Abstract
Zinc oxide nanoparticles (ZnO NPs) were synthesized by a precipitation method, and a new charring–foaming agent (CFA) N-ethanolamine triazine-piperazine, melamine polymer (ETPMP) was synthesized via nucleophilic substitution reaction by using cyanuric chloride, ethanolamine, piperazine, and melamine as precursor molecules. FTIR and energy-dispersive X-ray spectroscopy (EDS) studies were employed to characterize and confirm the synthesized ETPMP structure. New intumescent flame retardant epoxy coating compositions were prepared by adding ammonium polyphosphate (APP), ETPMP, and ZnO NPs into an epoxy resin. APP and ETPMP were fixed in a 2:1 w/w ratio and used as an intumescent flame-retardant (IFR) system. ZnO NPs were loaded as a synergistic agent in different amounts into the IFR coating system. The synergistic effects of ZnO NPs on IFR coatings were systematically evaluated by limited oxygen index (LOI) tests, vertical burning tests (UL-94 V), TGA, cone calorimeter tests, and SEM. The obtained results revealed that a small amount of ZnO NPs significantly increased the LOI values of the IFR coating and these coatings had a V-0 ratings in UL-94 V tests. From the TGA data, it is clear that the addition of ZnO NPs could change the thermal degradation behaviors of coatings with increasing char residue percentage at high temperatures. Cone calorimeter data reported that ZnO NPs could decrease the combustion parameters including peak heat release rates (PHRRs), and total heat release (THR) rates. The SEM results showed that ZnO NPs could enhance the strength and the compactness of the intumescent char, which restricted the flow of heat and oxygen.
Highlights
Wood is one of the most sustainable, aesthetically pleasing and environmentally friendly materials
The average crystalline size calculated by applying the Debye-Scherrer equation on the diffraction peaks was found to be 19.8 nm for zinc oxide particles synthesized from zinc acetate
The absorption band at 3428 cm−1 was caused by the O–H stretching mode, which shows a small amount of water absorbed by the Zinc oxide nanoparticles (ZnO NPs)
Summary
Wood is one of the most sustainable, aesthetically pleasing and environmentally friendly materials. The use of wood is limited by various safety requirements and regulations relating to its flammability and the propagation of fire characteristics To overcome this problem and maintain fire safety, fire-resistant coatings must be developed. Scientists have made great efforts to synthesize polymers that can exhibit both charring and foaming properties to solve this problem In this path, triazine molecules were chosen to prepare charring–foaming agents (CFAs), as it contains a high amount of nitrogen and carbon units [5,6,7]. Based on catalytic applications of ZnO, we selected it as a synergist, and we expect that it can show positive effects on flame retardancy of IFR systems [20,21,22,23,24]. The effects of ZnO on epoxy/IFR coatings were investigated by limited oxygen index (LOI) test, vertical burning tests (UL-94 V), TGA, cone calorimeter tests, and SEM
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