Nanostructured Fibre Composites, and Materials for Air Filtration

Abstract

Electrospinning is a method that can be used in the production of polymeric nanofibres. Polymer solution is drawn into nanosized fibres utilizing electric field. In addition to neat polymers, solutions containing additives and fillers can also be used to functionalize fibres for use in specific applications. In addition, the nanosized structure of electrospun fibre web has intrinsic properties which are suitable for various applications. The small fibre diameter, small pore size, and high surface area of the nanofibre web are properties that are advantageous for filtration applications. Electrospun nanofibres can be used as an effective layer in composite filter media.

This thesis studies the preparation of nanostructured fibre composites using the electrospinning method and using of such composites in air filtration applications. The formation of nanofibres using the electrospinning method was examined with neat and composite solutions; the preparation of composite materials containing nanofibre layer was investigated with modelling and in practice; and the use of composite materials in air filtration applications were explored. It was shown that the small fibre diameters that enable the slip-flow effect advantageous for filtration are easily achievable with the electrospinning method. The composite material was used in fibres to obtain intriguing properties, such as porosity throughout the fibre or photo catalytic activity. In some cases the use of composite solutions affected the fibre formation of the electrospinning process compared to neat polymeric solution.

Electrospun nanofibre layers had limited strength so they were produced onto substrates as an effective filtration layer. The preparation of such a layer can be accomplished with multi-nozzle electrospinning equipment as described within this thesis. The modelling of the electric field revealed that while the voltage affected the strength of the field, the overall nature and shape of the field was mainly dependent on the distance between the nozzles and the collector. The filtration efficiency of fibrous substrate clearly increased even with a very low amount of nanofibres, and efficiencies above 99 % were achieved with higher coating weights depending on the particle sizes used in the tests. Increasing the coating weight above 0.5 g/m2 showed no benefits, and instead raised the pressure drop to an unusable range.