Functionally‐modified egg white albumen hydrogels

Hydrogels were prepared by using egg white albumen (EWA) before and after chemical modification of its lysyl residues with ethylenediamine tetraacetic dianhydride (EDTAD) to incorporate carboxylic groups. This resulted in an increase in swelling ratio of the EWA hydrogels. The swelling ratio increased dramatically in deionized water substantially, more than in pH 7.4 buffer solution. The effects of medium pH, temperature and swelling were investigated, along with crosslinking of the gel network by glutaraldehyde (GLA), as well as acetone treatment. The gels denatured by acetone showed an insignificant increase in swelling ratio for the gels crosslinked with GLA during gel preparation, which is in contrast to the gels crosslinked subsequent to gel formation. The swelling behavior was positively affected by temperature and time. However, an insignificant effect of pH was observed due to electrostatic screening of the carboxylic groups by sodium ions in the buffer solution. Availability of various functional groups on EWA has resulted in adsorption of metals (Cu⁺² ions) and non‐metals (PO₄^?2 anions). Copyright © 2004 Society of Chemical Industry     

Characterization of strong polyelectrolyte hydrogels based on poly(vinyl alcohol)

Maleic anhydride (MA) was grafted onto both partially and fully hydrolyzed poly(vinyl alcohol) (PVA) in the presence of an initiator. Strong polyelectrolyte polymers were prepared by sulfonation of PVA–MA grafts. The sulfonation was completed by reaction of hydroxyl groups of PVA–MA grafts with two different sulfonating reagents (chlorosulfonic acid and pyridine sulfonic acid). The sulfonation degree was evaluated by acid–base titration and ¹H NMR analysis. The solution behaviour of the prepared grafts was evaluated from viscosity measurements. Four kinds of water‐insoluble PVA–MA and PVA–MA‐SO₃H hydrogels were prepared by heat treatment, physical gelation and chemical crosslinking with different weight ratios of N,N‐methylene bisacrylamide (MBA) crosslinker. The swelling parameters were measured for all prepared gels in deionized water and aqueous solutions at different pH values from 2 to 12 having constant ionic strength (I = 0.1). All gels exhibit a different swelling behaviour upon environmental pH changes. Copyright © 2004 Society of Chemical Industry     

Probing the degree of crosslinking of a cellulose based superabsorbing hydrogel through traditional and NMR techniques

The network structure of a cellulose-based superabsorbing material has been probed by using three different techniques: ¹³C solid state NMR, free swelling in water and uniaxial compression of water swollen samples. A good agreement between the three apporaches has been found in terms of concentration of crosslinks per unit volume.The results have been discussed taking into account that NMR technique is able to detect only chemically effective crosslinks while free swelling and compression are sensitive to elastically effective physical and chemical crosslinks.A depression of swelling capacity and an apparent increase of degree of crosslinking with time, promoted by ageing of the cellulosic material, has been experimentally evidenced and discussed in terms of development of intermolecular physical interactions.     

Preparation and swelling properties of semi‐IPN hydrogels based on chitosan‐g‐poly(acrylic acid) and phosphorylated polyvinyl alcohol

The phosphorylated poly(vinyl alcohol) (P‐PVA) samples with various substitution degrees were prepared through the esterification reaction of PVA and phosphoric acid. By using chitosan (CTS), acrylic acid (AA) and P‐PVA as raw materials, ammonium persulphate (APS) as an initiator and N,N‐methylenebisacrylamide as a crosslinker, the CTS‐g‐PAA/P‐PVA semi‐interpenetrated polymer network (IPN) ssuperabsorbent hydrogel was prepared in aqueous solution by the graft copolymerization of CTS and AA and followed by an interpenetrating and crosslinking of P‐PVA chains. The hydrogel was characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) techniques, and the influence of reaction variables, such as the substitution degree and content of P‐PVA on water absorbency were also investigated. FTIR and DSC results confirmed that PAA had been grafted onto CTS backbone and revealed the existence of phase separation and the formation of semi‐IPN network structure. SEM observations indicate that the incorporation of P‐PVA induced highly porous structure, and P‐PVA was uniformly dispersed in the polymeric network. Swelling results showed that CTS‐g‐PAA/P‐PVA semi‐IPN superabsorbent hydrogel exhibited improved swelling capability (421 g·g^?1 in distilled water and 55 g·g^?1 in 0.9 wt % NaCl solution) and swelling rate compared with CTS‐g‐PAA/PVA hydrogel (301 g·g^?1 in distilled water and 47 g·g^?1 in 0.9 wt % NaCl solution) due to the phosphorylation of PVA. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of monodisperse poly(vinyl alcohol) microspheres by heterogeneous surface saponification and iodine complex formation

Monodisperse poly(vinyl acetate) (PVAc) microspheres with high molecular weight obtained by suspension polymerization of vinyl acetate were saponified in alkaline aqueous solution to keep their spherical structure. The saponification was restricted on the surface of the PVAc microspheres and obtained particles had skin/core structure. Various poly(vinyl alcohol) (PVA) microspheres with different diameters and degrees of saponification (DSs) were obtained. The conversion of PVAc to PVA during the heterogeneous surface saponification time were examined by nuclear magnetic resonance spectroscopy and after 72 h hydrogel type PVA microspheres completely saponified were obtained. The crystal melting temperatures of the microspheres obtained by the saponification were measured a constant value of 238°C irrespective of varying DS, and the peaks became enlarged as reaction time. Iodine complexes were formed in saponified microspheres with DS of 41% and 99% by immersing them in I₂/KI aqueous solution and decomposed by the reduction of I₂ in the complexes to 2I^? using sodium sulfite to confirm whether the skin formed through the saponification was composed of PVA with high VA content. Obviously, characteristic blue color developments owing to I₅^?‐PVA complexes were observed in both saponified regions and a red in the PVAc core. Consequently, it was concluded that the PVA skins formed by heterogeneous surface saponification had high DSs. Such complexes endowed polymeric microspheres a good radiopacity which would be useful in clinical treatment of vascular diseases and were examined by X‐ray irradiation image. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation of water‐swollen hydrogel membranes for gas separation

Water‐swollen hydrogel (WSH) membranes for gas separation were prepared by the dip‐coating of asymmetric porous polyetherimide (PEI) membrane supports with poly(vinyl alcohol) (PVA)–glutaraldehyde (GA), followed by the crosslinking of the active layer by a solution method. Crosslinked PVA/GA film of different blend compositions (PVA/GA = 1/0.04, 0.06, 0.08, 0.10, 0.12 mol %) were characterized by differential scanning calorimetry (DSC) and their water‐swelling ratio. The swelling behavior of PVA/GA films of different blend compositions was dependent on the crosslinking density and chemical functional groups created by the reaction between PVA and GA, such as the acetal group, ether linkage, and unreacted pendent aldehydes in PVA. The permeation performances of the membranes swollen by the water vapor contained in a feed gas were investigated. The behavior of gas permeation through a WSH membrane was parallel to the swelling behavior of the PVA/GA film in water. The permeation rate of carbon dioxide through the WSH membranes was 10⁵ (cm³ cm^?2 s^?1 cmHg) and a CO₂/N₂ separation factor was about 80 at room temperature. The effect of the additive (potassium bicarbonate, KHCO₃) and catalyst (sodium arsenite, NaASO₂) on the permeation of gases through these WSH membranes was also studied. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1785–1791, 2001     

Hydrogels reinforced with nanoclays with improved response rate

Two series of semiinterpenetrating networks (SIPN) based on linear hydrophilic poly(vinyl alcohol) (PVA) and thermo‐responsive poly(N‐isopropylacrylamide) (PNIPA), physically crosslinked with inorganic clay, are presented. The hydrogels with different crosslinking densities were prepared by varying the content of clay from 1 to 6 wt % and contained linear interpenetrant, PVA in the range of 0.5–1.5 wt %. The effect of clay content on swelling/deswelling behavior and phase transition in PNIPA gels, as well as the feasibility of reinforcing the gels with high molecular weight PVA, were analyzed. The thermal response of hydrogels, followed by DSC, confirmed that the insertion of hydrophilic PVA did not have a significant effect on the onset of the volume phase transition temperature, while the response was faster. The equilibrium degree of swelling of SIPNs and PNIPA hydrogels was in the range of 9–79 and decreased with increasing content of clay. The internal morphology and surface wettability of the hydrogels were investigated by scanning electron microscope analysis and contact angle measurements, respectively. The network structural parameters of the PNIPA and SIPN nanocomposites hydrogels, such as the average molecular weight between crosslinks, M_c, and effective crosslinking density, N_e, were determined by dynamic mechanical analysis. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44535.     

Ring‐opening polymerization of epoxy end‐terminated poly(ethylene oxide) as a route to highly crosslinked materials with exceptional swelling behavior (II)

Highly swellable poly(ethylene oxide) (PEO) gels were prepared by anionic ring‐opening polymerization of diepoxy end‐capped PEO (3400 g mol^?1) and PEO (8000 g mol^?1) using dianionic glycerol and glycolic acid initiators at scales of up to 50 g diepoxide. The glycerol‐derived materials swell to almost 20 times their mass in water. The driving force for rapid swelling appears to arise during ‘crystallization’, as segments between crosslinks are forced to pack under conditions that create high‐energy domains within the material. Solvation and therefore swelling are driven by the release of the resulting packing energy. These observations may offer insight into methods for designing other highly swellable materials. When the polyfunctional initiators have groups with different reactivities (e.g. alkoxide versus carboxylate), as might be expected, the more nucleophilic functional group appears to dominate the ring‐opening polymerization process. Copyright © 2007 Society of Chemical Industry     

Poly(acrylamide‐co‐maleic acid) hydrogels for removal of Cr(VI) from aqueous solutions,Part 1: Synthesis and swelling characterization

The swelling behavior of poly (acrylamide‐co‐maleic acid) hydrogels has been investigated in distilled water at 30°C. The gels were characterized with respect to structural parameters, Fourier transform infrared, and thermogravimetric analysis. The gels showed fair pH‐dependent swelling and exhibited double “s”‐shaped curve between equilibrium water uptake and pH of the swelling media. The two pK_a values, as determined from the curve, were found to be 2.46 and 6.58. The activation energy of the water uptake process for plain and acid containing gels was found to be 7.93 and 3.26 kJ mol^?1 respectively. Similarly, the enthalpy of mixing between dry polymer and solvent showed positive values, thus indicting endothermic nature of the process, and the values increased from 10.06 to 16.29 kJ mol^?1 with increase in acid content from 2.1 × 10^?1 to 4.7 × 10^?1 mM respectively. There was an optimum initiator concentration 24.0 × 10^?2 mM and reaction temperature 60°C at which gels synthesized showed maximum absorbency. The dilution of the reaction mixture resulted in the formation of hydrogels with enhanced absorbency. Finally, the gels with varying content of monomer acid in the feed mixture showed different swelling behavior when studied in the medium of pH 1.0 and 7.0. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2759–2769, 2006     

Selected properties of pH‐sensitive,biodegradable chitosan–poly(vinyl alcohol) hydrogel

Chitosan and poly(vinyl alcohol) (PVA) were used to form a semi‐interpenetrating polymeric network with glutaraldehyde as the cross‐linker. The molecular weight and degree of deacetylation of the chitosan were 612 kDa and 72 %, respectively. The chemical bonds formed by the cross‐linking reaction and transition of these bonds in different pH media were investigated. The gelation property of the chitosan–PVA pregel solution and mechanical properties of the hydrogel were studied. The FTIR spectra of the hydrogel before and after swelling at pH 3 and pH 7 indicated formation of Schiff's base (C?N) and ? NH₃⁺. They also showed pH‐induced transition of C?N to C? N, and ? NH₃⁺ to ? NH₂, as well as the instability of the Schiff's base. The chitosan is essential for hydrogel formation through Schiff's base reaction between the amino groups of the chitosan and the aldehyde groups of the glutaraldehyde. The addition of PVA improved the mechanical properties of the hydrogel. However, PVA tends to leach out at longer swelling times in the acidic medium due to hydrolysis of the gel networks, Schiff's base. Copyright © 2004 Society of Chemical Industry     

Some peculiar properties of cross-linked polyvinyl alcohol (CL-PVA) related to the reticulation degree

Summary Unlike usual polyhydroxilic packing materials for liquid chromatography based on cross-linked agarose, CL-amylose and CL-dextrans (Sephadex), the cross-linked PVA gels exhibit an increase of swelling properties with the reticulation degree, up to a certain limit. Afterwards more advanced reticulation degrees induce a decrease in swelling capacities just as in case of other cross-linked polyhydroxilic polymers. This abnormal behaviour of CL-PVA was supposed as being due to the interchain hydrogen associations. IR spectra, X-ray data and 8 M urea treatments strongly supported our supposition pointing out a maximum association by hydrogen bonds in CL-PVA gels with a reduced degree of reticulation.Part of the paper was presented at the 29^th IUPAC Symposium Macro'83, Bucharest, ROMANIA, September 5–9, 1983.     

Novel shrinking–swelling hysteresis in DMSO/THF mixtures of copolymer gels containing sulphonate groups

The swelling volume of copolymer gels made from 2-(acrylamido)-2-methylpropanesulphonic acid (AMPS; electrolyte monomer), N,N-dimethylacrylamide (DMAA; comonomer) and N,N′-methylenebis(acrylamide) (BIS; crosslinker) was measured in mixtures of two organic solvents, dimethyl sulphoxide (DMSO) and tetrahydrofuran (THF) at 25°C. A volume phase transition was observed in the gels having 43·18mol% AMPS with different counterions K⁺, Na⁺ and H⁺, when the THF concentration in the mixture increased beyond a certain value. We observed a swelling-hysteresis between the shrinking and swelling curves, i.e. more DMSO was required to make a shrunk gel start to swell again than to cause the volume shrinking. This hysteresis stems from the formation of ion pairs and/or multiplets in the ionizable gels when the medium polarity is decreased. An excess of DMSO is required to reduce the ionization energy for making the shrunk gel swell again in the DMSO/THF mixture. These aggregates and multiplets do not seem to be entirely removed by the swelling process and act as additional physical crosslinks, so that the DMSO concentration required to induce the shrunk gel to swell becomes higher in the next swelling process, showing another hysteresis. The release of bound water from the solvating layer after shrinkage may be another possible reason for this hysteresis. © 1998 Society of Chemical Industry     

Preparation of ketoprofen‐loaded high‐molecular‐weight poly(vinyl alcohol) gels

High‐molecular‐weight atactic poly(vinyl alcohol) (a‐PVA) gels loaded with (R,S)‐2‐(3‐benzoylphenyl)propionic acid (ketoprofen) were prepared from 5, 6, 7, and 8 g/dL solutions of a‐PVA with a number‐average degree of polymerization of 4000 in an ethylene glycol/water mixture with an aging method to identify the effect of the initial polymer concentration on the swelling behavior, morphology, and thermal properties of a‐PVA gels. Then, the release behavior of ketoprofen from a‐PVA gels was investigated. As the polymer concentration decreased, the ability for network formation decreased, and the degree of swelling of the a‐PVA gels increased. In addition, the enthalpy increased with an increase in the a‐PVA concentration, but the melting temperatures of the gels prepared at different initial polymer concentrations were the same; this indicated that tighter gel networks would be formed by a higher polymer chain density. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation and characterization of hydroxyl ion-conducting interpenetrating polymer network based on PVA and PEI

Novel interpenetrating polymer networks (IPNs) and semi-interpenetrating polymeric networks (sIPNs) based on polyethyleneimine (PEI) and poly(vinyl alcohol) (PVA) have been prepared via crosslinking reactions with respective crosslinking agent, 1,4-dibromobutane and glutaraldehyde (GA). IPNs, sIPNs and PEI/PVA blend membranes are characterized in detail by Fourier transform Infrared attenuated total reflection (FTIR-ATR) spectroscopy, mechanical properties, water uptake, swelling ratio, field emission scanning electron microscope (FE-SEM), hydroxide ion (OH^?) conductivity. Moderate water uptake and swelling ratio are obtained by the IPN derived from PEI:PVA (1:1), achieving 78.4 and 36.8 %, respectively. And the IPN also shows an acceptable OH^? conductivity of 4.87 mS/cm at 80 °C.     

Superabsorbent composite. X. Effects of saponification on properties of polyacrylamide/attapulgite

A novel superabsorbent composite from acrylamide (AM) and attapulgite (APT), polyacrylamide/attapulgite (PAM/APT), was prepared by polymerizing AM with the existence of APT in aqueous solution, and then saponified with NaOH solution. Considering the impacts of hydrophilic groups (? COONa, ? COOH, and ? CONH₂) on properties of the PAM/APT composite, the effects of saponification mode, molar ratio of NaOH to AM and saponification time on water absorbency, hydrophilic group content, and surface morphology were investigated systematically. The results indicate that the two‐step adding NaOH mode is superior to that of the one‐step mode. Among the superabsorbent composite incorporated with 30 wt% APT, the composite saponified at 95°C for 2 h with the molar ratio of 0.6 for NaOH to AM acquired the highest water absorbencies of 1715g g^?1 and 87.8g g^?1 in distilled water and in 0.9 wt% NaCl solution, respectively. The molar ratio of various hydrophilic groups at this time was 10:3:11 for ? COONa, ? COOH, and ? CONH₂ determined using linear potentiometric titration method. POLYM. ENG. SCI. 46:1762–1767, 2006. © 2006 Society of Plastics Engineers.     

Study on ketalization reaction of polyvinylalcohol by ketones. I. Reaction between polyvinylalcohol and acetone

Ketalization reaction of polyvinylalcohol (PVA) by acetone, dimethylsulfoxide (DMSO) as solvent, under the presence of acidic catalyst, in homogeneous system was carried out and the synthesis of polyvinylketal with any ketalization degree was successfully performed. This reaction proceeds in bimolecular reaction, the equilibrium constant is ca. 0.07 at 40°C and roughly 10^?5 less compared with the acetalization reaction between PVA and aldehydes. Synthesis in aqueous media is difficult. However, the heat of reaction for both cases is 7.5 kcal/mol and both reactions are considered to proceed in an identical reaction mechanism. Ketalization reaction starts from isotactic OH portion and proceeds finally to syndiotactic OH portion, however, 100% ketalization is extremely difficult. The effects of water on reaction was confirmed both from theoretical and experimental viewpoints, and even though the presence of water lowers the degree of ketalization, it was observed that the presence of water below 0.1 mol against 1 mol of PVA will not significantly affect final ketalization degree. Polyvinylketals thus obtained are soluble in DMSO, dimethylformamide (DMF), and alcohols.     

The heterogeneous formalization of poly(vinyl alcohol) accompanying crosslinking reaction-II

Poly(vinyl alcohol) (PVA) films were allowed to react with formaldehyde in water containing salt and an acid catalyst (the heterogeneous formalization). The content of crosslinks increased with decreasing with decreasing acid concentration under fixed formaldehyde and salt concentrations. The crosslink contents of formalized PVA were estimated in terms of the degree of swelling of formalized and acetylated PVA in chloroform. The crosslink contents were calculated by means of FLORY's method. One crosslink per 100 units of vinyl alcohol was estimated to exist for the sample of the degree of swelling about 6.     

Photo‐Crosslinking Strategy Constructs Adhesive,Superabsorbent, and Tough PVA‐Based Hydrogel through Controlling the Balance of Cohesion and Adhesion

An ideal hydrogel with excellent adhesive performance has drawn much attention in research and applications. In this paper, a photo‐crosslinked polyvinyl alcohol bearing styrylpyridinium group/cellulose nanocrystals (PVA‐SbQ/CNC) composite hydrogel is designed through photo‐crosslinking technology for preventing the physical crosslinking of polyvinyl alcohol to maintain enough hydroxy groups in the hydrogel. Thus, the hydrogel exhibits excellent adhesive behavior not only for various solid substrates (plastics, rubbers, glasses, metals, and woods) but also muscle and fat. In addition, the formation mechanism, the swelling behavior, and mechanical strength are also investigated. Also, these results show that photo‐crosslinked PVA‐SbQ/CNC hydrogel possesses high swelling rate, super stretchability, and high toughness. Moreover, adhesive, mechanical, and swelling properties of PVA‐SbQ/CNC hydrogels can be changed with the increase of total incident light intensity. It is anticipated that the photo‐crosslinked PVA‐SbQ/CNC hydrogel would play a significant role in the applications of wound dressing, medical electrodes, tissue adhesives, portable equipment, and super absorbent materials. In this sense, the simple photo‐crosslinking strategy would provide new ideas for designing soft and adhesive materials through controlling the balance of cohesion and adhesion.     

Absorbent polyvinyl alcohol–sodium carboxymethyl cellulose hydrogels for propolis delivery in wound healing applications

Second degree burns require dressings to heal. The ideal dressing should keep a moist environment, have low cost, be elastic and have a bactericidal effect. The potential of PVA‐NaCMC (sodium carboxymethyl cellulose) gels to combine the mechanical and swelling properties of PVA with the flexibility and high water uptake of NaCMC and the antimicrobial characteristics of propolis is investigated. The freeze‐thawed gels were characterized by FTIR and DSC. Their swelling behavior, their mechanical response, the delivery of active compounds and their antimicrobial properties were also determined. The main findings of the FTIR analysis were that no chemical bonding occurred between the materials. The DSC analysis revealed that the addition of NaCMC to PVA lowered the PVA crystallinity, as did the addition of propolis, leading to a more deformable gel (as can be observed from the tensile tests results). This also resulted in a higher rate of delivery of active compounds, higher weight loss and higher fluid uptake than comparable PVA‐propolis systems, as shown by the swelling tests and by the propolis delivery tests. Samples with 15% propolis content or more inhibited S. aureus colonies with 80% reduction, and are therefore highly absorbent and compliant antimicrobial gels for wound healing. POLYM. ENG. SCI., 57:1224–1233, 2017. © 2017 Society of Plastics Engineers     

Synthesis of poly(vinyl benzal) from poly(vinyl alcohol) in nonaqueous medium

Poly(vinyl alcohol) (PVA) is soluble only in water and so some important derivatives like esters cannot be prepared from PVA. The 100% conversion of PVA to acetal is also elusive as there is strong intermolecular and intramolecular hydrogen bonding. However, PVA can be dissolved in a nonaqueous medium in the presence of a small amount of C₂H₅NO₃ · DMSO(EN · DMSO) and so a maximum extent of conversion may be possible. Here, we report the preparation of poly(vinyl benzal) (PVB) by acid-catalyzed homogeneous acetalization of PVA with benzaldehyde in a nonaqueous medium. The formation of PVB was confirmed by IR and ¹H-NMR spectra. The molecular mass of the polymer was determined by the GPC method. The PVB prepared had a degree of acetalization of 95 mol%. The glass transition temperature, T_g was measured from differential scanning calorimetric (DSC) thermograms. Thermal stabilities were checked by thermogravimetric analysis (TGA) and differential thermogravimetry (DTG). A possible mechanism of three-step thermal decomposition of PVB is proposed. © 1996 John Wiley & Sons, Inc.