THERMAL EFFECT ON THE UNIAXIAL TENSILE PROPERTIES AND STRUCTURE OF POLY (VINYL ALCOHOL) FILMS

Influence of heating or annealing at different temperatures from 25 to 140 °C on the uniaxial tensile properties of polyvinyl alcohol (PVA) thin films was investigated by using tensile testing method. It was observed that especially the shape of initial part (up to 10% strain) of the stress-strain curve changed significantly which indicates the formation of a transition point at a low strain value of around 1-2% strain with increasing anneal temperature. Besides, initial or Young’s modulus increased from 0.26 GPa to around 1 GPa as the temperature increased from 25 °C to around 100 °C and then it decreased slightly down to around 0.7 GPa. Ultimate tensile stress increased significantly from around 16 to 39 MPa. Moreover, toughness of the PVA films were improved from around 144*104 to 3942*104 J/m3 for the anneal temperatures from 80 to 130 °C. By using the FT-IR/ATR spectral results, the increase in tensile strength and toughness is assumed to be due to increase in the degree of crystallization and absorbance ratio of hydrogen bonded OH groups, that is, the increase in the more ordered structural units and reformation and/or breakage of intra- and inter-molecular hydrogen bonds during heating process

Uniaxial tensile and structural properties of poly(vinyl alcohol) films: The influence of heating and film thickness

Poly(vinyl alcohol) as pure or composite materials is widely used in the food and textile industries, andbiomedical applications due to some important properties such as uniaxial tensile, biocompatibility, and noncarcinogenicity. Investigation of the influence of the film thickness and heating on the uniaxial tensile, spectroscopic, and surface properties of PVA films investigated in this study is quite important for improving the properties of such materials and their applicability in different conditions. In this study, with the influence of heating, a necking behavior was observed at around 2% for thin films and 4-9% strain for thicker PVA films for which a kind of transition point at around 1-2% strain was observed. The mechanical strength of PVA films, strain at break, and Young's modulus were enhanced greatly as the temperature increased from 80 to around 110 degrees C, and then most of them decreased. The degree of crystallinity increased linearly with the heat temperature from around 36-40%. Although PVA thin films obtained a very smooth surface structure after being heated at 80 degrees C, with increasing heat temperature, the surface roughness of both thin and thick PVA films increased and the PVA thin films obtained more degraded film surface. (c) 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44915

Influence of heating on spectroscopic, mechanical, and thermal properties of reduced graphene oxide-poly(vinyl alcohol) composite films

The spectroscopic, uniaxial tensile, and thermal properties of reduced graphene oxide (rGO)-poly(vinyl) alcohol (PVA) composite films produced by using rGO synthesized using modified Hummer's method with varying weight ratio of rGO up to 10% were investigated by using an uniaxial tensile tester, Fourier Transform Infrared (Ft-IR)/Attenuated Total Reflectance (ATR) spectroscopy, and Differential Scanning Calorimeter (DSC) methods after heating process at different temperatures from room temperature to 200 degrees C. For unheated composite films, with increasing rGO weight ratio up to 10%, the Young's modulus of rGO-PVA films increased by approximately 2-3 times, conversely the strain at break values decreased greatly by about 40-50%. The heating process led to the significant improvement in the tensile strength and the Young's modulus, and great decrease in extensibility with respect to the unheated samples, e.g., the tensile strength and Young's modulus increased by 3-4 times and 8-10 times, respectively, for the heating temperatures up to 150 degrees C. With increasing heating temperature, the stress-strain curve of rGOPVA composite films turned from that of ductile and amorphous polymer to that of more brittle and rigid polymers. With increasing rGO content, the glass transition, the crystallization, and the melting temperatures increased and heating process generally shifted these temperatures to higher values. The great contribution of rGO content and the heating to the improvement of especially mechanical properties of rGO-PVA composite films thanks to the strong intermolecular interactions of rGO nanosheets with the PVA matrix molecules through hydrogen bonding and to the changes in the crystallinity ratio of PVA was shown in detail in the analysis of the spectral results. The relationship between the changes in the mechanical, structural, and thermal properties of the studied composite films was determined by using tensile testing, Ft-IR/ATR, and DSC methods. (C) 2018 Elsevier B.V. All rights reserved

Structural and tensile characteristics of reduced graphene oxide/poly (vinyl alcohol) composite films: Influence of ultraviolet irradiation

The influence of ultraviolet (UV) radiation on the structural and uniaxial tensile characteristics of reduced graphene oxide (rGO)/poly(vinyl alcohol) (PVA) composite films produced by using various contents (0-10 wt%) of rGO obtained by a microwave-assisted reduction process was investigated. With increasing rGO content, significant reinforcing effects of the rGO sheets were seen on the tensile characteristics of the unirradiated rGO/PVA composite films, that is, increases in the stiffness and rigidity and decreases in the strain at break values. After UV exposure times from minutes up to 1 hour, for all the rGO contents, the rGO/PVA composite films had improved tensile strength and modulus values as well as considerable improvement in the stress-strain behavior in spite of great decreases in the strain at break values. The structural changes responsible for the improvement in the tensile strength and Young's modulus of the rGO/PVA composite films were associated with the development of strong intermolecular interactions between the rGO sheets and the PVA polymer chains through the formation of hydrogen bonds. Deterioration of the mechanical characteristics, especially strain at break values, was mainly due to the photodegradation of the structural units induced by UV radiation leading to the formation of some free radicals caused by the chemical bond breakages in the polymer chains as well as the weakening of intermolecular interactions such as hydrogen bonds. Correlation between the changes in the tensile properties and the structure of the rGO/PVA composite films were sought by analyzing tensile testing, fourier transform infrared/attenuated total reflectance (FTIR/ATR), and UV-visible spectral results

Monitoring the film formation process of polystyrene/poly acrylamide (PS/PAAm) composite films annealed by IR heating

In this study, UV-visible (UVV) technique was used to probe the evolution of optical transmission during the film formation from composites of polystyrene (PS) latex particles and poly acrylamide (PAAm) films annealed by the infrared radiative heating (IRH) and convectional heating. Activation energies corresponding to the void closure and the interdiffusion stages were calculated. It was shown that the activation energy for the void closure processes of viscous flow from the composite films decreased considerably in IRH annealing technique. It was observed that IRH heating speeds up the film formation process and the decrease the required energy. POLYM. ENG. SCI., 58:353-360, 2018. (c) 2017 Society of Plastics Engineer

Electrodeposition of zinc and reduced graphene oxide on porous nickel electrodes for high performance supercapacitors

Electrochemical properties of porous nickel (Ni) foam, electrodeposited zinc (Zn) on Ni foam (Ni-Zn) and electrodeposited reduced graphene oxide (rGO) on Ni-Zn foam electrodes (Ni-Zn-rGO) in 6 M KOH electrolyte were investigated. Cyclic voltammetry (CV) and galvanostatic charge-discharge cycling (GCD) techniques were used to carry out the redox interactions, and cycling capacitive properties of the electrodes in KOH solution. Platinum (Pt) and gold (Au) foil were used as a counter electrode and the current collector in the electrochemical measurements, respectively. The specific capacitances of the electrodes were found from the GCD measurements as 155, 722 and 1820 F/g for Ni, Ni-Zn and Ni-Zn/rGO electrodes at the current density of 1 A/g, respectively. Scanning electron microscope (SEM) images of the three electrodes were also taken into account to associate all the electrochemical measurements. These results clearly show that specific capacitance values highly increased after the deposition of Zn and rGO to Ni electrode