A MOF / COF synergistically modified cellulose biomass composite flame retardant as well as a preparation method and application thereof

Abstract

The application discloses a kind of MOF / COF synergic modification cellulose biomass composite flame retardant and its preparation method and application, it is related to biomass-based flame retardant technical field.A kind of MOF / COF synergic modification cellulose biomass composite flame retardant preparation method, including the following steps: after pretreatment, cellulose biomass is modified with functional group, and functional group cellulose biomass carrier is obtained;With the functional group cellulose biomass carrier as substrate, by sequential growth method or one-pot method, MOF and COF are simultaneously loaded on it, and the MOF / COF synergic modification cellulose biomass composite flame retardant is obtained.The flame retardant proposed in the application gives full play to the efficient catalytic charring capacity of MOF, the excellent adsorption and stability characteristics of COF and the carbon source and carrier effect of cellulose biomass, and realizes the multiple flame retardant mechanism synergy of "physical barrier-catalytic charring-adsorption smoke suppression".

Description

Technical Field

[0001] This invention relates to the field of biomass-based flame retardant technology, and in particular to a MOF / COF synergistic modified cellulose biomass composite flame retardant, its preparation method, and its application. Background Technology

[0002] Polymer materials, characterized by their lightweight, corrosion resistance, and high plasticity, are widely used in automotive, electronics, medical, and construction industries. However, most polymer materials are flammable, posing fire safety hazards, thus requiring the addition of flame retardants to improve their fire resistance. While halogenated flame retardants are highly effective, they release toxic fumes and corrosive gases during combustion, causing secondary pollution, and their use is increasingly restricted by regulations. Developing novel, efficient, environmentally friendly, low-smoke, and low-toxicity flame retardants has become a current research focus. Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) are two emerging classes of porous materials that exhibit great potential in catalytic char formation and gas-phase flame retardancy due to their high specific surface area, tunable pore size, and functionalization capabilities. However, nanoscale MOF / COF particles are prone to agglomeration, making uniform dispersion in polymer matrices difficult, and their high synthesis cost limits their widespread application.

[0003] Cellulose-rich biomass, especially agricultural wastes such as sugarcane bagasse, corn stalks, and rice husks, is produced in huge quantities annually, is inexpensive, readily available, and renewable. The core component of these materials is cellulose, which has a rigid linear chain and abundant hydroxyl groups, providing a robust framework and numerous surface-active sites. By pretreatment (such as alkali treatment) to remove some hemicellulose and lignin, cellulose can be further purified, exposing more hydroxyl groups and forming a hierarchical porous structure, making it an ideal carrier material. Simultaneously, cellulose itself is also a highly efficient carbon source. Currently, most of this type of biomass is discarded or incinerated for low value, resulting in resource waste. Existing technologies mostly focus on the combination of single MOFs or COFs with biomass, failing to fully utilize the synergistic effect of MOFs and COFs. How to combine the catalytic activity of MOFs with the stable adsorption function of COFs, and rely on the natural structure of cellulose-based biomass, to construct a synergistic and multifunctional flame retardant is a problem urgently needing to be solved in this field. Summary of the Invention

[0004] This invention solves the problems of low flame retardant efficiency, poor smoke suppression and easy agglomeration of nanomaterials in the prior art. It provides a MOF / COF synergistic modified cellulosic biomass composite flame retardant, its preparation method and application. Through the functional complementarity and spatial synergy of MOF and COF, this invention realizes a multiple flame retardant mechanism of "catalytic char formation-adsorption of free radicals-physical barrier", which significantly improves flame retardant efficiency and smoke suppression performance.

[0005] The first objective of this invention is to provide a method for preparing a MOF / COF synergistic modified cellulosic biomass composite flame retardant, comprising the following steps: functionalizing pretreated cellulosic biomass to obtain a functionalized cellulosic biomass carrier; using the functionalized cellulosic biomass carrier as a substrate, simultaneously loading MOF and COF onto it via a sequential growth method or a one-pot method to obtain the MOF / COF synergistic modified cellulosic biomass composite flame retardant; wherein, the sequential growth method involves first growing a COF layer and then growing a MOF layer; the one-pot method involves simultaneously growing MOF and COF.

[0006] Preferably, the mass ratio of MOF to COF is 0.5:1 to 10.0:1, and based on the mass of the functionalized cellulose biomass carrier, the loading of MOF and COF in the cellulose biomass composite flame retardant is 60% to 95%.

[0007] Further preferred, the mass ratio of MOF to COF is 1.3:1 to 5.0:1, and based on the mass of the functionalized cellulose biomass carrier, the loading of MOF and COF in the cellulose biomass composite flame retardant is 65% to 95%.

[0008] Preferably, the functional group modification is carboxylation modification or amination modification.

[0009] Further preferably, the carboxylation modification uses a citric acid-sodium hypophosphite system or a butanetetracarboxylic acid-sodium hypophosphite system as the modifier, with an acid concentration of 5-10 wt% and a sodium hypophosphite addition amount of 30%-50% of the acid mass. The carboxylation modification steps are as follows: pretreated cellulose biomass is added to the modifier at a solid-liquid ratio of 1:10-1:30 g / mL, soaked at 25℃-40℃ for 1-3 hours, and then reacted at 150℃-180℃ for 5-15 minutes.

[0010] Further preferably, the modifier used in the amination modification is a solution of 3-aminopropyltriethoxysilane or polyethyleneimine, and the concentration of 3-aminopropyltriethoxysilane or polyethyleneimine in the modifier is 1-5 vol%. The amination modification steps are as follows: the pretreated cellulose biomass is added to the modifier at a solid-liquid ratio of 1:15 to 1:30 g / mL, and reacted at 60℃ to 80℃ for 4 to 8 hours.

[0011] Preferably, the cellulosic biomass is selected from one of sugarcane bagasse, corn stalks, rice husks, and wheat straw.

[0012] The pretreatment process includes the following steps: after washing, drying and crushing the cellulosic biomass, it is then subjected to alkali treatment and oxidative bleaching treatment in sequence to remove some hemicellulose and lignin, and to purify and activate the cellulose fibers.

[0013] The particle size of the cellulosic biomass is 50-100 mesh; the alkaline treatment uses a sodium hydroxide solution with a mass concentration of 5%-10%, the treatment temperature is 70℃-90℃, and the treatment time is 4-8 hours; the oxidative bleaching treatment uses a sodium chlorite solution with a pH of 3.5-5.0, the treatment temperature is 70℃-80℃, and the treatment time is 2-6 hours.

[0014] Preferably, the sequential growth method specifically includes the following steps: mixing the functionalized cellulose biomass carrier with the COF synthesis monomer, reacting by a solvothermal method at a reaction temperature of 100℃~120℃ for 48~72 hours, growing a COF layer on the functionalized cellulose biomass carrier to obtain a cellulose biomass@COF intermediate; then mixing the cellulose biomass@COF intermediate with a MOF synthesis precursor, reacting by a room temperature method or a solvothermal method, and growing an MOF layer in situ on the COF intermediate.

[0015] Further optimization, the sequential growth method specifically includes the following steps:

[0016] (1) The functionalized cellulose biomass carrier was dispersed in a solution of COF synthetic monomers, and the COF layer was preferentially grown by solvothermal method. The reaction temperature was 100℃~120℃ and the reaction time was 48~72 hours to obtain cellulose biomass@COF intermediate;

[0017] (2) Disperse the cellulose biomass@COF intermediate obtained in step (1) in a solution of MOF synthesis precursor, and grow MOF in situ on the surface or gap of COF layer by room temperature method or solvothermal method to obtain the MOF / COF synergistic modified cellulose biomass composite flame retardant.

[0018] In step (1), the solvent is a mixed solution of mesitylene / dioxane or DMF / acetonitrile with a volume ratio of 1:1.

[0019] In step (2), the solvent is selected from one or more of methanol, N,N-dimethylformamide (DMF), acetonitrile, and deionized water. The MOF synthesis precursor includes metal salt and organic ligand. The cellulose biomass@COF intermediate is first dispersed in the metal salt solution at a solid-liquid ratio of 1:10 to 1:100 g / mL, and ultrasonically treated at room temperature for 20 to 60 minutes, followed by shaking and impregnation for 1 to 4 hours. After adding the organic ligand solution, the reaction is carried out at 30°C for 12 hours by room temperature method or at 120°C for 12 hours by solvothermal method to obtain the MOF / COF synergistic modified cellulose biomass composite flame retardant.

[0020] The metal salt solution is specifically a methanol solution of the metal salt, with a concentration of 0.01~0.02 g / mL, preferably 0.0146 g / mL.

[0021] The organic ligand solution is a methanol solution of the organic ligand, and the concentration of the organic ligand solution is 0.03~0.04 g / mL. The concentration of the metal salt solution is preferably 0.0328 g / mL.

[0022] Preferably, the one-pot method specifically includes the following steps: placing the functionalized cellulose biomass carrier, MOF synthesis precursor, and COF synthesis monomer together in the same reaction system, and carrying out a one-step solvothermal reaction. The solvent is a mixed solution of mesitylene / dioxane or DMF / acetonitrile with a volume ratio of 1:1. The reaction temperature is 90°C, and the reaction time is 48 hours, thereby achieving the co-growth of MOF and COF on the carrier.

[0023] Further preferably, the COF is an imine-linked COF, and its monomer is selected from one or more of terephthalaldehyde, pyromellitic trimethylaldehyde, pyromellitic triamine, and p-phenylenediamine.

[0024] Further preferably, the MOF synthesis precursor comprises a metal salt and an organic ligand, wherein the molar ratio of the metal salt to the organic ligand is 1:2 to 1:8; the metal salt is selected from one of zinc salt, cobalt salt, aluminum salt, iron salt, and zirconium salt; and the organic ligand is selected from one of imidazole compounds and carboxylic acid compounds.

[0025] The second objective of this invention is to provide a MOF / COF synergistic modified cellulosic biomass composite flame retardant obtained by the preparation method described above, wherein the mass ratio of MOF to COF is 0.5:1 to 10.0:1, and based on the mass of the functionalized cellulosic biomass carrier, the loading of MOF and COF in the cellulosic biomass composite flame retardant is 60% to 95%.

[0026] Preferably, the mass ratio of MOF to COF is 1.3:1 to 5.0:1, and based on the mass of the functionalized cellulose biomass carrier, the loading of MOF and COF in the cellulose biomass composite flame retardant is 65% to 95%.

[0027] A third objective of this invention is to provide the application of the aforementioned cellulosic biomass composite flame retardant in the preparation of flame-retardant polymer composite materials.

[0028] Preferably, the flame-retardant polymer composite material comprises a polymer material, the cellulosic biomass composite flame retardant, and additives. The polymer material includes epoxy resin, polyethylene, polypropylene, polyurethane foam, polylactic acid, and rubber. The additives include accelerators and curing agents, etc.

[0029] Further optimization involves using the total mass of the flame-retardant polymer composite material as the standard, with the amount of flame retardant added being 2-4 wt%.

[0030] Further optimization is made by adding 3 wt% of flame retardant, based on the total mass of the flame retardant polymer composite material.

[0031] Compared with existing technologies, this invention has the following advantages: For the first time, this invention simultaneously combines MOF and COF with cellulosic biomass, constructing a multi-level structure of "biomass carrier - COF functional layer - MOF catalytic site," achieving a synergistic flame-retardant effect. This composite flame retardant can significantly reduce the polymer's heat release rate, total heat release, and total smoke release even at low addition levels, while maintaining good mechanical properties. It fully utilizes agricultural waste, the process is relatively green, and the product is environmentally friendly. Attached Figure Description

[0032] Figure 1 These are the infrared spectra of pretreated sugarcane bagasse P-SCB, carboxylated sugarcane bagasse C-SCB, intermediate SCB@TpPa-1, and composite flame retardant SCB@COF@ZIF-67 in Example 1 of this invention.

[0033] Figure 2 This is the infrared spectrum of the pretreated sugarcane bagasse and composite flame retardant SCB@ZIF-8@COF-LZU1 in Example 3 of this invention. Detailed Implementation

[0034] The following embodiments are further illustrations of the present invention, but not limitations thereof.

[0035] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention. Unless otherwise specified, the experimental materials and reagents used herein are commercially available products conventionally available in this field.

[0036] Unless otherwise specified, the term "loading amount" in this invention refers to the percentage of the mass of the loaded material (COF or MOF) based on the initial mass of the functionalized biomass carrier (such as C-SCB). The "mass ratio of MOF to COF" refers to the ratio of the absolute masses of the two materials actually loaded in the final composite flame retardant.

[0037] Example 1

[0038] The sequential growth method was used to prepare the SCB@COF@ZIF-67 composite flame retardant, and the steps are as follows:

[0039] (1) Grind and sieve the bagasse to obtain a 100-mesh powder, and dry it at 105℃ for 8 hours. Take 50 g of dried bagasse, add 500 mL of 5% NaOH solution, and mechanically stir the mixture in an 80℃ water bath for 6 hours. After cooling, filter and wash with water until neutral. Disperse the alkali-treated bagasse in 500 mL of an aqueous solution with pH=4.5 (adjusted with glacial acetic acid), add 5 g of sodium chlorite, and stir the mixture at 75℃ for 4 hours. After the reaction is complete, filter and wash with deionized water until no chloride ions are detected. Place the obtained product in a vacuum drying oven at 60℃ and dry for 48 hours to obtain pretreated bagasse P-SCB.

[0040] (2) Dissolve 60 g of citric acid and 24 g of sodium hypophosphite in 600 mL of deionized water to prepare a modifier of 10 wt% CA + 4 wt% SHP. Weigh 20 g of P-SCB and add it to the above modifier, then soak it at 30°C for 2 hours. Filter the soaked mixture to obtain a wet material, place it in a forced-air drying oven, and react it at 170°C for 8 minutes. Wash the reacted sample repeatedly with hot deionized water at 80°C until neutral, and finally dry it in a vacuum oven at 70°C for 12 hours to obtain carboxylated bagasse C-SCB.

[0041] (3) Dissolve 84 mg of trimesin (Tp) in 10 mL of a mixed solvent of trimesin / dioxane (v / v=5:5) (solution A); dissolve 54 mg of p-phenylenediamine (Pa-1) in 10 mL of the above mixed solvent (solution B). Disperse 0.5 g of C-SCB in solution A and sonicate for 30 minutes. Then, quickly pour solution B into the above mixture and gently shake to mix evenly. Transfer the mixture to a 50 mL hydrothermal reactor lined with polytetrafluoroethylene, seal it, and place it in an oven at 120°C for 72 hours. After the reaction, collect the solid product by filtration, extract with anhydrous acetone using a Soxhlet extractor, wash continuously for 24 hours, and finally activate in a vacuum oven at 120°C for 6 hours to obtain the sugarcane bagasse@TpPa-1 intermediate SCB@TpPa-1.

[0042] (4) Dissolve 0.73 g of cobalt nitrate hexahydrate in 50 mL of methanol (solution I); dissolve 1.64 g of 2-methylimidazole in 50 mL of methanol (solution II). Weigh 0.5 g of intermediate SCB@TpPa-1 and add it to solution I. Sonicate at room temperature for 30 minutes, then soak in a shaker at 150 rpm for 2 hours. Under vigorous stirring, quickly pour solution II into the above mixture, stir continuously for 10 minutes, and then allow to stand at 30°C for 12 hours. After the reaction is complete, wash four times with methanol by centrifugation, and finally dry in a vacuum oven at 60°C for 12 hours to obtain the sugarcane bagasse@TpPa-1@ZIF-67 ternary composite flame retardant SCB@COF@MOF. The intermediate and the final product were characterized and calculated by thermogravimetric analysis. The COF loading in the SCB@TpPa-1 intermediate obtained in this example is about 15% (based on the mass of C-SCB). Based on this, ZIF-67 was further grown, resulting in the final SCB@COF@MOF ternary composite flame retardant. In this flame retardant, the mass ratio of MOF to COF was approximately 5:1, and the total loading of MOF and COF was approximately 90% (based on the mass of C-SCB). Infrared spectroscopy was performed on pretreated bagasse P-SCB, carboxylated bagasse C-SCB, intermediate SCB@TpPa-1, and the composite flame retardant SCB@COF@ZIF-67. Figure 1 As can be seen in the C-SCB spectrum of carboxylated bagasse, at ~3500 cm⁻¹ -1 The left and right sides are cellulose OH and carboxylic acid OH, ~1730 cm -1 The left and right sides represent the C=O stretching vibrations of carboxylic acids or esters. In the spectrum of the intermediate SCB@TpPa-1, ~1620 cm⁻¹ -1 An absorption peak appeared, which is the characteristic stretching vibration peak of the C=N bond formed in the imine condensation reaction, ~1730 cm⁻¹. -1The C=O characteristic peak at this point is significantly weakened, indicating that the carboxyl group may have participated in interfacial interactions or undergone a reaction during the synthesis of COF. In the spectrum of the composite flame retardant SCB@COF@ZIF-67, the peak at ~1140 cm⁻¹ is significantly weakened. -1 ~990 cm -1 and ~750 cm -1 A series of characteristic absorption peaks belonging to the 2-methylimidazole ligand in ZIF-67 appeared in various locations.

[0043] Comparative Example 1

[0044] Same as Example 1, except that only SCB@TpPa-1 was synthesized and the MOF layer was not further grown.

[0045] Comparative Example 2

[0046] The SCB@ZIF-67 composite flame retardant was synthesized in the same way as in Example 1, except that carboxylated sugarcane bagasse C-SCB was used directly as a carrier to grow the MOF layer in step (4), without pre-growing the COF layer.

[0047] Example 2

[0048] The SCB@TpBD@ZIF-8 composite flame retardant was prepared by sequential growth method, the same as in Example 1, except that in step (2), 20 g of P-SCB was added to 600 mL of 3 vol% APTES / ethanol solution and reacted at 70°C for 6 hours. Afterwards, it was washed with ethanol and dried to obtain aminated sugarcane bagasse N-SCB. Using N-SCB as a carrier, a COF layer TpBD was grown according to the method in Example 1. Then, using the SCB@TpBD intermediate as a carrier, zinc nitrate hexahydrate as the metal salt, and 2-methylimidazole as the ligand, ZIF-8 was grown according to the room temperature method in Example 1. The mass ratio of MOF to COF was 3.8:1, resulting in the SCB@TpBD@ZIF-8 composite flame retardant. Thermogravimetric analysis showed that, based on the mass of the sugarcane bagasse carrier, the total loading of MOF and COF in the composite flame retardant obtained in this example was approximately 95%.

[0049] Example 3

[0050] The one-pot method for preparing SCB@ZIF-8@COF-LZU1 composite flame retardant comprises the following steps:

[0051] 1.0 g of pretreated sugarcane bagasse (pretreatment steps as in Example 1), 0.5 g of zinc nitrate hexahydrate, 1.0 g of 2-methylimidazole, 0.2 g of trimesaldehyde, and 0.15 g of p-phenylenediamine were dispersed in a DMF / acetonitrile (v / v=5:5) mixed solvent. The mixture was transferred to a reaction vessel and reacted at 90°C for 48 hours. After cooling, the mixture was washed sequentially with DMF and ethanol, and dried to obtain the SCB@ZIF-8@COF-LZU1 composite flame retardant. The mass ratio of MOF to COF was approximately 1.3:1. Based on the mass of the sugarcane bagasse carrier, the total loading of MOF and COF in the composite flame retardant obtained in this example was approximately 65% ​​by thermogravimetric analysis.

[0052] Infrared spectroscopy was performed on pretreated bagasse and SCB@ZIF-8@COF-LZU1 composite flame retardant. Figure 2 As can be seen, at ~1620 cm -1 The sharp absorption peak at ~1100 cm⁻¹ corresponds to the stretching vibration of the imine bond (C=N) in COF-LZU1. -1 and ~990 cm -1 The two characteristic absorption peaks appearing at ~740 cm⁻¹ belong to the CN stretching vibration of the imidazole ring in ZIF-8. -1 The sharp, strong peak that appears is due to the out-of-plane bending vibration of the ZIF-8 imidazole ring.

[0053] Example 4

[0054] The one-pot preparation method for SCB@ZIF-67@TpPa-1 composite flame retardant is as follows:

[0055] 0.5 g of carboxylated bagasse (pretreatment and carboxylation modification steps are the same as in Example 1) was weighed and dispersed together with 0.73 g of cobalt nitrate hexahydrate, 1.64 g of 2-methylimidazole, 84 mg of trimesaldehyde, and 54 mg of p-phenylenediamine in a 20 mL mixed solvent of trimesyl / dioxane (v / v=1:1). The mixture was sonicated for 30 minutes to ensure thorough dispersion, and then transferred to a 50 mL hydrothermal reactor lined with polytetrafluoroethylene. After sealing, the reactor was placed in a 90 °C oven for 48 hours. Post-treatment: After the reaction, the mixture was allowed to cool naturally to room temperature, and the solid product was collected by filtration. The product was washed repeatedly with methanol and acetone several times to thoroughly remove unreacted monomers, precursors, and solvents. Finally, the product was dried in a 60 °C vacuum oven for 12 hours to obtain the bagasse@ZIF-67@TpPa-1 composite flame retardant, denoted as SCB@MOF@COF (one-pot method). The mass ratio of MOF to COF is approximately 4:1. Based on thermogravimetric analysis and the mass of bagasse carrier, the total loading of MOF and COF in the composite flame retardant obtained in this embodiment is approximately 85%.

[0056] Example 5

[0057] Similar to Example 1, except that the carboxylation conditions in step (2) are 150°C for 5 minutes. Based on thermogravimetric analysis and the mass of the bagasse carrier, the total loading of MOF and COF in the composite flame retardant obtained in this example is approximately 82%.

[0058] Example 6

[0059] Similar to Example 1, except that the growth time of the COF layer TpPa-1 in step (3) is 48 hours and the growth temperature is 100℃. According to thermogravimetric analysis, based on the mass of the bagasse carrier, the total loading of MOF and COF in the composite flame retardant obtained in this example is about 68%.

[0060] Example 7

[0061] Similar to Example 1, except that in step (4), when growing ZIF-67, a solvothermal method was used, and the reaction system was placed in a 100 mL hydrothermal reactor and reacted at 120°C for 12 hours. According to thermogravimetric analysis, based on the mass of the bagasse carrier, the total loading of MOF and COF in the composite flame retardant obtained in this example is approximately 91%.

[0062] Example 8

[0063] Similar to Example 1, except that the carrier was replaced with corn stalks instead of bagasse. Based on thermogravimetric analysis and the mass of the corn stalk carrier, the total loading of MOF and COF in the composite flame retardant obtained in this example was approximately 77%.

[0064] Example 9

[0065] Similar to Example 3, except that the carrier was replaced with rice husk instead of bagasse. Based on thermogravimetric analysis and the mass of the rice husk carrier, the total loading of MOF and COF in the composite flame retardant obtained in this example was approximately 83%.

[0066] Example 10

[0067] Same as Example 1, except that:

[0068] (1) The sugarcane bagasse has a particle size of 50 mesh; the alkali treatment uses a 5% sodium hydroxide solution with a mass concentration of 5%, the treatment temperature is 70℃, and the treatment time is 8 hours; the oxidative bleaching treatment uses a sodium chlorite solution with a pH of 3.5, a treatment temperature of 70℃, and a treatment time of 6 hours.

[0069] (2) The modifier is a citric acid-sodium hypophosphite system. The concentration of acid in the modifier is 10 wt%, and the amount of sodium hypophosphite added is 50% of the acid mass. The modification steps are as follows: the pretreated sugarcane bagasse is added to the modifier at a solid-liquid ratio of 1:10 g / mL, soaked at 25℃ for 3 hours, and then reacted at 150℃ for 15 minutes.

[0070] (3) Same as step (3) in Example 1.

[0071] (4) The carboxylated bagasse@COF intermediate was first dispersed in a cobalt nitrate solution at a solid-liquid ratio of 1:10 g / mL, and the concentration of the cobalt nitrate solution was 0.01 g / mL. The mixture was ultrasonically treated at room temperature for 60 minutes, followed by shaking and impregnation for 4 hours. After adding 2-methylimidazole solution, the molar ratio of cobalt nitrate to 2-methylimidazole was 1:2. After stirring continuously for 10 minutes, the mixture was allowed to stand at 30°C for 12 hours. The mass ratio of MOF to COF was 1:0.5, and a MOF / COF synergistic modified bagasse flame retardant was obtained. Based on the mass of the bagasse carrier, the loading of MOF and COF in the composite flame retardant was 68%.

[0072] Example 11

[0073] Same as Example 1, except that:

[0074] (1) The sugarcane bagasse has a particle size of 100 mesh; the alkali treatment uses a 10% sodium hydroxide solution with a mass concentration of 10%, the treatment temperature is 90℃, and the treatment time is 4 hours; the oxidative bleaching treatment uses a sodium chlorite solution with a pH of 5.0, a treatment temperature of 80℃, and a treatment time of 2 hours.

[0075] (2) The modifier is a butanetetracarboxylic acid-sodium hypophosphite system. The concentration of acid in the modifier is 5 wt%, and the amount of sodium hypophosphite added is 30% of the acid mass. The carboxylation modification steps are as follows: the pretreated sugarcane bagasse is added to the modifier at a solid-liquid ratio of 1:30 g / mL, soaked at 40℃ for 1 hour, and then reacted at 180℃ for 5 minutes.

[0076] (3) Same as step (3) in Example 1.

[0077] (4) The modified sugarcane bagasse@COF intermediate was first dispersed in a cobalt nitrate solution at a solid-liquid ratio of 1:100 g / mL. The concentration of the cobalt nitrate solution was 0.02 g / mL. The mixture was ultrasonically treated at room temperature for 20 minutes, followed by shaking and impregnation for 1 hour. After adding 2-methylimidazole solution, the molar ratio of cobalt nitrate to 2-methylimidazole was 1:8. After stirring for 10 minutes, the mixture was allowed to stand at 30°C for 12 hours. The mass ratio of MOF to COF was 1:2. The MOF / COF synergistic modified sugarcane bagasse composite flame retardant was obtained. Based on the mass of the sugarcane bagasse carrier, the loading of MOF and COF in the composite flame retardant was 85%.

[0078] Application Example 1

[0079] The flame retardants prepared in Examples 1-4, 7, 8 and Comparative Examples 1-2 were compared with pure EP (epoxy resin E-51): 3 wt% of the composite flame retardant was mixed with epoxy resin E-51, and after ultrasonic dispersion and vacuum degassing, 80 wt% of curing agent methyltetrahydrophthalic anhydride and 0.8 wt% accelerator 2-ethyl-4-methylimidazolium were added. After mixing and degassing again, the mixture was poured into a mold and cured in a stepwise manner according to the program of 80℃ / 2 h + 120℃ / 2 h + 150℃ / 4 h. After demolding, composite material samples were obtained.

[0080] Table 1: Results of cone calorimeter test (50 kW / m²)

[0081] .

[0082] The test results above show that, compared with Comparative Examples 1 and 2, the cellulosic biomass composite flame retardant obtained in Example 1 has the best product performance. The two exhibit functional complementarity and spatial synergy in the "COF adsorption / barrier-MOF catalytic char formation" mechanism. Specifically, the porous structure of COF can adsorb molten polymers and capture gaseous free radicals, while providing a well-dispersed growth substrate for MOF; MOF, on the other hand, strongly catalyzes the formation of a denser and more stable graphitized carbon layer on the polymer and biomass carrier in the condensed phase. The MOF / COF synergistically modified cellulosic biomass composite flame retardant prepared in this invention possesses excellent flame retardant properties and smoke suppression effects.

[0083] The above description of the embodiments is only for the purpose of helping to understand the technical solution and core idea of ​​the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a MOF / COF synergistically modified cellulosic biomass composite flame retardant, characterized in that, The process includes the following steps: functionalizing pretreated cellulosic biomass to obtain a functionalized cellulosic biomass carrier; using the functionalized cellulosic biomass carrier as a substrate, simultaneously loading MOF and COF onto it via a sequential growth method or a one-pot method to obtain the MOF / COF synergistically modified cellulosic biomass composite flame retardant; wherein, the sequential growth method involves first growing a COF layer and then growing a MOF layer; the one-pot method involves simultaneously growing MOF and COF; the functionalization modification is carboxylation modification or amination modification; the COF is an imine-linked COF, and its synthetic monomers are trimesaldehyde and p-phenylenediamine; the MOF synthesis precursor includes a metal salt and an organic ligand, with a molar ratio of metal salt to organic ligand of 1:2 to 1:8; the metal salt is selected from zinc salt, cobalt salt, aluminum salt, iron salt, and zirconium salt; the organic ligand is dimethylimidazole.

2. The preparation method according to claim 1, characterized in that, The cellulose biomass is selected from one of sugarcane bagasse, corn stalks, rice husks, and wheat straw.

3. The preparation method according to claim 1, characterized in that, The sequential growth method specifically includes the following steps: mixing the functionalized cellulose biomass carrier with COF synthesis monomers, reacting via a solvothermal method at a reaction temperature of 100℃~120℃ for 48~72 hours, growing a COF layer on the functionalized cellulose biomass carrier to obtain a cellulose biomass@COF intermediate; then mixing the cellulose biomass@COF intermediate with a MOF synthesis precursor, reacting via a room temperature method or a solvothermal method, and growing an MOF layer in situ on the COF intermediate.

4. The preparation method according to claim 3, characterized in that, The specific conditions for the room temperature method or solvothermal method of growing MOF layers are as follows: for the room temperature method, the reaction is carried out at 30°C for 12 hours, and for the solvothermal method, the reaction is carried out at 120°C for 12 hours.

5. The preparation method according to claim 1, characterized in that, The one-pot method specifically includes the following steps: the functionalized cellulose biomass carrier, MOF synthesis precursor, and COF synthesis monomer are placed together in the same reaction system, and a one-step solvothermal reaction is carried out at a reaction temperature of 90°C and a reaction time of 48 hours, so that MOF and COF can co-grow on the carrier at the same time.

6. The MOF / COF synergistically modified cellulosic biomass composite flame retardant obtained by the preparation method according to claim 1, characterized in that, The mass ratio of MOF to COF is 0.5:1 to 10.0:

1. Based on the mass of the functionalized cellulose biomass carrier, the loading of MOF and COF in the cellulose biomass composite flame retardant is 60% to 95%.

7. The application of the cellulosic biomass composite flame retardant according to claim 6 in the preparation of flame-retardant polymer composite materials.

Images