Flame-retardant wood-plastic board and preparation method thereof

Abstract

The application discloses a kind of flame-retardant wood-plastic board and preparation method thereof, and relates to the technical field of wood-plastic board.The specific steps are as follows:S1: butyl acrylate, isooctyl acrylate and crosslinking agent are used as reaction monomers to prepare seed latex;the seed latex is subjected to shell polymerization with methyl methacrylate and flame-retardant monomers to obtain an ACR modifier;S2: polyvinyl chloride resin powder, wood powder, ACR modifier, lubricant, filler, plasticizer, stabilizer and coupling agent are uniformly mixed, and then subjected to double-helix melt extrusion and molding by vulcanizing machine to obtain the flame-retardant wood-plastic board.The wood-plastic board prepared by the application has good impact resistance and high flame-retardant performance, and can meet the A-level fireproof grade.

Description

Technical Field

[0001] This invention relates to the field of wood-plastic composite board technology, specifically a flame-retardant wood-plastic composite board and its preparation method. Background Technology

[0002] Wood-plastic composite board, also known as wood-plastic composite material, is made from wood-plastic fiber and thermoplastic resin as the main raw materials through melt blending, extrusion, and pressing. It has the characteristics of good weather resistance and high hardness. Since wood flour is a flammable material, the commonly used resin material is polyvinyl chloride (PVC). This resin has the characteristics of self-extinguishing after being removed from the flame and its limiting oxygen index can reach 45%, making it an excellent flame-retardant material. However, due to the "wick effect" and flammability of wood flour, even with the addition of PVC, its fire resistance rating can only reach B1. Since wood-plastic decoration is now widely used in engineering decoration, many projects have strict fire protection requirements and need to reach Class A, which requires the addition of a large amount of flame retardant. However, PVC is brittle, and the addition of a large amount of flame retardant will result in poor impact resistance of the prepared wood-plastic board, making it difficult to achieve a balance between flame retardancy and impact resistance.

[0003] In conclusion, solving the above problems and preparing a flame-retardant wood-plastic composite board is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a flame-retardant wood-plastic composite board and its preparation method, so as to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A method for preparing flame-retardant wood-plastic composite board includes the following steps: S1: Seed latex was prepared by using butyl acrylate, isooctyl acrylate, and crosslinking agent as reactive monomers; the seed latex was then subjected to shell polymerization with methyl methacrylate and flame retardant monomers to obtain ACR modifier; S2: Mix polyvinyl chloride resin powder, wood flour, ACR modifier, lubricant, filler, plasticizer, stabilizer, and coupling agent evenly, then melt-extrude the mixture in a twin-screw manner and press it into shape using a vulcanizing machine to obtain flame-retardant wood-plastic composite board.

[0006] Preferably, the flame-retardant wood-plastic composite board comprises the following raw materials, by weight: 100 parts polyvinyl chloride resin powder, 60-80 parts wood flour, 12-16 parts ACR modifier, 3-5 parts lubricant, 8-10 parts filler, 1-2 parts plasticizer, 4-6 parts stabilizer, and 0.5-1 part coupling agent. The polyvinyl chloride resin powder includes one or both of polyvinyl chloride and chlorinated polyvinyl chloride; the filler includes calcium carbonate and nanofiller in a mass ratio of 7~8:1; the nanofiller includes one or more of nano silica, nano clay, and nano magnesium hydroxide.

[0007] Preferred method for preparing ACR modifier includes the following steps: (1) under nitrogen atmosphere, butyl acrylate, isooctyl acrylate, crosslinking agent, sodium dodecyl sulfate, potassium carbonate and potassium persulfate are added to deionized water and mixed evenly. The mixture is stirred at 60-70°C for 2-3 hours to obtain seed latex; (2) methyl methacrylate, flame retardant monomer and sodium dodecyl sulfate are added to deionized water and mixed evenly to obtain emulsion solution; under nitrogen atmosphere, seed latex and potassium persulfate are added to deionized water and stirred at 60-70°C for 20-30 minutes; the emulsion solution is added dropwise at 70-80°C, and the addition rate is controlled at 1-2 drops / second. After the addition is completed, the mixture is stirred for 30-40 minutes, demulsified, filtered, washed and dried to obtain ACR modifier.

[0008] Preferably, the seed latex comprises the following raw materials in parts by weight: 35-40 parts butyl acrylate, 10-12 parts isooctyl acrylate, 1-1.4 parts crosslinking agent, 0.4-0.6 parts sodium dodecyl sulfate, 0.3-0.4 parts potassium carbonate, 0.2-0.3 parts potassium persulfate, and 30-40 parts deionized water; the ACR modifier comprises the following raw materials in parts by weight: 15-20 parts methyl methacrylate, 10-15 parts flame retardant monomer, 0.3-0.5 parts sodium dodecyl sulfate, 100 parts seed latex, 0.1-0.2 parts potassium persulfate, and 150-160 parts deionized water.

[0009] Preferredly, the preparation method of the crosslinking agent includes the following steps: (1) Under a nitrogen atmosphere, 4-tert-butylcatechol, enamine compounds, and paraformaldehyde are added to anhydrous ethanol and mixed evenly at 60~65℃, heated to 90~95℃ and stirred for 3~4h, the solvent is removed by vacuum evaporation, and dried to obtain the catechol derivative; (2) Under a nitrogen atmosphere, the catechol derivative and 4-vinylphenylboronic acid are added to dimethyl sulfoxide and mixed evenly, the pH is adjusted to 7.5~8, stirred for 12~16h at 25~30℃, the solvent is removed by vacuum evaporation, and dried to obtain the crosslinking agent.

[0010] Preferably, the raw materials for the catechol derivative include 4-tert-butylcatechol, enamine compounds, and paraformaldehyde in a ratio of 1 mol: 2.2~2.4 mol: 60~66 g; the raw materials for the crosslinking agent include catechol derivative and 4-vinylphenylboronic acid in a molar ratio of 1:1~1.2. The enamine compounds include one or two of 2-methylallylamine, 3-buten-1-amine, and 4-penten-1-amine.

[0011] The crosslinking agent is prepared by reacting 4-tert-butylcatechol and a primary amine in an enamine compound with paraformaldehyde in the presence of paraformaldehyde to obtain a catechol derivative containing two alkenyl groups. Further, the catechol groups are esterified with 4-vinylphenylboronic acid to obtain a trifunctional crosslinking agent. In the preparation of seed latex, the rubber particles generated by the polymerization of flexible monomers act as the core phase, playing a major role in improving toughness in the matrix. Appropriate crosslinking of the core phase can prevent polymer breakage when subjected to excessive voiding effects during impact. However, excessive crosslinking leads to fewer active groups available for shell reactions, making shell formation difficult and resulting in decreased impact toughness.

[0012] The crosslinking agent prepared in this invention has a trifunctional structure, which can ensure crosslinking density while providing reactive groups for the shell layer. It also contains a dynamic borate ester structure; on the one hand, the introduction of boron increases the flame retardancy of the matrix; on the other hand, its dynamic nature can control the crosslinking density of the core phase and allows for reversible fracture upon impact, absorbing impact energy and thus improving impact resistance. Regarding the selection of enamine compounds, choosing compounds with greater differences in double bond reactivity helps control the degree of crosslinking, improves toughness, ensures the retention of reactive double bonds on the core phase surface, and improves the grafting efficiency of the shell layer. The combination of 2-methylallylamine and 3-buten-1-amine, and the combination of 2-methylallylamine and 4-penten-1-amine, exhibit the best stability.

[0013] Preferred method for preparing the flame retardant monomer includes the following steps: (1) adding p-tert-butylbenzaldehyde, diethyl phosphite, and triethylenediamine to tetrahydrofuran and mixing evenly, stirring at 20-25°C for 2-3 hours, concentrating under reduced pressure, and purifying by column chromatography to obtain an α-hydroxyphosphite derivative; (2) adding the α-hydroxyphosphite derivative and triethylamine to dichloromethane and mixing evenly, stirring at -5-0°C for 1-1.5 hours, adding 35-40wt% acryloyl chloride dichloromethane solution dropwise, and after the addition is complete, raising the temperature to 30-35°C and continuing to stir for 10-12 hours, concentrating under reduced pressure, and purifying by column chromatography to obtain the flame retardant monomer.

[0014] Preferably, the α-hydroxyphosphate diethyl ester derivative comprises the following raw materials, by mass parts: 12-14 parts p-tert-butylbenzaldehyde, 13-15 parts diethyl phosphite, 3-4 parts triethylenediamine, and 100 parts tetrahydrofuran; the flame retardant monomer comprises the following raw materials, by mass parts: 23-25 ​​parts α-hydroxyphosphate diethyl ester derivative, 7-8 parts triethylamine, 100 parts dichloromethane, and 20 parts 35-40 wt% acryloyl chloride dichloromethane solution.

[0015] The flame-retardant monomer is prepared by reacting the aldehyde group in p-tert-butylbenzaldehyde with diethyl phosphite under the catalysis of triethylenediamine to obtain an α-hydroxydiethyl phosphate derivative. Further, the hydroxyl group of the α-hydroxydiethyl phosphate derivative undergoes an esterification reaction with acryloyl chloride dichloromethane under the catalysis of triethylamine to obtain an acrylate reactive monomer containing diethyl phosphate. The phosphate group exhibits excellent flame-retardant properties and has a strong polar interaction with the chlorine atoms of polyvinyl chloride, improving the compatibility of the ACR modifier with the matrix. Simultaneously, the introduced tert-butylbenzene structure is similar to the structure of the crosslinking agent in the core-phase preparation process, which helps the flame-retardant monomer preferentially attach to the crosslinking agent site, improving the shell structure formation efficiency. Furthermore, during the flame-retardant process, it facilitates the formation of a phosphorus-boron flame-retardant system with boron, significantly improving the flame-retardant effect.

[0016] Preferably, the temperature of the melt extrusion is 160~170℃; the vulcanizing temperature of the vulcanizing machine is 140~160℃, and the pressure is 10~15MPa.

[0017] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) The present invention uses butyl acrylate, isooctyl acrylate and crosslinking agent as flexible monomers to prepare seed latex, and methyl methacrylate and flame retardant monomers as shell layer. The resulting ACR modifier is added to wood-plastic composite board, which can significantly improve its flame retardant performance and impact resistance.

[0018] (2) The prepared crosslinking agent has a trifunctional structure and a dynamic borate ester structure with different activities, which can regulate the crosslinking density, improve toughness, and improve certain flame retardant properties.

[0019] (3) When the phosphate flame retardant monomer containing tert-butyl groups is introduced, the compatibility between the ACR modifier and the matrix can be further improved during shell polymerization, and the flame retardant performance can be significantly improved. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that the following quantities are by weight. There are no special restrictions on the manufacturers of the raw materials involved in this invention. Exemplary examples include: CAS number 98-29-3 for 4-tert-butylcatechol; CAS number 2878-14-0 for 2-methylallylamine; CAS number 2524-49-4 for 3-buten-1-amine; CAS number 22537-07-1 for 4-penten-1-amine; and paraformaldehyde, brand name 410, manufactured by Jinan Shi... Jitongda Chemical Co., Ltd. provides: CAS No. 2156-04-9 for 4-vinylphenylboronic acid; CAS No. 939-97-9 for p-tert-butylbenzaldehyde; CAS No. 762-04-9 for diethyl phosphite; CAS No. 814-68-6 for acryloyl chloride; CAS No. 141-32-2 for butyl acrylate; CAS No. 29590-42-9 for isooctyl acrylate; and CAS No. 80-62-6 for methyl methacrylate.

[0022] In each embodiment and comparative example, the polyvinyl chloride resin powder comprises polyvinyl chloride and chlorinated polyvinyl chloride in a mass ratio of 20:1. The polyvinyl chloride is of type SG-7, and the chlorinated polyvinyl chloride is of type R347 with a chlorine content ≥66.5%, provided by Shandong Gaoxin Chemical Co., Ltd.; the wood flour is of type 100 mesh; the lubricant is zinc stearate; the filler is calcium carbonate and nano-silica in a mass ratio of 8:1; the plasticizer is epoxidized soybean oil; the stabilizer is a calcium-zinc composite stabilizer; and the coupling agent is KH-570.

[0023] In the following examples, parts refer to parts by weight, and all raw materials mentioned above and others not mentioned are commercially available.

[0024] Example 1: The preparation method of flame-retardant wood-plastic composite board includes the following steps: Step 1: Preparation of crosslinking agent: (1) Under a nitrogen atmosphere, 4-tert-butylcatechol, enamine compounds (2-methylallylamine and 3-buten-1-amine in a molar ratio of 1:1) and paraformaldehyde were added to anhydrous ethanol in a ratio of 1 mol: 2.3 mol: 60 g and mixed evenly at 60 °C. The mixture was heated to 90 °C and stirred for 3 h. The solvent was removed by vacuum evaporation and the mixture was dried to obtain the catechol derivative; (2) Under a nitrogen atmosphere, the catechol derivative and 4-vinylphenylboronic acid were added to dimethyl sulfoxide in a molar ratio of 1:1.1 and mixed evenly. The pH was adjusted to 7.5~8 and the mixture was stirred for 12 h at 25 °C. The solvent was removed by vacuum evaporation and the mixture was dried to obtain the crosslinking agent; Step 2: Preparation of flame retardant monomer: (1) 13 parts of p-tert-butylbenzaldehyde, 14 parts of diethyl phosphite, and 3.5 parts of triethylenediamine were added to 100 parts of tetrahydrofuran and mixed evenly. The mixture was stirred at 25°C for 2 hours, concentrated under reduced pressure, and purified by column chromatography to obtain α-hydroxy phosphate diethyl ester derivative; (2) 24 parts of α-hydroxy phosphate diethyl ester derivative and 7.5 parts of triethylamine were added to 100 parts of dichloromethane and mixed evenly. The mixture was stirred at -5°C for 1 hour, and 20 parts of 38wt% acryloyl chloride dichloromethane solution were added dropwise. After the addition was completed, the temperature was raised to 35°C and the mixture was stirred for 12 hours. The mixture was concentrated under reduced pressure and purified by column chromatography to obtain flame retardant monomer; Step 3: Preparation of ACR Modifier: (1) Under a nitrogen atmosphere, 37 parts of butyl acrylate, 11 parts of isooctyl acrylate, 1.2 parts of crosslinking agent, 0.5 parts of sodium dodecyl sulfate, 0.3 parts of potassium carbonate, and 0.3 parts of potassium persulfate were added to 35 parts of deionized water and mixed evenly. The mixture was stirred at 65°C for 2 hours to obtain seed latex. (2) 17 parts of methyl methacrylate, 12 parts of flame retardant monomer, and 0.4 parts of sodium dodecyl sulfate were added to 70 parts of deionized water and mixed evenly to obtain an emulsion solution. Under a nitrogen atmosphere, 100 parts of seed latex and 0.2 parts of potassium persulfate were added to 80 parts of deionized water and stirred at 65°C for 25 minutes. The emulsion solution was added dropwise at 75°C, with the addition rate controlled at 1 drop / second. After the addition was completed, the mixture was stirred for 35 minutes. The emulsion was broken, filtered, washed, and dried to obtain ACR modifier. Step 4: Preparation of flame-retardant wood-plastic composite board: Mix 100 parts of polyvinyl chloride resin powder, 70 parts of wood flour, 14 parts of ACR modifier, 4 parts of lubricant, 9 parts of filler, 1.5 parts of plasticizer, 5 parts of stabilizer, and 0.5 parts of coupling agent evenly, and then melt-extrude at 170°C using a twin-screw method. Finally, press the mixture into shape in a vulcanizing machine at 160°C and 15MPa to obtain flame-retardant wood-plastic composite board.

[0025] Example 2: The preparation method of flame-retardant wood-plastic composite board includes the following steps: Step 1: Preparation of crosslinking agent: (1) Under a nitrogen atmosphere, 4-tert-butylcatechol, enamine compounds (2-methylallylamine and 4-penten-1-amine in a molar ratio of 1:1) and paraformaldehyde were added to anhydrous ethanol in a ratio of 1 mol: 2.3 mol: 60 g and mixed evenly at 60 °C. The mixture was heated to 90 °C and stirred for 3 h. The solvent was removed by vacuum evaporation and the mixture was dried to obtain the catechol derivative; (2) Under a nitrogen atmosphere, the catechol derivative and 4-vinylphenylboronic acid were added to dimethyl sulfoxide in a molar ratio of 1:1.1 and mixed evenly. The pH was adjusted to 7.5~8 and the mixture was stirred for 12 h at 25 °C. The solvent was removed by vacuum evaporation and the mixture was dried to obtain the crosslinking agent; Step 2: Preparation of flame retardant monomer: (1) 13 parts of p-tert-butylbenzaldehyde, 14 parts of diethyl phosphite, and 3.5 parts of triethylenediamine were added to 100 parts of tetrahydrofuran and mixed evenly. The mixture was stirred at 25°C for 2 hours, concentrated under reduced pressure, and purified by column chromatography to obtain α-hydroxy phosphate diethyl ester derivative; (2) 24 parts of α-hydroxy phosphate diethyl ester derivative and 7.5 parts of triethylamine were added to 100 parts of dichloromethane and mixed evenly. The mixture was stirred at -5°C for 1 hour, and 20 parts of 38wt% acryloyl chloride dichloromethane solution were added dropwise. After the addition was completed, the temperature was raised to 35°C and the mixture was stirred for 12 hours. The mixture was concentrated under reduced pressure and purified by column chromatography to obtain flame retardant monomer; Step 3: Preparation of ACR Modifier: (1) Under a nitrogen atmosphere, 37 parts of butyl acrylate, 11 parts of isooctyl acrylate, 1.2 parts of crosslinking agent, 0.5 parts of sodium dodecyl sulfate, 0.3 parts of potassium carbonate, and 0.3 parts of potassium persulfate were added to 35 parts of deionized water and mixed evenly. The mixture was stirred at 65°C for 2 hours to obtain seed latex. (2) 17 parts of methyl methacrylate, 12 parts of flame retardant monomer, and 0.4 parts of sodium dodecyl sulfate were added to 70 parts of deionized water and mixed evenly to obtain an emulsion solution. Under a nitrogen atmosphere, 100 parts of seed latex and 0.2 parts of potassium persulfate were added to 80 parts of deionized water and stirred at 65°C for 25 minutes. The emulsion solution was added dropwise at 75°C, with the addition rate controlled at 1 drop / second. After the addition was completed, the mixture was stirred for 35 minutes. The emulsion was broken, filtered, washed, and dried to obtain ACR modifier. Step 4: Preparation of flame-retardant wood-plastic composite board: Mix 100 parts of polyvinyl chloride resin powder, 70 parts of wood flour, 13 parts of ACR modifier, 4 parts of lubricant, 9 parts of filler, 1.5 parts of plasticizer, 5 parts of stabilizer, and 0.5 parts of coupling agent evenly, and then melt-extrude at 170°C using a twin-screw method. Finally, press the mixture into shape in a vulcanizing machine at 160°C and 15MPa to obtain flame-retardant wood-plastic composite board.

[0026] Example 3: The preparation method of flame-retardant wood-plastic composite board includes the following steps: Step 1: Preparation of crosslinking agent: (1) Under a nitrogen atmosphere, 4-tert-butylcatechol, enamine compound (2-methylallylamine), and paraformaldehyde were added to anhydrous ethanol in a ratio of 1 mol: 2.3 mol: 60 g and mixed evenly at 60 °C. The mixture was heated to 90 °C and stirred for 3 h. The solvent was removed by vacuum evaporation and the mixture was dried to obtain the catechol derivative; (2) Under a nitrogen atmosphere, the catechol derivative and 4-vinylphenylboronic acid were added to dimethyl sulfoxide in a molar ratio of 1:1.1 and mixed evenly. The pH was adjusted to 7.5~8 and the mixture was stirred for 12 h at 25 °C. The solvent was removed by vacuum evaporation and the mixture was dried to obtain the crosslinking agent; Step 2: Preparation of flame retardant monomer: (1) 13 parts of p-tert-butylbenzaldehyde, 14 parts of diethyl phosphite, and 3.5 parts of triethylenediamine were added to 100 parts of tetrahydrofuran and mixed evenly. The mixture was stirred at 25°C for 2 hours, concentrated under reduced pressure, and purified by column chromatography to obtain α-hydroxy phosphate diethyl ester derivative; (2) 24 parts of α-hydroxy phosphate diethyl ester derivative and 7.5 parts of triethylamine were added to 100 parts of dichloromethane and mixed evenly. The mixture was stirred at -5°C for 1 hour, and 20 parts of 38wt% acryloyl chloride dichloromethane solution were added dropwise. After the addition was completed, the temperature was raised to 35°C and the mixture was stirred for 12 hours. The mixture was concentrated under reduced pressure and purified by column chromatography to obtain flame retardant monomer; Step 3: Preparation of ACR Modifier: (1) Under a nitrogen atmosphere, 37 parts of butyl acrylate, 11 parts of isooctyl acrylate, 1.2 parts of crosslinking agent, 0.5 parts of sodium dodecyl sulfate, 0.3 parts of potassium carbonate, and 0.3 parts of potassium persulfate were added to 35 parts of deionized water and mixed evenly. The mixture was stirred at 65°C for 2 hours to obtain seed latex. (2) 17 parts of methyl methacrylate, 12 parts of flame retardant monomer, and 0.4 parts of sodium dodecyl sulfate were added to 70 parts of deionized water and mixed evenly to obtain an emulsion solution. Under a nitrogen atmosphere, 100 parts of seed latex and 0.2 parts of potassium persulfate were added to 80 parts of deionized water and stirred at 65°C for 25 minutes. The emulsion solution was added dropwise at 75°C, with the addition rate controlled at 1 drop / second. After the addition was completed, the mixture was stirred for 35 minutes. The emulsion was broken, filtered, washed, and dried to obtain ACR modifier. Step 4: Preparation of flame-retardant wood-plastic composite board: Mix 100 parts of polyvinyl chloride resin powder, 60-80 parts of wood flour, 12-16 parts of ACR modifier, 4 parts of lubricant, 9 parts of filler, 1.5 parts of plasticizer, 5 parts of stabilizer, and 0.5 parts of coupling agent evenly, and then melt-extrude at 170°C using a twin-screw method. Finally, press the mixture into shape in a vulcanizing machine at 160°C and 15MPa to obtain flame-retardant wood-plastic composite board.

[0027] Example 4: The preparation method of flame-retardant wood-plastic composite board includes the following steps: Step 1: Preparation of crosslinking agent: (1) Under a nitrogen atmosphere, 4-tert-butylcatechol, enamine compounds (2-methylallylamine and 3-buten-1-amine in a molar ratio of 1:1) and paraformaldehyde were added to anhydrous ethanol in a ratio of 1 mol: 2.3 mol: 60 g and mixed evenly at 60 °C. The mixture was heated to 90 °C and stirred for 3 h. The solvent was removed by vacuum evaporation and the mixture was dried to obtain the catechol derivative; (2) Under a nitrogen atmosphere, the catechol derivative and 4-vinylphenylboronic acid were added to dimethyl sulfoxide in a molar ratio of 1:1.1 and mixed evenly. The pH was adjusted to 7.5~8 and the mixture was stirred for 12 h at 25 °C. The solvent was removed by vacuum evaporation and the mixture was dried to obtain the crosslinking agent; Step 2: Preparation of flame retardant monomer: (1) 13 parts of p-tert-butylbenzaldehyde, 14 parts of diethyl phosphite, and 3.5 parts of triethylenediamine were added to 100 parts of tetrahydrofuran and mixed evenly. The mixture was stirred at 25°C for 2 hours, concentrated under reduced pressure, and purified by column chromatography to obtain α-hydroxy phosphate diethyl ester derivative; (2) 24 parts of α-hydroxy phosphate diethyl ester derivative and 7.5 parts of triethylamine were added to 100 parts of dichloromethane and mixed evenly. The mixture was stirred at -5°C for 1 hour, and 20 parts of 38wt% acryloyl chloride dichloromethane solution were added dropwise. After the addition was completed, the temperature was raised to 35°C and the mixture was stirred for 12 hours. The mixture was concentrated under reduced pressure and purified by column chromatography to obtain flame retardant monomer; Step 3: Preparation of ACR Modifier: (1) Under a nitrogen atmosphere, 37 parts of butyl acrylate, 11 parts of isooctyl acrylate, 1.2 parts of crosslinking agent, 0.5 parts of sodium dodecyl sulfate, 0.3 parts of potassium carbonate, and 0.3 parts of potassium persulfate were added to 35 parts of deionized water and mixed evenly. The mixture was stirred at 65°C for 2 hours to obtain seed latex. (2) 17 parts of methyl methacrylate, 12 parts of flame retardant monomer, and 0.4 parts of sodium dodecyl sulfate were added to 70 parts of deionized water and mixed evenly to obtain an emulsion solution. Under a nitrogen atmosphere, 100 parts of seed latex and 0.2 parts of potassium persulfate were added to 80 parts of deionized water and stirred at 65°C for 25 minutes. The emulsion solution was added dropwise at 75°C, with the addition rate controlled at 1 drop / second. After the addition was completed, the mixture was stirred for 35 minutes. The emulsion was broken, filtered, washed, and dried to obtain ACR modifier. Step 4: Preparation of flame-retardant wood-plastic composite board: Mix 100 parts of polyvinyl chloride resin powder, 80 parts of wood flour, 16 parts of ACR modifier, 4 parts of lubricant, 9 parts of filler, 1.5 parts of plasticizer, 5 parts of stabilizer, and 0.5 parts of coupling agent evenly, and then melt-extrude at 170°C using a twin-screw method. Finally, press the mixture into shape in a vulcanizing machine at 160°C and 15MPa to obtain flame-retardant wood-plastic composite board.

[0028] Comparative Example 1: Based on Example 1, without adding flame-retardant monomers, the remaining processes remain unchanged, as follows: Step 1: Preparation of crosslinking agent: (1) Under a nitrogen atmosphere, 4-tert-butylcatechol, enamine compounds (2-methylallylamine and 3-buten-1-amine in a molar ratio of 1:1) and paraformaldehyde were added to anhydrous ethanol in a ratio of 1 mol: 2.3 mol: 60 g and mixed evenly at 60 °C. The mixture was heated to 90 °C and stirred for 3 h. The solvent was removed by vacuum evaporation and the mixture was dried to obtain the catechol derivative; (2) Under a nitrogen atmosphere, the catechol derivative and 4-vinylphenylboronic acid were added to dimethyl sulfoxide in a molar ratio of 1:1.1 and mixed evenly. The pH was adjusted to 7.5~8 and the mixture was stirred for 12 h at 25 °C. The solvent was removed by vacuum evaporation and the mixture was dried to obtain the crosslinking agent; Step 2: Preparation of ACR Modifier: (1) Under a nitrogen atmosphere, 37 parts of butyl acrylate, 11 parts of isooctyl acrylate, 1.2 parts of crosslinking agent, 0.5 parts of sodium dodecyl sulfate, 0.3 parts of potassium carbonate, and 0.3 parts of potassium persulfate were added to 35 parts of deionized water and mixed evenly. The mixture was stirred at 65°C for 2 hours to obtain seed latex. (2) 29 parts of methyl methacrylate and 0.4 parts of sodium dodecyl sulfate were added to 70 parts of deionized water and mixed evenly to obtain an emulsion solution. Under a nitrogen atmosphere, 100 parts of seed latex and 0.2 parts of potassium persulfate were added to 80 parts of deionized water and stirred at 65°C for 25 minutes. The emulsion solution was added dropwise at 75°C, with the addition rate controlled at 1 drop / second. After the addition was completed, the mixture was stirred for 35 minutes. The emulsion was broken, filtered, washed, and dried to obtain ACR modifier. Step 3: Preparation of flame-retardant wood-plastic composite board: Mix 100 parts of polyvinyl chloride resin powder, 70 parts of wood flour, 14 parts of ACR modifier, 4 parts of lubricant, 9 parts of filler, 1.5 parts of plasticizer, 5 parts of stabilizer, and 0.5 parts of coupling agent evenly, and then melt-extrude at 170°C using a twin-screw method. Finally, press the mixture into shape in a vulcanizing machine at 160°C and 15MPa to obtain flame-retardant wood-plastic composite board.

[0029] Comparative Example 2: Based on Example 1, p-tert-butylbenzaldehyde was replaced with benzaldehyde in the preparation of the flame retardant monomer, while the rest of the process remained unchanged, as follows: Step 1: Preparation of crosslinking agent: (1) Under a nitrogen atmosphere, 4-tert-butylcatechol, enamine compounds (2-methylallylamine and 3-buten-1-amine in a molar ratio of 1:1) and paraformaldehyde were added to anhydrous ethanol in a ratio of 1 mol: 2.3 mol: 60 g and mixed evenly at 60 °C. The mixture was heated to 90 °C and stirred for 3 h. The solvent was removed by vacuum evaporation and the mixture was dried to obtain the catechol derivative; (2) Under a nitrogen atmosphere, the catechol derivative and 4-vinylphenylboronic acid were added to dimethyl sulfoxide in a molar ratio of 1:1.1 and mixed evenly. The pH was adjusted to 7.5~8 and the mixture was stirred for 12 h at 25 °C. The solvent was removed by vacuum evaporation and the mixture was dried to obtain the crosslinking agent; Step 2: Preparation of flame retardant monomer: (1) 10 parts of p-tert-butylbenzaldehyde, 14 parts of diethyl phosphite, and 3.5 parts of triethylenediamine were added to 100 parts of tetrahydrofuran and mixed evenly. The mixture was stirred at 25°C for 2 hours, concentrated under reduced pressure, and purified by column chromatography to obtain α-hydroxy phosphate diethyl ester derivative; (2) 24 parts of α-hydroxy phosphate diethyl ester derivative and 7.5 parts of triethylamine were added to 100 parts of dichloromethane and mixed evenly. The mixture was stirred at -5°C for 1 hour, and 20 parts of 38wt% acryloyl chloride dichloromethane solution were added dropwise. After the addition was completed, the temperature was raised to 35°C and the mixture was stirred for 12 hours. The mixture was concentrated under reduced pressure and purified by column chromatography to obtain flame retardant monomer; Step 3: Preparation of ACR Modifier: (1) Under a nitrogen atmosphere, 37 parts of butyl acrylate, 11 parts of isooctyl acrylate, 1.2 parts of crosslinking agent, 0.5 parts of sodium dodecyl sulfate, 0.3 parts of potassium carbonate, and 0.3 parts of potassium persulfate were added to 35 parts of deionized water and mixed evenly. The mixture was stirred at 65°C for 2 hours to obtain seed latex. (2) 17 parts of methyl methacrylate, 12 parts of flame retardant monomer, and 0.4 parts of sodium dodecyl sulfate were added to 70 parts of deionized water and mixed evenly to obtain an emulsion solution. Under a nitrogen atmosphere, 100 parts of seed latex and 0.2 parts of potassium persulfate were added to 80 parts of deionized water and stirred at 65°C for 25 minutes. The emulsion solution was added dropwise at 75°C, with the addition rate controlled at 1 drop / second. After the addition was completed, the mixture was stirred for 35 minutes. The emulsion was broken, filtered, washed, and dried to obtain ACR modifier. Step 4: Preparation of flame-retardant wood-plastic composite board: Mix 100 parts of polyvinyl chloride resin powder, 70 parts of wood flour, 14 parts of ACR modifier, 4 parts of lubricant, 9 parts of filler, 1.5 parts of plasticizer, 5 parts of stabilizer, and 0.5 parts of coupling agent evenly, and then melt-extrude at 170°C using a twin-screw method. Finally, press the mixture into shape in a vulcanizing machine at 160°C and 15MPa to obtain flame-retardant wood-plastic composite board.

[0030] Comparative Example 3: Based on Example 1, the crosslinking agent used was triallyl isocyanurate, and the remaining processes remained unchanged, as follows: Step 1: Preparation of flame retardant monomer: (1) 13 parts of p-tert-butylbenzaldehyde, 14 parts of diethyl phosphite, and 3.5 parts of triethylenediamine were added to 100 parts of tetrahydrofuran and mixed evenly. The mixture was stirred at 25°C for 2 hours, concentrated under reduced pressure, and purified by column chromatography to obtain α-hydroxy phosphate diethyl ester derivative; (2) 24 parts of α-hydroxy phosphate diethyl ester derivative and 7.5 parts of triethylamine were added to 100 parts of dichloromethane and mixed evenly. The mixture was stirred at -5°C for 1 hour, and 20 parts of 38wt% acryloyl chloride dichloromethane solution were added dropwise. After the addition was completed, the temperature was raised to 35°C and the mixture was stirred for 12 hours. The mixture was concentrated under reduced pressure and purified by column chromatography to obtain flame retardant monomer; Step 2: Preparation of ACR Modifier: (1) Under a nitrogen atmosphere, 37 parts of butyl acrylate, 11 parts of isooctyl acrylate, 1.2 parts of crosslinking agent (tracene propyl isocyanurate), 0.5 parts of sodium dodecyl sulfate, 0.3 parts of potassium carbonate, and 0.3 parts of potassium persulfate were added to 35 parts of deionized water and mixed evenly. The mixture was stirred at 65°C for 2 hours to obtain seed latex. (2) 17 parts of methyl methacrylate, 12 parts of flame retardant monomer, and 0.4 parts of sodium dodecyl sulfate were added to 70 parts of deionized water and mixed evenly to obtain an emulsion solution. Under a nitrogen atmosphere, 100 parts of seed latex and 0.2 parts of potassium persulfate were added to 80 parts of deionized water and stirred at 65°C for 25 minutes. The emulsion solution was added dropwise at 75°C, with the addition rate controlled at 1 drop / second. After the addition was completed, the mixture was stirred for another 35 minutes. The emulsion was broken, filtered, washed, and dried to obtain ACR modifier. Step 3: Preparation of flame-retardant wood-plastic composite board: Mix 100 parts of polyvinyl chloride resin powder, 70 parts of wood flour, 14 parts of ACR modifier, 4 parts of lubricant, 9 parts of filler, 1.5 parts of plasticizer, 5 parts of stabilizer, and 0.5 parts of coupling agent evenly, and then melt-extrude at 170°C using a twin-screw method. Finally, press the mixture into shape in a vulcanizing machine at 160°C and 15MPa to obtain flame-retardant wood-plastic composite board.

[0031] Comparative Example 4: Based on Example 1, the crosslinking agent used was dicyclopentenyl acrylate, and the remaining processes remained unchanged, as follows: Step 1: Preparation of flame retardant monomer: (1) 13 parts of p-tert-butylbenzaldehyde, 14 parts of diethyl phosphite, and 3.5 parts of triethylenediamine were added to 100 parts of tetrahydrofuran and mixed evenly. The mixture was stirred at 25°C for 2 hours, concentrated under reduced pressure, and purified by column chromatography to obtain α-hydroxy phosphate diethyl ester derivative; (2) 24 parts of α-hydroxy phosphate diethyl ester derivative and 7.5 parts of triethylamine were added to 100 parts of dichloromethane and mixed evenly. The mixture was stirred at -5°C for 1 hour, and 20 parts of 38wt% acryloyl chloride dichloromethane solution were added dropwise. After the addition was completed, the temperature was raised to 35°C and the mixture was stirred for 12 hours. The mixture was concentrated under reduced pressure and purified by column chromatography to obtain flame retardant monomer; Step 2: Preparation of ACR Modifier: (1) Under a nitrogen atmosphere, 37 parts of butyl acrylate, 11 parts of isooctyl acrylate, 1.2 parts of crosslinking agent (dicyclopentenyl acrylate), 0.5 parts of sodium dodecyl sulfate, 0.3 parts of potassium carbonate, and 0.3 parts of potassium persulfate were added to 35 parts of deionized water and mixed evenly. The mixture was stirred at 65°C for 2 hours to obtain seed latex. (2) 17 parts of methyl methacrylate, 12 parts of flame retardant monomer, and 0.4 parts of sodium dodecyl sulfate were added to 70 parts of deionized water and mixed evenly to obtain an emulsion solution. Under a nitrogen atmosphere, 100 parts of seed latex and 0.2 parts of potassium persulfate were added to 80 parts of deionized water and stirred at 65°C for 25 minutes. The emulsion solution was added dropwise at 75°C, with the addition rate controlled at 1 drop / second. After the addition was completed, the mixture was stirred for another 35 minutes. The emulsion was broken, filtered, washed, and dried to obtain ACR modifier. Step 3: Preparation of flame-retardant wood-plastic composite board: Mix 100 parts of polyvinyl chloride resin powder, 70 parts of wood flour, 14 parts of ACR modifier, 4 parts of lubricant, 9 parts of filler, 1.5 parts of plasticizer, 5 parts of stabilizer, and 0.5 parts of coupling agent evenly, and then melt-extrude at 170°C using a twin-screw method. Finally, press the mixture into shape in a vulcanizing machine at 160°C and 15MPa to obtain flame-retardant wood-plastic composite board.

[0032] Performance testing: (1) The impact resistance of the samples prepared in each embodiment and comparative example was tested according to GB / T-1043.1-2008; (2) The tensile properties of the samples prepared in each embodiment and comparative example were tested according to ASTM D638-2000, with a tensile speed of 20 mm / min; (3) The limiting oxygen index of the samples prepared in each embodiment and comparative example was tested according to the method of GB / T 2406.2-2009; The test data are shown in the table below:

[0033] Conclusion: As shown in the table, the ACR modifier obtained by preparing seed latex using butyl acrylate, isooctyl acrylate, and crosslinking agent as flexible monomers, and using methyl methacrylate and flame retardant monomers as shell layers, can significantly improve the flame retardant and impact resistance properties of wood-plastic composite boards, achieving a Class A fire rating.

[0034] In Comparative Example 1, no flame-retardant monomer was added, resulting in a significant decrease in flame-retardant performance and reduced compatibility between the ACR modifier and the matrix, leading to a decrease in impact strength. In Comparative Example 2, p-tert-butylbenzaldehyde was replaced with benzaldehyde, which reduced the shell structure formation efficiency and made it difficult to form a phosphorus-boron flame-retardant system, resulting in a decrease in impact strength and a slight reduction in flame-retardant performance. In Comparative Example 3, triallyl isocyanurate was used as the crosslinking agent. Due to the presence of equally active double bonds, the core layer crosslinking density was high, reducing the toughening effect. Furthermore, due to incomplete shell formation, compatibility was generally poor, resulting in a significant decrease in performance. In Comparative Example 4, dicyclopentenyl acrylate was used as the crosslinking agent, and its impact resistance was not as good as that of Example 1. This is because Example 1 contains a dynamic borate ester structure, which can better control the crosslinking density, allowing for reversible chain breakage.

[0035] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing flame-retardant wood-plastic composite board, characterized in that: Includes the following steps: S1: Seed latex was prepared by using butyl acrylate, isooctyl acrylate, and crosslinking agent as reactive monomers; ACR modifier was obtained by shell polymerization of seed latex with methyl methacrylate and flame retardant monomers. S2: Mix polyvinyl chloride resin powder, wood flour, ACR modifier, lubricant, filler, plasticizer, stabilizer, and coupling agent evenly, then melt-extrude the mixture in a twin-screw manner and press it into shape using a vulcanizing machine to obtain flame-retardant wood-plastic composite board.

2. The method for preparing a flame-retardant wood-plastic composite board according to claim 1, characterized in that: The flame-retardant wood-plastic composite board comprises the following raw materials, by weight: 100 parts polyvinyl chloride resin powder, 60-80 parts wood flour, 12-16 parts ACR modifier, 3-5 parts lubricant, 8-10 parts filler, 1-2 parts plasticizer, 4-6 parts stabilizer, and 0.5-1 part coupling agent. The polyvinyl chloride resin powder includes one or both of polyvinyl chloride and chlorinated polyvinyl chloride; the filler includes calcium carbonate and nanofiller in a mass ratio of 7~8:1; the nanofiller includes one or more of nano silica, nano clay, and nano magnesium hydroxide.

3. The method for preparing a flame-retardant wood-plastic composite board according to claim 1, characterized in that: The preparation method of the ACR modifier specifically includes the following steps: (1) Under a nitrogen atmosphere, butyl acrylate, isooctyl acrylate, crosslinking agent, sodium dodecyl sulfate, potassium carbonate, and potassium persulfate are added to deionized water in sequence and mixed evenly. The mixture is stirred at 60-70℃ for 2-3 hours to obtain seed latex; (2) Methyl methacrylate, flame retardant monomer, and sodium dodecyl sulfate are added to deionized water and mixed evenly to obtain an emulsion solution; Under a nitrogen atmosphere, seed latex and potassium persulfate are added to deionized water and stirred at 60-70℃ for 20-30 minutes; The emulsion solution is added dropwise at 70-80℃, and the addition rate is controlled at 1-2 drops / second. After the addition is completed, the mixture is stirred for 30-40 minutes, the emulsion is broken, filtered, washed, and dried to obtain the ACR modifier.

4. The method for preparing a flame-retardant wood-plastic composite board according to claim 3, characterized in that: The seed latex comprises the following raw materials, by weight: 35-40 parts butyl acrylate, 10-12 parts isooctyl acrylate, 1-1.4 parts crosslinking agent, 0.4-0.6 parts sodium dodecyl sulfate, 0.3-0.4 parts potassium carbonate, 0.2-0.3 parts potassium persulfate, and 30-40 parts deionized water; the ACR modifier comprises the following raw materials, by weight: 15-20 parts methyl methacrylate, 10-15 parts flame retardant monomer, 0.3-0.5 parts sodium dodecyl sulfate, 100 parts seed latex, 0.1-0.2 parts potassium persulfate, and 150-160 parts deionized water.

5. The method for preparing a flame-retardant wood-plastic composite board according to claim 1, characterized in that: The preparation method of the crosslinking agent includes the following steps: (1) Under a nitrogen atmosphere, 4-tert-butylcatechol, enamine compounds, and paraformaldehyde are added to anhydrous ethanol and mixed evenly at 60~65℃, heated to 90~95℃ and stirred for 3~4h, the solvent is removed by vacuum evaporation, and dried to obtain the catechol derivative; (2) Under a nitrogen atmosphere, the catechol derivative and 4-vinylphenylboronic acid are added to dimethyl sulfoxide and mixed evenly, the pH is adjusted to 7.5~8, stirred for 12~16h at 25~30℃, the solvent is removed by vacuum evaporation, and dried to obtain the crosslinking agent.

6. The method for preparing a flame-retardant wood-plastic composite board according to claim 5, characterized in that: The raw materials for the catechol derivative include 4-tert-butylcatechol, enamine compounds, and paraformaldehyde in a ratio of 1 mol: 2.2~2.4 mol: 60~66 g; the raw materials for the crosslinking agent include catechol derivative and 4-vinylphenylboronic acid in a molar ratio of 1:1~1.

2. The enamine compounds include one or two of 2-methylallylamine, 3-buten-1-amine, and 4-penten-1-amine.

7. The method for preparing a flame-retardant wood-plastic composite board according to claim 1, characterized in that: The preparation method of the flame retardant monomer includes the following steps: (1) p-tert-butylbenzaldehyde, diethyl phosphite, and triethylenediamine are added to tetrahydrofuran and mixed evenly. The mixture is stirred at 20-25°C for 2-3 hours, concentrated under reduced pressure, and purified by column chromatography to obtain α-hydroxy phosphate diethyl ester derivative; (2) α-hydroxy phosphate diethyl ester derivative and triethylamine are added to dichloromethane and mixed evenly. The mixture is stirred at -5-0°C for 1-1.5 hours. 35-40 wt% acryloyl chloride dichloromethane solution is added dropwise. After the addition is completed, the temperature is raised to 30-35°C and the mixture is stirred for 10-12 hours. The mixture is concentrated under reduced pressure and purified by column chromatography to obtain the flame retardant monomer.

8. The method for preparing a flame-retardant wood-plastic composite board according to claim 7, characterized in that: The α-hydroxyphosphate diethyl ester derivative comprises the following raw materials, by mass parts: 12-14 parts p-tert-butylbenzaldehyde, 13-15 parts diethyl phosphite, 3-4 parts triethylenediamine, and 100 parts tetrahydrofuran; the flame retardant monomer comprises the following raw materials, by mass parts: 23-25 ​​parts α-hydroxyphosphate diethyl ester derivative, 7-8 parts triethylamine, 100 parts dichloromethane, and 20 parts 35-40 wt% acryloyl chloride dichloromethane solution.

9. The method for preparing a flame-retardant wood-plastic composite board according to claim 1, characterized in that: The temperature of the melt extrusion is 160~170℃; the vulcanization temperature of the vulcanizing machine is 140~160℃, and the pressure is 10~15MPa.

10. A flame-retardant wood-plastic composite board prepared by the method of preparing a flame-retardant wood-plastic composite board according to any one of claims 1 to 9.

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