Mechanical Properties Of PVA Research Articles

Poly(vinyl alcohol) nanocomposites containing reduced graphene oxide coated with tannic acid for humidity sensor

Poly(vinyl alcohol) (PVA) nanocomposites were prepared by a solution casting method using a reduced graphene oxide coated with tannic acid (rGO-TA) as a filler. The rGO-TA was simply prepared by mixing tannic acid (TA) with graphene oxide (GO). The simple mixing process was found to be effective to reduce GO and to produce covalently-grafted TA layers on the reduced GO. The mechanical properties of PVA were much improved by the addition of rGO-TA because the TA layers increased the compatibility of the reduced GO with PVA matrix. For example, Young's modulus and elongation at break values of PVA were increased by 34.0 and 56.9%, respectively, by adding 1.0 wt% of rGO-TA. In addition, the PVA nanocomposites showed excellent humidity sensing properties over the wide relative humidity range and the long-term stability due to the conductive property of the reduced GO and the enhanced mechanical strength by the effective incorporation of rGO-TA into the PVA matrix.

Effect of Aluminium Nitrate Hydrate on the Crystalline, Thermal and Mechanical Properties of Poly(Vinyl Alcohol) Film

The effect of aluminium nitrate hydrate (Al(NO3)3·9H2O) on the crystalline, thermal and mechanical properties of PVA was studied in this paper. The interaction between Al(NO3)3·9H2O and PVA was investigated by Fourier transform infrared (FT-IR) spectroscopy. The influence of Al(NO3)3·9H2O on the crystalline, thermal, and mechanical properties of PVA was studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and tensile testing, respectively. The results indicated that Al(NO3)3·9H2O could form interaction with the hydroxyl group on PVA chain. The XRD studies revealed that the crystallites of PVA were destroyed by Al(NO3)3·9H2O. DSC studies showed that Al(NO3)3·9H2O could increase the flexibility of PVA chains and decrease the Tg of PVA. Tensile testing showed that after the addition of Al(NO3)3·9H2O the tensile strength of PVA film decreased and elongation at break increased. All these results show that Al(NO3)3·9H2O has a high plasticizing efficiency for PVA. However, Al(NO3)3·9H2O is a Lewis acid and the acidic property of Al(NO3)3·9H2O would cause the significant decrease of the thermal stability of PVA.

The overlooked role of reduced graphene oxide in the reinforcement of hydrophilic polymers

Mechanical properties of PVA are stabilized against moisture absorption by highly hydrophobic graphene.

High‐tensile‐strength polyvinyl alcohol films prepared from freeze/thaw cycled gels

ABSTRACTThe mechanical properties and molecular structure of a poly(vinyl alcohol) (PVA) film, which was obtained by eliminating water from a PVA hydrogel using repeated freeze/thaw cycles, were investigated by tensile tests, thermal analysis, and X‐ray diffraction measurements. The mechanical properties of PVA with 99.9% saponification were measured as a function of the number of freeze/thaw cycles performed. The tensile strength and Young's modulus increased and the elongation at break decreased with increasing freeze/thaw cycles. The tensile strength and Young's modulus of PVA films obtained after seven freeze/thaw cycles were as high as 255 MPa and 13.5 GPa after annealing at 130°C. Thermal analysis and X‐ray diffraction measurements revealed that this is because of a high crystallinity and a large crystallite size. A good relationship between the tensile strength and the glass transition temperature was obtained, regardless of the degree of saponification and annealing conditions. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40578.

Morphology and Properties of Poly(vinyl alcohol)/MMT Nanocomposite Prepared by Solid-state Shear Milling (S3M)

Poly(vinyl alcohol) (PVA)/montmorillonite (MMT) nanocomposites were prepared by combining solid-state shear milling (S3M) technology with melt intercalation. Compared with the composite obtained by simple melt intercalation, more MMT layers were exfoliated and apparently oriented along the injection molding direction in the nanocomposite prepared by combining S3M technology and melt intercalation, which greatly increased the orientation degree of MMT, resulting in the greater interactions between PVA and MMT layers. Simultaneously, this also promoted the orientation of PVA molecules and produced effective nucleation of the crystallization of PVA. Consequently, the thermal stability and mechanical properties of PVA were obviously improved. For instance, when the MMT content was 3 wt%, the tensile strength and modulus of the nanocomposite with MMT prepared by S3M were 98.9 MPa and 3.1 GPa, respectively, increasing by 52% and 63.2% compared with PVA.

The plasticizing effect of calcium nitrate on poly(vinyl alcohol)

AbstractCalcium nitrate (Ca(NO3)2) was used as the plasticizer to improve the properties of Poly(vinyl alcohol) (PVA). The interaction between Ca(NO3)2 and PVA was investigated by Fourier transform infrared (FTIR) spectroscopy. The influence of Ca(NO3)2 on the crystalline, thermal, and mechanical properties of PVA was studied by X‐Ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and tensile testing, respectively. FTIR studies showed that Ca(NO3)2 could strongly interact with PVA molecule and reduce the intensity of the hydrogen bonding between PVA molecules. The crystallization of PVA was interrupted and the degree of crystallinity of PVA decreased due to the strong interaction between Ca(NO3)2 and PVA. DSC studies showed that the glass transition temperature of PVA decreased with the addition of Ca(NO3)2. However, the thermal stability of PVA decreased with the addition of Ca(NO3)2. The mechanical properties of PVA was improved with the addition of Ca(NO3)2, PVA film became soft and ductile, with lower tensile strength and higher elongation at break compared with original PVA. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Poly(vinyl alcohol) Nanocomposites Filled with Poly(vinyl alcohol)-Grafted Graphene Oxide

We present a novel approach to the fabrication of advanced polymeric nanocomposites from poly(vinyl alcohol) (PVA) by incorporation of PVA-grafted graphene oxide. In this work, we have synthesized PVA-grafted graphene oxide (PVA-g-GO) for the strong interfacial adhesion of graphene oxide (GO) to the PVA matrix. It was found that the mechanical properties of PVA were greatly improved by incorporating PVA-g-GO. For example, the tensile strength and Young's modulus of the PVA nanocomposite films containing 1 wt % net GO in the PVA-g-GO significantly increased by 88 and 150%, respectively, as compared to unfilled PVA. The elongation at break was also increased by 22%, whereas the GO/PVA nanocomposite containing 1 wt % pristine GO was decreased by 15%. Therefore, the presence of the PVA-g-GO in the PVA matrix could make the PVA not only stronger but also tougher. The strong interfacial adhesion between PVA-g-GO and the PVA matrix was attributed to the good compatibility between PVA-g-GO and the matrix PVA as well as the hydrogen-bonding between them.

Poly(vinyl alcohol)/halloysite nanotubes bionanocomposite films: Properties and in vitro osteoblasts and fibroblasts response

In this study, transparent poly(vinyl alcohol) (PVA) and PVA/halloysite nanotubes (HNTs) bionanocomposite films were prepared by solution casting and glutaraldehyde (GA) crosslinking. The surface topography and chemistry of the films were characterized by atomic force microscopy (AFM) and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, respectively. Blending with HNTs induced changes in nanotopography and surface chemistry of PVA films. The mechanical properties of PVA were enhanced by the incorporated HNTs. The stain-induced crystallization was confirmed by DSC after tensile test. MC3T3-E1 osteoblast-like and NIH 3T3 fibroblast cells were cultured on neat PVA and PVA/HNTs films to evaluate the effects of surface nanotopography and composition on cell behavior. The observations indicated that MC3T3-E1 cell behavior strongly responded to surface nanotopography. On nanotube-dominant surface, cells exhibited a significantly higher level of adhesion than on neat PVA film, whereas neat PVA showed higher degree of osteoblast proliferation compared with PVA/HNTs. In vitro fibroblasts response demonstrated that both neat PVA and PVA/HNTs nanocomposite films were biocompatible and PVA/HNTs films favored to fibroblasts attach and growth below 7.5 wt % of HNTs incorporated. In summary, these results provided insights into understanding of PVA and PVA/HNTs bionanocomposite films in potential applications in bone tissue engineering and drug delivery systems.

Poly(vinyl alcohol) nanocomposites reinforced with cellulose fibrils isolated by high intensity ultrasonication

Cellulose fibrils in micro and nanoscales generated from biomass are relative new reinforcing materials for polymer composites, which have potential lightweight and high strength and are biodegradable. The objective of this study was to reinforce biodegradable polymers by cellulose fibrils generated from several cellulose sources by ultrasonic treatment in order to utilize biomass to fabricate high-value products. The geometrical characteristics of the fibrils were investigated by polarized light microscopy (PLM) and atomic force microscopy (AFM). The degree of fibrillation of the fibers evaluated by water retention value was significantly increased after treatment. The treated cellulose and separated fibrils were used to reinforce poly(vinyl alcohol) (PVA) to make biodegradable nanocomposites by film casting. The mechanical properties of PVA were significantly improved by most of the small fibrils. The morphological characteristics of the nanocomposites were investigated with PLM, scanning electron microscopy, and AFM.

Protein-functionalized carbon nanotube-polymer composites

We have developed fully integrated nanotube composite materials through the functionalization of multiwall carbon nanotubes (MWCNTs) by covalently attaching ferritin protein molecules onto the surface of MWCNTs. The investigation of the thermomechanical behavior was performed by dynamic mechanical thermal analysis. Results demonstrated dramatic enhancement in the mechanical properties of PVA, for example a 100%–110% increase in the modulus with the addition of 1.5 wt % of ferritin functionalized MWCNTs. Samples containing functionalized nanotubes showed a stronger influence on glass transition temperature in comparison to composites containing the same amount of nonfunctionalized nanotubes.

Temperature dependence of the morphology and mechanical properties of poly(vinyl alcohol) drawn films prepared by gelation/crystallization from solutions by X-ray and solid state 13C NMR

The morphology and mechanical properties of PVA were studied using atactic poly(vinyl alcohol) (at-PVA) dry gel films prepared by crystallization from solutions in dimethyl sulfoxide (Me 2SO) and water (H 2O) mixtures, in which Me 2SO/H 2O composition was set to be 60:40. The hot homogenized solution was quenched by pouring it into an aluminum tray controlled at −80°C, thus generating a gel. The crystal lattice modulus along the chain axis was measured by X-ray diffraction. The values were 200–220 GPa, which is independent of temperature up to 170°C. However, the values became lower with further increase in temperature and the value at 200°C became 133 GPa. This tendency is different from the previous reports showing rapid decrease in the crystal modulus at higher temperature than 120°C. The difference means that crystallites within the specimens prepared by quenching the solution (Me 2SO/H 2O=60:40) at −80°C are in much more stable state than those of the previous specimens. In spite of the temperature independence of the crystal modulus along the chain axis and the crystallinity, the storage modulus similar to Young's modulus decreases gradually with increasing temperature. To study the mechanical properties and molecular orientation of the present specimens with the stable crystallites, the orientational behavior of crystallites was estimated in terms of the orientation distribution function of crystallites, and Young's modulus was calculated by using the generalized orientation factors of crystallites and amorphous chain segments estimated from the orientation functions of crystallites and amorphous chain segments. In doing so, the theoretical calculation was carried out by using a three-dimensional model, in which the oriented crystalline layers are surrounded by an anisotropic amorphous phase and the strains of the two phases at the boundary are identical. The theoretical values were in good agreement with the experimental ones. The 13C NMR measurements suggested that the inter-molecular hydrogen bonds may be broken by drawing and the intra-molecular hydrogen bonds are more preferably formed in the mm and mr sequences with draw ratio but no marked difference in the structure exists between the crystalline and non-crystalline regions, as judged from the hydrogen bonding in the triad sequences. Even so, the spin–lattice relaxation time, T 1C, decreased drastically with increasing temperature reflecting drastic activity of chain mobility. Accordingly, the drastic decrease in Young's modulus (the storage modulus) is thought to be due to the fact that chain mobility in the amorphous phase becomes more pronounced as temperature increases.

Effect of crosslinking on the mechanical and thermal properties of poly(vinyl alcohol)

Poly(vinyl alcohol) was crosslinked with hexamethylene diisocyanate in solution. A broad range of degrees of crosslinking, from 1.7 up to 74mol% of reacted hydroxyl groups, was achieved. The variation of the thermal and mechanical properties of PVA with the crosslinking density show an initial decrease due to the diminution of the crystallinity of the system, caused by the crosslinking. After an abrupt rise at about 20%, the properties tend to level off independently on the increase of the crosslinking. This behaviour is explained as a result of the competitive action of at least three factors during the crosslinking: (i) weakening of the existing physical network due to hydrogen bonding; (ii) formation of a chemical network; and (iii) introduction of flexible moieties. The last factor is closely connected with the specific chemical structure of the crosslinker itself.