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Formaldehyde emissions from ULEF-and NAF-bonded commercial hardwood plywood as influenced by temperature and relative humidity

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Proceedings of the International Convention of Society of Wood Science and Technology and
United Nations Economic Commission for Europe – Timber Committee
October 11-14, 2010, Geneva, Switzerland
Paper WS-23 1 of 13
Formaldehyde Emissions from ULEF- and NAF-Bonded
Commercial Hardwood Plywood as Influenced by
Temperature and Relative Humidity
Charles R. Frihart
USDA Forest Products Laboratory
Madison, Wisconsin, USA
James M. Wescott
Heartland Resource Technologies
Waunakee, Wisconsin, USA
Michael J. Birkeland
Heartland Resource Technologies
Edgerton, Wisconsin, USA
Kyle M. Gonner
Heartland Resource Technologies
Madison, Wisconsin, USA
Abstract
It is well documented in the literature that temperature and humidity can influence formaldehyde
emissions from composite panels that are produced using urea-formaldehyde (UF) adhesives.
This work investigates the effect of temperature and humidity on newer, ultra-low emitting
formaldehyde urea formaldehyde (ULEF-UF) and no-added formaldehyde (NAF) adhesives. A
modified version of the EN 717-3 method to collect formaldehyde coupled with the acetyl-
acetone method to quantify formaldehyde emissions was used. Formaldehyde emissions from a
commercial CARB phase II compliant hardwood-plywood panel bonded with a ULEF-UF resin
increased greatly when panels were exposed to higher heat and humidity. Furthermore, the rate of
emission for ULEF-UF panels increased with longer exposure at 100% humidity. In contrast,
formaldehyde emissions from CARB phase II compliant hardwood-plywood bonded with a NAF
resin were relatively stable at different temperature and relative humidity conditions and
decreased over time. This work highlights the potential for long-term formaldehyde emissions
from the new ULEF-UF, CARB phase II compliant resin systems.
Keywords soy, urea formaldehyde, formaldehyde emissions, heat, humidity, ULEF
Proceedings of the International Convention of Society of Wood Science and Technology and
United Nations Economic Commission for Europe – Timber Committee
October 11-14, 2010, Geneva, Switzerland
Paper WS-23 2 of 13
Introduction
Increasing concerns over the quality of indoor air has led to recent changes in legislation and a
general preference for more stringent limits on the quantity of formaldehyde that can be emitted
from consumer products intended for indoor use. Wood composites bonded with urea-
formaldehyde (UF) adhesive have been identified as an important source of indoor formaldehyde
emissions (Battelle 1996). Formaldehyde release from interior wood composites has been a
longstanding issue, leading in the 1980s to the adoption of voluntary standards in the United
States and Europe that placed limits on formaldehyde emissions (ANSI 2009a,b, 2004; European
Standard 2002). These voluntary standards led to lower formaldehyde-emitting wood composites,
but in subsequent years, U.S. emissions from standard products stayed constant while products in
Europe and Japan moved to lower emission levels.
Recent standards adopted by the California Air Resources Board (CARB) are intended to
significantly reduce and regulate formaldehyde emissions in composite wood products (ATCM
2009). The CARB standard is also the basis for national legislation recently passed concerning
the emission of formaldehyde in interior wood composites (TSCA 2010). The new standards
have led to new UF adhesives with ultra-low formaldehyde emissions (ULEF-UF) (Dunkey
2005), and opened the door for no-added-formaldehyde (NAF) adhesives, such as soy-based
adhesives (Allen et al. 2010, Wescott et al. 2010), polymeric diphenylmethane diisocyanate, and
certain types of poly(vinyl acetate). Although both classes of adhesives, ULEF-UF and NAF, are
capable of passing the CARB phase II formaldehyde emissions limits, there is a concern about
the long-term emission potential of ULEF-UF adhesives when exposed to potentially higher
temperature or humidity levels than specified in the current testing methodology for measuring
formaldehyde emissions.
Although substantial progress has been made on ULEF-UF adhesives, the fundamental chemistry
of urea formaldehyde is relatively unchanged and may remain susceptible to hydrolysis. The
reaction of urea with formaldehyde first produces hydroxylmethyolated urea that then condenses
to yield methylene and dimethylene ether bridged urea polymers (Pizzi 2003, Meyer 1979).
Although these reactions are not unlike the steps to produce the other formaldehyde-containing
wood adhesives, the UF polymers are distinct in that they are susceptible to hydrolysis under
some normal use conditions (Myers 1986a). The reaction shown in Figure 1 for urea and
formaldehyde illustrates the problem with depolymerization in that it can yield additional free
formaldehyde, especially when free water is present.
Figure 1. The reaction of urea with formaldehyde to form the urea-formaldehyde polymer.
O
H H
O
H
2
N NH
2
+
O
N
HN
nH
2
O
+
Urea
Formaldehyde Urea-Formaldehyde Water
H
+
+
Proceedings of the International Convention of Society of Wood Science and Technology and
United Nations Economic Commission for Europe – Timber Committee
October 11-14, 2010, Geneva, Switzerland
Paper WS-23 3 of 13
The presence of free water in the composite panel, as in the case of higher humidity, tends to
drive the reverse reaction, yielding more free formaldehyde. Myers showed that formaldehyde
adsorbed onto wood reaches an emission plateau in about 7 days at 80% relative humidity (RH)
and 27°C, as does phenol-formaldehyde-bonded particleboard. In contrast, UF-bonded
particleboard emitted formaldehyde for over 30 days without reaching a plateau (Myers 1986b).
In addition, Myers’s own data and his analysis of the literature data showed that formaldehyde
emissions increase from UF-bonded wood composites at higher humidity and temperature
conditions (Myers 1985, Myers and Nagaoka 1981). This work was done with composites
bonded with more traditional UF-based adhesives; it is unclear if the new ULEF-UF systems
suffer from the same level of hydrolytic instability and subsequent high formaldehyde emissions.
Wood itself generates significant formaldehyde when exposed to certain conditions common to
the composite panel manufacturing process (Schäfer and Roffael 2000, Roffael 2006). This so-
called “native” formaldehyde has been shown to be transient and rapidly decreases to levels
below those set by the standards (Birkeland et al. 2010). Production of formaldehyde from wood
has been shown to occur at conditions of very high heat and would not be expected to be a
significant source of formaldehyde in composite wood products during service.
Currently, the primary standard test method in the United States for measuring and regulating
formaldehyde emissions in composite wood panels is the ASTM E 1333 (ASTM 2002) large
chamber test. Secondary methods can be also used; however, all methods must prove equivalence
to the primary method. In E 1333, samples are conditioned at 25°C and 50% RH for 7 days and
then tested at the same temperature and RH conditions. Based upon the available literature, some
questions arise regarding formaldehyde emissions from composite wood panels:
Given that the standard test method, ASTM E 1333, uses 25°C (77°F) and 50% relative
humidity, do these conditions represent all the exposure that interior composite wood products
will experience in service?
How do the formaldehyde emissions in CARB phase II certified composite wood products
bonded with ULEF-UF adhesives compare to those bonded with NAF adhesives over a range
of temperatures and relative humidity that they may reasonably experience in service?
This study focused on answering these questions, using a modified version of EN 717-3 to test
the effects of temperature and relative humidity on commercial CARB phase II compliant
plywood bonded with either ULEF-UF or NAF.
Methods
Samples
Plywood samples used for testing were 3/4-in.- (19-mm-) thick, seven-ply, hardwood plywood
with maple face and back and mixed softwood cores obtained from a commercial collaborator.
One plywood specimen was bonded with a ULEF-UF and one was bonded with a soy-based NAF
adhesive. Samples from both plywood specimens were tested in a small chamber by the
manufacturer and shown to be CARB phase II compliant (<0.05 ppm). Samples were wrapped
Proceedings of the International Convention of Society of Wood Science and Technology and
United Nations Economic Commission for Europe – Timber Committee
October 11-14, 2010, Geneva, Switzerland
Paper WS-23 4 of 13
and sealed in plastic within 24 h after hot-pressing and remained in plastic until testing by the
modified EN 717-3 method.
Modified EN 717-3 (WKI Bottle Method)
A modified version of the EN-717-3 was conducted in this study; Table 1 defines the specific
modifications used in this study. From other studies, the repeatability of this method gave a 4%
coefficient of variation.
Relative humidity was controlled as follows: 30% RH (with saturated MgCl2), 75% RH (with
saturated NaCl), and 100% RH (RO H2O) (Wexler 1961).
Table 1: Summary of modifications to EN-717-3
EN-717-3
Our method
Temperature
40°C
25°C and 35°C
Test duration
3 h
1–4 days
Relative humidity
(%)
100
30–100
Detailed Test Procedure
Using a Nalgene® 500-mL wide-mouth polypropylene bottle (Sigma Aldrich, Milwaukee,
Wiscsonsin), with cap modified with epoxy and a paper clip, 50 mL (via burette) of either H2O
(100% RH), saturated MgCl2 (30% RH), or saturated NaCl (75% RH) solution is placed in the
bottom. Three 1- by -in. samples are weighed to 0.1 g, stacked on top of each other (faces
together), and bound with a rubber band. The bound samples are then suspended above the
solution in the bottle by attaching the rubber band to the paper clip. The bottle is then kept in a
temperature/humidity controlled room (25°C) or in a water bath (35°C) for the allotted time (24,
48, or 96 h). The test bottles are then cooled in an ice water bath for 30 min, the samples removed
carefully, and the solution collected for analysis. The samples are analyzed for formaldehyde on
the same day using the acetyl-acetone method.
Acetyl-Acetone Method (ONORM 1992, Nash 1953, Belman 1963)
A calibration curve was generated using a standard formaldehyde solution prepared from 37%
formaldehyde (Sigma Aldrich, Milwaukee, Wisconsin) titrated to determine formaldehyde level.
A six-point calibration curve was generated using concentrations of 0 to 5.6 µg/mL formaldehyde
and yielding an R2 = 0.9998. The standards were analyzed as described below to obtain the
formaldehyde response. Equal parts (2 mL) of 0.4% acetyl-acetone (Fisher Scientific, Fair Lawn,
New Jersey), 20% ammonium acetate (Daigger Chemical, Vernon Hills, Illinois), and sample
solution were combined in a test tube. The mixture was heated to 40°C for 15 min in a water
bath, then cooled to 25°C. The cooled solution was placed in the dark for 1 h. The mixture was
then analyzed for absorbance with a spectrophotometer at a wavelength of 412 nm. The
formaldehyde concentration of the sample was determined based on the calibration curve as
described above. The results were converted to micrograms of formaldehyde emitted per gram of
wood. Standard solutions were run at 1, 10, and 30 µg/mL to cover the range of formaldehyde
Proceedings of the International Convention of Society of Wood Science and Technology and
United Nations Economic Commission for Europe – Timber Committee
October 11-14, 2010, Geneva, Switzerland
Paper WS-23 5 of 13
concentrations measured. Controls were run using the acetyl-acetone method with standard
formaldehyde levels in the presence of MgCl2 and NaCl to ensure no interference from the salts.
Figure 2: Sample set-up for
modified EN-717-3 method
Results and Discussion
A static formaldehyde emissions technique was employed to assess changes in emissions for
composite wood products as a function of temperature and humidity. The method was a modified
version of the EN 717-3 method. The modifications to this method are outlined in Table 1. The
purpose of the modifications was to allow the test to be run at various temperatures, relative
humidities, and durations to better understand the formaldehyde emission potential of composite
panels under a variety of possible exposures. The 100% humidity was higher than typical, but
accelerated tests are generally run under more severe conditions than normal exposures due to
shorter times under those conditions.
Two commercially produced decorative hardwood plywood specimens were evaluated in this
study. Both specimens were of the same construction, and the only variable was the adhesive
used to bond the veneers together to produce the final product. One specimen was bonded with a
ULEF-UF adhesive; the other specimen was bonded with a NAF soy-based system. Samples
from both specimens were tested by the manufacturer in a small chamber correlated to ASTM E
1333 prior to our testing, and both were shown to be CARB-phase II compliant.
The ASTM E 1333-96 “Large Chamber Method” and any correlated “Small Chamber Method”
per ASTM D 6007-02 must be run at 25°C and 50% relative humidity. It is likely that these
conditions may be typical for many homes in the United States, in particular, those that contain
Proceedings of the International Convention of Society of Wood Science and Technology and
United Nations Economic Commission for Europe – Timber Committee
October 11-14, 2010, Geneva, Switzerland
Paper WS-23 6 of 13
and operate an air conditioning system. However, there are many instances when these panels are
used within the interior of a home that they may be subjected to extended periods of time at
temperatures higher than 25°C and/or relative humidity levels higher than 50%. The data in
Figures 3a (www.weather.com) and 3b (www.cityrating.com/relativehumidity.asp) show that the
majority of the United States, in fact, is actually much higher than 50% RH. Most notably, during
the summer months, the southeastern region has substantially higher RH and temperature than the
test conditions (Table 2). It is this finding that led us to evaluate composite panel emissions as a
function of temperature and humidity.
15
35
79
0
10
20
30
40
50
60
70
80
90
21 -30
31 -40
41 -50
51 -60
61 -70
71 -80
81 -90
91 -100
Numb er of US Citie s in RH Range*
Relative Humidity Range s (% )
Relative Humidity AM
Figure 3a: AM relative humidity distribution of
137 U.S. Cities (Average = 79%)
6
9
11
65
45
1
0
0
0
10
20
30
40
50
60
70
21 -30
31 -40
41 -50
51 -60
61 -70
71 -80
81 -90
91 -100
Numb er of US Citie s in RH Range*
Relative Humidity Range s (% )
Relative Humidity PM
Figure 3b: PM relative humidity distribution of
137 U.S. cities (Average = 55%)
Proceedings of the International Convention of Society of Wood Science and Technology and
United Nations Economic Commission for Europe – Timber Committee
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Table 2: Summer temperature and relative humidity averages for
select U.S. cities
Ave. low temp.
Jun–Aug
F (°C))
AM
RH
(%)
Ave high temp
Jun–Aug
F (°C))
PM
RH
(%)
Chicago, IL
64 (18)
80
82 (28)
62
Fargo, ND
57 (14)
81
80 (27)
64
Houston, TX
75 (24)
90
93 (34)
63
Kansas City, MO
70 (18)
81
88 (31)
63
Las Vegas, NV
76 (24)
39
102 (39)
21
Los Angeles, CA
64 (18)
79
83 (28)
65
Miami, FL
76 (24)
83
91 (33)
61
New York, NY
66 (19)
72
80 (27)
56
Raleigh-Durham,
NC
67 (19) 85 86 (30) 54
Seattle, WA 55 (13) 83 73 (23) 62
Impact of Relative Humidity
In this section of the study, we used water (100% RH) and saturated solutions of MgCl2 (30%
RH) and NaCl (75% RH) to control the relative humidity inside the sample bottles. (See the
experimental section for details.) These experiments were run at both 25°C (77°F) and 35°C
(95°F). Table 3 shows the results.
Table 3: Formaldehyde emissions in (
µ
g CH2O/g wood) via modified
EN-717-3 method
Temp.
Days (°C) 30 75 100 30 75 100
125 1.8 3.6 5.8 0.7 0.7 1.6
225 4.2 6.0 16.7 1.2 1.6 2.9
425 5.6 11.4 50.8 1.4 2.4 4.0
135 3.1 8.9 24.0 0.5 2.4 4.5
235 5.2 15.5 54.2 0.7 2.7 5.0
435 9.1 31.3 178.1 2.1 4.4 5.3
% Relative Humidity
% Relative Humidity
ULEF-UF
NAF
To better analyze the data, several charts were constructed from the data shown in Table 3.
Figures 4a and 4b show emissions as a function of relative humidity for both the 25°C and 35°C
data sets. These results clearly show that the ULEF-UF panel emitted significantly higher
formaldehyde levels when subjected to higher relative humidity levels and that this was further
exacerbated by a concomitant increase in temperature.
Proceedings of the International Convention of Society of Wood Science and Technology and
United Nations Economic Commission for Europe – Timber Committee
October 11-14, 2010, Geneva, Switzerland
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0
10
20
30
40
50
60
020 40 60 80 100 120
CH2O Emissions (µg/g)
% Re lative Humidity @ 25 C
NAF
ULEF-UF
Figure 4a: Formaldehyde emissions at various relative humidity
levels at 25°C (4 day samples)
0
20
40
60
80
100
120
140
160
180
200
020 40 60 80 100 120
CH2O Emissions (µg/g)
% Re lative Humidity @ 35 C
NAF
ULEF-UF
Figure 4b: Formaldehyde emissions at various relative humidity
levels at 35°C (4 day samples)
Although it was expected that emission levels of panels produced with ULEF-UF adhesive would
increase more than those produced with NAF adhesive at increasing temperature and humidity,
the fact that the ULEF-UF panel emitted >33 times the amount of formaldehyde than the NAF
Proceedings of the International Convention of Society of Wood Science and Technology and
United Nations Economic Commission for Europe – Timber Committee
October 11-14, 2010, Geneva, Switzerland
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panel at 100% RH/35°C and the ULEF-UF panel’s emissions within its own set would increase
by >31 times (100% RH/35°C vs 30% RH/25°C) was quite surprising to us.
We were also interested in rate of emissions in this study. To assess rate of emissions, individual
samples were tested at 1-, 2-, and 4-day increments. Results of this study are shown in Figures 5
and 6 (note differences in scale for each set of figures). These results show that for all the NAF
samples, regardless of temperature or relative humidity, rate of formaldehyde emissions
decreased over time. This is a desired feature as this would suggest that emission levels will only
improve (reduce) over the life of the product. Interestingly, the ULEF-UF produced panel did not
show this behavior when subjected to the 100% relative humidity level, and even at the lower
humidity levels emission rates were either relatively flat or only slightly decreasing. The trends
were the same regardless of temperature, that is, emissions rate was roughly double at 4 days
what if was after only 1 day. This could be the result of scavenger consumption or possibly
sample equilibration and/or diffusion rates.
Another interesting aspect of these data is the apparent limited or fixed amount of “native”
formaldehyde present in these panels. With the NAF panels, this native formaldehyde appeared to
be released faster when the temperature was higher and the relative humidity was higher, hence
the emissions only increased from 4.5 to 5.3 from day 1 to day 4 within the 100% RH/35°C
sample set. It appears that once the native formaldehyde was extracted from the moist panel,
there was virtually no formaldehyde left in the panel, thus the total formaldehyde emitted did not
change substantially when the test duration was extended. The ULEF-UF panel was produced
from UF resin, and these resins are well known to hydrolyze and produce additional
formaldehyde; the NAF panel did not show this behavior.
The effect of temperature and humidity on formaldehyde emission reported in Table 3 is similar
to the effects seen by Myers and Nagaoka (1981). Using a dynamic chamber method and UF-
bonded particleboard, they showed that moving from 25°C and 30% RH to 25°C and 75% RH
resulted in an approximate two-fold increase in formaldehyde emissions. An examination of the
data in Table 3 shows that at 25°C, the increase from 30% to 75% RH yields a 2.0-, 1.4-, and 2.0-
fold increase in emissions for the 1-, 2-, and 4-day data, respectively.
Furthermore, when Myers and Nagaoka changed both temperature (from 25°C to 40°C) and RH
(from 30% to 75%), the resultant increase in formaldehyde emission was approximately six-fold.
An analysis of data from Table 3 shows that moving from 25°C and 30% RH to 35°C and 75%
RH yields a 4.9-, 3.7-, and 5.6-fold increase in emissions for the 1-, 2-, and 4-day data,
respectively.
Although Myers and Nagaoka (1981) did not conduct analyses at relative humidity levels above
75%, in a comprehensive literature survey, Myers was able to derive quantitative temperature and
relative humidity factors at a wide range of temperature and relative humidity conditions (Myers
1985). Based on these equations, the move from 30% to 90% RH at 25°C is predicted to yield a
three-fold increase in formaldehyde emissions. The data in Table 3 show that moving from 30%
to 100% RH at 25°C yields increases in formaldehyde emissions of 3.2, 4.0, and 9.1 fold for the
1-, 2-, and 4-day data, respectively. The 1-day data agree well with Myers prediction; however,
Proceedings of the International Convention of Society of Wood Science and Technology and
United Nations Economic Commission for Europe – Timber Committee
October 11-14, 2010, Geneva, Switzerland
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the longer test periods present increasing rates of formaldehyde emission. The mechanism for this
increase is currently unknown.
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
012345
Emissions Rate (ug/mL per day)
Days @ 25 C (ULEF-UF)
30%
75%
100%
Figure 5a: Emissions rate as a function of % relative humidity for
ULEF-UF panel at 25
°
C.
Figure 5b: Emissions rate as a function of % relative humidity for
NAF panel at 25
°
C.
Proceedings of the International Convention of Society of Wood Science and Technology and
United Nations Economic Commission for Europe – Timber Committee
October 11-14, 2010, Geneva, Switzerland
Paper WS-23 11 of 13
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
012345
Emissions Rate (ug/mL per day)
Days @ 35 C (ULEF-UF)
30%
75%
100%
Figure 6a: Emissions rate as a function of % relative humidity for
ULEF-UF panel at 35
°
C.
Figure 6b: Emissions rate as a function of % relative humidity for
NAF panels at 35
°
C.
Conclusions
Testing of formaldehyde emissions from CARB II compliant plywood panels using an ultra-low
emitting formaldehyde (ULEF) UF resin and a no-added-formaldehyde (NAF) resin carried out at
six different conditions (25°C at 30%, 75%, and 100% relative humidity, and 35°C at 30%, 75%,
and 100% relative humidity) using a modification of EN 717-3 has shown the following: (1) The
Proceedings of the International Convention of Society of Wood Science and Technology and
United Nations Economic Commission for Europe – Timber Committee
October 11-14, 2010, Geneva, Switzerland
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ULEF-UF product emitted more formaldehyde as the temperature and relative humidity
increased; at 100% humidity, there was an initial delay in this rise probably due to the
consumption of the scavenger. (2) The NAF plywood product showed that the total formaldehyde
emissions reached a plateau and decreased rapidly after only a few days under all test conditions.
Thus, neither the wood nor the NAF are providing any significant potential source of long-term
formaldehyde as a result of these increased heat and moisture conditions.
References
Allen, A J.; Spraul, B.K.; Wescott, J.M. 2010. Improved CARB II-compliant soy adhesives for
laminates. In: Wood Adhesives 2009. South Lake Tahoe, CA, Frihart, C.R.; Hunt, C.G.; Moon,
R.J. (eds.). Madison, WI: Forest Products Society. pp. 176-184.
ANSI. 2004. ANSI/HPVA standard HP-1-2004. American National Standard for hardwood
plywood and decorative plywood. Reston, VA: Hardwood Plywood and Veneer Association.
ANSI. 2009a. ANSI standard A208.1-2009. American National Standard for particleboard.
Gaithersburg, MD: The Composite Panel Association.
ANSI. 2009b. ANSI standard A208.2-2009. American National Standard for medium density
fiberboard (MDF) for interior applications. Gaithersburg, MD: The Composite Panel Association.
ASTM. 2002. ASTM standard E1333-96. Standard Test Method for determining formaldehyde
concentrations in air and emission rates from wood products using a large chamber. West
Conshohocken, PA: ASTM International.
ATCM. 2009. Airborne toxic control measure to reduce formaldehyde emissions from composite
wood products. Health and Safety Code: Title 17 California Code of Regulations, Section 93120-
93120.12.
Battelle. 1996. Determination of formaldehdye and toluene diisocyanate emissions from indoor
residential sources. Final Report, CARB Contract No. 93-315, Sacramento, CA. 119 pp.
Belman, S. 1963. The Fluormetric Determination of Formaldehyde. Anal. Chim. Acta 29:120.
Birkeland, M.J.; Lorenz, L.; Wescott, J.M.; Frihart, C.R. 2010. Determination of native (wood
derived) formaldehyde by the desiccator method in particleboards generated during panel
production. Holzfoschung 64:429–433.
Dunkey. M. 2005. Resins for ultra-low formaldehyde emission according to the Japanese F****
Quality. In: Wood Adhesives 2005. Madison, WI: Forest Products Society. pp. 343-349.
Proceedings of the International Convention of Society of Wood Science and Technology and
United Nations Economic Commission for Europe – Timber Committee
October 11-14, 2010, Geneva, Switzerland
Paper WS-23 13 of 13
European Standard. 2002. EN 13986. Wood-based panels for use in construction—
Characteristics, evaluation of conformity and marking. Brussels: European Committee for
Standardizations.
Meyer, B. 1979. Urea-formaldehyde resins. Reading, MA: Addison-Wesley Publishing
Company, Inc. pp. 128-129
Myers, G.E.; Nagaoka, M. 1981. Formaldehyde emission: methods of measurement and effects
of several particleboard variables. Wood Science 13:140-150.
Myers, G.E. 1985. The effects of temperature and humidity on formaldehyde emission from UF-
bonded boards: a literature critique. Forest Prod. J. 35(9):20-31.
Myers, G.E. 1986a. Resin hydrolysis and mechanisms of formaldehyde release from bonded
wood products. In: 1986 Forest Products Research Society Proceedings, Madison, WI, USA.
Myers, G.E. 1986b. Mechanisms of formaldehyde release from bonded wood products. In:
Meyer, B.; Andrews Kottes, B.A.; Reinhardt, R.M.. Formaldehyde release from wood products.
ACS Symposium Series 316; 1985 April 28-May 3; Miami Beach, FL: Washington, DC:
American Chemical Society. pp. 87-106
Nash, T. 1953. Colorimetric estimation of formaldehyde by means of the Hantzch reaction,
Biochem. J. 55:416–421.
ONORM. 1992. ONORM standard EN 120. Wood based panels—Determination of
formaldehyde contentExtraction method called the perforator method. Osterreichisches
Normungsinstitut (ON), Heinestraβe 38 A-1020 Wien, Vienna, Austria. pp. 5-6
Pizzi, A. 2003. Amino resin wood adhesives. In: Handbook of adhesive technology A. Pizzi and
K.L. Mittal (eds.). New York: Marcel Dekker Inc. pp. 541–572.
Roffael, E. 2006. Volatile organic compounds and formaldehyde in nature, wood and wood based
panels. Holz Roh Werkst. 64:144–149.
Schäfer, M.; Roffael, E. 2000. On the formaldehyde release of wood. Holz Roh Werkst. 58:259–
264.
TSCA. 2010. Toxic Substances Control Act of 1976. §1660, 15 U.S.C. 2601 §601 (2010).
Wescott, J.M.; Birkeland, M.J.; Yarvoski, J.; Brady, R. 2010. Recent advances in soy containing
PB and MDF. In: Wood Adhesives 2009. South Lake Tahoe, CA, Frihart, C.R.; Hunt, C.G.;
Moon, R.J. (eds.). Madison, WI: Forest Products Society. pp. 136-141.
Wexler, A. 1961. Humidity standards. TAPPI. V. 44, No. 6 pp. 180A. June 1961.
... It was unclear if the new lower emitting UF systems suffer from the same level of hydrolytic instability and subsequent high formaldehyde emissions. A similar study conducted on the formaldehyde emissions of ultra-lowemitting-formaldehyde (ULEF)– and NAF-bonded hardwood plywood (Frihart et al. 2010) showed that higher temperatures and humidity led to significantly higher formaldehyde emissions from plywood bonded with UF adhesive. The current article reports on particleboard with more extensive higher temperature and humidity condi- tions. ...
... The results were converted to micrograms of formaldehyde emitted per gram of wood. Previous work using the same saturated salt solutions showed that there was no interference from the salts on the formaldehyde concentrations (Frihart et al. 2010). ...
Article
Full-text available
It is well documented that temperature and humidity can influence formaldehyde emissions from composite panels that are produced using urea-formaldehyde (UF)-type adhesives. This work investigates the effect of temperature and humidity on newer commercial California Air Resources Board (CARB) phase II-compliant particleboard produced with UF-type adhesives. These results were compared with laboratory particleboards prepared with the no-added-formaldehyde (NAF) Soyad adhesive technology. A modified version of EN 717-3 ("Formaldehyde Release by the Flask Method." ÖNORM 1996) was used to collect formaldehyde emissions that were quantified using the acetylacetone method. The formaldehyde emissions from the commercial particleboard panel bonded with a UF-type resin increased greatly when panels were exposed to higher heat and humidity than in normal testing protocols. Furthermore, the rate of emission for these UF-bonded panels increased with longer exposure at 100 percent relative humidity. In contrast, formaldehyde emissions from particleboard bonded with the NAF adhesive were relatively stable and significantly lower compared with those bonded with UF at all temperature and relative humidity conditions. This work highlights the potential for increased long-tenn formaldehyde emissions even from the new UF CARB phase II-compliant adhesive systems.
... Paper WS-20 8 of 12 Wescott and Frihart 2008, Wescott et al. 2010). However, lower viscosity is valuable in certain applications; for example, spraying adhesives. ...
... Paper WS-20 9 of 12 under standard testing conditions, but also under elevated heat and humidity, which occur under common exposure conditions that the wood products may see (Frihart et al. 2010). Soy flour and PAE cross-linker involve less plant hazards than those adhesives containing formaldehyde or isocyanate. ...
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Synthetic adhesives, including urea-formaldehyde (UF) and phenol-formaldehyde (PF), have generally replaced biobased adhesives over the past 70 years because of their durability, low cost, and ease of use. However, in the past few years, concern about formaldehyde emissions, cost, and interest in biobased materials have renewed interest in soy adhesives. The use of soy adhesives can be broken into four stages: soy flour selection, dispersing/denaturating conditions, cross-linking chemistry, and bonding conditions. Generally soy flour is used because of its low cost, but the adhesive properties of the soy depend upon flour type, as well as adhesive formulation and processing conditions. For the flour to be used as an adhesive, it must be dispersed in a solvent, usually water. In this paper, we emphasized protein properties, as they are critical for forming good durable bonds. The dispersed proteins are globular because proteins fold in water so that the outer surface contains mainly hydrophilic groups, whereas hydrophobic groups prefer to be on the inside. Globular structures are sensitive to conditions, such as pH, added denaturants, temperature, and salts. Typically, soy proteins provide good adhesion to wood and other materials; however, these adhesives have poor water resistance without chemical cross-linking. Denaturants not only open or swell the protein globules to increase adhesion to the wood surfaces but also expose more sites for cross-linking these proteins. Soy adhesives, like most adhesives, need to be tailored to the application. Thus, an adhesive for plywood is very different from that for particleboard, and a core adhesive is different from a face adhesive for wood composites.
... Myers (1985) proposed an exponential relation between the steady-state HCHO emission rate and RH [53]. Prior studies reported that the HCHO emission rate had increased 6-9 times when RH increased from 30% to 100% [60,61]. Parthasarathy et al. (2011) said that the steady-state HCHO emission rate increased by 1.8 to 3.5 times after a rise in RH from 50% to 85% [55]. ...
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The adsorption of volatile organic compounds by building materials reduces the pollutant concentrations in indoor air. We collected three interior building materials with adsorption potentials—latex paint, micro-carbonized plywood, and moisture-buffering siding—used the sorptive building materials test (SBMT) to determine how much they reduced indoor formaldehyde (HCHO) concentrations, and then assessed the consequent reduction in human cancer risk from HCHO inhalation. Adsorption of HCHO by building materials significantly improved the effective ventilation efficiency. For example, the equivalent ventilation rate for Celite siding—used for humidity control—was 1.44 m³/(m²h) at 25C, 50% relative humidity (RH); the loading factor (L) was 0.4 m²/m³, and the HCHO concentration was 0.2 ppm; this effect is equivalent to a higher ventilation rate of approximately 0.6 air changes per hour in a typical Taiwanese dwelling. There was also a substantial reduction of risk in Case MCP-2 (Cin,te: 245 μg/m³, 30C, 50% RH): males: down 5.73 × 10⁻⁴; females: down 4.84 × 10⁻⁴). The selection of adsorptive building materials for interior surfaces, therefore, significantly reduces human inhalation of HCHO. Our findings should encourage developing and using innovative building materials that help improve indoor air quality and thus provide building occupants with healthier working and living environments. © 2019 Huang et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
... Myers [13] reviewed some available data and proposed a linear relation between steady state formaldehyde emission rate and RH. Frihart et al. [14,15] measured formaldehyde emissions from a UF-bonded particleboard and concluded that the emission rate increased 6e9 times when RH increased from 30% to 100%. Parthasarathy et al. [16] measured the steady state formaldehyde concentrations in the small environmental chamber and found that the increase of RH from 50% to 85% yielded a 1.8e3.5 times increase in formaldehyde emission rate. ...
... Although the original work and a mechanistic study used soy protein isolate (SPI) (Li et al. 2004, Zhong et al. 2007), soy flour is much more economically competitive. Performance of the soy flour-PAE adhesives has been reported Frihart et al. 2010aFrihart et al. , 2010bWescott et al. 2010), but only a limited number of studies have been published about the factors influencing the performance of these adhesives (Frihart et al. 2010a, Frihart andSatori 2013). Prior studies have shown that soy flour with 45 percent protein content provides less than a third of the wet bond strength provided by the SPI with over 90 percent protein content (Frihart 2011). ...
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Soy flour adhesives using a polyamidoamine-epichlorohydrin (PAE) polymeric coreactant are used increasingly as wood adhesives for interior products. Although these adhesives give good performance, higher bond strength under wet conditions is desirable. Wet strength is important for accelerated tests involving the internal forces generated by the swelling of wood and plasticization of the adhesive with increasing humidity. Soy proteins are globular due to their hydrophobicity; thus, it was expected that adding modifiers to open the protein structure should improve protein-protein and protein-wood interactions to help withstand both internal and external forces applied to the bond. Because modifiers have been shown to improve the performance of soy protein isolate adhesives, use of these modifiers has been examined as a way to improve soy flour adhesives. Protein-disrupting chaotropic agents (urea, guanidine hydrochloride, and dicyandiamide), surfactants (sodium dodecyl sulfate or cetyltrimethylammonium bromide), and the cosolvent propylene glycol were all expected to provide increased protein-protein and protein-PAE interactions. Improved interactions would make the soy flour adhesives durable enough to better pass wet bond strength tests specified for most interior bonded wood products. However, no substantial improvement was seen in cured wood bond strengths in wet conditions for soy flour adhesives by adding any of these modifiers with or without PAE polymer addition. These results led to a proposal that carbohydrates, about 45 percent by weight of soy flour, are interfering with obtaining greater adhesive bond strengths from the protein portion of the flour.
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This chapter contains sections titled: Introduction Scientific Analysis of the Problem Factors Affecting the Amount of Formaldehyde Emission Exposure Safe Level of Formaldehyde Exposure Evolution of Formaldehyde Emission Standards CARB Green Adhesive Formaldehyde Emission Standards Japanese JIS/JAS Formaldehyde Adhesive Emission Standards [21‐23] European Formaldehyde Emission Standards [24‐33] Standardization and Test Methods Different Standards and Test Methods
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Hot-pressing wood, particularly in the production of wood composites, generates significant ''native'' (wood-based) formaldehyde (FA), even in the absence of adhesive. The level of native FA relates directly to the time and temperature of hot-pressing. This native FA dissipates in a relatively short time and is not part of the long-term FA emission issue commonly associated with hydrolyzing urea-formaldehyde bonds. This paper demonstrates that the common desiccator/ chromotropic acid method is very specific for FA and is not influenced by other volatile compounds set free from wood during hot-pressing. Furthermore, it is shown that particle­ board produces native FA at high levels even in the absence of adhesives or in the presence of one type of no-added formaldehyde (NAF) adhesive. Soy-based adhesives sup­ press native FA emission and provide low FA emission levels in both the short and long term. This study highlights an often overlooked aspect that should be considered for emis­ sion testing: standardizing the time and conditions employed immediately after pressing and prior to the onset of emis­ sions testing. Addressing this issue in more detail would improve the reliability of correlation between data obtained by rapid process monitoring methods and emission measure­ ments in large chambers.
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An analysis has been conducted on available data related to temperature and humidity effects on formaldehyde concentrations that are produced by emission from particleboard and hardwood plywood paneling. Temperature changes are described by an exponential relation while a linear relation suffices for humidity effects. Large variations exist in the results from different investigators on different boards for the exponential temperature coefficients B ( minus 5620 degree to minus 12,480 degree K** minus **1) and for the linear humidity coefficients beta (0. 005% to 0. 038%** minus **1).
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In this paper I examine the available evidence for and against the influence of urea-formaldehyde (UF) resin hydrolysis on formaldehyde emis-sion from UF-bonded wood products. That evidence includes literature reports from 1950 through 1984 as well as unpublished results from my own recent studies. I have considered three related aspects: (a) the chemistry and hydrolytic stability of UF and phenol-formaldehyde (PF) mate-rials and rates of formaldehyde liberation from these materials, (b) the chemistry and hydrolytic sta-bility of formaldehyde-wood and UF-wood reaction products and rates of formaldehyde liberation from these products, and (c) the formaldehyde liberation behavior of UF and PF par-ticleboards. The primary conclusions are: (a) In an acid-catalyzed UF board, formaldehyde can exist in a wide variety of states, including dis-solved methylene glycol monomer and oligomers, parafonn, hexa, chemically bonded UF resin states, chemically bonded UF-wood states, cellulose hemi-formals and formals. Each of those states is a potential source of form-aldehyde emission by evaporation (methylene glycol) or initial hydroly-sis. At present, we cannot quantify the relative contributions of these states over time. (b) In a base-catalyzed PF board, formaldehyde states may include methylene glycol monomer and oligomer, chemically bonded PF resin states, chemically bonded PF-wood states, and cellulose hemiformals. Emission sources apparently include methylene glycol, cellulose hemiformals, and possibly phenolic methylols. (c) Diffusion processes very likely exert a major influence on panel emission rates and may involve movement of methylene glycol in the wood's moisture or of gaseous formaldehyde within the board or within the board-air interface.
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A sensitive fluorimetric procedure for formaldehyde has been developed. The method, which can measure 0.01 μg formaldehyde, is based on the Hantzsch reaction between acetylacetone, ammonia, and formaldehyde. The product, 3,5-diacetyl-I,4-dihydrolutidine, is colored yellow and fluoresces yellow green. Infra-red spectra indicate that this compound is ionic in dilute solution and aggregated in concentrated solution. The Hantzsch reaction may be extended for the assay of other aldehydes, amines, and β-diketones.RésuméL'auteur a mis au point une méthode fluorimétrique sensible pour le dosage du formaldéhyde. Ce procédé, basé sur la réaction de Hantzsch, entre acétylacétone, ammoniaque et formaldéhyde. permet de déterminer 0.01 μg de formaldehyde. Le produit deréaction,diacétyl-3,5-dihydro-l,4-lutidine, est jaune avec une fluorescence vert jaune. Cette réaction peut s'appliquer à d'autres aldéhydes, amines et β-dicétones.ZusammenfassungBeschriebung einer empfindlichen fluorometrischen Methode zur Bestimmung von Formaldehyd. Die Methode, die noch 0.01 μg Formaldehyd zu erfassen erlaubt, beruht auf der Reaktion nach Hantzsch zwischen Acetylaceton, Ammoniak und Formaldehyd. Das Reaktionsprodukt, 3,5-Diacetyl-1, 4-dihydrolutidin, ist gelb gefärbt und zeigt gelbgrune Fluoreszenz. Die Reaktion kann auch zur Bestimmung von anderen Aldehyden, von Aminen und β-Diketonen angewandt werden.
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The paper addresses the role of the main components of wood cellulose, hemicellulose, and lignin as well as of wood extractives as a potential source of formaldehyde. Lignin seems to have a higher emission potential than cellulose and hemicellulose. Moreover, the results reveal that on the one hand extractives release formaldehyde and on the other hand that certain wood extractives react with formaldehyde and hence act as a formaldehyde scavenger. Formaldehyde emanates from wood at temperatures as low as 40 degreesC. Higher temperatures increase the formaldehyde emission tremendously. Therefore, thermo-mechanical pulping enhances formaldehyde release exorbitantely. Differences in the formaldehyde emission between wood species are discussed and related to differences in their chemical composition.
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The emission of terpene compounds from vegetation is subject to seasonal and diurnal variations. Due to oxidation of terpene compounds simple aldehydes like formaldehyde can be formed. Insofar formaldehyde is an ubiquitous chemical. Due to its high reactivity it has a short half-life time. Wood and wood-based panels emit a low, but still detectable, amount of formaldehyde. The emission depends on exogenic (temperature, relative humidity, air exchange level) and endogenic (wood species, binder level, binder type, production conditions, etc.) factors. With the aging of boards formaldehyde release declines tremendously to reach very low level. Nevertheless, with low fuming binders wood-based panels with formaldehyde emission close to that of untreated wood can be prepared. Non-formaldehyde volatile organic compounds (VOCs) can be released from wood and wood-based panels. The emission rate depends on the wood species as well as on the boundary conditions (drying, storage, etc.). In the case of wood-based panels it depends also on the production factors as well as on the storage conditions. Methods to assess VOCs have been developed and regulations regarding the limits of emission values are under way.