Composite materials
Being intrinsically fire-resistant,
phenolic resins offer a better safety
margin without the need for flameretardant
additives or gel coats
high-volume production of parts that need to
EN45545 tests
Part of the EN45545 regulation specifies
resins easily meet even the most stringent HL3 category,” says
Pisipati. “High-strength bonds formed when phenolic systems cure
result in exceptional fire and high-temperature performance. This
also allows their use in a wide variety of manufacturing processes
without sacrificing fire performance.”
In real-world applications, Pisipati says phenolic resins can
meet HL3 performance requirements at a lower per part cost
than unsaturated polyesters. “These facts are making fabricators
take a second look at phenolics to meet the manufacturing, cost
and performance requirements of the industry,” he says.
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Ramesh Pisipati, Hexion
CELLOBOND PHENOLIC RESINS
Hexion has designed its Cellobond phenolic resins to enable
the rail industry to make composites that easily surpass fire
performance standards, irrespective of manufacturing process.
“Heavy fillers, in widespread use to improve polyester fire
performance, can easily drop out of solution during processing
and cause variable fire properties,” says Pat Colclough, Hexion’s
business manager for Northern Europe. “Intumescent gel coats
can be damaged and need precision coating to work effectively.
Choosing phenolic resins avoids these issues.”
He also says that unfilled phenolic resins provide big weight
savings over polyester and aluminium, benefitting fuel efficiency
and making them easier to install. He points out that phenolic
resins contain virtually undetectable levels of free formaldehyde,
and are styrene-free, future-proofing them regarding handling
and use. “Composites parts manufactured with Hexion phenolic
systems are fully competitive on cost and available globally
through an established network of suppliers,” adds Colclough.
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meet both cost and fire performance targets,” says Pisipati.
stringent fire standards.”
SMC performance
Sheet moulding compound (SMC) processes have also
meet exacting fire standards,” says Pisipati.
“Phenolics enable the fabrication of parts
that do not exhibit shrinkage in service and
tend not to distort at high temperatures. This
makes them good candidates for insulation
and exhaust shielding.”
Phenolic resins with ultra-low levels of
residual monomers have been introduced,
to minimize worker exposure to harmful
emissions. In 2018 Composites UK
recognised Hexion’s ultra-low emitting
phenolic resins with its Innovation Award.
a series of flammability tests for materials
to be used in trains. These tests check
performance along the axes of fire, flame
spread and toxicity and opacity of the fumes
produced on combustion. In addition, a
material’s heat release – as measured by a
cone calorimeter – is an important indicator
of how likely it is to contribute to flame spread.
In tests of a 2mm (0.08in)-thick phenolic
composite panel, composed of a Cellobond
resin grade from Hexion, the material performed well within the
specifications for HL3, for every aspect. “It is clear that phenolic
“The development of faster drying phenolic resin systems
as well as ultra-low free monomer systems has helped drive
the use of phenolic prepregs for parts that need to meet
been adapted to phenolic resins to produce composites
via a compression moulding process designed to maintain
target mechanical properties even after being exposed to
a fire. “Phenolic resins are key components that enable
such performance from SMC processes and are suited to
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