Encapsulation methods for photo-polymerisable self-healing formulations

The aim of this work is to encapsulate a self-healing photo-polymerisable material for aerospace applications. To meet the technical requirements of space applications - low and high temperatures: -120 degrees C (dark side) to+250 degrees C (solar side); UV radiations: 200-400nm; low pressure: 10(-4)Pa - we chose trimethylolpropane triacrylate as healing agent. This monomer polymerises at 190 degrees C. To avoid its earlier thermal polymerisation, an inhibitor was added to the monomer/photo-initiator formulation. Moreover, among several microencapsulation techniques tested, we chose the sol-gel process to form silica microcapsules containing the self-healing formulation. These microcapsules were characterised by different analysis (scanning electron microscopy (SEM), thermo gravimetric analysis (TGA), Fourier transform infra-red spectroscopy (FTIR), etc.) and satisfied our requirements (size 1-30m, thermal stability >250 degrees C). After the microcapsules breakage, the generation of poly(TMPTA) film by radical photopolymerisation of the released TMPTA monomer was proved by disappearance of the IR peak at 1635cm(-1) (assigned to TMPTA). The obtained film has a thermal stability above 300 degrees C.