1、Designation: D 570 98 (Reapproved 2005)Standard Test Method forWater Absorption of Plastics1This standard is issued under the fixed designation D 570; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A num
2、ber in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the relativerate of absorption of water by plastics when immersed. Thistest method is intend
3、ed 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 greater inthickness.1.2 The values given in SI units are to be regarded asstandard. The
4、 values stated in brackets 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 establish appro-priate safety and health practices and determine the applica-bility of
5、regulatory limitations prior to use.NOTE 1ISO 62 is technically equivalent to this test method.2. Referenced Documents2.1 ASTM Standards:D 647 Practice for Design of Molds for Test Specimens ofPlastic Molding Materials22.2 ISO Standard:ISO 62 PlasticsDetermination of Water Absorption33. Significance
6、 and Use3.1 This test method for 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 de
7、termined,as a guide to the effects 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 wat
8、er absorption values of various plas-tics can be made on the basis of values obtained in accordancewith 7.1 and 7.4.3.3 Ideal diffusion of liquids4into polymers is a function ofthe square root of immersion time. Time to saturation isstrongly dependent on specimen thickness. For example, Table1 shows
9、 the time to approximate time saturation 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 cha
10、nge in moisturecontent due to water 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 di
11、fferentthrough each edge and surface. 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
12、shapedspecimens: For materials of widely varying density, relationbetween water-absorption values on a volume as well as aweight basis may need to be considered.4. Apparatus4.1 BalanceAn analytical balance capable of reading0.0001 g.4.2 Oven, capable of maintaining uniform temperatures of50 6 3C 122
13、 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 thickness (see Note 2). Permissible variations in thicknessare 60.18 mm 60.007 in. for hot-molded and 60.30 mm60.012 in. for co
14、ld-molded or cast materials.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 edition approved Nov. 1, 2005. Published January 2006. Originallyapproved in 1940. Last previous edition a
15、pproved in 1998 as D 570 - 98.2Withdrawn.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.4Additional information regarding diffusion of liquids in polymers can be foundin the following references: (1) Diffusion, Mass Transfer in Fluid System
16、s, 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) “Permeation,Diffusion, and Sorption of Gases and Vapors,” R. M. Felder and G. S. Huvard, inMethods of Experimental Physics, Vol 16C, 1980, Academic
17、Press.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.NOTE 2The disk mold prescribed in the Molds for Disk TestSpecimens Section of Practice D 647 is suitable for molding disk testspecimens of thermosetting materials but not thermopl
18、astic 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-mmthickness. This test method and ISO 62 are technically equiva-lent when the test specimen described in 5.2 is used.5.3 The t
19、est 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 withmolded plastics is desired, specimens 3.2-mm 18-in. thickshould be used. Permissible variations in thickness shall be0.20 mm 60.008
20、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 under 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 tes
21、t 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 insidediameter, a rectangular specimen shall be cut 76 mm in lengthin the circumferential direction of the tube and 25.4 mm inwidth lengthwise of
22、 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. The cut edges shall be madesmooth by finishing with No. 0 or finer sandpaper or emerycloth. Sawing, machining, and sandpapering operations shal
23、lbe slow enough so that the material is not heated appreciably.NOTE 3If there is any oil on the surface of the specimen whenreceived or as a result of machining operations, wash the specimen witha cloth wet with gasoline to remove oil, wipe with a dry cloth, and allowto stand in air for2htopermit ev
24、aporation of the gasoline. If gasolineattacks the plastic, use some suitable solvent or detergent that willevaporate within the 2-h period.5.7 The dimensions listed in the following table for thevarious specimens shall be measured to the nearest 0.025 mm0.001 in. Dimensions not listed shall be measu
25、red within 0.8mm 6132 in.Type ofSpecimenDimensions to Be Measured to theNearest 0.025 mm 0.001 in.Molded disk thicknessSheet thicknessRod length and diameterTube inside and outside diameter, and wall thickness6. Conditioning6.1 Three specimens shall be conditioned as follows:6.1.1 Specimens of mater
26、ials whose water-absorption valuewould be appreciably affected by temperatures in the neigh-borhood of 110C 230F, shall be dried in an oven for 24 hat 50 6 3C 122 6 5.4F, cooled in a desiccator, and imme-diately weighed to the nearest 0.001 g.NOTE 4If a static charge interferes with the weighing, li
27、ghtly rub thesurface of the specimens with a grounded conductor.6.1.2 Specimens of materials, such as phenolic laminatedplastics and other products whose water-absorption value hasbeen shown not to be appreciably affected by temperatures upto 110C 230F, shall be dried in an oven for1hat105to110C 221
28、 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 at 50 6 3C 122 6 5.4F, cooled in a desic-cator, and immediately weighed to the nearest 0.001 g.7. Procedure7.1 Twenty-Four Hour ImmersionThe conditioned speci
29、-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 entirely 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 weigh
30、edto 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 wiping and weighed in the bottle.7.2 Two-Hour ImmersionFor all thicknesses of materialshaving a relatively high rate of absorption, and for thinspecimens of ot
31、her materials which may show a significantweight increase in 2 h, the specimens shall be tested asdescribed in 7.1 except that the time of immersion 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 wei
32、ghed again after 24 h.NOTE 5In using this test method the amount of water absorbed in 24h may be less than it would have been had the immersion not beeninterrupted.7.4 Long-Term ImmersionTo determine the total waterabsorbed when substantially saturated, the conditioned speci-mens shall be tested as
33、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 to the nearest 0.001g immediately, and then replaced in the water. The weighingsshall be repeated at the end of the first week and every twoweeks thereafter un
34、til 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 saturatedweight and the d
35、ry 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, the specimens sh
36、all 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 surfaceTABLE 1 Time to Saturation for Various Thickness of Nylon-6Thickness, mm Typical Time to 95 % Saturation, h1 1002 4003
37、.2 1 00010 10 00025 62 000D 570 98 (2005)2water removed with a dry cloth, and the specimens weighed tothe nearest 0.001 g immediately. If the specimen is116 in. orless in thickness, it shall be weighed in a weighing bottle.7.6 One-Half-Hour Boiling Water ImmersionFor allthicknesses of materials havi
38、ng a relatively high rate ofabsorption and for thin specimens of other materials whichmay show a significant weight increase in12 h, the specimensshall be tested as described in 7.5, except that the time ofimmersion shall be reduced to 30 6 1 min.7.7 Immersion at 50CThe conditioned specimens shallbe
39、 tested as described in 7.5, except that the time andtemperature of immersion shall be 48 6 1 h and 50 6 1C122.0 6 1.8F, respectively, and cooling in water beforeweighing shall be omitted.7.8 When data for comparison with absorption values forother plastics are desired, the 24-h immersion procedured
40、escribed in 7.1 and the equilibrium value determined in 7.4shall be used.8. Reconditioning8.1 When materials are known or suspected to contain anyappreciable amount of water-soluble ingredients, the speci-mens, after immersion, shall be weighed, and then recondi-tioned for the same time and temperat
41、ure as used in the originaldrying period. They shall then be cooled in a desiccator andimmediately reweighed. If the reconditioned weight is lowerthan the conditioned weight, the difference shall be consideredas water-soluble matter lost during the immersion test. For suchmaterials, the water-absorp
42、tion value shall be taken as the sumof the increase in weight on immersion and of the weight of thewater-soluble matter.9. Calculation and Report9.1 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,
43、measured inaccordance with 5.6, and reported to the nearest 0.025 mm0.001 in.,9.1.2 Conditioning time and temperature,9.1.3 Immersion procedure 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
44、follows:Increase in weight, % 5wet weight 2 conditioned weightconditioned weight31009.1.6 Percentage of soluble matter lost during immersion, ifdetermined, calculated to the nearest 0.01 % as follows (seeNote 6):Soluble matter lost, % 5conditioned weight 2 reconditioned weightconditioned weight3 100
45、NOTE 6When the weight on reconditioning the specimen after im-mersion in water exceeds the conditioned weight prior to immersion,report “none” 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. Th
46、e initial slope of this graph isproportional to the diffusion constant of water in the plastic.The plateau region with little or no change in weight as afunction of the square root of immersion time represents thesaturation water content of the plastic.NOTE 7Deviation from the initial slope and plat
47、eau model indicatesthat simple diffusion may be a poor model for determining water content.In such cases, additional studies are suggested to determine 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 observatio
48、ns as to warping, cracking, or changein appearance of the specimens.10. Precision and Bias510.1 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 var
49、iation (average of three replicates).WithinLaboratoriesBetweenLaboratoriesAverage absorption above1 % (2 materials)2.33 % 4.89 %Average absorption below0.2 % (1 material)9.01 % 16.63 %NOTE 8A round robin is currently under way to more completelydetermine repeatability and reproducibility of this test method.10.2 BiasNo justifiable statement on the bias of this testmethod can be made, since the true value of the propertycannot be established by an accepted referee method.11. Keywords11.
