New Flame Retardant for Transparent Intumescent Wood Coatings

Wood remains one of the most widely used building materials today. As a versatile material, wood is used in the construction of many structures, from residential homes to public-service buildings such as stadiums and high-rise buildings. However, wood lacks inherent fire resistance and cannot be used in public areas without appropriate fire protection. Pigmented fire-retardant wood coatings are commonly employed for this purpose. Beyond fire protection, however, coatings must also appeal to the aesthetic preferences of architects and building owners, offering an attractive and natural appearance. Clariant developed Exolit® 855 to meet this dual requirement. It is a completely transparent, nearly colorless solution that provides fire retardancy for transparent intumescent wood coatings, excellent fire resistance for all wood types, and scratch resistance. The product is based on a special formulation of liquid partial phosphoric acid esters. In combination with other components, it contains all reaction partners required for the intumescent reaction and reacts at lower temperatures than most conventional systems. The transparent intumescent coating can be applied to virtually all wood surfaces, including solid wood, medium-density fiberboard, particle board, plywood, and all other composite wood types.

Successfully Passed Fire Tests for Various Applications

Beyond its use as a building material, wood can also be used in decorative design as laminated wood varnish on various surfaces, such as "aluminum composite material" used in the interiors of passenger ships and yachts, or as lightweight yet sturdy honeycomb structures used in aircraft interior partition components (Figure 1). In all application areas, compliance with special fire test requirements tailored to the hazard levels in construction, shipbuilding, or aerospace applications is necessary. Using the same transparent intumescent formulation based on Exolit® 855, all fire tests conducted were successfully passed.

Specifications and Performance

The intumescent coating system consists of a two-component formulation. Part 1 comprises a special resin, several additives, and water. Part 2 contains Exolit 855, a hardener, and other components. The combined components, with a pot life of approximately 3 hours, can be easily applied using a spray gun or roller. The reference formulation provided by Clariant under a confidentiality agreement demonstrates excellent flow and leveling properties. The coating dries at ambient temperature, reaches dust-free condition after 4 hours, and becomes scratch-resistant after 24 hours. As always, an additional solvent-based topcoat provides protection against high humidity and direct water contact. When tested on a solid pine wood substrate (400g/m² wet) in a cone calorimeter test (iCone; 50kW; distance 25mm), the intumescent coating delivers excellent fire protection performance as shown in Figure 2. Over a 600-second test period (THR 600), total heat release is reduced by 98%, while the maximum average heat release rate decreases by 67% compared to an uncoated panel (Figure 2). In an SBI test on 13mm particle board coated with transparent intumescent paint, a "B-s1, d0" European classification is achieved.

Figure 1. Aircraft interior components

Figure 2. Reaction to fire—uncoated wood and wood coated with intumescent coating

Göknur Çıtır Sales Director Additives Business Unit Middle East and Turkey Clariant