Reinforcing polyamide 1212 with graphene oxide via a two-step melt compounding process

In this study, graphene oxide (GO) was synthesized from graphite powders via Hummers’ method. Polyamide 1212 (PA1212)/GO composites were prepared via a two-step melt compounding process. First, GO concentrates were prepared via solution coagulation. In this method, a GO solution was mixed with an ethanol-soluble polyamide solution. The resulting product was melt-compounded with a PA1212 matrix. This method enabled GO nanosheets to be well-dispersed in a PA1212 matrix. GO, which functioned as a nucleation template, exhibited heterogeneous nucleation effect in the PA1212 matrix because of its large specific surface area. The mechanical properties of the oriented PA1212/GO composites improved efficiently compared with those of pure PA1212. Crystal orientation degree and crystallinity in the composites increased slightly when GO was added after drawing. The composites’ reinforcing effect was mainly attributed to GO nanosheet alignment. These nanonsheets functioned as the nuclei to reinforce the entire oriented crystals.     

Enhanced thermal-conductive and anti-dripping properties of polyamide composites by 3D graphene structures at low filler content

In this work, 3D graphene structures constructed by graphene foam (GF) were introduced into polyamide-6 (PA6) matrix for the purpose of enhancing the thermal-conductive and anti-dripping properties of PA6 composites. The GF were prepared by one-step hydrothermal method. The PA6 composites were synthesized by in-situ thermal polycondensation method to realize PA6 chains covalently grafted onto the graphene sheets. The 3D interconnected graphene structure favored the formation of the consecutive thermal conductive paths or networks even at relatively low graphene loadings. As a result, the thermal conductivity was improved by 300% to 0.847 W·m⁻¹·K⁻¹ of PA6 composites at 2.0 wt% graphene loading from 0.210 W·m⁻¹·K⁻¹ of pure PA6 matrix. The presence of self-supported 3D structure alone with the covalently-grafted PA6 chains endowed the PA6 composites good anti-dripping properties.     

Synthesis and characterization of polyamide-6/graphite oxide nanocomposites

Polyamide-6/graphite oxide (PA6/GO) nanocomposites were synthesized using delamination/absorption method. The morphologies of the composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Both XRD and TEM showed that the GO sheets were completely exfoliated and distributed uniformly in PA6 matrix. Differential scanning calorimetry results revealed that the crystallization temperatures of the composites increased compared to that of pristine PA6, which was due to the heterogeneous nucleating effect of GO. However, the half-time of crystallization of the composites were evidently longer than that of pristine PA6, indicating an apparent decrease in the crystallization rate when GO was loaded into the polymer matrix. This was due to the constraining effect of layered GO on PA6 chains. The temperature of maximum decomposition rate was increased by 53 °C only by adding 5 wt% GO, and the maximum decomposition rate of the nanocomposites reduced greatly. The storage modulus (G′) and loss modulus (G″) curves shifted to higher modulus upon addition of 1–5 wt% of GO. With increasing GO loading, the shear viscosity of the nanocomposites gradually increased compared with pure PA6.     

氧化石墨烯/聚乙烯醇复合材料的纳米压痕实验及力学性能

为了研究氧化石墨烯(GO)对聚合物基复合材料力学性能的影响,通过溶液混合法制备了GO/聚乙烯醇(PVA)复合材料。然后,采用XRD、TEM、FTIR、DSC和纳米压痕实验等研究了GO/PVA复合材料的结构、界面结合性能、力学性能、蠕变行为和吸水膨胀率。结果表明:GO可以均匀分散在PVA基体中,二者之间主要通过氢键作用结合,具有较高的界面结合力;与纯PVA相比,1wt% GO/PVA复合材料的硬度和有效弹性模量分别提高了28.9%和23.3%,压入蠕变深度下降了19.8%;GO/PVA复合材料具有较低的无限剪切模量与瞬时剪切模量比,表明GO提高了PVA的蠕变抗力;GO的添加同时增加了GO/PVA复合材料的阻水性并降低了膨胀系数。吸湿纳米压痕实验结果表明:纯PVA的力学性能会随吸湿时间延长而下降,而GO/PVA复合材料吸湿72h后的力学性能基本保持不变。所得结论为石墨烯增强聚合物基复合材料的研究提供了理论指导。      

γ-Aminopropyl triethoxysilane functionalized graphene oxide for composites with high dielectric constant and low dielectric loss

A facile and efficient approach was developed to simultaneously functionalize and tune the reduction state of graphene oxide (GO) with γ-aminopropyl triethoxysilane (APTES) aided by NH₃ solution. X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy indicated that many surface groups of GO sheets were removed, and APTES were successfully functionalized onto GO sheets. The APTES-functionalized GO sheets (GO-APTES) were dispersed in water and further incorporated into nitrile butadiene rubber (NBR) by latex co-coagulation to form GO-APTES/NBR composites. These composites featured high degrees of exfoliation and intercalation of GO-APTES sheets throughout the NBR matrix. More significantly, the GO-APTES/NBR composites exhibited a relatively high dielectric constant (∼30.8) and a small loss factor (<0.04) at 1.0 kHz, combining with a good insulating property. The unique dielectric responses of GO-APTES/NBR composites open up the potential applications of these materials in resistive and capacitive field grading materials.     

用原位聚合法制备的PA6/GO纳米复合材料的结构和性能

以己内酰胺(CL)和6-氨基己酸(ACA)为聚合反应单体,用Hummers法制备氧化石墨烯(GO),再以GO为纳米填料用原位开环聚合法制备了GO改性PA6纳米复合材料(PA6/GO),并对PA6/GO纳米复合材料的结构及性能进行了研究。结果表明,PA6的黏均分子量达到104数量级,但加入过多的GO使PA6的分子量降低。形貌分析表明,GO均匀地分散在PA6基体中,并诱导了PA6基体的晶型由α晶型转变成γ晶型。同时,GO作为异相成核剂促进了PA6/GO复合材料中PA6基体的结晶,提高了PA6/GO复合材料的结晶度。拉伸测试结果表明,随着GO的加入PA6/GO纳米复合材料的拉伸强度先提高后降低,GO加入量为0.4份时拉伸强度达到最大值61.72 MPa,比纯PA6(48.52 MPa)提高了27.21%。导热性能分析表明含1.0份GO的PA6/GO纳米复合材料其50℃和100℃的热导率分别为0.317 W/(m·K)和0.280 W/(m·K),较纯PA6分别提高了33.19%和33.23%。     

Enhanced thermal resistance of phenolic resin composites at low loading of graphene oxide

By incorporating graphene oxide (GO) into phenolic resin (PR), GO/PR composites were prepared, and the effects of the content and reduction degree of GO on thermal resistance of GO/PR composites were studied. The peak degradation temperature of the PR was increased by about 14 °C with GO which was heat treated. The char yield of GO/PR composite at a GO weight fraction of 0.5% was about 11% greater than that of PR. The interactions such as covalent bonds and π–π stacking between GO and PR were regarded as the main reason for the enhancement. Located at the GO–PR interface, GO effectively anchored and structured PR molecular near the surfaces of GO sheets, and thus facilitated the formation of char. The superiority of GO/PR composites over PR in terms of thermal properties enhancement should also be related to the promoting graphitization by the addition of GO.     

In situ thermal reduction of graphene oxide for high electrical conductivity and low percolation threshold in polyamide 6 nanocomposites

Electrically conductive and thermally stable polyamide 6 (PA 6) nanocomposites were prepared through one-step in situ polymerization of ε-caprolactam monomer in the presence of electrically insulating and thermally unstable graphene oxide (GO) nanosheets. These nanocomposites show a low percolation threshold of ∼0.41 vol.% and high electrical conductivity of ∼0.028 S/m with only ∼1.64 vol.% of GO. Thermogravimetric analysis and X-ray photoelectron spectroscopy results of GO before and after thermal treatment at the polymerization temperature indicate that GO was reduced in situ during the polymerization process. X-ray diffraction patterns and scanning electron microscopy observation confirm the exfoliation of the reduced graphene oxide (RGO) in the PA 6 matrix. The low percolation threshold and high electrical conductivity are attributed to the large aspect ratio, high specific surface area and uniform dispersion of the RGO nanosheets in the matrix. In addition, although GO has a poor thermal stability, its PA 6 nanocomposite is thermally stable with a satisfactory thermal stability similar to those of neat PA 6 and PA 6/graphene nanocomposite. Such a one-step in situ polymerization and thermal reduction method shows significant potential for the mass production of electrically conductive polymer/RGO nanocomposites.     

Growing polystyrene chains from the surface of graphene layers via RAFT polymerization and the influence on their thermal properties

The polystyrene (PS) macromolecular chains were grafted on the surface of graphene layers by reversible addition-fragmentation chain transfer (RAFT) polymerization. In this procedure, a RAFT agent, 4-Cyano-4-[(dodecylsulfanylthiocarbonyl) sulfanyl] pentanoic acid, was used to functionalize the thermal reduced graphene oxide (TRGO) to obtain the precursor (TRGO-RAFT). It can be calculated that the grafting density of PS/graphene (PRG) composites was about 0.18 chains per 100 carbons. Successful in-plain attachment of RAFT agent to TRGO and PS chain to TRGO-RAFT was shown an influence on the thermal property of the PRG composites. The thermal conductivity (λ) improved from 0.150 W m⁻¹ K⁻¹ of neat PS to 0.250 W m⁻¹ K⁻¹ of PRG composites with 10 wt% graphene sheets loading. The thermal property of PRG composites increased due to the homogeneous dispersion and ordered arrangement of graphene sheets in PS matrix and the formation of PRG composites.     

The preparation of high performance and conductive poly (vinyl alcohol)/graphene nanocomposite via reducing graphite oxide with sodium hydrosulfite

Sodium hydrosulfite is used to reduce graphite oxide in current study. The preparation of poly (vinyl alcohol) (PVA)/graphene nanocomposites is realized using two simple steps: the synthesis of PVA/graphite oxide (GO) nanocomposites film and immersion of such a film in the reducing agent aqueous solution. This method prohibits the agglomeration of GO during direct reduction in PVA/GO aqueous solution, and opens a new way to scale up the production of graphene nanocomposites using a simple reducing agent. A 40% increase in tensile strength and 70% improvement in elongation at break have been obtained with only the addition of 0.7 wt.% of reduced graphite oxide. Furthermore, a good level of conductivity and a variation in the surface property of the prepared films have been observed for the composites containing graphene.     

Transparent and high gas barrier films based on poly(vinyl alcohol)/graphene oxide composites

Composites of poly(vinyl alcohol) (PVA) and graphene oxide (GO) were synthesized by a modified Hummers method and a solution-mixing method. GO was fully exfoliated in the PVA/GO composites. GO did not affect the crystallization of PVA during solvent evaporation. GO is itself an excellent gas barrier without any chemical reduction. The oxygen permeability of the PVA/GO (0.3 wt.%) composite coated film was 17 times lower than that of the pure poly(ethylene terephthalate) (PET) film, with 92% light transmittance at 550 nm. Composites of PVA and reduced graphene oxide (RGO) were synthesized by performing chemical reduction using hydrazine monohydrate. The oxygen permeability of the PVA/RGO (0.3 wt.%) composite coated film was 86 times lower than that of the pure PET film, with 73% light transmittance at 550 nm. The reduction of oxygen permeability was mainly attributed to the reduced oxygen solubility in the PVA/GO composite film, while it was attributed to both the reduced oxygen diffusivity and solubility in the PVA/RGO composite film.     

基于纳米银负载氧化石墨烯的新型聚乙烯复合材料

通过超声波辅助液相法将纳米银(AgNPs)与氧化石墨烯(GO)结合制得了一种新的负载纳米银的氧化石墨烯材料AgNPs@GO。分析表明在该材料中AgNPs主要被锚接在GO片层的含氧基团和缺陷上, 部分Ag单质被氧化为Ag ⁺离子并有部分GO被还原。AgNPs@GO能有效抑制铜绿假单胞菌生长, 其抑菌能力显著强于AgNPs和GO。将AgNPs@GO作为添加剂引入聚乙烯(PE)基体, 进一步制备了新型的AgNPs@GO掺杂PE复合材料0.48wt%-AgNPs@GO/PE, 相比PE和AgNPs掺杂PE复合材料, 0.48wt%-AgNPs@GO/PE具有更好的抑菌能力和更强的阻隔水蒸气性能, 并且在水和乙醇溶液中都具有较好的耐溶出性能。     

石墨烯/氰酸酯-环氧树脂复合材料的制备和性能

为优化石墨烯/氰酸酯(CE)复合材料的制备工艺并提高其韧性,制备了对苯二胺(PPD)功能化的氧化石墨烯(GO-PPD),分别以GO和GO-PPD为添加物,以CE和环氧树脂(质量比为7:3)共混物为基体树脂制备了GO/CE-环氧树脂和GO-PPD/CE-环氧树脂复合材料。采用红外和拉曼光谱表征GO和GO-PPD的结构,并研究了二者在溶剂中的溶解性。GO-PPD在乙醇等低沸点和低毒性的有机溶剂中表现出稳定的溶解性,与GO相比,GO-PPD明显改善了复合材料制备的工艺性。性能研究表明,GO和GO-PPD的加入均会降低基体树脂的固化温度,明显提高其力学性能和热性能,使基体树脂的介电常数和介电损耗显著增大,但仍然基本保持良好的耐湿热性和耐腐蚀性。石墨烯表面的化学性质影响石墨烯/CE-环氧树脂复合材料的综合性能,与GO相比,GO-PPD的加入能更明显提高复合材料的力学性能和耐热性。     

Multifold interface and multilevel crack propagation mechanisms of graphene oxide/polyurethane/epoxy membranes interlaminar-toughened carbon fiber-reinforced polymer composites

Graphene oxide/polyurethane/epoxy (GO/PU/EP) membranes were directly fabricated by functionalization of graphene oxide with epoxy-grafted polyurethane (GO-UE), and the interface correlation and crack propagation mechanisms in GO/PU/EP membranes interlaminar-toughened carbon fiber-reinforced polymer composites were investigated. The functionalized GO-UE with corrugation and scrolling nature of graphene sheets was evenly dispersed in GO/PU/EP membranes below 0.50 wt% loading. Mode I fracture toughness, flexural properties and interlaminar shear strength of GO/PU/EP membranes-toughened composites were enhanced in comparison with untoughened composites and PU/EP membranes-toughened composites, which was ascribed to the multifold interface bonding between the GO-UE layers, epoxy matrix and carbon fiber. Schematic models of multilevel crack propagations were proposed based on different crack extension directions to GO-UE and the morphology evolutions of GO-UE in the interlaminar region and at the carbon fiber interface in toughened composites, which highlighted the toughening mechanisms of crack pinning, crack deflection and separation between GO-UE layers.     

Thermal and electrical conductivity of Al(OH)<Subscript>3</Subscript> covered graphene oxide nanosheet/epoxy composites

Al(OH)₃ functionalized graphene composites (Al–GO) were prepared using a simple sol–gel method. In this protocol, graphene oxide (GO) was prepared according to the Hummers method and functionalized to enhance its reactivity with aluminum isopropoxide by a LiAlH₄ treatment. The functionalized graphene sheets were characterized by X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. These analyses confirmed that GO had been fabricated and the Al(OH)₃ layer could have a homogeneous distribution with large and dense coverage onto GO sheets. In addition, the thermal and electrical conductivity of the epoxy composites with GO and Al–GO fillers were measured. The thermal conductivities of the composites with graphene-based fillers were enhanced by the addition of fillers. In particular, the thermal conductivity of GO/epoxy composite containing 3 wt% was approximately two times higher than that of pure epoxy resin. In addition, the electrical conductivity of Al–GO embedded composites degenerated compared to GO composites.     

Crystallization,mechanical performance and hydrolytic degradation of poly(butylene succinate)/graphene oxide nanocomposites obtained via in situ polymerization

Poly(butylene succinate) (PBS)/graphene oxide (GO) nanocomposites were fabricated via in situ polymerization with very low GO content (from 0.03 to 0.5 wt%). The microstructures of the nanocomposites were characterized with Raman spectroscopy, fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), sedimentation experiments and atomic force microscopy (AFM). The results showed that PBS chains have been successfully grafted onto GO sheets during in-situ polymerization, accompanied by the thermo-reduction from GO to graphene. The grafted GO displayed a great nucleating effect on PBS crystallization, resulting in largely improved crystallization temperature and decreased spherules size. A simultaneous enhancement in tensile strength and elongation was achieved for PBS/GO nanocomposites fiber. Meanwhile, increase in hydrolytic degradation rate was also observed for these nanohybrids. Our result indicates that using very low content GO is a simple way to achieve good dispersion yet with remarkable property enhancement for polymer/GO nanocomposites.     

Preparation of Ferrioxalate Submicrorods/Graphene Composites and Their Photocatalytic Properties

Ferrioxalate submicrorods/graphene composites were synthesized through a simple solvothermal process in a mixture of ethylene glycol and water. The in situ growth of ferrioxalate submicrorods and the reduction of graphene oxide （GO） were completed in a one-step reaction. Fourier transform infrared and Raman spectroscopy confirmed the reduction of GO. Uniform rod-like ferrioxalates with diameter of about 600 nm and length of several micrometers were well distributed on the graphene sheets. As-obtained composites exhibited better photocatalytic properties than pure ferrioxalate submicrorods. The influence of different contents of GO on photocatalytic performance was also investigated. A possible photocatalytic mechanism of ferrioxalate submicrorods/graphene composites was proposed.     

Principles Governing Control of Aggregation and Dispersion of Graphene and Graphene Oxide in Polymer Melts

Controlling the structure of graphene and graphene oxide (GO) phases is vitally important for any of its widespread intended applications: highly ordered arrangements of nanoparticles are needed for thin-film or membrane applications of GO, dispersed nanoparticles for composite materials, and 3D porous arrangements for hydrogels. By combining coarse-grained molecular dynamics and newly developed accurate models of GO, the driving forces that lead to the various morphologies are resolved. Two hydrophilic polymers, poly(ethylene glycol) (PEG) and poly(vinyl alcohol) (PVA), are used to illustrate the thermodynamically stable morphologies of GO and relevant dispersion mechanisms. GO self-assembly can be controlled by changing the degree of oxidation, varying from fully aggregated over graphitic domains to intercalated assemblies with polymer bilayers between sheets. The long-term stability of a dispersion is extremely important for many commercial applications of GO composites. For any degree of oxidation, GO does not disperse in PVA as a thermodynamic equilibrium product, whereas in PEG dispersions are only thermodynamically stable for highly oxidized GO. These findings—validated against the extensive literature on GO systems in organic solvents—furnish quantitative explanations for the empirically unpredictable aggregation characteristics of GO and provide computational methods to design directed synthesis routes for diverse self-assemblies and applications.     

Pickering乳液技术制备纤维素纳米纤丝-还原氧化石墨烯/聚甲基丙烯酸甲酯电磁屏蔽复合材料

利用纤维素纳米纤丝（CNF）和氧化石墨烯（GO）共稳定的含有聚甲基丙烯酸甲酯（PMMA）的Pickering乳液法,并经抽滤、还原、热压等工艺制备高性能的纤维素纳米纤丝-还原氧化石墨烯/聚甲基丙烯酸甲酯（CNF-rGO/PMMA）电磁屏蔽复合材料。通过调节油相中聚合物的质量浓度、水油体积比,从而调控GO在复合材料中的质量分数。研究GO还原方式、质量分数及热压过程对所制备的CNF-rGO/PMMA电磁屏蔽复合材料的形貌结构与性能的影响。CNF-rGO/PMMA电磁屏蔽复合材料中GO经水合肼处理后有效还原为rGO,热压工艺使包裹在PMMA颗粒外的CNF-rGO片层与PMMA颗粒紧密堆积并形成交联的三维导电网络从而具有优异的导电率,在X波段不同频率（8.2~12.4 GHz）下具有良好的电磁屏蔽效能及稳定性,电磁屏蔽效能可达20 dB以上,可用于民用电磁屏蔽材料。      

Mechanical properties of epoxy composites filled with silane-functionalized graphene oxide

In this work, the effects of as-produced GO and silane functionalized GO (silane-f-GO) loading and silane functionalization on the mechanical properties of epoxy composites are investigated and compared. Such silane functionalization containing epoxy ended-groups is found to effectively improve the compatibility between the silane-f-GO and the epoxy matrix. Increased storage modulus, glass transition temperature, thermal stability, tensile and flexural properties and fracture toughness of epoxy composites filled with the silane-f-GO sheets are observed compared with those of the neat epoxy and GO/epoxy composites. These findings confirm the improved dispersion and interfacial interaction in the composites arising from covalent bonds between the silane-f-GO and the epoxy matrix. Moreover, several possible fracture mechanisms, i.e. crack pinning/deflection, crack bridging, and matrix plastic deformation initiated by the debonding/delamination of GO sheets, were identified and evaluated.