Flame-retardant pet material and preparation method and application thereof

Abstract

The application belongs to the technical field of high polymer materials, and discloses a kind of flame-retardant PET material and its preparation method and application, the raw material of flame-retardant PET material includes: PET resin 70-90 parts, modified lignin derivative 8-20 parts, functionalized boron nitride nanosheet 3-8 parts, lubricant 1-2 parts, antioxidant 0.2-1.5 parts by weight fraction;Modified lignin derivative is obtained by lignin sequentially through oxidative depolymerization, first group grafting and second group end group modification, the first group is at least one of triazine ring, amino and imino, and the second group is at least one of hydroxyl and carboxyl group.This application is modified with lignin as raw material, and the efficient synergistic flame-retardant system is constructed by collocating functionalized boron nitride nanosheet, and the environment-friendly flame-retardant PET material without phosphorus and halogen is created, which is in line with the current development trend of green and safe high polymer materials.

Description

Technical Field

[0001] This application belongs to the field of polymer materials technology, and specifically relates to a flame-retardant PET material, its preparation method and application. Background Technology

[0002] Polyethylene terephthalate (PET) resin, as a general-purpose engineering plastic with excellent comprehensive performance, is widely used in plastic products due to its good mechanical properties, processability, chemical resistance, and cost-effectiveness. With the increasing demands for material safety in related application fields, endowing PET resin with excellent flame-retardant properties has become a key requirement for its expanded applications. Currently, flame-retardant modification of PET resin is mostly achieved by adding halogen-based and phosphorus-based flame retardants. While this can improve the flame-retardant effect to some extent, the application of these traditional flame retardants has many drawbacks. Furthermore, existing modification schemes combining bio-based flame retardants and inorganic flame-retardant additives have not yet formed an efficient and compatible system, making it difficult to simultaneously consider the material's flame-retardant properties, environmental friendliness, processing performance, and stability in use. Summary of the Invention

[0003] This application aims to improve at least one technical problem in the background art.

[0004] The first aspect of this application provides a flame-retardant PET material, the raw materials of which include, by weight, 70-90 parts of PET resin, 8-20 parts of modified lignin derivative, 3-8 parts of functionalized boron nitride nanosheets, 1-2 parts of lubricant, and 0.2-1.5 parts of antioxidant. The modified lignin derivative is obtained by sequentially oxidative depolymerization of lignin, grafting of a first group, and modification of a second group end group. The first group is at least one of triazine ring, amino and imine, and the second group is at least one of hydroxyl and carboxyl groups. Functionalized boron nitride nanosheets were obtained by ultrasonic exfoliation and modification with silane coupling agents from hexagonal boron nitride.

[0005] The flame-retardant PET material provided in this application is made by compounding modified lignin derivatives and functionalized boron nitride nanosheets with PET resin as the matrix raw material, and combining them with lubricants and antioxidants. Each component is formulated in the corresponding weight proportions. The components work synergistically to give the material excellent phosphorus-free and halogen-free flame-retardant effect while retaining the original processing and mechanical properties of PET resin. At the same time, it improves the problem of poor compatibility and easy migration between traditional flame-retardant additives and PET matrix. The modified lignin derivative is made from lignin through oxidative depolymerization, grafting of the first group, and end-group modification of the second group. The grafted triazine ring, amino or imine group serves as a nitrogen-based flame-retardant functional group, which synergizes with the aromatic ring structure of lignin itself. The aromatic ring structure of lignin is easily carbonized at high temperatures to form a dense carbon layer (coke), which can play a role in blocking heat and oxygen in the condensed phase. The nitrogen-based flame-retardant functional group decomposes at high temperatures to release inert nitrogen-containing gas, which can dilute the combustible gas and oxygen in the combustion zone and capture the active free radicals generated during combustion, effectively blocking the chain reaction of gas-phase combustion. The hydroxyl or carboxyl groups modified at the end groups can improve the compatibility of the modified lignin derivative with the PET resin matrix, allowing it to be evenly dispersed in the matrix, ensuring the uniformity and long-lasting flame-retardant effect. Functionalized boron nitride nanosheets are prepared from hexagonal boron nitride through ultrasonic exfoliation and modification with a silane coupling agent. The boron nitride nanosheets obtained by ultrasonic exfoliation have a two-dimensional sheet structure. The modification with the silane coupling agent effectively improves its interfacial compatibility with the PET resin matrix, preventing the nanosheets from agglomerating in the matrix and enabling them to form a continuous sheet barrier network in the matrix. This network can physically block the escape of combustible gases and the entry of oxygen at high temperatures. At the same time, the boron element contained in the nanosheets can combine with the carbon layer formed by the carbonization of modified lignin derivatives to further densify the carbon layer structure and improve the thermal stability and barrier ability of the carbon layer. Modified lignin derivatives and functionalized boron nitride nanosheets form a nitrogen-carbon-boron synergistic flame retardant system. The two work together and complement each other to enhance each other during the flame retardant process. The modified lignin derivatives achieve dual flame retardant effects in both the gas phase and the condensed phase, while the functionalized boron nitride nanosheets focus on physical barrier and char layer reinforcement. The two-dimensional barrier network they form constructs a physical barrier between the gas phase and the condensed phase. The densification modification of the char layer by boron can significantly improve the char layer barrier effect formed by the modified lignin derivatives. This allows the entire flame retardant system to effectively block the combustion chain reaction in the gas phase and form a stable and dense barrier layer in the condensed phase, achieving dual flame retardant reinforcement in both the gas phase and the condensed phase, thereby improving the overall flame retardant performance of PET materials. Lubricant and antioxidant are used as auxiliary components. Lubricant can improve the fluidity of the material during melt processing, avoid problems such as material sticking during processing, and improve the processing and molding performance of the material. Antioxidant can inhibit the oxidative degradation of PET resin during high-temperature melt processing and subsequent use, and ensure the long-term stability of the material's mechanical properties and flame retardant properties. The components are combined according to the weight ratio of this application, so that the obtained flame retardant PET material has excellent flame retardant properties, processing performance and service stability.

[0006] Preferably, the lignin includes at least one of broadleaf lignin, coniferous lignin, herbaceous lignin, alkali lignin, and sulfate lignin.

[0007] Preferably, the first group is a triazine ring, and the second group is a hydroxyl group. The triazine ring, as a nitrogen-based flame-retardant functional group, possesses excellent thermal stability and high nitrogen content. Under high-temperature conditions, it can stably decompose and release inert nitrogen-containing gases, effectively diluting combustible gases and oxygen in the combustion zone. Simultaneously, it can effectively capture active free radicals generated during combustion, efficiently blocking the chain reaction of gas-phase combustion and exhibiting excellent gas-phase flame-retardant properties. The hydroxyl group can form hydrogen bonds with the ester groups in the PET resin molecular chain, significantly improving the interfacial compatibility between the modified lignin derivative and the PET resin matrix. This allows the modified lignin derivative to be uniformly dispersed within the PET resin matrix, ensuring the uniformity of the flame-retardant effect in all areas of the material and its long-lasting flame-retardant performance during use.

[0008] Preferably, the method for preparing modified lignin derivatives includes the following steps: Lignin was dispersed in a KOH solution with a pH of 13-14, and a catalyst and oxidant were added. The mixture was reacted at 90℃-110℃ for 3-4 hours to carry out oxidative depolymerization, yielding intermediate A. Intermediate A was mixed with melamine at a mass ratio of 1:(1.5-3), and then reacted under an inert atmosphere at 100℃-120℃ for 6-8 hours to graft the first group, thus obtaining intermediate B. Intermediate B was mixed with ethylene glycol at a molar ratio of 1:(1-1.2), and then reacted at 120℃-140℃ for 4-6 hours to carry out the second group end group modification. After separation and drying, the modified lignin derivative was obtained.

[0009] Preferably, the method for preparing functionalized boron nitride nanosheets includes the following steps: Hexagonal boron nitride was placed in a mixed liquid medium of anhydrous ethanol and water and ultrasonically exfoliated for 30-60 minutes at a power of 400W-600W to obtain a boron nitride nanosheet dispersion. A silane coupling agent was added to a boron nitride nanosheet dispersion, with a mass ratio of silane coupling agent to hexagonal boron nitride of 1:(0.08-0.15). The mixture was stirred at 50℃-60℃ for 2-3 hours. After centrifugation, washing, and drying, functionalized boron nitride nanosheets were obtained.

[0010] Preferably, the lubricant includes at least one of calcium stearate, ethylene bis-stearamide, and montan ester wax.

[0011] Preferably, the antioxidant includes at least one of hindered phenolic antioxidants and phosphite antioxidants.

[0012] The second aspect of this application provides a method for preparing the aforementioned flame-retardant PET material, comprising the following steps: PET resin, modified lignin derivative, functionalized boron nitride nanosheets, lubricant and antioxidant are mixed to obtain mixture A; Mixture A was subjected to ultrasonic and microwave treatment to obtain mixture B; The mixture B is melt-blended and extruded, then granulated to obtain flame-retardant PET material.

[0013] The parameters for ultrasonic treatment are: power of 300W-600W and time of 10min-30min.

[0014] The microwave processing parameters are: power 200W-400W, temperature 80℃-120℃, and time 5min-20min.

[0015] The temperature for melt blending extrusion is 240℃-270℃.

[0016] The third aspect of this application provides the application of the aforementioned flame-retardant PET material in the preparation of plastic products.

[0017] The beneficial effects of this application are as follows: This application uses lignin as a raw material for modification and combines it with functionalized boron nitride nanosheets to construct a highly efficient and synergistic flame-retardant system, creating a phosphorus-free and halogen-free environmentally friendly flame-retardant PET material, which aligns with the current development trend of green and safe polymer materials. Through the directional modification of lignin, the problems of poor compatibility and easy aggregation and migration between flame-retardant additives and the PET matrix are effectively solved, allowing the flame-retardant components to be uniformly dispersed in the material, ensuring a stable and long-lasting flame-retardant effect. The functionalized boron nitride nanosheets and modified lignin derivatives work together during the flame-retardant process to achieve dual flame-retardant enhancement in both the gas phase and condensed phase, significantly improving the flame-retardant performance of the material while maximizing the preservation of the original mechanical properties and processability of the PET resin, giving the material both excellent flame retardancy and good performance characteristics. This application not only realizes the high-value utilization of biomass resources but also meets the stringent requirements for material safety and comprehensive performance in plastic products, possessing broad practical application value and promising prospects for industrial promotion. Detailed Implementation

[0018] The present application will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Furthermore, it should be understood that after reading the contents of this application, those skilled in the art can make various alterations or modifications to this application, and these equivalent forms also fall within the scope defined by the appended claims.

[0019] Example 1 A flame-retardant PET material, the raw materials of which, by weight, include: 80 parts PET resin, 15 parts modified lignin derivative, 5 parts functionalized boron nitride nanosheets, 1.5 parts lubricant (ethylene bis-stearamide), and 0.8 parts antioxidant (hindered phenolic antioxidant 1010).

[0020] Among them, the modified lignin derivative is obtained by oxidative depolymerization of lignin (alkali lignin), grafting of the first group and modification of the second group end group in sequence. The first group is a triazine ring and the second group is a hydroxyl group. The preparation method of modified lignin derivatives includes the following steps: alkali lignin is dispersed in a KOH solution with a pH of 13.5, a catalyst (Fe2O3, amount 1% of the alkali lignin mass) and an oxidant (30wt% hydrogen peroxide, amount 20% of the alkali lignin mass) are added, and the mixture is reacted at 100℃ for 3.5h for oxidative depolymerization to obtain intermediate A; intermediate A is mixed with melamine at a mass ratio of 1:2.2, and then reacted at 110℃ under a nitrogen atmosphere for 7h for grafting of the first group to obtain intermediate B; intermediate B is mixed with ethylene glycol at a molar ratio of 1:1.1, and then reacted at 130℃ for 5h for end-group modification of the second group, followed by separation and drying to obtain the modified lignin derivative.

[0021] Functionalized boron nitride nanosheets were obtained by ultrasonic exfoliation of hexagonal boron nitride and modification with a silane coupling agent. The preparation method of functionalized boron nitride nanosheets includes the following steps: hexagonal boron nitride was placed in a mixed liquid medium of anhydrous ethanol and deionized water, and ultrasonically exfoliated for 45 min at 500 W to obtain a boron nitride nanosheet dispersion; a silane coupling agent (KH560) was added to the boron nitride nanosheet dispersion, with a mass ratio of silane coupling agent to hexagonal boron nitride of 1:0.12; the mixture was stirred and reacted at 55 °C for 2.5 h; after centrifugation, washing, and drying, functionalized boron nitride nanosheets were obtained.

[0022] The preparation method of this flame-retardant PET material includes the following steps: PET resin, modified lignin derivative, functionalized boron nitride nanosheets, lubricant and antioxidant were added to a high-speed mixer and mixed (1000 rpm for 15 min) to obtain mixture A; Mixture A was subjected to ultrasonic treatment (power 450W, time 20min) and microwave treatment (power 300W, temperature 100℃, time 15min) to obtain mixture B; Mixture B is fed into a twin-screw extruder for melt blending extrusion (temperature 250℃, screw speed 300rpm), granulated, to obtain flame-retardant PET material.

[0023] Example 2 A flame-retardant PET material, the raw materials of which, by weight, include: 75 parts PET resin, 12 parts modified lignin derivative, 4 parts functionalized boron nitride nanosheets, 1 part lubricant (calcium stearate), and 0.5 parts antioxidant (phosphite antioxidant 168).

[0024] Among them, the modified lignin derivative is obtained by lignin (broadleaf lignin) through oxidative depolymerization, grafting of the first group and modification of the second group end group in sequence. The first group is a triazine ring and the second group is a hydroxyl group. The preparation method of modified lignin derivatives includes the following steps: dispersing hardwood lignin in a KOH solution with pH 13, adding a catalyst (Fe2O3, amount 1% of the hardwood lignin mass) and an oxidant (30wt% hydrogen peroxide, amount 20% of the hardwood lignin mass), and reacting at 95℃ for 3h for oxidative depolymerization to obtain intermediate A; mixing intermediate A with melamine at a mass ratio of 1:1.8, and then reacting at 105℃ under a nitrogen atmosphere for 6.5h for grafting of the first group to obtain intermediate B; mixing intermediate B with ethylene glycol at a molar ratio of 1:1, and then reacting at 125℃ for 4.5h for end-group modification of the second group, followed by separation and drying to obtain the modified lignin derivative.

[0025] Functionalized boron nitride nanosheets were obtained by ultrasonic exfoliation of hexagonal boron nitride and modification with a silane coupling agent. The preparation method of functionalized boron nitride nanosheets includes the following steps: hexagonal boron nitride was placed in a mixed liquid medium of anhydrous ethanol and water, and ultrasonically exfoliated for 30 min at 400 W to obtain a boron nitride nanosheet dispersion; a silane coupling agent (KH550) was added to the boron nitride nanosheet dispersion, with a mass ratio of silane coupling agent to hexagonal boron nitride of 1:0.08; the mixture was stirred and reacted at 50 °C for 2 h; after centrifugation, washing, and drying, functionalized boron nitride nanosheets were obtained.

[0026] The preparation method of this flame-retardant PET material includes the following steps: PET resin, modified lignin derivatives, functionalized boron nitride nanosheets, lubricant and antioxidant were added to a high-speed mixer and mixed (800 rpm, 10 min) to obtain mixture A; Mixture A was subjected to ultrasonic treatment (300W power, 10min time) and microwave treatment (200W power, 80℃ temperature, 5min time) to obtain mixture B; Mixture B is fed into a twin-screw extruder for melt blending extrusion (temperature 240℃, screw speed 250rpm), granulation is performed, and flame-retardant PET material is obtained.

[0027] Example 3 A flame-retardant PET material, the raw materials of which, by weight, include: 85 parts PET resin, 18 parts modified lignin derivative, 6 parts functionalized boron nitride nanosheets, 2 parts lubricant (montan ester wax), and 1.2 parts antioxidant (hindered phenolic antioxidant 1010).

[0028] Among them, the modified lignin derivative is obtained by lignin (coniferous lignin) through oxidative depolymerization, grafting of the first group and modification of the second group end group in sequence. The first group is a triazine ring and the second group is a hydroxyl group. The preparation method of modified lignin derivatives includes the following steps: dispersing coniferous lignin in a KOH solution with pH 14, adding a catalyst (Fe2O3, amount 1% of the coniferous lignin mass) and an oxidant (30wt% hydrogen peroxide, amount 20% of the coniferous lignin mass), and reacting at 105℃ for 4h for oxidative depolymerization to obtain intermediate A; mixing intermediate A with melamine at a mass ratio of 1:2.8, and then reacting at 115℃ under a nitrogen atmosphere for 7.5h for grafting of the first group to obtain intermediate B; mixing intermediate B with ethylene glycol at a molar ratio of 1:1.2, and then reacting at 135℃ for 5.5h for end-group modification of the second group, followed by separation and drying to obtain the modified lignin derivative.

[0029] Functionalized boron nitride nanosheets were obtained by ultrasonic exfoliation of hexagonal boron nitride and modification with a silane coupling agent. The preparation method of functionalized boron nitride nanosheets includes the following steps: hexagonal boron nitride was placed in a mixed liquid medium of anhydrous ethanol and water, and ultrasonically exfoliated for 60 min at 600 W to obtain a boron nitride nanosheet dispersion; a silane coupling agent (KH560) was added to the boron nitride nanosheet dispersion, with a mass ratio of silane coupling agent to hexagonal boron nitride of 1:0.15; the mixture was stirred and reacted at 60 °C for 3 h; after centrifugation, washing, and drying, functionalized boron nitride nanosheets were obtained.

[0030] The preparation method of this flame-retardant PET material includes the following steps: PET resin, modified lignin derivatives, functionalized boron nitride nanosheets, lubricant and antioxidant were added to a high-speed mixer and mixed (1200 rpm, 20 min) to obtain mixture A; Mixture A was subjected to ultrasonic treatment (600W power, 30min time) and microwave treatment (400W power, 120℃ temperature, 20min time) to obtain mixture B; Mixture B is fed into a twin-screw extruder for melt blending extrusion (temperature 270℃, screw speed 350rpm), granulation is performed, and flame-retardant PET material is obtained.

[0031] Example 4 A flame-retardant PET material, the raw materials of which include, by weight, 78 parts PET resin, 10 parts modified lignin derivative, 3 parts functionalized boron nitride nanosheets, 1.2 parts lubricant (montan ester wax), and 0.6 parts antioxidant (a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:3).

[0032] Among them, the modified lignin derivative is obtained by lignin (broadleaf lignin) through oxidative depolymerization, grafting of the first group and modification of the second group end group in sequence. The first group is amino and the second group is carboxyl. The preparation method of modified lignin derivatives includes the following steps: dispersing hardwood lignin in a KOH solution with pH 13.2, adding a catalyst (Fe2O3, amount 1.0% of the hardwood lignin mass) and an oxidant (30wt% hydrogen peroxide, amount 20% of the hardwood lignin mass), and reacting at 98℃ for 3.2h for oxidative depolymerization to obtain intermediate A; mixing intermediate A with dicyandiamide at a mass ratio of 1:2.0, and then reacting at 108℃ under a nitrogen atmosphere for 6.8h for grafting of the first group to obtain intermediate B; mixing intermediate B with terephthalic acid at a molar ratio of 1:1.05, and then reacting at 128℃ for 4.8h for end-group modification of the second group, followed by separation and drying to obtain the modified lignin derivative.

[0033] The functionalized boron nitride nanosheets were obtained by ultrasonic exfoliation and modification with a silane coupling agent from hexagonal boron nitride. The preparation method of the functionalized boron nitride nanosheets was the same as in Example 1.

[0034] The preparation method of this flame-retardant PET material is the same as in Example 1.

[0035] Comparative Example 1 A PET material, differing from Example 1 in that it does not contain modified lignin derivatives. Otherwise, it is the same as Example 1.

[0036] Comparative Example 2 A PET material, differing from Example 1 in that it does not contain functionalized boron nitride nanosheets. Otherwise, it is the same as Example 1.

[0037] Comparative Example 3 A PET material, differing from Example 1 in that the modified lignin derivative comprises 30 parts by weight. Otherwise, it is the same as Example 1.

[0038] Comparative Example 4 A PET material, differing from Example 1 in that the functionalized boron nitride nanosheets comprise 15 parts by weight. Otherwise, it is the same as Example 1.

[0039] Comparative Example 5 A PET material differs from Example 1 in that the modified lignin derivative is obtained by grafting a first group onto lignin and modifying it with a second group end group, without undergoing oxidative depolymerization. Otherwise, it is the same as Example 1.

[0040] Comparative Example 6 A PET material differs from Example 1 in that the modified lignin derivative is obtained by oxidative depolymerization of lignin, without grafting of the first group and modification of the second group end groups. Otherwise, it is the same as Example 1.

[0041] Comparative Example 7 A PET material, differing from Example 1 in that alkali lignin is used instead of the modified lignin derivative. Otherwise, it is the same as Example 1.

[0042] Comparative Example 8 A PET material, differing from Example 1 in that: the functionalized boron nitride nanosheets are obtained by ultrasonic exfoliation of hexagonal boron nitride without modification by a silane coupling agent. Otherwise, it is the same as Example 1.

[0043] Comparative Example 9 A PET material, differing from Example 1 in that the first group in the modified lignin derivative is replaced with a cyano group. Otherwise, it is the same as Example 1.

[0044] Comparative Example 10 A PET material, differing from Example 1 in that the second group in the modified lignin derivative is replaced with an ester group. Otherwise, it is the same as Example 1.

[0045] The performance tests of the PET materials prepared in Examples 1-4 and Comparative Examples 1-10 are shown in Table 1.

[0046] Table 1 Referring to the data in Table 1, compared with Example 1, Comparative Example 1 lost its flame-retardant effect due to the absence of modified lignin derivatives. This fully demonstrates that modified lignin derivatives are the core component for achieving the flame-retardant function of this flame-retardant PET material. Their presence provides the material with basic flame-retardant ability, and their absence prevents the achievement of the expected flame-retardant effect. Compared with Example 1, Comparative Example 2 showed a significant decrease in flame-retardant performance due to the absence of functionalized boron nitride nanosheets. This indicates that functionalized boron nitride nanosheets and modified lignin derivatives can form a highly efficient synergistic flame-retardant system. Only through their combined action can the material achieve the ideal flame-retardant level; the absence of either component will affect the flame-retardant effect. Compared with Example 1, Comparative Example 3 used too much modified lignin derivative. Although the flame-retardant performance of the material was slightly improved, the mechanical properties declined significantly. This indicates that excessive addition of modified lignin derivatives will disrupt the overall performance balance of the material and affect its practical application value. Compared to Example 1, Comparative Example 4 showed an excessive amount of functionalized boron nitride nanosheets, resulting in a significant decrease in mechanical properties. This indicates that more functionalized boron nitride nanosheets are not necessarily better; a reasonable amount is needed to ensure that the material retains good mechanical properties while possessing excellent flame retardant properties. Compared to Example 1, Comparative Example 5 did not include an oxidative depolymerization step in the preparation of the modified lignin derivative, leading to a significant decrease in both flame retardant and mechanical properties. This demonstrates that the oxidative depolymerization step optimizes the molecular structure of lignin, making it more compatible with other components and laying the foundation for subsequent group grafting. The absence of this step affects the flame retardant efficiency and compatibility of the modified lignin derivative. Compared to Example 1, Comparative Example 6 only underwent oxidative depolymerization treatment without first-group grafting and second-group end-group modification, resulting in a decline in both flame retardant and mechanical properties. This proves that first-group grafting imparts good flame retardant ability to lignin, while second-group end-group modification improves its compatibility with PET resin. The combination of both allows the modified lignin derivative to fully exert its function. Compared to Example 1, Comparative Example 7 used unmodified alkali lignin instead of the modified lignin derivative, which itself has poor compatibility with PET resin and lacks sufficient flame retardant ability. Compared to Example 1, Comparative Example 8 involved only ultrasonic exfoliation of the functionalized boron nitride nanosheets without silane coupling agent modification, resulting in a significant decrease in the material's mechanical properties. This indicates that silane coupling agent modification can effectively reduce the surface energy of the boron nitride nanosheets, prevent their aggregation, improve their interfacial compatibility with PET resin, and fully utilize the flame-retardant effect of physical barrier. Compared to Example 1, Comparative Example 9 replaced the first group of the modified lignin derivative with a cyano group, leading to a significant decrease in the material's flame-retardant performance. This demonstrates that a suitable first group can effectively improve the material's flame-retardant efficiency. The cyano group cannot exert a good flame-retardant effect like triazine rings, amino groups, or imino groups, making it difficult for the material to achieve the expected flame-retardant effect.Compared with Example 1, Comparative Example 10 replaced the second group of the modified lignin derivative with an ester group, which also led to a decrease in the flame retardant properties of the material. This shows that the ester group cannot effectively improve the compatibility of the modified lignin derivative with PET resin, thereby affecting the full play of its flame retardant effect. Only a suitable end group structure can ensure the comprehensive performance of the material.

[0047] In the description of this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature.

[0048] The above description is only a preferred embodiment of this application. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of this application, and these improvements and additions should also be considered within the scope of protection of this application.

Claims

1. A flame-retardant PET material, characterized in that, Its raw materials, by weight, include: 70-90 parts PET resin, 8-20 parts modified lignin derivatives, 3-8 parts functionalized boron nitride nanosheets, 1-2 parts lubricant, and 0.2-1.5 parts antioxidant. The modified lignin derivative is obtained by sequentially oxidative depolymerization of lignin, grafting of a first group, and end-group modification of a second group. The first group is at least one of a triazine ring, an amino group, and an imine group, and the second group is at least one of a hydroxyl group and a carboxyl group. The functionalized boron nitride nanosheets are obtained by ultrasonic exfoliation and modification with a silane coupling agent from hexagonal boron nitride.

2. The flame-retardant PET material according to claim 1, characterized in that, The lignin includes at least one of broadleaf lignin, coniferous lignin, herbaceous lignin, alkali lignin, and sulfate lignin.

3. The flame-retardant PET material according to claim 1, characterized in that, The first group is a triazine ring, and the second group is a hydroxyl group.

4. The flame-retardant PET material according to claim 3, characterized in that, The preparation method of the modified lignin derivative includes the following steps: The lignin was dispersed in a KOH solution with a pH of 13-14, a catalyst and an oxidant were added, and the reaction was carried out at 90℃-110℃ for 3-4 hours to carry out the oxidative depolymerization, to obtain intermediate A; Intermediate A is mixed with melamine at a mass ratio of 1:(1.5-3), and then reacted under an inert atmosphere at 100℃-120℃ for 6-8 hours to graft the first group, thereby obtaining intermediate B. Intermediate B is mixed with ethylene glycol at a molar ratio of 1:(1-1.2), and then reacted at 120℃-140℃ for 4-6 hours to modify the second group end group. After separation and drying, the modified lignin derivative is obtained.

5. The flame-retardant PET material according to claim 1, characterized in that, The preparation method of the functionalized boron nitride nanosheets includes the following steps: The hexagonal boron nitride was placed in a mixed liquid medium of anhydrous ethanol and water and ultrasonically exfoliated for 30 min to 60 min at a power of 400 W to 600 W to obtain a boron nitride nanosheet dispersion. The silane coupling agent is added to the boron nitride nanosheet dispersion, wherein the mass ratio of the silane coupling agent to the hexagonal boron nitride is 1:(0.08-0.15). The mixture is stirred and reacted at 50℃-60℃ for 2-3 hours. After centrifugation, washing, and drying, the functionalized boron nitride nanosheets are obtained.

6. The flame-retardant PET material according to claim 1, characterized in that, The lubricant includes at least one of calcium stearate, ethylene bis-stearamide, and montan ester wax; And / or, the antioxidant includes at least one of hindered phenolic antioxidants and phosphite antioxidants.

7. The method for preparing the flame-retardant PET material according to any one of claims 1-6, characterized in that, Includes the following steps: The PET resin, the modified lignin derivative, the functionalized boron nitride nanosheets, the lubricant, and the antioxidant are mixed to obtain mixture A; The mixture A is subjected to ultrasonic and microwave treatment to obtain mixture B; The mixture B is melt-blended and extruded, then granulated to obtain the flame-retardant PET material.

8. The method for preparing flame-retardant PET material according to claim 7, characterized in that, The parameters for the ultrasonic treatment are: power of 300W-600W and time of 10min-30min; the parameters for the microwave treatment are: power of 200W-400W, temperature of 80℃-120℃ and time of 5min-20min.

9. The method for preparing flame-retardant PET material according to claim 7, characterized in that, The temperature of the melt blending extrusion is 240℃-270℃.

10. The use of the flame-retardant PET material as described in any one of claims 1-6 in the preparation of plastic articles.

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