Phosphorylated carboxyl chitosan nanosphere (at) Mxene antibacterial composite flame retardant

Abstract

The invention belongs to the field of functional nano composite materials based on polysaccharide compounds, and discloses a phosphorylated carboxyl chitosan nanosphere (at) Mxene antibacterial composite flame retardant, which is prepared by the following steps: reacting an aldehyde group compound with C2-site amino of water-soluble carboxyl chitosan to form Schiff base protection, then carrying out esterification reaction on C3-site hydroxyl of the water-soluble carboxyl chitosan by using a methanesulfonic acid / P2O5 system to form a phosphoric acid group, and then carrying out hydrolysis reaction on the phosphoric acid group to obtain the phosphorylated carboxyl chitosan nanosphere (at) Mxene antibacterial composite flame retardant. The preparation method comprises the following steps: preparing a PCCS dispersion liquid, removing C2-position Schiff base protection to obtain phosphorylated carboxyl chitosan (PCCS) with two acidic groups, treating the PCCS dispersion liquid by using an ultrasonic cell crusher to obtain PCCS submicron particles, preparing the PCCS nanosphere dispersion liquid by using an emulsion polymerization method, dropwise adding MXene nanosheets under microwave radiation, and carrying out electrostatic self-assembly to obtain the PCCS submicron particles. And preparing the phosphorylated carboxyl chitosan nanosphere (at) Mxene antibacterial composite flame retardant material. The antibacterial composite flame retardant prepared by the invention has huge application potential in the fields of flame retardance, fire prevention, lasting antibiosis, functional finishing and the like.

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] Currently, 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 released hydrogen halide is corrosive and can 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 generated volatile phosphorus compounds 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 light, oxygen, and humidity, resulting in the destruction of the molecular structure and the reduction of flame retardant activity. Silicon-based flame retardants also have limited applications due to their currently high cost. In the context of increasingly tight energy, green and environmentally friendly renewable resources have gradually gained people's favor. 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, renewable nature, biocompatibility, non-toxicity, non-irritation, long-lasting antibacterial ability, broad antibacterial spectrum, safety and hygiene. However, the strong hydrogen bond forces within and between chitosan molecules make it insoluble in water and common organic solvents, and can only be dissolved in acidic solutions. Acidic solutions are volatile, corrosive, and pollute the environment. At the same time, there is a lack of effective chemical bond cross-linking 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. Due to its relatively high carbon content, it can be used as a carbon source and a blowing 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 as well as 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 problems such as 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. 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, and have 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: 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, and then using the methanesulfonic acid / P 2 O 5 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 by 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 crosslinking 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.

[0006] Preferably, the C6 carboxyl group content of the water-soluble carboxymethyl 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, and the isoelectric point pH = 4.6-4.9. Its structural formula is as follows: 。

[0007] The present invention also provides a preparation method of the phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial composite flame retardant, which is carried out according to the following steps: (1) Dissolve water-soluble carboxymethyl chitosan in 1-(3-sulfonic acid)-propyl-3-methylimidazolium zinc chloride ([HO 3 S-(CH 2 ) 3 -mim]Cl-ZnCl 2 ) at 75-90 °C to prepare a carboxymethyl 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 carboxymethyl 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. Filter, wash ultrasonically with ethanol, and dry in vacuum to obtain carboxymethyl chitosan Schiff base; the aldehyde compound is citral, geranial or neral; (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 P 2 O 5 equally in 3 portions to the system and stir for 1-3 h to carry out a phosphorylation reaction. After the reaction, pour the product into ether for filtration and precipitation. Wash the filter cake 3-5 times with acetone, methanol, and ether respectively, and dry in vacuum 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, dry in vacuum, and ball mill to obtain phosphorylated carboxymethyl chitosan (PCCS); the mass ratio of carboxymethyl chitosan Schiff base to P 2 O 5 is 0.6:1-4; (3) Stir and disperse the phosphorylated carboxymethyl chitosan powder in absolute ethanol, and use an ultrasonic cell disruptor to perform ultrasonic cavitation treatment on the dispersion for 3 - 15 min to crush the phosphorylated carboxymethyl chitosan precipitate therein into submicron particles, and then dry in vacuum 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% (v / v) 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 volume ratio of 5 - 30:1 in a three - necked flask to form 60 mL of a homogeneous liquid, and 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 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 the reaction solution is centrifuged at a high speed of 8600 - 12500 rpm and the supernatant is discarded, and a freeze - drying protective agent solution with a mass concentration of 0.2 - 1.2% is added, and freeze - drying is carried out to obtain well - dispersed phosphorylated carboxymethyl chitosan nanospheres; the dialdehyde or dicarboxylic acid is dialdehyde - terminated polyethylene glycol (number - average molecular weight is 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. (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%, and 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. Place it in 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.

[0008] Preferably, in step (2), the phosphorylated carboxymethyl chitosan (PCCS) has a viscosity-average molecular weight of 49,300 to 94,100, a degree of phosphorylation at the C3 position of 40.26% to 63.74%, a degree of deacetylation at the C2 position of 91.23% to 94.52%, a carboxyl content at the C6 position of 74.68% to 89.72%, and a solubility in water of 10.17 to 17.89 g / 100 mL; the structural formula of the phosphorylated carboxymethyl chitosan is as follows: .

[0009] Preferably, in step (3), the ultrasonic cell disruptor has an operating frequency of 9 to 16 kHz and an ultrasonic power of 160 to 380 W.

[0010] Preferably, in step (4), the lyoprotectant is bovine serum albumin, dextran, Tween-80, glycine, L-serine, or citrate.

[0011] Preferably, in step (5), the microwave radiation power is 220 to 400 W, and the microwave radiation temperature is 80 to 105 °C.

[0012] Preferably, 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 to 0.2 mol / L.

[0013] Preferably, in step (5), the temperature of the microwave vacuum freeze-drying is -50 to -25 °C, the microwave power is 820 to 1600 W, and the vacuum degree is 15 to 22 Pa.

[0014] By optimizing the bath ratio of carboxymethyl chitosan Schiff base to methanesulfonic acid, the mass ratio of carboxymethyl chitosan Schiff base to P 2 O 5 the mass ratio, the ultrasonic cavitation treatment time and power, the amount of emulsifier, the amount of dialdehyde or diacid crosslinking agent, the reaction time and temperature, a series of phosphorylated carboxymethyl chitosan nanospheres with different degrees of phosphorylation and different particle sizes can be obtained.

[0015] Compared with the prior art, the preparation principle and advantages of the phosphorylated carboxymethyl chitosan nanosphere @Mxene antibacterial composite flame retardant in the present invention are as follows: 1. In the present invention, the Bronsted-Lewis acidic ionic liquid 1-(3-sulfonic acid)-propyl-3-methylimidazolium zinc chloride ([HO 3 S-(CH 2 ) 3 -mim]Cl-ZnCl 2) As the dissolution and reaction medium of carboxylated chitosan, 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 compounds can be absorbed by ionic liquid and propylene glycol respectively, promoting the forward progress of the Schiff base reaction; meanwhile, 1-(3-sulfonic acid)-propyl-3-methylimidazolium zinc chloride acidic ionic liquid 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, and effectively forming a Schiff base protection at the amino group at the C2 position of carboxylated chitosan, which helps the secondary hydroxyl group at the C3 position of carboxylated chitosan to react with P 2 O 5 to undergo phosphorylation substitution reaction, avoiding the consumption of 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 weight, 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.

[0016] 2. The present invention utilizes 1-(3-sulfonic acid)-propyl-3-methylimidazolium zinc chloride ([HO 3 S-(CH 2 ) 3 -mim]Cl-ZnCl 2 ) ionic liquid as the green solvent of carboxylated chitosan and the reaction medium for grafting aldehyde compounds. The ionic liquid has the advantages of non-toxic, pollution-free, stable physical and chemical properties, no evaporation pressure and non-volatility, green environmental protection, recyclability, etc.; meanwhile, 1-(3-sulfonic acid)-propyl-3-methylimidazolium zinc chloride ionic liquid can directly dissolve carboxylated chitosan at medium temperatures of 75-90 °C, without degrading and destroying the molecular chain of carboxylated chitosan, and after the reaction, adding absolute ethanol to the ionic liquid can precipitate the remaining carboxylated chitosan, and then the ionic liquid can be recycled after evaporating the absolute ethanol, which is environmentally friendly.

[0017] 3. The present invention utilizes methanesulfonic acid as an acidic catalyst. The H in its molecule + combines with the oxygen on the anhydride of phosphoric acid (P 2 O 5 ) (protonation), enhancing the positive charge of the phosphoric anhydride in P 2 O 5 , which is beneficial to attacking the secondary hydroxyl group at the C3 position of the Schiff base of nucleophilic reagent carboxylated chitosan to form a tetrahedral intermediate, and then losing a molecule of water, thereby generating phosphorylated carboxylated chitosan (PCCS). Phosphorylated carboxylated chitosan retains the amino group at the C2 position and can form a polycationic amino group, having good antibacterial activity. The nitrogen, phosphorus and other elements contained in PCCS can combine with the free radicals generated by thermal decomposition, thereby inhibiting the persistence of 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 flame.

[0018] 4. The present invention uses ultrasonic cavitation technology to process phosphorylated carboxymethyl chitosan. Through the cavitation effect generated by an ultrasonic cell disruptor in a 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 generate a strong disturbance effect, which can accelerate the particles, cause them to collide with each other and break the particles, thereby 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 reactivity 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 intermolecular 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.

[0019] 5. The present invention uses a freeze-drying protectant to obtain well-dispersed phosphorylated carboxymethyl chitosan nanoparticles by freeze-drying. The freeze-drying protectant reduces the formation and growth of ice crystals during the freezing process, avoiding physical damage to the sample; the freeze-drying protectant 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, reduce the crystallization process of water, and protect the sample; at the same time, the freeze-drying protectant can form hydrogen bonds with the sample molecules, replace the lost water molecules, and maintain the stability of the sample. The prepared phosphorylated carboxymethyl chitosan nanospheres have small particle size, uniform distribution, strong stability and high biological activity, and can realize the function of hydrogen bond force binding with MXene nanosheets and firmly grafting fiber materials through chemical bonds.

[0020] 6. Under the condition of microwave irradiation, the present invention drops Mxene nanosheets into the phosphorylated carboxymethyl chitosan nanosphere dispersion 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 absorption energy 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, the process is simple, saving reaction time and reducing energy consumption.

[0021] 7. The phosphorylated carboxyl chitosan nanosphere@Mxene composite flame retardant prepared by the present invention has excellent performance. The layered blocking effect of MXene nanosheets and the synergistic carbonization effect of MXene and PCCS nanospheres can form a dense protective carbon layer, thereby inhibiting the emission of smoke during combustion. At the same time, the MXene sheets provide a rich carbon source for it, and the amino group at the C2 position of the PCCS nanospheres provides ammonia gas as a gas source during combustion, achieving a synergistic intumescent flame retardant effect that combines the functions of acid source, carbon source, and gas source. The MXene in the composite flame retardant can effectively hinder the emission of gas products by changing the diffusion path of volatile substances, effectively inhibit the generation of smoke, and reduce the release of toxic or harmful gases such as CO and CO 2 etc. 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 carboxyl 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. It is a green and environmentally friendly bio-based flame retardant with great application prospects.

[0022] 8. The present invention puts the phosphorylated carboxyl chitosan nanosphere@Mxene composite material into an ultra-low temperature refrigerator for pre-freezing, and then performs microwave vacuum freeze-drying to obtain the composite flame retardant material. By pre-freezing, the freezing rate of water inside the phosphorylated carboxyl chitosan nanosphere@Mxene composite material is slowed down, thereby reducing the crystallization risk of water during freezing, helping to form a stable composite structure. At the same time, pre-freezing can also reduce crystallization and deformation during the freeze-drying process of the composite material, effectively avoiding the structural collapse of the composite material caused by the rapid removal of water, and significantly improving the stability of the phosphorylated carboxyl chitosan nanosphere@Mxene composite material. The present invention uses microwave vacuum freeze-drying to obtain the phosphorylated carboxyl chitosan nanosphere@Mxene antibacterial composite flame retardant material. By combining microwave drying and vacuum drying, the respective advantages can be fully utilized. The ice crystals generated inside the phosphorylated carboxyl 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 frozen material to be dried, quickly removing the water in the composite 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 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

[0023] Figure 1 is the schematic diagram for the preparation of carboxyl chitosan Schiff base of the present invention.

[0024] Figure 2It is the schematic diagram of the preparation of phosphorylated carboxymethyl chitosan (PCCS) of the present invention, and its starting material is carboxymethyl chitosan Schiff base.

[0025] Figure 3 It is the schematic diagram of the preparation of phosphorylated carboxymethyl chitosan (PCCS) nanospheres of the present invention, and its starting material is phosphorylated carboxymethyl chitosan.

[0026] Figure 4 It is the schematic diagram of the preparation of PCCS nanospheres@MXene antibacterial composite flame retardant of the present invention.

[0027] Figure 5 It is the transmission electron microscope image of phosphorylated carboxymethyl chitosan (PCCS) nanospheres in Test Item 3 of the present invention. (a) - (d) in the figure correspond to the samples of Comparative Example 2, Example 1, Example 3 and Example 4 respectively. Detailed implementation manners

[0028] For a better understanding of the technical features, objectives and beneficial effects of the present invention, the present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited to this embodiment.

[0029] In the following embodiments, the limiting oxygen index is the lowest oxygen concentration (volume percentage) required to maintain equilibrium combustion when the 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.

[0030] In the following embodiments, the test method for the minimum inhibitory concentration is as follows: The phosphorylated carboxymethyl chitosan nanospheres@Mxene antibacterial composite flame retardant dispersion liquids with mass concentrations of 0.078, 0.156, 0.313, 0.625, 1.25, 2.50, 5.0, 10.0 mg / mL are respectively prepared by the two-fold dilution method. Take a sterile test tube containing 8 mL of nutrient medium (adjust the pH = 5 with PBS buffer solution), and add 1 mL of the solution that has been diluted to 3.0×10 6CFU / mL bacterial suspension and 1 mL of phosphorylated carboxylated chitosan nanosphere@Mxene antibacterial composite flame retardant dispersion were added to make the mass concentration of the phosphorylated carboxylated chitosan nanosphere@Mxene antibacterial composite flame retardant dispersion 0.0078, 0.0156, 0.0313, 0.0625, 0.125, 0.25, 0.5, 1.0 mg / mL. Two tests were conducted in parallel for each mass concentration of the phosphorylated carboxylated chitosan nanosphere@Mxene antibacterial composite flame retardant dispersion. Another test tube containing the corresponding volume of nutrient medium with the phosphorylated carboxylated chitosan nanosphere@Mxene antibacterial composite flame retardant dispersion added (without bacterial suspension) was set as a blank control. The test tubes were placed in a constant temperature incubator and cultured at 37°C for 24 h, and then the absorbance of the solution was measured at 600 nm. Among them, the concentration at which there was no significant difference in absorbance between the experimental group and the control group was defined as the minimum inhibitory concentration (MIC).

[0031] I. Preparation of phosphorylated carboxylated chitosan nanosphere@Mxene antibacterial composite flame retardant Example 1

[0032] (1) Water-soluble carboxylated chitosan (with a carboxyl content at the C6 position of 76.15%, a degree of deacetylation of 95.03%, a viscosity-average molecular weight of 90,800, a water solubility of 16.82 g / 100 mL, and an isoelectric point pH = 4.9) was dissolved in 1-(3-sulfonic acid)-propyl-3-methylimidazolium zinc chloride ([HO 3 S-(CH 2 ) 3 -mim]Cl-ZnCl 2 ) at 78°C to prepare a 1% carboxylated chitosan solution. A propylene glycol solution of geranial was added dropwise within 12 min under continuous stirring. The mass ratio of water-soluble carboxylated chitosan to geranial was 1:1.5. Then, the mixture was heated and stirred at 65°C for 3 h. After cooling, 0.2 mol / L NaOH solution was added dropwise with stirring to adjust the pH to neutral. After suction filtration, ethanol ultrasonic washing, and vacuum drying, carboxylated chitosan Schiff base was obtained.

[0033] (2) At 4°C, carboxylated chitosan Schiff base was mixed with 58% methanesulfonic acid in a three-necked flask according to a bath ratio of 1 g:10 mL for dissolution. Then P 2 O 5 (the carboxylated chitosan Schiff base and P 2 O 5The mass ratio of 0.6:1 was added to the above mixture in three equal amounts and stirred for 1 h to carry out the phosphorylation reaction. After the reaction, the product was poured into ether for suction filtration to precipitate. The filter cake was washed three times with acetone, methanol, and ether respectively, and vacuum dried at 45 °C for 18 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 10 h, and then the ethanol was evaporated. It was precipitated with acetone, suction filtered, vacuum dried, and ball milled to obtain phosphorylated carboxymethyl chitosan (PCCS).

[0034] (3)The phosphorylated carboxymethyl chitosan powder was stirred and dispersed in absolute ethanol, and the dispersion was subjected to ultrasonic cavitation treatment for 5 min using an ultrasonic cell disruptor with a working frequency of 10 kHz and a power of 185 W, so that the phosphorylated carboxymethyl chitosan precipitate therein was crushed into submicron particles, and then 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 1.5% (v / v) to prepare a phosphorylated carboxymethyl chitosan acetic acid solution with a mass concentration of 1%.

[0035] (4)Liquid paraffin was mixed with emulsifier polysorbate-80 in a three-necked flask according to a volume ratio of 5:1 to form a 60 mL homogeneous liquid, and then 3 mL of the phosphorylated carboxymethyl chitosan acetic acid solution in step (3) was added dropwise within 4 min at a stirring speed of 260 rpm and continuously stirred for 2 h. A 0.08 mL oxalic acid solution with a mass concentration of 38% was added dropwise at a speed of 0.02 mL / min using an automatic syringe, and heated to 45 °C and stirred for 2.5 h to make the cationic amino group of phosphorylated carboxymethyl chitosan cross-link with the carboxyl group of oxalic acid to form nanoparticles, and the solution showed opalescence at this time; then the reaction solution was centrifuged at 9200 rpm at high speed and the supernatant was discarded, and a bovine serum albumin solution with a mass concentration of 0.4% was added, and freeze-dried to obtain well-dispersed phosphorylated carboxymethyl chitosan nanospheres.

[0036] (5)The phosphorylated carboxymethyl chitosan nanospheres in step (4) were dissolved in deionized water with a pH of 3.8 to prepare a nanodispersion with a mass concentration of 0.3%, and then a nanosheet dispersion of Mxene with a mass concentration of 0.15% was added dropwise so that the mass ratio of phosphorylated carboxymethyl chitosan nanospheres to Mxene nanosheets was 1.5:1, and stirred and reacted for 4 h under microwave radiation conditions (microwave radiation power was 260 W, microwave radiation temperature was 82 °C) to make the phosphorylated carboxymethyl chitosan nanospheres and Mxene nanosheets form hydrogen bond force and electrostatic self-assembly, placed in a -20 °C ultra-low temperature refrigerator for pre-freezing for 8 h, and then subjected to microwave vacuum freeze-drying (the temperature of microwave vacuum freeze-drying was -32 °C, microwave power was 940 W, and vacuum degree was 19 Pa) for 6 h to obtain a phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial composite flame retardant material.

[0037] 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.

[0038] Tested by 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.

[0039] After testing, the minimum inhibitory concentrations (MIC) of the phosphorylated carboxymethyl chitosan nanospheres@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%.

[0040] Example 2

[0041] (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) at 82 °C in 1-(3-sulfonic acid)-propyl-3-methylimidazolium zinc chloride ([HO 3 S-(CH 2 ) 3 -mim]Cl-ZnCl 2 ) to prepare a 1.5% carboxymethyl chitosan solution. Dropwise add the propylene glycol solution of neral within 15 min under continuous stirring. The mass ratio of water-soluble carboxymethyl chitosan to neral is 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. Filter by suction, wash with ethanol by ultrasound, and dry in vacuum to obtain carboxymethyl chitosan Schiff base.

[0042] (2) Dissolve the carboxymethyl chitosan Schiff base in a three-necked flask at a bath ratio of 1 g:12 mL with 65% methanesulfonic acid at 2 °C. Then add P 2 O 5 (the mass ratio of carboxymethyl chitosan Schiff base to P 2 O 5The mass ratio of (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 ether for suction filtration to obtain a precipitate. The filter cake was washed 4 times with acetone, methanol, and 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 the ethanol was evaporated. It was precipitated with acetone, suction filtered, vacuum dried, and ball milled to obtain phosphorylated carboxymethyl chitosan (PCCS).

[0043] (3)The phosphorylated carboxymethyl chitosan powder was stirred and dispersed in absolute ethanol, and 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 in it was crushed into submicron particles, and then 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%.

[0044] (4)Liquid paraffin and emulsifier polysorbate - 80 were mixed into 60 mL of a homogeneous liquid in a three - necked flask according to a volume ratio of 9:1. 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 continuously stirred for 3 h. A 0.12 mL solution of dialdehyde poly(ethylene glycol) with a mass concentration of 45% (number average molecular weight of 3820) 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 cross - link with the aldehyde group of dialdehyde poly(ethylene 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, and a dextran solution with a mass concentration of 0.8% was added, and freeze - dried to obtain well - dispersed phosphorylated carboxymethyl chitosan nanospheres.

[0045] (5) Dissolve the phosphorylated carboxymethyl chitosan nanospheres in step (4) in deionized water with pH = 4.0 to prepare a nano-dispersion with a mass concentration of 0.5%. Then, dropwise add a nano-dispersion of Mxene nanosheets with a mass concentration of 0.2% so that the mass ratio of phosphorylated carboxymethyl chitosan nanospheres to Mxene nanosheets is 2:1. Under microwave radiation conditions (microwave radiation power is 316 W, microwave radiation temperature is 90 °C), stir and react for 5 h to form hydrogen bond force and electrostatic self-assembly between phosphorylated carboxymethyl chitosan nanospheres and 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 phosphorylated carboxymethyl chitosan nanospheres@Mxene antibacterial composite flame retardant material.

[0046] 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.

[0047] 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.

[0048] After testing, the minimum inhibitory concentrations (MIC) of the phosphorylated carboxymethyl chitosan nanospheres@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%.

[0049] Example 3

[0050] (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) at 86 °C in 1-(3-sulfonic acid)-propyl-3-methylimidazolium zinc chloride ([HO 3 S-(CH 2 ) 3 -mim]Cl-ZnCl 2) It is formulated into a 2% carboxymethyl chitosan solution, and a propylene glycol solution of citral is added dropwise within 18 min under continuous stirring. The mass ratio of water-soluble carboxymethyl chitosan to citral is 1:3. Then, it is heated and stirred at 70 °C for 5 h. After cooling, 0.2 mol / L NaOH solution is added dropwise with stirring to adjust the pH to neutral. After filtration, ultrasonic washing with ethanol, and vacuum drying, carboxymethyl chitosan Schiff base is obtained.

[0051] (2) At 0 °C, carboxymethyl chitosan Schiff base is mixed with 70% methanesulfonic acid in a three-necked flask according to a bath ratio of 1 g:16 mL for dissolution. Then, P 2 O 5 (the mass ratio of carboxymethyl chitosan Schiff base to P 2 O 5 is 0.6:2) is added to the above mixture in three equal portions and stirred for 2 h to undergo phosphorylation reaction. After the reaction, the product is poured into ether for filtration and precipitation. The filter cake is washed 5 times with acetone, methanol, and ether respectively, and vacuum dried at 55 °C for 22 h to obtain phosphorylated carboxymethyl chitosan Schiff base powder; then it is placed in 0.1 mol / L hydrochloric acid ethanol solution, rotated and stirred for 14 h, and then ethanol is evaporated. It is precipitated with acetone, filtered, vacuum dried, and ball milled to obtain phosphorylated carboxymethyl chitosan (PCCS).

[0052] (3) The phosphorylated carboxymethyl chitosan powder is stirred and dispersed in absolute ethanol, and the dispersion is subjected to ultrasonic cavitation treatment for 12 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 is crushed into submicron particles, and then vacuum dried to obtain phosphorylated carboxymethyl chitosan submicron particles. The dried phosphorylated carboxymethyl chitosan submicron particles are stirred and dissolved in dilute acetic acid with a volume concentration of 3% (v / v) to be formulated into a 2% phosphorylated carboxymethyl chitosan acetic acid solution.

[0053] (4) Liquid paraffin and emulsifier polysorbate-80 are mixed in a three-necked flask according to a volume ratio of 14:1 to form 60 mL of a homogeneous liquid. Then, 4 mL of the phosphorylated carboxymethyl chitosan acetic acid solution in step (3) is added dropwise within 6 min at a stirring speed of 420 rpm and then continuously stirred for 3 h. 0.16 mL of a 50% malic acid solution is added dropwise at a speed of 0.04 mL / min using an automatic syringe, and heated to 50 °C and stirred 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 the solution shows opalescence at this time; then the reaction solution is centrifuged at 18560 rpm and the supernatant is discarded, and a 1% L-serine solution is added, and freeze-dried to obtain well-dispersed phosphorylated carboxymethyl chitosan nanospheres.

[0054] (5) Dissolve the phosphorylated carboxymethyl chitosan nanospheres in step (4) in deionized water with pH = 4.2 to prepare a nano-dispersion with a mass concentration of 0.8%. Then, dropwise add a nano-dispersion of Mxene nanosheets with a mass concentration of 0.3% so that the mass ratio of phosphorylated carboxymethyl chitosan nanospheres to Mxene nanosheets is 4:1. Under microwave radiation conditions (microwave radiation power is 375 W, microwave radiation temperature is 100 °C), stir and react for 6 h 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.

[0055] 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.

[0056] 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 102 nm and the Zeta potential is 42.51 mV.

[0057] 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%.

[0058] Example 4

[0059] (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) at 86 °C in 1-(3-sulfonic acid)-propyl-3-methylimidazolium zinc chloride ([HO 3 S-(CH 2 ) 3 -mim]Cl-ZnCl 2) It was formulated into a 2.5% (mass concentration) carboxymethyl chitosan solution. Under continuous stirring, a propylene glycol solution of citral was added dropwise within 18 min. The mass ratio of water-soluble carboxymethyl chitosan to citral was 1:4. Then, it was heated and stirred at 75 °C for 6 h. After cooling, 0.2 mol / L NaOH solution was added dropwise with stirring to adjust the pH to neutral. After suction filtration, ultrasonic washing with ethanol, and vacuum drying, carboxymethyl chitosan Schiff base was obtained.

[0060] (2) At 1 °C, carboxymethyl chitosan Schiff base was mixed with 76% (mass concentration) methanesulfonic acid in a three-necked flask according to a bath ratio of 1 g:16 mL for dissolution. Then, P 2 O 5 (the mass ratio of carboxymethyl chitosan Schiff base to P 2 O 5 was 0.6:3) was added to the above mixture in three equal portions and stirred for 2.5 h for phosphorylation reaction. After the reaction, the product was poured into ether for suction filtration and precipitation. The filter cake was washed 5 times with acetone, methanol, and ether respectively, and vacuum dried at 55 °C for 22 h to obtain phosphorylated carboxymethyl chitosan Schiff base powder; then it was placed in 0.1 mol / L hydrochloric acid ethanol solution, rotated and stirred for 15 h, and then ethanol was evaporated. It was precipitated with acetone, suction filtered, vacuum dried, and ball milled to obtain phosphorylated carboxymethyl chitosan (PCCS).

[0061] (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, and then 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 2.4% (mass concentration) phosphorylated carboxymethyl chitosan acetic acid solution.

[0062] (4) Liquid paraffin and emulsifier polysorbate-80 were mixed in a three-necked flask according to 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 50% (mass concentration) malic acid 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 make the cationic amino group of phosphorylated carboxymethyl chitosan cross-link with the carboxyl group of malic acid to form nanoparticles, and the solution showed opalescence at this time; then the reaction solution was centrifuged at 12160 rpm at high speed and the supernatant was discarded, and a 1% (mass concentration) citrate solution was added, and freeze-dried to obtain well-dispersed phosphorylated carboxymethyl chitosan nanospheres.

[0063] (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, dropwise add a 0.3% Mxene nanosheet dispersion so that the mass ratio of the phosphorylated carboxymethyl chitosan nanospheres to the 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 the phosphorylated carboxymethyl chitosan nanospheres and the 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 the phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial composite flame retardant material.

[0064] It was tested that the viscosity-average molecular weight of the phosphorylated carboxymethyl chitosan (PCCS) prepared in this example was 61,700, the degree of phosphorylation substitution at the C3 position was 60.53%, the degree of deacetylation at the C2 position was 92.91%, the carboxyl content at the C6 position was 83.08%, and the solubility in water was 16.37 g / 100 mL.

[0065] Tested by a dynamic light scattering particle size analyzer (DLS), the average particle size of the phosphorylated carboxymethyl chitosan nanospheres obtained in this example was 126 nm, and the Zeta potential was 39.20 mV.

[0066] It was tested that 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 were 0.0312 mg / mL and 0.0156 mg / mL respectively, and the limiting oxygen index was 41.3%.

[0067] Comparative Example 1 The phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial composite flame retardant was prepared in this comparative example under the same process conditions as in Example 3, with the difference that methanesulfonic acid was not added, that is, the 70% methanesulfonic acid in step (2) was replaced with an equal amount of deionized water.

[0068] It was tested that the viscosity-average molecular weight of the phosphorylated carboxymethyl chitosan (PCCS) prepared in this comparative example was 49,600, the degree of phosphorylation substitution at the C3 position was 30.17%, the degree of deacetylation at the C2 position was 93.84%, the carboxyl content at the C6 position was 88.13%, and the solubility in water was 16.22 g / 100 mL.

[0069] Tested by a dynamic light scattering particle size analyzer (DLS), the average particle size of the phosphorylated carboxymethyl chitosan nanospheres obtained in this comparative example was 145 nm, and the Zeta potential was 29.17 mV.

[0070] 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%.

[0071] Comparative Example 2 The phosphorylated carboxylated chitosan nanosphere@Mxene antibacterial composite flame retardant was prepared under the same process conditions as in Example 3, with the only difference being that malic acid was not added, that is, step (4) was adjusted as follows: 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. The mixture was 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, the reaction solution was centrifuged at 18560 rpm at high speed 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.

[0072] 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.

[0073] 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.

[0074] 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%.

[0075] II. Detection tests were carried out on the samples obtained in the above examples and comparative examples Test item 1: Test on the effect of the volume of malic acid solution on the particle size of the formed nanospheres According to 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 carboxylated chitosan nanospheres were detected by a dynamic light scattering particle size analyzer (DLS). The test results are shown in Table 1.

[0076] Table 1. Average particle size of phosphorylated carboxymethyl chitosan nanospheres

[0077]

[0078] As can be seen 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 added with 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 crosslink with the carboxyl group of malic acid, and further electrostatically assemble to form phosphorylated carboxymethyl chitosan nanospheres with smaller size, uniform particle size, low dispersion coefficient and strong stability, which have a wide range of applications.

[0079] Test item 2: Stability test of nanospheres Take 10 mL each of the phosphorylated carboxymethyl chitosan nanodispersion samples of Comparative Example 2 and Examples 2 - 4, respectively, and put them into 20 mL vials. Seal the vial mouths and place them at room temperature for 14 days. Measure the average particle size and Zeta potential of the phosphorylated carboxymethyl chitosan nanospheres at the specified time, and compare the appearance changes of each sample. The test results are shown in Table 2.

[0080] Table 2. Changes in particle size and potential of phosphorylated carboxymethyl chitosan nanospheres before and after standing for 14 days

[0081] 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 crosslinks with the carboxyl group of malic acid to form nanospheres, which significantly improves the particle size and stability of the nanospheres. The crosslinking 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, as well as more persistent 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 nanospheres@Mxene antibacterial composite flame retardant material.

[0082] Test item 3: Transmission electron microscopy analysis of phosphorylated carboxymethyl chitosan nanospheres 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.

[0083] It can be seen from Figure 5 that phosphorylated carboxymethyl chitosan molecules without adding malic acid solution can only self - crosslink to form nanoparticles. Due to the relatively large size of phosphorylated carboxymethyl chitosan molecules, there is a large steric hindrance, resulting in difficulties in the cross - linking reaction between the cationic amino groups in phosphorylated carboxymethyl chitosan molecules and the carboxyl groups on their own molecular chains. The formed nanoparticles are larger in size, and there is a phenomenon of local nanoparticle aggregation, with poor stability (see Figure 5 a). When malic acid solution is added 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).

[0084] In summary, through the reaction of aldehyde compounds with the C2 - position amino groups of water - soluble carboxymethyl chitosan (CCS) to form Schiff base protection, and then using the methanesulfonic acid / P 2 O 5 system to substitute the C3 - position hydroxyl group in the glucose unit of CCS with a phosphate group, phosphorylated carboxymethyl chitosan (PCCS) with two acidic groups is obtained. The PCCS dispersion is subjected to ultrasonic cavitation treatment using an ultrasonic cell disruptor to obtain PCCS sub - micron particles. Then, using dialdehyde or dibasic acid as a cross - linker, a PCCS nanosphere dispersion is prepared by emulsion polymerization, and MXene nanosheets are added dropwise under microwave radiation for electrostatic self - assembly to form a phosphorylated carboxymethyl chitosan nanosphere@Mxene antibacterial and flame - retardant composite with strong stability and high activity. The method of the present invention has a simple preparation process, mild and controllable reaction conditions. The prepared phosphorylated carboxymethyl chitosan nanospheres have small particle size, uniform size, good water solubility, biocompatibility, and degradability, and have characteristics such as environmental friendliness, green non - toxicity, etc., and have great application potential in the field of functional materials such as fire prevention and flame retardancy, and long - term antibacterial.

[0085] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. Phosphorylated carboxyl chitosan nanospheres @Mxene antibacterial composite flame retardant, characterized by: The phosphorylated carboxyl chitosan nanosphere @Mxene antibacterial composite flame retardant is prepared by reacting an aldehyde compound with the C2 amino group of a water-soluble carboxyl chitosan CCS to form a Schiff base protection, and then using a methanesulfonic acid / P2O5 system to esterify the C3 hydroxyl group in the glucose unit of the carboxyl chitosan Schiff base into a phosphate group, and then removing the chitosan C2 Schiff base protection to obtain phosphorylated carboxyl chitosan PCCS with two acidic groups, and using an ultrasonic cell crusher to perform ultrasonic cavitation treatment on the PCCS dispersion to obtain PCCS submicron particles, and then using dialdehyde or dibasic acid as a cross-linking agent to prepare PCCS nanospheres through an emulsion polymerization method, and then adding MXene nanosheets under microwave radiation for electrostatic self-assembly, and then obtaining the obtained particles through microwave vacuum freeze-drying.

2. The phosphorylated carboxyl chitosan nanosphere @Mxene antibacterial composite flame retardant according to claim 1, characterized in that: The water-soluble carboxyl chitosan has a C6 carboxyl content of 74.68-89.72%, a deacetylation degree of 94.62-98.75%, a viscosity-average molecular weight of 51,200-96,300, a solubility in water of 14.35-22.09 g / 100 mL, an isoelectric point pH of 4.6-4.9, and a structural formula as follows: 。 3. A method for preparing the phosphorylated carboxyl chitosan nanospheres @Mxene antibacterial composite flame retardant according to claim 1 or 2, characterized in that: The steps include: (1) Dissolving water-soluble carboxyl chitosan in 1-(3-sulfonic acid)-propyl-3-methylimidazolium chlorozincate at 75-90° C. to prepare a carboxyl chitosan solution with a mass concentration of 1-3%, and adding a propylene glycol solution of an aldehyde compound dropwise within 10-20 min under continuous stirring, wherein the mass ratio of water-soluble carboxyl chitosan to the aldehyde compound is 1:1-5, and then heating and stirring at 60-75° C. for 3-6 h, and then cooling and stirring and adding a 0.2 mol / L NaOH solution dropwise to adjust the pH to neutral, and filtering, washing with ethanol ultrasonic waves, and vacuum drying to obtain a carboxyl chitosan Schiff base; (2) Mix carboxy chitosan Schiff base with methanesulfonic acid of 56-82% in a three-necked flask at a bath ratio of 1g:8-20mL at 0-5°C to dissolve, then add P2O5 into the system in equal amounts for 3 times and stir for 1-3h to cause phosphating reaction, pour the product into ether for filtration and precipitation after the reaction, wash the filter cake with acetone, methanol and ether for 3-5 times respectively, and vacuum dry at 40-60°C for 18-24h to obtain phosphorylated carboxy chitosan Schiff base powder; then place it in 0.1mol / L hydrochloric acid ethanol solution, rotate and stir for 10-16h, then evaporate and remove ethanol, precipitate with acetone, filter, vacuum dry and ball mill to obtain phosphorylated carboxy chitosan PCCS; the mass ratio of carboxy chitosan Schiff base to P2O5 is 0.6:1-4; (3) stirring and dispersing the phosphorylated carboxyl chitosan powder in anhydrous ethanol, subjecting the dispersion to ultrasonic cavitation treatment for 3 to 15 minutes using an ultrasonic cell crusher to crush the phosphorylated carboxyl chitosan precipitate therein into submicron particles, and then vacuum drying to obtain phosphorylated carboxyl chitosan submicron particles; stirring and dissolving the dried phosphorylated carboxyl chitosan submicron particles in dilute acetic acid having a volume concentration of 1 to 4% to prepare a phosphorylated carboxyl chitosan acetic acid solution having a mass concentration of 0.8 to 3%; (4) Liquid paraffin is mixed with emulsifier polysorbate 80 in a three-necked flask at a volume ratio of 5 to 30:1 to form 60 mL of uniform liquid, and then 2 to 6 mL of phosphorylated carboxyl chitosan acetic acid solution in step (3) is added dropwise at a stirring speed of 200 to 500 rpm within 3 to 8 minutes, and then stirred for 2 to 5 hours. Dialdehyde or dihydrogen phosphate having a mass concentration of 35 to 60% is added dropwise at a rate of 0.02 to 0.05 mL / min using an automatic syringe. 0.08-0.2 mL of a primary acid solution is heated to 40-60° C. and stirred for reaction for 2-6 hours to allow the cationic amino groups of phosphorylated carboxyl chitosan to cross-link with the aldehyde groups and carboxyl groups of dialdehyde or dibasic acid to form nanoparticles, at which time the solution exhibits opalescence; the reaction solution is then centrifuged at 8600-12500 rpm and the supernatant is discarded, followed by the addition of a freeze-drying protective agent solution with a mass concentration of 0.2-1.2%, and freeze-drying to obtain phosphorylated carboxyl chitosan nanospheres; (5) The phosphorylated carboxyl chitosan nanospheres in step (4) are dissolved in deionized water with a pH value of 3.6 to 5.2 to prepare a nanodispersion with a mass concentration of 0.2 to 1%, and then a MXene nanosheet dispersion with a mass concentration of 0.1 to 0.4% is added dropwise, and the mixture is stirred for reaction for 4 to 8 hours under microwave irradiation conditions to allow the phosphorylated carboxyl chitosan nanospheres to form hydrogen bonds and electrostatic self-assembly with the MXene nanosheets, and the mixture is placed in a -30 to -18°C ultra-low temperature refrigerator for pre-freezing for 8 to 12 hours, and then subjected to microwave vacuum freeze drying for 6 to 10 hours to obtain a phosphorylated carboxyl chitosan nanosphere@MXene antibacterial composite flame retardant; the mass ratio of the phosphorylated carboxyl chitosan nanospheres to the MXene nanosheets is 1 to 6:

1.

4. The preparation method according to claim 3, characterized in that: The viscosity average molecular weight of the phosphorylated carboxyl chitosan PCCS in step (2) is 49,300 to 94,100, the degree of phosphate substitution at C3 is 40.26 to 63.74%, the degree of deacetylation at C2 is 91.23 to 94.52%, the carboxyl content at C6 is 74.68 to 89.72%, and the solubility in water is 10.17 to 17.89 g / 100 mL; the structural formula of the phosphorylated carboxyl chitosan is as follows: 。 5. The preparation method according to claim 3, characterized in that: In step (1), the aldehyde compound is citral, geranial or neral.

6. The preparation method according to claim 3, characterized in that: In step (4), the lyoprotectant is bovine serum albumin, dextran, Tween-80, glycine, L-serine or citrate, and the dialdehyde or dibasic acid is dialdehyde polyethylene glycol, oxalic acid or malic acid.

7. The preparation method according to claim 3, characterized in that: In step (4), the average particle size of the phosphorylated carboxyl chitosan nanospheres is 98-236 nm, and the Zeta potential is 26.44-42.91 mV.

8. The preparation method according to claim 3, characterized in that: In step (3), the operating 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.

9. The preparation method according to claim 3, characterized in that: In step (5), the pH of the nano-dispersion is adjusted by using acetic acid or sodium hydroxide solution with a concentration of 0.1 to 0.2 mol / L.

10. The preparation method according to claim 3, characterized in that: In step (5), the temperature of the microwave vacuum freeze drying is -50 to -25°C, the microwave power is 820 to 1600W, and the vacuum degree is 15 to 22Pa.

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