Phytic acid oligomers as bio-based crosslinkers for epoxy and polyol resins

Abstract In recent years, the chemical industry is not only striving to produce the best possible products for various applications, but the new products should ideally be based on renewable resources. The ideal case of "cradle to cradle" is generally not achievable in the coatings industry, as maximizing product life and preventing product degradation in the environment is usually one of the main goals of the coatings industry. Therefore, if the coatings industry wants to act sustainably, its efforts should be focused on renewable raw materials. This paper presents a process that makes the renewable raw material phytic acid easily accessible for conventional epoxy and polyol resin coating systems through hydrophobization- and oligomerization. Phytic acid, as a phosphorus reservoir in plants and with beneficial properties for corrosion protection and as a flame retardant, could be a new base for various coatings. In this work, a simple one-pot oligomerization of phytic acid with green mono- and difunctional alcohols is investigated. The aim of this work is to create a phytic acid hardener system based on renewable raw materials that can produce coatings with solvent-based epoxy and polyol binders as well as water-based epoxy binders. The successful reaction was observed by infrared, 1 H-NMR, and 31 P-NMR spectroscopy and the acid equivalent weight was determined by conductivity titration. The renewable curing agent was then used equivalently with different binder systems to prepare coatings. Crosslinking and glass transition temperature were monitored using oscillatory rheology. The coatings were applied to glass plates and the pendulum hardness was measured. A simple heating test followed by 31 P-NMR and IR spectroscopy was also performed to demonstrate the stability of phytic acid under reaction conditions.