A coated microcrystalline cellulose and a preparation method thereof, a biodegradable flame-retardant composite material and a preparation method and application thereof

Abstract

This invention belongs to the field of flame retardant materials technology, specifically relating to a coated microcrystalline cellulose and its preparation method, a biodegradable flame retardant composite material and its preparation method and application. The invention aims to combine the advantages of degradability, reinforcement, toughening, and flame retardancy in coated microcrystalline cellulose through structural design and adjustment. When used as a flame retardant, it improves the compatibility and dispersibility between the matrix and the flame retardant. Simultaneously, by selecting an organic flame retardant with high flame retardant efficiency and good compatibility with the matrix, and utilizing the interaction and individual advantages of these three components, the interfacial compatibility of each component can be improved, forming a flame-retardant biodegradable PBAT composite material with excellent flame retardancy, high tensile strength, high thermal stability, and maintained high toughness.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant materials technology, specifically relating to a coated microcrystalline cellulose and its preparation method, a biodegradable flame retardant composite material and its preparation method and application. Background Technology

[0002] Polybutylene terephthalate (PBAT) is a biodegradable synthetic material. Due to its excellent flexibility, processability, and biodegradability, PBAT has become an ideal alternative to petroleum-based plastics, enabling its application in other biodegradable polymer fields such as the food industry, pharmaceuticals, agricultural films, electronic components, and industrial equipment parts, making it a current research hotspot.

[0003] Although PBAT resin has garnered significant attention in the field of environmentally friendly materials due to its biodegradability, its limitations in flame-retardant applications cannot be ignored. Firstly, PBAT's molecular structure is primarily aliphatic-aromatic copolyester, with high hydrocarbon content and a lack of flame-retardant groups, resulting in extremely poor inherent flame retardancy. It is a flammable material, readily igniting rapidly under ignition and accompanied by dripping, exacerbating the spread of fire. Secondly, while traditional halogenated or phosphorus-based flame retardants can improve its flame-retardant properties, they have poor compatibility with PBAT, easily migrating and precipitating out, which not only reduces the material's mechanical properties but may also impair its biodegradability. Furthermore, existing bio-based flame-retardant systems (such as starch derivatives or phytic acid modifiers) struggle to form a continuous char layer in PBAT, failing to effectively isolate heat and oxygen during combustion. These shortcomings limit the application of PBAT in fields requiring high flame-retardant standards, such as electronics, electrical appliances, and building insulation, necessitating the development of novel modification technologies that balance flame retardancy, mechanical properties, and degradation characteristics.

[0004] Moreover, the current flame retardant-modified PBAT resin still has significant drawbacks: (1) traditional flame retardants have poor compatibility with PBAT, are prone to migration and precipitation, affecting mechanical properties and degradability; (2) inorganic flame retardants require high addition amounts (>30%) to be effective, but will seriously deteriorate processing fluidity and toughness; (3) bio-based flame retardants have low flame retardant efficiency; (4) PBAT resin has decreased thermal stability, decomposes at high temperatures leading to poor performance, and has poor melt flowability. These problems limit the application of PBAT composite materials in a wide range of fields. Summary of the Invention

[0005] The purpose of this invention is to provide a coated microcrystalline cellulose and its preparation method, a biodegradable flame-retardant composite material and its preparation method and application.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a coated microcrystalline cellulose, comprising a core layer and a coating layer; The core layer is microcrystalline cellulose; The coating layer is made of phytic acid-modified MOF material; A chemical bond is formed between the core layer and the coating layer.

[0007] Preferably, the mass ratio of the core layer to the covering layer is 0.5 to 5:1; The mass ratio of phytic acid to MOF material in the phytic acid-modified MOF material is 1~10:1; The MOF material includes ZIF-8, ZIF-67, UiO-66, UiO-67 or MIL-101.

[0008] This invention also provides a method for preparing the coated microcrystalline cellulose described in the above technical solution, comprising the following steps: Under stirring conditions, an aqueous phytic acid solution was added dropwise to a dispersion containing MOF materials to carry out the reaction, thereby obtaining phytic acid-modified MOF materials. Microcrystalline cellulose, a crosslinking agent, and a dispersion of phytic acid-modified MOF material are mixed and coated to obtain the coated microcrystalline cellulose.

[0009] Preferably, the mass ratio of phytic acid in the phytic acid aqueous solution to MOF material in the MOF material dispersion is 1~10:1; The reaction is carried out at a temperature of 10~50℃, under stirring conditions, and the stirring time is 3~8h.

[0010] Preferably, the mass ratio of the microcrystalline cellulose to the phytic acid-modified MOF material is 0.3~3:1; The mass ratio of the microcrystalline cellulose to the crosslinking agent is 0.1~2:1; The coating temperature is 10~50℃, the coating is carried out under stirring conditions, and the coating time is 5~24h.

[0011] The present invention also provides a biodegradable flame-retardant composite material, comprising polybutylene terephthalate and a flame retardant; The flame retardant includes phosphorus-containing flame retardants and auxiliary flame retardants; The auxiliary flame retardant is the coated microcrystalline cellulose described in the above technical solution or the coated microcrystalline cellulose prepared by the preparation method described in the above technical solution.

[0012] Preferably, by mass parts, the biodegradable flame-retardant composite material comprises 73-84 parts of polybutylene terephthalate-adipate, 15-20 parts of phosphorus-containing flame retardant, and 1-7 parts of auxiliary flame retardant.

[0013] Preferably, the phosphorus-containing flame retardant comprises phenylethyl bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

[0014] This invention also provides a method for preparing the biodegradable flame-retardant composite material described in the above technical solution, comprising the following steps: The biodegradable flame-retardant composite material is obtained by melting polybutylene terephthalate (PET) and a flame retardant.

[0015] The present invention also provides the application of the biodegradable flame-retardant composite material described in the above technical solution or the biodegradable flame-retardant composite material prepared by the preparation method described in the above technical solution in food, medicine, agricultural mulch film, electronic and electrical components and industrial equipment parts.

[0016] This invention provides a coated microcrystalline cellulose, comprising a core layer and a coating layer; the core layer is microcrystalline cellulose; the coating layer is made of phytic acid-modified MOF material; and a bond is formed between the core layer and the coating layer.

[0017] This invention aims to combine the advantages of biodegradability and flame retardancy by designing and adjusting the structure of coated microcrystalline cellulose. When used as a flame retardant, it improves the compatibility and dispersibility between the matrix and the flame retardant. At the same time, it selects organic flame retardants with high flame retardant efficiency and good compatibility with the matrix. By utilizing the interaction and advantages of the three, the interfacial compatibility of each component can be improved, forming a flame-retardant biodegradable PBAT composite material with excellent flame retardancy, high tensile strength, high thermal stability, and high toughness.

[0018] The mechanism of action of phytic acid / MOF-coated microcrystalline cellulose-modified PBAT composites can be explained from the following aspects: 1. Mechanism for improving flame retardant performance: Catalytic char formation and enhanced condensed phase: Phytic acid, as a phosphorus-rich acid source, decomposes at high temperatures to produce polyphosphoric acid, which can further catalyze the dehydration of cellulose and PBAT into char. Metal ions in MOF catalyze the cross-linking reaction of PBAT molecular chains, promoting the formation of a dense char layer. At the same time, cellulose, as the char-forming framework, together with MOF-derived metal oxides, constructs a dense char layer with a "reinforced concrete" structure, effectively isolating oxygen and heat.

[0019] Free radical capture and smoke suppression: Phytic acid releases phosphorus-containing free radicals during combustion and decomposition, which can capture active free radicals (such as ·OH, H·) generated during the combustion of the matrix. Furthermore, the transition metal elements in MOF can also capture free radicals at high temperatures, thus interrupting the chain combustion reaction.

[0020] Synergistic effect: The synergistic flame retardant effect of phytic acid and MOF can reduce the dripping phenomenon of the matrix and inhibit the release of toxic fumes.

[0021] 2. Mechanism for improving tensile strength: Chemical bonding network and physical crosslinking: Utilizing the abundant hydroxyl groups on the surface of microcrystalline fibers, chemical bonds are formed by the reaction of crosslinking agents with active sites or phosphate groups on phytic acid-modified MOFs, firmly connecting different components. This coating layer, acting as a "transition layer," has a modulus between that of rigid MOFs and flexible PBATs, effectively transferring external forces from the matrix to the interior of rigid particles, thus avoiding stress concentration.

[0022] Size effect: In-situ growth of MOFs on the cellulose surface typically forms a stable, rough structure, increasing the specific surface area. This enhances the physical anchoring and mechanical interlocking between the filler and the PBAT matrix. When the material is subjected to tensile forces, the rigid particles impede the slippage of molecular chains, thereby maintaining or improving the resistance to deformation.

[0023] 3. Toughening effect: Stress relief of rigid particles: Upon impact, the interface between rigid MOF particles and the PBAT matrix debonds, forming localized micro-voids. These voids can absorb a large amount of fracture energy and allow the matrix to undergo plastic deformation (shear yielding), thereby preventing rapid crack propagation and improving impact strength. In addition, the phytic acid / MOF coating layer, as a "transition layer," can effectively alleviate application concentration, prevent crack propagation, and achieve a toughening effect.

[0024] 4. Biodegradable retention function: The design principle of the fully bio-based material: Phytic acid and microcrystalline cellulose are both natural products. In soil or compost environments, water molecules can still freely permeate to the surface of the PBAT molecular chain, which is key to maintaining biodegradability.

[0025] Microbial affinity: Cellulose and phytic acid are carbon and nutrient sources that microorganisms prefer. The phytic acid / MOF layer coating the surface may become a "hotspot" for microbial colonization, accelerating the erosion of the material surface and exposing the internal PBAT ester bonds, thus ensuring that the degradation rate is not significantly reduced by the addition of "filler".

[0026] In summary, the phytic acid / MOF material-coated microcrystalline cellulose structure of this invention adopts the principle of "multi-scale structural design". Multi-level interface design: cellulose provides shape support as a rigid framework; phytic acid acts as a coupling agent to connect hydrophilic cellulose and hydrophobic PBAT or metal ions; MOF provides functionality and rigidity as nanoparticles.

[0027] Performance synergy mechanism: The rigidity of MOF increases the modulus, and phytic acid improves compatibility and flame retardancy. The two work together to avoid the common defect of inorganic fillers being "both rigid and brittle", achieving a balance between rigidity and toughness.

[0028] The unity of function and green environmental protection: halogen-free flame retardancy is achieved by utilizing the phosphorus element of phytic acid and the metal catalysis of MOF, while retaining the carbon-based advantages of bio-based materials. The degraded carbon structure (cellulose) and phytic acid can be converted into soil nutrients.

[0029] The microcrystalline cellulose hybrid particles (i.e. coated microcrystalline cellulose) and composite materials described in this invention have the characteristics of low cost, simple preparation process, biodegradability, and green environmental protection, which can expand their application to other biodegradable polymer fields such as food industry, pharmaceutical industry, agricultural mulch film, electronic and electrical components, and industrial equipment parts. Attached Figure Description

[0030] Figure 1 The infrared spectrum of the coated microcrystalline cellulose obtained in Example 1; Figure 2 Here is a SEM image of the coated microcrystalline cellulose obtained in Example 1; Figure 3 XPS image of the coated microcrystalline cellulose obtained in Example 1; Figure 4 This is an element mapping graph for pure MCC; Figure 5 This is an elemental mapping diagram of the coated microcrystalline cellulose obtained in Example 1. Detailed Implementation

[0031] This invention provides a coated microcrystalline cellulose, comprising a core layer and a coating layer; The core layer is microcrystalline cellulose; The coating layer is made of phytic acid-modified MOF material; A chemical bond is formed between the core layer and the coating layer.

[0032] In this invention, the preferred mass ratio of the core layer to the coating layer is 0.5 to 5:1, specifically 0.5:1, 1:1, 2:1, 3:1, 4:1, or 5:1; the preferred mass ratio of phytic acid to MOF material in the phytic acid-modified MOF material is 1 to 10:1, specifically 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1; the preferred MOF material includes ZIF-8, ZIF-67, UiO-66, UiO-67, or MIL-101.

[0033] This invention also provides a method for preparing the coated microcrystalline cellulose described in the above technical solution, comprising the following steps: Under stirring conditions, an aqueous phytic acid solution was added dropwise to a dispersion containing MOF materials to carry out the reaction, thereby obtaining phytic acid-modified MOF materials. Microcrystalline cellulose, a crosslinking agent, and a dispersion of phytic acid-modified MOF material are mixed and coated to obtain the coated microcrystalline cellulose.

[0034] In this invention, under stirring conditions, an aqueous solution of phytic acid is added dropwise to a dispersion containing MOF materials to carry out a reaction, thereby obtaining phytic acid-modified MOF materials.

[0035] In this invention, the mass ratio of phytic acid in the phytic acid aqueous solution to MOF material in the MOF material dispersion is preferably 1 to 10:1, specifically 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1.

[0036] In this invention, the preferred method for preparing the dispersion containing MOF material includes: dispersing the MOF material in deionized water and then sonicating it; the preferred ratio of MOF material to water is 1g:50mL; and the preferred sonication time is 30min.

[0037] In this invention, the MOF material is preferably obtained through preparation. The preparation method preferably includes: dissolving a metal salt and a ligand separately in methanol to obtain a metal salt solution and a ligand solution; mixing the metal salt solution and the ligand solution and reacting them to obtain the MOF material; the metal salt preferably includes zinc nitrate, cobalt acetate, zirconium chloride, or chromium nitrate; the ligand preferably includes 2-methylimidazole, terephthalic acid, or 4,4'-biphenyldicarboxylic acid; the molar ratio of the metal salt to the ligand is preferably 0.2~1:1; the reaction temperature is preferably 30°C; the reaction is preferably carried out under stirring conditions, and the stirring time is preferably 4 hours; after the reaction, it is also preferable to centrifuge and wash the obtained product with methanol, and then dry and grind it; there is no particular limitation on the number of centrifugation and washing cycles until the washing solution is neutral; the drying temperature is preferably 80°C, and the drying time is preferably 10~12 hours.

[0038] In this invention, the preferred method for preparing the phytic acid aqueous solution includes: diluting phytic acid with a mass concentration of 70% with water; the preferred ratio of phytic acid to water is 5g:10mL.

[0039] In this invention, the dropping rate is preferably 0.5~2 mL / min, specifically 0.5 mL / min, 1 mL / min, 1.5 mL / min, or 2 mL / min. In this invention, the reaction temperature is preferably 10~50℃, specifically 10℃, 20℃, 30℃, 40℃, or 50℃; the reaction is preferably carried out under stirring conditions, and the stirring time is preferably 3~8 h, specifically 3 h, 4 h, 5 h, 6 h, 7 h, or 8 h.

[0040] In this invention, after the reaction, it is preferable to further include extracting the obtained system multiple times with methanol and collecting the upper suspension; after separating the obtained suspension, the precipitate is washed with methanol by centrifugation until neutral, and then dried and ground; the drying temperature is preferably 80°C and the drying time is preferably 10~12h.

[0041] After obtaining the phytic acid-modified MOF material, the present invention mixes microcrystalline cellulose, crosslinking agent and dispersion of phytic acid-modified MOF material, and then coats the mixture to obtain the coated microcrystalline cellulose.

[0042] In this invention, the crosslinking agent preferably includes at least one of formaldehyde, glutaraldehyde, citric acid, epichlorohydrin, and isocyanate. In this invention, the abundant hydroxyl groups on the surface of the microcrystalline fiber are utilized to react with the active sites or phosphate groups on the phytic acid-modified MOF through the crosslinking agent, forming chemical bonds that firmly connect the different components.

[0043] In this invention, the mass ratio of microcrystalline cellulose to phytic acid-modified MOF material is preferably 0.3 to 3:1, specifically 0.3:1, 0.5:1, 1.0:1, 1.5:1, 2.0:1, 2.5:1, or 3:1; the mass ratio of microcrystalline cellulose to crosslinking agent is preferably 0.1 to 2:1, specifically 0.1:1, 0.3:1, 0.5:1, 1.0:1, 1.5:1, or 2.0:1.

[0044] In this invention, the preferred method for preparing the phytic acid-modified MOF material dispersion includes: dispersing the phytic acid-modified MOF material in methanol and then ultrasonicating it; the preferred ratio of the phytic acid-modified MOF material to methanol is 1 g: 60 mL; the preferred ultrasonication time is 30 min; the preferred mixing process includes: adding microcrystalline cellulose and formaldehyde to the phytic acid-modified MOF material dispersion, respectively. In this invention, the preferred coating temperature is 10~50℃, specifically 10℃, 20℃, 30℃, 40℃, or 50℃; the coating is preferably carried out under stirring conditions; and the preferred coating time is 5~24 h, specifically 5 h, 6 h, 12 h, 18 h, or 24 h.

[0045] In this invention, after coating, it is preferable to wash and filter the obtained product three times with a mixed solution of methanol and deionized water, then wash and filter it three times with deionized water until neutral; then dry it at 80°C for 10-12 hours and grind it.

[0046] The present invention also provides a biodegradable flame-retardant composite material, comprising polybutylene terephthalate (PBAT resin) and a flame retardant; The flame retardant includes phosphorus-containing flame retardants and auxiliary flame retardants; The auxiliary flame retardant is the biodegradable flame retardant described in the above technical solution or the coated microcrystalline cellulose prepared by the preparation method described in the above technical solution.

[0047] In this invention, the phosphorus-containing flame retardant preferably comprises phenylethyl bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DIDOPO). This invention selects the above-mentioned phosphorus-containing flame retardant because, based on the molecular structural characteristics of the phosphaphenanthrene group, it exhibits highly efficient flame retardant effects and excellent thermal stability. These compounds typically possess high thermal stability, effectively inhibiting combustion reactions, quenching flames, and diluting combustion gases, resulting in high flame retardant efficiency.

[0048] In this invention, the biodegradable flame-retardant composite material comprises, by weight parts, 73-84 parts of polybutylene terephthalate (PET), specifically 73, 75, 78, 80, 82, or 84 parts; 15-20 parts of phosphorus-containing flame retardant, specifically 15, 16, 17, 18, 19, or 20 parts; and 1-7 parts of auxiliary flame retardant, specifically 1, 2, 3, 4, 5, 6, or 7 parts.

[0049] This invention also provides a method for preparing the biodegradable flame-retardant composite material described in the above technical solution, comprising the following steps: The biodegradable flame-retardant composite material is obtained by melting polybutylene terephthalate (PET) and a flame retardant.

[0050] In this invention, the process prior to melting preferably includes drying and mixing the raw materials. The preferred drying method is to place the raw materials in a vacuum drying oven and store and dry them at 75-100°C for 10-20 hours. This invention does not impose any particular limitation on the mixing method, as long as the raw materials are mixed uniformly.

[0051] In this invention, the melting is preferably performed using a torque rheometer, and the preferred melting conditions include: a temperature of 170~210℃, specifically 170℃, 180℃, 190℃, 200℃, and 210℃; a rotational speed of 50~200 rpm, specifically 50 rpm, 100 rpm, 150 rpm, and 200 rpm; and a melting time of 5~15 min, specifically 5 min, 10 min, and 15 min. In this invention, after melting, the process preferably includes cooling, crushing, and drying; the drying temperature is preferably 100℃, and the drying time is preferably 5~10 hours.

[0052] In this invention, when performing performance testing on the biodegradable flame-retardant composite material, a vulcanization process is preferably included. In this invention, the vulcanization temperature is preferably 200~240℃, specifically 200℃, 210℃, 220℃, 230℃, or 240℃; the vulcanization is preferably carried out in a flat vulcanizing machine.

[0053] The present invention also provides the application of the biodegradable flame-retardant composite material described in the above technical solution or the biodegradable flame-retardant composite material prepared by the preparation method described in the above technical solution in food, medicine, agricultural mulch film, electronic and electrical components and industrial equipment parts.

[0054] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0055] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0056] Example 1 Preparation of ZIF-8: Weigh 2.88g of zinc nitrate and 3.98g of 2-methylimidazole and dissolve them in 30mL of methanol solution respectively. Then quickly mix the two solutions and stir magnetically at 30℃ for 4h. Wash the product with methanol solution and centrifuge 3 times until neutral. Dry it in an oven at 80℃ for 10h, grind it, and pack the powder into bags for later use. Phytic acid-modified ZIF-8: 1.0 g of the ZIF-8 powder obtained above was placed in a beaker, and 50 mL of deionized water was added. The mixture was ultrasonically dispersed for 30 min. 5.0 g of a 70% phytic acid (PA) solution was weighed and diluted with 10 mL of deionized water. The diluted phytic acid solution was slowly added dropwise (at a rate of 2 mL / min) to the ZIF-8 dispersion, and stirred at 25°C for 4 h. The reaction mixture was then extracted with methanol solution. After extraction, the solution separated into two layers: a white suspension on top and a pale yellow transparent solution on the bottom. The white suspension was placed in a beaker, and the lower pale yellow solution was extracted until extraction was complete. The white suspension was centrifuged, the waste liquid was discarded, and the precipitate was washed with methanol solution and centrifuged three times until neutral. The product was dried in an 80°C oven for 10 h, ground into powder, and then used as a powder to obtain the phytic acid-modified MOF material (PA-ZIF-8). PA-ZIF-8 coated microcrystalline cellulose: Dissolve 1.0g of the PA-ZIF-8 powder obtained above in 60mL of methanol and sonicate for 30min; then take 1.0g of microcrystalline cellulose (MCC) powder and 5mL of formaldehyde solution, and put them into the PA-ZIF-8 dispersion respectively. Stir at room temperature of 25℃ for 12h, wash and filter three times with a mixture of methanol and deionized water, and then wash and filter three times with deionized water until neutral. Place the final product in an oven at 80℃ and dry for 10-12h, grind, and bag the powder for later use to obtain coated microcrystalline cellulose (PA-ZIF-8@MCC), in which the mass ratio of phytic acid to MOF material is 3.5:1, and the mass ratio of core layer to coating layer is 1:1.

[0057] Example 2 Preparation of biodegradable flame-retardant composite materials; Raw materials include: 84 parts of PBAT resin and SYL GARD 184 from Jinhui Zhaolong High-Tech Co., Ltd. 15 parts of phosphorus-containing flame retardant, wherein the phosphorus-containing flame retardant is DIDOPO, the compound obtained in Example 1 of patent CN104086593A; One part of auxiliary flame retardant, which is the coated microcrystalline cellulose obtained in Example 1; All raw materials were vacuum dried at 85℃ for 12 hours; then placed in a mixing bag and thoroughly mixed for 5-10 minutes to obtain a mixed base material; the mixed base material was added to a torque rheometer and melt-mixed at 190℃ and 80rpm for 6 minutes, and the sample was taken out and cooled for later use; the obtained melt blend was pulverized by a high-efficiency crusher and dried at 85℃ for 12 hours to obtain a biodegradable composite material. The composite material was placed in a flat vulcanizing mold at 220°C to prepare standard vertical combustion, oxygen index, and mechanical specimens for performance testing.

[0058] Example 3 Biodegradable composite materials were prepared according to the method described in Example 2; The mixture contains 82 parts of PBAT resin, 15 parts of phosphorus-containing flame retardant, and 3 parts of auxiliary flame retardant.

[0059] Example 4 Biodegradable composite materials were prepared according to the method described in Example 2; The mixture contains 80 parts of PBAT resin, 15 parts of phosphorus-containing flame retardant, and 5 parts of auxiliary flame retardant.

[0060] Example 5 Biodegradable composite materials were prepared according to the method described in Example 2; The mixture contains 78 parts of PBAT resin, 15 parts of phosphorus-containing flame retardant, and 7 parts of auxiliary flame retardant.

[0061] Comparative Example 1 Biodegradable composite materials were prepared according to the method described in Example 2; It does not contain phosphorus-containing flame retardants or auxiliary flame retardants, i.e., blank PBAT resin.

[0062] Comparative Example 2 Biodegradable composite materials were prepared according to the method described in Example 2; It contains no auxiliary flame retardants, 85 parts of PBAT resin, and 15 parts of phosphorus-containing flame retardants.

[0063] Comparative Example 3 Biodegradable composite materials were prepared according to the method described in Example 2; It contains no auxiliary flame retardants, 80 parts of PBAT resin, and 20 parts of phosphorus-containing flame retardants.

[0064] Comparative Example 4 Biodegradable composite materials were prepared according to the method described in Example 2; This product does not include phosphorus-containing flame retardants, 99 parts of PBAT resin, and 1 part of auxiliary flame retardant.

[0065] Comparative Example 5 Biodegradable composite materials were prepared according to the method described in Example 2; This product does not include phosphorus-containing flame retardants, 97 parts of PBAT resin, and 3 parts of auxiliary flame retardants.

[0066] Comparative Example 6 Biodegradable composite materials were prepared according to the method described in Example 2; This product does not include phosphorus-containing flame retardants, 95 parts of PBAT resin, and 5 parts of auxiliary flame retardants.

[0067] Comparative Example 7 Biodegradable composite materials were prepared according to the method described in Example 2; This product does not include phosphorus-containing flame retardants, 93 parts of PBAT resin, and 7 parts of auxiliary flame retardants.

[0068] Performance testing Test Example 1 Figure 1 The infrared spectrum of the coated microcrystalline cellulose obtained in Example 1; Depend on Figure 1 It can be seen that the coated microcrystalline cellulose (PA-ZIF-8@MCC) provided by the present invention retains many of the same characteristic peaks of pure MCC, such as 3340, 2900, and 1653 cm⁻¹. -1 The peaks at these locations belong to the stretching vibration peak of OH, the stretching vibration peak of CH, and the bending vibration peak of the OH group, respectively. In addition to the characteristic peaks shared with pure MCC, new characteristic absorption peaks also clearly appear, such as at 864 cm⁻¹. -1 and 808cm -1 The peak at the position is attributed to the characteristic PO absorption peak of phytic acid molecules, confirming that PA-ZIF-8 molecules have been successfully coated onto the surface of MCC.

[0069] Figure 2 Here is a SEM image of the coated microcrystalline cellulose obtained in Example 1; Depend on Figure 2 It can be seen that the coated material surface is covered with regular and densely dispersed or clustered particles, achieving the designed structure. From Figure 2 As can be seen from (a1, a2), the microcrystalline cellulose before coating has a relatively smooth surface and a rod-shaped morphological structure with an orderly arrangement; Figure 2 (b1, b2) After coating, the microcrystalline cellulose hybrid particles are densely and uniformly attached to the surface of the particles, forming agglomerates.

[0070] Figure 3 XPS image of the coated microcrystalline cellulose obtained in Example 1; Table 1 shows the XPS data; Table 1 XPS Data

[0071] pass Figure 3 As shown in the XPS data in Table 1, pure MCC exhibits Og at binding energy positions of 532.75 eV and 286.81 eV. 1s and C 1s The peak; coated microcrystalline cellulose removes O 1s and C 1s In addition to the characteristic peaks, it also exhibits P 2s and Zn 2pCharacteristic peaks. Table 1 shows that, compared to pure MCC, PA-ZIF-8@MCC has a relative C content of 58.97%, a relative O content of 35.61%, and newly added N, Zn, and P elements with relative contents of 3.26%, 0.71%, and 1.45%, respectively. This further proves that PA-ZIF-8 has been coated onto microcrystalline cellulose. It further demonstrates that the preparation method provided by this invention can successfully prepare coated microcrystalline cellulose.

[0072] Figure 4 This is an element mapping graph of pure MCC. Figure 5 The elemental mapping diagram of the coated microcrystalline cellulose obtained in Example 1 is shown below. from Figure 4 , Figure 5 Elemental mapping analysis shows that the distribution of elements in both pure MCC and PA-ZIF-8@MCC is relatively uniform. Pure MCC contains only C and O elements, with a relative content (mole fraction) of 63.45% for C and 36.55% for O. PA-ZIF-8@MCC adds three new elements: N, P, and Zn, with relative contents of 58.97% for C, 35.61% for O, 3.26% for N, 1.45% for P, and 0.71% for Zn. Elemental scanning analysis reveals that the particles attached to the SEM image are PA-ZIF-8, which is uniformly distributed on the MCC surface. This, along with the results of infrared and XPS analyses, further confirms that PA-ZIF-8 is successfully coated onto microcrystalline cellulose, indicating that the preparation method provided by this invention can successfully prepare coated microcrystalline cellulose.

[0073] Test Example 2 To verify the mechanical and flame-retardant properties of the composite material prepared in this invention, the composite material prepared in the examples, the composite material in the comparative examples, and the pure PBAT matrix resin were subjected to vertical burning tests (UL-94 rating) according to national standard GB / T 2408-2008, and limiting oxygen index (LOI) tests according to national standard GB / T 2406-2008. Tensile strength, elongation at break, and other mechanical properties were tested according to GB / T 1040-2006. Detailed test results are shown in Tables 2 and 3. Table 2 Flame retardant performance test results

[0074] As shown in Table 2, pure PBAT matrix resin (Comparative Example 1) is easily combustible, drips severely, and has no flame retardant rating. In the composite systems with DIDOPO flame retardant introduced alone (Comparative Examples 2 and 3), the flame retardant performance and dripping phenomenon of the composite material are significantly improved, and the flame retardant rating reaches V-1 level in the UL-94 test, with an LOI of over 24%. In the composite systems with coated microcrystalline cellulose introduced alone (Comparative Examples 4-7), the ignition time is also significantly reduced, and the flame retardant performance is improved to some extent. Although a small amount of dripping is produced, it does not ignite the absorbent cotton. The PBAT / microcrystalline cellulose hybrid particle composite systems all reach V-1 level. With the combined use of DIDOPO flame retardant and coated microcrystalline cellulose (Examples 2-5), the flame retardant performance of the composite system is further improved. It cannot ignite the absorbent cotton, and no dripping occurs in Examples 3-5. The flame retardant rating reaches V-0 level, and the melt dripping phenomenon is significantly suppressed. The LOI value of Example 5 reaches 28.8%. Therefore, as can be seen from the above embodiments, the multi-level hybrid structure of microcrystalline cellulose and phosphorus-based flame retardants produce an excellent synergistic flame retardant effect, significantly improving the flame retardant performance compared to single-component systems. The flame retardant properties are significantly improved.

[0075] Table 3 Mechanical Performance Test Results

[0076] As shown in Table 3, compared with pure PBAT resin (Comparative Example 1), the tensile strength, flexural strength, and modulus of the material remained almost unchanged when DIDOPO flame retardant (Comparative Example 2) was added alone; however, the tensile strength, flexural strength, and modulus all increased to varying degrees when the coated microcrystalline cellulose hybrid particles from Example 1 (Comparative Example 6) were added alone. When DIDOPO and coated microcrystalline cellulose (Examples 2-5) were introduced together, the tensile strength, flexural strength, and elongation at break of the composite material generally increased gradually with the increase of the addition amount. Among them, the composite material of Example 5 achieved the best mechanical properties, with tensile strength, flexural modulus, flexural strength, and elongation at break all significantly increased compared with pure PBAT (Comparative Example 1). Therefore, when DIDOPO flame retardant and coated microcrystalline cellulose are used in combination, they can play a significant synergistic reinforcing and toughening role for biodegradable PBAT matrix resin.

[0077] Based on the test results in Tables 2 and 3, the DIDOPO phosphorus-based flame retardant and coated microcrystalline cellulose flame-retardant biodegradable PBAT composite material can significantly improve the flame retardant properties of the matrix, enhance its strength and modulus, and maintain high toughness. This demonstrates that the flame-retardant biodegradable PBAT composite material provided by this invention possesses excellent flame retardant properties and comprehensive mechanical properties.

[0078] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A coated microcrystalline cellulose, characterized in that, Includes the core layer and the cladding layer; The core layer is microcrystalline cellulose; The coating layer is made of phytic acid-modified MOF material; A chemical bond is formed between the core layer and the coating layer.

2. The coated microcrystalline cellulose according to claim 1, characterized in that, The mass ratio of the core layer to the cladding layer is 0.5 to 5:1; The mass ratio of phytic acid to MOF material in the phytic acid-modified MOF material is 1~10:1; The MOF material includes ZIF-8, ZIF-67, UiO-66, UiO-67 or MIL-101.

3. The method for preparing the coated microcrystalline cellulose according to claim 1 or 2, characterized in that, Includes the following steps: Under stirring conditions, an aqueous phytic acid solution was added dropwise to a dispersion containing MOF materials to carry out the reaction, thereby obtaining phytic acid-modified MOF materials. Microcrystalline cellulose, a crosslinking agent, and a dispersion of phytic acid-modified MOF material are mixed and coated to obtain the coated microcrystalline cellulose.

4. The preparation method according to claim 3, characterized in that, The mass ratio of phytic acid in the phytic acid aqueous solution to MOF material in the MOF material dispersion is 1~10:1; The reaction is carried out at a temperature of 10~50℃, under stirring conditions, and the stirring time is 3~8h.

5. The preparation method according to claim 3, characterized in that, The mass ratio of the microcrystalline cellulose to the phytic acid-modified MOF material is 0.3~3:1; The mass ratio of the microcrystalline cellulose to the crosslinking agent is 0.1~2:1; The coating temperature is 10~50℃, the coating is carried out under stirring conditions, and the coating time is 5~24h.

6. A biodegradable flame-retardant composite material, characterized in that, Including polybutylene terephthalate (PET) and flame retardants; The flame retardant includes phosphorus-containing flame retardants and auxiliary flame retardants; The auxiliary flame retardant is the coated microcrystalline cellulose according to claim 1 or 2, or the coated microcrystalline cellulose prepared by the preparation method according to any one of claims 3 to 5.

7. The biodegradable flame-retardant composite material according to claim 6, characterized in that, By weight, the biodegradable flame-retardant composite material comprises 73-84 parts of polybutylene terephthalate, 15-20 parts of phosphorus-containing flame retardant, and 1-7 parts of auxiliary flame retardant.

8. The biodegradable flame-retardant composite material according to claim 6, characterized in that, The phosphorus-containing flame retardant includes phenylethyl bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

9. The method for preparing the biodegradable flame-retardant composite material according to any one of claims 6 to 8, characterized in that, Includes the following steps: The biodegradable flame-retardant composite material is obtained by melting polybutylene terephthalate (PET) and a flame retardant.

10. The application of the biodegradable flame-retardant composite material according to any one of claims 6 to 8 or the biodegradable flame-retardant composite material prepared by the preparation method according to claim 9 in food, medicine, agricultural mulch film, electronic and electrical components and industrial equipment parts.

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