Study of the synergistic effect of boron nitride and carbon nanotubes in the improvement of thermal conductivity of epoxy composites

The enhancement of the thermal conductivity, keeping the electrical insulation, of epoxy thermosets through the addition of pristine and oxidized carbon nanotubes (CNTs) and microplatelets of boron nitride (BN) was studied. Two different epoxy resins were selected: a cycloaliphatic (ECC) epoxy resin and a glycidylic (DGEBA) epoxy resin. The characteristics of the composites prepared were evaluated and compared in terms of thermal, thermomechanical, rheological and electrical properties. Two different dispersion methods were used in the addition of pristine and oxidized CNTs depending on the type of epoxy resin used. Slight changes in the kinetics of the curing reaction were observed in the presence of the fillers. The addition of pristine CNTs led to a greater enhancement of the mechanical properties of the ECC composite whereas the oxidized CNTs presented a greater effect in the DGEBA matrix. The addition of CNTs alone led to a marked decrease of the electrical resistivity of the composites. Nevertheless, in the presence of BN, which is an electrically insulating material, it was possible to increase the proportion of pristine CNTs to 0.25 wt% in the formulation without deterioration of the electrical resistivity. A small but significant synergic effect was determined when both fillers were added together. Improvements of about 750% and 400% in thermal conductivity were obtained in comparison to the neat epoxy matrix for the ECC and DGEBA composites, respectively. © 2019 Society of Chemical Industry     

Preparation of liquid crystal 4'‐allyloxy‐biphenyl‐4‐ol functionalized MWCNTs and their application on improving mechanical and thermal properties of silicon resin

A liquid crystalline molecule, 4'‐allyloxy‐biphenyl‐4‐ol (AOBPO), was used to functionalize carbon nanotubers (CNTs) via physical means and chemical means, respectively. The physically functionalized CNTs (AOBPO‐CNTs) and chemically functionalized CNTs (AOBPO‐O‐CNTs) were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), fluorescent spectroscopy, and Raman spectroscopy. The two functionalized CNTs were mixed with silicone resin as fillers to fabricate organosilicone nanocomposites. Scanning electron microscopy (SEM) images indicated that the dispersion of CNTs in silicone resin and compatibility of CNTs with silicone resin were improved effectively after functionalization with liquid crystal via physical or chemical means. The thermal and mechanical properties testing indicated that, the chemically functionalized CNTs got a better effect in improvement of mechanical properties of silicon resin than the physically functionalized CNTs, whereas the physically functionalized CNTs was more applicable to enhance the thermal conductivity of silicon resin. The tensile strength of AOBPO‐O‐CNTs/silicon resin increased by 37.8% over that of neat CNTs/silicon resin when the mass fraction of AOBPO‐O‐CNTs was 1.0%, and the elastic modulus of AOBPO‐O‐CNTs/silicon resin increased by 32.8% over that of CNTs/silicon resin if it came up to 2.0%. The thermal conductivity of the resin filled with AOBPO‐CNTs was improved to be 1.176 W (m^?1 K^?1) at the mass fraction of 5.0%, which was enhanced more than 73.2% over that of CNTs/silicon resin. POLYM. ENG. SCI., 56:1118–1124, 2016. © 2016 Society of Plastics Engineers     

Manipulating matrices

Chemical resistance, high temperature capability, low emissions, high quality surface finish — fabricators of composite products may require many different features from the resins they use, depending on the application of the final product. George Marsh on the latest developments in resin and gel-coat technology.     

Cure study of epoxy resin reinforced with multiwalled carbon nanotubes by Raman and luminescence spectroscopy

Carbon nanotubes (CNTs) were annealed at high temperature under vacuum, followed by a chemical treatment using acids and ethylenediamine. The presence of acid and amine chemical groups on CNT surface was confirmed by infrared spectra. The amount of iron remaining in the CNTs after the treatments was evaluated by thermogravimetry and by energy dispersion spectroscopy. The crystalline property of CNTs was evaluated by Raman spectroscopy, showing that the acid treatment performed after the thermal treatment did not damage the nanotubes walls. Micrographs showed that the most dispersed CNTs were obtained after the amine functionalization step. The curing process of the neat resin and composites was studied by Raman and Luminescence spectroscopies and both techniques showed similar results. The presence of CNTs, functionalized or not, increased the cure degree of the epoxy resin when the same cure time was used in the comparison. Nanocomposites synthesized with annealed CNT and acid‐treated CNT had cure rates considerably higher at the beginning of the reaction. The difference in the cure rate was explained by means of the sample's homogeneity and the presence of chemical groups. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

碳纳米管改性填料对氟碳涂料性能的影响

采用混合酸和表面活性剂对碳纳米管表面进行改性处理,利用改性碳纳米管与不同的填料构造复合填料,并与FEVE氟碳树脂合成了碳纳米管改性复合氟碳材料,并将其涂覆在陶瓷基底上形成氟碳涂层。采用红外光谱（FTIR）对表面改性后的碳纳米管进行了表征分析,用扫描电镜（SEM）、接触角测量仪等仪器观察和测试了纳米复合氟碳涂层表面的微观结构及疏水性。研究结果表明：用混合酸和表面活性剂改性碳纳米管,碳纳米管的缠绕、团聚现象得到明显的改善,提高了其在氟碳树脂体系中的分散性能;当改性碳纳米管的量为0.75 g时,涂层的憎水性能较好。     

碳纳米管／环氧耐热复合材料性能研究

研究了碳纳米管／环氧树脂复合材料电性能、热氧老化性能和粘接性能。研究结果表明：添加量为2％时,复合材料的综合性能最优,表面电阻率和体积电阻率分别下降了9—10个数量级,剪切强度提高了12．33％,当老化时间达到200h,复合材料重量保持率仍有90％。制得的复合材料能够用于耐热胶粘剂和防静电材料。     

The effect of carbon nanotubes on the rheology and electrical resistivity of polyamide 12/high density polyethylene blends

Different melt mixing sequences were applied to incorporate multiwalled carbon nanotubes (CNTs) into blends prepared from high density polyethylene (PE) and polyamide 12 (PA). Electron microscopy, rheology and electrical resistivity were used to characterize the morphology and microstructure. At a composition of 75PA/25PE, presence of CNT at the interface promoted by premixing the CNTs in the PE phase, resulted in finer phase morphology and a decrease in the resistivity of up to five decades relative to other mixing procedures used. At a composition of 25PA/75PE, premixing the CNT in the PA phase resulted in their segregation inside and around the PA domains and a four decade lower resistivity. Interestingly, compounds that yielded the lowest resistivity were also characterized by increased low frequency melt storage modulus (G′) which indicates the existence of a correlation between the two properties.     

Decoration of multi-walled carbon nanotubes by polymer wrapping and its application in MWCNT/polyethylene composites

ABSTRACT: We dispersed the non-covalent functionalization of multi-walled carbon nanotubes (CNTs) with a polymer dispersant and obtained a powder of polymer-wrapped CNTs. The UV-vis absorption spectrum was used to investigate the optimal weight ratio of the CNTs and polymer dispersant. The powder of polymer-wrapped CNTs had improved the drawbacks of CNTs of being lightweight and difficult to process, and it can re-disperse in a solvent. Then, we blended the polymer-wrapped CNTs and polyethylene (PE) by melt-mixing and produced a conductive masterbatch and CNT/PE composites. The polymer-wrapped CNTs showed lower surface resistivity in composites than the raw CNTs. The scanning electron microscopy images also showed that the polymer-wrapped CNTs can disperse well in composites than the raw CNTs.     

纳米改性碳/酚醛树脂基复合材料性能研究

针对碳/酚醛树脂基复合材料层间剪切强度低的缺点,采用纳米填料进行改性。测试了2种纳米填料(纳米碳纤维、碳纳米管)改性后酚醛树脂的热解性能,研究了纳米填料对复合材料力学性能、烧蚀性能以及高温炭化后力学性能的影响,并观察分析了复合材料测试后的微观形貌。研究结果表明,纳米填料改性后,复合材料的力学性能、烧蚀性能均有所改善。其中,纳米碳纤维改性后复合材料的常温层间剪切强度达到24.9 MPa,氧乙炔线烧蚀率为22.75μm/s,质量烧蚀率为23.58 mg/s。纳米碳纤维表面粗糙,与树脂基体的界面强度高,因此其改性后的力学性能和烧蚀性能优于碳纳米管。     

Fabrication and electromagnetic interference shielding effectiveness of carbon nanotube reinforced carbon fiber/pyrolytic carbon composites

Carbon nanotube reinforced carbon fiber/pyrolytic carbon composites were fabricated by precursor infiltration and pyrolysis method and their electromagnetic interference shielding effectiveness (EMI SE) was investigated over the frequency range of 8.2–12.4 GHz (X-band). Carbon nanotubes (CNTs) were in situ formed through catalyzing hydrocarbon gases evaporating out of phenolic resin with nano-scaled Ni particles. The content of CNTs increased with the increase of Ni loadings (0.00, 0.50, 0.75 and 1.25 wt.%) in phenolic resin. Thermal gravimetrical analysis results showed that the carbon yield of phenolic resin increased with the addition of Ni catalyst. With the formation of CNTs, the EMI SE increased from 28.3 to 75.2 dB in X-band. The composite containing 5.0 wt.% CNTs showed an SE higher than 70 dB in the whole X-band.     

Effect of carbon nano-tubes on the corrosion resistance of alkyd coating immersed in sodium chloride solution

Effect of carbon nano-tubes (CNTs) on corrosion protection of carbon steel coated by alkyd resin and tested after immersion in 3.5% NaCl solution for different periods was evaluated by electrochemical impedance spectroscopy (EIS) measurements and scanning electron microscopy (SEM) investigations. Changes in the impedance characteristics of the systems were found to be greatly affected by the percentage of CNTs. Degradation of alkyd resin film without CNTs was observed after 72 h. On other hand no blisters, pin-holes and delamination were observed for alkyd resin containing 0.5% CNTs. It was found that CNTs improved the corrosion resistance and the adhesion strength of alkyd resin.     

Effect of deposited carbon nanotubes on interlaminar properties of carbon fiber‐reinforced epoxy composites using a developed spraying processing

Carbon fiber‐reinforced epoxy composites, with incorporated carboxylic multiwall carbon nanotubes (CNTs), were prepared using vacuum‐assisted resin infusion (VARI) molding, and the in‐plane and out‐of‐plane properties, including mode‐I (G_Ic) and mode‐II (G_IIc) interlaminar fracture toughness, interlaminar shear strength (ILSS), tensile, and flexural properties were measured. A novel spraying technique, which sprays a kind of epoxy resin E20 with high viscosity after spraying the CNTs, was adopted to deposit the CNTs on the surface of carbon fiber fabric. The E20 was used to anchor CNTs on the fabric surface, avoiding that the deposited CNTs were removed by the infusing resin during VARI process. The spraying processing, including spraying amount and spraying sequence, was optimized based on the distribution of CNTs on the fibers. After that, three composite specimen groups were fabricated using different carbon fiber fabrics, including as‐received, CNT‐deposited with E20, and CNT‐deposited without E20. The effects of CNTs on the processing quality and mechanical properties of carbon fiber‐reinforced polymer composites were studied. The experimental results show that all studied laminates have uniform thickness with designed values and no obvious defects form inside the laminates. Compared with the composite without CNTs, depositing CNTs with E20 increases by 24% in the average propagation G_Ic, by 11% in the propagation G_IIc and by 12% in the ILSS, while it preserves the in‐plane mechanical properties, However, depositing CNTs without E20 reduces interlaminar fracture toughness. These phenomena are attributed to the differences in the distribution of CNTs and the fiber/matrix interfacial bonding for different spraying processing. POLYM. COMPOS., 2013. © 2012 Society of Plastics Engineers     

Electrical and thermal conductivity and tensile and flexural properties of carbon nanotube/polycarbonate resins

Adding conductive carbon fillers to insulating thermoplastic polymers increases the resulting composite's electrical conductivity. Carbon nanotubes (CNTs) are very effective at increasing composite electrical conductivity at low loading levels without compromising composite tensile and flexural properties. In this study, varying amounts (2–8 wt %) of CNTs were added to polycarbonate (PC) by melt compounding, and the resulting composites were tested for electrical conductivity (1/electrical resistivity), thermal conductivity, and tensile and flexural properties. The percolation threshold was less than 1.4 vol % CNT, likely because of CNTs high aspect ratio (1000). The addition of CNT to PC increased the composite electrical and thermal conductivity and tensile and flexural modulus. The 6 wt % (4.2 vol %) CNT in PC resin had a good combination of properties for electrical conductivity applications. The electrical resistivity and thermal conductivity were 18 Ω‐cm and 0.28 W/m · K, respectively. The tensile modulus, ultimate tensile strength (UTS), and strain at UTS were 2.7 GPa, 56 MPa, and 2.8%, respectively. The flexural modulus, ultimate flexural strength, and strain at ultimate flexural strength were 3.6 GPa, 125 MPa, and 5.5%, respectively. Ductile tensile behavior is noted in pure PC and in samples containing up to 6 wt % CNT. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Improvements in the thermal conductivity and mechanical properties of phase‐change microcapsules with oxygen‐plasma‐modified multiwalled carbon nanotubes

The thermal properties and mechanical properties are the key factors of phase‐change microcapsules (microPCMs) in energy‐storage applications. In this study, microPCMs based on an n‐octadecane (C18) core and a melamine–urea–formaldehyde (MUF) shell supplemented with O₂‐plasma‐modified multiwalled carbon nanotubes (CNTs) were synthesized through in situ polymerization. Meanwhile, two different addition methods, the addition of modified CNTs into the emulsion system or into the polymer system, were compared and examined. Scanning electron microscopy micrographs showed that the microPCMs were spherical and had a broadened size distribution. Fourier transform infrared testing demonstrated that the modified CNTs did not affect C18 coated by MUF resin. The results indicate that the thermal conductivity and mechanical properties of the microPCMs were remarkably improved by the addition of a moderate amount of modified CNTs, but the heat enthalpy and encapsulated efficiency decreased slightly. Moreover, the thermal conductivity and mechanical properties of microPCMs modified with CNTs directly added to the polymer system were superior to those with CNTs added to emulsion system. In particular, when 0.2 g of modified CNTs were added to the polymer system, the thermal conductivity of the microPCMs was improved by 225%, and the breakage rates of the microPCMs at 4000 rpm for 5, 10, and 20 min decreased by 74, 72, and 60%, respectively, compared with that of the microPCMs without modified CNTs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45269.     

The sonication effect on CNT‐epoxy composites finally clarified

Carbon nanotube‐epoxy composites were prepared using amino‐functionalized CNTs and sonication as a mixing process. Different times and sonication powers were used for preparing composites in order to study how the sonication process may influence the curing reaction of both systems: neat epoxy resin and amino‐CNT/epoxy composite.The curing reaction was investigated with differential scanning calorimetry and the results were associated with analysis of gel permeation chromatography. The results showed that the effect of CNTs on the cure behavior of the epoxy resin depends on the sonication power. The sonication of neat resin with a 150 W powered device led to a molar mass reduction of the resin and an increase in the cure enthalpy. The CNT addition to this system reduced the cure enthalpy. However, when neat epoxy resin was sonicated with a 200 W powered device, the molar mass did not decrease (i.e., it was increased or was not changed) and the cure enthalpy did not increase (essentially it decreased or did not change). The CNT addition to such solutions did not reduce (i.e., it was increased or did not change) the cure enthalpy, which is a contrary result from that obtained with a 150 W powered device. POLYM. COMPOS., 38:1964–1973, 2017. © 2015 Society of Plastics Engineers     

Electrical Properties of an Ultralight Conductive Carbon Nanotube/Polymer Composite Foam Upon Compression

The variations of electrical property of an ultralight conductive carbon nanotube/polymer composite foam upon compression were investigated. It was found the sharp increase of volume resistivity and strain was generated by the same microstructural change, i.e., the damage of foam struts. Even the strain was increased to as high as 50%, the ultimate resistivity remained stable. Volume resistivity of the foam kept almost changeless under an invariant external mechanical field. The stable microstructure of the conductive network formed by contact of CNTs and the high endurance of samples' core regions endow the ultralight conductive foam with much stable electrical properties.     

酚醛树脂/混酸处理碳纳米管复合材料的制备与性能

本文对碳纳米管进行了酸氧化处理,并对酸氧化处理前后碳纳米管进行了红外和扫描电镜分析,发现酸氧化处理后的碳纳米管变疏松了,杂质也被有效地去除,并且在碳纳米管上引入了羧酸基、羟基等基团。采用溶液聚合法合成了酸氧化碳纳米管改性的酚醛树脂,采用FT-IR对树脂结构进行了表征,复合材料的冲击强度、剪切强度都呈现先增加后降低的趋势,当酸氧化碳纳米管含量为1.5 wt.%时,复合材料的冲击强度、剪切强度最大,分别为271KJ•m-2、72MPa,比改性前分别提高了41KJ•m-2、17MPa。     

碳纳米管的分散及其对酚醛树脂热性能的影响

利用机械分散与化学分散相结合的方法将碳纳米管(CNTs)在酚醛树脂(PF)溶液中进行分散,用透射电子显微镜对分散后的CNTs微观形态进行观察,利用表面张力和粘度对分散效果进行表征。结果表明,利用机械分散和化学分散相结合的方法能够对CNTs进行有效分散;随着分散时间的延长,分散效果趋于平稳。加入合适的表面活性剂可以降低分散体系的表面张力和粘度,提高分散效果;表面活性剂A对CNTs的分散效果最好。热性能分析表明,加入一定量的CNTs能够提高PF/CNTs体系的热性能。     

Effect of electrochemical anodization and growth time on continuous growth of carbon nanotubes on carbon fiber surface

Carbon nanotubes (CNTs)/carbon fiber (CF) reinforcements were prepared by chemical vapor deposition after electrochemical anodization and catalyst impregnation. The results showed that after the electrochemical anodization, the CFs were oxidatively etched and the surface roughness increased, which is helpful to form a uniform catalyst coating on the surface of CF. Under the current of 0.4 A and 0.6 A, CNTs can grow evenly on the surface of CF. Within a certain range, with the increase of growth time, the density and length of CNTs are improved. The CNTs/CF reinforcement prepared at the current intensity of 0.4 A and the growth time of 8 min has the best comprehensive performances compared with other as-fabricated samples. The tensile strength of the sample can reach a high value of 4.56 GPa, and the wettability of resin has an effective improvement.     

Structure and properties of polypropylene‐wrapped carbon nanotubes composite

By means of in situ graft method, polypropylene (PP)‐wrapped carbon nanotubes (CNTs) composite were prepared. Infrared spectroscopy (IR) results showed that there was covalent linkage between PP and CNTs via maleic anhydride (MAH) grafting. Owing to the uniform dispersion of CNTs and covalent adhesion between PP and CNTs, the tensile strength of PP‐wrapped CNTs composite was higher than that for neat PP by 110%, and a 74% increase as compared to the CNTs/PP (with the same CNTs content) composite. The further test showed a strong mechanical behavior with up to 113% increase in Young's modulus of the neat PP. Based on the uniform dispersion of CNTs, the electrical conductivity of PP‐wrapped CNTs composite increased sharply by up to seven orders of magnitude with 4 wt % CNT fillers. As a result, the volume resistivity was decreased with increase in the CNT content that could be governed in a percolation‐like power law with a relatively low percolation threshold. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009