Phosphorylated Carboxylated Chitosan Nanospheres@Mxene Antibacterial Composite Flame Retardant

Abstract

The present invention belongs to the field of functional nanocomposites based on polysaccharide compounds, and discloses a phosphorylated carboxyl chitosan nanosphere@Mxene antibacterial and flame retardant composite. It is prepared by reacting an aldehyde compound with the amino group at the C2 position of water-soluble carboxyl chitosan to form a Schiff base protection, then using the methanesulfonic acid / P2O5 system to esterify the hydroxyl group at its C3 position into a phosphate group, and then removing the Schiff base protection at the C2 position to obtain phosphorylated carboxyl chitosan (PCCS) with two acidic groups. An ultrasonic cell disruptor is used to treat the PCCS dispersion to obtain PCCS submicron particles, and then a PCCS nanosphere dispersion is prepared by emulsion polymerization. Under microwave radiation, MXene nanosheets are added dropwise for electrostatic self-assembly to prepare a phosphorylated carboxyl chitosan nanosphere@Mxene antibacterial and flame retardant composite material. The antibacterial and flame retardant composite prepared by the present invention has great application potential in the fields of flame retardant and fire prevention, long-lasting antibacterial, and functional finishing.

Description

Technical Field

[0001] The present invention discloses a phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial composite flame retardant, belonging to the field of functional nanocomposites based on polysaccharide compounds. Background Art

[0002] At present, the flame retardants commonly used in the domestic and foreign markets mainly include: inorganic flame retardants, halogen-based flame retardants, nitrogen-based flame retardants, phosphorus-based flame retardants, silicon-based flame retardants, etc. Among them: inorganic flame retardants need to be added at more than 30% to achieve a better flame retardant effect, and have poor compatibility with polymer materials, and need to be compatibilized. Halogen-based flame retardants have low cost, high stability, low addition amount, and good compatibility with the material body, but they generate a large amount of smoke during combustion, and the hydrogen halide released is corrosive and will produce toxic and carcinogenic substances. During the combustion process of organic phosphorus-based flame retardants, the decomposition of organic phosphorus promotes the formation of a dense carbon layer on the surface, reducing the contact probability between the polymer and oxygen. At the same time, the volatile phosphorus compounds generated can dilute the concentration of combustibles in the gas phase. However, under long-term outdoor use or complex environmental conditions, nitrogen and phosphorus-based flame retardants are easily affected by environmental factors such as ultraviolet rays, oxygen, and humidity, resulting in the destruction of the molecular structure and the reduction of flame retardant activity. Silicon-based flame retardants are also limited in application due to their high cost at present. In the context of increasingly scarce energy, green and environmentally friendly renewable resources have gradually attracted people's attention. As the second largest biomass polymer in nature, chitosan has gradually become a bio-based flame retardant to replace fossil energy raw materials due to its wide source, renewability, biocompatibility, non-toxicity, non-irritation, long-lasting antibacterial ability, broad antibacterial spectrum, safety and hygiene. However, the strong hydrogen bond force between and within chitosan molecules makes it insoluble in water and common organic solvents and can only be dissolved in acidic solutions. Acid solutions are volatile, corrosive, and pollute the environment. At the same time, there is a lack of effective chemical bond crosslinking between chitosan and other materials, and the flame retardant performance is limited, which greatly restricts the application range of chitosan.

[0003] Chitosan contains a large number of hydroxyl groups in its structure and can be used as a charring agent in polymer flame retardant systems. It has a certain flame retardant ability itself. By directly compounding it with acid source materials, an intumescent flame retardant (IFR) system can be formed. Because of its relatively high carbon content, it can be used as a carbon source and a foaming agent in the intumescent flame retardant system to achieve excellent flame retardant effects. Zeng et al. studied the pyrolysis mechanism of chitosan in a nitrogen atmosphere. Chitosan can not only be used as a carbon source but also act as a gas source in the intumescent flame retardant system [Zeng L T, Qin C Q, Wang L S, Li W. Volatile compounds formed from the pyrolysis of chitosan[J]. Carbohydrate Polymers, 2011, 83(4): 1553-1557]. Modifying chitosan by introducing phosphate groups, the phosphorus-containing chitosan flame retardant improves the thermal stability of the material in the high-temperature region and can effectively enhance the flame retardant performance. Li et al. prepared three different MXene-based nanocomposites by solution blending and dip coating methods. The research shows that MXene can significantly improve the anti-dripping performance of polymer combustion [Li L, Liu X, Wang J, et al. New application of MXene in polymer composites toward remarkable anti-dripping performance for flame retardancy[J]. Composites Part A, 2019, 127: 105649-105657]. In recent years, scholars at home and abroad have prepared composite flame retardant materials by synergistic flame retardancy of chitosan and MXene, giving full play to the high carbon content and biocompatibility of chitosan and the excellent thermal stability and controllable chemical properties of MXene. Lin et al. achieved the dual functionalization of polyurethane foam by layer-by-layer assembly of MXene / chitosan and antibacterial metal particles, obtaining excellent flame retardant and antibacterial properties [Bo L, Yin C A Y, Susan O, et al. Dual functionalisation of polyurethane foam for unprecedented flame retardancy and antibacterial properties using layer-by-layer assembly of MXene chitosan with antibacterial metal particles[J]. Composites Part B, 2022, 244: 1101471-1101479].Liu Bing et al. used two biobased materials, phytic acid (PA) and carboxymethyl chitosan (CMCS), to synthesize carboxymethyl chitosan phosphate (PA-CMCS) with good flame retardancy and no environmental pollution. PA-CMCS / PVA nanofiber membranes were obtained by electrospinning, and PA-CMCS / polyester fabrics were prepared by the coating method. They have good thermal stability and excellent char-forming ability, and the char residue rate of PA-CMCS reaches 45% when heated to 690 °C [Liu Bing. Research and Development of Biobased Flame Retardant Fabrics Based on Phytic Acid-Carboxymethyl Chitosan [D]. Jiangsu: Soochow University, 2022, 56-82]. However, the phosphorylated chitosan and its MXene composites obtained in the above research have the problems of fewer acidic groups, partial consumption of amino groups affecting antibacterial activity, lack of reactive groups, poor compatibility between the flame retardant coating and the matrix, affecting the air permeability and hand feeling of the fabric, easy to fall off by washing, unstable composite structure, and low flame retardancy grade. Therefore, it is urgent to develop new multifunctional chitosan biobased composite flame retardant materials. Summary of the Invention

[0004] In view of the above problems existing in the prior art, the purpose of the present invention is to provide a phosphorylated carboxyl chitosan nanosphere@Mxene antibacterial composite flame retardant, denoted as PCCS nanosphere@MXene antibacterial composite flame retardant. The phosphorylated carboxyl chitosan nanospheres have small particle size and uniform size, good water solubility, biocompatibility, degradability, and characteristics such as environmental friendliness and green non-toxicity, and have broad application prospects. The prepared PCCS nanosphere@MXene antibacterial composite flame retardant is green and environmentally friendly, has a stable structure, strong reactivity, and high flame retardancy and heat insulation, and can be used for functional materials such as fire prevention and flame retardancy and long-term antibacterial.

[0005] To achieve the above invention purpose, the technical scheme adopted by the present invention is as follows:

[0006] The present invention first provides a phosphorylated carboxyl chitosan nanosphere@Mxene antibacterial composite flame retardant, which is characterized in that: the antibacterial composite flame retardant is prepared by reacting an aldehyde compound with the amino group at the C2 position of water-soluble carboxyl chitosan (denoted as CCS) to form a Schiff base protection, then using a methanesulfonic acid / P2O5 system to esterify the hydroxyl group at the C3 position in the glucose unit of the carboxyl chitosan Schiff base into a phosphate group, and then removing the Schiff base protection at the C2 position of chitosan to obtain phosphorylated carboxyl chitosan (denoted as PCCS) with two acidic groups. The PCCS dispersion is subjected to ultrasonic cavitation treatment using an ultrasonic cell disruptor to obtain PCCS submicron particles, and then PCCS nanospheres are prepared by emulsion polymerization using a dialdehyde or a dicarboxylic acid as a cross-linking agent, and MXene nanosheets are added dropwise under microwave radiation for electrostatic self-assembly, and then microwave vacuum freeze-drying is carried out to obtain the product.

[0007] Preferably, the C6 carboxyl group content of the water-soluble carboxyl chitosan is 74.68 - 89.72%, the degree of deacetylation is 94.62 - 98.75%, the viscosity-average molecular weight is 51,200 - 96,300, the solubility in water is 14.35 - 22.09 g / 100 mL, the isoelectric point pH = 4.6 - 4.9, and its structural formula is as follows:

[0008] .

[0009] The present invention also provides a preparation method of the phosphorylated carboxyl chitosan nanosphere @Mxene antibacterial composite flame retardant, which is carried out according to the following steps:

[0010] (1) Dissolve water-soluble carboxyl chitosan in 1-(3-sulfonic acid)-propyl-3-methylimidazole zinc chloride ([HO3S-(CH2)3-mim]Cl-ZnCl2) at 75 - 90 °C to prepare a carboxyl chitosan solution with a mass concentration of 1 - 3%. Dropwise add a propylene glycol solution of an aldehyde compound within 10 - 20 min under continuous stirring. The mass ratio of water-soluble carboxyl chitosan to the aldehyde compound is 1:1 - 5, and then heat and stir at 60 - 75 °C for 3 - 6 h. After cooling, stir and dropwise add 0.2 mol / L NaOH solution to adjust the pH to neutral. Filter by suction, wash with ethanol by ultrasonic wave, and dry in vacuum to obtain carboxyl chitosan Schiff base; the aldehyde compound is citral, geranial or neral;

[0011] (2) Dissolve carboxyl chitosan Schiff base in a three-necked flask at a bath ratio of 1 g:8 - 20 mL and a mass concentration of 56 - 82% methanesulfonic acid at 0 - 5 °C. Then add P2O5 in three equal amounts to the system and stir for 1 - 3 h to carry out a phosphorylation reaction. After the reaction, pour the product into ether for suction filtration and precipitation. Wash the filter cake with acetone, methanol, and ether 3 - 5 times respectively, and dry in vacuum at 40 - 60 °C for 18 - 24 h to obtain phosphorylated carboxyl chitosan Schiff base powder; then place it in a 0.1 mol / L hydrochloric acid ethanol solution, rotate and stir for 10 - 16 h, then evaporate to remove ethanol, precipitate with acetone, filter by suction, dry in vacuum, and ball mill to obtain phosphorylated carboxyl chitosan (PCCS); the mass ratio of carboxyl chitosan Schiff base to P2O5 is 0.6:1 - 4;

[0012] (3) Stir and disperse phosphorylated carboxyl chitosan powder in absolute ethanol, and perform ultrasonic cavitation treatment on the dispersion for 3 - 15 min by an ultrasonic cell disruptor to crush the phosphorylated carboxyl chitosan precipitate therein into submicron particles, and then dry in vacuum to obtain phosphorylated carboxyl chitosan submicron particles; dissolve the dried phosphorylated carboxyl chitosan submicron particles in dilute acetic acid with a volume concentration of 1 - 4% (v / v) by stirring to prepare a phosphorylated carboxyl chitosan acetic acid solution with a mass concentration of 0.8 - 3%;

[0013] (4) Mix liquid paraffin and emulsifier polysorbate - 80 in a volume ratio of 5 - 30:1 in a three - necked flask to form 60 mL of a homogeneous liquid. Then, gradually add 2 - 6 mL of the phosphorylated carboxymethyl chitosan acetate solution in step (3) dropwise within 3 - 8 min under a stirring speed of 200 - 500 rpm and continue stirring for 2 - 5 h. Use an automatic syringe to drop 0.08 - 0.2 mL of a dialdehyde or dicarboxylic acid solution with a mass concentration of 35 - 60% at a speed of 0.02 - 0.05 mL / min, heat to 40 - 60 °C and stir - react for 2 - 6 h to make the cationic amino group of phosphorylated carboxymethyl chitosan cross - link with the aldehyde group and carboxyl group of the dialdehyde or dicarboxylic acid to form nanoparticles, and at this time the solution shows opalescence. Then, after the reaction solution is centrifuged at a high speed of 8600 - 12500 rpm and the supernatant is discarded, add a freeze - drying protective agent solution with a mass concentration of 0.2 - 1.2%, and freeze - dry to obtain well - dispersed phosphorylated carboxymethyl chitosan nanospheres; the dialdehyde or dicarboxylic acid is dialdehyde - terminated polyethylene glycol (number - average molecular weight of 1000 - 5400), oxalic acid or malic acid; the average particle size of the phosphorylated carboxymethyl chitosan nanospheres is 98 - 236 nm, and the Zeta potential is 26.44 - 42.91 mV;

[0014] (5) Dissolve the phosphorylated carboxymethyl chitosan nanospheres in step (4) in deionized water with pH = 3.6 - 5.2 to prepare a nanodispersion with a mass concentration of 0.2 - 1%. Then, gradually add a Mxene nanosheet dispersion with a mass concentration of 0.1 - 0.4% and stir - react for 4 - 8 h under microwave radiation conditions to make the phosphorylated carboxymethyl chitosan nanospheres form hydrogen - bond force and electrostatic self - assembly with Mxene nanosheets. Put it into a cryogenic refrigerator at - 30 - 18 °C for pre - freezing for 8 - 12 h, and then carry out microwave vacuum freeze - drying for 6 - 10 h to obtain a phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial and flame - retardant composite. The mass ratio of the phosphorylated carboxymethyl chitosan nanospheres to Mxene nanosheets is 1 - 6:1.

[0015] Preferably, in step (2), the viscosity - average molecular weight of the phosphorylated carboxymethyl chitosan (PCCS) is 49300 - 94100, the degree of phosphorylation substitution at the C3 position is 40.26 - 63.74%, the degree of deacetylation at the C2 position is 91.23 - 94.52%, the carboxyl content at the C6 position is 74.68 - 89.72%, and the solubility in water is 10.17 - 17.89 g / 100 mL; the structural formula of the phosphorylated carboxymethyl chitosan is as follows:

[0016] .

[0017] Preferably, in step (3), the working frequency of the ultrasonic cell disruptor is 9 - 16 kHz and the ultrasonic power is 160 - 380 W.

[0018] Preferably, in step (4), the lyoprotectant is bovine serum albumin, dextran, Tween-80, glycine, L-serine or citrate.

[0019] Preferably, in step (5), the microwave radiation power is 220 - 400 W, and the microwave radiation temperature is 80 - 105 °C.

[0020] Preferably, in step (5), the pH of the nano-dispersion is adjusted by acetic acid or sodium hydroxide solution with a concentration of 0.1 - 0.2 mol / L.

[0021] Preferably, in step (5), the temperature of the microwave vacuum freeze-drying is -50 to -25 °C, the microwave power is 820 - 1600 W, and the vacuum degree is 15 - 22 Pa.

[0022] By optimizing the bath ratio of carboxylated chitosan Schiff base to methanesulfonic acid, the mass ratio of carboxylated chitosan Schiff base to P2O5, the ultrasonic cavitation treatment time and power, the dosage of emulsifier, the dosage of dialdehyde or diacid cross-linking agent, the reaction time and temperature, a series of phosphorylated carboxylated chitosan nanospheres with different degrees of phosphate substitution and different particle sizes can be obtained.

[0023] Compared with the prior art, the preparation principle and advantages of the phosphorylated carboxylated chitosan nanosphere @Mxene antibacterial composite flame retardant in the present invention are as follows:

[0024] 1. In the present invention, Bronsted-Lewis acidic ionic liquid 1-(3-sulfonic acid)-propyl-3-methylimidazole zinc chloride ([HO3S-(CH2)3-mim]Cl-ZnCl2) is used as the dissolution and reaction medium for carboxylated chitosan. When the water generated during the Schiff base reaction between the amino group at the C2 position of carboxylated chitosan and the propylene glycol solution of aldehyde compound is absorbed by the ionic liquid and propylene glycol respectively, it promotes the forward progress of the Schiff base reaction; meanwhile, the acidic ionic liquid 1-(3-sulfonic acid)-propyl-3-methylimidazole zinc chloride makes the amino group at the C2 position of carboxylated chitosan carry a positive charge, enhancing the probability of nucleophilic reaction with aldehyde compounds, accelerating the reaction rate, effectively forming Schiff base protection at the amino group at the C2 position of carboxylated chitosan, and contributing to the phosphorylation substitution reaction between the secondary hydroxyl group at the C3 position of carboxylated chitosan and P2O5, avoiding the consumption of the amino group at the C2 position; in addition, the aldehyde compounds such as citral, geranial or neral used in the present invention have small molecular weights, low steric hindrance, are easy to contact and react with the amino group at the C2 position of chitosan, and are green, environmentally friendly, safe and non-toxic.

[0025] 2. The present invention uses 1-(3-sulfonic acid)-propyl-3-methylimidazolium zinc chloride ([HO3S-(CH2)3-mim]Cl-ZnCl2) ionic liquid as the green solvent for carboxymethyl chitosan and the reaction medium for grafting aldehyde compounds. The ionic liquid has 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, 1-(3-sulfonic acid)-propyl-3-methylimidazolium zinc chloride ionic liquid can directly dissolve carboxymethyl chitosan at medium temperatures of 75-90 °C, without degrading or destroying the molecular chain of carboxymethyl chitosan. After the reaction, adding anhydrous ethanol to the ionic liquid can precipitate the remaining carboxymethyl chitosan, and then evaporating the anhydrous ethanol can recycle the ionic liquid, which is environmentally friendly.

[0026] 3. The present invention uses methanesulfonic acid as an acidic catalyst. The H in its molecule + combines with the oxygen on the acid anhydride (P2O5) of phosphoric acid (protonation), enhancing the positive charge of the phosphoric anhydride in P2O5, which is beneficial to attacking the secondary hydroxyl group at the C3 position of the carboxymethyl chitosan Schiff base, forming a tetrahedral intermediate, and then losing a molecule of water, thus generating phosphorylated carboxymethyl chitosan (PCCS). Phosphorylated carboxymethyl chitosan retains the amino group at the C2 position and can form polycationic amino groups, having good antibacterial activity. The nitrogen, phosphorus and other elements contained in PCCS can combine with the free radicals generated by thermal decomposition, thus inhibiting the persistence of the thermal decomposition reaction. At the same time, the two acidic groups of carboxyl and phosphoric acid contained can dehydrate to form a dense and stable carbon layer during combustion, effectively preventing the spread of the flame.

[0027] 4. The present invention uses ultrasonic cavitation technology to treat phosphorylated carboxymethyl chitosan. Through the cavitation effect generated by an ultrasonic cell disruptor in the liquid, high-frequency alternating water pressure and high-intensity shear force are formed, causing the phosphorylated carboxymethyl chitosan particles to break. At the same time, the ultrasonic wave propagates in the liquid to produce a strong disturbance effect, which can accelerate the particles, causing them to collide with each other and break the particles, thus crushing the phosphorylated carboxymethyl chitosan precipitate into submicron particles, shortening the molecular chain of phosphorylated carboxymethyl chitosan, weakening the intermolecular hydrogen bond and other interaction forces, reducing the molecular arrangement regularity and crystallinity, increasing the accessibility and reaction activity of the active amino groups in the molecule, and showing the unique properties of low-molecular-weight chitosan. At the same time, low-molecular-weight phosphorylated carboxymethyl chitosan is easily cross-linked into spheres with dialdehyde or dibasic acid, and forms nanoparticles with small particle size and strong stability, effectively avoiding the intramolecular cross-linking of macromolecular chitosan due to high viscosity and easy entanglement and aggregation of molecular chains, which hinders the cross-linking of chitosan with dialdehyde or dibasic acid cross-linking agents.

[0028] 5. The present invention uses a lyoprotectant to obtain well-dispersed phosphorylated carboxymethyl chitosan nanoparticles through freeze-drying. The lyoprotectant reduces the formation and growth of ice crystals during the freezing process, avoiding physical damage to the sample. The lyoprotectant can increase the glass transition temperature of the sample, reduce the damage of ice crystals to the sample, and increase the viscosity of the solution, reducing the crystallization process of water to protect the sample. At the same time, the lyoprotectant can form hydrogen bonds with sample molecules to replace the lost water molecules and maintain the stability of the sample. The prepared phosphorylated carboxymethyl chitosan nanospheres have a small particle size, uniform distribution, strong stability, and high biological activity, and can achieve the functions of hydrogen bond force binding with MXene nanosheets and firmly grafting fiber materials through chemical bonds.

[0029] 6. Under microwave irradiation conditions, the present invention drops MXene nanosheets into the dispersion of phosphorylated carboxymethyl chitosan nanospheres for reaction. Due to the fast heating rate, short reaction time, and good uniformity of microwave irradiation, the phosphorylated carboxymethyl chitosan nanospheres are in full contact with the MXene lamellae, promoting the hydrogen bond force binding between the positively charged amino groups in the PCCS nanospheres and the -OH, -F, -O and other groups on the surface of MXene. At the same time, the radiation effect of microwave can enhance the energy absorption of PCCS nanospheres and MXene nanosheets, promote the movement between molecular chain segments, accelerate the multi-site cross-linking rate of PCCS nanospheres and MXene lamellae, with a simple process, saving reaction time and reducing energy consumption.

[0030] 7. The phosphorylated carboxymethyl chitosan nanosphere@Mxene composite flame retardant prepared by the present invention has excellent performance. The layered barrier effect of MXene nanosheets and the synergistic carbonization effect of MXene and PCCS nanospheres can form a dense protective carbon layer, thus inhibiting the emission of smoke during combustion. At the same time, the MXene lamellae provide a rich carbon source for it, and the amino group at the C2 position of the PCCS nanosphere provides ammonia gas as a gas source during combustion, realizing a synergistic intumescent flame retardant effect that combines the functions of acid source, carbon source, and gas source. MXene in the composite flame retardant can effectively hinder the emission of gas products by changing the diffusion path of volatiles, effectively inhibit the generation of smoke, and reduce the release of toxic or harmful gases such as CO and CO2. The addition of MXene nanosheets can enhance the structural stability of the composite flame retardant and further improve the flame retardant performance of the phosphorylated carboxymethyl chitosan nanosphere@Mxene composite material. At the same time, the PCCS nanosphere@MXene composite flame retardant does not use substances such as halogen elements and antimony oxide added in conventional flame retardants during the whole reaction, and will not produce toxic and corrosive gases, which is a green and environmentally friendly bio-based flame retardant with great application prospects.

[0031] 8. The phosphorylated carboxymethyl chitosan nanosphere@Mxene composite material of the present invention is pre-frozen in an ultra-low temperature refrigerator and then subjected to microwave vacuum freeze-drying to obtain a composite flame retardant material. By pre-freezing, the freezing rate of the water inside the phosphorylated carboxymethyl chitosan nanosphere@Mxene composite material is slowed down, thereby reducing the crystallization risk of water during freezing, which helps to form a stable composite structure. At the same time, pre-freezing can also reduce the crystallization and deformation during the freeze-drying process of the composite material, effectively avoiding the structural collapse caused by the rapid removal of water, and significantly improving the stability of the phosphorylated carboxymethyl chitosan nanosphere@Mxene composite material. The present invention uses microwave vacuum freeze-drying to obtain the phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial composite flame retardant material. By combining microwave drying and vacuum drying, the respective advantages can be fully exerted. The ice crystals generated inside the phosphorylated carboxymethyl chitosan nanosphere@Mxene composite material 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 in the composite material. Compared with the disadvantage of slow conventional heat conduction rate under vacuum, 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 composite material are evenly distributed, and the water drying rate is consistent, enhancing the structural strength of the composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is the schematic diagram of the preparation principle of the carboxymethyl chitosan Schiff base of the present invention.

[0033] Figure 2 is the schematic diagram of the preparation principle of phosphorylated carboxymethyl chitosan (PCCS) of the present invention, and its starting material is carboxymethyl chitosan Schiff base.

[0034] Figure 3 is the schematic diagram of the preparation principle of phosphorylated carboxymethyl chitosan (PCCS) nanospheres of the present invention, and its starting material is phosphorylated carboxymethyl chitosan.

[0035] Figure 4 is the schematic diagram of the preparation principle of PCCS nanospheres@MXene antibacterial composite flame retardant of the present invention.

[0036] Figure 5 is the transmission electron microscope image of phosphorylated carboxymethyl chitosan (PCCS) nanospheres in Test Item 3 of the present invention. The (a) - (d) in the figure correspond to the samples of Comparative Example 2, Example 1, Example 3, and Example 4 respectively. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] 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 this embodiment.

[0038] In the following examples, the limiting oxygen index is the lowest oxygen concentration (volume percentage) required to maintain equilibrium combustion when a test specimen is placed in a mixed gas of oxygen and nitrogen under specified conditions. The test of the limiting oxygen index is carried out on a JF-3 type oxygen index meter in accordance with ASTM D2863 standard.

[0039] In the following examples, the test method for the minimum inhibitory concentration is as follows: Phosphorylated carboxyl chitosan nanospheres@Mxene antibacterial composite flame retardant dispersions with mass concentrations of 0.078, 0.156, 0.313, 0.625, 1.25, 2.50, 5.0, 10.0 mg / mL are prepared by the two-fold dilution method respectively. Take sterile test tubes containing 8 mL of nutrient medium (adjust the pH = 5 with PBS buffer), and add 1 mL of the bacterial suspension diluted to 3.0×10 6 CFU / mL and 1 mL of the phosphorylated carboxyl chitosan nanospheres@Mxene antibacterial composite flame retardant dispersion respectively, so that the mass concentration of the phosphorylated carboxyl chitosan nanospheres@Mxene antibacterial composite flame retardant dispersion is 0.0078, 0.0156, 0.0313, 0.0625, 0.125, 0.25, 0.5, 1.0 mg / mL. Each mass concentration of the phosphorylated carboxyl chitosan nanospheres@Mxene antibacterial composite flame retardant dispersion is tested in parallel 2 times. Another test tube containing the corresponding volume of nutrient medium with the phosphorylated carboxyl chitosan nanospheres@Mxene antibacterial composite flame retardant dispersion added (without the bacterial suspension) is set as a blank control. Place the test tubes in a constant temperature incubator and culture at 37°C for 24 h, and then measure the absorbance of the solution at 600 nm. Among them, the concentration at which there is no significant difference in absorbance between the experimental group and the control group is defined as the minimum inhibitory concentration (MIC).

[0040] I. Preparation of phosphorylated carboxyl chitosan nanospheres@Mxene antibacterial composite flame retardant

[0041] Example 1

[0042] (1) Dissolve water-soluble carboxyl chitosan (the carboxyl content at the C6 position is 76.15%, the degree of deacetylation is 95.03%, the viscosity-average molecular weight is 90,800, the solubility in water is 16.82 g / 100 mL, and the isoelectric point pH = 4.9) in 1-(3-sulfonic acid)-propyl-3-methylimidazolium zinc chloride ([HO3S-(CH2)3-mim]Cl-ZnCl2) at 78°C to prepare a 1% carboxyl chitosan solution. Dropwise add a propylene glycol solution of geranial within 12 min under continuous stirring. The mass ratio of water-soluble carboxyl chitosan to geranial is 1:1.5. Then heat and stir at 65°C for 3 h. After cooling, stir and dropwise add 0.2 mol / L NaOH solution to adjust the pH to neutral. After suction filtration, ultrasonic washing with ethanol, and vacuum drying, carboxyl chitosan Schiff base is obtained.

[0043] (2) Dissolve carboxymethyl chitosan Schiff base in a three-necked flask at 4 °C in a bath ratio of 1 g:10 mL with methanesulfonic acid with a mass concentration of 58%. Then divide P2O5 (the mass ratio of carboxymethyl chitosan Schiff base to P2O5 is 0.6:1) into three equal portions and add them to the above mixture and stir for 1 h to carry out a phosphorylation reaction. After the reaction, pour the product into ether for suction filtration to precipitate. Wash the filter cake three times with acetone, methanol, and ether respectively, and vacuum dry at 45 °C for 18 h to obtain phosphorylated carboxymethyl chitosan Schiff base powder; then place it in a 0.1 mol / L hydrochloric acid ethanol solution, rotate and stir for 10 h, then evaporate to remove ethanol, precipitate with acetone, filter, vacuum dry, and ball mill to obtain phosphorylated carboxymethyl chitosan (PCCS).

[0044] (3) Stir and disperse the phosphorylated carboxymethyl chitosan powder in absolute ethanol, and use an ultrasonic cell disruptor with a working frequency of 10 kHz and a power of 185 W to perform ultrasonic cavitation treatment on the dispersion for 5 min to crush the phosphorylated carboxymethyl chitosan precipitate therein into submicron particles, and then vacuum dry to obtain phosphorylated carboxymethyl chitosan submicron particles; dissolve the dried phosphorylated carboxymethyl chitosan submicron particles by stirring in dilute acetic acid with a volume concentration of 1.5% (v / v) to prepare a phosphorylated carboxymethyl chitosan acetic acid solution with a mass concentration of 1%.

[0045] (4) Mix liquid paraffin and emulsifier polysorbate-80 in a volume ratio of 5:1 in a three-necked flask to form 60 mL of a homogeneous liquid. Then gradually add 3 mL of the phosphorylated carboxymethyl chitosan acetic acid solution in step (3) dropwise within 4 min at a stirring speed of 260 rpm and continue stirring for 2 h. Use an automatic syringe to drop 0.08 mL of oxalic acid solution with a mass concentration of 38% at a speed of 0.02 mL / min, heat to 45 °C and stir and react for 2.5 h to cause the cationic amino group of phosphorylated carboxymethyl chitosan to cross-link with the carboxyl group of oxalic acid to form nanoparticles, and at this time the solution shows opalescence; then after the reaction solution is centrifuged at 9200 rpm at high speed and the supernatant is discarded, add a bovine serum albumin solution with a mass concentration of 0.4%, and freeze-dry to obtain well-dispersed phosphorylated carboxymethyl chitosan nanospheres.

[0046] (5) Dissolve the phosphorylated carboxymethyl chitosan nanospheres in step (4) in deionized water with a pH of 3.8 to prepare a nanodispersion with a mass concentration of 0.3%. Then, dropwise add a 0.15% Mxene nanosheet dispersion so that the mass ratio of phosphorylated carboxymethyl chitosan nanospheres to Mxene nanosheets is 1.5:1. Under microwave radiation conditions (microwave radiation power is 260 W, microwave radiation temperature is 82 °C), stir and react for 4 h to form hydrogen bond forces and electrostatic self-assembly between phosphorylated carboxymethyl chitosan nanospheres and Mxene nanosheets. Place it in a -20 °C ultra-low temperature refrigerator for pre-freezing for 8 h, and then perform microwave vacuum freeze-drying (the temperature of microwave vacuum freeze-drying is -32 °C, microwave power is 940 W, and vacuum degree is 19 Pa) for 6 h to obtain a phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial composite flame retardant material.

[0047] After testing, the viscosity-average molecular weight of the phosphorylated carboxymethyl chitosan (PCCS) prepared in this example is 92,700, the degree of phosphorylation substitution at the C3 position is 46.13%, the degree of deacetylation at the C2 position is 92.06%, the carboxyl content at the C6 position is 75.83%, and the solubility in water is 12.06 g / 100 mL.

[0048] After testing with a dynamic light scattering particle size analyzer (DLS), the average particle size of the phosphorylated carboxymethyl chitosan nanospheres obtained in this example is 212 nm, and the Zeta potential is 28.51 mV.

[0049] After testing, the minimum inhibitory concentrations (MIC) of the phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial composite flame retardant material obtained in this example against Staphylococcus aureus and Escherichia coli are 0.0624 mg / mL and 0.0312 mg / mL respectively, and the limiting oxygen index is 35.6%.

[0050] Example 2

[0051] (1) Dissolve water-soluble carboxymethyl chitosan (carboxyl content at the C6 position is 78.39%, degree of deacetylation is 97.28%, viscosity-average molecular weight is 75,200, solubility in water is 19.05 g / 100 mL, isoelectric point pH = 4.7) in 1-(3-sulfonic acid)-propyl-3-methylimidazolium zinc chloride ([HO3S-(CH2)3-mim]Cl-ZnCl2) at 82 °C to prepare a 1.5% carboxymethyl chitosan solution. Dropwise add a propylene glycol solution of neral within 15 min under continuous stirring, with the mass ratio of water-soluble carboxymethyl chitosan to neral being 1:2. Then, heat and stir at 68 °C for 4 h. After cooling, stir and dropwise add 0.2 mol / L NaOH solution to adjust the pH to neutral. After filtration, ultrasonic washing with ethanol, and vacuum drying, carboxymethyl chitosan Schiff base is obtained.

[0052] (2) At 2 °C, carboxymethyl chitosan Schiff base was dissolved in a three-necked flask according to a bath ratio of 1 g:12 mL with methanesulfonic acid with a mass concentration of 65%. Then, P2O5 (the mass ratio of carboxymethyl chitosan Schiff base to P2O5 was 0.6:3) was added to the above mixture in three equal portions and stirred for 1.5 h to undergo a phosphorylation reaction. After the reaction, the product was poured into diethyl ether for suction filtration to obtain a precipitate. The filter cake was washed 4 times with acetone, methanol, and diethyl ether respectively, and vacuum dried at 50 °C for 20 h to obtain phosphorylated carboxymethyl chitosan Schiff base powder. Then, it was placed in a 0.1 mol / L hydrochloric acid ethanol solution, rotated and stirred for 12 h, and then ethanol was evaporated. It was precipitated with acetone, suction filtered, vacuum dried, and ball milled to obtain phosphorylated carboxymethyl chitosan (PCCS).

[0053] (3) The phosphorylated carboxymethyl chitosan powder was stirred and dispersed in absolute ethanol. The dispersion was subjected to ultrasonic cavitation treatment for 8 min using an ultrasonic cell disruptor with a working frequency of 12 kHz and a power of 260 W, so that the phosphorylated carboxymethyl chitosan precipitate therein was crushed into submicron particles. Then, it was vacuum dried to obtain phosphorylated carboxymethyl chitosan submicron particles. The dried phosphorylated carboxymethyl chitosan submicron particles were stirred and dissolved in dilute acetic acid with a volume concentration of 2.4% (v / v) to prepare a phosphorylated carboxymethyl chitosan acetic acid solution with a mass concentration of 1.5%.

[0054] (4) Liquid paraffin and emulsifier polysorbate-80 were mixed in a three-necked flask according to a volume ratio of 9:1 to form 60 mL of a homogeneous liquid. Then, 4 mL of the phosphorylated carboxymethyl chitosan acetic acid solution in step (3) was added dropwise within 5 min at a stirring speed of 385 rpm and then continuously stirred for 3 h. A 0.12 mL solution of dialdehyde polyethylene glycol (number average molecular weight of 3820) with a mass concentration of 45% was added dropwise at a speed of 0.04 mL / min using an automatic syringe, and heated to 50 °C and stirred for 3 h to cause the cationic amino group of phosphorylated carboxymethyl chitosan to crosslink with the aldehyde group of dialdehyde polyethylene glycol to form nanoparticles, and at this time the solution showed opalescence. Then, the reaction solution was centrifuged at 11680 rpm at high speed and the supernatant was discarded. A dextran solution with a mass concentration of 0.8% was added, and freeze drying was carried out to obtain well-dispersed phosphorylated carboxymethyl chitosan nanospheres.

[0055] (5) Dissolve the phosphorylated carboxymethyl chitosan nanospheres in step (4) in deionized water with a pH of 4.0 to prepare a nanodispersion with a mass concentration of 0.5%. Then, dropwise add a 0.2% Mxene nanosheet dispersion so that the mass ratio of the phosphorylated carboxymethyl chitosan nanospheres to the Mxene nanosheets is 2:1. Stir and react for 5 h under microwave radiation conditions (microwave radiation power is 316 W, microwave radiation temperature is 90 °C) to form hydrogen bond forces and electrostatic self-assembly between the phosphorylated carboxymethyl chitosan nanospheres and the Mxene nanosheets. Place it in a -24 °C ultra-low temperature refrigerator for pre-freezing for 10 h, and then perform microwave vacuum freeze-drying (the temperature of microwave vacuum freeze-drying is -40 °C, microwave power is 1280 W, and vacuum degree is 16 Pa) for 7 h to obtain the phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial composite flame retardant material.

[0056] After testing, the viscosity-average molecular weight of the phosphorylated carboxymethyl chitosan (PCCS) prepared in this example is 71,600, the degree of phosphorylation substitution at the C3 position is 53.31%, the degree of deacetylation at the C2 position is 92.86%, the carboxyl content at the C6 position is 79.04%, and the solubility in water is 13.57 g / 100 mL.

[0057] After testing by a dynamic light scattering particle size analyzer (DLS), the average particle size of the phosphorylated carboxymethyl chitosan nanospheres obtained in this example is 178 nm, and the Zeta potential is 33.17 mV.

[0058] After testing, the minimum inhibitory concentrations (MICs) of the phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial composite flame retardant material obtained in this example against Staphylococcus aureus and Escherichia coli are 0.0312 mg / mL and 0.0312 mg / mL, respectively, and the limiting oxygen index is 39.1%.

[0059] Example 3

[0060] (1) Dissolve water-soluble carboxymethyl chitosan (carboxyl content at the C6 position is 82.44%, degree of deacetylation is 98.12%, viscosity-average molecular weight is 52,600, solubility in water is 21.65 g / 100 mL, isoelectric point pH = 4.6) in 1-(3-sulfonic acid)-propyl-3-methylimidazole zinc chloride ([HO3S-(CH2)3-mim]Cl-ZnCl2) at 86 °C to prepare a 2% carboxymethyl chitosan solution. Dropwise add a propylene glycol solution of citral within 18 min under continuous stirring, with the mass ratio of water-soluble carboxymethyl chitosan to citral being 1:3. Then, heat and stir at 70 °C for 5 h. After cooling, stir and dropwise add 0.2 mol / L NaOH solution to adjust the pH to neutral. After filtration, ultrasonic washing with ethanol, and vacuum drying, carboxymethyl chitosan Schiff base is obtained.

[0061] (2) Dissolve carboxymethyl chitosan Schiff base in a three-necked flask at a bath ratio of 1 g:16 mL with 70% (mass concentration) methanesulfonic acid at 0 °C. Then divide P2O5 (the mass ratio of carboxymethyl chitosan Schiff base to P2O5 is 0.6:2) into three equal portions and add them to the above mixture in turn, stirring for 2 h to carry out the phosphorylation reaction. After the reaction, pour the product into ether for suction filtration to precipitate. Wash the filter cake 5 times with acetone, methanol, and ether respectively, and vacuum dry at 55 °C for 22 h to obtain phosphorylated carboxymethyl chitosan Schiff base powder. Then place it in a 0.1 mol / L hydrochloric acid ethanol solution, rotate and stir for 14 h, then evaporate to remove ethanol, precipitate with acetone, filter, vacuum dry, and ball mill to obtain phosphorylated carboxymethyl chitosan (PCCS).

[0062] (3) Stir and disperse the phosphorylated carboxymethyl chitosan powder in absolute ethanol, and use an ultrasonic cell disruptor with a working frequency of 15 kHz and a power of 350 W to perform ultrasonic cavitation treatment on the dispersion for 12 min to crush the phosphorylated carboxymethyl chitosan precipitate therein into submicron particles. Then vacuum dry to obtain phosphorylated carboxymethyl chitosan submicron particles. Stir and dissolve the dried phosphorylated carboxymethyl chitosan submicron particles in dilute acetic acid with a volume concentration of 3% (v / v) to prepare a phosphorylated carboxymethyl chitosan acetic acid solution with a mass concentration of 2%.

[0063] (4) Mix liquid paraffin and emulsifier polysorbate-80 in a three-necked flask according to a volume ratio of 14:1 to form 60 mL of a homogeneous liquid. Then add 4 mL of the phosphorylated carboxymethyl chitosan acetic acid solution in step (3) dropwise within 6 min at a stirring speed of 420 rpm and continue stirring for 3 h. Use an automatic syringe to drop 0.16 mL of a 50% (mass concentration) malic acid solution at a speed of 0.04 mL / min, heat to 50 °C and stir for 4 h to make the cationic amino group of phosphorylated carboxymethyl chitosan cross-link with the carboxyl group of malic acid to form nanoparticles, and at this time the solution shows opalescence. Then, after the reaction solution is centrifuged at 18560 rpm at high speed and the supernatant is discarded, add a 1% (mass concentration) L-serine solution, and freeze-dry to obtain well-dispersed phosphorylated carboxymethyl chitosan nanospheres.

[0064] (5) Dissolve the phosphorylated carboxymethyl chitosan nanospheres in step (4) in deionized water with a pH of 4.2 to prepare a nanodispersion with a mass concentration of 0.8%. Then, dropwise add a 0.3% Mxene nanosheet dispersion so that the mass ratio of phosphorylated carboxymethyl chitosan nanospheres to Mxene nanosheets is 4:1. Stir and react for 6 h under microwave radiation conditions (microwave radiation power is 375 W, microwave radiation temperature is 100 °C) to form hydrogen bond force and electrostatic self-assembly between phosphorylated carboxymethyl chitosan nanospheres and Mxene nanosheets. Place it in a -26 °C ultra-low temperature refrigerator for pre-freezing for 10 h, and then perform microwave vacuum freeze-drying (the temperature of microwave vacuum freeze-drying is -45 °C, microwave power is 1450 W, and vacuum degree is 15 Pa) for 8 h to obtain a phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial composite flame retardant material.

[0065] After testing, the viscosity-average molecular weight of the phosphorylated carboxymethyl chitosan (PCCS) prepared in this example is 50,300, the degree of phosphorylation substitution at the C3 position is 62.14%, the degree of deacetylation at the C2 position is 93.40%, the carboxyl content at the C6 position is 87.57%, and the solubility in water is 15.69 g / 100 mL.

[0066] After testing with a dynamic light scattering particle size analyzer (DLS), the average particle size of the phosphorylated carboxymethyl chitosan nanospheres obtained in this example is 102 nm, and the Zeta potential is 42.51 mV.

[0067] After testing, the minimum inhibitory concentrations (MIC) of the phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial composite flame retardant material obtained in this example against Staphylococcus aureus and Escherichia coli are 0.0156 mg / mL and 0.0156 mg / mL respectively, and the limiting oxygen index is 45.2%.

[0068] Example 4

[0069] (1) Dissolve water-soluble carboxymethyl chitosan (carboxyl content at the C6 position is 85.17%, degree of deacetylation is 97.62%, viscosity-average molecular weight is 58,400, solubility in water is 20.31 g / 100 mL, isoelectric point pH = 4.6) in 1-(3-sulfonic acid)-propyl-3-methylimidazolium zinc chloride ([HO3S-(CH2)3-mim]Cl-ZnCl2) at 86 °C to prepare a 2.5% carboxymethyl chitosan solution. Dropwise add a propylene glycol solution of citral within 18 min under continuous stirring, with the mass ratio of water-soluble carboxymethyl chitosan to citral being 1:4. Then, heat and stir at 75 °C for 6 h. After cooling, stir and add 0.2 mol / L NaOH solution to adjust the pH to neutral. After suction filtration, ethanol ultrasonic washing, and vacuum drying, carboxymethyl chitosan Schiff base is obtained.

[0070] (2) At 1 °C, carboxymethyl chitosan Schiff base was dissolved in a three-necked flask at a bath ratio of 1 g:16 mL with methanesulfonic acid with a mass concentration of 76%. Then, P2O5 (the mass ratio of carboxymethyl chitosan Schiff base to P2O5 was 0.6:3) was added to the above mixture in three equal portions and stirred for 2.5 h to undergo a phosphorylation reaction. After the reaction, the product was poured into diethyl ether for suction filtration to precipitate. The filter cake was washed 5 times with acetone, methanol, and diethyl ether respectively, and vacuum dried at 55 °C for 22 h to obtain phosphorylated carboxymethyl chitosan Schiff base powder. Then, it was placed in a 0.1 mol / L hydrochloric acid ethanol solution, rotated and stirred for 15 h, and then ethanol was evaporated. After precipitation with acetone, suction filtration, vacuum drying, and ball milling, phosphorylated carboxymethyl chitosan (PCCS) was obtained.

[0071] (3) The phosphorylated carboxymethyl chitosan powder was stirred and dispersed in absolute ethanol. The dispersion was subjected to ultrasonic cavitation treatment for 15 min using an ultrasonic cell disruptor with a working frequency of 15 kHz and a power of 350 W, so that the phosphorylated carboxymethyl chitosan precipitate therein was crushed into submicron particles. Then, it was vacuum dried to obtain phosphorylated carboxymethyl chitosan submicron particles. The dried phosphorylated carboxymethyl chitosan submicron particles were stirred and dissolved in dilute acetic acid with a volume concentration of 3% (v / v) to prepare a phosphorylated carboxymethyl chitosan acetic acid solution with a mass concentration of 2.4%.

[0072] (4) Liquid paraffin and emulsifier polysorbate-80 were mixed in a three-necked flask at a volume ratio of 19:1 to form 60 mL of a homogeneous liquid. Then, 5 mL of the phosphorylated carboxymethyl chitosan acetic acid solution in step (3) was added dropwise within 8 min at a stirring speed of 480 rpm and then continuously stirred for 4 h. A 0.2 mL solution of malic acid with a mass concentration of 50% was added dropwise at a speed of 0.05 mL / min using an automatic syringe, and heated to 55 °C and stirred for 5 h to cause the cationic amino group of phosphorylated carboxymethyl chitosan to crosslink with the carboxyl group of malic acid to form nanoparticles, and at this time the solution showed opalescence. Then, the reaction solution was centrifuged at a high speed of 12160 rpm and the supernatant was discarded. A citrate solution with a mass concentration of 1% was added, and freeze-dried to obtain well-dispersed phosphorylated carboxymethyl chitosan nanospheres.

[0073] (5) Dissolve the phosphorylated carboxymethyl chitosan nanospheres in step (4) in deionized water with a pH of 4.8 to prepare a nanodispersion with a mass concentration of 0.8%. Then, gradually add a 0.3% Mxene nanosheet dispersion drop by drop so that the mass ratio of phosphorylated carboxymethyl chitosan nanospheres to Mxene nanosheets is 5:1. Stir and react for 8 h under microwave radiation conditions (microwave radiation power is 380 W, microwave radiation temperature is 102 °C) to form hydrogen bond force and electrostatic self-assembly between phosphorylated carboxymethyl chitosan nanospheres and Mxene nanosheets. Place it in a -28 °C ultra-low temperature refrigerator for pre-freezing for 12 h, and then perform microwave vacuum freeze-drying (the temperature of microwave vacuum freeze-drying is -48 °C, microwave power is 1500 W, and vacuum degree is 15 Pa) for 9 h to obtain a phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial composite flame retardant material.

[0074] After testing, the viscosity-average molecular weight of the phosphorylated carboxymethyl chitosan (PCCS) prepared in this example is 61,700, the degree of phosphorylation substitution at the C3 position is 60.53%, the degree of deacetylation at the C2 position is 92.91%, the carboxyl content at the C6 position is 83.08%, and the solubility in water is 16.37 g / 100 mL.

[0075] After testing by a dynamic light scattering particle size analyzer (DLS), the average particle size of the phosphorylated carboxymethyl chitosan nanospheres obtained in this example is 126 nm, and the Zeta potential is 39.20 mV.

[0076] After testing, the minimum inhibitory concentrations (MICs) of the phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial composite flame retardant material obtained in this example against Staphylococcus aureus and Escherichia coli are 0.0312 mg / mL and 0.0156 mg / mL respectively, and the limiting oxygen index is 41.3%.

[0077] Comparative Example 1

[0078] This comparative example prepares a phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial composite flame retardant according to the same process conditions as in Example 3, with the only difference being that methanesulfonic acid is not added, that is, the 70% methanesulfonic acid in step (2) is replaced with an equal amount of deionized water.

[0079] After testing, the viscosity-average molecular weight of the phosphorylated carboxymethyl chitosan (PCCS) prepared in this comparative example is 49,600, the degree of phosphorylation substitution at the C3 position is 30.17%, the degree of deacetylation at the C2 position is 93.84%, the carboxyl content at the C6 position is 88.13%, and the solubility in water is 16.22 g / 100 mL.

[0080] After testing by a dynamic light scattering particle size analyzer (DLS), the average particle size of the phosphorylated carboxymethyl chitosan nanospheres obtained in this comparative example is 145 nm, and the Zeta potential is 29.17 mV.

[0081] After testing, the minimum inhibitory concentrations (MIC) of the phosphorylated carboxylated chitosan nanosphere@Mxene antibacterial composite flame retardant material obtained in this comparative example against Staphylococcus aureus and Escherichia coli were 0.1248 mg / mL and 0.1092 mg / mL, respectively, and the limiting oxygen index was 26.6%.

[0082] Comparative Example 2

[0083] The phosphorylated carboxylated chitosan nanosphere@Mxene antibacterial composite flame retardant was prepared in this comparative example under the same process conditions as in Example 3, except that malic acid was not added, that is, step (4) was adjusted to:

[0084] Liquid paraffin and emulsifier polysorbate-80 were mixed in a three-necked flask at a volume ratio of 14:1 to form 60 mL of a homogeneous liquid. Then, 4 mL of the phosphorylated carboxylated chitosan acetic acid solution in step (3) was added dropwise within 6 min at a stirring speed of 420 rpm and then continuously stirred for 3 h, and heated to 50 °C and stirred for 4 h to cause the self-crosslinking reaction of phosphorylated carboxylated chitosan molecules to form nanoparticles, and the solution showed opalescence at this time. Then, after the reaction solution was centrifuged at a high speed of 18560 rpm and the supernatant was discarded, a 1% L-serine solution was added, and freeze-drying was performed to obtain well-dispersed phosphorylated carboxylated chitosan nanospheres.

[0085] After testing, the viscosity-average molecular weight of the phosphorylated carboxylated chitosan (PCCS) prepared in this comparative example was 50,300, the degree of phosphorylation substitution at the C3 position was 62.14%, the degree of deacetylation at the C2 position was 93.40%, the carboxyl content at the C6 position was 87.57%, and the solubility in water was 15.69 g / 100 mL.

[0086] Tested by a dynamic light scattering particle size analyzer (DLS), the average particle size of the phosphorylated carboxylated chitosan nanoparticles obtained in this comparative example was 385 nm and the Zeta potential was 19.47 mV.

[0087] After testing, the minimum inhibitory concentrations (MIC) of the phosphorylated carboxylated chitosan nanosphere@Mxene antibacterial composite flame retardant material obtained in this comparative example against Staphylococcus aureus and Escherichia coli were 0.1092 mg / mL and 0.0936 mg / mL, respectively, and the limiting oxygen index was 29.1%.

[0088] II. Detection tests were carried out on the samples obtained in the above examples and comparative examples

[0089] Test item 1: Test on the influence of the volume of malic acid solution on the particle size of the formed nanospheres

[0090] Under the same process conditions as in Example 3, only the dropping volume of the malic acid solution in step (4) of Example 3 was adjusted (0 mL, 0.08 mL, 0.16 mL, 0.20 mL). The obtained phosphorylated carboxymethyl chitosan nanospheres were detected by a dynamic light scattering particle size analyzer (DLS). The test results are shown in Table 1.

[0091] Table 1. Average particle size of phosphorylated carboxymethyl chitosan nanospheres

[0092]

[0093] From the test data shown in Table 1, compared with the particle size of 385 nm of the phosphorylated carboxymethyl chitosan nanospheres obtained without adding malic acid, the average particle size of the phosphorylated carboxymethyl chitosan nanospheres with added malic acid is about 102 - 198 nm. The nanosize is significantly reduced and the distribution is more uniform, indicating that the cationic amino group of phosphorylated carboxymethyl chitosan can cross-link with the carboxyl group of malic acid and further form electrostatically assembled phosphorylated carboxymethyl chitosan nanospheres with smaller size, uniform particle size, low dispersion coefficient and strong stability, which have a wide range of applications.

[0094] Test item 2: Stability test of nanospheres

[0095] 10 mL of each of the phosphorylated carboxymethyl chitosan nanodispersion samples of Comparative Example 2 and Examples 2 - 4 were taken respectively, filled into 20 mL vials, the vial mouths were sealed, and they were placed at room temperature for 14 days. The average particle size and Zeta potential of the phosphorylated carboxymethyl chitosan nanospheres were measured at the specified time, and the appearance changes of each sample were compared. The test results are shown in Table 2.

[0096] Table 2. Changes in particle size and potential of phosphorylated carboxymethyl chitosan nanospheres before and after standing for 14 days

[0097]

[0098] The data in Table 2 show that by dropping different volumes of malic acid solution in the present invention, the cationic amino group of phosphorylated carboxymethyl chitosan cross-links with the carboxyl group of malic acid to form nanospheres, which significantly improves the particle size and stability of the nanospheres. The cross-linking and electrostatic self-assembly of the cationic amino group of phosphorylated carboxymethyl chitosan with the carboxyl group of malic acid and the ultrasonic cavitation treatment of the ultrasonic cell disruptor will significantly affect the particle size, potential, stability and functional effects of the nanospheres. By optimizing the ultrasonic cavitation treatment power and time and the dropping volume of the malic acid solution, the phosphorylated carboxymethyl chitosan nanospheres prepared in the present invention have more ideal particle size, potential and stability and more durable and efficient functionality, which is more conducive to the formation of hydrogen bond force and electrostatic self-assembly between the phosphorylated carboxymethyl chitosan nanospheres and MXene nanosheets, and obtaining a structurally stable phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial composite flame retardant material.

[0099] Test item 3: Transmission electron microscopy analysis of phosphorylated carboxymethyl chitosan nanospheres

[0100] The microscopic morphology of phosphorylated carboxymethyl chitosan nanospheres was observed by TEM. Four samples of phosphorylated carboxymethyl chitosan nanospheres were taken: the first was phosphorylated carboxymethyl chitosan nanospheres a with an average particle size of 385 nm obtained by the method of Comparative Example 2 without adding malic acid, the second was phosphorylated carboxymethyl chitosan nanospheres b with an average particle size of 212 nm obtained by the method of Example 1, the third was phosphorylated carboxymethyl chitosan nanospheres c with an average particle size of 102 nm obtained by the method of Example 3, and the fourth was phosphorylated carboxymethyl chitosan nanospheres d with an average particle size of 126 nm obtained by the method of Example 4. The test results are shown in turn in Figure 5 a - d.

[0101] It is shown that Figure 5 phosphorylated carboxymethyl chitosan molecules without adding malic acid solution can only self - crosslink to form nanoparticles. Due to the large size of phosphorylated carboxymethyl chitosan molecules, there is a large steric hindrance, which makes it difficult for the cationic amino groups in phosphorylated carboxymethyl chitosan molecules to cross - link with the carboxyl groups on their own molecular chains. The formed nanoparticles are large in size, and there is local nanoparticle aggregation, resulting in poor stability (see Figure 5 a). While adding malic acid solution as a cross - linker, due to the small size of malic acid molecules, it is easy to contact with macromolecular phosphorylated carboxymethyl chitosan. The hydroxyl groups and cationic amino groups in phosphorylated carboxymethyl chitosan molecules are prone to cross - link with the carboxyl groups of malic acid and electrostatically assemble to form stable, uniform and small - sized nanoparticles (see Figure 5 b - d).

[0102] In summary, Schiff base protection is formed by the reaction of aldehyde compounds with the C2 - position amino group of water - soluble carboxymethyl chitosan (CCS). Then, the C3 - position hydroxyl group in the glucose unit of CCS is substituted with a phosphate group using the methanesulfonic acid / P2O5 system to obtain phosphorylated carboxymethyl chitosan (PCCS) with two acidic groups. The PCCS dispersion is subjected to ultrasonic cavitation treatment using an ultrasonic cell disruptor to obtain PCCS sub - micron particles. Then, a PCCS nanosphere dispersion is prepared by emulsion polymerization using dialdehyde or dibasic acid as a cross - linker, and MXene nanosheets are added dropwise under microwave radiation for electrostatic self - assembly to form a phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial composite flame retardant with strong stability and high activity. The preparation process of the method of the present invention is simple, the reaction conditions are mild and controllable. The prepared phosphorylated carboxymethyl chitosan nanospheres have small particle size, uniform size, good water solubility, biocompatibility, degradability, and characteristics such as environmental friendliness and green non - toxicity, and have great application potential in the field of functional materials such as fire prevention and flame retardancy, and long - term antibacterial.

[0103] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. Phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial composite flame retardant, characterized in that: The phosphorylated carboxylated chitosan nanosphere@Mxene antibacterial composite flame retardant is obtained by the following steps: (1) Schiff base protection is formed by the reaction of an aldehyde compound with the C2-position amino group of water-soluble carboxylated chitosan CCS: Dissolve water-soluble carboxylated chitosan in 1-(3-sulfonic acid)-propyl-3-methylimidazolium zinc chloride at 75-90 °C to prepare a carboxylated chitosan solution with a mass concentration of 1-3%. Dropwise add the propylene glycol solution of the aldehyde compound within 10-20 min under continuous stirring. The mass ratio of water-soluble carboxylated chitosan to the aldehyde compound is 1:1-5. Then, heat and stir at 60-75 °C for 3-6 h. After cooling, stir and dropwise add 0.2 mol / L NaOH solution to adjust the pH to neutral. After filtration, ultrasonic washing with ethanol, and vacuum drying, carboxylated chitosan Schiff base is obtained; The aldehyde compound is citral, geranial or neral; the C6-position carboxyl content of the water-soluble carboxylated chitosan is 74.68-89.72%, the degree of deacetylation is 94.62-98.75%, the viscosity-average molecular weight is 51,200-96,300, the solubility in water is 14.35-22.09 g / 100 mL, the isoelectric point pH = 4.6-4.9, and its structural formula is as follows: ； (2) Use the methanesulfonic acid / P2O5 system to esterify the C3-position hydroxyl group in the glucose unit of carboxylated chitosan Schiff base into a phosphate group, and then remove the Schiff base protection at the C2 position of chitosan to obtain phosphorylated carboxylated chitosan PCCS with two acidic groups, (3) Use an ultrasonic cell disruptor to perform ultrasonic cavitation treatment on the PCCS dispersion to obtain PCCS submicron particles, (4) Prepare PCCS nanospheres by emulsion polymerization using a dialdehyde or a dicarboxylic acid as a cross-linking agent: Cross-link the cationic amino group of phosphorylated carboxylated chitosan with the aldehyde group and carboxyl group of the dialdehyde or dicarboxylic acid to form nanoparticles, and at this time, the solution shows opalescence; then, after the reaction solution is centrifuged at 8600-12500 rpm and the supernatant is discarded, add a freeze-drying protective agent solution with a mass concentration of 0.2-1.2%, and freeze-dry to obtain phosphorylated carboxylated chitosan nanospheres; the freeze-drying protective agent is bovine serum albumin, dextran, Tween-80, glycine, L-serine or citrate, and the dialdehyde or dicarboxylic acid is dialdehyde poly(ethylene glycol), oxalic acid or malic acid; (5) Under microwave radiation, dropwise add MXene nanosheets for electrostatic self-assembly, and then perform microwave vacuum freeze-drying to obtain it.

2. A preparation method of the phosphorylated carboxylated chitosan nanosphere @Mxene antibacterial composite flame retardant according to claim 1, characterized in that, It includes the following steps: (1) Dissolve water-soluble carboxylated chitosan in 1-(3-sulfonic acid)-propyl-3-methylimidazolium zinc chloride at 75-90 °C to prepare a carboxylated chitosan solution with a mass concentration of 1-3%. Dropwise add the propylene glycol solution of the aldehyde compound within 10-20 min under continuous stirring. The mass ratio of water-soluble carboxylated chitosan to the aldehyde compound is 1:1-5. Then, heat and stir at 60-75 °C for 3-6 h. After cooling, stir and dropwise add 0.2 mol / L NaOH solution to adjust the pH to neutral. After filtration, ultrasonic washing with ethanol, and vacuum drying, carboxylated chitosan Schiff base is obtained; (2) Dissolve carboxymethyl chitosan Schiff base in a three-necked flask at a bath ratio of 1 g: 8 - 20 mL with methanesulfonic acid with a mass concentration of 56 - 82% at 0 - 5 °C. Then add P2O5 into the system in three equal portions and stir for 1 - 3 h to carry out the phosphorylation reaction. After the reaction, pour the product into ether for suction filtration and precipitation. Wash the filter cake with acetone, methanol, and ether 3 - 5 times respectively, and vacuum dry at 40 - 60 °C for 18 - 24 h to obtain phosphorylated carboxymethyl chitosan Schiff base powder. Then place it in a 0.1 mol / L hydrochloric acid ethanol solution, rotate and stir for 10 - 16 h, then evaporate to remove ethanol, precipitate with acetone, filter, vacuum dry, and ball mill to obtain phosphorylated carboxymethyl chitosan PCCS; the mass ratio of the carboxymethyl chitosan Schiff base to P2O5 is 0.6:1 - 4; (3) Stir and disperse the phosphorylated carboxymethyl chitosan powder in absolute ethanol, and use an ultrasonic cell crusher to perform ultrasonic cavitation treatment on the dispersion for 3 - 15 min to crush the phosphorylated carboxymethyl chitosan precipitate in it into submicron particles, and then vacuum dry to obtain phosphorylated carboxymethyl chitosan submicron particles. Stir and dissolve the dried phosphorylated carboxymethyl chitosan submicron particles in dilute acetic acid with a volume concentration of 1 - 4% to prepare a phosphorylated carboxymethyl chitosan acetic acid solution with a mass concentration of 0.8 - 3%; (4) Mix liquid paraffin and emulsifier polysorbate - 80 in a three-necked flask at a volume ratio of 5 - 30:1 to form 60 mL of a homogeneous liquid. Then gradually add 2 - 6 mL of the phosphorylated carboxymethyl chitosan acetic acid solution in step (3) dropwise within 3 - 8 min at a stirring speed of 200 - 500 rpm, and continue to stir for 2 - 5 h. Use an automatic syringe to drop 0.08 - 0.2 mL of a dialdehyde or dicarboxylic acid solution with a mass concentration of 35 - 60% at a speed of 0.02 - 0.05 mL / min, heat to 40 - 60 °C, and stir and react for 2 - 6 h to cause the cationic amino group of the phosphorylated carboxymethyl chitosan to crosslink with the aldehyde group and carboxyl group of the dialdehyde or dicarboxylic acid to form nanoparticles, and at this time the solution shows opalescence. Then, after the reaction solution is centrifuged at 8600 - 12500 rpm and the supernatant is discarded, add a freeze-drying protectant solution with a mass concentration of 0.2 - 1.2%, and freeze-dry to obtain phosphorylated carboxymethyl chitosan nanospheres; (5) Dissolve the phosphorylated carboxymethyl chitosan nanospheres in step (4) in deionized water with a pH of 3.6 - 5.2 to prepare a nanodispersion with a mass concentration of 0.2 - 1%. Then gradually add a Mxene nanosheet dispersion with a mass concentration of 0.1 - 0.4%, and stir and react for 4 - 8 h under microwave radiation conditions to cause the phosphorylated carboxymethyl chitosan nanospheres and Mxene nanosheets to form hydrogen bond forces and electrostatic self-assembly. Place it in a - 30 - - 18 °C ultra-low temperature refrigerator for pre-freezing for 8 - 12 h, and then microwave vacuum freeze-dry for 6 - 10 h to obtain a phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial composite flame retardant; the mass ratio of the phosphorylated carboxymethyl chitosan nanospheres to Mxene nanosheets is 1 - 6:

1.

3. The preparation method according to claim 2, characterized in that: In step (2), the viscosity-average molecular weight of the phosphorylated carboxymethyl chitosan PCCS is 49,300 - 94,100, the degree of phosphorylation substitution at the C3 position is 40.26% - 63.74%, the degree of deacetylation at the C2 position is 91.23% - 94.52%, the carboxyl content at the C6 position is 74.68% - 89.72%, and the solubility in water is 10.17 - 17.89 g / 100 mL; the structural formula of the phosphorylated carboxymethyl chitosan is as follows: 。 4. The preparation method according to claim 2, characterized in that: In step (4), the average particle size of the phosphorylated carboxymethyl chitosan nanospheres is 98 - 236 nm, and the Zeta potential is 26.44 - 42.91 mV.

5. The preparation method according to claim 2, characterized in that: In step (3), the working frequency of the ultrasonic cell disruptor is 9 - 16 kHz, and the ultrasonic power is 160 - 380 W; in step (5), the microwave radiation power is 220 - 400 W, and the microwave radiation temperature is 80 - 105 °C.

6. The preparation method according to claim 2, characterized in that: In step (5), the pH of the nano-dispersion is adjusted by an acetic acid or sodium hydroxide solution with a concentration of 0.1 - 0.2 mol / L.

7. The preparation method according to claim 2, characterized in that: In step (5), the temperature of the microwave vacuum freeze-drying is -50 - -25 °C, the microwave power is 820 - 1600 W, and the vacuum degree is 15 - 22 Pa.

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