A benzoxazine/substituted borazine composite coating: A new resin for improving the corrosion resistance of the pristine benzoxazine coating applied on aluminum. (December 2018) - Renaud, Alexis
Graphical abstract: Highlights: Benzoxazine-substituted borazine coatings were applied on aluminum and thermally cured. Obtained microstructures show two phases, coarsening with the borazine concentration. The borazine derivative increases the hydrophobicity of the generated composite. Corrosion properties of the composites are strongly related to the microstructure. For the lowest concentration (0.5 wt% borazine) a durable corrosion barrier is obtained. Abstract: In this paper, laboratory synthesized Phenol-paraPhenyleneDiAmine (P-pPDA) benzoxazine containing different amounts of B-trimesityl-N-triphenylborazine was applied by spin coating on aluminum and thermally cured. The addition of the borazine derivative (borazine1 ) does not appear to modify the curing characteristics of the P-pPDA matrix itself as shown by FTIR, DSC and DEA analyses; however, some interactions - chemical and/or physical (co-crystallization) – between P-pPDA and borazine1 cannot be excluded. The microstructure of the composites is characterized by a two phase system consisting of a dispersion of nanosized (10–20 nm) clusters for the lowest borazine1 concentration (0.5 wt%), evolving towards bigger (100–200 nm), agglomerated clusters for higher borazine1 concentrations (3 wt%) and finally, continuous, dendritic structures within the P-pPDA matrix for the highest borazine1 concentration (10 wt%). The benzoxazine composite coating containing 0.5 wt% trimesitylborazine derivative showed a largely increased and durable ability to protect the aluminum substrate. It is shown that a highly capacitive behavior and durable barrier properties can be obtained for P-pPDA coatings containing such a low amount of borazine derivative homogeneously dispersed in the benzoxazine matrix. For concentrations of 3 wt%, as agglomeration took place and dendrites appeared for the highest concentration of borazine derivative (10 wt%), the corrosion resistance decreased with time.