United States National Risk Management

Environmental Protection Research Laboratory

Agency Research Triangle Park NC 27711

Research and Development EPA/600/SR-96/067 June 1996

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

Project Summary

Reconstituted engineered wood components (e.g., particleboard and medium-density fiberboard) are common

to several types of consumer wood

products (e.g., residential and readyto-assemble furniture and kitchen cabinets). 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 collaborating with the Indoor Environment

Management Branch of the U.S. Environmental Protection Agency’s Air Pollution Prevention and Control Division

in a project entitled, “The Application

of Pollution Prevention Techniques to

Reduce Indoor Air Emissions from

Composite Wood Products.” The research objectives are to characterize

indoor air emissions from engineered

wood products and to identify and

evaluate pollution prevention approaches for reducing indoor air emissions from these products.

The research has a five-phase approach: (1) evaluate existing data and

testing methodologies; (2) convene research planning meetings; (3) select

high-priority emissions sources; (4)

evaluate high-priority emissions

sources; and (5) develop and demonstrate pollution prevention approaches

for reducing indoor air emissions from

high-priority sources. The report summarizes information from the first two

phases of research. Information presented here will be used to select reconstituted wood components with various 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 documented in a separate report of the same

title (see Project Report ordering information at back).

Background

Several recent U.S. Environmental Protection Agency (EPA) studies have identified indoor air quality (IAQ) as one of the

most important environmental risks to the

Nation’s health. People spend approximately 90% of their time indoors in environments such as residences, public

buildings, and offices where concentrations of many pollutants are frequently

higher than outdoor urban air. Some indoor activities can lead to indoor air pollutant levels up to 1,000 times higher than

outdoor levels.

EPA’s Air Pollution Prevention and Control Division (APPCD) is responsible for

much of EPA’s indoor air engineering research and seeks to integrate IAQ and

pollution prevention (source reduction) into

a strategic approach to indoor source management. The research objective of

APPCD’s Indoor Environment Management Branch is to employ accepted pollution prevention techniques (e.g., process

modification and product reformulation) to

reduce indoor air contamination through

the development of “low-emitting materi-
2

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 improved IAQ, they do not prevent pollution;

furthermore, the pollution is simply transferred to another medium. Depending on

the source of indoor air pollution, another

approach is to focus on source management, ensuring that pollutants never enter

the indoor environment. In the Pollution

Prevention Act of 1990, Congress declared

that pollution should be prevented or reduced at the source whenever feasible.

Sources may be reduced by modifying

equipment, processes, and procedures; reformulating or redesigning products; substituting raw materials; and improving use

procedures. In multimedia pollution prevention, all environmental media are considered 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 cooperative agreement entitled, “The Application

of Pollution Prevention Techniques to Reduce Indoor Air Emissions from Composite Wood Products.” The objectives of this

research are first to characterize indoor

air emissions from engineered wood products and then to identify and evaluate

pollution prevention approaches (e.g., developing LEMs) for indoor use. This research 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 reducing indoor air emissions from selected

high-priority sources.

The report summarizes information collected in the first two phases of the project.

Information presented here, along with information from outside technical advisors,

will be used to select products for further

research. The technical advisors include

representatives of trade associations, industry, state government, academia, and

technical assistance providers. Extensive

source characterization will be carried out

on the selected products. Pollution prevention 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 prevention potential, and IAQ benefits of the pollution 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 coatings, and a variety of paper and plastic

laminates. Resins and wood used to manufacture engineered wood products and

their finishing materials are sources of organic emissions. The most commonly used

resins in the U.S. are phenol-formaldehyde, urea-formaldehyde, and methylenediphenyl diisocyanate (MDI). The different

chemistries of these resins result in different emissions characteristics. Types of finishing 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 preservatives. 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 pollution prevention opportunities such as

low-emitting or low-impact materials.

Indoor Air Emissions

In 1984, the U.S. Department of Housing and Urban Development (HUD) established 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.*

Many plywood and particleboard manufacturers changed their products to comply. Several studies evaluated various

sources of indoor air emissions and how

the emissions rates are affected by various parameters. One study concluded that

new building materials produced high emissions 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. Another indoor analysis suggested that building materials may be the main source of

organic compounds in the indoor environment: the total average concentration for

the most frequently identified compounds

in this study was 72.96 μg/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 engineered wood products.

Still other studies analyzed samples of

various engineered wood products. A National 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 concentrations, ranging from 156 μg/m3 at 24

hours to 2,520 μg/m3 at 120 hours, were

lower than for unfinished SYP substrates,

ranging from 2,880 μg/m3 at 24 hours to

918 μg/m3 at 120 hours]. Besides measuring organic emissions for water-damaged chipboard, which had a mean

formaldehyde concentration of about

0.0475 mg/m3, one study evaluated microbiological growth from water-damaged

chipboard samples, which revealed significant 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 presented 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 collected using different analytical test methods. Because methods used to collect

emissions data were study-dependent and

researchers presented emissions data differently, comparative conclusions could not

be drawn between the studies presented

in this report.

______________________________________________

* The HUD safety standards for certified plywood and

particleboard used in manufactured home construction 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 m2/m3),

and particleboard—0.13 ft2

/ft3 (0.43 m2/m3). Using

the operating conditions specified in FTM 2-1983

and the formaldehyde emissions rate equation, formaldehyde emissions rates are 0.13 mg/m2

 • h (2.66 x

10 -8 lb/ft2

 • h) for plywood and 0.43 mg/m2 • h (8.81 x

10 -8 lb/ft2 • h) for particleboard.
3

Pollution Prevention

Opportunities

Pollutants are managed most effectively

at their source. The major approaches are

chemical substitution, process changes,

and product redesign. Strategies vary depending 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 substituted. When product use or operation is

the major source of emissions, knowledge

of the relevant process is essential in developing emissions controls or redesigning 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 scavengers, and laminate or veneer use. These

pollution prevention and source management approaches are discussed briefly.

Alternatives to Wood Feedstock

The primary reason for including agricultural 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 engineered 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 composite panel products, such as insulation

board, particleboard, medium-density fiberboard, and hardboard. A global literature 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 developing countries where there is not enough

wood to cover the needs for fuelwood,

industrial wood, sawn wood, and woodbased engineered panels.

In the U.S., engineered panels are

manufactured primarily from wood. However, agricultural fibers are available that

have the potential to be used in engineered 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 Dakota 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-fortified urea-formaldehyde resins, phenolformaldehyde resins, and MDI resins.

While these alternative resins and additives 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 further 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 products. 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 systems; medium-density fiberboard products

use resins with formaldehyde-to-urea molar ratios higher than particleboard resins;

hardwood plywood products use the highest formaldehyde-to-urea molar ratios. The

nature of the product and process dictates which formaldehyde-to-urea molar

ratio to use. The molar ratio directly influences the ultimate strength the resin will

produce in the board; i.e., certain products 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 productivity or board quality, many North

American plants use scavengers with

urea-formaldehyde resins to reduce formaldehyde emissions. (Consequently, although 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 essentially 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 directly impacts the ultimate strength the

resin will produce in the board; i.e., certain 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 significant losses of resin efficiency (bond

strength) or productivity.

Most plants incorporate scavengers before pressing the panel. The most prevalent 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 metering and storage system for the scavenger

but does not provide flexibility in scavenger level for different products or conditions. A relatively new prepressing

scavenger method is combination blending, commonly called combi-blending.

Combination blending is the process by

which two liquid urea-formaldehyde resins

are used in combination to reduce formaldehyde emissions without a loss in board

properties or in production efficiency.

One advantage of combination blending over urea scavenger is that, unlike

simple urea, the scavenger resin has adhesive properties and contributes to bonding. 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
4

with the normal resin just before application 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 anhydrous 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 ammonia to formaldehyde forming a relatively 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 designed for other purposes, such as aesthetics, 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 humidity and temperature, reducing the potential for hydrolytic attack. However, note

that additional resins may be used as

adhesives to attach these covers to the

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, subject to

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

BULK RATE

POSTAGE & FEES PAID

EPA

PERMIT No. G-35

Official Business

Penalty for Private Use

$300

EPA/600/SR-96/067

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 include water-based contact cement, epoxy, and polyvinyl acetate.

A final report covering the research conducted under this cooperative agreement

between EPA and RTI will be issued upon

completion of the research in 1996. Additional information on indoor air emissions

from engineered wood products is available from studies presented in the full

report, which also presents additional information on resin chemistry. An evaluation of the health and environmental effects

was beyond the scope of work for this

project.