Plastic fuel tanks in automobiles are gaining
usage globally. Blow moulded or injection moulded
multi layer HDPE fuel tanks are most common. The
automotive industry has made significant developments
to meet the recent emission standards.
However this trend has not been increasing globally
in a geographically uniform pattern. Europe has
almost fully converted to these plastic fuel tanks,
with 92% automobiles of European origin fitted with
plastic fuel tanks. North America, with 75% usage,
is lagging behind. However, the Asian region is
lagging far behind, due to problems of economies.
One of the possible reasons is the smaller number
of car produced in different parts of Asia as compared
to Europe and North America. The use of plastic
fuel tank does not become economical at lower production
levels of an individual automobile company.
Another development in the auto segment has been
plastic fuel lines that convey fuel from the tank
to the engine compartment. Compared with existing
rubber and steel fuel lines, plastic fuel lines
are lighter in weight, lower in cost and often less
permeable. They are also available in many colors,
which make it easier to place, track and connect
fuel supplies. Interestingly, the automotive companies
are very slow in making the switch to plastic lines.
The slower pace stems from concerns by auto companies
over the ability of plastic fuel lines to meet strict
air emission standards, and to resist electrostatic
discharges (ESDs), which could ignite flammable
fuels. Automakers also need to be convinced that
fuel lines made of plastics can withstand the impact
of crashes at low winter temperatures and can resist
degradation from alcohol fuels. But polymer suppliers
and Tier One auto manufacturers have developed new
fuel line materials and designs, which they believe
can meet these challenges.
The most common polymer used in plastic fuel lines
is polyamide, often combined in multilayer structures
with fluorocarbon polymer barrier resins. Another
low-permeability material that has been paired with
polyamide in multilayer structures is polybutylene
naphthalate (PBN). Aliphatic polyketones have also
been promoted as fuel line materials. Some polymide
based fuel line formulations include low levels
of carbon nanotubes, which enhance ESD properties
without harming physical properties.
Complying with increasingly stringent antipollution
regulations is the biggest challenge faced by developers
of plastic fuel lines and other plastic fuel components
such as tanks, pumps, vapor recovery systems, filter
pipes and fuel rails. Of most concern to the global
auto industry are regulations in the U.S. state
of California that limit the levels of hydrocarbons
auto fuel system can release into the air. Among
them are the ZEV (zero emission vehicle), PZEV (partial
zero emission vehicle), and the CARB (California
Air Resource Board) LEV (low-emission vehicle) II
standards. Some of these rules have already taken
effect; others will be phased in over the next few
years. Because California has traditionally set
the pace for air pollution regulations in the rest
of the U.S. and elsewhere, most of the world's car
manufacturers are striving to meet the standards
in that state.
To meet the new air quality standards, plastic fuel
line manufacturers have developed structures that
reduce vapor permeation through their walls.
Atofina Chemicals Inc. has developed tubes made
from Rilsan line of polyamide 11 and 12, with barrier
properties enhanced by coextrusion with Kynar PVDF
(polyvinylidene difluoride). The layers are held
together with an adhesive tie resin. Features of
Atofina's new conductive grade of the Rilsan polyamide
12 polymer include a surface resistivity below 105
ohms which meets the conductivity requirements of
SAE standard 2260, and impact resistance down to
-40° C.
Dana Corp. has commenced production of new multilayer
plastic fuel line systems for automotive applications
in Europe, North America and South America. The
five-layer tubes have a PBN middle layer, two adhesive
layers, and nylon 12 internal and external layers.The
PBN-based materials are lower in permeation rates,
cost and weight than polyamide/fluoropolymer multilayer
fuel lines, and help in ahieving 2006 PZEV requirements.
In Japan, Ube Industries and Asahi Glass, have jointly
developed a two-layer fuel line material composed
of nylon 12 and a ETFE (ethylene tetra fluro ethylene
), a barrier resin. The two layers in their resin
system adhere strongly without the need for adhesive
tie layers, which can deteriorate over time and
cause delamination, and are reported to remain intact
and undetached even after 1,000 hours of immersion
in alcohol-based fuel. Other features include little
fuel permeation or vaporization, and excellent machinability
and chemical resistance.
DuPont's product line known as Selar RB amorphous
nylon can be dry blended with polyethylene to create
monolayer fuel tanks, fuel lines, filler necks and
filter housings that meet LEV II emission requirements.
SRI International is offering for license a high-performance
aliphatic polyketone, tradenamed Carilon, that combines
good chemical and permeation resistance with superior
impact strength and high-temperature performance.
New ways for improving the ESD properties of
fuel lines are also emerging. The typical approach
for making a plastic fuel line static dissipative
is to add graphite fibers to the resin formulation.
But this can degrade the polymer's properties,
particularly its impact strength. A newer practice
is to make fuel line resins conductive with much
smaller particles (carbon nanotubes).
Will these new material/product innovations accelerate
the use of plastics in fuel lines?
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