United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/SR-96/067 June 1996
4>EPA Project Summary
Sources and Factors Affecting
Indoor Emissions from
Engineered Wood Products:
Summary and Evaluation of
Current Literature
Sonji Turner, Cybele Martin, Robert Hetes, and Coleen Northeim
Reconstituted engineered wood com-
ponents (e.g., particleboard and me-
dium-density fiberboard) are common
to several types of consumer wood
products (e.g., residential and ready-
to-assemble furniture and kitchen cabi-
nets). The selection of resins used to
bind the components, coatings, and
laminates applied to the components
to produce the final products affects
emissions of formaldehyde and other
volatile organic compounds from the
products to the indoor environment.
Research Triangle Institute is collabo-
rating with the Indoor Environment
Management Branch of the U.S. Envi-
ronmental Protection Agency's Air Pol-
lution Prevention and Control Division
in a project entitled, "The Application
of Pollution Prevention Techniques to
Reduce Indoor Air Emissions from
Composite Wood Products." The re-
search objectives are to characterize
indoor air emissions from engineered
wood products and to identify and
evaluate pollution prevention ap-
proaches for reducing indoor air emis-
sions from these products.
The research has a five-phase ap-
proach: (1) evaluate existing data and
testing methodologies; (2) convene re-
search planning meetings; (3) select
high-priority emissions sources; (4)
evaluate high-priority emissions
sources; and (5) develop and demon-
strate pollution prevention approaches
for reducing indoor air emissions from
high-priority sources. The report sum-
marizes information from the first two
phases of research. Information pre-
sented here will be used to select re-
constituted wood components with vari-
ous finishing and resin systems for
initial emissions screening.
This Project Summary was developed
by EPA's National Risk Management
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Background
Several recent U.S. Environmental Pro-
tection Agency (EPA) studies have identi-
fied indoor air quality (IAQ) as one of the
most important environmental risks to the
Nation's health. People spend approxi-
mately 90% of their time indoors in envi-
ronments such as residences, public
buildings, and offices where concentra-
tions of many pollutants are frequently
higher than outdoor urban air. Some in-
door activities can lead to indoor air pol-
lutant levels up to 1,000 times higher than
outdoor levels.
EPA's Air Pollution Prevention and Con-
trol Division (APPCD) is responsible for
much of EPA's indoor air engineering re-
search and seeks to integrate IAQ and
pollution prevention (source reduction) into
a strategic approach to indoor source man-
agement. The research objective of
APPCD's Indoor Environment Manage-
ment Branch is to employ accepted pollu-
tion prevention techniques (e.g., process
modification and product reformulation) to
reduce indoor air contamination through
the development of "low-emitting materi-
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als" (LEMs). A LEM is designed to emit
fewer pollutants when used in the same
manner as another material in the same
indoor environment.
In the past, approaches for improving
IAQ have generally focused on mitigation
techniques, (e.g., increased or improved
ventilation and air cleaning) rather than
source reduction. Although these traditional
mitigation approaches can result in im-
proved IAQ, they do not prevent pollution;
furthermore, the pollution is simply trans-
ferred to another medium. Depending on
the source of indoor air pollution, another
approach is to focus on source manage-
ment, ensuring that pollutants never enter
the indoor environment. In the Pollution
Prevention Act of 1990, Congress declared
that pollution should be prevented or re-
duced at the source whenever feasible.
Sources may be reduced by modifying
equipment, processes, and procedures; re-
formulating or redesigning products; sub-
stituting raw materials; and improving use
procedures. In multimedia pollution pre-
vention, all environmental media are con-
sidered while avoiding transfer of risks or
pollution from one medium to another.
EPA Research on Engineered
Wood Products
The Research Triangle Institute (RTI) is
collaborating with APPCD in a coopera-
tive agreement entitled, "The Application
of Pollution Prevention Techniques to Re-
duce Indoor Air Emissions from Compos-
ite Wood Products." The objectives of this
research are first to characterize indoor
air emissions from engineered wood prod-
ucts and then to identify and evaluate
pollution prevention approaches (e.g., de-
veloping LEMs) for indoor use. This re-
search includes five phases: (1) evaluate
existing data and testing methodologies;
(2) convene a research planning meeting;
(3) select high-priority emissions sources;
(4) evaluate high-priority emissions
sources; and (5) develop and demonstrate
pollution prevention approaches for reduc-
ing indoor air emissions from selected
high-priority sources.
The report summarizes information col-
lected in the first two phases of the project.
Information presented here, along with in-
formation from outside technical advisors,
will be used to select products for further
research. The technical advisors include
representatives of trade associations, in-
dustry, state government, academia, and
technical assistance providers. Extensive
source characterization will be carried out
on the selected products. Pollution pre-
vention approaches will be identified and
applied. These improved products will be
evaluated through quantitative emissions
measurements to decide the technical and
economic feasibility, total pollution preven-
tion potential, and IAQ benefits of the pol-
lution prevention approaches.
Literature Summary
The literature summarized in the report
includes applicable material types, indoor
air emissions, and pollution prevention
opportunities.
Material Types
This cooperative research focuses on
indoor air emissions from engineered wood
products (e.g., furniture, cabinets, and
building materials). Raw materials used to
construct these products include wood,
glues, organic-based finishes and coat-
ings, and a variety of paper and plastic
laminates. Resins and wood used to manu-
facture engineered wood products and
their finishing materials are sources of or-
ganic emissions. The most commonly used
resins in the U.S. are phenol-formalde-
hyde, urea-formaldehyde, and methylene-
diphenyl diisocyanate (MDI). The different
chemistries of these resins result in differ-
ent emissions characteristics. Types of fin-
ishing materials used on engineered wood
materials include laminates, edge-bands,
adhesives for attaching laminates and
edge-bands, conversion varnish coatings,
paints, stains, fire retardants, and preser-
vatives. Some of these materials are
sources of organic emissions; others, such
as laminates or veneers, may help reduce
emissions. Evaluating and understanding
the indoor air emissions associated with
each of these raw materials are critical to
the development and evaluation of pollu-
tion prevention opportunities such as
low-emitting or low-impact materials.
Indoor Air Emissions
In 1984, the U.S. Department of Hous-
ing and Urban Development (HUD) estab-
lished formaldehyde product standards for
all plywood and particleboard materials
bonded with a resin system or coated with
surface finish containing formaldehyde
when installed in manufactured homes.*
* The HUD safety standards for certified plywood and
particleboard used in manufactured home construc-
tion require that formaldehyde emissions not exceed
0.2 ppm (0.246 mg/m3) from plywood and 0.3 ppm
(0.369 mg/m3) from particleboard, as measured by
the specified air chamber test, Large-Scale Test
Method FTM 2-1983. Individual engineered wood
products are tested in accordance with the following
loading ratios: plywood—0.29 ft2/ft3 (0.369 nf/m3),
and particleboard—0.13 ft2/ft3 (0.43 nf/m3). Using
the operating conditions specified in FTM 2-1983
and the formaldehyde emissions rate equation, form-
aldehyde emissions rates are 0.13 mg/m2 • h (2.66 x
10 8 Ib/ft2 • h) for plywood and 0.43 mg/m2 • h (8.81 x
10 »Ib/ft2 • h) for particleboard.
Many plywood and particleboard manu-
facturers changed their products to com-
ply. Several studies evaluated various
sources of indoor air emissions and how
the emissions rates are affected by vari-
ous parameters. One study concluded that
new building materials produced high emis-
sions levels, but with effective ventilation
these emissions could be reduced; the
maximum concentration of formaldehyde
reached 0.122 mg/m3 in the new office
building investigated for the study. An-
other indoor analysis suggested that build-
ing materials may be the main source of
organic compounds in the indoor environ-
ment: the total average concentration for
the most frequently identified compounds
in this study was 72.96 |ig/m3, and the
average arithmetic mean emissions rate
for all the identified compounds was 9.5
mg/m2 • h. Two other studies presented
predicted emissions rates and emissions
rate ranges, respectively, for several engi-
neered wood products.
Still other studies analyzed samples of
various engineered wood products. A Na-
tional Particleboard Association two-part
preliminary study analyzed emissions from
finished and unfinished engineered wood
products [for most of the finished samples
of southern yellow pine (SYP) substrates,
the total volatile organic compound con-
centrations, ranging from 156 |ig/m3 at 24
hours to 2,520 |ig/m3 at 120 hours, were
lower than for unfinished SYP substrates,
ranging from 2,880 |ig/m3 at 24 hours to
918 jag/m3 at 120 hours]. Besides mea-
suring organic emissions for water-dam-
aged chipboard, which had a mean
formaldehyde concentration of about
0.0475 mg/m3, one study evaluated mi-
crobiological growth from water-damaged
chipboard samples, which revealed sig-
nificant growth of fungi following water
damage (the results of these analyses are
presented in the full report). Although not
discussed in the full report, EPA performed
earlier research on a variety of consumer
products and building materials that pre-
sented emissions rate data and discussed
the effect of temperature and air exchange
on the emissions rate.
Reported information concerning organic
and formaldehyde emissions rates and
concentrations depended on the design
and objectives of each study. Emissions
data for each individual study were col-
lected using different analytical test meth-
ods. Because methods used to collect
emissions data were study-dependent and
researchers presented emissions data dif-
ferently, comparative conclusions could not
be drawn between the studies presented
in this report.
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Pollution Prevention
Opportunities
Pollutants are managed most effectively
at their source. The major approaches are
chemical substitution, process changes,
and product redesign. Strategies vary de-
pending on whether emissions are the
result of offgassing from construction or
finished materials (e.g., organics in wood
products) or product operation or use.
When offgassing is the major emissions
source, low-emitting materials may be sub-
stituted. When product use or operation is
the major source of emissions, knowledge
of the relevant process is essential in de-
veloping emissions controls or redesign-
ing the product to reduce emissions. In
either case, chemical substitution may be
warranted if a product or equipment is
found to emit chemicals shown to cause
serious human health or environmental
effects. Several possible approaches for
developing low-emitting materials are wood
alternatives, alternative resins and scav-
engers, and laminate or veneer use. These
pollution prevention and source manage-
ment approaches are discussed briefly.
Alternatives to Wood Feedstock
The primary reason for including agri-
cultural fiber sources (wood alternatives)
in this report is to identify their potential to
reduce indoor emissions from the use of
engineered wood products. However, data
on the indoor air emissions from engi-
neered agricultural products were not
found; therefore, emissions tests of these
products are required.
A potential alternative for wood used to
manufacture engineered wood products is
agricultural fiber. Agricultural fiber comes
from two main sources: agricultural crops
grown for fiber (e.g., kenaf) and residues
of crops grown for other purposes (e.g.,
wheat, cotton). Agricultural fibers are used
in many countries to manufacture com-
posite panel products, such as insulation
board, particleboard, medium-density fi-
berboard, and hardboard. A global litera-
ture search conducted at the U.S.
Department of Agriculture, found 1,039
citations on the use of agricultural fibers
for manufacturing composite panels. Many
of these applications are used in develop-
ing countries where there is not enough
wood to cover the needs for fuelwood,
industrial wood, sawn wood, and wood-
based engineered panels.
In the U.S., engineered panels are
manufactured primarily from wood. How-
ever, agricultural fibers are available that
have the potential to be used in engi-
neered panels; sources of these fibers
include bagasse, cereal straw, corn stalks
and cobs, cotton stalks, kenaf, rice husks,
rice straw, and sunflower hulls and stalks.
Recently, a plant was built in North Da-
kota that manufactures particleboard from
wheat straw and MDI resins.
Alternative Resins and
Scavengers
Several resin and additive approaches
exist for reducing formaldehyde board
emissions from urea-formaldehyde bonded
products, such as particleboard and
medium-density fiberboard. Included are
low molar ratio urea-formaldehyde resins,
the use of formaldehyde scavengers with
urea-formaldehyde resins, melamine-forti-
fied urea-formaldehyde resins, phenol-
formaldehyde resins, and MDI resins.
While these alternative resins and addi-
tives result in products with significantly
lower formaldehyde emissions, only low
molar ratio urea-formaldehyde resins and
formaldehyde scavengers have made a
significant penetration in the particleboard
and medium-density fiberboard industries.
Urea-formaldehyde resins are the most
commonly used adhesives for engineered
wood manufacture in the U.S.; second in
volume are phenol-formaldehyde resins.
MDI resins are the third most commonly
used type in the U.S. Originally, the
formaldehyde-to-urea molar ratio for the
urea-formaldehyde resin was 2.0. This
molar ratio corresponded to the number
of chemically reactive groups present in
the reagents. In the early 1980s, most
urea-formaldehyde resins marketed as
wood adhesive resins contained a molar
ratio of 1.8 although proof was available
that lowering the overall molar ratio fur-
ther reduced the potential for
postmanufacture formaldehyde release.
Nonetheless, progress has been made in
formulating low-molar ratio resins.
A wide range of molar ratio resins is
used in urea-formaldehyde bonded prod-
ucts. For particleboard, when a single resin
is used throughout the board, the
formaldehyde-to-urea molar ratio can fall
within the range set by the face/core sys-
tems; medium-density fiberboard products
use resins with formaldehyde-to-urea mo-
lar ratios higher than particleboard resins;
hardwood plywood products use the high-
est formaldehyde-to-urea molar ratios. The
nature of the product and process dic-
tates which formaldehyde-to-urea molar
ratio to use. The molar ratio directly influ-
ences the ultimate strength the resin will
produce in the board; i.e., certain prod-
ucts require higher molar ratio resins to
attain an adequate level of bond strength.
Often, formaldehyde emissions cannot
be sufficiently lowered with resin use alone.
To avoid incurring significant losses in pro-
ductivity or board quality, many North
American plants use scavengers with
urea-formaldehyde resins to reduce form-
aldehyde emissions. (Consequently, al-
though not exclusive, another potentially
beneficial impact for plants is reduced
formaldehyde exposure for workers.)
These scavengers fall into two categories:
scavengers that are incorporated before
pressing the panel and scavengers that
are incorporated after pressing. The basic
premise of the two approaches is essen-
tially the same: both approaches allow the
use of resins with a higher molar ratio and
all their attendant benefits while achieving
acceptable emissions by scavenging the
excess formaldehyde. The molar ratio di-
rectly impacts the ultimate strength the
resin will produce in the board; i.e., cer-
tain products require higher molar ratio
resins to attain an adequate level of bond
strength. Urea scavengers have been used
widely for many years. This method is
very effective in reducing formaldehyde
emissions with minimal impact on other
resin performance characteristics. It has
been used extensively where the use of
lower molar ratio resins resulted in signifi-
cant losses of resin efficiency (bond
strength) or productivity.
Most plants incorporate scavengers be-
fore pressing the panel. The most preva-
lent type of prepressing scavenger is
chemical urea. Another type of prepressing
scavenger is a scavenging wax emulsion
in which the scavenging chemicals are
added to the normal wax emulsion. (The
wax, a mixture of petroleum hydrocarbons,
is typically added as an emulsion to retard
the absorption of water by the board. Wax
emulsions are dispersions of very small
wax particles in water.) This approach
eliminates the need for a separate meter-
ing and storage system for the scavenger
but does not provide flexibility in scaven-
ger level for different products or condi-
tions. A relatively new prepressing
scavenger method is combination blend-
ing, commonly called combi-blending.
Combination blending is the process by
which two liquid urea-formaldehyde resins
are used in combination to reduce formal-
dehyde emissions without a loss in board
properties or in production efficiency.
One advantage of combination blend-
ing over urea scavenger is that, unlike
simple urea, the scavenger resin has ad-
hesive properties and contributes to bond-
ing. Consequently, it can be used to
replace part of the regular resin rather
than being an add-on. This can mean
significant savings in total additive cost.
Typically, the scavenger resin is combined
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with the normal resin just before applica-
tion to the wood, although good results
have also been achieved using separate
application of the two components. This
technology lends itself to batch mixing or
mixing in storage. Long-term contact of
the two components results in a mixture
that behaves similarly to a low molar ratio
resin.
Postpressing treatments are much less
common than prepressing treatments but
can be very effective. The most well known
of these is to gas the panels with anhy-
drous ammonia. Other techniques that
have been tried include the application of
liquid ammonia or ammonia salt solutions
to the board surface before stacking. All
three methods use the reactivity of am-
monia to formaldehyde forming a rela-
tively stable compound.
Source Management Approaches
Overlays on engineered wood products
include veneers, laminates, vinyl films,
decorative foils, high-pressure laminates,
and paper-based overlays. Although de-
signed for other purposes, such as aes-
thetics, these can serve as effective
barriers to emissions. For emissions to
occur, the compound must be present at
the surface and in contact with ambient
air. These overlays can also protect the
resins from drastic changes in relative hu-
midity and temperature, reducing the po-
tential for hydrolytic attack. However, note
that additional resins may be used as
adhesives to attach these covers to the
wood products. Both urea- and
phenol-formaldehyde resins have been
used for this purpose and, as a result,
increase the amount of resin present as a
potential source. Other adhesives used
for attaching laminates and veneers in-
clude water-based contact cement, ep-
oxy, and polyvinyl acetate.
A final report covering the research con-
ducted under this cooperative agreement
between EPA and RTI will be issued upon
completion of the research in 1996. Addi-
tional information on indoor air emissions
from engineered wood products is avail-
able from studies presented in the full
report, which also presents additional in-
formation on resin chemistry. An evalua-
tion of the health and environmental effects
was beyond the scope of work for this
project.
Sonji Turner, Cybele Martin, Robert Hetes, and Coleen Northeim are with Research
Triangle Institute, Research Triangle Park, NC 27709.
Elizabeth S. Howard is the EPA Project Officer (see below).
The complete report, entitled "Sources and Factors Affecting Indoor Emissions from
Engineered Wood Products,"(Order No. PB96-183876; Cost: $25.00, subjectto
change) will be available only from
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
National Risk Management
Research Laboratory (G-72)
Cincinnati, OH 45268
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POSTAGE & FEES PAID
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EPA/600/SR-96/067
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