Fibrilia polypropylene composite material

Abstract

The invention provides a fibrilia polypropylene composite material and a preparation method thereof. The composite material is formed by compounding the following components in percentage by weight: 30-50% of modified fibrilia, 30-50% of PP (polypropylene) fiber, 5-15% of PET (polyethylene terephthalate) fiber and 5-15% of GMT (glass mat reinforced plastics) board. The modified fibrilia is sprayed with a surface treatment solution containing a polycarboxylic derivative and metal ions, and a gel film is formed in a sodium alginate solution, so that the interfacial compatibility is improved. The PP fibers are subjected to surface grafting treatment so as to improve the binding force with other components. The GMT board is composed of polypropylene, glass fibers, an impregnating compound and a thermoelastomer, and the performance of the GMT board is optimized by adopting a specific preparation method. The preparation method of the composite material comprises the steps of opening, carding, needling, pressing and the like, and finally annealing treatment is carried out to improve the stability. The composite material has the advantages of light weight and excellent mechanical properties.

Description

Technical Field

[0001] The present invention belongs to the field of composite materials, and particularly relates to a hemp fiber polypropylene composite material. Background Art

[0002] Plant fiber composite materials not only have the advantages of wide sources, recyclability, degradability, and lighter weight, but also have relatively excellent mechanical, acoustic, and thermal and other physical properties. Plant hemp fibers have the characteristics of low cost, light weight, natural degradability, high specific strength, and high specific modulus, and are widely used in the preparation of fiber composite reinforcing materials. For example, in the automotive industry, hemp fiber composite boards have been developed to replace widely used synthetic reinforcing fiber boards such as glass fiber boards. For example, hemp fiber composite boards made of hemp fibers and polymer PP fibers have been well applied in automotive interior materials.

[0003] The invention patent application with the application publication number CN103131141A discloses a plant fiber particle-filled recycled polyester composite material and its preparation method. By chain-extending the polyester material and introducing plant fiber particles, the processing characteristics are improved, and while retaining the mechanical properties, the density of the composite material is reduced. However, relying on conventional compatibilizers to improve the bonding strength between components, there is still a large room for improvement in its mechanical properties.

[0004] The invention patent application with the application publication number CN104693606A discloses the application of a plant fiber-reinforced polypropylene composite material in the preparation of automotive parts. By introducing carboxylic acid groups on the surface of long plant fibers and generating fatty chains during polymer blending, the compatibility between plant fibers and polypropylene is improved. However, its pretreatment process requires solution soaking in a nitrogen atmosphere, which is difficult to promote.

[0005] Based on the above, it is necessary to develop a new hemp fiber polypropylene composite material to improve the compatibility and interaction force between plant fibers and polypropylene, so as to meet the lightweight requirements of the composite material without sacrificing its mechanical properties. Summary of the Invention

[0006] The main purpose of the present invention is to provide a hemp fiber polypropylene composite material, which is made lighter without reducing its mechanical properties. The secondary purpose is to improve the surface flatness of the hemp fiber composite material. The technical solution provided by the present invention is as follows: A ramie fiber polypropylene composite material, characterized in that: by weight percentage, it includes: 30-50% of modified ramie fibers, 30-50% of PP fibers, 5%-15% of PET fibers and is compounded with 5%-15% of GMT board as a whole; the preparation method of the modified ramie fibers includes: spraying a surface treatment solution on the surface of the ramie fibers, and after drying, placing the ramie fibers in a sodium alginate solution to form a gel film of the sodium alginate solution on the ramie fibers, and the surface treatment solution includes a polycarboxyl derivative and metal ions capable of cross-linking sodium alginate.

[0007] Preferably, the polycarboxyl derivative includes at least one of carboxymethyl chitosan, calcium disodium edetate, phthalic acid, and gambogic acid; preferably, the metal ions include at least one of calcium ions, copper ions, and zinc ions.

[0008] Furthermore, the surface treatment solution further includes: polyvinyl acetate glue, and the mass ratio of the polyvinyl acetate glue to the ramie fibers is 0.1-0.2:1.

[0009] Furthermore, the thickness of the gel film is 0.1-1 mm.

[0010] Furthermore, the surface of the PP fibers is grafted, and the preparation method includes: mixing the PP fibers with methylacrylic acid monomers in an aqueous suspension system, adding a strong oxidant to cause the methylacrylic acid monomers to undergo a grafting reaction with the surface of the PP fibers, with a grafting rate of more than 5%, and then washing the PP fibers with water and drying to a moisture content of 8-15%.

[0011] Furthermore, by weight percentage, the GMT board includes 75-85% of polypropylene, 5-10% of glass fiber, 5-10% of sizing agent, and 3-8% of thermoelastic body.

[0012] Furthermore, the preparation method of the GMT board includes applying a sizing agent on the surface of the glass fiber, and then placing the glass fiber, polypropylene, and thermoelastic body together in a heating device to heat up to melting, and then molding by pressing and cooling.

[0013] Furthermore, the sizing agent is an epoxy film-forming agent, and the thermoelastic body includes one of styrene-based, polyolefin-based, and polyurethane-based thermoelastic bodies.

[0014] The present invention also provides a preparation method of a ramie fiber polypropylene composite material, including the following steps: S01, by weight percentage, screen and accurately weigh 30-50% of ramie fibers, 30-50% of PP fibers, and 5%-15% of PET fibers and put them into a carding machine for carding treatment; S02, comb the carded fibers into a web with a density of 40-60 g / ㎡ using a carding machine; S03. Place the obtained net in a needling machine and needle it into a felt at a needle frequency of 400 - 800 Hz. S04. Place the obtained felt and GMT boards with a mass of 5% - 15% together in a board press, heat to 180 - 220 °C for 1 - 5 min, and press into a board under a pressure of 150 - 300 t.

[0015] Furthermore, anneal the board obtained by the above method to room temperature at 150 °C at a rate of 2 °C / min.

[0016] The advantages and beneficial effects of the present invention are as follows: 1. Spray a surface treatment solution containing polycarboxyl derivatives and metal ions on the surface of hemp fibers, and form a gel film in the sodium alginate solution to make the attachment of carboxyl groups more obvious, effectively improving the interfacial compatibility and interlayer bonding effect between hemp fibers, PP fibers, PET fibers and GMT boards, and adjusting the proportions of polypropylene, glass fiber, sizing agent and thermoelastic body in GMT boards to improve the overall performance of the composite material.

[0017] 2. Graft - treat the surface of PP fibers to make them undergo a graft reaction with methacrylic acid monomers, improving the bonding force between PP fibers, hemp fibers, PET fibers and GMT boards, and further enhancing the mechanical properties of the composite material. Brief Description of the Drawings

[0018] Figure 1 It is a schematic structural diagram of the product obtained by the present invention.

[0019] In the figure: 1 - composite felt, 2 - GMT board. Detailed Embodiments

[0020] The present invention provides a hemp fiber - polypropylene composite material, which is mainly composed of modified hemp fibers, PP (polypropylene) fibers and PET (ethylene terephthalate) fibers mixed in a certain proportion and compounded with GMT (glass fiber mat - reinforced thermoplastic resin) boards. Spray a surface treatment solution containing polycarboxyl derivatives and metal ions capable of cross - linking sodium alginate on the surface of hemp fibers. After drying, polycarboxyl derivatives and metal ions are evenly dispersed on the surface of hemp fibers. The polycarboxyl derivatives will undergo an esterification reaction with a large number of hydroxyl groups on the surface of hemp fibers to form aliphatic long chains. This chemical reaction can increase the active sites on the surface of hemp fibers and improve their compatibility with the resin matrix. The metal ions act as catalysts to accelerate the progress of the esterification reaction.

[0021] On the one hand, metal ions are used to catalyze the above esterification reaction, and on the other hand, they can serve as crosslinking agents for sodium alginate (SA). Sodium alginate is a natural polysaccharide macromolecule composed of multiple identical units connected by covalent bonds. It is easily soluble in water and can rapidly form a gel under mild conditions in the presence of cations such as calcium ions, and has good stability. After drying the above-mentioned hemp fibers, they are immersed in an aqueous solution of sodium alginate. In the gel film system, metal ions can also undergo an ion exchange reaction with sodium ions in sodium alginate, and at the same time promote the conversion of carboxyl groups on the sodium alginate molecular chain into active functional groups such as aldehyde groups or ketone groups. These active functional groups can further undergo a condensation reaction with hydroxyl groups on the surface of hemp fibers to form more stable chemical bonds. When the hemp fibers are placed in a sodium alginate solution, the polycarboxyl derivative also adjusts the pH to weakly acidic during this process. Under this condition, the carboxyl groups on the sodium alginate molecular chain are easily protonated and carry a positive charge, thereby increasing its affinity with the surface of hemp fibers. At this time, the temperature can be appropriately increased to enhance the movement and diffusion of the sodium alginate molecular chain, and promote its adsorption and crosslinking on the surface of hemp fibers. When a gel film is formed on the surface of hemp fibers from the sodium alginate solution, the polycarboxyl derivative therein will be enriched in the gel film. In this way, the polycarboxyl derivative can react with the hydroxyl groups on the surface of hemp fibers more quickly, further improving the interfacial bonding strength between the two.

[0022] As a preferred embodiment, a small amount of polyvinyl acetate glue (PVA) can also be added to the sodium alginate solution. PVA is a synthetic macromolecular material polymerized from vinyl acetate monomers and has good film-forming properties, adhesiveness, and stability. Similar to cellulose, PVA also has a large number of hydroxyl (-OH) groups, and these groups can form hydrogen bonds or chemical bonds (mainly referring to ester bonds) with polycarboxyl derivatives. The polycarboxyl derivative serves as a bridge to connect cellulose, sodium alginate, and PVA. Polyvinyl acetate glue and sodium alginate also form a complex through metal ions and carboxylic acid groups in sodium alginate, so that the polyvinyl acetate-sodium alginate-cellulose component forms an interpenetrating polymer network. In this network, sodium alginate and PVA molecules interpenetrate and entangle with each other, and are tightly connected through the crosslinking action of metal ions and the formation of intermolecular and intramolecular hydrogen bonds, thereby enhancing the interfacial bonding force of the material.

[0023] As a preferred embodiment, the thickness of the gel film is controlled between 0.1-1 mm. A thickness of 0.1-1 mm can ensure that the surface of the hemp fiber is fully covered by the sodium alginate solution, forming a uniform and continuous gel film. At the same time, it will not significantly increase the overall thickness of the hemp fiber, avoiding affecting the flexibility and strength of the fiber itself. It can be understood that an overly thin gel film has relatively weak effects in assisting the formation of an interpenetrating cross-linked network structure due to the limited amount of metal ions and polycarboxyl derivatives it can carry; while an overly thick gel film may lead to material defects such as cracks in the composite material during drying and subsequent hot pressing.

[0024] As a preferred embodiment, the PP fiber is grafted by adding a strong oxidant (such as potassium permanganate) to an aqueous suspension system and performing a free radical reaction with methyl methacrylate monomer. Optional auxiliary measures such as ultrasonic waves, mechanical stirring, plasma treatment, and radiation treatment can be used to improve and increase the active sites on the surface of the PP fiber, so that the grafting rate reaches more than 5%. Subsequently, the grafted PP fiber is washed with water to remove unreacted methyl methacrylate monomer and strong oxidant to prevent the strong oxidant from damaging the PP fiber. The grafted PP fiber is dried to a moisture content of 8-15% to maintain the performance and stability of the PP fiber.

[0025] In the hemp fiber polypropylene composite material, a small amount of polyethylene terephthalate (PET) is also added. The PET molecular structure contains polar groups, which can form strong interactions with the polycarboxyl derivatives and metal ions on the surface of the hemp fiber. PET can be used as a compatibilizer or plasticizer to improve the interfacial bonding force between PP and hemp fiber. Since PET itself has high strength and rigidity, it can also play a role as a skeleton in the composite material, supporting and dispersing stress, reducing the generation and propagation of cracks. PET has a high melting point and good thermal stability, and can maintain a stable form during the processing of the composite material. Its addition can improve the melt fluidity of the composite material, making the material easier to form during processing and reducing the generation of processing defects. In addition, the good interfacial bonding between PET and hemp fiber and PP matrix also helps the effective transfer of stress, further improving the mechanical properties of the material.

[0026] The ramie fiber polypropylene composite material is also thermally pressed and compounded with a certain mass of GMT sheet. The GMT sheet is a glass fiber reinforced thermoplastic composite material. The matrix material therein is PP, which provides basic strength and toughness; the reinforcing material is glass fiber (GF), which is used to improve the mechanical strength and stiffness of the sheet and improve the dimensional stability of the material. Its preparation method requires applying a sizing agent on the surface of GF. Here, an epoxy film-forming agent is used. The main function is to improve the interfacial bonding force between the glass fiber and the matrix material, promote the bonding between the PP resin and the glass fiber, and ensure the uniform distribution of GF in PP. A small amount of thermoelastic body is also added to the sheet. The main functions are: to improve the impact strength of the GMT sheet, reduce the breakage and crack generation of the material, and improve the toughness of the GMT sheet. The addition of the thermoelastic body makes the GMT sheet softer and easier to deform when subjected to external forces, thus avoiding brittle fracture. Adding these thermoelastic bodies to the GMT sheet can reduce the glass transition temperature of the material, reduce the viscosity and melting point of the GMT sheet in the molten state, making the material easier to process and form, so as to co-mold and extrude with the composite felt of PP / sodium alginate / cellulose.

[0027] The present invention also provides a preparation method of the ramie fiber polypropylene composite material. Accurately weigh ramie fiber, PP fiber and PET fiber and put them into a carding machine for carding. Mix the three fibers evenly and make the fibers loose. Then, through a combing machine, control its density to be a net-like structure of 40-60 g / ㎡. After transferring to a needling machine, needle it into a composite felt at a certain needle frequency. The fiber web is repeatedly punctured, and the frictional force between the fibers increases, thereby enhancing the bonding force between the fibers and forming a tightly structured felt-like material. Finally, place the composite felt and the GMT sheet together in a sheet press and make a composite sheet under high temperature and high pressure.

[0028] Optionally, the sheet obtained by the above method is also annealed at a certain temperature to eliminate the internal stress of the sheet and improve its dimensional stability.

[0029] The following combines examples to further describe the specific implementation manners of the present invention. The following examples are only used to more clearly illustrate the technical solutions of the present invention and cannot be used to limit the protection scope of the present invention.

[0030] Example 1: A ramie fiber polypropylene composite material, by weight percentage, its composition is: 32% modified ramie fiber, 48% PP fiber, 10% PET fiber and is compounded with 10% of GMT sheet as a whole.

[0031] The compounding method includes: carding ramie fiber, PP fiber and PET fiber into a net of 40 g / ㎡ after carding, needling it into a felt at 400 Hz, and then heating the composite felt and the GMT sheet together at 180 °C for 1 min and pressing it into a plate with a pressure of 150 t.

[0032] The preparation method of the modified hemp fiber includes spraying a surface treatment solution containing carboxymethyl chitosan (0.01 mol / L) and calcium ions (0.01 mol / L) on the surface of the hemp fiber. The mass ratio of the hemp fiber to the surface treatment solution is 1 / 1. After drying, the hemp fiber is placed in a sodium alginate solution, and the temperature is raised to 45 °C to form a gel film with a thickness of 0.1 mm on the hemp fiber.

[0033] Grafting is carried out on the surface of the PP fiber with a grafting rate of 5%. Then, the PP fiber is washed with water and dried to a moisture content of 8%.

[0034] The GMT sheet contains 82% polypropylene, 7% glass fiber, 6% sizing agent, and 5% styrene-based thermoelastic elastomer.

[0035] Example 2: A hemp fiber polypropylene composite material, by weight percentage, its composition is: 37% modified hemp fiber, 43% PP fiber, 15% PET fiber and is compounded with 5% GMT sheet into one body.

[0036] The composite method includes: loosening the hemp fiber, PP fiber and PET fiber and then carding them into a web of 50 g / ㎡, needling them into a felt at 600 Hz, and then heating the composite felt and the GMT sheet together at 200 °C for 3 min and pressing them into a board under a pressure of 200 t.

[0037] The preparation method of the modified hemp fiber includes spraying a surface treatment solution containing calcium disodium edetate (0.05 mol / L) and copper ions (0.05 mol / L) on the surface of the hemp fiber. The mass ratio of the hemp fiber to the surface treatment solution is 2 / 1. After drying, the hemp fiber is placed in a sodium alginate solution, and the temperature is raised to 50 °C to form a gel film with a thickness of 0.5 mm on the hemp fiber.

[0038] Grafting is carried out on the surface of the PP fiber with a grafting rate of 7%. Then, the PP fiber is washed with water and dried to a moisture content of 10%.

[0039] The GMT sheet contains 78% polypropylene, 9% glass fiber, 6% sizing agent, and 7% polyolefin-based thermoelastic elastomer.

[0040] Example 3: A hemp fiber polypropylene composite material, by weight percentage, its composition is: 48% modified hemp fiber, 32% PP fiber, 10% PET fiber and is compounded with 10% GMT sheet into one body.

[0041] The composite method includes: opening and carding ramie fibers, PP fibers and PET fibers into a web of 60 g / ㎡, needling it into a felt at 800 Hz, then heating the composite felt and GMT sheet together at 220 °C for 5 min, and pressing it into a board under a pressure of 300 t.

[0042] The preparation method of the modified ramie fibers includes spraying a surface treatment solution containing phthalic acid (0.10 mol / L) and zinc ions (0.10 mol / L) on the surface of the ramie fibers. The mass ratio of the ramie fibers to the surface treatment solution is 5 / 1. After drying, the ramie fibers are placed in a sodium alginate solution, and the temperature is raised to 55 °C to form a gel film with a thickness of 1 mm on the ramie fibers.

[0043] Grafting is carried out on the surface of the PP fibers with a grafting rate of 10%. Then the PP fibers are washed with water and dried to a moisture content of 15%.

[0044] The GMT sheet includes 85% polypropylene, 5% glass fiber, 6% sizing agent, and 4% styrene-based thermoelastic elastomer.

[0045] Example 4: A ramie fiber polypropylene composite material, by weight percentage, its composition is: 39% modified ramie fibers, 46% PP fibers, 5% PET fibers and is compounded with 10% GMT sheet into one body.

[0046] The composite method includes: opening and carding ramie fibers, PP fibers and PET fibers into a web of 45 g / ㎡, needling it into a felt at 500 Hz, then heating the composite felt and GMT sheet together at 190 °C for 2 min, and pressing it into a board under a pressure of 180 t.

[0047] The preparation method of the modified ramie fibers includes spraying a surface treatment solution containing gambogic acid (0.08 mol / L) and calcium ions (0.08 mol / L) on the surface of the ramie fibers. The mass ratio of the ramie fibers to the surface treatment solution is 3 / 1. After drying, the ramie fibers are placed in a sodium alginate solution, and the temperature is raised to 60 °C to form a gel film with a thickness of 0.8 mm on the ramie fibers.

[0048] Grafting is carried out on the surface of the PP fibers with a grafting rate of 6%. Then the PP fibers are washed with water and dried to a moisture content of 9%.

[0049] The GMT sheet includes 80% polypropylene, 8% glass fiber, 7% sizing agent, and 5% polyolefin-based thermoelastic elastomer.

[0050] Example 5: A ramie fiber polypropylene composite material, by weight percentage, its composition is: 41% modified ramie fibers, 39% PP fibers, 10% PET fibers and is compounded with 10% GMT sheet into one body.

[0051] The composite method includes: opening and carding ramie fibers, PP fibers, and PET fibers into a web of 55 g / ㎡, needling it into a felt at 700 Hz, then heating the composite felt and GMT board together at 210 °C for 4 min, and pressing it into a board under a pressure of 250 t.

[0052] The preparation method of the modified ramie fibers includes spraying a surface treatment solution containing carboxymethyl chitosan (0.04 mol / L) and copper ions (0.08 mol / L) on the surface of the ramie fibers. The mass ratio of the ramie fibers to the surface treatment solution is 4 / 1. After drying, the ramie fibers are placed in a sodium alginate solution, and the temperature is raised to 45 °C to form a gel film with a thickness of 0.6 mm on the ramie fibers.

[0053] Grafting is carried out on the surface of PP fibers with a grafting rate of 8%, and then the PP fibers are washed with water and dried to a moisture content of 11%.

[0054] The GMT board includes 76% polypropylene, 9% glass fiber, 8% sizing agent, and 7% polyurethane-based thermoelastic body.

[0055] Example 6: A ramie fiber polypropylene composite material, by weight percentage, its composition is: 44% modified ramie fibers, 35% PP fibers, 11% PET fibers, and is composite into one body with 10% GMT board.

[0056] The composite method includes: opening and carding ramie fibers, PP fibers, and PET fibers into a web of 40 g / ㎡, needling it into a felt at 400 Hz, then heating the composite felt and GMT board together at 180 °C for 1 min, and pressing it into a board under a pressure of 150 t.

[0057] The preparation method of the modified ramie fibers includes spraying a surface treatment solution containing calcium disodium edetate (0.02 mol / L) and zinc ions (0.10 mol / L) on the surface of the ramie fibers. The mass ratio of the ramie fibers to the surface treatment solution is 2 / 1. After drying, the ramie fibers are placed in a sodium alginate solution, and the temperature is raised to 50 °C to form a gel film with a thickness of 0.3 mm on the ramie fibers.

[0058] Grafting is carried out on the surface of PP fibers with a grafting rate of 6%, and then the PP fibers are washed with water and dried to a moisture content of 9%.

[0059] The GMT board includes 83% polypropylene, 6% glass fiber, 7% sizing agent, and 4% polyurethane-based thermoelastic body.

[0060] Example 7: A ramie fiber polypropylene composite material, by weight percentage, its composition is: 40% modified ramie fibers, 42% PP fibers, 8% PET fibers, and is composite into one body with 10% GMT board.

[0061] The composite method includes: opening and carding ramie fibers, PP fibers and PET fibers into a web of 60 g / m², needling into a felt at 800 Hz, then heating the composite felt and GMT sheet together at 220 °C for 5 min, pressing into a board under a pressure of 300 t, and annealing to room temperature at 150 °C at a rate of 2 °C / min.

[0062] The preparation method of the modified ramie fibers includes spraying a surface treatment solution containing phthalic acid (0.09 mol / L) and copper ions (0.09 mol / L) on the surface of the ramie fibers, with the mass ratio of ramie fibers to the surface treatment solution being 5 / 1. After drying, the ramie fibers are placed in a sodium alginate solution, and the temperature is raised to 50 °C to form a gel film with a thickness of 0.9 mm on the ramie fibers.

[0063] Grafting is carried out on the surface of PP fibers with a grafting rate of 9%, and then the PP fibers are washed with water and dried to a moisture content of 14%.

[0064] The GMT sheet includes 79% polypropylene, 8% glass fiber, 9% sizing agent, and 4% styrene-based thermoelastic elastomer.

[0065] Example 8: A ramie fiber polypropylene composite material, by weight percentage, its composition is: 36% modified ramie fibers, 44% PP fibers, 9% PET fibers and is compounded with 11% GMT sheet into one body.

[0066] The composite method includes: opening and carding ramie fibers, PP fibers and PET fibers into a web of 45 g / m², needling into a felt at 500 Hz, then heating the composite felt and GMT sheet together at 190 °C for 2 min, pressing into a board under a pressure of 180 t, and annealing to room temperature at 150 °C at a rate of 2 °C / min.

[0067] The preparation method of the modified ramie fibers includes spraying a surface treatment solution containing gambogic acid (0.07 mol / L) and calcium ions (0.10 mol / L) on the surface of the ramie fibers, with the mass ratio of ramie fibers to the surface treatment solution being 3 / 1. After drying, the ramie fibers are placed in a sodium alginate solution, and the temperature is raised to 55 °C to form a gel film with a thickness of 0.7 mm on the ramie fibers.

[0068] Grafting is carried out on the surface of PP fibers with a grafting rate of 7%, and then the PP fibers are washed with water and dried to a moisture content of 10%.

[0069] The GMT sheet includes 81% polypropylene, 10% glass fiber, 5% sizing agent, and 4% polyolefin-based thermoelastic elastomer.

[0070] Example 9: A ramie fiber polypropylene composite material, by weight percentage, its composition is: 47% modified ramie fiber, 33% PP fiber, 10% PET fiber and is compounded with 10% GMT sheet into one body.

[0071] The compounding method includes: opening and carding ramie fiber, PP fiber and PET fiber into a web of 55 g / ㎡, needling into felt at 700 Hz, then heating the compounded felt and GMT sheet together at 210 °C for 4 min, pressing into a plate at a pressure of 250 t, and annealing to room temperature at 150 °C at a rate of 2 °C / min.

[0072] The preparation method of the modified ramie fiber includes spraying a surface treatment solution containing carboxymethyl chitosan (0.03 mol / L) and copper ions (0.02 mol / L) on the surface of the ramie fiber, the mass ratio of the ramie fiber to the surface treatment solution is 4 / 1, after drying, putting the ramie fiber into sodium alginate solution, heating to 60 °C, and making the sodium alginate solution form a gel film with a thickness of 0.5 mm on the ramie fiber.

[0073] Grafting on the surface of PP fiber, the grafting rate is 8%, then washing the PP fiber with water and drying to a moisture content of 11%.

[0074] The GMT sheet includes 77% polypropylene, 9% glass fiber, 6% sizing agent, 8% polyurethane thermoelastic body.

[0075] Example 10: A ramie fiber polypropylene composite material, by weight percentage, its composition is: 35% modified ramie fiber, 45% PP fiber, 10% PET fiber and is compounded with 10% GMT sheet into one body.

[0076] The compounding method includes: opening and carding ramie fiber, PP fiber and PET fiber into a web of 40 g / ㎡, needling into felt at 400 Hz, then heating the compounded felt and GMT sheet together at 180 °C for 1 min, pressing into a plate at a pressure of 150 t, and annealing to room temperature at 150 °C at a rate of 2 °C / min.

[0077] The preparation method of the modified ramie fiber includes spraying a surface treatment solution containing calcium disodium ethylene diamine tetraacetate (0.02 mol / L) and zinc ions (0.01 mol / L) on the surface of the ramie fiber, the mass ratio of the ramie fiber to the surface treatment solution is 2 / 1, after drying, putting the ramie fiber into sodium alginate solution, heating to 60 °C, and making the sodium alginate solution form a gel film with a thickness of 0.2 mm on the ramie fiber.

[0078] Grafting on the surface of PP fiber, the grafting rate is 5%, then washing the PP fiber with water and drying to a moisture content of 8%.

[0079] The GMT sheet contains 84% polypropylene, 5% glass fiber, 8% sizing agent, and 3% polyolefin thermoelastic elastomer.

[0080] Performance analysis was conducted on the products obtained from the above examples and comparative examples, and the results are shown in the following table.

[0081] Among them: The test methods for flexural strength and flexural modulus are three-point bending tests, obtained according to the standard ASTM D790-17 "Standard Test Method for Flexural Properties of Reinforced and Non-Reinforced Plastics and Electrical Insulating Materials"; The test method for impact strength is GB / T1043.1:2008 "Plastics - Determination of Charpy impact properties - Part 1: Non-instrumented impact test"; The test method for surface flatness is ASTM D1604-63 "Method for Measuring Flatness of Plastic Sheets or Tubes". The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A ramie fiber polypropylene composite material, characterized in that: By weight percentage, it includes 30 - 50% of modified hemp fibers, 30 - 50% of PP fibers, 5% - 15% of PET fibers and is compounded with 5% - 15% of GMT board into one body; The preparation method of the modified hemp fibers includes: spraying a surface treatment solution on the surface of the hemp fibers, and after drying, placing the hemp fibers in a sodium alginate solution to form a gel film of the sodium alginate solution on the hemp fibers. The surface treatment solution includes polycarboxyl derivatives and metal ions capable of cross - linking sodium alginate.

2. The hemp fiber - polypropylene composite material according to claim 1, wherein: The polycarboxyl derivatives include at least one of carboxymethyl chitosan, calcium disodium ethylene diamine tetraacetate, phthalic acid, and gambogic acid; The metal ions include at least one of calcium ions, copper ions, and zinc ions.

3. The ramie fiber polypropylene composite material according to claim 1 or 2, characterized in that: The surface treatment solution further includes: polyvinyl acetate glue, and the mass ratio of the polyvinyl acetate glue to the hemp fibers is 0.1 - 0.2:

1.

4. The ramie fiber polypropylene composite material according to claim 3, wherein: The thickness of the gel film is 0.1 - 1 mm.

5. The ramie fiber polypropylene composite material according to claim 1, characterized in that: The surface of the PP fibers is grafted, and the preparation method includes: mixing the PP fibers with methacrylic acid monomers in an aqueous suspension system, adding a strong oxidant to cause a grafting reaction between the methacrylic acid monomers and the surface of the PP fibers, with a grafting rate of more than 5%, and then washing the PP fibers with water and drying to a moisture content of 8 - 15%.

6. The ramie fiber polypropylene composite material according to claim 1, characterized in that: By weight percentage, the GMT includes 75 - 85% of polypropylene, 5 - 10% of glass fiber, 5 - 10% of sizing agent, and 3 - 8% of thermo - elastomer.

7. The ramie fiber polypropylene composite material according to claim 6, characterized in that: The preparation method of the GMT board includes applying a sizing agent on the surface of the glass fiber, and then placing the glass fiber together with polypropylene and thermo - elastomer in a heating device to heat up to melting, and then molding by pressing and cooling.

8. The ramie fiber polypropylene composite material according to claim 7, wherein: The sizing agent is an epoxy film - forming agent, and the thermo - elastomer includes one of styrene - based, polyolefin - based, and polyurethane - based thermo - elastomers.

9. A method for preparing the ramie fiber polypropylene composite material according to claim 1, characterized in that, It includes the following steps: S01, by weight percentage, screen and accurately weigh 30 - 50% of hemp fibers, 30 - 50% of PP fibers, 5% - 15% of PET fibers and put them into a carding machine for carding treatment; S02, card the carded fibers with a carding machine into a web with a density of 40 - 60 g / ㎡; S03, place the obtained web in a needling machine and needle it into a felt at a needle frequency of 400 - 800 Hz; S04, place the obtained felt and GMT board with a mass of 5% - 15% together in a board press, heat to 180 - 220 °C for 1 - 5 min, and press into a board with a pressure of 150 - 300 t.

10. The preparation method of the ramie fiber polypropylene composite material according to claim 9, characterized in that: Anneal the obtained board at 150 °C at a rate of 2 °C / min to room temperature.

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