Liquid crystal polyester composition as well as preparation method and application thereof

Abstract

The invention relates to the technical field of polymer composite materials, in particular to a liquid crystal polyester composition. The liquid crystal polyester composition is prepared from the following components in parts by weight: 100 parts of liquid crystal polyester, 0.3 to 1 part of wheat straw cellulose, 0.1 to 0.6 part of polyethylene, 8 to 15 parts of filler and 0.5 to 2 parts of coupling agent. A combined system of the liquid crystal polyester, the wheat straw cellulose, the polyethylene, the filler and the coupling agent is selected, so that the mechanical property and the flowability of the liquid crystal polyester composition can be greatly improved, the wear resistance of a product can be improved, and a final product meets the application requirement of a high-speed light-load gear.

Description

Technical Field

[0001] The invention belongs to the field of polymer composite materials, and specifically relates to a liquid crystal polyester composition and a preparation method and application thereof. Background Art

[0002] Gears are usually used to transmit power and adjust speed in mechanical devices. When gears are working, power is transmitted through the contact between the tooth surfaces. The teeth are subjected to large alternating bending stress and contact stress, and there will be strong friction on the meshing tooth surfaces. When the meshing is uneven, impact force will also be generated. Therefore, the gear material should meet the following requirements: (1) high bending strength; (2) high hardness and wear resistance; (3) sufficient toughness.

[0003] Generally speaking, gears are made of metal materials and have high compressive strength and hardness, but there are also some shortcomings. For example, the metal has insufficient toughness, and the guide gear is easy to break when subjected to a large impact force. In addition, the manufacturing process of metal gears is complicated, resulting in low cost-effectiveness. Therefore, with the development of plastic industry technology, the field of gear transmission has gradually emerged with the trend of "replacing steel with plastic", and gear materials are no longer limited to metal.

[0004] Liquid crystal polyester is a polyarylate with a mesogen located in the main chain skeleton of the molecule. The presence of rigid mesogens makes the molecular chain of this type of polyester have a high degree of regularity. During melt processing, the viscosity of the polyester in the liquid crystal state is low, and the molecular chain is very easy to tend to form a highly oriented condensed structure. During the cooling process, due to the large rigidity of the molecular chain and the poor mobility of the chain segment, the relaxation time of the molecular chain segment is increased, so that the orientation can be retained, which also makes it have excellent rigidity, heat resistance and processability. However, the bending strength and impact strength of liquid crystal polyester are often difficult to take into account, and cannot meet the requirements of gear applications. In order to give full play to the characteristics of liquid crystal polyester materials, the inventors have conducted in-depth research on this material starting from modification. Summary of the invention

[0005] In view of the above technical problems, the present invention provides a liquid crystal polyester composition, which has good bending strength, impact strength, wear resistance and processability and can be used in high-speed and light-load gear transmission mechanisms.

[0006] The above technical problem of the present invention is solved by the following technical solution: a liquid crystal polyester composition, composed of the following components in parts by weight: 100 parts by weight of liquid crystal polyester, 0.3-1 parts by weight of wheat straw cellulose, 0.1-0.6 parts by weight of polyethylene, 8-15 parts by weight of filler, and 0.5-2 parts by weight of coupling agent.

[0007] Preferably, the liquid crystal polyester is composed of p-hydroxybenzoic acid, biphenol, terephthalic acid and isophthalic acid as repeating units.

[0008] Preferably, the molecular weight distribution range of the polyethylene is 25000-30000.

[0009] Preferably, the filler is a composite of talcum powder and nano-silicon dioxide in a mass ratio of (0.5-2):1.

[0010] More preferably, the average particle size of the talc is 20-30 μm, and the average particle size of the nano-silicon dioxide is 25-40 nm.

[0011] Preferably, the coupling agent is at least one of a silane coupling agent, a titanate coupling agent, and an aluminate coupling agent.

[0012] Preferably, the filler further comprises 0-1.5 parts by weight of an antioxidant.

[0013] To the above-mentioned liquid crystal polymer composition, glass fiber, boron nitride fiber, silicon nitride fiber, boron fiber, potassium titanate fiber, magnesium sulfate fiber, aluminum borate fiber, and metal fiber-like materials such as stainless steel, aluminum, titanium, and copper, or powdered fillers such as carbon black, graphite, silica, quartz powder, glass beads, calcium silicate, aluminum silicate, kaolin, antimony trioxide, aluminum oxide, calcium carbonate, magnesium carbonate, calcium sulfate, barium sulfate, silicon carbide, silicon nitride, boron nitride, and metal powder can also be added.

[0014] The second object of the present invention is to provide a method for preparing a liquid crystal polymer composition, which comprises: adding the above-mentioned liquid crystal polyester and polyethylene to a twin-screw extruder from a main feed port, and then adding the wheat straw cellulose, filler, and coupling agent from a side feed port, mixing the components evenly, and then extruding and granulating.

[0015] Preferably, the screw speed is 300-500 rpm and the extrusion temperature is 340-370°C.

[0016] The third object of the present invention is to provide an application of the above-mentioned liquid crystal polyester composition for high-speed and light-load gears.

[0017] The beneficial effects obtained by the technical solution of the present invention are as follows:

[0018] (1) The present invention mixes polyethylene with a certain molecular weight range having a small amount of double bonds and ether bonds with liquid crystal polyester, and the two undergo graft polymerization in a molten state, thereby breaking the high rigidity of the original molecular chain, making the molecular chain have a certain flexibility and better processability, but the bending strength of the material shows a downward trend. To this end, the inventors have found through repeated experiments that wheat straw cellulose can be physically cross-linked with liquid crystal polyester in a molten state, inducing crystallization of liquid crystal polyester and improving its crystallinity, which is beneficial to improving the bending properties of the liquid crystal polyester composite material.

[0019] (2) By adding a specific proportion of talcum powder and nano-silicon dioxide to the liquid crystal polyester, the flow processability of the liquid crystal polyester can be effectively improved while ensuring the mechanical properties of the liquid crystal polyester. In addition, the surface of nano-silicon dioxide contains a large number of hydroxyl groups and unsaturated residual bonds. Under the action of the coupling agent, it can undergo strong chemical adsorption with the surface of the liquid crystal polyester without agglomeration, forming a strong adsorption film layer, thereby further improving the wear resistance of the surface of the liquid crystal polyester. DETAILED DESCRIPTION

[0020] The implementation manner of the present invention is further described below in conjunction with specific examples.

[0021] Before further describing the specific embodiments of the present invention, it should be understood that the scope of the present invention includes but is not limited to the following specific embodiments. Generally, the terms used in the examples of the present invention are intended to describe specific embodiments rather than to limit the scope of the present invention. The test methods in the following examples that do not specify specific conditions are usually carried out under conventional conditions, and the raw materials whose sources are not particularly specified are usually conventional commercially available raw materials.

[0022] The liquid crystal polyester in the liquid crystal polyester composition can be a commercially available product or can be obtained by self-production. The self-production method is:

[0023] Add the reaction monomer, catalyst and acylating agent to the titanium alloy polymerization kettle; react at 130-150°C for 1-3h while stirring under nitrogen atmosphere, then heat to 300-400°C at a rate of 0.1-10°C / min. At 300-400°C, reduce the pressure to 1.0 mmHg in 0.1-0.5h, continue to react for 1-2h, and complete the polycondensation when the stirring torque reaches 15-20kg·cm; pressurize the polymerization kettle to 1.0-1.5kg / cm 2 The polymer is discharged into strips through a die having three circular discharge ports with a diameter of 10 mm, and then sliced ​​and crushed to obtain a liquid crystal polyester prepolymer; the prepolymer is placed in a nitrogen atmosphere and heat-treated in a rotary kiln at 250-300° C. for 12-48 hours to obtain a liquid crystal polyester.

[0024] The catalyst can be potassium acetate, sodium acetate, magnesium acetate, etc.

[0025] The acylating agent may be acetic anhydride, propionic anhydride, butyric anhydride or the like.

[0026] The liquid crystal polyester of the present invention is 20°C above the melting point and 1000 -s Melt index under shear rate conditions is 50-100cm 3 / 10min.

[0027] Liquid crystal polyester: the repeating units are p-hydroxybenzoic acid / biphenol / terephthalic acid / isophthalic acid, the molar ratio is 5:2.5:2.0:0.5, and the melt index is 60cm 3 / 10min, homemade according to the method described above.

[0028] The preparation method of the liquid crystal polyester composition of the embodiment and the comparative example is as follows: the liquid crystal polyester and polyethylene are added to the twin-screw extruder from the main feeding port, and then the wheat straw cellulose, filler and coupling agent are added from the side feeding port, and the components are mixed evenly and then extruded into granules, the screw speed is 300-500rpm, and the extrusion temperature is 340-370°C to obtain the liquid crystal polyester composition.

[0029] The properties of the liquid crystal polymer compositions provided in the embodiments and comparative examples of the present invention were measured according to the following test methods:

[0030] Bending strength: Prepare a specimen with a size of 170mm*10mm*4mm and test it according to ISO 178 standard;

[0031] Notched impact strength: Prepare a sample with a size of 170mm*10mm*4mm and test it according to ISO 180 / 1A standard;

[0032] Tensile strength: Prepare a sample with a size of 170mm*10mm*4mm and test it according to ISO 527-2 / 1A standard;

[0033] Wear scar width: Prepare a sample with a size of 35mm*7mm*4mm and test it according to GB / T3960-1983 standard.

[0034] Fluidity: spiral flow was used for characterization, the sample cross-sectional size was 5×1 mm, the molding temperature was 340°C, the molding speed was 30 mm / s, and the molding pressure was 35 bar.

[0035] Examples 1 to 7 provide a series of liquid crystal polyester compositions, whose formulations and relevant performance test results are shown in Table 1.

[0036] Table (1)

[0037]

[0038] Comparative Examples 1 to 7 provide a series of liquid crystal polyester compositions, whose formulations and relevant performance test results are shown in Table 2.

[0039] Table (2)

[0040]

[0041]

[0042] It can be seen from the data in Tables 1 and 2 that selecting a suitable combination system of liquid crystal polyester, wheat straw cellulose, polyethylene, filler and coupling agent can not only greatly improve the mechanical properties and fluidity of the liquid crystal polyester composition, but also improve the wear resistance of the product. It is further found that in order to achieve the above beneficial effects at the same time, the addition of each component is indispensable and the addition amount is also crucial.

Claims

1. A liquid crystal polyester composition, characterized in that: The invention is composed of the following components in parts by weight: 100 parts by weight of liquid crystal polyester, 0.3-1 parts by weight of wheat straw cellulose, 0.1-0.6 parts by weight of polyethylene, 8-15 parts by weight of filler and 0.2-2 parts by weight of coupling agent.

2. The liquid crystal polyester composition according to claim 1, characterized in that: The liquid crystal polyester is composed of p-hydroxybenzoic acid, biphenol, terephthalic acid and isophthalic acid as repeating units.

3. The liquid crystal polyester composition according to claim 1, characterized in that: The molecular weight distribution range of the polyethylene is 25000-30000.

4. The liquid crystal polyester composition according to claim 1, characterized in that: The filler is composited by talcum powder and nano silicon dioxide in a mass ratio of (0.5-2):

1.

5. The liquid crystal polyester composition according to claim 1, characterized in that: The coupling agent is at least one of a silane coupling agent, a titanate coupling agent, and an aluminate coupling agent.

6. The liquid crystal polyester composition according to claim 4, characterized in that: The average particle size of the talc powder is 20-30 μm, and the average particle size of the nano silicon dioxide is 25-40 nm.

7. The liquid crystal polyester composition according to claim 1, characterized in that: The filler also includes 0-1.5 parts by weight of an antioxidant.

8. A method for preparing a liquid crystal polyester composition, characterized in that: The liquid crystal polyester and polyethylene described in claim 1 are added to the twin-screw extruder from the main feed port, and then the wheat straw cellulose, filler and coupling agent are added from the side feed port. After the components are evenly mixed, they are extruded and granulated.

9. The method for preparing the liquid crystal polyester composition according to claim 8, characterized in that: The screw speed is 300-500rpm and the extrusion temperature is 340-370℃.

10. An application of the liquid crystal polyester composition according to claims 1 to 7, characterized in that: For high speed and lightly loaded gears.

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