Modified cardanol based colorless, transparent, hydrophobic and anti-corrosive polyurethane coating

Despite having unique functional properties, renewable resourced cardanol based polymers have limited usage in industrial coatings because of its dark brown or red color after polymerization. The current work reports the development of colorless, transparent, hydrophobic and corrosion resistant coating derived from cardanol 2,3-dihydroxy propyl ether (CPE) and modified with hydroxy-terminated polydimethylsiloxane (HTPDMS). CPE was synthesized to be used as a reactive aliphatic diol in forming polyurethane (CPU) and characterized. HTPDMS-CPU copolymers with multifunctional properties were prepared through copolymerization of 5, 10, 15, 20 wt% HTPDMS and CPE. HTPDMS-CPU coatings showed improved adhesion and hydrophobicity (>100°), enhanced transparency with easy readability underneath and a reasonable UV transmittance (92–96%). One distinct Tg and single phase surface morphology of HTPDMS10CPU and HTPDMS15CPU confirmed the good miscibility and compatibility of the system. Electrochemical Impedance Spectra (EIS), salt water immersion and salt spray studies revealed the anti-corrosive property of the copolymers with best performance at 10–15 wt% HTPDMS content. Thermogravimetric study showed almost no interference in thermal stability after the incorporation of HTPDMS into the system. The development of HTPDMS-CPU co-polymeric multifunctional coatings represents a more effective pathway to achieve multi-functional coatings with desirable hydrophobic, anti-corrosive and improved thermal stability.