Self-cooling outdoor wood-plastic material and preparation method thereof

Abstract

This application relates to the technical field of wood-plastic composite materials, specifically disclosing a self-cooling outdoor wood-plastic composite material and its preparation method. The self-cooling outdoor wood-plastic composite material includes a main board body and a self-cooling surface layer. The self-cooling surface layer covers the outer side of the main board body and comprises the following raw materials in parts by weight: 72-78 parts pure acrylic emulsion, 10-14 parts self-cooling emulsion, 12-16 parts rutile TiO2 slurry, 2-3 parts modified PE wax emulsion, 1-2 parts infrared functional filler, 0.2-0.4 parts dispersant, and 0.1-0.2 parts defoamer. This application can improve the self-cooling function of outdoor wood-plastic composite materials, helping to reduce thermal aging, deformation, and fading, and extend the service life of outdoor wood-plastic composite materials.

Description

Technical Field

[0001] This invention relates to the technical field of wood-plastic composite materials, and in particular to a self-cooling outdoor wood-plastic composite material and its preparation method. Background Technology

[0002] With the acceleration of urbanization and the continuous growth in demand for outdoor building decoration, wood-plastic composite materials, which combine the natural texture of wood with the corrosion resistance and weather resistance of plastics, are widely used in outdoor flooring, fences, landscape walkways, pavilions, and building facades. Traditional wood-plastic materials are usually made by melt blending and extrusion molding of plant fibers and thermoplastics, which to some extent solves the problems of solid wood being prone to decay, cracking, and insect infestation, thus extending the service life of the material.

[0003] However, in high-temperature or intense sunlight conditions during summer, existing outdoor wood-plastic composite materials generally suffer from excessively high surface temperatures. On one hand, the plastic components and some dark pigments in wood-plastic composites have high light absorption rates, causing a large amount of solar radiation energy to be converted into heat and accumulate on the material surface. On the other hand, traditional wood-plastic composites have low thermal conductivity, making it difficult for heat to be quickly conducted inwards. Furthermore, their generally low infrared emissivity makes it difficult for heat to dissipate effectively through thermal radiation. Excessively high surface temperatures can accelerate thermal aging, deformation, and fading of the material, shortening its service life.

[0004] Therefore, there is an urgent need to develop a new type of wood-plastic composite material with self-cooling function and suitable for outdoor environments. Summary of the Invention

[0005] In order to improve the self-cooling function of outdoor wood-plastic composite materials, this application provides a self-cooling outdoor wood-plastic composite material and its preparation method.

[0006] Firstly, this application provides a self-cooling outdoor wood-plastic composite material, which adopts the following technical solution: A self-cooling outdoor wood-plastic composite material includes a board body and a self-cooling surface layer. The self-cooling surface layer covers the outside of the board body and comprises the following raw materials in parts by weight: 72-78 parts of pure acrylic emulsion, 10-14 parts of self-cooling emulsion, 12-16 parts of rutile TiO2 slurry, 2-3 parts of modified PE wax emulsion, 1-2 parts of infrared functional filler, 0.2-0.4 parts of dispersant, and 0.1-0.2 parts of defoamer.

[0007] In one specific feasible embodiment, the self-cooling emulsion is prepared according to the following steps: Weigh the following raw materials: 50-70 parts methyl methacrylate, 25-40 parts butyl acrylate, 2-8 parts methacrylic acid, 40-60 parts deionized water, 0.5-2.0 parts anionic surfactant, 1.0-3.0 parts nonionic surfactant, and 0.3-0.8 parts initiator; According to the formula, methyl methacrylate, butyl acrylate and methacrylic acid are mixed evenly to obtain the oil phase; Deionized water was divided into two parts by mass ratio (7-8):(2-3). The first part of deionized water, anionic surfactant, and nonionic surfactant were mixed and added dropwise under stirring at 800-1200 rpm. After the addition was completed, stirring was continued for 10-20 min to obtain a pre-emulsion. The pre-emulsion was divided into a first pre-emulsion and a second pre-emulsion according to a mass ratio of (2-3):(17-18). The initiator was mixed evenly with the second part of deionized water to obtain an initiator solution. The initiator solution was then divided into a first initiator solution and a second initiator solution. Mix the first pre-emulsion and the first initiator solution, purge with nitrogen to remove oxygen, heat to 75-85℃, and react for 20-40 minutes to obtain seed micelles. Add the second pre-emulsion and the second initiator solution dropwise to the seed micelles. After the addition is complete, keep the reaction at the temperature for 1-2 hours, cool to 35-40℃, filter, and adjust the pH to 6.5-7.5 to obtain a self-cooling emulsion.

[0008] In one specific feasible implementation, the initiator solution is divided into a first initiator solution and a second initiator solution according to a mass ratio of (3-5):(5-7).

[0009] In one specific feasible implementation, the second part of the preemulsion and the second part of the initiator solution are added dropwise to the seed micelles at a uniform rate over 3.5-4.5 hours.

[0010] In one specific implementation, the infrared functional filler includes one or more of silicon carbide, hexagonal boron nitride, and cordierite powder.

[0011] In one specific implementation, the self-cooling surface layer further includes near-infrared reflective pigments and / or hollow glass microspheres.

[0012] In one specific implementation, the main body of the board includes a core layer and a transition layer, with the transition layer covering the outside of the core layer.

[0013] In one specific implementation, the core layer comprises, by weight, the following raw materials: 45-55 parts recycled thermoplastic, 35-45 parts wood flour, 1-4 parts PE-g-MAH, 0.1-0.3 parts antioxidant, and 0.5-1.5 parts ethylene bis-stearamide; and the transition layer comprises, by weight, the following raw materials: 55-65 parts thermoplastic, 25-35 parts wood flour, 4-6 parts SEBS-g-MAH, 1-1.5 parts silane coupling agent, and 0.2-0.8 parts titanate.

[0014] Secondly, this application provides a method for preparing a self-cooling outdoor wood-plastic composite material, which adopts the following technical solution: A method for preparing a self-cooling outdoor wood-plastic composite material includes the following steps: According to the formula, pure acrylic emulsion, self-cooling emulsion, rutile TiO2 slurry, modified PE wax emulsion, infrared functional filler, dispersant and defoamer are mixed evenly to obtain the surface raw material; The main raw material and the surface material of the board are co-extruded together. The main raw material forms the board body, and the surface material forms a self-cooling surface layer that wraps around the board body, thus obtaining a self-cooling outdoor wood-plastic composite material.

[0015] In summary, this application has the following beneficial effects: 1. This application adopts a board body and a self-cooling surface layer. The self-cooling surface layer uses pure acrylic emulsion, self-cooling emulsion, rutile TiO2 slurry, modified PE wax emulsion, infrared functional filler, dispersant and defoamer, which can improve the self-cooling function of outdoor wood-plastic composite materials, help reduce thermal aging, deformation and fading of outdoor wood-plastic composite materials, and extend their service life.

[0016] 2. In this application, silicon carbide, hexagonal boron nitride, and cordierite powder are preferred, which can form a dual cooling mechanism of reflection and radiation with the reflection function of photonic crystals, making up for the deficiency of single polymers in certain infrared bands and significantly improving the cooling effect at night and on cloudy days.

[0017] 3. The self-cooling surface layer of this application also includes near-infrared reflective pigments and / or hollow glass microspheres, which can further improve the self-cooling function of outdoor wood-plastic composite materials. Detailed Implementation

[0018] Unless otherwise specified, all raw materials used in this application are commercially available. Thermoplastic plastic, brand: LyondellBasell LR732001. Recycled thermoplastic plastic, which is recycled waste thermoplastic material with ash content ≤0.1%. PE-g-MAH, brand: Mitsui Chemicals NF908A (Japan). Antioxidant is Antioxidant 1010, CAS No. 6683-19-8. Ethylene bis-stearamide, CAS: 62-56-6, effective content 99%. Wood flour, 100 mesh, moisture content ≤1.0wt.%. Silicon carbide, model YY033, specification 3000-5000 mesh. SEBS-g-MAH, model: TSRC 7131. Silane coupling agent is KH-570. Titanate, NDZ-201, CAS No. 67691-13-8. Methyl methacrylate, CAS: 80-62-6, effective content 99%. Butyl acrylate, CAS: 141-42-2, effective content 99%. Methacrylic acid, CAS: 79-41-4, effective content 99%. Sodium dodecyl sulfate, CAS No. 7758-29-4, effective content 99%. Surfactant, model NP-40. Ammonium persulfate, AR grade. Hollow glass microspheres, model 3M S15 (USA). Near-infrared black pigment, model Ranbar Black P0086. Pure acrylic emulsion, purchased from Nanjing Danpei Chemical Co., Ltd., particle size distribution: 110-180nm. Rutile TiO2, effective content 98.5%, purchased from Qinghe County Chaotai Metal Materials Co., Ltd. Modified PE wax emulsion, model: BASF WE6. Dispersant, model: BYK-190. Defoamer, model: BYK-051N.

[0019] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0020] Example Example 1

[0021] This embodiment provides a self-cooling outdoor wood-plastic composite material, including a board body and a self-cooling surface layer. The self-cooling surface layer covers the outside of the board body and includes the following raw materials: 75 kg of pure acrylic emulsion, 12 kg of self-cooling emulsion, 14 kg of rutile TiO2 slurry, 2.5 kg of modified PE wax emulsion, 1.5 kg of silicon carbide, 0.3 kg of dispersant, and 0.15 kg of defoamer.

[0022] The main body of the board consists of a core layer and a transition layer, with the transition layer covering the outside of the core layer. The core layer comprises the following raw materials: 50 kg of recycled thermoplastic, 40 kg of wood flour, 2 kg of PE-g-MAH, 0.2 kg of antioxidant, and 1 kg of ethylene bis-stearamide. The transition layer comprises the following raw materials: 60 kg of thermoplastic, 30 kg of wood flour, 5 kg of SEBS-g-MAH, 1.2 kg of silane coupling agent, and 0.5 kg of titanate.

[0023] Self-cooling emulsions are prepared according to the following steps: Weigh the following raw materials: 60 kg of methyl methacrylate, 32.5 kg of butyl acrylate, 5 kg of methacrylic acid, 50 kg of deionized water, 1.25 kg of sodium dodecyl sulfate, 1.5 kg of surfactant, and 0.55 kg of ammonium persulfate.

[0024] According to the formula, methyl methacrylate, butyl acrylate and methacrylic acid are added to a container and magnetically stirred at room temperature for 15 minutes until they are mixed evenly to obtain the oil phase.

[0025] Deionized water was divided into two parts by mass ratio of 3:1. The first part of deionized water, anionic surfactant, and nonionic surfactant were added to a pre-emulsification tank and the oil phase was added dropwise at a uniform rate of 1000 rpm with the addition time controlled at 20 min. After the addition was completed, the mixture was stirred for another 15 min to obtain the pre-emulsion.

[0026] The pre-emulsion was divided into a first pre-emulsion and a second pre-emulsion at a mass ratio of 1:7. The initiator was mixed evenly with the second part of deionized water to obtain an initiator solution. The initiator solution was then divided into a first initiator solution and a second initiator solution at a mass ratio of 2:3.

[0027] The first pre-emulsion was added to a three-necked flask, followed by the first initiator solution. After purging with nitrogen for 30 minutes to remove oxygen, the temperature was raised to 80°C and reacted for 30 minutes to obtain seed micelles. The second pre-emulsion was then added dropwise to the seed micelles at a constant pressure dropping funnel. The second initiator solution was added dropwise simultaneously using a separate funnel over a period of 4 hours. After the addition was complete, the mixture was kept at this temperature for 1.5 hours, then cooled to between 35-40°C. The mixture was then passed through a 200-mesh stainless steel sieve, and the pH was adjusted to between 6.5-7.5 using ammonia or dilute NaOH solution to obtain a self-cooling emulsion.

[0028] Rutile TiO2 slurry is prepared according to the following steps: Add deionized water to the mixing tank, add rutile TiO2 powder to the deionized water while stirring at 500 rpm, stir evenly, pump into a horizontal sand mill, circulate and grind, stir and degas at low speed for 10 minutes, and pass through a 120-mesh sieve to obtain rutile TiO2 slurry.

[0029] This embodiment also provides a method for preparing a self-cooling outdoor wood-plastic composite material, including the following steps: According to the formula, pure acrylic emulsion, self-cooling emulsion, rutile TiO2 slurry, modified PE wax emulsion, silicon carbide, dispersant and defoamer are mixed evenly to obtain the surface material.

[0030] The raw materials are weighed according to the ratio of the core layer and the transition layer, and after mixing, the core layer raw materials and the transition layer raw materials are obtained.

[0031] The core layer material, transition layer material, and surface layer material are fed into three screw extruders, one independent and one collaborative. The materials are co-extruded through a stacked three-layer co-extrusion die, forming a self-cooling outdoor wood-plastic composite material. The core layer material forms the core layer, the transition layer material forms the transition layer surrounding the core layer, and the surface layer material forms the self-cooling surface layer surrounding the transition layer. The core layer screw extruder has the following temperature zones: Zone 1: 130-140℃; Zone 2: 150-160℃; Zone 3: 165-175℃; Die head temperature: 160-170℃; Screw speed: 350 rpm; Melt pressure: 8 MPa. The transition layer screw extruder has the following temperature zones: Zone 1: 125-135℃; Zone 2: 145-155℃; Zone 3: 150-160℃; Die head temperature: 155-165℃; Screw speed: 300 rpm; Melt pressure: 6 MPa. The surface screw extruder has a zone temperature of 150-160℃, a zone temperature of 165-175℃, a zone temperature of 170-180℃, a die head temperature of 165-175℃, a screw speed of 250 rpm, and a melt pressure of 10 MPa.

[0032] In this embodiment, the surface material uses an aqueous emulsion system, extruded via a surface screw extruder. The screw speed of the surface screw extruder is 250 rpm, and the melt pressure is 10 MPa. Under high-speed, high-pressure extrusion conditions, moisture is forcibly extracted in the extruder's exhaust section through a vacuum exhaust device, and residual moisture is essentially removed before the melt enters the die. Simultaneously, the modified PE wax emulsion acts as a lubricant and film-forming aid at high temperatures, helping the surface melt form a continuous and dense coating within the die. During co-extrusion, when the surface melt and transition layer melt are combined within the die, the surface layer thickness is controlled at 0.3-0.5 mm. This thin-layer structure facilitates the rapid dissipation of residual trace moisture, preventing the formation of bubbles or pinhole defects within the surface layer.

[0033] Example 2

[0034] The only difference between this embodiment and Embodiment 1 is that the self-cooling surface layer includes the following raw materials: 72 kg of pure acrylic emulsion, 10 kg of self-cooling emulsion, 12 kg of rutile TiO2 slurry, 2 kg of modified PE wax emulsion, 1 kg of silicon carbide, 0.2 kg of dispersant, and 0.1 kg of defoamer.

[0035] Example 3

[0036] The only difference between this embodiment and Embodiment 1 is that the self-cooling surface layer includes the following raw materials: 78 kg of pure acrylic emulsion, 14 kg of self-cooling emulsion, 16 kg of rutile TiO2 slurry, 3 kg of modified PE wax emulsion, 2 kg of silicon carbide, 0.4 kg of dispersant, and 0.2 kg of defoamer.

[0037] Example 4

[0038] The only difference between this embodiment and Embodiment 1 is that silicon carbide is replaced with an equal amount of hexagonal boron nitride.

[0039] Example 5

[0040] The only difference between this embodiment and Embodiment 1 is that an equal amount of cordierite powder is used to replace silicon carbide.

[0041] Example 6

[0042] The only difference between this embodiment and Embodiment 1 is that the core layer includes the following raw materials: 45 kg of recycled thermoplastic plastic, 35 kg of wood flour, 1 kg of PE-g-MAH, 0.1 kg of antioxidant, and 0.5 kg of ethylene bis-stearamide. The transition layer includes the following raw materials: 55 kg of thermoplastic plastic, 25 kg of wood flour, 4 kg of SEBS-g-MAH, 1 kg of silane coupling agent, and 0.2 kg of titanate.

[0043] Example 7

[0044] The only difference between this embodiment and Embodiment 1 is that the core layer comprises the following raw materials: 55 kg of recycled thermoplastic plastic, 45 kg of wood flour, 3 kg of PE-g-MAH, 0.3 kg of antioxidant, and 1.5 kg of ethylene bis-stearamide. The transition layer comprises the following raw materials: 65 kg of thermoplastic plastic, 35 kg of wood flour, 6 kg of SEBS-g-MAH, 1.5 kg of silane coupling agent, and 0.8 kg of titanate.

[0045] Example 8

[0046] The only difference between this embodiment and Example 1 is that, in the preparation step of the self-cooling emulsion, the following raw materials are weighed: 50 kg of methyl methacrylate, 25 kg of butyl acrylate, 2 kg of methacrylic acid, 40 kg of deionized water, 0.5 kg of sodium dodecyl sulfate, 1.0 kg of surfactant, and 0.3 kg of ammonium persulfate.

[0047] Example 9

[0048] The only difference between this embodiment and Embodiment 1 is that, in the preparation step of the self-cooling emulsion, the following raw materials are weighed: 70 kg of methyl methacrylate, 40 kg of butyl acrylate, 8 kg of methacrylic acid, 60 kg of deionized water, 2.0 kg of sodium dodecyl sulfate, 3.0 kg of surfactant, and 0.8 kg of ammonium persulfate.

[0049] Example 10

[0050] The only difference between this embodiment and Example 1 is that, in the preparation step of the self-cooling emulsion, methyl methacrylate, butyl acrylate, and methacrylic acid are added to a container according to the ratio, and magnetically stirred at room temperature for 15 minutes until uniform, to obtain the oil phase.

[0051] Deionized water was divided into two parts by mass ratio of 7:3. The first part of deionized water, anionic surfactant, and nonionic surfactant were added to a pre-emulsification tank and the oil phase was added dropwise at a uniform rate of 800 rpm with the addition time controlled at 10 min. After the addition was completed, the mixture was stirred for another 10 min to obtain the pre-emulsion.

[0052] The pre-emulsion was divided into a first pre-emulsion and a second pre-emulsion at a mass ratio of 1:9. The initiator was mixed evenly with the second part of deionized water to obtain an initiator solution. The initiator solution was then divided into a first initiator solution and a second initiator solution at a mass ratio of 3:7.

[0053] The first pre-emulsion was added to a three-necked flask, followed by the first initiator solution. After purging with nitrogen for 30 minutes to remove oxygen, the temperature was raised to 75°C and reacted for 20 minutes to obtain seed micelles. The second pre-emulsion was then added dropwise to the seed micelles at a constant pressure dropping funnel. The second initiator solution was added dropwise simultaneously using a separate funnel over a period of 3.5 hours. After the addition was complete, the mixture was kept at this temperature for 1 hour, then cooled to between 35-40°C. The mixture was then passed through a 200-mesh stainless steel sieve, and the pH was adjusted to between 6.5-7.5 using ammonia or dilute NaOH solution to obtain a self-cooling emulsion.

[0054] Example 11

[0055] The only difference between this embodiment and Example 1 is that, in the preparation step of the self-cooling emulsion, methyl methacrylate, butyl acrylate, and methacrylic acid are added to a container according to the ratio, and magnetically stirred at room temperature for 15 minutes until uniform, to obtain the oil phase.

[0056] Deionized water was divided into two parts by mass ratio of 4:1. The first part of deionized water, anionic surfactant, and nonionic surfactant were added to a pre-emulsification tank and the oil phase was added dropwise at a uniform rate of 1200 rpm with stirring. The dropwise addition time was controlled at 10 min. After the dropwise addition was completed, stirring was continued for 20 min to obtain the pre-emulsion.

[0057] The pre-emulsion was divided into a first pre-emulsion and a second pre-emulsion at a mass ratio of 3:17. The initiator was mixed evenly with the second part of deionized water to obtain an initiator solution. The initiator solution was then divided into a first initiator solution and a second initiator solution at a mass ratio of 1:1.

[0058] The first pre-emulsion was added to a three-necked flask, followed by the first initiator solution. After purging with nitrogen for 30 minutes to remove oxygen, the temperature was raised to 85°C and reacted for 40 minutes to obtain seed micelles. The second pre-emulsion was then added dropwise to the seed micelles at a constant pressure dropping funnel. The second initiator solution was added dropwise simultaneously using a separate funnel, with the addition time controlled at 4.5 hours. After the addition was complete, the mixture was kept at this temperature for 2 hours, then cooled to between 35-40°C. The mixture was then passed through a 200-mesh stainless steel sieve, and the pH was adjusted to between 6.5-7.5 using ammonia or dilute NaOH solution to obtain a self-cooling emulsion.

[0059] Example 12

[0060] The only difference between this embodiment and Embodiment 1 is that the self-cooling surface layer is coated on the outer side of the main body of the board. The self-cooling surface layer includes the following raw materials: 75 kg of pure acrylic emulsion, 12 kg of self-cooling emulsion, 14 kg of rutile TiO2 slurry, 2.5 kg of modified PE wax emulsion, 1.5 kg of silicon carbide, 0.3 kg of dispersant, 0.15 kg of defoamer, and 3 kg of hollow glass microspheres. In the preparation method of the self-cooling outdoor wood-plastic composite material: according to the formula, the pure acrylic emulsion, self-cooling emulsion, rutile TiO2 slurry, modified PE wax emulsion, silicon carbide, dispersant, defoamer, and hollow glass microspheres are mixed evenly to obtain the surface layer raw material.

[0061] Example 13

[0062] The only difference between this embodiment and Embodiment 1 is that the self-cooling surface layer is applied to the outer side of the main body of the board. The self-cooling surface layer comprises the following raw materials: 75 kg of pure acrylic emulsion, 12 kg of self-cooling emulsion, 14 kg of rutile TiO2 slurry, 2.5 kg of modified PE wax emulsion, 1.5 kg of silicon carbide, 0.3 kg of dispersant, 0.15 kg of defoamer, and 3 kg of near-infrared black pigment. In the preparation method of the self-cooling outdoor wood-plastic composite material: according to the specified ratio, the pure acrylic emulsion, self-cooling emulsion, rutile TiO2 slurry, modified PE wax emulsion, silicon carbide, dispersant, defoamer, and near-infrared black pigment are mixed evenly to obtain the surface layer raw material.

[0063] Comparative Example Comparative Example 1 The only difference between this comparative example and Example 1 is that, in the raw materials and preparation process of the self-cooling surface layer, an equal amount of pure acrylic emulsion is used to replace the self-cooling emulsion.

[0064] Comparative Example 2 The only difference between this comparative example and Example 1 is that, in the raw materials and preparation process of the self-cooling surface layer, an equal amount of silicon carbide is used to replace the self-cooling emulsion.

[0065] Comparative Example 3 The only difference between this comparative example and Example 1 is that the outdoor wood-plastic composite material in this comparative example only includes the main body of the board and does not include the surface layer.

[0066] Comparative Example 4 The only difference between this comparative example and Example 1 is that the outdoor wood-plastic composite material includes only the main body of the board and does not include the self-cooling surface layer. A water-based cooling coating (model LF-081) is applied to the surface of the main body of the board, and the coating thickness is the same as that of the self-cooling surface layer in Example 1. After curing at room temperature, a coated cooling wood-plastic composite material is obtained.

[0067] Performance testing The following performance tests were conducted on Examples 1-13 and Comparative Examples 1-4: According to GB / T25261-2018, the average solar reflectance of the prepared outdoor wood-plastic composite material in the 300-2500nm solar spectrum band was measured.

[0068] According to GB / T25261-2018, the average emissivity of the prepared outdoor wood-plastic composite material in the 8-13μm band was measured.

[0069] Prepare conventional dark-colored samples of the same size and color according to GB / T31389. In xenon lamp simulation, the irradiance is set to approximately 900-1000 W / m². 2 Under these conditions, the samples were laid horizontally and parallel, with a thick XPS insulation layer applied to the back to reduce heat conduction interference from the ground. A calibrated T-type thermocouple was embedded 1 mm below the center surface of the sample and connected to a data logger. The temperature was recorded every 10 minutes, and the average value of the temperature data measured within 3 hours was taken as the actual surface temperature under simulated exposure.

[0070] The test results are shown in Table 1.

[0071] Table 1

[0072] As can be seen from Example 1 and Comparative Examples 1-4, and Table 1, compared to Example 1, the average solar reflectance and average emissivity of Comparative Examples 1-4 are significantly lower, while the actual surface temperature under simulated sun exposure is significantly higher. This indicates that using the raw material ratio and preparation method of Example 1 can improve the self-cooling function of outdoor wood-plastic composite materials, helping to reduce thermal aging, deformation, and fading of outdoor wood-plastic composite materials, and extending their service life.

[0073] As can be seen from Examples 1-13 and Table 1, Examples 1-13 all exhibit high average solar reflectance and average emissivity, and their actual surface temperatures under simulated sun exposure are all low. This indicates that outdoor wood-plastic composite materials with excellent self-cooling properties can be prepared using the raw material ratios and preparation methods within the range of Examples 1-13.

[0074] Comparing the data from Example 1 and Comparative Example 13, it can be seen that the examples employing the self-cooling surface layer scheme of this application all exhibit significantly better solar reflectivity and infrared emissivity, and the surface temperature under simulated exposure is significantly reduced, indicating a synergistic effect among the components of this application. Regarding the possible mechanism of this synergistic effect, the applicant analyzes it based on the general principles of polymer physics and thermal radiation as follows: In this application, the copolymerization of methyl methacrylate and butyl acrylate in a self-cooling emulsion can regulate the glass transition temperature of polymer particles, enabling them to possess suitable deformation capabilities at wood-plastic processing temperatures. This facilitates the formation of a relatively compact packing morphology of particles on the surface, potentially contributing to the reflection of sunlight in specific wavelengths. The carboxyl groups provided by methacrylic acid impart surface polarity to the particles, helping to improve the dispersion stability of the particles in the emulsion system. The staged pre-emulsification and seed emulsion polymerization process effectively controls the polymerization rate and system viscosity, avoiding gelation or demulsification, and resulting in polymer microspheres with a relatively concentrated particle size distribution.

[0075] Furthermore, infrared functional fillers such as silicon carbide, hexagonal boron nitride, and cordierite powder possess high infrared emissivity. When introduced into the surface layer, they can synergistically work with the reflective function formed by the orderly arrangement of polymer microspheres, constructing a dual cooling mechanism combining reflection and radiation on the material surface. This dual mechanism may be one of the important reasons why the surface temperature of the embodiment was significantly lower than that of the comparative example under simulated exposure conditions.

[0076] It should be specifically noted that the above mechanism analysis is merely a reasonable speculation made by the inventors based on existing well-known scientific principles, intended to help understand the possible causes of the technical effects of this application, and does not constitute a limitation on the conditions necessary for the self-cooling function of the technical solution of this application. Those skilled in the art, based on the raw material composition, proportions, and preparation methods described in this application, can reproduce the technical solution of this application and achieve the expected cooling effect without relying on the above mechanism interpretation. Therefore, the presence or absence of this mechanism analysis and its degree of demonstration do not affect the full disclosure of the invention in this application.

[0077] Comparison of test data from various embodiments reveals that the self-cooling surface layer also includes near-infrared reflective pigments and / or hollow glass microspheres, which can further enhance the self-cooling function of outdoor wood-plastic composite materials. This is likely because the hollow glass microspheres and near-infrared reflective pigments construct a thermal resistance barrier on the surface, delaying heat conduction to the core layer, allowing more heat to remain on the surface and be radiated away by the infrared filler, thereby further reducing the peak surface temperature.

[0078] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A self-cooling outdoor wood-plastic composite material, characterized in that, The material comprises a main body and a self-cooling surface layer. The self-cooling surface layer covers the outer side of the main body and comprises the following raw materials in parts by weight: 72-78 parts of pure acrylic emulsion, 10-14 parts of self-cooling emulsion, 12-16 parts of rutile TiO2 slurry, 2-3 parts of modified PE wax emulsion, 1-2 parts of infrared functional filler, 0.2-0.4 parts of dispersant, and 0.1-0.2 parts of defoamer.

2. The self-cooling outdoor wood-plastic composite material according to claim 1, characterized in that, The self-cooling emulsion is prepared according to the following steps: Weigh the following raw materials: 50-70 parts methyl methacrylate, 25-40 parts butyl acrylate, 2-8 parts methacrylic acid, 40-60 parts deionized water, 0.5-2.0 parts anionic surfactant, 1.0-3.0 parts nonionic surfactant, and 0.3-0.8 parts initiator; According to the formula, methyl methacrylate, butyl acrylate and methacrylic acid are mixed evenly to obtain the oil phase; Deionized water was divided into two parts by mass ratio (7-8):(2-3). The first part of deionized water, anionic surfactant, and nonionic surfactant were mixed and added dropwise under stirring at 800-1200 rpm. After the addition was completed, stirring was continued for 10-20 min to obtain a pre-emulsion. The pre-emulsion was divided into a first pre-emulsion and a second pre-emulsion according to a mass ratio of (2-3):(17-18). The initiator was mixed evenly with the second part of deionized water to obtain an initiator solution. The initiator solution was then divided into a first initiator solution and a second initiator solution. Mix the first pre-emulsion and the first initiator solution, purge with nitrogen to remove oxygen, heat to 75-85℃, and react for 20-40 minutes to obtain seed micelles. Add the second pre-emulsion and the second initiator solution dropwise to the seed micelles. After the addition is complete, keep the reaction at the temperature for 1-2 hours, cool to 35-40℃, filter, and adjust the pH to 6.5-7.5 to obtain a self-cooling emulsion.

3. The self-cooling outdoor wood-plastic composite material according to claim 2, characterized in that, The initiator solution was divided into a first initiator solution and a second initiator solution according to a mass ratio of (3-5):(5-7).

4. The self-cooling outdoor wood-plastic composite material according to claim 2, characterized in that, The second part of the pre-emulsion and the second part of the initiator solution were added dropwise to the seed micelles at a uniform rate over 3.5-4.5 hours.

5. The self-cooling outdoor wood-plastic composite material according to claim 1, characterized in that, The infrared functional filler includes one or more of silicon carbide, hexagonal boron nitride, and cordierite powder.

6. The self-cooling outdoor wood-plastic composite material according to claim 1, characterized in that, The self-cooling surface layer also includes near-infrared reflective pigments and / or hollow glass microspheres.

7. The self-cooling outdoor wood-plastic composite material according to claim 1, characterized in that, The main body of the board includes a core layer and a transition layer, with the transition layer covering the outside of the core layer.

8. The self-cooling outdoor wood-plastic composite material according to claim 7, characterized in that, Based on the total weight of the core layer, the core layer comprises the following parts by weight of raw materials: 45-55 parts recycled thermoplastic, 35-45 parts wood flour, 1-4 parts PE-g-MAH, 0.1-0.3 parts antioxidant, and 0.5-1.5 parts ethylene bis-stearamide; based on the total weight of the transition layer, the transition layer comprises the following parts by weight of raw materials: 55-65 parts thermoplastic, 25-35 parts wood flour, 4-6 parts SEBS-g-MAH, 1-1.5 parts silane coupling agent, and 0.2-0.8 parts titanate.

9. A method for preparing a self-cooling outdoor wood-plastic composite material as described in any one of claims 1-8, characterized in that, Includes the following steps: According to the formula, pure acrylic emulsion, self-cooling emulsion, rutile TiO2 slurry, modified PE wax emulsion, infrared functional filler, dispersant and defoamer are mixed evenly to obtain the surface raw material; The main raw material and the surface material of the board are co-extruded together. The main raw material forms the board body, and the surface material forms a self-cooling surface layer that wraps around the board body, thus obtaining a self-cooling outdoor wood-plastic composite material.

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