Environmentally Friendly Hybrid Organic–Inorganic Halogen-Free Coatings for Wood Fire-Retardant Applications

Abstract

Wood and wood-based products are extensively used in the building sector due to their interesting combination of properties. Fire safety and fire spread, however, are of utmost concern for the protection of buildings. Therefore, in timber structures, wood must be treated with fire-retardant materials in order to improve its reaction to fire. This article highlights the flame retardancy of novel hybrid organic–inorganic halogen-free coatings applied on plywood substrates. For this purpose, either a huntite-rich mineral (H5) or its modified nano-Mg (OH)2 type form (H5-m), acting as an inorganic (nano) filler, was functionalized with reactive oligomers (ROs) and incorporated into a waterborne polymeric matrix. A water-soluble polymer (P (SSNa-co-GMAx)), combining its hydrophilic nature with functional epoxide groups, was used as the reactive oligomer in order to enhance the compatibility between the filler and the matrix. Among various coating compositions, the system composed of 13% polymeric matrix, 73% H5 and 14% ROs, which provided the best coating quality and flame retardancy, was selected for the coating of plywood on a larger scale in one or two layers. The results indicated that the novel plywood coating systems with the addition of ecological coating formulations (WF-13, WF-14 and WF-15), prepared at two layers, reached Euroclass B according to EN13501-1, which is the best possible for fire systems applied to wood.

Novel Hybrid Organic–Inorganic Polymeric Coatings Containing Phosphonium or Acidic Groups for Improving Flame Retardancy of Wood

“…The mineral huntite, H5, was kindly provided by the company Sibelco (Sibelco Hellas SA, Thessaloniki, Greece) and consisted of a huntite/hydromagnesite mixture, 88/12 wt./wt. %; the ratio was calculated by neglecting minor concentrations of other minerals, mostly dolomite [14,19,45]. Ultrapure water was obtained by means of an SG apparatus water purification unit.…”

“…In the last 40 years, the most predominant flame retardants (FRs) were halogenated flame retardants (HFRs). However, the production of carcinogens and the combustion process of those materials has led to the use of new halogen-free FRs in wood products, which are expected to be environmentally friendly and non-hazardous to human health [17][18][19]. These new flame-retardant additives involve phosphorus-, nitrogen-, silicone-, boron-, zinc-, iron-and aluminum-containing compounds.…”

Contemporary Fire Safety Engineering in Timber Structures: Challenges and Solutions

“…Flame-retardant interventions predominantly alter the timber surface or inherent chemical characteristics to attenuate its combustion rate and minimize heat release [59][60][61]. Scholars and industry experts have introduced various methodologies to bolster timber's resilience to fire [61][62][63][64][65]. One pivotal approach entails the utilization of specialized flameresistant surface coatings [66].…”

Preparation of a Flame-Retardant Curing Agent Based on Phytic Acid–Melamine Ion Crosslinking and Its Application in Wood Coatings

“…Therefore, it is necessary to carry out modifications of wood in order to improve its flame-retardant performance and reduce its fire hazard [ 5 , 6 ]. Inorganic flame retardants alone do not readily adhere to the surface of wood; as such, using a flame-retardant adhesive coating is currently the most used method for flame retardancy [ 7 , 8 ]. Flame-retardant coatings can improve not only the flame-retardant performance of wood but also the physical and chemical properties of the wood surface [ 9 ].…”