ASTM D2765-16(2024)
(Test Method)Standard Test Methods for Determination of Gel Content and Swell Ratio of Crosslinked Ethylene Plastics
Standard Test Methods for Determination of Gel Content and Swell Ratio of Crosslinked Ethylene Plastics
SIGNIFICANCE AND USE
5.1 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.
5.2 Extraction tests permit verification of the proper 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:
5.2.1 The filler is not soluble in either decahydronaphthalene or xylenes at the extraction temperature.
5.2.2 The amount of filler present in the compound either is known or will be determined by other means.
5.2.3 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 extractant remains clear and free of filler.
5.3 A suitable antioxidant is added to the extractant to inhibit possible oxidative degradation at the extraction temperatures.
5.4 Before proceeding with this test method, reference shall be made to the specification of the material being tested. Any test specimen preparation, conditioning, dimensions, or testing parameters, or a 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.
SCOPE
1.1 The gel content (insoluble fraction) produced in ethylene plastics by crosslinking is determined by extracting with solvents such as decahydronaphthalene or xylenes. The methods described herein are applicable to crosslinked ethylene plastics of all densities, including those containing fillers, and all provide corrections for the inert fillers present in some of those compounds.
1.2 Test Method A, which permits most complete extraction in least time, is to be used for referee tests, but two alternative nonreferee Test Methods B and C are also described. Test Method B differs from the referee test method only in sample preparation; that is, it requires use of shavings taken at selected points in cable insulation, for example, rather than the ground sample required by the referee test method. Because the shaved particles are larger, less total surface per sample is exposed to the extractant, so this test method ordinarily yields extraction values about 1 to 2 % lower than the referee method. Test Method C requires that a specimen in one piece be extracted in xylenes at a constant temperature of 110°C. At this temperature and with a one-piece specimen, even less extraction occurs (from 3 to 9 % less than the referee test method), this method permits swell ratio (a measure of the degree of crosslinking in the gel phase) be determined.
1.3 Extraction tests are made on articles of any shape. They have been particularly useful for electrical insulations since specimens can be selected from those portions of the insulation most susceptible to insufficient crosslinking.
1.4 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined.
Note 1: This test method is equivalent to ISO 10147, Method B. It is not equivalent to ISO 10147 in any other measurement or section.
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in Sections 6, 9, and 24.
1.6 This int...
General Information
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Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D2765 − 16 (Reapproved 2024)
Standard Test Methods for
Determination of Gel Content and Swell Ratio of
Crosslinked Ethylene Plastics
This standard is issued under the fixed designation D2765; 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.
not equivalent to ISO 10147 in any other measurement or section.
1. Scope*
1.5 This standard does not purport to address all of the
1.1 The gel content (insoluble fraction) produced in ethyl-
safety concerns, if any, associated with its use. It is the
ene plastics by crosslinking is determined by extracting with
responsibility of the user of this standard to establish appro-
solvents such as decahydronaphthalene or xylenes. The meth-
priate safety, health, and environmental practices and deter-
ods described herein are applicable to crosslinked ethylene
mine the applicability of regulatory limitations prior to use.
plastics of all densities, including those containing fillers, and
Specific precautionary statements are given in Sections 6, 9,
all provide corrections for the inert fillers present in some of
and 24.
those compounds.
1.6 This international standard was developed in accor-
1.2 Test Method A, which permits most complete extraction
dance with internationally recognized principles on standard-
in least time, is to be used for referee tests, but two alternative
ization established in the Decision on Principles for the
nonreferee Test Methods B and C are also described. Test
Development of International Standards, Guides and Recom-
Method B differs from the referee test method only in sample
mendations issued by the World Trade Organization Technical
preparation; that is, it requires use of shavings taken at selected
Barriers to Trade (TBT) Committee.
points in cable insulation, for example, rather than the ground
sample required by the referee test method. Because the shaved
2. Referenced Documents
particles are larger, less total surface per sample is exposed to
2.1 ASTM Standards:
the extractant, so this test method ordinarily yields extraction
D297 Test Methods for Rubber Products—Chemical Analy-
values about 1 to 2 % lower than the referee method. Test
sis
Method C requires that a specimen in one piece be extracted in
D618 Practice for Conditioning Plastics for Testing
xylenes at a constant temperature of 110°C. At this temperature
D883 Terminology Relating to Plastics
and with a one-piece specimen, even less extraction occurs
D1603 Test Method for Carbon Black Content in Olefin
(from 3 to 9 % less than the referee test method), this method
Plastics
permits swell ratio (a measure of the degree of crosslinking in
D1998 Specification for Polyethylene Upright Storage Tanks
the gel phase) be determined.
D3351 Test Method for Gel Count of Plastic Film (With-
1.3 Extraction tests are made on articles of any shape. They 3
drawn 2000)
have been particularly useful for electrical insulations since
E691 Practice for Conducting an Interlaboratory Study to
specimens can be selected from those portions of the insulation
Determine the Precision of a Test Method
most susceptible to insufficient crosslinking.
2.2 ISO Standard:
1.4 The values stated in either SI units or inch-pound units
ISO 10147 Pipes and Fittings Made of Crosslinked Poly-
are to be regarded separately as standard. The values stated in
ethylene (Pe-X)—Estimation of the Degree of Crosslink-
each system are not necessarily exact equivalents; therefore, to
ing by Determination of the Gel Content
ensure conformance with the standard, each system shall be
used independently of the other, and values from the two
3. Terminology
systems shall not be combined.
3.1 Definitions of Terms Specific to This Standard:
NOTE 1—This test method is equivalent to ISO 10147, Method B. It is
1 2
These test methods are under the jurisdiction of ASTM Committee D20 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Plastics and are the direct responsibility of Subcommittee D20.15 on Thermoplastic contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Materials. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Feb. 1, 2024. Published February 2024. Originally the ASTM website.
approved in 1968. Last previous edition approved in 2016 as D2765 – 16. DOI: The last approved version of this historical standard is referenced on
10.1520/D2765-16R24. www.astm.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2765 − 16 (2024)
3.1.1 gel content—the percentage by mass of polymer methods at altitudes greater than 1500 m (5000 ft) above sea
insoluble in a specified solvent after extraction under the level will observe lower boiling temperatures for the solvent
specified conditions. used. If this is observed it shall be noted in the results report.
3.1.2 swell ratio—the ratio of the gel volume in the swollen
TEST METHOD A (REFEREE TEST METHOD)
state to its volume in the unswollen state.
7. Apparatus
3.2 Terms as shown in Terminology D883 are applicable to
this test method. 7.1 The extraction apparatus shall be of the following
general type, as illustrated in Fig. 1:
4. Summary of Test Methods
7.1.1 Round-Bottom Flask, equipped with a suitable joint
that has been demonstrated to provide an essentially leak free
4.1 Specimens of the crosslinked ethylene plastic are
connection. For one or two determinations at one time, a
weighed and then immersed in the extracting solvent at the
500-mL flask is appropriate. For several determinations at one
temperature specified by the procedure selected and for the
time, but not exceeding six, a 2000-mL flask is suitable.
time designated by that procedure. After extraction, the speci-
7.1.2 Heating Mantle to fit the flask and with sufficient
mens are removed, dried, and reweighed as directed. The
heating capacity to boil decahydronaphthalene.
amount of material extracted is calculated and, if desired, swell
7.1.3 Reflux Condenser with ground-glass or cork joint to fit
ratio determined by the means described in alternative Test
into flask.
Method C.
7.1.4 Ring Stand and Appropriate Clamps.
5. Significance and Use
7.2 Grinding Equipment, suitable for reducing the sample to
5.1 Many important properties of crosslinked ethylene plas- a fineness between 30 and 60 mesh. A bench-top laboratory
mill is satisfactory, although any procedure which will produce
tics vary with the gel content. Hence, determination of the gel
content provides a means of both controlling the process and a sample of the required fineness without generating excessive
heat is acceptable.
rating the quality of finished products.
7.2.1 U.S. No. 30 and U.S. No. 60 Sieves.
5.2 Extraction tests permit verification of the proper gel
7.2.2 U.S. No. 120 Stainless Steel Wire Cloth.
content of any given crosslinked ethylene plastic and they also
7.3 Vacuum Oven, with vacuum source capable of creating
permit comparison between different crosslinked ethylene
plastics, including those containing fillers, provided that, for a vacuum of at least 710 mm (28 in.) Hg and equipped with a
thermometer capable of measuring to 150°C.
the latter, the following conditions are met:
5.2.1 The filler is not soluble in either decahydronaphtha-
7.4 Analytical Balance, capable of weighing to 0.0001 g.
lene or xylenes at the extraction temperature.
8. Reagents
5.2.2 The amount of filler present in the compound either is
known or will be determined by other means.
8.1 Decahydronaphthalene (Decalin), anhydrous, boiling
5.2.3 Sufficient crosslinking has been achieved to prevent
point 189 to 191°C.
migration of filler during the extraction. Usually it has been
8.2 Xylenes, ACS reagent grade, boiling point 138 to 141°C.
found that, at extraction levels up to 50 %, the extractant
8.3 Suitable stabilizers for the solvent include:
remains clear and free of filler.
8.3.1 2,2'-methylene-bis (4-methyl-6-tertiary butyl phenol)
5.3 A suitable antioxidant is added to the extractant to
(CAS# 119-47-1)
inhibit possible oxidative degradation at the extraction tem-
8.3.2 Tetrakis-(methylene-(3,5-di-(tert)-butyl-4-hydrocin-
peratures.
namate))methane (CAS# 6683-19-8)
5.4 Before proceeding with this test method, reference shall
8.3.3 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxy-
be made to the specification of the material being tested. Any
benzyl)benzene (CAS# 1709-70-2)
test specimen preparation, conditioning, dimensions, or testing
8.3.4 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-
parameters, or a combination thereof, covered in the materials
triazine-2,4,6(1h,3h,5h)-trione (CAS# 27676-62-6)
specification shall take precedence over those mentioned in this
9. Safety Precautions
test method. If there are no material specifications, then the
default conditions apply. 9.1 Xylenes and decahydronaphthalene are toxic and flam-
mable solvents and shall be handled carefully. Use only in a
6. Precautions
ventilated hood. Check the effectiveness of the hood before
starting the tests. Do not inhale the vapors. Excessive inhala-
6.1 This test method measures a much larger three –
tion of the vapors has been known to cause dizziness or
dimensional polymer network and is different than that mea-
headache, or both. In the event of excessive inhalation, seek
sured by Test Method D3351.
fresh clean air.
6.2 It has been reported that ultra-high molecular weight
polyethylene fails to completely dissolve in this procedure at 10. Test Specimens
times.
10.1 At least two specimens each containing 0.300 6 0.015
6.3 Atmospheric pressure affects the boiling temperature of g of ground polymer weighed to the nearest 0.0001 g shall be
solvents. It is possible that laboratories performing these test tested.
D2765 − 16 (2024)
A—Identification tag and fine wire attached to cage.
B—Reflux condenser.
C—Ring stand clamp.
D—Water inlet.
E—Joint.
F—Large-mouth round-bottom flask.
G—Variable transformer.
H—Water outlet.
I—Ring stand.
J—Decahydronaphthalene or xylene.
K—Heating mantle.
L—120-mesh wire cage containing the specimen.
NOTE 1—If a slightly higher degree of accuracy is desired (about 1 to 2 %) a modified Soxhlet Extractor may be employed wherein the specimen is
held in an extraction thimble. The extraction thimble, with extra-coarse fritted glass disk sealed in, will have 45-mm body diameter, 130-mm height or
1 3
equivalent (height must subsequently be cut to 75 mm). The fritted disk is extra-coarse with fused edge. Glass wool 13 to 19 mm thick ( ⁄2 to ⁄4 in.) will
be placed on the bottom of the extraction thimble to support one gram 30-60 mesh ground sample which is covered with 13 to 19 mm thick layer of glass
wool, a fritted glass disk and a small glass weight. The extraction thimble assembly rests upon the 55-mm portion of the thimble previously cut off, the
latter inserted into the modified Soxhlet Extractor.
FIG. 1 Extraction Apparatus
10.2 The test samples shall be ground to a fineness that will and stapling those folds. In that manner, a pouch open at the
pass through a 30-mesh sieve. Shake this sieved material over top is obtained. Weigh this pouch (W1).
a 60-mesh sieve and reject any material that passes through.
11.2 Place the ground and screened sample in the weighed
10.3 Test specimens originating from insulation cut from
pouch. Weigh the pouch and specimen (W2) to the nearest
wire shall be homogeneous and consist of an equal mixture of
0.0001 g. Fold over the open side of the pouch and staple the
samples representative of insulation nearest to the conductor
edge to form a cage. Weigh the cage and sample (W3).
and samples representative of insulation nearest the outer
NOTE 2—Compaction of specimens has been observed to negatively
periphery of the construction unless specific portions of the
affect the repeatability of this method. Avoid compaction of the specimens
insulation are being examined for insufficient crosslinking.
and the specimen cages.
11.3 Fill a round-bottom flask as described in 7.1.1 with
11. Procedure
enough solvent to immerse the 120-mesh cage and sample
11.1 Prepare a specimen holder by cutting a piece of
completely during extraction. Dissolve 1 % an appropriate
120-mesh stainless steel cloth measuring approximately 80 by
antioxidant (8.3) in the decahydronaphthalene or xylenes.
40 mm (3 by 1 ⁄2 in.). Fold this to form a square measuring
approximately 40 mm (1 ⁄2 in.). Fold two sides of this square
NOTE 3—A volume of 350-mL in a 500-mL flask or 1000-mL in a
closed by folding the cloth at the edges about 6 to 7 mm ( ⁄4 in.) 2000-mL flask has been found to be sufficient.
D2765 − 16 (2024)
11.4 Boil the decahydronaphthalene or xylenes vigorously 13. Report
enough to ensure good agitation of the solution. Twenty to 40
13.1 Report the following information:
drops/min from the condenser, while using 1000 g of solvent,
13.1.1 Complete identification of the compound,
is a satisfactory boiling rate. Suspend the cage and specimen in
13.1.2 Density of the polyethylene in the compound (usu-
the solvent so that the bottom edge of the cage is almost
ally as identified by its supplier),
touching the bottom of the flask. A small wire, attached to the
13.1.3 Weight percent of polyethylene in the compound or
cage and extending through the reflux condenser has been used
filler content (usually as identified by its supplier or determined
for suspending the cage. Extract the specimen for 6 h in
by the test methods identified in Note 7),
decahydronaphthalene or for 12 h in xylenes.
13.1.4 Percent extract; the value for each specimen and the
average for the sample,
NOTE 4—Since most of the extraction occurs within less than the
specified time, the period of extraction may be shortened for control tests
13.1.5 Solvent used, time of extraction, and any pertinent
on the basis of experience. If this is done, the time of extraction must be
sample preparation, and
reported. For referee tests, extraction time is to be as specified by this test
13.1.6 Any unusual or abnormal behavior observed during
method.
the test (6.3).
11.5 After extraction, place the cage and specimen imme-
diately in a vacuum oven preheated to 150°C. Dry the
TEST METHOD B (NONREFEREE TEST MET
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