Addressing Issues of Electrospinning Nanofibres on Textiles: Productivity, Perturbation and Adhesion

Academic and industrial interest for electrospinning raised in the 1990s. Textile is considered one of the most important field for the application of electrospun nanofibres, but at least three issues have to be solved in order to fulfil industrial requirements: up-scaling of electrospinning, process stability and nanofibres adhesion to textiles. Large-scale electrospinning systems should be designed to increase productivity, allowing continuous nanofibre production and deposition. One approach is the use of multi-nozzle electrospinning plant. In this work, several multi-nozzle electrospinning configurations (from 6 to 9 nozzles) were tested in order to study jet-jet interactions (electrostatic repulsion, alteration of whipping motion). A final electrospinning pilot plant equipped with 62 nozzles was designed and developed. Electrospun nanofibres were continuously deposited on a textile substrates, moved during electrospinning by a roll-to-roll system (Figure 1). The shifting speed of the substrate influenced thickness, porosity and density of the deposited nanofibre layers For filtration, clothing and protective textiles, electrospun nanofibres need to be deposited on a supporting substrate (usually textile materials such as woven fabrics or non-wovens) because of their limited mechanical properties. Textile materials are electrical insulator by nature. In this work, different process perturbations (i.e. stability of the jets, increase of Coulomb repulsive force between the jets, distribution of the deposition zones on the collector and nanofibre morphology) were observed when a non-conducting textile substrate (e.g. polypropylene non-woven) was used as nanofibre collector in multi-nozzle electrospinning. To minimize perturbations, adjustments in the process conditions were studied. The last challenge is to guarantee adhesion of nanofibres to textiles achieving satisfactory durability for practical uses. Adhesion of nanofibres to textile substrates was characterized by means of peeling tests. Investigations were carried out also for the comprehension of the factors that limit the adhesion. Textile processes, including plasma treatments, were proposed in order to enhance adhesion by pre-treating the textile substrates. In particular, after oxygen low-temperature plasma treatments, a polypropylene non-woven showed significant changes in wettability. The treatments results to increase adhesion energy and force of peeling tests. Adhesion between nanofibres and substrate were about 5-15 times higher for PEO nanofibre when deposited on a plasma treated PP non-woven, and about 2-5 times higher when PA6 nanofibres were used. The adhesion is low when a fabric composed of staple fibres is used as substrate. Even if treatments could improve the adhesion, optical microscopy observations on both nanofibre layer and fabric after peeling tests suggested that on staple fabrics the electrospun nanofibres were actually linked to few anchor points (i.e. protruding fibre) on the fabric surface. Therefore, surface hairiness of fabrics seems to be a critical limit for considerably improving adhesion, even if improvements can be promoted by the treatments. Hence, not all textile materials are suitable substrates for coating with electrospun nanofibres.