3D Printing with Flame-Retardant Materials

Fire damage is a multi-faceted menace. Capable of causing human casualties and injuries, widespread destruction and environmental pollution. Ensuring components aren’t prone to catching fire easily or propagating flames is of great importance for a variety of industries. Therefore, using materials that can prevent the spread of fire is often mandated.

Flame-retardant polymers are of particular importance in the aerospace and automotive industries. Slowing the spread of a fire in a car for example can allow time for its occupants to escape.

There are a handful of flame retardant materials available for 3D printing already. One example is PA 2441FR, a flame-retardant polyamide for use with laser sintering systems.

Recently Markforged released Onyx FR, a variant of their chopped carbon- nylon material. This material is suitable for building parts with exceptional mechanical properties.

What does ‘flame-retardant’ mean?

A flame-retardant material simply slows down the spread of fire. There are various mechanisms a material might use to do this, including:

• Using chemicals that react endothermically when heated. This means the chemical systems involved in the reaction essentially “absorb” heat, reducing temperatures and slowing fires.
• Releasing an inert gas, which acts to stifle the flames by cutting them off from oxygen.
• Having burning layers shield unburnt layers through the process of charring.

Note: Often ‘flame retardant’ is confused with ‘flame-resistant’. The latter of which refers to a material that completely resists catching on fire at all.

Why is it important?

Flame retardant materials are very important due to the obvious potential for damage fire possesses. An example of how they help can be seen in a 2009 UK government report. Implementing mandatory use of flame retardant materials resulted in significant fewer deaths and injuries.

While there were multiple other factors resulting in this reduction, it’s clear that materials that both passively and actively act to extinguish flames can be beneficial in preventing fires.

Where are these materials useful?

In general, any plastic components in close proximity to electrical current requires some form of fire resistance or retardancy. Wire nuts, junction boxes and internal supports for cables are all examples of components at risk of catching fire if an electrical issue occurs. Industrial machines, DIY tools and household equipment such as microwaves, toasters and dishwashers all contain flame retardant components.

In addition, the insides of vehicles, such as the interior of a plane or the cockpit of a race car, also need to prevent the spread of fire in order to protect their human occupants.

Markforged Onyx FR

Last year, Markforged released a fire-retardant variant of their Onyx material, called Onyx FR. This variant managed to get a rating of V-0 in the UL 94 Flammability rating, which is a US plastics flammability standard.

The testing process involved being set alight repeatedly with an external flame. To achieve the V-0 rating, it needed to exhibit the following properties:

• Burning for less than 10 seconds after the first and second burn. This demonstrates how quickly parts made with the material would stop burning.
• Afterglow after the second flame needed to last less than 30 seconds. This is a good guide on how quickly the part cools after being set on fire. The longer a part remains hot enough to glow, the more likely it is to reignite another part nearby.
• After being set on fire 10 times, no material was allowed to drip that would ignite cotton batting. Dripping material that can ignite other material is a sign that a component could ignite further fires in its immediate surroundings.
• The combustion could not consume the whole sample. This is a useful measure of how difficult it is for a flame to travel along the material.

Its V-0 rating allows Onyx FR to be used in many new environments. Coupled with its other qualities, including its strength, hardness, surface finish and heat tolerance, as well as the ability to reinforce resulting parts with strands of carbon fibre, Onyx FR is a versatile option for fire-sensitive tasks.

For more information on Markforged printers and consumables, contact us on 01926 333 777 or check out our contact us section.