Polyvinyl Alcohol Composites Research Articles

Effects of Partial Replacement of Eggshell Powder by Halloysite Nanotubes on the Properties of Polyvinyl Alcohol Composites

Polyvinyl alcohol (PVA)/eggshell powder (ESP) were prepared via solution casting method. The effects of gradual replacement of ESP by halloysite nanotubes (HNTs) were investigated based on tensile properties, physical properties and biodegradability. The main objective is to study the effect of hybrid fillers and also to compare the properties of PVA/ESP composite with conventional filler, HNT. The tensile properties decreased with increasing HNT loading. Scanning electron microscopy (SEM) studies showed that agglomeration of filler were present throughout the composites. Due to the presence of hydroxyl group on the outer and inner surface of HNT, the water absorption and water vapor transmisibility were found to increase with increasing HNTs loading. The biodegradability of film filled with HNT is lower compared to the film filled with ESP.

Structural mechanical and electrical property evaluation of nano cadmium oxide polyvinyl alcohol composites

In this work, the effect of nano cadmium oxide material on the physico-mechanical and electrical properties of polyvinyl alcohol (PVA) films was studied. A series of PVA/CdO nanocomposites with varying amounts of cadmium oxide (CdO) viz. 0, 0.5, 1.0 2.0 and 4.0 wt% have been prepared by solution casting method. The prepared polymer nanocomposites were analysed for XRD, SEM, FTIR and UV–vis spectra. Further, the tensile strength and elongation of these polymer nanocomposites were measured and compared with those of the neat polymer systems. UV–vis spectra showed that the absorbance increases with the increasing amount of nano CdO. The nano CdO particles are not agglomerated in the PVA matrix as observed from SEM images. The influence of frequency on the dielectric properties was studied at room temperature. The dielectric properties provide the information about the dielectric relaxation and possible interaction between the nano material and polymer matrix which can be exploited for microwave applications.

Preparation of SiC Fibers from Indonesian Natural Resource Prepared by Electrospinning Method

SiC fibers were prepared via electrospinning method. The starting materials were polyvinyl alcohol, sucrose, and SiO2. The SiO2 was extracted from natural pyrophyllite. In this work, we report the effect of polyvinyl alcohol and applied voltage on structural SiC fibers. The samples were then characterized using XRF, FTIR, and SEM-EDX. Based on the results of data analysis, it was shown that the optimum composition of polyvinyl alcohol in the SiC fibers was of 13.75% (w/v). It was also found that the SiC fibers had a smooth surface with a uniform diameter. Furthermore, the optimum applied voltage was set up at about 24 kV.

Special Issue on Wastewater Treatment and Reuse Technologies

Wastewater treatment allows for the safe disposal of municipal and industrial wastewater to protect public health and the ecosystem[...]

Preparation, dielectric and a.c. conductivity studies on chemically treated sisal powder filled polyvinyl alcohol biocomposites

In this paper, development and electrical characterization of sisal powder filled polyvinyl alcohol (PVA) composites is reported. Dielectric measurements were conducted on these composites on a LCR meter in the temperature range from 30 to 150°C and in the frequency range 1 kHz - 10 kHz. The effects of temperature and frequency variation on dielectric constant (ε’), dielectric dissipation factor (tan δ) and on a. c. conductivity (σa.c.) were determined. On increasing the filler content, dielectric constant increased, it was mainly due to motion of the dipolar groups of the interfacial polarization occurring in the composites. The conductivity increased with rise in temperature.Keywords: PVA, Electrical Properties, Dielectric Properties, Electrical Conductivity

Analysis of physical and magnetic properties of composite NdFeB bind with polyvinyl alcohol

The composite magnet NdFeB has been made using magnetic powder MQP-B and polyvinyl alcohol (PVA) as the binder. The mixing compositions of raw materials used are: 95 wt% NdFeB - 5 wt% PVA, 92.5 wt% NdFeB - 7.5 wt% PVA, 90 wt.% NdFeB - 10 wt% PVA, and 87.5 wt% NdFeB - 12.5 wt% PVA. Both raw materials are weighed according to the composition, and then mixed until homogeneous. Furthermore, pellet forming was made using dry pressing at 50 kgf/cm2 pressures and continued with drying at 100 °C and 10 mmbar for 4 hours. The characterization includes bulk density, hardness, compressive strength measurements, and magnetic properties testing. The characterization results show that the optimal composition of binder PVA is achieved at 5–7.5 wt% NdFeB composite magnet with following properties: bulk density = 5.21–5.25 g/cm3, hardness = 302.17 - 304.32 Hv, compressive strength = 25.17–3.17 kgf/cm2, magnetic flux = 1150-1170 Gauss, remanence = 70.90–74.97 emu/g or 4.7–5.0 kGauss, coercivity = 8.68–8.76 kOe, and energy product = 2.89–3.04 MgOe.

Influence of Polyvinyl Alcohol (PVA) Addition on Silica Membrane Performance Prepared from Rice Straw

The utilization and modification of silica from rice straw as the main ingredient of adsorbent has been studied. The aim of this study was to determine the optimum composition of PVA (polyvinyl alcohol): silica to produce adsorbents with excellent pore characteristics, optimum adsorption efficiency and optimum pH for methyl yellow adsorptions. X-Ray Fluorescence (XRF) analysis results showed that straw ash contains 82.12 % of silica (SiO2). SAA (Surface Area Analyzer) analysis showed optimum composition ratio 5:5 of PVA: silica with surface area of 1.503 m2/g. Besides, based on the pore size distribution of PVA: silica (5:5) showed the narrow pore size distribution with the largest pore cumulative volume of 2.8 x 10-3 cc/g. The optimum pH for Methanyl Yellow adsorption is pH 2 with adsorption capacity = 72.1346%.

Highly Structured Polyvinyl Alcohol Porous Carriers: Tuning Inherent Stability and Release Kinetics in Water.

Polyvinyl alcohol (PVA) porous carriers were prepared by means of ice templating of aqueous solutions containing of 90 kD and/or 16 kD PVA. The carriers were loaded with traces of a colored probe (methyl orange) to screen their release properties, once immersed in water. The carriers prepared from solutions containing 90 kD and 16 kD PVA resulted in intimate polymer mixtures, exhibiting physical properties that stand in between those of the bare 90 kD or 16 kD PVA end members. The freezing protocols employed were adapted to prepare carriers textured in the form of either monolithic scaffolds (directional constant freezing rate) or millimetric pellets (flash-freeze). Monolithic carriers remain stable in aqueous solution, and the probe release is governed by a swelling–diffusion mechanism. The kinetics of probe release can be tuned from minutes to hours by either increasing the total PVA content or the 90 kD-to-16 kD PVA ratio in the parent solution. In contrast, pellets (millimetric carriers) immersed in water release the probe on the scale of minutes, irrespective of the PVA content or composition. However, the PVA content and the 90 kD-to-16 kD PVA ratio dramatically affect the stability of the carriers. Depending on the formulation, these small carriers can develop swelling, erosion, or eventually massive dissolution.

Optimization of operating parameters for abrasion of areca sheath reinforced polymer composite: grey based Taguchi approach

Taguchi method has been widely and successfully used for more than two decades to improve the quality and performance of the product. In this research article, grey-based Taguchi method was implemented to optimize the operating parameters of dry sliding abrasive wear behavior of areca sheath fiber reinforced polyvinyl alcohol composites. Composites were prepared by incorporating randomly oriented benzyl chloride-modified areca sheath fibers taking 10, 20 and 30 wt% and experiments were conducted according to Taguchi’s L27 orthogonal array by considering three factors and three levels affecting the abrasion process using pin-on-disc apparatus. Grey relational analysis was utilized to optimize the multi-response tribological parameters. Analysis of variance was utilized to determine the importance of factors affecting wear the most. The specific wear rates for all the composites were also compared and discussed. The optimum process parameter which gives the best multiple response characteristics was found to be load 15 N, sliding velocity 0.392 m/s and filler content of 30 wt%. An improvement of 4.19% in GRG was observed after confirmation test which proves that the multiple performance characteristics of the natural fiber reinforced polymer composites can be adequately enhanced by this technique. Scanning electron micrographs were obtained at the optimum setting to support the findings.

A Novel ZnONPs/PVA-Functionalized Biomaterials for Bacterial Cells Immobilization and its Strengthening Effects on Quinoline Biodegradation

A novel bacterial cells immobilized carrier (ZnONPs/PVA), polyvinyl alcohol (PVA) composites decorated with ZnO nanoparticles (ZnO NPs), was prepared and used for immobilization of the strain Ochrobactrum sp. LC-1, and subsequently for quinoline degrading in water. Characterization of ZnONPs/PVA by using X-ray diffractometer and scanning electron microscopy demonstrated that ZnO NPs were coated on the surface of PVA cubes evenly and the bacterium grew well on the ZnONPs/PVA. Quinoline biodegradation results showed that the degradation effect of quinoline by ZnONPs/PVA immobilized cells was superior to the free cells significantly. The structure and physical properties of ZnNPs/PVA were maintained steady after the reuse of ZnNPs/PVA for cells immobilization several times. Reusability of the ZnONPs/PVA immobilized cells revealed that the quinoline removal ratio was above 97% within 8h under the conditions of pH neutral, 37°C when the initial quinoline concentration was 300mg/L.

Thermal conductivity of graphene oxide-enhanced polyvinyl alcohol composites depending on molecular interaction

Graphene oxide (GO) synthesized from graphite via oxidation and exfoliation is a graphene-like single-layer sheet with numerous oxygen groups and defects on the basal plane. In this study, GO is added as a filler in the polyvinyl alcohol (PVA) matrix for the purpose of improving thermal conductivity. GO is well dispersed in PVA aqueous solution, and GO/PVA composite films are easily prepared with various GO contents. The thermal conductivities of the polymer composites investigated in terms of GO content concentration, GO degree of oxidation, PVA degree of polymerization, and silica-bead packing in the GO/PVA composite. On the basis of phonon mean free path, the effect of oxygen groups in GO is discussed in relation to crystallinity of PVA and molecular interaction between GO and PVA. In addition, the phonon conductive path along the direction of thickness in the GO/PVA composite film is achieved via silica-bead packing.

The chemical composition and antioxidant and release properties of a black rice (Oryza sativa L.)-loaded chitosan and polyvinyl alcohol composite

A bioactive compound was successfully extracted from black rice (Oryza sativa L.) using a solvent extraction process. It was loaded into a chitosan and polyvinyl alcohol-based hydrogel composite at 10, 20 and 30wt%. The total phenolic content was estimated as 1–4mg GAE/g extraction. An SEM investigation revealed that the surface pores indicated interfacial adhesion between the bioactive compound and hydrogel composite. There was no significant change in thermal properties. Then, the bioactive compound loaded into the hydrogel composite presented swelling behavior of 600–1200% within 48h. With the presence of the bioactive compound in the hydrogel composite, greater antioxidant properties were present as investigated by DPPH, ABTS and FRAP assays. Furthermore, the in vitro release characteristic ranged from 60 to 80% for 60min. Preliminary investigation can be used to explain why a bioactive compound loaded into a chitosan and hydrogel composite has attracted interest in pharmaceutical and cosmetic research.

Suppressing Salt Transport through Composite Pervaporation Membranes for Brine Desalination

Pervaporation membranes have gained renewed interest in challenging feedwaters desalination, such as reverse osmosis (RO) concentrated brine wastewater. In this study, composite polyvinyl alcohol (PVA)/polyvinylidene fluoride (PVDF) pervaporation membranes were prepared for brine treatment. The composite membrane was firstly studied by adjusting the cross-linking density of PVA by glutaraldehyde: the membrane with higher cross-linking density exhibited much higher salt rejection efficiency for long-term operation. A trace of salt on the permeate side was found to diffuse through the membrane in the form of hydrated ions, following solution-diffusion mechanism. To further suppress the salt transport and achieve long-term stable operation, graphene oxide (GO) was incorporated into the PVA layer: the addition of GO had minor effects on water permeation but significantly suppressed the salt passage, compared to the pure PVA/PVDF membranes. In terms of brine wastewater containing organic/inorganic foulant, improved anti-fouling performance was also observed with GO-containing membranes. Furthermore, the highest flux of 28 L/m2h was obtained for the membrane with 0.1 wt. % of GO using 100 g/L NaCl as the feed at 65 °C by optimising the pervaporation rig, with permeate conductivity below 1.2 µS/cm over 24 h (equivalent to a salt rejection of >99.99%).

Three-dimensional graphene oxide and polyvinyl alcohol composites as structured activated carbons for capacitive desalination

Membrane capacitive deionization (MCDI) is a technique that is derived from conventional capacitive deionization (CDI). Additional ion-exchange membranes are included in the MCDI cell to prevent ion-expulsion and improve cyclability. As it stands, MCDI represents the most feasible option for large scale desalination to take place. In this work, we investigate the desalination performance of a novel structured activated carbon material synthesized from the assembly of polyvinyl alcohol (PVA) on graphene oxide (GO). A hydrothermal treatment causes self-assembly of the PVA covered GO sheets and the product is a polymeric framework supported by reduced GO sheets. A further activation process by KOH produces the structured activated carbon (AC). These new structured ACs possess unique morphologies and exhibit high adsorption capacities (>30mgg−1) which far surpass traditional ACs.

Low percolation threshold and enhanced electrical and dielectric properties of graphite powder/poly (vinyl alcohol) composites

Polyvinyl alcohol (PVA) composites with a conductive filler, graphite powder (GP) were prepared by solution casting process. GP remains well dispersed in the PVA composites as evidenced by the lack of the characteristic graphite reflection in the composites. SEM imaging show smooth fractured surfaces with graphite stacks and obvious debonding from the matrix in the GP/PVA composites. The dielectric dispersion and AC conductivity of the composite system exhibited a strong frequency dependence particularly in the vicinity of percolation threshold (fc ∼ 6 wt% = 2.65 vol%). A 150 times increase of dielectric permittivity and seven orders of magnitude higher conductivity were obtained by adding 2.65 vol% graphite powder in PVA indicating the efficient loading between the graphite and the matrix at percolation threshold which is well above the percolation threshold (fc = 0.41 vol%) for PVA/GOnP composites. Moreover, the dielectric properties were measured at about 30°C and 1 kHz. The values of permittivity and dielectric loss were found to increase with increasing graphite content. The percolative composites exhibit very low dielectric loss and leakage current density. Such GP/PVA flexible composites in tailored form might be important for many printing circuit board and capacitor applications in the age of device miniaturization. POLYM. COMPOS., 39:4400–4407, 2018. © 2017 Society of Plastics Engineers

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 have demonstrated Graphene oxide (GO) composite of polyvinyl 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. The issues were addressed by enhancing interfacial binding between PVA and GO, a covalent bond between the two is 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 highest improvement in tensile strength and swelling resistance was observed for a GO crosslinked with diacids due to the synergistic effect of reinforcement and crosslinking. Improvement of 225% and 234% in the tensile strength of PVA (31.19) MPa) was observed for 5%GO-PVA samples cross-linked with 6.25 mM adipic acid (AdA) and 7.5 mM succinic acid (SuA), respectively. For the same samples, water uptake was 44% (GO-AdA-CL-PVA) and 29.33% (GO-SuA-CL-PVA) compared to the uncross-linked PVA (359%).

MODIFIED ADHESIVE COMPOSITIONS BASED ON POLYVINYL ALCOHOL

The use of water soluble adhesives of both natural and synthetic origin, unlike adhesives on organic basis, contributes to solving problems of environmental protection and improvement of sanitary conditions. Therefore the purpose of the research is to make modifications of soluble polyvinyl alcohol adhesive compositions of various applications and forms of origin and evaluate their influence on technological and operational properties of adhesives. The research has the following results. Firstly, the authors have conducted the modification of polyvinyl alcohol water compositions by low-molecular (montmorillonite, wollastonite, phosphate acid) and high-macromolecular (starch) additives to improve technological and operational properties of the compositions. The viscosity of the composition was measured on Brookfield viscometer of type "DV-I". Cryo-processing (freezing) of the samples was carried applying a device for climatic testing "Kimura" KT70068. Adhesion was estimated by tensile strength during shear of glued wooden plates. Then, the influence of modifying additives on the properties of water-soluble adhesive compositions was determined. High-technological filled compositions based on polyvinyl alcohol, which are marked with improved working characteristics, particularly frost resistance were developed. Above mentioned compositions are stable for at least 4 cycles of "freezing – unfreezing" until the temperature –25 °C without significant viscosity change. This confirms the positive plasticizing impact of phosphoric acid on frost-resistance of the water-containing polyvinyl alcohol compositions. Adding of modified soluble starch to the compositions can regulate the technological characteristics of adhesives. It was made possible to reduce the content of polyvinyl alcohol in compositions without worsening of their adhesive properties. Adding the small quantities of mineral (nano) fillers in composition improves their adhesive properties without significant technological changes. The developed compositions are recommended for the glue production, which can be transported, stored and applied in the winter season.

Structural properties and temperature dependence dielectric properties of PVA-Al $$_2\mathrm{O}_3$$ 2 O 3 composite thin films

Thin films of polyvinyl alcohol (PVA)–aluminium oxide(Al\(_2\mathrm{O}_3\)) composite have been made by solution casting method. XRD, FESEM and FTIR techniques were used to characterize the prepared composite films for structural analysis. The existence of M–O bond was identified by FTIR. XRD study reveals that PVA composite has polycrystalline in nature. The morphological study shows the dispersion of Al\(_2\mathrm{O}_3\) particles on the surface of thin films. The effect of temperature and frequency on dielectric properties of PVA–Al\(_2\mathrm{O}_3\) composite was investigated and improvement of dielectric properties with temperature observed. AC conductivity is increased with temperature and maximum conductivity of \(3.20 \times 10^{-5}\) S/cm for PVAl-10% at 353 K is observed. Activation energy is evaluated from Arrhenius plot and found to lie in between 0.05 and 0.16 eV. Frequency exponent factor ‘s’ for Pristine PVA and PVAl-10% was calculated and found to lie in between 0 and 1. Impedance plots depict the semicircle at higher frequencies and residual tail at the lower frequencies and value of Rb is found to decrease till PVAl-10% and increased for further concentration. The prepared PVA–Al\(_2\mathrm{O}_3\) composites could be used in optoelectronic devices and thin film transistors as high k layer due to their high dielectric constant with low dielectric loss.

Low-temperature-cured highly conductive composite of Ag nanowires & polyvinyl alcohol**Project supported by the National Natural Science Foundation of China (Grant No. 61306080), the Natural Science Foundation of Hunan Province, China (Grant No. 2015JJ3143), and the Scientific and Technological Project of Hunan Provincial Development and Reform Commission, China.

Flexible conductive films were fabricated from a low-temperature-cured, highly conductive composite of silver nanowires (as conducting filler) and polyvinyl alcohol (PVA, as binder). Sheet resistance of 0.12 Ω/sq, conductivity of 2.63×104 S/cm, and contact resistance of 1.0 Ω/cm2 were measured in the films, along with excellent resistance to scratching and good flexibility, making them suitable electrical contact materials for flexible optoelectronic devices. Effects of curing temperature, curing duration, film thickness, and nanowire length on the film’s electrical properties were studied. Due to the abundance of hydroxyl groups on its molecular chains, the addition of PVA improves the film’s flexibility and resistance to scratching. Increased nanowire density and nanowire length benefit film conductance. Monte Carlo simulation was used to further explore the impact of these two parameters on the conductivity. It was observed that longer nanowires produce a higher length-ratio of conducting routes in the networks, giving better film conductivity.

Series resistance and interface states effects on the C–V and G/w–V characteristics in Au/(Co3O4-doped PVA)/n-Si structures at room temperature

Microwave-assisted method has been used for preparation of Co3O4 nanopowders. Then, Co3O4–doped polyvinyl alcohol (PVA) composites are deposited on n-Si wafer using spin coating method. The main electrical parameters of the Au/(Co3O4-doped PVA)/n-Si type Schotkky barrier diodes (SBDs) have been investigated by capacitance–voltage-frequency (C–V-f) and conductance–voltage-frequency (G/ω–V-f) measurements at room temperature and they were performed in the frequency range of 2 kHz–2 MHz and at (±4.5 V) by 50 mV steps. The XRD pattern of the as-prepared sample show that all diffraction peaks appeared in this pattern match very well with ICDD data and they can be readily indexed to the Co3O4 nanostructures, no other peaks were observed, which indicates the high purity of the sample. The effects of (Co3O4-doped PVA), series resistance (Rs) and surface states (Nss) on electrical characteristics have been investigated in detail. In order to eliminate the effect of Rs on high frequencies these measurements, the measured Cm and Gm/ω values were adjustment. The high values of Nss at low frequencies are responsible for the non-ideal behavior of C–V and G/ω–V characteristics. The obtained value of ND exponentially decreases; the value of ΦB (C–V) exponentially increases with increases frequency. Such behavior of ND and ΦB (C–V) are expected behavior and it is attributed to the particular density distribution of Nss, polarization processes and interfacial layer. Experimental results show that the C–V and G/ω–V characteristics of SBDs are affected not only in Nss and Rs but also interfacial polymer (Co3O4-doped PVA) layer.