Effect of the relative humidity on the fibre morphology of polyamide 4.6 and polyamide 6.9 nanofibres

To obtain uniform and reproducible nanofibres, it is important to understand the effect of the different electrospinning parameters on the nanofibre morphology. Even though a lot of literature is available on the electrospinning of nanofibres, only minor research has been performed on the effect of the relative humidity (RH). This paper investigates the influence of this parameter on the electrospinning process and fibre morphology of the hydrophilic polyamide 4.6 and the less hydrophilic polyamide 6.9. First, the electrospinning process and deposition area of the nanofibres is examined at 10, 50 and 70 % RH. Subsequently, the effect of the polyamide concentration and solvent ratio on the fibre morphology is investigated using scanning electron microscopy and differential scanning calorimetry. It was found that the nanofibre diameter decreased with increasing RH. This resulted in less stable crystals for polyamide 4.6 while electrospinning of polyamide 6.9 at higher RH led to slightly more stable crystals. In conclusion, the water affinity of a polymer is an important factor in predicting the nanofibre morphology at different humidities.     

聚酰胺复合膜的改性及其选择渗透性

非对称性的反渗透(RO)聚酰胺(PA)复合膜可以通过溶剂处理方法改性成为渗透汽化(PV)分离有机物水溶液的均相膜．实验选用了PA良溶剂(甲酸、乙酸、磷酸、盐酸、苯酚)作为PA膜的改性剂．溶剂改性条件(改性剂类型、浓度和处理时问)对改性膜的吸着性有明显影响．用质量分数8％的乙酸处理1h的PA膜，较之未改性膜，优先吸水性增强，对水的溶胀率SW增大，对异丙醇的溶胀率SIPA减小．乙酸处理的PA膜的SW与SIPA差值在所有溶剂处理的膜中最大，相应地PV分离IPA水溶液时，膜的分离因子和渗透通量也最大，处理过程溶剂分子与PA高分子链的接触和PA膜中微囊内高分子链段向外运行，是PA膜结构改变的主要因素．溶剂处理改变了膜的结构的机理能很好地解释非对称性RO膜的改性．     

Electrospinning of chitosan nanofibrous structures: feasibility study

In this paper a range of acid aqueous solutions are studied towards their suitability for developing chitosan nanofibres by electrospinning. It was found that parameters such as type of solvent, pH, concentration of chitosan, viscosity, charge density, applied voltage, solution flow rate, distance from nozzle tip to collector surface and time play a role in the characteristics of the obtained nanofibrous structures. After a preliminary study to select the most suitable composition of the chitosan containing solution (90% acetic acid), a detailed study was done to find the optimal conditions for chitosan nanofibrous structure development. Finally long-term experiments were performed, which showed that the formation of the nanofibrous structure distorts the electrical field.     

Preparation of PA12 microspheres with tunable morphology and size for use in SLS processing

Materials technology is currently a great challenge in selective laser sintering (SLS). The development of new method for the preparation of a variety of materials has drawn great attention from both industrial and academic organizations. In this work, we described a simple strategy to prepare polyamide 12 (PA12) microspheres through a modified phase-separation process. The phase separation was conducted by adding ethanol as a poor solvent into a formic acid solution of PA12 pellets with polyvinyl pyrrolidone as a dispersant. The mean diameters of the obtained PA12 microspheres, ranging from tens to hundreds of micrometers, were well controlled by adjusting the amount of ethanol and the phase separation temperature. Further investigation by differential scanning calorimetry demonstrated that the sintering window for PA12, between the onset temperatures of crystallization and melting, was drastically stretched during the microsphere formation process. The PA12 particle size and morphology, together with the wider sintering window of the microspheres, demonstrated that the obtained PA12 powder was suitable for SLS processing.     

Blends of poly(methyl methacrylate) and polyamides

The morphology of PMMA blends with different polyamides (PA-6, 6/9 and 12) was investigated by transmission electron microscopy, recognizing PA-6/PMMA as the most miscible pair. Blends of these polymers were prepared from solutions in m-cresol and formic acid and the morphology was highly dependent on the solvent. The morphology and the segregation degree of extruded PA-6/PMMA blends was investigated by scanning electron microscopy and dynamic-mechanical analysis. The compatibilization succeeded by the introduction of a block copolymer of polyamide and poly(ethylene oxide).     

Fabrication and characterization of PCL/gelatin composite nanofibrous scaffold for tissue engineering applications by electrospinning method

In the present study, composite nanofibrous tissue engineering-scaffold consisting of polycaprolactone and gelatin, was fabricated by electrospinning method, using a new cost-effective solvent mixture: chloroform/methanol for polycaprolactone (PCL) and acetic acid for gelatin. The morphology of the nanofibrous scaffold was investigated by using field emission scanning electron microscopy (FE-SEM) which clearly indicates that the morphology of nanofibers was influenced by the weight ratio of PCL to gelatin in the solution. Uniform fibers were produced only when the weight ratio of PCL/gelatin is sufficiently high (10:1). The scaffold was further characterized by Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric (TG) analysis, and X-ray diffraction (XRD). FT-IR and TG analysis indicated some interactions between PCL and gelatin molecules within the scaffold, while XRD results demonstrated crystalline nature of PCL/gelatin composite scaffold. Cytotoxicity effect of scaffold on L929 mouse fibroblast cells was evaluated by MTT assay and cell proliferation on the scaffold was confirmed by DNA quantification. Positive results of MTT assay and DNA quantification L929 mouse fibroblast cells indicated that the scaffold made from the combination of natural polymer (gelatin) and synthetic polymer (PCL) may serve as a good candidate for tissue engineering applications.     

Production of electrospun gelatin nanofiber by water-based co-solvent approach

In this study, gelatin, was successfully electrospun from a newly developed water-based co-solvent composed of ethyl acetate and acetic acid in water. Since natural polymers including gelatin exhibit limited solubility in water, toxic or highly acidic solvents are normally used to dissolve them for electrospinning. Instead of using those solvents, we used ethyl acetate in concert with acetic acid in water, and investigated the beneficial effect of its use in terms of the spinnability of the nanofiber and the acidity of the solvent. The replacement of acetic acid with ethyl acetate was observed to improve the spinnability of the nanofiber by reducing the surface tension of the solution as well as to increase the pH of the solvent significantly. The optimal composition of the co-solvent was found to correspond to a ratio of ethyl acetate to acetic acid of 2:3. Under this solvent condition, the gelatin could be dissolved at concentrations of up to ∼11 wt% and electrospun successfully to produce nanofibers with various diameters (47–145 nm on average) depending on the gelatin concentration. The water-based co-solvent method proposed herein may be useful for generating other nanofibrous natural polymers as well as being applicable in delivery systems for bioactive molecules within the nanofiber matrices.     

H_3PW_(12)O_(40)/PMMA/PA6夹层复合纳米纤维膜的制备及光催化性能

采用静电纺丝法制备了磷钨酸(H_3PW_(12)O_(40))/聚甲基丙烯酸甲酯(PMMA)/尼龙6(PA6)夹层复合纳米纤维膜,并通过扫描电镜、X射线能谱和红外光谱对其形貌和结构进行表征。结果显示,H_3PW_(12)O_(40)存在于夹层膜的上层与下层,且其Keggin结构未遭到破坏。与H_3PW_(12)O_(40)粉末和H_3PW_(12)O_(40)/PMMA复合纳米纤维膜相比,夹层膜对甲基橙(MO)具有更高的光催化活性。夹层纳米纤维膜易于回收并能重复使用,循环使用3次后光催化活性无明显下降,主要归咎于H_3PW_(12)O_(40)稳定地负载于纳米纤维膜中。因此,H_3PW_(12)O_(40)/PMMA/PA6夹层复合纳米纤维膜在水污染治理领域具有潜在的实际应用价值。     

Electrospun nanofibrous biodegradable polyester coatings on Bioglass-based glass-ceramics for tissue engineering

Biodegradable polymeric nanofibrous coatings were obtained by electrospinning different polymers onto sintered 45S5 Bioglass^®-based glass-ceramic pellets. The investigated polymers were poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) and a composite of poly(caprolactone) (PCL) and poly(ethylene oxide) (PEO) (PCL–PEO). The fibrous coatings morphology was evaluated by optical microscopy and scanning electron microscopy. The electrospinning process parameters were optimised to obtain reproducible coatings formed by a thin web of polymer nanofibres. In-vitro studies in simulated body fluid (SBF) were performed to investigate the bioactivity and mineralisation of the substrates by inducing the formation of hydroxyapatite (HA) on the nanofiber-coated pellets. HA crystals were detected on all samples after 7 days of immersion in SBF, however the morphology of the HA layer depended on the characteristic fibre diameter, which in turn was a function of the specific polymer-solvent system used. The bioactive and resorbable nanofibrous coatings can be used to tailor the surface topography of bioactive glass-ceramics for applications in tissue engineering scaffolds.     

Fabrication and characterization of PCL/gelatin/chitosan ternary nanofibrous composite scaffold for tissue engineering applications

In the present study, we have fabricated a ternary composite nanofibrous scaffold from PCL/gelatin/chitosan, by electrospinning technique, using a solvent system—chloroform/methanol for polycaprolactone (PCL) and acetic acid for gelatin and chitosan, for tissue engineering applications. Field emission scanning electron microscopy (FE-SEM) was used to investigate the fiber morphology of the scaffold and it was found that the fiber morphology was influenced by the concentrations of PCL, gelatin, and chitosan in polymer solution during electrospinning. X-ray diffraction, Fourier transform infrared, and thermogravimetric (TG) analysis results showed some interactions among the molecules of PCL, gelatin, and chitosan within the scaffold. In-vitro cell culture studies were done by seeding L929 mouse fibroblasts on fabricated composite scaffold, which confirmed the cell viability, high cell proliferation rate, and cell adhesion on composite scaffold as indicated by MTT assay, DNA quantification, and FE-SEM analysis of cell-scaffold construct. Thus, the ternary composite scaffold made from the combination of PCL (synthetic polymer), gelatin, and chitosan (natural polymer) may find potential application in tissue engineering.     

Advanced nanofibrous textile-based dressing material for treating chronic wounds

In the present work, an electrospun nanofibrous textile composed of polyurethane (PU), sodium bicarbonate (\(\hbox {NaHCO}_{3}\)) and pantothenic acid (PA) is developed for treating chronic wounds. Wounds are a common health problem and in particular, the chronic wounds such as vascular ulcers, diabetic ulcers and pressure ulcers cause a large number of morbidity and mortality. The main problems of the chronic wounds are prolonged inflammation phase and presence of acidic environment. These events deactivate the operation of growth factors and also the progression of natural healing mechanism. Hence, various types of advanced textile-based dressings are developed to address the clinical complications associated with chronic wound management. The prepared electrospun scaffolds were characterized to study their physicochemical and haemocompatible properties. The scanning electron microscopy micrographs depicted continuous, smooth-interconnected nanofibrous morphology of PU–NaHCO\(_{3}\)–PA scaffolds. The Fourier transform infrared spectroscopy spectra indicated the addition of NaHCO\(_{3}\) and PA-based hydrophilic chemical groups, which significantly enhanced the wettability of the composites. Further, the PU–NaHCO\(_{3}\)–PA composite membrane inferred to have a highly porous structure with the mean porosity of 79.4 ± 4.8%, which may provide a conducive environment for adherence and proliferation of skin cells. The composite scaffold also offers a highly haemocompatible surface by delaying coagulation of blood through contact activation pathways and by limiting red blood cells damage. Therefore, the excellent physicochemical properties, blood compatibility and the delivery of PA are anticipated to speed up the impaired healing process of chronic wounds.     

Nanofibre fabrication in a temperature and humidity controlled environment for improved fibre consistency

Fabricating nanofibres with reproducible characteristics is an important demand in the membrane industry in order to establish commercial viability. In this study, the effect of controlled atmospheric conditions on electrospun cellulose acetate (CA) nanofibres was evaluated for temperatures ranging 17.5–32.5 °C and relative humidity ranging 20–70%. CA solution (0.2 g/mL) in a solvent mixture of acetone/dimethylformamide/ethanol (2:2:1) was electrospun into nonwoven fibre mesh with the fibre diameter ranging from 150 nm to 1 μm. The resulting nanofibres were analysed by differential scanning calorimetry, showing a correlation of reducing melt enthalpy with increasing atmospheric temperature. The opposite was seen with increasing atmospheric humidity, which conferred increasing melt enthalpy. Analysis of scanning electron microscopy images provided a correlation of reducing average fibre diameter with increasing atmospheric temperature and increasing fibre diameter with increasing atmospheric humidity. These results correlate with the melt enthalpy results, suggesting that finer CA nanofibres infer a lower melt enthalpy. Together these studies provide strong evidence that the controlled atmospheric conditions affect the fibre diameter of the resulting electrospun nanofibres. A salient observation in this study was that increased humidity reduced the effect of fibre beading yielding a more consistent and therefore better quality of fibre. This has apparent implications for the reproducibility of nanofibre production and offers a new method of controlling fibre morphology. This study has highlighted the requirement to control atmospheric conditions during the electrospinning process to fabricate reproducible fibre mats.     

Electrospinning of gelatin and gelatin/poly(l-lactide) blend and its characteristics for wound dressing

Gelatin nanofibres were electrospun from its aqueous acetic acid solution. Electrospinning parameters, such as concentration of aqueous acetic acid and gelatin solutions, electric field and spinning distance, were examined to investigate the electrospinnability of gelatin solutions and the morphology of gelatin nanofibrous mats. Nanofibrous mats from poly(l-lactide) (PLLA) and gelatin/PLLA solutions were obtained. The electrospun mats showed controlled evaporative water loss, promoted fluid drainage ability, and excellent biocompatibility, and therefore have a potential application as wound dressing.     

Dynamics of absorbed water in model composites of polyamide 6 and carbon fibre evaluated by differential scanning calorimetry

The crystallization and subsequent melting behaviour of absorbed water in the model composites of polyamide 6 (PA6) and carbon fibre were investigated by differential scanning calorimetry (DSC) in comparison with those in neat PA6, using the small rectangular specimens exposed to water at 90 °C. In the DSC curves of PA6 any exothermic peaks of crystallization and endothermic ones of melting were not observed, but a step corresponding to glass transition was observed at about −30 °C during the heating process. Thus water absorbed by neat PA6 was recognized as non-freezing bound water which does not crystallize, probably due to the strong interaction with the polyamide chains. On the other hand, for the model composite several exothermic peaks were clearly observed at temperatures ranging from −10 to −20 °C, and their intensity was increased with increasing the fibre content. The distinct endothermic peaks were detected around at 0 °C during the reversed heating process. The glass transition temperature was not affected by adding the carbon fibre. Comparing with the result of neat PA6 indicates that in the model composite water exists in a state near free water, besides the non-freezing bound water dispersed in the matrix polyamide. It is further implied that water is mainly accumulated in the matrix/fibre interfacial region with some microstructural heterogeneties or defects, in which the water molecules can easily move under much weaker interaction with the polyamide chains.     

A comparative study on copper corrosion originated by formic and acetic acid vapours

The copper corrosion rate and products originated by the action of formic and acetic acid vapours at a 100% relative humidity were studied. Copper specimens were exposed to formic and acetic acid vapours for a period of 21 days. Five formic and acetic acid vapour concentrations (10, 50, 100, 200 and 300 ppm) were tested. Copper corrosion rates of up to 1300 mg m^–2 d^–1 (mmd) for formic acid and up to 2300 mmd for acetic acid were measured using a gravimetric method. The corrosion-product layers were characterised using electrochemical, X-ray powder diffraction and scanning electron microscopy techniques. Some of the compounds identified were: cuprite (Cu₂O), for both acids; cupric hydroxide monohydrate (Cu(OH)₂ · H₂O) and copper formate tetrahydrate (Cu(HCOO)₂ · 4H₂O), for formic acid; and copper acetate dihydrate (Cu(CH₃COO)₂ · 2H₂O) and copper hydroxide acetate dihydrate (Cu₄(OH)(CH₃COO)₇ · 2H₂O), for acetic acid.     

Tungstophosphoric acid supported onto hydrous zirconia: Physicochemical characterization and esterification of 1ℴ and 2ℴ alcohol

The Keggin type heteropolyacid, 12-tungstophosphoric acid (PW), was supported onto hydrous zirconia (Z) by impregnation method and designated as ZH₃. The ZH₃ was calcinated at 300°C and 500°C and designated as ZH₃₃ and ZH₃₅, respectively. The resulting materials were characterized by FTIR, diffuse reflectance spectroscopy (DRS), XRD, surface area measurement (BET method) and particle size distribution. The surface morphology was studied by scanning electron microscopy. The acidity of all materials was evaluated by carrying out chemisorption of ammonia and esterification of 1ℴ alcohol (n-butanol) with different acids like formic acid, acetic acid and propionic acid and 2ℴ alcohol (cyclohexanol, iso-butanol) with acetic acid. Above studies show the high dispersion of HPA in a non-crystalline form on the support as well as uniform distribution of particles of ZH₃ which contains 30% 12-tungstophosphoric acid. It also shows that when ZH₃ was calcinated at 500°C, it possesses highest acidity for both chemisorption of NH₃ as well as esterification reactions.     

Stereological analysis of the poly-(dl-lactide-co-glycolide) submicron sphere prepared by solvent/non-solvent chemical methods and centrifugal processing

Fine particles made of poly(lactide-co-glycolide) (DLPLG) are excellent candidates for controlled release of delivering drugs and genes, because of their degradable nature. The preparation of DLPLG submicron spheres poses serious challenges that are not necessarily present when preparing macroparticles. In the present paper, DLPLG powder is produced with chemical method using solvent/non-solvent systems with subsequent centrifugation of the solution. The samples were characterized by infrared spectroscopy (IR), scanning electron microscopy (SEM) and stereological analysis. By changing the aging time with non-solvent and time and velocity of the centrifugal processing, it is possible to influence on the morphology and uniformity of the copolymer particles. Powder of the series with short aging time with non-solvent and longest time and velocity of the centrifugal processing has smallest particles and highest uniformity, where mean particles sizes were between 150 nm and 230 nm depending on which stereological parameters are considered (D _max, maximal diameters, feret X or feret Y).     

溶液浓度和非溶剂比例对PVC膜形貌和疏水性能的影响

目的 研究溶液质量分数和非溶剂体积分数对PVC薄膜表面形貌和疏水性能的影响,以获得具有超疏水表面的PVC薄膜。方法 以四氢呋喃为良溶剂、乙醇为非溶剂,利用非溶剂诱导相分离的原理,采用旋涂法在玻璃基底上制备超疏水的聚氯乙烯（PVC）涂膜;通过对PVC样品的疏水性、表面形貌、结晶性能和热性能进行分析,探究溶液质量分数以及非溶剂的体积分数对PVC样品性能的影响。结果扫描电镜和接触角测试表明,添加一定体积分数的乙醇使得所制备的PVC样品形成了多孔膜层以及纳米级聚合物球粒,从而提高了PVC样品的疏水性。XRD测试结果表明,添加乙醇并不会改变PVC样品的无定形结构。结论 PVC溶液质量分数对所制备PVC样品的疏水性能和表面结构没有明显影响,乙醇体积分数为30%～40%时,可形成表面水接触角大于150°的超疏水表面。     

聚乳酸复合纳米纤维创面敷料的制备及性能

采用静电纺丝技术制备了聚乳酸(PLLA)纳米纤维毡、壳聚糖/PLLA纳米纤维毡和明胶/PLLA纳米纤维毡。利用扫描电镜(SEM)、图像分析软件等手段研究了纳米纤维微观形貌,并研究各种创面敷料的吸水性、保水性和水蒸汽通透性等性能。结果表明,壳聚糖/PLLA、明胶/PLLA复合纳米纤维毡的吸水性和保水性有显著提高,水蒸汽通透性略有下降,是理想的创面敷料材料。     

乳化添加非溶剂法制备复合高分子微胶囊的研究

利用Ｏ／Ｗ型乳化添非溶剂法，研究制备水溶性药物茶碱为核物质，乙基纤维素为壳物质的微胶囊的方法及特性。