Synthesis and application of soybean oil based photocurable polyurethane acrylates for aluminum coating

The aim of this work is to create a new bio-based photocurable oligomer by starting with soybean oil instead of petroleum-based chemicals. For this purpose, acrylic acid (AA) and epoxidized soybean oil (ESBO) were initially reacted. Then the obtained acrylated ESBO (AESBO) oligomer was reacted with the isocyanate groups of the 2,4-toluene diisocyanate - 2-hydroxyethyl methacrylate (TDI-HEMA) adduct. TDI was chosen as the isocyanate source since it is the most widely produced and used form of isocyanate in the global polyurethane industry. HEMA provided the hydroxyl and acrylate groups needed for UV curing and polyurethane production, respectively. Additionally, the oligomer is flexible due to the methyl side group of HEMA. The synthesized oligomer was characterized by Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC) analysis. The coating compositions included the produced TDI-HEMA modified AESBO oligomer, as well as a variety of reactive diluents and a photoinitiator. Then formulations were applied on aluminum plates by spray coating and cured by UV light. The impact of the type of reactive diluent on the film forming and coating performance were all searched. Overall results proved that the inclusion of reactive diluents in the coating formulations helped to increase the coating quality and performance by adjusting the crosslinking density resulting in enhancement in adhesion.