Low-temperature-resistant conductive polypropylene composite material constructed through split-phase network and preparation method of low-temperature-resistant conductive polypropylene composite material

Abstract

The invention discloses a low-temperature-resistant conductive polypropylene composite material constructed through a split-phase network and a preparation method thereof, and the low-temperature-resistant conductive polypropylene composite material comprises the following raw materials by weight: 35-40% of polypropylene, 5-10% of POE-g-MAH, 30-45% of a flexibilizer, 5-10% of carbon nanotubes, 3-5% of graphene, and 0.5-2.0% of a composite additive. The obtained polypropylene composite material has low-temperature toughness resistance and high conductivity, the density of the polypropylene composite material is 0.95-1.00 g / cm < 3 >, the melt flow rate is 1-8 g / 10 min, the simply supported beam notch impact strength (23 DEG C) is 30-80 kJ / m < 2 >, the simply supported beam notch impact strength (-50 DEG C) is 2-8 kJ / m < 2 >, and the surface resistance is 103-106. The material is especially suitable for the fields of automobile parts, electronic and electric appliance shells, cold-resistant special packages and the like.

Description

Technical Field

[0001] This invention relates to the field of polypropylene polymer composite materials technology, specifically to a low-temperature resistant conductive polypropylene composite material constructed through a phase-separated network and its preparation method. Background Technology

[0002] In recent years, with the rapid development of 5G / 6G communication, coverage and functionality have been continuously improved, leading to a growing demand for conductive materials capable of operating under extreme low-temperature conditions. Polypropylene (PP) is widely used in various industries due to its low cost, low density, good chemical resistance, and good processing performance. However, its low glass transition temperature (only -15~0℃) causes a sharp drop in impact strength at low temperatures, making it unsuitable for use in harsh environments. Furthermore, its inherent insulation properties further limit its application in scenarios requiring impact resistance and antistatic / conductive properties.

[0003] Currently, the main methods for improving the toughness of PP at low temperatures are to add elastomers (such as POE and EPDM) and to enhance its conductivity by adding high amounts of conductive fillers (such as carbon black CB and carbon nanotubes CNT). These methods typically employ a simple process of one-time melt blending of all components. However, when these two methods are used together, they can easily lead to uncontrolled phase structure. On the one hand, the addition of elastomers can encapsulate some of the conductive material, affecting its dispersion and consequently the construction of the conductive network. On the other hand, the tendency of conductive fillers to agglomerate and their uneven dispersion can lead to decreased material toughness and processing difficulties, creating a "performance contradiction."

[0004] CN 114524993 discloses an impact-resistant conductive polypropylene composite material. This invention adds conductive carbon black to polypropylene resin, giving the polypropylene conductive properties. Furthermore, modified magnesium sulfate whiskers are used to uniformly disperse the conductive carbon black, which not only improves conductivity but also reduces significant stress defects caused by carbon black agglomeration, thereby improving impact strength, especially low-temperature impact strength. CN 108586942A discloses a low-temperature resistant and antistatic glass fiber reinforced polypropylene material. Copolymer polypropylene, glass fiber reinforced masterbatch, and conductive masterbatch are added to a high-speed mixer and thoroughly mixed to obtain the low-temperature resistant and antistatic glass fiber reinforced polypropylene material. Masterbatch processing improves dispersion, and glass fiber enhances impact resistance. Although there have been reports on low-temperature conductive polypropylene, no related patents or papers have been found regarding multiphase dispersion control and resistance to ultra-low temperatures (around -50°C). Currently, in regions where temperatures remain below freezing and extremely low (< -30℃), packaging for precision parts or hazardous materials, as well as in the electronics and electrical appliance industries and new energy vehicle sectors, requires materials that simultaneously meet the requirements of conductivity and low-temperature resistance (surface resistivity ≤ 10). 5Ω, 2kg drop weight ≥300mm). Therefore, developing a polypropylene composite material that can simultaneously achieve excellent ultra-high temperature resistance and toughness, high electrical conductivity and controllable cost, and solving the problem of phase structure control in multiphase and multi-component systems, is an urgent problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a low-temperature resistant and highly conductive polypropylene composite material. Through a unique formula design and step-by-step processing technology, it cleverly solves the contradiction between toughness and conductivity, and achieves a synergistic improvement of the two properties.

[0006] Another objective of this invention is to provide the above-mentioned novel preparation method, which is simple in process and suitable for industrial mass production.

[0007] Another objective of this invention is to further expand the application of the above-mentioned composite materials in the fields of automobiles, electronics, 5G / 6G communications, etc.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A low-temperature resistant conductive polypropylene composite material constructed through a phase-separated network and its preparation method, comprising the following raw materials by weight percentage: Polypropylene 35-40% POE-g-MAH 5-10% Toughening agent 30-45% Carbon nanotubes 5-10% Graphene 3-5% Composite additives: 0.5-2.0%.

[0009] The polypropylene is one or more of ultra-high melt flow index copolymer polypropylene, high melt flow index copolymer polypropylene, and medium-high melt flow index copolymer polypropylene, preferably ultra-high melt flow index copolymer polypropylene, with a melt flow rate of 120-150 g / 10 min. High melt flow index polypropylene can effectively disperse the conductive material and toughening agent respectively when manufacturing A and B masterbatches, forming a relatively uniform conductive phase and toughening phase.

[0010] The toughening agent is at least one of POE elastomer and LDPE, preferably POE+LDPE used synergistically. The POE elastomer is preferably an ethylene-octene copolymer with a concentrated molecular weight distribution; 8-carbon POE elastomer can maintain good toughness at ultra-low temperatures. The polyethylene is preferably LDPE with a melt index of 20-30 g / 10 min (190℃, 5 kg). High melt index LDPE can form a mobile phase with good flowability when melted, allowing POE to be uniformly dispersed within it, better enhancing the interfacial interaction between the two, and maximizing the toughening effect through synergistic action.

[0011] The conductive material is at least one of carbon nanotubes and graphene. The carbon nanotubes preferably have a length of 20-30 μm and a diameter of 15-20 nm. Longer carbon nanotubes can better construct conductive channels in the form of "bridges," while smaller diameters can reduce electron scattering, improve electron conduction, and enhance conductivity. The graphene preferably has a bulk density of 0.55-0.75 g / cm³. 3 The scaly flakes can be better dispersed around the carbon nanotubes, thus effectively compensating for any potential defects between the "bridges".

[0012] The composite stabilizer is a mixture of antioxidants, lubricants, dispersants, and compatibilizers. Preferably, it is a combination of hindered phenols as the primary antioxidant and phosphite-based auxiliary antioxidants, and more preferably, a combination of external lubricants and low-molecular-weight dispersants. For better dispersion, a high-shear screw assembly is selected during production. Antioxidants and external lubricants effectively protect the material, prevent degradation, and meet the requirements for long-term storage. Low-molecular-weight dispersants and compatibilizers facilitate better material feeding and reduce the possibility of filler agglomeration, thereby ensuring the stability of dispersion and overall production.

[0013] The resulting polypropylene composite material possesses both low-temperature resistance and toughness, as well as high electrical conductivity, with a density of 0.95-1.00 g / cm³. 3 Melt flow rate 1-8 g / 10 min, notched impact strength of simply supported beam (23℃) 30-80 kJ / m 2 Notched impact strength of simply supported beam (-50℃): 2-8 kJ / m 2 The surface resistivity is 10^ 3 -10^ 6 .

[0014] A method for preparing a low-temperature resistant and conductive polypropylene composite material constructed through a phase-splitting network includes the following steps: First, polypropylene, toughening agent, graphene, and composite additives are thoroughly mixed in a high-speed mixer for 5±2 minutes. Then, the mixture is melt-blended and extruded through an extruder at 180-250℃, cooled, pelletized, and dried to obtain masterbatch A with toughening phase. Polypropylene, carbon nanotubes, POE-g-MAH and composite additives are then thoroughly mixed in a high-speed mixer for 5±2 minutes. The mixture is then melt-blended and extruded through an extruder at 180-250℃, cooled, pelletized and dried to obtain masterbatch B with a conductive phase. Finally, masterbatch A and masterbatch B are thoroughly mixed in a high-speed mixer at a certain ratio for 5±2 minutes. Then, the mixture is melt-blended and extruded through an extruder at 180-250℃, cooled, pelletized, and dried to obtain the low-temperature resistant conductive polypropylene composite material.

[0015] A low-temperature resistant conductive polypropylene composite material constructed through a phase-splitting network is suitable for components manufactured in harsh outdoor low-temperature environments; this material is particularly suitable for automotive parts, electronic and electrical housings, and cold-resistant special packaging.

[0016] Compared with traditional low-temperature resistant conductive polypropylene technology, the present invention has the following advantages: By adopting a unique process approach of "phase separation construction and final composite", the process and POE-g-MAH enable toughening and conductive additives to achieve a 1+1>2 effect during final melting, fundamentally solving the problem of mutual performance constraints in multiphase and multicomponent composite materials. The process is innovative.

[0017] By leveraging the dimensional synergistic effect of carbon nanotubes (one-dimensional) and graphene (two-dimensional), a highly efficient three-dimensional conductive network is constructed with a relatively low total filler content. This network exhibits significantly better conductivity than single-filler systems, at a lower cost, and with minimal impact on material properties. The final product successfully balances excellent low-temperature impact toughness with high conductivity.

[0018] The present invention provides a method for preparing low-temperature resistant conductive polypropylene composites. It uses conventional equipment, has a clear and straightforward process route, is suitable for industrial mass production, and has high practical value. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should all be covered within the protection scope of this invention.

[0020] The raw materials used in the specific implementation methods were all purchased from the market, and their specific sources are shown in Table 1 below: polypropylene M150RH (Ningbo Petrochemical) carbon nanotubes KNG-PG42 (Xiamen Kaina) graphene DRM-P005 (Xiamen Kaina) toughening agent Toughening agent 1: POE 8842 (Dow Chemical); Toughening agent 2: LDPE H1850H (Sinopec); Main antioxidant 1010 1010 Pentaerythritol Tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] (Lialon) Co-oxidant 168 168 Tris[2,4-di-tert-butylphenyl]phosphite (extremely easy to obtain) Lubricants, dispersants EBS Vinyl Distearate (Shanghai Youci); SW-907 (Debai Technology) Coupling agent KH-550 γ-aminopropyltriethoxysilane (commercially available) compatibilizer POE-g-MAH (Jia Yi Rong Polymer Co., Ltd.) The test methods for various properties of the material are as follows: Density: ISO 1183; Tensile strength: ISO 527; Flexural strength, flexural modulus: ISO 178; Notched impact strength: ISO 179; Low-temperature drop hammer impact, drop weight 2kg, thickness 3.2mm, temperature -50℃; Melt flow rate: ISO 1133, temperature 230℃, load 2.16KG; Surface resistivity, IEC 93.

[0021] According to the formula in Table 2, PP, toughening agent, graphene, and composite additives are added to a mixer and mixed at high speed for 5 minutes. Then, all of them are added from the main feed port at the following temperatures: 180℃-200℃, 190℃-210℃, 190℃-210℃, 200℃-220℃, 200℃-220℃, 190℃-210℃, 190℃-210℃, 200℃-230℃. The die temperature is 220℃. After cooling and pelletizing, masterbatch A containing the toughening phase is obtained.

[0022] According to the formula in Table 2, PP, carbon nanotubes, POE-g-MAH, and composite additives are added to a mixer and mixed at high speed for 5 minutes. Then, all of them are added from the main feed port at the following temperatures: 180℃-200℃, 190℃-210℃, 190℃-210℃, 200℃-220℃, 200℃-220℃, 190℃-210℃, 190℃-210℃, 200℃-220℃. The die temperature is 220℃. After cooling and pelletizing, masterbatch B containing the conductive phase is obtained.

[0023] Finally, masterbatch A and masterbatch B are added to the mixer and mixed at high speed for 5 minutes. Then, the mixture is added from the main feed port at the following temperatures: 180℃-200℃, 190℃-210℃, 190℃-210℃, 200℃-220℃, 200℃-220℃, 190℃-210℃, 190℃-210℃, 200℃-220℃. The die temperature is 220℃. After cooling and pelletizing, a low-temperature resistant conductive polypropylene composite material is obtained.

[0024] According to the formula in Table 3, PP, toughening agent, carbon nanotubes, graphene, and composite additives are mixed in one batch in a mixer and mixed at high speed for 5 minutes. Then, all of them are added from the main feed port at the following temperatures: 180℃-200℃, 190℃-210℃, 190℃-210℃, 200℃-220℃, 200℃-220℃, 190℃-210℃, 190℃-210℃, 200℃-230℃. The die temperature is 220℃. After cooling and pelletizing, polypropylene composite material is obtained.

[0025] Formulation components Example 1 Example 1 Example 2 Example 2 Example 3 Example 3 Example 4 Example 4 Example 5 Example 5 Example 6 Example 6 Masterbatch A Masterbatch B Masterbatch A Masterbatch B Masterbatch A Masterbatch B Masterbatch A Masterbatch B Masterbatch A Masterbatch B Masterbatch A Masterbatch B Copolymer polypropylene resin 18 38 18 35 18 35 16 32 13 30 10 26 carbon nanotubes 7 / 7 / 7 / 7 / 7 / 7 / graphene / / 2.4 0.6 / 3 / 3 / 3 5 POE-g-MAH / / / / / / 5 / 10 / 10 / Toughening agent 1 / 30 / 30 / 30 / 30 / 30 / 35 Toughening agent 2 / 5 / 5 / 5 / 5 / 5 / 5 1010 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 168 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 EBS 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 SW-907 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 KH-550 0.3 0.3 0.3 0.3 0.3 0.3 Formulation components Compare with Example 1 Compare with Example 2 Compare with Example 3 Copolymer polypropylene resin 56 53 48 carbon nanotubes 7 7 7 graphene / 3 3 Toughening agent 1 30 30 35 Toughening agent 2 5 5 5 1010 0.3 0.3 0.3 168 0.3 0.3 0.3 EBS 0.5 0.5 0.5 SW-907 0.5 0.5 0.5 KH-550 0.3 0.3 0.3 The granules from Examples 1-6 and Comparative Examples 1-3 were prepared into test specimens using an injection molding machine for mechanical property testing and surface resistance testing. The results are shown in Table 4.

[0026] performance <![CDATA[Density (g / cm 3 ).]]> Bending strength (MPa) Flexural modulus (MPa) Tensile strength (MPa) <![CDATA[Izod impact strength (23 °C, kJ / m 2 )]]> <![CDATA[Notch impact strength (-50 °C, kJ / m 2 ).]]> Surface resistivity (Ω) Melt flow rate (g / 10min) Low temperature drop weight (-50℃) Example 1 0.926 16.8 623 15.4 35 2.8 8.5*10^6 4.34 250 Example 2 0.934 16.4 600 15.9 37 2.9 2.3*10^6 3.68 250 Example 3 0.938 16.6 446 14.7 42 3.6 3.4*10^5 2.21 300 Example 4 0.947 13.84 424 13.9 47 3.8 5.4*10^4 1.88 300 Example 5 0.953 9.87 356 12.0 56 4.5 3.0*10^3 1.15 350 Example 6 0.968 10.11 374 12.2 53 4.3 8.0*10^3 ＜1 350 Compare with Example 1 0.931 16.20 734 16.2 34 2.6 5.9*10^7 3.74 200 Compare with Example 2 0.943 16.40 802 15.4 30 2.4 3.5*10^6 3.25 200 Compare with Example 3 0.945 10.24 423 10.9 47 4.2 6.7*10^6 ＜1 250 The following points can be observed from Examples 1-6: 1. The products made from the low-temperature resistant conductive polypropylene composite material obtained by this invention have a surface resistivity of 10^3, exhibiting good conductivity; the notched impact at 23℃ reaches 56 kJ / m2, the low-temperature impact at -50℃ reaches 4.5 kJ / m2, and a 2kg drop hammer can penetrate 350mm, demonstrating excellent low-temperature toughness.

[0027] 2. Comparing Examples 1 and 2 with Comparative Example 1, it can be seen that simply changing the process from a one-pot method to a two-step method does not have a significant effect. The conductivity and low-temperature resistance are only slightly improved. This shows that the simple two-step method still cannot solve the problem of dispersion and compatibility between various additives.

[0028] 3. Comparing Examples 3, 4, 5 and Comparative Example 2, it can be seen that the surface resistivity and low-temperature resistance of the material have increased significantly. In particular, in Example 5, the surface resistivity decreased from 10^6 to 10^3 compared to Comparative Example 2, the notched impact strength (-50℃, kJ / m2) increased from 2.4 kJ / m2 to 4.5 kJ / m2, and the drop height at -50℃ increased from 200mm to 350mm, showing a significant improvement in overall performance.

[0029] The material obtained by melt extrusion using a phase-separated network construction process exhibits superior low-temperature resistance and conductivity compared to the one-pot method. In masterbatch A, high melt index PP is used, allowing POE and LDPE to be fully dispersed under the influence of PP flowability, forming a micron-scale PP-POE and POE-LDPE double island structure, pre-constructing a complete toughening network. The addition of graphene can form a cross-linked network structure with the toughening agent, cleverly improving the system's compatibility and further enhancing its low-temperature resistance. In masterbatch B, high melt index PP is used, supplemented by strong shear force. In addition, POE-g-MAH is introduced. The MAH functional groups can interact with the CNT surface, promoting dispersion and forcibly dispersing the conductive material in PP, thus pre-constructing a primary conductive network in the PP matrix. In the final masterbatch mixing process, the graphene in masterbatch A can effectively compensate for the defects in the conductive network bridges and connect the conductive network throughout the entire surface; the POE-g-MAH in masterbatch B can effectively fuse with masterbatch A, allowing the compatibility of the entire system to reach the optimal state.

[0030] Therefore, when the last two phases are extruded and melted, they can effectively retain their own characteristics and combine well together, so as to better synergize toughening and conductivity, resulting in a 1+1>2 effect. This changes the traditional conclusion that "toughening must be insulating and conductivity must be brittle", and yields a polypropylene composite material that balances low temperature resistance and high conductivity.

[0031] 4. Comparing Examples 5 and 6, the latter showed a decrease in conductivity, indicating that the addition of graphene is limited. Appropriate graphene addition can further improve the conductivity of the composite material. This is because carbon nanotubes, during dispersion, may exhibit bridging defects or form a single conductive network, leading to maximizing conductivity or localized non-conductivity. By cleverly utilizing the dimensional synergistic effect of carbon nanotubes (one-dimensional) and graphene (two-dimensional), a highly efficient three-dimensional conductive network can be constructed with a lower total filler content, resulting in significantly better conductivity than a single filler system. When the amount of carbon nanotubes added is small, the conductive network is relatively simple and weak, with poor conductivity itself, and graphene cannot effectively achieve a synergistic effect (1+1>2). Conversely, when the amount of carbon nanotubes added is large, the conductive network is already relatively complete, and the addition of graphene is unlikely to bring about a qualitative change; it may even exacerbate the dispersion problem and affect the overall performance. Therefore, an appropriate amount of graphene, as an auxiliary conductive agent, can play a crucial role in enhancing the system's conductivity.

Claims

1. A low-temperature resistant conductive polypropylene composite material constructed through a phase-separated network, comprising the following raw materials by weight percentage: Polypropylene 35-40% POE-g-MAH 5-10% Toughening agent 30-45% Carbon nanotubes 5-10% Graphene 3-5% Composite additives: 0.5-2.0%.

2. The low-temperature resistant conductive polypropylene composite material constructed through a phase-separated network according to claim 1, characterized in that, The polypropylene is one or a blend of several of the following: ultra-high melt flow rate copolymer polypropylene (melt flow rate > 120 g / 10min (210℃, 2.16kg)), high melt flow rate copolymer polypropylene (melt flow rate > 90 g / 10min (210℃, 2.16kg)), and medium-high melt flow rate copolymer polypropylene (melt flow rate > 25 g / 10min (210℃, 2.16kg)).

3. The low-temperature resistant conductive polypropylene composite material constructed through a phase-separated network according to claim 1, characterized in that, The toughening agent is one or more of the following: octane POE synthesized from ethylene and 1-octene via metallocene catalysis, and high-melt-index polyethylene.

4. The low-temperature resistant conductive polypropylene composite material constructed through a phase-separated network according to claim 1, characterized in that, The carbon nanotubes have a diameter of 15-30 nm, a length of 10-20 μm, and a carbon content >98%; the graphene has a bulk density of 0.55-0.75 g / cm³. 3 Carbon content > 98%.

5. The low-temperature resistant conductive polypropylene composite material constructed through a phase-separated network according to claim 1, characterized in that, The composite additive comprises antioxidants, lubricants, and dispersants, wherein the antioxidant is selected from at least one of a primary antioxidant containing hindered phenols and a secondary antioxidant of phosphites; the lubricant includes at least one of metal soaps, fatty acid amides, and hydrocarbon lubricants; and the dispersant is a low molecular weight dispersant containing multiple functional groups.

6. A method for preparing a low-temperature resistant conductive polypropylene composite material constructed through a phase-separated network according to any one of claims 1 to 5, comprising the following steps: First, polypropylene, toughening agent, graphene, and composite additives are thoroughly mixed in a high-speed mixer for 5±2 minutes. Then, the mixture is melt-blended and extruded through an extruder at 180-250℃, cooled, pelletized, and dried to obtain masterbatch A with toughening phase. Polypropylene, carbon nanotubes, POE-g-MAH and composite additives are then thoroughly mixed in a high-speed mixer for 5±2 minutes. The mixture is then melt-blended and extruded through an extruder at 180-250℃, cooled, pelletized and dried to obtain masterbatch B with a conductive phase. Finally, masterbatch A and masterbatch B are thoroughly mixed in a high-speed mixer at a certain ratio for 5±2 minutes. Then, the mixture is melt-blended and extruded through an extruder at 180-250℃, cooled, pelletized, and dried to obtain the low-temperature resistant conductive polypropylene composite material.

7. The low-temperature resistant conductive polypropylene composite material constructed by a phase-splitting network according to any one of claims 1-5 is suitable for related components in harsh outdoor low-temperature environments.