A method of making a natural fiber web reinforced thermoplastic recyclable composite

Abstract

A preparation method of natural fiber web reinforced thermoplastic recyclable composite material, after cutting the three-dimensional natural fiber material, the surface is washed and sewn to reinforce; after water bath, wash with deionized water to neutral, place in different concentration of alkaline solution to form a large number of convex particles on the surface of the fiber; the cellulose fiber web is placed on the thermoplastic resin film, the uppermost layer is laid with thermoplastic resin film, and placed on the hot press, and the mold is opened to obtain the cellulose fiber web reinforced thermoplastic composite material; with high performance fiber reinforced thermoplastic composite material as upper and lower layers, the middle layer is cellulose fiber web reinforced thermoplastic composite material, and natural fiber web reinforced thermoplastic recyclable composite material is obtained. The natural fiber web is used as the reinforcing body, and the thermoplastic resin is used as the matrix. The composite material is prepared by controlling the material mass fraction, thickness, hot pressing temperature, hot pressing pressure and hot pressing time. The composite material has the advantages of low density, low price, environmental friendliness, repeated recycling and the like.

Description

A method for preparing a natural fiber web reinforced thermoplastic recyclable composite material Technical Field

[0001] This invention relates to the technical field of biomass composite materials, and in particular to a method for preparing a natural fiber web reinforced thermoplastic recyclable composite material. Background Technology

[0002] Composite materials possess advantages such as lightweight and high strength, corrosion resistance, acid and alkali resistance, salt spray resistance, aging resistance, impact resistance, and strong environmental adaptability, leading to their widespread application in various engineering fields. The preparation of natural plant fiber reinforced polymer composites primarily utilizes thermosetting resins, including epoxy resins, phenolic resins, and polyimides. Patent "CN105602268A" discloses a plant fiber reinforced bio-based thermosetting composite material and its preparation method. While the thermosetting resin exhibits good mechanical properties, the thermosetting composite material suffers from long molding times and difficulty in recycling, failing to meet the requirements of sustainable development.

[0003] Protective composite materials often employ high-performance fibers combined with resin to create stab-resistant units, which are then placed within the lining and rely on structural design to achieve the stab-resistant effect. Patent "CN101936684B" discloses a stab-resistant fiber composite material with an improved structure and its application, specifically involving the combination of a single-layer composite material made from high-performance fiber reinforcement and a resin matrix. While high-performance fibers possess high strength and high modulus, these materials are derived from non-renewable petroleum resources, resulting in high costs and a high carbon footprint.

[0004] Numerous three-dimensional network-like natural fibers exist in nature. Their naturally formed three-dimensional structure avoids the lengthy processes of traditional fabric processing and offers advantages such as abundant resources, biodegradability, and low cost. Composite materials prepared using natural three-dimensional fiber networks as reinforcing matrices exhibit high toughness and energy absorption. They can be combined with high-performance fibers to create hybrid composites for applications in personal protective equipment, such as stab-resistant vests and impact-resistant clothing. Developing composite materials using biomass fibers to replace some high-performance fibers and prepare hybrid composites with performance gradients can avoid the problems of excess performance and increased costs associated with homogeneous materials, while also achieving rational resource utilization and environmental protection. Patent "CN114932723A" discloses a method for preparing a lightweight composite material with variable thickness and performance gradients. This method uses high-performance fibers and compressed wood to prepare a hybrid composite material to bear loads. However, compressed wood is an anisotropic material, and its load-bearing capacity varies significantly under loads from different directions. Summary of the Invention

[0005] In view of the current application status of bio-based composite materials, the purpose of this invention is to provide a method for preparing a three-dimensional natural fiber reinforced thermoplastic composite material, which solves the problems of anisotropy and inconvenience of recycling of fiber reinforced laminate composite materials, and broadens the application field of new biomass fibers.

[0006] A method for preparing a natural fiber web reinforced thermoplastic recyclable composite material includes the following steps:

[0007] Step (1): Cut the three-dimensional natural fiber material into 6-10cm×6-10cm sizes and wash off the surface dust and impurities in running water; after air drying, sew it to reinforce it;

[0008] Step (2): Place the reinforced three-dimensional natural fiber material in a mixed solution at a bath ratio of 1:20-1:100, heat it in a constant temperature water bath at 80-100℃ for 1.5-2 hours, repeat 1-3 times to remove impurities in the fiber. After the water bath is completed, wash it with deionized water until neutral, and dry it in an oven for 4-8 hours to obtain a cellulose fiber web.

[0009] Step (3): Place the cellulose fiber web in alkaline solutions of different concentrations to dissolve hemicellulose and pectin, forming a large number of protruding particles on the fiber surface to increase surface roughness;

[0010] Step (4): Place the thermoplastic resin film on the bottom layer of the mold, place the cellulose fiber web on the thermoplastic resin film, and then lay the cellulose fiber web and thermoplastic resin film in sequence. Place the thermoplastic resin film on the top layer, and then place the mold sheet on top of the laid material to control the thickness. Spray the mold release agent on the mold that is close to the upper and lower surfaces of the material, place it on the hot press, and hot press it at a temperature of 90-150℃ and a pressure of 10-20MPa for 1-2 hours. After heating, let it close the mold and set the shape, and then cool it naturally under pressure for 6-12 hours. After that, open the mold to obtain the cellulose fiber web reinforced thermoplastic composite material.

[0011] Step (5): The high-performance fiber is laminated with the thermoplastic resin film to prepare the high-performance fiber reinforced composite material; the high-performance fiber reinforced composite material is used as the upper and lower layers, and the middle layer is the cellulose fiber network reinforced thermoplastic composite material to obtain the tough hybrid thermoplastic composite material, which is the natural fiber network reinforced thermoplastic recyclable composite material.

[0012] The present invention provides a method for preparing a natural fiber web reinforced thermoplastic recyclable composite material, which has the following advantages:

[0013] The natural three-dimensional fabric structure features fibers arranged at angles, uniformly distributed, and connected by fibers running through its thickness, forming a complex network structure. It possesses isotropic mechanical characteristics, enabling it to better withstand impacts from different directions.

[0014] Using natural fiber mesh as reinforcement and thermoplastic resin as matrix, composite materials are prepared by controlling the material mass fraction, thickness, hot pressing temperature, hot pressing pressure, and hot pressing time. They have advantages such as low density, low price, environmental friendliness, and recyclability.

[0015] When this biomass composite material is applied to the field of stab protection, it can be used as a toughening material and layered with high-performance fiberboard to prepare a hybrid composite material. The hybrid composite material relies on the high strength and high modulus of the high-performance fibers on the surface to hinder the penetration of the blade tip. When the blade tip continues to penetrate, the bio-based board has good energy dissipation and fracture toughness, which can effectively absorb impact loads, thereby reducing the amount of high-performance fibers used and achieving the purpose of reducing costs and weight. Attached Figure Description

[0016] Figure 1 is a schematic diagram of the hot pressing process of the present invention.

[0017] Figure 2 shows the appearance of the natural fiber web reinforced thermoplastic recyclable composite material obtained by selecting palm flakes;

[0018] Figure 3 shows the SEM image of the natural fiber web reinforced thermoplastic recyclable composite material obtained by selecting palm flakes;

[0019] Figure 4 is a schematic diagram of the puncture state of a natural fiber web reinforced thermoplastic recyclable composite material. Detailed Implementation

[0020] The present invention will now be described in detail with reference to specific embodiments. It should be understood that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific mass, temperature, time, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0021] A method for preparing a natural fiber web reinforced thermoplastic recyclable composite material includes the following steps:

[0022] Step (1): Cut the three-dimensional natural fiber material into 6-10cm×6-10cm sizes and wash the surface ash and impurities in running water; after air drying, sew it to reinforce it to prevent it from falling apart during the chemical treatment process;

[0023] Step (2): Place the reinforced three-dimensional fiber mesh in the mixed solution at a bath ratio of 1:20-1:100, and heat it in a constant temperature water bath at 80-100℃ for 1.5-2 hours. Repeat 1-3 times to remove impurities in the fiber. After the water bath is completed, wash it with deionized water until neutral, and dry it in an oven for 4-8 hours to obtain the cellulose fiber mesh. Adjust the porosity of the material according to the changes in the processing technology.

[0024] Step (3): Place the cellulose fiber web in alkaline solutions of different concentrations to dissolve hemicellulose and pectin, forming a large number of protruding particles on the fiber surface, increasing surface roughness and improving interfacial adhesion with thermoplastic resin.

[0025] Step (4): Place the thermoplastic resin film on the bottom layer of the mold, place the cellulose fiber web on the thermoplastic resin film, and then lay the cellulose fiber web and thermoplastic resin film in sequence. Place the thermoplastic resin film on the top layer, and then place the mold sheet on top of the laid material to control the thickness. Spray the mold release agent on the mold that is close to the upper and lower surfaces of the material, place it on the hot press, and hot press it at a temperature of 90-150℃ and a pressure of 10-20MPa for 1-2 hours. After heating, close the mold and let it cool naturally under pressure for 6-12 hours. Then open the mold to obtain the three-dimensional fiber web reinforced thermoplastic composite material.

[0026] Step (5): The high-performance fiber is laminated with the thermoplastic resin film to prepare the high-performance fiber reinforced composite material; the high-performance fiber reinforced composite material is used as the upper and lower layers, and the middle layer is the cellulose fiber network reinforced thermoplastic composite material to obtain the tough hybrid thermoplastic composite material, which is the natural fiber network reinforced thermoplastic recyclable composite material.

[0027] Preferably, the three-dimensional natural fiber material processed in step (1) of the present invention is one or more of palm flakes, loofah pulp, or radish peel.

[0028] Preferably, the sewing reinforcement method in step (1) of the present invention is sewing thread or resin bonding.

[0029] Preferably, the mixed solution in step (2) of the present invention is at least one of the following combinations: a mixed solution of sodium hydroxide and hydrogen peroxide, a mixed solution of sodium hydroxide and sodium sulfite, a mixed solution of sodium chlorite and glacial acetic acid, and a eutectic solvent composed of choline chloride and lactic acid, alanine and lactic acid, and betaine and lactic acid.

[0030] Preferably, in step (2) of the present invention, the mass percentage of hydrogen peroxide is 2 wt.%-4 wt.% and the mass percentage of sodium hydroxide is 4 wt.%-8 wt.%.

[0031] Preferably, the concentration of sodium hydroxide in step (3) of the present invention is 2% or 4% or 6% or 8% or 10% or 12%.

[0032] Preferably, the alkaline solution in step (3) of the present invention is at least one of sodium hydroxide, potassium hydroxide, and calcium hydroxide.

[0033] Preferably, the thermoplastic resin in step (4) of the present invention is at least one or more of polycarbonate, saline resin, thermoplastic epoxy resin, and polyamide; the thermoplastic resin is in sheet, granular or liquid form; the hot pressing temperature is set above the softening point or melting point of the thermoplastic resin; the mass percentage of the cellulose fiber web to the thermoplastic resin is 20%-60%, the fiber content in the composite material is 20%-50%, the volume of the thermoplastic resin is 50%-80%, and the length of the natural fiber is 5-10 cm.

[0034] Preferably, in step (5) of the present invention, the high-performance fiber layers are arranged in a cross-layout pattern at 0°, ±45°, and 90°. The thickness of the upper and lower layers can be the same or can vary in a gradient.

[0035] Preferably, the high-performance fiber in step (5) of the present invention is at least one of carbon fiber, glass fiber, and basalt fiber.

[0036] Use vernier calipers to measure the thickness of the material at multiple locations, avoiding areas where the thickness is significantly too large or too small. Then, take 5 sets of uniform data to calculate the average thickness. Use a balance to weigh the composite material, measure the length and width of the material, and calculate the density of each sample.

[0037] The prepared composite material was cut into samples and subjected to tensile fracture tests in accordance with GB / T3923.1-2013. The sample size was 50 mm long × 6 mm wide. The rising speed was set to 10 mm / min, the falling speed to 100 mm / min, and the decay rate to 80%. The fracture strength, elongation at break, and other data of the composite material were recorded, and the fracture strength and tensile modulus were calculated.

[0038] The composite material was subjected to a three-point bending test using a universal testing machine. The experiment was conducted in accordance with GB / T1449-2005 "Test Method for Bending Properties of Fiber Reinforced Plastics". The loading speed was 2 mm / min. The bending strength, bending modulus and other data of the composite material were calculated.

[0039] The impact toughness of the composite material was tested using the CXJD instrument from Jinhe Instruments. The test standard was based on GB / T1043-92, which involved notched pendulum impact. The impact energy absorbed at the point of fracture was recorded, and the average value was calculated as an indicator to evaluate the impact performance of the material.

[0040] Quasi-static puncture tests were conducted on composite materials using a universal testing machine. A schematic diagram of the hybrid composite material puncture test is shown in Figure 4. High-performance fiber-based composite materials and bio-based composite materials were laminated and bonded together and fixed in a fixture. The test tool moved downwards at a speed of 100 mm / min, puncturing the center of the sample. Data was recorded at a frequency of 30 Hz, yielding a displacement-load curve. The maximum load in the quasi-static test was defined as the quasi-static puncture strength. The slope of the initial straight line of the displacement-load curve was the quasi-static initial puncture modulus of the composite material. The ratio of energy absorbed by the material from initial contact with the tool to puncture of the lower surface to its thickness was defined as the work consumed per unit thickness. The puncture resistance of various composite material samples under quasi-static puncture tests was compared.

[0041] Example 1:

[0042] (1) Prepare a solution of 4% sodium hydroxide and 8% sodium sulfite by mass, with a bath ratio of 1:100. Weigh 20g of cut palm flakes, wash them under running water to remove surface dust and impurities, air dry them naturally, and then place them in the mixed solution. Heat them in a water bath at 90°C for 2 hours, repeat 3 times, and then dry them in an oven until constant weight.

[0043] (2) The portion of the palm fiber mesh with smaller fiber gaps after lignin removal was used as the experimental material. This material was cross-laminated with a thermoplastic sarin resin film and placed in a mold. The mold was then transferred between the upper and lower hot press plates of a hot press, and manual pressure was applied to prepare a composite material with a palm fiber mass fraction of 30%. The hot pressing process consisted of a hot pressing temperature of 100℃, a hot pressing pressure of 25MPa, a hot pressing time of 1 hour, and a pressurized cooling time of 2-5 hours. A schematic diagram of the hot pressing process is shown in Figure 1. The surface density of the selected sarin resin film was 130 g / m³. 2 The thickness is 0.1 mm, the tensile strength is 15.65 ± 0.98 MPa, and the elongation at break is 178.75 ± 11.08%.

[0044] Test results: The thickness of the palm fiber / salin composite material is 0.8 mm, and the density is 1.04 g / cm³. 3 The transverse tensile strength is 15-20 MPa, the longitudinal tensile strength is 18-20 MPa, the transverse tensile modulus is 350-500 MPa, the longitudinal tensile modulus is 480-550 MPa, the flexural strength is 5.6 MPa, the flexural modulus is 183.68 MPa, and the quasi-static puncture strength is 37 N.

[0045] Example 2:

[0046] (1) Prepare a solution of 4% sodium hydroxide and 8% sodium sulfite by mass, with a bath ratio of 1:100. Weigh 20g of cut palm flakes, wash them under running water to remove surface dust and impurities, air dry them naturally, and then place them in the mixed solution. Heat them in a water bath at 90°C for 2 hours, repeat 3 times, and then dry them in an oven until constant weight.

[0047] (2) The palm flakes after removing lignin were combined with thermoplastic resin film polycarbonate resin to prepare a composite material with a palm flake mass fraction of 30%. The hot pressing process was as follows: hot pressing temperature 140℃, hot pressing pressure 25MPa, hot pressing time 1h, and pressurized cooling time 2-5h.

[0048] Test Results: The surface morphology and cross-sectional SEM images of the palm fiber / polycarbonate composite material are shown in Figures 2 and 3, respectively. The fiber-reinforced composite material has a complete appearance, good molding, and no obvious surface defects. After alkali treatment, the number of hydrophilic groups in the fibers is reduced, resulting in a tighter bond with the matrix and effectively avoiding the problem of poor interfacial bonding between the fibers and the thermoplastic resin. The polycarbonate composite material has a thickness of 1.21 mm and a density of 1.12 g / cm³. 3 The transverse tensile strength is 50 MPa, the longitudinal tensile strength is 90 MPa, the flexural strength is 62.54 MPa, the flexural modulus is 725.75 MPa, the quasi-static puncture strength is 177 N, and the impact strength is 29.13 KJ / m. 2 .

[0049] Example 3:

[0050] (1) Prepare a solution of 1% sodium chlorite and 2% glacial acetic acid by mass, with a bath ratio of 1:40. Weigh 20g of the cut palm flakes, wash them under running water to remove surface dust and impurities, air dry them naturally, and then place them in the mixed solution. Heat them in a water bath at 100℃ for 2 hours, repeat 3 times, and then dry them in an oven until constant weight.

[0051] (2) The palm flakes after removing lignin were combined with thermoplastic resin film polycarbonate resin to prepare a composite material with a palm flake mass fraction of 30%. The hot pressing process was as follows: hot pressing temperature 130℃, hot pressing pressure 25MPa, hot pressing time 1h, and pressurized cooling time 2-5h.

[0052] Test results: The thickness of the palm fiber / polycarbonate composite material is 1.4 mm, and the density is 1.22 g / cm³. 3 The transverse tensile strength is 30 MPa, the flexural strength is 58.29 MPa, the flexural modulus is 543.16 MPa, the longitudinal tensile strength is 45 MPa, and the quasi-static puncture strength is 165 N.

[0053] Example 4:

[0054] (1) Prepare sodium hydroxide solutions of 2%, 6%, and 12% respectively, with a bath ratio of 1:20. Weigh 20g of the cut palm flakes, wash them under running water to remove surface dust and impurities, air dry them naturally, and then place them in the mixed solution. Treat them at room temperature for 2 hours, wash them with water, and then dry them in an oven to constant weight.

[0055] (2) Place the PC resin membrane in acetone liquid at 10wt%, and stir in a magnetic stirrer for 20-35h under sealed conditions at room temperature until the PC resin membrane is completely dissolved in the acetone reagent and no solid particles of resin membrane remain.

[0056] (3) The alkali-treated brown flakes with roughened surfaces are laid flat in an acetone / PC mixed solution and placed in a vacuum drying oven until the acetone is completely evaporated. The PC dissolved in the acetone combines with the brown flakes to prepare a composite material.

[0057] Test results: The composite material thickness is 1.4 mm, and the density is 1.32 g / cm³. 3 The transverse tensile strength is 35MPa, the flexural strength is 60MPa, and the quasi-static puncture strength is 180N.

[0058] Example 5:

[0059] (1) The surface density is 400 g / m 2 Carbon fiber plain weave fabric was cut to 15cm long x 6cm wide, laid flat, and placed in a mold. A thermoplastic resin PC film was then placed at the bottom of the mold, followed by the carbon fiber plain weave fabric. A hot press was then turned on, with the hot pressing temperature set to 200℃, the hot pressing pressure to 5MPa, and the hot pressing time to 0.5 hours. The pressurized cooling time was 2-5 hours. This process yielded two-layer and four-layer carbon fiber composite materials, with a carbon fiber mass fraction of 60%.

[0060] (2) The brown composite material prepared in Example 1 was used as the middle layer, and the two-layer and four-layer carbon fiber composite materials were used as the upper and lower layers, respectively. The composite material was cut into 4cm long × 4cm wide pieces and arranged in the mold according to the stacking order. PC film was laid between the composite material layers for bonding. The hot pressing temperature was 150℃ and the pressure was 1MPa to prepare the hybrid composite material. Quasi-static puncture test and dynamic puncture test were carried out.

[0061] Test results: The density of the laminated hybrid composite material is 1.12 g / cm³. 3 The thickness is 3.9-4.6 mm. When the sample thickness is 4.3 mm, the quasi-static puncture strength is 1308 N, the quasi-static initial modulus is 109.81 N / mm, and the work consumed per unit thickness is 0.41 J / mm.

[0062] Example 6:

[0063] (1) The composite material prepared in Example 2 was subjected to hot pressing recycling. The hot pressing process was as follows: hot pressing temperature 140℃, hot pressing pressure 25MPa, hot pressing time 1h, so that the thermoplastic resin was softened and impregnated with fibers again at high temperature. Then, it was cooled under pressure for 5-8h and tensile fracture test was performed.

[0064] Test results: The thickness of the palm fiber / polycarbonate composite material is 1.21 mm, and the density is 1.12 g / cm³. 3 The transverse tensile strength is 25 MPa, and the longitudinal tensile strength is 40 MPa.

[0065] Example 7:

[0066] (1) Prepare a solution of 1% sodium chlorite and 2% glacial acetic acid by mass, with a bath ratio of 1:40. Weigh 20g of the cut loofah sponge, wash it under running water to remove surface dust and impurities, air dry it naturally, and then place it in the mixed solution. Heat it in a water bath at 100℃ for 2 hours, repeat 3 times, and then dry it in an oven until constant weight.

[0067] (2) The lignin-free loofah fibers and thermoplastic resin film polycarbonate resin were used to prepare a composite material with a fiber mass fraction of 30%. The hot pressing process was as follows: hot pressing temperature 130℃, hot pressing pressure 25MPa, hot pressing time 1h, and pressurized cooling time 2-5h.

[0068] Test results: The density of the loofah sponge / polycarbonate composite material is 1.12 g / cm³. 3 The thickness is 1.0-1.2 mm. The transverse tensile strength is 35 MPa, and the longitudinal tensile strength is 45 MPa.

[0069] Example 8:

[0070] (1) Prepare a mixed solution of choline chloride and lactic acid with a weight ratio of 1:5. Stir continuously at 500 rpm for 2 hours at 60 degrees Celsius until a uniform and transparent liquid is formed to prepare a eutectic solvent system.

[0071] (2) Weigh 20g of cut flax fiber, wash it under running water to remove surface dust and impurities, air dry it naturally, then place it in a mixed solution at a solid-liquid ratio of 1:20, heat it in an oil bath at 120℃ for 2 hours, repeat 3 times, and dry it in an oven until constant weight.

[0072] (3) The linoleum fibers after lignin removal are combined with thermoplastic resin film polycarbonate resin to prepare a composite material with a fiber mass fraction of 30%. The hot pressing process is as follows: hot pressing temperature 130℃, hot pressing pressure 25MPa, hot pressing time 1h, and pressurized cooling time 2-5h.

[0073] Test results: The density of the flax / polycarbonate composite material is 1.18 g / cm³. 3 The thickness is 0.8-1.2 mm. The transverse tensile strength is 45 MPa, and the longitudinal tensile strength is 50 MPa.

[0074] Example 9:

[0075] (1) Prepare sodium hydroxide solutions of 2%, 6%, and 12% respectively, with a bath ratio of 1:20. Weigh 20g of the cut loofah sponge, wash it under running water to remove surface dust and impurities, air dry it naturally, and then place it in the mixed solution. Treat it at room temperature for 2 hours, wash it with water, and then dry it in an oven to constant weight.

[0076] (2) The lignin-removed loofah fibers were combined with thermoplastic resin film sarin resin to prepare a composite material with a fiber mass fraction of 30%. The hot pressing process was as follows: hot pressing temperature 100℃, hot pressing pressure 25MPa, hot pressing time 1h, and pressurized cooling time 2-5h.

[0077] Test results: The density of the flax / salin composite material is 1.12 g / cm³. 3 The transverse tensile strength is 25 MPa, and the longitudinal tensile strength is 30 MPa.

[0078] Example 10:

[0079] (1) Prepare potassium hydroxide solutions of 2%, 6%, and 12% respectively, with a bath ratio of 1:20. Weigh 20g of radish peel after cutting, wash it under running water to remove surface dust and impurities, air dry it naturally, and then place it in the mixed solution. Treat it at room temperature for 2 hours, wash it with water, and then dry it in an oven to constant weight.

[0080] (2) The radish peel after removing lignin was used to prepare a composite material with a fiber mass fraction of 30% by thermoplastic polycarbonate resin film. The hot pressing process was as follows: hot pressing temperature 140℃, hot pressing pressure 25MPa, hot pressing time 1h, and pressurized cooling time 2-5h.

[0081] Test results: The density of the radish peel / polycarbonate composite material is 1.21 g / cm³. 3 The transverse tensile strength is 35 MPa, and the longitudinal tensile strength is 45 MPa.

[0082] Comparative Example 1

[0083] Similar to Example 2, this comparative example uses natural fiber, loofah sponge, which has a natural mesh-like gap structure, as a reinforcing fiber to prepare composite materials, and conducts tensile fracture tests.

[0084] Test results: The composite material thickness is 1.12 mm, the transverse tensile strength is 15 MPa, and the longitudinal tensile strength is 20 MPa.

[0085] Comparative Example 2

[0086] Similar to Example 4, this comparative example uses carbon fiber plates instead of the intermediate three-dimensional fiber mesh reinforced thermoplastic composite material. The carbon fiber plates are made of three layers of carbon fiber plain weave fabric and polycarbonate, and the three layers of carbon fiber plates are bonded and pressed into a composite material.

[0087] Quasi-static puncture testing yielded the following results: thickness 4.1 mm, density 1.28 g / cm³. 3 The quasi-static puncture strength was 1166.39 N, the quasi-static initial modulus was 107.07 N / mm, and the work consumed per unit thickness was 0.36 J / mm, which was 12% lower than that of the example.

[0088] Comparative Example 3

[0089] Example 7 is basically the same, except that the material prepared in Example 7 is subjected to hot pressing recycling. The hot pressing process is as follows: hot pressing temperature 130°C, hot pressing pressure MPa, and hot pressing time 1h, so that the thermoplastic resin is softened and impregnated with fibers again at high temperature. After that, it is cooled under pressure for 5-8h and a tensile fracture test is performed.

[0090] Test results: The density of the composite material is 0.83 g / cm³. 3 The transverse tensile strength is 15 MPa and the longitudinal tensile strength is 25 MPa.

[0091] Comparative Example 4

[0092] Similar to Example 7, the material prepared in Example 7 was subjected to hot pressing for recycling. The hot pressing process was as follows: hot pressing temperature 130°C, hot pressing pressure 25MPa, and hot pressing time 1h, so that the thermoplastic resin would soften and be impregnated with fibers again at high temperature. After that, it was cooled under pressure for 5-8h and a tensile fracture test was performed.

[0093] Test results: The density of the composite material is 0.83 g / cm³. 3 The transverse tensile strength is 15 MPa and the longitudinal tensile strength is 25 MPa.

[0094] Comparative Example 5

[0095] Similar to Example 10, the material prepared in Example 10 was subjected to hot pressing for recycling. The hot pressing process was as follows: hot pressing temperature 130°C, hot pressing pressure 25MPa, and hot pressing time 1h, so that the thermoplastic resin could be softened and impregnated with fibers again at high temperature. After that, it was cooled under pressure for 5-8h and a tensile fracture test was performed.

[0096] Test results: The density of the composite material is 0.95 g / cm³. 3 The transverse tensile strength is 20 MPa and the longitudinal tensile strength is 25 MPa.

[0097] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for preparing a natural fiber web reinforced thermoplastic recyclable composite material, characterized in that... Includes the following steps: Step (1): Cut the three-dimensional natural fiber material into 6-10cm×6-10cm sizes and wash the surface ash and impurities in running water; after air drying, sew it to reinforce it; Step (2): Place the reinforced three-dimensional natural fiber material in a mixed solution at a bath ratio of 1:20-1:100 and heat it in a constant temperature water bath at 80-100℃ for 1.5-2 hours, repeating 1-3 times to remove impurities in the fiber. After the water bath, wash it with deionized water until neutral and dry it in an oven for 4-8 hours to obtain a cellulose fiber web; the mixed solution is a mixed solution of sodium hydroxide and hydrogen peroxide; Step (3): Place the cellulose fiber web in alkaline solutions of different concentrations to dissolve hemicellulose and pectin, forming a large number of protruding particles on the fiber surface to increase surface roughness; The alkaline solution is sodium hydroxide; Step (4): Place the thermoplastic resin film on the bottom layer of the mold, place the cellulose fiber web on the thermoplastic resin film, and then lay the cellulose fiber web and thermoplastic resin film in sequence. Place the thermoplastic resin film on the top layer. Then place the mold sheet on top of the laid material to control the thickness. Spray the mold release agent on the mold adjacent to the upper and lower surfaces of the material. Place it on a hot press and hot press it at a temperature of 90-150℃ and a pressure of 10-20MPa for 1-2 hours. After heating, close the mold and let it cool naturally under pressure for 6-12 hours. Then open the mold to obtain the cellulose fiber web reinforced thermoplastic composite material. Step (5): Laminate the high-performance fiber with the thermoplastic resin film to prepare the high-performance fiber reinforced composite material. Using high-performance fiber-reinforced composite materials as the upper and lower layers, and cellulose fiber mesh-reinforced thermoplastic composite materials as the middle layer, a tough hybrid thermoplastic composite material is obtained, which is a natural fiber mesh-reinforced thermoplastic recyclable composite material.

2. The method for preparing the natural fiber web reinforced thermoplastic recyclable composite material according to claim 1, characterized in that... The three-dimensional natural fiber material processed in step (1) is one or more of palm flakes, loofah sponge, or radish peel.

3. The method for preparing the natural fiber web reinforced thermoplastic recyclable composite material according to claim 1, characterized in that... The method of sewing reinforcement in step (1) is to use sewing thread or resin bonding.

4. The method for preparing the natural fiber web reinforced thermoplastic recyclable composite material according to claim 1, characterized in that... In step (2), the mass percentage of hydrogen peroxide is 2 wt.%-4 wt.%, and the mass percentage of sodium hydroxide is 4 wt.%-8 wt.%.

5. The method for preparing the natural fiber web reinforced thermoplastic recyclable composite material according to claim 1, characterized in that... In step (3), the concentration of sodium hydroxide is 2%, 4%, 6%, 8%, 10%, or 12%.

6. The method for preparing the natural fiber web reinforced thermoplastic recyclable composite material according to claim 1, characterized in that... The thermoplastic resin in step (4) is at least one or more of polycarbonate, saline resin, thermoplastic epoxy resin, and polyamide; the thermoplastic resin is in sheet, granular or liquid form; the hot pressing temperature is set above the softening point or melting point of the thermoplastic resin; the mass percentage of the cellulose fiber web to the thermoplastic resin is 20%-60%, the fiber content in the composite material is 20%-50%, the volume of the thermoplastic resin is 50%-80%, and the length of the natural fiber is 5-10 cm.

7. The method for preparing the natural fiber web reinforced thermoplastic recyclable composite material according to claim 1, characterized in that... In step (5), the high-performance fiber layers are arranged in a cross-layout pattern at 0°, ±45°, and 90°.

8. The method for preparing the natural fiber web reinforced thermoplastic recyclable composite material according to claim 1, characterized in that... The high-performance fiber in step (5) is at least one of carbon fiber, glass fiber, and basalt fiber.

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