Seed oils rich in linolenic acid as renewable feedstock for environment-friendly crosslinkers in powder coatings

In the work described, seed oils rich in linolenic acid were used fbr the s ynthesis of aliphatic oxiranes. The oils studied were linseed (Linum usitat issimum) oil, Canadian linseed oil and the oil of Lallemantia iberica. The oils contained 54.1, 60.2 and 68.0% of linolenic acid, respectively, and sh owed high theoretical iodine values of 211, 226 and 236 g/hg. Unsaturations in the oils were used to introduce epoxides by epoxidation with in situ ge nerated peroxyacetic acid. The epoxidized oils, showing high percentages of oxirane oxygen (9.4, 10.0 and 10.7%), were applied as crosslinkers in powd er-coating formulations. The major advantage of these types of crosslinkers is that they are neither toxic nor mutagenic, in contrast with the widely applied synthetic triglycidyl isocyanurate (TGIC) crosslinkers. However, tw o potential problems exist when aliphatic oxiranes are compared with conven tional TGIC systems. A decrease in glass transition temperature (T-g) of th e powder formulation and a higher degree of yellowing of the coating are of ten observed. In this paper the effects of rising oils containing high lino lenic acid contents on the yellowing of the coating and the T-g of the powd er, are studied. It appeared that aliphatic oxiranes are suitable as enviro nment-friendly crosslinkers in powder-coating systems. (C) 1999 Elsevier Sc ience B.V. All rights reserved.