Impact of functionality on properties of vegetable oil-based thermosetting coatings

Highly functional polyol resins of sucrose esters derived from soybean oil were synthesized and the properties of thermosets were determined after crosslinking with a commercial melamine-formaldehyde (MF) resin using an acid catalyst. As controls, a commercial soybean oil polyol resin and a typical commercial polyester polyol were used. A series of thermosets were made using MF loadings of 20%, 25%, 30% and 35% (wt. polyol) for all polyols studied. The high functionality of polyols from sucrose esters afforded much higher crosslink densities than the controls as determined by dynamic mechanical analysis (DMA). Interestingly, the storage moduli (E’) of sucrose ester-based thermosets was about an order of magnitude higher than that of the soybean oil-based thermosets. The glass transition temperature (Tg) of sucrose ester-based thermosets was about 90°C higher at 35% MF loading compared to the soybean-oil which was attributed to the high crosslink density. Coatings properties were also determined and the sucrose ester-based thermosets were found to be much harder in terms of König and pencil hardness versus the soybean oil thermosets and had a comparable hardness to the commercial polyester thermosets.