Jianjun Wang

Investigation of a-PVA/s-PVA hydrogels prepared by freezing-thawing method

The hydrogels of atactic poly (vinyl alcohol) (a-PVA) and syndiotactic poly (vinyl alcohol) (s-PVA) with different blend ratios were prepared by freezing-thawing processes. The effect of s-PVA on gelation behavior of the blend was investigated in terms of gelation temperature (Tgel) and hydrogel melting temperature (Tgm). And swelling behavior, crystallization, thermal properties, morphology of the blend hydrogels were also studied. With the increase of s-PVA, Tgel of the blend solution and Tgm of the blend hydrogels increase. Both crystallinity and crystallite dimensions based on the XRD profiles are nearly monotonically increasing functions of s-PVA content. FTIR results indicate the number of hydrogen bonds raises with s-PVA increasing. DSC results demonstrate s-PVA favors improvement of hydrogels thermal stability. According to SEM images of hydrogels, the increase of cross-linking caused by s-PVA in the blend hydrogels results in denser structure, which in turn leads to increased gel fraction (G) and Hardness. 50/50 (a-PVA/s-PVA) blend hydrogel has a denser structure with EWC of 73.6 %, hardness of 22.8 HA and Tm of 236.15 °C. The result indicates blending a-PVA and s-PVA is a useful method to form the hydrogel having good thermal stability and relative high degree of swelling.

Preparation and Antibacterial Activity of Poly (vinyl Alcohol)/Silk Fibroin Composite Nanofibers Containing Silver Nanoparticles

Silk fibroin (SF) and polyvinyl alcohol (PVA) solutions were prepared respectively by formic acid and deionized water as solvent, the solutions were then blended, and after that AgNO3 was added. The PVA/SF/AgNO3 solution was electrospun to form nanofibers. A number of particles were generated on the surface of nanofibers during electrospinning, which was confirmed by transmission electron microscopy (TEM). The diameter distribution of the nanofibers was narrow and the particles were nano-sized and well-dispersed. X-ray diffraction (XRD) patterns of the composite nanofibers indicated that the component of the nanoparticles was silver. By annealing the composite nanofibers at 155°C for 5 minutes, the silver nanoparticles possibly clustered into the larger size. The size of Ag nanoparticles was 2.25nm without post treatment, and this value increased to 3.76nm after the heat treatment. The antibacterial activity of the heat-treated PVA/SF composite nanofibers containing Ag nanoparticles was evaluated and the resultant nanofibers showed strong antimicrobial activity on Staphylococcus aureus and Escherichia coli. Moreover, the antibacterial PVA/SF composite nanofibers containing Ag nanoparticles have the possibility to be used in wound dressing due to the electrospun PVA nanofibers could preserve the web structure in water after the heat treatment.

Preparation of poly(vinyl alcohol) core/sheath micro/nano composite fibers containing silver nanowires

Micro/nano composite fibers with single microfibers as cores and nanofibers as sheaths, were successfully prepared by combining wet spinning with electrospinning. Poly(vinyl alcohol) (PVA) solution doped with silver nanowires (AgNWs) was wet spun to prepare PVA/AgNWs microfibers, and they were then functioned as the grounded collector during electrospinning process, on which nanofibers were deposited under the effect of electric field force to form a core/sheath structure. The PVA/AgNWs microfibers were part of the electrospinning device, as well as a component of the micro/nano composite fibers at the same time. The addition of a small amount of AgNWs increased the electrical conductivity of the core fibers, and led to the uniformly distributed nanofiber sheaths around the cores. The thickness of the nanofiber sheaths was controlled by the electrical conductivity of the PVA/AgNWs microfibers, and the conductivity was influenced by AgNWs content and fiber draw ratio. When AgNWs content was 0.75 wt%, the electrical conductivity of the PVA/AgNWs microfibers reached maximum, which was most beneficial to attract nanofibers. The carefully designed micro/nano composite fibers may have great potential in a broad range of fields.

Preparation and Characterization of pH-Responsive Poly(Vinyl-Alcohol)/Sodium Carboxymethylcellulose Nanofibers

pH-sensitivity nanofibers composited of poly (vinyl alcohol) (PVA) and sodium carboxymethylcellulose (Na-CMC) were prepared by electrospining. The structure, properties, and morphology of the nanofibers were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray differential (XRD), scanning electron microscopy (SEM) and pH-sensitivity testing. It was found that the reswelling of the nanofibers was pH-responsive and relied on the content of Na-CMC. FTIR spectroscopy of the nanofibers confirmed that hydrogen bonds were formed between PVA and Na-CMC which may cause the stable increase of pH-sensitivity. XRD peaks gradually weakened and broadened with the increase of Na-CMC content, indicating the decrease of crystallinity. Besides, the morphology of the PVA/ Na-CMC nanofibers was affected by the content of Na-CMC.

Pre-Oxidation Nanofibers from Acrylonitrile-Acrylamide Copolymers Synthesized by Solvent-Water Polymerization

Solvent-water suspension free-radical polymerization method was used to synthesize acrylonitrile(AN)-acrylamide(AM) copolymers in this paper. The copolymerization was carried out with azobisisobutyronitrile (AIBN) as an initiator and dimethysulfoxide (DMSO)/ water solution as solvents at a constant monomer ratio (AN:AM(wt)=85:15). The ratio(wt) AN:AM=100:0 was also be used for a comparison. The structure and properties of the copolymers was studied by fourier transform infrared (FT-IR), X-ray diffraction (XRD) and thermogravimetry(TG). The nanofibers were obtained by electrospinning AN-AM copolymer solution with N,N-Dimethyl acetamide(DMAc) as a solvent. Then, the fibers were pre-oxidized in relaxation state and in air by using an oven. The structure of pre-oxidized nanofibers was investigated by scanning electron microscopy (SEM) and FT-IR. The results showed that the ratio of dimethysulfoxide (DMSO)/water 50/50(v) was optimum for the copolymer properties and nanofiber spinnability as a carbon nanofiber precursor. The copolymer fibers only needed lower preoxidation temperature and shorter preoxidation time to reach the same degree of cyclization due to the introduction of AM.