Bagasse-based dendrimer modified nitrogen-phosphorus flame retardant as well as preparation method and application thereof

Abstract

The invention discloses a bagasse-based dendrimer modified nitrogen-phosphorus flame retardant as well as a preparation method and application thereof. The flame retardant is prepared by the following steps: (1) adding bagasse into a first solvent, adding an alkaline solution, heating and filtering to obtain cellulose and lignin; (2) suspending cellulose in a phosphoric acid solution, and adding an organic solvent and a catalyst to obtain phosphorylated cellulose; suspending the nitrogen-phosphorus cellulose in a second solvent, and adding a first dendrimer to obtain dendrimer modified nitrogen-phosphorus cellulose; (3) dissolving lignin in an alkali solution, and adding a second dendrimer and a formaldehyde solution to obtain dendrimer aminated lignin; dissolving the dendrimer-modified nitrogen-phosphorus lignin in a third solvent, and adding a phosphorus-containing compound to obtain dendrimer-modified nitrogen-phosphorus lignin; and (4) mixing the modified nitrogen-phosphorus cellulose and the modified nitrogen-phosphorus lignin to obtain the dendrimer modified nitrogen-phosphorus flame retardant. The bagasse-based modified nitrogen-phosphorus flame retardant is developed by utilizing the multifunctionality of the dendrimer, and the novel high-value utilization of the bagasse is embodied.

Description

Technical field:

[0001] The invention relates to the technical field of flame retardants, and in particular to a bagasse-based dendrimer-modified nitrogen-phosphorus flame retardant and a preparation method and application thereof. Background technology:

[0002] Bagasse is the waste of sugarcane sugar industry, accounting for about 1 / 3 of the mass of sugarcane, rich in cellulose, hemicellulose and lignin. Bagasse is an important wood fiber biomass resource in my country with large production, concentrated materials, cheap and easy to obtain and renewable, with an annual output of about 20 million tons. However, nowadays only a small part of bagasse is used for papermaking, and about 80% of bagasse is used as boiler fuel to provide heat and electricity for sugar factories. However, the steam and electricity provided by bagasse boilers in sugar factories can only meet the requirements of sugar production, and cannot be incorporated into the power grid for external supply, so the resource utilization value is not high. The burning and discarding of bagasse not only causes waste of resources, but also brings about problems such as environmental pollution. Making full use of bagasse to prepare high value-added products can reduce dependence on traditional fossil resources, reduce environmental pollution and greenhouse gas emissions, and conform to the concept of sustainable development.

[0003] The rapid development and expansion of modern industry and materials science have made the application of flame retardants more and more extensive. Halogen-containing flame retardants will cause secondary pollution in practical applications, so nitrogen-phosphorus halogen-free flame retardants are increasingly valued. In recent years, using bagasse as raw material, there has been some progress in the preparation of oligosaccharides, nanocellulose, carbon quantum dots and new high-value products of activated carbon, but there are few reports on the use of bagasse to prepare flame retardants. As a renewable resource, the use of bagasse should not be limited to traditional utilization methods. Exploring its new high-value utilization and developing a modified nitrogen-phosphorus flame retardant based on bagasse are very critical to improving the comprehensive utilization efficiency of sugarcane. Summary of the invention:

[0004] The invention solves the problems existing in the prior art. The invention provides a dendritic molecule-modified nitrogen-phosphorus flame retardant based on bagasse and a preparation method and application thereof. The invention expands the utilization methods and scope of bagasse. The flame retardant is simple to synthesize and has a good flame retardant effect, and has broad application prospects in PLA.

[0005] The first object of the present invention is to provide a dendrimer-modified nitrogen-phosphorus flame retardant based on bagasse, which is prepared by the following steps:

[0006] (1) adding the pretreated bagasse to a first solvent, adding an appropriate amount of an alkali solution, mixing evenly, then heating to reflux for reaction, cooling and filtering, washing the filter residue to neutrality, drying to obtain a powdered cellulose solid, collecting the filtrate, acidifying to obtain a precipitate, washing the precipitate to neutrality, and drying to obtain a powdered lignin solid;

[0007] (2) suspending the cellulose obtained in step (1) in a phosphoric acid solution, adding an organic solvent to assist dissolution, mixing uniformly, adding a catalyst, heating and stirring, filtering after cooling, and post-treating to obtain phosphorylated cellulose; then suspending the phosphorylated cellulose in a second solvent, adding the first dendrimer, heating and stirring, filtering after cooling, and post-treating to obtain dendrimer-modified nitrogen phosphocellulose;

[0008] (3) dissolving lignin in an alkaline solution, adding a second dendrimer and a formaldehyde solution, heating and stirring, modifying the dendrimer on the lignin through a Mannich reaction, adjusting the pH to acidic after cooling, filtering, and post-treating to obtain dendrimer aminated lignin; the dendrimer aminated lignin is dissolved in a third solvent, adding a phosphorus-containing compound, heating and stirring, cooling, filtering, and post-treating to obtain dendrimer-modified nitrogen-phosphorus lignin;

[0009] (4) The dendrimer-modified nitrogen-phosphorus cellulose and the dendrimer-modified nitrogen-phosphorus lignin are uniformly mixed to obtain a dendrimer-modified nitrogen-phosphorus flame retardant based on bagasse.

[0010] Preferably, the first solvent in step (1) is selected from one or more of water, ethanol, ethylene glycol, propanol, 1,2-butanediol and 1,4-butanediol, the base is selected from one or more of sodium hydroxide, potassium hydroxide, sodium ethoxide and ammonia water, the mass concentration of the alkaline solution is 10% to 20%, and the conditions for the heating reflux reaction are: reaction temperature 80°C to 120°C, heating time 0.5 to 6h.

[0011] The size of the bagasse proposed by the present invention is 100-20 meshes, and the specific steps of bagasse pretreatment are: grinding the bagasse and screening out powder, washing and drying, the drying temperature is 105°C, and the drying time is 12 hours. Adding an organic solvent to assist dissolution, and then using ultrasonic assisted pretreatment for 20-60 minutes. The acidifying agent of the filtrate is selected from one or more of hydrochloric acid, sulfuric acid, phosphoric acid, and acetic acid, the pH after acidification is 1-5, the standing temperature is 4°C-25°C, and the standing time is 2-16h.

[0012] Preferably, the solid-to-liquid ratio of bagasse to the first solvent in step (1) is 1:5-10 g / mL, and the volume ratio of the first solvent to the alkaline solution is 0.8-1.2: 1. More preferably, the volume ratio of the first solvent to the alkaline solution is 1:1.

[0013] Preferably, the mass concentration of the phosphoric acid solution in step (2) is 30% to 85%, the organic solvent is selected from one of ethanol, tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide and acetonitrile, the catalyst is selected from one of pyridine, N,N-dimethylaminopyridine, 4-pyrrolidinopyridine, 4-dimethylaminopyridine and imidazole, the solid-liquid ratio of cellulose to phosphoric acid solution is 1:1 to 4 g / mL, the volume ratio of phosphoric acid solution to organic solvent is 1:1 to 4, the amount of catalyst is 2% to 8% of the mass of cellulose, and the reaction conditions for synthesizing phosphorylated cellulose are: reaction temperature 50°C to 100°C, heating time 2 to 10 h.

[0014] More preferably, the amount of the catalyst is 5% of the mass of the cellulose.

[0015] Preferably, the second solvent in step (2) is selected from one or more of water, ethanol and N,N-dimethylformamide, the first dendrimer is selected from one of PAMAM G2-NH2 triethanolamine core, PAMAM G2-NH2 ethylenediamine core, PPI G2-NH2 and PLLG2-NH2, the solid-liquid ratio of phosphorylated cellulose to the second solvent is 0.075-0.150:1 g / mL, the mass ratio of phosphorylated cellulose to the first dendrimer is 5-7:1, and the conditions for synthesizing dendrimer-modified nitrogen phosphorus cellulose are: reaction temperature 60°C-100°C, heating time 5-12h. More preferably, the mass ratio of phosphorylated cellulose to the first dendrimer is 6:1.

[0016] Preferably, the mass concentration of the alkaline solution in step (3) is 8% to 12%, the second dendritic molecule is selected from one of PAMAM G2-NH2 triethanolamine core, PAMAM G2-NH2 ethylenediamine core, PPI G2-NH2 and PLL G2-NH2, the mass concentration of the formaldehyde solution is 35% to 40%, the solid-liquid ratio of lignin to the alkaline solution is 1:8 to 12 g / mL, the mass ratio of lignin to the second dendritic molecule is 5 to 7:1, and the mass ratio of lignin to the formaldehyde solution is 4 to 5:1. The conditions for synthesizing dendritic molecule aminated lignin are: reaction temperature 60°C to 80°C, heating time 3 to 6 hours.

[0017] Further preferably, the mass concentration of the alkaline solution in step (3) is 10%, the mass concentration of the formaldehyde solution is 37%, the solid-liquid ratio of lignin to the alkaline solution is 1:10 g / mL, the mass ratio of lignin to the second dendritic molecule is 6:1, and the mass ratio of lignin to the formaldehyde solution is 30:7.

[0018] Preferably, the third solvent in step (3) is selected from one or more of water, ethanol and N,N-dimethylformamide, the phosphorus-containing compound is selected from one of DOPO, DDP, dimethyl methylphosphonate and tributyl phosphate, the solid-liquid ratio of the dendrimer aminated lignin to the third solvent is 0.075-0.150:1 g / mL, the mass ratio of the dendrimer aminated lignin to the phosphorus-containing compound is 0.7-0.8:1, and the conditions for synthesizing the dendrimer modified nitrogen-phosphorus lignin are: reaction temperature 80° C.-120° C., heating time 5-8 h.

[0019] More preferably, the mass ratio of the dendrimer aminated lignin to the phosphorus-containing compound is 0.75:1.

[0020] Preferably, the mass ratio of the dendritic molecule-modified nitrogen phosphorus cellulose to the dendritic molecule-modified nitrogen phosphorus lignin in step (4) is 1:9 to 4:1. Further preferably, the mass ratio of the dendritic molecule-modified nitrogen phosphorus cellulose to the dendritic molecule-modified nitrogen phosphorus lignin in step (4) is 1:9 to 1:1.

[0021] The present invention also protects the use of the dendrimer-modified nitrogen-phosphorus flame retardant in the preparation of plastic products.

[0022] Preferably, the base material of the plastic product is PLA. Further preferably, the amount of the dendrimer-modified nitrogen-phosphorus flame retardant added to the base material is 1-10wt%. Still further preferably, the amount of the dendrimer-modified nitrogen-phosphorus flame retardant added to the base material is 8wt%.

[0023] Compared with the prior art, the present invention has the following advantages: the present invention utilizes the multifunctionality of dendritic molecules to develop a modified nitrogen-phosphorus flame retardant based on bagasse, embodies a new high-value utilization of bagasse, has simple synthesis, and improves the comprehensive utilization efficiency of sugarcane. Description of the drawings:

[0024] Figure 1 This is an infrared image of the dendritic molecular modified nitrogen phosphocellulose based on bagasse in Example 1 of the present invention.

[0025] Figure 2 This is an infrared image of the dendritic molecule-modified nitrogen-phosphorus lignin based on bagasse in Example 1 of the present invention. Specific implementation method:

[0026] The following examples are provided to further illustrate the present invention, rather than to limit the present invention.

[0027] Unless otherwise defined, all professional terms used hereinafter have the same meaning as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the experimental materials and reagents herein are conventional commercial products in the art.

[0028] Embodiment 1:

[0029] The preparation method of the dendrimer-modified nitrogen-phosphorus flame retardant based on bagasse comprises the following steps:

[0030] (1) Grind the bagasse and filter out the 100 mesh powder, and dry it at 105°C for 12 hours. Take 20g of dried bagasse, add 200mL of NaOH (10%) solution and 200mL of ethanol, and then ultrasonically pretreat for 20min. Next, reflux at 100°C for 2h, filter after cooling, wash the filter residue to neutrality, and dry at 105°C to obtain 7.74g of cellulose. Add 20% hydrochloric acid to the filtrate to adjust the pH to 1, let it stand at 4°C for 2h, then centrifuge at 3000rpm, collect the precipitate, wash it to neutrality, and dry it at 105°C to obtain 3.26g of lignin.

[0031] (2) Take 5g of dry cellulose, add 20mL of 30% phosphoric acid solution and 20mL of N,N-dimethylformamide, and then ultrasonically pretreat for 20min. After adding 0.25g of pyridine, react at 100℃ for 2h, filter after cooling, wash the filter residue to neutrality, and dry at 105℃ to obtain 4.01g of phosphorylated cellulose. Take another 3g of dry phosphorylated cellulose, add 20mL of water and 0.5g of PAMAM G2-NH2 (triethanolamine core), react at 80℃ for 5h, filter after cooling, wash the filter residue to neutrality, and dry at 105℃ to obtain 2.95g of dendrimer-modified nitrogen phosphorus cellulose.

[0032] Infrared testing of cellulose, phosphocellulose and dendrimer-modified nitrogen-phosphocellulose ( Figure 1 ), we can see that in the spectrum of phosphocellulose, around 2400cm-1 is the PH stretching vibration, and around 1000cm-1 is the PH bending vibration. In the spectrum of dendrimer-modified nitrogen-phosphorus cellulose, 3500-3300cm-1 is the characteristic absorption peak of the amino group, around 1500cm-1 is the main characteristic peak of the amide bond, and around 1200cm-1 is another characteristic absorption peak of the amide bond.

[0033] (3) Take 3g of dried lignin, dissolve it in 30mL of 10% sodium hydroxide solution, add water to adjust the pH to 10-11, heat it to 80℃, add 0.5g of PAMAM G2-NH2 (triethanolamine core) dropwise while stirring, then add 0.7g of 37% formaldehyde solution dropwise, and react for 3h. After cooling, add water, adjust the pH to 1 with hydrochloric acid, let stand at 4℃ for 16h, then filter, wash, and dry at 105℃ to obtain 1.86g of dendrimer aminated lignin. Take 1.5g of dried dendrimer-modified aminated lignin, dissolve it in 10mL of N,N-dimethylformamide, add 2g of DOPO, heat and stir at 120℃ for 5h, cool, slowly add dropwise to water, precipitate, then filter, wash, and dry at 105℃ to obtain 1.24g of dendrimer-modified nitrogen-phosphorus lignin.

[0034] Infrared testing of lignin, dendrimer-aminated lignin and dendrimer-modified nitrogen-phosphorus lignin ( Figure 2 ), we can see that in the spectrum of dendrimer aminated lignin, around 3400cm-1 is the characteristic absorption peak of amino group, and around 1200cm-1 is the characteristic absorption peak of amide bond. In the spectrum of dendrimer modified nitrogen-phosphorus lignin, 1200-1000cm-1 is the characteristic absorption peak of P=O and POC, and around 2900 is the characteristic absorption peak of CH on benzene ring.

[0035] (4) 0.2 g of dendrimer-modified nitrogen-phosphorus cellulose and 1.8 g of dendrimer-modified nitrogen-phosphorus lignin were uniformly mixed to obtain a dendrimer-modified nitrogen-phosphorus flame retardant based on bagasse.

[0036] Example 2

[0037] Same as Example 1, except that:

[0038] In step (4), 1 g of dendrimer-modified nitrogen-phosphorus cellulose and 1 g of dendrimer-modified nitrogen-phosphorus lignin are uniformly mixed to obtain a dendrimer-modified nitrogen-phosphorus flame retardant based on bagasse.

[0039] Example 3

[0040] Same as Example 1, except that:

[0041] In step (4), 1.6 g of dendrimer-modified nitrogen-phosphorus cellulose and 0.4 g of dendrimer-modified nitrogen-phosphorus lignin are uniformly mixed to obtain a dendrimer-modified nitrogen-phosphorus flame retardant based on bagasse.

[0042] Example 4

[0043] The preparation method of the dendrimer-modified nitrogen-phosphorus flame retardant based on bagasse comprises the following steps:

[0044] (1) Grind the bagasse and screen out a 20-mesh powder, and dry it at 105°C for 12 hours. Take 20g of dried bagasse, add 100mL of KOH (20%) solution and 100mL of propanol, and then ultrasonically pretreat for 60min. Next, reflux at 120°C for 6h, filter after cooling, wash the filter residue to neutrality, and dry at 105°C to obtain 6.91g of cellulose. Add 30% phosphoric acid to the filtrate to adjust the pH to 3, let it stand at 25°C for 16h, then centrifuge at 3000rpm, collect the precipitate, wash it to neutrality, and dry it at 105°C to obtain 3.52g of lignin.

[0045] (2) Take 5g of dry cellulose, add 5mL of 85% phosphoric acid solution and 20mL of ethanol, and then ultrasonically pretreat for 60min. After adding 0.25g of imidazole, react at 80℃ for 10h, filter after cooling, wash the filter residue to neutrality, and dry at 105℃ to obtain 3.77g of phosphorylated cellulose. Take another 3g of dry phosphorylated cellulose, add 10mL of water, 10mL of ethanol and 0.5g of PPIG2-NH2, react at 100℃ for 8h, filter after cooling, wash the filter residue to neutrality, and dry at 105℃ to obtain 2.56g of dendrimer-modified nitrogen phosphorus cellulose.

[0046] (3) Take 3g of dried lignin, dissolve it in 30mL of 10% sodium hydroxide solution, add water to adjust the pH to 10-11, heat to 60℃, add 0.5g of PPI G2-NH2 dropwise while stirring, then add 0.7g of 37% formaldehyde dropwise, and react for 6h. After cooling, add water, adjust the pH to 3 with hydrochloric acid, let stand at 4℃ for 16h, then filter, wash, and dry at 105℃ to obtain 2.12g of dendrimer aminated lignin. Take 1.5g of dried aminated lignin, dissolve it in 10mL of water and 10mL of ethanol, add 2g of DDP, heat and stir at 80℃ for 8h, cool, slowly add dropwise to water, precipitate, then filter, wash, and dry at 105℃ to obtain 1.10g of dendrimer modified nitrogen-phosphorus lignin.

[0047] (4) 1 g of dendrimer-modified nitrogen-phosphorus cellulose and 1 g of dendrimer-modified nitrogen-phosphorus lignin were uniformly mixed to obtain a dendrimer-modified nitrogen-phosphorus flame retardant based on bagasse.

[0048] The modified flame retardant prepared in Examples 1 to 4 was applied to PLA. PLA and the flame retardant were first dried in vacuum at 80° C. for 16 h, and then the dried PLA and the flame retardant (mass ratio 100:8) were added to a torque rheometer and mixed at 180° C. for 5 minutes.

[0049] Table 1: Performance test results of examples of dendrimer-modified nitrogen-phosphorus flame retardants based on bagasse

[0050]

[0051] Example 5

[0052] The same as Example 1, except that the dendrimers in step (2) and step (3) are both PAMAM G2-NH2 (ethylenediamine core).

[0053] Example 6

[0054] The same as Example 1, except that the dendrimers in step (2) and step (3) are both PPI G2-NH2.

[0055] Example 7

[0056] The same as Example 1, except that the dendrimer molecules in step (2) and step (3) are both PLL G2-NH2.

[0057] Example 8

[0058] Same as Example 1, except that:

[0059] The mass concentration of the alkaline solution in step (1) is 10%, and the conditions for the heating reflux reaction are: reaction temperature 80° C., heating time 6 h; the solid-liquid ratio of bagasse to the first solvent is 1:5 g / mL, and the volume ratio of the first solvent to the alkaline solution is 0.8:1.

[0060] Step (2) The mass concentration of the phosphoric acid solution is 30%, the solid-liquid ratio of cellulose to the phosphoric acid solution is 1:4 g / mL, the volume ratio of the phosphoric acid solution to the organic solvent is 1:4, the amount of the catalyst is 2% of the mass of the cellulose, and the reaction conditions for synthesizing phosphorylated cellulose are: reaction temperature 50°C, heating time 10 hours. The solid-liquid ratio of phosphorylated cellulose to the second solvent is 0.075:1 g / mL, the mass ratio of phosphorylated cellulose to the first dendrimer is 5:1, and the conditions for synthesizing dendrimer-modified nitrogen-phosphorus cellulose are: reaction temperature 60°C, heating time 12 hours.

[0061] In step (3), the mass concentration of the alkaline solution is 12%, the mass concentration of the formaldehyde solution is 35%, the solid-liquid ratio of lignin to the alkaline solution is 1:12 g / mL, the mass ratio of lignin to the second dendrimer is 5:1, the mass ratio of lignin to the formaldehyde solution is 4:1, and the conditions for synthesizing dendrimer aminated lignin are: reaction temperature 60°C, heating time 6h. The solid-liquid ratio of dendrimer aminated lignin to the third solvent is 0.075:1 g / mL, the mass ratio of dendrimer aminated lignin to the phosphorus-containing compound is 0.7:1, and the conditions for synthesizing dendrimer modified nitrogen-phosphorus lignin are: reaction temperature 80°C, heating time 8h.

[0062] Example 9

[0063] Same as Example 1, except that:

[0064] The mass concentration of the alkaline solution in step (1) is 20%, and the conditions for the heating reflux reaction are: reaction temperature 120° C., heating time 0.5 h; the solid-liquid ratio of bagasse to the first solvent is 1:10 g / mL, and the volume ratio of the first solvent to the alkaline solution is 1.2:1.

[0065] Step (2) The mass concentration of the phosphoric acid solution is 85%, the solid-liquid ratio of cellulose to the phosphoric acid solution is 1:1 g / mL, the volume ratio of the phosphoric acid solution to the organic solvent is 1:1, the amount of the catalyst is 8% of the mass of the cellulose, and the reaction conditions for synthesizing phosphorylated cellulose are: reaction temperature 100° C., heating time 2 h. The solid-liquid ratio of phosphorylated cellulose to the second solvent is 0.15:1 g / mL, the mass ratio of phosphorylated cellulose to the first dendrimer is 7:1, and the conditions for synthesizing dendrimer-modified nitrogen-phosphorus cellulose are: reaction temperature 100° C., heating time 5 h.

[0066] In step (3), the mass concentration of the alkaline solution is 8%, the mass concentration of the formaldehyde solution is 40%, the solid-liquid ratio of lignin to the alkaline solution is 1:8 g / mL, the mass ratio of lignin to the second dendrimer is 7:1, the mass ratio of lignin to the formaldehyde solution is 5:1, and the conditions for synthesizing dendrimer aminated lignin are: reaction temperature 80°C, heating time 3h. The solid-liquid ratio of dendrimer aminated lignin to the third solvent is 0.15:1 g / mL, the mass ratio of dendrimer aminated lignin to the phosphorus-containing compound is 0.8:1, and the conditions for synthesizing dendrimer modified nitrogen-phosphorus lignin are: reaction temperature 120°C, heating time 5h.

[0067] The description of the above embodiments is only used to help understand the technical solution and core ideas of the present invention. It should be pointed out that for technicians in this technical field, several improvements and modifications can be made to the present invention without departing from the principles of the present invention. These improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A dendrimer-modified nitrogen-phosphorus flame retardant based on bagasse, characterized in that: Prepared by the following steps: (1) adding the pretreated bagasse to a first solvent, adding an appropriate amount of an alkali solution, mixing evenly, then heating to reflux for reaction, cooling and filtering, washing the filter residue to neutrality, drying to obtain a powdered cellulose solid, collecting the filtrate, acidifying to obtain a precipitate, washing the precipitate to neutrality, and drying to obtain a powdered lignin solid; (2) suspending the cellulose obtained in step (1) in a phosphoric acid solution, adding an organic solvent to assist dissolution, mixing uniformly, adding a catalyst, heating and stirring, filtering after cooling, and post-treating to obtain phosphorylated cellulose; then suspending the phosphorylated cellulose in a second solvent, adding the first dendrimer, heating and stirring, filtering after cooling, and post-treating to obtain dendrimer-modified nitrogen phosphocellulose; (3) dissolving lignin in an alkaline solution, adding a second dendrimer and a formaldehyde solution, heating and stirring, modifying the dendrimer on the lignin through a Mannich reaction, adjusting the pH to acidic after cooling, filtering, and post-treating to obtain dendrimer aminated lignin; the dendrimer aminated lignin is dissolved in a third solvent, adding a phosphorus-containing compound, heating and stirring, cooling, filtering, and post-treating to obtain dendrimer-modified nitrogen-phosphorus lignin; (4) The dendrimer-modified nitrogen-phosphorus cellulose and the dendrimer-modified nitrogen-phosphorus lignin are uniformly mixed to obtain a dendrimer-modified nitrogen-phosphorus flame retardant based on bagasse.

2. The dendrimer-modified nitrogen-phosphorus flame retardant according to claim 1, characterized in that: The first solvent described in step (1) is selected from one or more of water, ethanol, ethylene glycol, propanol, 1,2-butanediol and 1,4-butanediol, the alkali is selected from one or more of sodium hydroxide, potassium hydroxide, sodium ethoxide and ammonia water, the mass concentration of the alkali solution is 10% to 20%, and the conditions for the heating reflux reaction are: reaction temperature 80°C to 120°C, heating time 0.5 to 6h.

3. The dendrimer-modified nitrogen-phosphorus flame retardant according to claim 1 or 2, characterized in that: The solid-to-liquid ratio of the bagasse to the first solvent in step (1) is 1:5-10 g / mL, and the volume ratio of the first solvent to the alkaline solution is 0.8-1.2:

1.

4. The dendrimer-modified nitrogen-phosphorus flame retardant according to claim 1, characterized in that: The mass concentration of the phosphoric acid solution in step (2) is 30% to 85%, the organic solvent is selected from one of ethanol, tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide and acetonitrile, the catalyst is selected from one of pyridine, N,N-dimethylaminopyridine, 4-pyrrolidinopyridine, 4-dimethylaminopyridine and imidazole, the solid-liquid ratio of cellulose to phosphoric acid solution is 1:1 to 4 g / mL, the volume ratio of phosphoric acid solution to organic solvent is 1:1 to 4, the amount of catalyst is 2% to 8% of the mass of cellulose, and the reaction conditions for synthesizing phosphorylated cellulose are: reaction temperature 50°C to 100°C, heating time 2 to 10 hours.

5. The dendrimer-modified nitrogen-phosphorus flame retardant according to claim 1 or 4, characterized in that: The second solvent described in step (2) is selected from one or more of water, ethanol and N,N-dimethylformamide, the first dendrimer is selected from one of PAMAM G2-NH2 triethanolamine core, PAMAM G2-NH2 ethylenediamine core, PPI G2-NH2 and PLL G2-NH2, the solid-liquid ratio of phosphorylated cellulose to the second solvent is 0.075-0.150:1 g / mL, the mass ratio of phosphorylated cellulose to the first dendrimer is 5-7:1, and the conditions for synthesizing dendrimer-modified nitrogen phosphocellulose are: reaction temperature 60°C-100°C, heating time 5-12h.

6. The dendrimer-modified nitrogen-phosphorus flame retardant according to claim 1, characterized in that: The mass concentration of the alkaline solution in step (3) is 8% to 12%, the second dendrimer is selected from one of PAMAM G2-NH2 triethanolamine core, PAMAMG2-NH2 ethylenediamine core, PPI G2-NH2 and PLL G2-NH2, the mass concentration of the formaldehyde solution is 35% to 40%, the solid-liquid ratio of lignin to the alkaline solution is 1:8 to 12 g / mL, the mass ratio of lignin to the second dendrimer is 5 to 7:1, the mass ratio of lignin to the formaldehyde solution is 4 to 5:1, and the conditions for synthesizing dendrimer aminated lignin are: reaction temperature 60°C to 80°C, heating time 3 to 6 hours.

7. The dendrimer-modified nitrogen-phosphorus flame retardant according to claim 1 or 6, characterized in that: The third solvent in step (3) is selected from one or more of water, ethanol and N,N-dimethylformamide, the phosphorus-containing compound is selected from one of DOPO, DDP, dimethyl methylphosphonate and tributyl phosphate, the solid-liquid ratio of the dendrimer aminated lignin to the third solvent is 0.075-0.150:1 g / mL, the mass ratio of the dendrimer aminated lignin to the phosphorus-containing compound is 0.7-0.8:1, and the conditions for synthesizing the dendrimer modified nitrogen-phosphorus lignin are: reaction temperature 80°C-120°C, heating time 5-8h.

8. The dendrimer-modified nitrogen-phosphorus flame retardant according to claim 1 or 2, characterized in that: The mass ratio of the dendrimer-modified nitrogen-phosphorus cellulose to the dendrimer-modified nitrogen-phosphorus lignin in step (4) is 1:9 to 4:

1.

9. Use of the dendrimer-modified nitrogen-phosphorus flame retardant according to any one of claims 1 to 8 in the preparation of plastic products.

10. The use according to claim 9, characterized in that: The base material of the plastic product is PLA.

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