Novel nanocomposites reinforced with hydroxylated poly(ether ether ketone)-grafted carbon nanotubes

High-performance poly(ether ether ketone) (PEEK) nanocomposites have been prepared via melt-blending by the incorporation of a hydroxylated polymer derivative (HPEEK) covalently grafted onto the surface of single-walled carbon nanotubes (SWCNTs). Their morphology, thermal, mechanical and electrical properties have been investigated and compared with the behaviour of composites reinforced with similar non-grafted fillers. Microscopic observations reveal that the grafting of the HPEEK onto the SWCNTs facilitates their dispersion within the matrix. The crystallization and melting temperature of PEEK decrease upon incorporation of the HPEEK-grafted SWCNTs, ascribed to the restrictions on polymer chain mobility imposed by the strong CNT-matrix interactions. The addition of these fillers leads to an exceptional increase in the thermal stability, storage modulus and glass transition temperature of the matrix. Tensile tests show unprecedented improvements in the Young's modulus, strength and toughness of the composites by the polymer grafting, attributed to a very effective load transfer achieved through covalent and hydrogen bonding. Electrical conductivity measurements indicate that the typical percolation behaviour takes place at very low SWCNT contents. In contrast, the thermal conductivity increases almost linearly with the filler loading. This approach is a simple, scalable and efficient method to improve the overall performance of thermoplastic nanocomposites for potential lightweight structural applications.