Reactive electrospinning of poly(vinyl alcohol) nanofibers

We aim to couple the electrospinning in‐line with solution chemistry to fabricate novel crosslinked polymer nanofibers. Poly(vinyl alcohol) (PVA) was used as a model polymer due to its high amount of hydroxyl groups. To obtain ideal parameters for electrospinning, pure PVA was explored primarily. To gain crosslinked fibers, PVA was first crosslinked partially with glutaraldehyde (GA) followed by transferring this precursor to a long hot tube which was used as reactor and then electrospun right before gelation. The preheating time and tube‐passing time were determined with viscometer and rheometer. The reactive as‐spun fibers could maintain their original morphology after water immersion due to their high crosslinking degree. The thermal stability and mechanical property of reactive as‐spun fibers were improved drastically compared with pure and GA vapor crosslinked PVA fibers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and characterization of graphene oxide/poly(vinyl alcohol) composite nanofibers via electrospinning

Graphene oxide (GO) was well dispersed in poly(vinyl alcohol) (PVA) diluted aqueous solution, and then the mixture was electrospun into GO/PVA composite nanofibers. Electron microscopy and Raman spectroscopy on the as‐prepared and calcined samples confirm the uniform distribution of GO sheets in the nanofibers. The thermal and mechanical properties of the nanofibers vary considerably with different GO filler contents. The decomposition temperatures of the GO/PVA composite nanofiber dropped by 38–50°C compared with pure PVA. A very small loading of 0.02 wt % GO increases the tensile strength of the nanofibers by 42 times. A porous 3D structure was realized by postcalcining nanofibers in H₂. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Studies of chitosan. I. Preparation and characterization of chitosan/poly(vinyl alcohol) blend films

Various blending ratios of chitosan/poly (vinyl alcohol) (CS/PVA) blend films were prepared by solution blend method in this study. The thermal properties and chemical structure characterization of the CS/PVA blend films were examined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and Fourier transform infrared (FTIR). Based upon the observation on the DSC thermal analysis, the melting point of PVA is decreased when the amount of CS in the blend film is increased. The FTIR absorption characteristic is changed when the amount of CS in the blend film is varied. Results of X‐ray diffraction (XRD) analysis indicate that the intensity of diffraction peak at 19° of PVA becomes lower and broader with increasing the amount of CS in the CS/PVA blend film. This trend illustrates that the existence of CS decreases the crystallinity of PVA. Although both PVA and CS are hydrophilic biodegradable polymers, the results of water contact angle measurement are still shown as high as 68° and 83° for PVA and for CS films, respectively. A minimum water contact angle (56°) was observed when the blend film contains 50 wt % CS. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

One-step fabrication of branched poly(vinyl alcohol) nanofibers by magnetic coaxial electrospinning

Branching has been emerging in 3-D interconnecting building blocks. Branched and hyperbranched poly(vinyl alcohol) (PVA) nanofibers were fabricated by coaxially electrospinning two-liquids under an alternating magnetic field in a facile manner. Both the PVA nanofiber trunks with diameter of 100–200 nm and the PVA nanofiber branches with diameter of 10–30 nm were formed in a single step. The length and the morphology of the branched PVA nanofibers could be controlled through a rational design of the magnetic field. The facile technique may readily be extended to prepare 3-D branched nanofibers from other materials such as various polymers and polymer–ceramic materials. Moreover, the multifunctional and multicomponent materials with branched nanostructure could be expected by using the magnetic coaxial electrospinning technique. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermal and structural characterization of nanofibers of poly(vinyl alcohol) produced by electrospinning

Poly(vinyl alcohol) (PVOH) was obtained from the alkaline hydrolysis of poly(vinyl acetate) (PVAc). Nonwoven membranes (mats) of PVOH nanofibers were produced by electrospinning of solutions of PVOH in water with and without aluminum chloride. The concentration of the PVOH/water solution was 12.4% w/v. The morphology of the mats was analyzed by scanning electron microscopy (SEM). The thermal properties and the degree of crystallinity of the nanofibers were measured by differential scanning calorimetry (DSC); the crystal structure of the mats was evaluated by wide‐angle X‐ray diffraction. The best nanofibers were obtained by electrospinning the PVOH/water solution with aluminum chloride (45% w/v) in which an electrical field of 3.0 kV/cm was applied. It was observed that the addition of the aluminum chloride and the increase in the applied electrical field decreased the number‐average nanofibers diameters. The mats without aluminum chloride had higher melting temperatures and higher degrees of crystallinity than the mats with the salt. The crystal structure of the mats was found to be monoclinic; however, the mats were neither highly oriented nor have a high degree of crystallinity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Pd/C embedded crosslinked polystyrene fibers as an efficient catalyst for Heck reactions

Pd/C embedded polystyrene fibers were successfully prepared by electrospinning. The polystyrene molecules were then cross-linked by paraformaldehyde in sulfuric acid to improve the solvent resistance of composite fibers. SEM images conformed the preparation of uniform and smooth composite fibers. FT-IR spectra demonstrated that the polystyrene molecules inside fibers have been sulphonated and crosslinked. Heck reactions were used to evaluate the catalytic performance of these novel composite fibers. The catalysis results show that this composite fiber mat catalyzed Heck reactions could be evidently promoted by using preferred reducing alcohol agent and solvent. Under the optimized reaction conditions, this composite fiber mat could effectively catalyze the Heck reactions of aromatic iodides with n-butyl acrylate to afford the products with satisfied yields. Especially, compared with the particulate Pd/C catalyst, the separation and recycling of this fibrous catalyst from the reaction mixture were significantly improved due to the larger fibrous structure. At last, this fiber catalyst was successfully reused for eight times with little loss of initial catalytic activity, which was even better than the pristine Pd/C catalyst. Hence, embedment of particulate supported metal catalysts inside the crosslinked polystyrene fibers can effectively improve their catalytic performance and handiness.     

Thermal and dynamic mechanical behavior of bionanocomposites: Fumed silica nanoparticles dispersed in poly(vinyl pyrrolidone), chitosan,and poly(vinyl alcohol)

Various bionanocomposites were prepared by dispersing fumed silica (SiO₂) nanoparticles in biocompatible polymers like poly(vinyl pyrrolidone) (PVP), chitosan (Chi), or poly(vinyl alcohol) (PVA). For the bionanocomposites preparation, a solvent evaporation method was followed. SEM micrographs verified fine dispersion of silica nanoparticles in all used polymer matrices of composites with low silica content. Sufficient interactions between the functional groups of the polymers and the surface hydroxyl groups of SiO₂ were revealed by FTIR measurements. These interactions favored fine dispersion of silica. Mechanical properties such as tensile strength and Young's modulus substantially increased with increasing the silica content in the bionanocomposites. Thermogravimetric analysis (TGA) showed that the polymer matrices were stabilized against thermal decomposition with the addition of fumed silica due to shielding effect, because for all bionanocomposites the temperature, corresponding to the maximum decomposition rate, progressively shifted to higher values with increasing the silica content. Finally, dynamic thermomechanical analysis (DMA) tests showed that for Chi/SiO₂ and PVA/SiO₂ nanocomposites the temperature of β‐relaxation observed in tanδ curves, corresponding to the glass transition temperature T_g, shifted to higher values with increasing the SiO₂ content. This fact indicates that because of the reported interactions, a nanoparticle/matrix interphase was formed in the surroundings of the filler, where the macromolecules showed limited segmental mobility. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of the tacticities of poly(vinyl alcohol) on the structure and morphology of poly(vinyl alcohol) nanowebs prepared by electrospinning

The effects of tacticities on the characteristics of poly(vinyl alcohol) (PVA) nanowebs prepared by an electrospinning technique were investigated. PVA webs composed of uniform nanofibers with syndiotactic dyad (s‐dyad) contents of 53.5 and 57.3% were successfully obtained with electrospinning. By changing processing parameters such as the initial polymer concentration, applied voltage, and tip‐to‐collector distance, we found suitable conditions for forming PVA webs with uniform nanofibers. PVAs of higher s‐dyad contents were prepared at a lower solution concentration and at a higher applied voltage because of the easy formation of syndiotactic PVA chain entanglements at a very low polymer concentration. The average diameter of the nanofibers in a PVA web with the higher s‐dyad content of 57.3% (ca. 240 nm) was thinner than that of the nanofibers in a PVA web with the lowers‐dyad content of 53.5% (ca. 270 nm). In addition, the crystallinity and thermal stability were greatly increased with an increase in the s‐dyad content. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation and properties of chitosan/poly(vinyl alcohol) blend foams for copper adsorption

A new form of polymer blend, macroporous chitosan/poly(vinyl alcohol) (PVA) foams made by a starch expansion process, exhibits the functionalities of chitosan while avoiding its poor mechanical properties and chemical instabilities. The appropriate conditions for foaming are discussed using both insoluble and water‐soluble chitosan. The chitosan/PVA foams demonstrated interconnected and open‐cell structures with large pore size from tens to hundreds of micrometers and high porosities from 73.6 to 84.3%. Glutaraldehyde was employed to improve the retention of chitosan and copper adsorption of the chitosan/PVA foams. While it increased the retention of chitosan and the adsorption capacities, glutaraldehyde decreased the pore size and porosity. The macroporous structure of the chitosan/PVA foams indicates extensive application prospects in terms of the considerable adsorption of heavy metal ions. Copyright © 2006 Society of Chemical Industry     

Synthesis of poly(vinyl propionate) from poly(vinyl alcohol) in nonaqueous medium using ethyl nitrate dimethyl sulfoxide as a catalyst

Poly(vinyl alcohol) (PVA) can be dissolved in a nonaqueous medium in the presence of catalytic concentration of ethyl nitrate dimethyl sulfoxide, C₂H₅ONO₂·DMSO. From the PVA solution, poly(vinyl propionate), PVPR was prepared by the homogeneous esterification of PVA with propionic acid. The ester thus formed contained some unconverted hydroxyl group. The formation of the ester was confirmed by the IR and ¹H‐NMR spectra. The molecular weight of the ester was determined by GPC and intrinsic viscosity (η) was determined by viscometric method. Glass transition temperature, T_g, was obtained from differential scanning calorimetric (DSC) analysis. Thermal stabilities of the ester were checked by thermogravimetric analysis (TGA) and differential thermogravimetric (DTG) analysis. The efficiency of the ester as a flow improver of crude oil was also examined. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5675–5679, 2006     

On the electrospinning of poly(vinyl alcohol) nanofiber mats: A revisit

Electrospinning was used to fabricate mats of poly(vinyl alcohol) (PVA; M_w = 72,000 Da, degree of hydrolysis ≈ 97.5–99.5) nanofibers from PVA solutions in reverse osmotic water. The effects of solution concentration, applied electrical potential, sonication, and collection distance on morphological appearance and diameters of the as‐spun fiber mats as well as those of the individual fibers were carefully investigated mainly by scanning electron microscopy. The effect of the distance from the center of the as‐spun fiber mat on morphological appearance and diameters of the as‐spun fibers was also investigated. The mechanical integrity of some as‐spun PVA fiber mats was also investigated. At all concentrations and applied electrical potentials investigated, the average diameters of the as‐spun PVA fibers ranged between 85 and 647 nm. The use of sonication to prepare a PVA solution caused the viscosity of the solution to decrease; hence, the observed decrease in the average diameters of the as‐spun fibers and the average diameters of the as‐spun fibers were practically the same throughout the as‐spun fiber mat. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Alumina nanofibers obtained from poly(vinyl alcohol)/boehmite nanocomposites

Poly(vinyl alcohol) (PVA)/boehmite nanocomposite (precursor) nanofibers were formed by electrospinning using a PVA aqueous solution of dispersed boehmite nanoparticles as the spinning solution. The alumina nanofibers were obtained by calcination of the precursor nanofibers between 500 and 1200°C. The specific surface area of the precursor nanofibers was around 6 m²/g, and that of the γ‐alumina nanofibers calcined at 500°C was around 300 m²/g. The specific surface areas and the fiber diameters were not affected by the alumina contents in the precursors. Also, the diameter of the alumina nanofibers was not affected by the calcination temperature of the precursor nanofibers. The pore characteristics of the alumina nanofibers decreased with increased calcination temperature due to the sintering, and nonporous α‐alumina nanofibers were obtained by calcination of the precursor nanofibers at 1200°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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

Chitosan and poly(vinyl alcohol) blend fibers were prepared by spinning their solution through a viscose‐type spinneret at 25°C into a coagulating bath containing aqueous NaOH and ethanol. The influence of coagulation solution composition on the spinning performance was discussed, and the intermolecular interactions of blend fibers were studied by infrared analysis (IR), X‐ray diffraction (XRD), and scanning electron micrograph (SEM) and by measurements of mechanical properties and water‐retention properties. The results demonstrated that the water‐retention properties and mechanical properties of the blend fibers increase due to the presence of PVA in the chitosan substract, and the mechanical strength of the blends is also related to PVA content and the degree of deacetylation of chitosan. The best mechanical strength values of the blend fibers, 1.82 cN/d (dry state) and 0.81 cN/d (wet state), were obtained when PVA content was 20 wt % and the degree of deacetylation of chitosan was 90.2%. The strength of the blend fibers, especially wet tenacity could be improved further by crosslinking with glutaraldehyde. The water‐retention values (WRV) of the blend fibers were between 170 and 241%, obviously higher than pure chitosan fiber (120%). The structure analysis indicated that there are strong interaction and good miscibility between chitosan and poly(vinyl alcohol) molecular resulted from intermolecular hydrogen bonds. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2558–2565, 2001     

Blend membranes of chitosan and poly(vinyl alcohol) in pervaporation dehydration of isopropanol and tetrahydrofuran

Blend membranes of a natural polymer, chitosan, with a synthetic polymer, poly(vinyl alcohol) (PVA), were prepared by solution casting and crosslinked with a urea formaldehyde/sulfuric acid (UFS) mixture. Chitosan was used as the base component in the blend system, whereas PVA concentration was varied from 20 to 60 wt %. Blend compatibility was studied by differential scanning calorimetry, and Fourier transform infrared spectroscopy was used to study membrane crosslinking. Membranes were tested for pervaporation dehydration of isopropanol and tetrahydrofuran (THF) at 30°C in close proximity to their azeotropic compositions. Membrane performance was assessed by calculating flux and selectivity. Swelling experiments performed in water + organic mixtures at 30°C were used to explain the pervaporation results. The blend membrane containing 20 wt % PVA when tested for 5 and 10 wt % water–containing THF and isopropanol feeds exhibited selectivity of 4203 and 17,991, respectively. Flux increased with increasing concentration of water in the feed. Selectivity was highest for the 20 wt % PVA‐containing blend membrane. The results of this study are unique in the sense that the crosslinking agent used—the UFS mixture—was novel. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1918–1926, 2007     

聚乳酸/聚乙烯醇纳米纤维的制备及结构

以二甲基亚砜为溶剂,制备不同配比的聚乳酸(PLLA)和聚乙烯醇(PVA)的混合溶液,静电纺丝制得PLLA/PVA纳米纤维。采用红外光谱仪、原子力显微镜等对PLLA/PVA纳米纤维结构与性能进行了表征。结果表明:PLLA/PVA纳米纤维中PVA上的羟基与PLLA上的羰基形成了氢键,PLLA与PVA之间存在一定的相互作用,但PLLA/PVA纳米纤维存在相分离现象;混合溶液的PLLA质量分数为11%,PVA质量分数为8%时可以得到较好的PLLA/PVA纳米纤维,但PVA质量分数为6%时出现液滴及珠丝,PVA质量分数为4%时,不能制得纳米纤维。     

Poly(vinyl alcohol) and poly(vinyl amine) blend membranes for isopropanol dehydration

Blended membranes of hydrophilic polymers poly(vinyl alcohol) (PVA) and poly(vinyl amine) (PVAm) were prepared and crosslinked with glutaraldehyde. The prepared membranes were characterized using infrared (attenuated total reflection mode) spectroscopy, differential scanning calorimetry, X‐ray diffractometry, and scanning electron microscopy measurements. Pervaporation performances of the membranes were evaluated for the separation of water‐isopropanol (IPA) mixtures. As the PVAm content increased from PVAm0 to PVAm1.5, the flux through a 70 μm film increased from 0.023 to 0.10 kg/m² h at an IPA/water feed ratio of 85/15 at 30 °C. The driving force for permeation of water increased due to the temperature but it has no effect on IPA permeation. Activation energies for the permeation of IPA and water were calculated to be 17.11 and 12.46 kJ/mol, respectively. Controlling the thickness of the blend membrane could improve the permeation flux with only a marginal reduction in the separation factor. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45572.     

Properties of branched and network poly(vinyl alcohols) prepared with poly(vinyl alcohol) having aldehyde groups at the chain ends

Branched and network poly(vinyl alcohols) (PVAs) were prepared with inter-acetalization of the PVA with aldehyde groups at the chain ends which was prepared by the cleavage of 1,2 glycol bonds in commercial PVA. The numbers of branches estimated from molecular weights were compared with those estimated by theory. Huggins' constant and crystallinity decreased with increasing branch number. Dissolution of branched PVAs into dimethylsulphoxide was not so easy compared with commercial PVA. The colour of branched PVA–iodine complex decreased rapidly with standing while that of commercial PVA decreased gradually. Network PVAs with Young's modulus of 1–8 MPa were prepared.     

Thermal characteristics of poly(vinyl alcohol) and poly(vinylpyrrolidone) IPNs

Interpenetrating polymer network (IPN) hydrogels based on poly(vinyl alcohol) (PVA) and 1‐vinyl‐2‐pyrrolidone (VP) were prepared by radical polymerization using 2,2‐dimethyl‐2‐phenylacetophenone (DMPAP) and methylene bisacrylicamide (MBAAm) as initiator and crosslinker, respectively. The thermal characterization of the IPNs was investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dielectric analysis (DEA). Depressions of the melting temperatures of PVA segments in IPNs were observed with increasing VP content via the DSC. The DEA was employed to ascertain the glass transition temperature (T_g) of IPNs. From the result of DEA, IPNs exhibited two T_gs indicating the presence of phase separation in the IPN. The thermal decomposition of IPNs was investigated using TGA and appeared at near 270°C. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1844–1847, 2002     

Synthesis and characterization of an interpenetrating polymer network composed of poly(methacrylic acid) and poly(vinyl alcohol)

Temperature and pH‐responsive interpenetrating polymer network (IPN) hydrogels, constructed with poly(methacrylic acid) (PMAA) and poly(vinyl alcohol) (PVA), by a sequential IPN method, were studied. The characterization of IPN hydrogels was investigated by Fourier‐transform infrared spectroscopy, differential scanning calorimetry (DSC) and swelling under various conditions. The IPN hydrogels exhibited relatively high swelling ratios, in the range 230–380 %, at 25 °C. The swelling ratios of the PMAA/PVA IPN hydrogels were pH and temperature dependent. DSC was used for the quantitative determination of the amounts of freezing and non‐freezing water. The amount of free water increased with increasing PMAA content in the IPN hydrogels. Copyright © 2004 Society of Chemical Industry