Mineral-based composition with deliquescent salt as flame retardant for melamine–urea–formaldehyde (MUF)-bonded wood composites

Abstract

A flame retardant composition (FRC) composed of a surface-treated calcium carbonate-based mineral, having high porosity and loaded with deliquescent calcium chloride, was assessed for its potential as a flame retardant. Two FRCs with 16% and 26% calcium chloride (dry solid) stored in the pore structure, respectively, were studied with respect to their ability to absorb and release free water and their efficacy in melamine-urea-formaldehyde (MUF)bonded wood composites was investigated. Water absorption capacity was determined by performing absorption tests at a temperature of 20°C and relative humidity (RH) of 65% and 95% and the water release behaviour was studied by performing thermogravimetric analysis. The FRCs have the capacity to hold substantial amounts of water (up to 60 wt. %), however still behave as a free-flowing powder. The influence of addition of 10 and 20 wt.% FRC in wood composites on reaction to fire and strength properties was determined by measuring the selfextinguishing time after flame exposure and internal bond strength, respectively. These effects were evaluated by comparing to ground calcium carbonate (GCC) and commercially available nitrogen containing phosphorus based fire retardant. Although the FRCs had a negative impact on internal bond strength, the results confirmed their flame retardant potential and showed that 10-15 % by weight of the flame retardant would be a good compromise, in terms of the trade-off between flame retardancy and mechanical properties. The synergistic effects of multiple flame retardancy reaction mechanisms due to the presence of inorganic minerals and a hygroscopic agent, CaCl2, are also discussed. The unique properties of the FRC, which allow to exploit the fire retardant potential of CaCl2 while at the same time eliminating the risk associated with the emission of hydrogen chloride gas during combustion, is confirmed by the results of FTIR spectroscopic analyses of the flue gas.

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

“…Hydroxyapatite‐based mineral consisting of 59 wt% of hydroxyapatite (HA) Ca 5 (PO 4 ) 3 (OH) and about 41 wt% calcium carbonate (CaCO 3 ) was provided by Omya International AG. The detailed characteristics of the material are provided in Ozyhar et al 19 …”

“…Furthermore, the industrial feasibility of this approach has been demonstrated in fiberboard products 18 . A promising mineral‐based fire‐retardant composition (FRC), consisting of a mineral carrier material and deliquescent salt for application in particle‐based wood composites has been further evaluated 19 . The authors demonstrated the efficacy of the mineral‐based FRC as a fire extinguisher and that the FRC can be easily incorporated into the structure of a particle‐based wood material.…”

“…Building on the promising results from the application of calcium carbonate and the mineral‐based FRC in wood‐based products, 15,16,18,19 this study investigates the use of another potential mineral for application in wood panels. Calcium hydrogen phosphate dihydrate (DCPD), a hydrated mineral, is proposed as a functional mineral additive for application in wood‐based composites, which is expected to exhibit fire‐retardant properties similar to other non‐halogenated inorganic phosphorous compounds, such as ammonium polyphosphate (APP) 20‐22 .…”

“…In addition, they can present a partial gas phase contribution to the flame extinguishing effect 23 . Similar to other hydrated minerals, such as ATH, magnesium oxides, or struvite often described as FR in connection to wood‐based materials, 8,24 DCPD is also expected to release water vapor in the event of fire, which can contribute to improved fire retardancy by diluting flammable gases, 19 in addition to the known char formation of polyphosphates. The fire‐retardant properties of DCPD have been previously demonstrated in cotton fabric 25 .…”

“…However, its application in wood‐based composites has not yet been investigated, to the best of our knowledge. The potential fire‐retardant effect of DCPD addition, as well as the effect of addition quantity on the mechanical properties, is compared to the previously reported FRC 19 . To this end, we investigated material compositions of 10‐, 20‐ and 30 wt% FR to determine the optimum addition amount in terms of fire retardancy and the mechanical properties.…”