Novel reinforced polyformaldehyde material and preparation method thereof

Abstract

The invention provides a reinforced polyformaldehyde material. The reinforced polyformaldehyde material comprises the following components in parts by weight: 100 parts of a polyformaldehyde matrix and 5-20 parts of a nano reinforced phase. 5-15 parts of a flexibilizer, 0.5-2 parts of an antioxidant, 0.5-2 parts of a lubricant, and 0.1-1 part of other auxiliary agents; wherein the nano reinforced phase comprises a nano reinforced phase with a specially modified surface and an unmodified nano reinforced phase. The invention also provides a preparation method of the novel reinforced polyformaldehyde material. The added nano reinforced phase comprises nano cellulose whiskers (CNWs) and nano titanium dioxide (TiO2), a composite system is obtained after surface modification treatment of a silane coupling agent, the compatibility between the nano reinforced phase and a polyformaldehyde matrix is improved, the reinforcing and toughening effects of nano particles are fully exerted, and under the combined action of other components, the flame-retardant performance of the composite material is improved, so that the flame-retardant performance of the composite material is improved, and the flame-retardant performance of the composite material is improved. The reinforcing and toughening effects of the polyformaldehyde material are improved, the original performance defects of the polyformaldehyde material are effectively overcome, the comprehensive performance of the polyformaldehyde material is improved, and the polyformaldehyde material has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of polymer material modification, specifically to a novel reinforced polyoxymethylene material and its preparation method. Background Technology

[0002] Polyoxymethylene (POM), as an important engineering plastic, possesses advantages such as high density, high crystallinity, excellent mechanical properties, good chemical corrosion resistance, outstanding wear resistance, and self-lubricating properties, making it widely used in many fields such as automotive manufacturing, electronics, and mechanical engineering. However, POM also has some limitations. For example, its high crystallinity leads to a relatively large molding shrinkage rate (up to 2%~3.5%), which easily causes warping during molding, affecting the dimensional accuracy and appearance quality of the finished product. Its impact toughness is relatively low, making it prone to brittle fracture under large impact forces, limiting its application in some applications requiring stringent material toughness. In addition, the heat resistance of POM needs improvement; its mechanical properties decrease significantly at high temperatures, thus affecting its application range and service life.

[0003] To overcome the aforementioned drawbacks of polyoxymethylene (POM), researchers have conducted extensive studies and explorations. Currently, common reinforcement modification methods include adding inorganic reinforcing materials such as glass fiber and carbon fiber to improve the strength and rigidity of POM; adding toughening agents, such as thermoplastic polyurethane elastomer (TPU) and ethylene-vinyl acetate copolymer (EVA), to improve its impact toughness; and using blending and copolymerization to introduce other polymers or monomers to alter the molecular structure and properties of POM. However, these existing reinforcement modification methods often have some problems, such as poor compatibility between the reinforcing materials and the POM matrix, resulting in limited improvement in the overall performance of the composite material; the addition of toughening agents, while improving toughness, may reduce the strength and rigidity of the material; and the blending and copolymerization processes are complex, require stringent processing conditions, have high production costs, and are difficult to scale up for industrial production. Therefore, developing a reinforcement modification method that can effectively improve the overall performance of POM while being simple in process, low in cost, and easy to industrialize is of significant practical importance. Summary of the Invention

[0004] The purpose of this invention is to provide a novel reinforced modified polyoxymethylene (POM) material and its preparation method. Through innovative formulation design and unique preparation process, the strength, toughness, heat resistance and dimensional stability of POM material are significantly improved, overcoming the shortcomings of the prior art and meeting the needs of the engineering field for high-performance POM materials.

[0005] The reinforced modified polyoxymethylene material of the present invention comprises the following components by weight: Polyoxymethylene matrix: 100 parts; Nano-reinforced phase: 5-20 parts; Toughening agent: 5-15 parts; Antioxidant: 0.5-2 parts; Lubricant: 0.5-2 parts; Other adjuvants: 0.1-1 part. The polyoxymethylene matrix is ​​a mixture of copolymerized polyoxymethylene and homopolymerized polyoxymethylene, and the weight ratio of copolymerized polyoxymethylene to homopolymerized polyoxymethylene is (40-60):(60-40). The polyoxymethylene matrix of this invention is a mixture of copolymeric polyoxymethylene and homopolymeric polyoxymethylene with different melt flow rates and molecular weight distributions. By optimizing the ratio of the two, the overall mechanical properties of the material are improved while ensuring its processing performance. Among them, copolymeric polyoxymethylene has better thermal stability and processing fluidity, while homopolymeric polyoxymethylene has higher strength and rigidity.

[0006] The nano-reinforcing phase includes nano-cellulose whiskers and nano-titanium dioxide, and the weight ratio of nano-cellulose whiskers to nano-titanium dioxide in the nano-reinforcing phase is (2-6):1. The surfaces of the nanocellulose whiskers and nano titanium dioxide are modified with a silane coupling agent. The nano-reinforcing phase described in this invention employs a composite system of nano-cellulose whiskers (CNWs) and nano-titanium dioxide (TiO2) with surface-modified treatment (forming covalent bonds on the surface to improve their dispersibility and stability). Nano-cellulose whiskers possess advantages such as high strength, high modulus, low density, good biocompatibility, and biodegradability, effectively enhancing the mechanical properties of polyoxymethylene (POM) matrices. Nano-titanium dioxide not only exhibits excellent photocatalytic properties, improving the material's weather resistance, but also, to some extent, improving its heat resistance. By surface-modifying nano-cellulose whiskers and nano-titanium dioxide, they achieve good compatibility with the POM matrix, are uniformly dispersed within the matrix, and fully leverage the reinforcing and toughening effects of the nanoparticles.

[0007] The toughening agent comprises maleic anhydride-grafted polyolefin elastomer and liquid rubber. The maleic anhydride-grafted polyolefin elastomer is a maleic anhydride-grafted ethylene-octene copolymer, and the liquid rubber is a liquid nitrile rubber. The toughening agent described in this invention is a compound system of maleic anhydride-grafted ethylene-octene copolymer (POE-g-MAH) and liquid nitrile rubber (L-NBR). Maleic anhydride-grafted ethylene-octene copolymer exhibits good flexibility and compatibilizing properties, improving the compatibility of the polyoxymethylene matrix with other components and enhancing the interfacial bonding strength of the composite material. Liquid nitrile rubber possesses high elasticity and good oil resistance, enabling it to form island structures within the polyoxymethylene matrix, effectively absorbing and dispersing impact energy and significantly improving the material's impact toughness. By optimizing the ratio of the two components, the toughening effect is maximized.

[0008] The antioxidant includes a compound system of hindered phenolic antioxidants and phosphite antioxidants; the lubricant includes a compound system of metal soaps and amide lubricants; and the other additives include at least one of light stabilizers and antistatic agents. The antioxidant described in this invention employs a synergistic system of hindered phenolic antioxidant 1010 and phosphite antioxidant 168. Hindered phenolic antioxidant 1010 can capture free radicals generated during the processing and use of polyoxymethylene (POM), terminating the chain reaction of oxidation. Phosphite antioxidant 168 can decompose hydroperoxides generated during the oxidation of POM, generating stable compounds, thereby inhibiting the thermal oxidative degradation of POM. The synergistic effect of these two agents significantly improves the antioxidant properties of POM materials and extends their service life.

[0009] The lubricant used in this invention is a composite lubricant of zinc stearate and ethylene bis-stearamide (EBS). Zinc stearate has excellent lubricating properties, which can reduce the melt viscosity of polyoxymethylene (POM) during processing and improve the material's fluidity; ethylene bis-stearamide has good internal and external lubrication effects, which can improve the material's release properties and prevent the material from sticking to the mold during processing. By using these two lubricants in combination, the processing performance of POM materials can be effectively improved.

[0010] Other additives described in this invention include appropriate amounts of light stabilizers and antistatic agents. Light stabilizers can absorb or quench ultraviolet light, preventing the polyoxymethylene (POM) material from aging and degrading under light conditions; antistatic agents can reduce the surface resistance of the POM material, preventing the accumulation of static electricity during processing and use, which could affect the material's performance and safety.

[0011] A method for preparing the novel reinforced polyoxymethylene material includes the following steps: Raw material pretreatment: Polyoxymethylene resin is vacuum dried at 80-100℃ for 4-6 hours, nanocellulose whiskers and nano titanium dioxide are dried at 100-120℃ for 2-3 hours, and toughening agents, antioxidants, lubricants and other additives are dried at room temperature for 1-2 hours. Surface modification treatment: Dryed nano-cellulose whiskers and nano-titanium dioxide were added to an appropriate amount of organic solvent, ultrasonically dispersed, and then silane coupling agent was added. The mixture was stirred and reacted to modify the surface of the nanoparticles. After the reaction was completed, the nano-cellulose whiskers and nano-titanium dioxide were obtained by centrifugation, washing and drying. Premixing: Pretreated polyoxymethylene resin, surface-modified nanocellulose whiskers and nano titanium dioxide, toughening agent, antioxidant, lubricant and other additives are added to a high-speed mixer and mixed at high speed; Melt blending extrusion: The premixed material is added to a twin-screw extruder for melt blending extrusion to obtain reinforced polyoxymethylene material. In the surface modification treatment step, the silane coupling agent used in the surface modification treatment is selected from any one of N-[3-(triethoxysilyl)propyl]imidazolium, 1H-1,2,4-triazol-3-ylpropyltriethoxysilane, N-[3-(triethoxysilyl)propyl]-1H-benzimidazole, N-[3-(triethoxysilyl)propyl]-4,5-dihydroimidazolium, 3-pyridinepropyltriethoxysilane, γ-aminopropyltriethoxysilane (KH-550), γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560), and γ-methacryloyloxypropyltrimethoxysilane (KH-570), and reacts at 50-70°C for 2-3 hours. The aforementioned high-speed mixing refers to mixing at a rotation speed of 1000-1500 r / min for 10-15 min. The melt blending extrusion is performed using a twin-screw extruder with an extrusion temperature range of 160-230℃ and a screw speed of 200-300 r / min. In some preferred embodiments, the preparation method of the novel reinforced modified polyoxymethylene material of the present invention includes the following steps: (1) Raw material pretreatment: Vacuum dry the polyoxymethylene resin at 80-100℃ for 4-6h to remove moisture and volatiles from the resin and prevent bubbles and hydrolysis during processing; Dry the nanocellulose whiskers and nano titanium dioxide at 100-120℃ for 2-3h to fully dehydrate them and improve their surface activity; Dry the toughening agent, antioxidant, lubricant and other additives at room temperature for 1-2h for later use.

[0012] (2) Surface modification treatment: The dried nano-cellulose whiskers and nano-titanium dioxide were added to an appropriate amount of organic solvent (any one of dimethyl sulfoxide, N-methylpyrrolidone, and dimethylformamide), and ultrasonically dispersed for 30-60 min to ensure uniform dispersion in the solvent. Then, an appropriate amount of silane coupling agent was added to covalently bond with the surface of the nano-reinforcing phase, improving its dispersibility and stability. The reaction was stirred at 50-70℃ for 2-3 h to modify the surface of the nanoparticles. After the reaction, the surface-modified nano-cellulose whiskers and nano-titanium dioxide were obtained through centrifugation, washing, and drying.

[0013] (3) Premixing: According to the above formula ratio, the pretreated polyoxymethylene resin, surface modified nano-cellulose whiskers and nano-titanium dioxide, toughening agent, antioxidant, lubricant and other additives are added to a high-speed mixer and mixed at a speed of 1000-1500r / min for 10-15min to ensure that the components are fully mixed and uniform, and a premix is ​​obtained.

[0014] (4) Melt Blending Extrusion: The premixed material is added to a twin-screw extruder for melt blending extrusion. The temperature settings for each section of the twin-screw extruder are as follows: Zone 1: 160-180℃, Zone 2: 180-200℃, Zone 3: 200-220℃, Zone 4: 220-230℃, Zone 5: 210-220℃; Screw speed: 200-300 r / min. During the extrusion process, the components are fully melted and mixed under high temperature and high shear force to form a uniform composite material. The extrudate is water-cooled, stretched, and pelletized to obtain granular products of the new reinforced modified polyoxymethylene material. Detailed Implementation

[0015] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0016] Example 1 (1) Raw material formula: 120.2

[0017] Preparation method: In some preferred embodiments, the preparation method of the novel reinforced modified polyoxymethylene material of the present invention includes the following steps: (1) Raw material pretreatment: Vacuum dry the polyoxymethylene resin at 80-100℃ for 5h to remove moisture and volatiles from the resin and prevent bubbles and hydrolysis during processing; Dry the nanocellulose whiskers and nano titanium dioxide at 110℃ for 3h to fully dehydrate them and improve their surface activity; Dry the toughening agent, antioxidant, lubricant and other additives at room temperature for 1h for later use.

[0018] (2) Surface modification treatment: The dried nano-cellulose whiskers and nano-titanium dioxide were added to an appropriate amount of organic solvent (N-methylpyrrolidone) and ultrasonically dispersed for 30-60 min to ensure uniform dispersion in the solvent. Then, an appropriate amount of silane coupling agent N-[3-(triethoxysilyl)propyl]-4,5-dihydroimidazole was added to covalently bond with the surface of the nano-reinforcing phase, improving its dispersibility and stability. The reaction was stirred at 50-70℃ for 2-3 h to modify the surface of the nanoparticles. After the reaction, the surface-modified nano-cellulose whiskers and nano-titanium dioxide were obtained through centrifugation, washing, and drying.

[0019] (3) Premixing: According to the above formula ratio, the pretreated polyoxymethylene resin, surface-modified nanocellulose whiskers and nano titanium dioxide, toughening agent, antioxidant, lubricant and other additives are added to a high-speed mixer and mixed at a speed of 1500r / min for 10min to ensure that the components are fully mixed and uniform, and a premix is ​​obtained.

[0020] (4) Melt Blending Extrusion: The premixed material is added to a twin-screw extruder for melt blending extrusion. The temperature settings for each section of the twin-screw extruder are as follows: Zone 1: 160-180℃; Zone 2: 180-200℃; Zone 3: 200-220℃; Zone 4: 220-230℃; Zone 5: 210-220℃; Screw speed: 300 r / min. During the extrusion process, the components are fully melted and mixed under high temperature and high shear force to form a uniform composite material. The extrudate is water-cooled, stretched, and pelletized to obtain granular products of the new reinforced modified polyoxymethylene material.

[0021] (5) Performance testing: The performance of the prepared novel reinforced modified polyoxymethylene material was tested, and the results are as follows: tensile strength was 84.3 MPa, flexural strength was 119.5 MPa, and cantilever beam notched impact strength was 15.3 kJ / m. 2 The heat distortion temperature (1.82 MPa) is 159℃, and the shrinkage rate is 1.2%.

[0022] Example 2 (1) Raw material formula:

[0023] (2) Preparation method: Same as in Example 1, except that the silane coupling agent is 1H-1,2,4-triazol-3-ylpropyltriethoxysilane.

[0024] (3) Performance tests: Tensile strength was 87.1 MPa, flexural strength was 123.2 MPa, and notched impact strength of the cantilever beam was 17.1 kJ / m. 2 The heat distortion temperature (1.82 MPa) is 164℃, and the shrinkage rate is 1.0%.

[0025] Example 3 (1) Raw material formula:

[0026] (2) Preparation method: Same as in Example 1, except that the silane coupling agent is N-[3-(triethoxysilyl)propyl]-1H-benzimidazole.

[0027] (3) Performance tests: tensile strength was 93.3 MPa, flexural strength was 139.1 MPa, and notched impact strength of the cantilever beam was 19.9 kJ / m. 2 The heat distortion temperature (1.82 MPa) is 168℃, and the shrinkage rate is 0.8%.

[0028] Example 4 (1) Raw material formula:

[0029] (2) Preparation method: Same as in Example 1, except that the silane coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0030] (3) Performance tests: Tensile strength was 78.7 MPa, flexural strength was 112.5 MPa, and notched impact strength of the cantilever beam was 14.1 kJ / m. 2 The heat distortion temperature (1.82 MPa) is 154℃, and the shrinkage rate is 1.5%.

[0031] Comparative Example 1 (2) Raw material formula:

[0032] (2) Preparation method: Except for not performing surface modification treatment on nanocellulose whiskers and nano titanium dioxide, the other preparation methods are the same as in Example 1.

[0033] (3) Performance tests: tensile strength was 65.7 MPa, flexural strength was 89.2 MPa, and notched impact strength of the cantilever beam was 11.2 kJ / m. 2 The heat distortion temperature (1.82 MPa) is 142℃, and the shrinkage rate is 2.2%.

[0034] Comparative Example 2 (1) Raw material formula:

[0035] (2) Preparation method: Same as in Example 1.

[0036] (3) Performance tests: Tensile strength was 69.2 MPa, flexural strength was 97.6 MPa, and notched impact strength of the cantilever beam was 12.1 kJ / m. 2 The heat distortion temperature (1.82 MPa) is 149℃, and the shrinkage rate is 1.8%.

[0037] The performance test results of Comparative Examples 1-4 and Comparative Examples 1-2 show that the novel reinforced modified polyoxymethylene material prepared by the present invention has significant advantages in tensile strength, flexural strength, impact toughness, heat distortion temperature and shrinkage rate by adopting surface-modified nano-reinforcing phase, optimized toughening agent system and reasonable formulation design and preparation process. It effectively overcomes the original performance defects of polyoxymethylene material, improves its comprehensive performance and has broad application prospects.

Claims

1. A reinforced polyoxymethylene material, characterized in that, By weight, it includes the following components: Polyoxymethylene matrix: 100 parts; Nano-reinforced phase: 5-20 parts; Toughening agent: 5-15 parts; Antioxidant: 0.5-2 parts; Lubricant: 0.5-2 parts; Other adjuvants: 0.1-1 part.

2. The reinforced polyoxymethylene material according to claim 1, characterized in that, The polyoxymethylene matrix is ​​a mixture of copolymerized polyoxymethylene and homopolymerized polyoxymethylene, and the weight ratio of copolymerized polyoxymethylene to homopolymerized polyoxymethylene is (40-60):(60-40).

3. The reinforced polyoxymethylene material according to claim 2, characterized in that, The nano-reinforcing phase includes nano-cellulose whiskers and nano-titanium dioxide, and the weight ratio of nano-cellulose whiskers to nano-titanium dioxide in the nano-reinforcing phase is (2-6):

1. The surfaces of the nanocellulose whiskers and nano titanium dioxide are modified with a silane coupling agent.

4. The reinforced polyoxymethylene material according to claim 1, characterized in that, The toughening agent comprises maleic anhydride-grafted polyolefin elastomer and liquid rubber.

5. The reinforced polyoxymethylene material according to claim 4, characterized in that, The maleic anhydride-grafted polyolefin elastomer is a maleic anhydride-grafted ethylene-octene copolymer, and the liquid rubber is a liquid nitrile rubber.

6. The reinforced polyoxymethylene material according to claim 1, characterized in that, The antioxidant includes a compound system of hindered phenolic antioxidants and phosphite antioxidants; the lubricant includes a compound system of metal soaps and amide lubricants; and the other additives include at least one of light stabilizers and antistatic agents.

7. A method for preparing the reinforced polyoxymethylene material according to any one of claims 1-6, characterized in that, Includes the following steps: Raw material pretreatment: Polyoxymethylene resin is vacuum dried at 80-100℃ for 4-6 hours, nanocellulose whiskers and nano titanium dioxide are dried at 100-120℃ for 2-3 hours, and toughening agents, antioxidants, lubricants and other additives are dried at room temperature for 1-2 hours. Surface modification treatment: Dryed nano-cellulose whiskers and nano-titanium dioxide were added to an appropriate amount of organic solvent, ultrasonically dispersed, and then silane coupling agent was added. The mixture was stirred and reacted to modify the surface of the nanoparticles. After the reaction was completed, the nano-cellulose whiskers and nano-titanium dioxide were obtained by centrifugation, washing and drying. Premixing: Pretreated polyoxymethylene resin, surface-modified nanocellulose whiskers and nano titanium dioxide, toughening agent, antioxidant, lubricant and other additives are added to a high-speed mixer and mixed at high speed; Melt blending extrusion: The premixed material is added to a twin-screw extruder for melt blending extrusion to obtain reinforced polyoxymethylene material.

8. The method according to claim 7, characterized in that, In the surface modification treatment step, the silane coupling agent used in the surface modification treatment is selected from any one of N-[3-(triethoxysilyl)propyl]imidazolium, 1H-1,2,4-triazol-3-ylpropyltriethoxysilane, N-[3-(triethoxysilyl)propyl]-1H-benzimidazole, N-[3-(triethoxysilyl)propyl]-4,5-dihydroimidazole, 3-pyridinepropyltriethoxysilane, γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane, and reacts at 50-70°C for 2-3 hours.

9. The method according to claim 7, characterized in that, The aforementioned high-speed mixing refers to mixing at a rotation speed of 1000-1500 r / min for 10-15 min.

10. The method according to claim 7, characterized in that, The melt blending extrusion is performed using a twin-screw extruder with an extrusion temperature range of 160-230℃ and a screw speed of 200-300 r / min.

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