A recent report describes the importance of varying the ratio of conventional flame-retardant additives and the scale of testing on the thermal and flammability/fire performance, of acrylic-based coatings.
Ammonium polyphosphate (APP) acid source, pentaerythritol (PER) carbonising agent, and expandable graphite (EG) blowing agent were used in intumescent coatings at various ratios. 1:1:3 or 1:3:1 or 3:1:1. Despite the different roles of APP, PER, and EG, in all the compositions, the physical mechanism of exfoliation of graphite played an important role in offering the fire protection.
With higher loadings of EG, the fire-resistance time was higher. However, there were clear differences in the protection extent when tested in a furnace under one-dimensional heat transfer conditions (bench-scale) as opposed to three-dimensional large-scale testing. Parameters that are not intrinsic to the coating system like char cohesion, cracking, delamination from the substrate, rapid and non-directional expansion, and even higher heat fluxes experienced by the edges of the I-steel section however all affect the fire performance.
This study was published in Progress in Organic Coatings Volume 150, January 2021.