Solid‐state 13C and 129Xe NMR study of poly(vinyl alcohol) and poly(vinyl alcohol)/lactosilated chitosan gels

Dry and hydrated poly(vinyl alcohol) (PVA) gels with 55% (a‐PVA) and 61% (s‐PVA) syndiotacticity and related PVA/lactyl chitosan (LC) blends have been investigated with ¹²⁹Xe and cross‐polarization/magic‐angle‐spinning ¹³C NMR techniques. Although the dry gels exhibit two broad ¹²⁹Xe resonances in the slow‐to‐intermediate exchange limit, both hydrated gels show three resonances. The corresponding dry blends exhibit two signals, the chemical shifts and line widths of which change with respect to those of pure PVA, whereas one (a‐PVA/LC) or two (s‐PVA/LC) signals appear in the spectra of the hydrated blends. A comparative analysis of the data demonstrates that LC rearranges the domains of the polymeric matrix in both the dry and hydrated blends according to the syndiotacticity of the PVA chains. Information on the molecular motions of the amorphous and swollen polymeric domains in the kilohertz range has been obtained from an analysis of the spin‐lattice relaxation times. These data indicate that the dynamics and arrangement of the PVA chains in the gels are strongly affected by their tacticity and the addition of the copolymer LC. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3123–3131, 2003     

Dynamic mechanical and dielectrical properties of poly(vinyl alcohol) and poly(vinyl alcohol)‐based nanocomposites

In this article we report on the investigation of the dynamics of poly(vinyl alcohol) (PVA) and PVA‐based composite films by means of dielectric spectroscopy and dynamic mechanical thermal analysis. Once the characterization of pure PVA was done, we studied the effect of a nanostructured magnetic filler (nanosized CoFe₂O₄ particles homogeneously dispersed within a sulfonated polystyrene matrix) on the dynamics of PVA. Our results suggest that the α‐relaxation process, corresponding to the glass transition of PVA, is affected by the filler. The glass‐transition temperature of PVA increases with filler content up to compositions of around 10 wt %, probably as a result of polymer–filler interactions that reduce the polymer chain mobility. For filler contents higher than 10 wt %, the glass‐transition temperature of PVA decreases as a result of the absorption of water that causes a plasticizing effect. The β‐ and γ‐relaxation processes of PVA are not affected by the filler as stated from both dynamic mechanical thermal analysis and dielectric spectroscopy. Nevertheless, both relaxation processes are greatly affected by the moisture content. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1968–1975, 2001     

Electrospinning and characterization of medium-molecular-weight poly(vinyl alcohol)/high-molecular-weight poly(vinyl alcohol)/montmorillonite nanofibers

Submicron fibers of medium-molecular-weight poly(vinyl alcohol) (MMW-PVA), high-molecular-weight poly(vinyl alcohol) (HMW-PVA), and montmorillonite clay (MMT) in aqueous solutions were prepared by electrospinning technique. The effect of HMW-PVA and MMT on the morphology and mechanical properties of the MMW-PVA/HMW-PVA/MMT nanofibers were investigated for the first time. Scanning electron microscopy, viscometer, tensile strength testing machine, thermal gravimetric analyzer (TGA), and transmission electron microscopy (TEM) were utilized to characterize the PVA/MMT nanofibers morphology and properties. The MMW-PVA/HMW-PVA ratios and MMT concentration played important roles in nanofiber's properties. TEM data demonstrated that exfoliated MMT layers were well distributed within nanofibers. It was also found that the mechanical property and thermal stability were increased with HMW-PVA and MMT contents.     

Mechanical and thermal properties of cryogels and foamed cryogels produced from aqueous solutions of poly(vinyl alcohol)

The effect of sodium chloride and technical-grade carbon (carbon black) on the mechanical and thermal properties of cryogels and foamed cryogels produced from homogeneous and heterogeneous (foamed) solutions of poly(vinyl alcohol) was studied.     

Characterization of poly(vinyl alcohol) during the emulsion polymerization of vinyl acetate using poly(vinyl alcohol) as emulsifier

During the emulsion polymerization of vinyl acetate (VAc) using poly(vinyl alcohol) (PVA) as stabilizer and potassium persulfate as initiator, the VAc reacts with PVA forming PVA-graft-PVAc. When the grafted polymer reaches a critical size it becomes water-insoluble and precipitates from the aqueous phase contributing to the formation of polymer particles. Since particle formation and therefore the properties of the final latex will depend on the degree of grafting, it is important to quantify and to characterize the grafted PVA. In this work, the quantitative separation and characterization of the grafted water-insoluble PVA was carried out by a two-step selective solubilization of the PVAc latex, first with acetonitrile to separate PVAc homopolymer, followed by water to separate the water-soluble PVA from the remaining acetonitrile-insoluble material. After the separation, the water-soluble and water-insoluble PVA were characterized by Fourier Transform Infrared (FTIR) spectroscopy and ¹H and ¹³C nuclear magnetic resonance (NMR) analyses, from which the details of the PVA-graft-PVAc structure were obtained. © 1996 John Wiley & Sons, Inc.     

Morphology assessment of chemically modified cryostructured poly(vinyl alcohol) hydrogel

The morphology of hydrogels based on poly(vinyl alcohol) (PVA) in their frozen hydrated state, modified with biologically active di- and multifunctional molecules was studied by scanning electron microscopy (SEM) with cryo-attachment. The porosity of samples was found to be more regular and ordered in the case of samples containing difunctional, and especially multifunctional carboxylic acids as compared to the neat PVA hydrogel. The morphology is dependent not only from the hydrogel composition but also the number of freezing-thawing cycles. Resulted highly porous and oriented structure has significant influence on materials properties, such as compressive stress and crosslinking density.     

Preparation and fluorescent properties of poly(vinyl alcohol) bearing coumarin

A novel water‐soluble fluorescent material was prepared via ring‐opening reaction between 4‐methyl‐7‐(2,3‐expoxypropoxy) coumarin (MEC) and poly(vinyl alcohol) (PVA). The fluorescent behaviors of this material (PVA–MEC) in solution, solid and film were studied in detail. The results showed that the fluorescence of PVA–MEC arose from isolated dye molecules and had a good film forming ability. In addition, the effects of acid/base environments on PVA–MEC were studied and the results showed that it was less affected by environment than 7‐HMC. Moreover, relative fluorescence intensity of PVA–MEC had an excellent linear response in the temperature range of 0–60°C. These observations suggest that PVA–MEC is an excellent fluorescent macromolecular material with a convenient method of preparation and had a good water‐soluble ability. Copyright © 2007 John Wiley & Sons, Ltd.     

Photocrosslinked methacrylated poly(vinyl alcohol)/hydroxyapatite nanocomposite hydrogels with enhanced mechanical strength and cell adhesion

Poly(vinyl alcohol) (PVA) hydrogels with high water content, good load‐bearing property, low frictional behavior as well as excellent biocompatibility have been considered as promising cartilage replacement materials. However, the lack of sufficient mechanical properties and cell adhesion are two critical barriers for their application as cartilage substitutes. To address these problems, herein, methacrylated PVA with low degree of substitution of methacryloyl group has been synthesized first. Then, methacrylated PVA‐glycidyl methacrylate/hydroxyapatite (PVA‐GMA/Hap) nanocomposite hydrogels have been developed by the photopolymerization approach subsequently. Markedly, both pure PVA‐GMA hydrogel and PVA‐GMA/Hap nanocomposite hydrogels exhibit excellent performance in compressive tests, and they are undamaged during compressive stress–strain tests. Moreover, compared to pure PVA‐GMA hydrogels, 8.5‐fold, 7.4‐fold, and 14.2‐fold increase in fracture stress, Young's modulus and toughness, respectively, can be obtained for PVA‐GMA/Hap nanocomposite hydrogels with 10 wt % Hap nanoparticles. These enhancements can be ascribed to the intrinsic property of PVA‐GMA and strong hydrogen bonding interactions between PVA‐GMA chain and Hap nanoparticles. More interestingly, significant improvement in the cell adhesion can also be successfully achieved by incorporation of Hap nanoparticles. These biocompatible nanocomposite hydrogels have great potential to be used as cartilage substitutes. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1882–1889     

Polyethylene-based nanocomposite: Structure and properties of poly(vinyl alcohol)/organofunctionalized Mg-doped fluorapatite hybrid

We report here the production and characterization of polymer nanocomposites (NC)s containing nanoceramics of organofunctionalized Mg-doped fluorapatite (MDFA) in a poly(vinyl alcohol) matrix. First, the MDFA materials were functionalized with N-trimellitylimido-L-leucine modifier through ultrasonic irradiation. The numerous experimental techniques like Fourier transform infrared spectroscopy, X-ray diffraction, atomic force microscopy, field emission scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis were applied to characterize the prepared materials. Thermal analysis of the obtained NCs showed an increase in thermal stability of the NCs when compared to the neat macromolecule.     

Equilibrium,kinetic, and thermodynamic studies of lead ion adsorption from mine wastewater onto MoS2-clinoptilolite composite

This work explored the potential of clinoptilolite, molybdenum sulphide (MoS₂), and MoS₂-clinoptilolite composite in lead (Pb) removal from aqueous medium and industrial mining wastewater. MoS₂-clinoptilolite composite was successfully prepared by a hydrothermal method. The surface properties, structure, and composition of the synthesized composite and the parent compounds were analyzed by scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. The removal efficiency of lead from aqueous solution was studied in batch-mode experiments. The MoS₂-clinoptilolite was used for the removal of Pb ions (50 mg/L) from an aqueous solution: ~100% of the Pb was removed with a MoS₂-clinoptilolite dose of 0.075 g, pH 6 at 328K within 90 min. The adsorption capacities of Pb onto MoS₂-clinoptilolite were found to be higher than those onto clinoptilolite. Metal ion adsorption behavior was well explained by the Freundlich model, that is, multilayer adsorption of Pb molecules occurred on the heterogeneous surface of adsorbents in case of clinoptilolite, while in the case of MoS₂-clinoptilolite, the Langmuir model was suitable, that is, the adsorption occurred on a monolayer surface. The rate of Pb adsorption was explained by pseudo-second-order model suggesting that the adsorption process is presumably chemisorption. Thermodynamic parameters such as ΔH°, ΔS°, and ΔG° were calculated, which indicated that the adsorption was spontaneous and exothermic in nature. The selectivity of each adsorbent for Pb was also tested by adding the adsorbents to real gold mine water which contains competitive metal ions.     

纳米羟基磷灰石/聚乙烯醇/明胶复合材料的结构和力学性能

采用机械共混法、原位化学合成法、原位水热法制备了一系列纳米羟基磷灰石/聚乙烯醇/明胶(n-HA/PVA/GEL)复合材料;利用X射线衍射仪、透射电镜及傅立叶变换红外光谱仪等分析了复合材料的结构;利用材料试验机测定了复合材料的力学性能.结果表明,利用原位水热法可使n-HA有效地在PVA高分子中均匀分散,并提高n-HA颗粒...     

A study of the microstructural and diffusion properties of poly(vinyl alcohol) cryogels containing surfactant supramolecular aggregates

Surfactant-containing poly(vinyl alcohol) (PVA) cryogels have been prepared by drying and reswelling hydrogel patches, previously obtained by the freeze/thaw procedure, in decyltrimethylammonium bromide (C10TAB) aqueous solutions. The microstructural and diffusive properties of the resulting material have been characterized by a combined experimental strategy. Gravimetric measurements show that the cryogel maximum swelling is not affected by the surfactant. The surfactant concentration within the cryogel, measured by ion chromatography, is the same as that in the rehydrating surfactant solution. Electron paramagnetic resonance (EPR) spin-probe and small-angle neutron scattering (SANS) measurements show that surfactant self-aggregation in the gel is similar to that in water, occurring at the same critical concentration and resulting in the formation of micellar aggregates whose structure is not affected by the cryogel polymeric scaffold. However, both the micelle intradiffusion coefficients, measured by PGSE-NMR, and the spin-probe correlation times, measured by EPR, indicate that dynamic processes in the hydrogel are much slower than in bulk water. A quantitative analysis of these results suggests that the cryogel polymer-poor domains, in which surfactant molecules are solubilized, have an average dimension of approximately 0.1 microm. Interestingly the experimental data also show that the polymer-poor phase contains more polymer than expected, suggesting that the spinodal decomposition, which occurs during the freezing step of cryogel preparation, is not complete or prevented by ice formation.     

Preparation and properties of poly(vinyl alcohol)/silica nanocomposites derived from copolymerization of vinyl silica nanoparticles and vinyl acetate

Nanocomposites of poly(vinyl alcohol)/silica nanoparticles (PVA-SNs) were prepared by in-situ radical copolymerization of vinyl silica nanoparticles functionalized by vinyltriethoxysilane (VTEOS) and vinyl acetate with benzoyl peroxide (BPO, i.e., initiator), subsequently saponified via direct hydrolysis with NaOH solution. The resulting vinyl silica nanoparticles, PVA-SNs were characterized by means of fourier transformation spectroscopy (FTIR), transmission electron microscopy (TEM) and the elemental analysis method. Effects of silica nanoparticles on viscosity and alcoholysis of PVA-SNs were studied by a ubbelohode capillary viscometer and the back titration method. The morphological structure of PVA-SN films was investigated by scanning electron microscopy (SEM). Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and tensile test were used to determine the thermal and mechanical properties of PVA-SN films. The results indicated that the content of vinyl groups on the surface of the vinyl silica nanoparticles was up to 3.02 mmol/g and vinyl silica nanoparticles had been successfully copolymerized with vinyl acetate. Furthermore, compared to pure PVA, silica nanoparticles bonded with polymer matrix in a low concentration affected the viscosity and alcoholysis of the PVA-SNs materials. At the same time, it resulted in the improvement of the thermal and mechanical properties of the PVA-SN materials due to a strong interaction between silica nanoparticles and the polymer matrix via a covalent bond. It could be found that the optical clarity of the membrane was changed through UV-Vis absorption spectrum due to the introduction of silica nanoparticles.     

Preparation of crosslinked polystyrene-supported ethylenediamine via a S-containing spacer and adsorption properties towards metal ions

Two novel chelating resins were prepared by anchoring ethylenediamine to crosslinked polystyrene via a spacer containing sulfide. Their structures were characterized by Fourier transform-infrared spectra (FTIR) and scanning electron microscopy (SEM). Porous structure parameters of the resins were measured by ASAP 2020 using BET and BJH methods. Their adsorption capacities for several heavy metal ions especially Hg²⁺ were investigated. The results showed that for the two resins, the more N contents did not mean the better adsorption capacity and the saturated adsorption capacity of poly(2-ethylenediamidomercaptomethylstyrene) (PSM-EDA) for Hg²⁺ could reach to 3.0 mmol/g at room temperature. Isothermal adsorptions of the resins for Hg²⁺ could be described by Langmuir formula. The adsorption mechanism of the resins for Hg²⁺, Cu²⁺ and Ag⁺ was confirmed by X-ray photoelectron spectroscopy (XPS) and FTIR.     

Study of cryostructuring of polymer systems: 28. Physicochemical properties and morphology of poly(vinyl alcohol) cryogels formed by multiple freezing-thawing

Macroporous viscoelastic poly(vinyl alcohol) (PVA) cryogels are prepared from aqueous concentrated (80–120 g/l) PVA solutions subjected to 1–5 cycles of cryogenic treatment (freezing at ?20°C for 19 h and subsequent thawing at a rate of 0.3°C/min). Shear moduli and fusion temperatures of corresponding samples are determined and the structure of thin sections is studied by optical microscopy with subsequent processing and analysis of images obtained. The previously described effect of a substantial increase in the rigidity and thermal stability of PVA cryogels resulted from the repeated freezing-thawing cycles is confirmed. The largest (jumpwise) changes in the physicochemical characteristics of such gels and their macroporous morphology take place after the second cycle of cryogenic treatment. Moreover, depending on the PVA concentration in the initial solution, the mean cross section of micropores increases by a factor of 2–3 and the total porosity of cryogel rises by a factor of 1.5–2; i.e., the imperfection of material increases. Nevertheless, this negative (from view-point of the integral properties of cryogel) effect is completely overpowered by processes of additional structuring, which result in the strengthening of polymer phase proceeding during the repeated freezing-thawing cycles.     

Dispersity and stability of foams obtained from poly(vinyl alcohol) solution and the properties of resulting foamed cryogels

Foams have been generated from aqueous poly(vinyl alcohol) solution by two different methods: dispersion (mechanical) method, i.e., by bubbling a gas through a porous medium into the aqueous poly(vinyl alcohol) solution, and the condensation (chemical) method, i.e., by performing a gas-generating reaction directly in the polymer solution. The effect of the formation method on foam stability and dispersity has been studied. The foam produced by the condensation method of foaming the aqueous poly(vinyl alcohol) solution with nitrogen is more stable and finely dispersed and has a higher expansion ratio than that obtained by bubbling the gas through the polymer solution. Foamed cryogels have been formed by freezing-thawing the foam resulting from the chemical reaction in the polymer solution. The values of the elasticity modulus, melting temperature, and thermal conductivity of the cryogels have been determined.     

Preparation and Properties of Poly（vinyl alcohol）/Chitosan Blend Bio-nanocomposites Reinforced by Cellulose Nanocrystals

The aim of this paper is to report the effect of the addition of cellulose nanocrystals（CNCs） on the mechanical, thermal and barrier properties of poly（vinyl alcohol）/chitosan（PVA/Cs） bio-nanocomposites films prepared through the solvent casting process. The characterizations of PVA/Cs/CNCs films were carried out in terms of X-ray diffraction（XRD）, transmission electron microscopy（TEM）, scanning electron microscopy（SEM）, thermogravimetric analysis（TGA and DTG）, oxygen transmission rate（OTR）, and tensile tests. TEM and SEM results showed that at low loading levels, CNCs were dispersed homogenously in the PVA/Cs matrix. The tensile strength and modulus in films increased from 55.1 MPa to 98.4 MPa and from 395 MPa to 690 MPa respectively, when CNCs content went from 0 wt% to 1.0 wt%. The thermal stability and oxygen barrier properties of PVA/Cs matrix were best enhanced at 1.0 wt% of CNCs loading. The enhanced properties attained by incorporating CNCs can be beneficial in various applications.     

Poly(vinyl acetate)/poly(vinyl alcohol)/montmorillonite nanocomposite microspheres prepared by suspension polymerization and saponification

Poly(vinyl acetate) (PVAc)–poly(vinyl alcohol)–montmorillonite (MMT) nanocomposite microspheres were prepared through suspension polymerization followed by the heterogeneous saponification. The effects of MMT on the polymerization rate and the saponification rate of PVAc were studied. It was found that the rate of polymerization decreased when MMT content was increased. However, the saponification rate of PVAc significantly increased in the presence of nanoclay particles. The XRD measurement illustrated that the clay particles are intercalated in the polymer matrix.