Synthesis and characterization of citric acid and itaconic acid-based two-pack polyurethane antimicrobial coatings

Polyurethane is one of the most versatile polymers in the industry. Polyurethane products include coatings, flexible foams, and elastomers. A polyurethane coating is a polyurethane layer applied to the surface of a substrate to protect it against corrosion, weathering, abrasion, microbial colonization, and other deteriorating processes. As mentioned in the literature, citric acid is a weak organic acid naturally present in limes, oranges, and lemons. Moreover, it acts as an antimicrobial agent by retarding the growth of bacteria, mold, yeast, and fungus. Also, itaconic acid has been shown to have an antimicrobial effect by inhibiting isocitrate lyase, the key enzyme of an essential pathway for microbial growth. In this research article, one polyester polyol was synthesized (propanetriol citrate polyester “PCE”) using citric acid and epichlorohydrin. In contrast, another polyester polyol [poly (1,2,3-propanetriol citrate-co-1,2,3-propanetriol itaconate) “PPCI”] was developed by reacting PCE with itaconic acid. The chemical structures of PCE and PPCI were confirmed by FTIR, H 1 NMR, GPC, acid value, and hydroxyl value. Further, two-pack polyurethane coatings based on these two polyester polyols and blocked polyisocyanates (hexamethylene diisocyanate “HDI” and toluene diisocyanate “TDI”) were formulated. These coatings were evaluated for their mechanical, chemical, thermal, anticorrosive, and antimicrobial properties. Studies on coating characteristics revealed that the gloss, adhesion, pencil hardness, and glass transition temperature of PCE-HTDI-based coatings were higher than that of PPCI-HDI-based coatings. Both PCE-HTDI and PPCI-HDI-based coatings showed good solvent resistance. The anticorrosive property in both the coating systems was alleviated with the increasing OH:NCO ratio. PPCI-HDI-based 2K polyurethane coatings showed better antimicrobial properties than PCE-HTDI-based 2K polyurethane coatings. Hence these coating systems have potential applications in the biomedical industry.