Preparation method of iron-silicon modified biochar flame retardant and preparation method of modified phenolic foam of iron-silicon modified biochar flame retardant

Abstract

The invention discloses a preparation method of an iron-silicon modified biochar flame retardant and a preparation method of modified phenolic foam of the iron-silicon modified biochar flame retardant, and belongs to the technical field of thermal protection. According to the scheme, the method comprises the following steps: hydrolyzing straw powder, washing and drying to obtain biochar; uniformly mixing biochar and a ferrous sulfate solution, filtering and drying to obtain iron modified biochar; and blending the iron-modified biochar, organic silicon and a halogen-free flame retardant to obtain the iron-silicon modified biochar flame retardant. Adding a basic catalyst into the molten phenol, uniformly stirring, adding paraformaldehyde in batches at a constant speed, and carrying out stepped reaction to obtain resole; reducing the temperature to 60-70 DEG C, dropwise adding a boric acid solution into the A-stage phenolic resin, carrying out constant-temperature reaction, and carrying out rotary evaporation to control the solid content of the resin to be 60-70%, so as to obtain boron modified phenolic resin; and blending the boron modified phenolic resin, the iron-silicon modified biochar flame retardant and a foaming aid, and performing foaming treatment to obtain the silicon modified biochar flame-retardant phenolic foam.

Description

Technical Field

[0001] The invention belongs to the technical field of thermal protection, and specifically relates to a method for preparing an iron-silicon modified biochar flame retardant and a method for preparing a modified phenolic foam thereof. Background Art

[0002] Traditional thermal insulation material polystyrene (PS) foam is widely used in the field of thermal insulation due to its low price, excellent thermal insulation performance, low water absorption, good impact resistance and other advantages, but the material itself has poor flame retardancy. Polyurethane (PU) foam has excellent thermal insulation performance and low water absorption, but it is expensive and has poor flame retardancy. It will produce a lot of harmful gases when burned, so the application of traditional thermal insulation materials is limited. With the rapid development of the construction industry, petrochemical industry, shipbuilding and other industries, light, fireproof and low-toxic materials are gradually favored by people. Among the commonly used thermal insulation foam materials, phenolic foam has advantages that other foam materials cannot match and is widely used. However, phenolic foam has problems such as poor toughness, high crushing rate and "smoldering". Summary of the invention

[0003] The present invention provides a method for preparing an iron-silicon modified biochar synergistic flame retardant and a method for preparing a modified phenolic foam thereof, using environmentally friendly biomass raw materials to prepare biochar, combining organic silicon with a halogen-free flame retardant, and preparing a green biomass flame retardant, which can improve the dispersibility of the flame retardant in the phenolic foam, improve the flame retardant performance of the phenolic foam, improve the problem of harmful gases being easily generated during the flame retardant process of the halogen-free flame retardant, and at the same time improve the toughness of the foam and reduce the crushing rate. The present invention can promote the further application of biomass materials in flame retardancy and open up a new way for flame retardancy of phenolic foam.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A method for preparing an iron-silicon modified biochar flame retardant comprises the following steps:

[0006] Step 1: hydrolyzing the straw powder, washing and drying it to obtain biochar;

[0007] Step 2: mixing the biochar and the ferrous sulfate solution, shaking, filtering and drying to obtain the iron-modified biochar;

[0008] Step three: blend the iron-modified biochar, organosilicon and halogen-free flame retardant to obtain an iron-silicon modified biochar flame retardant.

[0009] The mass ratio of the iron-modified biochar, the organosilicon and the halogen-free flame retardant is (1-5): (10-20): (1-10).

[0010] The straw powder is a combination of one or more of corn straw powder, wheat straw powder, furfural residue, peanut shell powder and rice straw powder.

[0011] The organosilicon is one or more of methylvinyl silicone oil, methylphenyl silicone oil, cyanide silicone oil, octamethylcyclotetrasiloxane, and dihydroxy-polydimethyldiphenylsiloxane; the halogen-free flame retardant includes one or more of triethyl phosphate, bisphenol A diphosphate, diethyl aluminum phosphinate, triphenyl phosphate, triphenol phosphate, and bisphenol A-bis(diphenyl phosphate).

[0012] A method for preparing an iron-silicon modified biochar flame retardant modified phenolic foam prepared by the preparation method comprises the following steps:

[0013] Step 1, synthesizing resol phenolic resin: adding an alkaline catalyst to melted phenol, stirring evenly, then adding paraformaldehyde in batches at a uniform speed, reacting at a temperature of 60-70° C. for 1-3 hours, then heating to 70-80° C. for 2-3 hours to obtain resol phenolic resin;

[0014] Step 2, synthesizing boron-modified phenolic resin: cooling the temperature to 60-70° C., dropping boric acid solution into the resol phenolic resin, performing constant temperature reaction for 4-8 hours by dropping with a dropping funnel, and controlling the solid content of the resin to 60%-70% by rotary evaporation to obtain a boron-modified phenolic resin;

[0015] Step 3: blend the boron-modified phenolic resin, the iron-silicon-modified biochar flame retardant and the foaming aid, stir at 500-1000 r / min for 1-3 min at room temperature, pour into a preheated foaming mold, and foam at 60-80°C for 10-120 min to obtain a silicon-modified biochar flame-retardant phenolic foam.

[0016] Furthermore, the molar ratio of the aldehyde group in the paraformaldehyde to the phenol group in the phenol is 1:1.5 to 1:2.0.

[0017] Furthermore, the alkaline catalyst includes one or more of potassium hydroxide, sodium hydroxide, and barium hydroxide.

[0018] Furthermore, the boric acid accounts for 3-10% of the mass of the resol phenolic resin; the solvent of the boric acid solution is one or more of methanol, ethanol, and isopropanol; and the boric acid accounts for 3-10% of the mass of the solvent.

[0019] Furthermore, the foaming aid includes a foaming agent, a curing agent and a surfactant; the mass ratio of the boron-modified phenolic resin, the iron-silicon modified biochar flame retardant, the foaming agent, the curing agent and the surfactant is 100:6-10:5-20:8-20:1-8.

[0020] The surfactant includes one or more of Tween-60, Tween-80, polysiloxane or polysiloxane surfactants; the foaming agent includes one or more of petroleum ether, n-pentane, n-hexane, isopentane, cyclopentane, n-butane, and dichloromethane; the curing agent is phosphoric acid, p-toluenesulfonic acid, hydroquinone and water in a ratio of (30-20):

[0021] A mixed acid of (100~90):(20~5):(20~30).

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The silicon element in the iron-silicon modified biochar and the boron element in the boron modified phenolic resin form a glassy covering layer at high temperature. The carbon layer generated by the synergistic biochar can effectively reduce the release of various polluting gases in the phenolic foam and improve the high temperature resistance and flame retardancy of the foam.

[0024] 2. The present invention uses renewable resource straw powder as raw material, and improves the high temperature resistance and flame retardancy of biochar by introducing silicon and phosphorus elements. The synergistic halogen-free flame retardant can obtain excellent flame retardant effect. Surface modification of biochar and ferrous sulfate solution can increase the specific surface area of ​​biochar, thereby improving the biochar's adsorption capacity for pollutant gases.

[0025] 3. The use of biomass raw materials to prepare biochar reduces material costs compared to adsorption materials such as carbon nanotubes and activated carbon, providing a high value-added utilization approach for biomass raw materials.

[0026] 4. The iron-silicon modified biochar synergistic flame retardant improves the flame retardancy of the foam, and the slag drop rate is reduced, which reduces the release of phosphorus-containing pollutants after adding halogen-free flame retardants and the release of pollutant gases from the foam itself; reduces production costs and makes full use of environmental resources. It can be applied to chemical companies and construction industries. Under the premise that the country has strict requirements on the flame retardancy of thermal insulation materials, phenolic foam with excellent self-flame retardant properties has broad market prospects. DETAILED DESCRIPTION

[0027] The technical solutions in the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] The raw materials of the present invention are all commercially available, and unless otherwise specified in the following examples, all are by weight.

[0029] Straw powder is a renewable resource. Biochar can be obtained by hydrothermal and pyrolysis. Biochar is porous and has good adsorption capacity. Compared with traditional adsorption materials such as activated carbon, zeolite biosieve and metal-organic framework, its cost is low and its availability is high. Therefore, biochar can be used as a renewable adsorption material with excellent price.

[0030] The preparation of biochar mainly includes hydrothermal method and pyrolysis method. Compared with pyrolysis method, the hydrothermal method has a higher aromatic structure retention rate. With the increase of heat treatment temperature, the content of polar groups in biochar decreases and the hydrophobicity increases. Compared with pyrolysis biochar, the H / C ratio is high and the aromatic structure retention rate is higher. The π~πEDA interaction occurs between the electron-deficient benzene ring in the halogen-free flame retardant and the aromatic layer of the biochar, which increases the binding rate of biochar and halogen-free flame retardant, improves the dispersibility of the flame retardant in the system, and achieves a better flame retardant effect.

[0031] The introduction of silicone into the system can make the viscosity of the foaming resin and the generation of bubbles more reasonable, so that the foaming agent can be dispersed in the entire emulsified system, thereby promoting the generation of bubbles. Silicone can act as a nucleating agent for bubbles, reducing the free energy in the nucleation process, thereby promoting the generation of foam pores. This can promote the formation of closed cells during the foaming process and improve the microstructure of the foam.

[0032] The present invention utilizes boric acid to modify phenolic resin, synthesizes phenolic resin with flexible boron-oxygen bonds, and physically blends it with an iron-silicon modified biochar flame retardant to improve the surface tension of the resin; the iron-silicon modified biochar synergistic halogen-free flame retardant is added to the boron-modified phenolic resin for foaming, and at high temperature, organic silicon and boron will form a glass layer, which together with the carbon layer can effectively prevent the release of pollutant gases, and at the same time can reduce the foam pulverization rate and improve the flame retardancy of the foam.

[0033] Example 1

[0034] A method for preparing an iron-silicon modified biochar flame retardant comprises the following steps:

[0035] Step 1: hydrolyze the straw powder in a hydrothermal reactor at 220°C for 7 hours, filter under reduced pressure, wash with ethanol and deionized water, and dry at 80°C for 12 hours to obtain biochar;

[0036] Step 2: Mix 1 g of biochar and 30 ml of ferrous sulfate solution (0.1 mol / L) prepared with deionized water and shake for 6 h, filter under reduced pressure, and dry at 105 °C for 6 h to obtain iron-modified biochar;

[0037] Step 3: Blend the iron-modified biochar, organosilicon and halogen-free flame retardant in a mass ratio of 1:10:1 to obtain an iron-silicon modified biochar flame retardant.

[0038] A method for preparing an iron-silicon modified biochar flame retardant modified phenolic foam prepared by the above method comprises the following steps:

[0039] Step 1, synthesizing resol phenolic resin: add alkaline catalyst to melted phenol, mix and stir evenly, then add polyformaldehyde in batches at a uniform speed, react at 60° C. for 3 h and at 70° C. for 2 h to obtain resol phenolic resin.

[0040] Step 2, synthesis of boron-modified phenolic resin: the temperature was lowered to 60°C, and the prepared boric acid solution (phenolic resin: boric acid: ethanol = 10:1:10) was added dropwise using a dropping funnel, and the reaction was carried out at a constant temperature for 4 hours. The solid content of the resin was controlled at 60% by rotary evaporation to obtain a boron-modified phenolic resin.

[0041] Step 3: Blend 100 parts of boron phenolic resin, 10 parts of iron-silicon modified biochar flame retardant, 8 parts of n-pentane, 15 parts of curing agent and 3 parts of surfactant by mass, and foam and cure at 60°C for 30 minutes to obtain silicon-modified biochar flame retardant phenolic foam. The material properties are shown in Appendix 1.

[0042] Example 2

[0043] A method for preparing an iron-silicon modified biochar flame retardant comprises the following steps:

[0044] Step 1: hydrolyze the straw powder in a hydrothermal reactor at 220°C for 7 hours, filter under reduced pressure, wash with ethanol and deionized water, and dry at 80°C for 12 hours to obtain biochar;

[0045] Step 2: Mix 1 g of biochar and 30 ml of ferrous sulfate solution (0.1 mol / L) prepared with deionized water and shake for 6 h, filter under reduced pressure, and dry at 105 °C for 6 h to obtain iron-modified biochar;

[0046] Step three, blending the iron-modified biochar, organosilicon and halogen-free flame retardant in a mass ratio of 1:10:2 to obtain an iron-silicon modified biochar flame retardant.

[0047] A method for preparing an iron-silicon modified biochar flame retardant modified phenolic foam prepared by the above method comprises the following steps:

[0048] Step 1, synthesizing resol phenolic resin: adding an alkaline catalyst to melted phenol, blending and stirring evenly, then adding paraformaldehyde in batches at a uniform speed, reacting at a temperature of 60° C. for 3 h and at 70° C. for 2 h to obtain resol phenolic resin;

[0049] Step 2, synthesis of boron-modified phenolic resin: the temperature was lowered to 60°C, and the prepared boric acid solution (phenolic resin: boric acid: ethanol = 10:1:10) was added dropwise using a dropping funnel, and the reaction was carried out at a constant temperature for 4 hours. The solid content of the resin was controlled at 60% by rotary evaporation to obtain a boron-modified phenolic resin.

[0050] Step 3: Blend 100 parts of boron phenolic resin, 10 parts of iron-silicon modified biochar flame retardant, 8 parts of n-pentane, 15 parts of curing agent and 3 parts of surfactant by mass, and foam and cure at 60°C for 30 minutes to obtain silicon-modified biochar flame retardant phenolic foam. The material properties are shown in Appendix 1.

[0051] Example 3

[0052] A method for preparing an iron-silicon modified biochar flame retardant comprises the following steps:

[0053] Step 1: hydrolyze the straw powder in a hydrothermal reactor at 220°C for 7 hours, filter under reduced pressure, wash with ethanol and deionized water, and dry at 80°C for 12 hours to obtain biochar;

[0054] Step 2: Mix 1 g of biochar and 30 ml of ferrous sulfate solution (0.1 mol / L) prepared with deionized water and shake for 6 h, filter under reduced pressure, and dry at 105 °C for 6 h to obtain iron-modified biochar;

[0055] Step three, blending the iron-modified biochar, organosilicon and halogen-free flame retardant in a mass ratio of 1:10:3 to obtain an iron-silicon modified biochar flame retardant.

[0056] A method for preparing an iron-silicon modified biochar flame retardant modified phenolic foam prepared by the above method comprises the following steps:

[0057] Step 1, synthesizing resol phenolic resin: adding an alkaline catalyst to melted phenol, blending and stirring evenly, then adding paraformaldehyde in batches at a uniform speed, reacting at a temperature of 60° C. for 3 h and at 70° C. for 2 h to obtain resol phenolic resin;

[0058] Step 2, synthesis of boron-modified phenolic resin: the temperature was lowered to 60°C, and the prepared boric acid solution (phenolic resin: boric acid: ethanol = 10:1:10) was added dropwise using a dropping funnel, and the reaction was carried out at a constant temperature for 4 hours. The solid content of the resin was controlled at 60% by rotary evaporation to obtain a boron-modified phenolic resin.

[0059] Step 3: Blend 100 parts of boron phenolic resin, 10 parts of iron-silicon modified biochar flame retardant, 8 parts of n-pentane, 15 parts of curing agent and 3 parts of surfactant by mass, and foam and cure at 60°C for 30 minutes to obtain silicon-modified biochar flame retardant phenolic foam. The material properties are shown in Appendix 1.

[0060] Example 4

[0061] A method for preparing an iron-silicon modified biochar flame retardant comprises the following steps:

[0062] Step 1: hydrolyze the straw powder in a hydrothermal reactor at 220°C for 7 hours, filter under reduced pressure, wash with ethanol and deionized water, and dry at 80°C for 12 hours to obtain biochar;

[0063] Step 2: Mix 1 g of biochar and 30 ml of ferrous sulfate solution (0.1 mol / L) prepared with deionized water and shake for 6 h, filter under reduced pressure, and dry at 105 °C for 6 h to obtain iron-modified biochar;

[0064] Step three, blending the iron-modified biochar, organosilicon and halogen-free flame retardant in a mass ratio of 1:10:4 to obtain an iron-silicon modified biochar flame retardant.

[0065] A method for preparing an iron-silicon modified biochar flame retardant modified phenolic foam prepared by the above method comprises the following steps:

[0066] Step 1, synthesizing resol phenolic resin: adding an alkaline catalyst to melted phenol, blending and stirring evenly, then adding paraformaldehyde in batches at a uniform speed, reacting at a temperature of 60° C. for 3 h and at 70° C. for 2 h to obtain resol phenolic resin;

[0067] Step 2, synthesizing boron-modified phenolic resin: cooling the temperature to 60°C, adding the prepared boric acid solution (phenolic resin: boric acid: ethanol = 10:1:10) dropwise using a dropping funnel, reacting at a constant temperature for 4 hours, and controlling the solid content of the resin at 60% by rotary evaporation to obtain a boron-modified phenolic resin;

[0068] Step 3: Blend 100 parts of boron phenolic resin, 10 parts of iron-silicon modified biochar flame retardant, 8 parts of n-pentane, 15 parts of curing agent and 3 parts of surfactant by mass, and foam and cure at 60°C for 30 minutes to obtain silicon-modified biochar flame retardant phenolic foam. The material properties are shown in Appendix 1.

[0069] Example 5

[0070] A method for preparing an iron-silicon modified biochar flame retardant comprises the following steps:

[0071] Step 1: hydrolyze the straw powder in a hydrothermal reactor at 220°C for 7 hours, filter under reduced pressure, wash with ethanol and deionized water, and dry at 80°C for 12 hours to obtain biochar;

[0072] Step 2: Mix 1 g of biochar and 30 ml of ferrous sulfate solution (0.1 mol / L) prepared with deionized water and shake for 6 h, filter under reduced pressure, and dry at 105 °C for 6 h to obtain iron-modified biochar;

[0073] Step three, blending the iron-modified biochar, organosilicon and halogen-free flame retardant in a mass ratio of 1:10:5 to obtain an iron-silicon modified biochar flame retardant.

[0074] A method for preparing an iron-silicon modified biochar flame retardant modified phenolic foam prepared by the above method comprises the following steps:

[0075] Step 1, synthesizing resol phenolic resin: adding an alkaline catalyst to melted phenol, blending and stirring evenly, then adding paraformaldehyde in batches at a uniform speed, reacting at a temperature of 60° C. for 3 h and at 70° C. for 2 h to obtain resol phenolic resin;

[0076] Step 2, synthesizing boron-modified phenolic resin: cooling the temperature to 60°C, adding the prepared boric acid solution (phenolic resin: boric acid: ethanol = 10:1:10) dropwise using a dropping funnel, reacting at a constant temperature for 4 hours, and controlling the solid content of the resin at 60% by rotary evaporation to obtain a boron-modified phenolic resin;

[0077] Step 3: Blend 100 parts of boron phenolic resin, 10 parts of iron-silicon modified biochar flame retardant, 8 parts of n-pentane, 15 parts of curing agent and 3 parts of surfactant by mass, and foam and cure at 60°C for 30 minutes to obtain silicon-modified biochar flame retardant phenolic foam. The material properties are shown in Appendix 1.

[0078] Example 6

[0079] A method for preparing an iron-silicon modified biochar flame retardant comprises the following steps:

[0080] Step 1: hydrolyze the straw powder in a hydrothermal reactor at 220°C for 7 hours, filter under reduced pressure, wash with ethanol and deionized water, and dry at 80°C for 12 hours to obtain biochar;

[0081] Step 2: Mix 1 g of biochar and 30 ml of ferrous sulfate solution (0.1 mol / L) prepared with deionized water and shake for 6 h, filter under reduced pressure, and dry at 105 °C for 6 h to obtain iron-modified biochar;

[0082] Step 3: Blend the iron-modified biochar, organosilicon and halogen-free flame retardant in a mass ratio of 1:10:6 to obtain an iron-silicon modified biochar flame retardant.

[0083] A method for preparing an iron-silicon modified biochar flame retardant modified phenolic foam prepared by the above method comprises the following steps:

[0084] Step 1, synthesizing resol phenolic resin: adding an alkaline catalyst to melted phenol, blending and stirring evenly, then adding paraformaldehyde in batches at a uniform speed, reacting at a temperature of 60° C. for 3 h and at 70° C. for 2 h to obtain resol phenolic resin;

[0085] Step 2, synthesis of boron-modified phenolic resin: the temperature was lowered to 60°C, and the prepared boric acid solution (phenolic resin: boric acid: ethanol = 10:1:10) was added dropwise using a dropping funnel, and the reaction was carried out at a constant temperature for 4 hours. The solid content of the resin was controlled at 60% by rotary evaporation to obtain a boron-modified phenolic resin.

[0086] Step 3: Blend 100 parts of boron phenolic resin, 10 parts of iron-silicon modified biochar flame retardant, 8 parts of n-pentane, 15 parts of curing agent and 3 parts of surfactant by mass, and foam and cure at 60°C for 30 minutes to obtain silicon-modified biochar flame retardant phenolic foam. The material properties are shown in Appendix 1.

[0087] Comparative Example 1

[0088] According to mass parts, 100 parts of phenolic resin, 8 parts of n-pentane, 15 parts of curing agent and 3 parts of surfactant were stirred at a rate of 1000 r / min for 3 minutes and then poured into a preheated foaming mold. The mold was foamed in an oven at 60°C for 60 minutes to obtain phenolic foam. The material properties are shown in Appendix 1.

[0089] Comparative Example 2

[0090] According to mass percentage, 100 parts of boron-modified phenolic resin, 8 parts of n-pentane, 15 parts of curing agent and 3 parts of surfactant were stirred at a rate of 1000 r / min for 3 minutes and then poured into a preheated foaming mold. The mold was foamed in an oven at 60°C for 60 minutes to obtain boron phenolic foam. The material properties are shown in Appendix 1.

[0091] Comparative Example 3

[0092] According to mass percentage, 100 parts of boron-modified phenolic resin, 8 parts of n-pentane, 15 parts of curing agent, 3 parts of surfactant and 10 parts of silicone were stirred at a rate of 1000 r / min for 3 minutes and then poured into a preheated foaming mold. The mold was foamed in an oven at 60°C for 60 minutes to obtain silicon-modified boron phenolic foam. The material properties are shown in Appendix 1.

[0093] Comparative Example 4

[0094] According to mass percentage, 100 parts of boron-modified phenolic resin, 8 parts of n-pentane, 15 parts of curing agent, 3 parts of surfactant, 10 parts of silicone and 4 parts of flame retardant were stirred at a rate of 1000 r / min for 3 minutes and poured into a preheated foaming mold. The mold was foamed in an oven at 60°C for 60 minutes to obtain silicon-modified boron phenolic flame retardant foam. The material properties are shown in Appendix 1.

[0095] As can be seen from Appendix 1, the present invention prepares a silicon-modified biochar flame-retardant phenolic foam material with smaller pores, more uniform pore distribution, reduced slag drop rate, increased limiting oxygen index, improved flame retardancy, and improved smoke suppression.

[0096] Appendix 1 Performance of different formulations of silicon-modified biochar synergistic CR-741 flame-retardant phenolic foam

[0097]

[0098] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for preparing an iron-silicon modified biochar flame retardant, characterized in that: The following steps are involved: Step 1: hydrolyzing the straw powder, washing and drying it to obtain biochar; Step 2: mixing the biochar and the ferrous sulfate solution, shaking, filtering and drying to obtain the iron-modified biochar; Step three: blend the iron-modified biochar, organosilicon and halogen-free flame retardant to obtain an iron-silicon modified biochar flame retardant.

2. The preparation method according to claim 1, characterized in that: The mass ratio of the iron-modified biochar, the organosilicon and the halogen-free flame retardant is (1-5): (10-20): (1-10).

3. The preparation method according to claim 1, characterized in that: The straw powder is a combination of one or more of corn straw powder, wheat straw powder, furfural residue, peanut shell powder and rice straw powder.

4. The preparation method according to claim 1, characterized in that: The organosilicon is one or more of methylvinyl silicone oil, methylphenyl silicone oil, cyanide silicone oil, octamethylcyclotetrasiloxane, and dihydroxy-polydimethyldiphenylsiloxane; the halogen-free flame retardant includes one or more of triethyl phosphate, bisphenol A diphosphate, diethyl aluminum phosphinate, triphenyl phosphate, triphenol phosphate, and bisphenol A-bis(diphenyl phosphate).

5. A method for preparing an iron-silicon modified biochar flame retardant modified phenolic foam prepared by the preparation method according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1, adding an alkaline catalyst to the melted phenol, stirring evenly, then adding paraformaldehyde in batches at a uniform speed to react at a temperature of 60 to 70° C. for 1 to 3 hours, then heating to 70 to 80° C. to react for 2 to 3 hours to obtain a resol phenolic resin; Step 2, cooling the temperature to 60-70° C., adding a boric acid solution dropwise to the resol phenolic resin for constant temperature reaction for 4-8 hours, and controlling the solid content of the resin to 60%-70% by rotary evaporation to obtain a boron-modified phenolic resin; Step 3: blend the boron-modified phenolic resin, the iron-silicon-modified biochar flame retardant and the foaming aid, and perform foaming treatment to obtain the silicon-modified biochar flame-retardant phenolic foam.

6. The preparation method according to claim 5, characterized in that: The molar ratio of the aldehyde group in the paraformaldehyde to the phenol group in the phenol is 1:1.5 to 1:2.

0.

7. The preparation method according to claim 5, characterized in that: The alkaline catalyst includes one or more of potassium hydroxide, sodium hydroxide and barium hydroxide.

8. The preparation method according to claim 5, characterized in that: The boric acid accounts for 3-10% of the mass of the resol phenolic resin; the solvent of the boric acid solution is a combination of one or more of methanol, ethanol and isopropanol; the boric acid accounts for 3-10% of the mass of the solvent.

9. The preparation method according to claim 5, characterized in that: The foaming aid comprises a foaming agent, a curing agent and a surfactant; the mass ratio of the boron-modified phenolic resin, the iron-silicon-modified biochar flame retardant, the foaming agent, the curing agent and the surfactant is 100:6-10:5-20:8-20:1-8.

10. The preparation method according to claim 5, characterized in that: The temperature of the foaming treatment is 60-80° C., and the time is 10-120 min.

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