Intumescent Coatings: Raw Materials, Performance Metrices & Test Requirements

TAGS: Wood Coatings Industrial Coatings Marine and Protective Coatings

Steel Building with Intumescent Coatings Fire is one of the most destructive forces known to man. Between 1993 and 2016, an average of 42 thousand people lost their lives annually in structure fires. While this is a sobering figure, the annual number of fire deaths each year has been steadily declining. This decline in annual deaths from fire has many drivers including:

Stricter building codes
Widespread use of fire detection and warning technology, and
Improvements in fire retardant materials

An important component of these advances in fire retardant materials are intumescent coatings. Intumescent coatings protect the substrate by rapidly expanding when exposed to heat and flame.

As intumescent coatings expand, they slow the spread of the flames and act as fire retardants. Fire retardant materials and fire resistant materials differ in the fact that fire resistance is a property of the material, meaning that it will not support flames. By slowing flame spread, fire retardant materials can protect both fire resistant and flammable materials from damage due to fire.

Go deeper to understand heat restistant and fire retardant coatings here »

Even non-flammable materials like concrete and steel can be damaged by heat and fire resulting in building collapse from loss of structural integrity. Both fire retardant and fire resistant materials are considered passive fire protections methods since they do not have to be activated like a manual or automatic sprinkler system.

Warehouse fire in Redlands, California showing the consequences of structural steel collapse due to fire
(Credits: KABC Television, Los Angeles, California)

What do you Need to Consider while Formulating Intumescent Coatings?

There are many parameters specific to the formulation of intumescent coatings. Among these factors are:

Fire protection performance required by government or industry guidelines,
Smoke and toxic gas released during a fire,
Corrosion resistance, and
The appearance of the applied coating.

These various factors are weighted differently depending on the end-use, but all are important. Formula ingredient selection is often limited by national or local regulations. For example, some regulations restrict halogen-containing components in fire retardant coatings.

Let's addresses how these factors affect the formulation and use of intumescent coatings by discussing raw materials, performance requirements, and commercially available coatings.

Formulation Elements of Intumescent Coatings

Intumescent coatings formulations require three elements to perform satisfactorily.

The first element is a char donor. The char donor supplies organic material which reacts under fire conditions to produce an inorganic carbonaceous inflammable layer.
An acid donor releases acid during a fire to activate the reactions leading to char formation. This may be an organic or inorganic acid.
Finally, a foaming agent is necessary to expand the inflammable char many times the thickness of the original coating layer. By expanding the char layer the coating can insulate the substrate from heat damage.

These combined elements can delay or prevent structural collapse, allowing more time for building evacuation and fire fighting.

There is a large variety of formulation materials which fulfill the three required functions for intumescent coatings. Which ones you choose will depend on the base resin system, curing mechanism, application method, and environmental service conditions the customer demands. National and regional regulations and industry requirements will also play a role in raw material selection.

Trying to describe in detail all the possible combinations of ingredients used to formulate intumescent coatings is beyond the scope of this article, so I will try to touch on some new and innovative materials. A material selection resource like SpecialChem is a good place to begin your product development process. As always, the final coating formulation must be thoroughly tested per your customer's requirements.

End-less Fire Protection Benefits with NeoGraf's Graphite Additives

Regulatory demands and growing consumer pressure are motivating manufacturers across a variety of markets to use solutions that can meet progressively complex environmental, safety, and regulatory standards. This is where NeoGraf Solutions’ GrafGuard® non-halogenated fire-stop additive stand out.

Manufactured from natural graphite flake, the proprietary processing for GrafGuard® expandable graphite inserts an expansion agent (or intercalant) between the parallel layer planes in the graphite. When exposed to elevated temperatures as low as 160°C, the intercalant decomposes to a gas that forcefully expands the layer planes apart, forming a highly effective carbon char layer. This resulting char protects the reactive coated substrate from the heat of the fire and minimizes the smoke generated from the burning of the substrate. In addition, the porous char layer allows for percolation of synergistic fire-retardant materials as they decompose during a fire.

GrafGuard® has successfully been incorporated into a wide variety of intumescent polymeric coating systems, including epoxies, latex, silicones, siloxanes, and polyurethanes. Find the suitable GrafGuard® grades for your application »

Boost Waterborne, Clear Intumescent Wood Coatings Capability

Waterborne coatings are at the forefront of most new technical coatings developments and intumescent coatings are no exception to the rule. One recent Clariant offering which facilitates waterborne, clear intumescent coatings for wood is Exolit® 855. This unique, proprietary mixture of clear liquid partial phosphoric acid esters is completely water-soluble, non-flammable and non-hygroscopic.

When formulated with a melamine-containing resin, Exolit® 855 contains all the reactants needed to make a waterborne intumescent clear coating for interior wood applications. If an exterior application is required, a clear topcoat should be applied over the intumescent coating.

Performance Metrics, Test Specifications and Regulatory Restrictions

There are many test specifications, building codes, insurance requirements, and environmental, safety and health regulations governing the uses and formulation of intumescent coatings. Test specifications are used to predict the performance of an intumescent coating in a fire in lieu of actually burning down a building. Customers, architects and regulators choose the relevant test specification depending on factors such as:

The duration of fire protection needed
The expected maximum temperature the fire will reach, and
The amount and composition of the smoke released by the coating

Insurance underwriters may also request specifications to minimize losses and maximize occupant safety. Stakeholders may often prohibit certain formulation components, for example, halogenated compounds, for environmental, health and safety reasons.

Most requirements for flame retardant coatings include test methods for:

Flame spread (how fast a flame propagates) and
Smoke generation (the density or relative toxicity of the smoke) of the coated substrate

A long-established test using both of these parameters is the ASTM E-84 test used for building products in the United States and adapted for use in many other countries. This test uses a long “flame tunnel” where one end of the sample is subjected to a gas flame, as the sample burns the optical density of the evolved smoke is measured. The rating for the sample is a combination of the length of the burning track and the smoke generation compared to two standards, one flammable and the other non-flammable.

ASTM E84 Test Method (Source: ROCKWOOL North America)
Considering the wide-ranging specifications and end uses for intumescent coatings it might be difficult to decide where to start formulating a new product. Coordination between your marketing colleagues and the product development team is essential to determine the best fit for your company.

Working with existing customers in the market space to find a solution for an unmet expectation could be the best entry point. Thoroughly research existing products and formulation ingredients, often the answer lies in using an existing ingredient in a novel way.

Commercial Coatings Examples

Hempafire Optima 500 to protect structural steel from cellulosic damage

Most manufacturers of industrial or marine and protective coatings offer intumescent coatings. These are a natural extension of product lines consisting of high corrosion or chemical resistant paints. Intumescent coatings often incorporate those properties as well or are designed to be combined with primers or topcoats with corrosion and/or chemical resistance.

One example is Hempel Hempafire Optima 500, this is a very low VOC waterborne thin film intumescent coating optimized to protect structural steel from damage due to cellulosic fires. This fast-drying acrylic coating supports higher productivity because of its fast-drying properties which require fewer coats to achieve the required levels of fire protection.

The market for intumescent coatings exceeded 985 million USD in 2019 and is expected to grow at 4.8% CAGR from 2020 to 2026. Even with the effects of the pandemic-driven global economic downturn considered, this forecast should still hold since many government-sponsored recovery programs include large investments in infrastructure, much of it using intumescent coatings. This growth will drive innovation and open the market to new players with novel and cost-effective solutions to the age-old problems of fire protection.

Find Suitable Flame/Fire Retardants for Coatings

View a wide range of flame/fire retardants available in the market today, analyze technical data of each product, get technical assistance or request samples.

Heat Resistant and Flame Retardant Coatings – Related Read

Intumescent Coatings: Material Selection & Formulation Tips