Preparation method of supercritical fluid microcellular foaming wood-plastic composite material

Abstract

The invention discloses a preparation method of a supercritical fluid microcellular foaming wood-plastic composite material, and belongs to the field of wood-plastic composite materials and manufacturing thereof. The invention aims to solve the problems of large cell size, low cell density, no more than 30wt.% of wood fiber content and unclear cell form regulation and control process control of a saturated filling foaming product in the existing wood-plastic composite material supercritical microcellular foaming injection molding technology. The method comprises the following steps: 1, preparing nucleating agent modified polymer granules; 2, preparing wood-plastic granules; and 3, preparing the microcellular foaming wood-plastic composite material. The method is used for preparing the supercritical fluid microcellular foaming wood-plastic composite material.

Description

Technical Field

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

[0002] Wood-plastic composites (WPCs) are green and environmentally friendly composite materials prepared by combining forestry processing residues with thermoplastic polymers. However, the high density and low toughness of WPCs severely limit their widespread application. Introducing a microporous structure into WPCs is an effective method to save costs, reduce density, and improve impact resistance, dimensional stability, sound insulation, heat insulation, and cushioning properties. Currently, WPCs are typically produced using chemical foaming methods, which not only result in large pore sizes and poor mechanical properties but also leave behind byproducts of foaming agent decomposition.

[0003] Supercritical fluids possess excellent solubility, high diffusivity, low viscosity, and are safe and inexpensive. They offer superior foaming effects compared to ordinary physical foaming agents and are safer and more environmentally friendly than chemical foaming agents, enabling microporous foamed products to combine high quality and environmental friendliness. Currently, obtaining microporous structures with small cell size and high cell density mainly relies on supercritical intermittent foaming. Existing technologies utilize supercritical fluid intermittent foaming technology to prepare microporous foamed wood-plastic composite products, such as publication numbers: CN116176086B, CN107759821A, CN106750486B, and CN107759821A. However, due to the long molding cycle and small sample size per foaming cycle of supercritical fluid intermittent foaming, it is difficult to put it into practical production.

[0004] Supercritical injection molding foaming technology, as a semi-automated technology with a short production cycle, is suitable for large-scale industrial production and is widely used in polymer microporous foamed materials. Currently, supercritical foaming technology for wood-plastic composites mainly employs saturated filling foaming methods. Although this introduces a microporous structure, it suffers from low weight loss, large cell size, low cell density, and unclear process control for cell morphology. Furthermore, the high wood fiber content leads to fiber agglomeration, causing a sharp increase in viscosity. High viscosity and strong yield stress significantly increase processing difficulty, easily resulting in insufficient mold filling and runner blockage during injection molding. The wood fiber content is generally no more than 30 wt.%, while increasing the wood fiber content is crucial for developing an ecological circular economy, improving product mechanical properties, and reducing production costs. Therefore, there are currently no publicly available publications on supercritical microporous foaming injection molding technology for wood-plastic composites with high wood fiber content. Summary of the Invention

[0005] This invention aims to address the problems of existing supercritical microporous foaming injection molding technology for wood-plastic composites, such as large cell size, low cell density, wood fiber content not exceeding 30 wt.%, and unclear process control for regulating cell morphology in saturated filled foamed products. Therefore, it provides a method for preparing supercritical fluid microporous foamed wood-plastic composites.

[0006] A method for preparing a supercritical fluid microporous foamed wood-plastic composite material, comprising the following steps:

[0007] I. Preparation of nucleating agent modified polymer granules:

[0008] Weigh out 1 to 20 parts by weight of nucleating agent, 80 to 99 parts by weight of thermoplastic polymer, 1 to 5 parts by weight of compatibilizer and 1 to 2 parts by weight of lubricant, and then perform high-speed mixing, high-speed extrusion granulation and drying in sequence to obtain nucleating agent modified polymer granules.

[0009] II. Preparation of wood-plastic granules:

[0010] Weigh out 10 to 60 parts by weight of wood fiber, 30 to 90 parts by weight of polymer granules modified with nucleating agent, 2 to 8 parts by weight of compatibilizer and 0.5 to 2 parts by weight of lubricant, and then perform high-speed mixing, granulation and drying in sequence to obtain wood-plastic granules;

[0011] III. Preparation of microporous foamed wood-plastic composite materials:

[0012] Wood-plastic granules are placed in an injection molding machine, and then supercritical fluid is injected into the injection molding machine. The mixture is then injected and molded according to a certain amount of melt to obtain a supercritical fluid microporous foamed wood-plastic composite material.

[0013] The beneficial effects of this invention are:

[0014] This invention utilizes supercritical fluid microporous foaming injection molding technology to prepare microporous foamed wood-plastic composites. It fully leverages the advantages of supercritical fluids, such as high solubility, high diffusivity, and environmental safety, to introduce a microporous structure while reducing the density of the wood-plastic composite. The resulting micropores effectively passivate cracks and improve impact toughness. Compared to traditional chemical foaming methods, the prepared microporous wood-plastic composite produces no byproducts of foaming agent decomposition, and features smaller pore sizes and higher pore density. Furthermore, microporous foamed wood-plastic products have a more pronounced wood-like texture than non-foamed wood-plastic products.

[0015] This invention employs an unsaturated filling foaming method, adjusting the degree of weight reduction through microporous foaming by controlling the actual melt ratio. It utilizes the plasticizing effect of supercritical fluid on the wood-plastic composite melt to improve the flow performance of the homogeneous melt in the mold cavity. The growth of cells compensates for the volume shrinkage caused by material shortage, resulting in microporous foamed wood-plastic composites with different weight reduction rates, ranging from 5% to 20% in density reduction, while saving 5% to 30% in raw material costs.

[0016] This invention utilizes compatibilizers to improve the interfacial compatibility between wood fibers and polymers, thereby increasing the wood fiber filler content and preparing wood-plastic composite materials with a wood fiber content of 10 wt.% to 60 wt.%. Furthermore, by utilizing the plasticizing effect of supercritical fluids and adjusting the injection molding machine temperature and foaming agent content, a high-content wood fiber microporous foamed composite material was successfully prepared. This breakthrough overcomes the current bottleneck that the wood fiber content in microporous foamed injection-molded wood-plastic composite materials is difficult to exceed 30 wt.%.

[0017] This invention modifies the polymer matrix through high-speed melt shear extrusion by adding nucleating agents. On one hand, it disperses inorganic nanoparticles with layered and polyhedral crystal structures, such as nano-montmorillonite, nano-titanium dioxide, nano-silica, and nano-zinc oxide, through high-speed shearing, improving the homogeneity of the system and promoting cell nucleation, thereby increasing the cell nucleation density. On the other hand, it treats polymer particles such as polytetrafluoroethylene, polyamide 6, polyethylene terephthalate, and polyphenylene sulfide in situ using microfibrillation technology, dispersing them in the thermoplastic matrix phase to form a three-dimensional network structure, which can significantly improve melt strength, thereby limiting cell growth and reducing cell size.

[0018] This invention regulates the cell morphology and mechanical properties of microporous foamed wood-plastic composites by adjusting process parameters of supercritical fluid microporous foaming injection molding, including injection molding machine screw temperature, nozzle temperature, system back pressure; supercritical fluid equipment injection pressure and foaming agent content; injection speed, injection pressure, holding pressure, holding time, cooling time, and mold temperature. It successfully produces microporous foamed wood-plastic composites with cell sizes ranging from 2μm to 30μm and cell densities of 10-1. 6 pcs / cm 3 ~10 9 pcs / cm 3 It is a microporous foamed wood-plastic composite material with excellent mechanical properties. It has broad application prospects in children's toys, interior furniture, automotive interiors and other fields. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the apparatus used in the present invention to prepare supercritical fluid microporous foamed wood-plastic composite material;

[0020] Figure 2 This is a scanning electron microscope image of the supercritical fluid microporous foamed wood-plastic composite material prepared in Example 1;

[0021] Figure 3 This is a scanning electron microscope image of the supercritical fluid microporous foamed wood-plastic composite material prepared in Example 2;

[0022] Figure 4 Scanning electron microscope (SEM) images of the saturated filled microporous foamed wood-plastic composite material prepared in Experiment 1 for comparison;

[0023] Figure 5 This is a scanning electron microscope image of the supercritical fluid microporous foamed wood-plastic composite material prepared in Example 3;

[0024] Figure 6 Scanning electron microscope (SEM) image of the microporous foamed wood-plastic composite material prepared in Experiment 2 without nucleating agent modification. Detailed Implementation

[0025] Specific implementation method one, combined with Figure 1 Detailed description: This embodiment describes a method for preparing a supercritical fluid microporous foamed wood-plastic composite material, which is carried out according to the following steps:

[0026] I. Preparation of nucleating agent modified polymer granules:

[0027] Weigh out 1 to 20 parts by weight of nucleating agent, 80 to 99 parts by weight of thermoplastic polymer, 1 to 5 parts by weight of compatibilizer and 1 to 2 parts by weight of lubricant, and then perform high-speed mixing, high-speed extrusion granulation and drying in sequence to obtain nucleating agent modified polymer granules.

[0028] II. Preparation of wood-plastic granules:

[0029] Weigh out 10 to 60 parts by weight of wood fiber, 30 to 90 parts by weight of polymer granules modified with nucleating agent, 2 to 8 parts by weight of compatibilizer and 0.5 to 2 parts by weight of lubricant, and then perform high-speed mixing, granulation and drying in sequence to obtain wood-plastic granules;

[0030] III. Preparation of microporous foamed wood-plastic composite materials:

[0031] Wood-plastic granules are placed in an injection molding machine, and then supercritical fluid is injected into the injection molding machine. The mixture is then injected and molded according to a certain amount of melt to obtain a supercritical fluid microporous foamed wood-plastic composite material.

[0032] In step three of this specific implementation method, the "certain melt amount" refers to setting a specific melt amount based on the density requirements of the foamed wood-plastic composite material.

[0033] The beneficial effects of this embodiment are:

[0034] This embodiment utilizes supercritical fluid microporous foaming injection molding technology to prepare microporous foamed wood-plastic composites. It fully leverages the advantages of supercritical fluids, such as high solubility, high diffusivity, and environmental safety, to introduce a microporous structure while reducing the density of the wood-plastic composite. The resulting micropores effectively passivate cracks and improve impact toughness. Compared to traditional chemical foaming methods, the prepared microporous wood-plastic composite produces no byproducts of foaming agent decomposition, and features smaller pore sizes and higher pore density. Furthermore, microporous foamed wood-plastic products have a more pronounced wood-like texture than non-foamed wood-plastic products.

[0035] This embodiment employs an unsaturated filling foaming method. By controlling the actual melt volume ratio, the degree of weight reduction through microporous foaming is adjusted. The plasticizing effect of supercritical fluid on the wood-plastic composite melt is utilized to improve the flow performance of the homogeneous melt in the mold cavity. The growth of cells compensates for the volume shrinkage caused by material shortage, thereby obtaining microporous foamed wood-plastic composites with different weight reduction rates. The density reduction ranges from 5% to 20%, while saving 5% to 30% of raw material costs.

[0036] This embodiment utilizes a compatibilizer to improve the interfacial compatibility between wood fibers and polymers, thereby increasing the wood fiber filler content and preparing wood-plastic composite materials with a wood fiber content of 10 wt.% to 60 wt.%. Furthermore, by utilizing the plasticizing effect of supercritical fluids and adjusting the injection molding machine temperature and foaming agent content, a high-content wood fiber microporous foamed composite material was successfully prepared. This overcomes the current bottleneck that the wood fiber content in microporous foamed injection-molded wood-plastic composite materials is difficult to exceed 30 wt.%.

[0037] This embodiment modifies the polymer matrix through high-speed melt shear extrusion by adding a nucleating agent. On one hand, it disperses inorganic nanoparticles with layered and polyhedral crystal structures, such as nano-montmorillonite, nano-titanium dioxide, nano-silica, and nano-zinc oxide, through high-speed shearing, improving the homogeneity of the system and promoting cell nucleation, thereby increasing the cell nucleation density. On the other hand, it treats polymer particles such as polytetrafluoroethylene, polyamide 6, polyethylene terephthalate, and polyphenylene sulfide in situ using microfibrillation technology, dispersing them in the thermoplastic matrix phase to form a three-dimensional network structure, which can significantly improve melt strength, thereby limiting cell growth and reducing cell size.

[0038] This embodiment controls the cell morphology and mechanical properties of microporous foamed wood-plastic composites by adjusting process parameters of supercritical fluid microporous foaming injection molding, including injection molding machine screw temperature, nozzle temperature, system back pressure; supercritical fluid equipment injection pressure and foaming agent content; injection speed, injection pressure, holding pressure, holding time, cooling time, and mold temperature. Cell sizes of 2μm to 30μm and cell densities of 10⁻⁶ were successfully prepared. 6 pcs / cm 3 ~10 9 pcs / cm 3 It is a microporous foamed wood-plastic composite material with excellent mechanical properties. It has broad application prospects in children's toys, interior furniture, automotive interiors and other fields.

[0039] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that: the nucleating agent mentioned in step one is polymer particles or inorganic nanoparticles with layered and polyhedral crystal structures; the thermoplastic polymer mentioned in step one is one or a combination of polyethylene, polypropylene, and polylactic acid; the compatibilizer mentioned in steps one and two is one or a combination of maleic anhydride-grafted polyethylene, maleic anhydride-grafted polypropylene, and maleic anhydride-grafted polylactic acid; the lubricant mentioned in steps one and two is one or a combination of polyethylene wax, stearic acid, paraffin wax, polypropylene wax, oxidized polyethylene wax, palm wax, lignite wax, and white oil; the thermoplastic polymer mentioned in step one is a dried thermoplastic polymer, specifically dried according to the following steps: drying the thermoplastic polymer at a temperature of 55℃~60℃ for 24h~48h. Everything else is the same as in Specific Implementation Method One.

[0040] When the nucleating agent described in this specific embodiment is an inorganic nanoparticle with a layered and polyhedral crystal structure, high-speed mixing mainly improves the dispersion uniformity; when the nucleating agent is a polymer particle, high-speed mixing transforms the polymer particle into filamentous polymer fibers, achieving a microfibrillation effect and forming a three-dimensional network structure.

[0041] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: the polymer particles are one or a combination of several of polytetrafluoroethylene, polyamide 6, polyethylene terephthalate, and polyphenylene sulfide; the inorganic nanoparticles with layered and polyhedral crystal structures are one or a combination of several of nano-montmorillonite, nano-titanium dioxide, nano-silica, and nano-zinc oxide. Everything else is the same as in Specific Implementation Method One or Two.

[0042] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: the total mass fraction of the wood fiber, nucleating agent-modified polymer granules, compatibilizer, and lubricant mentioned in step two is 100 parts; the wood fiber mentioned in step two is 40-150 mesh wood fiber; the wood fiber mentioned in step two is derived from one or a combination of several of agricultural and forestry processing residues and wastes; the wood fiber mentioned in step two is dried wood fiber, specifically dried according to the following steps: drying the wood fiber to a moisture content of less than 2% at a temperature of 100℃-106℃. Everything else is the same as in Specific Implementation Methods One to Three.

[0043] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the wood fiber mentioned in step two is one or a combination of wood flour, bamboo flour, and straw flour. Everything else is the same as in Specific Implementation Methods One to Four.

[0044] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in the following ways: The high-speed mixing described in steps one and two specifically utilizes a high-speed mixer, mixing for 5 to 30 minutes at a temperature of 20℃~80℃ and a rotation speed of 1000 r / min~3000 r / min; the high-speed extrusion granulation described in step one specifically utilizes a twin-screw extruder, performing high-speed melt extrusion granulation at a barrel temperature of 150℃~260℃, a die temperature of 150℃~260℃, and a screw rotation speed of 200 r / min~300 r / min; the granulation described in step two specifically utilizes a twin-screw extruder, performing melt extrusion granulation at a barrel temperature of 140℃~180℃, a die temperature of 150℃~180℃, and a screw rotation speed of 20 r / min~200 r / min; the drying described in steps one and two specifically involves drying at a temperature of 80℃~100℃ for 12 to 24 hours. The rest is the same as in specific implementation methods one to five.

[0045] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One through Six in that the injection molding process parameters described in step three are as follows: barrel temperature is 160℃~200℃, nozzle temperature is 170℃~220℃, screw speed is 40r / min~80r / min, and system back pressure is 10MPa~20MPa. Everything else is the same as in Specific Implementation Methods One through Six.

[0046] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: during the injection molding process described in Step Three, the wood-plastic granules sequentially pass through the melting stage, injection stage, holding pressure stage, cooling stage, and mold opening stage in the injection molding machine; the melting stage consists of a material plasticizing stage and an injection mixing stage, and the total time for the material plasticizing stage and the injection mixing stage is 5s to 30s; the injection stage is carried out under the conditions of an injection pressure of 3MPa to 17MPa and an injection speed of 53mm / s to 95mm / s; the holding pressure stage is specifically held for 0s to 30s under the conditions of a pressure of 4MPa to 12MPa; the cooling stage is specifically cooled for 5s to 30s under the conditions of a mold temperature of 30℃ to 40℃. Everything else is the same as in Specific Implementation Methods One to Seven.

[0047] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that: in step three, supercritical fluid is injected during the gas injection and mixing stage to obtain a gas-containing wood-plastic composite melt; the melt volume mentioned in step three is 70% to 100% of the theoretical melt volume; the theoretical melt volume is the total amount of material required to completely fill the mold cavity without foaming gas. Everything else is the same as in Specific Implementation Methods One to Eight.

[0048] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that: the injection pressure of the supercritical fluid in step three is 15MPa~30MPa; the supercritical fluid mentioned in step three is one or a combination of supercritical nitrogen and supercritical carbon dioxide; and the mass of the supercritical fluid is 0.5%~2% of the mass of the gas-containing wood-plastic composite melt. Everything else is the same as Specific Implementation Methods One to Nine.

[0049] The beneficial effects of the present invention are verified using the following embodiments:

[0050] Example 1:

[0051] A method for preparing a supercritical fluid microporous foamed wood-plastic composite material, comprising the following steps:

[0052] I. Preparation of nucleating agent modified polymer granules:

[0053] Weigh out 3 parts by weight of nucleating agent, 97 parts by weight of thermoplastic polymer, 2 parts by weight of compatibilizer and 1 part by weight of lubricant, and then perform high-speed mixing, high-speed extrusion granulation and drying in sequence to obtain nucleating agent modified polymer granules.

[0054] II. Preparation of wood-plastic granules:

[0055] Weigh out 40 parts by weight of wood fiber, 54 parts by weight of nucleating agent-modified polymer granules, 4 parts by weight of compatibilizer and 2 parts by weight of lubricant, and then perform high-speed mixing, granulation and drying in sequence to obtain wood-plastic granules.

[0056] III. Preparation of microporous foamed wood-plastic composite materials:

[0057] Wood-plastic granules are placed in an injection molding machine, and then supercritical fluid is injected into the injection molding machine. The mixture is then injected and molded according to a certain amount of melt to obtain a supercritical fluid microporous foamed wood-plastic composite material.

[0058] The nucleating agent mentioned in step one is nano-montmorillonite; the thermoplastic polymer mentioned in step one is polypropylene (T30S, Daqing Petrochemical); the compatibilizer mentioned in steps one and two is maleic anhydride-grafted polypropylene; the lubricant mentioned in steps one and two is a mixture of polyethylene wax and stearic acid in a mass ratio of 1:1; the thermoplastic polymer mentioned in step one is a dried thermoplastic polymer, specifically dried according to the following steps: the thermoplastic polymer is dried at a temperature of 60°C for 24 hours.

[0059] The wood fiber mentioned in step two is 80-100 mesh wood fiber; the wood fiber mentioned in step two is poplar wood powder; the wood fiber mentioned in step two is wood fiber after drying treatment, and specifically, it is dried according to the following steps: the wood fiber is dried for 24 hours at a temperature of 103±3℃ until the moisture content is 1%.

[0060] The high-speed mixing described in steps one and two specifically involves using a high-speed mixer to mix for 15 minutes at a temperature of 60°C and a rotation speed of 2000 r / min.

[0061] The high-speed extrusion granulation described in step one specifically involves using a twin-screw extruder to perform high-speed shear melt extrusion granulation under the following conditions: barrel temperature zones of 155℃, 175℃, 190℃, 190℃, 190℃, 190℃ and 190℃, die temperature of 180℃ and screw speed of 200r / min.

[0062] The granulation described in step two is specifically carried out using a twin-screw extruder, with the barrel temperature zone being 150℃, 165℃, 175℃, 175℃, 175℃, 175℃, 175℃, the die temperature being 160℃, and the screw speed being 50r / min.

[0063] The drying process described in steps one and two specifically involves drying at a temperature of 80°C for 12 hours.

[0064] The injection molding process parameters described in step three are as follows: the barrel temperature zones are 160℃, 170℃, 190℃, 190℃ and 190℃ respectively, the nozzle temperature is 180℃, the screw speed is 50r / min, and the system back pressure is 10MPa.

[0065] In step three, the wood-plastic granules undergo sequential processes in the injection molding machine: melting stage, injection stage, holding pressure stage, cooling stage, and mold opening stage. The melting stage consists of a material plasticizing stage and a gas injection mixing stage, with a total time of 15 seconds. The injection stage is performed at an injection pressure of 8 MPa and an injection speed of 84.8 mm / s. The holding pressure stage is specifically performed at a pressure of 4 MPa for 5 seconds. The cooling stage is specifically performed at a mold temperature of 40°C for 25 seconds.

[0066] In step three, supercritical fluid is injected during the gas injection and mixing stage to obtain a wood-plastic composite melt containing gas. The melt volume mentioned in step three is 26 mm, which is 81.25% of the theoretical melt volume. The theoretical melt volume is the total amount of material required to completely fill the mold cavity without foaming gas.

[0067] In step three, the injection pressure of the supercritical fluid is 20 MPa; the supercritical fluid mentioned in step three is supercritical nitrogen; and the mass of the supercritical fluid is 1% of the mass of the gas-containing wood-plastic composite melt.

[0068] Figure 2 This is a scanning electron microscope image of the supercritical fluid microporous foamed wood-plastic composite material prepared in Example 1;

[0069] Example 1: The supercritical fluid microporous foamed wood-plastic composite material prepared had a wood fiber content of 40 wt.% and a density of 0.85 g / cm³. 3 The weight reduction rate was 18.47%, the flexural strength was 46.03 MPa, the flexural modulus was 2.92 GPa, the tensile strength was 24.96 MPa, the tensile modulus was 2.41 GPa, and the impact strength was 11.97 KJ / m. 2 The average cell size was 24.32 μm, and the average cell density was 1.44 × 10⁻⁶. 7 pcs / cm 3 .

[0070] Example 2:

[0071] A method for preparing a supercritical fluid microporous foamed wood-plastic composite material, comprising the following steps:

[0072] I. Preparation of nucleating agent modified polymer granules:

[0073] Weigh out 1 part nucleating agent, 99 parts thermoplastic polymer, 4 parts compatibilizer and 1 part lubricant by mass, and then perform high-speed mixing, high-speed extrusion granulation and drying in sequence to obtain nucleating agent modified polymer granules.

[0074] II. Preparation of wood-plastic granules:

[0075] Weigh out 60 parts by weight of wood fiber, 34 parts by weight of nucleating agent-modified polymer granules, 4 parts by weight of compatibilizer and 2 parts by weight of lubricant, and then perform high-speed mixing, granulation and drying in sequence to obtain wood-plastic granules.

[0076] III. Preparation of microporous foamed wood-plastic composite materials:

[0077] Wood-plastic granules are placed in an injection molding machine, and then supercritical fluid is injected into the injection molding machine. The mixture is then injected and molded according to a certain amount of melt to obtain a supercritical fluid microporous foamed wood-plastic composite material.

[0078] The nucleating agent mentioned in step one is nano-titanium dioxide; the thermoplastic polymer mentioned in step one is polypropylene (T30S, Daqing Petrochemical); the compatibilizer mentioned in steps one and two is maleic anhydride-grafted polypropylene; the lubricant mentioned in steps one and two is a mixture of polyethylene wax and stearic acid in a mass ratio of 1:1; the thermoplastic polymer mentioned in step one is a dried thermoplastic polymer, specifically dried according to the following steps: the thermoplastic polymer is dried at a temperature of 60°C for 24 hours.

[0079] The wood fiber mentioned in step two is 80-100 mesh wood fiber; the wood fiber mentioned in step two is poplar wood powder; the wood fiber mentioned in step two is wood fiber after drying treatment, and specifically, it is dried according to the following steps: the wood fiber is dried for 24 hours at a temperature of 103±3℃ until the moisture content is 1%.

[0080] The high-speed mixing described in steps one and two specifically involves using a high-speed mixer to mix for 15 minutes at a temperature of 60°C and a rotation speed of 2000 r / min.

[0081] The high-speed extrusion granulation described in step one specifically involves using a twin-screw extruder to perform high-speed shear melt extrusion granulation under the following conditions: barrel temperature zones of 155℃, 175℃, 185℃, 185℃, 185℃, 185℃, 185℃, die temperature of 180℃, and screw speed of 200r / min.

[0082] The granulation described in step two is specifically carried out using a twin-screw extruder, with the barrel temperature zone being 150℃, 165℃, 175℃, 175℃, 175℃, 175℃, 175℃, the die temperature being 160℃, and the screw speed being 35r / min.

[0083] The drying process described in steps one and two specifically involves drying at a temperature of 80°C for 12 hours.

[0084] The injection molding process parameters described in step three are as follows: the barrel temperature zones are 160℃, 170℃, 190℃, 190℃ and 190℃ respectively, the nozzle temperature is 180℃, the screw speed is 50r / min, and the system back pressure is 10MPa.

[0085] In step three, the wood-plastic granules undergo a series of stages in the injection molding machine: melting, injection, holding pressure, cooling, and mold opening. The melting stage consists of a material plasticizing stage and a gas injection mixing stage, with a total time of 15 seconds. The injection stage is performed at an injection pressure of 11 MPa and an injection speed of 84.8 mm / s. The holding pressure stage is specifically performed at a pressure of 4 MPa for 5 seconds. The cooling stage is specifically performed at a mold temperature of 40°C for 25 seconds.

[0086] In step three, supercritical fluid is injected during the gas injection and mixing stage to obtain a wood-plastic composite melt containing gas. The melt volume mentioned in step three is 25mm, which is 78.13% of the theoretical melt volume. The theoretical melt volume is the total amount of material required to completely fill the mold cavity without foaming gas.

[0087] In step three, the injection pressure of the supercritical fluid is 20 MPa; the supercritical fluid mentioned in step three is supercritical nitrogen; and the mass of the supercritical fluid is 1% of the mass of the gas-containing wood-plastic composite melt.

[0088] Comparative Experiment 1: This comparative experiment differs from Example 2 in that the melt volume in step 3 is 32 mm, which is 100% of the theoretical melt volume; step 3 yields a saturated filled microporous foamed wood-plastic composite material. Everything else is the same as in Example 2.

[0089] Figure 3 This is a scanning electron microscope image of the supercritical fluid microporous foamed wood-plastic composite material prepared in Example 2; Figure 4 Scanning electron microscope (SEM) images of the saturated filled microporous foamed wood-plastic composite material prepared in Experiment 1 for comparison;

[0090] The supercritical fluid microporous foamed wood-plastic composite material prepared in Example 2 has a wood fiber content of 60 wt.% and a density of 1.01 g / cm³. 3 The weight reduction rate was 12.9%, the flexural strength was 74.35 MPa, the flexural modulus was 5.71 GPa, the tensile strength was 27.03 MPa, the tensile modulus was 3.01 GPa, and the impact strength was 9.54 KJ / m. 2 The average cell size is 5.27 μm, and the average cell density is 2.20 × 10⁻⁶. 8 pcs / cm 3 .

[0091] The saturated filled microporous foamed wood-plastic composite material prepared in Comparative Experiment 1 had a wood fiber content of 60 wt.% and a density of 1.10 g / cm³. 3The weight reduction rate was 5.2%, the flexural strength was 67.32 MPa, the flexural modulus was 4.13 GPa, the tensile strength was 21.89 MPa, the tensile modulus was 1.77 GPa, and the impact strength was 7.37 KJ / m. 2 The average cell size is 57.29 μm, and the average cell density is 5.76 × 10⁻⁶. 5 pcs / cm 3 .

[0092] Example 3:

[0093] A method for preparing a supercritical fluid microporous foamed wood-plastic composite material, comprising the following steps:

[0094] I. Preparation of nucleating agent modified polymer granules:

[0095] Weigh out 1 part nucleating agent, 99 parts thermoplastic polymer, 1 part compatibilizer and 1 part lubricant by mass, and then perform high-speed mixing, high-speed extrusion granulation and drying in sequence to obtain nucleating agent modified polymer granules.

[0096] II. Preparation of wood-plastic granules:

[0097] Weigh out 30 parts by weight of wood fiber, 64 parts by weight of nucleating agent-modified polymer granules, 4 parts by weight of compatibilizer and 2 parts by weight of lubricant, and then perform high-speed mixing, granulation and drying in sequence to obtain wood-plastic granules.

[0098] III. Preparation of microporous foamed wood-plastic composite materials:

[0099] Wood-plastic granules are placed in an injection molding machine, and then supercritical fluid is injected into the injection molding machine. The mixture is then injected and molded according to a certain amount of melt to obtain a supercritical fluid microporous foamed wood-plastic composite material.

[0100] The nucleating agent mentioned in step one is polytetrafluoroethylene; the thermoplastic polymer mentioned in step one is polypropylene (T30S, Daqing Petrochemical); the compatibilizer mentioned in steps one and two is maleic anhydride-grafted polypropylene; the lubricant mentioned in steps one and two is a mixture of polyethylene wax and stearic acid in a mass ratio of 1:1; the thermoplastic polymer mentioned in step one is a dried thermoplastic polymer, specifically dried according to the following steps: the thermoplastic polymer is dried at a temperature of 60°C for 24 hours.

[0101] The wood fiber mentioned in step two is 80-100 mesh wood fiber; the wood fiber mentioned in step two is poplar wood powder; the wood fiber mentioned in step two is wood fiber after drying treatment, and specifically, it is dried according to the following steps: the wood fiber is dried for 24 hours at a temperature of 103±3℃ until the moisture content is 1%.

[0102] The high-speed mixing described in steps one and two specifically involves using a high-speed mixer to mix for 15 minutes at a temperature of 60°C and a rotation speed of 2000 r / min.

[0103] The high-speed extrusion granulation described in step one specifically involves using a twin-screw extruder to perform high-speed shear melt extrusion granulation under the following conditions: barrel temperature zones of 175℃, 190℃, 200℃, 210℃, 210℃, 200℃, die temperature of 190℃, and screw speed of 200r / min.

[0104] The granulation described in step two is specifically carried out using a twin-screw extruder, with the barrel temperature zone being 150℃, 165℃, 175℃, 175℃, 175℃, 175℃, 175℃, the die temperature being 160℃, and the screw speed being 50r / min.

[0105] The drying process described in steps one and two specifically involves drying at a temperature of 80°C for 12 hours.

[0106] The injection molding process parameters described in step three are as follows: the barrel temperature zones are 160℃, 180℃, 185℃, 185℃ and 180℃ respectively, the nozzle temperature is 180℃, the screw speed is 50r / min, and the system back pressure is 10MPa.

[0107] In step three, the wood-plastic granules undergo a series of stages in the injection molding machine: melting, injection, holding pressure, cooling, and mold opening. The melting stage consists of a material plasticizing stage and a gas injection mixing stage, with a total time of 10 seconds. The injection stage is performed at an injection pressure of 7.5 MPa and an injection speed of 84.8 mm / s. The holding pressure stage is specifically performed at a pressure of 4 MPa for 15 seconds. The cooling stage is specifically performed at a mold temperature of 40°C for 25 seconds.

[0108] In step three, supercritical fluid is injected during the gas injection and mixing stage to obtain a wood-plastic composite melt containing gas. The melt volume mentioned in step three is 26 mm, which is 81.25% of the theoretical melt volume. The theoretical melt volume is the total amount of material required to completely fill the mold cavity without foaming gas.

[0109] In step three, the injection pressure of the supercritical fluid is 20 MPa; the supercritical fluid mentioned in step three is supercritical nitrogen; and the mass of the supercritical fluid is 1% of the mass of the gas-containing wood-plastic composite melt.

[0110] Comparative Experiment 2: This comparative experiment differs from Example 3 in that step 1 is omitted, and in step 2, the nucleating agent-modified polymer granules are replaced with thermoplastic polymers; step 3 yields microporous foamed wood-plastic composite materials without nucleating agent modification. Everything else is the same as in Example 3.

[0111] Figure 5 This is a scanning electron microscope image of the supercritical fluid microporous foamed wood-plastic composite material prepared in Example 3; Figure 6 Scanning electron microscope (SEM) image of the microporous foamed wood-plastic composite material prepared in Experiment 2 without nucleating agent modification;

[0112] The supercritical fluid microporous foamed wood-plastic composite material prepared in Example 3 has a wood fiber content of 30 wt.% and a density of 0.83 g / cm³. 3 The weight reduction rate was 17.5%, the tensile strength was 25.93 MPa, and the tensile modulus was 2.32 GPa; the flexural strength was 49.05 MPa, and the flexural modulus was 2.62 GPa; the impact strength was 23.69 KJ / m. 2 The average cell size was 29.59 μm, and the average cell density was 6.16 × 10⁻⁶. 6 pcs / cm 3 .

[0113] The microporous foamed wood-plastic composite material prepared in Comparative Experiment 2 without nucleating agent modification had a wood fiber content of 30 wt.% and a density of 0.81 g / cm³. 3 The weight reduction rate was 18.8%, the tensile strength was 25.19 MPa, the tensile modulus was 2.29 GPa; the flexural strength was 47.65 MPa, the flexural modulus was 2.55 GPa; and the impact strength was 17.49 KJ / m. 2 The average cell size was 89.35 μm, and the average cell density was 6.01 × 10⁻⁶. 5 pcs / cm 3 .

Claims

1. A method for preparing a supercritical fluid microporous foamed wood-plastic composite material, characterized in that... It is done in the following steps: I. Preparation of nucleating agent modified polymer granules: Weigh out 1 to 20 parts by weight of nucleating agent, 80 to 99 parts by weight of thermoplastic polymer, 1 to 5 parts by weight of compatibilizer and 1 to 2 parts by weight of lubricant, and then perform high-speed mixing, high-speed extrusion granulation and drying in sequence to obtain nucleating agent modified polymer granules. II. Preparation of wood-plastic granules: Weigh out 10 to 60 parts by weight of wood fiber, 30 to 90 parts by weight of polymer granules modified with nucleating agent, 2 to 8 parts by weight of compatibilizer and 0.5 to 2 parts by weight of lubricant, and then perform high-speed mixing, granulation and drying in sequence to obtain wood-plastic granules; III. Preparation of microporous foamed wood-plastic composite materials: Wood-plastic granules are placed in an injection molding machine, and then supercritical fluid is injected into the injection molding machine. The mixture is then injected and molded according to a certain amount of melt to obtain a supercritical fluid microporous foamed wood-plastic composite material.

2. The method for preparing a supercritical fluid microporous foamed wood-plastic composite material according to claim 1, characterized in that... The nucleating agent mentioned in step one is polymer particles or inorganic nanoparticles with layered and polyhedral crystal structures; the thermoplastic polymer mentioned in step one is one or a combination of polyethylene, polypropylene, and polylactic acid; the compatibilizer mentioned in steps one and two is one or a combination of maleic anhydride-grafted polyethylene, maleic anhydride-grafted polypropylene, and maleic anhydride-grafted polylactic acid; the lubricant mentioned in steps one and two is one or a combination of polyethylene wax, stearic acid, paraffin wax, polypropylene wax, oxidized polyethylene wax, palm wax, lignite wax, and white oil; the thermoplastic polymer mentioned in step one is a dried thermoplastic polymer, specifically dried according to the following steps: drying the thermoplastic polymer at a temperature of 55℃~60℃ for 24h~48h.

3. The method for preparing a supercritical fluid microporous foamed wood-plastic composite material according to claim 2, characterized in that... The polymer particles are one or a combination of polytetrafluoroethylene, polyamide 6, polyethylene terephthalate, and polyphenylene sulfide; the inorganic nanoparticles with layered and polyhedral crystal structures are one or a combination of nano-montmorillonite, nano-titanium dioxide, nano-silica, and nano-zinc oxide.

4. The method for preparing a supercritical fluid microporous foamed wood-plastic composite material according to claim 1, characterized in that... The total mass fraction of the wood fiber, nucleating agent-modified polymer granules, compatibilizer, and lubricant mentioned in step two is 100 parts; the wood fiber mentioned in step two is 40-150 mesh wood fiber; the wood fiber mentioned in step two is derived from one or a combination of several of agricultural and forestry processing residues and wastes; the wood fiber mentioned in step two is dried wood fiber, specifically dried according to the following steps: the wood fiber is dried to a moisture content of less than 2% at a temperature of 100℃-106℃.

5. The method for preparing a supercritical fluid microporous foamed wood-plastic composite material according to claim 4, characterized in that... The wood fiber mentioned in step two is one or a combination of wood flour, bamboo flour and straw flour.

6. The method for preparing a supercritical fluid microporous foamed wood-plastic composite material according to claim 1, characterized in that... The high-speed mixing described in steps one and two specifically involves using a high-speed mixer to mix for 5 to 30 minutes at a temperature of 20℃ to 80℃ and a rotation speed of 1000 r / min to 3000 r / min. The high-speed extrusion granulation described in step one specifically involves using a twin-screw extruder to melt-extrude and granulate at a barrel temperature of 150℃ to 260℃, a die temperature of 150℃ to 260℃, and a screw rotation speed of 200 r / min to 300 r / min. The granulation described in step two specifically involves using a twin-screw extruder to melt-extrude and granulate at a barrel temperature of 140℃ to 180℃, a die temperature of 150℃ to 180℃, and a screw rotation speed of 20 r / min to 200 r / min. The drying described in steps one and two specifically involves drying at a temperature of 80℃ to 100℃ for 12 to 24 hours.

7. The method for preparing a supercritical fluid microporous foamed wood-plastic composite material according to claim 1, characterized in that... The injection molding process parameters described in step three are as follows: barrel temperature is 160℃~200℃, nozzle temperature is 170℃~220℃, screw speed is 40r / min~80r / min, and system back pressure is 10MPa~20MPa.

8. The method for preparing a supercritical fluid microporous foamed wood-plastic composite material according to claim 7, characterized in that... In step three, the wood-plastic granules undergo a series of stages in the injection molding machine: melting, injection, holding pressure, cooling, and mold opening. The melting stage consists of a material plasticizing stage and a gas injection mixing stage, with a total time of 5 to 30 seconds. The injection stage is performed at an injection pressure of 3 to 17 MPa and an injection speed of 53 to 95 mm / s. The holding pressure stage is specifically performed at a pressure of 4 to 12 MPa for 0 to 30 seconds. The cooling stage is specifically performed at a mold temperature of 30 to 40 degrees Celsius for 5 to 30 seconds.

9. The method for preparing a supercritical fluid microporous foamed wood-plastic composite material according to claim 8, characterized in that... In step three, supercritical fluid is injected during the gas injection and mixing stage to obtain a gas-containing wood-plastic composite melt; the melt amount mentioned in step three is 70% to 100% of the theoretical melt amount; the theoretical melt amount is the total amount of material required to completely fill the mold cavity without foaming gas.

10. The method for preparing a supercritical fluid microporous foamed wood-plastic composite material according to claim 9, characterized in that... In step three, the injection pressure of the supercritical fluid is 15MPa~30MPa; the supercritical fluid mentioned in step three is one or a combination of supercritical nitrogen and supercritical carbon dioxide; the mass of the supercritical fluid is 0.5%~2% of the mass of the gas-containing wood-plastic composite melt.

Images