ASTM D7131-05

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An American National Standard
Designation:D7131–05
Standard Test Method for
Determination of Ion Exchange Capacity (IEC) in Grafted
Battery Separator
This standard is issued under the fixed designation D7131; 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 D1711 Terminology Relating to Electrical Insulation
E438 Specification for Glasses in Laboratory Apparatus
1.1 Thistestmethodevaluatesanimportantcharacteristicof
E1272 Specification for Laboratory Glass Graduated Cylin-
polyolefin or other fibrous nonwoven sheet material intended
ders
for use in alkaline battery separator applications. The hydro-
philic properties of the material are enhanced by grafting a
3. Terminology
functionalgroupontothepolyolefin,andthistestmethodisthe
3.1 Definitions:
primary test method to determine the treatment level, that is,
3.1.1 For definitions of textile terms, refer to Terminology
levelofmonomergraftedtothebasepolymer.Thistestmethod
D123.
can also be used for film or membranes
3.1.2 For definitions of electrical terms, refer to Terminol-
1.2 This test method is intended primarily for testing
ogy D1711.
copolymer-grafted polyolefin materials used as battery separa-
3.2 Definitions of Terms Specific to This Standard:
tors, but could be used for any grafted material. These
3.2.1 grafted battery separator, n—a sheet material whose
separators have radiation-initiated grafting of acrylic acid
fiber surface has been grafted to add a functional group to the
monomer (for example) onto a polyolefin base-web material to
base polymer of the fiber by some form of radiation, whereas
generate hydrophilic sites on the material. This process is a
these grafted sites are hydrophilic, thus increasing the sheet
very good method for surface modification of polymer mate-
material’s hydrophilic properties.
rials, and is used to make separators hydrophilic. Grafting can
3.2.2 ion-exchange capacity, n—the number of ionic sites
be accomplished by irradiation on common polymers such as
on the separator fiber surface that can participate in the
polyethylene, polypropylene and fluoropolymers with various
exchange process. The exchange capacity is expressed in
formsofenergy,suchasUV,gammarays,electronbeams(EB)
milliequivalents per gram.
or X-rays.
1.3 The values stated in SI units are to be regarded as the
4. Summary of Test Method
standard.
4.1 Apredetermined amount of separator in its acid form is
1.4 This standard does not purport to address all of the
added to a bottle with a potassium hydroxide (KOH) solution.
safety concerns, if any, associated with its use. It is the
The specimens are conditioned under a controlled temperature
responsibility of the user of this standard to establish appro-
for 2 h. After being allowed to cool, the amount of grafted
priate safety and health practices and to determine the
monomer functionality of the grafted surface in the sample can
applicability of regulatory limitations prior to use.
be determined by titration.
2. Referenced Documents 4.2 Results are calculated as milliequivalents per gram
2 (meq/g) using the appropriate equations.
2.1 ASTM Standards:
4.3 Sampling must be determined based on experience with
D123 Terminology Relating to Textiles
the separators uniformity and consistency of the grafting
process.
This test method is under the jurisdiction of ASTM Committee D09 on
Electrical and Electronic Insulating Materials and is the direct responsibility of
5. Significance and Use
Subcommittee D09.19 on Dielectric Sheet and Roll Products.
5.1 Nickel-metal hydride (Ni-MH) cells have a tendency to
Current edition approved March 1, 2005. Published March 2005. DOI: 10.1520/
D7131-05.
exhibit high rates of self-discharge that may be caused by
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contamination within a battery cell. The contamination source
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
has been shown to originate from electrode impurities. Grafted
Standards volume information, refer to the standard’s Document Summary page on
separators can trap and hold these impurities, thus reducing
the ASTM website.
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D7131–05
self-discharge rates and enhancing battery quality. This test 8.4 For each specimen, add 90 6 0.5 mL of distilled water
methoddeterminesanionicexchangecapacitythatcanbeused to each bottle as described in 6.2.
to quantify the lev
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