A novel approach utilising phosphorylated casein for fire-retardant and formaldehyde-free medium density wood fibreboards

Casein has been employed in composite materials as a flame retardant (FR). However, in the current research, casein has not been applied to a medium density fibreboard (MDF) material system, especially in a formaldehyde-free MDF material system, to investigate its impact on mechanical and fire-resistant performance. Polyamidoamine-epichlorohydrin (PAE) resin has been utilised as a binder to manufacture formaldehyde-free MDF samples in this research. Phosphorylation was conducted to enhance the flame-retardant ability of casein. This chemical treatment resulted in the significant improvement on the char-forming performance of the casein, leading to the dramatic reduction of the peak heat release rate (PHRR) by ⁓45% compared with non-treated casein. The char formation of the phosphorylated casein in the MDF sample also decreased its PHRR more effectively by ∼18% with the drop of the THR value (∼40 MJ/m2) than that of the casein. Besides, the addition of the phosphorylated casein to the MDF based on the PAE binder did not diminish the binder`s bonding performance, resulting in the improvement of the flexural modulus by ∼23% and flexural stress by ∼16%, while the IB strength retained compared with that of the control MDF sample. The current study clearly demonstrates that the jointly use of phosphorylated casein and PAE is a promising avenue to overcome one of the ongoing challenges in the MDF material system with regard to mitigating the reduction in mechanical performance associated with the introduction of flame-retardant materials.