Anticorrosive barrier coatings modified by core-shell rubber particles: effects on the property transients and premature crack initiation susceptibility of particle type and concentration

Protective epoxy coatings, as a result of their inherent brittleness, show insufficient resistance towards initiation and propagation of cracks, which can occur as early as during the curing process. To improve premature crack initiation resistance, it is essential to understand the underlying mechanisms. In this work, a solvent-based novolac epoxy, cured with a cycloaliphatic amine, was reinforced with either an epoxypropoxypropyl-terminated polydimethylsiloxane (PDMS), nanoparticles of strontium titanate (SrTiO3), or core-shell rubber (CSR) nanoparticles. The effects on coating property transients, curing-induced internal stress, and premature crack initiation susceptibility of the modifier types and CSR (MX 217 and MX 267) concentrations were investigated. In addition, using a digital microscope, the defect and crack morphology in coatings applied to rigid, flat substrates and inner 90-degree angles were characterized. Finally, to evaluate the anticorrosive barrier performance of the reinforced coatings, an electrochemical impedance spectroscopy analysis was employed. Despite a slightly reduced crack initiation susceptibility, the flexible PDMS chains, due to phase separation, resulted in a deteriorated barrier performance. The inclusion of SrTiO3 nanoparticles also led to a reduced anticorrosion performance, relative to a neat epoxy coating, with a slightly lower crack initiation susceptibility and a minor increase (around 0.2 MPa) in the average internal stress. For 5 wt% MX 217 and MX 267 CSR toughened coatings, the maximum internal stress and crack initiation susceptibility in the series, as well as an associated reduced corrosion resistance, were seen. In spite of a reduction in the elastic modulus, an improved barrier performance and a reduced internal stress and crack initiation susceptibility were observed for 25 wt% MX 217 and 37 wt% MX 267 CSR toughened coatings. To improve barrier properties and avoid premature crack initiation of epoxy coatings, guidelines on modifier selection are provided.