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Significance and Use
Many important properties of crosslinked ethylene plastics vary with the gel content. Hence, determination of the gel content provides a means of both controlling the process and rating the quality of finished products.
Extraction tests permit verification of the desired gel content of any given crosslinked ethylene plastic and they also permit comparison between different crosslinked ethylene plastics, including those containing fillers, provided that, for the latter, the following conditions are met: The filler is not soluble in xylene or toluene at the extraction temperature and the amount of filler present in the compound is known or can be determined.
Sufficient crosslinking has been achieved to prevent migration of filler during the extraction. Usually it has been found that, at extraction levels up to 50 %, the extraction solvent remains clear and free of filler.
Since some oxidative degradation of the material can occur at the extraction temperatures used in this procedure, despite the use of a closed cell which allows for minimal introduction of oxygen, a suitable antioxidant is added to the solvent to inhibit such degradation.
Before proceeding with this method, reference should be made to the specification of the material being tested. Any test specimen preparation, conditioning, dimensions, or testing parameters, or combination thereof, covered in the materials specification shall take precedence over those mentioned in this test method. If there are no material specifications, then the default conditions apply
1.1 The gel content of crosslinked ethylene plastics is determined by solvent extraction with xylene or toluene. This test method is applicable to ethylene plastics of all densities, including those containing fillers; provided the fillers are insoluble in the extraction solvent(s).
1.2 This test method uses pressurized liquid extraction (PLE) to increase the speed and reduce the amount of solvent required for solvent extraction. The results of this method are similar to Test Method D2765.
1.3 Extraction tests shall be performed on samples of any shape (see 7.2). Specimens shall be selected from those portions of the article most susceptible to insufficient crosslinking or selected from portions representative of the entire article. This test method has been developed for production and quality control of crosslinked polyethylene pipe but may be applicable to other products such as multilayer materials and fibers.
1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.5 This method makes use of minimal reagents and allows for solvent recovery and re-use. Due to the use of minimal reagents, health and safety concerns are minimized in comparison to other methods.
1.6 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.Specific precautionary statements are given in Section 10.
Note 1—There is no known ISO equivalent to this test method. This test method is similar to Test Method D2765.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D297 Test Methods for Rubber Products--Chemical Analysis
D618 Practice for Conditioning Plastics for Testing
D883 Terminology Relating to Plastics
D1603 Test Method for Carbon Black Content in Olefin Plastics
D2765 Test Methods for Determination of Gel Content and Swell Ratio of Crosslinked Ethylene Plastics
D3351 Test Method for Gel Count of Plastic Film
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
ICS Number Code 83.080.20 (Thermoplastic materials)