in situ synthesis of biopolyurethane nanocomposites reinforced with modified multiwalled carbon nanotubes
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Biopolyurethane nanocomposites reinforced with silane-modified multiwalled carbon nanotubes (s-MWCNT) were successfully prepared. The carbon nanotube surfaces were modified by means of functional amine groups via ozone oxidation followed by silanization. The surface structure of the s-MWCNTs was characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The s-MWCNTs were incorporated into a vegetable oil-based polyurethane (PU) network via covalent bonding to prepare PU nanocomposites. The effect of s-MWCNT loading on the morphology, thermomechanical, and tensile properties of the PU nanocomposites was studied. It was determined that the s-MWCNTs were dispersed effectively in the polymer matrix and that they improved the interfacial strength between the reinforcing nanotubes and the polymer matrix. Storage modulus, glass transition temperature, Young's modulus, and tensile strength of the nanocomposites increased with increasing s-MWCNT loading up to 0.8%. However, increasing the s-MWCNT content to 1.2 wt % resulted in a decrease in thermomechanical properties of the PU nanocomposites. This effect was attributed to the fact that at high s-MWCNT contents, the increased number of amine groups competed with the polyol's hydroxyl groups for isocyanate groups, causing a decrease in the integrity of the PU matrix. High s-MWCNT contents also facilitated aggregation of the nanotubes, causing a decrease in thermomechanical properties.