Technologies

Nano composite materials

Many aerospace applications require electrically conducting polymer based composites for static discharge, electrical bonding, interference shielding, primary and secondary power, and current return through the structure. Existing carbon fibre reinforced polymer composites are unable to achieve all these requirements due to the presence of insulating resin regions within the composite structure. Secondary conductive materials such as foils, wires, straps and/or coatings have typically been incorporated into the structure to improve the electrical properties and all of which require additional unwanted processing steps.

One of the objectives of the ADVITAC project is the improvement of electrical conductivity of composite laminates primarily in order to fulfil the requirements for lightning strike protection but also for electrical grounding, electrical bonding and EMI shielding.

Two lines of investigation have been highlighted for the improvement of the composite electrical conductivity using:

• Dispersed carbon nanotubes (CNT) in the resin matrix.
• Carbon nanofiller based “buckypapers”.

The first solution involves the addition of conductive particulates in the matrix itself. Recent studies have showed that a small amount of multi wall carbon nanotubes (MWCNT) relatively well dispersed into a polyester resin have the ability to reduce the resistivity of the liquid (and solid) polymer by several orders of magnitude.

The addition of MWCNT and other conductive nano-fillers such as carbon nanofibre (CNF) can increase the electrical conductivity of epoxies and BMI resins to a level sufficient to ensure electrical continuity within composite structures. The levels of nano fillers and the dispersion method can then be optimised for improved electrical conductivity. Several dispersion methods will be assessed, including high torque/ high shear mixing, horn sonication dispersion and shear dispersion using a triple rolls mill. The enhanced resins can be used in both the bulk composite as well as highly thermally conductive surface resin layers.

The second solution involves the manufacture of composite “buckypapers” using carbon nano fillers. The main material selected for use within this project will be carbon nanofibres (CNFs). However other types of nano reinforcements such as multi walled carbon nanotubes (MWCNTs) will also be assessed.

The manufacture of the papers consists of a low thickness of interwoven random distributed fibres or tubes manufactured using a suspension filtration process. The selected nano-materials (CNFs or MWCNTs) can also be treated in order to improve the electrical conductivity of the paper using graphitisation and metallisation processes.

Hybrid solutions using carbon nanopapers and metallic strings embedded by a fibre placement system will also be assessed.