Heat resistant and flame retardant coatings inhibit, suppress, or delay the production of flames from potentially flammable materials such as textiles and plastics. Flame retardants are essential for minimizing the impact of fires and consist of various chemicals with diverse properties and structures.

Heat resistant and flame retardant coatings exist extensively in the construction sector on materials such as plastic pipes and cables. Rising safety standards continue to drive the increase in global demand for flame retardants.

Common elements in flame retardants include bromine, phosphorus, and chlorine. The coatings also employ inorganic compounds, either alone or in combination with bromine, phosphorus, or nitrogen. Most flame retardants are designed for highly specialized applications, making their substitution difficult.

Flame retardants impede ignition by raising the threshold required to start a fire. They limit the spread of fire and suspend flashover, a "fireball" caused by the spontaneous combustion of heated gasses emitted from burning materials. The delay contributes to a reduction in fire intensity and increases time for appropriate action.

Today, the importance of flame retardants has accelerated significantly due to a greater level of fire hazards presented by assorted products and electronic devices found in modern homes. Public facilities such as hospitals, schools, and stadiums are equipped with more electronic products, making flame retardants a critical element for protecting vulnerable groups such as children and the elderly.

In response to concerns about the health and environmental impacts of flame retardants, numerous formerly common chemicals have been banned. Several modern flame retardants, specifically brominated compounds, are another source of public health debate because of limited information on their toxicity and potential effects.

Types of Heat Resistant and Flame Retardant Coatings

Flame retardants are categorized by their chemical makeup, including:

Brominated: Mainly used for their flame retardant properties. Brominated compounds are added to plastics without altering their properties, making them suitable for a broad range of applications. They exist in textiles, electronics, building materials, and other products.

Phosphorus: Used in mattresses comprised of foam, upholstered furniture, TV casings, textiles, and a plethora of plastic or rubber based products.

Nitrogen: Used in insulation, furniture foams, and electronics.

Chlorinated: Comparable to brominated compounds, chlorinated flame retardants have excellent thermal stability and are used to inhibit flame formation in products such as polyurethane foam, rubber, and flexible plastics.

Inorganic: Used as flame retardants with applications in plastics, paints, rubber, and similar products.

How Heat Resistant and Flame Retardant Coatings Work

As a piece of material burns, the flames produced represent combustion of flammable gasses given off via thermal decomposition (pyrolysis). In burning wood, pyrolysis is fueled by carbon dioxide, water vapor, and heat released during the combustion process. Flame retardants control the spread of the fire by impeding the pyrolysis process and are most effective in the ignition phase. Once a fire develops, the coatings have little effect.

Flame retardants containing bromine and chlorine (known as halogenated flame retardants) are designed to remove H and OH radicals during the ignition phase. Bromine or chlorine radicals, formed when the halogenated retardants heat, react with hydrocarbon molecules in the gas mixture. This process inhibits the gas phase combustion process and slows down or blocks ignition altogether.

Brominated and chlorinated compounds have different flame retardant properties. Bromine-hydrocarbon bonding properties are weaker in comparison to those of chlorine-hydrocarbon, resulting in easier release of bromine radicals when a material's temperature increases. The process occurs over a narrower temperature range, resulting in a higher bromine radical concentration and fire-stopping effectiveness.

Phosphorous flame retardants have a dissimilar effect and work in the solid phase of the combustible material instead of the gas phase. In the presence of a heat source, phosphorus flame retardants release phosphoric acid and promote charring. This process inhibits pyrolysis by cutting off fuel to the flame. Combination halogen/phosphorus compounds such as chloropropyl and chloroethyl use gas phase and solid phase mechanisms for fire retardation.

Inorganic flame retardants include aluminum trihydrate, magnesium hydroxide and boron compounds. Aluminum trihydrate works by decomposing to aluminum oxide at high temperatures and forming a nonflammable protective layer on the surface of a material, releasing water as steam. Magnesium hydroxide acts in a similar manner at higher temperatures. Nitrogen-based flame retardants cool the material and release nitrogen in a gaseous form to dilute the oxygen around it. Intumescent coatings avoid fire by expanding when heated to form an insulating layer between materials such as wood, plastic, steel and other materials. They also protect non-flammable materials, such as structural steel, from weakening due to the intense heat given off by a fire. The intended effect evades or delays structural collapse.

Applications

Flame retardants are employed in a wide range of applications, including:

• Adhesives
• Building and construction materials
• Carpets
• Electronics and electrical devices
• Furniture and furnishings
• Insulation
• Rubber
• Paint
• Plastics
• Polyurethane
• Textiles
• Transportation (planes, trains, automobiles)
• Wire & cable

Selecting Coatings

When purchasing flame retardant coatings, research the type of retardant appropriate for a particular function. Flame retardants are not interchangeable—some compounds and products work better than others for distinct applications. Check both the manufacturer's guidelines and applicable regulations to confirm the most effective choice. Federal, state, and local building and fire codes along with various regulations will align with the intended use.

Standards

SAE AMS3126 - Aluminum coating material, corrosion and heat resistant thermosetting

IEEE 817 - Test procedures for flame-retardant coatings applied to insulated cables in cables trays

References

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FORREST Technical Coatings | Sekisui Voltek, LLC | Victrex plc.