A Time Frequency-Based Approach for Defect Detection in Composites Using Nonstationary Thermal Wave Imaging

Russian Journal of Nondestructive Testing - Characterization of various industrial components without impairing their future utility increases the necessity of nondestructive testing (NDT)...     

Effect of non-ionic surfactants on thermomechanical properties of epoxy/multiwall carbon nanotubes composites

Epoxy/multiwall carbon nanotubes (MWCNTs) composites were investigated using three different non-ionic surfactants (BYK-110, Tween-80 and Nonidet-P40) separately as a modifier. The role of surfactants in dispersion of MWCNTs in the epoxy matrix was studied. Among three surfactants used, performance of Nonidet-P40 was found to be the best in improving the thermomechanical properties of the epoxy resin and achieving good dispersion of MWCNTs. The good dispersion of Nonidet-P40 modified MWCNT in the epoxy matrix is a result of the π–π interaction between π electrons of the Nonidet-P40 and π electron clouds of MWCNTs as well as H-bonding interaction between of Nonidet-P40 and the epoxy matrix. This type of interaction does not disturb the π electron clouds of MWCNTs as opposed to chemical functionalization strategy.     

Synthesis and characterization of novel hyperbranched alkyd and isocyanate trimer based high solid polyurethane coatings

In the present work, hyperbranched urethane alkyd high solid coatings were formulated by mixing hyperbranched alkyd and isocyanate trimer. Initially, a second generation hyperbranched polyol (HBP) was synthesized using dipentaerythritol (DPE) as a core material and 2,2-bis(methylol)propionic acid (BMPA) as a chain extender. This was reacted with varying concentrations of linseed oil fatty acid (LOFA) to make a series of hyperbranched alkyd (HBA) resins. Viscosity and volume solid of the HBA resins were measured. The resins were characterized by Fourier transform infrared (FTIR), and ¹³C Nuclear magnetic resonance (¹³C NMR) spectroscopic techniques. The hyperbranched alkyd resins containing varying amount unreacted hydroxyl groups were cured with hexamethylene diisocyanate (HDI) trimer (Desmodur N 3390) depending on their NCO: OH ratio to make hyperbranched urethane alkyd coatings. A series of such coatings were made by mixing HBA/isocyanate trimer (Desmodur N 3390) ratio with respect to the hydroxyl group present on the HBA. The performance of the coated specimens was evaluated by various techniques such as pull-off adhesion strength, tensile strength, abrasion resistance, scratch resistance, flexibility, and impact resistance tests. The weathering properties of the coated specimens were evaluated by UV-Weatherometer. Corrosion resistance of the coated specimens was evaluated by electrochemical impedance spectroscopy (EIS), salt spray, seawater immersion and humidity tests. It was observed that, there exists an optimum coating composition in terms of NCO: OH (HBA: Desmodur N 3390) ratio which showed excellent enhancement in terms of the mechanical, weathering and corrosion resistance properties than remaining coating compositions.