Lightweight high-performance wood-plastic composite material and preparation method thereof

Abstract

This invention relates to a lightweight, high-performance wood-plastic composite material and its preparation method, belonging to the field of wood-plastic composite material manufacturing. The invention addresses the problems of poor interfacial compatibility, low melt strength, and difficulty in controlling foaming and molding in traditional wood-plastic composite materials, which also fail to simultaneously achieve lightweight, suitable strength, and good toughness. The lightweight, high-performance wood-plastic composite material is a sandwich structure formed by segmented hot pressing in a one-step process. The sandwich structure consists of dense, high-strength surface layers on both sides and a foamed, buffered core layer in the middle. The method includes: 1. Core layer particle preparation; 2. Surface layer particle preparation; 3. Segmented hot pressing. This invention is used for lightweight, high-performance wood-plastic composite materials and their preparation.

Description

Technical Field

[0001] This invention belongs to the field of wood-plastic composite material manufacturing. Background Technology

[0002] Current research on wood-plastic composites mainly focuses on ordinary solid boards or single-foamed products. Conventional products are only suitable for non-load-bearing scenarios such as insulation, decoration, landscaping, and home improvement, limiting their application areas. Traditional non-foamed wood-plastic composites generally suffer from prominent problems such as high overall density, insufficient toughness, and weak comprehensive mechanical properties. Although foaming processes can effectively achieve lightweighting, the melt strength of the system is low, and defects such as large, unevenly distributed, and collapsed cells are prone to occur during molding, directly causing a significant reduction in the overall strength of the finished product. At the same time, existing single homogeneous wood-plastic systems cannot simultaneously meet the comprehensive requirements of lightweight, adaptable strength, and good toughness. Conventional physical modification methods cannot simultaneously achieve interface improvement, melt strength enhancement, and stable foaming synergistic adaptation, making it difficult to adapt to the needs of stable mass production of civil building materials in multiple scenarios. Summary of the Invention

[0003] This invention aims to address the problems of poor interfacial compatibility, low melt strength, and difficulty in controlling foaming and molding in traditional wood-plastic composite materials, as well as the inability to simultaneously achieve lightweight, suitable strength, and good toughness. In this way, it provides a lightweight high-performance wood-plastic composite material and its preparation method.

[0004] A lightweight high-performance wood-plastic composite material is a sandwich structure formed by segmented hot pressing in one step, wherein the two sides of the sandwich structure are dense high-strength surface layers and the middle is a foamed buffer core layer.

[0005] The foamed buffer core layer is prepared by mass fractions of 10 to 60 parts high-density polyethylene, 1 to 4 parts ionomer, 10 to 30 parts wood fiber, 1 to 3 parts lubricant, 1 to 3 parts maleic anhydride grafted polyethylene and 0 to 4 parts foaming agent.

[0006] The dense, high-strength surface layer is prepared by mass fractions of 30-90 parts high-density polyethylene, 1-10 parts ionomer, 1-10 parts montmorillonite, 1-3 parts lubricant, and 1-3 parts maleic anhydride-grafted polyethylene.

[0007] A method for preparing a lightweight, high-performance wood-plastic composite material, comprising the following steps:

[0008] I. Core layer fragment preparation:

[0009] ① Weigh out 10 to 60 parts of high-density polyethylene, 1 to 4 parts of ionomer, 10 to 30 parts of wood fiber, 1 to 3 parts of lubricant, 1 to 3 parts of maleic anhydride-grafted polyethylene and 0 to 4 parts of foaming agent by mass.

[0010] ② High-density polyethylene and ionomer are mixed at high speed and then fed into a single screw extruder for melt extrusion granulation to obtain toughened compatible matrix granules;

[0011] ③ The toughening compatibility matrix granules, wood fiber, lubricant, maleic anhydride grafted polyethylene and foaming agent are mixed at high speed, and then fed into a twin-screw extruder for melt extrusion granulation. Finally, they are dried to a moisture content of <2% to obtain core layer granules.

[0012] II. Preparation of surface fragments:

[0013] ① Weigh out 30 to 90 parts of high-density polyethylene, 1 to 10 parts of ionomer, 1 to 10 parts of montmorillonite, 1 to 3 parts of lubricant and 1 to 3 parts of maleic anhydride-grafted polyethylene by mass.

[0014] ② High-density polyethylene, ionomer, montmorillonite, lubricant and maleic anhydride-grafted polyethylene are mixed at high speed and then fed into a twin-screw extruder for melt extrusion granulation to obtain surface granules.

[0015] III. Segmented hot pressing:

[0016] Core and surface particles are layered into a mold in the order of surface, core, and surface, and then placed in a flat vulcanizing machine for segmented hot pressing to obtain a lightweight, high-performance wood-plastic composite material.

[0017] The beneficial effects of this invention are:

[0018] This invention addresses the problems of poor interfacial compatibility, low melt strength, and difficulty in controlling foaming in traditional wood-plastic composites by using ionomer interface regulation, secondary extrusion granulation, and segmented hot-pressing sandwich molding processes. It also overcomes the inability to simultaneously achieve lightweight, suitable strength, and good toughness. The invention achieves synergistic optimization of material structure and performance, with the following results:

[0019] 1. This invention forms a sandwich structure foamed wood-plastic composite material, achieving lightweight, cushioning, heat insulation, and structural integration;

[0020] 2. This invention introduces ionomers for interface regulation, which enhances the wood-plastic interface bonding through ionic and hydrogen bonds, significantly improving toughness and interlayer stability.

[0021] 3. The ionic polymer of this invention can significantly regulate melt strength and strain hardening behavior: by adding ionic polymer to form a reversible physical cross-linking network, the melt strength in the molten state is greatly improved, and the cracking, collapse and merging of cell walls are inhibited; at the same time, the melt exhibits a significant strain hardening effect, stabilizing cell growth and ensuring uniform cell size; the ionic polymer can also synergistically form a reinforcing network with wood fibers, further improving foaming uniformity and structural stability, making the core cell of the sandwich panel more regular, the surface and core layers more tightly bonded, and the overall mechanical properties more superior;

[0022] 4. This invention adopts a sandwich structure hot pressing molding method, which is different from the pure polymer single foaming structure, and achieves the effect of surface layer reinforcement and core layer weight reduction.

[0023] 5. The present invention has a high proportion of wood fiber, which can significantly reduce the cost of raw materials. It is green, renewable, and has outstanding environmental benefits. Its overall economic and environmental performance is significantly better than that of pure polymer foam materials.

[0024] 6. The process of this invention is stable, the equipment is universal, and it is suitable for industrial production, which broadens the application of wood-plastic composite materials in high-end structural and functional fields. Attached Figure Description

[0025] Figure 1 Optical electron microscope image of the cross-section of the foamed wood-plastic composite material prepared in Comparative Example 1;

[0026] Figure 2 Optical electron microscope image of the cross-section of the foamed wood-plastic composite material prepared in Comparative Example 4;

[0027] Figure 3 This is an optical electron microscope image of the cross-section of the foamed wood-plastic composite material prepared in Example 1;

[0028] Figure 4 The storage modulus and complex viscosity of the foamed buffer core layers prepared in Example 1 and Comparative Example 4 are shown. Detailed Implementation

[0029] Specific implementation method one: This implementation method is a lightweight high-performance wood-plastic composite material. The lightweight high-performance wood-plastic composite material is a sandwich structure formed by segmented hot pressing in one step. The sandwich structure has dense and high-strength surface layers on both sides and a foamed buffer core layer in the middle.

[0030] The foamed buffer core layer is prepared by mass fractions of 10 to 60 parts high-density polyethylene, 1 to 4 parts ionomer, 10 to 30 parts wood fiber, 1 to 3 parts lubricant, 1 to 3 parts maleic anhydride grafted polyethylene and 0 to 4 parts foaming agent.

[0031] The dense, high-strength surface layer is prepared by mass fractions of 30-90 parts high-density polyethylene, 1-10 parts ionomer, 1-10 parts montmorillonite, 1-3 parts lubricant, and 1-3 parts maleic anhydride-grafted polyethylene.

[0032] This embodiment uses high-density polyethylene (HDPE) as the matrix and wood fiber as the filler, forming a sandwich structure of a dense surface layer and a foamed core layer through chemical foaming and segmented hot pressing. Based on this, ionomers are introduced as interfacial compatibilizers and toughening agents to regulate the interface and optimize the performance of the composite material.

[0033] The beneficial effects of this embodiment are:

[0034] This embodiment addresses the problems of poor interfacial compatibility, low melt strength, and difficulty in controlling foaming in traditional wood-plastic composites by using ionomer interface regulation, secondary extrusion granulation, and segmented hot-pressing sandwich molding processes. It also overcomes the inability to simultaneously achieve lightweight, suitable strength, and good toughness. The result is a synergistic optimization of material structure and performance, with the following effects:

[0035] 1. This embodiment forms a sandwich structure foamed wood-plastic composite material, achieving lightweight, cushioning, heat insulation, and structural integration;

[0036] 2. This embodiment introduces ionomers for interface regulation, which enhances the wood-plastic interface bonding through ionic and hydrogen bonds, significantly improving toughness and interlayer stability.

[0037] 3. In this embodiment, the ionomer can significantly regulate melt strength and strain hardening behavior: by adding ionomer to form a reversible physical cross-linking network, the melt strength in the molten state is greatly improved, and the cracking, collapse and merging of cell walls are inhibited; at the same time, the melt exhibits a significant strain hardening effect, stabilizing cell growth and ensuring uniform cell size; the ionomer can also work with wood fibers to form a reinforcing network, further improving foaming uniformity and structural stability, making the core cell of the sandwich panel more regular, the surface and core layers more tightly bonded, and the overall mechanical properties more superior;

[0038] 4. This embodiment adopts a sandwich structure hot pressing molding method, which is different from the pure polymer single foaming structure, and achieves the effect of surface layer reinforcement and core layer weight reduction.

[0039] 5. This embodiment has a high proportion of wood fiber, which can significantly reduce raw material costs. It is green, renewable, and has outstanding environmental benefits. Its overall economic and environmental performance is significantly better than that of pure polymer foam materials.

[0040] 6. This implementation method features stable processes, universal equipment, and suitability for industrial production, thus broadening the application of wood-plastic composite materials in high-end structural and functional fields.

[0041] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the high-density polyethylene in the foamed buffer core layer and the dense high-strength surface layer exhibits a melt flow rate of 0.5 g / 10 min to 5 g / 10 min under conditions of 190°C and a weight load of 2.16 kg. Everything else is the same as in Specific Implementation Method One.

[0042] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the ionomers in the foamed buffer core layer and the dense high-strength surface layer are all sodium-based ethylene-methacrylic acid ionomers, zinc-based ethylene-methacrylic acid ionomers, ethylene-acrylic acid ion copolymers, or ionomer elastomers. Everything else is the same as in Specific Implementation Method One or Two.

[0043] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: the wood fiber in the foamed buffer core layer is one or a combination of several of the following: wood flour, rice husk flour, bamboo flour, straw flour, fruit shell flour, and bagasse, and the mesh size of the wood fiber is 60-200 mesh; the lubricant in the foamed buffer core layer and the dense high-strength surface layer is one or a combination of several of the following: polyethylene wax, polypropylene wax, paraffin wax, stearic acid, zinc stearate, and calcium stearate; the foaming agent in the foamed buffer core layer is azodicarbonamide or sodium bicarbonate. Everything else is the same as in Specific Implementation Methods One to Three.

[0044] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: the high-density polyethylene and ionomer in the foamed buffer core layer and the dense high-strength surface layer are obtained after drying at a temperature of 60℃~100℃ for 24h~48h; the wood fiber in the foamed buffer core layer is obtained after drying at a temperature of 80℃~110℃ until the moisture content is below 3%. Everything else is the same as in Specific Implementation Methods One to Four.

[0045] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the thickness of the dense, high-strength surface layer is 0.5mm to 1.2mm, and the thickness of the foamed buffer core layer is 3mm to 5mm. Everything else is the same as in Specific Implementation Methods One to Five.

[0046] Specific Implementation Method Seven: This implementation method provides a method for preparing a lightweight, high-performance wood-plastic composite material, which is carried out according to the following steps:

[0047] I. Core layer fragment preparation:

[0048] ① Weigh out 10 to 60 parts of high-density polyethylene, 1 to 4 parts of ionomer, 10 to 30 parts of wood fiber, 1 to 3 parts of lubricant, 1 to 3 parts of maleic anhydride-grafted polyethylene and 0 to 4 parts of foaming agent by mass.

[0049] ② High-density polyethylene and ionomer are mixed at high speed and then fed into a single screw extruder for melt extrusion granulation to obtain toughened compatible matrix granules;

[0050] ③ The toughening compatibility matrix granules, wood fiber, lubricant, maleic anhydride grafted polyethylene and foaming agent are mixed at high speed, and then fed into a twin-screw extruder for melt extrusion granulation. Finally, they are dried to a moisture content of <2% to obtain core layer granules.

[0051] II. Preparation of surface fragments:

[0052] ① Weigh out 30 to 90 parts of high-density polyethylene, 1 to 10 parts of ionomer, 1 to 10 parts of montmorillonite, 1 to 3 parts of lubricant and 1 to 3 parts of maleic anhydride-grafted polyethylene by mass.

[0053] ② High-density polyethylene, ionomer, montmorillonite, lubricant and maleic anhydride-grafted polyethylene are mixed at high speed and then fed into a twin-screw extruder for melt extrusion granulation to obtain surface granules.

[0054] III. Segmented hot pressing:

[0055] Core and surface particles are layered into a mold in the order of surface, core, and surface, and then placed in a flat vulcanizing machine for segmented hot pressing to obtain a lightweight, high-performance wood-plastic composite material.

[0056] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in the following ways: The high-speed mixing described in steps 1, 2, and 3 is performed at a rotation speed of 500 r / min to 1500 r / min for 3 to 8 minutes; the melt extrusion granulation described in steps 1, 2, is specifically performed at a temperature of 120℃ to 230℃ and a main machine rotation speed of 10 rpm to 20 rpm; the particle size of the toughening and compatibility matrix granules described in steps 1, 2, is 2 mm to 8 mm; the melt extrusion granulation described in steps 1, 3, is specifically performed at a temperature of 140℃ to 200℃ and a main machine rotation speed of 30 rpm to 60 rpm; the particle size of the core layer fragments described in steps 1, 3, is 2 mm to 8 mm. Everything else is the same as in Specific Implementation Method Seven.

[0057] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Seven or Eight in the following ways: The high-speed mixing in step two ② is performed at a rotation speed of 500 r / min to 1500 r / min for 3 to 8 minutes; the melt extrusion granulation in step two ② is specifically performed at a temperature of 150℃ to 170℃ and a main unit rotation speed of 10 rpm to 20 rpm; the particle size of the surface fragments in step two ② is 2 mm to 8 mm. Everything else is the same as in Specific Implementation Method Seven or Eight.

[0058] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods Seven to Nine in that the segmented hot pressing described in step three is performed as follows: First, maintain the temperature and pressure at 130℃~140℃ and 8MPa~12MPa for 5min~10min. Then, raise the temperature to 170℃~190℃ and maintain the temperature and pressure at 170℃~190℃ and 8MPa~12MPa for 10min~15min. Finally, maintain the pressure at 8MPa~12MPa and cool to room temperature for demolding. Everything else is the same as in Specific Implementation Methods Seven to Nine.

[0059] The beneficial effects of the present invention are verified using the following embodiments:

[0060] Example 1:

[0061] A method for preparing a lightweight, high-performance wood-plastic composite material, comprising the following steps:

[0062] I. Core layer fragment preparation:

[0063] ① Weigh out 58 parts high-density polyethylene, 4 parts ionomer, 30 parts wood fiber, 2 parts lubricant, 3 parts maleic anhydride grafted polyethylene and 3 parts foaming agent by weight.

[0064] The high-density polyethylene has a melt flow rate of 0.9 g / 10 min under the conditions of a temperature of 190°C and a weight load of 2.16 kg.

[0065] The ionomer is sodium-based ethylene-methacrylic acid ionomer (purchased from DuPont, model 8940).

[0066] The wood fiber is poplar wood powder, and the mesh size of the wood fiber is 120 mesh to 150 mesh;

[0067] The lubricant is a combination of polyethylene wax and stearic acid, and the mass ratio of polyethylene wax to stearic acid is 1:1.

[0068] The foaming agent is azodicarbonamide;

[0069] The high-density polyethylene and ionomer were obtained by drying at 60°C for 24 hours; the wood fiber was obtained by drying at 103°C until the moisture content was less than 3%.

[0070] ② Under the condition of a rotation speed of 1500 rpm, high-density polyethylene and ionomer are mixed at high speed for 5 minutes, and then fed into a single screw extruder. The mixture is melt-extruded and granulated under the conditions of zone 1 temperature of 150℃, 160℃, 170℃, 180℃, 170℃, 160℃ and 150℃ respectively, and main machine rotation speed of 15 rpm, to obtain toughened compatible matrix granules.

[0071] The toughening and compatible matrix granules have a particle size of 2mm to 8mm;

[0072] ③ At a speed of 1500 rpm, toughening compatibility matrix granules, wood fiber, lubricant, maleic anhydride grafted polyethylene and foaming agent are mixed at high speed for 5 minutes, and then fed into a twin-screw extruder. The mixture is melt-extruded and granulated at temperatures of 140℃, 140℃, 150℃, 150℃, 150℃, 140℃ and 140℃ in zones one to seven, respectively, and at a main extruder speed of 40 rpm. Finally, the mixture is dried at a temperature of 103℃ until the moisture content is <2% to obtain core layer granules.

[0073] The particle size of the core layer fragments is 2mm~8mm;

[0074] II. Preparation of surface fragments:

[0075] ① Weigh out 81 parts high-density polyethylene, 10 parts ionomer, 4 parts montmorillonite, 2 parts lubricant and 3 parts maleic anhydride-grafted polyethylene by mass.

[0076] The high-density polyethylene has a melt flow rate of 0.9 g / 10 min under the conditions of a temperature of 190°C and a weight load of 2.16 kg.

[0077] The ionomer is sodium-based ethylene-methacrylic acid ionomer (purchased from DuPont, model 8940).

[0078] The lubricant is a combination of polyethylene wax and stearic acid, and the mass ratio of polyethylene wax to stearic acid is 1:1.

[0079] Both the ionomer and the high-density polyethylene were obtained by drying at 60°C for 24 hours.

[0080] ② Under the condition of 1500 rpm, high-density polyethylene, ionomer, montmorillonite, lubricant and maleic anhydride grafted polyethylene are mixed at high speed for 8 minutes, and then fed into a twin-screw extruder. The mixture is melt-extruded and granulated under the conditions of zone 1 temperature of 155℃, 160℃, 160℃, 170℃, 170℃, 160℃ and 150℃ respectively, and main machine speed of 15 rpm, to obtain surface fragments.

[0081] The particle size of the surface fragments is 2mm to 8mm;

[0082] III. Segmented hot pressing:

[0083] Core layer fragments and surface layer fragments are laid into the mold in the order of surface layer, core layer, and surface layer. Then, the mold is placed in a flat vulcanizing machine. First, it is kept at 140℃ and 8MPa for 5 minutes. Then, the temperature is raised to 180℃ and kept at 10MPa for 10 minutes. Finally, it is kept under pressure and cooled to room temperature at 8MPa before demolding to obtain a lightweight high-performance wood-plastic composite material, namely foamed wood-plastic composite material.

[0084] The lightweight high-performance wood-plastic composite material is a sandwich structure formed by segmented hot pressing in one step. The sandwich structure has dense high-strength surface layers on both sides and a foamed buffer core layer in the middle. The thickness of the dense high-strength surface layers is 1 mm, and the thickness of the foamed buffer core layer is 4 mm.

[0085] Example 2: This example differs from Example 1 in that the addition of the foaming agent in step 1① is omitted, i.e., no foaming agent is added to the foamed buffer core layer. Everything else is the same as in Example 1.

[0086] Example 3: This example differs from Example 1 in that the number of parts of the foaming agent in step 1① is changed to 1 part. Everything else is the same as in Example 1.

[0087] Example 4: This example differs from Example 1 in that the number of parts of foaming agent in step 1① is changed to 2 parts. Everything else is the same as in Example 1.

[0088] Example 5: This example differs from Example 1 in that the number of parts of foaming agent in step 1① is changed to 4 parts. Everything else is the same as in Example 1.

[0089] Comparative Example 1: This comparative example differs from Example 1 in that the addition of ionomer and foaming agent in step 1① is omitted, i.e., no ionomer and foaming agent are added to the foamed buffer core layer. Everything else is the same as Example 1.

[0090] Comparative Example 2: This comparative example differs from Example 1 in that the addition of the ionomer in step 1① is omitted, i.e., no ionomer is added to the foamed buffer core layer; the number of parts of the foaming agent in step 1① is changed to 1 part. Everything else is the same as Example 1.

[0091] Comparative Example 3: This comparative example differs from Example 1 in that the addition of the ionomer in step 1① is omitted, i.e., no ionomer is added to the foamed buffer core layer; the number of parts of the foaming agent in step 1① is changed to 2 parts. Everything else is the same as Example 1.

[0092] Comparative Example 4: This comparative example differs from Example 1 in that the addition of the ionomer in step 1① is omitted, i.e., no ionomer is added to the foamed buffer core layer. Everything else is the same as Example 1.

[0093] Comparative Example 5: This comparative example differs from Example 1 in that the addition of the ionomer in step 1① is omitted, i.e., no ionomer is added to the foamed buffer core layer; the number of parts of the foaming agent in step 1① is changed to 4 parts. Everything else is the same as Example 1.

[0094] Impact and flexural properties of the foamed wood-plastic composites prepared in the examples and comparative examples were tested according to ASTM D790 standard; apparent density of the foamed wood-plastic composites prepared in the examples and comparative examples was tested according to GB / T 6343-2009 standard. The test results are shown in Table 1 below:

[0095] Table 1

[0096]

[0097] Figure 1 Optical electron microscope image of the cross-section of the foamed wood-plastic composite material prepared in Comparative Example 1; Figure 2 Optical electron microscope image of the cross-section of the foamed wood-plastic composite material prepared in Comparative Example 4; Figure 3 Optical electron microscope (OSE) images of the cross-section of the foamed wood-plastic composite material prepared in Example 1; from Table 1 and Figures 1 to 3 It can be seen that ionomers have a significant effect on regulating the cell size and mechanical properties of foamed wood-plastic composites. In the foaming system without ionomers, the cell size and wall thickness are uneven, and the cells are prone to collapse and merging, making the foaming process difficult to control stably. This results in low impact strength, significantly reduced flexural strength, and a substantial decrease in flexural modulus. Compared to the system without ionomers, the composite material with added ionomers has smaller cross-sectional cells, a complete closed-cell structure, and a uniform cell distribution, with no obvious cell collapse, merging, or interfacial debonding. In terms of mechanical properties, the impact strength, flexural strength, and flexural modulus of the ionomer-modified system are significantly improved, while the apparent density is reduced, exhibiting superior lightweighting and structural stability. Although the apparent density values ​​of some comparative examples (such as Comparative Example 4 and Comparative Example 5) are lower than those of the corresponding examples, these comparative examples only have lower apparent density values; the cell structure still suffers from severe unevenness, collapse, and merging problems, lacking a regular closed-cell structure. Their mechanical properties are far inferior to the examples, failing to achieve both lightweight and high-strength characteristics, and thus lacking stable foaming and practical application value. The above results indicate that ionomers can effectively enhance the interfacial bonding between resin and wood fiber, improve melt strength, and stabilize foaming nucleation and cell growth, thereby achieving efficient control over the microstructure and macroscopic properties of foamed wood-plastic composites.

[0098] right Figure 2 and Figure 3The obtained images were processed and the number of bubbles was counted. It was found that compared with Comparative Example 4 without the addition of ionomer, the number of bubbles in Example 1 with the addition of ionomer was 127 / cm. 3 Increased to 180 / cm 3 The average cell size decreased from 264.6 μm to 126.4 μm, the average cell density increased by more than an order of magnitude, the porosity decreased, and the cell distribution became more uniform. The system without ionomers had larger cell sizes, was prone to merging and collapse, and had poor structural stability. In contrast, ionomers significantly optimized cell morphology by controlling melt strength and strain hardening behavior, resulting in a stable foamed structure with smaller cell size, higher density, and more uniform porosity.

[0099] Figure 4 The storage modulus and complex viscosity diagrams of the foamed buffer core layers prepared in Example 1 and Comparative Example 4 are shown; from Figure 4 It can be seen that, in the low-frequency test range, the foamed buffer core layer of Example 1 with added ionomer exhibits a similar storage modulus (G′) to its complex viscosity (G′). The values ​​of G′ in Example 1 were significantly higher than those in Comparative Example 4 without the addition of ionic polymer, and both showed a consistent trend with changes in angular frequency. In the storage modulus curve, G′ in Example 1 was higher than that in Comparative Example 4 across the entire frequency range, and showed a stable upward trend with increasing angular frequency. This indicates that the introduction of the ionic polymer significantly enhanced the elastic response of the melt, forming a more stable physical cross-linked network structure. The elasticity and tensile strength of the melt were significantly improved, effectively suppressing the rupture and collapse of the cell walls during foaming. In the complex viscosity curve, the values ​​of G′ in Example 1 were significantly higher than those in Comparative Example 4 without the addition of ionic polymer, and both showed a consistent trend with changes in angular frequency. The viscosity of Example 1 was higher than that of Comparative Example 4 across the entire frequency range. Both examples exhibited shear-thinning behavior with increasing angular frequency, but Example 1 showed a higher overall viscosity level. This indicates that the ionomer significantly improved the melt flow resistance and viscoelastic stability, allowing for better gas encapsulation and delayed cell coalescence during foaming. This provides a key rheological basis for preparing foamed materials with high porosity and uniform, stable structure. By forming a reversible physical cross-linking network, the ionomer significantly improved the melt strength and strain hardening capacity of the system, effectively solving the problems of insufficient melt strength and easy cell collapse and coalescence in the foaming process of traditional wood-plastic composites.

Claims

1. A lightweight, high-performance wood-plastic composite material, characterized in that... The lightweight high-performance wood-plastic composite material is a sandwich structure formed by segmented hot pressing in one step. The sandwich structure has a dense and high-strength surface layer on both sides and a foamed buffer core layer in the middle. The foamed buffer core layer is prepared by mass fractions of 10 to 60 parts high-density polyethylene, 1 to 4 parts ionomer, 10 to 30 parts wood fiber, 1 to 3 parts lubricant, 1 to 3 parts maleic anhydride grafted polyethylene and 0 to 4 parts foaming agent. The dense, high-strength surface layer is prepared by mass fractions of 30-90 parts high-density polyethylene, 1-10 parts ionomer, 1-10 parts montmorillonite, 1-3 parts lubricant, and 1-3 parts maleic anhydride-grafted polyethylene.

2. The lightweight, high-performance wood-plastic composite material according to claim 1, characterized in that... The high-density polyethylene in the foamed buffer core layer and the dense high-strength surface layer has a melt flow rate of 0.5g / 10min to 5g / 10min under the conditions of a temperature of 190℃ and a weight load of 2.16kg.

3. The lightweight, high-performance wood-plastic composite material according to claim 1, characterized in that... The ionic polymers in the foamed buffer core layer and the dense high-strength surface layer are all sodium-based ethylene-methacrylic acid ionic polymers, zinc-based ethylene-methacrylic acid ionic polymers, ethylene-acrylic acid ionic copolymers, or ionomer elastomers.

4. The lightweight, high-performance wood-plastic composite material according to claim 1, characterized in that... The wood fiber in the foamed buffer core layer is one or a combination of several of the following: wood flour, rice husk flour, bamboo flour, straw flour, fruit shell flour, and bagasse, and the mesh size of the wood fiber is 60-200 mesh; the lubricant in the foamed buffer core layer and the dense high-strength surface layer is one or a combination of several of the following: polyethylene wax, polypropylene wax, paraffin wax, stearic acid, zinc stearate, and calcium stearate; the foaming agent in the foamed buffer core layer is azodicarbonamide or sodium bicarbonate.

5. A lightweight, high-performance wood-plastic composite material according to claim 1, characterized in that... The high-density polyethylene and ionomer in the foamed buffer core layer and the dense high-strength surface layer are obtained by drying at a temperature of 60℃~100℃ for 24h~48h; the wood fiber in the foamed buffer core layer is obtained by drying at a temperature of 80℃~110℃ until the moisture content is less than 3%.

6. The lightweight, high-performance wood-plastic composite material according to claim 1, characterized in that... The thickness of the dense, high-strength surface layer is 0.5mm to 1.2mm, and the thickness of the foamed buffer core layer is 3mm to 5mm.

7. The method for preparing a lightweight, high-performance wood-plastic composite material as described in claim 1, characterized in that... It is done in the following steps: I. Core layer fragment preparation: ① Weigh out 10 to 60 parts of high-density polyethylene, 1 to 4 parts of ionomer, 10 to 30 parts of wood fiber, 1 to 3 parts of lubricant, 1 to 3 parts of maleic anhydride-grafted polyethylene and 0 to 4 parts of foaming agent by mass. ② High-density polyethylene and ionomer are mixed at high speed and then fed into a single screw extruder for melt extrusion granulation to obtain toughened compatible matrix granules; ③ The toughening compatibility matrix granules, wood fiber, lubricant, maleic anhydride grafted polyethylene and foaming agent are mixed at high speed, and then fed into a twin-screw extruder for melt extrusion granulation. Finally, they are dried to a moisture content of <2% to obtain core layer granules. II. Preparation of surface fragments: ① Weigh out 30 to 90 parts of high-density polyethylene, 1 to 10 parts of ionomer, 1 to 10 parts of montmorillonite, 1 to 3 parts of lubricant and 1 to 3 parts of maleic anhydride-grafted polyethylene by mass. ② High-density polyethylene, ionomer, montmorillonite, lubricant and maleic anhydride-grafted polyethylene are mixed at high speed and then fed into a twin-screw extruder for melt extrusion granulation to obtain surface granules. III. Segmented hot pressing: Core and surface particles are layered into a mold in the order of surface, core, and surface, and then placed in a flat vulcanizing machine for segmented hot pressing to obtain a lightweight, high-performance wood-plastic composite material.

8. The method for preparing a lightweight, high-performance wood-plastic composite material according to claim 7, characterized in that... The high-speed mixing described in steps 1, 2, and 3 is carried out at a speed of 500 r / min to 1500 r / min for 3 to 8 minutes. The melt extrusion granulation described in steps 1 and 2 is carried out at a temperature of 120℃ to 230℃ and a main machine speed of 10 rpm to 20 rpm. The toughening and compatibility matrix granules described in steps 1 and 2 have a particle size of 2 mm to 8 mm. The melt extrusion granulation described in steps 1 and 3 is carried out at a temperature of 140℃ to 200℃ and a main machine speed of 30 rpm to 60 rpm. The core layer fragments described in steps 1 and 3 have a particle size of 2 mm to 8 mm.

9. The method for preparing a lightweight, high-performance wood-plastic composite material according to claim 7, characterized in that... The high-speed mixing described in step 2② is carried out at a speed of 500 r / min to 1500 r / min for 3 min to 8 min; the melt extrusion granulation described in step 2② is carried out at a temperature of 150℃ to 170℃ and a main machine speed of 10 rpm to 20 rpm; the particle size of the surface fragments described in step 2② is 2 mm to 8 mm.

10. The method for preparing a lightweight, high-performance wood-plastic composite material according to claim 7, characterized in that... The segmented hot pressing described in step three is carried out in the following steps: First, maintain the temperature and pressure at 130℃~140℃ and 8MPa~12MPa for 5min~10min. Then, raise the temperature to 170℃~190℃ and maintain the temperature and pressure at 170℃~190℃ and 8MPa~12MPa for 10min~15min. Finally, maintain the pressure at 8MPa~12MPa and cool to room temperature for demolding.

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