• Mehdi Salami-Kalajahi

      Articles written in Bulletin of Materials Science

    • Radical coupling of maleic anhydride onto graphite to fabricate oxidized graphene nanolayers

      Fatemeh Samadaei Mehdi Salami-Kalajahi Hossein Roghani-Mamaqani

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      Radical coupling was used to modify graphite with maleic anhydride (MAH). Azobisisobutyronitrile (AIBN) as radical generator activated MAH radically and it was reacted with defects at the surface of nanolayers. A set of batches with different reaction times (24, 48 and 72 h) were performed to obtain fully-modified nanolayers (GMA1, GMA2 and GMA3, respectively). Fourier transform infrared results approved the synthesis of MAHgrafted graphite. Thermogravimetric analysis showed that 5.9, 11.1 and 13.2 wt% of MAH was grafted onto the surface of GMA1, GMA2 and GMA3, respectively, and that was approved by X-ray photoelectron spectroscopy results. Also, X-ray diffraction patterns showed that $d$-spacing increased from 0.34 nm for graphite to 1.00 nm for all modified samples. However, GMA1 showed a weak peak related to graphite structure that disappeared when reaction time was increased. After modification with MAH, lamella flake structure of graphite was retained whereas the edges of sheets became distinguishable as depicted by scanning electron microscopy images. According to Raman spectra, modification progression resulted in more disorder structure of nanolayers due to grafting of MAH. Also, transmission electron microscopy images showed graphite as transparent layers while after modification, surface of nanolayers became folded due to the opposite effects of $\pi$-conjugated domains and electrostatic repulsion of oxygen-containing groups.

    • Preparation of polyurethane-acrylate and silica nanoparticle hybrid composites by a free radical network formation method


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      In this study, hybrid composites of polyurethane-acrylate (PUA) and silica nanoparticle were prepared by a radical method. For this aim, silica nanoparticles were chemically functionalized with 3-methacryloxypropyltrimethoxysilane. Polyurethane was synthesized and then modified with 2-hydroxyethyl methacrylate to yield PUA. Then, different amounts of modified-silica were used to prepare PUA composites by the addition of an ethylene glycol dimethacrylate crosslinker. Fourier-transform infrared spectroscopy confirmed the successful functionalization of silica nanoparticles and the prepa-ration of PUA. Structural investigation of the functionalized-nanoparticles and also nanocomposites was carried out using X-ray diffraction and electron microscopy. According to the thermal gravimetric analysis results, char residue of HSiO₂ is 86.6%, which decreases to 81.3% in the case of MSiO₂ as a result of its modifier degradation content of 5.3%. PUAS5 shows main decomposition temperatures of 396.5 and 454.9°C and also char content of 5.7% at 700°C. The high amount of MSiO₂ can also be resulted in higher degree of crosslinking and therefore higher thermal stabilities and char residue.

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