Plastic materials are generally considered to be excellent insulators. In addition to their high mechanical strength and low weight, they are especially suitable for the electric and electronics (E&E) market as well as the appliances and transportation industries.
Image Credit: NETZSCH-Gerätebau GmbH
One frequently used plastic material for this application derives from the polyamide family.
However, when near an ignition source, such as an electric spark, these materials are at risk of catching fire. The addition of flame retardants (FR) is one way to ensure appropriate fire safety.
Typically, it is desirable to only have a low amount of flame retardant present as to have a minimal influence on the plastic’s properties and processing behavior.
Like any additive, flame retardants increase the viscosity of polymer melts, which is a key parameter in the electronics industry where miniaturization and very thin walls are standard.
Initiated by just a single electric spark, even a starting fire can develop smoke. The general corrosiveness and toxicity of smoke observed are often a result of the halogenated polymers or flame retardants.
For that reason, specific non-halogenated flame retardants and graphite-based flame retardants are employed to eradicate these problems.
The TCC 918 Cone Calorimeter Saves Lives
Fire testing regulations are critical for limiting flammability and keeping the spread of fire at a level that can be suitably managed.
The “Reaction to Fire Test” in compliance with International Standard ISO 5660-1 and ASTM E1354 uses a Cone Calorimeter to evaluate the heat release rate and dynamic smoke production of a material sample.
The Cone Calorimeter is also crucial for determining the fire safety of recently developed materials.
Figure 1. TCC 918 Cone Calorimeter. Image Credit: NETZSCH-Gerätebau GmbH
How Different Flame Retardants Influence Fire Behavior
To evaluate the influence of different non-halogenated flame retardants on the fire behavior of PA 6, samples of the various compounds were injection molded into 100 x 100 x 4 mm3 plates and then tested via the TCC 918
For neat PA 6, PA 6 with graphite-based flame retardant and PA 6 with non-halogenated flame retardant, the heat release rate, mass loss and transmission as a function of time were studied (Figure 2).
Figure 2. a) Mass loss, b) heat release rate and c) transmission of a neat PA 6 (blue), PA 6 w/ graphite-based flame retardant (red) and PA 6 w/ non-halogenated flame retardant (green) (Source: BPI)
It can be considered that the PA6 sample with 20 wt% graphite-based flame retardant (red curve) presents the lowest loss of mass, as well as the bottom rate of heat and smoke release (lowest reduction in transmission) out of all the samples that were tested.
By way of contrast, the sample with 20 wt% non-halogenated flame retardant (green curve) acts in a similar manner to the neat PA 6 material (blue curve). In the case of the heat release, it exhibits somewhat reduced values, and the heat release stops earlier.
However, concerning transmission, the smoke emission is much greater than that of the neat PA 6.
This demonstrates that, in this particular case of PA6 as well as the FR loadings reviewed, the graphite-based flame retardant functions much better and considerably reduces the adverse effects a fire can have on its surrounding environment.
Additional information regarding the sample preparation and test setup will be detailed in an upcoming application note.
This information has been sourced, reviewed and adapted from materials provided by NETZSCH-Gerätebau GmbH.
For more information on this source, please visit NETZSCH-Gerätebau GmbH.