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

Ultrafine fibers of chitosan/poly(vinyl alcohol)/poly(vinyl pyrrolidone) (CS/PVA/PVP) were prepared via electrospinning. The structure and morphology of CS/PVA/PVP ultrafine fibers was characterized by the Fourier transform infrared (FT-IR) spectroscope and scanning electron microscope (SEM). Furthermore, the effects of the concentration of PVA, PVP and the electrospinning voltage on the morphology of ultrafine fibers were investigated the the SEM. When the concentration of PVA was at the range of 30wt%–40wt%, ultrafine fibers could be obtained. The diameter distributions of ultrafine fibers decreased when the electrospinning voltage increased from 20 to 30 kV. The rough surface fibers could be obtained after etching with CHCl₃.     

Photo-induced liquid crystal alignment of poly(vinyl cinnamate) and fluorinated polyimide blends

Liquid crystal(LC) alignment properties were mainly affected by surface properties of alignment layers. In our previous work, we prepared poly(vinyl cinnamate) (PVCi) and polyimide blend alignment layer for thermally stable LC alignment. In this work, we utilized fluorinated polyimide for blend alignment layers in order to modify surface properties of alignment layers. For this purpose, polyimides containing fluorine unit were synthesized and used for the blend alignment layers. Fluorine containing diamine, 4,4′-bis[2-(4-aminophenyl)hexafluoropropyl]-diphenyl ether(BDAF), is used for the polyimide synthesis. We prepared the fluorinated polyimide and PVCi blend alignment layers and investigated the effect of fluorine on the LC alignment properties and pretilt angle of LC.     

聚乙烯醇缩丁醛超滤膜的制备

用聚乙烯醇缩丁醛(PVB)作为本体高分子材料,用浸没沉淀相转化法制备PVB不对称超滤膜;扫描电镜照片显示所制膜的超滤结构.研究了PVB本体浓度、制膜间隙、凝胶浴温度以及乙酸添加剂等因素对PVB不对称超滤膜性能的影响;比较了乙酸及聚乙烯基吡咯烷酮(PVP)作为添加剂对大孔径PVB超滤膜皮层结构的影响.当PVB本体浓度为12%时,膜的纯水通量及牛血清白蛋白(BSA)溶液通量分别为876.4 L/(m2.h)和89.8 L/(m2.h),此时膜对BSA的截留率为96.8%;PVB膜纯水通量随着制膜间隙的增加及凝胶浴温度的上升而降低;乙酸及PVP的添加均提高了PVB超滤膜的纯水通量,通量增加幅度分别为136%和171%.     

Preparation of poly (vinyl alcohol) fibers strengthened using multiwalled carbon nanotubes functionalized with tea polyphenols

Poly (vinyl alcohol) (PVA) fibers were strengthened using multiwalled carbon nanotubes (MWCNTs) functionalized using a green modifier tea polyphenols (TP). MWCNTs were first modified using TP to increase their dispersity in dimethyl sulfoxide (DMSO)/water solution, and then PVA was added to the dispersion to form new dispersion of PVA/MWCNTs/TP/DMSO/water. The homogeneous dispersion was extruded through a spinning hole into cold methanol to form continuous fibers using gel-spinning process followed by a hot-drawing. The tensile strength of the well-oriented PVA/MWCNTs composite fibers containing merely 0.6 wt% of MWCNTs was surprisingly more than 2.6 times that of pure PVA fiber. Structure characterization showed that well-dispersed MWCNTs were caused by the interfacial interactions between PVA matrix and MWCNTs through the bridge effect of TP.     

Characterization of hydrogel blends of poly(vinyl pyrrolidone) and poly(vinyl alcohol-vinyl acetate)

Hydrogel blends were prepared from water-soluble polymers of poly(vinyl alcohol-vinyl acetate) and poly(vinyl pyrrolidone). The method of preparation was optimized and different compositions of blends were characterized. The effect of thermal treatment and the introduction of an aldehydic crosslinking agent in the blend was also studied. The swelling characteristics of the various compositions, their thermal behaviour and the state of water was examined. Mechanical properties of the hydrogels were determined and it was observed that blends containing glutaraldehyde produced materials with good mechanical integrity and high water contents.     

丙烯腈-丙烯酸共聚物超细纤维的制备及其pH响应性能的研究

以N,N-二甲基甲酰胺(DMF)为溶剂,通过气流-静电纺丝法制备了具有pH响应性能的丙烯腈-丙烯酸共聚物(Poly(AN-co-AA))超细纤维。利用扫描电镜(SEM)对超细纤维形貌进行表征,研究了聚合单体中丙烯酸(AA)的含量、纺丝溶液中L-苯丙氨酸(L-Phe)的含量和浸泡时间对Poly(AN-co-AA)超细纤维形貌的影响,并从缓冲溶液的pH值及其与纤维直径变化的可逆性等方面研究了Poly(AN-co-AA)超细纤维的pH响应性能,确定了制备具有pH响应性能的Poly(AN-co-AA)超细纤维的最佳工艺参数。     

Preparation and characterization of nano-hydroxyapatite/poly(vinyl alcohol) hydrogel biocomposite

Nano-hydroxyapatite (n-HA) was used to make a new hydrogel biocomposite with poly(vinyl alcohol) (PVA) by a unique technique. Fourier transform infrared absorption spectra (IR), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TG) and burning test were used to test the physical and chemical characteristics of the composite. Chemical binding between inorganic n-HA and poly(vinyl alcohol) was investigated and discussed. The results showed that the composite had good thermal stability and homogeneity. The n-HA crystals were uniformly distributed in the polymer matrix. The improved n-HA/PVA hydrogel could be used as an artificial articular cartilage, showing a promoting prospect.     

Comparison of porous poly (vinyl alcohol)/hydroxyapatite composite cryogels and cryogels immobilized on poly (vinyl alcohol) and polyurethane foams for removal of cadmium

Three novel adsorbents of hydroxyapatite/poly (vinyl alcohol) (HAp/PVA) cryogel, HAp/PVA cryogel immobilized on PVA foam and HAp/PVA cryogel immobilized on polyurethane (PU) foam have been investigated to compare the morphology and sorption performances for removal of cadmium. The adsorption kinetics was interpreted by double-exponential model, pseudo-first-order model and pseudo-second-order models. The equilibrium time was found to be 36, 24, and 12 h for cryogel, cryogel immobilized on PVA foam and PU foam, respectively. The adsorption was found to follow Langmuir isotherm model and the maximum sorption capacity was estimated to be 53.3, 53.1 and 47.7 mg g(-1) for cryogel, cryogel immobilized on PVA foam and PU foam. The effects of HAp/PVA ratio and drying method on cadmium sorption were also studied. The difference of adsorption kinetics model and equilibrium time among the three adsorbents was suggested to be ascribed to different pore size. Oven-dried HAp/PVA cryogel immobilized on PU foam was preferable due to short equilibrium time and good sorption ability.     

Dynamic mechanical characterization of hydrogel blends of poly(vinyl alcohol-vinyl acetate) with poly(acrylic acid) or poly(vinyl pyrrolidone)

Transparent hydrogels were prepared by blending solutions of poly(vinyl alcohol-vinyl acetate) with either poly(acrylic acid) or poly(vinyl pyrrolidone) in the presence of glutaraldehyde as a crosslinking agent. The network obtained from the poly(vinyl pyrrolidone) system was subjected to various thermal treatments, the effects of which have been studied. Dynamic mechanical analysis was used to characterize the hydrogels and to establish the suitability of these blends for use in biomedical applications. The swelling behaviour was followed under dynamic loads as well as by mass difference. Different frequencies were used to study the dynamic properties of the hydrogel blends which showed an increase in storage modulus with increasing frequency. A comparison of modulus values obtained dynamically were in agreement with data obtained mechanically in tension.This paper was accepted for publication after the 1995 Conference of the European Society of Biomaterials. Oporto, Portugal, 10–13 September.     

Melt-spun poly(tetrafluoroethylene) fibers

The recent discovery of melt-processable poly(tetrafluoroethylene) (PTFE) allows for common thermoplastic-polymer processing technologies to be applied to this unique polymer, which heretofore was considered to be highly intractable. In this paper, we report simple melt-spinning of monofilaments of a set of melt-processable (modified) PTFE grades with weight-average molar masses (M _w) ranging from 77 to 292 kg/mol. Fibers were spun at 380 °C at draw-down ratios of up to 2,750, yielding filaments of linear densities as low as 0.8 tex, corresponding to a diameter of ∼20 μm. The maximum Young’s modulus and tensile strength of as-spun fibers produced in this study were 91.7 cN/tex (1,972 MPa) and 12.0 cN/tex (258 MPa), respectively, accompanied by a strain to break of 24%.     

Preparation of CuS nanoparticles embedded in poly(vinyl alcohol) nanofibre via electrospinning

Poly(vinyl alcohol) (PVA)/CuS composite nanofibres were successfully prepared by electrospinning technique and gas-solid reaction. Scanning electron microscopic (SEM) images showed that the average diameter of PVA/CuS fibres was about 150–200 nm. Transmission electron microscopy (TEM) proved that a majority of CuS nanoparticles with an average diameter of about 15–25 nm are incorporated in the PVA fibres. X-ray diffraction (XRD) analyses and electron diffraction pattern also revealed the forming of CuS crystal structure in the PVA fibres.     

Graphite/poly (vinyl alcohol) hydrogel composite as porous ringy skirt for artificial cornea

Graphite/poly (vinyl alcohol) (PVA) hydrogel composites, which were designed as the porous ringy skirt surrounding the transparent core of a novel artificial cornea, were prepared by using the freeze/thawing process and the particle-leaching technique. The properties of the composites, including the water content, the mechanical strength, the porous architecture and the interactions between the graphite and PVA, were investigated. The tissue responses to the composite and pure PVA hydrogel were studied by in vivo implantation in the dorsal muscles of mice. The results showed that chemical interactions were present between the graphite and PVA in the composite, which benefited the combination of the two phases and enhanced the uniform distribution of graphite particles in the PVA matrix. However, the present of graphites in the PVA hydrogels reduced the tensile strength, elongation at break and water content of the composite. Moreover, the porous graphite/PVA hydrogel composite had interconnective pore structure with high porosity and enough mechanical strength. According to the histological analysis of 1 week and 12 weeks post-implantation, the graphite/PVA hydrogel composites showed less inflammatory reactions than the PVA hydrogels at the 1 week post-implantation. Moreover, compared to pure PVA hydrogel, the graphite/PVA hydrogel composite exhibited enhanced migration and infiltration of cells, and more neovascularization and tissue ingrowth. These in vivo characteristics will be beneficial for the long-term biofixation of artificial cornea. Therefore, the porous graphite/PVA hydrogel composite has a potential to be used as novel artificial cornea skirt.     

Effect of annealing on aqueous stability and elastic modulus of electrospun poly(vinyl alcohol) fibers

Electrospun poly(vinyl alcohol) (PVA) fibers rapidly dissolve in water. Their aqueous stability can be improved by annealing using a combination of controlled temperature and treatment time. The increase in aqueous stability of the PVA fibers is associated with an increase in PVA crystallinity and is defined by X-ray diffraction and the ratio of the Fourier transform infrared spectroscopy band intensities at 1141 and 1425 cm⁻¹. A ratio of intensity of these two infrared bands ≥2.5 or ~75% and above in the degree of crystallinity as determined by X-ray diffraction indicates fiber stability in water. Annealing treatment also results in an increase in the stiffness of the fibers. At a treatment temperature of 135 °C for 4 h, the elastic modulus of the fiber increased by 80%. This information is useful when these fibers are being considered for applications in an aqueous environment such as membrane filter or tissue scaffold.     

Gel-drawn fibres of poly(vinyl alcohol)

Semi-crystalline gels of several samples of poly(vinyl alcohol) were made from solutions in which the polymer concentration varied from 2.0 to 15.0%. Entanglement density in the material was in this way reduced from the melt entanglement density. When gels were partially dried and drawn isothermally the maximum draw ratio increased with drawing temperature up to 11 to 14 at 140 to 180 C. A meltcast film could be drawn to 6.8 times at 140 C. Drawn material had a crystallinity of 55 to 80%, while that of isotropic material was 20 to 55%. Gels of lower initial concentration (lower entanglement density) could be drawn to greater extensions at a given draw temperature and had better mechanical properties. Young's modulus increased with draw ratio to values very close to those for polyethylene fibres drawn by the same amount. Young's modulus was independent of drawing temperature or degree of crystallinity, but on comparing drawn gels of the same draw ratio, crystallinity and crystalline orientation, those of lower entanglement density had a higher Young's modulus.     

Preparation of poly(vinyl alcohol)-based separator with pore-forming additive for lithium-ion batteries

In this work, poly(vinyl alcohol) (PVA)-based separators with microporous structure were prepared from a casting solution composed of PVA resin, water as solvent, and poly(vinyl pyrrolidone) (PVP) polymer as pore controlling additive by non-solvent induced phase separation (NIPS) wet-process and investigated in lithium-ion batteries. The effects of PVP on the morphology and properties of the separator, such as porosity, electrolyte wettability, thermal stability and battery performance (discharge capacity, C-rate capability and cycleability) were systematically analyzed. Results show that PVP induced more pores on the bottom surfaces and the electrolyte uptake, ionic conductivity was further improved. Finally, a 10 wt% PVA-based separator with PVP solid content of 6 wt% exhibited greatly improved porosity, electrolyte uptake, ion conductivity and thermal resistance, resulting in the cell with high safety performance and matched electrochemical performance. The results demonstrated that the PVA-based separator with PVP as pore controlling additive can be a successful candidate serving as an effective separator for lithium-ion battery. Additionally, the present method of producing the microporous separator for LIBs is simple, environmentally benign and economically viable.     

Preparation and release characteristic of quercetin loaded poly(lactic acid) ultrafine fibers

In this study, poly(lactic acid) (PLA) ultrafine fibers have been prepared by electrospinning method using mix-solvent. The results showed that the variation of solvent ratio (N,N-dimethylformamide (DMF)/Dichloromethane (DCM)) could change the surface morphology of PLA nanofibers. By adjusting the solvent ratio, the quercetin release rate from the fiber membranes could be controlled. Furthermore, by adjusting the PLA concentration, the nanofibers without beads could be obtained. After addition of quercetin to polymer solution, the spindle-shaped beads on the fiber disappeared, but surface morphology of the fiber changed little with increase in quercetin dosage, and the release rate of quercetin increased with increase of quercetin dosage.     

高透明度聚乙烯醇水凝胶的制备、表征及透明机理研究

用二甲基亚砜(DMSO)水溶液通过冷冻/解冻法制备了高透明度聚乙烯醇(PVA)水凝胶,使用差示扫描量热仪(DSC)、紫外吸收光谱、力学性能分析仪、紫外-可见分光光度计等分析了DMSO浓度对聚乙烯醇水凝胶透光率的影响,并表征了PVA水凝胶的含水率、结晶度、力学性能等性质.结果表明,用含量为80%(质量分数)的DMSO水溶液制备的PVA水凝胶得到了高达(99.8±0.2)%透明度,其抗拉强度达到3MPa以上,断裂拉伸率＞600%.研究发现,DMSO与水形成的1DMSO/2H2O网络结构能够限制PVA分子在三维方向的结晶,同时能够促进二维方向PVA晶体的生长.当DMSO含量为80%时,溶液中DMSO与水的比例略＞1:2,存在少量未形成1:2网络结构的DMSO分子,该分子与PVA羟基形成氢键限制了PVA分子在二维方向的结晶,最终导致PVA水凝胶中PVA晶体的体积最小、PVA晶体的数目最多,从而得到了最高的水凝胶透明度和较好的力学性能.     

聚乙烯醇/玉米秸秆微晶纤维素复合膜的制备与性能

采用玉米秸秆微晶纤维素(CSCMC)作为增强剂,生物可降解材料聚乙烯醇(PVA)作为基体,制备了PVA/CSCMC复合膜材料,并对复合膜的结构、热稳定性能、力学性能进行了测试。结果表明,玉米秸秆微晶纤维素可增强复合膜材料的热稳定性能和力学性能。当CSCMC的质量分数为10%时增强效果最佳,与纯的PVA膜相比,复合膜的起始分解温度和最大重量损失率温度分别提高了19.25℃和17.17℃,拉伸强度提高了37.91%,断裂伸长率提高了58.93%。     

Preparation and characterization of poly(vinyl chloride) calcium carbonate nanocomposites via melt intercalation

Calcium carbonate was synthesized by in situ deposition technique and its nano size (35–60 nm) was confirmed by transmission electron microscopy (TEM). Composites of the filler CaCO₃ (micro and nano) and the matrix poly(vinyl chloride) (PVC) were prepared with different filler loadings (0–5 wt%) by melt intercalation. Brabender torque rheometer equipped with an internal mixer has been used for preparation of formulations for composites. The effect of filler content both nano- and micro level on the nanostructure and properties is reported here. The nanostructures were studied by wide angle X-ray diffraction and scanning electron microscopy. The mechanical, thermal, and dynamic mechanical properties of PVC/micro- and nano-CaCO₃ composites were characterized using universal testing machine, thermogravimetric analyzer, and dynamic mechanical analyzer. The results of thermal analysis indicated that the thermal stability of PVC/nano-CaCO₃ composites was improved as compared with corresponding microcomposites, and that of pristine PVC and maximum improvement was obtained at 1 and 3 phr loadings. However, the tensile strength decreased significantly with increase loading of both nano- and micro-CaCO₃, whereas storage modulus and glass transition temperature increased significantly.