Wicking properties of polyamide nanofibrous structures

The hydrophilicity of nanofibrous structures is a key characteristic for many applications. However due to the high porosity of the structures, it is difficult to measure this property with contact angle measurements. Therefore a characterisation through wicking behaviour is more appropriate. The ISO-norm on wicking behaviour needs some refining to account for the specific nature of the highly porous nanofibrous structures. This refined method is used on polyamide 6 nanofibrous structures with different diameters and on polyamide 6 nanofibres with an incorporated hydrophilic compound. It was found that the fibre diameter is the major characteristic which influences the wicking behaviour

Development and characterization of protein nanohydrogels for food applications

Fundação para a Ciência e Tecnologia, POPH-QREN and FSE (FCT, Portugal)EU Cost Actions FA090

Modifying the crack growth in a glass fiber reinforced epoxy by adding polyamide 6 nanofibers

Recently, several types of nanoparticles are frequently incorporated in reinforced epoxy resin composites. Since it is difficult to obtain a homogeneous dispersion of these nanoparticles, the mechanical improvement of the composites is very moderate. Thermoplastic nanofibrous structures can overcome this issue. Therefore, this paper investigated the effect of electrospun polyamide 6 nanofibrous structures on the mechanical properties of a glass fiber/epoxy composite. The nanofibers are incorporated in the glass fiber/epoxy composite as stand-alone interlayered structures and directly spun on the glass fiber reinforcement. Both incorporation procedures have no negative effect on the impregnation of the epoxy. Incorporation of nanofibers increases the stress at failure in the 0°-direction, the best results are obtained when the nanofibers are directly electrospun on the glass fibers. Optical microscopic images also demonstrate that nanofibers prevent delamination when a 90° crack reaches a neighbourly 0° ply. When the composites are loaded under 45°, it is proven that for an identical stress, the glass fiber composite with deposited nanofibers has less cracks than when interlayered nanofibrous structures are incorporated

The influence of nanofibres in composite materials

Nanofibres have by definition a diameter less than 500 nm, which is several times smaller than the conventional fibres. Because of their very small fibre diameter these fibrous materials have specific and unique characteristics such as a high surface-to-volume ratio and high porosity. Thanks to this these nanofibres can be used in a broad spectrum of applications such as liquid and air filtration, wound bandages and composites. Although the literature on nanofibre composites is restricted, nanofibres can have advantages for advanced composites. Composites reinforced with conventional glass or carbon fibres may have very high tensile strengths, but the impact resistance is sometimes limited. A second problem of these actual composites is the delamination of the several textile layers. Both problems can be reduced by using nanofibrous webs between the glass or carbon layers. In our research large polyamide nanofibrous structures (PA 6, PA6.6, PA 4.6 and PA 6.9) were produced on a multi-nozzle setup. Starting from these structures the effect of the nanofibres on the curing of a epoxy matrix was investigated by thermo analytical measurements using a differential scanning calorimeter. Changing the nanofibres characteristics, especially the polyamide type and fibre diameter, will affect the curing behaviour of the resin. Furthermore the influence of the amount of water absorbed through the nanofibrous webs is inquired, by making identical composite samples at different relative humidity’s. In the second part of the research glass fibre/polyamide nanofibre composites were produced on large scale by infusion. The polyamide nanofibres were brought into the composites as stand-alone structures as well as coatings on the glass fabrics. The tenacity of these composites is compared to glass fibre composites without nanofibres. This research gives a good overview of the curing behaviour of the resin affected by the nanofibrous webs on the one side and the advantages of nanofibres for high performance composites on the other side

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

Influence of the polyamide type and fibre diameter on the wicking height in nanofibrous structures

Due to the high porosity of nanofibrous structures, it is difficult to measure the hydrofilicity of the material with contact angle measurements. Therefore, a new method to examine the wicking behaviour of the structures is developed. This method is used on several structures, which differ in fibre diameter and polyamide type. The structures with the thickest nanofibres have the highest wicking rates. For different polyamide types, the capillary forces establish the wicking behaviour in the initial phase. Further in the process, it is determined by the capillary forces and the water absorption capacity of the bulk phase