Polymer Centre academics Dr Simon Hayes and Dr Patrick Smith have been investigating an application for thermally-cured polymers to heal defects in composite materials in aircrafts, by applying this technology through inkjet printing.
Composite materials, defined as materials made from two or more distinctive components which have different physical and chemical properties, are used in a variety of industries including the aerospace sector, due to their superior properties including high strength, durability and stiffness. However, an emerging problem with composites is the delamination, or separation, of internal layers. This leads to concealed damage within the material- a difficult problem to detect and treat. The use of self-healing polymers has been investigated for in situ repair of composite materials in airplanes.
Composite specimens for testing were produced from two different monomers, which were synthesised and inkjet printed in layers as 1% and 5% w/v solutions onto a PTFE base. Heat was applied under vacuum, initiating the thermal polymerisation of monomers via a series of Diels-Alder reactions to form polymers. It is this thermal polymerisation that is being used to promote self-healing between damaged layers.
The critical energy release and the interlaminar shear strength were assessed for each specimen. It was found that 5% samples showed superior interlaminar properties over control and 1% samples.
A thermal cycle analysis was conducted on the composite specimens. The results indicated that after heat treating, the 5% samples showed less of a reduction in interlaminar properties than the control and 1% samples. This suggests that some rebonding took place in the laminate layers due to polymerisation. Overall printing of the monomers followed by the application of heat to start the polymerisation, therefore the self-healing process, has been shown to have a beneficial effect on the composite material.
Original article: Inkjet Printing of Self-healing Polymers for Enhanced Composite Interlaminar Properties, Elliot Fleet, Yi Zhang, Simon Hayes and Patrick Smith, Journal of Materials Chemistry, 2015 3, pp 2283-2293
Article by Kathryn Murray; a PhD Student on the EPSRC Polymers, Soft Matter and Colloids CDT programme. For more information, please contact Dr Joe Gaunt at the Polymer Centre.