Preparation and curing of alkyd based on ricinoleic acid/melamine coatings

Three alkyd resins of high hydroxyl numbers based on ricinoleic acid, phthalic anhydride and glycerin, trimethylolpropane or ethoxylated pentaerythritol as polyol were prepared. Afterwards synthesized alkyds were made into baking enamels by blending with commercial melamine-formaldehyde resins (weight ratio of 70:30 based on dried mass). Alkyd/melamine resin mixtures were cured in a differential scanning calorimeter (DSC) under non-isothermal mode. Apparent degree of curing as a function of temperature was calculated from the curing enthalpies. Fourier transform infrared spectroscopy (FTIR) was used to identify characteristic peaks of resin mixtures before and after being cured. The gel content, hardness, elasticity and impact resistance of coated film cured at 150 °C for 60 min were measured. The onset of film thermal degradation, determined by thermogravimetric analysis (TGA) was observed at the temperatures from 281 to 330 °C. Based on the results obtained we suppose that the combinations of synthesized alkyds based on ricinoleic acid with used melamine resins could be employed as the compositions for the preparation of baking enamels.