Polypropylene composite material with stable size and high friction welding strength

Abstract

The invention belongs to the technical field of high polymer materials, and relates to a polypropylene composite material with stable size and high friction welding strength, which comprises the following components in parts by weight: 100 parts of polyolefin base material, 20-25 parts of flame retardant, 5-10 parts of glass fiber and 5-10 parts of talcum powder, the elasticity modulus of the glass fiber is greater than 90 GPa; the specific surface area of talcum powder is 3-5m < 2 > / g; the polyolefin base material is a mixture of maleic anhydride grafted modified polypropylene, high-crystallinity polypropylene and maleic anhydride grafted POE, and the crystallization enthalpy change of the high-crystallinity polypropylene is greater than 115J / g; the flame retardant is a mixture of poly (pentabromobenzyl acrylate) and silane-treated ammonium polyphosphate. Through the synergistic effect of components with specific performance parameters, the problem that in the prior art, after flame retardant modification and dimensional stability improvement, the friction welding strength of a polypropylene composite material is low is solved, and the polypropylene composite material has excellent dimensional stability and high friction welding strength and is suitable for relevant severe application scenes.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology and relates to a polypropylene composite material with dimensional stability and high friction welding strength. Background Technology

[0002] In numerous engineering applications, the demand for materials that combine dimensional stability and high friction welding strength is becoming increasingly urgent. This is particularly true in industries with extremely stringent material performance requirements, such as automotive manufacturing and electronics. The dimensional stability of materials is closely related to the assembly precision and long-term performance of products. If the material dimensions are unstable, precise fitting between components during product assembly can lead to problems such as excessive assembly gaps and inadequate sealing, thereby affecting the overall performance and reliability of the product and shortening its lifespan. High friction welding strength is a core element ensuring reliable component connections. Only with sufficient friction welding strength can components maintain a stable connection under various complex working environments, preventing malfunctions caused by loose connections and ensuring the safety and stability of the product.

[0003] Polypropylene composites have shown broad application prospects in the aforementioned fields due to their excellent comprehensive performance and low cost. However, current polypropylene composites still face many unresolved issues regarding dimensional stability, friction welding strength, and flame retardancy.

[0004] From the perspective of friction welding strength, polypropylene itself and commonly used toughening agents exhibit relatively high molecular chain flexibility. Studies have shown that this high molecular chain flexibility leads to friction hysteresis during friction welding. In high-frequency friction welding, due to friction hysteresis, the energy generated by friction cannot be effectively transferred to the welding surface, making it difficult to generate sufficient heat to melt the material and thus hindering the formation of a high-quality weld joint. To prepare materials that combine dimensional stability, a certain degree of toughness, and flame retardancy, it is inevitable to add toughening agents, minerals, flame retardants, and other substances that reduce friction welding strength. Coupled with the inherent flexibility of polypropylene's molecular chains, obtaining a material that meets various application requirements while improving friction welding strength has become a crucial problem that urgently needs to be solved.

[0005] From the perspective of dimensional stability, existing technologies include both methods of adding glass fiber to polypropylene composites and introductions to friction-welded glass fiber reinforced polypropylene materials. For example, literature (Dimensional stability and mechanical properties of GF-reinforced PP composites [J]. Engineering Plastics Application, 2017, 45 (5): 24-28, 56.), patent CN112759832B, and literature (Development of glass fiber reinforced flame-retardant polypropylene [J]. Engineering Plastics Application, 2015, 43 (8): 35-38.) all basically aim to prepare high-strength, high-dimensional-stability polypropylene materials by adding glass fiber. The addition of glass fiber can reduce the linear expansion coefficient of the material to a certain extent, which helps to improve dimensional stability. However, simply adding glass fiber can cause warping problems. Warping will cause the material to bend and deform after molding, resulting in the actual size of the material deviating from the design size; at the same time, due to the presence of warping, uneven welding strength and flash are likely to occur in various parts during friction welding.

[0006] In addition, existing technologies also include methods for adding talc to polypropylene composites. For example, in the literature (Study on shrinkage rate of automotive polypropylene materials [J]. Plastics Industry, 2018, 46 (10): 30-33.), the shrinkage rate of the material was significantly reduced by combining POE and talc; the literature (Influence of nucleating agents on the properties of inorganic filled polypropylene composite systems [J]. Plastics Industry, 2021, 49 (6): 45-50.) studied the influence of nucleating agents on dimensional stability and toughness in systems filled with a large amount of talc. Especially in the automotive industry, talc, as a commonly used filler mineral, plays an irreplaceable role in improving dimensional stability. Without involving friction welding, adding different contents of minerals such as talc can achieve material reinforcement, good dimensional stability and low warpage, thus becoming a commonly used material in industries such as home appliances and automobiles. However, the lamellar structure and large specific surface area of ​​talc give it high gas adsorption capacity, which can cause serious problems during friction welding. During friction welding, the material is locally heated, and the gas adsorbed on its surface expands and escapes, forming porosity defects inside the material. These porosity defects disrupt the internal structural integrity of the material, becoming stress concentration points and significantly reducing the friction weld strength. The addition of flame retardants presents similar problems to minerals: halogen-free phosphorus-nitrogen flame retardants are similar in properties to minerals and are prone to causing welding defects; while halogenated flame retardants, although mostly high-molecular-weight bromine-containing materials, exhibit varying effects on weld strength depending on the substrate due to differences in compatibility, wettability, and melting point.

[0007] In summary, existing polypropylene composite materials cannot simultaneously meet the requirements of dimensional stability, flame retardancy, and high friction weld strength. Therefore, it is necessary to develop a novel polypropylene composite material with both dimensional stability and high friction weld strength to overcome the shortcomings of existing technologies and meet the demand for high-performance materials in related fields. Summary of the Invention

[0008] The purpose of this invention is to solve the problems existing in the prior art and to provide a polypropylene composite material with dimensional stability and high friction welding strength.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A dimensionally stable polypropylene composite material with high friction welding strength, comprising, by weight, 100 parts of polyolefin base material, 20-25 parts of flame retardant, 5-10 parts of glass fiber and 5-10 parts of talc.

[0011] The polyolefin base material is a mixture of maleic anhydride-grafted modified polypropylene, highly crystalline polypropylene, and maleic anhydride-grafted POE. The crystallization enthalpy change of highly crystalline polypropylene is greater than 115 J / g.

[0012] The flame retardant is a mixture of polypentabromobenzyl acrylate and silane-treated ammonium polyphosphate;

[0013] The elastic modulus of glass fiber is greater than 90 GPa;

[0014] The specific surface area of ​​talc is 3-5m². 2 / g.

[0015] The high-modulus glass fiber used in this invention has high rigidity. Its high modulus can ensure small deformation during friction welding, which can effectively transmit high-frequency friction and minimize the friction hysteresis caused by the flexibility of toughening agents and polypropylene molecular chains. This increases the friction efficiency between interfaces and improves the friction welding strength.

[0016] The glass fiber of the present invention achieves the same linear expansion coefficient while reducing the amount of talc used, thereby reducing porosity defects caused by gas adsorption by talc.

[0017] The talc powder of the present invention reduces the amount of glass fiber used while achieving the same coefficient of linear expansion, thereby reducing warping caused by glass fiber.

[0018] This invention controls the specific surface area of ​​talc powder to be 3-5 m². 2 / g, because if the specific surface area of ​​talc is too large, it can adsorb more gas, which will produce pore defects on the welding surface during the friction welding process, affecting the final friction welding strength. If the specific surface area of ​​talc is too small, the particle size of talc will be too large, reducing the reinforcing filling efficiency and having an adverse effect on the final linear expansion coefficient of the composite material.

[0019] In the polyolefin matrix of this invention, the maleic anhydride grafting groups in the maleic anhydride-grafted modified polypropylene can combine with the polar groups of talc and glass fiber. This not only improves the compatibility of the polyolefin matrix with talc and glass fiber but also forms a certain bonding effect, thereby enhancing the interfacial bonding force between the filler and the matrix. This not only helps to improve the tensile strength after friction welding but also ensures that talc and glass fiber are uniformly dispersed to fully exert their linear expansion coefficient regulation effect, thus balancing the friction welding strength and dimensional stability of the composite material. High-crystallinity polypropylene, due to its high crystallinity, regular molecular structure, and small free volume, exhibits small dimensional changes after heating, effectively regulating the linear expansion coefficient of the composite material and maintaining it at a low level. Simultaneously, its regular structure resulting from high crystallinity provides high tensile stress after friction welding and cooling, thereby ensuring the friction welding strength. Maleic anhydride-grafted POE not only improves the toughness of materials, but as a component copolymerized from ethylene and α-olefins, its molecular chain has greater flexibility. It can also provide talc and glass fiber with a certain degree of freedom of movement during the crystallization shrinkage of polypropylene, reducing the orientation of glass fiber and talc caused by crystallization shrinkage, thereby inhibiting warping.

[0020] In the flame retardant of this invention, polypentabromobenzyl acrylate has a melting point of approximately 210°C, allowing it to melt during friction welding and wet the welding interface. Its polar groups provide good compatibility with talc, glass fiber, and maleic anhydride grafts, improving the problem of low friction welding strength caused by excessive flame retardant addition. Silane-treated ammonium polyphosphate, while enhancing compatibility with talc, decomposes at high temperatures to produce ammonia and phosphoric acid. This phosphoric acid promotes the charring of the benzene rings in the polypentabromobenzyl acrylate molecular structure, forming a carbon layer to isolate heat and oxygen supply, thus synergistically achieving dual flame retardant effects in the solid phase (charring barrier) and the gas phase (ammonia flame suppression). The two flame retardants work synergistically to achieve the charring barrier effect without the need for additional charring agents: Specifically, they utilize the highly char-forming benzyl ring of the pentabromobenzyl acrylate molecule. This structure first undergoes debromination to generate hydrogen bromide gas to inhibit free radical reactions, and its highly char-forming benzyl ring is then dehydrogenated by phosphoric acid substances to transform into a char layer.

[0021] As a preferred technical solution:

[0022] The polypropylene composite material described above, which is dimensionally stable and has high friction welding strength, comprises maleic anhydride-grafted modified polypropylene, highly crystalline polypropylene, and maleic anhydride-grafted POE in a mass ratio of 1:10:1.

[0023] The polypropylene composite material described above, which is dimensionally stable and has high friction welding strength, has a grafting rate of maleic anhydride-grafted modified polypropylene greater than 1%.

[0024] The polypropylene composite material described above, which is dimensionally stable and has high friction welding strength, has a maleic anhydride-grafted POE grafting rate greater than 0.7%.

[0025] The polypropylene composite material described above, which is dimensionally stable and has high friction welding strength, has a mass ratio of polypentabromobenzyl acrylate to silane-treated ammonium polyphosphate of 2:5.

[0026] As described in any of the preceding claims, a dimensionally stable polypropylene composite material with high friction weld strength has a tensile strength of 35-45 MPa and a notched impact strength of 17-25 kJ / m. 2 The friction welding strength is 19-25MPa, the linear expansion coefficient is 60-80μm / (m·℃) in the temperature range of -30℃ to 100℃, the warpage is ≤0.3mm, and the flame retardant rating is V-0.

[0027] Beneficial effects:

[0028] (1) This invention uses high-modulus glass fiber with an elastic modulus greater than 90 GPa and talc powder with a specific surface area of ​​3-5 m² / g, combined with polyolefin base material, to effectively reduce friction hysteresis and improve the friction welding strength of composite materials.

[0029] (2) In this invention, glass fiber and talc work together to reduce the warping problem caused by adding glass fiber alone and the porosity defect caused by adding talc alone, while achieving the required linear expansion coefficient, thereby improving the dimensional stability and welding strength of the composite material.

[0030] (3) The present invention controls the talc powder within a specific specific surface area range, which not only ensures its reinforcing filling efficiency and avoids adverse effects on the linear expansion coefficient of the composite material, but also reduces the amount of gas adsorption and lowers the probability of pore defects.

[0031] (4) The high modulus glass fiber used in this invention has high rigidity and small deformation during friction welding, which can effectively transmit high frequency friction and further ensure the strength of friction welding.

[0032] (5) The flame retardant combination of the present invention has little effect on the friction welding strength of the final material, while meeting the corresponding flame retardant requirements. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0034] To ensure that the performance of the substances used in each embodiment and comparative example is fully disclosed, the manufacturer information of the substances is specified in this invention; in addition, products from other manufacturers that conform to the limitations of this invention are also applicable.

[0035] The following are the test methods for the relevant performance indicators in each embodiment and comparative example:

[0036] Crystallization enthalpy change: The determination was carried out in accordance with GB / T 19466.3-2021 "Differential scanning calorimetry (DSC) for plastics - Part 3: Determination of melting and crystallization temperature and enthalpy", with the heating and cooling rate set at 20K / min.

[0037] Elastic modulus: Tested according to ASTM E1876:22 standard.

[0038] Tensile strength: Tested according to ISO 527-2:2012 standard, at a test rate of 50 mm / min.

[0039] Notched impact strength: tested according to ISO 179-1:2010 standard.

[0040] Friction welding strength: Tensile test specimens were first prepared by injection molding according to ISO 527-2:2012 standard, and the specimens were cut at 1 / 2. Then, the cut specimens were welded using friction welding equipment. The welding parameters were set as follows: pressure 3MPa, welding depth 0.3mm, amplitude 0.6mm. Finally, the tensile strength of the welded specimens was tested according to ISO 527-2:2012 standard, and the tensile strength was used as the friction welding strength data. The test rate was 50mm / min.

[0041] Linear expansion coefficient: Tested according to ISO 11359-2-2021 standard, using data from the temperature range of -30 to 100℃.

[0042] Warpage: In accordance with the requirements of the circular specimen in ASTM D955-21 standard, a plastic circular plate with a thickness of 3.2 mm and a diameter of 102 mm was prepared by injection molding. After the circular plate was cooled for 24 hours, it was placed on a flat surface with the gate side close to the horizontal plane. The distance between the farthest point of the circular plate from the gate and the horizontal plane was measured and used as the characteristic value of warpage. If the warpage is ≤0.3 mm, it is judged as no obvious warpage.

[0043] Flame retardancy rating: Tested according to GB / T 2408-2020 standard, with a sample thickness of 1.5mm.

[0044] Example 1

[0045] A method for preparing a polypropylene composite material with dimensional stability and high friction welding strength, comprising the following specific steps:

[0046] (1) Preparation of materials;

[0047] Polyolefin base material: composed of maleic anhydride-grafted modified polypropylene, highly crystalline polypropylene, and maleic anhydride-grafted POE in a mass ratio of 1:10:1; the maleic anhydride-grafted modified polypropylene is manufactured by Jia Yi Rong Polymer (Shanghai) Co., Ltd., with grade CMG5701 and a grafting rate of 1.03%; the highly crystalline polypropylene is manufactured by Sinopec Shanghai Petrochemical Co., Ltd., with grade PP M1200HS and a crystallization enthalpy change of 120J / g; the maleic anhydride-grafted POE is manufactured by Jia Yi Rong Polymer (Shanghai) Co., Ltd., with grade FB521A and a grafting rate of 0.71%;

[0048] Fiberglass: Manufacturer is Owens Corning (China) Investment Co., Ltd., brand name is WINDSTRAND® 4000, and elastic modulus is 91 GPa;

[0049] Talc: Manufacturer is ImerCare Group, brand name is ImerCare® 11T, specific surface area is 3m³ 2 / g;

[0050] Flame retardant: Composed of polypentabromobenzyl acrylate and silane-treated ammonium polyphosphate in a mass ratio of 2:5; the manufacturer of polypentabromobenzyl acrylate is Israel Chemicals, brand name FR-1025; the manufacturer of silane-treated ammonium polyphosphate is Qingyuan Pusefur Phosphate Chemical Co., Ltd., brand name APP231HS;

[0051] (2) After the polyolefin base material, glass fiber, talc powder and flame retardant are mixed evenly, they are extruded and granulated by a twin-screw extruder to obtain a polypropylene composite material with stable dimensions and high friction welding strength; wherein the rotation speed of the twin-screw extruder is 350-450 rpm and the extrusion temperature is 200-260℃.

[0052] The final polypropylene composite material with high dimensional stability and friction weld strength, by weight, comprises the following components: 100 parts polyolefin base material, 5 parts glass fiber, 5 parts talc, and 20 parts flame retardant. The tensile strength of this dimensionally stable polypropylene composite material with high friction weld strength is 38 MPa, and the notched impact strength is 25 kJ / m². 2The friction welding strength is 19MPa, the linear expansion coefficient is 74μm / (m·℃) in the temperature range of -30℃ to 100℃, there is no obvious warping, and the flame retardant rating is V-0.

[0053] Example 2

[0054] A method for preparing a polypropylene composite material with dimensional stability and high friction welding strength, comprising the following specific steps:

[0055] (1) Preparation of materials;

[0056] Polyolefin base material: composed of maleic anhydride-grafted modified polypropylene, highly crystalline polypropylene, and maleic anhydride-grafted POE in a mass ratio of 1:10:1; the maleic anhydride-grafted modified polypropylene is manufactured by Jia Yi Rong Polymer (Shanghai) Co., Ltd., with the grade CMG5701 and a grafting rate of 1.03%; the highly crystalline polypropylene is manufactured by Borealis Group, with the grade BorPure™ HJ311MO and a crystallization enthalpy change of 118 J / g; the maleic anhydride-grafted POE is manufactured by Jia Yi Rong Polymer (Shanghai) Co., Ltd., with the grade FB521A and a grafting rate of 0.71%;

[0057] Fiberglass: Manufacturer is Owens Corning (China) Investment Co., Ltd., brand name is WINDSTRAND® 5000, and elastic modulus is 95 GPa;

[0058] Talc: Manufacturer: Imercare Group, Brand: Imercare® Pharma 5T, Specific surface area: 4m³ 2 / g;

[0059] Flame retardant: Composed of polypentabromobenzyl acrylate and silane-treated ammonium polyphosphate in a mass ratio of 2:5; the manufacturer of polypentabromobenzyl acrylate is Shandong Rixing New Material Co., Ltd., brand name RX-1025; the manufacturer of silane-treated ammonium polyphosphate is Quzhou Weikai Chemical Co., Ltd., brand name Exflam APP 204;

[0060] (2) After the polyolefin base material, glass fiber, talc powder and flame retardant are mixed evenly, they are extruded and granulated by a twin-screw extruder to obtain a polypropylene composite material with stable dimensions and high friction welding strength; wherein the rotation speed of the twin-screw extruder is 350-450 rpm and the extrusion temperature is 200-260℃.

[0061] The final polypropylene composite material with high dimensional stability and friction weld strength, by weight, comprises the following components: 100 parts polyolefin matrix, 5 parts glass fiber, 10 parts talc, and 25 parts flame retardant. The tensile strength of this dimensionally stable polypropylene composite material with high friction weld strength is 35 MPa, and the notched impact strength is 21 kJ / m². 2The friction welding strength is 22MPa, the linear expansion coefficient is 80μm / (m·℃) in the temperature range of -30℃ to 100℃, there is no obvious warping, and the flame retardant rating is V-0.

[0062] Example 3

[0063] A method for preparing a polypropylene composite material with dimensional stability and high friction welding strength, comprising the following specific steps:

[0064] (1) Preparation of materials;

[0065] Polyolefin base material: composed of maleic anhydride-grafted modified polypropylene, highly crystalline polypropylene, and maleic anhydride-grafted POE in a mass ratio of 1:10:1; the maleic anhydride-grafted modified polypropylene is manufactured by Jia Yi Rong Polymer (Shanghai) Co., Ltd., with the grade CMG5701 and a grafting rate of 1.03%; the highly crystalline polypropylene is manufactured by Borealis Group, with the grade BorPure™ HJ311MO and a crystallization enthalpy change of 118 J / g; the maleic anhydride-grafted POE is manufactured by Jia Yi Rong Polymer (Shanghai) Co., Ltd., with the grade FB521A and a grafting rate of 0.71%;

[0066] Fiberglass: Manufacturer is Owens Corning (China) Investment Co., Ltd., brand name is WINDSTRAND® 5000, and elastic modulus is 95 GPa;

[0067] Talc: Manufacturer is Haimingsi Group, brand name is PLUSTALC® H50, specific surface area is 5m³ / g. 2 / g;

[0068] Flame retardant: Composed of polypentabromobenzyl acrylate and silane-treated ammonium polyphosphate in a mass ratio of 2:5; the manufacturer of polypentabromobenzyl acrylate is Israel Chemicals, brand name FR-1025; the manufacturer of silane-treated ammonium polyphosphate is Qingyuan Pusefur Phosphate Chemical Co., Ltd., brand name APP231HS;

[0069] (2) After the polyolefin base material, glass fiber, talc powder and flame retardant are mixed evenly, they are extruded and granulated by a twin-screw extruder to obtain a polypropylene composite material with stable dimensions and high friction welding strength; wherein the rotation speed of the twin-screw extruder is 350-450 rpm and the extrusion temperature is 200-260℃.

[0070] The final polypropylene composite material with high dimensional stability and friction weld strength, by weight, comprises the following components: 100 parts polyolefin matrix, 10 parts glass fiber, 5 parts talc, and 20 parts flame retardant. The tensile strength of this dimensionally stable polypropylene composite material with high friction weld strength is 45 MPa, and the notched impact strength is 19 kJ / m². 2The friction welding strength is 25MPa, the linear expansion coefficient is 60μm / (m·℃) in the temperature range of -30℃ to 100℃, there is no obvious warping, and the flame retardant rating is V-0.

[0071] Example 4

[0072] A method for preparing a polypropylene composite material with dimensional stability and high friction welding strength, comprising the following specific steps:

[0073] (1) Preparation of materials;

[0074] Polyolefin base material: composed of maleic anhydride-grafted modified polypropylene, highly crystalline polypropylene, and maleic anhydride-grafted POE in a mass ratio of 1:10:1; the maleic anhydride-grafted modified polypropylene is manufactured by Jia Yi Rong Polymer (Shanghai) Co., Ltd., with grade CMG5701 and a grafting rate of 1.03%; the highly crystalline polypropylene is manufactured by Sinopec Shanghai Petrochemical Co., Ltd., with grade PP M1200HS and a crystallization enthalpy change of 120J / g; the maleic anhydride-grafted POE is manufactured by Jia Yi Rong Polymer (Shanghai) Co., Ltd., with grade FB521A and a grafting rate of 0.71%;

[0075] Fiberglass: Manufacturer is China Jushi Co., Ltd., grade is E9, and elastic modulus is 101 GPa;

[0076] Talc: Manufacturer is Imercare Group, brand name is Imercare® Dolce, specific surface area is 5m³ / g. 2 / g;

[0077] Flame retardant: Composed of polypentabromobenzyl acrylate and silane-treated ammonium polyphosphate in a mass ratio of 2:5; the manufacturer of polypentabromobenzyl acrylate is Shandong Rixing New Material Co., Ltd., brand name RX-1025; the manufacturer of silane-treated ammonium polyphosphate is Quzhou Weikai Chemical Co., Ltd., brand name Exflam APP 204;

[0078] (2) After the polyolefin base material, glass fiber, talc powder and flame retardant are mixed evenly, they are extruded and granulated by a twin-screw extruder to obtain a polypropylene composite material with stable dimensions and high friction welding strength; wherein the rotation speed of the twin-screw extruder is 350-450 rpm and the extrusion temperature is 200-260℃.

[0079] The final polypropylene composite material with high dimensional stability and friction weld strength, by weight, comprises the following components: 100 parts polyolefin matrix, 10 parts glass fiber, 10 parts talc, and 25 parts flame retardant. The tensile strength of this dimensionally stable polypropylene composite material with high friction weld strength is 41 MPa, and the notched impact strength is 17 kJ / m². 2The friction welding strength is 25MPa, the linear expansion coefficient is 68μm / (m·℃) in the temperature range of -30℃ to 100℃, there is no obvious warping, and the flame retardant rating is V-0.

[0080] Comparative Example 1

[0081] The preparation method of a polypropylene composite material differs from that in Example 1 only in that the glass fiber is manufactured by China Jushi Co., Ltd., with the grade 540H (E-type glass fiber chopped strands) and an elastic modulus of 74 GPa.

[0082] The friction welding strength of the final polypropylene composite material was 15 MPa.

[0083] Compared with Comparative Example 1 and Example 1, the friction welding strength of polypropylene composite material was significantly reduced. This is because the elastic modulus of glass fiber is too low and its rigidity is insufficient. During the friction welding process, the deformation is large and it cannot effectively transmit high-frequency friction. It is difficult to minimize the friction hysteresis phenomenon, which means that the energy generated by friction cannot be efficiently transferred to the welding surface. The welding interface material cannot be fully melted to form a high-quality joint, thus resulting in a significant reduction in friction welding strength.

[0084] Comparative Example 2

[0085] The preparation method of a polypropylene composite material differs from that in Example 1 only in that the talc powder is manufactured by Haimingsi Group, with the brand name PLUSTALC H05 and a specific surface area of ​​12 m² / g.

[0086] The friction welding strength of the final polypropylene composite material was 13 MPa.

[0087] Compared with Example 1, the friction welding strength of the polypropylene composite material was significantly reduced. This is because the specific surface area of ​​talc powder is too high, and the amount of gas adsorbed increases significantly. During the friction welding process, the local heating of the material causes the adsorbed gas to expand and escape, forming a large number of pore defects at the welding interface and inside, which damages the structural integrity of the welded part and forms multiple stress concentration points, thus resulting in a significant decrease in friction welding strength.

[0088] Comparative Example 3

[0089] A method for preparing a polypropylene composite material differs from Example 3 only in that the amount of glass fiber added is adjusted in step (2).

[0090] The final polypropylene composite material contains 12 parts by weight of glass fiber; the warpage of the polypropylene composite material is 3 mm.

[0091] Compared with Comparative Example 3 and Example 3, the warpage of the polypropylene composite material was significantly increased. This is because the amount of glass fiber added was too high, which easily caused the material to warp, resulting in bending deformation after the material was molded, and thus a significant increase in warpage.

[0092] Comparative Example 4

[0093] A method for preparing a polypropylene composite material differs from Example 1 only in that the flame retardant is silane-treated ammonium polyphosphate.

[0094] The final polypropylene composite material has a friction welding strength of 15 MPa and a flame retardant rating of V-2.

[0095] Compared with Comparative Example 4 and Example 1, the friction welding strength of the polypropylene composite material was significantly reduced and the flame retardant performance was significantly worse. This is because the flame retardant used was only silane-treated ammonium polyphosphate, which has properties close to minerals and is prone to welding defects. At the same time, it lacks the melt wetting and compatibility enhancement effects of polypentabromobenzyl acrylate, which cannot improve the problem of low welding strength caused by flame retardant, and a single flame retardant is also difficult to meet the V-0 flame retardant requirements.

[0096] Comparative Example 5

[0097] A method for preparing a polypropylene composite material differs from Example 1 only in that the polyolefin base material does not contain highly crystalline polypropylene.

[0098] The final polypropylene composite material has a friction welding strength of 17 MPa and a linear expansion coefficient of 100 μm / (m·℃) in the temperature range of -30℃ to 100℃.

[0099] Compared with Comparative Example 5 and Example 1, the welding strength of the polypropylene composite material was reduced, while the coefficient of linear expansion was significantly increased. This is because there is no highly crystalline polypropylene in the polyolefin matrix, the crystallinity of the polyolefin matrix decreased, the free volume of molecules increased, and the size change was large under alternating heating and cooling, resulting in a significant increase in the coefficient of linear expansion. In addition, there was no sufficient tensile stress support after the friction weld cooled down, which ultimately led to a reduction in the friction weld strength.

[0100] Comparative Example 6

[0101] A method for preparing a polypropylene composite material differs from Example 1 only in that the polyolefin base material does not contain maleic anhydride-grafted modified polypropylene.

[0102] The final polypropylene composite material has a friction welding strength of 15 MPa and a linear expansion coefficient of 95 μm / (m·℃) in the temperature range of -30℃ to 100℃.

[0103] Compared with Comparative Example 6 and Example 1, the friction welding strength of the polypropylene composite material was significantly reduced and the linear expansion coefficient was significantly increased. This is because the maleic anhydride-grafted modified polypropylene was missing from the polyolefin matrix, resulting in decreased interfacial compatibility and insufficient bonding between the polyolefin matrix and talc and glass fiber. During friction welding, the interface could not form a stable bond, which led to a significant reduction in friction welding strength. At the same time, the insufficient compatibility prevented talc and glass fiber from being evenly dispersed in the material, making it difficult to fully exert their synergistic effect in regulating the linear expansion coefficient, ultimately resulting in a significant increase in the linear expansion coefficient.

[0104] Comparative Example 7

[0105] A method for preparing a polypropylene composite material, which differs from Example 1 only in that the flame retardant is polypentabromobenzyl acrylate (same as Example 1).

[0106] The final polypropylene composite material has a flame retardancy rating of V-1.

[0107] Compared with Comparative Example 7 and Example 1, the flame retardant performance of the polypropylene composite material was significantly worse. This is because the flame retardant used was only polypentabromobenzyl acrylate, which could only inhibit the free radical reaction by generating hydrogen bromide through debromination. It lacked the gas phase flame retardant effect of ammonia and the solid phase barrier effect of phosphoric acid promoting the carbonization of benzene rings, and thus could not achieve the dual flame retardant effect, resulting in a significant decrease in flame retardant efficiency.

[0108] Comparative Example 8

[0109] A method for preparing a polypropylene composite material differs from Example 1 only in that the polyolefin base material does not contain maleic anhydride grafted POE.

[0110] The final warpage with stable dimensions and high friction welding strength was 1.5 mm.

[0111] Compared with Comparative Example 8 and Example 1, the warpage of the polypropylene composite material was significantly increased. This is because the polyolefin matrix does not contain maleic anhydride-grafted POE, and lacks the support provided by its molecular chain flexibility. When polypropylene crystallizes and shrinks, talc and glass fiber do not have sufficient freedom of movement. The orientation caused by crystallization shrinkage cannot be weakened, and they cannot play a role in suppressing warpage, resulting in a significant increase in warpage.

Claims

1. A dimensionally stable polypropylene composite material with high friction welding strength, characterized in that, By weight, it includes 100 parts of polyolefin base material, 20-25 parts of flame retardant, 5-10 parts of glass fiber and 5-10 parts of talc. The polyolefin base material is a mixture of maleic anhydride-grafted modified polypropylene, highly crystalline polypropylene, and maleic anhydride-grafted POE. The crystallization enthalpy change of highly crystalline polypropylene is greater than 115 J / g. The flame retardant is a mixture of polypentabromobenzyl acrylate and silane-treated ammonium polyphosphate; The elastic modulus of glass fiber is greater than 90 GPa; The specific surface area of ​​talc is 3-5m². 2 / g.

2. The polypropylene composite material with dimensional stability and high friction welding strength according to claim 1, characterized in that, The mass ratio of maleic anhydride-grafted modified polypropylene, highly crystalline polypropylene, and maleic anhydride-grafted POE is 1:10:

1.

3. The polypropylene composite material with dimensional stability and high friction welding strength according to claim 1, characterized in that, The grafting rate of maleic anhydride-grafted modified polypropylene is greater than 1%.

4. The polypropylene composite material with dimensional stability and high friction welding strength according to claim 1, characterized in that, The grafting rate of maleic anhydride onto POE is greater than 0.7%.

5. The polypropylene composite material with dimensional stability and high friction welding strength according to claim 1, characterized in that, The mass ratio of polypentabromobenzyl acrylate to silane-treated ammonium polyphosphate is 2:

5.

6. A dimensionally stable polypropylene composite material with high friction weld strength according to any one of claims 1 to 5, characterized in that, The tensile strength of polypropylene composites is 35-45 MPa, and the notched impact strength is 17-25 kJ / m. 2 The friction welding strength is 19-25MPa, the linear expansion coefficient is 60-80μm / (m·℃) in the temperature range of -30℃ to 100℃, the warpage is ≤0.3mm, and the flame retardant rating is V-0.