Preparation and properties of PVA/PVP hydrogels containing chitosan by radiation

Radiation can induce chemical reactions to modify polymers even when they are in the solid state or at a low temperature. Radiation crosslinking can be easily adjusted by controlling the radiation dose and is reproducible. The finished product contains no residuals of substances required to initiate the chemical crosslinking, which can restrict its application possibilities. In these studies, hydrogels for wound dressing were made from a mixture of chitosan and polyvinyl alcohol (PVA)/poly‐N‐vinylpyrrolidone (PVP) by freezing and thawing, gamma‐ray irradiation, or combined freezing and thawing and gamma‐ray irradiation. The physical properties of the hydrogel, such as gelation, water absorptivity, and gel strength, were examined to evaluate the usefulness of the hydrogels for wound dressing. The PVA/PVP composition was 60:40, PVA/PVP–chitosan ratio was in the range 9:1–7:3, and the concentration of, PVA/PVP–chitosan as a solid was 15 wt %. A mixture of PVA/PVP–chitosan was exposed to gamma irradiation doses of 25, 35, 50, 60 and 70 kGy to evaluate the effect of irradiation dose on the physical properties of hydrogels. Water‐soluble chitosan was used in these experiment. The physical properties of the hydrogels, such as gelation and gel strength, were higher when the combination of freezing and thawing and irradiation were used rather than just freezing and thawing. The PVA/PVP–chitosan composition and irradiation dose had a greater influence on swelling than gel content. Swelling percent increased as the composition of chitosan in PVA/PVP–chitosan increased. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1787–1794, 2002     

Regimes of microstructural evolution as observed from rheology and surface morphology of crosslinked poly(vinyl alcohol) and hyaluronic acid blends during gelation

Hyaluronic acid (HA)‐based materials are being investigated because of their role in biological fluids and tissues. Poly(vinyl alcohol) (PVA) when blended with HA at different compositions leads to superior mechanical properties compared to pure HA. The PVAHA blend hydrogels are potential candidates for pharmaceutical, biomedical, and cosmetic applications. It is essential to understand the structure, gelation time, and morphological properties of these hydrogels. In this work, a blend system of PVA crosslinked with glutaraldehyde in the presence of HA is studied. Semidilute solutions of PVA and HA are blended, followed by gelation due to crosslinking. The crosslinked gels as well as the gel cast membranes were examined. The effect of HA on the gelation process is investigated using rheological characterization. It is shown that kinetics of gelation is influenced by HA content, though storage modulus of the gels is influenced marginally. The structural features of PVAHA gels were also probed with scanning electron microscopy and dynamic light scattering. It is argued that there is a complex interplay between intra‐ and intermolecular crosslinking of PVA and PVA–HA interactions during the gel formation. Based on the insights obtained from various probing techniques for PVAHA gels with different HA content, three broad structural features were identified. It is shown that the hydrogel is semi‐interpenetrating network at lower HA content (<10% HA), cocontinuous morphology at moderate HA content and with domains at high HA content (>20% HA). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41081.     

Radiation vulcanization of hydrogenated acrylonitrile butadiene rubber (HNBR)

Raw polymer and compound of hydrogenated acrylonitrile butadiene rubber (HNBR) were subjected to γ-ray irradiation. Crosslinking was found to be the main chemical reaction induced by irradiation; the ratio of chain scission to crosslinking as well as the does at which gelation occurred were determined from gel content measurements to be 0.41 and 3.8 Mrad, respectively. The excellent hot-air and oil-resistant properties should be retained because no formation of double bonds or changing of the nitrile groups were observed with in the optimum dose range. Desired mechanical properties of the vulcanizate may be conveniently obtained by controlling the radiation dose. © 1994 John Wiley & Sons, Inc.     

Synthesis of transparent fluorocarbon elastomers: Effect of crosslinker type and electron beam irradiation level on physical and mechanical behavior

Saturated fluorocarbon elastomers are very resistant to chemical reactions, including those of a crosslinking nature. In order to study proper methods of preparing these materials, Viton GLT was mixed with various levels of trimethylol propane trimethacrylate, TMPTM, and triallyl isocyanurate, Diak #7. After molding, the materials were subjected to electron beam irradiation. The glass transition, rubbery modulus, viscoelastic behavior, and equilibrium swelling were used to characterize the materials as a function of crosslinker and irradiation level. In general, the modulus and gel fraction increased with both crosslinker content and irradiation level. Mixtures of both crosslinking monomers produced an unexpected synergism, yielding higher tensile strength, and earlier onset of gelation.     

Electron‐beam curing of hydrogenated acrylonitrile–butadiene rubber

The electron‐beam‐induced crosslinking of hydrogenated acrylonitrile–butadiene rubber (HNBR) was investigated. HNBR sheets were exposed to electron‐beam irradiation in air at a room temperature of 25 ± 2°C over a dose range of 0–20 Mrad. An attempt was made to correlate the structure of the irradiated rubber with the properties. The ratio of chain scission to crosslinking and the gelation dose were determined by a method proposed elsewhere. The gel content and dynamic storage modulus increased with the radiation dose. Fourier transform infrared studies revealed the formation of double bonds and carbonyl and ether groups. These observations were further supported by a thermogravimetric analysis of the carbonaceous residue of irradiated HNBR. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 648–651, 2005     

Formation of the first injectable poly(vinyl alcohol) hydrogel by mixing of functional PVA precursors

In this study we describe the development of an injectable, in situ chemical hydrogel forming system. The gelation occurs under neutral pH and at room temperature immediately upon mixing of the two aqueous poly (vinyl alcohol) components specifically derivatized through carbamate linkages with aldehyde (PVA‐AL) and hydrazide (PVA‐HY) functional groups, respectively. Aldehyde and hydrazide pendant groups were incorporated with a low degree of substitution (DS) into the PVA backbone to keep PVA structural homogeneity minimally altered. As a result, the hydrazone crosslinks are formed rapidly between aldehyde and hydrazide pendant groups when the correspondingly modified PVA components are brought in contact as water solutions. To assess in situ hydrazone crosslinks formation for in vitro cytocompatibility, murine neuroblastoma N2a cells were suspended in cell culture medium with the dissolved PVA‐HY prior to addition to the PVA‐AL aqueous solution. Thus, the cells were chemically encapsulated in a polymer network that was formed by mixing of the corresponding aqueous solutions of PVA functional precursors. Biochemical analysis revealed that cells survived chemical crosslinking and remained viable in the hydrogel for 4 days of culture. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effects of crosslinking time and amount of sulfophthalic acid on properties of the sulfonated poly(vinyl alcohol) membrane

A proton‐exchange membrane for a direct methanol fuel cell was prepared by modifying the chemical structure of poly(vinyl alcohol) (PVA) via a sulfonation. The sulfonation was carried out by using sulfophthalic acid (sPTA) as a sulfonating agent. The sulfonated PVA membranes, with a variety of degrees of substitutions, were obtained by varying the crosslinking time and the amount of sulfonating agents. The chemical structure and thermal stability of the sulfonated PVA were characterized by using FTIR and thermogravimetric analysis techniques, respectively. The ion‐exchange capacity (IEC) and water uptake of the sulfonated membranes was evaluated by titration and gravimetry techniques, respectively. It was found that the IEC of the membrane increased with the amount of sPTA. Water uptakes of the membranes could either decrease or remain unchanged with the crosslinking time, depending on the amount of the sulfonating agent used. Methanol permeability values of the membranes treated with 10% sPTA were relatively low, comparing with that of the Nafion 115 membrane. Proton conductivity values of the sulfonated PVA membranes ranged between 0.024 and 0.035 S/cm and they did not remarkably change with the crosslinking time. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1931–1936, 2006     

PVA/Nano-SiO_2薄膜的制备表、征及性能研究

采用熔融法制备了聚乙烯醇(PVA)/纳米二氧化硅(nano-SiO2)薄膜。利用FTIR、DMA﹑AFM﹑水煮、DMSO煮等方法对薄膜进行了表征,并探讨了nano-SiO2对PVA薄膜的改性机理。结果表明:nano-SiO2的加入使PVA/nano-SiO2薄膜的储能模量和损耗模量均明显提高,其玻璃化转变温度随着nano-SiO2含量的增加先降低后升高;PVA/nano-SiO2薄膜中存在着由羟基脱水而产生的化学交联结构,这种结构影响着薄膜的各种性能。     

Synthesis,characterization and efficacy of chemically crosslinked PVA hydrogels for dermal wound healing in experimental animals

In this study, we have investigated the efficacy of crosslinked polyvinyl alcohol (PVA) hydrogel as a wound dressing material, using rat as the animal model. The hydrogel was synthesized by chemical crosslinking of PVA with potassium persulphate and the crosslinking reaction parameters were optimized. The developed hydrogel was found to possess excellent mechanical properties, high water absorption capacity, gel content, and optimum water vapor transmission rate, indicating its ability to act as an effective wound dressing material. The inherent nontoxic characteristics of PVA remained unaltered after crosslinking. The in vitro diffusion studies of bovine serum albumin (BSA) as model protein, indicated a relatively slow release of protein resulting from its microencapsulation in the polymeric matrix. For in vivo studies, full‐thickness excision wounds (2 × 2 cm²) were made on the dorsal surface of rats. The hydrogel was applied on the wound and changed at regular intervals. For comparison of wound healing ability, a radiation crosslinked PVA‐based hydrogel, “HiZel” was used as a reference control. The wounds treated with PVA hydrogel healed faster as indicated by an increased rate of wound contraction (16.5 days versus 22.0 in control group). Treatment with “Hizel” led to increase in hydroxyproline in the wound tissue, whereas treatment with PVA hydrogel led to increase in both hydroxyproline as well as hexosamine. This probably provides added strength to the tissue, thereby indicating that PVA hydrogel had higher efficacy than “Hizel”. The results suggest that chemically crosslinked PVA hydrogel could be used as an effective wound dressing material. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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     

改性聚乙烯醇膜的研究进展

聚乙烯醇（PVA）因其良好的化学稳定性、耐酸碱、耐有机溶剂性以及优异的成膜性和生物安全性,成为应用最广泛的亲水性膜材料之一。但亲水性PVA膜力学性能弱和耐水性能差等缺点严重限制其实际应用。近些年,人们通过共混、纳米复合、热处理、化学交联以及协同改性等方法对PVA膜进行了大量的改性研究工作并取得了众多成果。本文总结了不同PVA膜改性方法的特点及存在的问题,重点阐述了性能优异的填料在纳米复合改进PVA膜力学性能上的研究现状,简述了共混、热处理、化学交联对改性PVA膜的作用,强调了协同改性对提高PVA膜综合性能的重要意义,为设计和制备高性能的PVA膜提供一定的参考。指出改性后的PVA膜在水处理和食品包装领域具有良好的应用前景。     

Thermal and rheological properties of poly(vinyl alcohol) and water‐soluble chitosan hydrogels prepared by a combination of γ‐ray irradiation and freeze thawing

Poly(vinyl alcohol) (PVA)/water‐soluble chitosan (ws‐chitosan) hydrogels were prepared by a combination of γ‐irradiation and freeze thawing. The thermal and rheological properties of these hydrogels were compared with those of hydrogels prepared by pure irradiation and pure freeze thawing. Irradiation reduced the crystallinity of PVA, whereas freeze thawing increased it. Hydrogels made by freeze thawing followed by irradiation had higher degrees of crystallinity and higher melting temperatures than those made by irradiation followed by freeze thawing. ws‐Chitosan disrupted the ordered association of PVA molecules and decreased the thermal stability of both physical blends and hydrogels. All the hydrogels showed shear‐thinning behavior in the frequency range of 0.2–100 rad/s. Hydrogels made by freeze thawing dissolved into sol solutions at about 80°C, whereas those made by irradiation showed no temperature dependence up to 100°C. The chemical crosslinking density of the hydrogels made by irradiation followed by freeze thawing was much greater than that of hydrogels made by freeze thawing followed by irradiation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of gel spinning accompanied with cross‐linking using boric acid on the structure and properties of high‐molecular‐weight poly(vinyl alcohol) fiber

To enhance the thermal stability of poly(vinyl alcohol) (PVA) fiber, the fiber was prepared from the gel spinning of high molecular weight (HMW) PVA by using dimethyl sulfoxide/water (8/2, v/v) as a solvent, accompanied with the cross‐link by boric acid (B‐PVA). In addition, the structure and properties of the B‐PVA fiber were compared with those of the HMW PVA fiber obtained by using the same spinning system without cross‐linking (NB‐PVA). Through a series of experiments, it turned out that cross‐linking actualized by an optimum amount of boric acid (0.3 wt % based on PVA) and zone drawing caused significant changes in the properties of HMW PVA gel fiber. That is, cross‐linking increased thermal degradation temperatures at each degradation step and amounts of final residues, resulting in improving thermal properties of the PVA fiber. On the contrary, it was found that in the case of the B‐PVA fiber, some broadening of the original PVA unit cell occurred, which was identified by the peak shift to lower angle in X‐ray diffractogram. The tensile strength and Young's modulus of B‐PVA fiber with draw ratio of 15 are 23.1 and 308.3 g/d, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Application of chitosan solutions gelled by melB tyrosinase to water‐resistant adhesives

An investigation was undertaken on the application of dilute chitosan solutions gelled by melB tyrosinase‐catalyzed reaction with 3,4‐dihydroxyphenethylamine (dopamine). The tyrosinase‐catalyzed reaction with dopamine conferred water‐resistant adhesive properties to the semi‐dilute chitosan solutions. The viscosity of the chitosan solutions highly increased by the tyrosinase‐catalyzed quinone conversion and the subsequent nonenzymatic reactions of o‐quinones with amino groups of the chitosan chains. The viscosity of chitosan solutions highly increased in shorter reaction times by addition of melB tyrosinase. Therefore, in this study, the gelation of a chitosan solution was carried out without poly(ethylene glycol) (PEG), which was added for the gelation of chitosan solutions using mushroom tyrosinase. The highly viscous, gel‐like modified chitosan materials were allowed to spread onto the surfaces of the glass slides, which were tightly lapped together and were held under water. Tensile shear adhesive strength of over 400 kPa was observed for the modified chitosan samples. An increase in either amino group concentration of the chitosan solutions or molecular mass of the chitosan samples used effectively led to an increase in adhesive strength of the glass slides. Adhesive strength obtained by chitosan materials gelled enzymatically was higher than that obtained by a chitosan gel prepared with glutaraldehyde as a chemical crosslinking agent. In addition, the use of melB tyrosinase led to a sharp increase in adhesive strength in shorter reaction times without other additives such as PEG. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Enhancing mechanical properties of poly(vinyl alcohol) blown films by drawing and surface crosslinking

Thermal blowing of poly(vinyl alcohol) (PVA) film was successfully realized based on molecular complexation. Ways to enhance the performance of the PVA blown films (drawing and surface crosslinking) were studied. The experimental results showed that water exists in PVA films in different states through hydrogen bonds with PVA and other modifiers and influences the drawability of PVA films, as well as the structure and properties of the stretched films. When the initial water content of the film was higher than 35.0%, the draw ratio of the PVA film was quite large because of the effects of the bound water with PVA, as well as the plasticization of free water. With the increase of the initial water content in PVA, the free water content and draw ratio of the films increased but the strength of the films decreased because of the higher residual water in the films. Surface crosslinking can improve the stretchability of PVA films because more water remains in the films and disrupts the hydrogen bonding of PVA. In addition, crosslinking enhances the mechanical properties of stretched PVA films. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 774–779, 2005     

Preparation of PFSA‐PVA/PSf hollow fiber membrane for IPA/H2O pervaporation process

Using Na⁺ form of perfluorosulfonic acid (PFSA) and poly(vinyl alcohol) (PVA) as coating materials, polysulfone (PSf) hollow fiber ultrafiltration membrane as a substrate membrane, PFSA‐PVA/PSf hollow fiber composite membrane was fabricated by dip‐coating method. The membranes were post‐treated by two methods of heat treatment and by both heat treatment and chemical crosslinking. Maleic anhydride (MAC) aqueous solution was used as chemical crosslinking agent using 0.5 wt % H₂SO₄ as a catalyst. PFSA‐PVA/PSf hollow fiber composite membranes were used for the pervaporation (PV) separation of isopropanol (IPA)/H₂O mixture. Based on the experimental results, PFSA‐PVA/PSf hollow fiber composite membrane is suitable for the PV dehydration of IPA/H₂O solution. With the increment of heat treatment temperature, the separation factor increased and the total permeation flux decreased. The addition of PVA in PFSA‐PVA coating solution was favorable for the improvement of the separation factor of the composite membranes post‐treated by heat treatment. Compared with the membranes by heat treatment, the separation factors of the composite membranes post‐treated by both heat treatment and chemical crosslinking were evidently improved and reached to be about 520 for 95/5 IPA/water. The membranes post‐treated by heat had some cracks which disappeared after chemical crosslinking for a proper time. Effects of feed temperature on PV performance had some differences for the membranes with different composition of coating layer. The composite membranes with the higher mass fraction of PVA in PFSA‐PVA coating solution were more sensitive to temperature. It was concluded that the proper preparation conditions for the composite membranes were as follows: firstly, heated at 160°C for 1 h, then chemical crosslinking at 40°C for 3 h in 4% MAC aqueous solution. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of mixed solvent on gelation of poly(vinyl alcohol) solutions

The relationship between the polymer–solvent interaction and gelation behavior of poly(vinyl alcohol) (PVA) solutions prepared from ethylene glycol/water (EG/water) mixed solvents was investigated using a viscometer, light scattering, FTIR, X‐ray, and pulsed NMR analyses. The viscometric result showed that the affinity to PVA for water is higher than that for EG. The light scattering result showed that the spinodal decomposition rate of the PVA solution decreases rapidly as the water content in the EG/water mixed solvent is increased. On the other hand, the FTIR and X‐ray results both indicated that the crystallinity of the PVA gel decreases with water content. These results imply that the water molecules must improve the affinity of the solvent to PVA to inhibit the aggregation or crystallization of PVA chains. The pulsed NMR measurement results showed that the spin–spin relaxation times related to the polymer‐rich and polymer‐poor phases of the PVA gel increase, and the fractional amount of the polymer‐poor phase increases while that of the polymer‐rich phase decreases with increasing water content. These facts indicated that the increase in the mobility of PVA chains must give rise to the difficulty in chain aggregation of PVA solutions with increasing water content. Two transition temperatures were found in the phase transition of the polymer‐rich phase. The lower transition temperature was attributed to the destruction of the denser chain entanglements in the polymer‐rich phase and the higher transition temperature was mainly concerned with the melting of the crystallites. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1113–1120, 2001     

明胶胶凝对明胶化学交联反应的研究

以猪皮胶原为原料,研究了明胶凝胶化的机制以及主要影响因素分析了胶凝过程中化学成分及其含量、反应温度对交联反应的影响,探究胶原明胶化过程微观结构的变化规律,并通过研究物理凝胶、化学凝胶、混合凝胶的方式,观察在凝胶状态化学网络的储能剪切模量与三螺旋构象中明胶残基数量之间的关系,分析了明胶凝胶过程中的光学、力学、交联密度影响等因素,对三种不同的凝胶方式进行总结,从反应动力学、凝胶影响因素等角度分析其三螺旋结构的变化异同。     

Preparation and characterization by radiation of hydrogels of PVA and PVP containing Aloe vera

In these studies, hydrogels for wound dressing were made from a mixture of Aloe vera, poly(vinyl alcohol) (PVA) and poly(N‐vinylpyrrolidone) (PVP) by freeze‐thaw, gamma‐ray irradiation, or a two‐step process of freeze‐thaw and gamma‐ray irradiation. Physical properties, such as gelation, water absorptivity, gel strength and degree of water evaporation were examined to evaluate the applicability of these hydrogels to wound dressing. The PVA:PVP ratio was 6:4, and the dry weight of Aloe vera was in the range of 0.4‐1.2 wt %. The solid concentration of PVA/PVP/Aloe vera solution was 15 wt %. Mixtures of PVA/PVP/Aloe vera were exposed to gamma irradiation doses of 25, 35 and 50 kGy to evaluate the effect of irradiation dose on the physical properties of the hydrogels. Gel content and gel strength increased as the concentration of Aloe vera in PVA/PVP/Aloe vera decreased and as irradiation dose increased and freeze‐thaw was repeated. Swelling degree was inversely proportional to gel content and gel strength. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1612–1618, 2004     

Synergistic strengthening of composite films by crosslinking graphene oxide reinforcement and poly(vinyl alcohol) with dicarboxylic acids

High‐strength plastic materials with excellent biodegradability, non‐toxicity and economically wide availability are in high demand. Herein, we demonstrate graphene oxide (GO) composite of poly(vinyl alcohol) (PVA) as a potential bioplastic material by chemical crosslinking. For a potential bioplastic material, PVA has to be addressed for its high water absorbing capacity along with improvement in tensile strength and thermal stability. These issues were addressed by enhancing the interfacial binding between PVA and GO, covalent bonds between the two being introduced by crosslinking with dicarboxylic acids, namely succinic acid (SuA) and adipic acid (AdA). Crosslinking of neat PVA with dicarboxylic acids also resulted in enhanced swelling resistance and thermal stability. The greatest improvement in tensile strength and swelling resistance was observed for a GO crosslinked with diacids due to the synergistic effect of reinforcement and crosslinking. Improvements of 225 and 234% in the tensile strength of PVA (31.19 MPa) were observed for 5% GO–PVA samples crosslinked with 6.25 mmol AdA and 7.5 mmol SuA, respectively. For the same samples, water uptake was 44 and 29%, respectively, compared to the non‐crosslinked PVA (359%). © 2017 Society of Chemical Industry