Superior thermomechanical and wetting properties of ultrasonic dual mode mixing assisted epoxy-CNT nanocomposites

High-performance epoxy-carbon nanotube (CNT) nanocomposites were prepared by simultaneous use of ultrasonication and mechanical stirring. The dynamic and static mechanical properties and wetting properties of the nanocomposites were investigated. The dynamic mechanical analysis presented significant enhancement in storage modulus (approximately 124%) and glass transition temperature (approximately 25.6%) of epoxy-CNT nanocomposite at an optimized concentration of the CNT (0.25 wt%) possibly due to the formation of a strong interface between the epoxy and CNT. The tensile test results showed the significant improvement in tensile strength (approximately 47%) and Young’s modulus (approximately 40%) of the epoxy-CNT (0.25 wt%) nanocomposite without significantly affecting its stiffness. The homogeneous dispersion of CNTs in the epoxy matrix resulted in the significant enhancement in the dynamic and static mechanical properties of the nanocomposites. The hydrophilic character of the neat epoxy was tuned to a highly hydrophobic one by incorporation of CNTs in it. A direct relation between the average roughness of the tensile fracture surfaces and the contact angle of the nanocomposites was identified with respect to the concentration of the CNTs. These high-performance highly hydrophobic nanocomposites have the great potential to be used as the structural and functional materials in humid environments.

Functionalized multiwalled carbon nanotubes by loading phosphorylated chitosan

Novel flame-retardant phosphorylated chitosan-multiwalled carbon nanotubes (PCS-MWCNTs) were obtained by the loading of PCS on the surface of MWCNTs by a chemical deposition cross-linking method. A series of polyethylene terephthalate (PET) composites were prepared by melt compounding with MWCNTs or PCS-MWCNTs to investigate the flame-retardant properties. Field-emission scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared (FTIR) spectrometry were employed to characterize the morphology, chemical structure, and functionalization effect of MWCNTs. The coating degree and thermal stability of PCS-MWCNTs were investigated by thermogravimetric analysis (TGA). Thermal decomposition products after TGA and flame-retardant properties of PET composites were characterized by FTIR and CONE measurements, respectively. The results indicated that PCS is loaded on the MWCNT surface. Modified PCS-MWCNTs exhibited better dispersion and efficient flame retardancy. TGA data indicated that PCS-MWCNTs can enhance the onset temperature of PET and increase the amount of the char residues. The char residue with 1 wt% PCS-MWCNTs/PET increased from 12.62% (pure PET) to 15.46%. The analysis of the decomposition products and morphology of the char residue indicated that PCS-MWCNTs not only retain the effect of alternating couplet carbon (C) and physical barrier by MWCNTs, but also form P–C compounds, improving the flame retardancy of PET. CONE tests demonstrated that the PCS-MWCNTs lead to the efficient decrease in the flammability parameters, such as the heat release rate (HRR), total release heat rate (THR), total smoke production (TSP), mean mass loss rate (MMLR), and the total combustion time. The peak HRR value decreased from 513.22 kW m−2 to 341 kW m−2. The THR, TSP, and MMLR values decreased by 20.38 MJ m−2, 1.1 m2, and 1.32 g s−1, respectively. The total combustion time decreased by 98 s, from 388 s to 290 s, indicating that PCS-MWCNTs extinguish fire.

Effect of functionalization of multiwalled carbon nanotubes with aminated poly(ether sulfone) on thermal and mechanical properties of poly(ether ether ketone) nanocomposites

Multiwalled carbon nanotubes (MWCNTs) were functionalized with aminated poly(ether sulfone) (PES) through the amidation reaction. Characterizations by Fourier transform infrared spectroscopy and X-ray diffraction corroborated the success of grafting reaction. Raman spectra reveal that no further damage occurred after the anchoring of PES to the carboxylated MWCNTs. Transmission electron microscopy shows that PES functionalization resulted in better dispersion of MWCNTs than acid oxidation. Poly(ether ether ketone) (PEEK)/MWCNTs functionalized with PES (PES-MWCNTs) nanocomposites were fabricated by solution-mixing and compression-molding techniques. Thermogravimetric analysis indicates that PES-MWCNTs/PEEK nanocomposites have the highest degradation temperature and thermal stability. Furthermore, noticeable increases in the crystallization and melting temperature as well as in the degree of crystallinity were found from differential scanning calorimetry thermograms, attributed to the strong heterogeneous nucleating role of PES-MWCNTs. Tensile test presents that the attachment of PES to the surface of MWCNTs exceptionally improved the tensile strength and Young’s modulus, and obtained moderate elongation at break. Impact toughness test and dynamic mechanical analysis show that the addition of PES-MWCNTs greatly enhanced the toughness and storage modulus of PEEK, respectively. These results are attributed to improved dispersion of PES-MWCNTs and strong interfacial adhesion to matrix, which is evidenced by scanning electron microscopy.