Reinforcement of norbornene-based nanocomposites with norbornene functionalized multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWNTs) were functionalized with benzoic acid groups via an “on water” technique and further derivatized with norbornene groups. The norbornene groups grafted onto the MWNT surface were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and field-emission scanning electron microscopy (FE-SEM) to confirm covalent functionalization. Observations of suspensions and transmission electron microscopy (TEM) and SEM images of nanocomposites suggested improved dispersibility of norbornene-functionalized MWNTs (nMWNTs) in dicyclopentadiene/5-norbornene-2-carboxylic acid (DCPD/NCA) monomers relative to pristine MWNTs (pMWNTs). Cure kinetics and mechanical properties of MWNT/poly(DCPD/NCA) nanocomposites with various functionalized nanotube loadings (0.1–0.6 wt%) were investigated by means of differential scanning calorimetry (DSC), a universal testing machine (UTM), and dynamic mechanical analysis (DMA). It was found from DSC that the functionalized nanotubes have an acceleration effect on the cure process, which is likely related to enhanced heat transfer from the carbon nanotubes. The swelling ratio increased with increasing nanotube loading, revealing that the formation of crosslinks was hindered by the addition of nanotubes. The incorporation of the functionalized nanotubes resulted in improved Young’s modulus and yield strength compared with neat poly(DCPD/NCA), far beyond the enhancement with pMWNTs. Although a decrease in the elongation at break was observed as the nanotube loading increases, the tensile toughness remained almost unchanged up to 0.4 wt% nMWNT loading. Furthermore, the addition of the nMWNTs also shifted the glass transition toward higher temperatures. These enhancements are presumably attributed to better nanotube dispersion and stronger nanotube-matrix interfacial affinity.