Carbon nanotube gradient concentration distribution ABS composite material, preparation method and application thereof
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- WUHAN JINFA TECH CO LTD
- Filing Date
- 2026-04-30
- Publication Date
- 2026-06-30
AI Technical Summary
Traditional carbon nanotube-reinforced ABS materials suffer from carbon nanotube waste and decreased mechanical properties during laser marking processes. In particular, the uneven distribution of carbon nanotubes on the surface and inside leads to molding difficulties and increased energy consumption.
By employing a double-layer coated carbon nanotube, the polarity difference between the inner layer of the polar transition polymer and the ABS matrix, as well as the temperature gradient, is utilized to enrich the carbon nanotubes on the surface during injection molding, forming a gradient structure of high-concentration surface layer and low-concentration core layer. The controllable gradient distribution is achieved by using the fountain flow effect and viscosity gradient to assist the migration of carbon nanotubes.
It meets the requirements for surface laser marking with low addition amount, while improving the overall mechanical properties, reducing the amount of carbon nanotubes used, and reducing molding difficulty and energy consumption.
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Abstract
Description
Technical Field
[0001] This application relates to the field of polymer composite materials technology, and in particular to an ABS composite material with a gradient concentration distribution of carbon nanotubes, its preparation method and application. Background Technology
[0002] ABS plastic products are widely used in the automotive, electronics, and home appliance industries, often requiring simultaneous compliance with both surface laser marking and overall mechanical properties. Traditional carbon nanotube-reinforced ABS materials employ a uniform dispersion design, meaning carbon nanotubes are evenly added throughout the ABS matrix. However, this approach has the following drawbacks: Laser marking primarily occurs on the surface of products, typically at a depth of 50-200 μm. However, carbon nanotubes are uniformly dispersed throughout the matrix, preventing a large number of internal carbon nanotubes from effectively participating in the laser marking process, thus wasting expensive additives. Furthermore, when the carbon nanotube content exceeds 1.5 wt%, the toughness of ABS material significantly decreases, making it impossible to simultaneously meet the requirements for surface laser marking effectiveness and overall mechanical properties. Moreover, high carbon nanotube content substantially increases melt viscosity, leading to processing problems such as difficult molding and increased energy consumption. Summary of the Invention
[0003] The purpose of this invention is to overcome the defects and shortcomings of existing ABS and provide an ABS composite material that can achieve a controllable gradient distribution of carbon nanotubes, with carbon nanotubes enriched on the material surface to meet the requirements of surface laser marking, while also having good overall mechanical properties.
[0004] Another object of the present invention is to provide a method for preparing ABS composite material.
[0005] Another object of the present invention is to provide an ABS injection molded part with a gradient concentration distribution of carbon nanotubes.
[0006] The above-mentioned objective of this invention is achieved through the following technical solution: This invention provides an ABS composite material comprising the following components by weight: 100 parts of ABS resin 0.8–2.0 parts of double-layer coated carbon nanotubes, 0.3–0.8 parts of small molecule rheology modifier, Nucleating agent 0.1–0.3 parts, The ABS resin has a shear thinning index n = 0.35-0.45, a weight-average molecular weight Mw of 120,000-180,000, and a dispersity Mw / Mn = 2.5-4.0. The double-layer coated carbon nanotubes comprise carbon nanotubes, a polar transition polymer inner layer, and a compatible polymer outer layer stacked sequentially; the polar transition polymer inner layer is an N-isopropylacrylamide (PNIPAM) copolymer, which contains NIPAM units, acrylic acid units, and hydroxyl-containing acrylate units; the compatible polymer outer layer is a PMMA and / or SAN copolymer.
[0007] The ABS composite material of the present invention uses ABS resin as a matrix and adds double-layer coated carbon nanotubes. During the injection molding stage, the carbon nanotubes are transported to the surface area through the fountain flow effect. During the cooling and curing process, the polarity difference between the inner layer of the polar transition polymer and the ABS matrix, as well as the temperature gradient between the surface layer and the core layer, are used to make the carbon nanotubes preferentially undergo phase separation and enrichment on the surface layer, while maintaining a relatively uniform dispersion in the core layer, forming a continuous gradient structure of 'high concentration surface layer - low concentration core layer'. This ensures mechanical properties with a low amount of carbon nanotubes added, while also meeting the requirements for surface laser marking.
[0008] Specifically, the double-layer coated carbon nanotubes of the present invention include carbon nanotubes, a polar transition polymer inner layer, and a compatible polymer outer layer stacked sequentially; enabling the carbon nanotubes to exhibit differentiated dispersion states in different temperature regions: the high mixing entropy in the high-temperature region (core layer) keeps the carbon nanotubes uniformly dispersed, while the reduced mixing entropy in the low-temperature region (surface layer) enhances the polarity mismatch effect, resulting in the enrichment of carbon nanotubes.
[0009] The inner layer of the polar transition polymer is a PNIPAM copolymer containing acrylic copolymer units and hydroxyl-containing acrylate copolymer units, which acts as a polar buffer layer coating the surface of carbon nanotubes. The acrylic units (carboxyl groups) and hydroxyethyl acrylate units (hydroxyl groups) in this copolymer provide a significant polarity difference from the ABS matrix, while the NIPAM units provide appropriate segmental flexibility and good adhesion to the carbon nanotube surface. During the high-temperature, high-shear stage of injection molding, the outer PMMA and / or SAN copolymer provides good compatibility with the ABS matrix, allowing the carbon nanotubes to be uniformly dispersed in the melt. The fountain effect during molding causes the melt to tumble and deposit from the center of the flow front towards the mold wall, transporting some of the carbon nanotubes to the surface region. When the melt begins to cool, the surface temperature drops rapidly (below 100°C within 0-2 seconds). Because the inner layer of the PNIPAM copolymer, after modification by copolymerization of acrylic acid and hydroxyethyl acrylate, contains a large number of carboxyl and hydroxyl functional groups, its polarity is much higher than that of the SAN continuous phase of the ABS matrix. It should be noted that although pure PNIPAM exhibits LCST temperature response characteristics in aqueous solution, this mechanism does not apply in the high-temperature polymer melt system of this invention (far exceeding the LCST temperature). The driving force for carbon nanotube enrichment towards the surface mainly originates from: the drastic decrease in the contribution of mixing entropy during cooling, and the significant enhancement of the enthalpy-driven phase separation tendency caused by polarity differences, leading to in-situ phase separation and enrichment of carbon nanotubes in the surface region; while in the core layer, due to the higher temperature (maintained at 150-180℃), the contribution of mixing entropy remains relatively large, the polarity mismatch effect is weak, and the carbon nanotubes remain relatively uniformly dispersed. As the surface layer rapidly solidifies, this gradient distribution is frozen, thus forming a continuous gradient structure of 'high-concentration surface layer - low-concentration core layer'.
[0010] Furthermore, this invention controls the rheological properties of the ABS resin, utilizing a viscosity gradient to assist the migration of carbon nanotubes to the surface. By employing ABS resin with a specific shear thinning index and a small-molecule rheology modifier, the melt viscosity is significantly reduced under high shear conditions during the injection molding stage, making it easier for carbon nanotubes to disperse and oriented. Under low shear conditions during the holding and cooling stages, the viscosity recovers rapidly, but the viscosity difference between the surface and core layers provides the driving force for carbon nanotube migration.
[0011] Meanwhile, by controlling the molecular weight distribution of ABS and adding a specific amount of nucleating agent, the melt is made to have moderate thixotropy. Thixotropy causes the viscosity of the melt to increase over time under static or low-shear conditions. This time dependence provides a time window for the formation of carbon nanotube gradients: in the early stage of cooling (e.g., 0-5 seconds), the surface temperature drops rapidly, the polarity mismatch effect is enhanced, and carbon nanotubes undergo phase separation and enrichment in the surface region, while the core temperature remains high, and the carbon nanotubes remain dispersed; in the middle and late stages of cooling (e.g., 5-15 seconds), the surface is completely solidified, the core viscosity gradually increases, and the gradient distribution is 'frozen'.
[0012] During the cooling process of the product, the surface temperature drops rapidly, the viscosity rises sharply, and it solidifies quickly, while the core temperature decreases slowly and the viscosity increases more gradually. This spatiotemporal coupling effect of temperature and viscosity results in different dispersion states of carbon nanotubes in the surface and core layers: due to the low temperature and low mixing entropy in the surface layer, the polarity mismatch effect is strong, leading to phase separation and enrichment of carbon nanotubes; while in the core layer, due to the high temperature and high mixing entropy, the polarity mismatch effect is weak, resulting in a more uniform dispersion of carbon nanotubes. As the surface layer rapidly solidifies, this gradient distribution is frozen.
[0013] In some embodiments, the ABS resin has a weight content of not less than 90 wt% in the ABS composite material.
[0014] In some embodiments, the carbon nanotubes are multi-walled carbon nanotubes (MWCNTs) with an outer diameter of 10-20 nm and a length of 10-30 μm.
[0015] The outer diameter was determined by transmission electron microscopy (TEM) with an accelerating voltage of 200 kV. At least 50 well-dispersed carbon nanotubes were randomly selected, and the distance between the outer walls of each tube was measured using image analysis software to calculate the average outer diameter. The TEM sample preparation method was as follows: carbon nanotubes were ultrasonically dispersed in anhydrous ethanol (approximately 0.1 mg / mL, ultrasonic for 20 min), and a drop was placed on a copper grid of a carbon support film. After drying at room temperature, the sample was measured.
[0016] The length was determined by scanning electron microscopy (SEM) with an accelerating voltage of 10-15 kV. At least 50 carbon nanotubes were randomly selected, and the end-to-end distance of each tube was measured to calculate the average length. SEM sample preparation method: The above dispersion was dropped onto a conductive silicon wafer, dried, and then sputtered with gold using an ion sputtering instrument.
[0017] In some embodiments, the content of the double-layer coated carbon nanotubes that can achieve the purpose of the present invention can be any range between 0.8 parts, 1 part, 1.2 parts, 1.4 parts, 1.6 parts, 1.8 parts, 2 parts or more of the component content.
[0018] In some embodiments, the content of the small molecule rheology modifier that enables the present invention to achieve its objective can be any range between 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, or 0.8 parts or more of the component content.
[0019] In some embodiments, the nucleating agent content that enables the present invention to achieve its purpose can be any one of 0.1 parts, 0.15 parts, 0.2 parts, 0.25 parts or 0.3 parts or any range between two of these.
[0020] Preferably, the shear thinning index n of the ABS resin is any one of 0.35, 0.36, 0.37, 0.38, 0.39, 0.4, 0.41, 0.42, 0.43, 0.44 and 0.45 or any range between two of these.
[0021] Preferably, the weight-average molecular weight Mw of the ABS resin is any one of 120,000, 130,000, 140,000, 150,000, 160,000, 170,000 and 180,000 or any range between two of these.
[0022] Preferably, the dispersion Mw / Mn of the ABS resin is any one of 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9 and 4.0 or any range between two of these.
[0023] In some embodiments, the double-layered carbon nanotubes constitute 0.75-1.9% of the mass of the ABS composite material.
[0024] In some embodiments, the mass ratio of NIPAM monomer, acrylic monomer and hydroxyethyl acrylate monomer in the PNIPAM copolymer is (8-12):(1.5-4.2):(0.3-0.8); preferably, the mass ratio is 10:(2.4-4):(0.3-0.8).
[0025] In some embodiments, the PNIPAM copolymer is grafted onto the surface of the carbon nanotubes, and the grafting amount is 30-50 wt% of the mass of the carbon nanotubes.
[0026] Preferably, the grafting amount of the PNIPAM copolymer is any one of 30wt%, 32wt%, 34wt%, 36wt%, 38wt%, 40wt%, 42wt%, 44wt%, 46wt%, 48wt%, and 50wt%, or any range between two of them.
[0027] In some embodiments, the copolymer of the PMMA monomer or SAN monomer is grafted onto the PNIPAM copolymer, and the grafting amount is 10-20 wt% of the mass of the carbon nanotubes.
[0028] Preferably, the grafting amount of the PMMA and / or SAN copolymer is any value within a range of 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, and 20wt%, or any value between both.
[0029] In some embodiments, the small molecule rheology modifier is at least one selected from low molecular weight polyethylene wax, low molecular weight polypropylene wax, glyceryl monostearate, or EBS wax (ethylene bis-stearamide), preferably low molecular weight polyethylene wax and / or low molecular weight polypropylene wax, with Mn of 1400-2500; more preferably, Mn of 1800-2300. The Mn is determined by high-temperature gel permeation chromatography.
[0030] In some embodiments, the nucleating agent is at least one of nano-talc, sorbitol-based nucleating agents (such as dibenzylsorbitol), phosphate ester nucleating agents (such as NA-11), or nano-calcium carbonate, with a D50 particle size of 800-1200 nm. The D50 particle size is determined using a laser particle size analyzer according to the method of standard ISO 13320:2020.
[0031] In some embodiments, the mixture also includes: 0.3-0.5 parts of antioxidant, 0.2-0.4 parts of lubricant, and 0.1-2.5 parts of colorant.
[0032] Preferably, the antioxidant includes at least one of hindered phenolic antioxidants, amine antioxidants, hydroxylamine antioxidants, or benzofuranone antioxidants, or a combination thereof with an auxiliary antioxidant; preferably, it is a hindered phenolic antioxidant, specifically, the hindered phenolic antioxidant may be selected from at least one of antioxidant 1010 (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]), antioxidant 1076 (octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), or antioxidant 264 (2,6-di-tert-butyl-4-methylphenol). The auxiliary antioxidant may be selected from at least one of antioxidant 168 (tris(2,4-di-tert-butylphenyl) phosphite), antioxidant 626 (bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite), antioxidant DLTDP (dilauryl thiodipropionate), or antioxidant DSTDP (distearate thiodipropionate).
[0033] Preferably, the lubricant is selected from at least one of calcium stearate, zinc stearate, magnesium stearate, or pentaerythritol stearate.
[0034] Preferably, the colorant is selected from at least one of titanium dioxide-based white masterbatch, carbon black masterbatch, or organic pigment masterbatch.
[0035] In some embodiments, the preparation steps of the double-layer coated carbon nanotubes are as follows: S1, Functional modification of carbon nanotubes: Carbon nanotubes are oxidized by strong acid to obtain oxidized carbon nanotubes; the oxidized carbon nanotubes are subjected to silanol condensation reaction with an amino-containing silane coupling agent to obtain aminated carbon nanotubes. S2, Surface-grafted PNIPAM copolymer: After dispersing the aminated carbon nanotubes in an organic solvent, a carboxylic acid azo initiator, a carbodiimide condensing agent and a nucleophilic catalyst are added to carry out a coupling reaction, and the carbon nanotubes with surface-fixed initiator are obtained by drying. The carbon nanotubes with the surface-fixed initiator, NIPAM monomer, acrylic monomer and hydroxyl-containing acrylate comonomer are mixed evenly and heated at 65-75°C under an inert atmosphere to carry out an in-situ free radical polymerization reaction to obtain PNIPAM copolymer grafted carbon nanotubes. S3, grafted compatible polymer: After dispersing the PNIPAM copolymer grafted carbon nanotubes in an organic solvent, 2-bromoisobutyryl bromide and an acid-binding agent are added to cause the hydroxyl groups in the PNIPAM copolymer to undergo an esterification reaction with 2-bromoisobutyryl bromide, thereby covalently fixing the ATRP initiating group to the surface of the PNIPAM layer. PNIPAM copolymer grafted with ATRP initiating groups on its surface is dispersed in an organic solvent, and MMA monomer or a mixture of styrene and acrylonitrile and ATRP catalyst are added. Under an inert atmosphere, the reaction is carried out at 85-95°C for 4-6 hours, so that the initiation sites on the surface of the PNIPAM layer initiate ATRP polymerization, thereby connecting PMMA and / or SAN copolymers to the PNIPAM copolymer.
[0036] In some embodiments, in step S1, the strong acid is selected from concentrated sulfuric acid and / or concentrated nitric acid. The amino-containing silane coupling agent is selected from at least one of γ-aminopropyltriethoxysilane (APTES), γ-aminopropyltrimethoxysilane (APTMS), or N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.
[0037] In some embodiments, the mass-to-volume ratio of the PNIPAM copolymer-grafted carbon nanotubes (PNIPAM-CNT) and PMMA monomer or styrene and acrylonitrile mixture is 0.15-0.22 g / mL, which can achieve a grafting amount of PMMA or SAN of 10-20 wt% of the mass of the carbon nanotubes.
[0038] In some embodiments, the mass ratio of the mixture of styrene and acrylonitrile is (6-8):(2-4).
[0039] In some embodiments, in step S2, the carboxylate azo initiator is at least one selected from 4,4'-azobis(4-cyanopentanoic acid) (ACPA), 4,4'-azobis(dimethyl 4-cyanopentanoate), or 2,2'-azobis(2-methylbutyric acid). Preferably, the mass ratio of the carboxylate azo initiator to the aminated carbon nanotube is (0.5-1):1.
[0040] In some embodiments, the carbodiimide condensing agent is selected from at least one of dicyclohexylcarbodiimide (DCC), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC), or diisopropylcarbodiimide (DIC). Preferably, the mass ratio of the carbodiimide condensing agent to the aminated carbon nanotubes is (0.7-1.5):1.
[0041] In some embodiments, the nucleophilic catalyst is selected from at least one of 4-dimethylaminopyridine (DMAP), 4-pyrrolidinylpyridine (PPY), or 1-hydroxybenzotriazole (HOBt). Preferably, the mass ratio of the nucleophilic catalyst to the aminated carbon nanotubes is (0.1-0.3):1.
[0042] In some embodiments, the ATRP catalyst is selected from a complex of CuBr and 2,2'-bipyridine, preferably in a mass ratio of 1:(1.5-3).
[0043] In some embodiments, the acid-binding agent is selected from triethylamine.
[0044] In some embodiments, in step S1, the condensation reaction is carried out at 75-85°C for 10-15 hours. In some embodiments, in step S2, the coupling reaction is carried out at room temperature for 22-26 hours.
[0045] In some embodiments, in step S3, the esterification reaction conditions are: reacting at 0-5°C for 1-2 hours, then heating to room temperature for 2-4 hours.
[0046] This invention provides a method for preparing ABS composite material, comprising the following steps: premixing each component raw material uniformly, melt blending, extrusion granulation, and obtaining the ABS composite material.
[0047] In some embodiments, the melt blending is processed using an extruder, with temperatures from the feed section to the die head of: 165-175°C, 180-190°C, 195-205°C, 205-215°C, 210-220°C, and 205-215°C. The screw speed is 300-450 rpm, and the feed rate is 15-25 kg / h.
[0048] This invention provides an ABS injection molded part with a gradient concentration distribution of carbon nanotubes, which is injection molded using the ABS composite material.
[0049] In some embodiments, injection molding is performed using an injection molding machine, with the following barrel temperatures set: feed section 170-180°C, compression section 185-195°C, metering section 200-210°C, and nozzle 205-215°C. The cavity surface is 75-90°C, and the mold body is 30-50°C, creating a temperature gradient.
[0050] The injection parameters are as follows: injection speed 40-60 mm / s, injection pressure 90-120 MPa, holding pressure 60-80 MPa, holding time 5-10 seconds, and cooling time 15-40 seconds.
[0051] Compared with the prior art, the beneficial effects of the present invention are: This invention provides an ABS composite material in which double-layered carbon nanotubes are added to a specific ABS resin. During the processing and cooling process, the polarity difference between the inner layer of the polar transition polymer and the ABS matrix, as well as the temperature gradient between the surface layer and the core layer, are utilized to cause the carbon nanotubes to preferentially undergo phase separation and enrichment on the surface layer, while maintaining a relatively uniform dispersion in the core layer. This forms a continuous gradient structure of 'high concentration surface layer - low concentration core layer', thereby ensuring mechanical properties with a low amount of carbon nanotubes added, while also meeting the requirements for laser marking on the surface layer. Detailed Implementation
[0052] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.
[0053] The raw materials for the examples and comparative examples are as follows: ABS resin: ABS-1: Shear thinning index n=0.40, weight average molecular weight Mw is 150,000, dispersity Mw / Mn=3.0; produced by Chi Mei Industrial Co., Ltd., grade PA-757K.
[0054] ABS-2: Shear thinning index n=0.38, weight average molecular weight Mw is 160000, dispersity Mw / Mn=3.3; produced by Zhenjiang Chimei Chemical Co., Ltd., grade PA-765A.
[0055] ABS-3: Shear thinning index n=0.42, weight average molecular weight Mw is 140000, dispersity Mw / Mn=2.8; produced by Shanghai Kumho Rili Plastics Co., Ltd., grade 750SW.
[0056] ABS-4: Shear thinning index n=0.30, weight average molecular weight Mw is 180000, dispersity Mw / Mn=3.0; manufactured by LG Chem, grade AF-312.
[0057] ABS-5: Shear thinning index n=0.40, weight average molecular weight Mw is 220000, dispersity Mw / Mn=5.2; produced by Formosa Plastics, grade AG-15A1.
[0058] The shear thinning index test standard for the above-mentioned ABS resin is ISO 11443-2014, with a temperature of 220℃ and a shear rate range of 100. 5000s -1 The weight-average molecular weight Mw was determined by GPC method, using polystyrene as the standard; the dispersity Mw / Mn was determined by GPC method.
[0059] Nucleating agent: Nucleating agent-1: Nano talc powder, D50 particle size 1000 nm, Jiangxi Guangyuan Chemical Co., Ltd., HS-768.
[0060] Nucleating agent-2: Dibenzyl sorbitol nucleating agent, obtained by grinding and screening with a D50 particle size of 900 nm, Milliken Chemical Company, Millad NX8000.
[0061] Rheology modifiers: Rheology Modifier-1: Low molecular weight polyethylene wax, Mn=2000, Honeywell, AC 8A.
[0062] Rheology modifier-2: Low molecular weight polypropylene wax, Mn=2200, Clariant, Licowax PP230.
[0063] Lubricant: Calcium stearate, commercially available.
[0064] Antioxidant: Antioxidant 1010 and Antioxidant 168, in a mass ratio of 1:1.
[0065] Pigment: Titanium dioxide-based white masterbatch, Polymer Polymer (Suzhou) Co., Ltd., OnColor WhiteD9T58865.
[0066] Double-layer coated carbon nanotubes: TRC-CNT-1: PMMA-PNIPAM-CNT, with PNIPAM grafting amount of 40% and PMMA grafting amount of 15%. The mass ratio of NIPAM monomer, acrylic acid monomer and hydroxyethyl acrylate monomer in the PNIPAM is 10:2.5:0.5.
[0067] TRC-CNT-2: PMMA-PNIPAM-CNT, with PNIPAM grafting amount of 45% and PMMA grafting amount of 12%. The mass ratio of NIPAM monomer, acrylic acid monomer and hydroxyethyl acrylate monomer in the PNIPAM is 10:2.5:0.5.
[0068] TRC-CNT-3: PMMA-PNIPAM-CNT, with PNIPAM grafting amount of 35% and PMMA grafting amount of 18%. The mass ratio of NIPAM monomer, acrylic acid monomer and hydroxyethyl acrylate monomer in the PNIPAM is 10:2.5:0.5.
[0069] TRC-CNT-4: SAN-PNIPAM-CNT, with PNIPAM grafting amount of 40% and SAN grafting amount of 15%. The mass ratio of NIPAM monomer, acrylic acid monomer and hydroxyethyl acrylate monomer in the PNIPAM is 10:2.5:0.5.
[0070] TRC-CNT-5: PMMA-PNIPAM-CNT, with PNIPAM grafting amount of 40% and PMMA grafting amount of 15%. The mass ratio of NIPAM monomer, acrylic acid monomer and hydroxyethyl acrylate monomer in the PNIPAM is 10:3:0.5.
[0071] TRC-CNT-6: PMMA-PNIPAM-CNT, with PNIPAM grafting amount of 40% and PMMA grafting amount of 15%. The mass ratio of NIPAM monomer, acrylic acid monomer and hydroxyethyl acrylate monomer in the PNIPAM is 10:4:0.5.
[0072] TRC-CNT-7: PMMA-PNIPAM-CNT, with PNIPAM grafting amount of 40% and PMMA grafting amount of 15%. The mass ratio of NIPAM monomer, acrylic acid monomer and hydroxyethyl acrylate monomer in the PNIPAM is 10:1.5:0.5.
[0073] TRC-CNT-8: PMMA-PNIPAM-CNT, with PNIPAM grafting amount of 40% and PMMA grafting amount of 15%. The PNIPAM does not contain acrylic acid monomers, and the mass ratio of NIPAM monomer to hydroxyethyl acrylate monomer is 10:0.5.
[0074] PNIPAM-CNT: PNIPAM-modified CNT, with PNIPAM grafting amount of 40%.
[0075] PMMA-CNT: Carbon nanotubes grafted with only PMMA (without PNIPAM inner layer), with a PMMA grafting amount of 15%.
[0076] The preparation steps of the TRC-CNT-1 to TRC-CNT-3 bilayer coated carbon nanotubes are as follows: S1, Functionalization of carbon nanotubes: 5.0 g of carbon nanotubes (XFM13 Xianfeng Nano) were added to a mixture of 150 mL of concentrated sulfuric acid and 50 mL of concentrated nitric acid and refluxed at 80 °C for 4 hours to introduce oxygen-containing functional groups such as carboxyl and hydroxyl groups. The product was washed with deionized water until neutral, filtered, and vacuum dried to obtain carbon nanotubes (O-CNT). O-CNT (3.0 g) was dispersed in anhydrous ethanol (200 mL), and APTES (6 mL) was added. The mixture was refluxed at 80 °C for 12 hours. After hydrolysis, the triethoxysilyl groups of APTES underwent a silanol condensation reaction with the hydroxyl groups on the surface of carbon nanotubes to form Si-O covalent bonds, introducing amino groups onto the surface of carbon nanotubes. The product was washed with ethanol, centrifuged, and vacuum dried to obtain aminated carbon nanotubes (NH2-CNT).
[0077] S2, Surface-grafted PNIPAM copolymer inner layer: Aminated carbon nanotubes (NH2-CNT, 2.0 g) were dispersed in anhydrous dichloromethane (150 mL), and 4,4'-azobis(4-cyanopentanoic acid) (ACPA, 1.5 g), condensing agent dicyclohexylcarbodiimide (DCC, 2.0 g), and catalyst 4-dimethylaminopyridine (DMAP, 0.3 g) were added. The reaction was carried out at room temperature for 24 hours, so that the carboxyl group (-COOH) in ACPA molecule reacted with the amino group (-NH2) on the surface of carbon nanotube to form amide bond (-CO-NH-), thereby covalently bonding the azo initiator to the surface of carbon nanotube. The product was washed with dichloromethane and methanol, and vacuum dried to obtain carbon nanotubes (ACPA-CNT) with surface-fixed initiator.
[0078] ACPA-CNT (1.5 g) was dispersed in deionized water (300 mL), and NIPAM monomer (10.0 g) and the formulated amounts of acrylic acid and hydroxyethyl acrylate (mass ratio 10:2.5:0.5) were added. Acrylic acid was used to adjust the polarity and chain segment flexibility of the polymer inner layer, while hydroxyethyl acrylate provided hydroxyl sites for subsequent grafting reactions. Under nitrogen protection, the mixture was heated to 70 °C. The azo groups on the surface of the carbon nanotubes decomposed to generate free radicals, which initiated free radical polymerization of NIPAM and the comonomer in situ on the surface, forming a covalently bonded PNIPAM shell. The reaction lasted 6-12 hours. The polymerization reaction started from the initiation sites on the carbon nanotube surface, and the polymer chains were connected to the carbon nanotubes through covalent bonds. The polymer chains did not detach after washing, yielding PNIPAM-CNT. By adjusting the amount of NIPAM monomer added and the polymerization reaction time, the grafting amount of PNIPAM could be adjusted within the range of 30% to 50%.
[0079] The grafting amount of PNIPAM was determined by thermogravimetric analysis (TGA) according to ASTM E1131-20. The test conditions were: nitrogen atmosphere, heating rate of 10℃ / min, temperature range of 25-800℃. The grafting amount was calculated from the polymer decomposition weight loss.
[0080] S3, outer layer grafted with compatible polymer: S3a, Immobilization of ATRP initiating groups: PNIPAM-CNT (1.5 g) was dispersed in anhydrous tetrahydrofuran (100 mL), and triethylamine (0.8 mL) was added. 2-bromoisobutyryl bromide (0.5 mL) was slowly added dropwise under ice bath conditions (0-5 °C). After the addition was complete, the reaction was carried out at 0-5 °C for 1 h, and then the temperature was raised to room temperature for another 3 h. This allowed the hydroxyl groups (-OH) of the hydroxyethyl acrylate copolymer units in the PNIPAM copolymer to undergo an acylation reaction with 2-bromoisobutyryl bromide, forming ester bonds (-O-CO-C(CH3)2Br), thereby introducing ATRP initiating groups onto the surface of the PNIPAM layer. The product was washed with tetrahydrofuran and methanol, and then vacuum dried to obtain PNIPAM-CNT (BiBB-PNIPAM-CNT) with surface-immobilized ATRP initiating groups.
[0081] S3b, Surface-Initiated ATRP Polymerization: BiBB-PNIPAM-CNT (1.5 g) was dispersed in anhydrous toluene (100 mL), and MMA monomer (8 mL), CuBr (0.08 g), and 2,2'-bipyridine (0.15 g) were added. Under nitrogen protection, the reaction was carried out at 90 °C for 5 hours. MMA initiated controlled polymerization from the ATRP initiation sites on the surface of the PNIPAM layer, forming a covalently grafted thin PMMA layer (number average molecular weight Mn = 5000-8000, thickness 3-6 nm). The product was washed with toluene and methanol and dried under vacuum to obtain TRC-CNT (PMMA-PNIPAM-CNT). By adjusting the amount of MMA monomer added and the polymerization reaction time, the amount of PMMA grafted can be adjusted within the range of 10% to 20%.
[0082] The amount of PMMA grafted was determined by thermogravimetric analysis (TGA). The thickness was directly observed and determined by high-resolution transmission electron microscopy (HRTEM); the number-average molecular weight (Mn) was determined by collecting the free homopolymer generated simultaneously in the reaction system and performing gel permeation chromatography (GPC).
[0083] The preparation method of the TRC-CNT-4 bilayer coated carbon nanotubes differs from that of the TRC-CNT-1 only in that, in step S3b, the MMA monomer (8 mL) is replaced with an equal volume of a mixture of styrene and acrylonitrile (mass ratio 7:3).
[0084] The preparation method of TRC-CNT-5 differs from that of TRC-CNT-1 only in that, in step S2, the mass ratio of NIPAM monomer, acrylic monomer and hydroxyethyl acrylate monomer is adjusted to 10:3:0.5.
[0085] The only difference between the preparation method of TRC-CNT-6 and the preparation method of TRC-CNT-1 is that in step S2, the mass ratio of NIPAM monomer, acrylic acid monomer and hydroxyethyl acrylate monomer is adjusted to 10:4:0.5.
[0086] The preparation method of TRC-CNT-7 differs from that of TRC-CNT-1 only in that, in step S2, the mass ratio of NIPAM monomer, acrylic monomer and hydroxyethyl acrylate monomer is adjusted to 10:1.5:0.5.
[0087] The preparation method of TRC-CNT-8 differs from that of TRC-CNT-1 in that: in step S2, no acrylic acid monomer is added, and only NIPAM monomer and hydroxyethyl acrylate monomer (mass ratio 10:0.5) are copolymerized.
[0088] The preparation method of PNIPAM-CNT differs from that of TRC-CNT-1 in that it only performs steps S1 and S2, without performing step S3 (i.e. without grafting a compatible polymer outer layer), and directly obtains PNIPAM copolymer-grafted carbon nanotubes (PNIPAM-CNT).
[0089] The preparation method of the PMMA-CNT includes the following steps: S1, the preparation of aminated carbon nanotubes (NH2-CNT) is the same as step S1 in the preparation method of TRC-CNT-1; S2, grafted compatible polymer outer layer; Specifically, NH2-CNT (2.0 g) was dispersed in anhydrous tetrahydrofuran (100 mL), and triethylamine (0.8 mL) was added. 2-bromoisobutyryl bromide (0.5 mL) was slowly added dropwise under ice bath conditions (0-5 °C). After the addition was complete, the reaction was continued at 0-5 °C for 1 h, and then the temperature was raised to room temperature for another 3 h. This allowed the amino groups on the surface of the carbon nanotubes to react with 2-bromoisobutyryl bromide, forming amide bonds and introducing ATRP initiating groups. The product was washed with tetrahydrofuran and methanol, and then vacuum dried to obtain carbon nanotubes with ATRP initiating groups fixed on the surface. Then, 1.5 g of this product was dispersed in anhydrous toluene (100 mL), and MMA monomer (8 mL), CuBr (0.08 g), and 2,2'-bipyridine (0.15 g) were added. The reaction was carried out at 90 °C for 5 h under nitrogen protection to obtain PMMA-CNT.
[0090] The following examples and comparative examples illustrate the preparation method of ABS composite materials, which includes the following steps: premixing each component raw material in a high-speed mixer for 15 minutes at a speed of 1000 rpm and a mixing temperature controlled at 70°C until the premixing is uniform; adding the premixed material to a twin-screw extruder for melt blending and extrusion granulation to obtain the ABS composite material.
[0091] The temperature range of the twin-screw extruder from the feed section to the die head is: 170℃, 185℃, 200℃, 210℃, 215℃, 210℃. The screw speed is 375 rpm, and the feeding rate is 20 kg / h.
[0092] The following examples and comparative examples of ABS injection molded parts with gradient carbon nanotube concentration distributions were injection molded using the aforementioned ABS composite material. Specifically, the above-mentioned granules were added to the hopper of the injection molding machine and plasticized in the barrel; the barrel temperatures were set sequentially as follows: 170℃, 185℃, 200℃, 210℃, 205℃; the cavity surface was 80℃, and the mold body was 40℃, forming a temperature gradient. The injection speed was 50 mm / s, the injection pressure was 100 MPa, the holding pressure was 70 MPa, the holding time was 8 seconds, and the cooling time was 25 seconds.
[0093] Examples 1-14 This embodiment provides a series of ABS composite materials, the components of which are shown in Table 1 by mass.
[0094] Table 1
[0095] Comparative Examples 1-5 This comparative example provides a series of ABS composite materials, the components of which are shown in Table 2 by mass parts.
[0096] Table 2
[0097] Performance testing The ABS composite materials of the above embodiments and comparative examples were injection molded into standard test plates with a thickness of 3 mm, and the following performance tests were conducted. The structures are shown in Table 3.
[0098] 1. Gradient structure representation: ABS composite material was injection molded into 3 mm thick strips, which were then cut along their thickness direction. Ultrathin sections with a width of 70-100 nm were prepared using an ultrathin slicer. The distribution of TRC-CNTs was observed using a transmission electron microscope (accelerating voltage 200 kV). The carbon nanotubes appeared dark due to their high electron density.
[0099] Specifically, 10 fields of view were selected in each of the surface layer, transition layer, and core layer. The number density of TRC-CNTs was statistically analyzed using image analysis software and converted into the density gradient ratio of the surface layer, transition layer, and core layer. The surface layer is the region 0-0.2 mm from the surface of the product; the transition layer is the region 0.2-0.8 mm from the surface; and the core layer is the central region 0.8-1.5 mm from the surface.
[0100] 2. Laser marking performance test: The test conditions were as follows: Laser: 1064 nm fiber laser, power 20 W, frequency 20 kHz, scanning speed 1000 mm / s.
[0101] Laser marking contrast measurement: Use a colorimeter to measure the L* value of the laser marking area and the background area. Contrast = L*marking / L*background.
[0102] Line width measurement: Using an optical microscope and image analysis software, 20 points are randomly measured along the laser line, and the average line width and standard deviation are calculated.
[0103] 3. Mechanical property testing: Tensile strength: Refer to standard ISO 527-2:2012, tensile speed 50 mm / min.
[0104] Notched impact strength: Refer to standard ISO 179-1:2010, type A notch.
[0105] Table 3
[0106] The results show that the ABS composite material of the present invention can form a continuous gradient structure of "high concentration surface layer - low concentration core layer", ensuring mechanical properties with low carbon nanotube addition, while meeting the requirements of surface laser marking. Specifically, its laser marking contrast is ≥5.8, linewidth deviation is ≤2.5μm, tensile strength is ≥54.5MPa, impact strength is ≥23.6kJ / m², and the concentration gradient ratio is (5.2-6.9):(2.1-3.2):1.
[0107] As can be seen from Examples 1 and 7-9, the PNIPAM polar transition polymer inner layer prepared with a specific concentration of acrylic monomer is beneficial to the concentration gradient ratio and enhances the contrast of laser marking. Compared with Example 1, when Comparative Examples 1-2 used ABS resin with a lower shear thinning index or ABS resin with excessive dispersion, the concentration gradient ratio decreased, and effective migration and enrichment of carbon nanotubes in the surface region were not achieved. This resulted in low contrast of laser marking, large linewidth deviation, and poor mechanical properties.
[0108] In Comparative Example 3, TRC-CNT-8 without acrylic units was used. Due to the lack of carboxyl groups provided by acrylic units in the PNIPAM copolymer, the polarity of the polar transition layer was insufficient, relying only on the hydroxyl groups of hydroxyethyl acrylate. The polarity difference between the polar transition layer and the ABS matrix was small, resulting in insufficient enthalpy-driven phase separation during cooling. Only a weak carbon nanotube gradient distribution (gradient ratio of 1.5:1.2:1) was formed, leading to poor laser marking effect and mechanical properties.
[0109] Comparative Example 4's carbon nanotubes lacked a PMMA or SAN compatible polymer outer layer. Due to the lack of a compatible outer layer matching the ABS matrix, the carbon nanotubes exhibited poor dispersibility and severe agglomeration during the melt blending stage. Although the polarity difference of the inner layer of the PNIPAM copolymer still caused the carbon nanotube agglomerates to show a certain surface migration trend (concentration gradient ratio 2.5:1.5:1), the resulting agglomerates formed a gradient distribution of micron-sized agglomerates rather than a uniform gradient distribution of individual nanotubes. This uneven distribution of agglomerates on the surface led to drastic fluctuations in the carbon nanotube concentration in the laser-treated area, and the agglomerates, acting as stress concentration points, severely weakened the mechanical properties.
[0110] Comparative Example 5 uses modified carbon nanotubes with only a PMMA outer layer (without a PNIPAM polar transition inner layer). Although the PMMA layer provides good compatibility with the ABS matrix, resulting in good dispersion of carbon nanotubes during the melt blending stage, the lack of a polar transition inner layer means there is no driving force for migration to the surface during cooling. As a result, the carbon nanotubes are uniformly dispersed (gradient ratio 1.1:1.0:1), leading to poor laser marking effect and mechanical properties.
[0111] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.
Claims
1. An ABS composite material, characterized by, Includes the following components by mass: 100 parts of ABS resin 0.8–2.0 parts of double-layer coated carbon nanotubes, 0.3–0.8 parts of small molecule rheology modifier, Nucleating agent 0.1–0.3 parts, The ABS resin has a shear thinning index n = 0.35-0.45, a weight-average molecular weight Mw of 120,000-180,000, and a dispersity Mw / Mn = 2.5-4.
0. The double-layer coated carbon nanotubes comprise a carbon nanotube, a polar transition polymer inner layer, and a compatible polymer outer layer, which are sequentially coated. The polar transition polymer inner layer is a PNIPAM copolymer containing NIPAM units, acrylic units, and hydroxyl-containing acrylate units. The compatible polymer outer layer is a PMMA and / or SAN copolymer.
2. The ABS composite material as described in claim 1, characterized in that, The mass ratio of NIPAM monomer, acrylic monomer and hydroxyethyl acrylate monomer in the PNIPAM copolymer is (8-12):(1.5-4.2):(0.3-0.8), preferably 10:(2.4-4):(0.3-0.8).
3. The ABS composite material as described in claim 1, characterized in that, The PNIPAM copolymer is grafted onto the surface of the carbon nanotubes, and the grafting amount is 30-50 wt% of the mass of the carbon nanotubes; and / or, The PMMA and / or SAN copolymer is grafted onto the PNIPAM copolymer, and the grafting amount is 10-20 wt% of the mass of the carbon nanotubes.
4. The ABS composite material as described in claim 1, characterized in that, The small molecule rheology modifier is at least one of low molecular weight polyethylene wax, low molecular weight polypropylene wax, glyceryl monostearate, and EBS wax.
5. The ABS composite material as described in claim 1, characterized in that, The nucleating agent is at least one of nano-talc, sorbitol-based nucleating agents, phosphate ester nucleating agents, and nano-calcium carbonate.
6. The ABS composite material as described in claim 1, characterized in that, Also includes: Antioxidant 0.3-0.5 parts, lubricant 0.2-0.4 parts, colorant 0.1-2.5 parts.
7. The ABS composite material as described in claim 1, characterized in that, The preparation steps of the double-layer coated carbon nanotubes are as follows: S1, Functional modification of carbon nanotubes: Carbon nanotubes are oxidized by strong acid to obtain oxidized carbon nanotubes; The carbon nanotubes were subjected to a silanol condensation reaction with an amino-containing silane coupling agent to obtain amino-modified carbon nanotubes. S2, Surface-grafted PNIPAM copolymer: After dispersing the aminated carbon nanotubes in an organic solvent, a carboxylic acid azo initiator, a carbodiimide condensing agent and a nucleophilic catalyst are added to carry out a coupling reaction, and the carbon nanotubes with surface-fixed initiator are obtained by drying. The carbon nanotubes with the surface-fixed initiator, NIPAM monomer, acrylic monomer and hydroxyl-containing acrylate comonomer are mixed evenly and heated at 65-75°C for 6-12 hours under an inert atmosphere to obtain PNIPAM copolymer grafted carbon nanotubes. S3, grafted compatible polymer: After dispersing the PNIPAM copolymer grafted carbon nanotubes in an organic solvent, 2-bromoisobutyryl bromide and an acid-binding agent are added to cause the hydroxyl groups in the PNIPAM copolymer to undergo an esterification reaction with 2-bromoisobutyryl bromide, thereby covalently fixing the ATRP initiating groups to the surface of the PNIPAM layer. PNIPAM copolymer grafted with ATRP initiating groups on its surface is dispersed in an organic solvent, and MMA monomer or a mixture of styrene and acrylonitrile and ATRP catalyst are added. Under an inert atmosphere, the reaction is carried out at 85-95°C for 4-6 hours to initiate ATRP polymerization at the initiation sites on the surface of the PNIPAM layer, thereby connecting PMMA and / or SAN copolymers to the PNIPAM copolymer.
8. The ABS composite material as described in claim 7, characterized in that, In step S1, the conditions for the condensation reaction are: reaction at 75-85℃ for 10-15 hours; In step S2, the coupling reaction conditions are: reaction at room temperature for 22-26 hours; In step S3, the esterification reaction conditions are as follows: react at 0-5℃ for 1-2 hours, then raise the temperature to room temperature and react for 2-4 hours.
9. A method for preparing the ABS composite material according to any one of claims 1-8, characterized in that, The process includes the following steps: premixing each component raw material evenly, melt blending, extrusion granulation, and obtaining the ABS composite material.
10. An ABS injection molded part with a gradient concentration distribution of carbon nanotubes, characterized in that, Injection molding using the ABS composite material described in any one of claims 1-8.