Preparation of polyimide/siloxane‐functionalized graphene oxide composite films with high mechanical properties and thermal stability via in situ polymerization

An effective approach to prepare polyimide/siloxane‐functionalized graphene oxide composite films is reported. The siloxane‐functionalized graphene oxide was obtained by treating graphene oxide (GO) with 1,3‐bis(3‐aminopropyl)‐1,1,3,3‐tetra‐methyldisiloxane (DSX) to obtain DSX‐GO nanosheets, which provided a starting platform for in situ fabrication of the composites by grafting polyimide (PI) chains at the reactive sites of functional DSX‐GO nanosheets. DSX‐GO bonded with the PI matrix through amide linkage to form PI‐DSX‐GO films, in which DSX‐GO exhibited excellent dispersibility and compatibility. It is demonstrated that the obvious reinforcing effect of GO to PI in mechanical properties and thermal stability for PI‐DSX‐GO is obtained. The tensile strength of a composite film containing 1.0 wt% DSX‐GO was 2.8 times greater than that of neat PI films, and Young's modulus was 6.3 times than that of neat PI films. Furthermore, the decomposition temperature of the composite for 5% weight loss was approximately 30 °C higher than that of neat PI films. © 2015 Society of Chemical Industry     

Effects of crosslinking agents on the physical properties of polyimide/amino‐functionalized graphene oxide hybrid films

The effects of crosslinking agents (crosslinkers) on polyimide (PI)/graphene oxide (GO) hybrid films were extensively investigated. The surface of GO was modified with amino groups using 4‐aminobenzylamine to improve compatibility with pyromellitic dianhydride/4,4′‐oxydianiline PI, and two kinds of crosslinkers were used: tris(4‐aminophenyl)amine and 1,3,5‐triazine‐2,4,6‐triamine (melamine). The mechanical, thermal and optical properties of the PI hybrid films were investigated. In particular, the transparency and physical properties of the PI hybrid films containing amino‐functionalized GO with homogeneous dispersion were improved. As the content of the crosslinker increased, a crosslinking network was formed between the PI chains, and the stiffness of the hybrid films was increased. The glass transition temperature, heat resistance and mechanical properties were also enhanced. The PI hybrids prepared with a rigid crosslinker exhibited higher optical transparency due to the reduction of the intermolecular charge transfer interactions with increasing interchain spacing between the PI chains. © 2018 Society of Chemical Industry     

Improvement of thermal and mechanical properties by control of formulations in rigid polyurethane foams from polyols functionalized with graphene oxide

This article addresses the optimization of water-blown rigid polyurethane (RPU) foams obtained from a polyol functionalized with graphene oxide (GO). For this purpose, a series of RPU foams are herein synthesized by varying either the isocyanate index, the contents of catalyst or the contents of surfactant, or a combination of these three components. The modifications introduced in the formulation are based on the effect of GO on the reaction kinetics. These strategies are mainly focused on the increase of both isocyanate conversion and polymerization reaction, which decrease for the foams containing GO. Density, cellular structure, thermal conductivity, and mechanical properties of the resulting foams are herein investigated. The results show how controlling PU formulation allows to improve both the thermal and the mechanical behavior in these RPU foams containing GO. The highest cell size reduction of 25% and the lowest thermal conductivity are obtained for the sample with a simultaneous increase in isocyanate index, catalyst content, and surfactant content. Moreover, the adequate combination of these components leads to a high improvement of 59% of the relative Young's modulus and of 54% of the relative collapse stress. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47474.     

聚偏氟乙烯/石墨烯复合材料的制备及性能研究

用溶液共混法制备出聚偏氟乙烯/氧化石墨烯复合材料(PVDF/GO)，经高温热压将GO还原得到聚偏氟乙烯/还原氧化石墨烯复合材料(PVDF/rGO)。研究了填料种类及含量对复合材料电学性能、热稳定性和力学性能的影响。结果表明：随GO和rGO的添加，两种复合材料的介电常数(ε _r)均变大、介电损耗(tanδ)变化不大；低含量下GO和rGO均能提高PVDF的热稳定性，但rGO对PVDF性能的改善效果更好；随填料含量从0增加到8%(质量)，100 Hz下PVDF/rGO复合材料的ε _r从3.60增加到38.30，PVDF/rGO[4%(质量)]复合材料失重率为5%的分解温度较纯PVDF提高了6.44℃。rGO增强了PVDF的刚性，PVDF/rGO复合材料的拉伸强度先增大后减小，杨氏模量逐渐增大，当rGO含量为4%(质量)时拉伸强度最大，拉伸强度和弹性模量分别较纯PVDF提高了35.30%、22.58%。但GO和rGO都降低了复合材料的击穿场强。     

Characterization and performance of dodecyl amine functionalized graphene oxide and dodecyl amine functionalized graphene/high‐density polyethylene nanocomposites: A comparative study

Dodecyl amine (DA) functionalized graphene oxide(DA‐GO) and dodecyl amine functionalized reduced graphene oxide (DA‐RGO) were produced by using amidation reaction and chemical reduction, then two kinds of well dispersed DA‐GO/high‐density polyethylene (HDPE) and DA‐RGO/HDPE nanocomposites were prepared by solution mixing method and hot‐pressing process. Thermogravimetric, X‐ray photoelectron spectroscopy, Fourier transforms infrared spectroscopy, X‐ray diffractions, and Raman spectroscopy analyses showed that DA was successfully grafted onto the graphene oxide surface by uncleophilic substitution and the amidation reaction, which increased the intragallery spacing of graphite oxide, resulting in the uniform dispersion of DA‐GO and DA‐RGO in the nonpolar xylene solvent. Morphological analysis of nanocomposites showed that both DA‐GO and DA‐RGO were homogeneously dispersed in HDPE matrix and formed strong interfacial interaction. Although the crystallinity, dynamic mechanical, gas barrier, and thermal stability properties of HDPE were significantly improved by addition of small amount of DA‐GO or DA‐RGO, the performance comparison of DA‐GO/HDPE and DA‐RGO/HDPE nanocomposites indicated that the reduction of DA‐GO was not necessary because the interfacial adhesion and aspect ratio of graphene sheets had hardly changed after reduction, which resulting in almost the same properties between DA‐GO/HDPE and DA‐RGO/HDPE nanocomposites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39803.     

In situ polymerization of bio‐based thermosetting polyurethane/graphene oxide nanocomposites

Novel bio‐based polyurethane/graphene oxide (GO) nanocomposites have been successfully synthesized from biorenewable epoxidized soybean‐castor oil fatty acid‐based polyols with considerable improvement in mechanical and thermal properties. The GO was synthesized via a modified pressurized oxidation method, and was investigated using Raman spectra, AFM and XPS, respectively. The toughening mechanism of GO in the bio‐based polyurethane matrix was explored. The elongation at break and toughness of polyurethane were increased by 1.3 and 0.8 times with incorporation of 0.4 wt % GO, respectively. However, insignificant changes in both mechanical strength and modulus were observed by adding GO. The results from thermal analysis indicated that the GO acts as new secondary soft segments in the polyurethane which lead to a considerable decrease in the glass transition temperature and crosslink density. The SEM morphology of the fracture surface after tensile testing showed a considerable aggregation of graphene oxide at concentrations above 0.4 wt %. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41751.     

Photovoltaic and UV detector applications of ZnS/rGO nanocomposites synthesized by a green method

The effect of graphene concentration on the photovoltaic and UV detector applications of ZnS/graphene nanocomposites was investigated. The nanocomposites were synthesized by a green, cost-effective, and simple co-precipitation method with different graphene concentrations (5, 10, and 15 wt%) using L-cysteine amino acid as a surfactant and graphene oxide (GO) powder as a graphene source. Transmission electron microscopy (TEM) images showed that the ZnS NPs were decorated on GO sheets and the GO caused a significant decrease in ZnS diameter size. The results of X-ray diffraction (XRD) patterns, Raman, and Fourier transform infrared (FTIR) spectroscopy indicated that the GO sheets were changed into reduced graphene oxide (rGO) during synthesis process. Therefore, L-cysteine amino acid played its role as a reducing agent to reduce the GO. Photovoltaic measurements showed that the graphene caused to increase the efficiency of solar-cell application of ZnS/rGO nanocomposites. In addition, our observation showed that the nanocomposites were suitable as ultraviolet (UV) detectors and graphene concentration increased the responsibility of the detectors.     

Preparation of functional reduced graphene oxide and its influence on the properties of polyimide composites

Homogeneous dispersion and strong filler–matrix interfacial interactions were vital factors for graphene for enhancing the properties of polymer composites. To improve the dispersion of graphene in the polymer matrix and enhance the interfacial interactions, graphene oxide (GO), as an important precursor of graphene, was functionalized with amine‐terminated poly(ethylene glycol) (PEG–NH₂) to prepare GO–poly(ethylene glycol) (PEG). Then, GO–PEG was further reduced to prepare modified reduced graphene oxide (rGO)–PEG with N₂H₄·H₂O. The success of the modification was confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis, and Raman spectroscopy. Different loadings of rGO–PEG were introduced into polyimide (PI) to produce composites via in situ polymerization and a thermal reduction process. The modification of PEG–NH₂ on the surface of rGO inhibited its reaggregation and improved the filler–matrix interfacial interactions. The properties of the composites were enhanced by the incorporation of rGO–PEG. With the addition of 1.0 wt % rGO–PEG, the tensile strength of PI increased by 81.5%, and the electrical conductivity increased by eight orders of magnitude. This significant improvement was attributed to the homogeneous dispersion of rGO–PEG and its strong filler–matrix interfacial interactions. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45119.     

氧化石墨烯改性环氧树脂涂料的制备及防腐性能

环氧树脂在溶剂蒸发过程中容易产生微孔,影响其防腐蚀性能。为了提高其对腐蚀介质的阻碍能力,本文采用密闭氧化法制备氧化石墨烯,再利用湿式转移法将氧化石墨烯水溶液分散在环氧树脂中,制备氧化石墨烯/环氧树脂防腐涂料。通过红外光谱（FTIR）、X射线衍射（XRD）和拉曼光谱（Raman）分析氧化石墨烯的结构变化,利用开路电位测试（OCP）、水接触角、腐蚀形貌和气体透过率分析氧化石墨烯/环氧树脂涂料的防腐性能。结果表明,氧化石墨烯/环氧树脂（GO/EP）涂料的开路电位和水接触角分别为0.181V和86.12°,与纯环氧树脂涂料相比,分别提高了0.066V和10.5°;当GO/EP浸泡在3.5%NaCl溶液中腐蚀20天后,表面仅产生了粗糙化,涂层稳定性好,屏障性能强;与EP涂层相比,GO/EP涂层的O₂和H₂O渗透率分别降低了51.2%和65.5%。     

氧化石墨烯对SiO2多孔陶瓷吸波性能的影响

采用颗粒堆积法,以石英砂为骨料,甲基纤维素为黏结剂干压成型后,在1300℃保温1 h烧结制备得到SiO₂多孔陶瓷样品。通过对样品吸波性能的测试,发现样品的吸波带较宽达到9 GHz,反射率约-3 dB。经过浸渍氧化石墨烯后,样品的吸波性能发生较大改变。在氧化石墨烯质量分数为0.004%时,由于氧化石墨烯的涡流损耗,样品的吸波性能较纯SiO₂多孔陶瓷样品的吸波性能提高75%,反射率达到-5 dB。过量的氧化石墨烯使多孔陶瓷样品呈现出对电磁波的全反射。     

Influence of structure of amines on the properties of amines‐modified reduced graphene oxide/polyimide composites

Graphene oxide (GO), as an important precursor of graphene, was functionalized using alkyl‐amines with different structure and then reduced to prepare reduced amines grafted graphene oxide (RAGOs) by N₂H₄ · H₂O. The successful chemical amidation reaction between amine groups of alkyl‐amines and carboxyl groups of GO was confirmed by Fourier transform infrared (FTIR), X‐ray photoelectron spectroscopy (XPS), and thermal gravimetric analysis (TGA). Then RAGOs/polyimide nanocomposites were prepared via in situ polymerization and thermal curing process with different loadings of RAGOs. The modification of amine chains lead to homogenous dispersion of RAGOs in the composites and it formed strong interfacial adhesion between RAGOs and the polymer matrix. The mechanical and electrical properties of polyimide (PI) were significantly improved by incorporation of a small amount of RAGOs, the influence of structure of amines grafted on RAGOs on the enhancement effects of composites was discussed. The research results indicated that the proper structure of amine could effectively enhance the properties of composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43820.     

Polyimide foams with ultralow dielectric constants

To explore ultralow dielectric constant polyimide, the crosslinked polyimide foams (PIFs) were prepared from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA), 4,4′‐oxydianiline (ODA), and 2,4,6‐triaminopyrimidine (TAP) via a poly(ester–amine salt) (PEAS) process. FTIR measurements indicated that TAP did not yield a negative effect on imidization of PEAS precursors. SEM measurement revealed the homogeneous cell structure. Through using TAP as a crosslinking monomer, the mechanical properties of PIFs could be improved in comparison with uncrosslinked BTDA/ODA based PIF. The crosslinked PIFs still exhibited excellent thermal stability with 5% weight loss temperatures higher than 520°C. In the field with frequency higher than 100 Hz, the dielectric constants of the obtained PIFs ranged from 1.77 to 2.4, and the dielectric losses were smaller than 3 × 10^?2 at 25–150°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1734–1740, 2006     

Fabrication of isocyanate‐based polyimide foam by a postgrafting method

Density and flame retardancy controlled isocyanate‐based polyimide foam was prepared by a postgrafting method. The first solution containing prepolymer that was synthesized by dianhydride and overdose isocyanates was added into the second solution containing dianhydride derivatives, water, catalysts, and surfactants. The possible reactions during preparation are discussed. The obtained Fourier transform infrared spectra indicate that an increased amount of imide rings was generated with increasing molar ratio of the anhydride/isocyanate groups. The size and walls of the cells became smaller and thinner with less carbon dioxide (CO₂) escaping into the air during the first solution preparation process, as shown in scanning electron microscopy images. The thermogravimetric analysis curves demonstrated that the 5% weight loss temperature (T_5%) was greater than 289 °C, and the residual weight retention at 800 °C was more than 45%. In addition, differential thermogravimetry curves demonstrated that the thermal stability decreased with more byproducts in polyimide foams. The limiting oxygen index increased gradually from 30.63% ± 0.56 to 48% ± 0.50 with increasing molar ratio of the anhydride/isocyanate groups. Meanwhile, the density of obtained polyimide foams ranged from 38.31 kg/m³ ± 0.90 to 99.53 kg/m³ ± 10.85. When the molar ratio of anhydride/isocyanate groups ranged from 0.4 to 0.8, the prepared isocyanate‐based polyimide foams all exhibit both great flame retardancy and lower density. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44240.     

Radiation synthesis of graphene oxide/composite hydrogels and their ability for potential dye adsorption from wastewater

A high yield of graphene oxide (GO) was chemically synthesized from graphite powder utilizing adjusted Hummer's method. The contents of acidic functional groups in GO were determined using potentiometric titration. Composite hydrogels dependent on graphene oxide/poly(2-acrylamido-2-methylpropanesulfonic acid)/polyvinyl alcohol (GO/PAMPS/PVA) were synthesized utilizing a ⁶⁰Co gamma irradiation source at different doses. The synthesized graphene oxide and composite hydrogels were portrayed via X-ray diffraction, thermogravimetric analysis, and Fourier transform infrared analysis. The morphology of composite hydrogels was characterized by scanning electron microscope. The gel % and swelling % for the prepared hydrogel demonstrated that the swelling % of hydrogel increased with raising AMPS content. Whereas the increment of GO and increasing the irradiation dose lead to a reduction in the swelling %. The influences of pH, GO percentage, initial dye concentration, the adsorbent dosage, contact time, and temperature on the adsorption of basic blue 3 dye were evaluated and the adsorption capacity was 194.6 mg/g at optimum conditions; pH = 6, GO/PAMPS/PVA composite hydrogels with 5 wt% of GO, initial dye concentration = 200 mg/L, adsorbent dose = 0.1 g, solution volume = 50 mL after 360 min at room temperature (25°C). The adsorption of dye onto the GO/PAMPS/PVA composite hydrogels follows Pseudo-second-order adsorption kinetics, fits the Freundlich adsorption isotherm model.     

The preparation and properties of polystyrene/functionalized graphene nanocomposite foams using supercritical carbon dioxide

In this work, polystyrene (PS)/functionalized graphene nanocomposite foams were prepared using supercritical carbon dioxide. Thermally reduced graphene oxide (TRG) and graphene oxide (GO) were incorporated into the PS. Subsequently, the nanocomposites were foamed with supercritical CO₂. The morphology and properties of the nanocomposites and the nucleation efficiency of functionalized graphene in foaming PS are discussed. Compared with GO, TRG exhibited a higher nucleation efficiency and more effective cell expansion inhibition thanks to its larger surface area and better exfoliated structure. It is suggested that the factors that have a significant influence on the nucleation efficiency of TRG and GO originate from the differences in surface properties and chemical structure. Furthermore, PS/TRG nanocomposites and their nanocomposite foams also possess good electrical properties which enable them to be used as lightweight functional materials.© 2012 Society of Chemical Industry     

Preparation and the controlled release effect study of graphene oxide-modified poly(ε-caprolactone)

Functionalized graphene oxide-modified poly(ε-caprolactone) composites ((graphene oxide)GO/PCL) were successfully synthesized by Steglich esterification for drug applications of controlled release. Lomefloxacin (LMF) was selected as a model drug to investigate its controlled release properties. The controlled release effect of the LMF-contained pills of the GO/PCL and polylactic acid blend was evaluated. In contrast to the pure PCL, GO/PCL could effectively adjust the time of drug release and release the drug at a constant rate, achieving the controlled release requirements. Furthermore, different additive amounts of graphene oxide have different effects on adjusting the time of controlled release, while the best result obtained under the ratio is 4% GO/PCL as carrier of drug. Thus, high-quality drug carrier materials are obtained which are more suitable for clinical use. Exploring the optimum addition of graphene oxide is very significant for the development of GO/PCL carrier material.     

Microstructural and mechanical characteristics of graphene oxide-fly ash cenosphere hybrid reinforced epoxy resin composites

An experimental investigation into the influence of incorporation of graphene oxide (GO) and fly ash cenospheres (FACs) on the mechanical properties of epoxy resin (EP) composites. Two fillers were studied: GO-FAC hybrid and single GO. The GO-FAC hybrid was synthesized using a solution blending method, and characterized by FTIR, XRD, and scanning electron microscope (SEM). The modified EP composite specimens were prepared by adding different contents of GO and GO-FAC hybrid. The investigation showed that the FACs were successfully carried on the GO layer. The experimental data indicated that the addition of GO-FAC hybrid effectively improved the tensile property and the wear resistance of the EP composites, superior to the addition of single GO samples. The best tensile properties and lowest wear rate of EP composites were obtained when the hybrid content was 0.5 wt %. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 47173.     

氧化石墨烯改性水性半合成液压支架用浓缩液的制备与性能

通过化学法对氧化石墨烯（GO）中的羧基进行活化,然后在一定条件下使其与油酸三乙醇胺（MDLO）末端的羟基反应,制备GO接枝改性油酸三乙醇胺酯（MDLO-GO）;最后将水、KOH、EDTA混合均匀后再依次加入蓖钾皂、MDLO-GO、乳化剂及消泡剂等,制备得到GO接枝改性半合成液压支架用浓缩液（GO-HDSF）。红外光谱和X射线光电子能谱的测试结果表明GO被成功接枝到MDLO分子链上;此外,其他性能测试结果表明,随GO添加量增多GO-HDSF浓缩液黏度逐渐增大,且耐腐蚀性、润滑性逐渐提高;当GO的添加量为0.004%（质量分数）时,GO-HDSF的耐腐蚀电位增大到83mV,电流密度减小到6.5×10^-6A/cm²;GO-HDSF的最大无卡咬负荷PB值最大达到了481N。相比于未经氧化石墨烯改性的浓缩液,GO-HDSF的润滑性提高了11.9%,防腐蚀性提高了97.6%,同时耐高温、低温性能也显著提高。     

A study of the effects of the matrix epoxy resin and graphene oxide (GO) manufacturing process on the tensile behaviour of GO-epoxy nanocomposites

This work comprises a study of the reinforcement capacity provided by the addition of different types of nano-reinforcements of graphene oxide (GO) to epoxy matrices. A range of nanocomposites, resulting from the use of two epoxy matrices (a mono-component system and a bi-component system) and different types of GOs, at different weight percentages were studied and tensile tests were performed on specimens of these materials in order to quantify the variations in their elastic constants and tensile strength. The GO reinforcements used were obtained by means of the modified Hummers method followed by thermal reduction at different temperatures. The aim was to quantify the effect of carbon/oxygen ratio on the reinforcement capacity of GO in order to optimise the manufacturing process. The stiffness of the nanocomposites improved with the addition of TRGO for both matrices, but the tensile strength depended on the matrix.     

纳米二氧化硅/氧化石墨烯复合物对普通硅酸盐水泥力学性能的影响

氧化石墨烯(GO)在水泥中的分散性较差,限制了其提高水泥基复合材料性能。采用溶胶-凝胶法制备了纳米二氧化硅/氧化石墨烯复合物(GOS),在模拟的水泥孔隙溶液中对比了GO和GOS的分散稳定性;同时,制备了添加纳米片的水泥浆体,研究了GO和GOS对其力学性能的影响。结果表明:GOS在水泥环境中的分散稳定性明显优于GO;与对照组相比,GO/水泥基复合材料的28 d抗折和抗压强度分别提高了20.48%和13.14%,而GOS/水泥基复合材料分别提高了35.42%和23.90%。微观分析表明,GO/水泥基复合材料内部形成花状水化晶体,GOS/水泥基复合材料内部的水化晶体彼此交联,结构致密,降低了水泥脆性,提高了韧性。