Morphology study of polyamide 6.9 nanofibres electrospun under steady state conditions

Abstract

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