Boron-doped phosphorus-nitrogen type synergistic flame-retardant polylactic acid non-woven fabric and finishing process thereof

Abstract

This invention relates to the field of flame-retardant fabrics, and more particularly to a boron-doped phosphorus-nitrogen synergistic flame-retardant polylactic acid (PLA) nonwoven fabric and its finishing process. Technical problem: When performing flame-retardant treatment on PLA nonwoven fabrics, phosphorus-containing intumescent flame retardants have advantages such as low toxicity, environmental friendliness, and smoke suppression, becoming the development direction for PLA flame retardancy. However, they involve complex processing techniques, limiting large-scale production. Technical solution: A boron-doped phosphorus-nitrogen synergistic flame-retardant PLA nonwoven fabric is obtained by treating PLA nonwoven fabric with a flame-retardant treatment solution. This invention utilizes phytic acid as a raw material to prepare the flame-retardant treatment solution. Phytic acid has the advantages of being non-toxic, non-polluting, and biocompatible. Therefore, reacting it with triethanolamine and inorganic boric acid can yield a flame-retardant treatment solution exhibiting synergistic effects such as phosphorus-nitrogen, boron-nitrogen, and phosphorus-nitrogen-boron, promoting the carbonization of PLA fibers, and giving the PLA nonwoven fabric high flame-retardant effect and anti-dripping properties.

Description

Technical Field

[0001] This invention relates to the field of flame-retardant fabrics, and more particularly to a boron-doped phosphorus-nitrogen synergistic flame-retardant polylactic acid nonwoven fabric and its finishing process. Background Technology

[0002] Polylactic acid (PLA) nonwoven fabric is a special material; it is made of PLA fibers and does not require a weaving process. This gives it many characteristics and applications. It has good breathability and moisture absorption, making it suitable for dressings and bandages in the medical field. Furthermore, it can be used to make eco-friendly bags and biodegradable packaging materials. The nonwoven structure of PLA nonwoven fabric also provides it with high strength and durability, making it suitable for construction, home furnishings, and automotive interiors. PLA is a new generation of biocompatible and biodegradable environmentally friendly material, widely used in packaging materials, biomaterials, and woven fibers, and is receiving increasing attention. However, its products have poor thermal stability and flame retardancy, and are prone to producing molten droplets during combustion, making it difficult to meet [standard requirements]. The lack of consumer demand for flame-retardant properties in polylactic acid (PLA) textiles has severely limited its application in the textile industry. Flame retardancy for PLA materials mainly focuses on PLA composites such as PLA plastics, often achieved by adding flame retardants to PLA particles. Direct flame retardancy of PLA textiles is less common. When treating PLA nonwovens with flame retardants, phosphorus-containing intumescent flame retardants offer advantages such as low toxicity, environmental friendliness, and smoke suppression, making them a promising development direction for PLA flame retardancy. Cyclic phosphate compounds are used to improve the flame retardancy of PLA knitted fabrics, but these methods are prone to dripping. Phytic acid and chitosan are used to achieve matrix flame retardancy through layer-by-layer self-assembly, but this involves complex processing techniques, limiting large-scale production. Summary of the Invention

[0003] To overcome the shortcomings of polylactic acid (PLA) nonwoven fabrics, such as poor flame retardant performance and easy dripping during combustion, phosphorus-containing intumescent flame retardants have become the development direction of PLA flame retardants due to their advantages of low toxicity, environmental friendliness, and smoke suppression. Cyclic phosphate ester compounds are used to improve the flame retardancy of PLA knitted fabrics, but they are prone to dripping. Phytic acid and chitosan are used to achieve flame retardancy of the matrix through layer-by-layer self-assembly, but this involves complex processing technology, which limits large-scale production.

[0004] The technical solution of this invention is as follows: a boron-doped phosphorus-nitrogen synergistic flame-retardant polylactic acid nonwoven fabric, obtained by treating polylactic acid nonwoven fabric with a flame-retardant treatment solution. The polylactic acid nonwoven fabric is made from polylactic acid chips, with a weight of 80g per square meter. The main component of the flame-retardant treatment solution is boron-doped phosphorus-nitrogen synergistic flame retardant BTP. The flame-retardant treatment solution is prepared by mixing and reacting the following components in parts by weight: 6.2 parts boric acid, 44.7 parts triethanolamine, 264 parts phytic acid, 240 parts urea, and 830-840 parts water. The treatment process of the flame-retardant treatment solution on the polylactic acid nonwoven fabric is a pad-baking process.

[0005] Preferred, polylactic acid (PLA) is a new generation of biocompatible and biodegradable environmentally friendly material. PLA is widely used in packaging materials, biomaterials, and textile fibers, and is receiving increasing attention. However, its products have poor thermal stability and flame retardant properties, and are prone to producing molten droplets during combustion, making it difficult to meet consumer requirements for the flame retardant performance of PLA textiles. This greatly limits its application in the textile industry. Flame retardancy for PLA materials mainly focuses on the flame retardancy of PLA composites, such as PLA plastics, and often involves adding flame retardants to PLA particles to improve the flame retardant performance of PLA composites. Direct flame retardancy for PLA textiles is less common. Phosphorus-containing intumescent flame retardants have advantages such as low toxicity, environmental friendliness, and smoke suppression, making them a promising development direction for PLA flame retardancy. Cyclic phosphate compounds improve the flame retardancy of polylactic acid (PLA) knitted fabrics, but they are prone to dripping. While phytic acid and chitosan can be used to achieve matrix flame retardancy through layer-by-layer self-assembly, this involves complex processing techniques that limit large-scale production. Phytic acid, a biomass polyphosphate compound extracted from plants, has a phosphorus content as high as approximately 28%. It is non-toxic, non-polluting, and biocompatible, and is widely used in anti-corrosion treatment, self-assembled membranes, biosensors, and cation exchange resins. Therefore, reacting phytic acid with triethanolamine and inorganic boric acid yields a flame-retardant treatment liquid exhibiting synergistic effects such as phosphorus-nitrogen, boron-nitrogen, and phosphorus-nitrogen-boron, promoting the carbonization of PLA fibers and resulting in PLA nonwoven fabrics with high flame retardant performance and anti-dripping properties.

[0006] Preferably, polylactic acid nonwoven fabric is manufactured through the following steps:

[0007] S1: Pre-crystallize polylactic acid chips at 90-120 degrees Celsius;

[0008] S2: Dry the polylactic acid chips at 90-115 degrees Celsius for 3-6 hours;

[0009] S3: The dried polylactic acid chips are melted and extruded using a screw extruder, wherein the temperature of the molten polylactic acid is controlled between 190-220 degrees Celsius;

[0010] S4: The molten polylactic acid melt is conveyed to the spinneret, and the spinneret is used to extrude the melt into filaments;

[0011] S5: The formed filaments are cooled uniformly at an environment of 15-25 degrees Celsius;

[0012] S6: The high-speed airflow of the drawer is used to draw the cooled filaments, forming long filaments that are evenly spread on the moving mesh curtain to form a fiber web;

[0013] S7: The obtained fiber web is fed to a hot rolling mill for hot rolling bonding to form polylactic acid nonwoven fabric. The temperature of the hot rolling rolls of the hot rolling mill is 150 degrees Celsius, and the mill linear pressure is greater than 100 N per square millimeter.

[0014] Preferably, using a high-speed airflow nozzle to stretch the filaments can improve the orientation of the continuous filaments, resulting in higher fiber strength and increased tensile strength of the polylactic acid nonwoven fabric. Using a hot rolling mill with a hot roll temperature of 150 degrees Celsius and a rolling mill line pressure greater than 100 N per square millimeter can achieve the most suitable bonding strength between the continuous filaments.

[0015] A finishing process for boron-doped phosphorus-nitrogen synergistic flame-retardant polylactic acid nonwoven fabric includes the following steps:

[0016] S1: Polylactic acid nonwoven fabric pretreatment, which treats the polylactic acid nonwoven fabric so that it can be mixed with BTP flame retardant;

[0017] S2: Synthesis of BTP flame retardant, using phytic acid, triethanolamine and inorganic boric acid to synthesize boron-doped phosphorus-nitrogen type synergistic flame retardant BTP;

[0018] S3: Using the synthesized boron-doped phosphorus-nitrogen synergistic flame retardant BTP to finish polylactic acid nonwoven fabric, a phosphorus-nitrogen synergistic flame retardant polylactic acid nonwoven fabric is synthesized.

[0019] Preferably, the pretreatment of polylactic acid nonwoven fabric includes the following steps:

[0020] S1: Immerse the polylactic acid nonwoven fabric completely in the washing solution, where the amount of detergent is 2 g / L, the mass ratio of polylactic acid nonwoven fabric to washing solution is 1:50, the temperature of the washing solution is 60 degrees Celsius, and the immersion time is sixty minutes.

[0021] S2: After soaking the polylactic acid nonwoven fabric in the washing solution, wash the polylactic acid nonwoven fabric thoroughly with clean water.

[0022] S3: After washing, dry the polylactic acid nonwoven fabric at 80 degrees Celsius and wait for use.

[0023] Preferably, the synthesis of boron-doped phosphorus-nitrogen synergistic flame retardant BTP includes the following steps:

[0024] S1: Add 6.2 parts by weight of boric acid and 44.7 parts by weight of triethanolamine to a container and stir. The temperature inside the container is 140 degrees Celsius during stirring, and the stirring time is three hours.

[0025] S2: After stirring, cool to 130 degrees Celsius, add 264 parts by weight of phytic acid, and stir for three hours to obtain a milky white viscous liquid.

[0026] S3: Add 240 parts by weight of urea to the obtained milky white viscous liquid, maintain the temperature at 100 degrees Celsius, and stir for two hours to obtain the crude product of boron-doped phosphorus-nitrogen synergistic flame retardant BTP.

[0027] Preferably, the above steps are used as the synthetic route for boron-doped phosphorus-nitrogen synergistic flame retardant BTP. This synthetic method is simple and easy to implement, the raw materials are readily available, and there is no pollution emission.

[0028] Preferably, when mixing boric acid and triethanolamine, the heating and stirring are performed using the reflux method; after adding phytic acid, the heating and stirring are performed using the reflux method; and after adding urea, the heating and stirring are performed using the reflux method.

[0029] Preferably, when preparing the crude product of boron-doped phosphorus-nitrogen synergistic flame retardant BTP, the condensation reflux method can be used to stabilize the internal temperature of the container, which can effectively achieve energy saving and reduce the risk of leakage.

[0030] Preferably, after obtaining the crude product of boron-doped phosphorus-nitrogen synergistic flame retardant BTP, the crude product is subjected to precipitation, filtration and washing in sequence using anhydrous ethanol and acetone to remove unreacted reactants and obtain pure boron-doped phosphorus-nitrogen synergistic flame retardant BTP.

[0031] Preferably, filtering and drying the crude product of boron-doped phosphorus-nitrogen synergistic flame retardant BTP can remove moisture, which facilitates the transportation and storage of the boron-doped phosphorus-nitrogen synergistic flame retardant BTP. Furthermore, it allows for more accurate calculation of the amount of phosphorus-nitrogen synergistic flame retardant BTP used during application.

[0032] Preferably, after obtaining pure boron-doped phosphorus-nitrogen synergistic flame retardant BTP, the pure boron-doped phosphorus-nitrogen synergistic flame retardant BTP is dried using a freeze dryer to obtain a white solid product, boron-doped phosphorus-nitrogen synergistic flame retardant BTP. The control parameters of the freeze dryer are: temperature of -50 degrees Celsius, drying time of 24 hours, and pressure of 8 Pascals.

[0033] As a preferred option, the chemical formula for the synthesis of boron-doped phosphorus-nitrogen synergistic flame retardant BTP is:

[0034]

[0035] Preferably, the boron-doped phosphorus-nitrogen synergistic flame retardant BTP can lower the initial decomposition temperature of polylactic acid (PLA) nonwoven fabric from 299.1 degrees Celsius to 183.1 degrees Celsius, promoting the decomposition of PLA. Furthermore, it can increase the thermal stability of PLA fibers during the high-temperature thermal decomposition process, reducing the mass loss of PLA fibers. It can also catalyze the dehydration of PLA fibers, forming a dense char layer. This char layer inhibits the transmission of combustible gases and the diffusion of oxygen, resulting in PLA nonwoven fabric treated with boron-doped phosphorus-nitrogen synergistic flame retardant BTP exhibiting good flame retardant properties. Simultaneously, the flame retardant system composed of boron-doped phosphorus-nitrogen synergistic flame retardant BTP and PLA fibers can decompose into non-flammable gases such as water, ammonia, and carbon dioxide upon heating, diluting the combustible gases and thus providing an auxiliary flame retardant effect.

[0036] Preferably, when finishing polylactic acid nonwoven fabrics using the synthesized boron-doped phosphorus-nitrogen synergistic flame retardant BTP, the following steps are included:

[0037] S1: The synthesized boron-doped phosphorus-nitrogen synergistic flame retardant BTP is dissolved into a flame retardant treatment solution with a mass fraction of 40%; and a dicyandiamide catalyst with a mass fraction of 4% is added to it. The mass ratio of the flame retardant treatment solution to polylactic acid nonwoven fabric is 20:1.

[0038] S2: The flame retardant treatment liquid is used to impregnate polylactic acid nonwoven fabric. The parameters of the impregnation treatment are: two dips and two nips, the padding rate is 70% to 80%, the first impregnation time is 5 minutes, and the second impregnation time is 3 minutes.

[0039] S3: Dry the impregnated polylactic acid nonwoven fabric at an environment of 80 to 100 degrees Celsius for a drying time of three to five minutes.

[0040] S4: Bake the dried polylactic acid nonwoven fabric at 170 degrees Celsius for three minutes.

[0041] Preferably, the flame-retardant treatment of polylactic acid nonwoven fabric through the above steps results in the addition of 11.01% (wt%) phosphorus (P), 18.12% (wt%) nitrogen (N), and 10.90% (wt%) boron (B) to the surface of the polylactic acid nonwoven fabric, in addition to the original 25.03% (wt%) carbon and 34.97% (wt%) oxygen. The presence and adhesion of these elements provide the flame-retardant properties of the polylactic acid nonwoven fabric. The presence and adhesion of nitrogen and boron elements result in synergistic effects such as phosphorus-nitrogen, boron-nitrogen, and phosphorus-nitrogen-boron on the polylactic acid nonwoven fabric, which promotes the carbonization of polylactic acid fibers in the polylactic acid nonwoven fabric and further improves the flame-retardant effect and anti-dripping properties of the polylactic acid nonwoven fabric.

[0042] The beneficial effects of this invention are:

[0043] 1. Compared with existing technologies that use phosphorus-containing intumescent flame retardants to treat polylactic acid (PLA) nonwoven fabrics, phosphorus-containing intumescent flame retardants have advantages such as low toxicity, environmental friendliness, and smoke suppression, making them the development direction for PLA flame retardancy. Cyclic phosphate ester compounds are used to improve the flame retardancy of PLA knitted fabrics, but they are prone to dripping. Phytic acid and chitosan are used to achieve matrix flame retardancy through layer-by-layer self-assembly, but this involves complex processing technology, which limits large-scale production. This treatment method uses phytic acid as a raw material to prepare a flame retardant treatment liquid. Phytic acid is a biomass polyphosphate compound extracted from plants, with a phosphorus content as high as about 28%. It has the advantages of being non-toxic, non-polluting, and biocompatible, and is widely used in anti-corrosion treatment, self-assembled membranes, biosensors, cation exchange resins, and other fields. Therefore, by reacting it with triethanolamine and inorganic boric acid, a flame retardant treatment liquid with synergistic effects such as phosphorus-nitrogen, boron-nitrogen, and phosphorus-nitrogen-boron can be obtained, which promotes the carbonization of PLA fibers, giving PLA nonwoven fabrics higher flame retardant effect and anti-dripping performance.

[0044] 2. Boron-doped phosphorus-nitrogen synergistic flame retardant BTP can lower the initial decomposition temperature of polylactic acid (PLA) nonwoven fabric from 299.1 degrees Celsius to 183.1 degrees Celsius, promoting PLA decomposition. Furthermore, it can increase the thermal stability of PLA fibers during the high-temperature thermal decomposition process, reducing PLA fiber mass loss. It can also catalyze PLA fiber dehydration, forming a dense char layer. This char layer inhibits the transmission of combustible gases and the diffusion of oxygen, resulting in PLA nonwoven fabric treated with boron-doped phosphorus-nitrogen synergistic flame retardant BTP exhibiting good flame retardant properties. Simultaneously, the flame retardant system composed of boron-doped phosphorus-nitrogen synergistic flame retardant BTP and PLA fibers can decompose into non-flammable gases such as water, ammonia, and carbon dioxide upon heating, diluting combustible gases and thus providing an auxiliary flame retardant effect.

[0045] 3. The flame-retardant treatment of polylactic acid (PLA) nonwoven fabric through the above steps removes the original 25.03% (wt%) carbon and 34.97% (wt%) oxygen from the surface of the PLA nonwoven fabric, and adds 11.01% (wt%) phosphorus (P), 18.12% (wt%) nitrogen (N), and 10.90% (wt%) boron (B). The presence and adhesion of these elements provide the flame-retardant properties of PLA nonwoven fabric. The presence and adhesion of nitrogen and boron elements result in synergistic effects such as phosphorus-nitrogen, boron-nitrogen, and phosphorus-nitrogen-boron on the PLA nonwoven fabric, promoting the carbonization of PLA fibers in the PLA nonwoven fabric and further improving the flame-retardant effect and anti-dripping properties of the PLA nonwoven fabric. Attached Figure Description

[0046] Figure 1 The diagram shows a process flow diagram of the production of polylactic acid nonwoven fabric in the boron-doped phosphorus-nitrogen type synergistic flame-retardant polylactic acid nonwoven fabric of the present invention.

[0047] Figure 2 The diagram shows a flow chart of the finishing process for the boron-doped phosphorus-nitrogen type synergistic flame-retardant polylactic acid nonwoven fabric of the present invention.

[0048] Figure 3 The diagram shows a schematic of the synthesis process of boron-doped phosphorus-nitrogen synergistic flame retardant BTP in the finishing process of boron-doped phosphorus-nitrogen synergistic flame retardant polylactic acid nonwoven fabric of the present invention.

[0049] Figure 4 The diagram illustrates the principle of synthesizing boron-doped phosphorus-nitrogen synergistic flame retardant BTP in the finishing process of boron-doped phosphorus-nitrogen synergistic flame retardant polylactic acid nonwoven fabric according to the present invention. Detailed Implementation

[0050] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0051] Please see Figure 1 This invention provides an embodiment: a boron-doped phosphorus-nitrogen synergistic flame-retardant polylactic acid (PLA) nonwoven fabric, obtained by treating PLA nonwoven fabric with a flame-retardant treatment solution. The PLA nonwoven fabric is made from PLA chips, with a weight of 80g per square meter. The main component of the flame-retardant treatment solution is a boron-doped phosphorus-nitrogen synergistic flame retardant (BTP). The flame-retardant treatment solution is prepared by mixing and reacting the following components in parts by weight: 6.2 parts boric acid, 44.7 parts triethanolamine, 264 parts phytic acid, 240 parts urea, and 830-840 parts water. The treatment process of the flame-retardant treatment solution on the PLA nonwoven fabric is a pad-baking process.

[0052] Preferred, polylactic acid (PLA) is a new generation of biocompatible and biodegradable environmentally friendly material. PLA is widely used in packaging materials, biomaterials, and textile fibers, and is receiving increasing attention. However, its products have poor thermal stability and flame retardant properties, and are prone to producing molten droplets during combustion, making it difficult to meet consumer requirements for the flame retardant performance of PLA textiles. This greatly limits its application in the textile industry. Flame retardancy for PLA materials mainly focuses on the flame retardancy of PLA composites, such as PLA plastics, and often involves adding flame retardants to PLA particles to improve the flame retardant performance of PLA composites. Direct flame retardancy for PLA textiles is less common. Phosphorus-containing intumescent flame retardants have advantages such as low toxicity, environmental friendliness, and smoke suppression, making them a promising development direction for PLA flame retardancy. Cyclic phosphate compounds improve the flame retardancy of polylactic acid (PLA) knitted fabrics, but they are prone to dripping. While phytic acid and chitosan can be used to achieve matrix flame retardancy through layer-by-layer self-assembly, this involves complex processing techniques that limit large-scale production. Phytic acid, a biomass polyphosphate compound extracted from plants, has a phosphorus content as high as approximately 28%. It is non-toxic, non-polluting, and biocompatible, and is widely used in anti-corrosion treatment, self-assembled membranes, biosensors, and cation exchange resins. Therefore, reacting phytic acid with triethanolamine and inorganic boric acid yields a flame-retardant treatment liquid exhibiting synergistic effects such as phosphorus-nitrogen, boron-nitrogen, and phosphorus-nitrogen-boron, promoting the carbonization of PLA fibers and resulting in PLA nonwoven fabrics with high flame retardant performance and anti-dripping properties.

[0053] Preferably, polylactic acid nonwoven fabric is manufactured through the following steps:

[0054] S1: Pre-crystallize polylactic acid chips at 90-120 degrees Celsius;

[0055] S2: Dry the polylactic acid chips at 90-115 degrees Celsius for 3-6 hours;

[0056] S3: The dried polylactic acid chips are melted and extruded using a screw extruder, wherein the temperature of the molten polylactic acid is controlled between 190-220 degrees Celsius;

[0057] S4: The molten polylactic acid melt is conveyed to the spinneret, and the spinneret is used to extrude the melt into filaments;

[0058] S5: The formed filaments are cooled uniformly at an environment of 15-25 degrees Celsius;

[0059] S6: The high-speed airflow of the drawer is used to draw the cooled filaments, forming long filaments that are evenly spread on the moving mesh curtain to form a fiber web;

[0060] S7: The obtained fiber web is fed to a hot rolling mill for hot rolling bonding to form polylactic acid nonwoven fabric. The temperature of the hot rolling rolls of the hot rolling mill is 150 degrees Celsius, and the mill linear pressure is greater than 100 N per square millimeter.

[0061] Preferably, using a high-speed airflow nozzle to stretch the filaments can improve the orientation of the continuous filaments, resulting in higher fiber strength and increased tensile strength of the polylactic acid nonwoven fabric. Using a hot rolling mill with a hot roll temperature of 150 degrees Celsius and a rolling mill line pressure greater than 100 N per square millimeter can achieve the most suitable bonding strength between the continuous filaments.

[0062] Please see Figure 2-4 This invention provides an embodiment: a finishing process for boron-doped phosphorus-nitrogen synergistic flame-retardant polylactic acid nonwoven fabric, comprising the following steps:

[0063] S1: Polylactic acid nonwoven fabric pretreatment, which treats the polylactic acid nonwoven fabric so that it can be mixed with BTP flame retardant;

[0064] S2: Synthesis of BTP flame retardant, using phytic acid, triethanolamine and inorganic boric acid to synthesize boron-doped phosphorus-nitrogen type synergistic flame retardant BTP;

[0065] S3: Using the synthesized boron-doped phosphorus-nitrogen synergistic flame retardant BTP to finish polylactic acid nonwoven fabric, a phosphorus-nitrogen synergistic flame retardant polylactic acid nonwoven fabric is synthesized.

[0066] Preferably, the pretreatment of polylactic acid nonwoven fabric includes the following steps:

[0067] S1: Immerse the polylactic acid nonwoven fabric completely in the washing solution, where the amount of detergent is 2 g / L, the mass ratio of polylactic acid nonwoven fabric to washing solution is 1:50, the temperature of the washing solution is 60 degrees Celsius, and the immersion time is sixty minutes.

[0068] S2: After soaking the polylactic acid nonwoven fabric in the washing solution, wash the polylactic acid nonwoven fabric thoroughly with clean water.

[0069] S3: After washing, dry the polylactic acid nonwoven fabric at 80 degrees Celsius and wait for use.

[0070] Preferably, the synthesis of boron-doped phosphorus-nitrogen synergistic flame retardant BTP includes the following steps:

[0071] S1: Add 6.2 parts by weight of boric acid and 44.7 parts by weight of triethanolamine to a container and stir. The temperature inside the container is 140 degrees Celsius during stirring, and the stirring time is three hours.

[0072] S2: After stirring, cool to 130 degrees Celsius, add 264 parts by weight of phytic acid, and stir for three hours to obtain a milky white viscous liquid.

[0073] S3: Add 240 parts by weight of urea to the obtained milky white viscous liquid, maintain the temperature at 100 degrees Celsius, and stir for two hours to obtain the crude product of boron-doped phosphorus-nitrogen synergistic flame retardant BTP.

[0074] Preferably, the above steps are used as the synthetic route for boron-doped phosphorus-nitrogen synergistic flame retardant BTP. This synthetic method is simple and easy to implement, the raw materials are readily available, and there is no pollution emission.

[0075] Preferably, when mixing boric acid and triethanolamine, the heating and stirring are performed using the reflux method; after adding phytic acid, the heating and stirring are performed using the reflux method; and after adding urea, the heating and stirring are performed using the reflux method.

[0076] Preferably, when preparing the crude product of boron-doped phosphorus-nitrogen synergistic flame retardant BTP, the condensation reflux method can be used to stabilize the internal temperature of the container, which can effectively achieve energy saving and reduce the risk of leakage.

[0077] Preferably, after obtaining the crude product of boron-doped phosphorus-nitrogen synergistic flame retardant BTP, the crude product is subjected to precipitation, filtration and washing in sequence using anhydrous ethanol and acetone to remove unreacted reactants and obtain pure boron-doped phosphorus-nitrogen synergistic flame retardant BTP.

[0078] Preferably, filtering and drying the crude product of boron-doped phosphorus-nitrogen synergistic flame retardant BTP can remove moisture, which facilitates the transportation and storage of the boron-doped phosphorus-nitrogen synergistic flame retardant BTP. Furthermore, it allows for more accurate calculation of the amount of phosphorus-nitrogen synergistic flame retardant BTP used during application.

[0079] Preferably, after obtaining pure boron-doped phosphorus-nitrogen synergistic flame retardant BTP, the pure boron-doped phosphorus-nitrogen synergistic flame retardant BTP is dried using a freeze dryer to obtain a white solid product, boron-doped phosphorus-nitrogen synergistic flame retardant BTP. The control parameters of the freeze dryer are: temperature of -50 degrees Celsius, drying time of 24 hours, and pressure of 8 Pascals.

[0080] As a preferred option, the chemical formula for the synthesis of boron-doped phosphorus-nitrogen synergistic flame retardant BTP is:

[0081]

[0082] Preferably, the boron-doped phosphorus-nitrogen synergistic flame retardant BTP can lower the initial decomposition temperature of polylactic acid (PLA) nonwoven fabric from 299.1 degrees Celsius to 183.1 degrees Celsius, promoting the decomposition of PLA. Furthermore, it can increase the thermal stability of PLA fibers during the high-temperature thermal decomposition process, reducing the mass loss of PLA fibers. It can also catalyze the dehydration of PLA fibers, forming a dense char layer. This char layer inhibits the transmission of combustible gases and the diffusion of oxygen, resulting in PLA nonwoven fabric treated with boron-doped phosphorus-nitrogen synergistic flame retardant BTP exhibiting good flame retardant properties. Simultaneously, the flame retardant system composed of boron-doped phosphorus-nitrogen synergistic flame retardant BTP and PLA fibers can decompose into non-flammable gases such as water, ammonia, and carbon dioxide upon heating, diluting the combustible gases and thus providing an auxiliary flame retardant effect.

[0083] Preferably, when finishing polylactic acid nonwoven fabrics using the synthesized boron-doped phosphorus-nitrogen synergistic flame retardant BTP, the following steps are included:

[0084] S1: The synthesized boron-doped phosphorus-nitrogen synergistic flame retardant BTP is dissolved into a flame retardant treatment solution with a mass fraction of 40%; and a dicyandiamide catalyst with a mass fraction of 4% is added to it. The mass ratio of the flame retardant treatment solution to polylactic acid nonwoven fabric is 20:1.

[0085] S2: The flame retardant treatment liquid is used to impregnate polylactic acid nonwoven fabric. The parameters of the impregnation treatment are: two dips and two nips, the padding rate is 70% to 80%, the first impregnation time is 5 minutes, and the second impregnation time is 3 minutes.

[0086] S3: Dry the impregnated polylactic acid nonwoven fabric at an environment of 80 to 100 degrees Celsius for a drying time of three to five minutes.

[0087] S4: Bake the dried polylactic acid nonwoven fabric at 170 degrees Celsius for three minutes.

[0088] Preferably, the flame-retardant treatment of polylactic acid nonwoven fabric through the above steps results in the addition of 11.01% (wt%) phosphorus (P), 18.12% (wt%) nitrogen (N), and 10.90% (wt%) boron (B) to the surface of the polylactic acid nonwoven fabric, in addition to the original 25.03% (wt%) carbon and 34.97% (wt%) oxygen. The presence and adhesion of these elements provide the flame-retardant properties of the polylactic acid nonwoven fabric. The presence and adhesion of nitrogen and boron elements result in synergistic effects such as phosphorus-nitrogen, boron-nitrogen, and phosphorus-nitrogen-boron on the polylactic acid nonwoven fabric, which promotes the carbonization of polylactic acid fibers in the polylactic acid nonwoven fabric and further improves the flame-retardant effect and anti-dripping properties of the polylactic acid nonwoven fabric.

[0089] Through the above steps, a flame-retardant treatment liquid is prepared using phytic acid as a raw material. Phytic acid is a biomass polyphosphate compound extracted from plants, with a phosphorus content as high as about 28%. It has the advantages of being non-toxic, non-polluting, and biocompatible, and is widely used in anti-corrosion treatment, self-assembled membranes, biosensors, cation exchange resins, and other fields. Therefore, reacting it with triethanolamine and inorganic boric acid can yield a flame-retardant treatment liquid exhibiting synergistic effects such as phosphorus-nitrogen, boron-nitrogen, and phosphorus-nitrogen-boron, which promotes the carbonization of polylactic acid fibers, making polylactic acid nonwovens... The fabric exhibits high flame retardancy and anti-dripping properties. Boron-doped phosphorus-nitrogen synergistic flame retardant BTP can lower the initial decomposition temperature of polylactic acid (PLA) nonwoven fabric from 299.1 degrees Celsius to 183.1 degrees Celsius, promoting PLA decomposition. Furthermore, it increases the thermal stability of PLA fibers during high-temperature thermal decomposition, reducing mass loss. It also catalyzes PLA fiber dehydration, forming a dense char layer. This char layer inhibits the transmission of combustible gases and oxygen diffusion, resulting in a more robust and effective flame retardant product. Polylactic acid (PLA) nonwoven fabric treated with the synergistic flame retardant BTP exhibits good flame retardant properties. Furthermore, the flame retardant system composed of boron-doped phosphorus-nitrogen synergistic flame retardant BTP and PLA fibers can decompose into non-flammable gases such as water, ammonia, and carbon dioxide upon heating, thus diluting flammable gases and providing auxiliary flame retardant effects. Through the above steps of flame retardant treatment on PLA nonwoven fabric, the original 25.03% (wt%) carbon and 34.97% (wt%) oxygen elements are removed from the surface of the PLA nonwoven fabric. The addition of 11.01% (wt%) phosphorus (P), 18.12% (wt%) nitrogen (N), and 10.90% (wt%) boron (B) provides flame retardant properties to polylactic acid nonwoven fabrics. The presence and adhesion of nitrogen and boron elements result in synergistic effects such as phosphorus-nitrogen, boron-nitrogen, and phosphorus-nitrogen-boron on the polylactic acid nonwoven fabric, promoting the carbonization of polylactic acid fibers in the polylactic acid nonwoven fabric and further improving the flame retardant effect and anti-dripping properties of the polylactic acid nonwoven fabric.

[0090] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A boron-doped phosphorus-nitrogen synergistic flame-retardant polylactic acid nonwoven fabric; characterized in that: It is obtained by treating polylactic acid nonwoven fabric with a flame retardant treatment solution. The polylactic acid nonwoven fabric is made of polylactic acid chips, and the weight of each square meter of polylactic acid nonwoven fabric is 80g. The main component of the flame retardant treatment solution is boron-doped phosphorus-nitrogen type synergistic flame retardant BTP. The flame retardant treatment solution is prepared by mixing and reacting the following components in parts by weight: 6.2 parts boric acid, 44.7 parts triethanolamine, 264 parts phytic acid, 240 parts urea and 830-840 parts water. The treatment process of the flame retardant treatment solution on the polylactic acid nonwoven fabric is a pad baking process. The chemical formula for the synthesis of boron-doped phosphorus-nitrogen synergistic flame retardant BTP is as follows:

2. The boron-doped phosphorus-nitrogen synergistic flame-retardant polylactic acid nonwoven fabric according to claim 1, characterized in that: Polylactic acid nonwoven fabric is made through the following steps: S1: Pre-crystallize polylactic acid chips at 90-120 degrees Celsius; S2: Dry the polylactic acid chips at 90-115 degrees Celsius for 3-6 hours; S3: The dried polylactic acid chips are melted and extruded using a screw extruder, wherein the temperature of the molten polylactic acid is controlled between 190-220 degrees Celsius; S4: The molten polylactic acid melt is conveyed to the spinneret, and the spinneret is used to extrude the melt into filaments; S5: The formed filaments are cooled uniformly at an environment of 15-25 degrees Celsius; S6: The high-speed airflow of the drawer is used to draw the cooled filaments, forming long filaments that are evenly spread on the moving mesh curtain to form a fiber web; S7: The obtained fiber web is fed to a hot rolling mill for hot rolling bonding to form polylactic acid nonwoven fabric. The temperature of the hot rolling rolls of the hot rolling mill is 150 degrees Celsius, and the mill linear pressure is greater than 100 N per square millimeter.

3. The boron-doped phosphorus-nitrogen synergistic flame-retardant polylactic acid nonwoven fabric according to claim 1, characterized in that: Its finishing process includes the following steps: S1: Polylactic acid nonwoven fabric pretreatment, which treats the polylactic acid nonwoven fabric so that it can be mixed with BTP flame retardant; S2: Synthesis of BTP flame retardant, using phytic acid, triethanolamine and inorganic boric acid to synthesize boron-doped phosphorus-nitrogen type synergistic flame retardant BTP; S3: Using the synthesized boron-doped phosphorus-nitrogen synergistic flame retardant BTP to finish polylactic acid nonwoven fabric, a phosphorus-nitrogen synergistic flame retardant polylactic acid nonwoven fabric is synthesized.

4. The boron-doped phosphorus-nitrogen synergistic flame-retardant polylactic acid nonwoven fabric according to claim 3, characterized in that: The pretreatment of polylactic acid nonwoven fabrics includes the following steps: S1: Immerse the polylactic acid nonwoven fabric completely in the washing solution, where the amount of detergent is 2 g / L, the mass ratio of polylactic acid nonwoven fabric to washing solution is 1:50, the temperature of the washing solution is 60 degrees Celsius, and the immersion time is sixty minutes. S2: After soaking the polylactic acid nonwoven fabric in the washing solution, wash the polylactic acid nonwoven fabric thoroughly with clean water. S3: After washing, dry the polylactic acid nonwoven fabric at 80 degrees Celsius and wait for use.

5. The boron-doped phosphorus-nitrogen synergistic flame-retardant polylactic acid nonwoven fabric according to claim 4, characterized in that: The synthesis of boron-doped phosphorus-nitrogen synergistic flame retardant BTP includes the following steps: S1: Add 6.2 parts by weight of boric acid and 44.7 parts by weight of triethanolamine to a container and stir. The temperature inside the container is 140 degrees Celsius during stirring, and the stirring time is three hours. S2: After stirring, cool to 130 degrees Celsius, add 264 parts by weight of phytic acid, and stir for three hours to obtain a milky white viscous liquid. S3: Add 240 parts by weight of urea to the obtained milky white viscous liquid, maintain the temperature at 100 degrees Celsius, and stir for two hours to obtain the crude product of boron-doped phosphorus-nitrogen synergistic flame retardant BTP.

6. The boron-doped phosphorus-nitrogen synergistic flame-retardant polylactic acid nonwoven fabric according to claim 5, characterized in that: When mixing boric acid and triethanolamine, the reflux heating method was used for heating and stirring. After adding phytic acid, the reflux heating method was used for heating and stirring. After adding urea, the reflux heating method was used for heating and stirring.

7. The boron-doped phosphorus-nitrogen synergistic flame-retardant polylactic acid nonwoven fabric according to claim 6, characterized in that: After obtaining the crude product of boron-doped phosphorus-nitrogen synergistic flame retardant BTP, the crude product was subjected to precipitation, filtration and washing with anhydrous ethanol and acetone in sequence to remove unreacted reactants and obtain pure boron-doped phosphorus-nitrogen synergistic flame retardant BTP.

8. The boron-doped phosphorus-nitrogen synergistic flame-retardant polylactic acid nonwoven fabric according to claim 7, characterized in that: After obtaining pure boron-doped phosphorus-nitrogen synergistic flame retardant BTP, the pure boron-doped phosphorus-nitrogen synergistic flame retardant BTP was dried using a freeze dryer to obtain a white solid product, boron-doped phosphorus-nitrogen synergistic flame retardant BTP. The control parameters of the freeze dryer were: temperature of -50 degrees Celsius, drying time of 24 hours, and pressure of 8 Pascals.

9. The boron-doped phosphorus-nitrogen synergistic flame-retardant polylactic acid nonwoven fabric according to claim 8, characterized in that: When using the synthesized boron-doped phosphorus-nitrogen synergistic flame retardant BTP to finish polylactic acid nonwoven fabrics, the following steps are included: S1: The synthesized boron-doped phosphorus-nitrogen synergistic flame retardant BTP is dissolved into a flame retardant treatment solution with a mass fraction of 40%; and a dicyandiamide catalyst with a mass fraction of 4% is added to it. The mass ratio of the flame retardant treatment solution to polylactic acid nonwoven fabric is 20:

1. S2: The flame retardant treatment liquid is used to impregnate polylactic acid nonwoven fabric. The parameters of the impregnation treatment are: two dips and two nips, the padding rate is 70% to 80%, the first impregnation time is 5 minutes, and the second impregnation time is 3 minutes. S3: Dry the impregnated polylactic acid nonwoven fabric at an environment of 80 to 100 degrees Celsius for a drying time of three to five minutes. S4: Bake the dried polylactic acid nonwoven fabric at 170 degrees Celsius for three minutes.

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