Cross-linked PVA Research Articles

Influence of gamma irradiation on polymerization of pyrrole and glucose oxidase immobilization onto poly (pyrrole)/poly (vinyl alcohol) matrix

This paper describes the immobilization of glucose oxidase, GOx onto polymer matrix comprising of poly(pyrrole), PPy and poly(vinyl alcohol), PVA using gamma irradiation technique. Py/PVA-GOx film was prepared by spreading PVA:GOx, 1:1 solution onto dried pyrrole film and exposed to gamma irradiation from cobalt 60 source at doses ranging from 0 to 60 kGy. The films were subjected to structural and morphological analyses by using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Scanning electron microscope (SEM), Field emission scanning electron microscope (FESEM) and Atomic-force microscopy (AFM) techniques. Similar studies were also made on pristine pyrrole film which served as control. The SEM and FTIR spectra of Py/PVA-GOx film revealed that pyrrole has been successfully polymerized through irradiation-induced reactions. The results on the morphological properties of the samples characterize using FESEM, SEM and AFM further confirmed the occurrence of radiation-induced modification of Py/PVA-GOx film. The FTIR spectra showed the existence of intermolecular interaction between polymer matrix and GOx indicating that GOx had been successfully immobilized onto Ppy/PVA matrix by radiation-induced reactions. Results revealed that radiation induced reactions such as polymerization of pyrrole, crosslinking of PVA, grafting between the adjacent PVA and pyrrole molecules as well as immobilization of GOx onto Ppy/PVA matrix occurred simultaneously upon gamma irradiation. The optimum dose for GOx immobilization in the polymer matrix found to be 40 kGy. Therefore it is clear that this irradiation technique offered a simple single process to produce Py/PVA-GOx film without additional crosslinking and polymerization agents.

Effect of nanostructured carbon coatings on the electrochemical performance of Li1.4Ni0.5Mn0.5O2+x -based cathode materials.

Nanocomposites of Li1.4Ni0.5Mn0.5O2+x and amorphous carbon were obtained by the pyrolysis of linear and cross-linked poly(vinyl alcohol) (PVA) in presence of Li1.4Ni0.5Mn0.5O2+x. In the case of linear PVA, the formation of nanostructured carbon coatings on Li1.4Ni0.5Mn0.5O2+x particles is observed, while for cross-linked PVA islands of mesoporous carbon are located on the boundaries of Li1.4Ni0.5Mn0.5O2+x particles. The presence of the carbon framework leads to a decrease of the polarization upon cycling and of the charge transfer resistance and to an increase in the apparent Li+ diffusion coefficient from 10−16 cm2·s−1 (pure Li1.4Ni0.5Mn0.5O2+x) to 10−13 cm2·s−1. The nanosized carbon coatings also reduce the deep electrochemical degradation of Li1.4Ni0.5Mn0.5O2+x during electrochemical cycling. The nanocomposite obtained by the pyrolysis of linear PVA demonstrates higher values of the apparent lithium diffusion coefficient, a higher specific capacity and lower values of charge transfer resistance, which can be related to the more uniform carbon coatings and to the significant content of sp2-hybridized carbon detected by XPS and by Raman spectroscopy.

Modification of the surface of superparamagnetic iron oxide nanoparticles to enable their safe application in humans.

Combined individually tailored methods for diagnosis and therapy (theragnostics) could be beneficial in destructive diseases, such as rheumatoid arthritis. Nanoparticles are promising candidates for theragnostics due to their excellent biocompatibility. Nanoparticle modifications, such as improved surface coating, are in development to meet various requirements, although safety concerns mean that modified nanoparticles require further review before their use in medical applications is permitted. We have previously demonstrated that iron oxide nanoparticles with amino-polyvinyl alcohol (a-PVA) adsorbed on their surfaces have the unwanted effect of increasing human immune cell cytokine secretion. We hypothesized that this immune response was caused by free-floating PVA. The aim of the present study was to prevent unwanted immune reactions by further surface modification of the a-PVA nanoparticles. After cross-linking of PVA to nanoparticles to produce PVA-grafted nanoparticles, and reduction of their zeta potential, the effects on cell viability and cytokine secretion were analyzed. PVA-grafted nanoparticles still stimulated elevated cytokine secretion from human immune cells; however, this was inhibited after reduction of the zeta potential. In conclusion, covalent cross-linking of PVA to nanoparticles and adjustment of the surface charge rendered them nontoxic to immune cells, nonimmunogenic, and potentially suitable for use as theragnostic agents.

Synthesis of cross-linked PVA membranes embedded with multi-wall carbon nanotubes and their application to esterification of acetic acid with methanol

The present study focused on the performance enhancement of cross-linked PVA membrane using citric acid as the cross-linking agent, and by incorporation of treated multi-wall carbon nanotubes (TCN). Hybrid membranes were synthesized and applied as a separation element in a membrane reactor to improve the esterification of acetic acid with methanol in which Amberlyst 15 was used as the catalyst. The properties of the membranes were investigated by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, scanning electronic microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), derivative thermal gravimetry (DTG), differential scanning calorimetry (DSC), and tensile test. Moreover, swelling of prepared membranes at 25°C was found for a quaternary feed solution. Results showed that the acid conversion rate was improved with the increasing TCN content of the membranes. It was also indicated that the hybrid membranes had good separating properties for removing water from the reaction mixture. The final conversion of acid was increased from 52.30% to 99.25% using the membrane with 2wt.% TCN instead of the pure membrane at optimized condition and 4h of operation. The operating conditions were optimized as the initial methanol to acetic acid molar ratio of 4:1, reaction temperature of 70°C and catalyst loading of 15wt.% relative to acetic acid.

Mechanical Properties and Interfacial Interaction of Modified Calcium Sulfate Whisker/Poly(Vinyl Chloride) Composites

Calcium sulfate whiskers (CSWs) modified with glutaraldehyde-crosslinked poly(vinyl alcohol) (PVA) or traditional surface modifiers, including silane coupling agent, titanate coupling agent and stearic acid, were used to strengthen poly(vinyl chloride) (PVC), and the morphologies, mechanical and heat resistant properties of the resulting composites were compared. The results clearly show that glutaraldehyde cross-linked PVA modified CSW/PVC composite (cPVA@CSW/PVC) has the strongest interfacial interaction, good and stable mechanical and heat resistant properties. Nielsen's modified Kerner's equation for Young's modulus is better than other models examined for the CSW/PVC composites. The half debonding angle θ of cPVA@CSW/PVC composite is lower than that of other composites except silane coupling agent modified CSW/PVC composites, indicating a very strong interfacial adhesion between cPVA@CSW and PVC. In general, cross-linked PVA is effective and environmentally friendly in modifying inorganic fillers.

Microparticulate poly(vinyl alcohol) hydrogel formulations for embedding and controlled release of polyethylenimine (PEI)-based nanoparticles.

The present paper for the first time describes the embedding of polymeric PEI-based polyplexes and lipopolyplexes into poly(vinyl alcohol) (PVA) hydrogels, to establish novel Nanoparticles-in-Microparticle Delivery Systems (NiMDS). Through modification of various parameters including different PVA molecular weights and concentrations, different emulsifiers and defined numbers of freeze-thaw cycles for physical PVA crosslinking, sustained release devices are also obtained. Beyond favourable alterations of important physicochemical/biological nanoparticle properties and the possibility for prolonged storage as easy-to-handle formulation (dry powder), we show that these NiMDS also allow the tailormade, fine-tuned, long-term release of fully active nanoparticles in possible therapeutic applications.

Electrochemical Performance of Graphite-Silicon Alloy Composite Anodes Using Cross-Linked Poly(vinyl alcohol) Binder for Lithium-Ion Batteries

The growing demand for rechargeable batteries requires a great improvement in the energy density of current lithium-ion batteries. In order to increase the energy density of lithium-ion batteries, silicon anode materials have been actively studied, because they exhibit a high theoretical capacity, a low reduction potential, are environmentally benign and are low cost.1 However, they suffer from substantial volume changes during cycling, which are highly detrimental to the cycling stability of lithium-ion batteries. The mechanical stresses caused by repeated volume changes can fracture the electrode, which results in poor electrical contacts between the active materials, electronic conductors and current collector. To solve these problems, many studies have been carried out by different approaches such as controlling the particle size and morphology, alloying with inert metals, embedding silicon in a conductive material, and applying several functional binders. In order to obtain the silicon-based composite anodes with high capacity and good cycling stability, we synthesized silicon alloy that was composed of silicon nanoparticles embedded in Al-Fe-Ti-Ni matrix phases. Using these silicon alloy material, we prepared the composite electrodes composed of graphite powder and silicon alloy particles. In these composite anodes, poly(vinyl alcohol) (PVA)s with different degree of cross-linking were employed as polymer binders. The effect of degree of cross-linking on interfacial adhesion and cycling performance of the composite electrodes was investigated to identify optimum processing condition. A systematic study demonstrated that the appropriate cross-linking of PVA made the electrodes mechanically strong and remarkably improved the cycling stability of the electrodes.

Embedded Ceria Nanoparticles in Crosslinked PVA Electrospun Nanofibers as Optical Sensors for Radicals.

This work presents a new nanocomposite of cerium oxide (ceria) nanoparticles embedded in electrospun PVA nanofibers for optical sensing of radicals in solutions. Our ceria nanoparticles are synthesized to have O-vacancies which are the receptors for the radicals extracted from peroxide in water solution. Ceria nanoparticles are embedded insitu in PVA solution and then formed as nanofibers using an electrospinning technique. The formed nanocomposite emits visible fluorescent emissions under 430 nm excitation, due to the active ceria nanoparticles with fluorescent Ce3+ ionization states. When the formed nanocomposite is in contact with peroxide solution, the fluorescence emission intensity peak has been found to be reduced with increasing concentration of peroxide or the corresponding radicals through a fluorescence quenching mechanism. The fluorescence intensity peak is found to be reduced to more than 30% of its original value at a peroxide weight concentration up to 27%. This work could be helpful in further applications of radicals sensing using a solid mat through biomedical and environmental monitoring applications.

Facile preparation of cross-linked porous poly(vinyl alcohol) nanofibers by electrospinning

Abstracts We reported a facile strategy for fabricating cross-linked poly(vinyl alcohol) (PVA) nanofibers with internal nanopore structure. PVA nanofibers encapsulated with Fe3O4 nanoparticles were produced by electrospinning, in which nanopores were generated by removal of Fe3O4 particle template and cross-linking of PVA simultaneously. The cross-linked PVA nanofibers had enhanced thermal stability compared with that of the as-spun pure ones. It is shown that the pores were uniformly distributed all over the fibers, with an average size of 12 nm. This new method, which can be used to prepare nanoporous PVA nanofibers simply at low cost, is suitable for practical applications.

Highly improved reverse osmosis performance of novel PVA/DGEBA cross-linked membranes by incorporation of Pluronic F-127 and MWCNTs for water desalination

A novel Poly (vinyl alcohol) (PVA) reverse osmosis (RO) membrane with unique performance and characteristics was synthesized for water desalination. PVA thin film nanocomposite (TFN) membranes were fabricated by the infusion of Pluronic F-127 and multi-wall carbon nano-tubes (MWCNTs) in a single layer crosslinked by bisphenol A diglycidyl ether (DGEBA). The overall RO performance of the membranes including hydrophilicity, surface roughness, water permeability, salt rejection, chlorine resistance and biofouling resistance was evaluated using a dead end RO filtration unit. The incorporation of Pluronic F-127 and MWCNTs improved the overall RO performance of the membranes. It was found that the modified membranes surface became smoother and highly hydrophilic compared to the pristine PVA membranes surfaces. This study indicated that the membranes that contain 0.08 and 0.1wt% MWCNTs provided excellent permeation, salt rejection, Chlorine and biofouling resistance and mechanical strength. The most striking result to emerge from this study is that the overall RO performance enhancement has transpired while utilizing PVA as an active RO separation layer without a polymeric or ceramic substrate. This study shows that proper crosslinking of PVA coupled with mechanical strength enhancement overcomes the common PVA drawbacks, mainly swelling and rupture under very high pressure.

Fabrication and characterization of poly(vinyl alcohol)-TiO2 nanocomposite films for orthopedic applications

Poly(vinyl alcohol) (PVA) is reinforced with TiO2 nanoparticles in order to enhance thermo-mechanical stabilities, surface characteristics and osteoblastic cell adhesion. PVA–TiO2 nanocomposite films with desirable mechanical, thermal and biocompatible properties are fabricated through solution casting method followed by de-hydrothermal cross-linking treatment. The composition of TiO2 nanoparticles was standardized to achieve mechanically stable nanocomposite films, based on tensile strength measurements composition of TiO2 is determined as optimal at 3wt%. PVA–TiO2 nanocomposite films were characterized by Scanning electron microscopy, Energy dispersive spectroscopy, Atomic force microscopy, Ultra violet and Fourier transform infrared spectroscopic techniques. Elemental mapping studies substantiate incorporation of TiO2 nanoparticles within the PVA matrix. Dimensional stability evaluated by soaking films in SBF for 24h insinuates the role of TiO2 in the direction of controlling degree of swelling. In-vitro bioactivity test and cell adhesion results also predict that presence of TiO2 is advantageous to enhance apatite growth and promote cell-substrate interaction. SEM studies illustrate improved surface morphology of PVA–TiO2 nanocomposite film with homogenously distributed TiO2 nanoparticles, which help to enhance thermo-mechanical behavior. TiO2 nanoparticles construct cell-adhesive hydrophilic nano-domains that act as potential cell adhesion sites and promotes osteointegration. Bio compatibility studies proved that thermally cross-linked PVA is non-toxic in relation to PVA cross-linked with glutaraldehyde. Cytotoxicity and cell adhesion of nanocomposite films evaluated through cell viability (MMT) assay and crystal violet staining revealed that PVA-3wt% TiO2nanocomposite could act as an excellent composite and hence suitable to be used in bone implant applications.

Cross-linked nanocomposite hydrogels based on cellulose nanocrystals and PVA: Mechanical properties and creep recovery

Cellulose nanocrystal (CNC) reinforced poly(vinyl alcohol) (PVA) hydrogels with a water content of ∼92% were successfully prepared with glutaraldehyde (GA) as a cross-linker. The effects of the CNC content on the thermal stability, swelling ratio and mechanical and viscoelastic properties of the cross-linked hydrogels were investigated. The compressive strength at 60% strain for the hydrogels with 1wt% CNCs increased by 303%, from 17.5kPa to 53kPa. The creep results showed that the addition of CNCs decreased the creep elasticity due to molecular chain restriction. The almost complete strain recovery (∼97%) after fixed load removal for 15min was observed from the hydrogels with CNCs, compared with 92% strain recovery of the neat cross-linked PVA hydrogels. The incorporation of CNCs did not affect the swelling ratio and thermal stability of the hydrogels. These results suggest the cross-linked CNC-PVA hydrogels have potential for use in biomedical and tissue engineering applications.

Frictional properties of physically cross-linked PVA hydrogels as artificial cartilage

Abstract Physically cross-linked PVA gels (freeze-thawed PVA gel and cast-dried PVA gel) are used as biocompatible materials since special chemicals were not used in their preparation. Cast-dried PVA gels are therefore promising as candidate materials for artificial cartilage because of their excellent frictional property. In this study, three types of gels-freeze-thawed gels, cast-dried gels and hybrid gels which are laminated gels consisting of both cast-dried layer and freeze-thawed layer were prepared and analyzed. The frictional behaviors of these three PVA hydrogels were examined in reciprocating test. Further, the effects of sterilization with ethanol on frictional behaviors of these PVA hydrogels were evaluated.

Preparation and properties of polyacrylamide/polyvinyl alcohol physical double network hydrogel

A novel physical double network hydrogel (PDN gel) composed of physically cross-linked PVA and hydrophobically associated polyacrylamide (HAPAM) has been successfully prepared by one-pot in situ polymerization and subsequent freeze–thaw cycling.

Properties and Applications of Polyvinyl Alcohol, Halloysite Nanotubes and Their Nanocomposites

The aim of this review was to analyze/investigate the synthesis, properties, and applications of polyvinyl alcohol–halloysite nanotubes (PVA–HNT), and their nanocomposites. Different polymers with versatile properties are attractive because of their introduction and potential uses in many fields. Synthetic polymers, such as PVA, natural polymers like alginate, starch, chitosan, or any material with these components have prominent status as important and degradable materials with biocompatibility properties. These materials have been developed in the 1980s and are remarkable because of their recyclability and consideration of the natural continuation of their physical and chemical properties. The fabrication of PVA–HNT nanocomposites can be a potential way to address some of PVA’s limitations. Such nanocomposites have excellent mechanical properties and thermal stability. PVA–HNT nanocomposites have been reported earlier, but without proper HNT individualization and PVA modifications. The properties of PVA–HNT for medicinal and biomedical use are attracting an increasing amount of attention for medical applications, such as wound dressings, drug delivery, targeted-tissue transportation systems, and soft biomaterial implants. The demand for alternative polymeric medical devices has also increased substantially around the world. This paper reviews individualized HNT addition along with crosslinking of PVA for various biomedical applications that have been previously reported in literature, thereby showing the attainability, modification of characteristics, and goals underlying the blending process with PVA.

New approach to the synthesis of a functional macroporous poly(vinyl alcohol) network and design of boronate affinity sorbent for protein separation

A new method for preparation of a functional macroporous crosslinked polyvinyl alcohol (MP-PVA) matrix in aqueous media without usage of an outer porogen has been elaborated. The method includes PVA oxidation by sodium periodate followed by (a) self-crosslinking of the oxidized PVA and (b) glutaraldehyde crosslinking. MP-PVA represents a highly crosslinked matrix that is non-swellable in water and common organic solvents and has a high pore volume and pore surface and contains reactive aldehyde groups. Surface topography of MP-PVA has revealed its heterogeneous globule-like structure with open macropores of about 100–300nm in diameter and large pores of about several microns. Dynamic light scattering study has elucidated the phase separation during the self-crosslinking step as the main factor responsible for macroporous structure generation. Boronate affinity sorbent has been designed by means of immobilization of aminophenylboronic acid via aldehyde groups of MP-PVA matrix, and its applicability for quantification of glycated and non-glycated haemoglobin in human blood of diabetics patients has been demonstrated. The proposed approach to the preparation of the functional macroporous MP-PVA matrix may be promising for designing new macroporous sorbents and monoliths for affinity ligands immobilization and separation of hydrophilic macromolecules.

High filtration performance thin film nanofibrous composite membrane prepared by electrospraying technique and hot-pressing treatment

For conventional powder coating technology, powder coating materials were directly coated onto the target surface and then heated and cured to form a coat. Inspired by this technology, a facile route for fabrication of thin film nanofibrous composite (TFNC) membrane consisting of a nanofibrous substrate and a hydrophilic barrier layer was developed by electrospraying poly(vinyl alcohol) (PVA) nanobeads onto the electrospun polyacrylonitrile (PAN) substrate and following by hot-pressing treatment assisted by moistening absorption. Water molecules from absorbed moisture acted as “plasticizer” and could facilitate PVA melting. The moistened electrosprayed PVA nanobeads could be easily melted or softened to be pressed imperceptibly into an integrated barrier film on the supporting layer at a certain temperature. The depositing time of PVA electrospraying, moistcuring time, thermal treatment temperature and time were optimized to achieve an integrated, nonporous PVA barrier layer. The resulting barrier layer was chemically crosslinked and its filtration performance can be finely controlled by different PVA crosslinking degree. Especially, the optimized PVA/PAN TFNC membrane possessed high ultrafiltration performance in BSA filtration tests with water flux 173.0L/m2h and rejection above 98.0% at low feeding pressure 0.3MPa. This work may provide a practical feasibility for water filtration application.

Modification of polyurethane by the lateral cross-linking using a modified poly(vinyl alcohol) for the improvement of tensile strength and the control of water vapor permeation

The hydroxyl groups of poly(vinyl alcohol) (PVA) was capped with phenylisocyanate, ethylisocyanate, or octylisocyanate to reduce the hydrophilicity and to improve the compatibility with organic solvent. The modified PVA was used to laterally cross-link the polyurethane (PU), and a Control PU series containing free modified PVA was also prepared for comparison. The PVA cross-linking significantly improved the tensile strength, whereas the Control series did not. The thermal properties (T g , T m , and ΔH m ) did not change with the incorporation of PVA cross-linking. The breaking strain of the PU series was not affected by the PVA cross-linking. The shape recovery and shape retention of the PU series remained high with the increase of PVA content. The low-temperature flexibilities of PU series was not changed by the PVA cross-linking, whereas the water vapor permeability was reduced by the PVA cross-linking.

Synthesis of Magnetic Nanoparticles Incorporated Smart Gel.

In this work, we prepared new poly(vinyl alcohol) (PVA) based magnetic-pH responsive smart gels comprised of nickel nanoparticles and cross-linked PVA with a pH responsive poly(methyl methacrylic acid) (PMAA) (designated as (PVA-PMAA/Ni-NCGs). We developed a strategy based on the modification of PVA with glycidyl methacrylate (GMA) groups, which has the advantage of being highly efficient in preparing cross-linked PVA with pH responsive polymer chains. The PVA(GMA)-PMAA/Ni-NCGs were characterized by X-ray diffraction, scanning electron microscopy, magnetic measurements and thermogravimetric analysis. We report the relationship between macroscopic properties like the swelling ratio and the network microstructure of PVA(GMA)-PMAA/Ni-NCGs. Swelling in water and drying in air were alternately repeated, in which water was exchanged by new water before each swelling experiment. The PVA(GMA)-PMAA/Ni-NCGs can respond to a magnetic field and the pH changes of an environment. We present an example showing that PVA(GMA)-PMAA/Ni-NCGs can be innovatively exploited as a polymeric material in the application of controlled drug release.

A novel surface modification for calcium sulfate whisker used for reinforcement of poly(vinyl chloride)

A novel technique is developed in this study to modify the surface of calcium sulfate whisker (CSW) for the preparation of high-performance CSW/poly(vinyl chloride) (PVC) composites. The CSW coated with poly(vinyl alcohol) (PVA) and then cross-linked by glutaraldehyde is used to strengthen PVC, and the surface morphology and mechanical properties of CSW/PVC composites are investigated. It shows that the mechanical properties of the cross-linked PVA modified CSW/PVC (cPVA@CSW/PVC) composites are significantly improved, their yield strength, breaking strength, tensile modulus and elongation at break are 65.7 MPa, 53.5 MPa, 1772 MPa and 225 %, with an increase of 7.2, 13.1, 7.6 and 8.2 % as compared with that of the unmodified CSW/PVC composites, respectively. The improvement in the mechanical properties can be attributed to the strong interfacial adhesion between cPVA@CSW and PVC matrix, because the modified CSW has abundant hydroxyl groups that can produce a strong interaction with PVC. This method is simple and inexpensive, and can be applied in large scale.