Improvement of fire protection properties of epoxy coatings with cobalt-zinc based metal-organic frameworks and siloxane co-loaded alginate fibers as nano-reinforcing agents

Abstract

Alginate fibers (ORF), as an organic fiber, have the natural advantage of good compatibility with epoxy resins. However, it is unable to adequately serve as a reinforcing residual char at high temperature due to its greater tendency to form amorphous char. To address this shortcoming, Co, Zn-MOF was uniformly immobilized on the surface of ORF, which accelerated the transformation of resin matrices to stabilized carbonaceous materials. Simultaneously, the Co, Zn-MOF could induce the conversion of the ORF into residual carbon and retain its fiber structure, thus serving the purpose of reinforcing the residual carbon. After that, the organosilicon was loaded on the surface of ORF/Co,Zn-MOF to obtain ORF/Co,Zn-MOF@Si composite flame retardant, which could form a stable silicon network at high temperature, thus effectively slowing down the heat transfer process. The experimental results proved that the ORF@Co,Zn-MOF@Si filled EP exhibited maximum tensile strength (12.2 ± 0.51 Mpa) and impact strength (18.3 ± 0.56 KJ/m²). Further, the ORF@Co,Zn-MOF@Si/EP composite coating had a significantly lower backside temperature (166.4 °C) than other coatings, signaling optimum thermal insulation efficiency. It is worth mentioning that the ORF@Co,Zn-MOF@Si/EP samples achieved a significant residual carbon retention rate (31.9 %) in the heat loss assessment session, which is attributed to the catalytic effect of Co and Zn ions on carbon generation within the Co,Zn-MOF framework. The expansion height and expansion rate of the ORF@Co,Zn-MOF@Si/EP sample were 19.60 mm and 15.2, highlighting a significant enhancement in foaming behavior. Besides, some fibrous structures can be clearly observed in the carbon layer of ORF@Co,Zn-MOF@Si/EP, which can be explained by the catalytic carbon-forming effect of Co,Zn-MOF and the protective effect of silicon network.