Preparation method and application of intumescent bio-based flame retardant

Abstract

The present invention belongs to the field of functional chitosan derivatives based on polysaccharide compounds, and discloses a preparation method and application of an intumescent bio-based flame retardant. The flame retardant is prepared by dissolving dicarboxyl chitosan in ionic liquid 1-butyl-3-methylimidazole acetate, adding an inhibitor and an initiator, and reacting the mixture with N-hydroxymethyl acrylamide under microwave radiation. Then, phytic acid is added to react the C6 position of the dicarboxyl chitosan with the PO4 in the phytic acid molecule under the action of a catalyst. 3‑ The bio-based flame retardant prepared by this invention contains a large number of phosphate, carboxyl, and cationic amino groups, and is environmentally friendly, highly effective in flame retardancy and fire protection, highly reactive, and exhibits antibacterial activity. It has great potential for application in flame retardancy, fire protection, healthcare, textiles, clothing, and new materials.

Description

Technical Field

[0001] The invention belongs to the field of functional chitosan derivatives based on polysaccharide compounds, discloses a preparation method and application of an intumescent bio-based flame retardant, and particularly relates to a flame-retardant and antibacterial fabric grafted and modified with N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid. Background Art

[0002] With the development of science and technology and the continuous improvement of environmental protection requirements, people are paying more and more attention to renewable, environmentally friendly and non-toxic flame retardants. Bio-based materials derived from nature are gradually being used in the field of flame retardancy as a substitute for traditional flame retardants because of their advantages of being non-toxic, green, environmentally friendly, highly biocompatible and renewable. Chitosan-based flame retardants prepared from chitosan, the second largest biomass resource in nature, have attracted widespread attention. Chitosan can improve the thermal stability of polymers to a certain extent, thereby improving their flame retardant properties, but it cannot improve the flame retardant grade of the material. It is often necessary to introduce flame retardant elements to improve the flame retardant properties [Hao Fengling, Geng Weitao, Zhang Jian, et al. Research progress of chitosan-based flame retardants [J]. Wool Textile Technology, 2019, 47(2): 80-85]. Chitosan is a natural, environmentally friendly, high-carbon polymer. The nitrogen element contained in its molecules enables it to be used as a foaming agent in intumescent flame retardant systems. By directly compounding chitosan with acid source materials, an intumescent flame retardant (IFR) system can be formed. The intumescent flame retardant system (composed of an acid source, a carbon source, and a foaming agent) is valued for its excellent flame retardant properties. In the presence of flame or high temperature, the intumescent flame retardant coating can quickly produce foam and bubbles, thereby forming a dense, porous and stable carbon layer. This carbon layer can effectively block flames and block the transfer of heat, fuel and oxygen, thereby significantly improving fire safety.

[0003] Phytic acid is a biomass that can be extracted from plant seeds such as grains and soybeans. It is abundant and renewable. The six phosphate groups in phytic acid's structure provide an important role as an acid source in intumescent flame retardants. When phytic acid is pyrolyzed, it produces a large amount of phosphate derivatives, which not only promote the dehydration and carbonization of the carbon source but also capture free radicals, thereby improving the flame retardant properties of the entire system [Wei An, Zou Yongjin, Sun Lixian. Research Progress of Phosphorus-Containing Bio-Based Flame Retardants [J]. Modern Chemical Industry, 2025, 45(2): 57-62]. Fang et al. investigated the LBL assembly coating of fully bio-based intumescent flame retardant (IFR) CS / PA coating on polyester / cotton blended fabrics. After 20 times of CS / PA coating and LBL assembly, the limiting oxygen index (LOI) value of the polyester / cotton blended fabric reached 29.2%, and the dripping of molten droplets was eliminated. However, CS / PA lacks chemical bonding with the fabric, and the electrostatic force formed is weak, and it is easy to fall off after washing, resulting in poor flame retardancy and durability of the polyester / cotton blended fabric coated with CS / PA [Yinchun F, Weihao S, Junwei L, et al. Eco-friendly flame retardant and dripping-resistant of polyester / cotton blend fabrics through layer-by-layer assembly fully bio-based chitosan / phytic acid coating[J]. International Journal of Biological Macromolecules, 2021, 175: 140-146].Zhang et al. deposited an environmentally friendly flame retardant coating composed of a bio-based intumescent flame retardant system (chitosan and phytic acid) and metal ions on cotton fabric. The metal ions were used as catalysts for the dehydrogenation reaction to increase the amount of carbonization formed. The synergistic effect of the intumescent flame retardant system and the metal ions was used to effectively improve the thermal stability and flame retardant properties of cotton fabrics through the dip-roll-dry method. However, the flame retardant treatment had an adverse effect on the whiteness, tensile strength and softness of the fabric, and the metal ions posed certain human safety risks, which limited the use of bio-based intumescent flame retardants [Zhang Z, Ma Z, Leng Q, et al. Eco-friendly flame retardant coating deposited on cotton fabrics from bio-based chitosan, phytic acid and divalent metalions [J]. International Journal of Biological Macromolecules, 2019, 140: 303-310]. The flame retardant efficiency and durability of bio-based materials when used alone as flame retardants need to be improved. In addition, the lack of active groups that react with fabric cross-linking leads to easy detachment during washing and poor flame retardant durability, which limits their application areas. Currently, the main method for finishing fabrics with chitosan and phytic acid composite flame retardants is to construct a flame-retardant coating using layer-by-layer assembly (LBL) or padding. This flame retardant coating not only affects the fabric's wearability, such as breathability, feel, strength, and whiteness, but is also not washable and cannot provide long-term flame retardancy and thermal insulation. Therefore, the development of a green and environmentally friendly bio-based flame retardant that can firmly bond with fabrics through a grafting reaction, imparting long-lasting and highly effective flame retardancy and fire protection, as well as antimicrobial activity, is urgent. Summary of the Invention

[0004] In view of the above problems in the prior art, the first object of the present invention is to provide a method for preparing an N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid (NMA-DCCS-PA) intumescent bio-based flame retardant. The present invention involves a substitution reaction between dicarboxyl chitosan (DCCS) and N-hydroxymethyl acrylamide (NMA), and a reaction between the -OH group at the C6 position of the dicarboxyl chitosan and the PO4 in the phytic acid molecule. 3-Esterification reactions are performed to enrich NMA-DCCS-PA with a large number of groups, such as phosphates, carboxyl groups, cationic amino groups, and unsaturated double bonds. This results in high reactivity, excellent biocompatibility, and dual fire-retardant and highly effective antibacterial properties. A second objective of the present invention is to provide a method for preparing intumescent bio-based flame retardant-modified fabrics. The carboxyl groups and unsaturated double bonds in NMA-DCCS-PA react with the amino groups of protein fibers and the hydroxyl groups of cellulose fibers to undergo amide and nucleophilic addition reactions, respectively. This modified fabric, produced without the use of any chemical crosslinking agents, is safe and hygienic, exhibits high chemical crosslinking strength, and exhibits long-lasting functionality. The fabric has significant potential for application in flame retardancy, long-lasting antibacterial, and other related fields.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is as follows:

[0006] The present invention first discloses an intumescent bio-based flame retardant, which is characterized in that: the intumescent bio-based flame retardant is N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid (NMA-DCCS-PA), which is prepared by dissolving dicarboxyl chitosan (DCCS) in ionic liquid 1-butyl-3-methylimidazolium acetate ([Bmim][Ac]), adding an inhibitor and an initiator to react with N-hydroxymethyl acrylamide (NMA) under microwave radiation, and then adding phytic acid (PA) to react with the C6 position of dicarboxyl chitosan with the PO4 in the phytic acid molecule under the action of a catalyst. 3- Esterification reaction is carried out to obtain.

[0007] Preferably, the dicarboxyl chitosan has a C2 and C3 carboxyl content of 45.31-68.57%, a deacetylation degree of 61.27-83.42%, a viscosity-average molecular weight of 35,200-86,300, a solubility in water of 9.12-17.35 g / 100 mL, an isoelectric point pH of 4.2-4.6, and a structural formula of the dicarboxyl chitosan as follows:

[0008] .

[0009] The method for preparing the intumescent bio-based flame retardant of the present invention comprises the following steps:

[0010] (1) Dissolve dicarboxyl chitosan (DCCS) in 1-butyl-3-methylimidazole acetate at 65-85°C to prepare a dicarboxyl chitosan solution with a mass concentration of 0.8-2.5%. Add N-hydroxymethyl acrylamide (NMA) under continuous stirring and dissolve for 20-40 minutes. The mass ratio of dicarboxyl chitosan to N-hydroxymethyl acrylamide is 1:1-3. Then add an inhibitor and an initiator to dissolve. Then stir and react under microwave irradiation for 8-20 minutes. After cooling, add methanol and stir for 3-8 minutes to obtain a reaction solution. The obtained precipitate is added into acetone for precipitation, and is ultrasonically washed with a mixture of acetone and ethanol in a volume ratio of 2:1, and then vacuum dried at 40-60°C for 18-24 hours to obtain a light yellow solid N-hydroxymethyl acrylamide-dicarboxyl chitosan; the polymerization inhibitor is 2,6-di-tert-butyl-p-cresol, hydroquinone or 4-methoxyphenol, and the mass ratio of dicarboxyl chitosan to the polymerization inhibitor is 1:0.008-0.015; the initiator is ammonium persulfate, ammonium chloride or potassium persulfate, and the mass ratio of dicarboxyl chitosan to the initiator is 1:0.12-0.68.

[0011] (2) N-hydroxymethyl acrylamide-dicarboxyl chitosan was mixed with phytic acid solution of pH=3.6-4.2 in a three-necked flask at 55-65°C in a bath ratio of 1g:30-50mL to dissolve the mixture, wherein the mass ratio of N-hydroxymethyl acrylamide-dicarboxyl chitosan to phytic acid was 1.8-3.2:1; the catalyst was then added to the mixture, and the mixture was condensed and refluxed at 70-85°C for 1-4h to allow the -OH group on the C6 position of the dicarboxyl chitosan to react with the PO4 3- An esterification reaction occurs, and after the reaction is completed, the product is poured into acetone and filtered to precipitate. The precipitate is placed in an ultra-low temperature refrigerator at -40 to -20°C for pre-freezing for 5 to 10 hours, then subjected to microwave vacuum freeze-drying for 24 to 48 hours, rinsed with ethanol to remove impurities 3 to 5 times, and then vacuum-dried at 40 to 50°C for 8 to 12 hours to obtain a yellow solid N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid (NMA-DCCS-PA), which is an intumescent bio-based flame retardant. The catalyst is 4-dimethylaminopyridine (DMAP) or dicyclohexylcarbodiimide (DCC), and the mass concentration of the catalyst added to the mixed solution is 1 to 2.5%.

[0012] Preferably, the viscosity-average molecular weight of the N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid (NMA-DCCS-PA) in step (2) is 51,400 to 103,600, the carboxyl content at the C2 and C3 positions is 40.73 to 62.49%, the degree of substitution of N-hydroxymethyl acrylamide at the C6 position is 23.16 to 39.51%, the degree of substitution of phytic acid at the C6 position is 45.20 to 63.15%, the degree of deacetylation is 50.23 to 71.31%, and the solubility in water is 7.62 to 15.08 g / 100 mL. The structural formula of the N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid is as follows:

[0013] .

[0014] Preferably, in step (1), the power of the microwave radiation is 480-860 W, and the microwave radiation temperature is 90-150° C.

[0015] Preferably, in step (2), the pH of the phytic acid solution is adjusted by acetic acid or sodium hydroxide solution with a concentration of 0.06 to 0.1 mol / L.

[0016] Preferably, in step (2), the temperature of the microwave vacuum freeze-drying is -100 to -60°C, the microwave power is 1580 to 2600W, and the vacuum degree is 8 to 15Pa.

[0017] The present invention further discloses a method for preparing an intumescent bio-based flame retardant modified fabric, comprising the following steps:

[0018] S1. Adding the cellulose fiber fabric after scouring, desizing or degumming to an aqueous solution of the intumescent bio-based flame retardant with a mass concentration of 0.5-2% at a bath ratio of 1 g: 20-30 mL to obtain a fabric-flame retardant composite solution;

[0019] Alternatively, the protein fiber fabric after scouring, desizing or degumming is added to an aqueous solution of the intumescent bio-based flame retardant with a mass concentration of 0.5-2% at a bath ratio of 1 g: 20-30 mL, the pH is adjusted to 4.0-4.6 (adjusted by a sodium hydroxide solution with a concentration of 0.1-0.3 mol / L), and the mixture is stirred at 50-65° C. for 1-3 hours to allow the NMA-DCCS-PA molecules to undergo an amide cross-linking reaction with the protein fabric to obtain a fabric-flame retardant composite liquid;

[0020] Adding an alkaline catalyst to the fabric-flame retardant composite liquid and dissolving it, and then continuously stirring and reacting it at 60-80° C. for 1-3 hours to allow the NMA-DCCS-PA molecules to undergo a nucleophilic addition reaction with the fabric, thereby grafting the flame retardant coating on the fabric surface; using an electric padder to perform double dipping and double padding to ensure that the liquid carrying rate of the fabric with the flame retardant coating is 80-100%;

[0021] The alkaline catalyst is sodium carbonate, sodium bicarbonate or sodium hydroxide, and the mass concentration of the alkaline catalyst in the aqueous solution of the intumescent bio-based flame retardant is 1.2-3%.

[0022] S2. Pre-drying the flame retardant-coated fabric obtained in step S1 at 70-80° C. for 15-30 minutes, and then baking at 120-150° C. for 3-5 minutes. The resulting product is filtered and washed with a mixture of acetone and ethanol in a volume ratio of 1:1 to remove unreacted NMA-DCCS-PA. The product is then washed with deionized water, dehydrated, and vacuum-dried to obtain an intumescent bio-based flame retardant-modified fabric.

[0023] Preferably, the grafting rate of NMA-DCCS-PA in the intumescent bio-based flame retardant modified fabric is 8.94-24.18%.

[0024] By optimizing the mass ratio of N-hydroxymethylacrylamide-dicarboxylic chitosan to phytic acid in NMA-DCCS-PA, the amount of catalyst, the esterification reaction time, the mass concentration of NMA-DCCS-PA solution, the amount of alkaline catalyst, the grafting (including amide cross-linking reaction and nucleophilic addition reaction) reaction time and temperature in the preparation of modified fabrics, a series of NMA-DCCS-PA flame retardants with different N-hydroxymethylacrylamide substitution degrees and phytic acid substitution degrees as well as functional modified fabrics with different grafting rates can be obtained.

[0025] Compared with the prior art, the preparation principle and advantages of the intumescent bio-based flame retardant NMA-DCCS-PA and the modified fabric based thereon in the present invention are as follows:

[0026] 1. The present invention uses the ionic liquid 1-butyl-3-methylimidazolium acetate ([Bmim][Ac]) as a dissolving and reaction medium for dicarboxy chitosan. The water produced during the nucleophilic substitution reaction between the primary hydroxyl group at the C6 position of dicarboxy chitosan and the hydroxyl group in N-methylol acrylamide can be completely absorbed by the ionic liquid, thereby promoting the forward progress of the substitution reaction. At the same time, 1-butyl-3-methylimidazolium acetate imparts a positive charge to the amino group at the C2 position of dicarboxy chitosan, thereby enhancing the probability of nucleophilic reaction with N-methylol acrylamide, accelerating the reaction rate, and promoting an increase in the degree of substitution of N-methylol acrylamide at the C6 position of dicarboxy chitosan. At the same time, the phenolic polymerization inhibitor used in the present invention will be oxidized to the corresponding quinone in the presence of oxygen, reducing the activity of free radicals, thereby preventing the polymerization reaction of the N-methylol acrylamide monomer and increasing the degree of substitution of N-methylol acrylamide at the C6 position of dicarboxy chitosan. The initiators used in the present invention, such as ammonium persulfate, ammonium chloride or potassium persulfate, have good water solubility, small molecular weight and low steric hindrance. They generate active free radicals by decomposition, which initiate the affinity substitution reaction between carboxyl chitosan and N-hydroxymethyl acrylamide, thereby accelerating the substitution reaction rate.

[0027] 2. The present invention utilizes the ionic liquid 1-butyl-3-methylimidazolium acetate ([Bmim][Ac]) as a green solvent for dicarboxy chitosan and a reaction medium for grafting N-hydroxymethyl acrylamide. The ionic liquid has the advantages of being non-toxic and pollution-free, having stable physical and chemical properties, having no vapor pressure and being non-volatile, being green and environmentally friendly, and being recyclable. Furthermore, the dicarboxy chitosan is directly dissolved in the 1-butyl-3-methylimidazolium acetate at a moderate temperature (65-85° C.), and its molecular structure does not undergo derivatization or degradation, thereby maintaining the amphoteric polyelectrolyte properties and excellent biocompatibility of the dicarboxy chitosan. Furthermore, after the reaction is completed, anhydrous ethanol can be added to the ionic liquid to precipitate the remaining dicarboxy chitosan. After evaporating and removing the anhydrous ethanol, the ionic liquid can be recycled, thereby being environmentally friendly.

[0028] 3. The N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid flame retardant prepared by the present invention has excellent performance. Both dicarboxyl chitosan and N-hydroxymethyl acrylamide provide rich carbon sources. The amino group on the C2 position of dicarboxyl chitosan produces ammonia and other gases as a gas source during the combustion process. The two carboxyl groups can improve the carbonization effect of chitosan. The molecular structure of phytic acid consists of 6 phosphate groups esterified with 6 hydroxyl groups on the inositol ring to form 6 phosphate bonds. The esterification of these hydroxyl groups makes phytic acid a highly phosphorylated compound with excellent flame retardant properties. The acidic groups such as carboxyl and phosphoric acid contained in NMA-DCCS-PA can be dehydrated to form a dense and stable carbon layer when exposed to high temperature or flame, thereby suppressing smoke emissions during the combustion process. At the same time, a large amount of phosphoric acid derivatives are produced during pyrolysis, which can not only promote the dehydration and carbonization of the carbon source, but also capture free radicals and improve the overall flame retardant properties. N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid is a highly effective intumescent flame retardant that combines acid, carbon, and gas sources. It produces no toxic or corrosive gases and is environmentally friendly. Furthermore, the NMA-DCCS-PA molecule retains the amino group at the C2 position and can form a polycationic amino group, exhibiting highly effective antimicrobial activity.

[0029] 4. The present invention reacts dicarboxyl chitosan with N-methylol acrylamide under microwave irradiation conditions in the presence of a polymerization inhibitor and an initiator. Due to the rapid heating rate, short reaction time, and good uniformity of microwave irradiation, the dicarboxyl chitosan and N-methylol acrylamide are fully contacted, promoting an affinity substitution reaction between the primary hydroxyl group at the C6 position of the dicarboxyl chitosan and the hydroxyl group in the N-methylol acrylamide. Simultaneously, the microwave radiation enhances the energy absorption of the dicarboxyl chitosan and N-methylol acrylamide reactants, promotes movement between molecular segments, and accelerates the substitution reaction rate of the dicarboxyl chitosan and N-methylol acrylamide. The process is simple, saves reaction time, reduces energy consumption, and increases the degree of substitution of N-methylol acrylamide at the C6 position of the dicarboxyl chitosan.

[0030] 5. The present invention dissolves N-hydroxymethyl acrylamide-dicarboxyl chitosan in phytic acid (PA) solution, and under the action of catalyst, the -OH group on the C6 position of dicarboxyl chitosan reacts with the PO4 in the phytic acid molecule. 3- The esterification reaction occurs, and the catalyst 4-dimethylaminopyridine (DMAP) or dicyclohexylcarbodiimide (DCC) used is suitable for catalyzing the esterification reaction of polysaccharides with large steric hindrance. It plays the role of catalytic reaction and water absorbent at the same time, completely absorbing the water product of the esterification reaction, promoting the reversible esterification reaction to the direction of ester formation, significantly accelerating the esterification reaction rate of N-hydroxymethylacrylamide-dicarboxyl chitosan and phytic acid, and improving the phytic acid substitution degree at the C6 position of N-hydroxymethylacrylamide-dicarboxyl chitosan.

[0031] 6. The present invention puts N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid into a cryogenic refrigerator for pre-freezing, and then microwave vacuum freeze-drying is used to obtain an intumescent flame retardant. The water freezing speed inside N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid is slowed down by pre-freezing, so as to reduce the crystallization risk of water during freezing, and it is helpful to form a stable intumescent flame retardant structure. Pre-freezing can also reduce crystallization and deformation during flame retardant freeze drying, effectively avoiding the rapid removal of moisture and causing the structural collapse of intumescent flame retardant, and significantly improving the structural stability of NMA-DCCS-PA. The present invention utilizes microwave vacuum freeze drying to obtain N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid intumescent bio-based flame retardant material, microwave drying and vacuum drying are combined, and respective advantages can be fully utilized, the ice crystals generated inside the NMA-DCCS-PA flame retardant during pre-freezing are sublimated and dried below vacuum and eutectic temperature, and latent heat of sublimation is provided to the material to be dried in a frozen state by a microwave generator, and the moisture of the material is quickly removed. Compared with the disadvantage of slow conventional heat conduction rate under vacuum state, the drying time is shortened and the drying efficiency is improved. The microwave vacuum freeze drying temperature is uniform, the water molecules in the flame retardant are evenly distributed, the moisture drying rate is consistent, and the structural strength of the intumescent bio-based flame retardant is enhanced.

[0032] 7. The present invention conducts a grafting reaction between NMA-DCCS-PA molecules and protein fiber fabrics under acidic conditions of pH = 4.0 to 4.6. The positively charged NMA-DCCS-PA molecules enhance the probability of contacting negatively charged protein fiber fabrics (protein fiber fabrics have a negative charge at an isoelectric point of pH lower than 4.0 to 4.6), thereby promoting the amide cross-linking reaction rate between the two. After adding an alkaline catalyst to the solution, the unsaturated double bonds in the NMA-DCCS-PA molecules can also undergo nucleophilic addition reactions with the hydroxyl groups in the protein fiber fabrics, thereby forming multi-site chemical bonds on the fabric surface, resulting in strong water wash resistance and a high grafting rate. No chemical cross-linking agent is used in the entire grafting reaction, thereby avoiding the negative impact of cross-linking agent coating on the excellent properties of the fabric and human health. The NMA-DCCS-PA molecules are uniformly penetrated into the fabric by a padding method and cross-linked on the fiber surface to form a strong flame-retardant coating, exhibiting excellent flame retardant and antibacterial properties without affecting the wearing performance of the fabric. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of the preparation principle of the N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid intumescent flame retardant of the present invention.

[0034] Figure 2 This is a schematic diagram of the preparation principle of the NMA-DCCS-PA flame retardant grafted silk fabric of the present invention.

[0035] Figure 3 This is a scanning electron microscope image of the silk fabric modified with the NMA-DCCS-PA flame retardant in Test Item 2 of the present invention, where a, b, and c correspond to the unmodified silk fabric, the silk fabric modified by the method of Example 2, and the silk fabric modified by the method of Example 3, respectively. DETAILED DESCRIPTION

[0036] In order to better understand the technical features, objectives and beneficial effects of the present invention, the present invention is further described below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited to the following embodiments.

[0037] 1. Preparation of intumescent bio-based flame retardant NMA-DCCS-PA and modified fabrics based on it

[0038] Example 1

[0039] In this example, NMA-DCCS-PA was prepared according to the following steps:

[0040] (1) 2 g of dicarboxyl chitosan (carboxyl content at C2 and C3 positions is 46.74%, deacetylation degree is 65.38%, viscosity average molecular weight is 81,700, solubility in water is 9.63 g / 100 mL, isoelectric point pH = 4.6) was dissolved in 1-butyl-3-methylimidazole acetate at 82 ° C to prepare a dicarboxyl chitosan solution with a mass concentration of 1%. N-hydroxymethyl acrylamide was added under continuous stirring and dissolved for 25 min. The mass ratio of dicarboxyl chitosan to N-hydroxymethyl acrylamide was 1:1. Then, an inhibitor 2 was added. 6-di-tert-butyl-p-cresol (the mass ratio of dicarboxyl chitosan to inhibitor is 1:0.008) and initiator ammonium chloride (the mass ratio of dicarboxyl chitosan to initiator is 1:0.18) were dissolved, and then stirred for reaction under microwave irradiation conditions (microwave radiation power is 500 W, microwave radiation temperature is 95°C) for 10 minutes. After cooling, 16 mL of methanol was added and stirred for 3 minutes to obtain a reaction solution; the reaction solution was added to 90 mL of acetone for precipitation, and the obtained precipitate was ultrasonically washed with a mixture of acetone and ethanol with a volume ratio of 2:1, and then vacuum dried at 40°C for 18 hours to obtain a light yellow solid N-hydroxymethyl acrylamide-dicarboxyl chitosan.

[0041] (2) N-hydroxymethyl acrylamide-dicarboxyl chitosan was mixed with a phytic acid solution of pH=4.2 in a three-necked flask at a bath ratio of 1g:35mL at 55°C to dissolve the mixture. The mass ratio of N-hydroxymethyl acrylamide-dicarboxyl chitosan to phytic acid was 3:1. Then, the catalyst dicyclohexylcarbodiimide (DCC) was added to the above mixture (the mass concentration of the catalyst added to the mixture was 1.2%), and condensed and refluxed at 72°C for 1.5h to allow the -OH on the C6 position of the dicarboxyl chitosan to react with the PO4 in the phytic acid molecule. 3- An esterification reaction occurs. After the reaction is completed, the product is poured into acetone and filtered to precipitate. The precipitate is placed in a -22°C ultra-low temperature refrigerator for precooling for 6 hours, and then subjected to microwave vacuum freeze-drying for 30 hours (the temperature of microwave vacuum freeze-drying is -68°C, the microwave power is 1620W, and the vacuum degree is 13Pa). It is washed with ethanol to remove impurities three times, and then vacuum-dried at 40°C for 8 hours to obtain a yellow solid N-hydroxymethylacrylamide-dicarboxylic chitosan-phytic acid (NMA-DCCS-PA), which is an intumescent bio-based flame retardant.

[0042] The intumescent bio-based flame retardant obtained in this example was applied to functionally modified cotton fabrics, and the specific steps were as follows:

[0043] S1. The scour-desized cotton fabric was added to a 0.8% NMA-DCCS-PA aqueous solution at a bath ratio of 1 g:25 mL. Then, after dissolving the alkaline catalyst sodium hydroxide (the mass concentration of the alkaline catalyst in the NMA-DCCS-PA aqueous solution was 1.5%), the mixture was stirred continuously at 65°C for 1 hour to allow the NMA-DCCS-PA molecules to undergo a nucleophilic addition reaction with the cotton fabric, thereby grafting a flame retardant coating on the surface of the cotton fabric. The flame retardant coating was then double-dipped and double-rolled using an electric padder to achieve a liquid carrying rate of 85% for the cotton fabric.

[0044] S2. The flame retardant-coated cotton fabric obtained in step S1 was pre-baked at 72° C. for 18 min, and then baked at 140° C. for 3 min. The resulting product was filtered and washed with a mixture of acetone and ethanol in a volume ratio of 1:1 to remove unreacted NMA-DCCS-PA. The product was then washed with deionized water, dehydrated, and vacuum-dried to obtain an intumescent bio-based flame retardant-modified cotton fabric.

[0045] The test results show that the viscosity-average molecular weight of the N-hydroxymethyl acrylamide-dicarboxy chitosan-phytic acid (NMA-DCCS-PA) prepared in this example is 96,500, the carboxyl content at the C2 and C3 positions is 42.37%, the substitution degree of N-hydroxymethyl acrylamide at the C6 position is 27.14%, the substitution degree of phytic acid at the C6 position is 46.91%, the deacetylation degree is 56.08%, and the solubility in water is 8.14 g / 100 mL.

[0046] Testing showed that the grafting rate of the intumescent bio-based flame retardant-modified cotton fabric obtained in this embodiment was 9.21%, the breaking strength of the modified cotton fabric was 386.6N, the wrinkle recovery angle was 191.7°, and the air permeability was 416.5mm / s. After 100 washes, the limiting oxygen index of the modified cotton fabric was 33.9%, the antibacterial rate against Staphylococcus aureus was 92.84%, and the antibacterial rate against Escherichia coli was 93.71%.

[0047] Example 2

[0048] In this example, NMA-DCCS-PA was prepared according to the following steps:

[0049] (1) 2 g of dicarboxyl chitosan (carboxyl content at C2 and C3 positions of 51.06%, deacetylation degree of 70.38%, viscosity-average molecular weight of 68,200, solubility in water of 12.35 g / 100 mL, isoelectric point pH = 4.4) was dissolved in 1-butyl-3-methylimidazole acetate at 75 ° C to prepare a dicarboxyl chitosan solution with a mass concentration of 1.5%. N-hydroxymethyl acrylamide was added under continuous stirring and dissolved for 30 min. The mass ratio of dicarboxyl chitosan to N-hydroxymethyl acrylamide was 1:2. Then, an inhibitor 2 was added. 6-di-tert-butyl-p-cresol (the mass ratio of dicarboxyl chitosan to inhibitor is 1:0.009) and initiator potassium persulfate (the mass ratio of dicarboxyl chitosan to initiator is 1:0.32) were dissolved, and then stirred for reaction for 15 minutes under microwave irradiation conditions (microwave radiation power is 640 W, microwave radiation temperature is 120°C). After cooling, 18 mL of methanol was added and stirred for 5 minutes to obtain a reaction solution; the reaction solution was added to 100 mL of acetone for precipitation, and the obtained precipitate was ultrasonically washed with a mixture of acetone and ethanol with a volume ratio of 2:1, and then vacuum dried at 45°C for 20 hours to obtain a light yellow solid N-hydroxymethyl acrylamide-dicarboxyl chitosan.

[0050] (2) N-hydroxymethyl acrylamide-dicarboxyl chitosan was mixed with a phytic acid solution of pH=3.8 in a three-necked flask at a bath ratio of 1g:40mL at 60°C to dissolve the mixture. The mass ratio of N-hydroxymethyl acrylamide-dicarboxyl chitosan to phytic acid was 2:1. Then, the catalyst dicyclohexylcarbodiimide (DCC) was added to the above mixture (the mass concentration of the catalyst added to the mixture was 1.6%), and refluxed at 80°C for 2h to allow the -OH on the C6 position of the dicarboxyl chitosan to react with the PO4 in the phytic acid molecule. 3- An esterification reaction occurs. After the reaction is completed, the product is poured into acetone and filtered to precipitate. The precipitate is placed in a -28°C ultra-low temperature refrigerator for precooling for 8 hours, and then subjected to microwave vacuum freeze-drying for 36 hours (the temperature of microwave vacuum freeze-drying is -75°C, the microwave power is 1860W, and the vacuum degree is 10Pa). It is washed with ethanol to remove impurities 4 times, and then vacuum-dried at 45°C for 9 hours to obtain a yellow solid N-hydroxymethyl acrylamide-dicarboxylic chitosan-phytic acid (NMA-DCCS-PA), which is an intumescent bio-based flame retardant.

[0051] The intumescent bio-based flame retardant obtained in this example is applied to functionally modified silk fabrics, and the specific steps are as follows:

[0052] S1. The scouring and degumming silk fabric was added to a 1.2% mass concentration NMA-DCCS-PA aqueous solution at a bath ratio of 1 g:25 mL. The pH was adjusted to an acidic condition of pH = 4.2 with a 0.2 mol / L sodium hydroxide solution and the mixture was stirred and reacted at 55°C for 1.5 hours to allow the NMA-DCCS-PA molecules to undergo an amide cross-linking reaction with the silk fabric. Then, after the alkaline catalyst sodium carbonate was added and dissolved (the mass concentration of the alkaline catalyst in the NMA-DCCS-PA aqueous solution was 1.8%), the mixture was stirred and reacted at 70°C for 1.5 hours to allow the NMA-DCCS-PA molecules to undergo a nucleophilic addition reaction with the silk fabric again, and a flame retardant coating was grafted on the surface of the silk fabric. The silk fabric with the flame retardant coating was subjected to two dipping and two rolling processes using an electric padder to achieve a liquid carrying rate of 90%.

[0053] S2. The silk fabric with the flame retardant coating obtained in step S1 was pre-baked at 75° C. for 20 min, and then baked at 120° C. for 4 min. The resulting product was filtered and washed with a mixture of acetone and ethanol in a volume ratio of 1:1 to remove unreacted NMA-DCCS-PA. The product was then washed with deionized water, dehydrated, and vacuum-dried to obtain an intumescent bio-based flame retardant-modified silk fabric.

[0054] Tests showed that the viscosity-average molecular weight of the N-hydroxymethyl acrylamide-dicarboxy chitosan-phytic acid (NMA-DCCS-PA) prepared in this example was 84,300, the carboxyl content at the C2 and C3 positions was 47.09%, the degree of substitution of N-hydroxymethyl acrylamide at the C6 position was 29.85%, the degree of substitution of phytic acid at the C6 position was 53.70%, the degree of deacetylation was 64.54%, and the solubility in water was 10.51 g / 100 mL.

[0055] Testing showed that the grafting rate of the intumescent bio-based flame retardant-modified silk fabric obtained in this embodiment was 13.18%, the breaking strength of the modified silk fabric was 470.5N, the wrinkle recovery angle was 185.2°, and the air permeability was 553.7mm / s. After 100 washes, the limiting oxygen index of the modified silk fabric was 37.8%, the antibacterial rate against Staphylococcus aureus was 93.61%, and the antibacterial rate against Escherichia coli was 95.66%.

[0056] Example 3

[0057] In this example, NMA-DCCS-PA was prepared according to the following steps:

[0058] (1) 2 g of dicarboxyl chitosan (carboxyl content at C2 and C3 positions of 63.52%, deacetylation degree of 81.17%, viscosity-average molecular weight of 42,400, solubility in water of 16.83 g / 100 mL, isoelectric point pH = 4.2) was dissolved in 1-butyl-3-methylimidazole acetate at 68 ° C to prepare a dicarboxyl chitosan solution with a mass concentration of 2%. N-hydroxymethyl acrylamide was added under continuous stirring and dissolved for 35 min. The mass ratio of dicarboxyl chitosan to N-hydroxymethyl acrylamide was 1:2.5. Then, the polymerization inhibitor 4-methoxyphenol (dicarboxyl chitosan and polymerization inhibitor) was added. The reaction mixture was stirred for 18 minutes under microwave irradiation (microwave radiation power of 720 W, microwave irradiation temperature of 140°C). After cooling, 20 mL of methanol was added and stirred for 6 minutes to obtain a reaction solution. The reaction solution was added to 120 mL of acetone for precipitation. The obtained precipitate was ultrasonically washed with a mixture of acetone and ethanol in a volume ratio of 2:1, and then vacuum dried at 50°C for 22 hours to obtain a light yellow solid N-hydroxymethyl acrylamide-dicarboxy chitosan.

[0059] (2) At 60°C, N-hydroxymethylacrylamide-dicarboxyl chitosan was mixed with a phytic acid (PA) solution of pH = 4.0 in a three-necked flask at a bath ratio of 1g:50mL to dissolve the mixture, and the mass ratio of N-hydroxymethylacrylamide-dicarboxyl chitosan to phytic acid was 2.4:1. Then, the catalyst 4-dimethylaminopyridine (DMAP) was added to the above mixture (the mass concentration of the catalyst added to the mixture was 2%), and refluxed at 80°C for 3h to allow the -OH on the C6 position of N-hydroxymethylacrylamide-dicarboxyl chitosan to react with the PO4 in the phytic acid molecule. 3- An esterification reaction occurs. After the reaction is completed, the product is poured into acetone and filtered to precipitate. The precipitate is placed in a -30°C ultra-low temperature refrigerator for precooling for 9 hours, and then subjected to microwave vacuum freeze-drying for 42 hours (the temperature of microwave vacuum freeze-drying is -80°C, the microwave power is 2280W, and the vacuum degree is 8Pa). It is washed with ethanol to remove impurities 5 times, and then vacuum-dried at 45°C for 10 hours to obtain a yellow solid N-hydroxymethyl acrylamide-dicarboxylic chitosan-phytic acid (NMA-DCCS-PA), which is an intumescent bio-based flame retardant.

[0060] The intumescent bio-based flame retardant obtained in this example is applied to functionally modified silk fabrics, and the specific steps are as follows:

[0061] S1. The scouring and degumming silk fabric was added to a 1.5% mass concentration NMA-DCCS-PA aqueous solution at a bath ratio of 1 g:30 mL. The pH was adjusted to an acidic condition of 4.4 with a sodium hydroxide solution having a concentration of 0.12 mol / L. The mixture was stirred and reacted at 60°C for 2 hours to allow the NMA-DCCS-PA molecules to undergo an amide cross-linking reaction with the silk fabric. Then, an alkaline catalyst, sodium bicarbonate, was added and dissolved (the mass concentration of the alkaline catalyst in the NMA-DCCS-PA aqueous solution was 2.4%). The mixture was stirred and reacted at 80°C for 2 hours to allow the NMA-DCCS-PA molecules to undergo a nucleophilic addition reaction with the silk fabric, thereby grafting a flame retardant coating on the surface of the silk fabric. The silk fabric with the flame retardant coating was subjected to two dipping and two rolling processes using an electric padder, so that the liquid carrying rate of the silk fabric was 95%.

[0062] S2. The silk fabric with the flame retardant coating obtained in step S1 was pre-baked at 75° C. for 25 minutes and then baked at 120° C. for 5 minutes. The resulting product was filtered and washed with a mixture of acetone and ethanol in a volume ratio of 1:1 to remove unreacted NMA-DCCS-PA. The product was then washed with deionized water, dehydrated, and vacuum-dried to obtain an intumescent bio-based flame retardant-modified silk fabric.

[0063] Tests showed that the viscosity-average molecular weight of the N-hydroxymethyl acrylamide-dicarboxy chitosan-phytic acid (NMA-DCCS-PA) prepared in this example was 51,700, the carboxyl content at the C2 and C3 positions was 58.11%, the degree of substitution of N-hydroxymethyl acrylamide at the C6 position was 37.82%, the degree of substitution of phytic acid at the C6 position was 61.94%, the degree of deacetylation was 70.35%, and the solubility in water was 14.57 g / 100 mL.

[0064] Testing showed that the intumescent bio-based flame retardant-modified silk fabric obtained in this embodiment had a grafting rate of 24.06%, a breaking strength of 492.7 N, a wrinkle recovery angle of 215.6°, and an air permeability of 537.1 mm / s. After 100 washes, the limited oxygen index of the modified silk fabric was 44.6%, and the antibacterial rate against Staphylococcus aureus was 96.28%, and the antibacterial rate against Escherichia coli was 97.46%.

[0065] Example 4

[0066] In this example, NMA-DCCS-PA was prepared according to the following steps:

[0067] (1) 2 g of dicarboxyl chitosan (carboxyl content at C2 and C3 positions of 63.52%, deacetylation degree of 81.17%, viscosity-average molecular weight of 42,400, solubility in water of 16.83 g / 100 mL, isoelectric point pH = 4.2) was dissolved in 1-butyl-3-methylimidazole acetate at 68 ° C to prepare a dicarboxyl chitosan solution with a mass concentration of 2%. N-hydroxymethyl acrylamide was added under continuous stirring and dissolved for 35 min. The mass ratio of dicarboxyl chitosan to N-hydroxymethyl acrylamide was 1:2.5. Then, the polymerization inhibitor 4-methoxyphenol (dicarboxyl chitosan and polymerization inhibitor) was added. The reaction mixture was stirred for 18 minutes under microwave irradiation (microwave radiation power of 720 W, microwave irradiation temperature of 140°C). After cooling, 20 mL of methanol was added and stirred for 6 minutes to obtain a reaction solution. The reaction solution was added to 120 mL of acetone for precipitation. The obtained precipitate was ultrasonically washed with a mixture of acetone and ethanol in a volume ratio of 2:1, and then vacuum dried at 50°C for 22 hours to obtain a light yellow solid N-hydroxymethyl acrylamide-dicarboxy chitosan.

[0068] (2) N-hydroxymethylacrylamide-dicarboxyl chitosan was mixed with a phytic acid solution of pH=4.0 in a three-necked flask at a bath ratio of 1g:50mL at 60°C to dissolve the mixture. The mass ratio of N-hydroxymethylacrylamide-dicarboxyl chitosan to phytic acid was 2.4:1. The catalyst 4-dimethylaminopyridine (DMAP) was then added to the mixture (the mass concentration of the catalyst added to the mixture was 2%), and the mixture was condensed and refluxed at 80°C for 3h to allow the -OH group at the C6 position of N-hydroxymethylacrylamide-dicarboxyl chitosan to react with the PO4 in the phytic acid molecule. 3- An esterification reaction occurs. After the reaction is completed, the product is poured into acetone and filtered to precipitate. The precipitate is placed in a -30°C ultra-low temperature refrigerator for precooling for 9 hours, and then subjected to microwave vacuum freeze-drying for 42 hours (the temperature of microwave vacuum freeze-drying is -80°C, the microwave power is 2280W, and the vacuum degree is 8Pa). It is washed with ethanol to remove impurities 5 times, and then vacuum-dried at 45°C for 10 hours to obtain a yellow solid N-hydroxymethyl acrylamide-dicarboxylic chitosan-phytic acid (NMA-DCCS-PA), which is an intumescent bio-based flame retardant.

[0069] The intumescent bio-based flame retardant obtained in this example is applied to functionally modified wool fabrics, and the specific steps are as follows:

[0070] S1. The scour-desized wool fabric was added to a 1.5% mass concentration NMA-DCCS-PA aqueous solution at a bath ratio of 1 g:30 mL. The pH was adjusted to an acidic condition of 4.4 with a 0.2 mol / L sodium hydroxide solution and the mixture was stirred at 60°C for 2 h to allow the NMA-DCCS-PA molecules to undergo an amide cross-linking reaction with the wool fabric. Then, an alkaline catalyst, sodium bicarbonate, was added and dissolved (the mass concentration of the alkaline catalyst in the NMA-DCCS-PA aqueous solution was 2.4%). The mixture was stirred at 80°C for 2.5 h to allow the NMA-DCCS-PA molecules to undergo a nucleophilic addition reaction with the wool fabric, thereby grafting a flame retardant coating on the surface of the wool fabric. The wool fabric with the flame retardant coating was dipped and rolled twice using an electric padder to achieve a liquid carrying rate of 100%.

[0071] S2. The wool fabric with the flame retardant coating obtained in step S1 was pre-baked at 78° C. for 25 minutes and then baked at 130° C. for 5 minutes. The resulting product was filtered and washed with a mixture of acetone and ethanol in a volume ratio of 1:1 to remove unreacted NMA-DCCS-PA. The product was then washed with deionized water, dehydrated, and vacuum-dried to obtain an intumescent bio-based flame retardant-modified wool fabric.

[0072] Tests showed that the viscosity-average molecular weight of the N-hydroxymethyl acrylamide-dicarboxy chitosan-phytic acid (NMA-DCCS-PA) prepared in this example was 51,700, the carboxyl content at the C2 and C3 positions was 58.11%, the degree of substitution of N-hydroxymethyl acrylamide at the C6 position was 37.82%, the degree of substitution of phytic acid at the C6 position was 61.94%, the degree of deacetylation was 70.35%, and the solubility in water was 14.57 g / 100 mL.

[0073] Testing showed that the grafting rate of the intumescent bio-based flame retardant-modified wool fabric obtained in this embodiment was 20.47%, the breaking strength of the modified wool fabric was 419.2N, the wrinkle recovery angle was 207.5°, and the air permeability was 517.6mm / s; after 100 washes, the limiting oxygen index of the modified wool fabric was 40.5%, the antibacterial rate against Staphylococcus aureus was 94.36%, and the antibacterial rate against Escherichia coli was 95.94%.

[0074] Comparative Example 1

[0075] In this comparative example, NMA-DCCS-PA was prepared using the same process and conditions as in Example 3, except that the amount of initiator added in step (1) was 0.

[0076] The flame retardant obtained in this comparative example was applied to functionally modified silk fabrics using the same process and conditions as in Example 3.

[0077] Tests showed that the viscosity-average molecular weight of the N-hydroxymethyl acrylamide-dicarboxy chitosan-phytic acid (NMA-DCCS-PA) prepared in this example was 48,900, the carboxyl content at the C2 and C3 positions was 59.26%, the degree of substitution of N-hydroxymethyl acrylamide at the C6 position was 14.73%, the degree of substitution of phytic acid at the C6 position was 60.30%, the degree of deacetylation was 68.92%, and the solubility in water was 12.76 g / 100 mL.

[0078] Testing showed that the grafting rate of the intumescent bio-based flame retardant-modified silk fabric obtained in this embodiment was 12.38%, the breaking strength of the modified silk fabric was 459.1N, the wrinkle recovery angle was 172.3°, and the air permeability was 556.2mm / s. After 100 washes, the limiting oxygen index of the modified silk fabric was 34.3%, the antibacterial rate against Staphylococcus aureus was 93.09%, and the antibacterial rate against Escherichia coli was 94.17%.

[0079] Comparative Example 2

[0080] Performance tests of fabrics not modified with intumescent bio-based flame retardants:

[0081] (1) After testing, the unmodified cotton fabric (i.e., the scouring and desizing cotton fabric used in Example 1) had a breaking strength of 357.4 N, a wrinkle recovery angle of 162.7°, and an air permeability of 430.4 mm / s. After 100 washes, the limiting oxygen index of the unmodified cotton fabric was 17.5%, the antibacterial rate against Staphylococcus aureus was 26.51%, and the antibacterial rate against Escherichia coli was 19.18%.

[0082] (2) After testing, the unmodified silk fabric (i.e., the scouring and desizing silk fabric used in Examples 2 and 3) had a breaking strength of 439.5 N, a wrinkle recovery angle of 150.6°, and an air permeability of 571.4 mm / s. After 100 washes, the limiting oxygen index of the unmodified silk fabric was 22.3%, the antibacterial rate against Staphylococcus aureus was 22.75%, and the antibacterial rate against Escherichia coli was 24.08%.

[0083] (3) After testing, the unmodified wool fabric (i.e., the wool fabric after scouring and desizing used in Example 4) had a breaking strength of 402.3 N, a wrinkle recovery angle of 177.5°, and an air permeability of 534.8 mm / s; after 100 washes, the unmodified wool fabric had a limiting oxygen index of 25.7%, an antibacterial rate against Staphylococcus aureus of 28.64%, and an antibacterial rate against Escherichia coli of 25.17%.

[0084] In the above examples and comparative examples: the breaking strength was tested according to GB / T3923.2-1998 "Tensile Properties of Textile Fabrics", with a sample clamping length of 10 cm and a tensile speed of 100 mm / min; the wrinkle recovery angle was tested according to GB / T 3819-1997 "Determination of Crease Recovery of Textile Fabrics"; and the air permeability was tested according to GB / T 5453-1997 "Determination of Air Permeability of Textile Fabrics" with a test area of ​​25 cm. 2 , test air pressure 100pa; the limiting oxygen index is tested on a JF-3 oxygen index meter in accordance with ASTMD2863 standard; the antibacterial rate against Staphylococcus aureus and Escherichia coli is tested in accordance with GB / T 20944.3-2008 "Evaluation of antibacterial properties of textiles Part 3: Oscillation method" standard.

[0085] 2. Testing the samples obtained in the above examples

[0086] Test Item 1: Cone Calorimetry Analysis of Silk Fabric Modified with Intumescent Bio-based Flame Retardant

[0087] The fire behavior of the modified silk fabrics was analyzed using a cone calorimeter. Three silk fabric samples were collected: the first was the unmodified silk fabric sample (control sample) from Comparative Example 2; the second was a silk fabric modified with an NMA-DCCS-PA intumescent bio-based flame retardant, obtained according to Example 2; and the third was a silk fabric modified with an NMA-DCCS-PA intumescent bio-based flame retardant, obtained according to Example 3. The test results are shown in Table 1.

[0088] Table 1. Cone calorimeter test results of bio-based flame retardant modified silk fabrics

[0089]

[0090] Time to ignition (TTI), peak HRR (PHRR) and total heat release (THR) are several important parameters of combustion behavior during the combustion of textile materials. The unmodified silk fabric reaches PHRR at 8s and burns out at 38s. The TTI, PHRR and THR values ​​are 8s, 78.763KW / m 2 and 5.012MJ / m 2 Obviously, silk fabric is a very flammable fiber material. The silk fabric modified with NMA-DCCS-PA bio-based flame retardant in Example 3 reached PHRR at 31s and burned out at 65s, with the burning time increased by 71.05% compared with the unmodified silk fabric. The TTI, PHRR and THR values ​​were 31s, 36.131KW / m 2 and 2.908MJ / m 2, PHRR and THR values ​​were reduced by 54.13% and 41.98% respectively compared with the unmodified silk fabric. This shows that NMA-DCCS-PA bio-based flame retardant graft coating can effectively reduce PHRR and THR during silk fabric combustion and prevent the rapid heat release of silk. At the same time, Table 1 shows that the total smoke production (TSP) value of silk fabric modified with NMA-DCCS-PA bio-based flame retardant is 0.049m 2 , than the unmodified silk fabric (0.298m 2 ) was 83.56% lower. Furthermore, modification with the bio-based flame retardant NMA-DCCS-PA also reduced CO and CO2 emissions (PCO, PCO2). This indicates that the acidic groups, such as carboxyl and phosphoric acid, contained in NMA-DCCS-PA can dehydrate to form a dense and stable carbon layer when exposed to high temperatures or flames, thereby suppressing smoke emissions during combustion. Furthermore, pyrolysis produces a large amount of phosphoric acid derivatives, which not only promote the dehydration and carbonization of the carbon source but also capture free radicals, enhancing the flame retardancy of the modified fabric. This indicates that N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid is a highly efficient intumescent flame retardant that combines the effects of an acid source, a carbon source, and a gas source. NMA-DCCS-PA grafted onto the surface of fabrics can effectively enhance the flame retardancy of textiles.

[0091] Test Item 2: Scanning Electron Microscope Analysis of Silk Fabric Modified with NMA-DCCS-PA Bio-based Flame Retardant

[0092] SEM was used to observe the micromorphology of unmodified silk fabrics and modified silk fabrics with different grafting ratios. Three silk fabric samples were collected: the first was silk fabric a obtained after scouring and degumming (blank control sample), the second was modified silk fabric b obtained by grafting silk fabric with NMA-DCCS-PA intumescent bio-based flame retardant according to the method of Example 2, with a grafting ratio of 13.18%, and the third was modified silk fabric c obtained by grafting silk fabric with NMA-DCCS-PA intumescent bio-based flame retardant according to the method of Example 3, with a grafting ratio of 24.06%. The test results are shown in Table 1. Figure 3 (a)~(c).

[0093] Depend on Figure 3 It can be seen that the surface of the original silk fiber a is relatively smooth and flat, with a small amount of unremoved sericin; while the surface of the silk fiber b after grafting with the NMA-DCCS-PA intumescent bio-based flame retardant is coated with many lumps (see Figure 3 b), and with the increase of the grafting rate of NMA-DCCS-PA flame retardant, the NMA-DCCS-PA molecules grafted on the surface of silk fibers gradually cross-link to form a relatively uniform flame retardant film (see Figure 3c) At the same time, the surface of the modified silk becomes relatively rough, which indicates that the NMA-DCCS-PA molecules are firmly bonded to the silk fibers through a chemical grafting reaction and cross-linked and deposited on the surface of the silk fibers, with strong water resistance and long-lasting flame retardant and antibacterial effects.

[0094] In summary, dicarboxyl chitosan (DCCS) was dissolved in the ionic liquid 1-butyl-3-methylimidazolium acetate ([Bmim][Ac]), and an inhibitor and an initiator were added to react with N-hydroxymethyl acrylamide (NMA) under microwave irradiation to undergo nucleophilic substitution reaction. Then, phytic acid (PA) was added to react with the C6 position of dicarboxyl chitosan to form a nucleophilic substitution reaction with the PO4 in the phytic acid molecule. 3- An esterification reaction occurs to produce an intumescent bio-based flame retardant, N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid (NMA-DCCS-PA). The unsaturated double bonds and carboxyl groups in the NMA-DCCS-PA molecule then undergo nucleophilic addition and amide crosslinking reactions with the hydroxyl and amino groups of the fabric, respectively, to chemically graft the NMA-DCCS-PA onto the fabric surface. This results in a functionally modified fabric that is human-friendly, safe, comfortable, highly flame-retardant, and has long-lasting antibacterial properties. The intumescent bio-based flame retardant prepared by the present invention contains a large number of carboxyl groups, phosphate groups, cationic amino groups, and unsaturated double bonds. It is environmentally friendly, highly reactive, and firmly chemically bonds to the fabric without the use of chemical crosslinkers. It remains washable and environmentally friendly, exhibiting multifunctional properties such as flame retardancy and fire protection, as well as long-lasting antibacterial properties. It is low-cost and easily marketable and applicable.

[0095] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An intumescent bio-based flame retardant, characterized in that: The intumescent bio-based flame retardant is N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid, which is prepared by dissolving dicarboxyl chitosan in ionic liquid 1-butyl-3-methylimidazolium acetate, adding a polymerization inhibitor and an initiator to react with N-hydroxymethyl acrylamide under microwave radiation to obtain N-hydroxymethyl acrylamide-dicarboxyl chitosan; then mixing N-hydroxymethyl acrylamide-dicarboxyl chitosan with phytic acid solution to obtain a mixed solution, adding a catalyst to the mixed solution to react the -OH group at the C6 position of the dicarboxyl chitosan with the PO4 in the phytic acid molecule. 3- Esterification reaction is carried out to obtain: The mass ratio of dicarboxyl chitosan to N-hydroxymethyl acrylamide is 1:1-3, and the mass ratio of N-hydroxymethyl acrylamide-dicarboxyl chitosan to phytic acid is 1.8-3.2:1; The dicarboxyl chitosan has a C2 and C3 carboxyl content of 45.31-68.57%, a deacetylation degree of 61.27-83.42%, a viscosity-average molecular weight of 35,200-86,300, a solubility in water of 9.12-17.35 g / 100 mL, an isoelectric point pH of 4.2-4.6, and a structural formula of the dicarboxyl chitosan as follows: ； The polymerization inhibitor is 2,6-di-tert-butyl-p-cresol, hydroquinone or 4-methoxyphenol, and the mass ratio of dicarboxyl chitosan to the polymerization inhibitor is 1:0.008-0.015; the initiator is ammonium persulfate or potassium persulfate, and the mass ratio of dicarboxyl chitosan to the initiator is 1:0.12-0.68; the catalyst is 4-dimethylaminopyridine or dicyclohexylcarbodiimide, and the mass concentration of the catalyst added to the mixed solution is 1-2.5%.

2. A method for preparing the intumescent bio-based flame retardant according to claim 1, characterized in that: The steps include: (1) Dissolve dicarboxyl chitosan in 1-butyl-3-methylimidazole acetate at 65-85°C to prepare a dicarboxyl chitosan solution with a mass concentration of 0.8-2.5%, add N-hydroxymethyl acrylamide and dissolve it for 20-40 minutes under continuous stirring, then add an inhibitor and an initiator to dissolve them, and then stir and react under microwave irradiation for 8-20 minutes. After cooling, add methanol and stir for 3-8 minutes to obtain a reaction solution; add the reaction solution to acetone for precipitation, and the obtained precipitate is ultrasonically washed with a mixture of acetone and ethanol in a volume ratio of 2:1, and then vacuum-dried at 40-60°C for 18-24 hours to obtain N-hydroxymethyl acrylamide-dicarboxyl chitosan; (2) N-hydroxymethyl acrylamide-dicarboxyl chitosan was mixed with phytic acid solution of pH=3.6-4.2 in a three-necked flask at 55-65°C in a bath ratio of 1g:30-50mL to dissolve the mixture; then the catalyst was added to the mixture, and the mixture was condensed and refluxed at 70-85°C for 1-4h to allow the -OH on the C6 position of the dicarboxyl chitosan to react with the PO4 in the phytic acid molecule. 3- An esterification reaction occurs. After the reaction is completed, the product is poured into acetone and filtered to precipitate. The precipitate is placed in an ultra-low temperature refrigerator at -40 to -20°C for pre-freezing for 5 to 10 hours, and then subjected to microwave vacuum freeze-drying for 24 to 48 hours. Ethanol is used for rinsing and impurity removal for 3 to 5 times, and then vacuum-dried at 40 to 50°C for 8 to 12 hours to obtain solid N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid, which is an intumescent bio-based flame retardant.

3. The preparation method according to claim 2, wherein: The viscosity-average molecular weight of the N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid in step (2) is 51,400 to 103,600, the carboxyl content at the C2 and C3 positions is 40.73 to 62.49%, the degree of substitution of N-hydroxymethyl acrylamide at the C6 position is 23.16 to 39.51%, the degree of substitution of phytic acid at the C6 position is 45.20 to 63.15%, the degree of deacetylation is 50.23 to 71.31%, and the solubility in water is 7.62 to 15.08 g / 100 mL.

4. The preparation method according to claim 2, wherein: In step (1), the power of the microwave radiation is 480 to 860 W and the temperature is 90 to 150° C.; in step (2), the pH of the phytic acid solution is adjusted by using acetic acid or sodium hydroxide solution with a concentration of 0.06 to 0.1 mol / L; in step (2), the temperature of the microwave vacuum freeze-drying is -100 to -60° C., the microwave power is 1580 to 2600 W, and the vacuum degree is 8 to 15 Pa.

5. A method for preparing an intumescent bio-based flame retardant modified fabric, characterized in that: The steps include: S1. Adding the cellulose fiber fabric after scouring, desizing or degumming to an aqueous solution of the intumescent bio-based flame retardant according to claim 1 or 2 with a mass concentration of 0.5-2% at a bath ratio of 1 g: 20-30 mL to obtain a fabric-flame retardant composite liquid; Alternatively, the protein fiber fabric after scouring, desizing or degumming is added to an aqueous solution of the intumescent bio-based flame retardant according to claim 1 or 2 with a mass concentration of 0.5-2% at a bath ratio of 1 g: 20-30 mL, the pH is adjusted to 4.0-4.6, and the mixture is stirred continuously at 50-65° C. for 1-3 hours to allow the N-hydroxymethyl acrylamide-dicarboxylic chitosan-phytic acid molecules to undergo an amide cross-linking reaction with the protein fabric to obtain a fabric-flame retardant composite liquid; Adding an alkaline catalyst to the fabric-flame retardant composite liquid and dissolving it, and then continuously stirring and reacting it at 60-80° C. for 1-3 hours, so that the N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid molecules react with the fabric through a nucleophilic addition reaction, thereby grafting the flame retardant coating on the fabric surface; Use an electric padder to perform double dipping and double padding to make the liquid carrying rate of the fabric with flame retardant coating 80-100%; The alkaline catalyst is sodium carbonate, sodium bicarbonate or sodium hydroxide, and the mass concentration of the alkaline catalyst in the aqueous solution of the intumescent bio-based flame retardant is 1.2-3%; S2. Pre-drying the flame retardant-coated fabric obtained in step S1 at 70-80° C. for 15-30 min, and then baking at 120-150° C. for 3-5 min. The resulting product is filtered and washed with a mixture of acetone and ethanol in a volume ratio of 1:1 to remove unreacted N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid. The product is then washed with deionized water, dehydrated, and vacuum-dried to obtain an intumescent bio-based flame retardant-modified fabric.

6. The preparation method according to claim 5, characterized in that: The grafting rate of N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid in the intumescent bio-based flame retardant modified fabric is 8.94-24.18%.

7. An intumescent bio-based flame retardant modified fabric prepared by the preparation method according to claim 5 or 6.

8. Use of the intumescent bio-based flame retardant modified fabric according to claim 7 in flame retardancy, fire protection and long-lasting antibacterial properties.

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