Investigating the long term effects of immersion in salt solution on the protective properties of bio-content polyurethane coatings

摘要

One of the ways to protect metals against corrosion is to coat them with polymers which act as an ionic (mainly) barrier and/or contain inhibitors. In consequence the redox reactions are hindered and corrosion is reduced to negligible (passivation current) rate. However, polymers undergo various processes of degradation in the harsh environments where some coatings are used utilization. So for long term protection it is important to know different mechanisms of the polymer degradation. A popular type of anti-corrosive organic coatings is based on polyurethane. The degradation of these with a biomass component has been investigated in this work The resins were synthesized using pre-polymer and single-step method. Castor oil was added to the systems thereby contributing to lowering the amount of artificial chemical compounds in the final product. The samples were subjected to immersion in 3% NaCl solution, for different periods of time. Several types of measurements were made to investigate the long term effects of immersion. The main monitoring method was DC resistance which is directly associated with barrier properties. SEM images obtained before and after immersion enabled observation of the topographical changes. DMA was employed to verify some of mechanical properties and determine glass transition temperatures for different coatings. It emerged that coatings with the greater amount of castor oil exhibited the highest DC resistance. As the result of immersion some pits and cracks in the surface were revealed by SEM imaging. DMA results showed that increase of castor oil content in PU coatings cause both higher cross link density and higher glass transition temperature.