1、Designation: D7238 06 (Reapproved 2012)Standard Test Method forEffect of Exposure of Unreinforced PolyolefinGeomembrane Using Fluorescent UV CondensationApparatus1This standard is issued under the fixed designation D7238; the number immediately following the designation indicates the year oforiginal
2、 adoption or, in the case of revision, 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 This standard covers the specific procedures and testconditions tha
3、t are applicable for exposure of unreinforcedpolyolefin geomembranes to fluorescent UV radiation andcondensation.NOTE 1Polyolefin geomembranes include high density polyethylene(HDPE), linear low density polyethylene (LLDPE), flexible polyproply-ene (fPP), etc.1.2 Test specimens are exposed to fluore
4、scent UVA 340lamps under controlled environmental conditions. UVA 340lamps are standard for this method.NOTE 2Other types of fluorescent UV lamps, such as UVB-313, canalso be used based upon discussion between involved parties. However, ifthe test is ran with another type of fluorescent UV lamps, su
5、ch asUVB-313, this should be considered as a deviation from the standard andclearly stated in the test report. UVB-313 and UVA-340 fluorescent lampsgenerate different amount of radiant power in different wavelength ranges;thus, the photochemical effects caused by these different lamps may vary.1.3 T
6、his method covers the conditions under which theexposure is to be performed and the test methods for evaluatingthe effects of fluorescent UV, heat and moisture in the form ofcondensation on geomembranes. General guidance is given inPractices G151 and G154.1.4 The values listed in SI units are to be
7、regarded as thestandard.1.5 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 regulatory limitations prio
8、r to use.2. Referenced Documents2.1 ASTM Standards:2D1238 Test Method for Melt Flow Rates of Thermoplasticsby Extrusion PlastometerD5885 Test Method for Oxidative Induction Time of Poly-olefin Geosynthetics by High-Pressure Differential Scan-ning CalorimetryD6693 Test Method for Determining Tensile
9、Properties ofNonreinforced Polyethylene and Nonreinforced FlexiblePolypropylene GeomembranesG113 Terminology Relating to Natural and Artificial Weath-ering Tests of Nonmetallic MaterialsG151 Practice for Exposing Nonmetallic Materials in Accel-erated Test Devices that Use Laboratory Light SourcesG15
10、4 Practice for Operating Fluorescent LightApparatus forUV Exposure of Nonmetallic MaterialsG156 Practice for Selecting and Characterizing WeatheringReference Materials3. Terminology3.1 Definitions: (According to Terminology G113).3.1.1 control, nAmaterial which is of similar compositionand construct
11、ion to the test material used for comparison,exposed at the same time.3.1.2 irradiance, nthe radiant power per unit area incidenton a receiver, typically reported in units of W/(m2.nm) atspecified wavelength of measurement or in W/m2in a specifiedspectral range.3.1.3 reference material, nA material
12、with known perfor-mance.3.1.4 ultraviolet regions, nThe UV region of the spectrumis divided into three regions: UVA, radiation in wavelengths1This test method is under the jurisdiction of ASTM Committee D35 onGeosynthetics and is the direct responsibility of Subcommittee D35.02 on Endur-ance Propert
13、ies.Current edition approved July 1, 2012. Published July 2012. DOI: 10.1520/D7238-06R20122For 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 to the standards Document Sum
14、mary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1between 315 nm and 400 nm; UVB, radiation in wavelengthsbetween 280 nm and 315 nm; and UVC, radiation in wave-lengths shorter than 280 nm (Ref. CIE Publicati
15、on No. 20(1972).4. Summary of Test Method4.1 Geomembrane coupons are exposed to repetitive cyclesconsisting of ultraviolet radiation at a specified temperaturefollowed by moisture in the form of condensation at a specifiedtemperature in the absence of ultraviolet radiation.4.2 The UV source is provi
16、ded by fluorescent UVA-340lamps, with lamp emissions peaking at 343 nm.4.3 Water vapor shall be generated by heating water andfilling the chamber with hot vapor, which then is made tocondense on the front of the test coupons. The reverse side ofthe coupons is exposed to the cooling influence of ambi
17、entroom air.4.4 While this standard prescribes a particular set of expo-sure conditions, such conditions may be varied by agreementbetween the parties involved in the agreement or contract. Suchvariation may include the irradiance, the selection of thefluorescent UV lamps; the duration of the UV and
18、 condensa-tion exposure periods; the temperature of UV exposure; and thetemperature of the condensation exposure.4.5 The periodically removed coupons are cut into testspecimens, appropriately tested and the results compared tounexposed samples for determination of a percent retained foreach property
19、 evaluated5. Significance and Use5.1 The use of this apparatus is intended to induce propertychanges associated with the end use conditions, including theeffects of the UV portion of sunlight, moisture, and heat.Exposures are not intended to simulate the deterioration causedby localized weather phen
20、omena, such as atmosphericpollution, biological attack, and saltwater exposure.NOTE 3Refer to Practice G151 for cautionary guidance applicable tolaboratory weathering devices.5.2 Variation in results may be expected when operatingconditions are varied within the accepted limits of this method.5.3 Te
21、st data for one thickness of a geomembrane can not beused as data for other thickness geomembranes made with thesame formula (polymer, pigment and stabilizers) since thedegradation is thickness related.NOTE 4It is recommended that a similar material of known perfor-mance (a control) be exposed simul
22、taneously with the test material toprovide a standard for comparative purposes. When control material isused in the test program, it is recommended only one coupon be used foreach UV exposure period to allow for OIT testing.6. Apparatus6.1 Fluorescent UV/Condensation apparatus, complyingwith Practic
23、es G151 and G154.6.2 Unless otherwise specified, the spectral power distribu-tion of the fluorescent UV lamp shall conform to the require-ments in Practice G154 for a UVA-340 lamp.6.3 The apparatus must include a feed-back-loop controllerand be capable of controlling the irradiance level within theg
24、uidelines set in Practice G154, Table X2.3, OperationalFluctuations On Exposure Conditions.6.4 Exposure Chamber Location:6.4.1 The apparatus shall be located in an area maintained attemperature range between 18 and 27C (64 and 81F)measured at a maximum distance of 150 mm (5.9 in) from theplane door
25、of the apparatus.6.4.2 It is recommended that the apparatus be located atleast 0.3 m (12 in) from walls or other test devices. Nearby heatsources, such as ovens or heated test devices, shall be avoidedor shielded, because such sources can influence the results.6.4.3 The room where the apparatus is l
26、ocated shall beadequately ventilated to remove the heat and moisture pro-duced and to maintain the temperatures specified in 6.4.1.6.5 Instrument Calibration:6.5.1 To ensure standardization and accuracy, the instru-ments associated with the exposure apparatus (that is, timers,thermometers, UV sensor
27、s, radiometers) require recurrent cali-bration to ensure repeatability of test results. The calibrationfrequency recommended by the equipment manufacturershould be used.NOTE 5It is recommended that a weathering reference material shouldbe evaluated at least once per year to assess the operation of t
28、he device.Practice G156 describes procedures for selecting and characterizingweathering reference materials used to establish consistency of operatingconditions in a laboratory accelerated test.7. Test Coupons7.1 The number of coupons should be sufficient to producefive Test Methods D6693 specimens
29、from the exposure areasfor each exposure period.7.2 Prepare the test coupons so that the longer dimension ofthe test coupon is the machine direction of the test material.7.3 Since the thickness of a coupon may markedly affect theresults, thickness of the test and control coupon shall be within6 10%
30、of the nominal dimensions.7.4 Retain adequate unexposed material for the determina-tion of unexposed properties (tested one time to form thebaseline for comparison of the exposed material properties).8. Procedure8.1 Attach the coupons, backed by an aluminum panel, tothe coupon holders in the equipme
31、nt in such a manner that thespecimens are not subjected to any applied stress.NOTE 6Some UV fluorescent devices have a central stiffening bar onthe holder. To ensure that the entire coupon is exposed to ultravioletradiation, this bar should be removed prior to the start of the exposurecycle.8.2 Plac
32、e the coupon holders in the exposure device with thedesired surfaces facing the lamps. If the coupons do notcompletely occupy the racks, fill the empty spaces with blankpanels to maintain proper test conditions within the chamber.8.3 The extreme right-and left-hand coupon holders shall beequipped wi
33、th blank aluminum panels and shall not be used forcoupon exposure.D7238 06 (2012)28.4 Program the exposure device to achieve the followingexposure conditions.8.4.1 20 hours of UV with an uninsulated black paneltemperature set point of 75 C (167 F) alternating with 4 hourscondensation at 60 C (140 F)
34、, uninsulated black paneltemperature set point. See Practice G154, Table X2.3 for themaximum allowable operational fluctuation of the temperaturesetting.8.4.2 Unless otherwise specified, apparatus with irradiancecontrol shall be set at the control point at an irradiance level of0.78 W/(m2.nm) at 340
35、 nm. See Practice G154, Table X2.3 forthe maximum allowable operational fluctuation of the irradi-ance setting.8.4.3 If the operational fluctuation is greater than the maxi-mum allowable from either the temperature and irradiancesetting at the control sensor during equilibrium operation, thetest mus
36、t be discontinued until the problem is solved.NOTE 7Refer to Practice G154, Table X2.1, Note 1 for historical setpoint information.8.5 Reposition coupons horizontally once a week by (1)moving the two extreme right hand coupon holders to the farleft of the exposure area, and (2) sliding the remaining
37、 couponholders to the right.8.6 The exposure duration shall be 400, 800, 1200, 1600,and 2000 hours of UV or longer until sufficient change isobtained to establish trends in behavior. The total exposuretimes (UV time plus condensation time) corresponding to theseUV exposures are 480, 960, 1440, 1920
38、and 2400 hours,respectively8.7 Remove the appropriate number of coupons (see 7.1)ateach exposure time for material evaluation.9. Evaluation of Changes in Material Properties9.1 Test methods to be utilized in the evaluation process9.1.1 Test methods to be utilized in the evaluation processfor both un
39、exposed (file) and exposed coupons include highpressure oxidative induction time (HP-OIT) (Test MethodD5885), tensile strength (Test Method D6693) and melt index(Test Method D1238).9.2 Measurements on unexposed coupons.9.2.1 Determine the HP-OIT of the unexposed geomem-brane material as the base lin
40、e value. Test three replicates anduse the average of three values in the calculations.9.2.2 Determine the breaking strength and percent breakelongation of five replicate specimens in the machine direction,as directed in Test Method D6693. Use the average values inthe calculations.9.2.3 Determine the
41、 melt index (Test Method D1238) using190/2.16 on three replicate specimens. Use the average meltindex value in the calculations.9.3 Measurements on exposed coupons.9.3.1 Take three specimens from the centrally located areasof the removed coupons to determine the HP-OIT values.Calculate the average v
42、alue. The test method shall be same asthe one used in 9.2.1.9.3.2 Cut centrally located Test Method D6693 test speci-mens from the removed coupons, and test them accordingly.Determine breaking strength and percent break elongation atbreak of the five tensile specimens. Calculate the averagevalues of
43、 each property.9.3.3 Determine the melt index values of the three removedcoupons according to Test Method D1238 and calculate anaverage value. The test condition shall be same as that used insection 9.2.3.NOTE 8Tensile properties (Test Method D6693) and melt index (TestMethod D1238) may not show sub
44、stantial changes within 1600 hours ofUV exposure9.4 Calculate the percent retained values of HP-OIT, break-ing strength, percent break elongation and melt index at eachexposure time.10. Report10.1 Report the following information:10.1.1 Type of lamp.10.1.2 Report irradiance in W/(m2.nm), or radiant
45、exposurein J/(m2.nm), and the wavelength in which measurements weremade.10.1.3 Coupon repositioning procedure, if different from theprocedure described in 8.5.10.1.4 Alisting of the results for the exposed tested couponsfor each exposure time and the results for the unexposedmaterial.10.1.5 A listin
46、g of the percent retained values for eachexposure time.10.1.6 Graphs of the percent retained values against expo-sure times and appropriate curve fitting so as to establish trendsin the behavior.10.1.7 A statement indicating whether the fluorescent UVapparatus has been calibrated in accordance with
47、the manufac-tures recommendations.11. Precision and Bias11.1 The precision of the test is being evaluated.12. Keywords12.1 accelerated; geomembrane; fluorescent UV; tempera-ture; ultravioletD7238 06 (2012)3ASTM International takes no position respecting the validity of any patent rights asserted in
48、connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the res
49、ponsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is co
