2018-05 North Dakota State

National Association of Corrosion Engineers (NACE) International estimated the global cost of corrosion to be US$2.5 trillion in 2016, equivalent to roughly 3.4% percent of the global GDP. They also found that 15-35% of the cost of damage could be saved by implementing corrosion prevention technologies. Coating is one of the most important methods to protect metallic structures from corrosion. In addition to the barrier, anticorrosion, and strong bonding properties provided by a general-purpose metal coating, coatings for metallic heritage preservation should also be easily removable under a suitable conditions when needed. Currently this type of coatings is still lacking. In this project, a thermally reversible coating was developed based on the Diels-Alder (DA) reaction and retro-DA (rDA) reaction. The DA bonds, which link resin polymer chains together to form a strong coating, undergo the rDA reaction under elevated temperatures to allow coating softening and removal. Cellulose nanofibers and an electroactive compound were also incorporated in the coating to improve its mechanical and anticorrosion properties. To enable the DA and rDA reactions in the coating, furfuryl functional groups were connected to cellulose nanofibers, epoxy resin, and an electroactive compound through chemical synthesis. After mixing bismaleimide with these functionalized compounds, the DA reaction occurred and a thermally reversible coating was produced. Coating was prepared on steel test panels using different formulations and coating thickness. Coating hardness, solvent resistance, impedance, thermal property, and corrosion resistance were investigated. Differential scanning calorimetry and actual scraping tests confirmed the rDA reaction and that coating could be removed at elevated temperatures. The incorporated functionalized cellulose nanofibers increased the solvent resistance and rubbing resistance of the coating by increasing mechanical strength of the coating.

Images of six metal plates showing varying amounts of rust coverage.

Coated steel panels before and after the prohesion test.
A: 1 mil FFER/FFEC/bismaleimide coating; AA: A sample after the test;
B: 1 mil FFER/FFEC/FFCNF/bismaleimide; BB: B sample after the test;
C: 2 mil FFER/FFEC/FFCNF/bismaleimide coating; CC: C sample after the test.

Corrosion resistance of the coating was investigated by electrochemical impedance spectroscopy and prohesion (salt spray) tests. The results shows that the incorporation of the cellulose nanofibers can increase impedance of the coating, but lead to a higher number of coating defects, which deteriorate corrosion resistance of the coating. Further research can be conducted to improve the dispersion of the nanofibers in the coating to increase coating homogeneity and reduce coating defects. Research to reduce or even eliminate the brown color of the coating is also desirable.

National Center for Preservation Technology and Training
645 University Parkway
Natchitoches, LA 71457

Email: ncptt[at]nps.gov
Phone: (318) 356-7444
Fax: (318) 356-9119