聚乙烯醇/壳聚糖共混膜渗透汽化性能研究

制备了聚乙烯醇(PVA)/壳聚糖(CS)共混膜,用渗透汽化膜技术实现了甲醇/碳酸二甲酯二元共沸物的有效分离,研究了共混组成、操作温度、原料组成对膜分离性能的影响,结果表明,随着共混膜中CS含量的增加,膜的渗透通量增大,分离系数先增大后减小,当共混膜中CS含量为66%时,该膜具有优异的渗透汽化性能,有较大渗透汽化分离指数PSI值=660.8g/(m2.h).操作温度升高,膜的渗透通量增大,分离系数略微减小;随着原料中甲醇含量的增大,膜的渗透通量增大,分离系数减小.该共混膜在分离甲醇/碳酸二甲酯二元共沸物时得到的渗透侧甲醇的浓度远大于对应饱和蒸汽的浓度,表明用膜法渗透汽化分离是优于精馏分离的.     

Metformin hydrochloride-loaded poly(vinyl alcohol) composites as drug delivery systems

A straightforward method is proposed for the preparation of drug-loaded biocompatible polymer composites based on the freeze drying technique. The solution of poly(vinyl alcohol) (PVA) and metformin hydrochloride (MH) is frozen using liquid nitrogen and the ice crystals are removed by sublimation through freeze drying, which results in the formation of MH-loaded PVA composite. By controlling the PVA concentration in the solution, both MH-loaded PVA fibers and porous products can be obtained. The synthesized MH-loaded PVA composites are characterized with scanning electron microscopy (SEM), powder X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The drug release behavior of the as-prepared products is studied to reveal their potential use in drug delivery system.     

Dielectric properties of montmorillonite clay filled poly(vinyl alcohol)/poly(ethylene oxide) blend nanocomposites

Organic–inorganic nanocomposites of poly(vinyl alcohol) (PVA)–poly(ethylene oxide) (PEO) blend filled with montmorillonite (MMT) nanoclay up to 10 wt.% concentration were synthesized by aqueous solution-cast technique. The complex dielectric function, electrical conductivity, electric modulus and impedance spectra of the nanocomposites were measured in the frequency range 20 Hz–1 MHz at ambient temperature. A direct correlation was observed between the real part of dielectric function and the mean relaxation time of the polymer chain segmental dynamics, with the exfoliated and intercalated MMT clay structures, and the extent of miscibility between PVA and PEO due to hydrogen bonded bridging through exfoliated MMT clay nanosheets. The large increase of dielectric relaxation time revealed that the dispersed exfoliated nanoscale MMT clay in the polymers blend matrix produces a large hindrance to the polymer chain dynamics. Results confirm that the real part of dielectric function of the nanocomposites can be tailored by varying amount of MMT clay filler for their use as nanodielectric materials in the microelectronic technology.     

Antibiotic drug release behavior of poly (vinyl alcohol)/sodium alginate hydrogels

Poly (vinyl alcohol)/sodium alginate hydrogels were prepared by freeze-thaw followed by calcium ion crosslinking. Chloramphenicol release behavior from the poly (vinyl alcohol)/sodium alginate hydrogels in mimic conditions of gastrointestinal tract was examined. The effects of composition, number of freeze-thaw cycles and calcium ion concentration on drug release process were investigated. The results showed that the cumulative release amount of chloramphenicol from the hydrogels (crosslinked through 4 freeze-thaw cycles and immersed in 2 % calcium chloride solution) decreased from 84.3 % to 72.3 % as sodium alginate content increased from 0 % to 75 %. For the hydrogels containing 50 % sodium alginate and immersed in 2 % calcium chloride solution after the freeze-thaw cycles, cumulative release amount of chloramphenicol decreased from 83.5 % to 76.6 % as the freeze-thaw cycles increased from 2 to 6. Cumulative release amount of chloramphenicol from the hydrogels containing 50 % sodium alginate and with 4 freeze-thaw cycles decreased from 79.8 % to 75.6 % when concentration of calcium chloride solution increased from 1 % to 4 %.     

Optical properties of poly(vinyl chloride)/poly(ethylene oxide) blend

The relatively high dielectric constant poly(vinyl chloride) (PVC) was blended with poly(ethylene oxide) (PEO) polymer electrolytes to improve their electrical conductivity from the optical spectra of the given polymeric system. The optical properties in the UV–visible region of PVC polymer containing 0%, 20%, 50% and 70% by weight PEO are reported. The optical results obtained were analyzed in terms of the absorption formula for non-crystalline materials. The absorption coefficient and the optical band energy gap (E_opt) have been obtained from direct allowed transitions in k-space at room temperature. The width of the tail of localized states in the band gap (ΔE) was evaluated using the Urbach-edges method. It was found that both (E_opt) and (ΔE) vary with the concentration of the PEO complex in the polymer matrix. In addition, a correlation between the energy gap and the ac-conductivity as a function of PEO complex concentration is also reported.     

甘蔗渣微晶纤维素增强聚乙烯醇复合膜的性能研究

以甘蔗渣微晶纤维素(BCMC)作为增强材料,聚乙烯醇(PVA)作为基体,制备了BCMC/PVA复合膜材料,并对复合膜的结构、热稳定性能、力学性能进行了测试。结果表明,甘蔗渣微晶纤维素增强复合膜材料的热稳定性能和力学性能。当BCMC的质量分数为5%时增强效果最佳,与纯PVA膜相比,起始分解温度和最大重量损失率温度分别增加了11.71℃和36.86℃,拉伸强度提高了17.52%,断裂伸长率提高了29.58%。     

Optical study of poly(vinyl alcohol)/hydroxypropyl methylcellulose blends

The proposal in this study was to evaluate the optical properties of different biopolymers films. The materials used were poly(vinyl alcohol) (PVA) and hydroxypropyl methylcellulose (HPMC). PVA/HPMC blends were prepared by casting technique. Variations in the group coordination in the infrared region were followed. The effects of HPMC concentrations on the optical properties of the PVA films were studied by near infrared, ultraviolet/visible, transmittance, and reflectance in the spectral region 200–2500 nm. Absorption, transmittance, and reflectance spectra were used for the determination of the optical constants. The study has been also extended to include the changes in the optical parameters including the band tail width and band gap energies and extinction coefficient for the investigated films. The results indicate that the optical band gap was derived from Tauc’s extrapolation and decreases with the HPMC contents. The obtained optical parameters were found to be strongly affected by HPMC contents.     

Preparation and characterization of chitosan/poly(vinyl alcohol)/poly(vinyl pyrrolidone) electrospun fibers

Ultrafine fibers of chitosan/poly(vinyl alcohol)/poly(vinyl pyrrolidone) (CS/PVA/PVP) were prepared via electrospinning. The structure and morphology of CS/PVA/PVP ultrafine fibers was characterized by the Fourier transform infrared (FT-IR) spectroscope and scanning electron microscope (SEM). Furthermore, the effects of the concentration of PVA, PVP and the electrospinning voltage on the morphology of ultrafine fibers were investigated the the SEM. When the concentration of PVA was at the range of 30wt%–40wt%, ultrafine fibers could be obtained. The diameter distributions of ultrafine fibers decreased when the electrospinning voltage increased from 20 to 30 kV. The rough surface fibers could be obtained after etching with CHCl₃.     

Investigation on the panchromaticity of silver-doped poly(vinyl alcohol)/acrylamide photopolymer

An investigation on the panchromaticity of a silver-doped poly(vinyl alcohol)/acrylamide photopolymer system is presented in this paper. Frequency-doubled Nd:YAG (532 nm) and Ar? (488 nm) lasers were used for the characterization of the films. Previous studies using an He-Ne laser (632.8 nm) showed that plane-wave transmission grating with a high diffraction efficiency of 75% could be stored in the optimized film. From the present study, it was noted that transmission gratings with 70% diffraction efficiency could be recorded using Ar? and Nd:YAG lasers, thereby elucidating the possibility of using the developed photopolymer system as a competent panchromatic recording medium.     

Enhancement of poly(3,4-ethylenedioxy thiophene)/poly(styrene sulfonate) properties by poly(vinyl alcohol) and doping agent as conductive nano-thin film for electronic application

In this work, the integration of the useful concepts of polymer blending and doping agent to simultaneously improve various properties of poly(3,4-ethylene dioxy thiophene) poly(styrene sulfonate) (PEDOT:PSS) nano-thin films was shown. According to the polymer-blending concept, insulating poly(vinyl alcohol) (PVA) has a good deal of potential to be utilized as a filler to improve the critical properties of the PEDOT:PSS matrix, especially conductivity, wettability, and thermal and mechanical properties. At the appropriate amount of PVA, 0.08 wt%, it acts as a binder to improve the connection network between PEDOT:PSS chains, leading to a maximum conductivity of 1.18 S/cm, and also providing a good contact angle of 8.8°. The transmission of the films decreased with increasing PVA content; however, all specimens still showed excellent transmittance values of more than 80 %. The thermal stability and the resistance to abrasion of the nano-thin conductive films were improved by strong covalent bonds between PVA and PSS, which were verified by TGA and a scratching test, respectively. In addition, the relationship of PEDOT:PSS properties versus various amounts of insulating PVA for practical usage for specific electronic fields were shown. Use of the doping agent quinoxaline was aimed to particularly enhance the conductivity of PEDOT:PSS. The highest conductivity (2.75 S/cm) was achieved when 0.5 wt% quinoxaline was added into 0.08 wt% PVA/PEDOT:PSS while the other properties were not significantly altered.     

聚乙烯醇/纳米氧化锌复合材料的非等温结晶动力学

为了研究聚乙烯醇/纳米氧化锌复合材料的结晶性能,通过熔融共混挤出的方法制备了复合材料,并在差示扫描量热分析(DSC)的基础上通过Jeziomy法和Liu法研究了聚乙烯醇薄膜和聚乙烯醇/纳米氧化锌复合材料的非等温结晶动力学行为.结果表明,聚乙烯醇薄膜和聚乙烯醇/纳米氧化锌复合材料的非等温结晶行为强烈地依赖于冷却速率,随着冷却速率的提高,结晶速率常数增大,结晶的不完善程度也增大.在相同的冷却速率下,复合体系的Avrami指数n值和结晶速率常数Z。较大,晶体的完善程度较高.要达到相同的结晶度,复合材料所需的冷却速率要小于聚乙烯醇薄膜,即纳米氧化锌的加入使材料中聚乙烯醇的结晶速率增加,对聚乙烯醇具有异相成核作用.     

Comparison of porous poly (vinyl alcohol)/hydroxyapatite composite cryogels and cryogels immobilized on poly (vinyl alcohol) and polyurethane foams for removal of cadmium

Three novel adsorbents of hydroxyapatite/poly (vinyl alcohol) (HAp/PVA) cryogel, HAp/PVA cryogel immobilized on PVA foam and HAp/PVA cryogel immobilized on polyurethane (PU) foam have been investigated to compare the morphology and sorption performances for removal of cadmium. The adsorption kinetics was interpreted by double-exponential model, pseudo-first-order model and pseudo-second-order models. The equilibrium time was found to be 36, 24, and 12 h for cryogel, cryogel immobilized on PVA foam and PU foam, respectively. The adsorption was found to follow Langmuir isotherm model and the maximum sorption capacity was estimated to be 53.3, 53.1 and 47.7 mg g(-1) for cryogel, cryogel immobilized on PVA foam and PU foam. The effects of HAp/PVA ratio and drying method on cadmium sorption were also studied. The difference of adsorption kinetics model and equilibrium time among the three adsorbents was suggested to be ascribed to different pore size. Oven-dried HAp/PVA cryogel immobilized on PU foam was preferable due to short equilibrium time and good sorption ability.     

Facile one-pot synthesis of iron oxide nanoparticles cross-linked magnetic poly(vinyl alcohol) gel beads for drug delivery

In this paper, a facile one-pot strategy for scalable synthesis of robust magnetic poly(vinyl alcohol) (mPVA) gel beads is developed. Through dropwise addition of mixed aqueous solution of iron salts and PVA solution into alkaline (e.g., ammonia, NaOH, and KOH) solution, mPVA gel beads with uniform size and excellent superparamagnetic property can be fabricated based on the simultaneous formation of magnetic iron oxide nanoparticles (MIONs) and cross-link of PVA chains. Moreover, this approach can be extended to prepare dual- or multiresponsive gel beads through simply adding functional fillers into PVA solution (e.g., mPVA-PNIPAM gel beads that possess both magnetic and temperature responsibilities can be readily prepared by adding temperature responsive poly(N-isopropylacrylamide) (PNIPAM) into PVA solution). It is found that that the obtained mPVA gel beads exhibit high drug loading level (e.g., above 70%) after the treatment of freezing-thawing. Drug release experiments reveal that the drug release rate and amount of the mPVA gel beads can be tuned by operating the external magnetic field and adjusting the concentration of iron oxide nanoparticles and temperature (for mPVA-PNIPAM gel beads). The present work is of interest for opening up enormous opportunities to make full use of magnetic gel beads in drug delivery and other applications, because of their facile availability, cost-effective productivity, and tunable drug release performance.     

Further investigations on a poly(vinyl alcohol)- polyelectrolyte chemically selective optical film

The ionomer poly(vinylbenzyltrimethylammonium chloride) has been blended with cross-linked poly(vinyl alcohol) to form optically clear composites that can be covalently linked as thin films to oxide surfaces. Films are characterized using spectroscopic ellipsometry with refractive index (n) and extinction coefficient (k) data presented for wavelengths 300 to 1100 nm. A refractive index of 1.54 and average thickness of 709 nm are typical of an air dry film prepared by spin-coating. Dynamic in situ ellipsometry results for films exposed to 0.1 M KNO(3) and 1.0 mM Fe(CN)(6)(-3) are presented. Upon initial exposure to 0.1 M KNO(3), an air dry film expands by about 160% and stabilizes in size and refractive index at about 18 hours. Ion exchange of film cationic groups with ferricyanide is marked by slight film contraction, presumably due to electrostatic cross-linking by the multivalent anion. These films are useful in the spectroelectrochemical sensor with our newly developed fluorescence detection mode, as demonstrated by results of the reversible incorporation of the fluorescent anion fluorescein.     

Transparent and high gas barrier films based on poly(vinyl alcohol)/graphene oxide composites

Composites of poly(vinyl alcohol) (PVA) and graphene oxide (GO) were synthesized by a modified Hummers method and a solution-mixing method. GO was fully exfoliated in the PVA/GO composites. GO did not affect the crystallization of PVA during solvent evaporation. GO is itself an excellent gas barrier without any chemical reduction. The oxygen permeability of the PVA/GO (0.3 wt.%) composite coated film was 17 times lower than that of the pure poly(ethylene terephthalate) (PET) film, with 92% light transmittance at 550 nm. Composites of PVA and reduced graphene oxide (RGO) were synthesized by performing chemical reduction using hydrazine monohydrate. The oxygen permeability of the PVA/RGO (0.3 wt.%) composite coated film was 86 times lower than that of the pure PET film, with 73% light transmittance at 550 nm. The reduction of oxygen permeability was mainly attributed to the reduced oxygen solubility in the PVA/GO composite film, while it was attributed to both the reduced oxygen diffusivity and solubility in the PVA/RGO composite film.