The influence of dehydration on the interfacial bonding,microstructure and mechanical properties of poly(vinyl alcohol)/graphene oxide nanocomposites

The relationship between the interfacial bonding, microstructure and mechanical properties of the poly(vinyl alcohol)/graphene oxide nanocomposites (PVA/GO) has been investigated by controlling the water content through a dehydration process. The interfacial bonding in PVA/GO was predominantly by hydrogen bonds which were strongly affected by the dehydration process. Micro-voids in the microstructure formed after dehydration due to the shrinkage of the fibrils. A variety of hydrogen bonds including water–water, water–GO and water–PVA can be replaced with the strong PVA–GO interfacial bond resulting in a transition from ductile to brittle fracture. The tensile modulus and strength properties of the PVA and PVA/GO increased as the amount of residual water reduced, while the fracture strain was decreased. The surface mechanical properties of PVA/GO measured by nanoindentation showed broadly similar trends with water content as the bulk mechanical properties. However, there was a threshold value of approximately 3 wt.% water below which the surface mechanical properties decrease slightly. The indentation modulus was higher than the tensile modulus by a factor of at least three. The combined influence of the microstructure and the distribution of water in the nanocomposite is considered to be responsible for this.     

Mechanical,thermal, and structural properties of uniaxially drawn polylactic acid/halloysite nanocomposites

The effect of solid-state drawing at different conditions including drawing ratio (DR), drawing temperature (DT), and drawing speed (DS) on mechanical, thermal, and structural properties of polylactic acid (PLA)/halloysite nanotubes (HNTs) composites were studied. PLA/HNTs composite films were prepared by melt mixing process followed by compression molding. Subsequently, drawing was performed using a tensile testing machine. Field emission scanning electron microscopy confirmed alignment and orientation of polymer chains and HNTs after stretching. Thermal and mechanical analysis of the drawn films revealed that glass transition temperature, crystallinity, ultimate tensile strength, and Young's modulus were enhanced by increasing DR, DT, and DS. However, toughness was decreased by increasing DR and DS and increased by increasing DT. In addition, the drawn nanocomposites showed superior mechanical and thermal properties compared to the drawn neat PLA films indicating the high efficiency of solid-state drawing and positive effect of HNTs. Therefore, this study could be helpful to introduce an approach to enhance the properties of biopolymers and renewable polymers by uniaxial drawing.     

Superabsorbent,Breathable Graphene Oxide-Based Nanocomposite Hydrogel as a Dense Membrane for Use in Protective Clothing

This study examines the synthesis, fabrication and characterization of poly acrylamido methyl propane sulfonic acid (PAMPS)/graphene oxide (GO) nanocomposites. PAMPS-GO nanocomposite hydrogel was synthesized by radical initiated polymerization and its swelling properties, water vapor permeability (WVP), and stress-strain behavior were evaluated. The swelling behavior of hydrogel nanocomposites were improved at the presence of 0.2 wt% GO, as confirmed by water uptake experiments. It should be noted that as GO loading increased, so did the WVP of the hydrogel. The stress-strain test also revealed that the incorporation of just 0.1% of GO raised the tensile strength and young modulus of the hydrogels by 42% and 37% respectively. These fabricated dense membranes can have applications in protective clothing and wound dressing.     

Improving interfacial interaction of l‐phenylalanine‐functionalized graphene nanofiller and poly(vinyl alcohol) nanocomposites for obtaining significant membrane properties: Morphology,thermal, and mechanical studies

In polymer nanocomposite synthesis, the challenges are achieving well dispersion of nanofiller and its maximum interfacial interaction with polymer matrix at low loading percent. In this study, the preparation of poly (vinyl alcohol) (PVA) nanocomposites with l ‐phenylalanine‐functionalized graphene (f‐graphene) using a simple water solution processing method is reported. Graphene layers were functionalized with l ‐phenylalanine amino acid as a biocompatible and environmentally friendly modifier. The obtained PVA/f‐graphene nanocomposite membranes were smooth, uniform, and flexible. Efficient interaction was found between f‐graphene and PVA matrix, which caused significant improvement in mechanical and thermal properties of the graphene‐based nanocomposite with homogeneous dispersion. POLYM. COMPOS., 37:1924–1935, 2016. © 2015 Society of Plastics Engineers     

Electromagnetic interference shielding properties of graphene quantum-dots reinforced poly(vinyl alcohol)/polypyrrole blend nanocomposites

Graphene quantum dots (GQDs) reinforced poly(vinyl alcohol) (PVA)/polypyrrole (WPPy) nanocomposite films with various GQDs loadings were synthesized using the versatile solvent casting method. The structural and morphological properties of PVA/WPPy/GQDs nanocomposite films were investigated by employing Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The thermogravimetric analysis revealed enhanced thermal stability of synthesized nanocomposites while enhanced dielectric properties were also observed. The maximum dielectric constant value for PVA/WPPy/GQDs nanocomposite films was observed to be ε = 6,311.85 (50 Hz, 150°C). The electromagnetic interference (EMI) shielding effectiveness (SE) of nanocomposite films was determined in the X-band (8–12 GHz) and Ku-band (12–18 GHz) frequency region. The EMI SE was found to be increased from 0.8 dB for the pure PVA film to 9.8 dB for the PVA/WPPy/GQDs nanocomposite film containing 10 wt% GQDs loading. The enhanced EMI shielding efficiency of nanocomposite films has resulted from the homogenous dispersion of GQDs in PVA/WPPy blend nanocomposites. Thus, the prepared nanocomposites are envisioned to utilize as a lightweight, flexible, and low-cost material for EMI shielding applications.     

Nanofibrillated cellulose,poly(vinyl alcohol), montmorillonite clay hybrid nanocomposites with superior barrier and thermomechanical properties

Nanocomposites of poly(vinyl alcohol) (PVA), nanofibrillated cellulose (NFC), and montmorillonite (MMT) clay were prepared via solvent casting. In addition to investigating the effect of clay loading, PVA matrices crosslinked with poly(acrylic acid) (PAA) were prepared and compared with linear (noncrosslinked) PVA nanocomposites. ¹³C NMR and infrared spectroscopy confirmed the presence of crosslinks. Scanning electron microscopy revealed effective NFC and MMT clay dispersion throughout the nanocomposites, while X‐ray diffraction highlighted the effectiveness of PAA to encourage clay dispersion. MMT clay provided a barrier against the diffusion of water and oxygen (molecules) through the nanocomposite films. Permeability and adsorption were further reduced by crosslinking, while oxygen barrier properties were remarkably enhanced at elevated relative humidities. Thermal stability of the PVA segments was strengthened by the presence of MMT clay and crosslinks. MMT clay–reinforced PVA and NFC within the films, increasing the Young's modulus, tensile strength, and glass transition temperature. Crosslinking further enhanced the thermomechanical properties by imparting physical restraints on polymer chain segments, providing elasticity, and ductility. The hybrid films were successfully reinforced at elevated humidities, with nanocomposites displaying enhanced storage moduli and near‐complete recovery. POLYM. COMPOS., 35:1117–1131, 2014. © 2013 Society of Plastics Engineers     

A chitosan/poly(vinyl alcohol) nanocomposite film reinforced with natural halloysite nanotubes

Biodegradable polymer/clay nanocomposites have attracted tremendous attentions because of their excellent properties and ecofriendly advantages. In this article, a series of nanocomposite films were prepared by introducing of halloysite nanotubes (HTs) into chitosan (CS)/poly(vinyl alcohol) (PVA) matrix using the solution casting method, and the effect of HT as nanofillers on the properties of polymer/HT nanocomposites was explored. The results indicated that the tensile strength of CS/PVA/HT3 and elongation at break of CS/PVA/HT2 sharply increased by 39.72% and 26.14% in comparison with the pure CS/PVA film, respectively. The water resistance and thermal stability of polymer/HT nanocomposites were also improved compared with the pure CS/PVA film, but the optical property of the nanocomposite films was not affected by introducing HT into the CS/PVA matrix. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Improving the mechanical properties of graphene oxide based materials by covalent attachment of polymer chains

We report on the modification of graphene oxide (GO) with poly(vinyl alcohol) (PVA) leading to the mechanical improvement of GO based materials. First, GO was covalently functionalised with PVA by esterification of carboxylic groups on GO with hydroxyl groups of PVA resulting in functionalised f-(PVA)GO. This was carried out for PVA of six different molecular weights. This functionalised graphene oxide could be formed into a paper-like material by vacuum filtration. Papers prepared from f-(PVA)GO showed significant increases in mechanical properties compared to those prepared with GO or with simple mixtures of GO and PVA. The best performance was achieved for PVA functional groups with molecular weights between 50 and 150 kg/mol. Improvements in Young’s moduli of 60% and tensile strength of 400% were observed relative to GO-only paper. The improved mechanical properties are attributed to enhanced inter-flake stress transfer due to the covalently bonded PVA. Second, functionalised f-(PVA)GO was used as filler in PVA-based composites. The application of a pre-selection method allowed the use of only the largest functionalised f-(PVA)GO flakes. This resulted in substantially reinforced PVA–f-(PVA)GO composites. Both modulus and strength increased by 40% relative to the pure polymer for f-(PVA)GO loadings below 0.3 vol.%.     

Preparation of graphene/poly(vinyl alcohol) nanocomposites with enhanced mechanical properties and water resistance

The control and dispersal of graphene nanosheets in polymer hosts are challenges in the development of high‐performance graphene‐based nanocomposites due to the strong interlayer cohesive energy and surface inertia. Here we report a simple and practical approach to synthesize graphene‐reinforced poly(vinyl alcohol) (PVA) composite films by incorporating graphene oxide and graphene into PVA aqueous solution. The resulting nanocomposites revealed increases of up to 212% in tensile strength and 34% in elongation at break with only 0.5 wt% graphene content. Water absorption measurements showed that the water absorption ratio of the graphene/PVA composites decreased from 105.2 to 48.8%, and the barrier properties were obviously improved. Contact angle measurements showed that the composites were hydrophobic (θ > 90°) in contrast to the highly hydrophilic (θ < 90°) pure PVA. Copyright © 2011 Society of Chemical Industry     

Structure evolution of melt‐spun poly(vinyl alcohol) fibers during hot‐drawing

The drawability of melt‐spun poly(vinyl alcohol) (PVA) fibers and its structure evolution during hot‐drawing process were studied by differential scanning calorimetry (DSC), two dimensional X‐ray diffraction (2‐D WAXD) and dynamic mechanical analysis (DMA). The results showed that the water content of PVA fibers should be controlled before hot‐drawing and the proper drying condition was drying at 200°C for 3 min. PVA fibers with excellent mechanical properties could be obtained by drawing at 200°C and 100 mm/min. The melt point and crystallinity of PVA fibers increased with the draw ratio increasing. The 2‐D WAXD patterns of PVA fibers changed from circular scattering pattern to sharp diffraction point, confirming the change of PVA fibers from random orientation to high degree orientation. Accordingly, the tensile strength of PVA fibers enhanced by hot‐drawing, reaching 1.85 GPa when the draw ratio was 16. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and characterization of graphene/poly(vinyl alcohol) nanocomposites

Graphene (GE)‐based nanocomposites are emerging as a new class of materials that hold promise for many applications. In this article, we present a general approach for the preparation of GE/poly(vinyl alcohol) (PVA) nanocomposites. The basic strategy involved the preparation of graphite oxide from graphite, complete exfoliation of graphite oxide into graphene oxide sheets, followed by reduction to GE nanosheets, and finally, the preparation of the GE/PVA nanocomposites by a simple solution‐mixing method. The synthesized products were characterized by X‐ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetry, and differential scanning calorimetry analysis. The GE nanosheets were well dispersed in the PVA matrix, and the restacking of the GE sheets was effectively prevented. Because of the strong interfacial interaction between PVA and GE, which mainly resulted from the hydrogen‐bond interaction, together with the improvement in the PVA crystallinity, the mechanical properties and thermal stability of the nanocomposites were obviously improved. The tensile strength was increased from 23 MPa for PVA to 49.5 MPa for the nanocomposite with a 3.25 wt % GE loading. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characterization of graphene oxide/poly(vinyl alcohol) composite nanofibers via electrospinning

Graphene oxide (GO) was well dispersed in poly(vinyl alcohol) (PVA) diluted aqueous solution, and then the mixture was electrospun into GO/PVA composite nanofibers. Electron microscopy and Raman spectroscopy on the as‐prepared and calcined samples confirm the uniform distribution of GO sheets in the nanofibers. The thermal and mechanical properties of the nanofibers vary considerably with different GO filler contents. The decomposition temperatures of the GO/PVA composite nanofiber dropped by 38–50°C compared with pure PVA. A very small loading of 0.02 wt % GO increases the tensile strength of the nanofibers by 42 times. A porous 3D structure was realized by postcalcining nanofibers in H₂. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and characterization of PVA-g-GO/PVA/PAN composite membrane for pervaporation desalination

Graphene oxide (GO) has extensive applications in membrane-based separations, but its dispersion in the membrane has always been a problem due to the presence of π–π interactions in GO nanosheets. In this study, a grafting reaction was designed by using poly (vinyl alcohol) (PVA) for GO grafting modification and poly (vinyl alcohol)-g-graphene oxide (PVA-g-GO) nanocomposites were synthesized. The grafting material to GO was the same as the basic separation polymer material. PVA-g-GO showed better dispersibility and hydrophilicity than GO, and a series of composite membranes were prepared using a polyacrylonitrile (PAN) ultrafiltration (UF) membrane as a substrate. PVA-g-GO nanocomposites and membranes were characterized by using X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), water contact angle, scanning electron microscopy (SEM), etc. The addition of PVA-g-GO improved both the separation performance and anti-swelling property of the composite membrane, and the PVA-g-GO/PVA/PAN composite membrane loaded with 2 wt.% PVA-g-GO obtained a high flux of 4.46 kg/m² · h and a high rejection of 99.99% when dehydrating 3.5 wt.% NaCl solution at 30°C by pervaporation.     

Synergistic strengthening of composite films by crosslinking graphene oxide reinforcement and poly(vinyl alcohol) with dicarboxylic acids

High‐strength plastic materials with excellent biodegradability, non‐toxicity and economically wide availability are in high demand. Herein, we demonstrate graphene oxide (GO) composite of poly(vinyl alcohol) (PVA) as a potential bioplastic material by chemical crosslinking. For a potential bioplastic material, PVA has to be addressed for its high water absorbing capacity along with improvement in tensile strength and thermal stability. These issues were addressed by enhancing the interfacial binding between PVA and GO, covalent bonds between the two being introduced by crosslinking with dicarboxylic acids, namely succinic acid (SuA) and adipic acid (AdA). Crosslinking of neat PVA with dicarboxylic acids also resulted in enhanced swelling resistance and thermal stability. The greatest improvement in tensile strength and swelling resistance was observed for a GO crosslinked with diacids due to the synergistic effect of reinforcement and crosslinking. Improvements of 225 and 234% in the tensile strength of PVA (31.19 MPa) were observed for 5% GO–PVA samples crosslinked with 6.25 mmol AdA and 7.5 mmol SuA, respectively. For the same samples, water uptake was 44 and 29%, respectively, compared to the non‐crosslinked PVA (359%). © 2017 Society of Chemical Industry     

Synergistic effect of α‐ZrP and graphene oxide nanofillers on the gas barrier properties of PVA films

Two types of 2D nanofillers, α‐zirconium phosphate (α‐ZrP) and graphene oxide (GO), were synthesized and incorporated into poly(vinyl alcohol) (PVA) with 1 wt % loading level at various α‐ZrP:GO (Z:G = 5:1, 2:1, 1:1, 1:2, and 1:5) ratios. The resulting nanocomposites were tested for barrier properties by casting films from solution. The structure and morphology of α‐ZrP and GO were characterized by Fourier‐transform infrared spectroscopy, atomic force microscope, scanning electron microscopy, transmission electron microscopy, and X‐ray diffraction, which demonstrated successful preparation of exfoliated α‐ZrP and GO. The physical characteristics of the nanocomposite films, including thermal, mechanical, and gas barrier properties were investigated. The results indicated that the tensile strength, Young's modulus, and elongation at break of the PVA nanocomposite films with Z:G hybrid nanofiller improved compared to neat PVA. The glass transition temperature, melting temperature, and crystallinity also increased. Consequently there appears to be a synergistic effect with these two types of nanofillers that formed a specific macro structure of a “wall.” This macrostructure resulted in excellent O₂ gas barrier properties with the PVA/Z:G‐5:1 nanocomposite films having the best performance. The of the PVA/Z:G‐5:1 nanocomposite decreased from 1.835 × 10^?16 to 0.587 × 10^?16 cm³ cm cm^?2 s^?1 Pa^?1 compared with neat PVA. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46455.     

Carbon nanoparticles/polyvinyl alcohol composites with enhanced optical,thermal, mechanical,and flame-retardant properties

In this work, polyvinyl alcohol (PVA) is chemically bonded to carbon nanoparticles (CNPs) by a very simple and versatile solution casting method. Five different kinds of CNPs/PVA composite films were prepared; 0.5, 1.0, 1.5, 2.0, and 3.0 wt% CNPs dispersed in PVA. The as-prepared samples were characterized using various characterization techniques. The resulting nanocomposites proved to possess homogeneity and better mechanical, thermal, optical, and flame-retardant properties than pure PVA. Most of the CNPs with average particle size ≤100 nm were homogeneously dispersed in the PVA matrix showing fluorescence in the violet color zone. The crystallinity of the nanocomposites show a decline in the diffraction intensity as compared to pure PVA which results from the dwelling of CNPs inside the gaps of stacked-layer chains of PVA. The mechanical properties of nanocomposites indicated enhancement in toughness, elastic modulus and tensile strength with an increase in CNPs contents. The assessment for flame-retardant properties was carried out through cone calorimetry. The results show a decrease in both total heat release rate (THRR) and peak heat release rate (pHRR) of the resulting nanocomposites as compared to pure PVA. The superior properties of the CNPs/PVA composites stemmed from the good interfacial bonding between the CNPs and PVA matrix.     

聚乙烯醇／蒙脱土复合材料的结构与性能研究

采用熔融插层法制备了聚乙烯醇(PVA)／蒙脱土(MMT)复合材料。通过X射线衍射仪和透射电镜对复合材料的结构进行表征，结果表明所得复合材料为剥离型或部分剥离型结构。热重测试、电子拉力试验和水溶性试验结果显示聚乙烯醇／蒙脱土纳米复合材料与纯聚乙烯醇相比，其加工热稳定性、综合力学性能以及耐水性能都得到了明显提高。     

Preparation of high-strength and high-modulus poly(vinyl alcohol) fibers by crosslinking wet spinning/multistep drawing method

This study is mainly focused on the preparation of high-strength and high-modulus poly(vinyl alcohol) (PVA) fibers by crosslinking wet spinning and multistep drawing. High strength as well as high modulus can be achieved by introduction of the crosslinks into the oriented chains to reduce entanglement degree and slippage between chains. The relationships between mechanical properties and fine structure of the drawn fibers were examined based on results of measurements of tensile property, thermal property, dynamic viscoelasticity, crystallinity, and orientation. The strength and Young's modulus of the drawn fibers are approximated to 1.82 and 51.76 GPa, respectively. The fiber has a sharp melting peak temperature that appeared at 236.7°C in the differential scanning calorimeter (DSC) curve. Our results indicate the multistep drawing procedure is superior to the conventional one-step drawing procedure. These excellent mechanical properties can be directly attributed to their high orientation of the amorphous chains. © 1994 John Wiley & Sons, Inc.     

Thin polymer films based on poly(vinyl alcohol) containing graphene oxide and reduced graphene oxide with functional properties

In this article, the effect of the addition of graphene oxide (GO) and reduced graphene oxide (rGO) on the mechanical properties, thermal stability, and electrical conductivity of polyvinyl alcohol (PVA) has been investigated. Different weight percentages of nanofillers ranging from 0.5 to 5 wt% have been combined with PVA. The ultrasonic technique has been applied to disperse nanofillers in the PVA solution. The nanocomposite films have been prepared via solution casting technique and the dispersion of nanofillers into the PVA has been studied through optical microscopy. The microstructure, crystallization behavior, and interfacial interaction were characterized through X-ray diffraction and Fourier transform infrared spectroscopy. Differential scanning calorimetry (DSC) and thermogravimetric analysis have been applied to study the thermal properties of the prepared nanocomposites. The DSC results revealed that the crystallization temperature and melting temperature were enhanced in the presence of GO nanofiller. Besides, the tensile strength at break was improved along with the addition of GO; however, elongation at break for PVA/GO and PVA/rGO was diminished. Moreover, all specimens showed insulating behavior and the only sample was electrically conducting, which contain a high amount of rGO (5 wt%).     

Mechanical Properties of Single-Layer Diamond Reinforced Poly(vinyl alcohol) Nanocomposites through Atomistic Simulation

Low-dimensional carbon nanostructures are ideal nanofillers to reinforce the mechanical performance of polymer nanocomposites due to their excellent mechanical properties. Through molecular dynamics simulations, the mechanical performance of poly(vinyl alchohol) (PVA) nanocomposites reinforced with a single-layer diamond – diamane is investigated. It is found the PVA/diamane exhibits similar interfacial strengths and pull-out characteristics with the PVA/bilayer-graphene counterpart. Specifically, when the nanofiller is fully embedded in the nanocomposite, it is unable to deform simultaneously with the PVA matrix due to the weak interfacial load transfer efficiency, thus the enhancement effect is not significant. In comparison, diamane can effectively promote the tensile properties of the nanocomposite when it has a laminated structure as it deforms simultaneously with the matrix. With this configuration, the interlayer sp³ bonds endows diamane with a much higher resistance under compression and shear tests, thus the nanocomposite can reach very high compressive and shear stress. Overall, enhancement on the mechanical interlocking at the interface as triggered by surface functionalization is only effective for the fully embedded nanofiller. This work provides a fundamental understanding of the mechanical properties of PVA nanocomposites reinforced by diamane, which can shed lights on the design and preparation of next generation high-performance nanocomposites.