Title

Post-treatment and enhancement for coatings formed by spontaneous polymerization on aluminum

Date of Completion

January 2001

Keywords

Engineering, Chemical|Engineering, Materials Science

Degree

Ph.D.

Abstract

Post-treatment and modification of a new process to form protective coatings on aluminum have been studied. This coating process S-Poly® is based on spontaneous polymerization on aluminum and other metals. The polymer coating studied here was formed from styrene, n-phenyl maleimide (NPMI), bismaleimide (BMI), and 2-(methacryloyloxy) ethyl acetoacetate (MEA). Both optimization of the process and the characterization of changes in coating structure after polymerization were investigated. It was seen that the coating successfully changed into an adherent film through controlled rinsing and drying with the aid of a coalescing solvent, and drying at a high temperature (>170°C) enhanced the performance of the coating in terms of corrosion resistance and adhesion. It was revealed that improvements could be attributed to removing surface water on the substrate and forming a dense protective layer by means of thermal crosslinking of β-diketone functional groups in the coating. The reaction mechanism associated with evolution of acetone, carbon dioxide, and acetoacetic acid was reported. The resultant coatings showed adhesion strength over 30 MPa in torsional test and corrosion free for 3000 hours exposure in salt fog spray test (ASTM B-117). Furthermore, a new coating system incorporating N-isobutoxymethyl acrylamide (BAM) was developed. The new system became crosslinked at temperatures below 150°C through the interaction between BAM and β-diketone groups. The resultant coating obtained desired performance without the damage to mechanical properties of some aluminum alloys, which is caused by high temperature drying. It is also reported that the use of a corrosion inhibitor Nitrolotris (methylene) triphosphonic acid (NTMP) resulted in superior corrosion resistance and adhesion, especially wet adhesion of the coating formed from this new system. ^