JEC COMPOSITES MAGAZINE - Issue #91 - August/September 2014 - 58

polyurethane

Fig. 1: Urethane bond

lives in various forms: at home (hose
insulation, kitchen utensils, sofas,
mattresses, etc.), at the office (chairs,
equipment enclosures, furniture wheels,
etc.), in leisure or sports activities (ski
equipment, surf boards, bicycle seats,
outsoles of sneakers, etc.) or in industries (automotive sector, construction,
coatings, etc.). The polyurethane market
is divided in three big blocks: flexible
foams (widely used in the furniture
industry, mattresses or automotive
seating), rigid foams (used in global
insulation systems) and CASE polyurethanes (coating, adhesives, sealant and
elastomers used in coatings, sneaker
outsoles and automotive applications).
In all these fields, the polyurethane
industry is facing new challenges mainly
related to legislation and the environment, especially the control of volatile
organic compound (VOC) emissions,
the use of flame-retardant agents free
of halogenated derivatives, the use of
blowing agents harmless to the ozone
layer and polyurethane recycling methods.

Volatile organic
compounds (VOCs)
VOC control is becoming more important in close spaces such as building or
vehicle interiors. However, the danger
of emissions is considerably higher in
cars since the heat effect produced by
the solar radiation is five times higher
inside a vehicle than inside a building.
As a result, European automotive manufacturers are pushing more restrictive
specifications for VOC emissions inside
cars.

Polyurethane foams are one of the main
components found inside a car, being
part of the seats and headrests. Polyurethane manufacturers are thus working to
develop new formulations which minimize VOC emissions. Work has been
done in areas such as the elimination of
antioxidant additive emissions in polyol
and isocyanate, the reduction of styrene
acrylonitrile monomers in copolymer
polyols and the replacement of amines
used as additives in polyurethane formulation. Several catalyst combinations
are used in the formulation of polyurethane to establish a balance between
the main chemical reactions, namely
the "gelation" reaction (isocyanate
with polyol) and the "blow" reaction
(isocyanate with water). Traditionally,
amines have been the most commonly
used catalysts in the production of flexible polyurethane foams, but the negative effects of some amines in terms of
VOCs emissions have been documented
in several papers. As a result, polyurethane formulations with reduced VOC
emissions have been investigated and
developed, while maintaining or even
improving the quality and processability
of the foam.

Flame-retardant agents
Some flame-retardant agents also
contribute to the VOC emissions of
polyurethanes. Brominated flameretardant agents, especially polybrominated diphenyl ether compounds
(PBDEs), were widely used to reduce
the speed of flame propagation in
various plastic products such as flexible
polyurethane foams. However, several
tests have shown that PBDEs are gradually released in the environment and
can be toxic for human health. In 2004,
the European Union prohibited the use
of pentabromodiphenyl ether (pentaBDE) and octabromodiphenyl ether
(octaBDE), which were also prohibited
in the American market the same year.
A third compound, decabromodiphenyl
ether, was prohibited in the EU in 2008.
Nowadays, organophosphate flame
retardants (OPFRs) are used as substi-

58 jec composites magazine / No91 August - September 2014

tutes for the pentaBDE mixture. OPFRs
are present in the environment and
were detected at high concentrations in
residential dust, which suggests a generalized human exposition. The effects
of some of these compounds on health,
especially 1, tris (1,3-dichloro-2-propyl) phosphate (TDCPP), are being
evaluated by the California Department
of Toxic Substances Control. There are
alternatives to this type of compounds,
such as the use of nanomaterials or
melamine-based compounds as flame
retardants. In any case, the industry
must face the continuous challenge of
obtaining polyurethane formulations
that comply with the increasingly restrictive fire regulations and, at the same
time, do not involve any risks for human
health.

Blowing agents
Polyurethane foam manufacturers
also face the challenge of meeting user
requirements for more sustainable and
environmentally friendly materials and
processes. In this area, the use of environmentally sustainable blowing agents
is especially significant. Using blowing
agents with an ozone depletion potential equal to zero is not enough; blowing
agents are also required to have a low
global warming potential (GWP).
After its entry into force in 1989, the
Montreal Protocol significantly influ-

Fig. 2: Blowing agents used in the plastics industry
[Source: Special Chem On line paper April 2010
(Understanding Polyurethane 2011 course)]

JEC COMPOSITES MAGAZINE - Issue #91 - August/September 2014

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #91 - August/September 2014