The demand for high-performance plastic foams is expanding all across a broad spectrum of market sectors, including transportation, electronics, healthcare, industrial equipment, consumer appliances, building and construction, footwear and sporting goods. The main reason for the expanding usage is that these materials offer the light weight and cushioning properties of conventional foams, plus various combinations of special features, such as exceptional strength, heat and flame resistance, sound damping, chemical inertness and biocompatibility.
Polymers used in high-performance
foams include polyurethanes, polyolefins, silicones,
fluoropolymers, styrenics and engineering resins.
Some of these materials possess intrinsically
superior mechanical, thermal or chemical properties;
others are made that way by chemical modifications
in their polymer chains, cross linking treatments,
or the use of special additives. Foaming of
high-performance materials is done with standard
methods such as chemical blowing agents and
physical blowing agents (hydrocarbons or fluorocarbons
are typical ones).
High-performance foams compete with non-foamed
thermoplastics, metals, and natural and synthetic
rubber. The foams are used in such parts as
gaskets, seals, heat shields, shock and vibration
cushions, prosthetic devices, and EMI/RFI shields
for electronic equipment.
Polyurethanes
make up the largest segment of high-performance
foams. When suitably formulated and processed,
these materials provide the following advantages:
- High resistance to compression set, which
makes them useful for gaskets, seals and cushions.
- Efficient energy absorption, thus providing
high resiliency, good vibration damping and
impact attenuation.
- Low outgassing, that eliminates fogging
in auto interiors.
- A broad service temperature range. One supplier
features products that can be used between
-40°C and 90°C.
- Inherent flame retardance in many cases.
- High chemical and environmental resistance,
which minimizes damage from ozone and UV light.
In the automotive sector, high-performance
polyurethane foams are used in air conditioner
vent gaskets, spare tire mounts, tail-light
gaskets, cup holders, engine vibration mounts,
dashboard impact pads, gas tank isolator pads,
and instrument cluster gaskets.
In communications, pads made of urethane foams
protect the fragile LCD assemblies of cell phones.
In desktop and laptop computers, these foams
are used in thermal insulation, EMI/RFI shielding
and battery shock absorbers.
Noise absorption is another outlet for the urethane
materials. In this application they are used
in headliners and panels for automobiles, ventilation
ducts of commercial aircraft, off-road vehicles,
appliances, air compressors and snowmobiles.
The healthcare industry employs high-performance
urethane foams for custom orthopedic equipment
and prosthetic padding.
Lower end polyurethanes have long been used
as cushioning in furniture, but in a new trend,
specialized polyurethane foams, that combine
the properties of both cushions and the underlying
metal springs, are being introduced. As a result,
these foams eliminate the need for the metal
springs and the labor-intensive process of installing
them.
The
major high-performance of Polyolefin
is: crosslinked polyethylene elastomers
and plastomers. (Plastomers have a specific
gravity of 0.89 and above; elastomers have a
specific gravity below 0.89.) Foamed PP has
some specialized uses, particularly in low-density
packaging. Polyolefin foams, which possess exceptional
tensile and elongation properties, look and
feel like rubber but process like other polyethylene
resins. They can easily be thermoformed or laminated
to other materials.
In the automotive sector, foamed polyolefins
are gaining ground due to their weight saving
properties and easy recyclability. Uses of the
foams in this industry include door panels,
sound-absorbing hood liners and instrument panel
laminates.
In footwear, the ruggedness and impact-absorption
features of foamed polyolefins are making them
useful as shoe insoles and ski boot linings.
Construction applications of the foamed polyolefins
include thermal insulators, sealants against
moisture and dust, impact and vibration attenuators,
and underlays for parquet floors.
In consumer goods such as luggage, toys, helmets
and sporting gear, foamed polyolefins function
as shock absorbers, thermal insulation, and
pressure distributors.
Silicone
foams are known for
their resistance to temperature extremes, UV
light, ozone and extreme mechanical stress.
They are also flame retardant and highly resistant
to compression set and creep. The properties
of silicone foams make them particularly useful
inside commercial aircraft, where they are used
as thermal and noise insulators, cargo fire
barriers, carpet underlay, and HVAC (heating,
ventilation and air conditioning) gaskets and
seals.
In electronics, silicone foams find applications
in EMP/RFI shielding, vibration and thermal
insulation.
Mass transit is another market for silicone
foams. Among their uses in that sector are gasketing,
sealing, sound dampening and cushioning.
Because silicone foams maintain their dimensional
stability when exposed to sterilizing agents
such as dry heat, steam, electron beam and gamma
radiation, they are often used in medical components.
These include body contact surfaces for sonogram
equipment and surfaces for rubber articles intended
for repeated use.
PVDF is the
most common high-performance fluoropolymer.
It is inherently flame retardant and can be
made in a closed-cell structure that gives it
very low thermal conductivity. Foamed PVDF also
features low gas and moisture permeability,
plus resistance to UV, most chemicals and ionizing
radiation.
Manufacturers of foamed fluoropolymers are targeting
applications in aircraft insulation, particularly
for ducts and air conditioning. In industry,
the foams are suited for applications in seals
for chemically harsh environments, and in the
floats of chemical tanks. PVDF can be made in
very high purity, so that it is less likely
to contaminate industrial chemical formulations
than other foams. Its flame retardance is also
an asset in manufacturing situations where fire
hazards are present.
EPS foam has long had a role in low-cost packaging, but it is also widely used in the construction industry. In this area it finds applications in structural insulation panels, roofing systems, floors, walls and ceilings, geofoams (ground-fill materials), cold storage systems, and below-grade foundations. Producers of EPS for construction emphasize its energy efficiency, stability, versatility and ease of installation. They also point out that the foams are not manufactured with blowing agents that contribute to global warming.
Engineering
resins (ETP) are on the higher end
of the performance spectrum. Foaming these materials
preserves most of their useful features, while
introducing the advantage of lightweight.
A foamed material such as expanded PC, for example,
has the typical polycarbonate properties of
high impact resistance, high-temperature and
flame resistance, low water absorption and good
electrical properties. But EPC sheets are only
about half the weight of comparable size solid
polycarbonate sheets. Among the uses of EPC
sheets are roof insulation for automobiles,
housings for office machines, traveling cases
for sports equipment, sterilizable trays for
medical laboratories, and backlit highway signs.
High-performance foams are
benefiting from several trends. First, manufacturers
are building lighter weight transportation vehicles
for greater fuel economy. They are also producing
lighter cell phones, computers and other electronic
devices, which appeal to consumers. But manufacturers
are unwilling to sacrifice quality or durability
for weight savings, which is creating opportunities
for structural and insulating components that
are both low in density and rugged. In addition,
many industrial processes are operating at higher
and higher temperatures, where energy efficiency
is greatest. Consequently, there is a growing
demand for insulation, gaskets, seals and jacketing
that can stand up to these rigorous conditions.
Industry sources say these trends have not yet
run their course, forecasting continued vibrant
growth for high-performance foams, at least
for the next few years
|