approaches to impart flame-retardant properties to polyester are mainly divided into two categories: intrinsic flame-retardant modification and finishing.

[0004] Intrinsic flame-retardant modification involves introducing flame-retardant monomers or agents during the polymerization and spinning stages of polyester, embedding the flame-retardant components into the fiber matrix through copolymerization or blending. Copolymerization typically uses diacid or diol monomers containing flame-retardant elements such as phosphorus and nitrogen to participate in esterification-condensation reactions, integrating the flame-retardant structure into the PET macromolecular backbone. Blending involves physically adding small-molecule flame retardants or nano-flame-retardant fillers to the spinning melt. Intrinsically modified flame-retardant polyester offers advantages such as long-lasting flame retardancy and excellent wash resistance; however, its production process is complex and technically demanding. Furthermore, the introduction of comonomers often alters the crystallization behavior and thermal transition temperature of polyester, adversely affecting the fiber's spinnability and final mechanical properties. More importantly, these methods primarily target the ignition and sustained combustion processes of polyester, offering limited effectiveness in suppressing the more significant secondary risk of melt dripping.

[0005] Finishing processes impart flame-retardant properties to polyester fabrics during the finished product stage through impregnation, coating, and other techniques. This method is flexible, simple, and relatively cost-effective, making it suitable for multi-variety, small-batch production scenarios. Traditional flame-retardant finishing systems primarily utilize halogen-antimony oxide synergistic systems and organophosphates. However, halogenated flame retardants release large amounts of toxic and corrosive hydrogen halide gases during combustion, leading to their gradual restriction under international environmental regulations. Furthermore, the bonding between ordinary phosphate flame retardants and the polyester matrix is ​​mostly physical adsorption, lacking strong chemical bonds. This results in a significant decrease in flame-retardant performance after several washes, failing to meet the wash resistance requirements of household textiles. In addition, conventional finishing coatings also fail to fundamentally solve the dripping problem during polyester combustion—under the high temperature of a flame, the polyester matrix softens and flows, causing the surface coating to sag and crack, losing its protective function.

[0006] In recent years, shear-thickening fluids (STFs) have attracted widespread attention in the field of personal protective equipment due to their unique rate / stress response characteristics. Under normal conditions, STFs behave as flowable liquids, but when subjected to high-speed impacts or strong shear stress, their viscosity can increase dramatically by several orders of magnitude instantaneously, even transforming into a near-solid state, thereby absorbing and dissipating large amounts of energy. Based on this principle, researchers have attempted to composite STFs onto the surfaces of high-performance fibers to improve their impact resistance and puncture resistance. However, research on applying STFs to the flame-retardant field of fabrics, especially to address the problem of polyester melt dripping, is still in its early stages.

[0007] In summary, developing a technical solution that combines highly efficient flame retardancy with reliable anti-dripping properties, while also possessing good washability and not significantly damaging the original processing characteristics and wearing comfort of polyester, is a technical bottleneck that urgently needs to be overcome in the field of flame-retardant textile materials. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for preparing highly efficient flame-retardant synthetic fibers.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: This invention first proposes a method for preparing high-efficiency flame-retardant synthetic fibers, comprising the following steps: a. Using 65-70 parts of non-flammable ionic liquid as the dispersion medium, 25-30 parts of surface-modified nano silica as the dispersion phase, and 3-5 parts of organic montmorillonite as the flame retardant synergist, after multi-stage dispersion, 2-3 parts of waterborne polyurethane crosslinking agent are added and mixed evenly to obtain an ionic liquid-based shear thickening fluid. b. Pre-treat PET fibers or fabrics to remove surface oil and sizing agents; c. Immerse the pretreated PET fibers or fabrics in an ionic liquid-based shear thickening fluid, and use a padding process to make the ionic liquid-based shear thickening fluid uniformly adhere to the fiber surface as a coating liquid to construct an STF sheath layer and form a core-sheath structure. d. The impregnated fibers are pre-dried and then cured by baking to obtain high-efficiency flame-retardant synthetic fibers; The surface-modified nano-silica and organo-modified montmorillonite need to be vacuum dried at 120°C for 4 hours, then mixed with 0.5-0.8 parts of anhydrous ethanol dilution of KH-550 silane coupling agent, stirred at 1500 rpm for 20 minutes, and then dried at 105°C for 2 hours to activate.

[0010] Preferably, the ionic liquid is 1-butyl-3-methylimidazolium tetrafluoroborate or 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate; the surface-modified nano-silica is oleophilic, with a particle size of 15-20 nm and a specific surface area of ​​200±20 m². 2 / g; the organomodified montmorillonite is sodium-based modified, with d001 ≥ 2.5nm and particle size ≤ 5μm.

[0011] Preferably, the multi-stage dispersion in step a specifically involves: first, high-speed dispersion at 2000 rpm for 30 minutes, then cyclic sand milling at 1500 rpm 5 times, and finally ultrasonic treatment at 600W power for 20 minutes, followed by vacuum degassing at room temperature for 30 minutes.

[0012] Preferably, the dip rolling process parameters in step c are: roll pressure 0.2-0.3MPa, machine speed 10-15m / min, two dip and two rolling process, and the roll residue rate is controlled between 70-80%.

[0013] Preferably, the pre-baking temperature in step d is 80-100℃ and the time is 4-6 minutes; the baking and curing temperature is 140-160℃ and the time is 2-4 minutes.

[0014] Preferably, step b further includes argon plasma surface treatment of the pretreated PET fibers or fabrics, with a treatment power of 200W, a time of 60 seconds, and a pressure of 20Pa.

[0015] The present invention also proposes a high-efficiency flame-retardant synthetic fiber prepared by the aforementioned preparation method.

[0016] Surface-modified nano-silica achieves anti-dripping through a shear-thickening effect. After modification with KH-550 silane coupling agent, the surface of SiO2 particles changes from hydrophilic to oleophilic, improving compatibility with hydrophobic ionic liquids and preventing aggregation. When heated or impacted, these nanoparticles rapidly aggregate to form clusters, causing a sharp increase in fluid viscosity and instantaneous hardening on the fiber surface, physically preventing dripping.

[0017] Organic montmorillonite (OMMT) migrates to the surface during combustion, and its lamellae act as a physical barrier. At the same time, it can act as a char-forming catalyst, working synergistically with phosphorus-containing flame retardants or ionic liquids to form a denser and stronger intumescent char layer, effectively insulating against heat and oxygen.

[0018] Non-flammable ionic liquids have extremely high thermal stability and act as solvents for SiO2 and OMMT. When burned, they can form dense carbon. Their unique ionic structure provides an ideal medium environment for the dispersion of nanoparticles and the triggering of shear thickening effects.

[0019] Compared with the prior art, the beneficial effects of the present invention are: 1. In existing technologies, whether intrinsic copolymerization or post-treatment coating, the mechanism of action mainly focuses on chemical aspects such as capturing free radicals and promoting char formation, lacking effective mechanical resistance to the physical flow of polyester after it softens due to heat. This invention creatively introduces a shear-thickening fluid system using ionic liquid as the medium and modified nano-silica as the dispersed phase. When exposed to the high temperature of a flame, this intelligent fluid instantly undergoes a violent shear-thickening effect, its viscosity increasing exponentially, transforming directly from a flowable liquid state into a robust, near-solid armor. This phase change behavior triggered by thermal stress provides a powerful physical constraint, tightly binding the softened polyester matrix and preventing the formation and dripping of melt, achieving a leap from passive chemical flame retardancy to active physical confinement.

[0020] 2. Conventional flame-retardant finishing processes primarily rely on physical adsorption, resulting in weak interfacial bonding between the coating and the fiber matrix. After repeated washing, the flame-retardant function rapidly deteriorates. This invention employs a precise chemical bonding system: First, the silane coupling agent KH-550 acts as a molecular bridge, hydrolyzing at one end and condensing with the hydroxyl groups on the surface of nano-SiO2 to complete the organic modification of the inorganic particles; the other end exposes highly active amino groups. During the baking process, the active groups at both ends of the waterborne polyurethane crosslinking agent undergo crosslinking and curing reactions with the polar groups on the plasma-activated PET fiber surface and the amino groups of KH-550, respectively. Thus, a strong covalent bond is formed between the rigid inorganic STF particles and the flexible organic fiber matrix, permanently anchoring the functional coating and achieving a high degree of unity between long-lasting flame retardancy and anti-dripping properties.

[0021] 3. Existing technologies often rely on halogen compounds to achieve flame retardant efficiency, releasing toxic gases during combustion and posing serious secondary environmental and safety risks. This invention uses a non-flammable ionic liquid as the dispersion medium and base liquid, eliminating the inherent combustion hazard of the coating itself. Furthermore, its nitrogen-rich cationic structure exhibits a significant synergistic char-forming effect with organic montmorillonite at high temperatures: the two-dimensional sheets of montmorillonite act as the char layer framework, while the pyrolysis products of the ionic liquid provide the expansion driving force and supplementary carbon source for the char layer. Together, they generate a dense, continuous, and high-strength expanded char layer on the fiber surface. This highly efficient physical barrier can rapidly isolate oxygen and heat, terminating the combustion chain reaction. The entire process is halogen-free, low-smoke, and low-toxicity, aligning with the development trend of green textile chemicals.

[0022] In summary, this invention solves the problem of polyester melt dripping by establishing a novel phase change thickening-physical confinement mechanism and utilizing the intelligent response characteristics of shear-thickening fluids; it anchors the functional coating to the fiber surface by using a chemical bridging network constructed with silane coupling agent and waterborne polyurethane, overcoming the bottleneck of poor water resistance in traditional finishing processes; at the same time, it leverages the synergistic char-forming effect of ionic liquid and organic montmorillonite to form a highly efficient expanded char layer, achieving the goal of halogen-free, low-smoke, and low-toxicity green flame retardant. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0024] Example 1: This embodiment provides a method for preparing high-efficiency flame-retardant synthetic fibers, the specific steps of which are as follows: Nanofiller pretreatment: Weigh 28 parts of oleophilic surface-modified nano-silica and 4 parts of organomodified montmorillonite, mix them evenly, and place them in a vacuum drying oven to dry at 120℃ for 4 hours. Weigh 0.6 parts of KH-550 silane coupling agent and dilute it with 6 parts of anhydrous ethanol.

[0025] The dried nanofiller was added to a high-speed disperser, and the coupling agent ethanol solution was slowly sprayed at 1500 rpm. The mixture was stirred for 20 minutes and then dried at 105°C for 2 hours to activate it.

[0026] Preparation of ionic liquid-based shear-thickening fluid: Weigh 67 parts of [BMIM]BF4 ionic liquid and add it to the material tank of a high-speed disperser, and heat it to 60°C. Add the pretreated nanofiller in 3 batches at a speed of 2000 rpm, with an interval of 10 minutes between each batch. After all the fillers are added, continue high-speed dispersion for 30 minutes.

[0027] The mixture was transferred to a horizontal sand mill and circulated for 5 cycles at 1500 rpm, with the temperature controlled to not exceed 40℃.

[0028] After sand milling, the mixture was ultrasonically treated at 600W for 20 minutes, and then vacuum degassed at room temperature and -0.08MPa for 30 minutes. Finally, 2.4 parts of waterborne polyurethane crosslinking agent were slowly added at 500rpm and stirred for 15 minutes until homogeneous.

[0029] PET fiber pretreatment: Wash 100 parts of PET fiber in 80℃ deionized water for 30 minutes to remove surface oil and slurry, rinse with clean water and dry at 100℃.

[0030] Pulping Coating: Ionic liquid-based shear-thickening fluid is poured into the trough of the padding mill and heated to 40°C. The pretreated PET fibers are then introduced into the padding mill, using a two-dip, two-roll process with a roll pressure of 0.25 MPa, a speed of 12 m / min, and a roll allowance of 75%.

[0031] Pre-drying and baking: The impregnated PET fibers are immediately fed into a hot air pre-drying machine and pre-dried at 90°C for 5 minutes. Then they are transferred to a baking machine and baked at 150°C for 3 minutes to cure. After natural cooling to room temperature, the finished product is obtained.

[0032] Example 2: This embodiment is basically the same as Embodiment 1, except that: the formulation of the ionic liquid-based shear thickening fluid is 468 parts of [BMIM]BF4, 29 parts of surface-modified nano silica, 3 parts of organic montmorillonite, 0.6 parts of KH-550, and 2.4 parts of waterborne polyurethane crosslinking agent.

[0033] Example 3: This embodiment is basically the same as Embodiment 1, except that 1.5 parts of multi-walled carbon nanotubes (diameter 8-15nm) are used to replace 4 parts of organomodified montmorillonite.

[0034] Example 4: This embodiment is basically the same as embodiment 1, except that: after the PET fabric pretreatment, an argon plasma surface treatment step is added, with a treatment power of 200W, a time of 60 seconds, and a gas pressure of 20Pa.

[0035] Comparative Example 1: Ordinary untreated 150D / 48F plain weave PET fabric.

[0036] Comparative Example 2: CEPPA copolymer flame-retardant PET fabric with a phosphorus content of 1.0% is prepared by conventional copolymerization-spinning process.

[0037] Comparative Example 3: This comparative example is basically the same as Example 1, except that no aqueous polyurethane crosslinking agent is added to the ionic liquid-based shear thickening fluid.

[0038] Performance testing: The fibers obtained from the above experimental group were manufactured as 150D / 48F plain weave with a weight of 120g / m². 2 After processing the PET fabric, tests were conducted on limiting oxygen index, vertical flammability, anti-dripping properties, and tensile strength. The results are as follows: Data Analysis: This test, through a comparative experiment involving four sets of examples and three sets of comparative examples, systematically verified the comprehensive performance advantages of the core-sheath structure technology route based on ionic liquid-based shear-thickening fluid. The core data conclusions are as follows: In terms of flame retardancy and anti-dripping properties, the average limiting oxygen index (LOI) of the samples from this invention reached 33.8%, a 61% improvement compared to ordinary PET (21.0%) and a 12.3% improvement compared to traditional CEPPA copolymer flame-retardant PET (30.1%). In Example 3, carbon nanotubes were used to replace montmorillonite as a synergist, further increasing the LOI to 35.2%, demonstrating excellent potential for formulation optimization.

[0039] A qualitative breakthrough has been achieved in anti-dripping performance: no molten drips were produced during the combustion of all tested samples, completely solving the industry pain point that traditional copolymer flame-retardant PET still has a small amount of molten drips, and achieving the highest flame retardant standard of UL-94V-0.

[0040] Regarding the retention of mechanical properties, the average breaking strength of the samples from this invention is 3.4 cN / dtex, retaining 85% of the original strength of ordinary PET fibers, which is 13.3% higher than that of traditional copolymer flame-retardant PET (3.0 cN / dtex). This is due to the design of maintaining a pure PET structure in the core layer, avoiding the damage to the molecular chains caused by adding flame retardants to the bulk.

[0041] Regarding wash resistance and durability, the samples with added water-based polyurethane crosslinking agent maintained an LOI between 28.5% and 30.5% after 20 standard water washes, all maintaining a V-0 rating. In Example 4, after plasma surface treatment, the LOI reached 30.5% after water washing, with performance retention increasing to 90.5%. In contrast, the LOI of Comparative Example 3, without crosslinking agent, plummeted to 24.8% after water washing, indicating a decrease in flame retardancy, fully validating the crucial role of the crosslinking curing system in coating adhesion.

[0042] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing high-efficiency flame-retardant synthetic fibers, characterized in that, Includes the following steps: a. Using 65-70 parts of non-flammable ionic liquid as the dispersion medium, 25-30 parts of surface-modified nano silica as the dispersion phase, and 3-5 parts of organic montmorillonite as the flame retardant synergist, after multi-stage dispersion, 2-3 parts of waterborne polyurethane crosslinking agent are added and mixed evenly to obtain an ionic liquid-based shear thickening fluid. b. Pre-treat PET fibers or fabrics to remove surface oil and sizing agents; c. Immerse the pretreated PET fibers or fabrics in an ionic liquid-based shear thickening fluid, and use a padding process to make the ionic liquid-based shear thickening fluid uniformly adhere to the fiber surface as a coating liquid to construct an STF sheath layer and form a core-sheath structure. d. The impregnated fibers are pre-dried and then cured by baking to obtain high-efficiency flame-retardant synthetic fibers; The surface-modified nano-silica and organo-modified montmorillonite need to be vacuum dried at 120°C for 4 hours, then mixed with 0.5-0.8 parts of anhydrous ethanol dilution of KH-550 silane coupling agent, stirred at 1500 rpm for 20 minutes, and then dried at 105°C for 2 hours to activate.

2. The ionic liquid is 1-butyl-3-methylimidazolium tetrafluoroborate or 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate; the surface-modified nano-silica is oleophilic, with a particle size of 15-20 nm and a specific surface area of ​​200±20 m². 2 / g; the organomodified montmorillonite is sodium-based modified, with d001 ≥ 2.5nm and particle size ≤ 5μm.

3. The preparation method according to claim 1, characterized in that, The multi-stage dispersion described in step a is as follows: first, high-speed dispersion at 2000 rpm for 30 minutes, then cyclic sand milling at 1500 rpm 5 times, and finally ultrasonic treatment at 600W power for 20 minutes, followed by vacuum degassing at room temperature for 30 minutes.

4. The preparation method according to claim 1, characterized in that, The immersion rolling process parameters in step c are: roll pressure 0.2-0.3MPa, machine speed 10-15m / min, two-immersion two-rolling process, and control of the roll residue rate between 70-80%.

5. The preparation method according to claim 1, characterized in that, The pre-baking temperature in step d is 80-100℃, and the time is 4-6 minutes; the baking and curing temperature is 140-160℃, and the time is 2-4 minutes.

6. The preparation method according to claim 1, characterized in that, Step b also includes argon plasma surface treatment of the pretreated PET fibers or fabrics, with a treatment power of 200W, a time of 60 seconds, and a pressure of 20Pa.

7. A high-efficiency flame-retardant synthetic fiber prepared by the preparation method according to any one of claims 1-6.

Images