An enhanced polyoxymethylene composition with low TVOC, its preparation method and application

Abstract

The present invention provides a reinforced polyoxymethylene composition with low TVOC, its preparation method and application, belonging to the technical field of engineering plastics. The reinforced polyoxymethylene composition of the present invention comprises the following components in parts by weight: 100 parts of polyoxymethylene, 2 - 6 parts of acid-modified polyolefin, 15 - 40 parts of glass fiber, and 0.5 - 1 part of antioxidant; the melt flow rate of the polyoxymethylene is 2.5 - 27 g / 10 min; the acid-modified polyolefin is a polyolefin modified with an unsaturated carboxylic acid. Through the synergistic effect of components such as polyoxymethylene with a specific melt flow rate, acid-modified polyolefin, and glass fiber, the present invention reduces the decomposition of polyoxymethylene, improves the bonding force between the glass fiber and the organic components, realizes the reduction of the TVOC content, improves the strength of the reinforced polyoxymethylene composition, and the TVOC of the prepared reinforced polyoxymethylene composition is ≤ 36 ugC / g, and the tensile strength is ≥ 118 MPa.

Description

Technical Field

[0001] The present invention relates to the technical field of engineering plastics, and in particular to a reinforced polyoxymethylene composition with low TVOC, a preparation method thereof, and an application thereof. Background Art

[0002] Polyoxymethylene resin (POM) has excellent mechanical properties, dimensional stability, chemical resistance, wear resistance, especially the fatigue resistance and self-lubricating property are the highest among all thermoplastics. However, in the face of some application fields with higher wear resistance requirements (such as components such as gears, bearings, window and door pulleys, bushings, etc.), there are still defects in insufficient wear resistance, and at the same time, the strength of POM is not high, resulting in limitations in some applications with high performance requirements.

[0003] In order to improve the rigidity of the material, glass fiber is generally added for reinforcement. However, in the system of glass fiber reinforced polyoxymethylene, due to the presence of glass fiber, the friction between the material and the screw and barrel during extrusion and injection molding increases, which more easily causes the decomposition of the polyoxymethylene material, releases formaldehyde, and further makes the content of total volatile organic compounds (TVOC) too high. For some products with wear resistance requirements, polytetrafluoroethylene, silicone oil, molybdenum disulfide, etc. are often added for wear resistance modification. However, the wear resistance modifier will also cause the TVOC of the material to be too high, and the strength of the material is low.

[0004] Chinese Patent Application CN 108948642 A discloses a polyoxymethylene composition and a preparation method thereof, including components such as polyoxymethylene, ultra-high molecular weight polyethylene modified glass fiber, odor adsorption masterbatch, molybdenum disulfide, etc. The odor adsorption masterbatch includes multiple components such as high-density polyethylene, hydrophobic diatomaceous earth, hydrophobic activated carbon, needle-shaped zeolite molecular sieve, zinc ricinoleate, nano-silica, calcium stearate, melamine, etc.; the odor of the material is reduced by the odor adsorption masterbatch, and the wear resistance and mechanical properties of the material are improved by the ultra-high molecular weight polyethylene modified glass fiber. However, the components of the odor adsorption masterbatch are complex, including a variety of inorganic materials, which will also bring more negative impacts on the mechanical properties of polyoxymethylene when added into the polyoxymethylene matrix. The tensile strength of the polyoxymethylene composition is only 111-128 MPa. In addition, the odor adsorption masterbatch has limited adsorption effect on TVOC, and the TVOC of the prepared polyoxymethylene composition is still too high, only reaching 37-39 ugC / g, still not meeting the use requirements of low TVOC in practical applications.

[0005] Therefore, there is a need to provide a reinforced polyoxymethylene composition with both high tensile strength and low TVOC. Summary of the Invention

[0006] The object of the present invention is to overcome the defects of low tensile strength and high TVOC in the prior art, and to provide a reinforced polyoxymethylene composition with low TVOC. Through the synergistic effect of POM with a specific melt flow rate, glass fiber, and acid-modified polyolefin and other components, the reinforced polyoxymethylene composition of the present invention has both high tensile strength and low TVOC content.

[0007] Another object of the present invention is to provide a preparation method of the above-mentioned reinforced polyoxymethylene composition.

[0008] Another object of the present invention is to provide an application of the above-mentioned reinforced polyoxymethylene composition.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] A reinforced polyoxymethylene composition, comprising the following components in parts by weight:

[0011]

[0012] The melt flow rate of the polyoxymethylene under the conditions of 190 °C and 2.16 kg is 2.5-27 g / 10 min;

[0013] The acid-modified polyolefin is a polyolefin modified with an unsaturated carboxylic acid.

[0014] In the present invention, the acid-modified polyolefin contains a certain amount of carboxyl groups, and the carboxyl groups can act on the C-O bonds of the polyoxymethylene, so that the acid-modified polyolefin is dispersed on the surface layer of the material, reducing the shear force suffered by the polyoxymethylene during extrusion and injection molding, and thus reducing the decomposition of the polyoxymethylene, thereby achieving the reduction of TVOC.

[0015] During the preparation process of the glass fiber, a small amount of hydroxyl groups will remain. The carboxyl groups in the acid-modified polyolefin can interact with the remaining hydroxyl groups of the glass fiber, improving the bonding force between the glass fiber and the organic components, reducing the friction between the reinforced polyoxymethylene material and the screw and barrel due to the presence of the glass fiber, and further reducing the content of TVOC in the reinforced polyoxymethylene composition; at the same time, the interaction between the carboxyl groups in the acid-modified polyolefin and the hydroxyl groups in the glass fiber further improves the reinforcing effect of the glass fiber in the polyoxymethylene system of the present invention, so that the strength of the reinforced polyoxymethylene composition of the present invention is excellent.

[0016] In addition, the melt flow rate of polyoxymethylene should be within an appropriate range. The inventors have found through research that when the melt flow rate of polyoxymethylene is 2.5 - 27 g / 10 min under the conditions of 190 °C and 2.16 kg, the synergistic effect among polyoxymethylene, acid-modified polyolefin, and glass fiber components is significantly better, and it is possible to achieve high strength of the material while maintaining low TVOC. When the melt flow rate of polyoxymethylene is too low, the acid-modified polyolefin cannot be effectively dispersed in the polyoxymethylene system, and at this time, the acid-modified polyolefin cannot play a role in improving the TVOC of the system; when the melt flow rate of polyoxymethylene is too high, there will also be a situation where polyoxymethylene acts alone with glass fiber, and the acid-modified polyolefin does not act at the interface between the two, resulting in an insignificant improvement in the strength of the material and a low tensile strength.

[0017] The test standard for the melt flow rate of polyoxymethylene is ISO 1133-1:2011.

[0018] Preferably, the melt flow rate of the polyoxymethylene is 9 - 14 g / 10 min under the conditions of 190 °C and 2.16 kg.

[0019] Preferably, the weight-average molecular weight of the polyoxymethylene is 80,000 - 200,000.

[0020] Preferably, the acid value of the acid-modified polyolefin is 10 - 20 (mg CH3ONa / g).

[0021] The test method for the acid value of the acid-modified polyolefin is acid-base titration: Titrate the acid-modified polyolefin with 0.1 mol / L CH3ONa solution, and calculate the acid value of the acid-modified polyolefin through the titration end point. Take a certain amount of acid-modified polyolefin, add it to 50 ml of chloroform, completely dissolve it, add bromophenol blue indicator, shake well, and then titrate with CH3ONa solution. Stop titration when the solution changes from yellow to blue, and calculate the acid value. "mg CH3ONa / g" represents the milligrams of sodium methoxide required to neutralize 1 g of the sample.

[0022] The acid value of the acid-modified polyolefin should be within an appropriate range, neither too large nor too small. The inventors have found through research that when the acid value of the acid-modified polyolefin is too small, the improvement in reducing the decomposition of polyoxymethylene and enhancing the binding force of glass fiber is limited; when the acid value of the acid-modified polyolefin is too large, due to its too strong acidity, its own acidity will promote the decomposition of polyoxymethylene, resulting in too high TVOC content and deterioration of the mechanical properties of the polyoxymethylene material.

[0023] The acid-modified polyolefin can be prepared by the following method:

[0024] Under the action of a radical initiator, mix unsaturated carboxylic acid and polyolefin, and obtain the acid-modified polyolefin through melt extrusion.

[0025] Optionally, in the preparation of the acid-modified polyolefin, the weight ratio of the unsaturated carboxylic acid to the polyolefin is (5-20):100.

[0026] Preferably, the unsaturated carboxylic acid is a monocarboxylic acid or a dicarboxylic acid containing an unsaturated double bond.

[0027] Optionally, the unsaturated carboxylic acid is at least one of itaconic acid, crotonic acid, and maleic acid.

[0028] Preferably, the polyolefin is polyethylene and / or polypropylene.

[0029] Preferably, the weight-average molecular weight of the polyolefin is 100,000-200,000.

[0030] The molecular weight of the acid-modified polyolefin needs to be in a suitable range. When the molecular weight of the acid-modified polyolefin is too large, its own fluidity is too poor, and it cannot be effectively dispersed in polyoxymethylene to play the role of reducing TVOC; when the molecular weight of the acid-modified polyolefin is too small, the chance of its own collision increases, and the reaction between each other increases, resulting in a decrease in the content of terminal carboxyl groups, and it cannot play the role of reducing TVOC and improving mechanical properties.

[0031] The radical initiator can be a conventional radical initiator in the art, such as a peroxide initiator.

[0032] Optionally, the radical initiator can be at least one of dicumyl peroxide (DCP) and benzoyl peroxide (BPO).

[0033] Conventional types of glass fibers in the art can all be applied to the reinforced polyoxymethylene composition of the present invention.

[0034] Preferably, the diameter of the glass fiber is 10-10.5 μm.

[0035] Preferably, the antioxidant includes a main antioxidant and a co-antioxidant. The main antioxidant is a hindered phenol antioxidant, and the co-antioxidant is a phosphite antioxidant and / or a thioether antioxidant.

[0036] Preferably, the weight ratio of the main antioxidant to the co-antioxidant in the antioxidant is 1:(0.5-1).

[0037] Optionally, the hindered phenol antioxidant is at least one of bis[3-(1,1-dimethylethyl)-4-hydroxy-5-methylphenylpropanoic acid] triethylene glycol and pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0038] Optionally, the phosphite antioxidant is at least one of tris(2,4-di-tert-butylphenyl) phosphite and bis(2,4-dicumylphenyl)pentaerythritol diphosphite.

[0039] Optionally, the thioether antioxidant is at least one of pentaerythritol tetrakis(3-laurylthiopropionate) and distearyl thiodipropionate.

[0040] Preferably, the reinforced polyoxymethylene composition comprises the following components in parts by weight:

[0041]

[0042] The present invention also protects a method for preparing the above-mentioned reinforced polyoxymethylene composition, which comprises the following steps:

[0043] Mix polyoxymethylene, acid-modified polyolefin, and antioxidant, and add the mixture to the main feeding port of an extruder. Add glass fiber to the side feeding port of the extruder, and after melt mixing and extrusion granulation, the reinforced polyoxymethylene composition is obtained.

[0044] Preferably, the extruder is a twin-screw extruder.

[0045] Preferably, the temperatures of the respective barrels of the twin-screw extruder from the feeding port to the head are: 150-170°C, 160-180°C, 160-180°C, 160-180°C, 170-190°C, 170-190°C, 170-190°C, 180-200°C, 180-200°C, 180-200°C. The screw speed is 250-400 revolutions per minute, the feeding rate is 50-200 kg / h, and the vacuum degree is (-0.1)-0 MPa.

[0046] The present invention also protects the application of the above-mentioned reinforced polyoxymethylene composition in the preparation of wear-resistant parts such as gears, bearings, window and door pulleys, and bushings.

[0047] Compared with the prior art, the beneficial effects of the present invention are:

[0048] The present invention develops a reinforced polyoxymethylene composition with low TVOC and high strength. By introducing an acid-modified polyolefin containing carboxyl groups, on the one hand, it acts on the C-O bonds of polyoxymethylene, reducing the decomposition of polyoxymethylene and lowering the TVOC content. On the other hand, the carboxyl groups in the acid-modified polyolefin interact with the residual hydroxyl groups of glass fiber, improving the bonding force between the glass fiber and the organic components, further reducing the TVOC content in the reinforced polyoxymethylene composition and increasing the strength of the reinforced polyoxymethylene composition. By using polyoxymethylene with an appropriate melt flow rate, the synergistic effect of the acid-modified polyolefin and glass fiber in the polyoxymethylene matrix is significantly better, and it is possible to achieve high strength while maintaining low TVOC. The TVOC of the reinforced polyoxymethylene composition prepared by the present invention is ≤ 36 μgC / g, and the tensile strength is ≥ 118 MPa. Detailed Embodiments

[0049] To better illustrate the purpose, technical solution and advantages of the present invention, the following will further illustrate the present invention with specific examples, but the examples do not limit the present invention in any form. The sources of raw materials used in the examples and comparative examples of the present invention are as follows:

[0050] Polyoxymethylene:

[0051] POM-1, Formosa Plastics Corporation, FM025, melt flow rate at 190 °C and 2.16 kg is 2.5 g / 10 min, weight average molecular weight is 200,000;

[0052] POM-2, Formosa Plastics Corporation, FM090, melt flow rate at 190 °C and 2.16 kg is 9 g / 10 min, weight average molecular weight is 160,000;

[0053] POM-3, Polyplastics M140-44, melt flow rate at 190 °C and 2.16 kg is 14 g / 10 min, weight average molecular weight is 130,000;

[0054] POM-4, Formosa Plastics Corporation, FM270, melt flow rate at 190 °C and 2.16 kg is 27 g / 10 min, weight average molecular weight is 80,000;

[0055] POM-5, Asahi Kasei POM 3010, melt flow rate at 190 °C and 2.16 kg is 2.5 g / 10 min, weight average molecular weight is 45,000;

[0056] POM-6, Polyplastics M450-44, melt flow rate at 190 °C and 2.16 kg is 45 g / 10 min, weight average molecular weight is 65,000;

[0057] POM-7, Celanese Hostaform M10AE, has a melt flow rate of 1 g / 10 min at 190 °C under a load of 2.16 kg, and a weight-average molecular weight of 230,000.

[0058] Acid-modified polyolefin: Self-made. Method: Under the action of DCP, an unsaturated carboxylic acid and a polyolefin are mixed and added to a single-screw extruder. The extrusion temperature is 160 - 200 °C, the screw speed is 25 revolutions per minute, and the acid-modified polyolefin is obtained by extrusion.

[0059] By adjusting the mixing weight ratio of the unsaturated carboxylic acid to the polyolefin, acid-modified polyolefins with different acid values are obtained. Prepared:

[0060] Acid-modified polyolefin - 1, the unsaturated carboxylic acid is itaconic acid, the polyolefin is polyethylene with a molecular weight of 100,000, and the acid value is 10 (mg CH3ONa / g);

[0061] Acid-modified polyolefin - 2, the unsaturated carboxylic acid is itaconic acid, the polyolefin is polyethylene with a molecular weight of 100,000, and the acid value is 20 (mg CH3ONa / g);

[0062] Acid-modified polyolefin - 3, the unsaturated carboxylic acid is itaconic acid, the polyolefin is polyethylene with a molecular weight of 100,000, and the acid value is 23 (mg CH3ONa / g);

[0063] Acid-modified polyolefin - 4, the unsaturated carboxylic acid is maleic acid, the polyolefin is polyethylene with a molecular weight of 200,000, and the acid value is 15 (mg CH3ONa / g);

[0064] Commercially available products can also be used for acid-modified polyolefins. For example, acid-modified polyolefin - 5, Mitsui Chemicals, Inc. LUBMER LY1040, with an acid value of 12 (mg CH3ONa / g);

[0065] Anhydride-modified polyolefin: Self-made. The difference from the self-making method of acid-modified polyolefin - 4 is that maleic acid is replaced by maleic anhydride;

[0066] Unmodified polyolefin: High molecular weight polyolefin, Mitsui Chemicals, Inc. L4000;

[0067] Glass fiber: Taishan Fiberglass Co., Ltd. ECS10 - 3.0 - T445, with a diameter of 10 μm;

[0068] Antioxidant: A mixture of IRGANOX 245 (hindered phenol antioxidant) and SONOX 168 (phosphite antioxidant) in a mass ratio of 3:2.

[0069] Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the technical field. Unless otherwise specified, the reagents and materials used in the present invention are commercially available.

[0070] Examples 1 to 15

[0071] Examples 1 to 15 provide a reinforced polyoxymethylene composition, and the component contents are shown in Table 1. The preparation method is as follows:

[0072] Mix the other components except glass fiber according to Table 1, add them to the main feeding port of the twin-screw extruder, add the glass fiber to the side feeding port of the extruder, and after melting and mixing, extrude and pelletize. The temperatures of each barrel of the twin-screw extruder from the feeding port to the head are respectively: 150 - 170 °C, 160 - 180 °C, 160 - 180 °C, 160 - 180 °C, 170 - 190 °C, 170 - 190 °C, 170 - 190 °C, 180 - 200 °C, 180 - 200 °C, 180 - 200 °C. The screw speed is 250 - 400 revolutions per minute, the feeding amount is 50 - 200 kg / h, and the vacuum degree is (-0.1) - 0 MPa, to obtain the reinforced polyoxymethylene composition.

[0073] Table 1

[0074]

[0075] Comparative Examples 1 to 6

[0076] Comparative Examples 1 to 6 provide a reinforced polyoxymethylene composition, and the component contents are shown in Table 2. The preparation method is as follows:

[0077] Mix the other components except glass fiber according to Table 2, add them to the main feeding port of the twin-screw extruder, add the glass fiber to the side feeding port of the extruder, and after melting and mixing, extrude and pelletize. The temperatures of each barrel of the twin-screw extruder from the feeding port to the head are respectively: 150 - 170 °C, 160 - 180 °C, 160 - 180 °C, 160 - 180 °C, 170 - 190 °C, 170 - 190 °C, 170 - 190 °C, 180 - 200 °C, 180 - 200 °C, 180 - 200 °C. The screw speed is 250 - 400 revolutions per minute, the feeding amount is 50 - 200 kg / h, and the vacuum degree is (-0.1) - 0 MPa, to obtain the reinforced polyoxymethylene composition.

[0078] Table 2

[0079]

[0080]

[0081] Performance test

[0082] The performance of the reinforced polyoxymethylene compositions prepared in the examples and comparative examples was tested. The specific method is as follows:

[0083] TVOC: The test standard is PV3341-1995;

[0084] Tensile strength: The test standard is ISO 527-2-2012, and the test speed is 10 mm / min.

[0085] The test results of the examples are shown in Table 3, and the test results of the comparative examples are shown in Table 4.

[0086] Table 3

[0087]

[0088] Table 4

[0089]

[0090] According to the test results in Table 3, the TVOC of the reinforced polyoxymethylene compositions prepared in each example of the present application is ≤36 μgC / g, and the tensile strength is ≥118 MPa; for the reinforced polyoxymethylene compositions of some examples, the TVOC is ≤24 μgC / g, and the tensile strength is ≥128 MPa.

[0091] From Examples 1 to 5, it can be seen that polyoxymethylene can produce good synergistic effects with acid-modified polyolefins and glass fiber components at a melt flow rate of 2.5 to 27 g / 10 min, which is significantly better, achieving high strength of the material while maintaining low TVOC; when the melt flow rate of polyoxymethylene is 9 to 14 g / 10 min, the reinforced polyoxymethylene composition has a lower TVOC while maintaining a relatively high tensile strength. In Comparative Example 5, the melt flow rate of polyoxymethylene is too high, and polyoxymethylene acts alone with glass fiber, and acid-modified polyolefins do not act at the interface between the two, resulting in an insignificant improvement in the strength of the material, a relatively low tensile strength, poor thermal stability of polyoxymethylene, and high TVOC; in Comparative Example 6, the melt flow rate of polyoxymethylene is too low, and acid-modified polyolefins cannot be effectively dispersed in the polyoxymethylene system, and at this time, acid-modified polyolefins cannot play a role in improving the TVOC of the system.

[0092] According to the test results of Example 1 and Example 5, when the melt flow rate of polyoxymethylene is within an appropriate range and the molecular weight is relatively low, the TVOC of the prepared reinforced polyoxymethylene composition is relatively high.

[0093] According to Embodiment 1, Embodiments 2 to 9, it can be seen that the TVOC of the reinforced polyoxymethylene composition of Embodiment 7 is relatively higher and the tensile strength is relatively lower. This is because when the acid value of the acid-modified polyolefin exceeds 20 mg CH3ONa / g, due to its too strong acidity, its own acidity will promote the decomposition of polyoxymethylene, resulting in too high TVOC content and a decrease in the mechanical properties of the polyoxymethylene material.

[0094] In Embodiments 10 to 16, the reinforced polyoxymethylene compositions prepared in Embodiments 10, 12, 13, and 15 have both lower TVOC, TVOC ≤ 24 μgC / g, and higher tensile strength, tensile strength ≥ 128 MPa. Therefore, it is preferred that the acid-modified polyolefin in the strong polyoxymethylene composition is 3 to 6 parts and the glass fiber is 25 to 35 parts.

[0095] In Comparative Example 1, an acid anhydride-modified polyolefin was used to replace the acid-modified polyolefin. Compared with Embodiment 8, the TVOC of the reinforced polyoxymethylene composition of Comparative Example 1 was too high and the tensile strength was lower. This is because the acid anhydride emits a strong pungent odor during the modification process, and the residual acid anhydride will affect the appearance of the product and at the same time produce an unpleasant odor, which has a negative impact on the final TVOC of the system. In Comparative Example 2, an unmodified polyolefin was used to replace the acid-modified polyolefin, and the TVOC of the prepared reinforced polyoxymethylene composition was very high and the tensile strength was poor.

[0096] According to Comparative Examples 3 and 4, it can be seen that when the addition amount of the acid-modified polyolefin is too low or too high, it will have a negative impact on TVOC and tensile strength, and it is impossible to prepare a reinforced polyoxymethylene composition with both low TVOC and high tensile strength.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An enhanced polyoxymethylene composition, characterized in that, Comprising the following components in parts by weight: 100 parts of polyoxymethylene, 2 - 6 parts of acid - modified polyolefin, 15 - 40 parts of glass fiber, 0.5 - 1 part of antioxidant; The melt flow rate of the polyoxymethylene under the conditions of 190 °C and 2.16 kg is 2.5 - 27 g / 10 min, and the test standard is ISO1133 - 1:2011; The acid - modified polyolefin is a polyolefin modified by an unsaturated carboxylic acid; the polyolefin is polyethylene and / or polypropylene, and the weight - average molecular weight of the polyolefin is 100000 - 200000; the unsaturated carboxylic acid is at least one of itaconic acid, crotonic acid, and maleic acid.

2. The reinforced polyoxymethylene composition according to claim 1, wherein The melt flow rate of the polyoxymethylene under the conditions of 190 °C and 2.16 kg is 9 - 14 g / 10 min.

3. The reinforced polyoxymethylene composition according to claim 1, wherein The weight - average molecular weight of the polyoxymethylene is 80000 - 200000.

4. The reinforced polyoxymethylene composition according to claim 1, characterized in that, The acid value of the acid - modified polyolefin is 10 - 20 mg CH3ONa / g.

5. The reinforced polyoxymethylene composition according to claim 1, wherein Reinforced polyoxymethylene composition, characterized in that it comprises the following components in parts by weight: 100 parts of polyoxymethylene, 3 - 6 parts of acid - modified polyolefin, 25 - 35 parts of glass fiber, 0.5 - 1 part of antioxidant.

6. The preparation method of the reinforced polyoxymethylene composition according to any one of claims 1 to 5, characterized in that, Comprising the following steps: Mix the polyoxymethylene, acid - modified polyolefin, and antioxidant and add them to the main feeding port of the extruder, add the glass fiber to the side feeding port of the extruder, and after melt - mixing and extrusion granulation, obtain the reinforced polyoxymethylene composition.

7. Use of the reinforced polyoxymethylene composition according to any one of claims 1 - 5 in the preparation of gears, bearings, window and door pulleys, and bushings.

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