Morphology study of polyamide 6.9 nanofibres electrospun under steady state conditions

This research investigates the electrospinning prerequisites for polyamide 6.9 and the influence of different electrospin parameters on the fibre morphology. Polyamide 6.9 is a seldom used polyamide though with specific properties such as the lowest water absorption of all polyamides. This can, for example, be advantageous for nanofibres in composite applications. Acetic acid/formic acid solvent mixtures prove to be very suitable for the steady state electrospinning of PA 6.9, with the formic acid serving the solubility of the PA 6.9 and the acetic acid serving the appropriate solution characteristics for obtaining steady state. Steady state behaviour means no irregularities in the nanofibrous structures and a high reproducibility A limited range of polymer concentrations, solvent ratios and process parameters results in steady state electrospinning. The combination of those parameters is determined by the viscosity, surface tension and electric properties of the electrospinning solutions. Different steady state tables showing the limits within a varying polymer concentration and solvent ratio that allow for the production of nanofibres are composed. Sequentially the influence of the main solution and process parameters on the fibre diameter (using SEM) and thermal behaviour (using DSC and XRD) is investigated. The polymer concentration has a significant effect on the morphology of the nanofibres: the average PA 6.9 diameter and the fraction less stable crystal phase increase with increasing polymer concentration. The effect of the solvent ratio is less obvious. The process parameters only have a minor effect on the nanofibres. The applied voltage and TCD show no influence on the nanofibre morphology. The flow rate has a small influence on the fibres, but the difference in diameters is small compared to the differences found with varying polymer concentration. It can be concluded that the polymer concentration is the key parameter to alter the fibre morphology of PA 6.9 nanofibres

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Performance assessment of functionalized electrospun nanofibres for removal of pathogens

Perfonnance Assessment of Functionalized Electrospun Nanofibres for Removal of PathogensKeywords: functionalised nanofibre, pathogen removal, membrane filtration. The c1ectrospinning technique is a process for making continuous nanofibrcs in a nonwoven fonn. This process spins fibres ranging from 80 om diameter to several hundred nanometers. The non-woven structure is produced by app lying a high voltage to the anode, submerged in a spinn ing solution. This produces a charged jet of fluid when the electrical force is highcr than the surface tension of the solution and the fibres are collected on a grounded aluminum plate. Nanofibres have a small pore size and a large surface area to volume ratio compared to nonwovens (this ratio for a nanofibre can be as large as 1000 times of that of a microfibre). This, together with their low density and interconnected open pore structure. make the nanofibre nonwoven appropriate for a wide variety of filtration applications (Huang et al.. 2003). Due to the large effective surface areas. nanofibres can carry functional agents with different properties. such as biocidcs. With microfiltration membranes it is possible to retain suspended solids and micro-organisms. The added value of the tested nanofibre microfiltration membranes functionalized with silver nanoparticles (nAg) or other biocides to pathogen removal was studied. The biocides used in this study are commercially available. WSCP for example. is used as a cooling tower biocide and is applied directly into the water. Silver nanoparticles are nowadays implemented in a wide variety of consumer products for antimicrobial controL The aim of the study is to examine the effectiveness of different biocides and the possibility to electrospin them in a steady state nanofibre membrane. The results show that due to the silver nanoparticles and the funct ionalisation with biocides in the functionalized membrane a higher efficiency (3.9 10giO - 5,5 10glO) could be achieved. Further, the removal of pathogens is a factor 100 (2 10g10) higher with a WSCP (5%) than conventional microfihration. Functionalisation with Ag nanoparticles gave a 4 10gi0 removal. It is generally known that these particles only have effect on gram negative bacteria such as E. coli. WSCP and bronopol are bactericides that can be applicd on c1ectrospun nanofibres and it has also effect on gram positive bacteria (Chen et aI., 2008). The removal with a non-functionalised membrane is not as good as other micro-filtration studies. With other commercial membranes a 2 log I 0 - 4 logl 0 removal is possible (Zodrow et al.. 2009)

Functionalized nanofiber membranes for disinfection of water

Nowadays, water is often disinfected with biocides which can result in the formation of harmful by-products. Therefore new developments in water treatment are needed. One of such new developments is presented in this study. Nanofiber membranes produced by the electrospinning technique offer great potential in water filtration. Nanofiber structures have a small pore size, a large specific surface area and interconnected open pore structure which makes them appropriate for water filtration. However, the pathogen removal efficiency is not yet satisfactory. To improve this, disinfectants as a functional agent on nanofiber membranes were used in this study. The pathogen removal of the functionalized membranes was evaluated with wastewater from a general hospital with ca. 107 culturable organisms per 100 ml before filtration. Pathogen removal of about 4 to 5,5 log10 is possible with selected biocides. This is higher than a nanofibers membrane without disinfectant, which gives a removal of 2 log10 and commercial membranes with a removal of 3 to 4 log10. In addition to this, the biocides stay immobilized inside the membrane and only a limited fraction (10%) leaches into the water

Electrospun nanofiber membranes functionalized with antibacterial particles

Electrospinning is the most efficient method for the production of nanofibrous structures, which have unique characteristics such as high porosity, high absorption capacity, small pore size and high specific surface area. Thanks to this, they can be used as filtration membranes. Nanofiber membranes have high clean water permeability values, however the pathogen removal efficiency is currently not satisfactory. For this reason, we functionalized the membranes with antibacterial particles, such as silver nanoparticles and commercial biocides, by adding them into the spinning solution. Afterwards, the membranes were characterized to study the effect of the functionalization on the fiber diameter and pathogen removal efficiency. The distribution of the silver nanoparticles was studied with SEM and TEM images. TEM-images showed that the silver nanoparticles are trapped inside the nanofibers. SEM-images confirmed that the average fiber diameter is not affected by the functionalization. To evaluate the removal of pathogens, water samples were taken from waste water from a general hospital (107 – 108 colony forming units per 100 ml) and were filtered with different membranes. A non functionalized nanofiber membrane could not achieve the same reduction in culturable organisms as commercial membranes (2 log10 – 4 log10 removal). Higher reduction was reached when silver nanoparticles were added to the membrane. A 3 log10 – 4 log10 removal was reached by adding silver nanoparticles to the spinning solution. Nanofiber membranes with biocides as functionalization agents achieved even a much higher reduction, up to 5,5 log10, which is competitive with commercial membranes currently on the market. In conclusion, the electrospinning process allows the functionalization of nanofiber membranes with antibacterial particles. This highly improves the pathogen removal efficiency of the membranes