Biodegradable amylose films reinforced by graphene oxide and polyvinyl alcohol

Graphene oxide/amylose (GO/amylose) composite films with different amounts of graphene oxide (GO), glycerol and polyvinyl alcohol (PVA) were prepared by a solution casting method. The structure, morphologies, and properties of the films were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis, UV–vis spectroscopy and tensile tests. The results indicated good dispersion of the GO nanosheets in the GO/amylose composite films and consequently a significant improvement in their mechanical properties. The addition of GO increased the tensile strength of the GO/amylose films, significantly. When glycerol was used as a plasticizer, the elongation at break of the films increased. When PVA was also added to the composite films, the films were mechanically strong and flexible. The incorporation of GO also decreased the moisture absorbability and UV transmittance of the films. The stability of the GO/amylose films in acidic and alkaline solutions was also studied and the films had excellent stability in both acidic and alkaline aqueous mediums.     

Graphene oxides nanosheets mediation of poly(vinyl alcohol) films in tuning their structural and opto-mechanical attributes

Herein, we report successful incorporation of graphene oxide (GO) nanosheets into poly(vinyl alcohol) (PVA) matrix by employing solution casting method. The effect of GO loadings on structural, optical and mechanical properties of PVA films was investigated. Most of the optical properties of such films are reported for the first time in the present study. On incorporating GO nanosheets into PVA matrix, the properties of nanocomposites were changed entirely. The tensile strength and Young’s modulus of nanocomposites were enhanced. Alongside, a variation in absorption edge, direct/indirect band gap, Urbach energy, refractive index, optical dielectric constant, optical conductivity and dispersion parameters were noticed. The band gap and dispersion parameters were calculated using Tauc’s and Wemple–DiDomenico models, respectively. Helpin–Tsai and mixture rule models were employed to calculate Young’s modulus. The applied models reinforced the experimental results in the present study. Advanced analytical techniques were employed to characterize the nanocomposites films. The prepared nanocomposites might be used in designing the opto-electronic devices.     

Nylon-6/Graphene composites modified through polymeric modification of graphene

The covalent functionalization of graphene oxide (GO) with poly(vinyl alcohol) (PVA) via ester linkages (GO-es-PVA) as well as the characterization of modified graphene based Nylon-6 (PA6) composite prepared by solution mixing techniques was examined. The anchoring of PVA chains on GO sheets was confirmed by XPS and FTIR measurements. The resulting functionalized sample became soluble in formic acid, allowing solution-phase processing for preparation of PA6/GO composites. Answering to the efficient polymer-chain grafting, a homogeneously dispersion of GO sheets in PA6 matrix and a dramatic improvement of interface adhesion between nanosheets and matrix were observed in PA6/GO-es-PVA composites by SEM and TEM. The depressed crystallization of PA6 chains in PA6/GO-es-PVA composites was investigated by their DSC and XRD results.     

透明LED石墨烯/苯基硅橡胶复合封装材料

采用化学接枝技术,利用硅烷偶联剂γ-氨丙基三乙氧基硅烷（KH-550）、水合肼改性氧化石墨烯（GO）制备功能型石墨烯（FG）。将FG与苯基硅橡胶混合,采用氢化硅烷化法,在铂催化剂作用下制备了一种发光二极管（LED）封装用FG/苯基硅橡胶复合材料,考察了改性后FG结构、表面官能团变化以及其用量对FG/苯基硅橡胶复合材料力学性能及光学性能的影响,并分析了FG/苯基硅橡胶复合材料的微观相态及其热稳定性。结果表明:经KH-550改性后的FG表面附有特殊官能团,能提高其在苯基硅橡胶中的分散性。当苯基硅橡胶中引入0.010 0wt% FG时,FG/苯基硅橡胶复合封装材料的透光率仍可达到85%以上,耐紫外老化性能和力学性有明显提高。FG/苯基硅橡胶复合材料的热分解温度为690 ℃、GO/苯基硅橡胶复合材料的热分解温度为623 ℃,而纯苯基硅橡胶的热分解温度为491 ℃,且FG/苯基硅橡胶复合材料的放热量始终比纯苯基硅橡胶略低。苯基硅橡胶中引入0.010 0wt% 改性的FG,材料热分解温度提高了200 ℃,放热量有所减少,能更好满足功能型LED复合封装材料热稳定性能要求。      

Composite Microgels Created by Complexation between Polyvinyl Alcohol and Graphene Oxide in Compressed Double‐Emulsion Drops

Microgels, microparticles made of hydrogels, show fast diffusion kinetics and high reconfigurability while maintaining the advantages of hydrogels, being useful for various applications. Here, presented is a new microfluidic strategy for producing polymer‐graphene oxide (GO) composite microgels without chemical cues or a temperature swing for gelation. As a main component of microgels, polymers that are able to form hydrogen bonds, such as polyvinyl alcohol (PVA), are used. In the mixture of PVA and GO, GO is tethered by PVA through hydrogen bonding. When the mixture is rapidly concentrated in the core of double‐emulsion drops by osmotic‐pressure‐driven water pumping, PVA‐tethered GO sheets form a nematic phase with a planar alignment. In addition, the GO sheets are linked by additional hydrogen bonds, leading to a sol–gel transition. Therefore, the PVA–GO composite remains undissolved when it is directly exposed to water by oil‐shell rupture. These composite microgels can be also produced using poly(ethylene oxide) or poly(acrylic acid), instead of PVA. In addition, the microgels can be functionalized by incorporating other polymers in the presence of the hydrogel‐forming polymers. It is shown that the multicomponent microgels made from a mixture of polyacrylamide, PVA, and GO show an excellent adsorption capacity for impurities.     

Simple photoreduction of graphene oxide nanosheet under mild conditions

Graphene oxide (GO) nanosheets were reduced by UV irradiation in H2 or N2 under mild conditions (at room temperature) without a photocatalyst. Photoreduction proceeded even in an aqueous suspension of nanosheets. The GO nanosheets reduced by this method were analyzed by X-ray photoelectron spectroscopy and Raman spectroscopy. It was found that epoxy groups attached to the interiors of aromatic domains of the GO nanosheet were destroyed during UV irradiation to form relatively large sp2 islands resulting in a high conductivity. I-V curves were measured by conductive atomic force microscopy (AFM; perpendicular to a single nanosheet) and a two-electrode system (parallel to the nanosheet). They revealed that photoreduced GO nanosheets have high conductivities, whereas nonreduced GO nanosheets are nearly insulating. Ag+ adsorbed on GO nanosheets promoted the photoreduction. This photoreduction method was very useful for photopatterning a conducting section of micrometer size on insulating GO. The developed photoreduction process based on a photoreaction will extend the applications of GO to many fields because it can be performed in mild conditions without a photocatalyst.     

氧化石墨烯纳米片/环氧树脂复合材料的制备与性能

氧化石墨烯(GO)是石墨烯重要的衍生物之一,通过氧化和超声波分散制备了GO纳米片/环氧树脂复合材料。采用XRD、拉曼光谱、FTIR和TEM表征了GO纳米片的结构与形貌,研究了GO纳米片用量对GO纳米片/环氧树脂复合材料热稳定性、力学性能及介电性能的影响。结果表明:GO纳米片的加入提高了GO纳米片/环氧树脂复合材料失热稳定性;随着GO纳米片填充量的增加,GO纳米片/环氧树脂复合材料的冲击强度和抗弯性能先提高后降低,其介电常数和介电损耗则先减小后增加。GO纳米片填充量为0.3wt%的GO纳米片/环氧树脂复合材料的失重5%时的热分解温度由纯环氧树脂的400.2℃提高到424.5℃,而冲击强度和弯曲强度分别在GO纳米片填充量为0.2wt%和0.3wt%时达到最大,冲击强度由纯环氧树脂的10.5kJ/m2提高到19.7kJ/m2,弯曲强度由80.5 MPa提高到104.0 MPa。     

Enhancements of the mechanical properties and thermal conductivity of carboxylated acrylonitrile butadiene rubber with the addition of graphene oxide

Graphene oxide (GO)/carboxylated acrylonitrile butadiene rubber (xNBR) vulcanizates were prepared in this study by mixing exfoliated GO aqueous dispersion with xNBR latex. The GO monolayers were exfoliated from natural flake graphite by Hummers' method. This study shows that GO could be dispersed homogeneously in xNBR matrix up to 1.2 vol.%. Adding GO nanosheets has a great effect on the mechanical, thermal stability, thermal conductivity, and thermal diffusivity of GO/xNBR vulcanizates. With the incorporation of GO nanosheets, the thermal stability, thermal conductivity, and thermal diffusivity of GO/xNBR vulcanizates increased significantly. The mechanical property of GO/xNBR vulcanizates reached its peak with 1.2 vol.% of GO content. The addition of 1.2 vol.% of GO nanosheets largely enhanced the tensile strength and modulus at 100 % elongation of xNBR by more than 370 and 230 %, respectively. The thermal conductivity and diffusivity of the GO/xNBR vulcanizates with 1.6 vol.% of GO had 1.4- and 1.2-fold improvements, respectively, compared to that of unfilled xNBR vulcanizate.     

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。      

氧化石墨烯纳米片层对水泥基复合材料的增韧效果及作用机制

通过氧化和超声波分散制备了氧化石墨烯（GO）纳米片层分散体系,研究了GO纳米片层对水泥基复合材料的增韧效果及作用机制。用EDS、FTIR、XRD、SEM和AFM对GO纳米片层的结构进行了表征。研究结果表明：所得GO含氧量为32.3wt%,GO纳米片层的厚度为6 nm左右,在GO片层表面含有羟基、羧基和磺酸基等活性基团。水泥基复合材料的SEM形貌及力学性能测定结果表明：当GO掺量为0.03wt%时,GO能够使水泥水化产物形成花朵状晶体,并使水泥基复合材料的拉伸强度、抗折强度和压缩强度比对照样品分别提高了65.5%、60.7%和38.9%。提出了GO纳米片层对水泥水化产物的模板调控机制,揭示了花状晶体的形成过程。     

氧化石墨烯负载无纺布复合膜的制备及光热转换性能

氧化石墨烯(GO)是一种性能良好的光热转换材料,广泛用于海水淡化、光电转换和太阳能利用等领域。为了测试GO负载无纺布膜(GO膜)和聚乙烯醇-氧化石墨烯无纺布复合膜(PVA-GO复合膜)的光热水蒸发特性,通过改进Hummers方法制备GO,选取了纤维素和聚酯类型的无纺布,通过浸泡-超声法制得GO膜和PVA-GO复合膜。运用紫外-可见-近红外光谱仪分析了GO膜和PVA-GO复合膜的吸光性能,并通过电子天平测量GO膜和PVA-GO复合膜的蒸发水量。由于PVA具有亲水性,能增大膜的吸水性,因而PVA加入会使蒸发水量增大。通过SEM分析GO膜和PVA-GO复合膜表面特征,发现无添加PVA的GO膜是纤维丝状结构,且纤维清晰可见。加入PVA后,纤维被PVA包裹,说明膜对光的吸收能力增强。当加入6wt% PVA时,无纺布纤维被PVA完全包裹。当用氙灯对两种膜进行水蒸发实验时,GO膜的蒸发速率达到了1.67 kg/(m2·h),PVA-GO复合膜的蒸发速率达到了1.85 kg/(m2·h)。此外,GO膜中出现GO层状结构,在紫外-可见-近红外光谱分析中表现出较好的吸光能力,在光热蒸发实验中表现出较好的光热转换能力。PVA-GO复合膜在PVA质量浓度为4wt%时有较好的光热转换性能和吸光性。      

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.     

Preparation and properties of polystyrene nanocomposites with graphite oxide and graphene as flame retardants

In this study, graphite oxides (GOs) with different oxidation degrees and graphene nanosheets were prepared by a modified Hummers method and thermal exfoliation of the prepared GO, respectively. Polystyrene (PS)/GO and PS/graphene nanocomposites were prepared via melt blending. X-ray diffraction results showed that GOs and graphene were exfoliated in the PS composites. It could be observed from the scanning electron microscope images that GOs and graphene were well dispersed throughout the matrix without obvious aggregates. Dynamic mechanical thermal analysis suggested that the storage modulus for the PS/GO1 and PS/graphene nanocomposites was efficiently improved due to the low oxygen content of GO1 and the elimination of the oxygen groups from GO. The flammability of nanocomposites was evaluated by thermal gravimetric analysis and cone calorimetry. The results suggested that both the thermal stability and the reduction in peak heat release rate (PHRR) decreased with the increasing of the oxygen groups in GOs or graphene. The optimal flammability was obtained with the graphene (5 wt%), in which case the reduction in the PHRR is almost 50 % as compared to PS.     

Facile and size-controllable preparation of graphene oxide nanosheets using high shear method and ultrasonic method

ABSTRACT

The lateral size of the graphene oxide (GO) nanosheets could be controlled by preparation method, and a simple and effective strategy to adjust the lateral size of GO nanosheets by selecting suitable method is presented. The high shear method was introduced to produce GO nanosheets, and the GO nanosheets (few micrometres) prepared by high shear method is about one order of magnitude larger than GO nanosheets (few hundred nanometres) obtained by ultrasonic method, as evidenced by atomic force microscopy. The FTIR, XPS and Raman analysis revealed that there are no distinct differences in composition and functional groups between the GO nanosheets produced by high shear method and ultrasonic method. The cavitation in the procedure of ultrasonic method is favourable for GO exfoliation, but it also could result in damage to GO nanosheets. The shearing force in the process of high shear method is effective for GO delamination with minimal fragmentation. The results indicated that the high shear method proposed in this paper is an efficient exfoliation means to produce single-layer GO nanosheets.     

Morphology, mechanical and thermal properties of graphene-reinforced poly(butylene succinate) nanocomposites

Graphene nanosheets (GNSs) reinforced poly(butylene succinate) (PBS) nanocomposites are facilely obtained by a solution-based processing method. Graphene nanosheets, which are derived from chemically reduced graphite oxide (GO), are characterized by AFM, TEM, XRD and Raman spectra. The state of dispersion of the GNSs in the PBS matrix is examined by SEM observations that reveals homogeneous distribution of GNSs in PBS matrix. A 21% increase in tensile strength and a 24% improvement of storage modulus are achieved by addition of 2.0 wt% of GNS. The electrical conductivity and thermal stability of the graphene-based nanocomposite are also improved. DSC measurement indicates that the presence of graphene sheets does not have a remarkable impact on the crystallinity of the nanocomposites. Therefore, the high performances of the nanocomposites are mainly attributed to the uniform dispersion of GNSs in the polymer matrix and strong interfacial interactions between both components.     

Synergistic effects of hydrophilic nano-SiO2/graphene oxide @ copolymer nanocomposites in tanning leather

The near-spherical silica nanoparticles with polyvinyl alcohol (denoted as PVA-SiO₂) or polyethylene glycol (denoted as PEG-SiO₂) as surface modifiers were loaded onto graphene oxide nanosheets (denoted as GO) to prepare PVA(PEG)-SiO₂-GO nanocomposites. The nanocomposites well dispersed in water were then compounded with maleic anhydride (MA) - acrylic acid (AA) copolymer (denoted as PMAAA) to prepare new nanocomposite tanning agents (denoted as PVA(PEG)-SiO₂-GO/PMAAA). The hydrothermal stability, thickness increase, mechanical properties, flame retardancy and antistatic property, etc. of the leather tanned with PVA(PEG)-SiO₂-GO/PMAAA were founded to be improved in a significant way compared with those of the leather tanned with the commercial acrylic resin (CHINATAN OM) and pure PMAAA copolymer tanning agents. The acquired excellent tanning properties may be related to the synergistic tanning effects of near-spherical silica nanoparticles and thin-layered graphene oxide nanosheets in leather tanning process. Especially, the highest shrinkage temperature of the wet-white sheepskin tanned with PVA-SiO₂-GO/PMAAA reached 71 ^◦C and the thickness increase reached 190% without chrome tanning agents.     

Improving the thermal and mechanical properties of silicone polymer by incorporating functionalized graphene oxide

Functionalized graphene oxide (FGO) was produced by reacting graphene oxide nanosheets with vinyl trimethoxy silane (VTMS). The results confirmed the attachment of VTMS molecules to the surface of GO sheets by Si–O–C bonding. The introduction of VTMS molecules led to an excellent dispersibility in tetrahydrofuran and to the complete exfoliation of FGO with a thickness of about 1.19 nm. Meanwhile, FGO/silicone polymer composites were prepared by solution blending method. The incorporation of 0.5 wt% of FGO in silicone polymer improved remarkably the thermal stability, tensile strength, and thermal conductivity of the silicone polymer composite, due to the homogeneous dispersion of FGO in the composites as well as to the strong interfacial adhesion with silicone polymer matrix. Tensile strength and thermal conductivity of the FGO/silicone polymer composite were increased by 95.6 and 78.3 %, respectively, with the addition of 0.5 wt% FGO. The 5 % weight loss temperature of the composite at 0.5 wt% FGO loading was detected 26.1 °C higher than that of silicone polymer.     

How can graphene reduce the flammability of polymer nanocomposites?

Nanocomposites based on poly(vinyl alcohol) (PVA) and graphene nanosheets have been prepared by polymer solution blending and their flame retardant properties have been evaluated by a cone calorimetry test. It has been shown that there is a strong influence of graphene nanosheets on the fire behaviour of the composites with a significant reduction in peak heat release rate (PHRR) and a much longer time to ignition. Compared to pure PVA, the PHRR of PVA filled with 3 wt.% graphene is reduced by 49%. The flame retardancy of graphene for PVA matrix surpasses that of both Na-MMT and MWNTs with the same addition content. Such a remarkable behaviour might be explained by the forming of a compact, dense and uniform char during combustion.     

Acacia stabilized polyaniline dispersions: preparation, properties and blending with poly(vinyl alcohol)

Polyaniline (PANI) dispersion in water has been prepared by using industrially produced and cheaper stabilizer, namely gum acacia — dried exudates from a species of acacia tree. Gum acacia stabilized PANI particles can be easily isolated from the aniline polymerization reaction mixture and then re-dispersed in water. By increasing the content of gum acacia — in the polyaniline-gum acacia (PANI-ACACIA) redispersable composite from 42 to 70 wt.% it is possible to diminish the average particle diameter from 450 nm to 200 nm and lower its size distribution. The suitability of the dispersion for blending with water-soluble polymers, such as for example poly(vinyl alcohol) (PVA) has also been tested. The composite PANI-ACACIA containing 60 wt.% of gum acacia has yielded the best blends with PVA with the conductivity in the range of 10^− 4 to 10^− 5 S/cm.     

Preparation and properties of substrate PVA-GO composite membrane for solar photothermal conversion

Solar thermal desalination (STD) is a promising and sustainable techno- logy for extracting clean water resources. Whereas recent studies to improve STD performance primarily focus on interfacial solar evaporation, a non-traditional bottom heating method was designed in this study. Herein, we prepared the polyvinyl alcohol/graphene oxide (PVA-GO) composite membrane and adhered to the bottom of a beaker using crystallized PVA. The GO was loaded on a non-woven fabric and different concentrations of PVA were compared for their effect on the evaporation efficiency. The results showed that the addition of PVA increased the evaporation rate. The surface characteristic of GO membrane without PVA was a fibrous filamentous structure as observed by SEM, whereby the fibers were clearly visible. When the PVA concentration reached 6%, the non-woven fiber was completely wrapped by PVA. Under the action of a fixed light intensity, the photothermal conversion rates of GO, 2% PVA-GO, 4% PVA-GO and 6% PVA-GO membrane device could reach 39.93%, 42.61%, 45.10% and 47.00%, respectively, and the evaporation rates were 0.83, 0.88, 0.94 and 0.98 kg·m⁻²·h⁻¹, respectively. In addition, the PVA-GO composite membrane showed an excellent stability, which has significance for industrial application.