Development of bio-based polyester-urethane-acrylate (PUA) from citric acid for UV-curable coatings

A novel UV-curable hyperbranched polyester-urethane-acrylate (PUA) resin was successfully synthesized using citric acid as a core bio-based material and ester-urethane-acrylate linkage as the arm and was applied on both wood and metal substrates. Citric acid was employed as a functionality-enhancing bio-based monomer for coating applications. This resin (PUA) was synthesized from citric acid (CA)-based polyester-polyol (CAP) and subsequently reacted with isophorone diisocyanate (IPDI) and end-capped with 2-hydroxyethylmethacrylate (HEMA) to form a tetra-functional acrylate precursor (UCAP). Fourier-transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (H-1-NMR) and gel permeation chromatography (GPC) were used to characterize the citric acid-based polyester-urethane-acrylate (UCAP). This oligomer was formulated with a reactive diluent and a photoinitiator (UCAP PUA), applied on both wood and metal substrates and cured under UV-radiation. The mechanical, chemical and thermal properties of the coated substrates were investigated and compared to a commercial urethane acrylate (CUA). The mechanical properties such as crosscut adhesion, pencil hardness, impact strength and flexibility showed comparable results. Even though the chemical resistance and free film properties of the synthesized urethane acrylate (UCAP) were found to be inferior, the thermal properties were observed to be superior. [GRAPHICS]