JEC COMPOSITES MAGAZINE - Issue #144 - January/February 2022 - 41

FEATURE
fire retardant
Consider fire requirements
when specifying composites
erIc MouSSIaux,
VP Technology
Exel Composites
In applications where the risk of fire is a factor, such as in transportation,
building, and construction, fire performance becomes the primary
consideration when specifying composite solutions. Exel Composites
explains how fire considerations influence composite design.
are toxic, and waste is classified as hazardous,
making their disposal costly.
G
enerally, there are three main fire performance
considerations for manufacturers.
These are how difficult it is for
the material to ignite, how fast the fire spreads,
and how much heat it generates. Next, how
much smoke will develop and how quickly?
Finally, how toxic is the smoke and how quickly
can it cause harm? These considerations are
typically referred to as FST, fire smoke and
toxicity, properties.
With these considerations in mind, it is common
for composites manufacturers to incorporate
flame retardant additives into the
materials. The nature of these additives varies
depending on the application in question and
any relevant regulatory requirements.
Traditional approach
Halogenated compounds are a broad category
of flame retardant additives that were traditionally
seen as the first choice for composites
manufacturers because of their high efficiency
and relatively low cost. Halogenated additives
work by eliminating the highly-reactive free
radicals generated in the thermal decomposition
of polymers during combustion. By hampering
oxidation reactions in the combustion
process, they can effectively kill the flames.
Brominated and chlorinated additives, occasionally
helped with synergists such as
antimony trioxide, are still used in heavily-corrosive
environments. However, they are
becoming increasingly banned for use in many
common applications because of their adverse
side effects. Several halogenated substances
present health hazards, the produced smokes
Modern approach
New trends in adding flame retardant properties
to composites are based on the use of
non-halogenated substances such as aluminium
trihydrate (ATH) and metal hydroxides,
including magnesium and phosphorus-based
compounds. ATH additives are now the most
widely used non-halogenated flame retardants
because, despite being less effective than halogens,
they are far less toxic when they burn.
They operate by releasing water molecules in
an endothermic reaction during the combustion
process. These water molecules quench
the surface of the surrounding materials,
providing flame retardancy and smoke suppression.
Furthermore, unlike halogenated
products, ATH additives do not give off toxic
smoke when burned.
The downside of ATH, being much less effective
in hampering the fire, is that higher
quantities are needed to meet the increasingly
stringent fire requirements in many applications.
Very high filler loadings negatively
affect mechanical performance because there
is less room for reinforcing fibres, and also influence
long-term behaviour in difficult environments.
Very high resin viscosities, changed
reactivities, and important pultrusion pulling
forces require narrow process windows and
tight process control. Special consideration
needs to be given to geometrical product details
and the highest level of tooling quality is
required to successfully produce such parts.
Ultimately, when specifying composites for
applications where fire must be considered, a
balance must be struck between the desired
mechanical properties and meeting the relevant
fire safety tests. While this might initially
seem like a daunting prospect, this challenge
can be overcome by working with a knowledgeable
partner who understands all these
considerations and can propose the most suitable
solution available.
This is particularly crucial in applications
such as train transportation, where fire requirements
vary depending on whether the
train will travel overground or underground
and whether the composite materials will be
used internally or externally. In Europe, trains
have three hazard levels and, as we move up
through them, the level of FST requirements
increases.
As a consequence, navigating all the necessary
fire requirements and knowing what tests to
apply can be extremely complicated. As FST
demands will affect most other properties and
have considerable effect on processing, they
should be discussed in very early stages of each
new enquiry. Exel Composites has the expertise
and manufacturing capabilities to guide
customers through it and produce the most
suitable composite solution for a given application.
More
information:
Fire considerations influence composite design
www.exelcomposites.com
N°144 January - February 2022 / jec composites magazine
41
Feature Construction
http://www.exelcomposites.com
JEC COMPOSITES MAGAZINE - Issue #144 - January/February 2022

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