Eggshells: A novel bio-filler for intumescent flame-retardant coatings

•Eggshell, a novel bio-filler for intumescent flame-retardant coatings.•Addition of bio-filler improved the fire protection and adhesion of coating.•Combinations of Al(OH)3, Mg(OH)2 and CES reduced the surface spread of flame.•CES has a great potential for use as eco-friendly filler for intumescent coating.

The aim of this study was to develop intumescent flame-retardant coatings that incorporate chicken eggshell (CES) waste as a novel eco-friendly bio-filler. Three flame-retardant additives, namely, ammonium polyphosphate phase II, pentaerythritol and melamine were mixed with flame-retardant fillers and acrylic binder to synthesize the intumescent coatings. The fire performance of the coatings was evaluated in accordance with ‘BS 476: Part 6-Fire Propagation’ and ‘BS 476: Part 7-Surface Spread of Flame’ test standards. It was found that 4 out of 5 of the coated specimens (B, C, D and E) neither showed surface spread of flame nor any afterglow combustion upon fire exposure. The addition of 5.0 wt% and 2.5 wt% eggshell bio-filler into formulations B and E, respectively, improved fire protection due to char formation, with better morphology, height and structure of the protecting shield. The filler compositions of samples D (3.4 wt% TiO2/3.3 wt% Al(OH)3/3.3 wt% Mg(OH)2) and E (2.5 wt% TiO2/2.5 wt% Al(OH)3/2.5 wt% Mg(OH)2/2.5 wt% CES) applied at a thickness of 1.5 ± 0.2 mm achieved the lowest fire propagation index with a value of 4.5 and 5.0, respectively (BS 476 Part 6, Class 0 materials) which indicates excellent fire-stopping properties. The results showed that the coatings were effective in fire protection, with good qualities of water resistance, thermal stability, and adhesion strength. Significantly, coating E (with CES) has proved to be efficient in the protection of plywood against fire.