Preparation method of nano material composite flame retardant plastic

Abstract

The invention provides a method for preparing a flame-retardant plastic composited with nanomaterials. The preparation method comprises the following preparation steps: providing graphene oxide, ammonium polyphosphate and a plastic matrix, wherein the plastic matrix contains polar groups; functionalizing the graphene oxide to obtain graphene oxide with active functional groups introduced on the surface; activating the ammonium polyphosphate to obtain ammonium polyphosphate with functional groups on the surface, wherein the functional groups can react with the active functional groups; grafting the functionalized graphene oxide with the activated ammonium polyphosphate to obtain a flame retardant of graphene oxide grafted with ammonium polyphosphate; mixing the flame retardant with a mass percentage of 5-25% and the plastic matrix with a mass percentage of 70-90% to obtain a flame-retardant plastic composited with nanomaterials. The flame retardant is obtained by grafting ammonium polyphosphate onto graphene oxide, and the two produce a synergistic effect, which greatly improves flame retardancy, thermal stability and compatibility with the plastic matrix.

Description

Technical Field

[0001] The invention relates to the technical field of plastic preparation, and in particular to a method for preparing a nano material composite flame retardant plastic. Background Art

[0002] The requirements for flame retardant properties of plastic materials are increasing in key areas such as electronics, construction and transportation. To achieve this goal, the addition of flame retardants has become an effective strategy to improve the fire safety of plastic materials. However, the selection and application of flame retardants face many challenges, including flame retardant efficiency, environmental impact, material performance impact and cost.

[0003] Among traditional flame retardants, brominated flame retardants are known for their high flame retardant efficiency, but their application is greatly limited because they contain halogen elements, which can easily color plastic materials and do not meet current environmental protection requirements. Although phosphorus-based flame retardants can provide a certain flame retardant effect, they often cause a sharp drop in the performance of modified plastics, thus limiting their scope of application.

[0004] In recent years, sulfonate flame retardants have gradually gained favor among researchers due to their high efficiency, low impact on the physical properties of modified materials, and low impact on the light transmittance of polycarbonate. At the same time, although silicon-based flame retardants are expensive, their excellent synergistic flame retardant effect and low impact on material properties make them irreplaceable in some high-end applications, especially liquid silicon-based flame retardants, which can provide effective flame retardant properties while maintaining the transparency of the material.

[0005] However, with the tightening of regulations, the sustainability requirements for flame retardants are also increasing. Therefore, it is urgent to develop new and efficient flame retardants to meet the needs of flame retardant plastics in different fields. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a method for preparing a flame-retardant plastic composited with nanomaterials, comprising the following preparation steps:

[0007] Providing graphene oxide, ammonium polyphosphate and a plastic matrix, wherein the plastic matrix contains a polar group;

[0008] Functionalizing the graphene oxide to obtain graphene oxide with active functional groups introduced on the surface;

[0009] Activating the ammonium polyphosphate to obtain an ammonium polyphosphate having functional groups on the surface, wherein the functional groups are capable of reacting with the active functional groups;

[0010] The functionalized graphene oxide is subjected to a grafting reaction with the activated ammonium polyphosphate to obtain a flame retardant of the graphene oxide grafted with the ammonium polyphosphate;

[0011] The flame retardant with a mass percentage of 5-25% and the plastic matrix with a mass percentage of 70-90% are mixed to obtain the nano material composite flame retardant plastic.

[0012] Optionally, the ammonium polyphosphate is formed by mixing a first ammonium polyphosphate and a second ammonium polyphosphate;

[0013] The molecular weight of the first ammonium polyphosphate is any value in the range of 1000-1500 Daltons, and the molecular weight of the second ammonium polyphosphate is any value in the range of 2000-4000 Daltons.

[0014] Optionally, the step of grafting the functionalized graphene oxide with the activated ammonium polyphosphate to obtain a flame retardant of graphene oxide grafted with ammonium polyphosphate comprises the following steps:

[0015] Mixing the activated first ammonium polyphosphate and the functionalized graphene oxide in a first preset solvent to obtain a first mixed solution;

[0016] Adding a first catalyst to the first mixed solution, and performing an initial grafting reaction under first reaction conditions, so that the first ammonium polyphosphate is preferentially grafted onto the edge of the graphene oxide, to obtain a first reaction mixture;

[0017] post-treating the first reaction mixture to obtain a first reaction product;

[0018] Mixing the activated second ammonium polyphosphate and the first reaction product in a second preset solvent to obtain a second mixed solution;

[0019] adding a second catalyst to the second mixed solution, and performing a subsequent grafting reaction under second reaction conditions, so that the second ammonium polyphosphate is preferentially grafted onto the basal surface of the graphene oxide, to obtain a second reaction mixture;

[0020] The second reaction mixture is post-treated to obtain a second reaction product.

[0021] Optionally, the activating treatment of the ammonium polyphosphate to obtain the ammonium polyphosphate having functional groups on the surface comprises the following steps:

[0022] dissolving the ammonium polyphosphate in a polar organic solvent;

[0023] The ammonium polyphosphate is functionalized by an esterification reaction or an amidation reaction to introduce the functional group on the surface of the ammonium polyphosphate, wherein the functional group is an ester group or an amide group.

[0024] Optionally, the flame retardant in an amount of 5-25% by mass and the plastic matrix in an amount of 70-90% by mass are mixed to obtain a flame retardant plastic composited with nanomaterials, comprising the following steps:

[0025] Premixing 5-25% by mass of the flame retardant, 70-90% by mass of the plastic matrix, and a first preset additive at a first preset temperature to obtain a premix;

[0026] The premix and the second preset additive are melt-blended at a second preset temperature to obtain the flame retardant plastic.

[0027] Optionally, neither the first preset additive nor the second preset additive contains an interface compatibilizer.

[0028] According to the scheme of the present invention, first, reactive functional groups such as hydroxyl and carboxyl are added to graphene oxide; then, ammonium polyphosphate is activated to make it easier to react with the functional groups of graphene oxide. After that, the two are tightly combined through a grafting reaction to form a stable chemical bond. This combination not only combines the flame retardant advantages of both, but also produces a significant synergistic effect. During combustion, a more stable and dense carbon layer can be formed, which effectively prevents the spread of flames and greatly improves the flame retardant performance. At the same time, this flame retardant is evenly dispersed in the plastic and has good compatibility, ensuring that its flame retardant effect is maximized. In the formula, the flame retardant accounts for 5-25%, and the plastic matrix accounts for 70-90%. This ratio not only ensures the flame retardant effect, but also does not affect the original performance of the plastic, achieving a balance between flame retardancy and performance.

[0029] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic flow chart of a method for preparing a flame-retardant plastic composited with nanomaterials according to an embodiment of the present invention is shown;

[0031] Figure 2 The Raman spectra of the graphene oxide after functionalization treatment, the ammonium polyphosphate after activation treatment, and the graphene oxide grafted with ammonium polyphosphate in Example 1 of the present invention are shown;

[0032] Figure 3 Raman spectra of graphene oxide and graphene oxide grafted with the first ammonium polyphosphate and the second ammonium polyphosphate according to Example 2 of the present invention are shown. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0034] Figure 1 FIG. 1 is a schematic flow chart of a method for preparing a flame retardant plastic composite of nanomaterials according to an embodiment of the present invention. Figure 1 As shown, the preparation method comprises:

[0035] Step S100, providing graphene oxide, ammonium polyphosphate and a plastic matrix, wherein the plastic matrix contains polar groups;

[0036] Step S200, functionalizing graphene oxide to obtain graphene oxide with active functional groups introduced on the surface;

[0037] Step S300, performing activation treatment on the ammonium polyphosphate to obtain an ammonium polyphosphate having functional groups on the surface, wherein the functional groups can react with the active functional groups;

[0038] Step S400, performing a grafting reaction on the functionalized graphene oxide and the activated ammonium polyphosphate to obtain a flame retardant of graphene oxide grafted with ammonium polyphosphate;

[0039] Step S500 , mixing 5-25% by mass of a flame retardant and 70-90% by mass of a plastic matrix to obtain a nano-material composite flame retardant plastic.

[0040] According to the scheme of the present invention, by grafting ammonium polyphosphate on graphene oxide, the flame retardant prepared not only integrates the flame retardant properties of graphene oxide and ammonium polyphosphate, but also produces a significant synergistic effect. This synergistic effect is mainly reflected in the following aspects: Enhanced flame retardancy. Graphene oxide uses its unique lamellar structure as a physical barrier to effectively isolate oxygen and heat, while ammonium polyphosphate forms a stable carbon layer during combustion through chemical reactions. After the two are combined, a denser barrier layer can be formed, which greatly slows down the spread of flames and significantly improves the flame retardant properties of flame-retardant plastics. Improve the stability of the carbon layer. The carbon layer formed by ammonium polyphosphate becomes more stable and dense under the reinforcement of the lamellar structure of graphene oxide. This structure can effectively prevent the carbon layer from breaking under the impact of flames, thereby further enhancing the flame retardant effect. Improve the dispersibility and compatibility of flame retardants. The large specific surface area and excellent dispersibility of graphene oxide, combined with the activation treatment of ammonium polyphosphate, enable the flame retardant to be evenly distributed in the plastic matrix, ensuring the uniformity and stability of the flame retardant effect. Complementary flame retardant mechanism. The physical barrier of graphene oxide and the chemical carbon layer of ammonium polyphosphate complement each other to form a multi-layered flame retardant system. When a fire occurs, both can respond quickly and effectively prevent the spread of flames.

[0041] By functionalizing graphene oxide, active functional groups such as hydroxyl and carboxyl are introduced, which not only enhances its chemical reactivity with ammonium polyphosphate, but also provides more reaction sites for grafting reaction. At the same time, functionalization also improves the dispersibility and compatibility of graphene oxide in plastics. On the other hand, ammonium polyphosphate is activated to have more functional groups in its molecular structure that match the functional groups of graphene oxide, such as ester groups and carboxyl groups. These functional groups can form stable chemical bonds, such as ester bonds and amide bonds, with the functional groups of graphene oxide. The functionalized graphene oxide undergoes a grafting reaction with the activated ammonium polyphosphate to form a chemical bond, so that the two are tightly combined. This combination not only enhances the overall stability and durability of the flame retardant, but also further improves the dispersibility and compatibility of the flame retardant in plastics, thereby ensuring that it can be evenly distributed and exert the best flame retardant effect. Therefore, this method, which combines the advantages of the two flame retardant components and achieves a tight combination through chemical bonding, effectively improves the performance of flame retardant plastics.

[0042] In addition, the mass percentage of the flame retardant is 5-25%, and the mass percentage of the plastic matrix is ​​70-90%. Such a ratio is intended to achieve a balance between the flame retardant performance and the performance of the plastic matrix. Within this ratio range, the flame retardant can fully exert its flame retardant effect while maintaining good processability and physical properties of the plastic matrix.

[0043] Functionalization of graphene oxide and activation of ammonium polyphosphate are key steps in the preparation of high-performance flame-retardant composites. Functionalized graphene oxide provides grafting sites for ammonium polyphosphate, which not only affects the interfacial interaction between ammonium polyphosphate and graphene oxide, but also directly affects the bonding strength between the flame retardant and the substrate, thus affecting the overall flame retardant performance.

[0044] In order to enhance the binding force between the flame retardant and the substrate, it is expected that functionalization and activation can form a stable chemical bond, such as a covalent bond or an ionic bond, between ammonium polyphosphate and graphene oxide. The formation of these chemical bonds can significantly enhance the interaction between the flame retardant and the substrate, so that the flame retardant can be more firmly attached to the surface of the substrate and is not easy to fall off. At the same time, while forming chemical bonds, physical adsorption such as van der Waals forces and hydrogen bonds also enhance the binding force between the flame retardant and the substrate to a certain extent, thereby improving the stability of the flame retardant.

[0045] In order to optimize the flame retardant properties, it is necessary to control the grafting position and grafting density of ammonium polyphosphate. The edge of graphene oxide is an ideal position for grafting ammonium polyphosphate due to its high reactivity. This is because the carbon atoms at the edge are unsaturated and are more likely to form stable chemical bonds with ammonium polyphosphate. In addition, the defect sites on the surface of graphene oxide, such as vacancies, cracks or functional groups, also provide highly active grafting sites for ammonium polyphosphate. These defect sites not only enhance the interaction between the flame retardant and graphene oxide, but also help improve the flame retardant properties.

[0046] However, too high a grafting density will increase the steric hindrance between ammonium polyphosphate molecules, affecting their arrangement and orientation on the graphene oxide surface, thereby adversely affecting the performance of the composite material of graphene oxide grafted with ammonium polyphosphate. Therefore, during the preparation process, the grafting density needs to be precisely controlled to ensure the best interaction between ammonium polyphosphate and graphene oxide while maintaining the stability and performance of the composite material.

[0047] Therefore, by precisely controlling the functionalization of graphene oxide and the activation process of ammonium polyphosphate, as well as the grafting reaction, the grafting position and grafting density are optimized to prepare a composite material with excellent flame retardant properties and good interfacial compatibility with the plastic matrix.

[0048] In order to achieve the above purpose, in some embodiments, in the above step S100, graphene oxide can be prepared by existing technologies such as oxidation exfoliation, chemical vapor deposition, oxidation substitution, electrolytic exfoliation, etc., or it can be directly purchased. It should be noted that whether it is prepared by an existing preparation method or directly purchased, it needs to meet the following requirements: 1) The purity of the graphene oxide needs to be greater than 90wt%, preferably more than 99wt%, to ensure its good flame retardant properties. 2) The graphene oxide flakes are in the range of 10nm-10μm. Too small flakes will lead to a decrease in flame retardant properties, while too large flakes will affect its dispersibility in the plastic matrix. 3) The thickness of graphene oxide is in the range of 0.5nm-2nm. This is because thinner graphene oxide has better barrier properties and higher specific surface area, which is conducive to improving flame retardant properties.

[0049] Ammonium polyphosphate can be purchased directly, such as ammonium polyphosphate produced by Clariant, with product grades of Exolit AP 435 or Exolit AP 740. The purity of the ammonium polyphosphate should be greater than 90wt%, preferably greater than 99wt%, to ensure the effect of its activation treatment and the performance of the final flame retardant. The basic structural formula of ammonium polyphosphate is as follows:

[0050]

[0051] The plastic matrix may be, for example, polyvinyl chloride, polyvinylidene fluoride, polyamide, polyester, etc. The plastic matrix contains polar groups, which can interact with ammonium polyphosphate and functionalized graphene oxide, thereby enhancing the bonding force between the flame retardant and the plastic matrix and the flame retardant effect.

[0052] In the above step S200, chemical methods such as nitric acid treatment or introduction of functional group reagents can be used to introduce active functional groups such as carboxyl, hydroxyl or amino groups on the surface of graphene oxide. These functional groups will serve as active sites for grafting reactions.

[0053] The above step S300 specifically includes the following steps: dissolving ammonium polyphosphate in a polar organic solvent; functionalizing the ammonium polyphosphate through an esterification reaction or an amidation reaction to introduce a functional group on the surface of the ammonium polyphosphate, wherein the functional group is an ester group or an amide group.

[0054] In the step of dissolving ammonium polyphosphate in a polar organic solvent, the polar organic solvent may be, for example, ethanol, acetone, chloroform, methanol or dimethylformamide, etc. These solvents should be able to dissolve ammonium polyphosphate well and not have a negative impact on the subsequent activation reaction.

[0055] The esterification reaction and amidation reaction can use existing methods, and the above technical purpose can be achieved by adjusting some parameters. The esterification reaction can include, for example:

[0056] Step S301, prepare an esterification agent. The esterification agent is a compound containing a carboxyl group or an alcoholic hydroxyl group, such as anhydride, carboxylic acid or alcohol.

[0057] Step S302, under a certain temperature and in the presence of a catalyst, an esterification agent is added dropwise to a solution of ammonium polyphosphate. The catalyst can be sulfuric acid, hydrochloric acid or an organic acid, etc. The ammonium polyphosphate can be pretreated, such as surface hydroxylation, to enhance the subsequent reactivity with the esterification agent.

[0058] Step S303, stirring the reaction mixture to allow the ammonium polyphosphate and the esterification agent to fully react.

[0059] Step S304, after the reaction is completed, remove the excess solvent and unreacted reagents by distillation or extraction.

[0060] In the above step S302, the temperature may vary depending on the type of catalyst. In a specific embodiment, when the catalyst is sulfuric acid or hydrochloric acid, the temperature is any value in the range of 80° C.-100° C. The molar ratio of the catalyst to the esterification agent is any value in the range of 0.1-5:100.

[0061] The amidation reaction may include, for example:

[0062] Step S310, prepare an amidation reagent. The amidation reagent is usually a compound containing an amino group, such as amines or ammonia.

[0063] Step S320, adding an amidation agent dropwise into the ammonium polyphosphate solution at a certain temperature in the presence of a catalyst, wherein the catalyst may be, for example, an organic metal catalyst or an acidic catalyst.

[0064] Step S330, stirring the reaction mixture to allow the ammonium polyphosphate and the amidation reagent to fully react.

[0065] Step S340, after the reaction is completed, remove the excess solvent and unreacted reagents by filtering, distilling or extracting.

[0066] In step S320, when the catalyst is an organic metal catalyst such as a palladium catalyst, a copper catalyst, etc., the corresponding temperature is any value between 30° C. and 60° C. When the catalyst is an acidic catalyst such as sulfuric acid, phosphoric acid, etc., the corresponding temperature is any value between 60° C. and 120° C.

[0067] It should be emphasized that in the embodiments of the present invention, ester groups or amide groups need to be introduced into ammonium polyphosphate instead of other functional groups such as aldehyde groups, ketone groups, etc. The reason is that ester groups and amide groups have high chemical stability and can maintain structural stability under different environmental conditions, which is crucial for the performance of flame retardants. In addition, ester groups and amide groups can react chemically with functional groups on the surface of graphene oxide to form stable chemical bonds, thereby achieving effective grafting of ammonium polyphosphate and graphene oxide.

[0068] When other functional groups such as aldehyde groups and ketone groups are introduced into ammonium polyphosphate, although the functional groups have high reactivity, they are prone to decomposition or degradation during long-term storage or use, thus affecting the performance of the flame retardant. In addition, these other functional groups cannot react effectively with the functional groups on the surface of graphene oxide, or the chemical bonds formed are not stable enough, resulting in weak binding between the flame retardant and graphene oxide, which is easy to fall off or decompose.

[0069] There are also some functional groups that do not have good flame retardant properties, or their introduction will have a negative impact on the flame retardant properties of the flame retardant, thus failing to meet the performance requirements of the flame retardant in this patented technology. For example, although amino groups can be combined with certain flame retardant elements such as phosphorus and nitrogen to form effective flame retardant groups, amino groups alone do not have good flame retardant properties. In addition, amino groups will participate in oxidation reactions at high temperatures to produce harmful gases, thereby causing harm to the environment and human health. Another example is alkenyl, which is a group containing a carbon-carbon double bond. This group has a high reactivity. However, during the preparation of the flame retardant, the alkenyl group will have unnecessary side reactions with other components, resulting in changes in the composition and structure of the flame retardant, thereby reducing its flame retardant properties.

[0070] Therefore, the inventors have found through a large number of experimental verifications that when the functional groups introduced on the surface of ammonium polyphosphate are ester groups or amide groups, the performance in all aspects is optimal or better.

[0071] In the above embodiments, as long as ammonium polyphosphate can be successfully grafted onto graphene oxide and mixed into a plastic matrix as a flame retardant, a higher flame retardant effect and good compatibility between the flame retardant and the plastic matrix can be achieved.

[0072] However, since the reactivity and steric hindrance of the edge and defect positions of graphene oxide are different from those of the basal plane positions of graphene oxide, it is necessary to make full use of the structural characteristics of graphene oxide and the characteristics of different positions in order to achieve the best performance of the flame retardant. In order to achieve this goal, the inventors of the present application have creatively thought of grafting ammonium polyphosphate with a smaller molecular weight at the edge and defect positions of graphene oxide, and grafting ammonium polyphosphate with a larger molecular weight at the basal plane positions of graphene oxide.

[0073] Since the edges and defect positions of graphene oxide have higher reactivity and greater steric hindrance, it is easier for small molecular weight ammonium polyphosphate to be successfully grafted here. Small molecular weight ammonium polyphosphate is easier to match these positions in terms of geometric size, so that effective chemical reactions occur. This grafting method can ensure that the flame retardant forms stable chemical bonds at the edges and defect positions of graphene oxide, thereby improving the stability and durability of the flame retardant. In addition, grafting large molecular weight ammonium polyphosphate at the basal plane position of graphene oxide can further enhance the performance of the flame retardant. Large molecular weight ammonium polyphosphate has longer molecular chains and more functional groups, which can form more complex interactions with the basal plane position. This grafting method can not only improve the dispersibility and stability of the flame retardant at the basal plane position of graphene oxide, but also increase the interaction force between the flame retardant and the plastic matrix, thereby enhancing the dispersibility and stability of the flame retardant in the plastic matrix. In addition, by grafting ammonium polyphosphate of different molecular weights at different positions, the flame retardant can be evenly distributed on the surface of graphene oxide. This distribution method can ensure the uniformity of the flame retardant in the material, thereby improving the overall flame retardant performance of the material.

[0074] Therefore, by grafting small molecular weight ammonium polyphosphate on the edge and defect positions of graphene oxide and grafting large molecular weight ammonium polyphosphate on the basal plane, the structural characteristics of graphene oxide and the characteristics of different positions can be fully utilized to achieve the best performance of the flame retardant. This design method can not only improve the stability and durability of the flame retardant, but also enhance the dispersion and stability of the flame retardant in the polymer, thereby improving the overall flame retardant performance of the material.

[0075] In order to achieve the technical purpose of grafting smaller molecular weight ammonium polyphosphate onto the edge and defect positions of graphene oxide and grafting larger molecular weight ammonium polyphosphate onto the basal plane of graphene oxide, the inventors of the present application have developed the following scheme after a large number of experimental verifications.

[0076] Two ammonium polyphosphates with different molecular weights are selected, one of which has a molecular weight ranging from 1000 to 1500 Daltons, such as 1000 Daltons, 1100 Daltons, 1200 Daltons or 1500 Daltons, or any other value from 1000 to 1500 Daltons, and the ammonium polyphosphate is recorded as the first ammonium polyphosphate. The other ammonium polyphosphate has a molecular weight ranging from 2000 to 4000 Daltons, such as 2000 Daltons, 3000 Daltons or 4000 Daltons, or any other value from 2000 to 4000 Daltons, and the ammonium polyphosphate is recorded as the second ammonium polyphosphate.

[0077] The molecular weight of the first ammonium polyphosphate is selected to be any value in the range of 1000-1500 daltons, and this molecular weight range can ensure that the ammonium polyphosphate molecule has enough steric hindrance to adapt to the structural limitations of the edge and defect positions of graphene oxide, while maintaining high reactivity. Moreover, the ammonium polyphosphate of this molecular weight usually has high reactivity, and its functional group is more likely to react with the active sites on the surface of graphene oxide to form stable chemical bonding. Too small molecular weight such as 300-500 daltons causes the molecule to be too simple, and the reactivity is insufficient, while too large molecular weight such as 2000-3000 daltons increases steric hindrance and reduces reaction efficiency. Moreover, in the plastic matrix, the ammonium polyphosphate molecules (1000-1500 daltons) of appropriate size are more easily evenly dispersed to prevent the occurrence of agglomeration, which helps to improve the stability and dispersibility of the flame retardant, thereby improving the overall performance of the material.

[0078] The molecular weight of the second ammonium polyphosphate is selected to be any value in the range of 2000-4000 Dalton. This molecular weight range can ensure that the ammonium polyphosphate molecule has sufficient length and functional group number at the basal plane position of graphene oxide, so as to form enough interactions with the basal plane, and realize stable and effective grafting. Moreover, the molecular weight within this range is moderate, which can avoid the insufficient grafting stability caused by too small molecular weight, and also prevent the increase of steric hindrance and the increase of grafting difficulty caused by too large molecular weight. In addition, within this molecular weight range, the ammonium polyphosphate molecule can form a denser carbon layer when burning, providing a better flame retardant effect. Too small molecular weight such as 500-1500 Dalton cannot form a sufficiently stable carbon layer when burning, and too large molecular weight such as 5000-10000 Dalton causes the carbon layer to be too thick, affecting the mechanical properties and processing properties of the material.

[0079] Therefore, by selecting ammonium polyphosphate with different molecular weights for grafting, a gradient distribution of the flame retardant on the surface of graphene oxide can be achieved. This gradient distribution can further optimize the performance of the flame retardant and enable it to play a better role.

[0080] In step S300, the functionalized graphene oxide is subjected to a grafting reaction with the activated ammonium polyphosphate to obtain a flame retardant of graphene oxide grafted with ammonium polyphosphate, and the method comprises:

[0081] Step S301, mixing the activated first ammonium polyphosphate and the functionalized graphene oxide in a first preset solvent to obtain a first mixed solution;

[0082] Step S302, adding a first catalyst to the first mixed solution, and performing an initial grafting reaction under a first reaction condition, so that the first ammonium polyphosphate is preferentially grafted onto the edge of the graphene oxide, to obtain a first reaction mixture;

[0083] Step S303, post-treating the first reaction mixture to obtain a first reaction product;

[0084] Step S304, mixing the activated second ammonium polyphosphate and the first reaction product in a second preset solvent to obtain a second mixed solution;

[0085] Step S305, adding a second catalyst to the second mixed solution, and performing a subsequent grafting reaction under a second reaction condition, so that the second ammonium polyphosphate is preferentially grafted onto the basal surface of the graphene oxide, to obtain a second reaction mixture;

[0086] Step S306, post-treating the second reaction mixture to obtain a second reaction product.

[0087] The embodiment of the present invention successfully uses a two-step grafting method to graft the first ammonium polyphosphate to the edge position and defect position of graphene oxide, and grafts the second ammonium polyphosphate to the basal position of graphene oxide. This scheme was determined by the inventor after a large number of experimental verifications. Initially, the inventor tried to mix the two ammonium polyphosphates together for a one-step grafting reaction, but found that no matter how the reaction parameters, such as catalyst, reaction temperature and reaction time, were adjusted, the ideal flame retardant effect could not be obtained.

[0088] Based on this, the inventors have creatively proposed a two-step grafting method. The reason why this method can successfully obtain an ideal flame retardant is that the second ammonium polyphosphate with a large molecular weight faces great difficulties when directly grafted to the basal plane of graphene oxide due to its long molecular chain and large steric hindrance. This is because the basal plane of graphene oxide has higher steric hindrance and fewer active sites compared to the edge and defect positions. On the contrary, the first ammonium polyphosphate with a small molecular weight is easier to enter the edge and defect positions of graphene oxide due to its short molecular chain and small steric hindrance, and reacts with the active sites at these positions. Therefore, in the first step of the grafting reaction, the first ammonium polyphosphate with a small molecular weight is preferentially selected for grafting to ensure that a stable grafting structure is formed at the edge and defect positions of graphene oxide. After completing the first step, the edge and defect positions of graphene oxide have been occupied by the first ammonium polyphosphate with a small molecular weight, forming a preliminary grafting structure. In the second step of grafting reaction, a second ammonium polyphosphate with a large molecular weight is added to the reaction system. Since the steric hindrance of the edge position and the defect position has been occupied, the ammonium polyphosphate with a large molecular weight will be more easily guided to the basal plane position of graphene oxide for grafting. This is because the basal plane position has a larger space and more potential active sites for the large molecular weight ammonium polyphosphate to be grafted relative to the occupied edge and defect positions.

[0089] In addition, the two-step grafting method also helps to optimize the efficiency and stability of the grafting reaction. First, the first ammonium polyphosphate with a small molecular weight is grafted to form a stable grafted structure at the edge position and defect position of graphene oxide, providing a good foundation for the subsequent grafting of ammonium polyphosphate with a large molecular weight. At the same time, the two-step grafting can also avoid the competitive reactions and side reactions that may occur when two ammonium polyphosphates with different molecular weights are added simultaneously in a one-step reaction, thereby improving the efficiency of the grafting reaction and the purity of the product. Therefore, the two-step grafting method is based on the fact that ammonium polyphosphate with a large molecular weight is not easy to graft to the basal plane of graphene oxide. By first grafting a small molecular weight ammonium polyphosphate to form a stable grafted structure, and then guiding the large molecular weight ammonium polyphosphate to be grafted to the basal plane position, the efficiency and stability of the grafting reaction are optimized.

[0090] In some embodiments, in the above step S301, the first preset solvent is selected as an amide, halogen compound or sulfoxide polar aprotic solvent. Amide polar aprotic solvents can be selected as N, N-dimethylformamide, N-methylpyrrolidone, etc., for example. Halogen polar aprotic solvents can be selected as 1,2-dichloroethane, ethyl bromide, propyl bromide, etc. Sulfoxide polar aprotic solvents can be selected as dimethyl sulfoxide, diethyl sulfone, etc. The first preset solvent is selected as an amide, halogen compound or sulfoxide polar aprotic solvent, and its polarity can be well matched with the functionalized graphene oxide and the activated ammonium polyphosphate. This polarity matching helps the solvent to better dissolve and disperse these substances, thereby promoting the grafting reaction. In addition, in the grafting reaction, these solvents can effectively dissolve graphene oxide and ammonium polyphosphate, making them more susceptible to interaction and grafting reactions. In addition, amide, halogen compound and sulfoxide solvents usually have high chemical stability and are not prone to decomposition or unnecessary reactions with other substances during the grafting reaction, which helps maintain the stability and purity of the reaction system, thereby improving the success rate of the grafting reaction and the purity of the product. In addition, the extremely weak acidity and alkalinity of these solvents help maintain the pH value of the reaction system stable, avoiding unnecessary acid-base effects on reactants and products.

[0091] The molar ratio of the first ammonium polyphosphate to graphene oxide in the first mixed solution is any value in the range of 10-80:1. The molar ratio can be, for example, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1 or 80:1, or any other value in the range of 10-80:1. Within this molar ratio range, the first ammonium polyphosphate can form an appropriate grafting density and coverage at the edge and defect positions of graphene oxide. A too low molar ratio of 1-5:1 results in incomplete grafting at the edge and defect positions of graphene oxide, affecting the effectiveness of the flame retardant, while a too high molar ratio of 90-150:1 results in excessive grafting, causing the ammonium polyphosphate molecules to crowd each other, affecting its distribution and stability on the surface of graphene oxide. Moreover, after the first grafting reaction is completed, the appropriate molar ratio can also provide a good basis for the subsequent grafting reaction. In the second grafting reaction, the second ammonium polyphosphate with a large molecular weight needs to be grafted to the basal plane of graphene oxide. If the molar ratio of the first ammonium polyphosphate in the first grafting reaction is too high, it may occupy too many active sites and affect the progress of the second grafting reaction. If the molar ratio is too low, there may not be enough active sites for the second ammonium polyphosphate with a large molecular weight to be grafted.

[0092] Of course, the molar ratio of the first ammonium polyphosphate and graphene oxide is related to the type of the first preset solvent. When the first preset solvent is selected as an amide polar aprotic solvent, the molar ratio of the first ammonium polyphosphate and graphene oxide in the first mixed solution is any value in the range of 10-50:1, for example, it can be 10:1, 20:1, 30:1, 40:1 or 50:1, or any other value in the range of 10-50:1.

[0093] When the first preset solvent is selected as a polar aprotic solvent of a halogen compound, the molar ratio of the first ammonium polyphosphate and graphene oxide in the first mixed solution is any value in the range of 20-80:1, for example, it can be 20:1, 30:1, 40:1, 50:1, 60:1, 70:1 or 80:1, or any other value in the range of 20-80:1.

[0094] When the first preset solvent is selected as a sulfoxide-based polar aprotic solvent, the molar ratio of the first ammonium polyphosphate to graphene oxide in the first mixed solution is any value in the range of 10-30:1, for example, it can be 10:1, 20:1 or 30:1, or any other value in the range of 10-30:1.

[0095] In step S302, the reaction temperature in the first reaction condition is any value in the range of 100° C.-300° C., for example, it can be 100° C., 200° C. or 300° C., or any value in the range of 100° C.-300° C. The reaction time in the first reaction condition is any value in the range of 2 h-4 h, for example, it can be 2 h, 3 h or 4 h. The first catalyst is selected as a copper-based, iron-based or palladium-based organometallic catalyst.

[0096] The organic ligand of the copper-based organometallic catalyst may be, for example, a phosphine ligand, an amine ligand, pyridine and its derivative ligands, etc. The phosphine ligand may be, for example, diphenylphosphine, tricyclohexylphosphine, etc. The amine ligand may be, for example, N,N-dimethylethylenediamine, N-methylpyrrolidone, etc. When the first catalyst is selected as a copper-based organometallic catalyst, the reaction temperature in the first reaction condition is any value in the range of 150°C-250°C, for example, 150°C, 200°C or 250°C, or any other value in the range of 150°C-250°C.

[0097] The organic ligand of the iron-based organometallic catalyst may be, for example, pyridine and its derivatives, nitrogen heterocyclic carbene, porphyrin, Schiff base, etc. The organic ligand of pyridine and its derivatives may be, for example, 2,6-di-tert-butyl-4-methylpyridine. The nitrogen heterocyclic carbene organic ligand may be, for example, 1,3-di-tert-butyl-4,5-dihydroimidazole-2-ylide. The porphyrin organic ligand may be, for example, tetraphenylporphyrin iron. When the first catalyst is selected as an iron-based organometallic catalyst, the reaction temperature in the first reaction condition is any value between 100°C and 200°C, for example, 100°C, 150°C or 200°C, or any other value in the range of 100°C to 200°C.

[0098] The organic ligand of the palladium-based organometallic catalyst may be, for example, a phosphine ligand, an N-heterocyclic carbene ligand, a pyridine and its derivative ligand, an olefin ligand, etc. The phosphine ligand may be, for example, triphenylphosphine, tri(o-methylphenyl)phosphine (P(o-Tol)3). The N-heterocyclic carbene ligand may be, for example, 1,3-di-tert-butyl-4,5-dihydroimidazole-2-ylidene. The pyridine and its derivative ligand may be, for example, 2,6-diisopropylpyridine. When the first catalyst is selected as a palladium-based organometallic catalyst, the reaction temperature in the first reaction condition is any value between 200°C and 300°C, for example, 200°C, 250°C or 300°C, or any other value in the range of 200°C to 200°C.

[0099] In step S303, the post-processing steps include filtering, washing, drying, purification, etc. These post-processing steps are conventional techniques and will not be described in detail here.

[0100] After the above steps S301 to S303, the first grafting process is completed, and the graphene oxide grafted with the first ammonium polyphosphate is obtained. This first reaction product will be used as the raw material for the second grafting reaction, and is used to further graft the second ammonium polyphosphate with a large molecular weight to achieve optimized flame retardant properties.

[0101] In step S304, the second preset solvent is also selected as an amide, a halogen compound or a sulfoxide polar aprotic solvent. The second preset solvent may be consistent with the first preset solvent, or may be inconsistent, but both are amides, halogen compounds or sulfoxide polar aprotic solvents. In this way, since the properties of the two solvents are similar, the stability of the reaction system can be ensured when used, and this stability is very important for maintaining the activity of the catalyst, controlling the reaction rate and preventing unnecessary side reactions. In addition, since both solvents are polar aprotic solvents, they have good solubility and compatibility for functionalized graphene oxide and ammonium polyphosphate, which helps to ensure that the reactants are fully dispersed and mixed in the solvent, thereby improving the efficiency and uniformity of the reaction.

[0102] The molar ratio of the second ammonium polyphosphate to the first reaction product in the second mixed solution is any value in the range of 15-40:1, for example, it can be 15:1, 20:1, 30:1, 35:1 or 40:1, or any other value in the range of 15-40:1.

[0103] When the second preset solvent is different, the corresponding molar ratio of the second ammonium polyphosphate to the first reaction product is different. When the second preset solvent is selected as an amide polar aprotic solvent, the molar ratio of the second ammonium polyphosphate to the first reaction product is any value in the range of 15-25:1, for example, it can be 15:1, 20:1, or 25:1, or any other value in 15-25:1. When the second preset solvent is selected as a halogen compound polar aprotic solvent, the molar ratio of the second ammonium polyphosphate to the first reaction product is any value in the range of 25-40:1, for example, it can be 25:1, 30:1 or 40:1, or any other value in 25-40:1. When the second preset solvent is selected as a sulfoxide polar aprotic solvent, the molar ratio of the second ammonium polyphosphate to the first reaction product is any value in the range of 15-25:1, for example, it can be 15:1, 20:1, or 25:1, or any other value in 15-25:1.

[0104] In step S305, the reaction temperature in the second reaction condition is any value in the range of 60°C-80°C, for example, 60°C, 70°C or 80°C, or any other value in the range of 60°C-80°C. The reaction time in the second reaction condition is any value in the range of 4h-8h, for example, 4h, 5h, 6h, 7h or 8h, or any other value in the range of 4h-8h. The second catalyst is selected to be an iridium-based or rhodium-based organometallic catalyst.

[0105] The organic ligand of the iridium-based organometallic catalyst may be, for example, a phosphine ligand, an N-heterocyclic carbene ligand, a pyridine and its derivative ligand, an olefin ligand, etc. The phosphine ligand may be, for example, diphenylphosphine, tricyclohexylphosphine, etc. The N-heterocyclic carbene ligand may be, for example, 1,3-di-tert-butyl-4,5-dihydroimidazole-2-ylidene. The pyridine and its derivative ligand may be, for example, 2,6-diisopropylpyridine. When the second catalyst is selected as an iridium-based organometallic catalyst, the reaction temperature in the second reaction condition is any value between 70°C and 80°C, for example, 70°C, 75°C or 80°C, or any other value in the range of 70°C to 80°C.

[0106] The organic ligand of the rhodium-based organometallic catalyst may be, for example, a Phosphine ligand, an N-HeterocyclicCarbenes ligand, etc. The Phosphine ligand may be, for example, triphenylphosphine, diphenylphosphine, trihydroxymethylphosphine, etc. The N-HeterocyclicCarbenes ligand may be, for example, 1,3-diisopropyl-4,5-dimethyl. When the second catalyst is a rhodium-based organometallic catalyst, the reaction temperature in the second reaction condition is any value between 60°C and 70°C, for example, 60°C, 65°C or 70°C, or any other value between 60°C and 70°C.

[0107] In the above step S306, the post-processing steps include reaction quenching, product separation, purification, drying, etc. These post-processing steps are conventional techniques and will not be described in detail here.

[0108] In the above-mentioned steps S301 to S306, although the first catalyst and the second catalyst are of different specific types, they are all selected as metal organic catalysts. Metal organic catalysts usually have similar catalytic mechanisms, that is, the reaction is promoted by the interaction between the metal center and the substrate. This similar catalytic mechanism means that in the two-step grafting reaction, although the specific catalysts are different, they can work together to promote the smooth progress of the grafting reaction. Since both types of catalysts belong to the general category of metal organic catalysts, they usually respond similarly to reaction conditions (such as temperature, pressure, solvent, etc.). Therefore, when optimizing the reaction conditions, the needs of the two types of catalysts can be considered at the same time, and it is easier to find an optimal condition suitable for the entire grafting reaction system.

[0109] In addition, different temperature ranges are set for the first grafting reaction and the second grafting reaction, because different catalysts exhibit optimal catalytic activity within their specific temperature ranges. By precisely adjusting the reaction temperature, the reaction conditions of each step can be optimized, thereby improving the efficiency of the overall grafting reaction and the quality of the product.

[0110] In the first step of the grafting reaction, a higher temperature is selected to promote the grafting of small molecular weight ammonium polyphosphate at the edge of graphene oxide. This is because high temperature can increase the thermal motion speed of molecules, thereby increasing the collision probability of small molecules with the active sites on the edge of graphene oxide, which is conducive to the formation and growth of grafted chains. In addition, high temperature conditions can also help reduce the activation energy of the reaction, promote the reaction, and help eliminate some adverse side reactions, thereby improving the purity and performance of the product.

[0111] In the second step of grafting reaction, a lower temperature is selected to graft the high molecular weight ammonium polyphosphate on the basal plane of graphene oxide. This is because the high molecular weight ammonium polyphosphate may undergo structural changes or degradation due to excessive thermal motion at high temperatures, affecting its grafting effect and functionality. At lower temperatures, the macromolecules can maintain good structural stability, which is conducive to their orderly grafting on the basal plane of graphene oxide. In addition, low temperature conditions also help control the reaction rate, prevent overreaction or side reactions, and ensure that the grafting process is more controllable and efficient.

[0112] By setting different temperature ranges for the two-step grafting reaction and optimizing the reaction conditions of each step, it is ensured that the small molecular weight first ammonium polyphosphate and the large molecular weight second ammonium polyphosphate are grafted on the edge and basal plane of graphene oxide, respectively, to achieve precise molecular regulation and functional design.

[0113] In the process of manufacturing flame-retardant plastics, the addition of flame retardants is a crucial step. In order to ensure the efficient and stable flame retardant effect of flame retardants, attention must be paid to their changes during the mixing process with the plastic matrix. In addition, it is also critical to ensure that the addition of flame retardants does not significantly affect the mechanical properties and processing properties of the plastic matrix. Therefore, when manufacturing flame-retardant plastics, it is necessary to carefully control the entire production process to ensure the compatibility and stability of flame retardants and plastic matrices, so as to produce flame-retardant plastics that have excellent flame retardant properties while maintaining the original mechanical and processing properties.

[0114] By using the existing method for manufacturing flame-retardant plastics, as long as the amount of flame retardant and plastic matrix is ​​controlled, the flame-retardant plastics manufactured can have excellent flame retardant properties and basically maintain the original mechanical and processing properties to a certain extent. However, in order to further improve the flame retardant properties, mechanical properties and processing properties of flame-retardant plastics, the inventors have developed the following manufacturing method. This step S500 includes:

[0115] Step S501, premixing 5-25% by mass of a flame retardant, 70-90% by mass of a plastic matrix, and a first preset additive at a first preset temperature to obtain a premix;

[0116] Step S502, melt-blending the premixture and the second preset additive at a second preset temperature to obtain a flame retardant plastic, wherein the second preset temperature is greater than the first preset temperature.

[0117] In this embodiment, a premix is ​​prepared first and then melt blending is performed, so that the flame retardant can be preliminarily dispersed in the plastic matrix during the premixing process, and the compatibility between the flame retardant and the plastic matrix is ​​improved. By premixing, the flame retardant can be better dispersed in the plastic matrix before melt blending, thereby avoiding the problem of agglomeration or uneven dispersion during melt blending. In addition, the temperature control of the two steps of premixing and melt blending is optimized respectively to adapt to the processing requirements of different materials. Premixing is performed at a first preset temperature, so that the flame retardant can be preliminarily combined with the plastic matrix, and the influence of high temperature on material properties is reduced. Melt blending is performed at a second preset temperature, which can ensure that the material is completely melted and mixed evenly, thereby improving the stability and uniformity of the flame retardant plastic. In addition, by the synergistic effect of the two steps of premixing and melt blending, it can be ensured that the flame retardant is evenly distributed in the plastic matrix, thereby improving the flame retardant performance and mechanical properties of the flame retardant plastic. At the same time, this preparation method can also reduce waste and loss in the production process and improve the quality and consistency of the product.

[0118] In the above step S501, the first preset additive includes one or more of a dispersant, a lubricant, an antioxidant and an antistatic agent. The mass percentage of the dispersant is any value in the range of 0.1%-1%, for example, 0.1%, 0.5% or 1%. The mass percentage of the lubricant is any value in the range of 0.5%-4%, for example, 0.5%, 1%, 2% or 4%. The mass percentage of the antioxidant is any value in the range of 0.1%-3%, for example, 0.1%, 0.5%, 1%, 2% or 3%. The mass percentage of the antistatic agent is any value in the range of 0.05%-0.3%, for example, 0.05%, 0.1%, 0.2% or 0.3%. The mass percentage of the flame retardant can be, for example, 5%, 10%, 15%, 20% or 25%, or any other value in the range of 5%-25%. The mass percentage of the plastic matrix may be, for example, 70%, 80%, 85% or 90%, or any other value in the range of 70%-90%.

[0119] The first preset temperature is selected to be greater than the softening point of the plastic matrix and less than the thermal decomposition temperature of the flame retardant and the additive, which can ensure that the plastic matrix is ​​fully softened during the mixing process while maintaining the stability and effectiveness of the flame retardant and the additive. In some embodiments, the first preset temperature can be any value between 20°C and 200°C, for example, it can be 20°C, 50°C, 100°C, 150°C or 200°C, or any other value between 20°C and 200°C. At the first preset temperature, the first ammonium polyphosphate with a smaller molecular weight can still be grafted relatively stably at the edge position of graphene oxide without being affected by heat. The premixing in step S501 can be carried out in a premixer, and the premixer can be, for example, a horizontal belt mixer or a conical mixer.

[0120] In the above step S502, the premix and the second preset additive are heated to a second preset temperature and fully mixed under the action of stirring or shearing force. Melt blending is usually carried out in a dedicated melt blending device, such as a melt blender or an extruder. These devices can provide appropriate temperature and shearing force to achieve efficient mixing and dispersion.

[0121] The mass percentage of the premixture is any value in the range of 60%-80%, for example, it can be 60%, 70% or 80%. The second preset additive includes one or more of a plasticizer, a colorant and a filler. The mass percentage of the plasticizer is any value in the range of 5%-20%, for example, it can be 5%, 10%, 15% or 20%, or any other value in the range of 5%-20%. The mass percentage of the colorant is any value in the range of 0.1%-5%, for example, it can be 0.1%, 1%, 3% or 5%, or any other value in the range of 0.1%-5%. The mass percentage of the filler is any value in the range of 10%-25%, for example, it can be 10%, 15% or 25%, or any other value in the range of 10%-25%.

[0122] The second preset temperature is any value in the range of 150°C-300°C, for example, 150°C, 200°C or 300°C, or any other value in the range of 150°C-300°C. The second preset temperature needs to be high enough to completely melt the plastic matrix and fully mix with the additive, but not too high to avoid thermal degradation or thermal decomposition. For polyvinyl chloride plastics, the melt blending temperature is 160°C-190°C. For some high-temperature plastics such as nylon, the melt blending temperature reaches 250°C-300°C.

[0123] In order to verify the technical effects described in the embodiments of the present invention, specific embodiments and comparative examples are described in detail below.

[0124] Embodiment 1:

[0125] This embodiment provides a method for preparing a flame retardant, and the method for preparing the flame retardant comprises:

[0126] Step S111, treating graphene oxide with nitric acid to introduce carboxyl groups and hydroxyl groups on the graphene oxide. The graphene oxide was purchased from Angstron Materials Inc.;

[0127] Step S112, dissolving ammonium polyphosphate in a dimethylformamide solvent, and functionalizing the ammonium polyphosphate by an esterification reaction to introduce ester groups on the surface of the ammonium polyphosphate, wherein the molecular weight of the ammonium polyphosphate is 2000-4000 Daltons;

[0128] Step S113, mixing the product obtained in step S111 and the product obtained in step S112 in dimethylformamide, adding an iridium phosphine complex catalyst after mixing evenly, and reacting at 70° C. for 3 hours, post-treating the product obtained by the reaction to obtain graphene oxide grafted with ammonium polyphosphate.

[0129] Embodiment 2:

[0130] In this embodiment, the preparation method of the flame retardant includes:

[0131] Step S121, treating graphene oxide with nitric acid to introduce carboxyl groups and hydroxyl groups on the graphene oxide. The graphene oxide was purchased from Angstron Materials Inc.;

[0132] Step S122, dissolving the first ammonium polyphosphate and the second ammonium polyphosphate in a dimethylformamide solvent respectively, and functionalizing the ammonium polyphosphates respectively by an esterification reaction, so as to introduce ester groups on the surfaces of the first ammonium polyphosphate and the second ammonium polyphosphate;

[0133] Step S123, mixing the first ammonium polyphosphate obtained in step S122 and the product obtained in step S121 in dimethylformamide, adding a copper phosphine complex catalyst after mixing evenly, and reacting at 200° C. for 1.5 hours to obtain a first reaction product, in which the first ammonium polyphosphate is preferentially grafted to the edge and defect positions of graphene oxide;

[0134] Step S124, mixing the first reaction product and the second ammonium polyphosphate obtained in step S122 in dimethylformamide, adding an iridium phosphine complex catalyst after mixing evenly, and reacting at 70° C. for 3 hours, post-treating the product obtained by the reaction to obtain a second reaction product, in which the first ammonium polyphosphate is grafted to the edge and defect positions of graphene oxide, and the second ammonium polyphosphate is grafted to the basal plane position of graphene oxide.

[0135] Embodiment three:

[0136] The difference between the third embodiment and the second embodiment is that the third embodiment adds a preparation process of the flame retardant plastic. The preparation of the flame retardant plastic includes:

[0137] Step S131, premixing 10% by mass of the flame retardant obtained in Example 2, 85% by mass of the polyamide plastic, 0.7% by mass of the dispersant, 2% by mass of the lubricant, 2% by mass of the antioxidant, and 0.3% by mass of the antistatic agent at 95° C. to obtain a premix;

[0138] Step S132, melt-blending 70% by mass of the premix, 10% by mass of the plasticizer, and 20% by mass of the filler at 200°C to obtain a flame-retardant plastic.

[0139] Embodiment 4:

[0140] The difference between the fourth embodiment and the second embodiment is that the fourth embodiment adds a preparation process of the flame retardant plastic. The preparation of the flame retardant plastic includes the following steps:

[0141] 10% by mass of the flame retardant obtained in Example 2, 85% by mass of polyamide plastic, 0.7% by mass of a dispersant, 2% by mass of a lubricant, 2% by mass of an antioxidant, and 0.3% by mass of an antistatic agent are uniformly mixed to obtain a mixture;

[0142] 70% by mass of the mixture, 10% by mass of the plasticizer, and 20% by mass of the filler are melt-blended at 200° C. to obtain a flame-retardant plastic.

[0143] Embodiment five:

[0144] The difference between the fifth embodiment and the second embodiment is that in the fifth embodiment, step S123 and step S124 are replaced by the following steps: the first ammonium polyphosphate obtained in step S122, the second ammonium polyphosphate and the product obtained in step S121 are mixed in dimethylformamide, and after mixing evenly, an iridium phosphine complex catalyst is added, and the mixture is reacted at 70° C. for 3 hours, and the product obtained by the reaction is post-treated to obtain a reaction product.

[0145] Comparative Example 1:

[0146] The difference between the comparative example 1 and the embodiment 1 is that in the comparative example 1, graphene oxide is directly used as a flame retardant, and the flame retardant is mixed with a plastic matrix to obtain a flame retardant plastic, wherein the mass percentage of graphene oxide and plastic matrix is ​​the same as that of the embodiment 1.

[0147] Figure 2The Raman spectra of graphene oxide after functionalization treatment, ammonium polyphosphate after activation treatment, and graphene oxide grafted with ammonium polyphosphate according to Example 1 of the present invention are shown. Figure 2 As shown in the figure, the functionalized graphene oxide is marked as C-GO, the activated ammonium polyphosphate is marked as PPA0, and the graphene oxide grafted with ammonium polyphosphate is marked as C-GO / PPA0. In the Raman spectrum, C-GO shows different vibration peaks at specific locations: at 3430 cm -1 The vibration peak of hydroxyl group appears at 1716cm -1 The vibration peak of carbon-oxygen double bond appears at 2912cm -1 The OH vibration peak of the carboxyl group appears at 1637 cm -1 The G peak of graphene oxide appears at 1375 cm -1 The D peak of graphene oxide appears at . It can be seen that hydroxyl groups and carboxyl groups are successfully introduced into graphene oxide in the above step S111.

[0148] See also Figure 2 In the Raman spectrum, PPA0 exhibits different vibration peaks at specific locations: at 3012 cm -1 The vibration peak of NH bond appears at 1716cm -1 The vibration peak of carbon-oxygen double bond appears at 1042cm -1 The carbon-oxygen single bond vibration peak appears at 1070 cm -1 The vibration peak of PO bond appears at 3012cm. It can be seen that the ester group was successfully introduced into ammonium polyphosphate in the above step S112. C-GO / PPA0 exhibits different vibration peaks at specific locations: -1 The vibration peak of NH bond appears at 1637cm -1 The G peak of graphene oxide appears at 1375 cm -1 The D peak of graphene oxide appears at 1070 cm -1 The vibration peak of the PO bond appears at . It can be seen that the ammonium polyphosphate is successfully grafted onto the graphene oxide in the above step S113.

[0149] Figure 3 The Raman spectra of graphene oxide and graphene oxide grafted with the first ammonium polyphosphate and the second ammonium polyphosphate in Example 2 of the present invention are shown. Figure 3 As shown, the graphene oxide is marked as Y-GO, the graphene oxide is not functionalized, and the graphene oxide grafted with the first ammonium polyphosphate and the second ammonium polyphosphate is marked as Y-GO / PPA1 / PPA2. In the Raman spectrum, Y-GO / PPA1 / PPA2 has a higher peak at 3012 cm-1 than Y-GO. -1 、1178cm -1and 1070cm -1 At 3012cm, there are three more vibration peaks, and at the same time, the G peak and D peak of graphene oxide shifted. -1 The vibration peak of the NH bond is at 1070cm -1 The vibration peak of the PO bond is at 1178 cm -1 The vibration peak of P=O bond appears at Figure 3 Analysis shows that since PPA1 is mainly grafted at the edge and defect positions of GO, it affects the D peak of GO. The grafting of PPA1 leads to an increase in the defects of GO and an increase in the intensity of the D peak. PPA2 is grafted at the basal plane of GO, so it affects the G peak of GO. Since PPA2 has a large molecular weight, its grafting causes local structural changes in the basal plane of GO, thereby causing the displacement and intensity change of the G peak. In addition, new vibration peaks related to functional groups unique to PPA1 and PPA2, such as PO bonds and P=O bonds, appear in the Raman spectrum. This shows that the first ammonium polyphosphate was successfully grafted at the edge and defect positions of graphene oxide, and the second ammonium polyphosphate was successfully grafted at the basal plane position.

[0150] Table 1 below shows the flame retardancy, thermal stability, physical properties, etc. of Examples 1 to 4 and 5.

[0151] Table 1

[0152] LOI% UL-94 Classification Tensile strength / MPa Melt index (g / 10min) Embodiment 1 38.2 V-1 / / Embodiment 2 52.3 V-0 / / Embodiment 3 50.1 V-0 34.9 7.0 Embodiment 4 43.8 V-0 33.8 6.5 Embodiment 5 35.0 V-1 / / Comparative Example 1 17.3 HB 20.6 5.6

[0153] See Table 1, LOI% represents the limiting oxygen index (volume fraction). The higher the LOI value, the better the flame retardant performance. According to the UL94 standard, the flame retardant performance of plastic materials is divided into multiple levels, including V-0, V-1, V-2, HB, 5VA and 5VB, etc. These levels reflect factors such as the burning speed of the material when it is subjected to flames, the length of flame spread, and whether the dripping material ignites the absorbent cotton. For example, the V-0 level means that the material is extinguished within 10 seconds in the vertical burning test, and no burning material drips to ignite the absorbent cotton below.

[0154] As shown in Table 1, grafting ammonium polyphosphate on graphene oxide can significantly improve the flame retardant properties and tensile strength of the flame retardant plastic, ensuring good flame retardant effect while ensuring good mechanical properties. In addition, grafting the first ammonium polyphosphate on the edge and defect position of graphene oxide and grafting the second ammonium polyphosphate on the base surface can also significantly improve the flame retardant effect. From the melt index, it can be seen that the flame retardant plastic has good processing performance.

[0155] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0156] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a flame-retardant plastic composited with nanomaterials, characterized in that: The method comprises the following preparation steps: Providing graphene oxide, ammonium polyphosphate and a plastic matrix, wherein the plastic matrix contains a polar group; Functionalizing the graphene oxide to obtain graphene oxide with active functional groups introduced on the surface; Activating the ammonium polyphosphate to obtain an ammonium polyphosphate having a functional group on the surface, wherein the functional group can react with the active functional group, and the functional group is an ester group or an amide group; The functionalized graphene oxide is subjected to a grafting reaction with the activated ammonium polyphosphate to obtain a flame retardant of the graphene oxide grafted with the ammonium polyphosphate; The flame retardant with a mass percentage of 5-25% and the plastic matrix with a mass percentage of 70-90% are mixed to obtain the nano material composite flame retardant plastic.

2. The preparation method according to claim 1, characterized in that: The ammonium polyphosphate is formed by mixing a first ammonium polyphosphate and a second ammonium polyphosphate; The molecular weight of the first ammonium polyphosphate is any value in the range of 1000-1500 Daltons, and the molecular weight of the second ammonium polyphosphate is any value in the range of 2000-4000 Daltons.

3. The preparation method according to claim 2, characterized in that: The method of grafting the functionalized graphene oxide with the activated ammonium polyphosphate to obtain a flame retardant of graphene oxide grafted with ammonium polyphosphate comprises the following steps: Mixing the activated first ammonium polyphosphate and the functionalized graphene oxide in a first preset solvent to obtain a first mixed solution; Adding a first catalyst to the first mixed solution, and performing an initial grafting reaction under first reaction conditions, so that the first ammonium polyphosphate is preferentially grafted onto the edge of the graphene oxide, to obtain a first reaction mixture; post-treating the first reaction mixture to obtain a first reaction product; Mixing the activated second ammonium polyphosphate and the first reaction product in a second preset solvent to obtain a second mixed solution; adding a second catalyst to the second mixed solution, and performing a subsequent grafting reaction under second reaction conditions, so that the second ammonium polyphosphate is preferentially grafted onto the basal surface of the graphene oxide, to obtain a second reaction mixture; The second reaction mixture is post-treated to obtain a second reaction product.

4. The preparation method according to claim 3, characterized in that: The molar ratio of the first ammonium polyphosphate to the graphene oxide in the first mixed solution is any value in the range of 10-80:1, the reaction temperature in the first reaction condition is any value in the range of 100° C.-300° C., and the reaction time is any value in the range of 2 h-4 h; The molar ratio of the second ammonium polyphosphate to the first reaction product in the second mixed solution is any value in the range of 15-40:1, the reaction temperature in the second reaction condition is any value in the range of 60°C-80°C, and the reaction time is any value in the range of 4h-8h.

5. The preparation method according to claim 4, characterized in that: The first preset solvent and the second preset solvent are both selected as polar aprotic solvents of amides, halogen compounds or sulfoxides; The first catalyst is selected as a copper-based, iron-based or palladium-based organic metal catalyst, and the second catalyst is selected as an iridium-based or rhodium-based organic metal catalyst.

6. The preparation method according to claim 5, characterized in that: When the first preset solvent is an amide polar aprotic solvent, the molar ratio of the first ammonium polyphosphate to the graphene oxide in the first mixed solution is any value in the range of 10-50:1; When the first preset solvent is a halogen compound-based polar aprotic solvent, the molar ratio of the first ammonium polyphosphate to the graphene oxide in the first mixed solution is any value in the range of 20-80:1; When the first preset solvent is selected as a sulfoxide-based polar aprotic solvent, the molar ratio of the first ammonium polyphosphate to the graphene oxide in the first mixed solution is any value in the range of 10-30:

1.

7. The preparation method according to claim 5, characterized in that: When the second preset solvent is an amide polar aprotic solvent, the molar ratio of the second ammonium polyphosphate to the first reaction product is any value in the range of 15-25:1; When the second preset solvent is selected as a halogen compound-based polar aprotic solvent, the molar ratio of the second ammonium polyphosphate to the first reaction product is any value in the range of 25-40:1; When the second preset solvent is selected as a sulfoxide-based polar aprotic solvent, the molar ratio of the second ammonium polyphosphate to the first reaction product is any value in the range of 15-25:

1.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The method of subjecting the ammonium polyphosphate to activation treatment to obtain ammonium polyphosphate having functional groups on the surface comprises the following steps: dissolving the ammonium polyphosphate in a polar organic solvent; The ammonium polyphosphate is functionalized by an esterification reaction or an amidation reaction to introduce the functional group on the surface of the ammonium polyphosphate, wherein the functional group is an ester group or an amide group.

9. The preparation method according to any one of claims 1 to 7, characterized in that: The method of mixing 5-25% by mass of a flame retardant and 70-90% by mass of a plastic matrix to obtain a nano-material composite flame retardant plastic comprises the following steps: Premixing 5-25% by mass of the flame retardant, 70-90% by mass of the plastic matrix, and a first preset additive at a first preset temperature to obtain a premix; The premix and the second preset additive are melt-blended at a second preset temperature to obtain the flame retardant plastic.

10. The preparation method according to claim 9, characterized in that: The first predetermined additive and the second predetermined additive do not contain an interface compatibilizer.

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