PVA Solution Research Articles

Green synthesis of silver nanoparticles from Thymus vulgaris and Sambucus nigra extracts in poly (vinyl alcohol) nanofiber matrix: In vitro evaluation

In the current study, silver nanoparticles (AgNPs) green synthesized from Thymus vulgaris (Thyme) and Sambucus nigra (black elderberry) (BE) extracts and added into poly (vinyl alcohol) (PVA) solution to achieve antibacterial, biocompatible, and bioactive nanofibers through electrospinning technique. The absorbance peaks of AgNPs were found at 450 nm in the ultraviolet–visible (UV-Vis) spectrum, and AgNPs were found in (111) d-spacing in high-resolution transmission electron microscope (HRTEM). The average particle sizes were measured as 66.30 ± 7.70 nm and 20.03 ± 4.80 nm for ThymeAgNPs and BEAgNPs, respectively. 1 and 2 wt% content of the AgNPs were added into the PVA solution and electrospun at 9 kV voltage and 5 ml/hr flow rate. The fiber morphologies were investigated with the help of scanning electron microscopy (SEM) and HRTEM, and a decrease in the fiber diameter and the porosity of the fibers was obviously observed. Chemical bond analysis was done using Fourier transform infrared (FTIR), and the thermal behavior of the fiber was examined with a differential scanning calorimeter (DSC). X-ray diffraction (XRD) and HRTEM provide the presence of AgNPs in PVA nanofibers. According to antibacterial activity investigations the inhibition growth effect against Escherichia coli (E. coli) of PVA/ThymeAgNPs was 11.6 % higher than that of PVA/BEAgNPs. The cell cytotoxicity tests at different concentrations with L929 cells revealed better performance in PVA/Thyme nanofibers.

Solvent-Controlled Strategy for Color-Tunable Fluorescence Carbon Dots and Their Application in Light-Emitting Diodes

Carbon dots (CDs) offer tremendous advantages in the fields such as bioimaging, sensing, biomedicine, catalysis, information encryption, and optoelectronics. However, the inherent challenge is synthesizing CDs with a full-spectrum emission, as most CDs typically produce only blue or green emissions, which severely hinder further investigation into their fluorescence mechanism and restrict their broader applications in light-emitting diodes (LEDs). In this work, we reported a solvent-controlled strategy for the preparation of multicolor CDs with blue, yellow, and red emissions, using o-phenylenediamine (oPD) and ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6) as precursors. The detailed characterizations proved that a solvent with a lower boiling point and lower solubility of precursors resulted in a higher degree of dehydration and carbonization process, thereby increasing carbon cores with sp2-conjugated domains and nitrogen doping and further reducing the bandgap energies, causing a significant redshift emission from blue to red. The underlying fluorescence mechanism of the prepared multicolor CDs was contributed to the surface state. Eventually, blue-, yellow-, and red-emitting CDs based on poly(vinyl alcohol) (PVA) films and colorful LEDs devices were fabricated by dispersing the as-synthesized CDs into a PVA solution. The proposed solvent-controlled strategy for multicolor CDs preparation will be helpful for fully utilizing the advantages of CDs and expanding their applications.

Polymer-Mediated Crack Suppression in Deposit of Nanoellipsoids.

Uniform distribution of particles and crack suppression in dried particulate deposits are major challenges for applications in coating and printing technologies. To address this, we investigated the impact of the addition of a water-soluble polymer, poly(vinyl alcohol) (PVA), on the evaporative self-assembly and kinetics of crack formation in deposits of anisotropic colloids. The fluid flow inside the drying drop is significantly altered due to polymer-mediated adsorption of ellipsoids to the drop surface. The competition between outward capillary flow and Marangoni flow developed in the drying colloid-polymer dispersion drop dictates the distribution of particles in the final dried patterns. The deposits formed by drying drops of ellipsoids dispersed in PVA solutions show three distinct patterns depending on the PVA concentration. A transition from ring-like deposit to uniform deposition with intermittent cracks was observed for a critical PVA concentration of 0.3 wt %. Radial as well as annular cracks were observed in the case of no PVA, while only annular cracks were formed in the dried patterns as the PVA content increased, thus indicating the change of capillary stresses in the films. Analyses of the particle dynamics and deposition patterns confirmed the effectiveness of gelation-driven crack prevention. This method offers a facile and straightforward solution for obtaining crack-free coatings in drying-mediated colloidal nanoparticle assembly.

Skin-inspired ultra-tough, self-healing anisotropic wood-based electronic skin for multidimensional sensing

Skin is a flexible and stretchable sensor composed of anisotropic dermis (DM) and repairable epidermis (EM). It repairs itself when damaged and has a multi-dimensional sensing system that can assist the body in performing some complex multi-dimensional movements. Inspired by skin, we utilized natural wood as the skeleton and for the first time designed a low-cost, double-layer structure wood-based electronic skin (wood-eskin). Simple chemical treatments were employed to directionally regulate the ray structure of natural wood and to enhance its porosity. Subsequently, physical freeze-thawing was employed to facilitate the formation of an entangled network structure between the PVA solution and the wood nanofibers. Wood-eskin with multi-dimensional sensing was obtained by further introducing ions by immersing in salt solution. In comparison to the majority of contemporary bionic e-skins, wood-eskin exhibits superior mechanical properties. Additionally, it is capable of performing complex deformations, such as bending and knotting. After fracture, wood-eskin can also repair itself and recover ∼94 % of its mechanical properties. The oriented arrangement of cellulose nanofiber channels gives wood-eskin a multidimensional sensing capability that can be used to monitor more complex body movements. The low-cost, biodegradable wood-eskin exhibits similar functionality to human skin, and its potential for biomedical and bionic robotics applications is considerable.

Long-Term Drying Shrinkage Strain of Engineered Cementitious Composite Concrete Contains Polymeric Fibers

The lack of concrete tensile stress endurance led to the invention of engineered cementitious composite. However, the absence of gravel from the mixture in addition to the high binder content may lead to high shrinkage strain. Therefore, a radical solution to this problem is worth to be anticipated. The importance of this research lies in investigating the long-term drying shrinkage strain of the engineered cementitious composite since there is a lack of information regarding this behavior. Mixes of 30 and 60 MPa strengths were produced with polyvinyl alcohol fibers PVA-ECC and polypropylene fibers PP-ECC. The drying shrinkage strain of PVA-ECC mixes has been compared to PP-ECC mixes for both short term (0–28 days) and long term (0–360 days). Results indicated that all PVA-ECC mixes exhibited lower drying shrinkage strains than PP-ECC mixes. The ultimate drying shrinkage strain was recorded to be 1200 microstrain at 28 days. The increment in drying shrinkage strain after 28 days was 5.6% in PVA-ECC mixes when compared to that in PP-ECC mixes which was 6.77%. For high strength levels, the drying shrinkage strain at the age of 360 days declared a reduction of 3.5% for PVA-ECC compared to PP-ECC mixes. Also, it was lower for mixes with 60 MPa (6.3%) than for mixes with 30 MPa (7.6%). Therefore, despite the higher cement content for mixes with 60 MPa strength, the higher fiber volume fraction and the higher PVA solution percentage restricted the drying shrinkage strain increment. The research also addresses some mechanical tests of engineered cementitious composite concrete such as compressive strength, flexural strength, and strain capacity that may provide a strong relation to the drying shrinkage behavior of the different mixes. The scanning electron microscope images were involved in this research to declare the impact of fiber types on the microstructure of the ECC mixes.

Ice growth inhibition by poly(vinyl alcohol): Insights from near-infrared spectroscopy and molecular dynamics simulation

Poly(vinyl alcohol) (PVA) is a well-known ice recrystallization inhibitor, yet its antifreeze mechanism remains debated. Here, the mechanism of PVA is elucidated by means of near-infrared spectroscopy and molecular dynamics (MD) simulations. Analysis of the spectra of PVA solutions during the ice growth process reveals a dynamic interaction conversion from PVA-water to PVA-ice, indicating that PVA inhibits ice growth by directly binding to ice. Moreover, we observed OH binding to the ice surface through one or two hydrogen bonds but did not witness the previously reported formation of three hydrogen bonds when the OH group perfectly embeds into the ice crystal lattice. In addition, the spectral feature of CH2 groups of PVA indirectly indicates their significant contribution to inhibiting ice growth through hydrophobic interactions. The MD simulations further confirm the effective roles of both OH and CH2 groups for inhibiting ice growth.

Construction of interfacial interlocking structure in epoxy composites with enhanced mechanical performance and ultraviolet resistance

Replacing carbon fibers with organic fibers to reinforce the polymer matrix has become a promising development direction in the preparation of structural composites owing to its low density and cost, but the mechanical performance of organic fibers restricts their further application. Herein, poly(vinyl alcohol) (PVA) fibers were utilized to reinforce the epoxy resin (EP) through the incorporation of zinc oxide nanoparticles (ZnO NPs) in PVA solution (PVAS), and high-strength composite for 122.3 MPa with interfacial interlocking structure was successfully fabricated via vacuum assisted resin transfer molding (VARTM). ZnO NPs were coated on the PVA fibers and enhanced the surface roughness, which improved the mechanical performance of the composite. In comparison with untreated composites, the interlaminar shear strength (ILSS) of composites displayed a significant increase, from 99.4 MPa to 122.3 MPa, resulting from improved interfacial bonding and reduced interfacial gap. Simultaneously, the incorporation of ZnO NPs efficiently enhanced the ultraviolet (UV) resistance.

Synthesis of PVA/TiO2 Composite Layer over Conductive Textile Sheet Using Electrospinning Method for Enhancing Self-Cleaning Properties

The present research used the electrospinning method to apply a polyvinyl alcohol/titanium dioxide (PVA/TiO2) layer over a conductive textile (70 % polyester and 30 % cotton) sheet. PVA with 10, 12.5, and 15 g concentrations was mixed into 100 ml distilled water. Then, each PVA solution was mixed with 1.5 wt.% of TiO2. Afterward, the electrospinning method applied a PVA/TiO2 composite onto a conductive textile sheet. Various characterizations were conducted, such as resistivity, scanning electron microscopy (SEM), Fourier transforming infrared (FTIR), and photocatalytic activity. The resistivity result is 9.5, 10, and 10  for A, B, and C samples. According to SEM investigation, higher PVA concentration leads to higher fiber sizes around 0.65 µm. An increase in PVA content does not affect the bands that were formed. The size of the fiber diameter contributed to the photocatalytic activity of MB. A smaller fiber diameter could enhance photocatalytic activity.

Cryostructuring of Polymeric Systems: 67 Properties and Microstructure of Poly(Vinyl Alcohol) Cryogels Formed in the Presence of Phenol or Bis-Phenols Introduced into the Aqueous Polymeric Solutions Prior to Their Freeze-Thaw Processing.

Poly(vinyl alcohol) (PVA) physical cryogels that contained the additives of o-, m-, and p-bis-phenols or phenol were prepared, and their physico-chemical characteristics and macroporous morphology and the solute release dynamics were evaluated. These phenolic additives caused changes in the viscosity of initial PVA solutions before their freeze-thaw processing and facilitated the growth in the rigidity of the resultant cryogels, while their heat endurance decreased. The magnitude of the effects depended on the interposition of phenolic hydroxyls in the molecules of the used additives and was stipulated by their H-bonding with PVA OH-groups. Subsequent rinsing of such "primary" cryogels with pure water led to the lowering of their rigidity. The average size of macropores inside these heterophase gels also depended on the additive type. It was found also that the release of phenolic substances from the additive-containing cryogels occurred via virtually a free diffusion mechanism; therefore, drug delivery systems such as PVA cryogels loaded with either pyrocatechol, resorcinol, hydroquinone, or phenol, upon the in vitro agar diffusion tests, exhibited antibacterial activity typical of these phenols. The promising biomedical potential of the studied nanocomposite gel materials is supposed.

Cross-linked poly(vinyl alcohol)/citric acid electrospun fibers containing imidazolium ionic liquid with enhanced antiadhesive and antimicrobial properties

Patients in hospital environments are susceptible to bacterial colonization, which can lead to infections. In this study, electrospun fibers were manufactured using poly(vinyl alcohol) (PVA) crosslinked with citric acid (CA) and incorporating the ionic liquid (IL) 1-hexadecyl-3-methylimidazolium chloride (C16MImCl) to prevent microbial growth and biofilm formation. The presence of CA and IL reduced the surface tension of the PVA solution (12% w/v) from 52.07 mN/m to 35.84 mN/m. CA was introduced into PVA solutions, and the resulting fibers were thermally crosslinked through esterification between PVA hydroxyl groups and CA. X-ray photoelectron spectroscopy (XPS) confirmed the presence of IL on the fiber surfaces. The IL acted as a surfactant, imparting plasticity to the electrospun fibers and enhancing homogeneity and mechanical properties. Before crosslinking, the PVA/CA/IL fibers exhibited an elongation at break (%) of approximately 140%, a tensile strength of 5.3 MPa, and an elastic modulus of 18.2 MPa. After cross-linking, the elongation at break reduced to 86%, the tensile strength increased to 7.6 MPa, and the elastic modulus increased to 88 MPa. Mechanical measurements confirmed the thermal crosslinking of the fibers, primarily because of the increased elastic modulus. Adhesion and proliferation tests with Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa) indicated reduced bacterial adhesion and growth on the PVA/CA/IL fibers. Antimicrobial assays further confirmed a 50.73% and 69.42% increase in bactericidal activity against S. aureus and P. aeruginosa, respectively. The PVA/CA/IL fibers exhibit promising potential for producing antimicrobial materials to prevent the attachment and proliferation of microbial strains on solid surfaces.

Investigation of the effects of cellulose nanofiber on the properties of poly(vinyl alcohol) crosslinked by 2,5-furandicarboxylic acid

Bio-based and biodegradable materials have received special interests in recent years as a replacement for petroleum-based plastics. Poly(vinyl alcohol) (PVA), cellulose nanofiber (CNF), and 2,5-furandicarboxylic acid (FDCA) are typical examples among these environmentally friendly molecules. In this study, we investigated the synergistic effects of CNF reinforcement and crosslinking with FDCA on the properties of PVA. The composite films were prepared via a straightforward mechanical-dispersion method, wherein CNF was incorporated into a PVA solution and subsequently crosslinked with FDCA. Comprehensive characterizations, including Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-IR), X-ray diffraction (XRD), Thermal Gravimetric Analysis/Differential Thermal Gravimetric Analysis (TGA/DTGA), Differential Scanning Calorimetry (DSC), tensile testing, and morphological studies, were performed to assess the impact of these modifications. Our findings revealed significant enhancements in the mechanical and thermal properties of the composites. Notably, the tensile strength of the PVA-c-FDCA/CNF composite with 2% CNF reached 37.08 MPa, representing a twofold increase compared to both crosslinked PVA (16.84 MPa) and unmodified PVA (14.57 MPa). TGA/DTGA analysis demonstrated improved thermal stability, with the degradation temperature reaching 371°C, compared to the 298°C observed for PVA. DSC and XRD results indicated a reduction in PVA crystallinity after crosslinking and blending with CNF. Scanning electron microscopy (SEM) images showed good compatibility between PVA and CNF. This study underscores the potential of CNF reinforcement and FDCA crosslinking as a viable strategy to enhance the mechanical properties of PVA-based materials.

Lignocellulosic full-components hydrogelation using steam-exploded corn stover

The non-dissolving strategy utilizes green steam explosion method to pretreat corn stover, and then directly blend it with PVA solution to fabricate a lignocellulose-based hydrogel, which avoids component separation, modification, and dissolution.

Development and characterization of antibacterial 3D porous hydroxyapatite-gelatin-PVA scaffolds containing zinc oxide nanoparticles

There is still a need to develop hydroxyapatite (HAp)/gelatin-based porous scaffolds to provide a hybrid system with structural and biochemical properties equivalent to those of bone. Here, we fabricated and characterized 3D hybrid scaffolds composed of HAp nanoparticles synthesized in situ in gelatin and PVA solutions and loaded with combustionally synthesized (10 wt%) zinc oxide nanoparticles (ZnO NPs) to ensure their homogeneous embedding in the polymer matrices. The phase analysis, composition, morphological and microstructural properties of ZnO NPs and freeze-dried hybrid scaffolds were studied. The compressive strength, porosity, swelling capacity, degradation rate, and antibacterial activity of the hybrid scaffolds were measured. The fabricated 3D scaffolds showed high porosity of up to 78 % with a pore size of about 50–300 μm, good mechanical strength in the range of about 55 kPa, high swelling capacity of up to 505 %, and long-term degradation rate of about 22–25 % for up to 35 days. ZnO NPs have a pure phase and a quasi-spherical shape with a size of about 78 ± 25 nm structure and there are no significant differences between the physicochemical properties of ZnO-free scaffolds and ZnO-loaded scaffolds. Incorporation of ZnO NPs into the scaffolds enhanced their antibacterial response against pathogenic Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). This work provides advanced 3D porous hybrid bone scaffolds with favorable mechanical performance and antibacterial activity for bone repair and regeneration.

Low-Viscous, Dilute Phase Adhesive from Dense Polyphenolic Coacervates of Poly(vinyl alcohol) and Tannic acid.

This study explores a polyphenolic coacervate, named VATA, formed by poly(vinyl alcohol) (PVA) and tannic acid (TA). Distinct from conventional studies that have focused on the bottom, dense phase of coacervates, this research emphasizes the top, dilute phase, low-viscous coacervate liquid termed liquid-VATA (l-VATA). Due to TA's capability of intermolecular association as well as adhesiveness, phenomena not typically observed in the upper dilute phase of standard polyelectrolyte-based coacervates are revealed. At first glance, the dilute phase l-VATA coacervate resembles a water-like, low-viscous mixture solution of PVA, TA, and PVA/TA complexes. However, analysis shows that nearly all of the TA molecules associate with PVA chains, forming PVA/TA complexes. Furthermore, supraparticular association was observed between PVA/TA complex nanoparticles upon applying external shear force. A broad survey of shear rate and strain showed that the solution exhibited sequential shear-thickening, followed by shear-thinning behavior. The water-like, low viscosity of l-VATA unexpectedly reveals robust adhesiveness and thus able to lift an entire mouse using just a single human hair strand. Even in cases of failure, no interfacial failure was detected between mouse and human hair. In addition to enabling hair-to-hair bonding, our study also showcases the efficacy of l-VATA in facilitating hair-to-skin adhesion. The results illustrate how the lower viscosity of l-VATA can be exploited for a wide range of industrial and cosmetic applications, allowing the formulation of thin, uniform adhesive layers, something unachievable with the dense, viscous VATA glue. Thus, this study highlights the importance of investigating the top dilute phase of coacervates, shedding light on an area often underestimated compared to the bottom dense phase reported in prevalent coacervate studies.

Development of MEAs Using Mesoporous Carbon Fibers as Cathode Carbon Supports

Introduction Mesoporous carbon (MC) has recently been paid more attention to as a carbon support for polymer electrolyte fuel cells (PEFCs), which are promising energy technologies for a future decarbonized society, since it is used in TOYOTA MIRAI. We have also been developing MC materials, whose diameter is slightly less than 10 nm, since 2006. More recently, we have developed MC fibers (MCFs) using an electrospinning method. Although MCF can form a sheet, it can be milled to powder. Comparing to our MC, MCF was found to be easily milled to smaller carbon particles. Then, we are interested in a correlation between IV performance and three dimensional structure of cathode layers made of different MC based powder. The aim of this study is to find important parameters to develop the cathode layer to achieve high IV performance. In this study, we synthesized MCF followed by ball-milling to the smaller carbon particles and evaluated the IV performance and structure of MCF based cathode layers. The detailed comparison to MC cathode layers1 was performed. Experimental MCFs were made by electrospinning of the precursor solution containing a surfactant (Pluronic F127) and carbon precursors (phloroglucinol dihydrate, formaldehyde, and triethyl orthoacetate) dissolved in the acid water/ethanol solution, and PVA solution. The obtained MCF precursor sheet was heated in the oven for polymerization of carbon precursors, and then heated up to 8 h by stepwise in the oven under the nitrogen atmosphere in order to decompose Pluronic F127 and carbonized precursors. MCF sheets were milled to small particles by hands and then zirconia balls at 450 rpm and 800 rpm. Pt nanoparticles were deposited on MCF powder by using Pt(acac)2 as a precursor. MEAs with 1cm2 electrodes were fabricated on the Nafion212 membrane. Prepared MCF based catalysts were used for the cathode, and 46.5% Pt/KB (TEC10E50E) was used for the anode. Results and discussion IV performance of MEAs with different cathodes, such as 46.5% Pt/KB (TEC10E50E), 33%Pt/MC, and 32%Pt/MCF, were evaluated and compared. When each overvoltage was evaluated separately, high ohmic overvoltage was seen for MEA with 33%Pt/MC. However, it was reduced for MEA with 32%Pt/MCF. When carbon particles size was compared between the two, MCF was found to be milled into much smaller particles as seen Figure 1. The resulting smaller particles most likely reduced the contact resistance between the particles.Diffusion overvoltage was found to be lowered when 33%Pt/MC and 32%Pt/MCF were used in the cathode. In order to find out a mechanism of the resulting low diffusion overvoltage, the cathode structure was three dimensionally evaluated using FIB-SEM and 3D imaging software. Relatively larger pores were seen in 33%Pt/MC and 32%Pt/MCF cathodes than in 46.5% Pt/KB (TEC10E50E) cathode. Such large pores or/and mesopores might be positively work for mass diffusion, but the mechanism for low diffusion overvoltage is still under the study.

Active and intelligent packaging films based on PVA/Chitosan/Zinc oxide nanoparticles/Sweet purple potato extract as pH sensing and antibacterial wraps

With growing concerns about the environmental impact of petroleum-based products, researchers are exploring new materials for food packaging. One promising avenue is the use of nanotechnology and natural materials. In this study, active and intelligent composite films were developed by solvent casting method using polyvinyl alcohol (P), chitosan (C), zinc oxide nanoparticles (Z), and sweet purple potato extract (S). The results demonstrated that C and Z did not affect the pH-based structural transformation of pigment (S)-containing PVA solutions. SEM microstructural observation revealed a uniform distribution of zinc oxide nanoparticles in the polymeric matrix. The addition of C and Z to the composite film improved its thermal, water barrier, and antibacterial and antioxidant properties. The tensile strength of the neat film (P) was 13.0 MPa and increased to 30.8 MPa for PCZS composite film because of the good interaction between PVA and the additives. The strong antimicrobial activity of PCZS composite films against environmental pathogens was validated by antimicrobial barrier analysis. Additionally, the functional composite film (PCZS) efficiently detected chicken freshness as a function of pH change. These findings suggest that the PCZS film has great potential as a smart and active food packaging material or as an antimicrobial wrap.

Electrocatalytic activation of peroxomonosulfate (PMS) under aerobic condition for the remediation of oil sands process water: Insight into one-pot synergistic coupling of PMS electro-activation and heterogeneous electro-Fenton processes

Alkaline industrial effluents possess a different challenge during treatment by advanced oxidation processes due to the reduction in redox potential of hydroxyl radical (•OH) in basic media. Herein, electrocatalytic peroxomonosulfate activation (EC-PMS), which synergistically couples an early-stage PMS electro-activation (E-PMS) with subsequent heterogeneous electro-Fenton oxidation (HEF) catalyzed by Fe-modified biochar (BC-Fe) was investigated for enhanced degradation and mineralization of organics in oil sands process water (OSPW). The EC-PMS was first studied for the degradation of surrogate naphthenic acids (NAs) (5-phenylvalveric acid, (PVA)) as a synthetic process water and complete degradation of 50 mg L−1 PVA solution was achieved within very short treatment time (0.5 h) with excellent mineralization (>70 % TOC removal) in 6 h. The efficiency of EC-PMS for PVA degradation was affected by the applied current density, PMS, and catalyst dosage. The organic degradation, electroparamagnetic resonance spectrometry, quenching and chemical probe experiments showed that sulfate radical (SO4•−) generated by E-PMS was the dominant radical oxidant for the degradation of PVA, contributing over 93 %, whereas •OH produced from BC-Fe decomposition of electrogenerated H2O2 in HEF was responsible for the mineralization of the organic solution at the later stage of the coupled process. The EC-PMS showed excellent reusability and was effective for the treatment of real OSPW, achieving complete degradation of real NAs in OSPW and relatively good mineralization of the water. Analysis of the EC-PMS treated OSPW did not simulate any response during the bioactivity assay test using a macrophage cell line, indicating the complete detoxification of the water.

Rice husk-based cellulose nanocrystal/poly(vinyl alcohol) composite film for the removal of Cu (II) cation from aqueous solution

Abstract In this study, a nanocomposite film comprising poly(vinyl alcohol) (PVA) and rice husk-derived cellulose nanocrystals (CNC) was introduced as a novel sorbent for removing copper (II) cations. First, CNC was isolated from neat rice husk, and then these particles with many ratios compared to PVA (2, 4, 6, and 10 wt.%) were added to the PVA solution to render the nanocomposite films. The obtained films were evaluated using scanning electron microscopy, Fourier-transform infrared spectroscopy, and water uptake tests. The optimal condition for the sorbent preparation was 10 wt.% of CNCs to PVA. The maximum ion adsorption percentage of the PVA/CNC 10 % film reached 55 % after 3 h exposure to 70 ppm Cu (II) ion solution at 25 °C. This research suggested a facile and feasible fabrication method of a nanocomposite film, considered a potential sorbent for the adsorption of copper (II) ions.

Role of hydrodynamic conditions and type of foam stabilizer for antifoam efficiency

The effects of antifoam and surfactant concentration on the foamability of solutions of an anionic (SLES) and nonionic (Brij 35) surfactants and a series of polyvinyl alcohols with 88% and 98% degree of hydrolysis and molecular masses between 31 and 205 kDa, were studied. Three methods which differ in the way of air incorporation were used for foaming – Bartsch test, shake test and Ultra Turrax. Mixed silicone oil-silica particles antifoam was studied. The antifoam was introduced in the foaming solution as pre-dispersed in organic solvent or as antifoam-in-water emulsion. It was shown that the antifoam is very active in the fast foaming methods (Bartsch and shake tests) for the slow adsorbing polymers PVA and has no any activity in the slow foaming method (Ultra Turrax) for the fast adsorbing surfactants with electrostatic stabilization (SLES). The efficiency of pre-dispersed in organic solvent antifoam is much higher as compared to that of emulsified antifoam, due to the faster segregation of the silica particles and silicone oil in the emulsified antifoam. The antifoam efficiency increases with antifoam concentration and with lowering the surfactant concentration. In a given foaming method, the antifoam efficiency is the highest in PVA solutions with 98% DH, intermediate for PVA with 88% DH and Brij 35, and the lowest for SLES solutions. At a certain degree of hydrolysis, the molecular mass of PVA has no significant effect on the antifoam activity. Good correlation between the antifoam efficiency and the stability of the pseudo emulsion film formed between the antifoam globule and the bubble surface is established, showing that the electrostatic repulsion is more efficient to prevent the entering of the antifoam globules on the air-water interface, as compared to the steric repulsion.

Defect free pervaporation mixed matrix membranes fabricated on ZIF-8 surface segregation substrates

Mixed matrix membranes (MMMs), which incorporate porous particles into polymer matrix, were a promising approach to overcome the inherent trade-off effect of polymeric membranes. Controllable and easily scalable membrane fabrication strategies remained a challenge for the development of defect-free pervaporation MMMs. In this work, to avoid defects formed by particle exposure in MMMs, forced surface segregation of ZIF-8 on a substrate was achieved by vapor-assisted non-solvent induced phase separation (NIPS) process. Subsequently, ZIF-8 ‘islands’ on the substrate surface were sealed with PVA solution and defect-free dense MMMs were successfully prepared. The surface segregation of ZIF-8 was proved by scanning electron microscope (SEM), X-Ray diffraction (XRD) and fourier transform infrared (FTIR). The prepared MMMs showed an increase in flux of 162% and an increase in separation factor of 299% compared to the pristine membranes. It was expected that this strategy of inducing particles to undergo forced surface segregation could be extended to the preparation of other membranes.