Nanocomposites based on thermosetting polyurethane matrix and chemically modified multiwalled carbon nanotubes

The nanocomposites based on thermosetting polyurethane (PU) matrix with 0.01–0.25 wt.% of multiwalled carbon nanotubes (MWCNTs), containing carboxyl, lactone or phenol groups on their surface, were prepared and explored. Their structural peculiarities by AFM, TEM and SEM, the thermodynamic miscibility, the dynamic (by DMA) and static mechanical properties as well as the dynamic heterogeneity and creep resistance (by creep rate spectroscopy, CRS) of the nanocomposites have been investigated. It was found that the functional groups for PU attachment that were covalently bonded to the MWCNT lattice possessed superior mechanical performance to the functional groups that were immobilised through van der Waals forces to the MWCNT surface. The thermodynamic calculations have shown that free energy of interaction between the carbon nanotubes with functionalized surfaces and PU matrix is negative for all types of nanofillers that assume the thermodynamic stability of these composites and high adhesion of PU to carbon nanotubes. The strong dependence between matrix dynamics and variations in the nanotube surface chemistry was demonstrated via the combined DMA-CRS approach. Only direct covalent bonding of the PU matrix to carbon nanotube lattice, which is free from fulvic acids, results in the dramatic changes in its glass transition dynamics even at low nanofiller content. Due to the change in fundamental interaction at the interfaces, two- or three-fold enhancement in the dynamic and static mechanical properties may be attained for low filler content thermosetting PU-MWCNT nanocomposites compared with those of neat PU matrix.