ASTM D6869-03
(Test Method)Standard Test Method for Coulometric and Volumetric Determination of Moisture in Plastics Using the Karl Fischer Reaction (the Reaction of Iodine with Water)
Standard Test Method for Coulometric and Volumetric Determination of Moisture in Plastics Using the Karl Fischer Reaction (the Reaction of Iodine with Water)
SIGNIFICANCE AND USE
Moisture will affect the processability of some plastics. High moisture content causes surface imperfections (that is, splay or bubbling) or degradation by hydrolysis. Low moisture (with high temperature) causes polymerization.
The physical properties of some plastics are affected by the moisture content.
SCOPE
1.1 This method uses the reaction of Iodine (I 2) with water (Karl Fischer Reaction) to determine the amount of moisture in a polymer sample.
1.2 This test method is intended to be used for the determination of moisture in most plastics. Plastics containing volatile components such as residual monomers and plasticizers are capable of releasing components that will interfere with the I2/water reaction.
1.3 This method is suitable for measuring moisture over the range of 0.005 to 100 %. Sample size shall be adjusted to obtain an accurate moisture measurement.
1.4 The values stated in SI units are regarded as the standard.
Note 1—This standard is technically equivalent to ISO 15512 Method B.
1.5 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.
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Designation:D6869–03
Standard Test Method for
Coulometric and Volumetric Determination of Moisture in
Plastics Using the Karl Fischer Reaction (the Reaction of
Iodine with Water)
This standard is issued under the fixed designation D6869; 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 collected in the solution within the titration cell is determined
using the reaction of water with I .
1.1 This method uses the reaction of Iodine (I ) with water 2
3.2 Endpoint detection is made by instrumented methods.
(Karl Fischer Reaction) to determine the amount of moisture in
2 Determination of the moisture present is made using the
a polymer sample.
reaction of I with water.
1.2 This test method is intended to be used for the determi-
3.3 Coulometric instruments use Faraday’s law to measure
nation of moisture in most plastics. Plastics containing volatile
the moisture present with 10.71 Coulombs (C) of generating
components such as residual monomers and plasticizers are
- -
current corresponding to 1 mg of water (2I → I+2e ).
capable of releasing components that will interfere with the 2
Volumetric instruments measure the volume of solution con-
I /water reaction.
taining I that is required to keep the current constant.
1.3 This method is suitable for measuring moisture over the
range of 0.005 to 100 %. Sample size shall be adjusted to
4. Significance and Use
obtain an accurate moisture measurement.
4.1 Moisture will affect the processability of some plastics.
1.4 The values stated in SI units are regarded as the
High moisture content causes surface imperfections (that is,
standard.
splay or bubbling) or degradation by hydrolysis. Low moisture
NOTE 1—This standard is technically equivalent to ISO 15512 Method
(with high temperature) causes polymerization.
B.
4.2 The physical properties of some plastics are affected by
1.5 This standard does not purport to address all of the
the moisture content.
safety concerns, if any, associated with its use. It is the
5. Interferences
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica- 5.1 Some compounds, such as aldehydes and ketones,
bility of regulatory limitations prior to use.
interfere in the determination of moisture content using this
method.
2. Referenced Documents
6. Apparatus
2.1 ISO Document:
ISO 15512 Plastics—Determination of Water Content 6.1 Heating Unit, consisting of an oven capable of heating
the sample to approximately 300°C, a furnace tube, a tempera-
3. Summary of Test Method
turecontrolunit,acarriergasflowmeter,anddesiccatingtubes
3.1 Samples are heated to vaporize water that is transported
for the carrier gas.
by a nitrogen carrier gas to the titration cell. The moisture
6.2 SamplePan(Boat),normallyaglasssampleboatorboat
manufactured of a suitable material to transfer the oven heat to
the sample. It is permitted to use aluminum foil as a disposable
This test method is under the jurisdiction ofASTM Committee D20 on Plastics
liner for the sample pan.
and is the direct responsibility of Subcommittee D20.70.01 on Physical Methods.
6.3 Titration Unit, consisting of a control unit, titration cell
Current edition approved July 10, 2003. Published August 2003. DOI: 10.1520/
with a solution cathode, platinum electrode, and solution
D6869-03.
See Appendix X1, History of Reagents Associated With the Karl Fischer
stirring capability.This apparatus has the capability to generate
Reaction, for an explanation of coulometric and volumetric techniques as well as an
or deliver iodine to react stoiciometrically with the moisture
explanation of the Karl Fischer Reaction and Karl Fischer Reagents.
3 present in the titration cell. The current or volume required to
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036. generate the iodine converts to micrograms of water present.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6869–03
The percent moisture in the sample is then calculated based on 10.2 Pourapproximately200mL(oranamountspecifiedby
the sample weight used and is given as a direct digital readout. the manufacturer) of generator (anode) solution into the
6.4 Analytical Balance, capable of weighing 0.1 mg (four titration cell.
decimal place balance). 10.3 Add 10 mL of cathode solution to the cathode cell.
6.5 Glass Capillary (Micropipette), used to measure a
NOTE 3—The condition of both anode and cathode solutions are
known amount of water, typically 2 mg (2000 µg).
determined by the appearance of the fluids. The solutions must be light
amber in color.As solutions age, viscosity will increase and solution color
7. Reagents and Materials
will turn dark. The instrument will indicate solution integrity by the
“background” value titration rate. Do not analyze samples containing low
7.1 Anode (Generator) Solution, per manufacturer’s recom-
moisture content if the “background” value is greater than 0.10 µg/s.
mendation.
7.2 Cathode Solution, per manufacturer’s recommendation. 10.4 Turn the cell power switch on. If the cell potential
shows a negative value, indicating that the anode solution
NOTE 2—Hydranal or similar anode and cathode solutions are recom-
contains excess iodine, add approximately 50 to 200 µL of
mended. These reagents do not contain pyridine, are less toxic, and have
neutralization solution or check solution.
no offensive odor.
10.5 Disconnect the tube connecting the vaporizer unit to
7.3 Silica Gel, granules, approximately 2 mm, desiccant for
the titration cell. Set nitrogen flow rate to achieve steady
drying tube of titration assembly (if applicable).
bubbling of nitrogen to the titration cell. (Aflow rate of 200 to
7.4 Special Grease, as supplied by manufacturer for ground
300 mL/min is recommended.)
glass joints.
10.6 Lift the titration cell and agitate the solution by gently
7.5 Molecular Sieve, or suitable desiccant (for drying the
swirling the cell to remove any residual water from the walls.
nitrogen carrier gas stream).
Stir the solution for a minute in the Titration Mode to dry and
7.6 Nitrogen Gas (N ), containing less than 5 µg/g of water.
stabilize the inner atmosphere.
7.7 Neutralization Solution, or check solution (per manu-
10.7 Reconnect the tube from the vaporizer unit to the
facturer’s recommendation).
titration cell. Keep the carrier gas flow on during the whole
titration. The instrument is now ready for sample analysis.
8. Hazards
10.8 Set the oven and furnace tube temperature as required
8.1 Due to the low quantities of water measured, maximum
to obtain accurate results for the plastic to be tested. The
care shall be exercised at all times to avoid contaminating the
temperature is set so that the analysis is completed in a short
sample with water from the sample container, the atmosphere
time period, yet eliminating the generation of water from
or transfer equipment. Hygroscopic resin samples shall be
thermal degradation of the sample. Selection of Optimum
protected from the atmosphere.
Heating Temperature is discussed below.
8.2 Due to the high temperatures and the chemicals in-
10.9 Selection of Optimum Heating Temperature:
volved in this test method, safe lab practices must be followed
10.9.1 Select optimum heating temperature for material to
at all times.
be tested by carrying out tests in several different temperatures
to make a curve as shown in Fig. 1.
9. Sampling, Test Specimens, and Test Units
10.9.1.1 In the range from 1 to 2, the water in the sample is
9.1 Unless otherwise agreed upon by interested parties or
not vaporized sufficiently so that the water content indicated
described in a specification, the material shall be sampled
increases in proportion to the temperature.
statistically or the sample shall come from a process that is in
10.9.1.2 Between 2 and 3, the water content measured
statistical control.
appears nearly constant and is considered the optimum heating
9.2 Samples that will determine the moisture of a larger lot
temperature range for determining moisture content.
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