1、Designation: F3203 16Standard Test Method forDetermination of Gel Content of Crosslinked Polyethylene(PEX) Pipes and Tubing1This standard is issued under the fixed designation F3203; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 The gel content of pipe and tubing produced fromcrosslinked polyethylene plastics as described in Specific
3、ationF876 and other pipe or tubing standards is determined byextracting with solvents such as xylenes. A test method forquantitative determination of gel content is described herein.The method is applicable to PEX pipe and tubing of alldensities, including those containing fillers, and providescorre
4、ction for the inert fillers present in some of thosecompounds.1.2 Continuous extraction (see definition in Section 3)isused in this method to test the gel content of crosslinkedpolyethylene specimens. Continuous extraction when used fortesting gel content has the advantages of decreased the cost oft
5、esting, increased accuracy and consistency of results, anddecreased test time. This is because extraction with a puresolvent is more efficient than extraction with a partiallysaturated solvent.1.3 While extraction tests may be made on articles of anyshape, this test method is applicable for determin
6、ing the gelcontent of crosslinked polyethylene pipes and tubing.1.4 This test method makes use of xylenes or alternativesolvents which have lower toxicity than xylenes. The alterna-tive solvents are also potentially beneficial from an economicand environmental viewpoint. Xylenes are used for referee
7、tests.1.5 The values stated in SI units are to be regarded asstandard. The inch-pound units in brackets are for informationonly1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish a
8、ppro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D883 Terminology Relating to PlasticsD1603 Test Method for Carbon Black Content in OlefinPlasticsD2765 Test Methods for Determination of Gel Cont
9、ent andSwell Ratio of Crosslinked Ethylene PlasticsD7567 Test Method for Determining Gel Content in Cross-linked Ethylene Plastics Using Pressurized Liquid Extrac-tion (Withdrawn 2015)3E691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodF876 Specification
10、for Crosslinked Polyethylene (PEX) Tub-ing2.2 ISO Standard:4ISO 10147 Pipes and Fittings Made of Crosslinked Polyeth-ylene (Pe-X) Estimation of the Degree of Crosslinkingby Determination of the Gel Content3. Terminology3.1 Terms as shown in Terminology D883 are applicable tothis test method.3.2 Defi
11、nitions of Terms Specific to This Standard:3.2.1 continuous extractor, ntest apparatus for performinga continuous extraction.3.2.1.1 DiscussionSoxhlet, Knofler-Bohm, and Kum-agawa extractors are examples of continuous extractors. Acontinuous extractor has three main components which are aboiling fla
12、sk or vessel for the solvent, a condenser, and asiphon cup. There are various designs for the siphon cup; theSoxhlet, Knofler-Bohm, and Kumagawa designs are the mostcommon.1This test method is under the jurisdiction of ASTM Committee F17 on PlasticPiping Systems and is the direct responsibility of S
13、ubcommittee F17.40 on TestMethods.Current edition approved Aug. 1, 2016. Published September 2016. DOI:10.1520/F3203162For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer t
14、o the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.4Available from International Organization for Standardization (ISO), ISOCentral Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,Geneva, Swi
15、tzerland, http:/www.iso.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.2 continuous extraction, nan extraction performed in acontinuous extractor where a solvent (normally xylenes) isheated in a vessel and boils forming vapor
16、s, the vapors rise andcondense on a condenser to form droplets, the droplets fall intoa cup where one or more specimens are placed, there thesolvent in the tray dissolves some of the un-crosslinkedpolyethylene in the specimens, and when the cup holding thespecimens is filled with solvent, the solven
17、t now containingsome of the un-crosslinked polyethylene drains out through asiphon tube back into the vessel where it started. The solventand the sample specimens in the cup are kept warm by solventvapor rising toward the condenser. The extraction steps repeatautomatically and continuously as long a
18、s heat is applied to thevessel holding the solvent. Because only the solvent evaporatesand not the material dissolved in it, the concentration ofun-crosslinked polyethylene in the boiling solvent increases,while the concentration of un-crosslinked polyethylene in thespecimens continually decreases.3
19、.2.3 gel content, nthe percentage by mass of polymerinsoluble in a specified solvent after extraction under thespecified conditions.4. Summary of Test Method4.1 Specimens of the crosslinked ethylene plastic areprepared, weighed and then extracted using a heated extractionsolvent in a continuous extr
20、actor for the time designated by theprocedure. After extraction, the specimens are removed fromthe continuous extractor, dried, and weighed as directed. Thegel content is calculated using the final and initial specimenweights as directed in the calculations section of this testmethod.5. Significance
21、 and Use5.1 Many important properties of crosslinked ethylene plas-tics vary with the gel content. Hence, determination of the gelcontent provides a basis for controlling production processesand a means of establishing the quality of finished products.5.2 Extraction tests permit verification of the
22、proper gelcontent of any given crosslinked ethylene plastic and they alsopermit comparison between different crosslinked ethyleneplastics, including those containing fillers, provided that, forthe latter, the following conditions are met:5.2.1 The filler is not soluble in the solvent used in thismet
23、hod at the extraction temperature.5.2.2 The amount of filler present in the compound either isknown or can be determined.5.2.3 Sufficient crosslinking has been achieved to preventmigration of filler during the extraction. It has been found that,at gel content above 30 %, the solvent remains clear an
24、d free offiller.5.3 Since some oxidative degradation of the material andsolvent may occur at the reflux temperature of the solvents, asuitable antioxidant is added to the solvent to inhibit suchdegradation.5.4 This test method is normally used for specimens con-sisting of an equal representation of
25、the entire cross section ofthe product, but may also be used to examine specific portionsof a product for differences in extent of cross-linking whencompared to either a product standard or another sample.5.5 This test method is intended for testing crosslinkedpolyethylene compounds that are not hyg
26、roscopic. If com-pounds that are hygroscopic are tested using this method,specimen conditioning before and after extraction is required.5.6 This standard differs from test methods Test MethodsD2765, and Test Method D7567 which also describe proce-dures for determining the gel content of crosslinked
27、polyeth-ylene. It allows for the use of naphthenic blend or isoparaffinsolvent as an alternative to xylenes. Xylenes are the onlysolvent allowed to be used for referee tests. The preferredmethod of sample preparation in this standard is to use a latheto create thin ribbons of PEX material. This stan
28、dard requiresthe use of a continuous extractor in order to provide consistentresults and to allow for reliable solvent re-use. Specializedspecimen holders are used to minimize variability resultingfrom loss of specimen particles.NOTE 1Pressurized extraction techniques have been found to yielduseful
29、results in a shorter time frame, however not all grades of PEXtolerate the elevated extraction temperatures without substantial degrada-tion. For this reason pressurized extraction techniques are recommendedfor control tests only if it is possible to determine that the crosslinkedmatrix of the PEX d
30、oes not break down at the temperature of extraction6. Conditioning6.1 ConditioningConditioning of the test specimens is notrequired, unless specified by the manufacturer of the materialbeing sampled.6.2 Test ConditionsTest conditions do not affect results,with the exception of atmospheric pressure.
31、Conduct tests in alaboratory with atmospheric pressure greater than 80 kPa (lessthan 6000 ft above average sea level).NOTE 2The altitude above sea level of the lab will influence theatmospheric pressure, which in turn will affect the boiling temperature ofthe solvent used and the rate at which it wi
32、ll be able to extractun-crosslinked polyethylene from the matrix.7. Apparatus7.1 Continuous Extractor, of the following general type, asillustrated in Fig. 1. Further information regarding possiblesources of components is included in the Appendix X3.7.1.1 Boiling Flask, with a ground-glass joint. Th
33、e flaskmay be either flat bottom or round bottom. For one or twodeterminations at a time, the minimum appropriate size is 500-mL. For routine testing with several determinations at onetime, but not exceeding six, a 2000-mL flask is suitable.7.1.2 Heating Mantle or Hot Plate, to fit the flask and wit
34、hsufficient heating capacity to boil the solvent used. If a flatbottom flask is used a hotplate shall be used instead of aheating mantle, and shall have sufficient heating capacity toboil the solvent used.7.1.3 Extractor Cup, with a ground-glass joint to fit theboiling flask, a large mouth ground-gl
35、ass joint on the top andsufficient capacity to hold specimen cages as described in7.3.2. The extractor cup shall be of a jacketed design so that thespecimens are extracted at as near as possible to the boilingtemperature of the solvent. The extractor cup and the boilingF3203 162flask must be of mate
36、d capacity, as the boiling flask must havesufficient solvent in to safely be used as the extractor cup fillsand drains. The extractor cup will be described with differentnames by laboratory glassware suppliers. These names includemodified Soxhlet extractor, jacketed Soxhlet extractor, andKnofler-Boh
37、m extractor. Review appendix X3.3 for supplierinformation.7.1.4 Reflux Condenser, with ground-glass joint to fit intothe extractor cup. This will typically be an Allihn or Dimrothcondenser.7.1.5 Ring Stand and Appropriate Clamps7.2 Lathe, Drill Press, Plane or Planer, suitable for reduc-ing the samp
38、le to a thickness of 0.15 to 0.05 mm. A bench toplathe is preferred, although any procedure which will producea sample of the required fineness without generating excessiveheat is acceptable. Appendix X2 presents examples of devicessuitable for sample preparation.7.3 Specimen Holders or Cages:7.3.1
39、Specimen Holders, of the general type illustrated inFig. 2, machined aluminum with an internal volume of 6 to 7cm3. The recommended design consists of two end caps and aspacer ring. The end caps shall be held together either by rareearth (samarium cobalt) magnets or a threaded connection tothe space
40、r ring. The end caps shall have US No. 150 stainlesssteel wire mesh nested inside of the openings. The wire meshis held between the spacer ring and the end caps to preventspecimen particles from escaping when the specimen holder isclosed. The exposed surface area of the wire mesh in the endcaps shal
41、l be a minimum of 11 cm2. Individual specimenholders are identified by an engraved number or letter on theend caps. Specimen holders are reusable. Construction draw-ings for suitable specimen holders are available in AppendixX1.7.3.2 Specimen Cages, made from U.S. No 150 stainlesssteel wire cloth. P
42、repare specimen cages by cutting pieces ofstainless steel wire cloth measuring 80 by 50 mm (3 by 2 in.).Fold these in half to form rectangles measuring approximately40 by 50 mm (112 by 2 in.) Fold two sides of these rectanglesclosed by folding at the edges about 6 to 7 mm (14 in.). In thismanner, ca
43、ges open at the top is obtained. Specimen cages maybe reused several times provided that they are completely freeof any polymer residue and do not have holes in them thatwould allow specimen particles to escape.7.4 Oven, capable of heating specimen holders to 150C(300F) with temperature indication.
44、This oven shall be of suchconstruction and design to maximize air circulation. Convec-tion toaster ovens sold for kitchen use have been found to beadequate provided they are used in a fume hood. Alternativelya vacuum oven may be used.7.5 Analytical Balance, , minimum capacity of 100 g andcapable of
45、weighing to 6 0.0001 g.7.6 Wood Block, 62 mm (212 in.) by 37 mm (112 in.) by 37mm (112 in.).7.7 Timer, capable of timing intervals up to 10 hours,accurate to 6 30 s per hour or better, and with an audible alarmat the completion of the timed interval.8. Reagents8.1 Extraction solvent, xylenes are the
46、 preferred solvent andmust be used for referee tests; however any one of thefollowing solvents may be used for control tests:8.1.1 Naphthenic hydrocarbon blend, boiling range 113 to145C. See Appendix X4.8.1.2 Isoparaffn solvent, boiling range 155 to 180C. SeeAppendix X4.8.1.3 Xylenes, ACS reagent gr
47、ade, boiling point 138 to141C.8.1.4 Comparison tests using xylenes and any alternativesolvent must be made. Gel content percentage values obtainedusing alternatives to xylenes tend to be 1.0 and 3.0% higherthan those obtained with xylenes.8.2 Antioxidant, the following or equivalent phenolic anti-ox
48、idant shall be used in combination blends or by themselves.The antioxidants selected may be obtained from commercialFIG. 1 Continuous ExtractorF3203 163suppliers and are not required to be reagent grade, as there is noexpectation that minor impurities will influence results:8.2.1 2,2-methylene-bis(4
49、-methyl-6-tertiary butyl phenol)(CAS#119-47-1)8.2.2 Tetrakis-(methylene-(3,5-di-(tert)-butyl-4- hydrocin-namate)methane (CAS# 6683-19-8)8.2.3 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4- hydroxy-benzyl)benzene (CAS #:1709-70-2)8.2.4 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1h,3h,5h)-trione (CAS# 27676-62-6)9. Safety Precautions9.1 The solvents used for extractions are toxic and flam-mable and as such must be handled carefully. Use only in aventilated hood. Check the effectiveness of the hood beforestarting tests. Keep away from
