Fabrication of self-ameliorating microphases between composite plies by inkjet printing

Inkjet printing has been extensively explored as a manufacturing technique over the last two decades due to its ability to precisely print pico-litre droplets according to predefined patterns without masks. It is an attractive method for many areas such as printed electronics [1] and tissue engineered scaffolds [2] on account of its minimum waste generation. The main consideration for using inkjet printing is in the physical and rheological properties of inks which are composed of either solutions or suspensions. Viscosity and surface tension are the most important factors which determine the printability of inks [3].

Composites are of increasing interest due to their light weight and relatively high mechanical properties such as tensile strength and flexural modulus. A reinforced fibre or other filler is embedded into the composite with the aim of improving their strength and stiffness-to-weight ratio [4]. However, the trade-off for this gain in mechanical strength is their poor performance under impact loading which leads to delamination. In order to extend the lifetime of this material, researchers began investigating self-repairing strategies; numerous self-healing materials with different healing mechanisms have been reported to date [5]. In this study, a new method is presented that uses inkjet printing to deposit, or fabricate, self-ameliorating agents between composite plies prior to the curing cycle.

A research grade inkjet printer was used to place self-ameliorating agents onto the surfaces of carbon fibre reinforced epoxy pre-pregs. The interface between the plies is likely to be the main source of micro-cracks hence this strategic deposition imparts multifunctional properties whilst enhancing its structural integrity in service. The self-ameliorating agents took the form of standard polymers, which need to be classified as M15P and M20P at this stage (due to IP application which will be finalised in time for the conference). The addition of the agents contributed to improved properties in the interlaminar shear modulus and Mode I interlaminar fracture toughness (GIc).