Preparation And Characterization Of Reactive Liquid Rubber-toughened Epoxy/Functionalized Carbon Nanotube Nanocomposites

Carbon nanotubes (CNTs) are considered as reinforcement for polymer matrix because of the remarkable physical, chemical and electrical properties with small dimensions and high aspects. Carboxyl-modified multi-walled carbon nanotubes (MWCNT-COOHs) were successfully prepared by modifying MWCNTs with nitric acid and then incorporated into the carboxyl-terminated butadiene-acrylonitrile (CTBN) toughened diglycidyl ether of bisphenol A (DGEBA), and amino-modified MWCNTs (MWCNT-NH2s) were incorporated into amino-terminated butadiene-acrylonitrile (ATBN) toughened DGEBA resins.Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and Raman spectrum (Raman) were used to characterization the structure of MWCNT-COOH and MWCNT-NH2. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), universal material tester, TGA and scanning electronic microscopy (SEM) were used to study the curing behaviors, glass transition temperatures (Tgs), mechanical properties, thermal stabilities and cryo-fracture surfaces of DGEBA/CTBN/MWCNT-COOH and DGEBA/ATBN/MWCNT-NH2nanocomposites.FT-IR spectrum of MWCNT-COOHs showed peaks at around3435cm-1and1714cm-1respectively assigned to the O-H stretching vibrations and C=O stretching vibrations, TGA curve of MWCNT-COOHs showed more weight loss above250℃than that of MWCNTs, and Raman spectrum showed a higher defect rate, indicating that MWCNTs were successfully modified with the introduction of the carboxyl functionalities. DSC kinetic studies showed that the active energy (Ea) decreased with the increase of MWCNT-COOH content, indicating that MWCNT-COOHs act as catalysts and facilitate the curing reaction. The maximum tensile and flexural properties were obtained at MWCNT-COOH concentration of0.5wt.%with uniform dispersion. Nevertheless, at higher concentrations, MWCNT-COOHs agglomerated in the viscous epoxy/CTBN system and resulted in the decreasing of mechanical properties. DMA results revealed that Tg of rubber-toughened epoxy nanocomposites lowered with MWCNT-COOH contents. Phase-separation phenomenon and a homogeneous dispersion of nanocomposites at lower comcentration were observed.FT-IR spectrum of MWCNT-NH2showed peaks at around3437cm-1assigned to N-H stretching,1540cm-1and1508cm-1respectively assigned to the-N-H stretching vibrations and bending vibrations, TGA curve of MWCNT-COOHs showed weight loss above250℃, proving the existence of amino groups at the surface of MWCNT-NH2. DSC kenetic studies showed that MWCNT-NH2could lower the Ea and facilitate the curing reaction. It is observed that tensile strength, Young’s modulus, flexural strength and flexural modulus of DGEBA/ATBN/MWCNT-NH2nanocomposites increased with increase of MWCNT-NH2, however the elogationg at break decreased. Tgs measured by DSC rescanning showed a highest value at0.5wt.%content of MWCNT-NH2because of the restriction of polymer chains by MWCNT-NH2, but the value decreased for the agglomerates with increase of MWCNT-NH2. SEM images also displayed phase-separation phenomenons and agglomerates. Meanwhile, there were stronge interactions between MWCNT-NH2and ATBN-toughened epoxy.