ASTM D2765-01(2006)
(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
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 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 can be determined.
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.
Since some oxidative degradation of the material can occur at the reflux temperature of the extractants, a suitable antioxidant is added to the extractant to inhibit such degradation.
Before proceeding with this test method, reference should 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 can be determined by extracting with solvents such as decahydronaphthalene or xylenes. Such extraction test methods are described herein. They 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. The first of these 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. The second of the alternative test methods requires that a specimen in one piece be extracted in xylenes at a constant temperature of 110C. At this temperature and with a one-piece specimen, even less extraction occurs (from 3 to 9 % less than the referee test method) but swell ratio (a measure of the degree of crosslinking in the gel phase) can be determined.
1.3 Extraction tests can be made on articles of any shape. They have been particularly useful for electrical insulations since specimens may be selected from those portions of the insulation most susceptible to insufficient crosslinking.
1.4 The values stated in SI units are to be regarded as standard. The inch-pound units in brackets are for information only. ISO 10147 is similar to this test, but is not equivalent.
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 Sections , , and .
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Designation:D2765–01 (Reapproved 2006)
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.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* bility of regulatory limitations prior to use. Specific precau-
tionary statements are given in Sections 6, 10, and 25.
1.1 The gel content (insoluble fraction) produced in ethyl-
ene plastics by crosslinking can be determined by extracting
2. Referenced Documents
with solvents such as decahydronaphthalene or xylenes. Such
2.1 ASTM Standards:
extraction test methods are described herein. They are appli-
D297 TestMethodsforRubberProducts—ChemicalAnaly-
cabletocrosslinkedethyleneplasticsofalldensities,including
sis
thosecontainingfillers,andallprovidecorrectionsfortheinert
D618 Practice for Conditioning Plastics for Testing
fillers present in some of those compounds.
D883 Terminology Relating to Plastics
1.2 TestMethodA,whichpermitsmostcompleteextraction
D1603 Test Method for Carbon Black Content in Olefin
in least time, is to be used for referee tests, but two alternative
Plastics
nonreferee Test Methods B and C are also described. The first
D1998 Specification for Polyethylene Upright Storage
of these differs from the referee test method only in sample
Tanks
preparation;thatis,itrequiresuseofshavingstakenatselected
D3351 Test Method for Gel Count of Plastic Film
points in cable insulation, for example, rather than the ground
E691 Practice for Conducting an Interlaboratory Study to
samplerequiredbytherefereetestmethod.Becausetheshaved
Determine the Precision of a Test Method
particles are larger, less total surface per sample is exposed to
the extractant, so this test method ordinarily yields extraction
3. Terminology
values about 1 to 2% lower than the referee method. The
3.1 Definitions of Terms Specific to This Standard:
second of the alternative test methods requires that a specimen
3.1.1 gel content—the percentage by mass of polymer
in one piece be extracted in xylenes at a constant temperature
insoluble in a specified solvent after extraction under the
of 110°C. At this temperature and with a one-piece specimen,
specified conditions.
evenlessextractionoccurs(from3to9%lessthanthereferee
3.1.2 soluble—capable of being loosened or dissolved, sus-
test method) but swell ratio (a measure of the degree of
ceptibleofbeingdissolvedinorasifinafluid.(SeeWebster’s
crosslinking in the gel phase) can be determined.
Ninth New Collegiate Dictionary, 1988.)
1.3 Extraction tests can be made on articles of any shape.
3.1.3 swell ratio—theratioofthegelvolumeintheswollen
They have been particularly useful for electrical insulations
state to its volume in the unswollen state.
since specimens may be selected from those portions of the
3.2 Terms as shown in Terminology D883 are applicable to
insulation most susceptible to insufficient crosslinking.
this test method.
1.4 The values stated in SI units are to be regarded as
standard. The inch-pound units in brackets are for information
4. Summary of Test Methods
only.
4.1 Specimens of the crosslinked ethylene plastic are
NOTE 1—ISO 10147 is similar to this test, but is not equivalent.
weighed and then immersed in the extracting solvent at the
temperature specified by the procedure selected and for the
1.5 This standard does not purport to address all of the
time designated by that procedure.After extraction, the speci-
safety concerns, if any, associated with its use. It is the
mens are removed, dried, and reweighed as directed. The
responsibility of the user of this standard to establish appro-
amountofmaterialextractediscalculatedand,ifdesired,swell
priate safety and health practices and determine the applica-
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 responsibilityofSubcommittee D20.15onThermoplastic 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 April 1, 2006. Published April 2006. Originally the ASTM website.
approved in 1968. Last previous edition approved in 2001 as D2765–01. DOI: Withdrawn. The last approved version of this historical standard is referenced
10.1520/D2765-01R06. on 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.
D2765–01 (2006)
ratio also may be determined by the means described in 500-mLflask is appropriate. For several determinations at one
alternative Test Method C. time, but not exceeding six, a 2000-mL flask is suitable.
8.1.2 Heating Mantle to fit the flask and with sufficient
5. Significance and Use
heating capacity to boil decahydronaphthalene (boiling point
5.1 Many important properties of crosslinked ethylene plas- 190 to 193°C) or xylenes (boiling point 138 to 141°C).
tics vary with the gel content. Hence, determination of the gel 8.1.3 Reflux Condenser with ground-glass or cork joint to
content provides a means of both controlling the process and fit into flask.
rating the quality of finished products. 8.1.4 Ring Stand and Appropriate Clamps.
5.2 Extraction tests permit verification of the proper gel 8.2 Grinding Equipment,suitableforreducingthesampleto
content of any given crosslinked ethylene plastic and they also a fineness between 30 and 60 mesh. A bench-top laboratory
4,5
permit comparison between different crosslinked ethylene mill is satisfactory, although any procedure which will
plastics, including those containing fillers, provided that, for produce a sample of the required fineness without generating
the latter, the following conditions are met: excessive heat may be used.
5.2.1 The filler is not soluble in either decahydronaphtha- 8.2.1 U.S. No. 30 and U.S. No. 60 Sieves.
lene or xylenes at the extraction temperature. 8.2.2 U.S. No. 120 Stainless Steel Wire Cloth.
8.3 Vacuum Oven, with vacuum source capable of creating
5.2.2 The amount of filler present in the compound either is
known or can be determined. a vacuum of at least 710 mm [28 in.] Hg and equipped with a
thermometer capable of measuring 150°C.
5.2.3 Sufficient crosslinking has been achieved to prevent
migration of filler during the extraction. Usually it has been 8.4 Analytical Balance, capable of weighing to 0.001 g.
found that, at extraction levels up to 50%, the extractant
NOTE 2—If a slightly higher degree of accuracy is desired (about 1 to
remains clear and free of filler.
2%) a modified Soxhlet Extractor; Kontes Catalog No. 586100-0023,
5.3 Since some oxidative degradation of the material can
Size C, Kontes Glass Co., Vineland, NJ or equivalent may be employed
occur at the reflux temperature of the extractants, a suitable wherein the specimen is held in an extraction thimble. The extraction
thimble, with extra-coarse fritted glass disk sealed in; Kontes 586500-
antioxidant is added to the extractant to inhibit such degrada-
0023, 45-mm body diameter, 130-mm height or equivalent (height must
tion.
subsequently be cut to 75 mm).The fritted disk is extra-coarse with fused
5.4 Before proceeding with this test method, reference
edge;Kontes952000-4025,40-mmdiameterorequivalent.Glasswool13
shouldbemadetothespecificationofthematerialbeingtested.
1 3
to19mmthick[ ⁄2to ⁄4in.]placedonthebottomoftheextractionthimble
Any test specimen preparation, conditioning, dimensions, or
tosupportonegram30–60meshgroundsamplewhichiscoveredwith13
testing parameters, or a combination thereof, covered in the
to 19 mm thick layer of glass wool, a fritted glass disk and a small glass
materials specification shall take precedence over those men- weight.The extraction thimble assembly rests upon the 55-mm portion of
thethimblepreviouslycutoff,thelatterinsertedintothemodifiedSoxhlet.
tioned in this test method. If there are no material specifica-
tions, then the default conditions apply.
9. Reagents
6. Precautions
9.1 Decahydronaphthalene, anhydrous, boiling point 189 to
191°C.
6.1 This test method measures a much larger three –
9.2 Xylenes,ACSreagentgrade,boilingpoint138to141°C.
dimensional polymer network than that measured by Test
5,6
9.3 2,28-methylene-bis (4-methyl-6-tertiary butyl phenol)
Method D3351 and should not be confused with it.
6.2 It has been reported that crosslinked ultra-high molecu-
10. Safety Precautions
lar weight polyethylene fails to completely dissolve in this
10.1 Xylenesanddecahydronaphthalenearetoxicandflam-
procedure at times.
mable solvents and as such should be handled carefully. Use
7. Conditioning
only in a ventilated hood. Check the effectiveness of the hood
before starting the tests. Do not inhale the vapors. Excessive
7.1 Conditioning—Condition the test specimens at 23 6
inhalation of the vapors may cause dizziness or headache, or
2°C [73.4 6 3.6°F] for not less than 40 h prior to test in
both. In the event of excessive inhalation, seek fresh clean air.
accordance with ProcedureAof Practice D618, for those tests
where conditioning is required. In cases of disagreement, the
11. Test Specimens
tolerance shall be 6 1°C [61.8°F].
11.1 At least two specimens each containing 0.300 6 0.015
7.2 Test Conditions—Prepare samples in the standard labo-
g of ground polymer weighed to the nearest 0.001 g shall be
ratory atmosphere of 23 6 2°C [73.4 6 3.6°F], unless
tested.
otherwise specified in the test methods. In cases of disagree-
ment, the tolerance shall be 61°C [61.8°F].
AWiley Cutting Mill, Intermediate Model, or equivalent, Catalog No. 08-338,
TEST METHOD A (REFEREE TEST METHOD)
available from Fisher Scientific Co., 711 Forbes Ave., Pittsburgh, PA 15219, has
been found satisfactory for this purpose.
8. Apparatus
If you are aware of alternative suppliers, please provide this information to
ASTM International Headquarters. Your comments will receive careful consider-
8.1 The extraction apparatus shall be of the following
ation at a meeting of the responsible technical committee, which you may attend.
general type, as illustrated in Fig. 1:
Antioxidant,availablefromCytecunderthetradenameCyanox2246,hasbeen
8.1.1 Round-Bottom Flask, with large-mouth ground-glass
foundsatisfactoryforthispurpose.CytecIndustries,PolymerAdditiveDepartment,
or cork joint. For one or two determinations at one time, a 5 Garret Mountain Plaza, West Paterson, NJ 07424.
D2765–01 (2006)
A—Identification tag and fine wire attached to cage.
B—Reflux condenser.
C—Ring stand clamp.
D—Water inlet.
E—Ground-glass or cork 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.
FIG. 1 Extraction Apparatus
11.2 The test samples shall be ground to a fineness that will 12.3 Fill a round-bottom flask as described in 8.1.1 with
pass through a 30-mesh sieve. Shake this sieved material over enough solvent to immerse the 120-mesh cage and sample
a 60-mesh sieve and reject any material that passes through. completely. Three hundred fifty grams in a 500-mL flask or
11.3 Test specimens originating from insulation cut from 1000 g in a 2000-mL flask is sufficient. Dissolve 1% of
wire should be homogeneous and consist of an equal mixture antioxidant in the decahydronaphthalene or xylenes to inhibit
ofsamplesrepresentativeofinsulationnearesttotheconductor further crosslinking of the specimen.
and samples representative of insulation nearest the outer 12.4 Boil the decahydronaphthalene or xylenes vigorously
periphery of the construction unless specific portions of the enough to ensure good agitation of the solution. Twenty to 40
insulation are being examined for insufficient crosslinking. drops/min from the condenser, while using 1000 g of solvent,
isasatisfactoryboilingrate.Suspendthecageandspecimenin
12. Procedure the solvent so that the bottom edge of the cage is almost
touching the bottom of the flask.Asmall wire, attached to the
12.1 Prepare a specimen holder by cutting a piece of
cage and extending through the reflux condenser can be used
120-mesh stainless steel cloth measuring approximately 80 by
for suspending the cage. Extract the specimen for6hin
40 mm [3 by 1 ⁄2 in.]. Fold this to form a square measuring
decahydronaphthalene or for 12 h in xylenes.
approximately 40 mm [1 ⁄2 in.]. Fold two sides of this square
closedbyfoldingtheclothattheedgesabout6to7mm[ ⁄4in.]
NOTE 3—Since most of the extraction occurs within less than the
and stapling those folds. In that manner, a pouch open at the specified time, the period of extraction may be shortened for control tests
on the basis of experience. If this is done, the time of extraction must be
top is obtained. Weigh this pouch (W1).
reported. For referee tests, extraction time is to be as specified by this test
12.2 Place approximately 0.3 g of the ground and screened
method.
sample in the weighed pouch. Weigh the pouch and specimen
(W2). Fold over the open side of the pouch and staple the edge 12.5 After extraction, place the cage and specimen imme-
to form a cage. Weigh the cage and sample (W3). diately in a vacuum oven preheated to 150°C. Dry the
D2765–01 (2006)
specimentoconstantweightunderatleast710mm[28in.]Hg TEST METHOD B (NONREFEREE TEST METHOD)
vacuum. Cool and weigh (W4). If the compound absorbs
15. Scope
moisture, cool the specimen in a desiccator before weighing.
15.1 This modification of the referee test method was
NOTE 4—It has been reported that drying time sometimes can be
developed particularly for wire and cable insulations and
materiallyshortenedifthecageandsamplearecooledfor15minandthen
differs from the referee test method only in specimen prepara-
are placed either on a suspended screen or on lint-free absorbent material
tion.
to remove excess solvent before being put into the vacuum drying oven.
15.2 In using this alternative test method, it should be
12.6 If extraction tests are regularly made, the apparatus
recognized that the values obtained may be lower than those
may be left assembled and the extracting solvent (containing
obtained by referee Test MethodAfor the reason given in 1.2.
inhibitor as directed) may be reused until it darkens. However,
16. Test Specimens
if there is any doubt abou
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