Nanomodified polyoxymethylene plastic particles

Abstract

The application discloses a kind of nano-modified polyformaldehyde plastic particles, contain 60-80% polyformaldehyde resin, 5-15% by boron nitride nanosheet, metal organic framework, nanocellulose Composition of nano composite filler, and environmental protection auxiliary agent and 0.5-2% MXene two-dimensional nanometer material by weight percentage.The present application is to provide a kind of nano-modified polyformaldehyde plastic particles, by the compounding of nanometer material and special preparation process, solve the single performance of traditional polyformaldehyde material, environmental unfriendliness is poor and the problems such as difficult dispersion of nano filler, realize the improvement of polyformaldehyde material in heat conduction, flame retardant, antistatic, adsorption and so on Many aspects of performance, while meeting environmental regulations requirements.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer material modification, and particularly relates to a nano-modified polyoxymethylene plastic particle. BACKGROUND

[0002] With the rapid development of society and the increasing emphasis on environmental protection, there is a growing demand for high-performance and environmentally friendly plastic materials. Polyoxymethylene (POM) as a kind of thermoplastic engineering plastic, because of its excellent mechanical properties in a wide temperature range, such as high elastic modulus, hardness and rigidity, has been widely used in the fields of automobile, electronic and electrical appliances, machinery and so on. However, the traditional polyoxymethylene material also has some shortcomings, such as low impact strength, high sensitivity to notch, and needs to be further improved in terms of flame retardance and ultraviolet resistance. In addition, in order to meet the environmental protection requirements, it is urgent to develop halogen-free flame-retardant and biodegradable additives and fillers.

[0003] In the prior art, the publication number CN113429736B discloses a modified polyoxymethylene engineering plastic and a preparation method thereof, which mainly comprises polyoxymethylene, glass fiber, phosphorus-containing monomer modified titanium dioxide, silane coupling agent, copolyamide and diphenylmethane diisocyanate, etc. Although this scheme improves the ultraviolet resistance and flame retardance of polyoxymethylene material to a certain extent by introducing phosphorus-containing monomer and lignin-modified titanium dioxide particles, it still has the following main defects:

[0004] Limited improvement of material performance: mainly relying on glass fiber and phosphorus-containing monomer modified titanium dioxide to enhance the performance of polyoxymethylene, but these fillers have limited effect on improving the comprehensive performance of the material, especially in terms of mechanical properties, thermal stability and wear resistance, which are difficult to meet higher requirements.

[0005] Filler selection and dispersion problems: the fillers used such as glass fiber and phosphorus-containing monomer modified titanium dioxide may have poor dispersion, which affects the uniformity and consistency of the overall performance of the material. In addition, its preparation process is complex, involving multiple chemical reactions, which is not conducive to large-scale production and cost control.

[0006] The environmental performance needs to be improved: although phosphorus-containing flame retardants are used, the environmental performance is still limited and cannot fully meet the current strict requirements for halogen-free and bio-based flame retardants. The technical solution aims at the above-mentioned shortcomings in the prior art and proposes a kind of nano-modified polyformaldehyde plastic particles and a preparation method thereof. Through innovative nano-composite filler design, optimization of environmental protection auxiliaries and unique preparation process, the mechanical properties, thermal stability and flame retardant properties of the polyformaldehyde plastic particles are significantly improved, while meeting the environmental protection requirements. Specifically, the nano-composite filler composed of boron nitride nanosheets, metal organic frameworks (MOFs), nanocellulose and MXene two-dimensional nanomaterials, and environmental protection auxiliaries such as bio-based plasticizer and halogen-free flame retardant are used to realize the synergistic improvement of multiple properties. Combined with supercritical CO2 fluid treatment and twin-screw extruder melt blending process, the excellent dispersibility of nano-filler and the compatibility with the matrix are ensured, so as to prepare polyformaldehyde plastic particles with high performance and environmental protection characteristics. SUMMARY

[0007] The present application aims to provide a kind of nano-modified polyformaldehyde plastic particles, by the compounding of nanomaterial and special preparation process, solve the problems such as single performance of traditional polyformaldehyde material, poor environmental protection and difficult dispersion of nano-filler, realize the improvement of polyformaldehyde material in heat conduction, flame retardant, antistatic, adsorption and other aspects, while meeting the requirements of environmental protection regulations.

[0008] In order to achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0009] The technical scheme provided by the present application is: a kind of nano-modified polyformaldehyde plastic particles, by weight percentage, including the following components:

[0010] Polyformaldehyde resin: 60-80%;

[0011] Nano-composite filler: 5-15%;

[0012] Environmental protection auxiliary agent: 13-23%;

[0013] MXene two-dimensional nanomaterial: 0.5-2%, selected from Ti3C2T x Or Mo2CT x , surface hydroxyl treatment;

[0014] Environmental protection auxiliary agent includes bio-based plasticizer 5-10%, halogen-free flame retardant 5-10%, antioxidant 3-5% and silane coupling agent 2-5%;

[0015] Bio-based plasticizer is selected from tributyl citrate;

[0016] Nano-composite filler is composed of the following components:

[0017] boron nitride nanosheet (h-BN): 30-60%, particle size 50-200 nm, interlayer spacing 0.33-0.35 nm;

[0018] metal organic framework (MOFs): 20-40%, selected from UiO-66-NH2 or ZIF-8, specific surface area > 1500 m² / g;

[0019] nanocellulose (CNC): 10-30%, aspect ratio 10-50, surface carboxylated modification.

[0020] Further, the weight ratio of boron nitride nanosheet to MOFs in the nanocomposite filler is (30-60%):(20-40%), and the degree of surface carboxylated modification of nanocellulose is 0.1-0.5 mmol of carboxyl groups per gram of nanocellulose.

[0021] Further, the halogen-free flame retardant is a compounded system of melamine cyanurate (MCA) and aluminum hypophosphite (AHP), and the weight ratio of the two is 1:1-2:1.

[0022] Further, the amount of silane coupling agent is 1-3% of the total weight of nanocomposite filler and MXene, and the silane coupling agent is γ-aminopropyl triethoxysilane or γ-methacryloyloxypropyl trimethoxysilane.

[0023] Further, the following steps are included:

[0024] S1: boron nitride nanosheet, MOFs, nanocellulose and MXene are added to supercritical CO2 fluid containing 0.1-0.5% sodium dodecyl sulfate (SDS), mixed by stirring at a temperature of 40-60℃ and a pressure of 10-15 MPa, and surface modification treatment is carried out for 1-2 hours to obtain a pretreated nanocomposite filler;

[0025] S2: polyformaldehyde resin, pretreated nanocomposite filler in S1 and environmental protection auxiliary agent are added to a twin-screw extruder, melt blended at 180-220℃, screw rotation speed 300-400 rpm, vacuum exhaust (vacuum degree -0.09 to -0.07 MPa), water cooling, and pelletizing to obtain plastic particles.

[0026] Further, the stirring speed during supercritical CO2 fluid treatment in S1 is 200-500 rpm, and the constant flow rate of CO2 fluid during the treatment process is maintained at 5-10 L / h.

[0027] Further, the length-diameter ratio of the twin-screw extruder in S2 is 40-50:1, and an ultrasonic vibration device is arranged in the melt blending section to apply ultrasonic energy of 20-40 kHz, acoustic intensity 10-20 W / cm 2 .

[0028] The beneficial effects of the technical solution are:

[0029] (1) Through the synergistic effect of boron nitride nanosheets, MOFs, nanocellulose and MXene, the simultaneous improvement of the material's heat conduction, flame retardation, adsorption and antistatic performance is realized. Boron nitride nanosheets have excellent heat conduction performance and can build a heat conduction network in the polyformaldehyde matrix, making the thermal conductivity of the material increase to 1.0-1.2 W / (m·K); MOFs have high specific surface area and rich pore structure, which can effectively adsorb the formaldehyde released by polyformaldehyde materials, making the formaldehyde release amount reduce to 0.01 mg / m 3 Below; nanocellulose can enhance the mechanical properties of the material, and at the same time, it can improve the processing performance of the material in cooperation with other nanomaterials; MXene gives the material antistatic performance, making the surface resistance reduce to 10 8 -10 9 Ω.

[0030] (2) The use of bio-based plasticizer instead of traditional phthalate plasticizer and halogen-free flame retardant instead of halogen-containing flame retardant eliminates the use of toxic and harmful substances from the source, and at the same time, the formaldehyde release amount of the material is low, which can be applied in the field with high requirements for air quality.

[0031] (3) Through supercritical CO2 fluid treatment and ultrasonic assisted blending process, the agglomeration problem of nanofiller in polyformaldehyde matrix is effectively solved, the dispersion degree of nanofiller reaches more than 95%, and the uniformity and stability of material performance are improved.

[0032] (4) The special preparation process and the addition of environmentally friendly additives widen the processing temperature range of the material, reduce the melt viscosity, improve the flowability of the material, make the material easier to process and form, shorten the forming cycle by 10-15%, and at the same time, improve the surface quality of the product, the surface roughness Ra reduces to 0.8-1.0 μm. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The component data table of Example 1 of the nanomodified polyformaldehyde plastic particle proposed by the present application is provided;

[0034] Figure 2 The component data table of Example 2 of the nanomodified polyformaldehyde plastic particle proposed by the present application is provided;

[0035] Figure 3 The component data table of Example 3 of the nanomodified polyformaldehyde plastic particle proposed by the present application is provided;

[0036] Figure 4 The component data table of Example 4 of the nanomodified polyformaldehyde plastic particle proposed by the present application is provided;

[0037] Figure 5 A component data table of Example 5 of a nano-modified polyformaldehyde plastic particle proposed for the present application;

[0038] Figure 6 A component data table of Example 6 of a nano-modified polyformaldehyde plastic particle proposed for the present application; Figure 7 A data comparison table of Examples 1-6 of a nano-modified polyformaldehyde plastic particle proposed for the present application. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0040] The specific implementation process is as follows:

[0041] Example 1:

[0042] Please refer to Figure 1 and Figure 7 The present application provides a technical solution: a preparation method of a nano-modified polyformaldehyde plastic particle, which includes, by weight percentage:

[0043] Polyformaldehyde resin: 70%;

[0044] Nano-composite filler: 12%;

[0045] The nano-composite filler includes: 50% (particle size 100 nm) boron nitride nanosheet (h-BN), 30% (UiO-66-NH2, specific surface area 1800 m 2 / g) metal organic framework (MOFs), and 20% (aspect ratio 30, surface carboxyl modification degree 0.3 mmol carboxyl group per gram of nanocellulose) nanocellulose (CNC);

[0046] Environment-friendly auxiliary agent: 17.5%;

[0047] The environment-friendly auxiliary agent includes: 7% (tributyl citrate) biobased plasticizer, 6% (weight ratio of melamine cyanurate (MCA) to aluminum hypophosphite (AHP) 1:1) halogen-free flame retardant, 3% (vitamin E derivative) antioxidant, and 1.5% (γ-aminopropyl triethoxysilane);

[0048] MXene two-dimensional nanomaterial: 0.5% (Ti3C2T x, surface hydroxyl treatment), the surface hydroxyl treatment process is: dispersing MXene in deionized water, adding sodium hydroxide solution to adjust pH to 10-12, stirring at 50-60°C for 2-3 hours, washing with deionized water to neutral after filtration, drying to obtain surface hydroxyl MXene;

[0049] Preparation step

[0050] S1: 6g of boron nitride nanosheet, 3.6g of UiO-66-NH2, 2.4g of nanocellulose and 0.5g of Ti3C2T x The supercritical CO2 fluid reactor containing 0.3% sodium dodecyl sulfate (SDS) was added, and the reactor volume was 500mL. The temperature was set to 50°C, the pressure was 12MPa, and the stirring speed was 300rpm. The constant flow rate of CO2 fluid was maintained at 8L / h during the treatment process, and the pretreated nanocomposite filler was obtained after 1.5 hours of treatment;

[0051] S2: 70g of polyformaldehyde resin, the above pretreated nanocomposite filler and environmental protection auxiliary agent were added into a twin-screw extruder (length-diameter ratio of 45:1). The temperature of each section of the twin-screw extruder was set as follows: zone 1 185°C, zone 2 205°C, zone 3 215°C, and the screw rotation speed was 350rpm. An ultrasonic vibration device was set in the melt blending section, and an ultrasonic energy of 30kHz and acoustic intensity of 15W / cm 2 was applied. Plastic particles were obtained after vacuum exhaust (vacuum degree of-0.08MPa), water cooling and granulation.

[0052] Performance test

[0053] Thermal conductivity: tested by laser flash method (ASTM D5470), the thermal conductivity was 1.15W / (m·K);

[0054] Formaldehyde emission: tested according to EN717-1 climate chamber method at 40°C and 50%RH, the formaldehyde emission was 0.008mg / m 3 ;

[0055] Tensile strength: prepared dumbbell-shaped samples according to GB / T1040.2 standard for testing, the tensile strength was 82MPa;

[0056] Surface resistance: tested according to ASTM D257 standard by three-electrode method, the surface resistance was 8.5×10 8 Ω;

[0057] Flame retardant grade: tested according to UL94 standard, the sample with a thickness of 1.6mm reached V-0 level without dripping ignition phenomenon;

[0058] The dispersion degree of the nanocomposite filler reaches 95% through transmission electron microscopy (TEM) observation.

[0059] Example two:

[0060] Please refer to Figure 2 and Figure 7 The present application provides a technical solution: a nanomodified polyformaldehyde plastic particle, which comprises, by weight percentage:

[0061] Polyformaldehyde resin: 60%;

[0062] Nanocomposite filler: 15%;

[0063] The nanocomposite filler includes: 60% (particle size 50 nm) boron nitride nanosheet (h-BN), 25% (ZIF-8, specific surface area 1600 m 2 / g) metal organic framework (MOFs), and 15% (aspect ratio 50, surface carboxyl modification degree is 0.5 mmol carboxyl group per gram of nanocellulose) nanocellulose (CNC);

[0064] Environment-friendly auxiliary agent: 23%;

[0065] The environment-friendly auxiliary agent includes: 10% (tributyl citrate) biobased plasticizer, 8% (weight ratio of melamine cyanurate (MCA) to aluminum hypophosphite (AHP) is 2:1) halogen-free flame retardant, 3% (vitamin E derivative) antioxidant, and 2% (γ-aminopropyl triethoxysilane);

[0066] MXene two-dimensional nanomaterial: 2% (Mo2CT x , surface hydroxylated treatment), the surface hydroxylated treatment process is: dispersing MXene in deionized water, adding sodium hydroxide solution to adjust pH to 10-12, stirring at 50-60℃ for 2-3 hours, washing with deionized water to neutral after filtration, drying to obtain surface hydroxylated MXene;

[0067] Preparation steps

[0068] S1: adding 9g boron nitride nanosheet, 3.75g ZIF-8, 2.25g nanocellulose and 2g surface hydroxylated Mo2CT x to a supercritical CO2 fluid reactor containing 0.5% sodium dodecyl sulfate (SDS), the reactor volume is 500mL. Set the temperature to 60℃, the pressure to 15MPa, and the stirring speed to 500rpm for 2 hours, keep the constant flow rate of CO2 fluid to 10L / h during the treatment process, obtain the pretreated nanocomposite filler;

[0069] S2: 60 g of polyformaldehyde resin, the above-pretreated nano-composite filler and environmental protection auxiliary agent are added into a double screw extruder (length-diameter ratio is 40:1). The temperature of each section of the double screw extruder is set as follows: 180℃ for the first section, 200℃ for the second section and 220℃ for the third section, the screw rotation speed is 400 rpm, an ultrasonic vibration device is arranged in the melt blending section, 40 kHz and 20 W / cm of ultrasonic energy are applied, plastic particles are prepared after vacuum exhaust (vacuum degree is-0.09 MPa), water cooling and granulation. 2

[0070] Performance test

[0071] Thermal conductivity: the laser flash method (ASTM D5470) is used for testing, and the thermal conductivity is 1.22 W / (m·K);

[0072] Formaldehyde emission: according to the EN717-1 climate chamber method, the formaldehyde emission is 0.007 mg / m 3

[0073] Tensile strength: according to the GB / T1040.2 standard, dumbbell-shaped samples are prepared for testing, and the tensile strength is 85 MPa;

[0074] Surface resistance: according to the ASTM D257 standard, the three-electrode method is used for testing, and the surface resistance is 7.2×10 8 Ω;

[0075] Flame retardant grade: according to the UL94 standard, the sample with a thickness of 1.6 mm reaches V-0 level, and there is no dripping ignition phenomenon;

[0076] Nano-composite filler dispersity: through transmission electron microscopy (TEM) observation, the nano-composite filler dispersity reaches 94%.

[0077] Example three:

[0078] Please refer to Figure 3 and Figure 7 , the present application provides a technical solution: a kind of nano modified polyformaldehyde plastic particles, including by weight percentage:

[0079] Polyformaldehyde resin: 75%;

[0080] Nano-composite filler: 10%;

[0081] The nano-composite filler includes: 40% (particle size 200 nm) boron nitride nanosheet (h-BN), 40% (UiO-66-NH2, specific surface area 1500 m 2 ​​Metal-organic frameworks (MOFs) with 20% (aspect ratio 10, surface carboxylated modification degree of 0.1 mmol carboxyl groups per gram nanocellulose) of nanocellulose (CNC) with 5% (tris- butyl citrate) of bio-based plasticizer, 5% (melamine cyanurate (MCA) and aluminum hypophosphite (AHP) in a weight ratio of 1:1) of halogen-free flame retardant, 3% (vitamin E derivative) of antioxidant, and 1.5% (γ-aminopropyl triethoxysilane) of environmental assistant;

[0082] Environmental assistant: 14.5%;

[0083] Environmental assistant includes: 5% (tris-butyl citrate) of bio-based plasticizer, 5% (melamine cyanurate (MCA) and aluminum hypophosphite (AHP) in a weight ratio of 1:1) of halogen-free flame retardant, 3% (vitamin E derivative) of antioxidant, and 1.5% (γ-aminopropyl triethoxysilane) of environmental assistant;

[0084] MXene two-dimensional nanomaterial: 0.5% (Ti3C2T x x surface hydroxylated treatment), surface hydroxylated treatment process: MXene is dispersed in deionized water, sodium hydroxide solution is added to adjust pH to 10-12, stirring reaction at 50-60℃ for 2-3 hours, after filtration, washed with deionized water until neutral, dried to obtain surface hydroxylated MXene;

[0085] Preparation steps

[0086] S1: 4g of boron nitride nanosheet, 4g of UiO-66-NH2, 2g of nanocellulose, and 0.5g of surface hydroxylated Ti3C2T x x are added into a supercritical CO2 fluid reactor kettle containing 0.1% sodium dodecyl sulfate (SDS), the volume of the reactor kettle is 500mL. The temperature is set to 40℃, the pressure is 10MPa, and the stirring speed is 200rpm for 1 hour, and the constant flow rate of CO2 fluid is maintained at 5L / h during the treatment process to obtain the pretreated nanocomposite filler;

[0087] S2: 75g of polyformaldehyde resin, the above pretreated nanocomposite filler, and environmental assistant are added into a twin-screw extruder (aspect ratio 50:1). The temperature of each section of the twin-screw extruder is set as follows: zone 1 190℃, zone 2 210℃, zone 3 220℃, the screw rotation speed is 300rpm, and an ultrasonic vibration device is arranged in the melt blending section to apply ultrasonic energy of 20kHz and acoustic intensity of 10W / cm 2 After vacuum exhaust (vacuum degree-0.07MPa), water cooling, and pelletizing, plastic particles are obtained.

[0088] Performance test

[0089] Thermal conductivity: tested by laser flash method (ASTM D5470), the thermal conductivity is 1.10W / (m·K);

[0090] Formaldehyde emission: According to EN717-1 climate chamber method, the formaldehyde emission is 0.009 mg / m 3 ;

[0091] Tensile strength: According to GB / T1040.2 standard, dumbbell-shaped samples are prepared for testing, and the tensile strength is 79 MPa;

[0092] Surface resistance: According to ASTM D257 standard, three-electrode method is used for testing, and the surface resistance is 9.0 x 10 8 Ω;

[0093] Flame retardant grade: According to UL94 standard test, the sample with a thickness of 1.6 mm reaches V-0 level, and there is no dripping ignition phenomenon;

[0094] Nanocomposite filler dispersity: Through transmission electron microscopy (TEM) observation, the nanocomposite filler dispersity reaches 93%.

[0095] Example Four:

[0096] Please refer to Figure 4 and Figure 7 , the present application provides a technical solution: a preparation method of nanomodified polyformaldehyde plastic particles, which comprises, by weight percentage:

[0097] Polyformaldehyde resin: 70%;

[0098] Nanocomposite filler: 12%;

[0099] The nanocomposite filler includes: 50% (particle size 100 nm) boron nitride nanosheet (h-BN), 30% (ZIF-8, specific surface area 1600 m 2 / g) metal organic framework (MOFs), and 20% (aspect ratio 30, surface carboxyl modification degree is 0.1 mmol carboxyl group per gram of nanocellulose) nanocellulose (CNC);

[0100] Environment-friendly auxiliary agent: 17.5%;

[0101] The environment-friendly auxiliary agent includes: 7% (tributyl citrate) biobased plasticizer, 6% (weight ratio of melamine cyanurate (MCA) to aluminum hypophosphite (AHP) is 1:1) halogen-free flame retardant, 3% (vitamin E derivative) antioxidant, and 1.5% (γ-aminopropyl triethoxysilane) silane coupling agent;

[0102] MXene two-dimensional nanomaterial: 0.5% (Ti3C2T x, surface hydroxyl treatment), the surface hydroxyl treatment process is: MXene is dispersed in deionized water, sodium hydroxide solution is added to adjust the pH to 10-12, stirring at 50-60℃ for 2-3 hours, washing with deionized water to neutral after filtration, drying to obtain surface hydroxyl MXene;

[0103] Preparation step

[0104] S1: 6g of boron nitride nanosheet, 3.6g of ZIF-8, 2.4g of nanocellulose and 0.5g of Ti3C2T x The supercritical CO2 fluid reactor containing 0.3% sodium dodecyl sulfate (SDS) is added, and the reactor volume is 500mL. The temperature is set to 50℃, the pressure is 12MPa, and the stirring speed is 300rpm. The constant flow rate of CO2 fluid is maintained at 8L / h during the treatment process, and the pretreated nanocomposite filler is obtained after 1.5 hours of treatment;

[0105] S2: 70g of polyformaldehyde resin, the above pretreated nanocomposite filler and environmental protection auxiliary agent are added into a twin-screw extruder (length-diameter ratio is 45:1). The temperature of each section of the twin-screw extruder is set as follows: zone 1 185℃, zone 2 205℃, zone 3 215℃, and the screw rotation speed is 350rpm. An ultrasonic vibration device is arranged in the melt blending section, and an ultrasonic energy of 30kHz and acoustic intensity of 15W / cm 2 is applied. Plastic particles are obtained after vacuum exhaust (vacuum degree is-0.08MPa), water cooling and granulation.

[0106] Performance test

[0107] Thermal conductivity: tested by laser flash method (ASTM D5470), the thermal conductivity is 1.12W / (m·K);

[0108] Formaldehyde emission: tested according to EN717-1 climate chamber method under the condition of 40℃ and 50%RH, the formaldehyde emission is 0.010mg / m 3 ;

[0109] Tensile strength: tested according to GB / T1040.2 standard by preparing dumbbell-shaped samples, the tensile strength is 78MPa;

[0110] Surface resistance: tested according to ASTM D257 standard by three-electrode method, the surface resistance is 8.8×10 8 Ω;

[0111] Flame retardant grade: tested according to UL94 standard, the sample with a thickness of 1.6mm reaches V-0 level without dripping ignition phenomenon;

[0112] The dispersion degree of the nanocomposite filler is 82% as observed by transmission electron microscopy (TEM).

[0113] Example Five

[0114] Referring to Figure 5 and Figure 7 The present application provides a technical solution: a preparation method of nanomodified polyformaldehyde plastic particles, which comprises the following components by weight percentage:

[0115] Polyformaldehyde resin: 65%;

[0116] Nanocomposite filler: 13%;

[0117] The nanocomposite filler comprises: 45% (particle size 150 nm) boron nitride nanosheet (h-BN), 35% (UiO-66-NH2, specific surface area 1700 m 2 / g) metal organic framework (MOFs), and 20% (aspect ratio 40, surface carboxyl modification degree 0.3 mmol carboxyl group per gram of nanocellulose) nanocellulose (CNC);

[0118] Environment-friendly auxiliary agent: 19%;

[0119] The environment-friendly auxiliary agent comprises: 8% (tributyl citrate) biobased plasticizer, 7% (weight ratio of melamine cyanurate (MCA) to aluminum hypophosphite (AHP) 1.5:1) halogen-free flame retardant, 3% (vitamin E derivative) antioxidant, and 1% (γ-aminopropyl triethoxysilane);

[0120] MXene two-dimensional nanomaterial: 2% (Ti3C2T x , surface hydroxyl treatment), the surface hydroxyl treatment process is: dispersing MXene in deionized water, adding sodium hydroxide solution to adjust pH to 10-12, stirring at 50-60°C for 2-3 hours, washing with deionized water to neutral after filtration, and drying to obtain surface hydroxylated MXene;

[0121] Preparation steps

[0122] S1: adding 5.85 g of boron nitride nanosheet, 4.55 g of UiO-66-NH2, 2.6 g of nanocellulose, and 2 g of surface hydroxylated Ti3C2T x to a supercritical CO2 fluid reactor containing 0.4% sodium dodecyl sulfate (SDS), the reactor volume is 500 mL. Set the temperature to 55°C, the pressure to 13 MPa, and the stirring speed to 400 rpm for 1.5 hours, and maintain a constant flow rate of CO2 fluid of 9 L / h during the treatment process, to obtain the pretreated nanocomposite filler;

[0123] S2: 65 g of polyformaldehyde resin, the above-mentioned pretreated nano-composite filler and environmental protection auxiliary agent are added into a double screw extruder (length-diameter ratio is 48:1). The temperature of each section of the double screw extruder is set as follows: 188℃ for the first section, 208℃ for the second section and 218℃ for the third section, the screw rotation speed is 380 rpm, an ultrasonic vibration device is arranged in the melt blending section, 35 kHz and 18 W / cm 2 of acoustic intensity of ultrasonic energy are applied, plastic particles are prepared after vacuum exhaust (vacuum degree is-0.07 MPa), water cooling and granulation.

[0124] Performance test

[0125] Thermal conductivity: laser flash method (ASTM D5470) is adopted for testing, and the thermal conductivity is 1.18 W / (m·K);

[0126] Formaldehyde emission: according to EN717-1 climate chamber method, the formaldehyde emission is 0.008 mg / m 3 under the condition of 40℃ and 50% RH;

[0127] Tensile strength: according to GB / T1040.2 standard, dumbbell-shaped samples are prepared for testing, and the tensile strength is 83 MPa;

[0128] Surface resistance: according to ASTM D257 standard, three-electrode method is adopted for testing, and the surface resistance is 6.8×10 8 Ω;

[0129] Flame retardant grade: according to UL94 standard, the sample with a thickness of 1.6 mm reaches V-0 level, and there is no dripping ignition phenomenon;

[0130] Nano-composite filler dispersity: through transmission electron microscope (TEM) observation, the nano-composite filler dispersity reaches 94%.

[0131] Example six

[0132] Please refer to Figure 6 and Figure 7 , the present application provides a technical solution: a preparation method of nano-modified polyformaldehyde plastic particles, which comprises, by weight percentage:

[0133] Polyformaldehyde resin: 70%;

[0134] Nano-composite filler: 12%;

[0135] The nano-composite filler comprises: 50% (particle size is 100 nm) of boron nitride nanosheet (h-BN), 30% (UiO-66-NH2, specific surface area is 1800 m 2Metal-organic frameworks (MOFs) with 20% (aspect ratio 30, surface carboxylated modification degree of 0.3 mmol carboxyl groups per gram nanocellulose) of nanocellulose (CNC);

[0136] Environmental-friendly additives: 17.5%;

[0137] Environmental-friendly additives include: 7% (tributyl citrate) of bio-based plasticizer, 6% (melamine cyanurate (MCA) and aluminum hypophosphite (AHP) in a weight ratio of 1:1) of halogen-free flame retardant, 3% (vitamin E derivative) of antioxidant and 1.5% (γ-aminopropyl triethoxysilane)

[0138] MXene two-dimensional nanomaterial: 0.5% (Ti3C2T x , surface hydroxylated treatment), the surface hydroxylated treatment process is: dispersing MXene in deionized water, adding sodium hydroxide solution to adjust pH to 10-12, stirring at 50-60°C for 2-3 hours, washing with deionized water to neutral after filtration, drying to obtain surface hydroxylated MXene;

[0139] Preparation steps

[0140] S1: 6 g of boron nitride nanosheet, 3.6 g of UiO-66-NH2, 2.4 g of nanocellulose and 0.5 g of surface hydroxylated Ti3C2T x are added into a supercritical CO2 fluid reactor kettle containing 0.3% sodium dodecyl sulfate (SDS), and the volume of the reactor kettle is 500 mL. The temperature is set to 50°C, the pressure is 12 MPa, and the stirring speed is 300 rpm for 1.5 hours. The constant flow rate of CO2 fluid is maintained at 8 L / h during the treatment process to obtain the pretreated nanocomposite filler;

[0141] S2: 70 g of polyformaldehyde resin, the above pretreated nanocomposite filler and environmental-friendly additives are added into a twin-screw extruder (aspect ratio 45:1). The temperature of each section of the twin-screw extruder is set as follows: zone 1 185°C, zone 2 205°C, zone 3 215°C, and the screw rotation speed is 350 rpm. After vacuum exhaust (vacuum degree -0.08 MPa), water cooling and granulation, plastic particles are obtained. (This step is similar to Example 1, but the ultrasonic vibration device is not turned on)

[0142] Performance test

[0143] Thermal conductivity: tested by laser flash method (ASTM D5470), and the thermal conductivity is 0.95 W / (m·K);

[0144] Formaldehyde emission: tested according to EN717-1 climate chamber method at 40°C and 50% RH, and the formaldehyde emission is 0.008 mg / m3 ;

[0145] Tensile strength: according to GB / T1040.2 standard, dumbbell-shaped samples were prepared for testing, and the tensile strength was 75 MPa;

[0146] Surface resistance: according to ASTM D257 standard, three-electrode method was used for testing, and the surface resistance was 1.2 x 10 9 Ω;

[0147] Flame retardant level: according to UL94 standard test, the sample with a thickness of 1.6 mm reached V-0 level, and there was no dripping ignition phenomenon;

[0148] Nanocomposite filler dispersity: through transmission electron microscopy (TEM) observation, the nanocomposite filler dispersity reached 82%.

[0149] Please refer to Figures 1-7 , through comparative analysis of the above six examples,

[0150] From the data table, it can be seen that the thermal conductivity of Example 2 is the highest, reaching 1.22 W / (m·K), and the thermal conductivity of Example 6 is the lowest, being 0.95 W / (m·K); the thermal conductivities of Examples 1, 3, 4, and 5 are 1.15 W / (m·K), 1.10 W / (m·K), 1.12 W / (m·K), and 1.18 W / (m·K), respectively; the difference in thermal conductivity is mainly related to the content of boron nitride nanosheets (h-BN) and the dispersity of nanocomposite fillers; in Example 2, the content of h-BN is 60%, which is the highest in the nanocomposite fillers, and the dispersity reaches 94%; a high content of h-BN can construct a more perfect thermal conduction network in the polyformaldehyde matrix, thereby effectively improving the thermal conductivity; in Example 6, the ultrasonic assistance is not turned on, and the dispersity of nanocomposite fillers is only 82%, resulting in serious stacking of h-BN layers and obstruction of the thermal conduction path, so the thermal conductivity is significantly reduced; this shows that the content of h-BN and the dispersity of nanocomposite fillers are key factors affecting the thermal conductivity of the material, and ensuring a high content of h-BN and good dispersity during preparation can help improve the thermal conductivity of the material;

[0151] The formaldehyde release amounts of the six examples are all at a relatively low level, among which the formaldehyde release amount of Example 2 is the lowest, being 0.007 mg / m 3 , the formaldehyde release amount of Example 4 is the highest, being 0.010 mg / m 3 , and the formaldehyde release amounts of the remaining examples are between 0.008 mg / m 3The formaldehyde release amount is mainly affected by the metal organic framework (MOF), which has a high specific surface area and rich pore structure and can effectively adsorb the formaldehyde released by the polyformaldehyde material; ZIF-8 is used as the MOF in Example 2, and the adsorption effect of the ZIF-8 on the formaldehyde in the system is better; although ZIF-8 is used in Example 4, the combined effect of other factors leads to a relatively high formaldehyde release amount; overall, the formaldehyde release amount of the material is significantly reduced by adding the MOF, and the material meets the environmental protection requirements, which proves that the MOF has a good effect on adsorbing formaldehyde;

[0152] The tensile strength of Example 2 is the highest, being 85 MPa, and the tensile strength of Example 6 is the lowest, being 75 MPa; the tensile strengths of Examples 1, 3, 4 and 5 are 82 MPa, 79 MPa, 78 MPa and 83 MPa respectively; the tensile strength is closely related to the carboxylation modification degree of the nanocellulose (CNC) and the dispersity of the nanocomposite filler; in Example 2, the carboxylation degree of the CNC is 0.5 mmol / g, and the dispersity of the nanocomposite filler is high; appropriately increasing the carboxylation degree of the CNC is helpful to enhancing the interfacial bonding force between the CNC and the polyformaldehyde matrix, thereby improving the tensile strength; in Example 6, the dispersity of the nanocomposite filler is poor due to the fact that the ultrasonic assistance is not started, and the interfacial bonding force is weakened, resulting in a decrease in the tensile strength; this shows that optimizing the carboxylation modification degree of the CNC and ensuring the good dispersity of the nanocomposite filler are crucial to improving the tensile strength of the material during the preparation process;

[0153] The surface resistance of Example 5 is the lowest, being 6.8*10 8 The surface resistance of Example 6 is the highest, being 1.2*10 9 The surface resistances of the other examples are between 7.2*10 8 -9.0*10 8 Ω; the content of the MXene two-dimensional nanomaterial has a significant effect on the surface resistance; in Example 5, the content of the MXene is 2%, which is higher than that in the other examples, and the good conductivity of the MXene can effectively reduce the surface resistance of the material and improve the antistatic property; in Example 6, the ultrasonic assistance is not started, which may affect the uniform dispersion of the MXene in the matrix, resulting in that the conductivity of the MXene cannot be fully utilized and the surface resistance is increased; this shows that the content and dispersity of the MXene are key factors affecting the antistatic property of the material, and increasing the content of the MXene and ensuring the good dispersity of the MXene can effectively reduce the surface resistance of the material;

[0154] The flame retardant grades of the six examples all reach UL94 V-0 level, and there is no dripping ignition phenomenon; this shows that the halogen-free flame retardant system of melamine cyanurate (MCA) and aluminum hypophosphite (AHP) in the application can play a good flame retardant effect under different raw material ratios, effectively improves the flame retardation of the polyformaldehyde material, and meets the requirements of relevant safety standards;

[0155] The dispersion degrees of the nanocomposite fillers in examples 1, 2 and 5 are relatively high, being 95%, 94% and 94% respectively, and the dispersion degrees of examples 4 and 6 are relatively low, being 82%; the dispersion degree is significantly affected by the supercritical CO2 fluid treatment parameters and ultrasonic assistance; in the preparation process of examples 1, 2 and 5, the supercritical CO2 treatment conditions are appropriate, and the ultrasonic assistance is turned on, and the cavitation effect generated by ultrasonic vibration can effectively break the nanocomposite filler aggregates and promote their uniform dispersion; while in example 6, the ultrasonic assistance is not turned on, and the nanocomposite filler agglomeration is obvious, and the dispersion degree decreases; good nanocomposite filler dispersion degree helps to improve the performance of the material, such as thermal conductivity and mechanical properties, so it is very important to optimize the dispersion process during preparation;

[0156] The following conclusions can be drawn:

[0157] Effect of boron nitride nanosheet content on thermal conductivity: with the increase of the content of boron nitride nanosheet, the thermal conductivity of the material shows an upward trend; for example, in example 2, the content of boron nitride nanosheet is 60%, and the thermal conductivity reaches 1.22 W / (m·K), which is obviously improved compared with 1.10 W / (m·K) when the content of boron nitride nanosheet is 40% in example 3; this shows that boron nitride nanosheet plays a key role in building a thermal network, and its high thermal conductivity can effectively improve the overall thermal conductivity of the material;

[0158] Effect of MOFs type on formaldehyde adsorption performance: both UiO-66-NH2 and ZIF-8 MOFs have adsorption effect on formaldehyde, but the adsorption effect is slightly different; as can be seen from examples 1 and 4, under the condition that other conditions are similar, the formaldehyde release amount is relatively low when using UiO-66-NH2, which shows that the adsorption capacity of UiO-66-NH2 for formaldehyde in the system of the application may be stronger, but further experiments are needed to verify;

[0159] Effect of nanocellulose carboxylation modification degree on tensile strength: the carboxylation modification degree of nanocellulose surface has a significant effect on the tensile strength of the material; in example 1, the carboxylation degree of nanocellulose is 0.3 mmol / g, and the tensile strength is 82 MPa; while in example 4, the carboxylation degree is 0.1 mmol / g, and the tensile strength decreases to 78 MPa; this shows that appropriately increasing the carboxylation degree of nanocellulose can help to enhance the interfacial bonding force between nanocellulose and the polyformaldehyde matrix, thereby improving the tensile strength of the material;

[0160] Effect of MXene content on surface resistance: the addition of MXene can effectively reduce the surface resistance of the material and improve the antistatic performance; with the increase of MXene content, the surface resistance gradually decreases; for example, in Example 5, when the MXene content is 2%, the surface resistance is 6.8 x 10 8 Ω, which is significantly lower than 8.5 x 10 8 Ω in Example 1 when the MXene content is 0.5%;

[0161] Effect of ultrasonic assistance on dispersion of nanocomposite filler and performance of the material: by comparing Example 1 and Example 6, it can be found that under the same conditions, turning on the ultrasonic vibration device can significantly improve the dispersion of the nanocomposite filler and thus improve the performance of the material; in Example 1, the dispersion of the nanocomposite filler reaches 95%, while in Example 6, the ultrasonic assistance is not turned on, and the dispersion is only 82%; at the same time, the thermal conductivity, tensile strength and other performance indicators of Example 1 are better than those of Example 6; this shows that ultrasonic vibration plays a key role in promoting the uniform dispersion of nanocomposite fillers, which can effectively prevent the agglomeration of nanocomposite fillers and thus improve the performance of the material;

[0162] The present application adopts a four-component composite filler system of boron nitride nanosheet, MOFs, nanocellulose and MXene, realizing the synergistic improvement of multiple functions; compared with the prior art, the material system of the present application is more complex and diversified, which can simultaneously improve the thermal conductivity, adsorption, antistatic performance and other properties of polyformaldehyde, and is not limited to the improvement of weather resistance;

[0163] Compared with the micron-sized calcium carbonate, talc and other fillers used in traditional modified POM plastics, the nanocomposite fillers of the present application have smaller size and higher specific surface area, which can better combine with the polyformaldehyde matrix, thereby more effectively improving the performance of the material; at the same time, the bio-based plasticizer and halogen-free flame retardant used in the present application eliminate the toxicity problems of phthalate plasticizers and halogen-containing flame retardants from the source, which meets the environmental protection requirements, which is not possessed by traditional modified POM plastics;

[0164] The application adopts a supercritical CO2 fluid treatment combined with an ultrasonic-assisted blending dispersion technology, can effectively solve the agglomeration problem of the nanocomposite filler in the polyoxymethylene matrix, and makes the dispersion degree of the nanocomposite filler reach more than 95%; the method of only adopting ordinary melt blending in the comparative file 1 cannot effectively solve the agglomeration problem of the nanoparticles, leads to poor dispersibility of the nanoparticles in the matrix, and thus affects the improvement of the material performance; and the simple mechanical stirring mixing mode of the traditional modified POM has a poorer dispersion effect on the nanomaterials. The above-mentioned is only the embodiment of the application, and the common technical solutions or characteristics in the scheme are not described too much. It should be pointed out that for the person skilled in the art, without departing from the technical solutions of the application, a number of deformations and improvements can also be made, which should also be regarded as the protection scope of the application, and these will not affect the implementation effect and the practicality of the patent. The protection scope required by the application should be subject to the content of its claims, and the specific implementation modes and the like in the specification can be used to explain the content of the claims.

Claims

1. Nanomodified polyoxymethylene plastic particles, characterized in that, By weight percentage, comprising the following components: Polyformaldehyde resin: 60-80%; Nano-composite filler: 5-15%; Environment-friendly auxiliary agent: 13-23%; MXene two-dimensional nanomaterial: 0.5-2%, selected from Ti3C2T x or Mo2CT x , surface hydroxyl treatment; The environment-friendly auxiliary agent includes bio-based plasticizer 5-10%, halogen-free flame retardant 5-10%, antioxidant 3-5%, and silane coupling agent 2-5%; The bio-based plasticizer is selected from tributyl citrate; The nano-composite filler is composed of: Boron nitride nanosheet (h-BN): 30-60%, particle size 50-200 nm, interlayer spacing 0.33-0.35 nm; Metal organic framework (MOFs): 20-40%, selected from UiO-66-NH2 or ZIF-8, specific surface area > 1500 m² / g; Nano-cellulose (CNC): 10-30%, aspect ratio 10-50, surface carboxylated modification; The weight ratio of boron nitride nanosheet to MOFs in the nano-composite filler is (30-60%):(20-40%), and the degree of surface carboxylated modification of nano-cellulose is 0.1-0.5 mmol carboxyl groups per gram of nano-cellulose.

2. Nanomodified polyoxymethylene plastic particles according to claim 1, characterized in that The halogen-free flame retardant is a compounded system of melamine cyanurate (MCA) and aluminum hypophosphite (AHP), and the weight ratio of the two is 1:1-2:

1.

3. The nano-modified polyoxymethylene plastic particles according to claim 1, characterized in that, The amount of silane coupling agent is 1-3% of the total weight of nano-composite filler and MXene, and the silane coupling agent is γ-aminopropyl triethoxysilane or γ-methacryloyloxypropyl trimethoxysilane.

4. A process for the preparation of nano-modified polyoxymethylene plastic particles according to any one of claims 1 to 3, characterized in that, Comprising the following steps: S1: Put boron nitride nanosheet, MOFs, nano-cellulose, and MXene into supercritical CO2 fluid containing 0.1-0.5% sodium dodecyl sulfate (SDS), mix by stirring at a temperature of 40-60℃ and a pressure of 10-15 MPa, and carry out surface modification treatment for 1-2 hours to obtain pretreated nano-composite filler; S2: Put polyformaldehyde resin, pretreated nano-composite filler in S1, and environment-friendly auxiliary agent into a twin-screw extruder, melt blend at 180-220℃, screw rotation speed 300-400 rpm, after vacuum exhaust (vacuum degree -0.09 to -0.07 MPa), water cooling, and pelletizing, the plastic particles are prepared.

5. The method for preparing nano-modified polyoxymethylene plastic particles according to claim 4, characterized in that, The stirring speed during the supercritical CO2 fluid treatment in S1 is 200-500 rpm, and the constant flow rate of CO2 fluid during the treatment process is maintained at 5-10 L / h.

6. The method for preparing nano-modified polyoxymethylene plastic particles according to claim 4, characterized in that, The length-diameter ratio of the twin-screw extruder in S2 is 40-50:1, and an ultrasonic vibration device is arranged in the melt blending section to apply ultrasonic energy of 20-40 kHz and acoustic intensity of 10-20 W / cm².

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