A halogen-free flame retardant based on coffee grounds and preparation method thereof

Abstract

The present invention relates to the technical field of halogen-free flame retardants, and in particular to a halogen-free flame retardant based on coffee grounds and a preparation method thereof. The method comprises the following steps: firstly washing the coffee grounds with water and alkali to remove impurities in the coffee grounds and to form more active groups on the surface of the coffee grounds, then grafting polyethyleneimine to the surface of the coffee grounds through a silane coupling agent, and finally combining the aluminum dihydrogen phosphate on the surface of the coffee grounds by utilizing the electrostatic attraction between polyethyleneimine and aluminum dihydrogen phosphate. The flame retardant prepared by the present invention can realize the resource utilization of coffee grounds waste, will not cause harm to the environment and human body, and is green and environmentally friendly.

Description

Technical Field

[0001] The invention relates to the technical field of halogen-free flame retardants, and in particular to a halogen-free flame retardant based on coffee grounds and a preparation method thereof. Background Art

[0002] With the rapid development of modern industry and life, various materials are widely used in the fields of construction, electronics, transportation, textiles, etc. However, most of these materials are flammable. Once a fire occurs, the fire will spread rapidly, causing huge loss of life and property and environmental pollution. According to statistics, the economic losses caused by fires around the world are as high as billions of dollars each year. The occurrence of numerous fire accidents highlights the key role of flame retardants in preventing fires and reducing fire hazards. Flame retardants can effectively inhibit or delay the combustion process of materials, buy precious time for personnel evacuation and fire rescue, and are indispensable additives for ensuring public safety and safe use of materials.

[0003] Halogen flame retardants (such as bromine and chlorine) have long dominated the flame retardant market due to their efficient flame retardant properties. During their combustion, halogen atoms can capture free radicals in the combustion reaction, thereby interrupting the chain reaction of combustion and achieving a flame retardant effect. However, halogen flame retardants pose serious environmental and health risks. When a fire occurs, the combustion of halogen flame retardants will release a large amount of toxic and harmful gases, such as dioxins, hydrogen bromide, and hydrogen chloride. Dioxin is a strong carcinogen that causes irreversible damage to the human immune system, endocrine system, and reproductive system; while acidic gases such as hydrogen bromide and hydrogen chloride are corrosive and can irritate the human respiratory tract, eyes, etc., and can also corrode firefighting equipment and buildings, exacerbating losses after a fire. In addition, halogen flame retardants are difficult to degrade and will continue to accumulate in the environment, causing damage to the ecological balance.

[0004] Coffee, as a popular drink in the world, produces a large amount of coffee grounds every year. According to statistics, the global production of coffee grounds is as high as millions of tons per year. At present, most coffee grounds are disposed of by landfill or incineration, which not only occupies a large amount of land resources, but also causes environmental pollution and waste of resources. However, coffee grounds are rich in organic components such as cellulose, hemicellulose, and lignin, which give coffee grounds potential application value.

[0005] In recent years, researchers have begun to explore the resource utilization of coffee grounds in many fields, such as the preparation of biofuels, adsorbents, soil conditioners, etc. However, in the field of flame retardants, the application research of coffee grounds is relatively small and has not yet been fully developed and utilized. Summary of the invention

[0006] In order to overcome the above problems of the prior art, the present invention provides a halogen-free flame retardant based on coffee grounds and a preparation method thereof. The flame retardant prepared by the present invention can realize the resource utilization of coffee grounds waste, does not cause harm to the environment and human body, and is green and environmentally friendly.

[0007] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions: A method for preparing a halogen-free flame retardant based on coffee grounds comprises the following steps: 1) Rinse the coffee grounds with deionized water to remove surface impurities and soluble substances, dry them to constant weight, and then grind them through a 100-200 mesh sieve to obtain pretreated coffee grounds; 2) soaking the coffee grounds in an alkali solution for alkali treatment, then washing with deionized water until neutral, and then drying to a constant weight to obtain alkali-treated coffee grounds; 3) adding the epoxy silane coupling agent to a mixed solution of ethanol and water, stirring and hydrolyzing to obtain a hydrolyzate, adding the alkali-treated coffee grounds to the hydrolyzate, heating and stirring to react, and obtaining the coupling agent-modified coffee grounds; 4) adding polyethyleneimine into deionized water and stirring to dissolve to obtain polyethyleneimine solution, adding coupling agent-modified coffee grounds into the polyethyleneimine solution, heating and stirring to react to obtain polyethyleneimine-modified coffee grounds; 5) adding polyethyleneimine modified coffee grounds into deionized water, dispersing them evenly by ultrasonic oscillation, then adding glutaraldehyde, adding sodium hydroxide solution to adjust the pH value of the solution to 8-9, heating and stirring to react, and obtaining surface cross-linked modified coffee grounds; 6) Add aluminum dihydrogen phosphate into deionized water, stir and dissolve to obtain an aluminum dihydrogen phosphate solution, soak the surface cross-linked modified coffee grounds in the aluminum dihydrogen phosphate solution, stir and disperse them evenly, let them stand, filter and separate, wash and dry to obtain a halogen-free flame retardant.

[0008] The present invention uses coffee grounds as a flame retardant. Coffee grounds contain a large amount of carbon elements. Under conditions such as high temperature, coffee grounds will undergo a pyrolysis and carbonization reaction to form a carbon layer with a certain flame retardant effect. This layer of carbon can isolate oxygen and heat, prevent the further spread of combustion, and thus play a flame retardant role. In addition, mineral elements such as potassium, calcium, and magnesium exist in coffee grounds. These elements can promote the carbonization of coffee grounds during the combustion process, improve the stability and density of the carbon layer, and enhance the flame retardant effect. At the same time, they may also participate in some chemical reactions during combustion, reduce the concentration of free radicals in the combustion system, and thus slow down the combustion rate.

[0009] However, the technical problem faced by using coffee grounds as flame retardants is that coffee grounds will decompose more rapidly and the carbon layer structure will be destroyed in a high temperature environment, resulting in a decrease in the flame retardant performance of coffee grounds, limiting its application in a high temperature environment. In order to solve this technical problem, the present invention modifies the coffee grounds, first rinses the coffee grounds with deionized water, effectively removes surface impurities and soluble substances, and prevents these impurities from interfering with the formation of the carbon layer in subsequent reactions, thereby providing a cleaner basic raw material for subsequent processing, helping to improve the purity of the final prepared flame retardant, and then optimizing its flame retardant performance. Alkali solution immersion can produce more active groups on the surface of coffee grounds, which is beneficial to the subsequent grafting reaction.

[0010] Then, a silane coupling agent is used to graft an epoxy silane coupling agent onto the surface of the coffee grounds. This step is the basis of the entire modification process. The silane coupling agent molecule has a special structure. One end can chemically react with groups such as hydroxyl groups on the surface of the coffee grounds, and the other end introduces an epoxy functional group. In this way, the epoxy functional group is successfully loaded onto the surface of the coffee grounds. This process changes the surface chemical properties of the coffee grounds, giving them active sites for further reactions, laying the foundation for the subsequent grafting of polyethyleneimine, while also enhancing the binding force between the coffee grounds and the subsequently introduced substances, and improving the stability of the overall structure. The newly introduced epoxy functional groups on the surface of the coffee grounds react with the amino groups on the polyethyleneimine molecules, and polyethyleneimine is grafted onto the surface of the coffee grounds through a ring-opening reaction.

[0011] Polyethyleneimine plays a vital dual role in the entire system: On the one hand, electrostatic binding of dihydrogen phosphate ions: After grafting with polyethyleneimine, the surface of the coffee grounds is positively charged. Based on the principle of electrostatic attraction, the positively charged coffee grounds can tightly bind to the negatively charged dihydrogen phosphate ions. In a high temperature environment, the dihydrogen phosphate ions will undergo a series of chemical changes and eventually form a glassy cross-linked product. This cross-linked product has excellent thermal insulation properties and can form an effective thermal insulation barrier on the surface of the material to prevent heat from transferring to the inside, thereby slowing down the thermal decomposition rate of the material and protecting the carbon layer. On the other hand, to enhance structural stability: glutaraldehyde is used to cross-link polyethyleneimine, and this process constructs a three-dimensional network structure of polyimide. Under the action of this three-dimensional network structure, the structural stability of the coffee grounds carbon layer is greatly improved. The coffee grounds carbon layer, which was originally prone to cracking and structural destruction at high temperatures, can maintain a relatively complete shape under the support and restraint of the three-dimensional network, and is not prone to structural deformation and cracking. This not only improves the thermal stability of the material, but also ensures that the flame retardant can continue to work in a high temperature environment, avoiding the failure of flame retardant properties due to structural damage.

[0012] The present invention develops a halogen-free flame retardant based on coffee grounds. From an environmental protection perspective, it can effectively solve the problem of coffee grounds disposal, reduce environmental pollution, and realize the resource utilization of waste; at the same time, it avoids the environmental and health risks brought by halogen flame retardants, which is in line with the concepts of green chemistry and sustainable development. On the economic level, coffee grounds are widely available and low-cost. Using them as raw materials to prepare flame retardants can reduce production costs and improve product competitiveness. From the perspective of technological innovation, it has opened up a new direction for the research and development of flame retardants, enriched the types of halogen-free flame retardants, and is expected to promote technological progress in the flame retardant industry and meet the needs of different fields for high-performance, environmentally friendly flame retardants.

[0013] Preferably, in step 2), the alkali solution is a sodium hydroxide solution, and the concentration of the sodium hydroxide solution is 2.0-5.0%.

[0014] Preferably, in step 3), the reaction temperature is 40-50° C. and the reaction time is 3-7 h.

[0015] Preferably, in step 4), the mass ratio of the coupling agent-modified coffee grounds to polyethyleneimine is 1:0.2-0.8.

[0016] Preferably, in step 4), the reaction temperature is 80-85° C. and the reaction time is 5-10 h.

[0017] Preferably, in step 5), the amount of glutaraldehyde added is 0.1-0.5 wt % of the polyethyleneimine-modified coffee grounds.

[0018] Preferably, in step 5), the reaction temperature is 30-50° C. and the reaction time is 10-15 h.

[0019] Preferably, in step 6), the mass ratio of the surface cross-linked modified coffee grounds to aluminum dihydrogen phosphate is 1:0.1-0.5.

[0020] Preferably, in step 6), the standing time is 3-6 hours.

[0021] A halogen-free flame retardant based on coffee grounds is prepared by the method.

[0022] The present invention has the following beneficial effects: 1) Realize the resource utilization of coffee grounds waste, which will not cause harm to the environment and human body, and is green and environmentally friendly; 2) By modifying the coffee grounds, the flame retardant formed by the coffee grounds has good thermal stability, thus achieving a good flame retardant effect. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with specific embodiments. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are generally only embodiments of a part of the present invention, rather than all embodiments. Therefore, based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work should fall within the scope of protection of the present invention.

[0024] Unless otherwise specified, the raw materials used in the examples of the present invention are all commercially available or available to those skilled in the art; unless otherwise specified, the methods used in the examples of the present invention are all methods known to those skilled in the art.

[0025] Example 1: A method for preparing a halogen-free flame retardant based on coffee grounds, comprising the following steps: 1) Rinse the coffee grounds with deionized water to remove surface impurities and soluble substances, dry them to constant weight, and then grind them through a 200-mesh sieve to obtain pretreated coffee grounds; 2) Soaking the coffee grounds in a 4.0% sodium hydroxide solution for 2 hours, then washing with deionized water until neutral, and then drying to constant weight to obtain alkali-treated coffee grounds; 3) adding epoxy silane coupling agent KH-560 to a mixed solvent at a mass volume ratio of 1 g / 50 mL, wherein the mixed solvent is a mixture of ethanol and water at a volume ratio of 1:0.5, stirring and hydrolyzing to obtain a hydrolyzate, adding alkali-treated coffee grounds to the hydrolyzate at a mass volume ratio of 1 g / 100 mL, heating and stirring to react, the reaction temperature is 45° C., and the reaction time is 5 h, to obtain coupling agent-modified coffee grounds; 4) adding polyethyleneimine into deionized water and stirring to dissolve to prepare a polyethyleneimine solution with a concentration of 0.5 wt%, adding coupling agent-modified coffee grounds into the polyethyleneimine solution, wherein the mass ratio of coupling agent-modified coffee grounds to polyethyleneimine is 1:0.7, heating and stirring to react, the reaction temperature is 83° C., and the reaction time is 7 h, to obtain polyethyleneimine-modified coffee grounds; 5) adding polyethyleneimine-modified coffee grounds into deionized water at a mass volume ratio of 1 g / 80 mL, dispersing the grounds uniformly by ultrasonic oscillation, and then adding glutaraldehyde in an amount of 0.4 wt % of the polyethyleneimine-modified coffee grounds, adding sodium hydroxide solution to adjust the pH value of the solution to 8.5, heating and stirring the reaction at a reaction temperature of 40° C. for a reaction time of 14 h to obtain surface cross-linked modified coffee grounds; 6) Aluminum dihydrogen phosphate was added into deionized water at a mass volume ratio of 1 g / 60 mL, and the mixture was stirred to dissolve to obtain an aluminum dihydrogen phosphate solution. The surface cross-linked modified coffee grounds were immersed in the aluminum dihydrogen phosphate solution, and the mass ratio of the surface cross-linked modified coffee grounds to aluminum dihydrogen phosphate was 1:0.4. The mixture was stirred to be evenly dispersed, and the mixture was allowed to stand for 5 hours. The mixture was filtered, separated, washed, and dried to obtain a halogen-free flame retardant.

[0026] Example 2: A method for preparing a halogen-free flame retardant based on coffee grounds, comprising the following steps: 1) Rinse the coffee grounds with deionized water to remove surface impurities and soluble substances, dry them to constant weight, and then grind them through a 100-mesh sieve to obtain pretreated coffee grounds; 2) Soaking the coffee grounds in a 3.0% sodium hydroxide solution for 2 hours, then washing with deionized water until neutral, and then drying to constant weight to obtain alkali-treated coffee grounds; 3) adding epoxy silane coupling agent KH-560 to a mixed solvent at a mass volume ratio of 1 g / 50 mL, wherein the mixed solvent is a mixture of ethanol and water at a volume ratio of 1:0.5, stirring and hydrolyzing to obtain a hydrolyzate, adding alkali-treated coffee grounds to the hydrolyzate at a mass volume ratio of 1 g / 100 mL, heating and stirring to react, the reaction temperature is 45° C., and the reaction time is 4 hours to obtain coupling agent-modified coffee grounds; 4) adding polyethyleneimine into deionized water and stirring to dissolve to prepare a polyethyleneimine solution with a concentration of 0.5 wt%, adding coupling agent-modified coffee grounds into the polyethyleneimine solution, wherein the mass ratio of coupling agent-modified coffee grounds to polyethyleneimine is 1:0.3, heating and stirring to react, the reaction temperature is 83° C., and the reaction time is 6 h, to obtain polyethyleneimine-modified coffee grounds; 5) adding polyethyleneimine-modified coffee grounds into deionized water at a mass volume ratio of 1 g / 80 mL, dispersing the grounds uniformly by ultrasonic oscillation, and then adding glutaraldehyde in an amount of 0.2 wt % of the polyethyleneimine-modified coffee grounds, adding sodium hydroxide solution to adjust the pH value of the solution to 8.5, heating and stirring the reaction at a reaction temperature of 40° C. for a reaction time of 11 h to obtain surface cross-linked modified coffee grounds; 6) Aluminum dihydrogen phosphate was added into deionized water at a mass volume ratio of 1 g / 60 mL, and the mixture was stirred to dissolve to obtain an aluminum dihydrogen phosphate solution. The surface cross-linked modified coffee grounds were immersed in the aluminum dihydrogen phosphate solution, and the mass ratio of the surface cross-linked modified coffee grounds to aluminum dihydrogen phosphate was 1:0.2. The mixture was stirred to be evenly dispersed, and the mixture was allowed to stand for 4 hours. After filtering, separation, washing and drying, a halogen-free flame retardant was obtained.

[0027] Example 3: A method for preparing a halogen-free flame retardant based on coffee grounds, comprising the following steps: 1) Rinse the coffee grounds with deionized water to remove surface impurities and soluble substances, dry them to constant weight, and then grind them through a 200-mesh sieve to obtain pretreated coffee grounds; 2) Soaking the coffee grounds in a 3.0% sodium hydroxide solution for 2 hours, then washing with deionized water until neutral, and then drying to constant weight to obtain alkali-treated coffee grounds; 3) adding epoxy silane coupling agent KH-560 to a mixed solvent at a mass volume ratio of 1 g / 50 mL, wherein the mixed solvent is a mixture of ethanol and water at a volume ratio of 1:0.5, stirring and hydrolyzing to obtain a hydrolyzate, adding alkali-treated coffee grounds to the hydrolyzate at a mass volume ratio of 1 g / 100 mL, heating and stirring to react, the reaction temperature is 45° C., and the reaction time is 5 h, to obtain coupling agent-modified coffee grounds; 4) adding polyethyleneimine into deionized water, stirring and dissolving to prepare a polyethyleneimine solution with a concentration of 0.5 wt%, adding coupling agent-modified coffee grounds into the polyethyleneimine solution, wherein the mass ratio of coupling agent-modified coffee grounds to polyethyleneimine is 1:0.5, heating and stirring to react, the reaction temperature is 83° C., and the reaction time is 7 h, to obtain polyethyleneimine-modified coffee grounds; 5) adding polyethyleneimine-modified coffee grounds into deionized water at a mass volume ratio of 1 g / 80 mL, dispersing the grounds uniformly by ultrasonic oscillation, and then adding glutaraldehyde in an amount of 0.3 wt % of the polyethyleneimine-modified coffee grounds, adding sodium hydroxide solution to adjust the pH value of the solution to 8.5, heating and stirring the reaction at a reaction temperature of 40° C. for a reaction time of 12 h to obtain surface cross-linked modified coffee grounds; 6) Aluminum dihydrogen phosphate was added into deionized water at a mass volume ratio of 1 g / 60 mL, and the mixture was stirred to dissolve to obtain an aluminum dihydrogen phosphate solution. The surface cross-linked modified coffee grounds were immersed in the aluminum dihydrogen phosphate solution, and the mass ratio of the surface cross-linked modified coffee grounds to aluminum dihydrogen phosphate was 1:0.3. The mixture was stirred to be evenly dispersed, and the mixture was allowed to stand for 4.5 hours. After filtration separation, washing and drying, a halogen-free flame retardant was obtained.

[0028] Example 4: A method for preparing a halogen-free flame retardant based on coffee grounds, comprising the following steps: 1) Rinse the coffee grounds with deionized water to remove surface impurities and soluble substances, dry them to constant weight, and then grind them through a 200-mesh sieve to obtain pretreated coffee grounds; 2) Soaking the coffee grounds in a 5.0% sodium hydroxide solution for 2 hours, then washing with deionized water until neutral, and then drying to constant weight to obtain alkali-treated coffee grounds; 3) adding epoxy silane coupling agent KH-560 to a mixed solvent at a mass volume ratio of 1 g / 50 mL, wherein the mixed solvent is a mixture of ethanol and water at a volume ratio of 1:0.5, stirring and hydrolyzing to obtain a hydrolyzate, adding alkali-treated coffee grounds to the hydrolyzate at a mass volume ratio of 1 g / 100 mL, heating and stirring to react, the reaction temperature is 50° C., and the reaction time is 7 hours to obtain coupling agent-modified coffee grounds; 4) adding polyethyleneimine into deionized water, stirring and dissolving to prepare a polyethyleneimine solution with a concentration of 0.5 wt%, adding coupling agent-modified coffee grounds into the polyethyleneimine solution, wherein the mass ratio of coupling agent-modified coffee grounds to polyethyleneimine is 1:0.8, heating and stirring to react, the reaction temperature is 85° C., and the reaction time is 10 h, to obtain polyethyleneimine-modified coffee grounds; 5) adding polyethyleneimine-modified coffee grounds into deionized water at a mass volume ratio of 1 g / 80 mL, dispersing the grounds uniformly by ultrasonic oscillation, and then adding glutaraldehyde in an amount of 0.5 wt % of the polyethyleneimine-modified coffee grounds, adding sodium hydroxide solution to adjust the pH value of the solution to 9, heating and stirring the reaction at a reaction temperature of 50° C. for a reaction time of 15 h to obtain surface cross-linked modified coffee grounds; 6) Aluminum dihydrogen phosphate was added into deionized water at a mass volume ratio of 1 g / 60 mL, and the mixture was stirred to dissolve to obtain an aluminum dihydrogen phosphate solution. The surface cross-linked modified coffee grounds were immersed in the aluminum dihydrogen phosphate solution, and the mass ratio of the surface cross-linked modified coffee grounds to aluminum dihydrogen phosphate was 1:0.5. The mixture was stirred to be evenly dispersed, and the mixture was allowed to stand for 6 hours. After filtering, separation, washing and drying, a halogen-free flame retardant was obtained.

[0029] Example 5: A method for preparing a halogen-free flame retardant based on coffee grounds, comprising the following steps: 1) Rinse the coffee grounds with deionized water to remove surface impurities and soluble substances, dry them to constant weight, and then grind them through a 100-mesh sieve to obtain pretreated coffee grounds; 2) Soaking the coffee grounds in a 2.0% sodium hydroxide solution for 2 hours, then washing with deionized water until neutral, and then drying to a constant weight to obtain alkali-treated coffee grounds; 3) adding epoxy silane coupling agent KH-560 to a mixed solvent at a mass volume ratio of 1 g / 50 mL, wherein the mixed solvent is a mixture of ethanol and water at a volume ratio of 1:0.5, stirring and hydrolyzing to obtain a hydrolyzate, adding alkali-treated coffee grounds to the hydrolyzate at a mass volume ratio of 1 g / 100 mL, heating and stirring to react, the reaction temperature is 40° C., and the reaction time is 3 h to obtain coupling agent-modified coffee grounds; 4) adding polyethyleneimine into deionized water, stirring and dissolving to prepare a polyethyleneimine solution with a concentration of 0.5 wt%, adding coupling agent-modified coffee grounds into the polyethyleneimine solution, wherein the mass ratio of coupling agent-modified coffee grounds to polyethyleneimine is 1:0.2, heating and stirring to react, the reaction temperature is 80° C., and the reaction time is 5 h, to obtain polyethyleneimine-modified coffee grounds; 5) adding polyethyleneimine-modified coffee grounds into deionized water at a mass volume ratio of 1 g / 80 mL, dispersing the grounds uniformly by ultrasonic oscillation, and then adding glutaraldehyde in an amount of 0.1 wt % of the polyethyleneimine-modified coffee grounds, adding sodium hydroxide solution to adjust the pH value of the solution to 8, heating and stirring the reaction at a reaction temperature of 30° C. for a reaction time of 10 h to obtain surface cross-linked modified coffee grounds; 6) Aluminum dihydrogen phosphate was added into deionized water at a mass volume ratio of 1 g / 60 mL, and the mixture was stirred to dissolve to obtain an aluminum dihydrogen phosphate solution. The surface cross-linked modified coffee grounds were immersed in the aluminum dihydrogen phosphate solution, and the mass ratio of the surface cross-linked modified coffee grounds to aluminum dihydrogen phosphate was 1:0.1. The mixture was stirred to be evenly dispersed, and the mixture was allowed to stand for 3 hours. The mixture was filtered, separated, washed, and dried to obtain a halogen-free flame retardant.

[0030] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is: Step 4 is omitted, i.e., polyethyleneimine is not grafted onto the surface of the coffee grounds; The remaining steps are the same as those in Example 1.

[0031] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is: Step 5) is omitted, i.e., the polyethyleneimine-modified coffee grounds are not cross-linked using a glutaraldehyde cross-linking agent; The remaining steps are the same as those in Example 1.

[0032] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that: Step 6 is omitted), that is, aluminum dihydrogen phosphate is not used to perform surface treatment on the surface cross-linked modified coffee grounds; The remaining steps are the same as those in Example 1.

[0033] Performance Testing The halogen-free flame retardants prepared in the examples and comparative examples were added to the polypropylene masterbatch, the amount of the halogen-free flame retardant added was 10wt% of the polypropylene masterbatch, and the mixture was stirred and mixed evenly, and then melt blended at 195°C for 10 minutes, and then pressed and molded, and cooled and solidified at room temperature for 5 hours to obtain a polypropylene flame retardant material, and the flame retardant properties and mechanical properties of the polypropylene flame retardant material were tested. Then, the material without adding the flame retardant to the polypropylene was used as a blank sample, and the flame retardant effect and mechanical properties of the blank sample were tested.

[0034] 1. Flame retardant performance test: The flame retardant performance is tested by the limiting oxygen index (LOI). The sample is fixed vertically in the combustion tube, and a mixed flow of oxygen and nitrogen is introduced. The sample at the top of the airflow is ignited, and the oxygen concentration is adjusted until a specific combustion behavior is observed. The higher the LOI value, the better the flame retardant performance of the material. Generally, LOI < 21% is a flammable material, 21% ≤ LOI < 26% is a combustible material, and LOI ≥ 26% is a flame retardant material.

[0035] 2. Mechanical properties test: The mechanical strength of polypropylene materials is tested to test the effect of adding flame retardants on the mechanical properties of polypropylene materials. Use an electronic universal testing machine to clamp the polypropylene sample on the testing machine fixture, stretch it at a constant rate, measure the force and displacement data during the stretching process, and obtain the tensile strength. The tensile strength reflects the ability of the material to resist tensile damage. The higher the tensile strength, the better the mechanical properties of the material.

[0036]

[0037] The above test shows that the flame retardant properties of the flame retardants prepared in Examples 1-5 are significantly better than those of Comparative Examples 1-3 and the blank sample, indicating that the flame retardant prepared in the present invention can achieve a good flame retardant effect. The mechanical strength test of the polypropylene material shows that adding the coffee grounds halogen-free flame retardant to the polypropylene material has little effect on the mechanical properties of the polypropylene material.

[0038] The above are only preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be regarded as limiting the present invention, and the protection scope of the present invention should be based on the scope defined by the claims. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a halogen-free flame retardant based on coffee grounds, characterized in that: The following steps are involved: 1) Rinse the coffee grounds with deionized water to remove surface impurities and soluble substances, dry them to constant weight, and then grind them through a 100-200 mesh sieve to obtain pretreated coffee grounds; 2) soaking the coffee grounds in an alkali solution for alkali treatment, then washing with deionized water until neutral, and then drying to a constant weight to obtain alkali-treated coffee grounds; 3) adding the epoxy silane coupling agent to a mixed solution of ethanol and water, stirring and hydrolyzing to obtain a hydrolyzate, adding the alkali-treated coffee grounds to the hydrolyzate, heating and stirring to react, and obtaining coupling agent-modified coffee grounds; 4) adding polyethyleneimine into deionized water and stirring to dissolve to obtain polyethyleneimine solution, adding coupling agent-modified coffee grounds into the polyethyleneimine solution, heating and stirring to react to obtain polyethyleneimine-modified coffee grounds; 5) adding polyethyleneimine-modified coffee grounds into deionized water, dispersing them evenly by ultrasonic oscillation, then adding glutaraldehyde, adding sodium hydroxide solution to adjust the pH value of the solution to 8-9, heating and stirring to react, and obtaining surface cross-linked modified coffee grounds; 6) Add aluminum dihydrogen phosphate into deionized water, stir and dissolve to obtain an aluminum dihydrogen phosphate solution, soak the surface cross-linked modified coffee grounds in the aluminum dihydrogen phosphate solution, stir and disperse them evenly, let them stand, filter and separate, wash and dry to obtain a halogen-free flame retardant.

2. The method for preparing a halogen-free flame retardant based on coffee grounds according to claim 1, characterized in that: In the step 2), the alkali solution is a sodium hydroxide solution, and the concentration of the sodium hydroxide solution is 2.0-5.0%.

3. The method for preparing a halogen-free flame retardant based on coffee grounds according to claim 1, characterized in that: In the step 3), the reaction temperature is 40-50° C. and the reaction time is 3-7 hours.

4. The method for preparing a halogen-free flame retardant based on coffee grounds according to claim 1, characterized in that: In the step 4), the mass ratio of the coupling agent-modified coffee grounds to the polyethyleneimine is 1:0.2-0.

8.

5. The method for preparing a halogen-free flame retardant based on coffee grounds according to claim 1, characterized in that: In the step 4), the reaction temperature is 80-85° C. and the reaction time is 5-10 h.

6. The method for preparing a halogen-free flame retardant based on coffee grounds according to claim 1, characterized in that: In the step 5), the amount of glutaraldehyde added is 0.1-0.5wt% of the polyethyleneimine-modified coffee grounds.

7. The method for preparing a halogen-free flame retardant based on coffee grounds according to claim 1, characterized in that: In the step 5), the reaction temperature is 30-50° C. and the reaction time is 10-15 h.

8. The method for preparing a halogen-free flame retardant based on coffee grounds according to claim 1, characterized in that: In the step 6), the mass ratio of the surface cross-linked modified coffee grounds to aluminum dihydrogen phosphate is 1:0.1-0.

5.

9. The method for preparing a halogen-free flame retardant based on coffee grounds according to claim 1, characterized in that: In the step 6), the standing time is 3-6 hours.

10. A halogen-free flame retardant based on coffee grounds, characterized in that: The method is prepared by any one of claims 1 to 9.

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