High Strength and High Modulus Electrospun Nanofibres

Abstract

In the last two decades, a rapidly growing polymer processing technology, electrospinning, has attracted great interests as it provides a viable and simple method to create ultra-fine continuous fibres. Despite the potential utilization of electrospun nanofibres in many fields, their success is limited so far due to their poor mechanical properties compared to corresponding textile fibres made from the same polymers, which is mainly ascribed to the low degree of orientation and chain extension of the macromolecules along the fibre axis in such fibres. In this thesis, first an in-depth review of the mechanical properties of electrospun fibres and recent developed methodologies to generate high strength and high modulus nanofibres will be presented. In the experimental work, electrospinning of rigid polymer PPTA was attempted and mechanical properties of obtained fibres were evaluated (Chapter 3). It was shown that the electrospinning process cannot be easily operated in a controllable and continuous manner although some high performance fibres were obtained. Chapter 4 dealt with the electrospinning of reactive mesogens (liquid crystal monomers) by employing polymers (PMMA and PA6) as matrix. The mechanical properties of the resulting composite nanofibres (PA6/RM257) showed dependence on the reactive mesogen (RM257) content and the phase separation between PA6 and RM257. In Chapter 5, a high performance polymer BPDA/PDA/ODA was synthesized and electrospun; the nanofibres were characterized using FTIR and WAXD and their mechanical tests were carried out based on unidirectional mats and multifilament bundles. A Weibull modulus based 7 model was introduced to estimate the tensile strength of single nanofibres in such bundles. Subsequently, composites based on BPO nanofibres in a rubbery thermoplastic matrix were fabricated and evaluated in Chapter 7 using composite mechanics theories for off-axis properties and „Rule of Mixture‟ which were used to back-calculate the Young‟s modulus of single BPO nanofibres. From this it could be concluded that the developed co-polyimide BPO nanofibres exhibit among the highest mechanical properties of electrospun nanofibres reported in literature so far. It can be concluded that the electrospun BPO co-polyimide nanofibres and p-aramid fibres possess among the highest mechanical properties reported for electrospun fibres so far.