In this work, maize starch was used to demonstrate a novel method which enables the preparation of starch films and coatings with good thickness control. 5% starch in de-ionized water (w/v) was ...gelatinized at 120
°C for 30
min, subsequently small quantities of dispersant and ethanol were added and subjected to ultrasonic disruption to make a stable modified starch solution. Electrohydrodynamic behavior of this solution was studied and optimum conditions for film preparation were determined. The solution was then electrosprayed in the cone-jet mode and films were collected on a rotating plate. Film thickness was investigated by electron microscopy. Films of varying thickness were prepared by varying the electrospraying time and their characteristics are compared with solvent-cast films.
The selection of a desirable solvent or solvent system as the carrier of a particular polymer is fundamental for the optimisation of electrospinning. Solvent selection is pivotal in determining the ...critical minimum solution concentration to allow the transition from electrospraying to electrospinning, thereby significantly affecting solution spinnability and the morphology of the electrospun fibres. 28 solvents diversely positioned on the Teas graph were studied for their solubility and electrospinnability for making polymethylsilsesquioxane (PMSQ) solutions. The results are combined and mapped on the Teas graph using different colour codes. Based on this new spinnability–solubility map, various solvent systems for PMSQ are methodically developed. Solvents are selected to produce binary solvent systems that have solvent parameters close to a good single solvent for electrospinning of the polymer solution. This work shows that solvents of high solubility do not necessarily produce solutions good for electrospinning. Polymethylsilsesquioxane solutions of the same concentration in solvents of partial solubility showed better spinnability than solutions in solvents of high solubility. A methanol–propanol binary solvent system produced electrospun fibres with high surface porosity, showing that high volatility and high vapour pressure difference among solvents mixed can induce phase separation in electrospinning. It is noteworthy that the binary solvent system mixing 2-nitropropane (high solubility) and dimethylsulphoxide (non-solvent), neither of which exhibited high volatility, also produced highly porous electrospun fibres. This demonstrates that phase separation can be induced by solubility difference in the electrospun polymer solution.
Display omitted
Core-sheath fibres of two polymers were generated using a novel set-up where rotating speed and pressure can be varied at ambient temperature. The specially designed spinneret consists of inner and ...outer chambers which can accommodate two polymers and other additives. The new methodology was demonstrated using poly(ethylene oxide) and poly(methylmethacrylate) (PMMA). Dyes were used as colouring agents for the polymers to verify core-sheath formation, and optical, scanning and fluorescent microscopy of the formed fibres confirmed the presence of a core-sheath combination. The core diameter obtained was in the range 5–10 μm and the sheath fibre diameter was 20–30 μm. The core/sheath diameter can be pre-set by selecting the forming conditions. To show the flexibility of the new method, nanoparticle containing PMMA fibres were also produced using the new device and incorporation of the nanoparticles in the sheath and core of the fibres was verified by electron microscopy and energy-dispersive X-ray spectroscopy analysis. A high yield of fibre was obtained and with more severe forming conditions the size of core-sheath fibres generated can be reduced to the nanoscale. Thus, the new process has a real capability of manufacturing a wide variety of novel functional materials and structures in a single scalable set-up.
Display omitted
•Core-sheath polymer fibres are formed in a novel way.•A new twin-reservoir device has been designed and constructed to enable this.•The device was subjected to pressurised gyration.•Microstructural characterisation confirms core-sheath fibre formation.•Nanoparticles have been successfully incorporated in the product.
Academic and industrial research on nanofibres is an area of increasing global interest, as seen in the continuously multiplying number of research papers and patents and the broadening range of ...chemical, medical, electrical and environmental applications. This in turn expands the size of the market opportunity and is reflected in the significant rise of entrepreneurial activities and investments in the field. Electrospinning is probably the most researched top-down method to form nanofibres from a remarkable range of organic and inorganic materials. It is well known and discussed in many comprehensive studies, so why this review? As we read about yet another "novel" method producing multifunctional nanomaterials in grams or milligrams in the laboratory, there is hardly any research addressing how these methods can be safely, consistently and cost-effectively up-scaled. Despite two decades of governmental and private investment, the productivity of nanofibre forming methods is still struggling to meet the increasing demand. This hinders the further integration of nanofibres into practical large-scale applications and limits current uses to niche-markets. Looking into history, this large gap between supply and demand of synthetic fibres was seen and addressed in conventional textile production a century ago. The remarkable achievement was accomplished via extensive collaborative research between academia and industry, applying ingenious solutions and technological convergence from polymer chemistry, physical chemistry, materials science and engineering disciplines. Looking into the present, current advances in electrospinning and nanofibre production are showing similar interdisciplinary technological convergence, and knowledge of industrial textile processing is being combined with new developments in nanofibre forming methods. Moreover, many important parameters in electrospinning and nanofibre spinning methods overlap parameters extensively studied in industrial fibre processing. Thus, this review combines interdisciplinary knowledge from the academia and industry to facilitate technological convergence and offers insight for upscaling electrospinning and nanofibre production. It will examine advances in electrospinning within a framework of large-scale fibre production as well as alternative nanofibre forming methods, providing a comprehensive comparison of conventional and contemporary fibre forming technologies. This study intends to stimulate interest in addressing the issue of scale-up alongside novel developments and applications in nanofibre research.
Cellulose derivatives are an attractive sustainable material used frequently in biomaterials, however their solubility in safe, green solvents is not widely exploited. In this work three cellulose ...derivatives; ethyl cellulose, cellulose acetate and carboxymethyl cellulose were subjected to electrohydrodynamic processing. All were processed with safe, environmentally friendly solvents; ethanol, acetone and water. Ethyl cellulose was electrospun and an interesting transitional region was identified. The morphological changes from particles with tails to thick fibres were charted from 17 to 25 wt% solutions. The concentration and solvent composition of cellulose acetate (CA) solutions were then changed; increasing the concentration also increased fibre size. At 10 wt% CA, with acetone only, fibres with heavy beading were produced. In an attempt to incorporate water in the binary solvent system to reduce the acetone content, 80:20 acetone/water solvent system was used. It was noted that for the same concentration of CA (10 wt%), the beading was reduced. Finally, carboxymethyl cellulose was electrospun with poly(ethylene oxide), with the molecular weight and polymer compositions changed and the morphology observed.
•Starch and starch–polymer were subjected to the new process of pressurised gyration.•Product features were dependent on composition, rheology, gyration speed and pressure.•Aligned continuous 160nm ...diameter polymer fibres containing starch beads were obtained.•Structural characteristics of the starch–polymer mixtures confirmed their properties.
This work investigates the rheology and spinning of starch and starch-loaded poly(ethylene oxide) (PEO) by pressurised gyration in order to prepare nanofibres. The spinning dope's rheological properties played a crucial role in fibre formation. Newtonian behaviour is observed in 1–20wt% starch suspensions and non-Newtonian behaviour is found in all the PEO–starch mixtures. Pressurised gyration of the starch suspensions produced beads only but PEO–starch mixtures generated fibres. The fibre diameter of the PEO–starch samples is shown to be a function of polymer concentration and rotating speed of the gyration system. Fibre formation can only be facilitated below a certain working pressure. The concentration of starch in the PEO–starch mixtures is crucial in defining whether beaded or continuous fibres were generated and this is related to the composition of the spinning dope. FT-IR, XRD and microscopy studies indicated very good miscibility of starch and PEO in the nanofibres. The storage modulus of the PEO–starch were also studied as a function of temperature (30–150°C) and showed interesting results but it was not possible to deduce general trends valid for the entire temperature range.
Co-electrospinning has demonstrated that polymer solutions below the entanglement concentration can be made into fibers as an encapsulated core in an electrospinnable sheath solution containing a ...carrier/template polymer. The carrier polymer may require removal at a later stage. This work shows for the first time that without increasing the polymer concentration/molecular weight or needing a template polymer, simply infusing a liquid in the core nozzle can cause the sheath polymer solution (viscosity <20 mPa s) to electrospin instead of electrospray in a coaxial electrified jet. Different from coelectrospinning, the core liquid can be a common solvent such as water and does not require a readily electrospinnable carrier polymer. The process was not limited to one core liquid system; infusing solvents and nonsolvents with different properties in the core generated either beaded fibers or continuous fibers from the sheath solution. The process of fiber formation instead of particle breakup was attributed to the relaxation time of the elastic polymer sheath solution becoming longer than the growth rate of the Rayleigh instability in the compound jet upon the infusion of a second solvent in the core. Key parameters of the process included high surface tension of the core liquid (e.g., water and glycerol), high interfacial tension between the core and the sheath liquids, and electrohydrodynamic operating parameters such as flow rate and applied voltage. Given that charge was transferred from the sheath solution to the core liquid, differences in the dielectric constant and electrical conductivity of the core liquids showed little influence on the process. Fibers also formed irrespective of the miscibility and solubility of the solvent, though in the case of a nonsolvent, a lower miscibility was desirable to minimize polymer precipitation at the core–sheath interface. The process was investigated using poly(lactide-co-glycolide) as a model system, with polycaprolactone and polymethylsilsesquioxane systems presented as two additional examples. This work documents new roles of solvents in coaxial electrohydrodynamic processes and presents a useful method to obtain micro- and nanofibers from low-viscosity solutions without using a template polymer.
. At ambient temperature (22°C), these bubbles were very stable with their size remaining almost unchanged for 160 min. The
influence of higher temperatures such as the human body temperature (37°C) ...on the size and stability of the microbubbles was
also explored. It was found that the mean bubble diameter fell rapidly to begin with but then stabilized at 1–2 μm after 20 min., The use of phospholipid-coated microbubbles for medical applications is gaining considerable attention. However, the preparation
of lipid-coated microbubble suspensions containing the ideal size and size distribution of bubbles still represents a considerable
challenge. The most commonly used preparation methods of sonication and mechanical agitation result in the generation of polydisperse
microbubbles with diameters ranging from less than 1 μm to greater than 50 μm. Efforts have been made via distinctly different
techniques such as microfluidic and electrohydrodynamic bubbling to prepare lipid-coated microbubbles with diameters less
than 10 μm and with a narrow size distribution, and recent results have been highly promising. In this paper, we describe
a detailed investigation of the latter method that essentially combines liquid and air flow, and an applied electric field
to generate microbubbles. A parametric plot was constructed between the air flow rate (, ) to identify suitable flow rate regimes for the preparation of phospholipid-coated microbubbles with a mean diameter of 6.6 μm
and a standard deviation of 2.5 μm. The parametric plot has also helped in developing a scaling equation between the bubble
diameter and the ratio, ) and the lipid suspension flow rate (
Antibiotics have been used to control the aquatic environment in both therapeutic and prophylactic ways. Antibiotics are particularly difficult to extract due to their strong interactions with ...biological matrices. In this study, UPLC-MS/MS method was developed and validated for quantitative confirmatory analysis of multi-class antibiotics residues in fish and shrimp. Fourteen antibiotics belonging to sulphonamides, β-lactams, quinolones, sulfones and macrolides were determined within one chromatographic run. The samples were suspended in 0.1 M HCl, and the analytes were extracted into ethyl acetate. The extracts were defatted with cyclohexane. The limits of quantification (LOQ) ranged from 0.24 to 1.32 µg kg−1 for fish and 0.42–1.62 µg kg−1 for shrimp samples. The recoveries ranged from 75 to 105%. The method was applied to the analysis of farmed freshwater Tilapia fish (Oreochromis niloticus) and shrimp (Penaeus monodon) collected in Sri Lanka. Sulfacetamide (4.31 ± 0.70 µg kg−1) and sulfamethoxypyridazine (0.75 ± 0.15 µg kg−1) were detected in the fish, and sulfapyridine (0.21–0.56 µg kg−1) and sulfadoxine (0.35–1.44 µg kg−1) were detected in the shrimp samples. The concentrations complied with the EU regulation limits for veterinary drug residues in seafood and did not pose a risk in terms of food safety.
PDF
