Three well-tuned procedures were used for thermal improvement of epoxy resin (E). Accordingly, graphene xerogel (GX) was used as nanofiller in the matrix of E. Additionally, (3-isocyanatopropyl)triethoxysilanemodified E (IE) or tetraethyl orthosilicate (TEOS) oligomer-modified E (TE) was incorporated into a hybrid structure of graphene-containing silica/siloxane network. For this purpose, a bifunctional silane coupling agent of 1,1 0 -(hexane-1,6-diyl)bis(3-(3-(trimethoxysilyl)propyl)urea) (HDBTMSPU) was synthesized. GX was obtained by incorporation of HDBTMSPU-modified graphene oxide (FGO) into xerogel structure using HDBTMSPU and TEOS. Modified resins, FGO, HDBTMSPU, and TEOS were also used in preparation of hybrid products. Thermal stability and char residue of the composites were compared. GO modification was approved by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Raman, X-ray diffraction, and thermogravimetric analysis results. Hybrid composite of IE, FGO, and silica/siloxane network shows higher thermal properties. Char residue is increased by 16.93 % by loading of only 1 wt% of FGO in this hybrid product.
Graphical Abstract
Thermal properties of epoxy resin (E) were improved by its incorporation into silica/siloxane network in the presence of carbon nanotube (CNT). At first, CNT xerogel (CNTX)/E composite was prepared by curing E in the presence of CNTX. Then, E is modified with (3-isocyanatopropyl)triethoxysilane (IE) or tetraethyl orthosilicate (TEOS) oligomer (TE) for its incorporation into a hybrid network of CNT-containing silica/siloxane network. For this purpose, a bifunctional modifier of 1,1 0 -(hexane-1,6-diyl)bis(3-(3-(trimethoxysilyl)propyl)urea) (HDBTMSPU) was synthesized. CNTX was prepared by incorporation of HDBTMSPU-modified CNT (FCNT) into silica/siloxane network by using HDBTMSPU and TEOS. IE (TE), FGO, HDBTMSPU, and TEOS were also used in the preparation of hybrid products. Three types of composites were compared in their thermal degradation temperature and char content. Functionalization of CNT was confirmed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Raman, X-ray diffraction (XRD), and thermogravimetric analysis (TGA) results. Xerogel formation was proved by Raman, XRD, and N 2 adsorption and desorption isotherms. TGA results showed that the hybrid of IE, FCNT, and silica/ siloxane network shows higher thermal properties. Char residue is increased 17.54 % by only 4 wt% loading of FCNT in IE resin (IEGX1). Formation of xerogel network around CNT was observed by scanning and transmission electron microscopies.
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