Flame-retardant wood-plastic composite material

Abstract

The invention belongs to the field of wood-plastic composite materials, and discloses a flame-retardant wood-plastic composite material which comprises the following raw materials: wood flour, a plastic matrix, modified aluminum hydroxide, modified magnesium hydroxide, a flame retardant, a coupling agent, a lubricant and an antioxidant. According to the flame-retardant wood-plastic composite material disclosed by some examples of the invention, by optimizing a flame retardant compounding system and a surface modification process, the flame-retardant properties are as follows: the oxygen index is greater than or equal to 32%, and the UL-94 vertical combustion reaches V-0 level; mechanical properties are as follows: the bending strength is greater than or equal to 28MPa, and the tensile strength is greater than or equal to 18MPa; the durability is as follows: the water absorption is lt; and the turnover frequency of the building template is more than or equal to 15 (the turnover frequency of the traditional WPC template is less than or equal to 8). The flame retardant property and the mechanical property are synergistically improved, meanwhile, the production cost is reduced, and the method is suitable for large-scale application of building templates.

Description

Technical Field

[0001] The invention belongs to the field of wood-plastic composite materials, and particularly relates to a flame-retardant wood-plastic composite material. Background Art

[0002] Wood-Plastic Composite (WPC), an environmentally friendly building material composed of wood fibers (such as wood flour and bamboo powder) and thermoplastics (such as polyethylene and polypropylene), combines the processability of wood with the corrosion resistance of plastic. It is widely used in outdoor flooring, guardrails, decorative panels, and other applications. Compared to pure wood, WPC offers advantages such as moisture resistance, insect resistance, and recyclability, making it particularly well-suited to the trend of green building. However, both the wood fibers and the plastic matrix in traditional WPC are combustible materials, with a limiting oxygen index (LOI) generally below 22%. When exposed to open flames, they easily burn and release large amounts of smoke, posing a high risk of fire spread. This limitation severely limits its application in applications such as building formwork and high-rise building exterior walls, which require strict fire resistance ratings (such as Class B1 and above in GB 8624-2012, "Classification of Combustion Performance of Building Materials and Products"), and has become a key technical bottleneck hindering its market expansion.

[0003] To improve the flame retardancy of WPC, existing technologies primarily employ the addition of inorganic flame retardants (such as aluminum hydroxide and magnesium hydroxide) or intumescent flame retardants (such as ammonium polyphosphate and pentaerythritol). For example, Chinese patent application CN102731935A discloses a WPC with 30% aluminum hydroxide added, but its flexural strength decreases by over 40% compared to the unadded WPC, and the high loading leads to poor processing fluidity. Chinese patent application CN103709623A attempts to improve flame retardancy by compounding magnesium hydroxide with zinc borate, but the flame retardant exhibits poor interfacial adhesion with the substrate and easily agglomerates during extrusion, resulting in surface defects and uneven mechanical properties. Furthermore, some studies have employed coating with red phosphorus or nano-montmorillonite for modification. While these methods can reduce the amount of flame retardant required, red phosphorus readily absorbs moisture and releases toxic phosphine gas, making dispersion of nanomaterials difficult and limiting their practical application. All of the above solutions face the contradiction of "flame retardancy-mechanics-cost" being difficult to optimize in a coordinated manner: improving flame retardancy efficiency often comes at the expense of material strength or increasing production costs, while low-cost flame retardant systems are difficult to meet the dual requirements of building formwork for bearing capacity and durability.

[0004] As the construction industry's requirements for construction safety and formwork turnover efficiency become increasingly stringent, the heavy weight of traditional steel formwork and the susceptibility to deformation and mildew of bamboo and wood formwork have become increasingly prominent, creating an urgent need for lightweight, high-strength, and flame-retardant alternatives. However, existing WPC building formwork, due to its insufficient flame retardancy, is easily ignited by common fire sources on construction sites, such as high-temperature welding and electric welding sparks. Burning also produces molten droplets, posing a risk of secondary ignition. Furthermore, building formwork must withstand the lateral pressure of concrete pouring and the impact of repeated assembly and disassembly, placing stringent demands on the material's flexural strength (≥25MPa), water absorption (<3%), and weather resistance. Therefore, developing a wood-plastic composite material with efficient flame retardant dispersion, stable mechanical properties, and environmental friendliness, and achieving its large-scale application in building formwork, has become a pressing need for technological advancement in this field. Summary of the Invention

[0005] The object of the present invention is to overcome at least one disadvantage of the prior art and provide a flame retardant wood-plastic composite material.

[0006] The technical solution adopted by the present invention is: The first aspect of the present invention provides: A flame retardant wood-plastic composite material comprising the following components in parts by weight: Wood flour: 30-50 parts, plastic matrix: 40-60 parts, silane coupling agent surface modified aluminum hydroxide: 10-15 parts, stearic acid surface modified magnesium hydroxide: 5-10 parts, flame retardant: 5-9 parts, coupling agent: appropriate amount, lubricant: appropriate amount, antioxidant: appropriate amount.

[0007] In some examples, the plastic matrix is selected from at least one of high-density polyethylene (HDPE), polypropylene (PP), or polyvinyl chloride (PVC).

[0008] In some examples, the flame retardant includes 3 to 5 parts of zinc borate and 2 to 4 parts of red phosphorus, and the red phosphorus is microencapsulated red phosphorus.

[0009] In some examples, the coating layer of the microencapsulated red phosphorus is phenolic resin or melamine resin, and the coating rate is ≥90%.

[0010] In some examples, the coupling agent is used in an amount of 2 to 4 parts.

[0011] In some examples, the coupling agent includes at least one of maleic anhydride grafted polyethylene (MAPE) or maleic anhydride grafted polypropylene (MAPP).

[0012] In some examples, the amount of the lubricant is 1 to 2 parts.

[0013] In some examples, the lubricant is selected from one of calcium stearate, zinc stearate, or polyethylene wax.

[0014] In some examples, the amount of the antioxidant is 0.5 to 1 part.

[0015] In some examples, the antioxidant is at least one selected from the group consisting of antioxidant 1010 (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 1076 (octadecylβ-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), BHT (butylated hydroxytoluene), 168 (tris[2,4-di-tert-butylphenyl]phosphite), DLTDP (dilauryl thiodipropionate), DSTDP (distearyl thiodipropionate) and antioxidant 4010NA.

[0016] In some examples, the silane coupling agent is selected from at least one of KH550, KH560, and KH570.

[0017] In some examples, the amount of the silane coupling agent used is 1 to 2% by mass of the aluminum hydroxide.

[0018] In some examples, the preparation method of the silane coupling agent surface-modified aluminum hydroxide is: fully mixing aluminum hydroxide and a silane coupling agent in a high-speed mixer at 70-85°C.

[0019] In some examples, the preparation method of the silane coupling agent surface-modified aluminum hydroxide is: mixing aluminum hydroxide and a silane coupling agent in a high-speed mixer at 70 to 85° C. for 20 to 40 minutes at a mixing speed of 800 to 1200 rpm.

[0020] In some examples, the amount of stearic acid added is 1.5-3% by mass of the magnesium hydroxide.

[0021] In some examples, the preparation method of the stearic acid surface-modified magnesium hydroxide is: fully ball-milling magnesium hydroxide and stearic acid in a ball mill.

[0022] In some examples, the preparation method of the stearic acid surface-modified magnesium hydroxide is: ball milling magnesium hydroxide and stearic acid in a ball mill for 1 to 2 hours, with a ball-to-material ratio of 5:1 and a ball milling speed of 200 to 300 rpm.

[0023] In some examples, the wood flour has at least one of the following characteristics: At least one selected from pine wood powder, bamboo powder and straw powder; Moisture content ≤1%; The particle size is 80-120 mesh.

[0024] In some embodiments, the preparation method includes: S1) crushing the plastic matrix into particles with a particle size of ≤5 mm; S2) adding wood flour, plastic matrix, modified aluminum hydroxide, modified magnesium hydroxide, flame retardant coupling agent, lubricant and antioxidant into a high-speed mixer and mixing uniformly to obtain a mixture; S3) feeding the mixed material into a twin-screw extruder, melt-blending and then extruding into pellets, the temperature of each zone of the twin-screw extruder is: zone 1 160-165°C, zone 2 170-175°C, zone 3 180-185°C, zone 4 175-180°C, and the die head temperature is 170-175°C; S4) forming the granulated composite material particles through a template extruder and cooling them to obtain a flame retardant wood-plastic composite material.

[0025] In some embodiments, the mixing temperature of the high-speed mixer is 50-70°C.

[0026] In some embodiments, the mixing time of the high-speed mixer is 10 to 15 minutes.

[0027] In some embodiments, the mixing temperature of the high-speed mixer is 50-70° C., and the mixing time is 10-15 minutes.

[0028] In some examples, the screw speed of the twin-screw extruder is 200-300 rpm.

[0029] In some examples, the die plate extruder molding extrusion temperature is 170-190° C., and the pressure is 8-12 MPa.

[0030] The above features can be combined arbitrarily unless they conflict with each other.

[0031] The second aspect of the present invention provides: A flame-retardant building profile, the main body of which is the flame-retardant wood-plastic composite material described in the first aspect of the present invention.

[0032] In some examples, the surface of the flame-retardant wood-plastic composite material is coated with a flame-retardant-waterproof coating, and the coating is composed of the following components in parts by weight: Polyurethane resin: 85-90 parts; Ammonium polyphosphate: 5-8 parts; Nano silicon dioxide: 3-5 parts; Dispersant: 1-2 parts; The coating has a coating thickness of 0.2 to 0.5 mm.

[0033] In some examples, the dispersant is selected from sodium polyacrylate (PAAS), polycarboxylate ether (PCE), alkylphenol phosphate, sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), polyoxyethylene ethers (Tween, Triton series), sodium silicate, potassium silicate, sodium hexametaphosphate (SHMP), sodium tripolyphosphate (STPP), polyurethane dispersant, polyether modified polysiloxane, acrylic copolymer, modified cellulose, starch derivatives, nanosilica, carbon nanotubes, BYK-110 / 111, BYK-180 / 181, BYK-190 / 192, BYK-2155, EFKA-4010 / 4015, EFKA-4580, EFKA-7701, Dispex® AA4040, Dispex® Ultra PX 4585, EFKA® FA 4612, DOWANOL™ DPnB, TEGO Dispers At least one of 710, TEGODispers 685, Solsperse 32000, KUSMILLAN 911, Shanghai Changfeng CF-550, and CF-10.

[0034] In some examples, the flame retardant building profile is a multi-layer composite design, including: Middle layer: fiber reinforced layer, thickness accounts for 10-15%, fiber length is 3-5mm; Core layer: composed of the flame-retardant wood-plastic composite material according to claim 1, with a thickness accounting for 75-85%; Surface layer: High-density polyethylene layer containing weathering agent.

[0035] The beneficial effects of the present invention are: By optimizing the flame retardant compounding system and surface modification process, some examples of flame-retardant wood-plastic composite materials in this invention achieve flame retardancy with an oxygen index ≥32% and a UL-94 V-0 vertical combustion rating. They also exhibit mechanical resistance with a flexural strength ≥28 MPa and a tensile strength ≥18 MPa. They also exhibit durability with a water absorption rate <2% and a building formwork turnover rate ≥15 times (compared to ≤8 times for conventional WPC formwork). This achieves a synergistic improvement in both flame retardancy and mechanical properties while reducing production costs, making it suitable for large-scale application in building formwork. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a cross-sectional view of a flame-retardant wood-plastic building template, in which the reference numerals represent: 1 HDPE layer, 2 basalt fiber reinforcement layer, 3 the flame-retardant wood-plastic of the present invention. DETAILED DESCRIPTION

[0037] A flame retardant wood-plastic composite material comprising the following components in parts by weight: Wood flour: 30-50 parts, plastic matrix: 40-60 parts, silane coupling agent surface modified aluminum hydroxide: 10-15 parts, stearic acid surface modified magnesium hydroxide: 5-10 parts, flame retardant: 5-9 parts, coupling agent: appropriate amount, lubricant: appropriate amount, antioxidant: appropriate amount.

[0038] In some examples, the plastic matrix is selected from at least one of high-density polyethylene (HDPE), polypropylene (PP), or polyvinyl chloride (PVC).

[0039] In some examples, the flame retardant includes 3 to 5 parts of zinc borate and 2 to 4 parts of red phosphorus, and the red phosphorus is microencapsulated red phosphorus.

[0040] In some examples, the coating layer of the microencapsulated red phosphorus is phenolic resin or melamine resin, and the coating rate is ≥90%.

[0041] In some examples, the coupling agent is used in an amount of 2 to 4 parts.

[0042] In some examples, the coupling agent includes at least one of maleic anhydride grafted polyethylene (MAPE) or maleic anhydride grafted polypropylene (MAPP).

[0043] The role of the lubricant is to facilitate processing, and its amount can be adjusted accordingly as needed. In some examples, the amount of the lubricant is 1 to 2 parts.

[0044] There is no particular requirement for the type of lubricant, and it can be a commonly used lubricant in the art. In some examples, the lubricant is selected from one of calcium stearate, zinc stearate, or polyethylene wax.

[0045] The amount of the antioxidant can be adjusted accordingly as needed. In some examples, the amount of the antioxidant is 0.5 to 1 part.

[0046] There are no particular requirements for the type of antioxidant, and it can be a commonly used antioxidant in the art. In some examples, the antioxidant is at least one selected from the group consisting of antioxidant 1010 (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 1076 (octadecylβ-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), BHT (butylated hydroxytoluene), 168 (tris[2,4-di-tert-butylphenyl]phosphite), DLTDP (dilauryl thiodipropionate), DSTDP (distearyl thiodipropionate), and antioxidant 4010NA.

[0047] In some examples, the silane coupling agent is selected from at least one of KH550, KH560, and KH570. These silane coupling agents have better effects.

[0048] In some examples, the amount of silane coupling agent used is 1-2% of the mass of aluminum hydroxide, which can fully modify the aluminum hydroxide without causing waste.

[0049] In some examples, the preparation method of the silane coupling agent surface-modified aluminum hydroxide is: fully mixing aluminum hydroxide and a silane coupling agent in a high-speed mixer at 70-85°C.

[0050] In some examples, the preparation method of the silane coupling agent surface-modified aluminum hydroxide is: mixing aluminum hydroxide and a silane coupling agent in a high-speed mixer at 70 to 85° C. for 20 to 40 minutes at a mixing speed of 800 to 1200 rpm.

[0051] In some examples, the amount of stearic acid added is 1.5-3% of the mass of the magnesium hydroxide, which can fully modify the magnesium hydroxide without causing waste.

[0052] In some examples, the preparation method of the stearic acid surface-modified magnesium hydroxide is: fully ball-milling magnesium hydroxide and stearic acid in a ball mill.

[0053] In some examples, the preparation method of the stearic acid surface-modified magnesium hydroxide is: ball milling magnesium hydroxide and stearic acid in a ball mill for 1 to 2 hours, with a ball-to-material ratio of 5:1 and a ball milling speed of 200 to 300 rpm.

[0054] In some examples, the wood flour has at least one of the following characteristics: At least one selected from pine wood powder, bamboo powder and straw powder; Moisture content ≤1%; The particle size is 80-120 mesh.

[0055] In some embodiments, the preparation method includes: S1) crushing the plastic matrix into particles with a particle size of ≤5 mm; S2) adding wood flour, plastic matrix, modified aluminum hydroxide, modified magnesium hydroxide, flame retardant coupling agent, lubricant and antioxidant into a high-speed mixer and mixing uniformly to obtain a mixture; S3) feeding the mixed material into a twin-screw extruder, melt-blending and then extruding into pellets, the temperature of each zone of the twin-screw extruder is: zone 1 160-165°C, zone 2 170-175°C, zone 3 180-185°C, zone 4 175-180°C, and the die head temperature is 170-175°C; S4) forming the granulated composite material particles through a template extruder and cooling them to obtain a flame retardant wood-plastic composite material.

[0056] In some embodiments, the mixing temperature of the high-speed mixer is 50-70°C.

[0057] In some embodiments, the mixing time of the high-speed mixer is 10 to 15 minutes.

[0058] In some embodiments, the mixing temperature of the high-speed mixer is 50-70° C., and the mixing time is 10-15 minutes.

[0059] In some examples, the screw speed of the twin-screw extruder is 200-300 rpm.

[0060] In some examples, the die plate extruder molding extrusion temperature is 170-190° C., and the pressure is 8-12 MPa.

[0061] The above features can be combined arbitrarily unless they conflict with each other.

[0062] In the following examples, unless otherwise specified, parts are by weight or mass, and the amount added is by mass.

[0063] The preparation method of aluminum hydroxide surface modified with a silane coupling agent is as follows: aluminum hydroxide and a silane coupling agent are mixed in a high-speed mixer at 70 to 85° C. for 20 to 40 minutes at a mixing speed of 800 to 1200 rpm.

[0064] The preparation method of stearic acid surface-modified magnesium hydroxide is as follows: magnesium hydroxide and stearic acid are ball-milled in a ball mill for 1 to 2 hours, with a ball-to-material ratio of 5:1 and a ball-milling speed of 200 to 300 rpm.

[0065] The technical solution of the present invention is further illustrated below with reference to examples.

[0066] In the following examples, the test standards for different performances are as follows: Oxygen index: GB / T 2406.2-2009; Vertical burning grade: ASTM D3801; Bending strength: GB / T 9341-2008; Water absorption: GB / T 17657-2013; Number of turnover uses: GB / T 29418-2012.

[0067] For the sake of comparison, the composition of flame retardant and waterproof coating is unified as follows: Polyurethane resin: 88 parts; ammonium polyphosphate: 7 parts; nano-silicon dioxide: 4 parts; dispersant (BY-164): 1 part.

[0068] Example 1 Formula (parts by weight): Wood flour: 40 parts (pine flour, 100 mesh, moisture content 0.8%) Plastic matrix: 50 parts HDPE (80% recycled material) Modified aluminum hydroxide: 12 parts (treated with KH550, added at 1.5%) Modified magnesium hydroxide: 8 parts (treated with stearic acid, added at 2%) Zinc borate: 4 parts Microcapsule red phosphorus: 3 parts (phenolic resin coated, coating rate 92%) MAPE coupling agent: 3 parts Calcium stearate: 1.5 parts Antioxidant 1010: 0.8 parts.

[0069] Preparation process: 1. Dry the wood flour at 105℃ for 5 hours and sieve to 80-120 mesh; 2. Modified aluminum hydroxide and KH550 were mixed at 80°C and 1000 rpm for 30 minutes; 3. Ball mill the modified magnesium hydroxide and stearic acid for 1.5 hours (ball to material ratio 5:1, speed 250 rpm); 4. All ingredients were mixed at high speed at 60°C for 12 minutes; 5. Twin-screw extruder for blending and granulation (temperature: zone 1 165°C, zone 2 175°C, zone 3 185°C, zone 4 180°C, die head 175°C, speed 250 rpm); 6. Extrusion molding into building formwork (temperature 180°C, pressure 10 MPa), surface coating with polyurethane-ammonium polyphosphate coating (thickness 0.3 mm, curing temperature 70°C, time 40 minutes).

[0070] Performance testing: Oxygen index: 33.5%; UL-94 vertical combustion: V-0 (no dripping, self-extinguishing time ≤ 3 seconds); Flexural strength: 29.2MPa; Tensile strength: 19.1MPa; Water absorption rate: 1.8%; Number of turnovers: 16 times.

[0071] Example 2 Formula (parts by weight): Wood powder: 30 parts (bamboo powder, 80 mesh, moisture content 0.5%) Plastic matrix: PP 60 parts (recycled materials account for 70%) Modified aluminum hydroxide: 10 parts (KH560 treated, addition amount 1.0%) Modified magnesium hydroxide: 5 parts (treated with stearic acid, added at 3.0%) Zinc borate: 3 parts Microencapsulated red phosphorus: 2 parts MAPP coupling agent: 2 parts.

[0072] Performance testing: Oxygen index 32.1%, UL-94 V-0 grade, flexural strength 26.8MPa, water absorption 1.5%, turnover number 15 times.

[0073] Example 3 Formula (parts by weight): Wood flour: 50 parts (straw powder, 120 mesh, moisture content 1.0%) Plastic matrix: PVC 40 parts (90% recycled materials) Modified aluminum hydroxide: 15 parts (KH570 treated, added 2%) Modified magnesium hydroxide: 10 parts (treated with stearic acid, added at 1.5%) Zinc borate: 5 parts Microencapsulated red phosphorus: 4 parts.

[0074] Performance testing: Oxygen index 34.0%, UL-94 V-0 grade, flexural strength 27.5MPa, water absorption 2.0%, turnover number 15 times.

[0075] Comparative Example 1: Formula: Same as Example 1, but aluminum hydroxide / magnesium hydroxide is not surface treated.

[0076] Performance testing: Oxygen index 28.5%, UL-94 V-2 grade (molten droplets ignite absorbent cotton); Flexural strength 21.4MPa, tensile strength 14.2MPa; The flame retardant agglomerates obviously and the extruded surface is rough.

[0077] Comparative Example 2 Formula: Same as Example 1, but without adding zinc borate and red phosphorus.

[0078] Performance testing: Oxygen index 26.7%, UL-94 V-2 grade (burning time > 30 seconds); The bending strength is 24.3MPa, but a large amount of molten droplets are produced during combustion.

[0079] Example 4: Multi-layer composite template Structural design: Core layer: composite material of Example 1, thickness accounting for 80%; Surface layer: HDPE layer (containing 2% UV-531), thickness accounting for 5%; Middle layer: basalt fiber reinforced layer (average fiber length 4mm), accounting for 5% of the thickness.

[0080] The overall structure diagram is as follows Figure 1 shown.

[0081] Performance improvements: Flexural strength increased to 32.1MPa; UV aging resistance (QUV test 500 hours, color difference ΔE ≤ 3.0); The turnover rate is increased to 20 times.

[0082] Example 5 Preparation process: Same as Example 1, but omitting the surface coating.

[0083] Performance testing: Oxygen index 30.5% (only the base flame retardant), UL-94 V-1 grade; Water absorption rate 4.2% (does not meet the ≤2% requirement); Number of turnovers: 9 (missing coating resulted in cracking of the template edge).

[0084] The performance comparison of different instances is shown in Table 1.

[0085] Table 1. Performance comparison of different instances index Example 1 Comparative Example 1 Comparative Example 2 Example 5 Oxygen index (%) 33.5 28.5 26.7 30.5 UL-94 rating V-0 V-2 V-2 V-1 Flexural strength (MPa) 29.2 21.4 24.3 27.8 Water absorption rate (%) 1.8 2.5 2.1 4.2 Turnover rate 16 7 10 9 in conclusion 1. Necessity of modified flame retardants and synergistic systems: 1) Comparative Examples 1 / 2 show that when the flame retardant is not modified or the synergist is missing, the oxygen index decreases by 5-7% and the mechanical properties decrease by 20%-30%; 2) Synergists (zinc borate + red phosphorus) achieve gas-phase-condensed phase synergistic flame retardancy through catalytic carbonization and free radical capture.

[0086] ,Key functions of surface coating: 1) Example 5 shows that the water absorption rate exceeds the standard (>4%) when the coating is not applied, and the number of turnovers is less than 10 times; 2) Polyurethane-ammonium polyphosphate coating can seal surface pores and inhibit burning droplets.

[0087] The above is a further detailed description of the present invention and should not be considered as a limitation on the specific implementation of the present invention. For those skilled in the art, simple deductions or substitutions that do not depart from the concept of the present invention are within the scope of protection of the present invention.

Claims

1. A flame retardant wood-plastic composite material, characterized in that: The following components are included by weight: Wood flour: 30-50 parts, plastic matrix: 40-60 parts, silane coupling agent surface modified aluminum hydroxide: 10-15 parts, stearic acid surface modified magnesium hydroxide: 5-10 parts, flame retardant: 5-9 parts, coupling agent: appropriate amount, lubricant: appropriate amount, antioxidant: appropriate amount.

2. The flame retardant wood-plastic composite material according to claim 1, characterized in that: The flame retardant comprises 3 to 5 parts of zinc borate and 2 to 4 parts of red phosphorus, and the red phosphorus is microencapsulated red phosphorus.

3. The flame retardant wood-plastic composite material according to claim 1, characterized in that: The plastic matrix is selected from at least one of high-density polyethylene (HDPE), polypropylene (PP) or polyvinyl chloride (PVC).

4. The flame retardant wood-plastic composite material according to claim 1, characterized in that: The silane coupling agent is selected from at least one of KH550, KH560 and KH570; and / or The amount of silane coupling agent used is 1-2% of the mass of aluminum hydroxide; and / or The preparation method of the silane coupling agent surface-modified aluminum hydroxide is as follows: fully mixing the aluminum hydroxide and the silane coupling agent in a high-speed mixer at 70-85° C.

5. The flame retardant wood-plastic composite material according to claim 1, characterized in that: The amount of stearic acid added is 1.5-3% of the mass of magnesium hydroxide; and / or The preparation method of the stearic acid surface-modified magnesium hydroxide comprises the following steps: fully milling magnesium hydroxide and stearic acid in a ball mill.

6. The flame retardant wood-plastic composite material according to claim 1, characterized in that: The wood flour has at least one of the following characteristics: At least one selected from pine wood powder, bamboo powder and straw powder; Moisture content ≤1%; The particle size is 80-120 mesh.

7. The flame retardant wood-plastic composite material according to claim 1, characterized in that: The preparation method thereof comprises: S1) crushing the plastic matrix into particles with a particle size of ≤5 mm; S2) adding wood flour, plastic matrix, modified aluminum hydroxide, modified magnesium hydroxide, flame retardant coupling agent, lubricant and antioxidant into a high-speed mixer and mixing uniformly to obtain a mixture; S3) feeding the mixed material into a twin-screw extruder, melt-blending and then extruding into pellets, the temperature of each zone of the twin-screw extruder is: zone 1 160-165°C, zone 2 170-175°C, zone 3 180-185°C, zone 4 175-180°C, and the die head temperature is 170-175°C; S4) forming the granulated composite material particles through a template extruder and cooling them to obtain a flame retardant wood-plastic composite material.

8. A flame retardant building profile, characterized in that: The main body is the flame-retardant wood-plastic composite material as claimed in claim 1.

9. The flame retardant building profile according to claim 8, characterized in that: The surface of the flame-retardant wood-plastic composite material is coated with a flame-retardant-waterproof coating, and the coating is composed of the following components in parts by mass: Polyurethane resin: 85-90 parts; Ammonium polyphosphate: 5-8 parts; Nano silicon dioxide: 3-5 parts; Dispersant: 1-2 parts; The coating has a coating thickness of 0.2 to 0.5 mm.

10. The flame retardant building profile according to claim 8, characterized in that: The flame retardant building profile is a multi-layer composite design, including: Middle layer: fiber reinforced layer, thickness accounts for 10-15%, fiber length is 3-5mm; Core layer: composed of the flame-retardant wood-plastic composite material according to claim 1, with a thickness accounting for 75-85%; Surface layer: High-density polyethylene layer containing weathering agent.

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