1、Designation: D7238 06 (Reapproved 2017)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 run 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 amounts of radiant power in different wavelengthranges; thus, the photochemical effects caused by these different lampsmay 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.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBa
9、rriers to Trade (TBT) Committee.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 f
10、or Determining Tensile 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 Labo
11、ratory Light SourcesG154 Practice for Operating Fluorescent Ultraviolet (UV)Lamp Apparatus for Exposure of Nonmetallic MaterialsG156 Practice for Selecting and Characterizing WeatheringReference Materials3. Terminology3.1 Definitions: (According to Terminology G113.)3.1.1 control, na material which
12、is of similar compositionand construction 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.
13、3.1.3 reference material, na material 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 Sub
14、committee D35.02 on Endur-ance Properties.Current edition approved July 1, 2017. Published July 2017. Originally approvedin 2006. Last previous edition approved in 2012 as D7238 06 (2012). DOI:10.1520/D7238-06R17.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Cu
15、stomer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was dev
16、eloped in 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.1between 315 nm an
17、d 400 nm; UVB, radiation in wavelengthsbetween 280 nm and 315 nm; and UVC, radiation in wave-lengths shorter than 280 nm (Ref. CIE Publication No. 20(1972).4. Summary of Test Method4.1 Geomembrane coupons are exposed to repetitive cyclesconsisting of ultraviolet radiation at a specified temperaturef
18、ollowed by moisture in the form of condensation at a specifiedtemperature in the absence of ultraviolet radiation.4.2 The UV source is provided 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
19、, which then is made tocondense on the front of the test coupons. The reverse side ofthe coupons is exposed to the cooling influence of ambientroom air.4.4 While this standard prescribes a particular set of expo-sure conditions, such conditions may be varied by agreementbetween the parties involved
20、in the agreement or contract. Suchvariation may include the irradiance, the selection of thefluorescent UV lamps, the duration of the UV and condensationexposure periods, the temperature of UV exposure, and thetemperature of the condensation exposure.4.5 The periodically removed coupons are cut into
21、 testspecimens, appropriately tested, and the results compared tounexposed samples for determination of a percent retained foreach property evaluated.5. Significance and Use5.1 The use of this apparatus is intended to induce propertychanges associated with the end-use conditions, including theeffect
22、s of the UV portion of sunlight, moisture, and heat.Exposures are not intended to simulate the deterioration causedby localized weather phenomena, such as atmosphericpollution, biological attack, and saltwater exposure.NOTE 3Refer to Practice G151 for cautionary guidance applicable tolaboratory weat
23、hering devices.5.2 Variation in results may be expected when operatingconditions are varied within the accepted limits of this method.5.3 Test data for one thickness of a geomembrane cannot beused as data for other thickness geomembranes made with thesame formula (polymer, pigment, and stabilizers)
24、since thedegradation is thickness related.NOTE 4It is recommended that a similar material of known perfor-mance (a control) be exposed simultaneously with the test material toprovide a standard for comparative purposes. When control material isused in the test program, it is recommended only one cou
25、pon be used foreach UV exposure period to allow for OIT testing.6. Apparatus6.1 Fluorescent UV/Condensation Apparatus, complyingwith Practices 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
26、 for a UVA-340 lamp.6.3 The apparatus must include a feedback loop controllerand be capable of controlling the irradiance level within theguidelines 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
27、an area maintained attemperature range between 18 and 27 C (64 and 81 F)measured at a maximum distance of 150 mm (5.9 in.) from theplane door 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. Nearbyheat sources, such as ov
28、ens or heated test devices, shall beavoided or shielded because such sources can influence theresults.6.4.3 The room where the apparatus is located 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
29、.5.1 To ensure standardization and accuracy, the instru-ments associated with the exposure apparatus (that is, timers,thermometers, UV sensors, radiometers) require recurrent cali-bration to ensure repeatability of test results. The calibrationfrequency recommended by the equipment manufacturershoul
30、d be used.NOTE 5It is recommended that a weathering reference material shouldbe evaluated at least once per year to assess the operation of the device.Practice G156 describes procedures for selecting and characterizingweathering reference materials used to establish consistency of operatingcondition
31、s in a laboratory accelerated test.7. Test Coupons7.1 The number of coupons should be sufficient to producefive Test Method D6693 specimens from the exposure areas foreach exposure period.7.2 Prepare the test coupons so that the longer dimension ofthe test coupon is the machine direction of the test
32、 material.7.3 Since the thickness of a coupon may markedly affect theresults, thickness of the test and control coupon shall be within610 % of the nominal dimensions.7.4 Retain adequate unexposed material for the determina-tion of unexposed properties (tested one time to form thebaseline for compari
33、son of the exposed material properties).8. Procedure8.1 Attach the coupons, backed by an aluminum panel, tothe coupon holders in the equipment 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 e
34、nsure that the entire coupon is exposed to ultravioletradiation, this bar should be removed prior to the start of the exposurecycle.8.2 Place 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 w
35、ith blankpanels to maintain proper test conditions within the chamber.D7238 06 (2017)28.3 The extreme right- and left-hand coupon holders shallbe equipped with blank aluminum panels and shall not be usedfor coupon exposure.8.4 Program the exposure device to achieve the followingexposure conditions.8
36、.4.1 Twenty (20) h of UV with an uninsulated black paneltemperature set point of 75 C (167 F) alternating with 4 hcondensation at 60 C (140 F), uninsulated black paneltemperature set point. See Practice G154, Table X2.3 for themaximum allowable operational fluctuation of the temperaturesetting.8.4.2
37、 Unless otherwise specified, apparatus with irradiancecontrol shall be set at the control point at an irradiance level of0.78 W/(m2.nm) at 340 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
38、 than the maxi-mum allowable from either the temperature and irradiancesetting at the control sensor during equilibrium operation, thetest must 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 hori
39、zontally 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 couponholders to the right.8.6 The exposure duration shall be 400, 800, 1200, 1600,and 2000 h of UV or longer until sufficient change is obtainedto establish
40、 trends in behavior. The total exposure times (UVtime plus condensation time) corresponding to these UVexposures are 480, 960, 1440, 1920 and 2400 h, respectively.8.7 Remove the appropriate number of coupons (see 7.1)ateach exposure time for material evaluation.9. Evaluation of Changes in Material P
41、roperties9.1 Test Methods to be Utilized in the Evaluation Process:9.1.1 Test methods to be utilized in the evaluation processfor both unexposed (file) and exposed coupons include high-pressure oxidative induction time (HP-OIT) (Test MethodD5885), tensile strength (Test Method D6693), and melt index
42、(Test Method D1238).9.2 Measurements on Unexposed Coupons:9.2.1 Determine the HP-OIT of the unexposed geomem-brane material as the baseline 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 re
43、plicate specimens in the machine direction,as directed in Test Method D6693. Use the average values inthe calculations.9.2.3 Determine the 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 Coupon
44、s:9.3.1 Take three specimens from the centrally located areasof the removed coupons to determine the HP-OIT values.Calculate the average value. 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
45、accordingly.Determine breaking strength and percent break elongation atbreak of the five tensile specimens. Calculate the averagevalues of 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
46、shall be same as that used insection 9.2.3.NOTE 8Tensile properties (Test Method D6693) and melt index (TestMethod D1238) may not show substantial changes within 1600 h of UVexposure.9.4 Calculate the percent retained values of HP-OIT, break-ing strength, percent break elongation, and melt index at
47、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 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.
48、4 Alisting of the results for the exposed tested couponsfor each exposure time and the results for the unexposedmaterial.10.1.5 A listing 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 e
49、stablish trendsin the behavior.10.1.7 A statement indicating whether the fluorescent UVapparatus has been calibrated in accordance with the manufac-tures recommendations.11. Precision and Bias11.1 The precision of the test is being evaluated.12. Keywords12.1 accelerated; fluorescent UV; geomembrane; tempera-ture; ultravioletD7238 06 (2017)3ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity
copyright@ 2008-2019 麦多课文库（www.mydoc123.com）网站版权所有
备案/许可证编号：苏ICP备17064731号-1