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 woodproducts (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 EnvironmentManagement 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 fromComposite Wood Products.” The research objectives are to characterize indoor air emissions from engineered wood products and to identify andevaluate pollution prevention approaches for reducing indoor air emissions from these products.

The research has a five-phase approach: (1) evaluate existing data andtesting methodologies; (2) convene research planning meetings; (3) select high-priority emissions sources; (4) evaluate high-priority emissionssources; and (5) develop and demonstrate pollution prevention approaches for reducing indoor air emissions fromhigh-priority sources. The report summarizes information from the first twophases 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 ofthe research project that is fully documented in a separate report of the sametitle (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 theNation’s health. People spend approximately 90% of their time indoors in environments such as residences, publicbuildings, and offices where concentrations of many pollutants are frequentlyhigher 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 formuch of EPA’s indoor air engineering research and seeks to integrate IAQ and pollution prevention (source reduction) intoa strategic approach to indoor source management. The research objective ofAPPCD’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 traditionalmitigation 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, anotherapproach is to focus on source management, ensuring that pollutants never enter

the indoor environment. In the Pollution Prevention Act of 1990, Congress declaredthat pollution should be prevented or reduced at the source whenever feasible. Sources may be reduced by modifyingequipment, processes, and procedures; reformulating or redesigning products; substituting raw materials; and improving useprocedures. 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) iscollaborating with APPCD in a cooperative agreement entitled, “The Applicationof Pollution Prevention Techniques to Reduce Indoor Air Emissions from Composite Wood Products.” The objectives of this

research are first to characterize indoorair emissions from engineered wood products and then to identify and evaluatepollution 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 demonstratepollution 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 includerepresentatives of trade associations, industry, state government, academia, and technical assistance providers. Extensive

source characterization will be carried outon 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 andeconomic 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 andtheir finishing materials are sources of organic emissions. The most commonly usedresins 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 tothe 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 howthe emissions rates are affected by various parameters. One study concluded thatnew building materials produced high emissions levels, but with effective ventilation these emissions could be reduced; the maximum concentration of formaldehyde reached 0.122 mg/m 3in the new officebuilding investigated for the study. Another indoor analysis suggested that building materials may be the main source oforganic compounds in the indoor environment: the total average concentration for the most frequently identified compounds in this study was 72.96 μ g/m 3 , and the average arithmetic mean emissions rate for all the identified compounds was 9.5 mg/m 2 • h. Two other studies presented predicted emissions rates and emissionsrate ranges, respectively, for several engineered wood products.

Still other studies analyzed samples ofvarious 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 μ g/m 3 at 24 hours to 2,520 μ g/m 3at 120 hours, were lower than for unfinished SYP substrates, ranging from 2,880 μ g/m 3at 24 hours to

918 μ g/m 3at 120 hours]. Besides measuring organic emissions for water-damaged chipboard, which had a mean formaldehyde concentration of about 0.0475 mg/m 3 , one study evaluated microbiological growth from water-damagedchipboard 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 consumerproducts 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. Emissionsdata for each individual study were collected using different analytical test methods. Because methods used to collect emissions data were study-dependent andresearchers 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/m 3 ) from plywood and 0.3 ppm (0.369 mg/m 3 ) 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 ft 2 /ft 3 (0.369 m 2 /m 3 ), and particleboard—0.13 ft 2 /ft 3 (0.43 m 2 /m 3 ). Using the operating conditions specified in FTM 2-1983and the formaldehyde emissions rate equation, formaldehyde emissions rates are 0.13 mg/m 2• h (2.66 x

10 -8 lb/ft 2 • h) for plywood and 0.43 mg/m 2• h (8.81 x

10 -8lb/ft 2 • 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 emissionssource, low-emitting materials may be substituted. When product use or operation is the major source of emissions, knowledgeof 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 woodalternatives, alternative resins and scavengers, and laminate or veneer use. Thesepollution 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, dataon 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 usedin many countries to manufacture composite panel products, such as insulationboard, 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. Manyof 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 aremanufactured primarily from wood. However, agricultural fibers are available thathave 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 withurea-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 availablethat 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 isused in urea-formaldehyde bonded products. For particleboard, when a single resin is used throughout the board, the formaldehyde-to-urea molar ratio can fallwithin the range set by the face/core systems; medium-density fiberboard productsuse resins with formaldehyde-to-urea molar ratios higher than particleboard resins;hardwood plywood products use the highest formaldehyde-to-urea molar ratios. Thenature of the product and process dictates which formaldehyde-to-urea molarratio to use. The molar ratio directly influences the ultimate strength the resin willproduce 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 withurea-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 basicpremise 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 theexcess formaldehyde. The molar ratio directly impacts the ultimate strength theresin 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 oflower 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 approacheliminates the need for a separate metering and storage system for the scavengerbut does not provide flexibility in scavenger level for different products or conditions. A relatively new prepressingscavenger 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, unlikesimple 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 combined4with 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 knownof 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. Allthree 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 theresins 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
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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 usedfor 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 uponcompletion of the research in 1996. Additional information on indoor air emissionsfrom engineered wood products is available from studies presented in the fullreport, 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.