Processing of Composites Based on Thermosets

A closely related method to the in situ polymerisation processing of composites is based on epoxy resins thermosets. In this approach, CNTs can be dispersed in a liquid epoxy precursor and then the mixtures can be cured by the addition of hardener, such as triethylene tetramine (TETA), and the application of temperature or pressure. In most cases, the epoxy monomer exists in liquid state, facilitating nanotube dispersion. Curing is then carried out to 

Widely used industrial approaches for the produetion of polymer fibres and yarns, such as coagulation spinning and electrospinning, have also been utilised for the fabrication of polymer nanotube eomposites. In coagulation spinning, for example, composite fibres ean be produced by an injection of surfactant-stabilised nanotube dispersion in water into a rotating bath of polymer e.g. PVA) dissolved in water sueh that nanotube and polymer dispersions flowed in the same direction at the point of injection. In this case, polymer molecules replace surfactant molecules on the nanotube surface, thus destabilising the nanotubes dispersion whieh eollapses to form a fibre. These fibres can then be retrieved from the bath, rinsed and dried. 

In a similar study, Sen et formed fibre-based membranes. They were spun from SWNT dispersed in either polystyrene or polyurethane with a 3 cm needle-plate gap. In this work, the solution was pumped slowly out of a needle under application of 15 kV. Spinning was continued for 1 h until the counterelectrode was covered in a membrane built up from the spun fibres. 

In a more recent work, MWNTs have been incorporated into surface-modified, reactive P(St-co-GMA) nanofibres by electrospinning. Then resulting nanofibres have been functionalised with epoxide groups and added to the epoxy matrix producing reinforced epoxy resins. The polymer composites have demonstrated over a 20% increase in flexural modulus, when compared with neat epoxy, despite a very low composite fibre weight fraction (at approximately 0.2% by a single-layer fibrous mat). The increase is attributed to the combined effect of the well-dispersed MWNTs and the surface chemistry of the electrospun fibres that enabled an effective cross-linking between the polymer matrix and the nanofibres. 

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Common traditional approaches for the fabrication of CNT-polymer composites include solution processing of composites, melt spinning, melt processing, in situ polymerization, processing of composites based on thermosets, electrospinning and coagulation spinning for composite fibers and yam production [92]. 

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