Nanofiber reinforced polyformaldehyde composite material and preparation method thereof

Abstract

The invention discloses a nanofiber reinforced polyformaldehyde composite material and a preparation method thereof. The nanofiber reinforced polyformaldehyde composite material comprises the following raw material components in percentage by mass: 55-74% of a polyformaldehyde matrix; 11%-19% of polyketone resin; 5%-10% of a sulfur-free vulcanized elastomer; 8%-15% of a modified compound; 1%-3% of a silver nanowire; the invention relates to the technical field of composite materials. According to the nanofiber reinforced polyformaldehyde composite material and the preparation method thereof, the compound fibers provide an adhesion carrier for the boron nitride nanosheets, the strength of the composite material is improved, a heat conduction network is formed, the composite material has good flame retardance and heat conductivity, the continuity of the heat conduction network is guaranteed in cooperation with the silver nanowires, and the heat dissipation capacity of the composite material is improved; by combining the sulfur-free vulcanized elastomer and the polyketone resin, the elasticity and toughness of the composite material are improved, the notch impact strength is improved, the nanofibers are oriented in an electric field orientation mode, and the tensile strength and bending strength of the composite material are further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, in particular to a nanofiber reinforced polyoxymethylene composite material and a preparation method thereof. Background Art

[0002] Polyoxymethylene, a high-density, highly crystalline linear polymer, is an engineering plastic. It boasts high strength and modulus, excellent resistance to wear, chemical attack, creep, fatigue, and dimensional stability. It is an ideal replacement for copper, zinc, aluminum, and their alloys, and is widely used in the automotive, electrical, electronics, machinery, and chemical industries. Polyoxymethylene exhibits high strength but poor toughness and is notch-sensitive, leading to a shift toward high-end modified polyoxymethylene, typically in the form of composite materials.

[0003] When it comes to nanofiber selection for nanofiber-reinforced polyoxymethylene composites, carbon nanofibers and nylon 6 nanofibers are the primary choices. Carbon nanofibers bond with polyoxymethylene through hydrogen bonding, increasing tensile strength and modulus, and improving crystallinity. Adding 0.5% carbon nanofibers increases tensile strength by 20.5%, storage modulus by 127%, and loss modulus by 58%. Nylon 6 nanofibers, produced by electrospinning, have amide groups that form hydrogen bonds with the ether bonds of polyoxymethylene, enhancing compatibility. The addition of nylon 6 not only improves impact and flexural strength but also promotes heterogeneous nucleation, lowering the melt blending temperature and preventing polyoxymethylene depolymerization. However, these two types of nanofiber-reinforced composites are reinforced using a single fiber, resulting in a single function and still failing to meet ideal tensile strength and toughness requirements.

[0004] In view of this, a nanofiber reinforced polyoxymethylene composite material and a preparation method thereof are proposed. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the present invention provides a nanofiber reinforced polyformaldehyde composite material and a preparation method thereof, which solves the problem that the existing nanofiber reinforced polyformaldehyde composite material has a single function and still cannot meet the ideal requirements in terms of tensile strength and toughness.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions: A nanofiber reinforced polyoxymethylene composite material, the raw material components of which include, by mass percentage: Polyoxymethylene matrix: 55% to 74%; Polyketone resin: 11% to 19%; Sulfur-free vulcanized elastomer: 5% to 10%; Modified complex: 8% to 15%; Silver nanowires: 1% to 3%.

[0007] The present invention is further configured as follows: the raw material components of the sulfur-free vulcanized elastomer include ethylene-methacrylate glycidyl copolymer, thermoplastic polyurethane, polylactic acid, hexamethylene diisocyanate, stannous octoate and antioxidant 1010, and the mass ratio of the ethylene-methacrylate glycidyl copolymer, thermoplastic polyurethane, polylactic acid, hexamethylene diisocyanate, stannous octoate and antioxidant 1010 is: 75-85:8-12:3-5:2-5:0.1-0.5:0.2-0.4.

[0008] The present invention is further configured as follows: the raw material components of the modified composite include composite fiber, boron nitride nanosheets, ammonium polyphosphate, phytic acid and KH-550 coupling agent, and the mass ratio of the composite fiber, boron nitride nanosheets, ammonium polyphosphate and phytic acid is: 75-92:1-3:5-8:2-5.

[0009] The present invention is further configured as follows: the particle size of the boron nitride nanosheets is 90-100 nm, and the purity is greater than 99%; The particle size of the ammonium polyphosphate is less than 5 μm; The purity of the phytic acid is greater than 98%.

[0010] The present invention is further configured as follows: the composite fiber includes nanocellulose and lignin nanofibers, and the mass ratio of the nanocellulose to the lignin nanofibers is 3-5:1-2.

[0011] The present invention is further configured as follows: the nanocellulose is wood pulp fiber; The lignin nanofiber is alkali lignin.

[0012] The present invention is further configured as follows: the diameter of the silver nanowires is 150-200 nm.

[0013] The present invention also discloses a nanofiber reinforced polyoxymethylene composite material, the preparation method of which specifically comprises the following steps: Step 1, fiber compounding and modification: Nanocellulose and lignin nanofibers are dispersed in deionized water, dispersed at 4000-5000 rpm for 10-12 minutes by a high-speed shearing machine, and then boron nitride nanosheets dispersed in ethanol are added. The mixture is treated in a high-voltage electrostatic field of 5-10 kV / mm for 15-30 minutes. Ammonium polyphosphate, phytic acid and KH-550 coupling agent are added, and the mixture is stirred and reacted at 80°C for 1-2 hours. After freeze-drying and hot pressing, a modified composite sheet is obtained, and the modified composite sheet is crushed into fragments with a particle size of less than 100 μm using a high-speed shearing machine as a modified composite. Step 2: Mixing and extruding: The polyoxymethylene matrix, polyketone resin, sulfur-free vulcanized elastomer, modified compound and silver nanowires are fed into a twin-screw extruder at a feeding zone of 170°C, a melting zone of 180°C, a mixing zone of 190°C, and an extrusion zone of 200°C, and extruded at a speed of 150-180 rpm. Step 3: Electric field orientation: A 5-8 kV / cm pulsed high voltage electric field with a frequency of 10-15 Hz is applied in the extrusion zone to orient the modified reset body along the shear stress direction; Step 4: Gradient cooling molding: The composite material in the extrusion zone is prepared into a composite product by injection molding or compression molding. After cooling to below the glass transition temperature at a rate of 80°C / min, the product is placed in an oven and annealed at 120°C for 1.5-2 hours to obtain a composite product.

[0014] The present invention provides a nanofiber-reinforced polyoxymethylene composite material and a preparation method thereof. It has the following beneficial effects: The present invention provides an attachment carrier for boron nitride nanosheets through compounding fibers, thereby improving the strength of the composite material while forming a thermal conductive network with good flame retardancy and thermal conductivity. Silver nanowires are used to ensure the continuity of the thermal conductive network and improve the heat dissipation capacity of the composite material. The combination of sulfur-free vulcanized elastomer and polyketone resin improves the elasticity and toughness of the composite material while achieving an improvement in notched impact strength. The nanofibers are then oriented through electric field orientation to further improve the tensile strength and flexural strength of the composite material, thereby achieving diversified functions and applicable scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The present invention provides a schematic diagram of the preparation process of the nanofiber reinforced polyoxymethylene composite material. DETAILED DESCRIPTION

[0016] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0017] See also Figure 1 , the embodiment of the present invention provides the following technical solutions: Example 1 A nanofiber reinforced polyoxymethylene composite material, the raw material components of which include, by mass percentage: Polyoxymethylene matrix: 55%; Polyketone resin: 19%; Sulfur-free vulcanized elastomer: 10%. The raw material components of the sulfur-free vulcanized elastomer include ethylene-glycidyl methacrylate copolymer, thermoplastic polyurethane, polylactic acid, hexamethylene diisocyanate, stannous octoate and antioxidant 1010. The mass ratio of ethylene-glycidyl methacrylate copolymer, thermoplastic polyurethane, polylactic acid, hexamethylene diisocyanate, stannous octoate and antioxidant 1010 is 75:12:3:2:0.1:0.2. Modified composite: 15%. The raw materials of the modified composite include composite fiber, boron nitride nanosheets, ammonium polyphosphate, phytic acid and KH-550 coupling agent. The particle size of the boron nitride nanosheets is 90 nm and the purity is greater than 99%. The particle size of the ammonium polyphosphate is less than 5 μm. The purity of the phytic acid is greater than 98%. The mass ratio of the composite fiber, boron nitride nanosheets, ammonium polyphosphate and phytic acid is 75:3:5:5. The composite fiber includes nanocellulose and lignin nanofibers. The nanocellulose is wood pulp fiber, and the lignin nanofiber is alkali lignin. The mass ratio of nanocellulose to lignin nanofiber is 3:2. Silver nanowires: 1%, the diameter of the silver nanowires is 150nm.

[0018] To further clarify, the processing methods for sulfur-free vulcanized elastomers include: At 45°C, ethylene-glycidyl methacrylate copolymer and thermoplastic polyurethane were mixed in a high-speed mixer at 1500 rpm for 25 minutes, and then polylactic acid was added and mixed for 8 minutes. Hexamethylene diisocyanate, stannous octoate and antioxidant 1010 were added and mixed for 10 minutes. The elastomer was then injection molded in a twin-screw extruder to obtain a sulfur-free vulcanized elastomer. The parameters of the twin-screw extruder were as follows: screw diameter 40 mm, aspect ratio 60:1, feeding zone 170°C, melting zone 180°C, mixing zone 190°C, and extrusion zone 200°C. The hexamethylene diisocyanate reacted with hydroxyl or amino groups in the thermoplastic polyurethane to form urethane cross-linked bonds.

[0019] The preparation method of the nanofiber reinforced polyoxymethylene composite material specifically comprises the following steps: Step 1, fiber compounding and modification: Nanocellulose and lignin nanofibers are dispersed in deionized water, dispersed at 4000 rpm for 12 minutes by a high-speed shearing machine, and then boron nitride nanosheets dispersed in ethanol are added. The mixture is treated in a high-voltage electrostatic field of 5 kV / mm for 30 minutes. Ammonium polyphosphate, phytic acid and KH-550 coupling agent are added, and the mixture is stirred and reacted at 80°C for 1 hour. The mixture is freeze-dried and hot-pressed at a temperature of 120°C and a pressure of 10 MPa to obtain a modified composite sheet. The modified composite sheet is crushed into fragments with a particle size of less than 100 μm using a high-speed shearing machine as a modified reset body; Step 2, mixing and extrusion: the polyoxymethylene matrix, polyketone resin, sulfur-free vulcanized elastomer, modified compound and silver nanowires were put into a twin-screw extruder with a screw diameter of 40 mm, an aspect ratio of 60:1, a feeding zone of 170°C, a melting zone of 180°C, a mixing zone of 190°C, and an extrusion zone of 200°C, and extruded at a speed of 150 rpm; Step 3: Electric field orientation: A 5kV / cm pulsed high voltage electric field with a frequency of 15Hz is applied in the extrusion area to orient the modified reset body along the shear stress direction; Step 4: Gradient cooling molding: The composite material in the extrusion zone is prepared by injection molding or compression molding to prepare a composite product. After cooling to below the glass transition temperature at a rate of 80°C / min, the product is placed in an oven and annealed at 120°C for 1.5 hours to obtain a composite product.

[0020] Example 2 The difference between this embodiment and the first embodiment is that the raw material components of the nanofiber-reinforced polyoxymethylene composite material include, by mass percentage, the following: Polyoxymethylene matrix: 62%; Polyketone resin: 15%; Sulfur-free vulcanized elastomer: 8%, its raw material components are ethylene-glycidyl methacrylate copolymer, thermoplastic polyurethane, polylactic acid, hexamethylene diisocyanate, stannous octoate and antioxidant 1010 in the mass ratio of 79:9:4:3:0.3:0.3; Modified composite: 12%, the particle size of its raw material component boron nitride nanosheets is 95nm, the mass ratio of composite fiber, boron nitride nanosheets, ammonium polyphosphate and phytic acid is: 83:2:7:3, and the mass ratio of nanocellulose and lignin nanofibers is: 4:1; Silver nanowires: 3%, the diameter of the silver nanowires is 180nm.

[0021] The preparation method of the nanofiber reinforced polyoxymethylene composite material specifically comprises the following steps: Step 1, fiber compounding and modification: Nanocellulose and lignin nanofibers are dispersed in deionized water, dispersed at 4500 rpm for 11 minutes by a high-speed shearing machine, and then boron nitride nanosheets dispersed in ethanol are added. The mixture is treated in a high-voltage electrostatic field of 8 kV / mm for 25 minutes. Ammonium polyphosphate, phytic acid and KH-550 coupling agent are added, and the mixture is stirred and reacted at 80°C for 1.5 hours. The mixture is freeze-dried and hot-pressed at a temperature of 120°C and a pressure of 10 MPa to obtain a modified composite sheet. The modified composite sheet is crushed into fragments with a particle size of less than 100 μm using a high-speed shearing machine as a modified reset body; Step 2: Mixing and extrusion: The polyoxymethylene matrix, polyketone resin, sulfur-free vulcanized elastomer, modified compound and silver nanowires were fed into a twin-screw extruder at a feeding zone of 170°C, a melting zone of 180°C, a mixing zone of 190°C, and an extrusion zone of 200°C, and extruded at a speed of 170 rpm. Step 3: Electric field orientation: A 7kV / cm pulsed high voltage electric field with a frequency of 14Hz is applied in the extrusion zone to orient the modified reset body along the shear stress direction; Step 4: Gradient cooling molding: The composite material in the extrusion zone is prepared by injection molding or compression molding to prepare a composite product. After cooling to below the glass transition temperature at a rate of 80°C / min, the product is placed in an oven and annealed at 120°C for 1.8 hours to obtain a composite product.

[0022] Example 3 The difference between this embodiment and the first embodiment is that the raw material components of the nanofiber-reinforced polyoxymethylene composite material include, by mass percentage, the following: Polyoxymethylene matrix: 74%; Polyketone resin: 11%; Sulfur-free vulcanized elastomer: 5%, its raw material components are ethylene-glycidyl methacrylate copolymer, thermoplastic polyurethane, polylactic acid, hexamethylene diisocyanate, stannous octoate and antioxidant 1010 in the mass ratio of 85:8:5:5:0.5:0.4; Modified composite: 8%, the particle size of its raw material component boron nitride nanosheets is 100nm, the mass ratio of composite fiber, boron nitride nanosheets, ammonium polyphosphate and phytic acid is: 92:1:8:2, and the mass ratio of nanocellulose and lignin nanofibers is: 5:1; Silver nanowires: 2%, the diameter of the silver nanowires is 200nm.

[0023] The preparation method of the nanofiber reinforced polyoxymethylene composite material specifically comprises the following steps: Step 1, fiber compounding and modification: Nanocellulose and lignin nanofibers are dispersed in deionized water, dispersed at 5000 rpm for 10 minutes by a high-speed shearing machine, and then boron nitride nanosheets dispersed in ethanol are added. The mixture is treated in a high-voltage electrostatic field of 10 kV / mm for 15 minutes. Ammonium polyphosphate, phytic acid and KH-550 coupling agent are added, and the mixture is stirred and reacted at 80°C for 2 hours. The mixture is freeze-dried and hot-pressed at a temperature of 120°C and a pressure of 10 MPa to obtain a modified composite sheet. The modified composite sheet is crushed into fragments with a particle size of less than 100 μm using a high-speed shearing machine as a modified reset body; Step 2: Mixing and extrusion: The polyoxymethylene matrix, polyketone resin, sulfur-free vulcanized elastomer, modified compound and silver nanowires were fed into a twin-screw extruder at a feeding zone of 170°C, a melting zone of 180°C, a mixing zone of 190°C, and an extrusion zone of 200°C, and extruded at a speed of 180 rpm. Step 3: Electric field orientation: Apply a pulsed high voltage electric field of 8 kV / cm at a frequency of 10 Hz in the extrusion zone to orient the modified reset body along the shear stress direction; Step 4: Gradient cooling molding: The composite material in the extrusion zone is prepared by injection molding or compression molding to prepare a composite product. After cooling to below the glass transition temperature at a rate of 80°C / min, the product is placed in an oven and annealed at 120°C for 2 hours to obtain a composite product.

[0024] The composite materials obtained in Examples 1, 2, and 3 were used as samples to test tensile strength, flexural modulus, impact strength, and flame retardancy. The tensile strength was tested at a tensile rate of 5 mm / min, the flexural modulus was tested by a three-point bending method, the notched impact strength was tested by an Izod impact test, and the flame retardancy was tested by a vertical burning method according to the UL94 standard. The test results are shown in Table 1. tensile strength flexural modulus Impact strength flame retardancy Example 1 189MPa 13499MPa 65J / m V-0 Example 2 198MPa 14586MPa 78J / m V-0 Example 3 157MPa 12125MPa 61J / m V-0 Table 1 As can be seen from Table 1, the composite materials obtained according to the methods provided in Examples 1, 2 and 3 have excellent tensile strength, flexural modulus and impact strength. It can be judged that the composite materials have the advantage of high toughness and excellent flame retardant effect.

[0025] As can be seen from Examples 1, 2, and 3, the present invention also introduces silver nanowires and boron nitride nanosheets, both of which have good thermal conductivity. Therefore, the thermal conductivity of the composite materials obtained in the above three examples was tested using a steady-state heat flow method. The test results are shown in Table 2: Thermal conductivity (W / m·K) Example 1 1.23 Example 2 1.51 Example 3 1.10 Table 2 As can be seen from Table 2, the composite material product obtained according to the method provided by the present invention has good thermal conductivity.

[0026] Simulation Experiment 1 The carbon fiber reinforced wear-resistant polyoxymethylene ZF137TQ produced by Yuyao Changshi and the carbon fiber reinforced polyoxymethylene CH-20 produced by Japan Polyplastics were used as comparative examples, and the tensile strength, flexural modulus, impact strength and flame retardancy tests were compared with the composite material prepared in Example 2 of the present invention. The comparison results are shown in Table 3: index Example 2 ZF137TQ CH-20 tensile strength 198MPa 116MPa 166MPa flexural modulus 14586MPa 8823MPa 12159MPa Impact strength 78J / m 55J / m 58J / m flame retardancy V-0 none none Table 3 As can be seen from Table 3, the composite material product obtained according to the method provided in Example 2 has flame retardancy, and its tensile strength and toughness-related indicators are greatly improved compared to conventional carbon fiber reinforced polyoxymethylene.

[0027] Simulation Experiment 2 The tensile strength, flexural modulus, impact strength and flame retardancy of the composite material prepared in Example 2 of the present invention were compared with the nylon 6 nanofiber reinforced polyoxymethylene material 6V0M produced by Domo, Germany, as a comparative example. The comparison results are shown in Table 4: index Example 2 6V0M tensile strength 198MPa 78MPa flexural modulus 14586MPa 3359MPa Impact strength 78J / m 29J / m flame retardancy V-0 none Table 4 As can be seen from Table 4, the composite material product obtained according to the method provided in Example 2 has flame retardancy, and its tensile strength and toughness-related indicators are greatly improved compared with conventional nylon 6 nanofiber reinforced polyoxymethylene.

[0028] In summary, it can be seen that the composite material provided by the present invention shows obvious advantages in notched impact strength and flexural modulus compared with traditional nano-reinforced polyoxymethylene materials, and has the functions of flame retardancy and thermal conductivity, which can meet the diverse application needs in more scenarios.

[0029] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A nanofiber reinforced polyoxymethylene composite material, characterized in that: The raw material components include by mass percentage: Polyoxymethylene matrix: 55% to 74%; Polyketone resin: 11% to 19%; Sulfur-free vulcanized elastomer: 5% to 10%; Modified complex: 8% to 15%; Silver nanowires: 1% to 3%.

2. The nanofiber reinforced polyoxymethylene composite material according to claim 1, characterized in that: The raw material components of the sulfur-free vulcanized elastomer include ethylene-methacrylate glycidyl copolymer, thermoplastic polyurethane, polylactic acid, hexamethylene diisocyanate, stannous octoate and antioxidant 1010, and the mass ratio of the ethylene-methacrylate glycidyl copolymer, thermoplastic polyurethane, polylactic acid, hexamethylene diisocyanate, stannous octoate and antioxidant 1010 is: 75-85:8-12:3-5:2-5:0.1-0.5:0.2-0.

4.

3. The nanofiber reinforced polyoxymethylene composite material according to claim 1, characterized in that: The raw material components of the modified composite include composite fiber, boron nitride nanosheets, ammonium polyphosphate, phytic acid and KH-550 coupling agent, and the mass ratio of the composite fiber, boron nitride nanosheets, ammonium polyphosphate and phytic acid is 75-92:1-3:5-8:2-5.

4. The nanofiber reinforced polyoxymethylene composite material according to claim 2, characterized in that: The particle size of the boron nitride nanosheets is 90-100 nm, and the purity is greater than 99%; The particle size of the ammonium polyphosphate is less than 5 μm; The purity of the phytic acid is greater than 98%.

5. The nanofiber reinforced polyoxymethylene composite material according to claim 3, characterized in that: The composite fiber comprises nanocellulose and lignin nanofibers, and the mass ratio of the nanocellulose to the lignin nanofibers is 3-5:1-2.

6. The nanofiber reinforced polyoxymethylene composite material according to claim 5, characterized in that: The nanocellulose is wood pulp fiber; The lignin nanofiber is alkali lignin.

7. The nanofiber reinforced polyoxymethylene composite material according to claim 1, characterized in that: The diameter of the silver nanowire is 150-200 nm.

8. A nanofiber reinforced polyoxymethylene composite material according to any one of claims 1 to 7, characterized in that: The preparation method specifically comprises the following steps: Step 1, fiber compounding and modification: Nanocellulose and lignin nanofibers are dispersed in deionized water, dispersed at 4000-5000 rpm for 10-12 minutes by a high-speed shearing machine, and then boron nitride nanosheets dispersed in ethanol are added. The mixture is treated in a high-voltage electrostatic field of 5-10 kV / mm for 15-30 minutes. Ammonium polyphosphate, phytic acid and KH-550 coupling agent are added, and the mixture is stirred and reacted at 80°C for 1-2 hours. After freeze-drying and hot pressing, a modified composite sheet is obtained, and the modified composite sheet is crushed into fragments with a particle size of less than 100 μm using a high-speed shearing machine as a modified composite. Step 2: Mixing and extrusion: put the polyoxymethylene matrix, polyketone resin, sulfur-free vulcanized elastomer, modified compound and silver nanowires into a twin-screw extruder with a feeding zone of 170°C, a melting zone of 180°C, a mixing zone of 190°C, and an extrusion zone of 200°C, and extrude at a speed of 150-180 rpm; Step 3: Electric field orientation: A 5-8 kV / cm pulsed high voltage electric field with a frequency of 10-15 Hz is applied in the extrusion zone to orient the modified reset body along the shear stress direction; Step 4: Gradient cooling molding: The composite material in the extrusion zone is prepared into a composite product by injection molding or compression molding. After cooling to below the glass transition temperature at a rate of 80°C / min, the product is placed in an oven and annealed at 120°C for 1.5-2 hours to obtain a composite product.

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