Flame Retardants in Plastics: Past and Present

Flame Retardants in Plastics: Past and Present

Flame retardants are a class of chemicals specifically designed to provide passive fire protection to polymers in specific fire risk situations. The fire protection provided by flame retardants can vary from flame retardation, slowing the growth of flame spread/heat release to reducing smoke and toxic gases. When properly selected and used, flame retardants can be used to implement a variety of safety measures. It is important to remember that each flame retardant solution must be customized for a specific polymer and specific testing. In other words, flame retardants are chemicals used in thermoplastics, thermosets, textiles and coatings to prevent or resist the spread of fire.

Flame retardants are a type of polymer additive that is added to plastics during the manufacturing process to bring specific benefits to the plastic that the base polymer cannot provide on its own (e.g., better mechanical, thermal, or electrical properties, color, oxygen or UV protection). An important point to understand is that there is no one universal flame retardant, because a material that works well with a polymer in one particular test may not work with the same polymer in another test, or with a different polymer in the same test. Each flame retardant application must have a specific test for a specific polymer. Developing new flame retardant applications requires proper research and careful observation of polymer chemistry, polymer thermal decomposition behavior, and flame retardant mechanisms.

The global flame retardants industry market size was USD 7.2 billion in 2022, growing at a CAGR of about 5.1% and is expected to reach USD 9.7 billion by 2028. Important applications include aerospace, automotive, electronic and electrical products, carpets, textiles, mass transportation (trains, ships, and subways), building and construction, military, and wire and cable.

The most common flame retardants are brominated flame retardants, which are widely used due to their great efficacy in a wide range of polymers and applications, as well as their low cost. These materials were known as early as the 1930s and have proven to be effective. However, the use of some flame retardants raised environmental and health concerns and had to be discontinued. For example, polychlorinated biphenyls (PCBs) were banned in 1977 after they were found to be toxic. The EU banned several PBDEs in 2008, 10 years after PBDEs were found to accumulate in breast milk in Sweden.

As far as environmental issues are concerned, two major environmental events have captured the public's attention and led to a general rejection of chemicals in the Western world. These include the Great Smog of London (UK, 1952) and the Cuyahoga River Fire (near Cleveland, Ohio, USA, 1969), where incorrect handling of the chemicals led to the river "catching fire" and causing a large number of deaths. 2006 saw the last major producer of PentaBDE and OctaBDE (Great Lakes Chemical Company, now part of Chemtura) voluntarily withdrawing both of these chemicals from the market. In 2006, the last major producer of PentaBDE and OctaBDE (Great Lakes Chemical Corporation, now part of Chemtura) voluntarily withdrew both chemicals, and the U.S. Environmental Protection Agency (EPA) tightly regulated them to ensure that there would be no significant new uses for them.

In addition to this, in May 2012, the Chicago Tribune published an informative article calling for a ban on the use of the entire class of flame retardants. In the article, the Chicago Tribune mentioned that toxic chemicals used in plastic products have been linked to serious health problems, including cancer, developmental issues, neurological deficiencies, and impaired fertility.

Considering the drawbacks of flame retardants mentioned above, flame retardants that have been used for decades, such as brominated diphenyl ethers (BDEs) and hexabromocyclododecane (HBCD), will no longer be allowed to be used after the end of 2013 or 2014.

In light of all these concerns, flame retardant manufacturers are considering the introduction of a number of different flame retardants that are not harmful to the environment and do not cause health problems.

What's new with flame retardants?

With the banning of brominated flame retardants, many companies have introduced new alternatives. In many cases, the alternative is a polymerized brominated polymer or a non-halogenated flame retardant. This is because polymeric materials tend to have a much lower environmental impact (low bioaccumulation and toxicity) than small molecule materials. The use of polymeric flame retardants is likely to continue as flame retardant manufacturers continue to advance this technology. In fact, from a production standpoint, polymerized flame retardants offer a number of advantages over the flame retardants they replace. Specifically, they may be easier to melt compound into plastics and provide a better balance of properties in the final plastic product, which will be a polymer/polymer blend rather than a polymer with fillers/additives.

New Commercial Non-Halogenated Flame Retardants

The first class of new non-halogenated flame retardants are polymeric/isomeric phosphonate compounds. All of these additives and oligomers can be melted, compounded with other polymers or used directly as inherently flame retardant materials. They have been used in a wide range of applications such as fibers, electronics, transportation (aerospace, trains), building and construction. The most effective polymers appear to be those that contain oxygen in the polymer backbone, including polycarbonates, polyesters [unsaturated, polyethylene terephthalate, polybutylene terephthalate], thermoplastic polyurethanes and epoxy resins.

Protective Coatings - Novel Flame Retardant Methods

Another method of achieving flame retardant protection in thermoplastic materials is the use of protective coatings. There are two main methods associated with thermoplastics. The first is the use of infrared reflective coatings on thermoplastics so that the material never heats up enough to thermally decompose and ignite.

The other method of protective coating is the use of layer-by-layer (LbL) coatings. This method has been used successfully on textiles and foams.

Flame Retardants for Plastic Additive Manufacturing

In the past year, a completely new technology has opened up new markets, new applications, and the potential to bring plastic product manufacturing to even more companies. The technology that has caused this explosion is additive manufacturing or 3D printing. Additive manufacturing technology has the potential to bring plastic customized parts, designs, and shapes within reach, in many ways very similar to the way the printing press has made text more ubiquitous.

The question is how did flame retardants come about?

The answer can be found in the application of printed parts. More specifically, it's a matter of examining the uses of the printed parts and any fire risks associated with those uses.

If you are just printing a toy or a neat shape that will be used as a model, then any plastic that is compatible with the 3D printing process is acceptable. However, if you are making a customized enclosure or custom parts for an electronic application, then there may be an associated fire risk.  If there is a potential for short circuiting near the plastic part, then flame retardancy may be required, and common thermoplastics used for 3D printing (typically HIPS or ABS) may not be able to meet this need.

In addition to all of these developments in the field of flame retardants, there have been various conferences held internationally where experts in the field have come together to discuss how to make flame retardants that do not pose a threat to the environment and biological health. We all agree that flame retardants are necessary because they prevent fires, but flame retardant manufacturers should try and come up with formulations that do not jeopardize the health of all living things while ensuring environmental safety.

The above is the introduction of the past and present content of the flame retardant, if you want to continue to discuss with us, welcome to contact us!