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.     

Functionalized multi-walled carbon nanotubes with hyperbranched aromatic polyamide for poly(methyl methacrylate) composites

Multi-walled carbon nanotubes (MWCNTs) were functionalized with hyperbranched aromatic polyamide (HAP) by in situ polymerization and by the AB ₂ approach to enhance the mechanical properties of poly(methylmethacrylate) (PMMA) composites. Various concentrations of HAP-functionalized MWCNTs (HAP-f-MWCNTs) were used to prepare HAP-f-MWCNT-reinforced PMMA composite films. The covalent attachment of HAP to the MWCNTs, as achieved by in situ functionalization, resulted in effective dispersion of the MWCNTs in the PMMA matrix, thus enhancing the mechanical and thermal properties of the composite films. The breaking stress of the composites increased largely with the HAP-f-MWCNT loading.     

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%.     

Preparation of poly(vinyl acetate)/clay and poly(vinyl acetate)/poly(vinyl alcohol)/clay microspheres

Poly(vinyl acetate) (PVAc)/poly(vinyl alcohol)(PVA)/montmorillonite (MMT) clay nanocomposite microspheres with a core/shell structure have been developed via a suspension polymerization approach. In order to prepare the PVAc/MMT and PVAc/PVA/MMT nanocomposite microspheres, which are promising precursor of PVA/MMT nanocomposite microspheres, suspension polymerization of vinyl acetate with organophilic MMT and heterogeneous saponification were conducted. A quaternary ammonium salt, cetyltrimethylammonium bromide, was mixed with the MMT in the monomer phase prior to the suspension polymerization. The rate of conversion decreased with an increase in MMT concentration. The incorporation of MMT into the PVAc was verified by FT-IR spectroscopy. Organic vinyl acetate monomers were intercalated into the interlayer regions of organophilic clay hosts and followed by suspension polymerization. Partially saponified PVA/MMT nanocomposite microspheres with a core/shell structure were successfully prepared by heterogeneous saponification.     

Column study of cadmium adsorption onto poly(vinyl alcohol)/hydroxyapatite composite cryogel

Macroporous PVA/HAp composite cryogel was studied for cadmium removal in a fixed-bed column. The cryogel was made through a freeze-thawing process. The morphology of the cryogel was measured. The adsorption performance of the cryogel in the column was examined by varying bed height and HAp amount in PVA cryogel. The maximum adsorption capacity and exhaustion time were determined from the breakthrough curves. The experimental data was described using Adams-Bohart model. Bed height did not exert a large influence on the maximum adsorption capacity and exhaustion time. The kinetic rate constant and the adsorption capacity of the bed were found to be affected by HAp amount.     

Characterization and electrochemical properties of poly(aniline-co-o-methoxyaniline)/multi-walled carbon nanotubes composites synthesized by solid-state method

The composites of copolymers of aniline (An) and o-methoxyaniline (OMA) with multi-walled carbon nanotubes, named as copolymers/MWNT, (poly(An-co-OMA)/MWNT) were prepared by solid-state synthesis method at room temperature. The homopolymers/MWNT composites were synthesized for comparison. The structure and morphology of these composites were characterized by FT-IR spectroscopy, UV-Vis absorption spectroscopy, X-ray diffraction (XRD) and TEM. The electrochemical performances of the composites were investigated by galvanostatic charge-discharge, cyclic voltammetry (CV) and cycle life measurements. The results from FT-IR and UV-Vis spectra showed that different molar ratio of [An]/[OMA] in reaction system has great influence on the oxidation degree, conjugation length and doping level of the copolymers in these composites. The presence of MWNT in the composites was confirmed from the characteristic peaks of MWNT in XRD patterns and the enwrapped MWNT in TEM images. The TEM images further indicates that the MWNT uniformly distributed and enwrapped with polymer in the case of composite from molar ratio of [An]/[OMA]=1:1. The results also showed that the morphology, crystallinity and solubility of composites were highly affected by the incorporation of OMA unit copolymer chain. The results from electrochemical performances suggested that the molar ratio of [An]/[OMA]=3:1 in reaction system can make the obtained composites displayed a higher specific capacitance, good rate ability and cycling stability.     

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.     

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.     

Fabrication of poly(vinyl alcohol) nanofibers by wire electrode-incorporated electrospinning

Wire electrodes for needleless electrospinning consist of stainless steel wires in place of cylinder electrodes. The effects of different numbers of constituent stainless steel wires on the morphology and diameter of polyvinyl alcohol (PVA) fibers are examined. With 1, 2, 3, or 4 stainless steel wires being twisted as wire electrodes, an 8, 10, or 12 wt.% polyvinyl alcohol (PVA) solution is electrospun into PVA nanofibers by using a needleless electrospinning machine. The morphology and diameter of PVA nanofibers is observed by scanning electron microscopy. The combination of the number of stainless steel wires (two), PVA solution (10 wt.%), and the collecting distance (10 cm) results in the finest diameter and an evenly formed fiber morphology. In addition, the nanofibers exhibit a wide range of diameters when electrospun with an electrode consisting of more than two stainless steel wires. Compared with the cylinder electrode, the use of a wire electrode can form nanofibers, which results in a more even morphology.     

Unique crystallization behavior of multi-walled carbon nanotube filled poly(lactic acid)

Although poly(lactic acid) (PLA) possesses many desirable properties such as miscible, reproducible, nontoxic, and biodegradable properties, extremely slow crystallization rate is a weak point in comparison with other commercial thermoplastics. Addition of nucleating agents can be a good method to increase the overall crystallization rate and multi-walled carbon nanotube (MWCNT) is generally known as a good nucleating agent as well as reinforcement. MWCNT reinforced PLA nanocomposites were prepared by melt blending and the unique nucleation and crystallization behaviors of pure PLA and MWCNT/PLA nanocomposites were investigated. Slow homogeneous nucleation and crystallization behavior of the pure PLA and fast heterogeneous crystallization behavior of MWCNT/PLA nanocomposites were observed. Crystallization behavior of MWCNT/PLA nanocomposites was irrespective of cooling rate and the peculiar behavior was due to fast heterogeneous crystallization caused by the nucleating effect of MWCNT and fast PLA chain mobility.     

Preparation and characterization of nanoscaled poly(vinyl alcohol) fibers via electrospinning

Nanoscaled PVA fibers were prepared by electrospinning. This paper described the electrospinning process, the processing conditions, fiber morphology, and some potential applications of the PVA nano-fibers. PVA fibers with various diameters (50–250 nm) were obtained by changing solution concentration, voltage and tip to collector distance (TCD). The major factor was the concentration of PVA solution which affected the fiber diameter evidently. Increasing the concentration, the fiber diameter was increased, and the amount of beads was reduced even to 0%. The fibers were found be efficiently crosslinked by glyoxal during the curing process. Phosphoric acid was used as a catalyst activator to reduce strength losses during crosslinking. Scanning electron micrograph (SEM) and differential scanning calorimetric (DSC) techniques were employed to characterize the morphology and crosslinking of PVA fibers. It was found that the primary factor which affected the crosslinking density was the content of chemical crosslinking agent.     

Structural investigation of anionic functional poly(vinyl alcohol) doped polypyrrole nanospheres

This article reports on a facile route for the preparation of polypyrrole nanospheres with improved water solubility, ordering and conductivity in the presence of a polyelectrolyte, such as phosphorylated polyvinyl alcohol. The phosphorylated polyvinyl alcohol (PPVA) was used as both the stabilizer and the dopant in the chemical oxidative polymerization of pyrrole. The resulting PPVA doped polypyrrole (PPy) nanocomposites (PPy-PPVA) were characterized with FTIR, TGA, SEM and AFM techniques. The electrical conductivity of polymer was measured by four-point probe method. Our observation and results suggest a plausible formation mechanism of PPy nanospheres, PPVA micelle might have functioned as ‘template’ during the polymerization of pyrrole monomers, meanwhile, the PPy chains doped with phosphate group. It was found that the size decreased and their dispersion stability in water increased with the increasing feeding ratio of PPVA. The conductivity of PPy with different morphologies was also measured and compared. When the PPVA: pyrrole feeding ratio ranged from 20 to 50 wt%, the PPy-PPVA nanoparticles showed spherical shape with excellent uniformity, good electrical conductivity (up to 33.1 S·cm^?1), and weakly temperature dependent conductivity. It’s worth mentioning that the PPy-PPVA nanocomposite prepared in high PPVA feeding ratio has been well-dispersed for more than 24 months, which indicates its significant dispersion stability.     

Supramolecular composite of single-walled carbon nanotubes with oligo(p-phenyleneethynylene)s-graft-poly(ethyleneoxide)s

Poly(p-phenyleneethynylene)s, composed of a rigid backbone with alternating arylenes and ethynylenes, exhibit high conductivity and chemical stability, and thus they have huge potentials for various applications, including chemosensors, electronic and photonic devices. In spite of numerous interesting applications to date, not many researches concerning oligo(p-phenyleneethynylene)s-graft-poly(ethylene oxide)s (OPEs-g-PEOs) have been carried out, let alone their complexation behaviors with carbon nanomaterials. In this article, we present the synthesis of OPEs-g-PEOs and characterize its morphological and spectral properties by various characterization techniques. We have investigated the interaction of OPEs-g-PEOs with single-walled carbon nanotubes (SWNTs) using various characterization techniques, such as UV-visible, photoluminescence, and Raman spectroscopy, along with SEM, TEM, and POM. In this way, we have successfully demonstrated that OPEs-g-PEOs provide a useful means to modify the physical properties of CNTs, especially in terms of their solubility in common organic solvents.     

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.     

Electrospinning of fucoidan/chitosan/poly(vinyl alcohol) scaffolds for vascular tissue engineering

The formation of thrombosis has limited the applications of small diameter vascular in cardiovascular diseases. In order to improve the anticoagulant activities of scaffolds, this study combined fucoidan with CS/PVA and investigated the complete physicochemical and mechanical characterization of the scaffolds to evaluate the feasibility of Fucoidan/CS/PVA scaffolds used in vascular tissue engineering. The SEM graphs show a well defined and interconnected pore structure and the nanofiber diameters are ranging from 341 nm to 482 nm. After immersing in PBS for 5 days, the tensile strength of the crosslinked scaffolds was 722±38 kPa while the elongation at break was 35.5±1.6 %. Besides, added with fucoidan, the scafflolds showed lower rate of plate adhesion (14.75±2.10 %) and markedly prolonged the APTT and TT. Furthermore, owing to the great water uptake ability, sufficient porosity, enhanced drug release and low cytotoxicity, the Fucoidan/CS/PVA scaffolds might be used for vascular tissue engineering with good prospect.     

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.     

Organic-inorganic hybrid of chitosan/poly (vinyl alcohol) containing yttrium(III) membrane for the removal of Cr(VI)

In this present study, an organic-inorganic hybrid membrane was prepared by embedding yttrium(III) into chitosan matrix for the removal of Cr(VI) from aqueous solutions. Several techniques, including fourier infrared spectrum (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD), and transmission electron microscope (TEM) are employed to characterize the properties of the membrane. The mechanical properties of the membrane were also examined. The chitosan/poly(vinyl alcohol) containing yttrium(III) (CY) membrane was experimentally used for the removal of Cr(VI) ions from aqueous solution under the optimized conditions. The results showed that the adsorption capacity for the removal of Cr(VI) ions was enhanced when yttrium(III) was introduced. The adsorption data from the experiment were fit well by Langmuir isotherm. Based on Langmuir model, q _m was calculated to be 38.48 mg g^?1. Kinetic study results indicated that the adsorption process followed a pseudo-second-order kinetics.     

Synthesis and characterization of electrically conductive composite films of polypyrrole/poly(acrylonitrile-co-styrene)

Homogeneus Polypyrrole (PPy)/poly(acrylonitrile-co-styrene) (SAN) composite thin films were prepared by chemical polymerization of pyrrole on poly(acrylonitrile-co-styrene) matrix. Ce (IV) is used as an oxidant for in-situ polymerizion of pyrrole on SAN matrix, having an advantageous over the impregnation method. The formation and incorporation of PPy in the copolymer matrix were confirmed by FTIR-ATR and UV-Visible spectrophotometric measurements. Thermal analyses showed that after polymerization of Py in copolymer matrix, thermal behavior of SAN was changed and derivative of weight loss at this temperature was increased by increasing of PPy content. XPS and FTIR-ATR analysis of composite films indicated cerium salt with nitrate ion acted as a dopant. The increase in the AC electrical conductivity of the PPy/SAN composites over pure SAN was observed. At lower frequency up to 10⁵ Hz, conductivity was shown an independent behavior from frequency; but at high frequencies (10⁵–10⁷ Hz), dependence on frequency was explained by polaron and bipolaron formations of PPy. The dispersion of PPy particles in copolymer matrix was proven by SEM, AFM and digital camera. By the increase of PPy content in the composite films, increase in AC conductivities, and decrease in dielectric constants and loss were observed.     

Carbon nanotube/poly(vinyl alcohol) fibers with a sheath-core structure prepared by wet spinning

A method for manufacturing sheath-core structured fibers was developed using wet spinning techniques. The core portion of a fiber was prepared using a carbon nanotube (CNT) solution while the sheath used a fiber-forming polymer such as polyvinyl alcohol (PVA). Preparation methods of CNT solutions were investigated and it was found that dispersivity and concentration played an important role in the formation and spinning of fiber??s core. CNT solution prepared using a surfactant with high molecular weight such as sodium lignosulfonate (SLS) was most effective and the CNT concentration was as high as 30 g/l. Fiber processing conditions were optimized and it was determined that stretching fibers in the coagulation bath was a significant step in the formation of a solid and well structured core. Drawn fibers were so strong and flexible that they could be woven into a fabric for potential use as a pressure sensor. These results are relevant for practical applications, such as the development of large-area fabric sensors. Furthermore, the described procedure to produce sheath-core CNT fibers is scalable as wet spinning methods have been widely used in the fiber industry.