硫化锌掺锰/聚乙烯醇复合纳米纤维的制备与表征

利用静电纺丝法与气固反应相结合, 成功地制备了硫化锌掺锰/聚乙烯醇复合纳米纤维, 并对所制备的复合物进行了表征, 探讨了复合物的结构及其性能.     

A nanofibrous composite membrane of PLGA-chitosan/PVA prepared by electrospinning

Tissue engineering scaffolds produced by electrospinning feature a structural similarity to the natural extracellular matrix. In this study, poly(lactide-co-glycolide) (PLGA) and chitosan/poly(vinyl alcohol) (PVA) were simultaneously electrospun from two different syringes and mixed on the rotating drum to prepare the nanofibrous composite membrane. The composite membrane was crosslinked by glutaraldehyde vapor to maintain its mechanical properties and fiber morphology in wet stage. Morphology, shrinkage, absorption in phosphate buffered solution (PBS) and mechanical properties of the electrospun membranes were characterized. Fibroblast viability on electrospun membranes was discussed by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay and cell morphology after 7 days of culture. Results indicated that the PBS absorption of the composite membranes, no matter crosslinked or not, was higher than the electrospun PLGA membrane due to the introduction of hydrophilic components, chitosan and PVA. After crosslinking, the composite membrane had a little shrinkage after incubating in PBS. The crosslinked composite membrane also showed moderate tensile properties. Cell culture suggested that electrospun PLGA-chitosan/PVA membrane tended to promote fibroblast attachment and proliferation. It was assumed that the nanofibrous composite membrane of electrospun PLGA-chitosan/PVA could be potentially used for skin reconstruction.     

Fragrance encapsulation in polymeric matrices by emulsion electrospinning

We present the successful application of emulsion electrospinning for the encapsulation of a model for highly volatile fragrances, namely (R)-(+)-limonene in a poly(vinyl alcohol) (PVA) fibrous matrix. The influence of the emulsion formulation and of its colloidal properties on the fiber morphology, as well as on the limonene encapsulation efficiency, is described. The release profile of the fragrance from the electrospun nanofibers over a fifteen days range shows that this type of nanofibrous matrices with a high fragrance loading capacity is of great potential for applications in various fields, such as cosmetics or food packaging.     

Electrospinning and characterization of poly(vinyl alcohol)/chitosan oligosaccharide/clay nanocomposite nanofibers in aqueous solutions

Submicron fibers of the composite of poly(vinyl alcohol) (PVA), chitosan oligosaccharide [COS, (1→4)2-amino-2-deoxy-β-d-glucose], and montmorillonite clay (MMT) were prepared using electrospinning method with aqueous solutions. Scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), thermal gravimetric analyzer, and tensile strength testing machine (Zwick) were utilized to characterize the PVA/COS/MMT nanofiber mats morphology and properties. The PVA/COS ratio and MMT concentration play important roles in nanofiber mat properties. XRD and TEM data demonstrated that exfoliated MMT layers were well-distributed within nanofiber. It was also found that the mechanical property and thermal stability were increased with COS and MMT contents.     

Anti-trade-off in dehydration of ethanol by novel PVA/APTEOS hybrid membranes

Novel organic–inorganic hybrid membranes were prepared through sol–gel reaction of poly(vinyl alcohol) (PVA) with γ-aminopropyl-triethoxysilane (APTEOS) for pervaporation (PV) separation of ethanol/water mixtures. The membranes were characterized by FTIR, EDX, WXRD and PALS. The amorphous region of the hybrid membranes increased with increasing APTEOS content, and both the free volume and the hydrophilicity of the hybrid membranes increased when APTEOS content was less than 5 wt%. The swelling degree of the hybrid membranes has been restrained in an aqueous solution owing to the formation of hydrogen and covalent bonds in the membrane matrix. Permeation flux increased remarkably with APTEOS content increasing, and water permselectivity increased at the same time, the trade-off between the permeation flux and water permselectivity of the hybrid membranes was broken. The sorption selectivity increased with increasing temperature, and decreased with increasing water content. In addition, the diffusion selectivity and diffusion coefficient of the permeants through the hybrid membranes were investigated. The hybrid membrane containing 5 wt% APTEOS has highest separation factor of 536.7 at 50 °C and permeation flux of 0.0355 kg m⁻² h⁻¹ in PV separation of 5 wt% water in the feed.     

Stabilization of electrospun poly(vinyl alcohol) nanofibrous mats in aqueous solutions

<正>The stability ofpoly(vinyl alcohol)(PVA) nanofibrous mats in water media was improved by post-electrospinning treatments.Bifunctional glutaraldehyde(GA) in methanol was used as a crosslinking agent to stabilize PVA nanofiber,but fiber twinning was observed frequently,and the highly porous structure of PVA nanofibrous mats was destroyed when the crosslinked fiber was soaked in water.To overcome this shortcoming,chitosan(CS) was introduced into the PVA spinning solution to prepare PVA/CS composite nanofibers.Their treatment in GA/methanol solution could retain the fiber morphology of PVA/CS nanofibers and porous structure of PVA/CS nanofibrous mats even if they were soaked in aqueous solutions for 1 month.Scanning electron microscopy(SEM),X-ray diffraction(XRD),thermal gravimetric analysis(TGA) and differential scanning calorimetry(DSC) were applied to characterize the physicochemical structure and thermal properties of PVA nanofibers.It was found that the water resistance of PVA nanofibrous mats was enhanced because of the improvement of the degree of crosslinking and crystallinity in the electrospun PVA fibers after soaking in GA/methanol solution.     

Alkaline Zn-air and Al-air cells based on novel solid PVA/PAA polymer electrolyte membranes

High ionic conducting solid polymer electrolyte membranes (SPEM) had been successfully prepared from poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA). The solution casting method yielded highly hydrophilic membranes with uniform structure that were suitable for electrochemical applications. The room temperature ionic conductivity of the alkaline PVA/PAA polymer electrolyte membranes was in the range of 0.142–0.301 S cm⁻¹ depending on the composition. The cyclic voltammetry analysis was carried out using Zn|SPEM|Zn and Al|SPEM|Al cells. The analysis results revealed the excellent electrochemical stability of these newly developed alkaline solid PVA/PAA polymer electrolyte membranes. Metal-air fuel cells were also prepared from the alkaline solid PVA/PAA polymer electrolyte membranes. The electrochemical cell performance was evaluated based on Zn-air and Al-air cells at C/10 and C/5 discharge rates. The experimental results exhibited high percent of utilization for metal powders at room temperature. It was up to 90% for Zn-air cell when assembled with PVA:PAA = 10:7.5 polymer electrolyte membrane and discharged at C/10 rate. The power density could be as high as 50 mW cm⁻² at room temperature. However, the cell percent utilization was reduced to 73% with the same composition electrolyte membrane when C/5 discharge rate was tested.     

Preparation and study of PPV/PVA nanofibers via electrospinning PPV precursor alcohol solution

We have found a simple method to prepare poly(phenylene vinylene) (PPV) nanofibers via electrospinning PPV precursor alcohol solution under annealed at 180 °C in a N₂ atmosphere. The nanofibers are uniform in diameter and long in decimeter magnitudes with resistance in decay, which makes them have potential applications in optical and electronic devices. The morphology can be better controlled by blend PPV precursor solution with poly(vinylalcohol) (PVA) aqueous solution. The fluorescence spectrum of PPV/PVA nanofibers exhibited appreciable blue shift, which made it possible to fabricate nanofibers with fluorescence from yellow-green to blue.     

Study of charge storage in the nanofibrous poly(ethylene terephthalate) electrets prepared by electrospinning or by corona discharge method

In this paper, the charge storage performance of electrospun poly(ethylene terephthalate) (PET) mats with high specific surface area was evaluated in comparison to that of PET film electrets. Corona discharge method was used to charge the electrospun PET mats and PET films. The surface potential decay measurements revealed that the corona charged РЕТ mats had higher initial values for the normalized surface potential compared to the РЕТ electret films. A tendency for stabilization of the electret charge to one and the same value for all charged samples (mats and films) after the 50th day was observed. The peaks at 90 °C in the thermally stimulated current (TSC) spectra of uncharged and charged in corona discharge electrospun PET mats were observed and attributed to a relaxation of the separated space charges, the dipole disorientation or injected charges within the bulk. It was found that the value of the storage charge in a corona charged electrospun PET mats was higher than that in PET mats prepared by electrospinning.     

Preparation and Characterization of PVA Hidrogels Nanofibers

Summary: Poly(vinyl alcohol) (PVA) is a biomaterial that has interesting features for applications in soft tissue replacement due to its similarities in the mechanical properties of such tissues. This paper describes the preparation and characterization of PVA fibers obtained by electrospinning and crosslinked with potassium persulfate as thermoinitiator. These PVA fibers were characterized by Scanning Electron Microscopy (SEM) and Optical Microscopy (OM) to analyze the morphology of the spun samples. Finally, Fourier Transform Infrared Spectroscopy (FTIR) and differential scanning calorimetry (DSC) were performed and the results showed that the biomaterial was partially cross-linked, which indicates a potential use for dermal regeneration applications. The morphology of the fibers indicated that structural changes occurred in the biomaterial after thermal crosslinking.     

细菌纤维素(BC)增强PVA/PVP复合水凝胶的制备及性能表征

通过冷冻-熔融法制备了细菌纤维素/聚乙烯醇/聚乙烯吡咯烷酮(BC/PVA/PVP)双网络复合水凝胶,并采用X射线衍射,红外光谱,扫描电镜,力学性能测试等手段对凝胶的结构和性能进行表征.研究发现PVA、PVP通过氢键作用均匀地吸附于纤维微丝周围,将BC纤维有效地分开,因而干燥后的复合凝胶在热水中浸泡后仍可恢复原状;X射线...     

Immobilization of Acidithiobacillus ferrooxidans with complex of PVA and sodium alginate

A new Acidithiobacillus ferrooxidans cell immobilization technique utilizing the complex of PVA solution and sodium alginate solution crosslinked by Ca(NO₃)₂ as entrapment medium is reported. The mixture of A. ferrooxidans suspension and the entrapment complex were extruded into a solution of Ca(NO₃)₂ (1-5%) to form beads, then the beads were frozen at −20 °C for 1-2 days and thawed at room temperature. The forming mechanism, characteristic of this immobilized beads and the factors affecting activity of immobilized cells were also discussed. A maximum oxidation rate of 4.6 g Fe²⁺/(L h) was achieved in batch cultures by these immobilized cells. Precipitation formed during culture process was analyzed. The forming mechanism of this precipitation and how this precipitation affects the whole system were also discussed. In addition, the immobilization technique is operated simply, and the gel beads have high stability even under non-sterile conditions. So its application on an industrial scale would be more practicable.     

ITO Electrode Modified by α‐K6[P2W18O62] Hybrid Nanofibers for Nitrite Determination

A promising nitrite sensor based on one‐dimensional polyoxometalate hybrid nanofibers was prepared and developed by electrospinning of a mixture of poly(vinyl alcohol) and α‐K₆[P₂W₁₈O₆₂]?14H₂O (P₂W₁₈) onto the surface of an indium tin oxide (ITO) electrode. After thermal crosslinking, the P₂W₁₈ hybrid nanofibers are insoluble in aqueous solutions even after a period of 24 hours, which ensures the electrochemical stability of the P₂W₁₈ hybrid nanofiber‐modified ITO electrode. The cyclic voltammetry results have demonstrated that the P₂W₁₈ hybrid nanofiber‐modified ITO electrode exhibits excellent electrocatalytic activity toward the reduction of nitrite in acidic solutions. Additionally, long‐term stability and reproducibility have been observed.     

Novel stand-alone PVA mixed matrix membranes conjugated with graphene oxide for highly improved reverse osmosis performance

In this research, an innovative Poly (vinyl alcohol) (PVA) reverse osmosis (RO) membrane with exceptional attributes was fabricated. Graphene Oxide (GO) nanosheets and Pluronic F-127 were infused within crosslinked PVA to fabricate thin film mixed matrix membranes. The newly synthesized membranes were evaluated in terms of several parameters like surface roughness, hydrophilicity, salt rejection, water permeability, Chlorine tolerance and anti-biofouling property, utilizing a dead-end RO filtration unit. Typical characterization techniques were used to assess the characteristics of the membranes. These include SEM, AFM, contact angle measurements and mechanical strength analysis. The conjugation of Pluronic F-127 and GO enhanced the overall performance of the membranes. The modified membranes surfaces had less roughness and higher hydrophilicity in comparison with the unmodified ones. This research showed that membranes that contained 0.08 wt% and 0.1 wt% GO exhibited superior selectivity, mechanical strength, Chlorine tolerance and anti-biofouling property. The truly significant outcome to evolve from this investigation is that improvements have been accomplished while PVA was used as a stand-alone RO layer without the use of any substrate. This study showed that crosslinking of PVA and modifying it with proper fillers overcame the common PVA downsides, primarily swelling and rupture under exceptionally high pressure.     

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.     

Fabrication of electrospun poly(methyl methacrylate) nanofibrous membranes by statistical approach for application in enzyme immobilization

Response surface methodology based on a five-level, five-variable central composite rotatable design was used to model the average diameter of electrospun poly(methyl methacrylate) nanofibers. The effects studied include polymer concentration, distance, temperature, flow rate, and voltage. Fiber diameter was correlated to these variables by using a second-order polynomial function at a 95% confidence level. The analysis confirmed that polymer concentration, temperature, flow rate, and voltage were the significant factors affecting the diameter with the first three being the most significant ones. Also, no interaction effect terms were found to be significant. The coefficient of determination of the model was found to be 0.9443. The predicted fiber diameters were in agreement with the experimental results. The adequacy of the model was examined using additional independent experiments that were not employed in the model generation to fabricate 100–500 nm fibers with the average absolute relative deviation being 3.55%. A minimum fiber diameter of 36 nm was established and could be validated by experiments. When used for immobilization of Candida rugosa lipase by adsorption, the nanofibrous membranes provided enzyme loading as high as 332 mg lipase/g fibers, which is 5.2 times the reported maximum value.     

Free volume related fluorescent behavior in electron beam irradiated chalcone doped PVA

Effect of electron irradiation on the free volume related microstructural and optical properties of chalcone doped Poly(vinyl alcohol) composite films have been studied using FTIR, UV-Visible, XRD and Positron Annihilation techniques. The FTIR spectral study shows that the irradiation induces the crosslinking within the composite. Using UV-Visible absorption spectra the optical energy band gap and activation energies were estimated and the variation of these parameters suggests the existence of defects and molecular ordering within the irradiated composite. XRD diffractograms reveal that the crosslinking enhances the crystallinity of the sample. In this cross-linked polymer composite the fluorescence enhancement has been observed in the fluorescence spectral study. The Positron annihilation result suggests that the irradiation affects the free volume properties and crosslinking hinders the chalcone chromophore molecular rotation. Under this restricted condition the chromophore molecules likely to emit enhanced fluorescence and its mobility is directly related to the free volume around it.     

Enhanced dehumidification performance of PVA membranes by tuning the water state through incorporating organophosphorus acid

A novel thin film composite membrane with superior propylene dehumidification performance was prepared by coating a high hydrophilic organophosphorus acid ethylene diamine tetra(methylene phosphonic acid) (EDTMPA) doped poly(vinyl alcohol) (PVA) on polysulfone (PS) hollow fiber membranes. Experimental studies and molecular dynamics simulations were combined to probe the existing states and the transport mechanism of water in the membranes. Water vapor sorption experiments revealed that the enhanced dehumidification performance was governed by the diffusion process. Water states and water distribution were investigated by molecular dynamics simulation. At low EDTMPA content (<10 wt.%), states of the water were not obviously changed and the increase of water diffusion coefficient was mainly attributed to enlarged free volume of the membrane. At high EDTMPA content (10–30 wt.%), the increase in the water diffusion coefficient mainly arose from the variations in the water states. Strong interaction between PVA and EDTMPA reduced the amount of water that bounded to the PVA and increased the proportion of free water. The diffusion coefficients of water increased with increasing proportion of free water, since the mobility of free water was higher than that of bound water. The permeance of water reached 997.7 GPU for the PVA–EDTMPA/PS membrane with a 20 wt.% EDTMPA content when the proportion of free water was the highest, and the separation factor increased to infinity.     

Polydopamine- and polyDOPA-coated electrospun poly(vinyl alcohol) nanofibrous membranes for cationic dye removal

Mussel adhesive proteins including special functional groups, such as dopamine and 3,4-dihydroxy-l-phenylalanine (DOPA), exhibit strong adhesion and have thus been used in numerous applications. As a novel dye adsorbent for wastewater treatment, this study examineed poly(vinyl alcohol) (PVA) nanofibrous membranes (NFMs) fabricated via electrospinning and then coated with polydopamine (pDA) or polyDOPA through a simple dip coating process in dopamine or DOPA solution to examine. The surface morphology, chemical composition and hydrophilicty of PVA NFMs coated with pDA or polyDOPA were compared using scanning electron microscopy (SEM), UV photoelectron spectrometry (XPS) and contact angle analyzer, respectively. The thermal degradation temperatures of the PVA NFMs were increased significantly by about 100 °C due to the radical scavenging ability of pDA and pDOPA. Also, the differences in the adsorption performance toward a cationic dye, methylene blue (MB), for polydopamine- or polyDOPA-coated PVA NFMs were evaluated using a UV–Visible spectrophotometer. Finally, a recyclability test was conducted to confirm the applicability as a dye adsorbent.     

Development of electrospun poly(vinyl alcohol) fibers immobilizing lipase highly activated by alkyl-silicate for flow-through reactors

Electrospun fibrous membranes composed of poly(vinyl alcohol) (PVA) fibers of approximately 1 μm in diameter, and immobilizing highly activated lipase entrapped in silicate cages with smaller dimensions than the fibers, were developed; and their feasibility as a component of flow-through reactors was studied. The electrospun PVA fibers were prepared from a mixture of PVA solution and a sol obtained from silicon alkoxide(s)—either tetramethoxysilane (TMOS) or dimethyldimethoxysilane (DMDMOS), or both, containing lipase. The fastest initial transesterification rate converting (s)-glycidol to glycidyl n-butyrate with vinyl n-butyrate in batchwise reactions was accomplished by treatment of lipase using the sol obtained from DMDMOS and TMOS together. The values were 4.5-, 21.8-, and 1.8-fold faster than those of systems using lipases that were either non-modified or modified using TMOS alone or DMDMOS alone, respectively. The higher activity of the lipase modified using both DMDMOS and TMOS and immobilized in PVA fibers resulted in a flow-through reactor having a higher degree of conversion at the same retention time compared with that using immobilized non-modified lipase. These results show the feasibility of flow-through reactors composed of electrospun PVA fibers immobilizing lipase highly activated by alkyl-silicate.