ASTM D7191-05
(Test Method)Standard Test Method for Determination of Moisture in Plastics by Relative Humidity Sensor
Standard Test Method for Determination of Moisture in Plastics by Relative Humidity Sensor
SIGNIFICANCE AND USE
This test method is intended for use as a control, acceptance, and assessment test.
Moisture can seriously affect the processability of plastics. It is possible that high moisture content will cause surface imperfections (that is, splay or bubbling) or degradation by hydrolysis. Low moisture (with high temperature) has been known to cause solid phase polymerization.
The physical properties of some plastics are greatly affected by the moisture content.
SCOPE
1.1 This test method covers the quantitative determination of water down to 20 ppm in plastics using a relative humidity sensor.
1.2 Values stated in SI units are to be regarded as standard.
1.3 Specimens tested in this test method can reach or exceed 250°C, use caution when handling them after testing has completed.
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.Note 1
There is no similar or equivalent ISO standard.
General Information
Relations
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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:D7191–05
Standard Test Method for
Determination of Moisture in Plastics by Relative Humidity
Sensor
This standard is issued under the fixed designation D7191; 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 headspace into the sensor manifold. In the sensor manifold, the
carriergasiscooledtoallowhigh-boilingvolatilestocondense
1.1 This test method covers the quantitative determination
on a hydrophobic filter. The filter’s hydrophobic properties
of water down to 20 ppm in plastics using a relative humidity
allow the moisture in the carrier gas to pass through and then
sensor.
be measured as an increase in potential at the relative humidity
1.2 Values stated in SI units are to be regarded as standard.
sensor. This sensor signal is integrated over time to provide a
1.3 Specimenstestedinthistestmethodcanreachorexceed
measurementofthetotalmassofwaterinthesample.Thetotal
250°C, use caution when handling them after testing has
moisture is then divided by sample mass to yield moisture
completed.
content.
1.4 This standard does not purport to address all of the
4.2 This test method utilizes a sealed, airtight flow system
safety concerns, if any, associated with its use. It is the
that prevents contamination of the analyzer from water present
responsibility of the user of this standard to establish appro-
in the atmosphere.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
5. Significance and Use
NOTE 1—There is no similar or equivalent ISO standard.
5.1 This test method is intended for use as a control,
acceptance, and assessment test.
2. Referenced Documents
5.2 Moisture can seriously affect the processability of plas-
2.1 ASTM Standards:
tics. It is possible that high moisture content will cause surface
D1193 Specification for Reagent Water
imperfections (that is, splay or bubbling) or degradation by
D883 Terminology Relating to Plastics
hydrolysis. Low moisture (with high temperature) has been
D1600 Terminology for Abbreviated Terms Relating to
known to cause solid phase polymerization.
Plastics
5.3 The physical properties of some plastics are greatly
D6869 Test Method for Coulometric and Volumetric Deter-
affected by the moisture content.
mination of Moisture in Plastics Using the Karl Fischer
Reaction (the Reaction of Iodine with Water) 6. Interferences
6.1 Elevated concentrations of some common solvents such
3. Terminology
as methanol, ethanol and acetone will give biased high read-
3.1 Definitions—Thedefinitionsusedinthistestmethodare
ings due to their polar characteristics and ability to permeate
in accordance with Terminology D883.
the thermoset polymer layers of the relative humidity sensor.
4. Summary of Test Method
7. Apparatus
4.1 Asample is loaded into a septum-capped glass vial that
7.1 Moisture Analyzer , an apparatus that consists of:
is moved into a heater to evolve the volatiles from the sample
7.1.1 Flow Regulator,capableofmaintainingthecarriergas
into the headspace.Acoaxial needle, or two needle set, pierces
flow rate within the manufacturer’s specified conditions.
the septum of the vial as it enters the heater. A dry carrier gas
7.1.2 Flow Meter, capable of measuring the carrier gas flow
then flows into the vial and carries the evolved volatiles in the
rate in accordance with the manufacturer’s specified condi-
tions.
1 7.1.3 Manifold, which provides:
This test method is under the jurisdiction ofASTM Committee D20 on Plastics
and is the direct responsibility of Subcommittee D20.70 on Analytical Methods.
Current edition approved November 1, 2005. Published November 2005. DOI:
10.1520/D7191-05. The sole source of supply of the apparatus known to the committee at this time
2 th
For referenced ASTM standards, visit the ASTM website, www.astm.org, or isArizona Instrument, 1912 West 4 Street, Tempe,AZ 85281. If you are aware of
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM alternative suppliers, please provide this information to ASTM International
Standards volume information, refer to the standard’s Document Summary page on Headquarters.Your comments will receive careful consideration at a meeting of the
the ASTM website. responsible technical committee, which you may attend.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D7191–05
7.1.3.1 A thermally stable port for mounting and operation 10.2 Perform the vial heater calibration in accordance with
of the relative humidity sensor. the manufacturer’s instructions.
7.1.3.2 Inlet and outlet ports for the carrier gas.
10.3 If the results are not within the acceptable range,
7.1.3.3 A cold trap filter loop which filters out particulates contact the analyzer manufacturer.
and re-condensed high boiling volatiles.
10.4 Perform the RH sensor verification daily in accordance
7.1.3.4 A port for mounting the coaxial needle, or two
with the manufacturer’s instructions by way of using a capil-
needle set.
lary tube (see 8.1) filled with water (see 8.4) or other method
7.1.4 Coaxial Needle, a needle which has a dual flow path
as specified by the instrument manufacturer.
allowing the carrier gas to flow into the sample vial and then
10.5 If the RH sensor verification result is not within the
back into the manifold, or a two needle set configured to allow
acceptable range, perform the RH sensor calibration in accor-
inflow into the sample vial through one needle and outflow
dance with the manufacturer’s instructions using a capillary
from the sample vial through the second needle.
tube (see 8.1) filled with water (see 8.4) or other method as
7.1.5 Relative Humidity (RH) Sensor, a capacitive sensing
specified by the instrument manufacturer.
element that measures the relative humidity of the carrier gas
10.6 Repeat step 10.4 to verify RH sensor calibration.
coming into the manifold.
10.7 If results are not within the acceptable range, contact
7.1.6 Sample Vial Heater, capable of maintaining the
the analyzer manufacturer.
sample vial temperature within 1°C of the programmed tem-
perature between 25°C and 275°C.
11. Procedure
7.1.7 Microcontroller, which provides:
11.1 Sample Analysis:
7.1.7.1 Capability of integrating and converting the RH
11.1.1 Turn on the analyzer.
sensor signal.
11.1.2 Establish carrier gas flow in accordance with the
7.1.7.2 Capability of controlling the temperature of the
manufacturer’s specifications.
sample vial heater and sensor manifold.
11.1.3 Program the analyzer with the appropriate test con-
7.2 Balance, external, with 1-mg readability.
ditions.
8. Reagents and Materials
NOTE 2—Suggested test conditions are listed in Appendix X1. If test
conditions for a specific material are not listed inAppendix X1, they will
8.1 Capillary Tubes—NIST-traceable at the desired total
have to be determined experimentally as described inAppendix X2 or by
mass of water, typically 1000 µg, or other qualified water
contacting the analyzer manufacturer.
standard devices.
8.2 Sample Vials—70-mm tall and 25-mL capacity. 11.1.4 Place a clean vial on the balance and tare it.
8.3 Sample Vial Septa—polytetrafluoroethylene (PTFE)- 11.1.5 RefertoTableX2.1andplacetheappropriateamount
coated silicone. of sample in the vial keeping in mind that the vial must remain
8.4 Water—Unless otherwise indicated, references to water less than half full.
shall be understood to mean reagent water as defined by Type
11.1.6 Place the vial with sample back on the balance and
II of Specification D1193. reweigh.
8.5
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.