Alcohol Composites Research Articles

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

Effects of enhanced hydrogen bonding on the mechanical properties of poly (vinyl alcohol)/carbon nanotubes nanocomposites

In this study, poly (vinyl alcohol) (PVA) composites reinforced by multiwall carbon nanotubes (MWCNTs) functionalized with either phenolic hydroxyl groups (MWCNTs-f-OH) or PVP molecule (PVP@MWCNTs) were fabricated. The objective was to elucidate the effect of different MWCNTs surface functionalization on the mechanical properties of the nanocomposites. It was found that both of PVP@MWCNTs and MWCNTs-f-OH had a good dispersion in PVA matrix. However, the MWCNTs-f-OH had stronger effective interfacial interaction with PVA matrix than PVP@MWCNTs, owe to the formation of hydrogen bonds between MWCNTs-f-OH and PVA. The stress-strain measurements showed that the Young’s modulus and tensile strength of MWCNTs-f-OH/PVA with only 1.0 wt.% contents increased by 200 and 100% compare with that of PVA, respectively. The findings of this experimental study emphasized the critical role of MWCNTs surface morphology in determining the mechanical properties of nanocomposites, and shed new light on understanding and advancing the properties of carbon nanotube based composites.

Ultrahigh dielectric constant and low loss of highly-aligned graphene aerogel/poly(vinyl alcohol) composites with insulating barriers

A novel two-step route to prepare graphene aerogel (GA)/poly(vinyl alcohol) (PVA) composites with exceptional dielectric performance is reported. The composites obtained from the initial unidirectional freeze casting possess a highly-aligned, conducting graphene skeleton with an ultralow density, a high porosity and remarkable thermal stability, showing ultrahigh dielectric constants combined with moderate losses. The losses are significantly reduced by means of PVA barriers introduced between the neighboring conductive main skeletons of the aligned GA/PVA networks in the 2nd freeze casting process. The insulating barriers effectively block the current leakage by removing the transversely interconnected, conductive ligaments. The compaction of barrier-shielded, porous GA/PVA composites yield fully consolidated, solid composites which deliver both exceptional dielectric constants and very stable, low losses. The approach developed here paves the way for rational design and assembly of GA/PVA composites as a lightweight, tunable and high-performance dielectric material, satisfying various requirements for emerging applications.

A09 イオン液体/ポリビニルアルコール複合体の超音波応答挙動

A09 イオン液体/ポリビニルアルコール複合体の超音波応答挙動

Seasonal changes in the preen wax composition of the Herring gull Larus argentatus

The preen gland produces oily secretion, which smeared onto a bird’s plumage improves its maintenance. The main components of the secretion are waxes, and its composition often changes during the year. The aim of this study was to determine the differences in the chemical composition of preen waxes in adult herring gulls Larus argentatus, captured in Poland in winter and in the breeding season. Preen gland secretions of herring gulls consist of monoester waxes, composed of about 29 saturated C7–C16 fatty acids and about 51 saturated C11–C20 alcohols. Unbranched-octanoic acid and n-hexadecanol dominated fatty acid and alcohol fractions, respectively, but 2-methyl-branched compounds were numerous in all individuals. The chemical compositions of fatty acids and alcohols differ between winter and the breeding season. In breeding gulls, 2-monomethyl-branched fatty acids were lower in content or could not be found, contrary to herring gulls in winter, where 2-monomethyl-substituted fatty acids were the second most abundant among all the fatty acids. Breeding gulls had also a higher content of n-octanoic acid and n-hexadecanol and a lower content of 2,6- and 2,8-dimethyl-substituted fatty acids than individuals caught during the winter. Differences in fatty acid composition were greater in breeding males, which incubate more often at night than breeding females. Hence, chemical changes in the preen wax composition in males may have evolved as additional nocturnal protection against mammalian predators which use olfaction to detect their prey and which are more active at night; however, this needs to be tested. Olfactory-based mate recognition in the colony also cannot be excluded at this stage of experimentation.

A facile method to prepare flexible boron nitride/poly(vinyl alcohol) composites with enhanced thermal conductivity

Polymer infiltrating filler-network has been actively researched recently to obtain composite materials with enhanced thermal conductivities. However, the long infiltration time blocks its wide application. In this study, we prepared hexagonal boron nitride (h-BN)/poly(vinyl alcohol) (PVA) composite by combining polymer infiltration with filler diffusion through the polymer to reduce infiltration time and form heat conduction paths. Base on this process, the maximum thermal conductivities of the obtained h-BN/PVA composites were 1.63 W/m·K and 8.44 W/m·K along the through-plane and in-plane directions, respectively. In addition, the composites displayed excellent heat dissipation performance when attached on top of a light emitting diode (LED) light strip. The research results indicate our approach is facile and capable of fabricating high performance thermal interface materials.

Desert Plants Leaf-surface Wax as Eco-friendly Lubricant Additive for an Aluminumon- steel Contact

The friction behavior of leaf-surface wax of two desert plants, Ammopiptanthus mongolicus and Reaumuria soongorica, as additives were evaluated on an aluminum-on-steel system, glycerol and molybdenum-dithiocarbamate (MoDTC) as compaire additive. A Gas chromatography-mass spectrometry (GC-MS) analysis system was performed to identify the composition of Ammopiptanthus mongolicus leaf wax. Scanning electron microscopy and X-ray photoelectron spectroscopy(XPS) were employed to explore the friction mechanisms of Ammopiptanthus mongolicus leaf-surface wax. The poly-alpha-olefin (PAO) containing leaf-surface wax showed a better friction reducing and wear resistance properties than that of containing glycerol and MoDTC, respectively. The results show that the leaf-surface wax of desert plants could effectively reduce the friction and wear of aluminum-on-steel sliding pairs compared with the PAO containing MoDTC, and glycerol as additives. Especially, Ammopiptanthus mongolicus showed high performance anti-wear and friction reducing properties. The excellent tribological properties were attributed to the wax composition of leafsurface fatty acid, alcohol, and esters.

Macro- and microstructural tracking of ageing-related changes of papaverine hydrochloride-loaded electrospun nanofibrous buccal sheets

Electrospun papaverine hydrochloride-loaded nanofibrous sheets consist of hydroxypropyl cellulose/poly(vinyl alcohol) composite were prepared for buccal administration for cerebral ischemia. The nanofibrous drug delivery system was subjected to accelerated stability test for four weeks in order to scrutinize the solid state changes relating to the stress induced (40±2°C/75±5% relative humidity) physical ageing. Micro- and macrostructural alterations were detected using scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and positron annihilation lifetime spectroscopy (PALS). Significant changes were revealed at both supramolecular and macroscopic levels. Microscopic morphology uncovered major morphological transitions. Subtle variations of Raman and FTIR spectra indicated that the local chemical environment of papaverine was altered suggesting a partial phase transition of the active. Discrete o-Ps lifetimes and lifetime-distributions unveiled a two-step ageing process of the drug carrier. In addition to the tracking of the glassy-to-rubbery transition of the fiber forming polymers, the Raman spectroscopy enabled monitoring the kinetics of the phase transition observed.

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.

In-situ reduced graphene oxide-polyvinyl alcohol composite coatings as protective layers on magnesium substrates

A simple and feasible method was developed to fabricate in-situ reduced graphene oxide-polyvinyl alcohol composite (GO-PVA) coatings as protective layers on magnesium substrates. Polyvinyl alcohol was used as an in-situ reductant to transform GO into reduced GO. Contiguous and uniform GO-PVA coatings were prepared on magnesium substrates by dip-coating method, and were further thermally treated at 120°C under ambient condition to obtain in-situ reduced GO-PVA coatings. Owing to the reducing effect of PVA, thermal treatment at low temperature led to effective in-situ reduction of GO as confirmed by XRD, Raman, FTIR and XPS tests. The corrosion current density of magnesium substrates in 3.5wt% NaCl solution could be lowered to its 1/25 when using in-situ reduced GO-PVA coatings as protective layers.

Suspended carbon black fluids reinforcing and toughening of poly(vinyl alcohol) composites

A convenient and green approach was utilized to prepare the suspended carbon black fluids (SCBF) using carboxylic CB nanoparticles with diameters of 15nm as the core and poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-b-PPO-b-PEO) as surface modifier via hydrogen bonding interaction. It was found that when the total polymer content (strongly adsorbed layer and weakly adsorbed or free layer) was greater than 60wt%, the SCBF exhibited liquid-like behavior without solvent. More interestingly, the flow mechanism mainly related to surface polymer content, which greatly differed from ionically or covalently nanofluids systems. Besides, the thermal, dispersibility, electrical conductivity properties and rheological behaviors, as well as microstructure of SCBF were systematically investigated using various methods. Moreover, the SCBF as fillers were used to prepare SCBF/Poly(vinyl alcohol) (PVA) composites for producing the simultaneous reinforcement and plasticization effect due to the unique fluidity of SCBF and interfacial interactions between the PVA molecules and SCBF via hydrogen bondings.

Development and characterization study of silk fibre reinforced poly(vinyl alcohol) composites

The current study aims to explore the use of a low cost technique to develop biodegradable composite films of poly(vinyl alcohol) (PVA) reinforced with silk fibre. The composite films were fabricated by varying the weight percentage of silk fibres and PVA, using the solution casting technique and evaluated for their mechanical and bio-degradable properties. The films were further subjected to characterization by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and atomic force microscopy techniques (AFM). The prepared film composites showed enhanced mechanical properties as compared to the pure PVA film. From the XRD studies, the composite films exhibited improved crystallinity, when compared to the pristine sample. The dispersion of fibres in the matrix was revealed by SEM. The thermal properties of the film composites increased with the increasing concentration of silk fibre. Moreover, the soil burial experiments revealed that the degradation rate improved with the addition of silk fibre, thus making it suitable in the packaging sector, without causing any ecological damage owing to its disposable property.

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.

Novel radiochromic dosimeters based on Calcein dye for high dose applications

New compositions of radio-chromic solutions and polyvinyl alcohol (PVA) films containing different concentrations of Calcein dye have been introduced as high dose dosimeter. The dosimeters were irradiated with gamma rays from C60o source at doses from 5 to 30kGy for film and from 0.25 to 1kGy for solution. UV/vis spectrophotometry was used to investigate the absorbance (optical density) of unirradiated and irradiated films and solutions in terms of absorbance at 493nm for film and 496nm for solution. The effects of scan temperature, relative humidity and stability of the response of films and solutions after irradiation were investigated. The results show that these films could be used as dosimeter in industrial radiation processing. The useful dose range of developed Calcein-PVA film and solution dosimeters is in the range of 5–20kGy and 0.25–1kGy respectively

Improved mechanical and wear resistance properties of silicon carbide/poly (vinyl alcohol) composites by silane coupling agents

In this work, the surface coated silicon carbide (SiC) obtained by dispersing it in silane coupling agent/ethanol solutions of different concentrations was used as a filler in poly (vinyl alcohol)(PVA) and the composites of (PVA)/SiC were prepared by melt process. The structure and properties of PVA/SiC composites were studied by Fourier‐transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), mechanical and wear resistance tests in detail. The silane coupling agent was hydrolyzed under acidic conditions, and as a result, large number of hydroxyl and amino groups were generated, which could form hydrogen bonds with hydroxyl groups of the PVA molecular chains, this effect subsequently improved the interactions between the filler and matrix. The surface modified SiC particles dispersed well in PVA matrix resulting a good compatibility with the matrix. For the PVA/SiC composites with the same content of SiC filler, both tensile strength and elongation at break improved with the increase of silane coupling agent concentration. In addition, a good improvement in the wear resistance of the PVA/SiC composites was also achieved compared with the neat PVA/SiC composite. POLYM. COMPOS., 39:3849–3857, 2018. © 2017 Society of Plastics Engineers

A comparative study of the nutritional values, volatiles compounds, and sensory qualities of pea pastes cooked in iron pot and clay pot

In the current study, the nutritional values, volatiles compounds, and sensory qualities of pea pastes cooked in iron pot and clay pot were compared. Results showed that the iron pot-cooked pea pastes contained profoundly more iron, total sugar, and starch than the clay pot-cooked ones, and the effects were found related to iron ion by comparing the results between clay pot-cooked pastes with and without iron ion addition. Samples prepared with the two utensils demonstrated similar contents of protein, polyphenol, and tannin, but differed in the composition of some volatile alcohols, alkanes, aldehydes, ketones, esters, and organic acids. The clay pot-cooked samples had higher score of “color,” “mouthfeel,” “taste,” and “overall quality” than the iron pot-cooked pastes. In conclusion, iron pot can allow the production of iron-enriched pea pastes whose sensory qualities are remarkably lower than those of the clay pot-cooked samples but are still in the acceptable range. Practical applications Iron utensil plays an important role in modern food industry due to its durability and convenience to handle. Cooking with iron pot is a simple and useful method of dietary iron fortification for the prevention of iron-deficiency anemia in developing countries. Pea paste is a popular legume food with high nutritional value and good palatability. Traditional pea paste producers believe cooking with clay pots can give rise to product with more desirable features than using iron pots. However, there were no scientific evidences regarding the effects of cooking utensils on pea paste qualities. It has been proved in the current study that iron pot can allow the production of iron-enriched pea pastes whose sensory qualities are remarkably lower than those of the clay pot-cooked samples but are still in acceptable range.

Electromechanical properties of a yarn strain sensor with graphene-sheath/polyurethane-core

This paper reports on the fabrication of a new yarn strain sensor based on commonly used polyurethane yarn which is easily incorporated into textile structures by using textile technologies for wearable applications. By integrating graphene/poly(vinyl alcohol) composites as the conductive sheath around yarn, and polyurethane yarn as the elastic core by using a layer-by-layer assembly method that is simple, scalable and low in cost, the merits of both types of materials are incorporated to fabricate sensors with enhanced performance. The combined effects of graphene concentration and number of coatings on sensor properties are elucidated, and on that basis, the electromechanical properties can be modified by adjusting the parameters. The sensors are characterized in terms of sensitivity, resistivity, linearity, repeatability, hysteresis and thermal stability. There are two sensors (graphene concentration of 0.8 wt% and 1.0 wt%, and 12 and 9 cycles of coating respectively) with high sensitivity (gauge factor of 28.48 and 86.86, respectively), good linearity between the change in relative resistance and applied strain (correlation coefficient of 0.95 and 0.97, respectively), good repeatability (repeatability error of 2.03% and 1.81%, respectively), low hysteresis (hysteresis error of 7.03% and 9.08%, respectively) and excellent thermal stability (within the range of 25 °C–310 °C).

Development of poly(vinyl alcohol)/wood-derived biochar composites for use in pressure sensor applications

Carbon-based electrically conductive polymer composites have been considered as promising materials for piezoresistive pressure and strain sensors. The objective of this work is to investigate the behaviors of wood-derived biochar-filled polyvinyl alcohol (PVA) composites as pressure sensors. Composites of polyvinyl alcohol and wood-derived biochar were prepared by a solution casting method. The research found that with elevated pressure from 0 to 358 kPa, the electrical resistance of PVA/biochar composite sensors with 8, 10, and 12 wt% biochar content (to 10% PVA solution by weight) gradually decreased by 92, 98, and 99%, respectively. Also, the effects of sensor thickness (0.40, 0.50, and 0.60 mm) and temperature (from −20 to 70 °C) were investigated. Results indicated that effect of thickness was most influential in the 8 wt% PVA/biochar sensors. Higher temperature (40–70 °C) enhanced the sensor voltage output, while lower temperature (−5 to −20 °C) reduced the piezoresistive effects.

Solubility and preferential solvation of econazole nitrate in binary solvent mixtures of methanol, ethanol and 1,4-dioxane in water

The solubility of econazole nitrate in binary mixed solvents of (methanol+water, ethanol+water and 1,4-dioxane+water) were measured experimentally via the isothermal dissolution equilibrium method in the temperature range of (278.15–318.15) K under 101.2kPa. For the (1,4-dioxane+water) system, at a certain composition of 1,4-dioxane, the solubility of econazole nitrate increased with an increase in temperature; nevertheless at the same temperature, they increased at first and then decreased with an increase in mass fraction of 1,4-dioxane. At the same temperature and mass fraction of methanol, ethanol or 1,4-dioxane, the solubility of econazole nitrate was greater in (methanol+water) than in the other two mixed solvents. The solubility values were correlated by using Jouyban-Acree model, and the dissolution enthalpies of the dissolution process were computed. Preferential solvation parameters of econazole nitrate were also derived by means of the inverse Kirkwood-Buff integrals method. The preferential solvation parameter by water δx1,3 is negative in water-rich mixtures but positive in compositions from 0.31 to 1.0 in mole fraction of methanol and from 0.24 to 1.0 in mole fraction of ethanol. It is conjecturable that in intermediate composition of alcohol and alcohol-rich mixtures the interaction by acidic hydrogen-bonding by methanol/ethanol on the basic sites of econazole nitrate played a relevant role in the drug solvation. However in 1,4-dioxane (1)+water (2) mixtures with 0.18<x1<0.50 positive δx1,3 values were observed, but with 0.50<x1<1.0 negative δx1,3 values were observed again. The solubility data presented in this work expand the physicochemical information about drugs in binary aqueous-co-solvent mixtures.

Effect of varying hydrolysis time on extraction of spherical bacterial cellulose nanocrystals as a reinforcing agent for poly(vinyl alcohol) composites

Bacterial cellulose nanocrystal (BCNC) was prepared from bacterial cellulose (BC) using acid hydrolysis for 12, 24 and 72 h. The effect of the BCNC was estimated as a means of reinforcing the poly(vinyl alcohol) (PVA) matrix in terms of mechanical and thermal properties. The effect of the hydrolysis time on BCNC extraction was evaluated by considering morphology, changes in chemical functional groups, crystallinity and thermal stability. Atomic force microscopy (AFM) images revealed the diameters of spherical cellulosic particles were in the range 16–35 nm with the smaller ones resulting from a longer hydrolysis treatment time. Fourier transform infrared (FTIR) spectroscopy showed no changes in the functional groups between BC and BCNC samples for all hydrolysis extraction times. However, X-ray diffraction (XRD) proved that the crystallinity of the BCNC increased up to 87% in comparison with the BC. The thermal stability of nanocellulose decreased over a longer hydrolysis period. Furthermore, the BCNC showed an improved effect on the PVA matrix in both tensile and thermal analysis. Therefore, BCNC obtained by acid hydrolysis for 24 h could be used as a reinforcing agent for material industries.