Preparation of monodisperse poly(vinyl alcohol) (PVA) nanoparticles by dispersion polymerization and heterogeneous surface saponification

Monodisperse poly(vinyl alcohol) (PVA)/poly(vinyl acetate) (PVAc) nanoparticles with a skin-core structure were prepared through heterogeneous surface saponification of PVAc nanoparticles. For the preparation of PVAc nanoparticles with a uniform particle size distribution, vinyl acetate (VAc) was dispersion polymerized in a mixed solvent of ethanol and water using PVA with a low degree of saponification as a stabilizer. Increase of the amount of ethanol in media, the resulting PVAc nanoparticle size increases due to increasing solubility of VAc and oligomer PVAc. To preserve the sphericity and size uniformity of PVAc nanoparticles, we restricted saponification to the surface of the nanoparticles by using a small amount of aqueous sodium hydroxide solution. To determine the proper concentration of alkali solution for heterogeneous saponification, monodisperse PVAc nanoparticles were saponified with different concentrations of alkali solution at 25 °C for 0.5–3.0 h. The PVA/PVAc nanoparticles obtained by the heterogeneous saponification with 4 % (relative to the amount of the VAc) alkali solution for 2.0 h were uniformly shaped and monodispersed with diameter ranging from 428 to 615 nm. Transmission electron microscopy (TEM) confirmed the spherical nature and regular skin-core structure of the PVA/PVAc nanoparticles.     

Preparation of syndiotactic poly(vinyl alcohol) embolic particles with radiopacity

A suspension copolymerization in the presence of aqueous radiopaque nanoparticles was used to prepare poly(vinyl pivalate/vinyl acetate) (P(VPi/VAc)) nanocomposite microspheres for embolic materials. To generate nanocomposite microspheres with radiopacity, various radiopaque nanoparticles (TiO₂, Ti, Ag, Au and Pt) were added to P(VPi/VAc) copolymer. The P(VPi/VAc)/nanoparticles microspheres with radiopacity were then saponified in alkali solution, leading to syndiotactic poly(vinyl alcohol) (s-PVA)/nanoparticles microspheres with radiopacity of which degree of saponification (DS) was up to 99.8 %. The saponification time of P(VPi/VAc)/nanoparticles microspheres decreased with increasing the amount of nanoparticles. Computed tomography (CT) analysis revealed that s-PVA/TiO₂ and s-PVA/Ti microspheres had good radiopacity.     

Preparation of high molecular weight atactic poly(vinyl alcohol) by photo-induced bulk polymerization of vinyl acetate

Vinyl acetate was polymerized in ultraviolet-ray initiated bulk system at low temperatures using 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN) or 2,2′-azobis(isobutyronitrile) (AIBN) as the photoinitiator, respectively. High molecular weight (HMW) poly(vinyl alcohol) (PVA) having number-average degree of polymerization (P _n ) of 3,900–7,800 and syndiotactic diad (S-diad) content of 52.5–54.0% could be prepared by complete saponification of synthesized linear poly(vinyl acetate) (PVAc) havingP _n of 5,900–9,400 obtained at conversion of below 30%.P _n of PVA using ADMVN was larger than that of PVA using AIBN. On the other hand, conversion of the former was smaller than that of the latter, and it was found that the initiation rate of the ADMVN was lower than that of AIBN. This could be explained by a fact that the rate of photolysis of AIBN is faster than that of ADMVN due to the higher quantum yield or dissociation rate constant of AIBN than that of ADMVN. TheP _n , syndiotacticity, and whiteness of PVA from PVAc polymerized at lower temperatures were superior to those of PVA from PVAc polymerized at higher temperatures.     

Preparation of poly(vinyl alcohol)/silver-zeolite composite hydrogels by UV-irradiation

Poly(vinyl alcohol) (PVA)/Ag-zeolite nanocomposite hydrogels were prepared by UV irradiation using PVA solution mixed with Ag-zeolite nanoparticles. Physical properties and changes in morphology of the PVA/Ag-zeolite hydrogels were investigated. The PVA/Ag-zeolite hydrogels were prepared at a PVA concentration of 9 wt% with a UV irradiation distance of 15 cm, where gel fraction and swelling ratio were optimized. Hardness of the PVA/Ag-zeolite hydrogels decreased with increasing amounts of Ag-zeolite, reaching that of soft elastomer when the amount of Ag-zeolite was 5 % by weight. The PVA/Ag-zeolite hydrogels showed strong antimicrobial activities against Staphylococcus aureus and Klebsiella pneumoniae, inducing a reduction of bacteria of over 99.9 % at a Ag-zeolite content of 3 wt%.     

Fabrication of homogeneous multi-walled carbon nanotube/poly (vinyl alcohol) composite films using for microwave absorption application

Poly (vinyl alcohol) (PVA)/multi walled carbon nanotubes (MWNT) nanocomposite films were fabricated and their microwave absorption behavior were evaluated using vector network analyzer in the frequency range of 8–12 GHz (Xband). The uniform, stable dispersion and well oriented MWNT within the PVA matrix were achieved through using sodium dodecyl sulfate (SDS) as dispersing agent. The surface morphology of the PVA/SDS/MWNT films was examined by scanning electron microscope (SEM). The SEM analysis of the film samples revealed the uniform appearance in the whole surfaces of the fabricated composite films. However, some roughness on the surface was observed due to the presence of MWNT in the film structure. The PVA/SDS/MWNT films show significant increase in microwave absorption which is improved by increasing the MWNT content. The PVA/SDS/MWNT nanocomposite film sample with MWNT loading of 10 wt% showed the maximum and the relatively high microwave absorption of 28.00 dB at the frequency of 8.6 GHz.     

Low temperature suspension polymerization of methyl methacrylate for the preparation of high molecular weight poly(methyl methacrylate)/silver nanocomposite microspheres

In order to prepare high molecular weight poly(methyl methacrylate) (PMMA)/silver nanocomposite microspheres, methyl methacrylate was suspension-polymerized in the presence of silver nanoparticles at low temperature with 2,2′-azobis(2,4-dimethylvaleronitrile) as an initiator. The rate of conversion was increased by increasing the initiator concentration. When silver nanoparticles were added, the rate of polymerization decreased slightly. High monomer conversion (about 85 %) was obtained in spite of low polymerization temperature of 30°C. Under controlled conditions, PMMA/silver microspheres with various number-average degrees of polymerization (6,000–37,000) were prepared. Morphology studies revealed that except for normal suspension microspheres with a smooth surface, a golf ball-like appearance of the microspheres was observed, due to the migration and aggregation of the hydrophilic silver nanoparticles at the sublayer beneath the microsphere’s surface.     

Preparation of poly(vinyl alcohol)/ZrO2 composite nanofibers via co-axial electrospinning with higher ZrO2 particle content

Poly(vinyl alcohol) (PVA)/zirconium oxide (ZrO₂) composite nanofibers with a skin-core structure were prepared and the effect of ZrO₂ particle content on uniform web formation was investigated. The optimized polymer concentration, tip to collector distance, and applied voltage for electrospinning were 11 wt%, 12 cm, and 20 kV, respectively. Skin-core PVA/ZrO₂ composite nanofibers containing up to 12 wt% ZrO₂ were successfully prepared, but it was difficult to obtain PVA/ZrO₂ composite nanofiber webs via conventional electrospinning. Increasing the amount of ZrO₂ caused the morphology of the PVA/ZrO₂ composite nanofibers to become a non-uniform nanoweb with irregular nanofiber diameters. While it was difficult to obtain a uniform nanofiber web containing a content of ZrO₂ over 6 wt% for conventional electrospinning, a more uniform nanofiber web could be obtained at up to 9 wt% ZrO₂ using a skin-core dual nozzle. More uniform webs could also be obtained when ZrO₂ was in the skin rather than the core.     

Preparation and UV-protective property of PVAc/ZnO and PVAc/TiO<Subscript>2</Subscript> microcapsules/poly(lactic acid) nanocomposites

The poly(vinyl acetate) (PVAc)/zinc oxide (ZnO) microcapsule and PVAc/titanium dioxide (TiO₂) microcapsule were synthesized via in-situ emulsion polymerization method. The PVAc/ZnO microcapsule and PVAc/TiO₂ microcapsule were characterized by fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis(TG), transmission electron microscopy (TEM), and UV-visible spectroscopy (UV-vis). Effect of PVAc/ZnO microcapsule and PVAc/TiO₂ microcapsule on properties of poly(lactic acid) (PLA) was evaluated by UV-vis, SEM and mechanical properties test. The results showed that the addition of PVAc/ZnO and PVAc/TiO₂ microcapsules as a UV-blocking additive could significantly enhance UV-blocking property of PLA/PVAc/ZnO microcapsule composites and PLA/PVAc/TiO₂ microcapsule composites compared with pure PLA, PLA/ZnO composites and PLA/TiO₂ composites. The mechanical properties of PLA/PVAc/ZnO microcapsule composites were better than those of PLA/ZnO composites due to good dispersability and compatibility of PVAc/ZnO microcapsule in PLA matrix. Also, the mechanical properties of PLA/PVAc/TiO₂ microcapsule composites were better than those of pure PLA and PLA/TiO₂ composites. This study demonstrates the great potentials of the intrinsically UV shield additive PVAc/ZnO and PVAc/TiO₂ microcapsules in the application of high performance matrix resin and composite material.     

Preparation and photochromism of poly(methyl methacrylate) microspheres containing spirooxazine

Photochromic poly(methyl methacrylate) (PMMA)/spirooxazine microspheres were prepared by in situ suspension polymerization and those photochromic behaviors were investigated. When UV irradiation was subjected to the PMMA/spirooxazine microspheres, the reflection spectra generated by photochromic reaction was clearly observed and its reversible decoloration behaviors responded rapidly in the dark. Photochromic microspheres prepared in this work, could be used to photochromic fabrics such as microcapsules for fragrant finishing of fabrics, as well as those are could be applied in sensing materials.     

Studies on a novel polyacrylonitrile copolymer/cellulose acetate blending water absorbency fiber

Polyacrylonitrile copolymer (CPAN) was obtained by water-deposit polymerization, using acrylonitrile (AN), vinyl acetate (VAc), potential crosslinking moiety (hydropropyl acrylate, HQ) as monomer, NaClO₃ as initiator. CPAN was blended with cellulose acetate (CA) to prepare CPAN/CA blending fiber via wet spinning. The fiber was post-crosslinked and hydrolyzed to get water absorbency fiber. The structures and properties of the fibers were studied and the results showed that potential crosslinking moiety was necessary in making CPAN/CA blending water absorbency fiber. The saponification reaction was accelerated after blended with CA and the interfacial microvoids enhanced the water absorbency ability.     

The effect of multi-walled carbon nanotubes on the molecular orientation of poly(vinyl alcohol) in drawn composite films

Poly(vinyl alcohol) (PVA)/multi-walled carbon nanotube (MWNT) composite films were prepared by casting a DMSO solution of PVA and MWNTs, whereby the MWNTs were dispersed by sonication. A significant improvement in the mechanical properties of the PVA drawn films was achieved by the addition of a small amount of MWNTs. The initial modulus and the tensile strength of the PVA drawn film increased by 30% and 45% respectively, with the addition of 1 wt% MWNTs, which are close to those calculated from the rule of mixtures, and were strongly dependent upon the orientation of the PVA matrix. The mechanical properties, however, were not improved with a further increase in the MWNT content. The orientation of MWNTs in the composite was not well developed compared to that of the PVA matrix. This result suggests that the improvement of the molecular orientation of the PVA matrix plays a major role in the increase of the mechanical properties of the drawn PVA/MWNT composite films.     

Pervaporation separation of dimethyl carbonate/methanol binary mixtures with poly(vinyl alcohol)-perfluorslulfonic acid/poly(acrylonitrile) hollow fiber composite membranes

Using poly(vinyl alcohol) (PVA) and perfluorslulfonic acid (PFSA) as coating materials, poly(acrylonitrile) (PAN) hollow fiber ultrafiltration membrane as substrate, PVA-PFSA/PAN composite membranes were fabricated by dip-coating method. The fabricated composite membranes were used to the separation of dimethyl carbonate (DMC)/methanol (MeOH) binary mixtures by pervaporation process. SEM images verify that the coated layer is well combined with substrate and the thickness nearly linearly increases with the coating solution concentration. The separation factor increases but at cost of the decline of permeation flux when the concentration of the coating solution or its PVA mass fraction increase. The permeation flux increases and separation factor slightly increases with the feed temperature increasing at 30–60 °C. The increase of feed MeOH concentration leads to an improvement of permeation flux and a decline of separation factor.     

Preparation of new polymer nanocomposites based on poly(lactic acid)/fatty nitrogen compounds modified clay by a solution casting process

In this study, different organoclays (OMMTs) were prepared using various fatty nitrogen compounds (FNCs) and natural clay, sodium montmorillonite (MMT). The clay modification was carried out by stirring the clay particles in an aqueous solution of fatty amides (FA), fatty hydroxamic acids (FHA), and carbonyl difatty amides (CDFA). These OMMTs were then used for nanocomposites production to improve the property balance of poly(lactic acid) (PLA) by solution casting process. All sets of OMMTs and nanocomposites were characterized using various apparatuses. In the nanocomposites, where the clay surface is pretreated with FA, FHA and CDFA, the basal spacing of the clay increased to 2.94, 3.26 and 3.80 nm, respectively The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results confirmed the production of nanocomposites. PLA modified clay nanocomposites show higher thermal stability and significant improvement of mechanical properties in comparison with pure PLA.     

Titanium dioxide nanofibers prepared by using electrospinning method

The synthesis of titanium dioxide nanofibers with 200–300 nm diameter was presented. The new inorganic-organic hybrid nanofibers were prepared by sol-gel processing and electrospinning technique using a viscous solution of titanium isopropoxide (TiP)/poly(vinyl acetate) (PVAc). Pure titanium dioxide nanofibers were obtained by high temperature calcination of the inorganic-organic composite fibers. SEM, FT-IR, and WAXD techniques were employed to characterize these nanofibers. The titanium dioxide nanostructured fibers have rougher surface and smaller diameter compare with PVAc/TiP composite nanofibers. The anatase to rutile phase transformation occurred when the calcination temperature was increased from 600 °C to 1000 °C.     

The effect of casting solvent on the structural characteristics and miscibility of regenerated silk fibroin/Poly(vinyl alcohol) blends

Regenerated silk fibroin(SF)/Poly(vinyl alcohol)[PVA] blend films were prepared using different casting solvents, water and formic acid, to elucidate the effect of casting solvent on the structure and miscibility of SF/PVA blends. FTIR and XRD measurement suggested thatβ-sheet conformation of SF was not changed by addition of PVA in case of formic acid casting and the casting solvent determined the crystallized component of SF/PVA, leading to a different trend in the overall crystallinity between the two blends. The casting solvent had a dominant role in deciding phase behavior and molecular miscibility of blend films. SEM observation and DMTA measurement elucidated that water solvent produced phase-separated blend films while formic acid yielded one phase blend films with partial miscibility in molecular level indicating that the miscibility of SF blend can be improved by choosing a proper co-solvent.     

Effect of aldehydes crosslinkers on properties of bacterial cellulose-poly(vinyl alcohol) (BC/PVA) nanocomposite hydrogels

The effects of the aldehydes crosslinkers on properties of the BC/PVA nanocomposite hydrogels were investigated. BC as the reinforcement and PVA as the matrix materials of the BC/PVA nanocomposite hydrogels, the hydrogels were prepared in coagulating bath of sodium sulfate and cross-linked with kinds of aldehydes. The hydrogels were characterized by Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), Equilibrium swelling ratio (ESR) tests, mechanical properties tests, thermo-gravimetric analysis (TGA) and X-ray diffraction (XRD) analysis. It was found that the dialdehyde (glyoxal, glutaraldehyde) crosslinkers were more efficient than monoaldehyde (formaldehyde, acetaldehyde) crosslinkers. The ESR, mechanical properties of the BC/PVA nanocomposite hydrogels were obviously influenced by aldehydes crosslinkers. However, their thermo stability and crystallinity were scarcely influenced. The nanocomposite hydrogels described in this study provides information for further development and optimization of a variety of nanofiber-polymer matrix composite hydrogels.     

Preparation and properties of antibacterial Poly(vinyl alcohol) nanofibers by nanoparticles

Poly(vinyl alcohol) (PVA)/Ag-zeolite nanofiber webs were prepared with different concentrations of Ag-zeolite nanoparticles by the electrospinning technique. Scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), transmission electron microscopy (TEM), Fourier transform-infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Instron, and antibacterial activities analysis were utilized to characterize the morphology and properties of the PVA/Ag-zeolite nanofiber webs. The study results showed that the polymer concentration, applied voltages and tip-to-collector distances were the main factors influencing the morphology of the electrospun nanofiber webs. The introduction of Ag-zeolite nanoparticles improved the mechanical properties and thermal stability of the PVA nanofiber webs. TEM data demonstrated that the Ag-zeolite nanoparticles were well distributed within the nanofiber. FTIR revealed a possible interaction between the PVA matrix and the Ag-zeolite nanoparticles. These fibers showed an antibacterial efficacy of 99.8 % and over against Staphylococcus aureus and Klebsiella pneumoniae at Ag-zeolite concentrations of 1 % and over, because of the presence of the silver nanoparticles in the zeolite.     

Poly(vinylidene fluoride)/poly(ethylene-co-vinyl acetate) (20/80) blend. II. Crystalline structure and morphology

We investigated the effect of ethylene and vinyl acetate (20/80 mole ratio) copolymer (EVAc80) content in poly(vinylidene fluoride) (PVDF/EVAc80) blends and also varying isothermal crystallization temperatures on the crystalline structure and morphology, and surface topography using different spectroscopic and microscopic techniques. As crystallization temperature increases for the same blend composition, the lamellar splay type spherulite is changed to the concentric ring-banded spherulite, and then to the spiral-ringed spherulite with further increasing temperature. With increasing EVAc80 content in the PVDF/EVAc80 blends, the temperature range, where spiral-ringed spherulites and lamellar splay typeγ-spherulites are present predominantly, becomes much broader. Furthermore, the non-textured spherulite was observed more at highest crystallization temperature with increasing EVAc80 content. The band spacing between bright and dark zone and periodicity between ridge and valley increase with increasing amorphous EVAc80 content.     

Electrospun poly(tetrafluoroethylene) nanofiber membranes from PTFE-PVA-BA-H<Subscript>2</Subscript>O gel-spinning solutions

As a kind of high-performance fibers, PTFE fiber has been widely used in many fields because of its unique characteristics. In this study, the poly(tetrafloroethylene) (PTFE) nanofibers manufactured by electrospinning method was reported. The gel-spinning solution of poly(tetrafluoroethylene)/poly(vinyl alcohol)/boric acid (PTFE/PVA/BA), which was prepared by the gel process of the mixture of PTFE, PVA, BA and redistilled water, was electrospun to form PTFE/PVA/BA composite nanofibers. After calcinating, the PTFE nanofibers with diameters of 200 nm to 1000 nm were obtained. The fibers before and after calcinating were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), FT-IR spectrum analysis and X-ray photoelectron spectroscopy (XPS), respectively, and the mechanical and hydrophobic properties of the fibers were also investigated. The results showed that the PTFE nanofiber membranes could be electrospun effectively used the gel-spinning solution of PTFE/PVA/BA, and may realize the applications in the fields of high-temperature filtration, catalyst supports, battery separator and so on.     

SiO2-kaolinite affecting the surface properties of ternary poly(vinyl chloride)/silica/kaolinite nanocomposites

The products from the dispersion of nanoscale particulates such as the layered clays or the spherical inorganic minerals within the polymeric matrices are called polymeric nanocomposites. In this paper, we prepared poly(vinyl chloride) (PVC) based nanocomposites containing SiO₂-kaolinite by melt compounding. The influence of SiO₂-kaolinite on the surface properties of PVC was investigated by the use of various surface analysis techniques including a ttenuated total reflectance spectroscopy (ATR), wide angle X-ray diffractometry (WAXD), atomic force microscopy (AFM), scanning electron microscopy (SEM), electron dispersive X-ray spectrometer (EDX), contact angle measurement (CAM), and reflectance spectroscopy (RS). ATR spectroscopy showed possible interaction between layered kaolinite and PVC at surface. Microscopic methods illustrated an increased surface roughness compared to the pure PVC. Contact angle measurements of the resultant PVC nanocomposites demonstrated that the wettability of substrates depends on the surface interactions between kaolinite layers and PVC matrix. Optical properties of nanocomposite films were finally measured by the aid of reflectance spectrophotometer. It can be seen from optical studies that reflectance values were increased after incorporation of SiO₂-kaolinite in nanocomposite.