The effect of pigment volume concentration on self-stratification and physico-mechanical properties of solvent-free silicone/epoxy coating systems

Self-stratifying coatings facilitate segregation of two distinct and inter connected coating layers with complimentary properties in a single shot application. This novel process thus obviates the need for multiple coating steps. In the current work, we report the effect of pigmentation on self-stratification of a solvent-free coating system comprising incompatible polymer blends of epoxy and silicone resins. The resins were pigmented to impart anticorrosive properties to the epoxy layer (pigment volume concentration, PVC of 10, 20 and 30% using red iron oxide) and weathering resistance to the silicone resin using TiO2 (a fixed PVC of 10%). A series of complimentary analytical techniques were employed to probe the degree of stratification of the cured coating at different length scales, namely contact angle goniometry, attenuated total reflectance-Fourier transformed infrared spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. There were evidence of TiO2 migrating towards epoxy and iron oxide towards silicone resin, even though, the pigments were properly dispersed in their corresponding resins. This implied significant effect of PVC on stratification of epoxy and silicone resins. Rheological studies were employed to epoxy, silicone resin and their pigmented mixture to understand the curing behaviour as well as to understand its effect on stratification process. We also scrutinized the outcome of constrained stratification on thermo/mechanical and anticorrosive performance of the coatings. Contact angle values obtained for top surfaces of all PVC, i.e., 10, 20 & 30 stratified coatings were found to be > 106 degrees and shows hydrophobicity and the bottom coat was found to be < 50 degrees which is more hydrophilic in 20 & 30 PVCs coatings. The 20 PVC coating showed clear stratification, optimal anticorrosive and hydrophobic properties as revealed by electrochemical impedance spectroscopy and contact angle goniometry studies, respectively.

Automated summary

Self-stratifying coatings allow for the segregation of different coating layers in a single application, eliminating the need for multiple coating steps. This study investigates the effect of pigmentation on the stratification of epoxy and silicone resins in a solvent-free coating system. The results show that the pigment volume concentration has a significant impact on the stratification of the resins. Analytical techniques such as contact angle measurement, infrared spectroscopy, electron microscopy, and X-ray spectroscopy were used to study the degree of stratification at different length scales. Rheological studies were also conducted to understand the curing behavior and its effect on stratification. The findings suggest that a PVC of 20% achieves the optimal stratification, anticorrosive, and hydrophobic properties.