Evaluating the use of calcium hydrogen phosphate dihydrate as a mineral-based fire retardant for application in melamine-urea-formaldehyde (MUF)-bonded wood-based composite materials

Calcium hydrogen phosphate dihydrate (DCPD) was evaluated for its potential as a mineral fire retardant (FR) for application in melamine-urea-formaldehyde (MUF)-bonded wood composites. The efficacy as FR was studied in melamine-urea-formaldehyde (MUF)-bonded three-layer particleboard as a function of addition quantities of 10-, 20- and 30 wt%. Resistance to fire and mechanical properties were determined by measuring the self-extinguishing time after flame exposure and internal bond strength, respectively. Combustion behavior was examined on samples with 20 wt% DCPD addition by performing cone calorimetry experiments. The efficacy of DCPD was evaluated by determining the heat release, total heat release rate, smoke production, and smoke production rate and compared to another promising mineral-based fire-retardant composition (FRC) based on hydroxyapatite (HA) with deliquescent salt and HA alone. The effect of FR on the curing behavior of MUF in relation to mechanical properties was determined through viscosity measurements of MUF with 10 wt% addition of FR. The results confirmed the fire-retardant characteristics of DCPD in wood composites, albeit at higher application rates when compared to the FRC, however with no negative impact on resin curing time or mechanical strength. Based on the demonstrated compatibility in MUF, DCPD is considered a promising mineral extender of other FRs for application in UF-based wood composites.