Composite materials, made from resins reinforced with glass
fibre, are widely used to make moulded parts for the transport, electrical
and construction industries. But they tend to burn easily, emitting
toxic smoke and fumes. A group of companies in Spain and France got
together to investigate how these resins could be used both to meet
strict new fire regulations and to make them suitable for automated
Transport, electrical, construction sectors.
The potential market for fire-resistant composites has been
estimated at E500 million. With further potential in the aviation
New regulations on fire safety in public places
are putting heavy demands on the manufacturers of composite materials.
Composites consist of fibres (commonly glass) embedded in a resin.
Because they are light in weight and can be moulded into complex shapes,
composites are widely used in public transport vehicles such as aircraft,
buses, trains and ships, as well as in public buildings.
But resins tend to burn easily, emitting toxic gases and smoke. As
a result, many composites used in the transport industry are failing
to meet the new requirements. Fire-resistant additives go part way
to solving the flammability problem, but it is proving more difficult
to reduce the emission of smoke and gases.
Among the more promising materials are the phenolic resins, which
are intrinsically fire-resistant and emit low levels of gases and
smoke. But until now it has not been possible to use phenolic resins
in the moulding processes favoured by industrial processors.
One approach is to make composite components by "hand lay-up",
placing the fibres in the mould by hand and brushing in one of several
commercial resins treated with flame retardants. But there are environmental
and health problems associated with handling volatile gases, flammable
solvents and glass fibres. And it is harder to achieve a consistent
product when composites are made by hand.
Resin transfer moulding
It was against this background that Mariskone, a Spanish manufacturer
of glass-fibre composite parts, initiated a CRAFT project to tackle
the problem. They wanted to develop a range of resins that both
met the new fire standards and could be moulded by a process known
as resin transfer moulding (RTM).
"Resin transfer moulding is prevalent in the electronics, corrosion-resistance,
recreational vehicle and consumer markets because it produces two
finished sides and the highest-quality surface technically achievable,"
explains Nerea Markaide of project coordinator INASMET, a materials
research centre in San Sebastian. In RTM the resin is mixed with
a catalyst and injected by vacuum, or under pressure, into a closed
mould containing fibre matting. Because the mould is sealed, there
is a reduced risk of toxic emissions. The process can be automated
and is suitable for short or medium-length productions runs of 500
to 10 000 mouldings a year.
When the project began, Mariskone were producing parts by hand
lay-up or spray lay-up, a process in which a mixture of resin and
chopped fibres is sprayed into the mould and compacted by hand.
Another partner, Defi 22, design and produce composite parts for
the rail sector using vacuum and compression injection moulding
as well as RTM. The two processors worked closely with clients Ikusi,
who make electronic security systems and tele-indicators, and GEC
Alsthom one of the leading manufacturers of trains. The group also
included Isojet, who make equipment for low-pressure injection moulding
and polyurethane casting.
INASMET investigated RTM for the manufacture of flat panels, with
a range of selected resins. The panels were tested for fire reaction,
smoke density, toxic emissions and flammability, as well as mechanical
strength, chemical resistance, and thermal and ultraviolet ageing.
Similar experiments were also carried out on more complex moulded
Different resins subjected to a reactivity
test (ASTM D-2471) to discard the resins which are unsuitable
for the RTM technology.
As a result of the research, the consortium have defined a design
methodology for the use of fire-resistant composites in RTM. It
covers choice of materials (fibres and resins) for different applications,
processing conditions and design of the mould.
The most suitable resins for RTM turn out to be modified unsaturated
polyester resins, though their smoke emission is still not completely
satisfactory. Modified acrylics are suitable when the glass fibre
content is below 5-10%, but this diminishes their mechanical properties.
Mouldings made from phenolic resins, despite the research efforts
of the large companies who produce them, tend to lose their shape
over long periods when made by an RTM process. "The dimensional
stability is one of the problems of the phenolic resins not completely
solved until now," says Mrs Markaide. "However the additional advantages
make phenolics particularly attractive for applications where there
is a requirement for optimum fire and smoke behaviour. And the manufacturers
are developing new materials with improved dimensional properties,
to get into the potentially huge market for fire-resistant resins."
The effects on the partners have been very positive, with all of
them reporting increased business and growth. Mariskone are planning
to double their production capacity and the expansion will be entirely
accounted for by RTM, a process they had not used before. Ikusi
will replace some of their metal parts by moulded components supplied
by Mariskone. Defi 22 have adopted RTM as their standard process
for all medium-sized parts, some of which will be supplied to GEC
Alsthom. Isojet have been investigating suitable machines for RTM
processing and are developing a mixing head specifically devised
to inject fire resistant resins.
With almost half of all composite materials destined for the bus,
rail and mass-transit, marine, electrical and construction sectors,
the potential market for fire-resistant composites has been estimated
at e500 million with further potential in the aviation industry.