ASTM D6902-04(2011)

Standard Test Method for Laboratory Measurement of Formaldehyde Evolved During the Curing of Melamine-Formaldehyde-Based Coatings

SIGNIFICANCE AND USE
This test method measures the amount of formaldehyde that is evolved from a coating containing melamine-formaldehyde resin(s) during cure at elevated temperature. Cure formaldehyde results from a side-reaction during cross-linking of functionalized polymers with melamine-formaldehyde resins. Cure formaldehyde is evolved in the final bake or cure oven, when the coating temperature is high enough to initiate cross-linking. Formaldehyde can be released from a coating during application, solvent flash-off and cure. Free formaldehyde is primarily evolved during coating application and solvent flash-off. Test Method D1979 measures “free formaldehyde” in amino resins and Test Method D6191 measures formaldehyde evolved from coatings at ambient temperature. This method measures only the formaldehyde released during heat cure, which is primarily “cure formaldehyde.”
This test method is not intended to duplicate the evolved formaldehyde from an industrial process, but serves as a reproducible comparative laboratory evaluation.
This test method has not been evaluated with catalyzed coating systems that cure at or below 40°C, such as those used by the wood-finishing industry, and would likely require special adaptation for this application.
SCOPE
1.1 This test method is for the determination of formaldehyde evolved from melamine-formaldehyde-based coatings during the cure step. The results may be used to determine the “cure formaldehyde” evolved from a sample under controlled laboratory conditions.
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.3 This test method is capable of measuring from 500 μg/g to 22 000 μg formaldehyde/g dry coating under the test conditions specified (3 000 ml/min total flow, 50 ml/min DNPH tube flow). The ratio of total flow to DNPH tube flow could be adjusted to extend the range of the method.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 31-May-2011
• ICS: 83.080.10 - Thermosetting materials
• Technical Committee: D01 - Paint and Related Coatings, Materials, and Applications
• Drafting Committee: D01.21 - Chemical Analysis of Paints and Paint Materials

Relations

• Replaces: ASTM D6902-04e1 - Standard Test Method for Laboratory Measurement of Formaldehyde Evolved During the Curing of Melamine-Formaldehyde-Based Coatings
• Effective Date: 01-Jun-2011

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D6902 − 04 (Reapproved 2011)
Standard Test Method for
Laboratory Measurement of Formaldehyde Evolved During
the Curing of Melamine-Formaldehyde-Based Coatings
This standard is issued under the fixed designation D6902; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
1.1 This test method is for the determination of formalde- 3.1 Definitions of Terms Specific to This Standard:
hyde evolved from melamine-formaldehyde-based coatings 3.1.1 cure formaldehyde, n—the formaldehyde generated as
during the cure step. The results may be used to determine the the result of a chemical reaction during coating curing.
“cure formaldehyde” evolved from a sample under controlled
3.1.2 free formaldehyde, n—the residual formaldehyde in a
laboratory conditions.
coating due to the raw materials.
1.2 The values stated in SI units are to be regarded as the
4. Summary of Test Method
standard. The values given in parentheses are for information
only.
4.1 Approximately 0.2 g of coating formulation is placed in
an aluminum foil pan, dried in a vacuum oven at 40°C (to
1.3 This test method is capable of measuring from 500 µg/g
remove free formaldehyde and solvents) and then baked at the
to 22 000 µg formaldehyde/g dry coating under the test
optimum process cure temperature for 30 min. Formaldehyde
conditions specified (3 000 ml/min total flow, 50 ml/min
emissions are collected from the cure chamber on a DNPH/
DNPH tube flow). The ratio of total flow to DNPH tube flow
Silica tube, which is then extracted and the extract analyzed by
could be adjusted to extend the range of the method.
HPLC/UV. The amount of formaldehyde evolved from the
1.4 This standard does not purport to address all of the
coating during the cure step is calculated on both a wet-weight
safety concerns, if any, associated with its use. It is the
and dry-weight basis. The test is run in triplicate plus a blank
responsibility of the user of this standard to establish appro-
and system standard.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
5. Significance and Use
2. Referenced Documents
5.1 This test method measures the amount of formaldehyde
that is evolved from a coating containing melamine-
2.1 ASTM Standards:
formaldehyde resin(s) during cure at elevated temperature.
D362 SpecificationforIndustrialGradeToluene(Withdrawn
Cure formaldehyde results from a side-reaction during cross-
1989)
linking of functionalized polymers with melamine-
D1979 Test Method for Free Formaldehyde Content of
formaldehyde resins. Cure formaldehyde is evolved in the final
Amino Resins (Withdrawn 2006)
bake or cure oven, when the coating temperature is high
D6191 Test Method for Measurement of Evolved Formalde-
enough to initiate cross-linking. Formaldehyde can be released
hyde from Water Reducible Air-Dry Coatings
from a coating during application, solvent flash-off and cure.
E691 Practice for Conducting an Interlaboratory Study to
Free formaldehyde is primarily evolved during coating appli-
Determine the Precision of a Test Method
cation and solvent flash-off. Test Method D1979 measures
“free formaldehyde” in amino resins and Test Method D6191
measures formaldehyde evolved from coatings at ambient
This test method is under the jurisdiction of ASTM Committee D01 on Paint
and Related Coatings, Materials, andApplications and is the direct responsibility of
temperature. This method measures only the formaldehyde
Subcommittee D01.21 on Chemical Analysis of Paints and Paint Materials.
released during heat cure, which is primarily “cure formalde-
Current edition approved June 1, 2011. Published June 2011. Originally
ε1
hyde.”
approved in 2003. Last previous edition approved in 2004 as D6902 – 04 . DOI:
10.1520/D6902-04R11.
5.2 Thistestmethodisnotintendedtoduplicatetheevolved
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
formaldehyde from an industrial process, but serves as a
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on reproducible comparative laboratory evaluation.
the ASTM website.
5.3 This test method has not been evaluated with catalyzed
The last approved version of this historical standard is referenced on
www.astm.org. coating systems that cure at or below 40°C, such as those used
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6902 − 04 (2011)
by the wood-finishing industry, and would likely require 7. Reagents and Materials
special adaptation for this application.
7.1 Purity of Reagents—Use reagent grade chemicals in all
tests, unless otherwise specified. Other grades may be used,
6. Apparatus
provided it is first ascertained that the reagent is sufficiently
high purity to permit its use without lessening the accuracy of
6.1 High Pressure Liquid Chromatograph (HPLC), either a
the determination.
gradient or isocratic system. A gradient system is preferred
when other aldehydes or ketones are present.
7.2 Toluene, technical grade, Specification D362.
NOTE 1—The system shall be equipped with a temperature-controlled
7.3 Tetrahydrofuran, HPLC Grade.
column oven. A liquid autosampler is optional.
7.4 Water, HPLC Grade.
6.2 Column,aC ODS packed with 5-µm pellicular beads
7.5 Acetonitrile, HPLC Grade.
with the dimensions of approximately 4 mm by 75 or 150 mm.
A 2-cm guard column packed with the same material is 7.6 DNPH-Silica Cartridge, Waters Sep-Pak Cartridges,
recommended to protect the analytical column. Part # WAT037500.
7.7 Formaldehyde/2,4-dinitrophenylhydrazone (DNPH)
6.3 Detector, UV/VIS detector capable of measuring absor-
Complex, may be purchased or prepared in the laboratory.
bance at 360 nm.
7.8 Calcium Nitrate Tetrahydrate, reagent grade.
6.4 Integrator, peak integration system.
7.9 Paraformaldehyde, reagent grade.
6.5 Air Sampling Pump, an air sampling pump with the
capability of maintaining a constant flow rate between 3 and 4
8. Hazards
L/min. Both an inlet and outlet port must be available for
measuring flow. An SKC AirCheck Sampler Model 224-
8.1 Check the supplier’s Material Safety Data Sheet
PCXR8 has been found suitable.
(MSDS) on all chemicals before use.
6.6 Flow Meters—An in-line mass flow meter or flow
9. Preparation of Apparatus
sensor capable of measuring 30 to 120 mL/min with at least
9.1 Install the column in the chromatograph following the
3 % accuracy. A flow meter or bubble meter capable of
manufacturer’s directions and establish the operating condi-
measuring 3 to 4 L/min with at least 5 % accuracy.
tions required to give the desired separation (see Table 1).
6.7 Glass Purge Chamber—A glass purge chamber with a
Allow sufficient time for the instrument to reach equilibrium as
mouth at least 60 mm wide and a lid with an air-tight gasket
indicated by a stable baseline.
seal. One liter reaction flask, reaction flask head with two
9.2 Purge Chamber Set Up:
threads, two 5029 tetrafluorethylene polymer bushings and
9.2.1 Assemble apparatus (empty purge chamber, impinger,
FETFE O-Ring and 124 mm anodized 2 piece clamp, Ace
pump, flow meters and valving) as shown in Fig. 1 with a
Glass part numbers 6511-53, 6513-SP, and 6508-6.
DNPH cartridge in line (use two DNPH cartridges for water-
6.8 Valves—Two metering valves to adjust split flow rate.
borne coatings and paraformaldehyde calibration check).
One valve must be constructed of stainless steel. A Swagelok
9.2.2 Add500gofcalciumnitratetetrahydrateto250mLof
506-1-316 has been found suitable.
reagentgradewatertoformanearsaturatedsolution.Placethis
6.9 Aluminum Foil Dishes, 58 mm in diameter by 18 mm mixture in the constant humidity Insert the Sherer Impinger so
high with a smooth (planar) bottom surface.
that the solution is 8 in. above the bottom of the impinger tip.
Mark the solution level on the impinger.
6.10 Forced Draft Oven, oven, capable of maintaining
160°C (320°F), of adequate size to accommodate one or more
NOTE 2—This calcium nitrate tetrahydrate solution ensures a constant
humidityof55 %.Addwaterwhenthesolutionlevelfallsbelowthemark.
purge chambers.
6.11 Vacuum Oven, capable of maintaining 40°C and a
vacuum of 0.1 to 0.2 Barr (~100 mm Hg).
TABLE 1 Instrument Conditions
6.12 Volumetric Glassware, various volumetric flasks and
Detector UV/VIS Absorbance 360 nm
pipettes for preparation of calibration standards. Also, 5-mL
Column (Isocratic) C ODS4by75mm
volumetric flasks for sample elution. Mobile Phase (Isocratic) Water/Acetonitrile/Tetrahydrofuran
65/30/5 volume/volume
6.13 Analytical Balance—Four-place analytical balance ca-
Column (Gradient) C ODS 4 by 150 mm
Mobile Phase (Gradient) Water/Acetonitrile/Tetrahydrofuran
pable of measuring to 60.1mg (0.0001 g).
A: 65/30/10 volume/volume
B: 40/60/0 volume/volume
6.14 Sherer Impinger Diffuser, A 25 mm dia, 275 mL with
100%Afor 1 min then linear gradient
impinger stopper, Ace Glass part number 7538-29 has been
to 100%Bin10min
found suitable.
Flow Rate 1.5 mL/min
Column Temperature 40°C
6.15 Water Trap, 1000 mL vacuum flask with stopper.
Run Time (Isocratic) 10 min
Run Time (Gradient) 15 min
6.16 Thermometer, thermocouple with temperature readout
Injection Volume 10 to 20 µL
calibrated in range of 50°F to 400°F.
D6902 − 04 (2011)
FIG. 1 Page Chamber Set-Up
9.2.3 Adjust the forced draft oven so that the pan tempera- 10.2 Determination of Relative Response Factors—The re-
ture is set at the coating manufacturers recommended optimum sponsefactorrelativetothestandardisdeterminedbymeansof
process cure temperature 62°F (usually with the range of 260 the following procedure. It is good practice to determine the
to 310°F for automotive coatings). Use a thermocouple taped relative retention time daily or with each series of determina-
to the bottom of the pan to measure pan temperature. tions.
10.2.1 Prepare a minimum four-point standard curve of
9.2.4 Adjust pump flow rate to 3.0 to 3.5 L/min.
9.2.5 Adjust valves A and B until the DNPH Cartridge has Formaldehyde-DNPH derivative in acetonitrile, ranging from
a flow of 50 mL/min. 0.1 to 10 µg/mL as formaldehyde. Recommended curve 0.1,
9.2.6 Check pump flow rate to ensure it is still in the proper 1.0, 5.0 and 10 µg/mL.
range. Recommended starting flows; Pump 3.0 L/min, DNPH 10.2.2 Inject a 10 to 20 µL aliquot of the standard mixture
Cartridge 50 mL/min (1:60 split). into the HPLC. At the end of the chromatographic run,
calibrate the integrator by following the manufacturer’s proce-
10. Calibration
dure for external standard calibration. If this capability is not
available, refer to the following calculations. See Figs. 2 and 3
10.1 Use the information in Table 1 as a guide to select the
conditions that give the necessary resolution of formaldehyde- for typical chromatograms using the three listed columns.
10.2.3 The response factor of each analyte is calculated as
DNPH derivative from interferences in the samples.
follows:
A
analyte
R 5 (1)
analyte
C
analyte
D6902 − 04 (2011)
FIG. 2 Isocratic Separation of C -C Aldehyde and Ketone Derivatives
1 3
FIG. 3 Gradient Separation of C -C Aldehyde and Ketone Derivatives
1 9
where: 10.3 System Integrity:
R = response factor for the analyte being calibrated, 10.3.1 System Blank—Follow procedure (Section 11) below
analyte
C = concentration of formaldehyde in mg/mL, and
only using a blank aluminum foil dish. Result should be below
analyte
A = peak area for the analyte being calibrated.
analyte detection for formaldehyde.
10.3.2 System Standard—Follow procedure beginning at
10.2.4 Calculate the average response factor for all concen-
trations and the correlation coefficient for calibration curve. If 10.2, using two DNPH cartridges and an oven temperature of
150°C.Add4.0 60.5mgofparaformaldehydetoacoolempty
the correlation coefficient is not 0.9999 or greater, repeat
calibration process. pan and record weight to nearest 0.1 mg. Total formaldehyde
D6902 − 04 (2011)
measured should be equal to the amount of paraformaldehyde 11.1.4 Measure 0.2 6 0.05 g of coating formulation into a
used 65 %, with less than a 1 % breakthrough to the second tared aluminum foil dish using a syringe by measuring the
cartridge. Analyze system standard on a minimum daily basis.
weight of the syringe before and after dispensing the coating.
Record weight of the dispensed coating on Bench Data Sheet
11. Procedure
(Fig. 4).
11.1 Prepare Coating Specimens:
11.1.4.1 For solventborne coatings add 1.5 mLof toluene to
11.1.1 Mix the coating sample, preferably on a mechanical
disperse the coating evenly on the bottom of the dish.
shaker or roller for solventborne and by hand for waterborne
11.1.4.2 For waterborne coatings add one mL of distilled
coatings, until homogeneous. If air bubbles become entrapped,
water, swirling pan until the coating formulation is fully
stir by hand until air has been removed.
wetted.Add one mLof ethanol again swirling the pan until the
11.1.2 Rinse aluminum foil dishes (6.9) with toluene, wipe
coating is fully dispersed.
dry with a lint-free cloth then bake at cure temperature and
11.1.5 Place dish immediately into a level vacuum oven set
time. Place dishes in a desiccator to cool after baking.
11.1.3 Record the weight of three dry aluminum foil dishes. at 40°C.
FIG. 4 Bench Data Sheet
D6902 − 04 (2011)
11.1.6 Repeat steps 11.1.3 – 11.1.5 two more times. Then A 35mL
analyte
Formaldehyde, µg/tube 5 (2)
evacuate the oven to 0.1 to 0.2 Barr (100 mm Hg). R
analyte
11.1.7 Allow specimens to dry in vacuum oven for1hat
where:
40°C.
A = area of the analyte peak, and
analyte
11.1.8 Remove the dishes from the vacuum oven and place
R = average response factor for all standards in cali-
analyte
in a covered container at room temperature. Specimens should
bration curve (as determined in 10.2.4).
not stand for more than 72 h between solvent evaporation and
NOTE 6—Mid-range bracketing standards must fall within 65 % of a
curing.
calibration standard.
NOTE 3—For applications where a clearcoat is applied on top of a
12.2 Record Formaldehyde concentrations (µg/tube) on
basecoat, it is recommended that the procedure be followed through step
Bench Data Sheets.
11.1.8 for the basecoat then return to step 11.1.4 and apply the clear
...