1、Designation: D570 98 (Reapproved 2018)Standard Test Method forWater Absorption of Plastics1This standard is issued under the fixed designation D570; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A numbe
2、r in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 This test method covers the determination of the relat
3、iverate of absorption of water by plastics when immersed. Thistest method is intended to apply to the testing of all types ofplastics, including cast, hot-molded, and cold-molded resinousproducts, and both homogeneous and laminated plastics in rodand tube form and in sheets 0.13 mm (0.005 in.) or gr
4、eater inthickness.1.2 The values given in SI units are to be regarded asstandard. The values stated in parentheses are for informationonly.1.3 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
5、 establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Princ
6、iples for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ISO Standard:ISO 62 PlasticsDetermination of Water Absorption23. Significance and Use3.1 This test method for
7、rate of water absorption has twochief functions: first, as a guide to the proportion of waterabsorbed by a material and consequently, in those cases wherethe relationships between moisture and electrical or mechanicalproperties, dimensions, or appearance have been determined,as a guide to the effect
8、s of exposure to water or humidconditions on such properties; and second, as a control test onthe uniformity of a product. This second function is particu-larly applicable to sheet, rod, and tube arms when the test ismade on the finished product.3.2 Comparison of water absorption values of various p
9、las-tics can be made on the basis of values obtained in accordancewith 7.1 and 7.4.3.3 Ideal diffusion of liquids3into polymers is a function ofthe square root of immersion time. Time to saturation isstrongly dependent on specimen thickness. For example, Table1 shows the time to approximate time sat
10、uration for variousthickness of nylon-6.3.4 The moisture content of a plastic is very intimatelyrelated to such properties as electrical insulation resistance,dielectric losses, mechanical strength, appearance, and dimen-sions. The effect upon these properties of change in moisturecontent due to wat
11、er absorption depends largely on the type ofexposure (by immersion in water or by exposure to highhumidity), shape of the part, and inherent properties of theplastic. With nonhomogeneous materials, such as laminatedforms, the rate of water absorption may be widely differentthrough each edge and surf
12、ace. Even for otherwise homoge-neous materials, it may be slightly greater through cut edgesthan through molded surfaces. Consequently, attempts tocorrelate water absorption with the surface area must generallybe limited to closely related materials and to similarly shapedspecimens: For materials of
13、 widely varying density, relationbetween water-absorption values on a volume as well as aweight basis may need to be considered.1This test method is under the jurisdiction ofASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.50 on Durability of Plastics.Current editio
14、n approved Aug. 1, 2018. Published August 2018. Originallyapproved in 1940. Last previous edition approved in 2010 as D570 - 98 (2010)1.DOI: 10.1520/D0570-98R18.2Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.3Additional
15、information regarding diffusion of liquids in polymers can be foundin the following references: (1) Diffusion, Mass Transfer in Fluid Systems,E.L.Cussler, Cambridge University Press, 1985, ISBN 0-521-29846-6, (2) Diffusion inPolymers, J. Crank and G. S. Park, Academic Press, 1968, and (3) “Permeatio
16、n,Diffusion, and Sorption of Gases and Vapors,” R. M. Felder and G. S. Huvard, inMethods of Experimental Physics, Vol 16C, 1980, Academic Press.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed i
17、n accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.14. Apparatus4.1 BalanceAn
18、 analytical balance capable of reading0.0001 g.4.2 Oven, capable of maintaining uniform temperatures of50 6 3C (122 6 5.4F) and of 105 to 110C (221 to 230F).5. Test Specimen5.1 The test specimen for molded plastics shall be in theform of a disk 50.8 mm (2 in.) in diameter and 3.2 mm (18 in.)in thick
19、ness. Permissible variations in thickness are 60.18 mm(60.007 in.) for hot-molded and 60.30 mm (60.012 in.) forcold-molded or cast materials.5.2 ISO Standard SpecimenThe test specimen for homo-geneous plastics shall be 60 by 60 by 1 mm. Tolerance for the60-mm dimension is 62mmand60.05 mm for the 1-m
20、mthickness. This test method and ISO 62 are technically equiva-lent when the test specimen described in 5.2 is used.5.3 The test specimen for sheets shall be in the form of a bar76.2 mm (3 in.) long by 25.4 mm (1 in.) wide by the thicknessof the material. When comparison of absorption values withmol
21、ded plastics is desired, specimens 3.2-mm (18-in.) thickshould be used. Permissible variations in thickness shall be0.20 mm (60.008 in.) except for materials which have greaterstandard commercial tolerances.5.4 The test specimen for rods shall be 25.4-mm (1-in.) longfor rods 25.4 mm in diameter or u
22、nder and 12.7-mm (12-in.)long for larger-diameter rods. The diameter of the specimenshall be the diameter of the finished rod.5.5 The test specimen for tubes less than 76 mm (3 in.) ininside diameter shall be the full section of the tube and25.4-mm (1-in.) long. For tubes 76 mm (3 in.) or more in in
23、sidediameter, a rectangular specimen shall be cut 76 mm in lengthin the circumferential direction of the tube and 25.4 mm inwidth lengthwise of the tube.5.6 The test specimens for sheets, rods, and tubes shall bemachined, sawed, or sheared from the sample so as to havesmooth edges free from cracks.
24、The cut edges shall be madesmooth by finishing with No. 0 or finer sandpaper or emerycloth. Sawing, machining, and sandpapering operations shallbe slow enough so that the material is not heated appreciably.NOTE 1If there is any oil on the surface of the specimen whenreceived or as a result of machin
25、ing operations, wash the specimen witha cloth wet with gasoline to remove oil, wipe with a dry cloth, and allowto stand in air for2htopermit evaporation of the gasoline. If gasolineattacks the plastic, use some suitable solvent or detergent that willevaporate within the 2-h period.5.7 The dimensions
26、 listed in the following table for thevarious specimens shall be measured to the nearest 0.025 mm(0.001 in.). Dimensions not listed shall be measured within 0.8mm (6132 in.).Type ofSpecimenDimensions to Be Measured totheNearest 0.025 mm (0.001 in.)Molded disk thicknessSheet thicknessRod length and d
27、iameterTube inside and outside diameter, andwall thickness6. Conditioning6.1 Three specimens shall be conditioned as follows:6.1.1 Specimens of materials whose water-absorption valuewould be appreciably affected by temperatures in the neigh-borhood of 110C (230F), shall be dried in an oven for 24 ha
28、t 50 6 3C (122 6 5.4F), cooled in a desiccator, and imme-diately weighed to the nearest 0.001 g.NOTE 2If a static charge interferes with the weighing, lightly rub thesurface of the specimens with a grounded conductor.6.1.2 Specimens of materials, such as phenolic laminatedplastics and other products
29、 whose water-absorption value hasbeen shown not to be appreciably affected by temperatures upto 110C (230F), shall be dried in an oven for1hat105to110C (221 to 230F).6.1.3 When data for comparison with absorption values forother plastics are desired, the specimens shall be dried in anoven for 24 h a
30、t 50 6 3C (122 6 5.4F), cooled in adesiccator, and immediately weighed to the nearest 0.001 g.7. Procedure7.1 Twenty-Four Hour ImmersionThe conditioned speci-mens shall be placed in a container of distilled water main-tained at a temperature of 23 6 1C (73.4 6 1.8F), and shallrest on edge and be ent
31、irely immersed. At the end of 24, +12,0 h, the specimens shall be removed from the water one at atime, all surface water wiped off with a dry cloth, and weighedto the nearest 0.001 g immediately. If the specimen is116 in. orless in thickness, it shall be put in a weighing bottle immedi-ately after w
32、iping and weighed in the bottle.7.2 Two-Hour ImmersionFor all thicknesses of materialshaving a relatively high rate of absorption, and for thinspecimens of other materials which may show a significantweight increase in 2 h, the specimens shall be tested asdescribed in 7.1 except that the time of imm
33、ersion shall bereduced to 120 6 4 min.7.3 Repeated ImmersionA specimen may be weighed tothe nearest 0.001 g after 2-h immersion, replaced in the water,and weighed again after 24 h.NOTE 3In using this test method the amount of water absorbed in 24h may be less than it would have been had the immersio
34、n not beeninterrupted.7.4 Long-Term ImmersionTo determine the total waterabsorbed when substantially saturated, the conditioned speci-mens shall be tested as described in 7.1 except that at the endof 24 h they shall be removed from the water, wiped free ofsurface moisture with a dry cloth, weighed t
35、o the nearest 0.001TABLE 1 Time to Saturation for Various Thickness of Nylon-6Thickness, mmTypical Time to 95 %Saturation, h1 1002 4003.2 1 00010 10 00025 62 000D570 98 (2018)2g immediately, and then replaced in the water. The weighingsshall be repeated at the end of the first week and every twoweek
36、s thereafter until the increase in weight per two-weekperiod, as shown by three consecutive weighings, averages lessthan 1 % of the total increase in weight or 5 mg, whichever isgreater; the specimen shall then be considered substantiallysaturated. The difference between the substantially saturatedw
37、eight and the dry weight shall be considered as the waterabsorbed when substantially saturated.7.5 Two-Hour Boiling Water ImmersionThe conditionedspecimens shall be placed in a container of boiling distilledwater, and shall be supported on edge and be entirely im-mersed. At the end of 120 6 4 min, t
38、he specimens shall beremoved from the water and cooled in distilled water main-tained at room temperature. After 15 6 1 min, the specimensshall be removed from the water, one at a time, all surfacewater removed with a dry cloth, and the specimens weighed tothe nearest 0.001 g immediately. If the spe
39、cimen is116 in. orless in thickness, it shall be weighed in a weighing bottle.7.6 One-Half-Hour Boiling Water ImmersionFor all thick-nesses of materials having a relatively high rate of absorptionand for thin specimens of other materials which may show asignificant weight increase in12 h, the specim
40、ens shall betested as described in 7.5, except that the time of immersionshall be reduced to 30 6 1 min.7.7 Immersion at 50CThe conditioned specimens shallbe tested as described in 7.5, except that the time andtemperature of immersion shall be 48 6 1 h and 50 6 1C(122.0 6 1.8F), respectively, and co
41、oling in water beforeweighing shall be omitted.7.8 When data for comparison with absorption values forother plastics are desired, the 24-h immersion proceduredescribed in 7.1 and the equilibrium value determined in 7.4shall be used.8. Reconditioning8.1 When materials are known or suspected to contai
42、n anyappreciable amount of water-soluble ingredients, thespecimens, after immersion, shall be weighed, and then recon-ditioned for the same time and temperature as used in theoriginal drying period. They shall then be cooled in a desicca-tor and immediately reweighed. If the reconditioned weight isl
43、ower than the conditioned weight, the difference shall beconsidered as water-soluble matter lost during the immersiontest. For such materials, the water-absorption value shall betaken as the sum of the increase in weight on immersion and ofthe weight of the water-soluble matter.9. Calculation and Re
44、port9.1 The report shall include the values for each specimenand the average for the three specimens as follows:9.1.1 Dimensions of the specimens before test, measured inaccordance with 5.6, and reported to the nearest 0.025 mm(0.001 in.),9.1.2 Conditioning time and temperature,9.1.3 Immersion proce
45、dure used,9.1.4 Time of immersion (long-term immersion procedureonly),9.1.5 Percentage increase in weight during immersion, cal-culated to the nearest 0.01 % as follows:Increase in weight, % 5wet weight 2 conditioned weightconditioned weight31009.1.6 Percentage of soluble matter lost during immersio
46、n, ifdetermined, calculated to the nearest 0.01 % as follows (seeNote 4):Soluble matter lost, %5conditioned weight 2 reconditioned weightconditioned weight3100NOTE 4When the weight on reconditioning the specimen afterimmersion in water exceeds the conditioned weight prior to immersion,report “none”
47、under 9.1.6.9.1.7 For long-term immersion procedure only, prepare agraph of the increase in weight as a function of the square rootof each immersion time. The initial slope of this graph isproportional to the diffusion constant of water in the plastic.The plateau region with little or no change in w
48、eight as afunction of the square root of immersion time represents thesaturation water content of the plastic.NOTE 5Deviation from the initial slope and plateau model indicatesthat simple diffusion may be a poor model for determining water content.In such cases, additional studies are suggested to d
49、etermine a better modelfor water absorption.9.1.8 The percentage of water absorbed, which is the sum ofthe values in 9.1.5 and 9.1.6, and9.1.9 Any observations as to warping, cracking, or changein appearance of the specimens.10. Precision and Bias410.1 PrecisionAn interlaboratory test program was car-ried out using the procedure outlined in 7.1, involving threelaboratories and three materials.Analysis of this data yields thefollowing coefficients of variation (average of three replicates).WithinLaboratoriesBetweenLaboratoriesAverage absorpti
