Effect of incorporating carbon- and silicon-based nanomaterials on the physico-chemical properties of a structural epoxy adhesive

Various carbon-based (i.e. carbon nanofibres (CNF), cellulose nanocrystals and graphite nanopowder) and silicon-based nanomaterials (i.e. silica nanopowder and MMT nanoclay) were incorporated into neat structural epoxy (NE) adhesive (Sikadur (R)-30) at 0.5, 1.0 and 1.5% by weight and mixed using a simple and cost-effective approach to produce the nanomaterial-modified epoxy adhesives (NMEAs). The impact of incorporating these nanomaterials into the NE on its chemical composition was investigated using Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. X-ray diffraction (XRD) measurements were also used to identify the changes in the physical structure (i.e. the degree of crystallinity) that may occur in the NE with the addition of nanomaterials. Furthermore, the microstructure of the NE and NMEAs (in terms of the degree of dispersibility of the nanoparticles through the matrix) was investigated through scanning electron microscopy (SEM) analysis. A porosity analysis was also conducted across all samples. The results obtained from various tests were correlated to investigate the changes that occurred in the different properties of the matrix and the corresponding nanocomposites effectively and more critically. The SEM images showed some particle agglomeration, which increased with increasing wt%. An increase in the % porosity ratio of all nanocomposites over that of the NE was also observed, accompanied by a decrease in crystallinity compared to the NE. As per the FTIR spectroscopy, the chemical bonds in the NE and carbon-based NMEAs were observed to have different intensities, which were changed in the NMEAs, with the type and wt. % of the nanomaterials. No new bonds were formed by incorporating any of the nanomaterials (i.e. carbon- and silicon-based), except when adding 1.0 wt% CNF, where a bond at 1710 cm-1 was observed indicating a new C--O stretching bond. As shown by Raman spectroscopy, all CNF and graphite NMEAs exhibited higher ID/IG values than those of the corresponding pristine materials.