Synthesis of castor oil-based polyols applicable in acrylated polyurethane coating with improved mechanical properties

The study focuses on the synthesis of polyurethane (PU)-based coating from modified castor oil (CO) via an in situ polymerization process. CO was modified by employing multiple process steps, that included epoxidation, followed by transesterification and acrylation to get the required polyol for PU synthesis. The structural properties were studied using Fourier transform infrared and H-1 NMR spectra. Thermogravimetric analysis (TGA) and differential scanning calorimetry revealed an increase in the final degradation temperature and glass transition temperature from 358 and -46.58 degrees C to 368 and -37.43 degrees C respectively after transesterification followed by acrylation of epoxidized CO. Hydroxyl value, acid value, amine value and viscosity were observed to change from 208 mg/KOH, 1.75, 13.09 and 428 mPa s to 233 mg/KOH, 1.16, 19.53 and 318 mPa s after transesterification and acrylation of epoxidized CO. Paint formulations at variable OH:NCO ratios like 1:0.9, 1:1 and 1:1.1 were optimized by following the cross-cut tape test, lap-shear test, abrasion resistance test and pencil hardness test. Crosslinking density of the paint samples was calculated and the morphological properties of the optimized coating sample were studied using a scanning electron microscope. TGA was carried out to study the thermal properties of the coating. (c) 2022 Society of Chemical Industry.