Preparation method and application of intumescent bio-based flame retardant

Abstract

The 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, and the intumescent bio-based flame retardant is prepared by the following steps: dissolving dicarboxyl chitosan in weakly acidic ionic liquid 1-butyl-3-methylimidazole acetate; the preparation method comprises the following steps: adding a polymerization inhibitor and an initiator to carry out substitution reaction with N-hydroxymethyl acrylamide under microwave radiation, and then adding phytic acid to carry out esterification reaction on-OH on the C6 site of dicarboxyl chitosan and PO4 < 3-> in phytic acid molecules under the action of a catalyst to obtain N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid (NMA-DCCS-PA). The prepared bio-based flame retardant contains a large number of phosphate radicals, carboxyl groups, cationic amino groups and other groups, is environmentally friendly, efficient in flame retardance and fire prevention and high in reaction activity, has antibacterial activity and has huge application potential in the fields of flame retardance and fire prevention, medical treatment and public health, textile and clothing, new materials and the like.

Description

Technical Field

[0001] 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, and particularly relates to a flame retardant and antibacterial fabric grafted and modified with N-methylolacrylamide-dicarboxyl chitosan-phytic acid. Background Art

[0002] With the development of science and technology and the continuous improvement of environmental protection requirements, people pay more and more attention to renewable, environmentally friendly and non-toxic flame retardants. Bio-based materials derived from nature, due to their non-toxic, harmless, green, high biocompatibility and renewable advantages, are gradually applied in the flame retardant field as substitutes for traditional flame retardants. Chitosan-based flame retardants prepared from chitosan, the second largest biomass resource in nature, have received extensive attention. Chitosan can improve the thermal stability of polymers to a certain extent and enhance their flame retardant properties, but it cannot improve the flame retardant grade of materials, and it is often necessary to introduce flame retardant elements to improve the flame retardant properties [Hao Fengling, Geng Weitao, Zhang Jian, etc. Research progress of chitosan-based flame retardants [J]. Wool Textile Journal, 2019, 47(2): 80-85]. As a natural and environmentally friendly polymer with a high carbon content, the nitrogen element contained in the molecule of chitosan makes it used as a blowing agent in the intumescent flame retardant system. 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 blowing agent) has received attention due to its excellent flame retardant properties. In a flame or high-temperature environment, the intumescent flame retardant coating can quickly generate foam and bubbles, and then form a dense, porous and stable carbon layer. This carbon layer can effectively block the flame and block the transfer of heat, fuel and oxygen, thus significantly improving the fire safety.

[0003] Phytic acid is a kind of biomass that can be extracted from plant seeds such as grains and soybeans, with rich and renewable sources. The six phosphate groups in the phytic acid structure play an important role as an acid source in intumescent flame retardants. When phytic acid pyrolyzes, a large number of phosphoric acid derivatives are produced, which can not only promote the dehydration and carbonization of the carbon source, but also capture free radicals, thus improving the flame retardancy of the whole 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. explored the coating of the LBL component constructed by the fully bio-based intumescent flame retardant (IFR) CS / PA on polyester-cotton blended fabrics. The limiting oxygen index (LOI) value of the polyester-cotton blended fabrics assembled by 20 times of CS / PA coating LBL reached 29.2%, and the dripping of molten droplets was eliminated. However, there is no chemical bond between CS / PA and the fabric, and the electrostatic force formed is weak, and it is easy to fall off by washing, resulting in poor flame retardant durability of the polyester-cotton blended fabrics with CS / PA coating [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 fabrics. The metal ions were used as catalysts for dehydrogenation reactions to increase the amount of char formation. The thermal stability and flame retardancy of cotton fabrics were effectively improved through the synergistic effect of the intumescent flame retardant system and metal ions by the dip-roll-dry method. However, the flame retardant treatment had an adverse impact on the whiteness, tensile strength, and softness of the fabric, and there were certain human safety hazards associated with the metal ions, 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 metal ions[J]. International Journal of Biological Macromolecules, 2019, 140:303-310]. The flame retardancy efficiency and durability of bio-based materials used alone as flame retardants need to be improved, and they lack reactive groups for cross-linking reactions with fabrics, resulting in problems such as easy shedding during washing and poor flame retardant durability, which limits their application fields. Currently, the methods for finishing fabrics with chitosan and phytic acid composite flame retardants mainly use layer-by-layer self-assembly (LBL) or padding to construct flame retardant modification layers. The flame retardant coatings not only affect the service performance of fabrics such as breathability, handfeel, strength, and whiteness, but also are not resistant to washing and cannot provide long-term flame retardant and heat insulation protection. Therefore, it is urgent to develop a green and environmentally friendly bio-based flame retardant that can firmly bind with fabrics through grafting reactions, endow fabrics with long-lasting and efficient flame retardant and fire prevention properties, and have antibacterial activity. Summary of the Invention

[0004] In view of the above problems existing in the prior art, the first object of the present invention is to provide a preparation method of an N-methylolacrylamide-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-methylolacrylamide (NMA), and the -OH at the C6 position of dicarboxyl chitosan reacts with PO4 in the phytic acid molecule 3-An esterification reaction is carried out to make NMA-DCCS-PA contain a large number of groups such as phosphate groups, carboxyl groups, cationic amino groups, and unsaturated double bonds. It has high reaction activity, good biocompatibility, and has the dual effects of fire prevention and high-efficiency antibacterial. The second object of the present invention is to provide a preparation method of an intumescent bio-based flame retardant modified fabric. The carboxyl groups and unsaturated double bonds in NMA-DCCS-PA can respectively undergo amide and nucleophilic addition reactions with the amino groups of protein fibers and the hydroxyl groups of cellulose fibers, and a modified fabric can be obtained without using any chemical cross-linking agents. It is safe and hygienic, has high chemical bond cross-linking fastness, and long-lasting functions, and has great application potential in related fields such as flame retardant and fire prevention, and long-term antibacterial.

[0005] To achieve the above-mentioned invention purposes, the technical solutions adopted by the present invention are as follows: The present invention first discloses an intumescent bio-based flame retardant, which is characterized in that: the intumescent bio-based flame retardant is N-methylolacrylamide-dicarboxyl chitosan-phytic acid (NMA-DCCS-PA). Dissolve dicarboxyl chitosan (DCCS) in the weak acidic ionic liquid 1-butyl-3-methylimidazolium acetate ([Bmim][Ac]), add a polymerization inhibitor and an initiator, and carry out a substitution reaction with N-methylolacrylamide (NMA) under microwave irradiation, and then add phytic acid (PA). Under the action of a catalyst, the -OH at the C6 position of dicarboxyl chitosan reacts with PO4 in the phytic acid molecule 3- to carry out an esterification reaction to obtain it.

[0006] Preferably, the carboxyl group contents at the C2 and C3 positions of the dicarboxyl chitosan are 45.31-68.57%, the degree of deacetylation is 61.27-83.42%, the viscosity-average molecular weight is 35,200-86,300, the solubility in water is 9.12-17.35 g / 100 mL, and the isoelectric point pH = 4.2-4.6. The structural formula of the dicarboxyl chitosan is as follows: .

[0007] The preparation method of the intumescent bio-based flame retardant described in the present invention includes the following steps: (1) Dissolve dicarboxyl chitosan (DCCS) in 1-butyl-3-methylimidazolium acetate at 65-85 °C to prepare a dicarboxyl chitosan solution with a mass concentration of 0.8-2.5%. Add N-hydroxymethylacrylamide (NMA) and dissolve it for 20-40 min under continuous stirring. The mass ratio of dicarboxyl chitosan to N-hydroxymethylacrylamide is 1:1-3. Then add an inhibitor and an initiator for dissolution, and then stir and react for 8-20 min under microwave irradiation. After cooling, add methanol and stir for 3-8 min to obtain a reaction solution. Add the reaction solution to acetone for precipitation. The obtained precipitate is ultrasonically washed with a mixed solution of acetone and ethanol with a volume ratio of 2:1, and then vacuum dried at 40-60 °C for 18-24 h to obtain a light yellow solid, N-hydroxymethylacrylamide-dicarboxyl chitosan; the inhibitor is 2,6-di-tert-butyl-p-cresol, hydroquinone or 4-methoxyphenol, and the mass ratio of dicarboxyl chitosan to the 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.

[0008] (2) At 55-65 °C, mix N-hydroxymethylacrylamide-dicarboxyl chitosan with a bath ratio of 1 g:30-50 mL and a phytic acid solution with pH = 3.6-4.2 in a three-necked flask for dissolution to obtain a mixed solution. The mass ratio of N-hydroxymethylacrylamide-dicarboxyl chitosan to phytic acid is 1.8-3.2:1; then add a catalyst to the mixed solution and carry out condensation reflux at 70-85 °C for 1-4 h to make the -OH at the C6 position of dicarboxyl chitosan react with PO4 3- in phytic acid molecules to undergo an esterification reaction. After the reaction is completed, pour the product into acetone for suction filtration and precipitation. Put the precipitate into a cryogenic refrigerator at -40--20 °C for pre-freezing for 5-10 h, and then carry out microwave vacuum freeze-drying for 24-48 h. Use ethanol to wash and remove impurities 3-5 times, and then vacuum dry at 40-50 °C for 8-12 h to obtain a yellow solid, N-hydroxymethylacrylamide-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 1-2.5%.

[0009] Preferably, in step (2), the viscosity-average molecular weight of N-methylolacrylamide-dicarboxyl chitosan-phytic acid (NMA-DCCS-PA) is 51,400 - 103,600, the carboxyl group contents at C2 and C3 positions are 40.73% - 62.49%, the substitution degree of N-methylolacrylamide at C6 position is 23.16% - 39.51%, the substitution degree of phytic acid at C6 position is 45.20% - 63.15%, the degree of deacetylation is 50.23% - 71.31%, and the solubility in water is 7.62 - 15.08 g / 100 mL; the structural formula of N-methylolacrylamide-dicarboxyl chitosan-phytic acid is as follows: 。

[0010] Preferably, in step (1), the power of the microwave radiation is 480 - 860 W, and the microwave radiation temperature is 90 - 150 °C.

[0011] Preferably, in step (2), the pH of the phytic acid solution is adjusted with acetic acid or sodium hydroxide solution with a concentration of 0.06 - 0.1 mol / L.

[0012] Preferably, in step (2), the temperature of the microwave vacuum freeze-drying is -100 - -60 °C, the microwave power is 1580 - 2600 W, and the vacuum degree is 8 - 15 Pa.

[0013] The present invention further discloses a preparation method of an intumescent bio-based flame retardant modified fabric, comprising the following steps: S1. Add the scoured and desized or degummed cellulose fiber fabric into the aqueous solution of the intumescent bio-based flame retardant with a mass concentration of 0.5% - 2% according to a bath ratio of 1 g:20 - 30 mL to obtain a fabric-flame retardant composite liquid; Or, add the scoured and desized or degummed protein fiber fabric into the aqueous solution of the intumescent bio-based flame retardant with a mass concentration of 0.5% - 2% according to a bath ratio of 1 g:20 - 30 mL, adjust the pH to 4.0 - 4.6 (adjusted with sodium hydroxide solution with a concentration of 0.1 - 0.3 mol / L) and continuously stir and react at 50 - 65 °C for 1 - 3 h to make the NMA-DCCS-PA molecules carry out amide crosslinking reaction with the protein fabric to obtain a fabric-flame retardant composite liquid; Add an alkaline catalyst to dissolve in the fabric-flame retardant composite liquid and continuously stir and react at 60 - 80 °C for 1 - 3 h to make the NMA-DCCS-PA molecules carry out nucleophilic addition reaction with the fabric and graft a flame retardant coating on the fabric surface; use an electric padding mangle for two-bath two-roll padding to make the liquor pickup rate of the fabric with the flame retardant coating be 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%.

[0014] S2. Bake the fabric with the flame retardant coating obtained in step S1 at 70-80 °C for 15-30 min, and then bake it at 120-150 °C for 3-5 min. The obtained product is filtered and washed with a mixed solution of acetone and ethanol with a volume ratio of 1:1 to remove the unreacted and combined NMA-DCCS-PA, and then washed with deionized water, dehydrated, and vacuum dried to obtain the intumescent bio-based flame retardant modified fabric.

[0015] Preferably, the grafting rate of NMA-DCCS-PA in the intumescent bio-based flame retardant modified fabric is 8.94-24.18%.

[0016] By optimizing the mass ratio of N-hydroxymethylacrylamide-bis-carboxyl chitosan to phytic acid in NMA-DCCS-PA, the catalyst dosage, the esterification reaction time, and the mass concentration of the NMA-DCCS-PA solution, the alkaline catalyst dosage, the grafting (including amide cross-linking reaction and nucleophilic addition reaction) reaction time and temperature in the preparation of the modified fabric, a series of NMA-DCCS-PA flame retardants with different degrees of N-hydroxymethylacrylamide substitution and phytic acid substitution and functional modified fabrics with different grafting rates can be obtained.

[0017] Compared with the prior art, the preparation principles and advantages of the intumescent bio-based flame retardant NMA-DCCS-PA and the modified fabric based on it in the present invention are as follows: 1. In the present invention, the weak acidic ionic liquid 1-butyl-3-methylimidazolium acetate ([Bmim][Ac]) is used as the dissolution and reaction medium for bis-carboxyl chitosan. The water generated during the nucleophilic substitution reaction between the primary hydroxyl group at the C6 position of bis-carboxyl chitosan and the hydroxyl group in N-hydroxymethylacrylamide can be completely absorbed by the ionic liquid, promoting the forward progress of the substitution reaction; at the same time, 1-butyl-3-methylimidazolium acetate makes the amino group at the C2 position of bis-carboxyl chitosan carry a positive charge, enhancing the probability of nucleophilic reaction with N-hydroxymethylacrylamide, accelerating the reaction rate, and promoting the increase in the degree of N-hydroxymethylacrylamide substitution at the C6 position of bis-carboxyl chitosan; at the same time, the phenolic 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 N-hydroxymethylacrylamide monomers and enhancing the degree of N-hydroxymethylacrylamide substitution at the C6 position of bis-carboxyl chitosan. The initiators such as ammonium persulfate, ammonium chloride or potassium persulfate used in the present invention have good water solubility, small molecular weight and low steric hindrance. By decomposing to generate active free radicals, they initiate the affinity substitution reaction between carboxyl chitosan and N-hydroxymethylacrylamide, accelerating the substitution reaction rate.

[0018] 2. The present invention utilizes the weakly acidic ionic liquid 1-butyl-3-methylimidazolium acetate ([Bmim][Ac]) as the green solvent for dicarboxylated chitosan and the reaction medium for grafting N-hydroxymethylacrylamide. Ionic liquids have the advantages of being non-toxic, pollution-free, having stable physical and chemical properties, no evaporation pressure and non-volatility, being environmentally friendly, and recyclable. At the same time, dicarboxylated chitosan is directly dissolved in 1-butyl-3-methylimidazolium acetate at a medium temperature (65 - 85 °C), and its molecular structure does not undergo derivatization and degradation, maintaining the amphoteric polyelectrolyte characteristics and excellent biocompatibility of dicarboxylated chitosan. After the reaction, adding absolute ethanol to the ionic liquid can precipitate the remaining dicarboxylated chitosan, and the ionic liquid can be recycled after evaporating the absolute ethanol, which is environmentally friendly.

[0019] 3. The N-hydroxymethylacrylamide-dicarboxylated chitosan-phytic acid flame retardant prepared by the present invention has excellent performance. Both dicarboxylated chitosan and N-hydroxymethylacrylamide provide abundant carbon sources. The amino group at the C2 position of dicarboxylated chitosan generates ammonia gas during combustion as a gas source, and the two carboxyl groups can improve the carbon formation effect of chitosan. The molecular structure of phytic acid is formed by esterifying 6 phosphate groups with 6 hydroxyl groups on the inositol ring to form 6 phosphate ester 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 dehydrate to form a dense and stable carbon layer at high temperature or when exposed to flame, thereby inhibiting the smoke emission during combustion. At the same time, a large number of phosphoric acid derivatives are generated during pyrolysis, which can not only promote the dehydration and carbonization of the carbon source but also capture free radicals, enhancing the overall flame retardant performance. N-hydroxymethylacrylamide-dicarboxylated chitosan-phytic acid is a highly efficient intumescent flame retardant that combines acid source, carbon source, and gas source in one, and does not produce toxic and corrosive gases, being environmentally friendly. In addition, the amino group at the C2 position is retained in the NMA-DCCS-PA molecule and can form a polycationic amino group, having high antibacterial activity.

[0020] 4. The present invention reacts dicarboxylated chitosan with N-hydroxymethylacrylamide under the action of a polymerization inhibitor and an initiator under microwave irradiation conditions. Due to the fast heating rate, short reaction time, and good uniformity of microwave irradiation, dicarboxylated chitosan and N-hydroxymethylacrylamide are in full contact, promoting the nucleophilic substitution reaction between the primary hydroxyl group at the C6 position of dicarboxylated chitosan and the hydroxyl group in N-hydroxymethylacrylamide. At the same time, the radiation effect of microwave can enhance the energy absorption of the reactants of dicarboxylated chitosan and N-hydroxymethylacrylamide, promote the movement between molecular chain segments, accelerate the substitution reaction rate of dicarboxylated chitosan and N-hydroxymethylacrylamide, the process is simple, saving reaction time and reducing energy consumption, and improving the substitution degree of N-hydroxymethylacrylamide at the C6 position of dicarboxylated chitosan.

[0021] 5. The present invention dissolves N-hydroxymethylacrylamide-dicarboxyl chitosan in phytic acid (PA) solution, and under the action of a catalyst, the -OH at the C6 position of dicarboxyl chitosan reacts with PO4 in the phytic acid molecule 3- to carry out an esterification reaction. The catalysts used, 4-dimethylaminopyridine (DMAP) or dicyclohexylcarbodiimide (DCC), are suitable for the catalytic esterification reaction of polysaccharides with large steric hindrance, and at the same time play the role of catalytic reaction and water absorbent, completely absorbing the water generated by the esterification reaction product, promoting the esterification reversible reaction to proceed in the direction of forming esters, significantly accelerating the esterification reaction rate of N-hydroxymethylacrylamide-dicarboxyl chitosan and phytic acid, and increasing the phytic acid substitution degree at the C6 position of N-hydroxymethylacrylamide-dicarboxyl chitosan.

[0022] 6. The present invention puts N-hydroxymethylacrylamide-dicarboxyl chitosan-phytic acid into a ultra-low temperature refrigerator for pre-freezing, and then carries out microwave vacuum freeze-drying to obtain an intumescent flame retardant. By pre-freezing, the freezing rate of the water inside N-hydroxymethylacrylamide-dicarboxyl chitosan-phytic acid is slowed down, thereby reducing the crystallization risk of water during freezing, helping to form a stable structure of the intumescent flame retardant. At the same time, pre-freezing can also reduce the crystallization and deformation during the freeze-drying of the flame retardant, effectively avoiding the structural collapse of the intumescent flame retardant caused by the rapid removal of water, and significantly improving the structural stability of NMA-DCCS-PA. The present invention uses microwave vacuum freeze-drying to obtain an N-hydroxymethylacrylamide-dicarboxyl chitosan-phytic acid intumescent bio-based flame retardant material. By combining microwave drying and vacuum drying, the respective advantages can be fully exerted. The ice crystals generated inside the NMA-DCCS-PA flame retardant during pre-freezing are sublimated and dried under vacuum and below the eutectic temperature, and the microwave generator provides the latent heat of sublimation to the material to be dried in a frozen state, quickly removing the water of the material. Compared with the disadvantage of slow conventional heat conduction rate in a vacuum state, the drying time is shortened and the drying efficiency is improved. The temperature of microwave vacuum freeze-drying is uniform, the water molecules in the flame retardant are evenly distributed, and the water drying rate is consistent, enhancing the structural strength of the intumescent bio-based flame retardant.

[0023] 7. Under the acidic condition of pH = 4.0 - 4.6, the NMA-DCCS-PA molecules react with the protein fiber fabric. The positively charged NMA-DCCS-PA molecules enhance the probability of contacting the negatively charged protein fiber fabric (the protein fiber fabric has a negative charge because its isoelectric point pH is lower than 4.0 - 4.6), 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 fabric, thereby forming multi-site chemical bond binding on the fabric surface, with strong wash resistance and high grafting rate. No chemical cross-linking agent is used in the whole grafting reaction, avoiding the negative impacts of cross-linking agent coating on the excellent properties of the fabric and human health. The NMA-DCCS-PA molecules uniformly penetrate into the fabric interior through the padding method and cross-link into a firm flame-retardant coating on the fiber surface, showing excellent flame-retardant and antibacterial properties without affecting the wearing performance of the fabric. Description of the Drawings

[0024] Figure 1 It is the schematic diagram of the preparation principle of the N-hydroxymethylacrylamide-bis-carboxyl chitosan-phytic acid intumescent flame retardant of the present invention.

[0025] Figure 2 It is the schematic diagram of the preparation principle of the NMA-DCCS-PA flame retardant grafted on silk fabric of the present invention.

[0026] Figure 3 It is the scanning electron micrograph of the NMA-DCCS-PA flame retardant modified silk fabric in Test Item 2 of the present invention. In the figure, a, b, and c respectively 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. Detailed Embodiments

[0027] For a better understanding of the technical features, objectives, and beneficial effects of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but the present invention is not limited to the following embodiments.

[0028] I. Preparation of the intumescent bio-based flame retardant NMA-DCCS-PA and the modified fabric based on it Example 1 The NMA-DCCS-PA is prepared according to the following steps in this example: (1) Dissolve 2 g of dicarboxyl chitosan (the carboxyl content at C2 and C3 positions is 46.74%, the degree of deacetylation is 65.38%, the viscosity-average molecular weight is 81,700, the solubility in water is 9.63 g / 100 mL, and the isoelectric point pH = 4.6) in 1-butyl-3-methylimidazolium acetate at 82 °C to prepare a 1% dicarboxyl chitosan solution. Add N-hydroxymethylacrylamide and dissolve for 25 min under continuous stirring. The mass ratio of dicarboxyl chitosan to N-hydroxymethylacrylamide is 1:1. Then add the inhibitor 2,6-di-tert-butyl-p-cresol (the mass ratio of dicarboxyl chitosan to the inhibitor is 1:0.008) and the initiator ammonium chloride (the mass ratio of dicarboxyl chitosan to the initiator is 1:0.18) for dissolution. Then stir and react for 10 min under microwave radiation conditions (microwave radiation power is 500 W, microwave radiation temperature is 95 °C). After cooling, add 16 mL of methanol and stir for 3 min to obtain a reaction solution. Add the reaction solution to 90 mL of acetone for precipitation. The obtained precipitate is ultrasonically washed with a mixed solution of acetone and ethanol with a volume ratio of 2:1, and then vacuum dried at 40 °C for 18 h to obtain a light yellow solid N-hydroxymethylacrylamide-dicarboxyl chitosan.

[0029] (2) At 55 °C, mix N-hydroxymethylacrylamide-dicarboxyl chitosan with a bath ratio of 1 g:35 mL and a phytic acid solution with pH = 4.2 in a three-necked flask for dissolution to obtain a mixed solution. The mass ratio of N-hydroxymethylacrylamide-dicarboxyl chitosan to phytic acid is 3:1. Then add the catalyst dicyclohexylcarbodiimide (DCC) to the above mixed solution (the mass concentration of the catalyst added to the mixed solution is 1.2%), and reflux under condensation at 72 °C for 1.5 h to make the -OH on the C6 position of dicarboxyl chitosan react with PO4 in the phytic acid molecule 3- to undergo an esterification reaction. After the reaction, pour the product into acetone for suction filtration and precipitation. The precipitate is pre-cooled in a -22 °C ultra-low temperature refrigerator for 6 h, and then microwave vacuum freeze-dried for 30 h (the temperature of microwave vacuum freeze-drying is -68 °C, the microwave power is 1620 W, and the vacuum degree is 13 Pa). Use ethanol to wash and remove impurities 3 times, and then vacuum dry at 40 °C for 8 h to obtain a yellow solid N-hydroxymethylacrylamide-dicarboxyl chitosan-phytic acid (NMA-DCCS-PA), which is the intumescent bio-based flame retardant.

[0030] Apply the intumescent bio-based flame retardant obtained in this example to the functional modified cotton fabric. The specific steps are as follows: S1. Add the scoured and desized cotton fabric to an aqueous solution of NMA-DCCS-PA with a mass concentration of 0.8% at a bath ratio of 1 g:25 mL. Then add the alkaline catalyst sodium hydroxide to dissolve it (the mass concentration of the alkaline catalyst in the NMA-DCCS-PA aqueous solution is 1.5%), and continuously stir and react at 65 °C for 1 h to carry out a nucleophilic addition reaction between NMA-DCCS-PA molecules and the cotton fabric, and graft a flame retardant coating on the surface of the cotton fabric. Use an electric padding mangle to dip and pad twice to make the liquor pickup rate of the cotton fabric with the flame retardant coating 85%.

[0031] S2. Pre-dry the cotton fabric with the flame retardant coating obtained in step S1 at 72 °C for 18 min, then cure it at 140 °C for 3 min. Filter and wash the obtained product with a mixed solution of acetone and ethanol with a volume ratio of 1:1 to remove unreacted and bound NMA-DCCS-PA, and then wash it with deionized water, dehydrate it, and dry it in vacuum to obtain the intumescent bio-based flame retardant modified cotton fabric.

[0032] After testing, the viscosity-average molecular weight of N-hydroxymethylacrylamide-dicarboxyl chitosan-phytic acid (NMA-DCCS-PA) prepared in this example is 96,500, the carboxyl content at C2 and C3 positions is 42.37%, the substitution degree of N-hydroxymethylacrylamide at C6 position is 27.14%, the substitution degree of phytic acid at C6 position is 46.91%, the deacetylation degree is 56.08%, and the solubility in water is 8.14 g / 100 mL.

[0033] After testing, the grafting rate of the intumescent bio-based flame retardant modified cotton fabric obtained in this example is 9.21%, the breaking strength of the modified cotton fabric is 386.6 N, the crease recovery angle is 191.7°, and the air permeability is 416.5 mm / s; after 100 washes, the limiting oxygen index of the modified cotton fabric is 33.9%, the antibacterial rate against Staphylococcus aureus is 92.84%, and the antibacterial rate against Escherichia coli is 93.71%.

[0034] Example 2 This example prepares NMA-DCCS-PA according to the following steps: (1) Dissolve 2 g of dicarboxyl chitosan (the carboxyl content at C2 and C3 positions is 51.06%, the degree of deacetylation is 70.38%, the viscosity-average molecular weight is 68,200, the solubility in water is 12.35 g / 100 mL, and the isoelectric point pH = 4.4) in 1-butyl-3-methylimidazolium acetate at 75 °C to prepare a 1.5% dicarboxyl chitosan solution. Add N-hydroxymethylacrylamide and dissolve for 30 min under continuous stirring. The mass ratio of dicarboxyl chitosan to N-hydroxymethylacrylamide is 1:2. Then add the inhibitor 2,6-di-tert-butyl-p-cresol (the mass ratio of dicarboxyl chitosan to the inhibitor is 1:0.009) and the initiator potassium persulfate (the mass ratio of dicarboxyl chitosan to the initiator is 1:0.32) and dissolve. Then stir and react for 15 min under microwave irradiation conditions (microwave irradiation power is 640 W, microwave irradiation temperature is 120 °C). After cooling, add 18 mL of methanol and stir for 5 min to obtain a reaction solution. Add the reaction solution to 100 mL of acetone for precipitation. The obtained precipitate is ultrasonically washed with a mixed solution of acetone and ethanol with a volume ratio of 2:1, and then vacuum dried at 45 °C for 20 h to obtain a light yellow solid N-hydroxymethylacrylamide-dicarboxyl chitosan.

[0035] (2) At 60 °C, mix N-hydroxymethylacrylamide-dicarboxyl chitosan with a bath ratio of 1 g:40 mL and a phytic acid solution with pH = 3.8 in a three-necked flask for dissolution to obtain a mixed solution. The mass ratio of N-hydroxymethylacrylamide-dicarboxyl chitosan to phytic acid is 2:1. Then add the catalyst dicyclohexylcarbodiimide (DCC) to the above mixed solution (the mass concentration of the catalyst added to the mixed solution is 1.6%), and reflux with condensation at 80 °C for 2 h to make the -OH on the C6 position of dicarboxyl chitosan react with PO4 3- in phytic acid molecules to undergo an esterification reaction. After the reaction, pour the product into acetone for suction filtration and precipitation. The precipitate is pre-cooled in a -28 °C ultra-low temperature refrigerator for 8 h, and then subjected to microwave vacuum freeze-drying for 36 h (the temperature of microwave vacuum freeze-drying is -75 °C, the microwave power is 1860 W, and the vacuum degree is 10 Pa). Use ethanol to wash and remove impurities 4 times, and then vacuum dry at 45 °C for 9 h to obtain a yellow solid N-hydroxymethylacrylamide-dicarboxyl chitosan-phytic acid (NMA-DCCS-PA), which is the intumescent bio-based flame retardant.

[0036] Apply the intumescent bio-based flame retardant obtained in this example to the functional modified silk fabric. The specific steps are as follows: S1. Add the degummed silk fabric after scouring and degumming to an aqueous solution of NMA-DCCS-PA with a mass concentration of 1.2% according to a liquor ratio of 1 g:25 mL. Adjust it to an acidic condition with a pH of 4.2 using a sodium hydroxide solution with a concentration of 0.2 mol / L and continuously stir and react at 55 °C for 1.5 h to carry out an amide cross-linking reaction between NMA-DCCS-PA molecules and the silk fabric. Then add sodium carbonate as an alkaline catalyst to dissolve it (the mass concentration of the alkaline catalyst in the NMA-DCCS-PA aqueous solution is 1.8%) and continuously stir and react at 70 °C for 1.5 h to cause a nucleophilic addition reaction between NMA-DCCS-PA molecules and the silk fabric again, and graft and form a flame retardant coating on the surface of the silk fabric. Use an electric padding mangle to dip and pad twice to make the liquor pickup rate of the silk fabric with the flame retardant coating be 90%.

[0037] S2. Pre-dry the silk fabric with the flame retardant coating obtained in step S1 at 75 °C for 20 min, and then cure it at 120 °C for 4 min. Filter and wash the obtained product with a mixed solution of acetone and ethanol with a volume ratio of 1:1 to remove the unreacted and bound NMA-DCCS-PA, then wash it with deionized water, dehydrate it, and vacuum dry it to obtain the intumescent bio-based flame retardant modified silk fabric.

[0038] After testing, the viscosity-average molecular weight of N-hydroxymethylacrylamide-dicarboxyl chitosan-phytic acid (NMA-DCCS-PA) prepared in this example is 84,300, the carboxyl content at C2 and C3 positions is 47.09%, the substitution degree of N-hydroxymethylacrylamide at C6 position is 29.85%, the substitution degree of phytic acid at C6 position is 53.70%, the deacetylation degree is 64.54%, and the solubility in water is 10.51 g / 100 mL.

[0039] After testing, the grafting rate of the intumescent bio-based flame retardant modified silk fabric obtained in this example is 13.18%, the breaking strength of the modified silk fabric is 470.5 N, the crease recovery angle is 185.2°, and the air permeability is 553.7 mm / s; after 100 washes with water, the limiting oxygen index of the modified silk fabric is 37.8%, the antibacterial rate against Staphylococcus aureus is 93.61%, and the antibacterial rate against Escherichia coli is 95.66%.

[0040] Example 3 This example prepares NMA-DCCS-PA according to the following steps: (1) Dissolve 2 g of dicarboxyl chitosan (the carboxyl content at C2 and C3 positions is 63.52%, the degree of deacetylation is 81.17%, the viscosity-average molecular weight is 42,400, the solubility in water is 16.83 g / 100 mL, and the isoelectric point pH = 4.2) in 1-butyl-3-methylimidazolium acetate at 68 °C to prepare a 2% dicarboxyl chitosan solution. Add N-hydroxymethylacrylamide and dissolve it for 35 min under continuous stirring. The mass ratio of dicarboxyl chitosan to N-hydroxymethylacrylamide is 1:2.5. Then add the inhibitor 4-methoxyphenol (the mass ratio of dicarboxyl chitosan to the inhibitor is 1:0.012) and the initiator ammonium persulfate (the mass ratio of dicarboxyl chitosan to the initiator is 1:0.42) and dissolve them. Then stir and react for 18 min under microwave radiation conditions (the microwave radiation power is 720 W, and the microwave radiation temperature is 140 °C). After cooling, add 20 mL of methanol and stir for 6 min to obtain a reaction solution. Add the reaction solution to 120 mL of acetone for precipitation. The obtained precipitate is ultrasonically washed with a mixed solution of acetone and ethanol with a volume ratio of 2:1, and then vacuum dried at 50 °C for 22 h to obtain a light yellow solid N-hydroxymethylacrylamide-dicarboxyl chitosan.

[0041] (2) At 60 °C, mix N-hydroxymethylacrylamide-dicarboxyl chitosan with a bath ratio of 1 g:50 mL and a phytic acid (PA) solution with pH = 4.0 in a three-necked flask for dissolution to obtain a mixed solution. The mass ratio of N-hydroxymethylacrylamide-dicarboxyl chitosan to phytic acid is 2.4:1. Then add the catalyst 4-dimethylaminopyridine (DMAP) to the above mixed solution (the mass concentration of the catalyst added to the mixed solution is 2%), and reflux under condensation at 80 °C for 3 h to make the -OH on the C6 position of N-hydroxymethylacrylamide-dicarboxyl chitosan react with PO4 in the phytic acid molecule 3- to undergo an esterification reaction. After the reaction, pour the product into acetone for suction filtration and precipitation. The precipitate is pre-cooled in a -30 °C ultra-low temperature refrigerator for 9 h, and then microwave vacuum freeze-dried for 42 h (the temperature of microwave vacuum freeze-drying is -80 °C, the microwave power is 2280 W, and the vacuum degree is 8 Pa). Use ethanol to wash and remove impurities 5 times, and then vacuum dry at 45 °C for 10 h to obtain a yellow solid N-hydroxymethylacrylamide-dicarboxyl chitosan-phytic acid (NMA-DCCS-PA), which is an intumescent bio-based flame retardant.

[0042] Apply the intumescent bio-based flame retardant obtained in this example to functional modified silk fabrics. The specific steps are as follows: S1. The degummed silk fabric after scouring and degumming was added to an aqueous solution of NMA-DCCS-PA with a mass concentration of 1.5% according to a liquor ratio of 1 g:30 mL, adjusted to an acidic condition with a pH of 4.4 by a sodium hydroxide solution with a concentration of 0.12 mol / L, and continuously stirred and reacted at 60 °C for 2 h to allow the NMA-DCCS-PA molecules to undergo an amide crosslinking reaction with the silk fabric. Then, a basic catalyst sodium bicarbonate was added and dissolved (the mass concentration of the basic catalyst in the NMA-DCCS-PA aqueous solution was 2.4%), and the reaction was continuously stirred at 80 °C for 2 h 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 padded twice with an electric padding mangle to make the liquor pickup rate 95%.

[0043] S2. The silk fabric with the flame retardant coating obtained in step S1 was pre-dried at 75 °C for 25 min, then baked at 120 °C for 5 min. The obtained product was filtered and washed with a mixed solution of acetone and ethanol with a volume ratio of 1:1 to remove the unreacted and bound NMA-DCCS-PA, then washed with deionized water, dehydrated, and vacuum dried to obtain the intumescent bio-based flame retardant modified silk fabric.

[0044] After testing, the viscosity-average molecular weight of N-hydroxymethylacrylamide-dicarboxyl chitosan-phytic acid (NMA-DCCS-PA) prepared in this example was 51,700, the carboxyl content at C2 and C3 positions was 58.11%, the substitution degree of N-hydroxymethylacrylamide at C6 position was 37.82%, the substitution degree of phytic acid at C6 position was 61.94%, the degree of deacetylation was 70.35%, and the solubility in water was 14.57 g / 100 mL.

[0045] After testing, the grafting rate of the intumescent bio-based flame retardant modified silk fabric obtained in this example was 24.06%, the breaking strength of the modified silk fabric was 492.7 N, the crease recovery angle was 215.6°, and the air permeability was 537.1 mm / s; after 100 washes, the limiting oxygen index of the modified silk fabric was 44.6%, the antibacterial rate against Staphylococcus aureus was 96.28%, and the antibacterial rate against Escherichia coli was 97.46%.

[0046] Example 4 In this example, NMA-DCCS-PA was prepared according to the following steps: (1) Dissolve 2 g of dicarboxyl chitosan (the carboxyl content at C2 and C3 positions is 63.52%, the degree of deacetylation is 81.17%, the viscosity-average molecular weight is 42,400, the solubility in water is 16.83 g / 100 mL, and the isoelectric point pH = 4.2) in 1-butyl-3-methylimidazolium acetate at 68 °C to prepare a 2% dicarboxyl chitosan solution. Add N-hydroxymethylacrylamide and dissolve for 35 min under continuous stirring. The mass ratio of dicarboxyl chitosan to N-hydroxymethylacrylamide is 1:2.5. Then add the inhibitor 4-methoxyphenol (the mass ratio of dicarboxyl chitosan to the inhibitor is 1:0.012) and the initiator ammonium persulfate (the mass ratio of dicarboxyl chitosan to the initiator is 1:0.42) for dissolution. Then stir and react for 18 min under microwave radiation conditions (microwave radiation power is 720 W, microwave radiation temperature is 140 °C). After cooling, add 20 mL of methanol and stir for 6 min to obtain a reaction solution. Add the reaction solution to 120 mL of acetone for precipitation. The obtained precipitate is ultrasonically washed with a mixed solution of acetone and ethanol with a volume ratio of 2:1, and then vacuum dried at 50 °C for 22 h to obtain a light yellow solid N-hydroxymethylacrylamide-dicarboxyl chitosan.

[0047] (2) At 60 °C, mix N-hydroxymethylacrylamide-dicarboxyl chitosan with a bath ratio of 1 g:50 mL and a phytic acid solution with pH = 4.0 in a three-necked flask for dissolution to obtain a mixed solution. The mass ratio of N-hydroxymethylacrylamide-dicarboxyl chitosan to phytic acid is 2.4:1. Then add the catalyst 4-dimethylaminopyridine (DMAP) to the above mixed solution (the mass concentration of the catalyst added to the mixed solution is 2%). Reflux with condensation at 80 °C for 3 h to make the -OH on the C6 position of N-hydroxymethylacrylamide-dicarboxyl chitosan react with PO4 in the phytic acid molecule 3- to undergo an esterification reaction. After the reaction, pour the product into acetone for suction filtration and precipitation. The precipitate is pre-cooled in a -30 °C ultra-low temperature refrigerator for 9 h, and then subjected to microwave vacuum freeze-drying for 42 h (the temperature of microwave vacuum freeze-drying is -80 °C, the microwave power is 2280 W, and the vacuum degree is 8 Pa). Use ethanol to wash and remove impurities 5 times, and then vacuum dry at 45 °C for 10 h to obtain a yellow solid N-hydroxymethylacrylamide-dicarboxyl chitosan-phytic acid (NMA-DCCS-PA), which is an intumescent bio-based flame retardant.

[0048] Apply the intumescent bio-based flame retardant obtained in this example to the functional modified wool fabric. The specific steps are as follows: S1. Add the scoured and desized wool fabric into an aqueous solution of NMA-DCCS-PA with a mass concentration of 1.5% at a bath ratio of 1 g:30 mL. Adjust it to an acidic condition with a pH of 4.4 using a sodium hydroxide solution with a concentration of 0.2 mol / L and continuously stir and react at 60 °C for 2 h to allow the amide cross-linking reaction between NMA-DCCS-PA molecules and the wool fabric. Then add sodium bicarbonate as an alkaline catalyst to dissolve it (the mass concentration of the alkaline catalyst in the NMA-DCCS-PA aqueous solution is 2.4%) and continuously stir and react at 80 °C for 2.5 h to allow the nucleophilic addition reaction between NMA-DCCS-PA molecules and the wool fabric again, grafting to form a flame retardant coating on the surface of the wool fabric. Use an electric padding mangle for two-dip two-roll to make the liquor pickup rate of the wool fabric with the flame retardant coating 100%.

[0049] S2. Pre-dry the wool fabric with the flame retardant coating obtained in step S1 at 78 °C for 25 min, then cure it at 130 °C for 5 min. Filter and wash the obtained product with a mixed solution of acetone and ethanol with a volume ratio of 1:1 to remove the unreacted and bound NMA-DCCS-PA, then wash it with deionized water, dehydrate, and vacuum dry it to obtain the intumescent bio-based flame retardant modified wool fabric.

[0050] After testing, the viscosity-average molecular weight of N-methylolacrylamide-bis-carboxyl chitosan-phytic acid (NMA-DCCS-PA) prepared in this example is 51,700, the carboxyl content at C2 and C3 positions is 58.11%, the substitution degree of N-methylolacrylamide at C6 position is 37.82%, the substitution degree of phytic acid at C6 position is 61.94%, the deacetylation degree is 70.35%, and the solubility in water is 14.57 g / 100 mL.

[0051] After testing, the grafting rate of the intumescent bio-based flame retardant modified wool fabric obtained in this example is 20.47%, the breaking strength of the modified wool fabric is 419.2 N, the crease recovery angle is 207.5°, and the air permeability is 517.6 mm / s; after 100 washes, the limiting oxygen index of the modified wool fabric is 40.5%, the antibacterial rate against Staphylococcus aureus is 94.36%, and the antibacterial rate against Escherichia coli is 95.94%.

[0052] Comparative Example 1 In this comparative example, NMA-DCCS-PA was prepared by the same process method and conditions as in Example 3, with the only difference being that the initiator addition amount in step (1) was 0.

[0053] Apply the flame retardant obtained in this comparative example to the functional modified silk fabric by the same process method and conditions as in Example 3.

[0054] After testing, the viscosity-average molecular weight of N-hydroxymethylacrylamide-dicarboxyl chitosan-phytic acid (NMA-DCCS-PA) prepared in this example is 48,900, the carboxyl content at C2 and C3 positions is 59.26%, the substitution degree of N-hydroxymethylacrylamide at C6 position is 14.73%, the substitution degree of phytic acid at C6 position is 60.30%, the degree of deacetylation is 68.92%, and the solubility in water is 12.76 g / 100 mL.

[0055] After testing, the grafting rate of the intumescent bio-based flame retardant modified silk fabric obtained in this example is 12.38%, the breaking strength of the modified silk fabric is 459.1 N, the wrinkle recovery angle is 172.3°, and the air permeability is 556.2 mm / s; after 100 washes, the limiting oxygen index of the modified silk fabric is 34.3%, the antibacterial rate against Staphylococcus aureus is 93.09%, and the antibacterial rate against Escherichia coli is 94.17%.

[0056] Comparative Example 2 Performance test of the fabric unmodified by the intumescent bio-based flame retardant: (1) After testing, the breaking strength of the unmodified cotton fabric (i.e., the scoured and desized cotton fabric used in Example 1) is 357.4 N, the wrinkle recovery angle is 162.7°, and the air permeability is 430.4 mm / s; after 100 washes, the limiting oxygen index of the unmodified cotton fabric is 17.5%, the antibacterial rate against Staphylococcus aureus is 26.51%, and the antibacterial rate against Escherichia coli is 19.18%.

[0057] (2) After testing, the breaking strength of the unmodified silk fabric (i.e., the scoured and desized silk fabric used in Examples 2 and 3) is 439.5 N, the wrinkle recovery angle is 150.6°, and the air permeability is 571.4 mm / s; after 100 washes, the limiting oxygen index of the unmodified silk fabric is 22.3%, the antibacterial rate against Staphylococcus aureus is 22.75%, and the antibacterial rate against Escherichia coli is 24.08%.

[0058] (3) After testing, the breaking strength of the unmodified wool fabric (i.e., the scoured and desized wool fabric used in Example 4) is 402.3 N, the wrinkle recovery angle is 177.5°, and the air permeability is 534.8 mm / s; after 100 washes, the limiting oxygen index of the unmodified wool fabric is 25.7%, the antibacterial rate against Staphylococcus aureus is 28.64%, and the antibacterial rate against Escherichia coli is 25.17%.

[0059] In the above-mentioned examples and comparative examples: The breaking strength was tested according to the standard of GB / T 3923.2—1998 "Textiles - Tensile properties of fabrics", with the sample clamping length of 10 cm and the tensile speed of 100 mm / min; The crease recovery angle was tested according to the standard of GB / T 3819—1997 "Textiles - Determination of crease recovery of fabrics"; The air permeability was tested according to the standard of GB / T 5453—1997 "Textiles - Determination of air permeability of fabrics", with the test area of 25 cm 2 , and the test air pressure of 100 Pa; The limiting oxygen index was tested on a JF-3 type oxygen index meter according to the ASTM D2863 standard; The antibacterial rates against Staphylococcus aureus and Escherichia coli were tested according to the standard of GB / T 20944.3—2008 "Evaluation of antibacterial properties of textiles - Part 3: Oscillation method".

[0060] II. Detection tests were carried out on the samples obtained in the above-mentioned examples Test item 1: Cone calorimetry analysis of intumescent bio-based flame retardant modified silk fabrics The fire behavior of the modified silk fabrics was analyzed by a cone calorimeter. Three samples of silk fabrics were taken. The first one was the unmodified silk fabric sample (control sample) in Comparative Example 2, the second one was the NMA-DCCS-PA intumescent bio-based flame retardant modified silk fabric obtained by the method of Example 2, and the third one was the NMA-DCCS-PA intumescent bio-based flame retardant modified silk fabric obtained by the method of Example 3. The test results are shown in Table 1.

[0061] Table 1. Cone calorimeter test results of bio-based flame retardant modified silk fabrics

[0062] The ignition time (TTI), peak heat release rate (PHRR), and total heat release (THR) are several important parameters of the combustion behavior during the combustion process of textile materials. The unmodified silk fabric reached the PHRR at 8 s and burned out at 38 s. The values of TTI, PHRR, and THR were 8 s, 78.763 KW / m 2 and 5.012 MJ / m 2 , obviously, silk fabric is a highly flammable fiber material. The NMA-DCCS-PA bio-based flame retardant modified silk fabric of Example 3 reached the PHRR at 31 s and burned out at 65 s. The burning time increased by 71.05% compared with the unmodified silk fabric. The values of TTI, PHRR, and THR were 31 s, 36.131 KW / m 2 and 2.908 MJ / m 2, the PHRR and THR values are reduced by 54.13% and 41.98% respectively compared with the unmodified silk fabric. This indicates that the grafting coating of the NMA-DCCS-PA bio-based flame retardant can effectively reduce the PHRR and THR during the combustion process of silk fabric and prevent the rapid heat release of silk. At the same time, Table 1 shows that the total smoke production (TSP) value of the NMA-DCCS-PA bio-based flame retardant modified silk fabric is 0.049 m 2 , which is 83.56% lower than that of the unmodified silk fabric (0.298 m 2 ). Meanwhile, the modification with the NMA-DCCS-PA bio-based flame retardant also reduces the release amounts of CO and CO2 (PCO, PCO2). This shows that the carboxyl groups, phosphoric acid and other acidic groups contained in NMA-DCCS-PA can dehydrate to form a dense and stable carbon layer at high temperature or when exposed to flame, thereby inhibiting the smoke emission during the combustion process. At the same time, a large number of phosphoric acid derivatives are generated during pyrolysis, which can not only promote the dehydration and carbonization of the carbon source, but also capture free radicals, improving the flame retardant performance of the modified fabric. It can be seen that N-hydroxymethylacrylamide-dicarboxyl chitosan-phytic acid is a highly efficient intumescent flame retardant integrating acid source, carbon source and gas source, and the grafting of NMA-DCCS-PA on the fabric surface can effectively improve the flame retardant and fire prevention ability of textiles.

[0063] Test item 2: Scanning electron microscopy analysis of NMA-DCCS-PA bio-based flame retardant modified silk fabric SEM was used to observe the microtopography of the unmodified silk fabric and the modified silk fabrics with different grafting rates. Three samples of silk fabric were taken: the first was silk fabric a obtained after scouring and degumming treatment (blank control sample), the second was modified silk fabric b with a grafting rate of 13.18% obtained by grafting silk fabric with the NMA-DCCS-PA intumescent bio-based flame retardant according to the method of Example 2, and the third was modified silk fabric c with a grafting rate of 24.06% obtained by grafting silk fabric with the NMA-DCCS-PA intumescent bio-based flame retardant according to the method of Example 3. The test results are shown in Figure 3 (a) - (c) in turn.

[0064] It can be seen from Figure 3 that the surface of the original silk fiber a is relatively smooth and flat, and there are a small number of sericin that have not been removed; while after grafting with the NMA-DCCS-PA intumescent bio-based flame retardant, many lumps are coated on the surface of silk fiber b (see Figure 3 b), and with the increase of the grafting rate of the NMA-DCCS-PA flame retardant, the NMA-DCCS-PA molecules grafted on the surface of the silk fiber gradually crosslink to form a relatively uniform flame retardant film (see Figure 3(c). Meanwhile, the surface of the modified silk becomes relatively rough, indicating that the NMA-DCCS-PA molecules are firmly bonded to the silk fibers through chemical grafting reactions and cross-linked and deposited on the surface of the silk fibers, with strong wash resistance and long-lasting flame retardant and antibacterial effects.

[0065] In summary, by dissolving dicarboxyl chitosan (DCCS) in the weak acidic ionic liquid 1-butyl-3-methylimidazolium acetate ([Bmim][Ac]), adding an inhibitor and an initiator to carry out a nucleophilic substitution reaction with N-hydroxymethyl acrylamide (NMA) under microwave irradiation, and then adding phytic acid (PA), the -OH at the C6 position of dicarboxyl chitosan reacts with PO4 in the phytic acid molecule 3- to undergo an esterification reaction, preparing the intumescent bio-based flame retardant N-hydroxymethyl acrylamide-dicarboxyl chitosan-phytic acid (NMA-DCCS-PA); then, by using the nucleophilic addition and amide cross-linking reactions of the unsaturated double bonds and carboxyl groups in the NMA-DCCS-PA molecules with the hydroxyl and amino groups of the fabric respectively, the NMA-DCCS-PA is chemically grafted on the surface of the fabric, obtaining a functional modified fabric that is affinity to the human body, safe and comfortable, highly flame retardant and fireproof, and has a long-lasting antibacterial property. The intumescent bio-based flame retardant prepared by the present invention contains a large number of groups such as carboxyl groups, phosphate groups, cationic amino groups, and unsaturated double bonds, is green and environmentally friendly, has high reaction activity, is firmly chemically bonded to the fabric, does not use chemical cross-linking agents, does not fall off after washing, is green and environmentally friendly, and at the same time has multiple functions such as flame retardant and fireproof, and long-lasting antibacterial, has a low cost, and is easy to promote and apply.

[0066] The above are only the 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 principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An intumescent bio-based flame retardant, characterized in that: The intumescent bio-based flame retardant described above is N-hydroxymethylacrylamide-bicarboxyl chitosan-phytic acid, which is prepared by dissolving bicarboxyl chitosan in the weakly acidic ionic liquid 1-butyl-3-methylimidazolium acetate, adding an inhibitor and an initiator, and carrying out a substitution reaction with N-hydroxymethylacrylamide under microwave radiation. Then, phytic acid is added and an esterification reaction occurs between the -OH at the C6 position of bicarboxyl chitosan and the PO4 3- in the phytic acid molecule under the action of a catalyst to obtain the product.

2. The intumescent bio-based flame retardant according to claim 1, wherein: The carboxyl contents at C2 and C3 positions of the dicarboxyl chitosan are 45.31 - 68.57%, the degree of deacetylation is 61.27 - 83.42%, the viscosity-average molecular weight is 35,200 - 86,300, the solubility in water is 9.12 - 17.35 g / 100 mL, and the isoelectric point pH = 4.2 - 4.

6. The structural formula of the dicarboxyl chitosan is as follows: 。 3. A method for preparing the intumescent bio-based flame retardant according to claim 1 or 2, characterized in that, It includes the following steps: (1) Dissolve the dicarboxyl chitosan in 1-butyl-3-methylimidazolium acetate at 65 - 85 °C to prepare a dicarboxyl chitosan solution with a mass concentration of 0.8 - 2.5%. Add N-hydroxymethylacrylamide and dissolve for 20 - 40 min under continuous stirring. The mass ratio of dicarboxyl chitosan to N-hydroxymethylacrylamide is 1:1 - 3. Then add an inhibitor and an initiator for dissolution, and then stir and react for 8 - 20 min under microwave radiation conditions. After cooling, add methanol and stir for 3 - 8 min to obtain a reaction solution; add the reaction solution to acetone for precipitation, and ultrasonically wash the obtained precipitate with a mixed solution of acetone and ethanol with a volume ratio of 2:1, and then vacuum dry at 40 - 60 °C for 18 - 24 h to obtain N-hydroxymethylacrylamide-dicarboxyl chitosan; (2) At 55-65 °C, N-hydroxymethylacrylamide-dicarboxyl chitosan is mixed with phytic acid solution with a bath ratio of 1 g: 30-50 mL and pH = 3.6-4.2 in a three-necked flask for dissolution to obtain a mixed solution. The mass ratio of N-hydroxymethylacrylamide-dicarboxyl chitosan to phytic acid is 1.8-3.2:1; then a catalyst is added to the mixed solution, and the mixture is refluxed under condensation at 70-85 °C for 1-4 h to make the -OH on the C6 position of dicarboxyl chitosan react with PO4 in the phytic acid molecule 3- to undergo an esterification reaction. After the reaction, the product is poured into acetone for suction filtration and precipitation. The precipitate is placed in a cryogenic refrigerator at -40 to -20 °C for pre-freezing for 5-10 h, and then freeze-dried by microwave vacuum for 24-48 h. It is washed with ethanol for impurity removal 3-5 times, and then vacuum dried at 40-50 °C for 8-12 h to obtain solid N-hydroxymethylacrylamide-dicarboxyl chitosan-phytic acid, which is the intumescent bio-based flame retardant.

4. The preparation method according to claim 3, characterized in that: In step (1), the inhibitor is 2,6-di-tert-butyl-p-cresol, hydroquinone or 4-methoxyphenol, and the mass ratio of dicarboxyl chitosan to the 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; in step (2), the catalyst is 4-dimethylaminopyridine or dicyclohexylcarbodiimide, and the mass concentration of the catalyst added to the mixed solution is 1 - 2.5%.

5. The preparation method according to claim 3, characterized in that: In step (2), the viscosity-average molecular weight of the N-hydroxymethylacrylamide-dicarboxyl chitosan-phytic acid is 51,400 - 103,600, the carboxyl contents at C2 and C3 positions are 40.73 - 62.49%, the substitution degree of N-hydroxymethylacrylamide at C6 position is 23.16 - 39.51%, the substitution degree of phytic acid at C6 position is 45.20 - 63.15%, the degree of deacetylation is 50.23 - 71.31%, and the solubility in water is 7.62 - 15.08 g / 100 mL; the structural formula of the N-hydroxymethylacrylamide-dicarboxyl chitosan-phytic acid is as follows: 。 6. The preparation method according to claim 3, characterized in that: In step (1), the power of the microwave radiation is 480 - 860 W and the temperature is 90 - 150 °C; in step (2), the pH of the phytic acid solution is adjusted with acetic acid or sodium hydroxide solution with a concentration of 0.06 - 0.1 mol / L; in step (2), the temperature of the microwave vacuum freeze-drying is -100 - -60 °C, the microwave power is 1580 - 2600 W, and the vacuum degree is 8 - 15 Pa.

7. A preparation method of an intumescent bio-based flame retardant modified fabric, characterized in that, It includes the following steps: S1. Add the scoured and desized or degummed cellulose fiber fabric to the aqueous solution of the intumescent bio-based flame retardant described in claim 1 or 2 with a mass concentration of 0.5 - 2% according to a bath ratio of 1 g:20 - 30 mL to obtain a fabric-flame retardant composite solution; Alternatively, add the protein fiber fabric after scouring and desizing or degumming to the aqueous solution of the intumescent bio-based flame retardant described in claim 1 or 2 at a bath ratio of 1 g: 20-30 mL, adjust the pH to 4.0-4.6 and continuously stir and react at 50-65 °C for 1-3 h to carry out an amide cross-linking reaction between the N-hydroxymethylacrylamide-bicarboxyl chitosan-phytic acid molecule and the protein fabric to obtain a fabric-flame retardant composite liquid; Add an alkaline catalyst to the fabric-flame retardant composite liquid and dissolve it, then continuously stir and react at 60-80 °C for 1-3 h to carry out a nucleophilic addition reaction between the N-hydroxymethylacrylamide-bicarboxyl chitosan-phytic acid molecule and the fabric, and graft a flame retardant coating on the fabric surface; Use an electric padding mangle to dip and pad twice to make the liquor pickup rate of the fabric with the flame retardant coating be 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-bake the fabric with the flame retardant coating obtained in step S1 at 70-80 °C for 15-30 min, then bake it at 120-150 °C for 3-5 min. Filter and wash the obtained product with a mixed solution of acetone and ethanol with a volume ratio of 1:1 to remove the unreacted and bound N-hydroxymethylacrylamide-bicarboxyl chitosan-phytic acid, then wash it with deionized water, dehydrate it, and dry it in vacuum to obtain the intumescent bio-based flame retardant modified fabric.

8. The preparation method according to claim 7, characterized in that: The grafting rate of N-hydroxymethylacrylamide-bicarboxyl chitosan-phytic acid in the intumescent bio-based flame retardant modified fabric is 8.94-24.18%.

9. An intumescent bio-based flame retardant modified fabric prepared by the preparation method described in claim 7 or 8.

10. An application of the intumescent bio-based flame retardant modified fabric described in claim 9 in flame retardancy and long-term antibacterial.

Images