Enhanced Mechanical Properties and Fire Resistance of Epoxy/Nanoclay Composite Coatings for Advanced Steel Protection

Abstract

This study investigates the enhancement of mechanical strength and flame retardancy in epoxy-based nanocomposite coatings reinforced with organically modified nanoclay (I.30E) at different concentrations (1, 3, 5 and 7 wt%). The coatings were systematically characterized to assess their mechanical performance, fire resistance, and thermal stability. Results showed that incorporating nanoclay significantly improved the fire retardant properties of the epoxy coatings. The Limiting Oxygen Index (LOI) increased from 21.3 % (pure epoxy) to 24.5, 26.3, 28.5 and 27.0 % for 1, 3, 5 and 7 % nanoclay, respectively. The best flame-retardant performance was observed at 5 wt% nanoclay, which achieved a UL-94 V0 rating, indicating self-extinguishing behavior and minimal dripping. Mechanical properties also exhibited notable improvements. Tensile strength increased from 45 MPa (pure epoxy) to 53, 61, 67 and 62 MPa for 1, 3, 5 and 7 % nanoclay, respectively. Similarly, impact strength improved from 15.2 (pure epoxy) to 20.8, 25.3, 28.7 and 26.5 J/m as the nanoclay content increased. Hardness and scratch resistance were also enhanced, with a maximum increase of 38 % in relative hardness and 133 % in scratch resistance at 5 wt% nanoclay. However, at 7 wt% nanoclay, mechanical performance slightly declined, suggesting a possible agglomeration effect at higher concentrations. Thermal analysis (TGA) revealed that char residue at 700 °C increased by 10, 15, 20 and 18 % for 1, 3, 5 and 7 % nanoclay, respectively, further confirming the improved fire resistance. SEM and XRD analyses demonstrated that nanoclay was well-dispersed in the epoxy matrix at lower concentrations, but slight aggregation was observed at 7 wt%, reducing its reinforcing efficiency. These findings highlight the significant potential of nanoclay-reinforced epoxy coatings for applications requiring enhanced fire resistance, mechanical durability, and thermal stability.

HIGHLIGHTS

• Epoxy coatings were reinforced with 1 - 7 wt% nanoclay I.30E, showing significant improvements in mechanical strength and flame retardancy.
• The optimal concentration of 5 wt% nanoclay yielded the best performance: Tensile strength increased by 49 %, and impact strength by 88 % compared to pure epoxy.
• The composite achieved UL-94 V0 rating and LOI of 28.5 %, indicating excellent self-extinguishing flame resistance.
• Thermal stability improved, with Tmax rising to 395 °C and char residue reaching 22%, demonstrating enhanced fire barrier formation.
• SEM and XRD analyses confirmed good nanoclay dispersion at 5 wt%, while higher concentrations led to agglomeration and performance decline.

GRAPHICAL ABSTRACT