ASTM D7131-05

Nickel-metal hydride (Ni-MH) cells have a tendency to exhibit high rates of self-discharge that may be caused by contamination within a battery cell. The contamination source has been shown to originate from electrode impurities. Grafted separators can trap and hold these impurities, thus reducing self-discharge rates and enhancing battery quality. This test method determines an ionic exchange capacity that can be used to quantify the level of grafting of a separator.

This method is useful for research, quality control, and material specifications.

1.1 This test method evaluates an important characteristic of polyolefin or other fibrous nonwoven sheet material intended for use in alkaline battery separator applications. The hydrophilic properties of the material are enhanced by grafting a functional group onto the polyolefin, and this test method is the primary test method to determine the treatment level, that is, level of monomer grafted to the base polymer. This test method can also be used for film or membranes

1.2 This test method is intended primarily for testing copolymer-grafted polyolefin materials used as battery separators, but could be used for any grafted material. These separators have radiation-initiated grafting of acrylic acid monomer (for example) onto a polyolefin base-web material to generate hydrophilic sites on the material. This process is a very good method for surface modification of polymer materials, and is used to make separators hydrophilic. Grafting can be accomplished by irradiation on common polymers such as polyethylene, polypropylene and fluoropolymers with various forms of energy, such as UV, gamma rays, electron beams (EB) or X-rays..

1.3 The values stated in SI units are to be regarded as the standard.

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 to determine the applicability of regulatory limitations prior to use.