Carbon nanotube/polyurethane nanocomposites with surface-modified nanostructures

Polymeric nanocomposites are strong alternatives for filled polymers (containing fillers) or blends. Due to certain properties, such as high Young’s modulus, good tensile strength and carbonic nature, it is more economical to use nanotubes instead of metals. Although nanotubes do not interact easily with other materials, chemical modifications can still make them to interact favorably with other materials. Uniform distribution and improved adhesion of nanotubes are important issues that must be paid attention for successful synthesis of nanocomposites. The main goal of the present work is to make a uniform distribution and proper interaction between the PU matrix and CNTs. Therefore, carboxylic functional groups were created on the surface of nanotubes using acid and plasma treatment methods and the properties of resulting nanocomposites were studied. FTIR results corroborated that the micro-phase separation values increased by 7% in acid-modified and 3% in plasma-modified nanocomposites compared to its unmodified counterpart. The frequency sweep analysis proved that the surface modification of CNT promotes the non-terminal behavior and viscosity upturn at low frequencies and this effect was more noticeable in acid-treated samples compared to plasma-treated ones. The DMA analysis results confirmed that surface modification at low content of CNT decreases the Tg of a soft segment-rich phase, whereas at higher content of CNT, surface modification increases this value. Electrical conductivity measurement illustrated that the electrical percolation threshold in acid-modified nanocomposites was decreased by 35% and in plasma-modified nanocomposites by 19% compared with its untreated counterpart.