ASTM G178-2009 Standard Practice for Determining the Activation Spectrum of a Material (Wavelength Sensitivity to an Exposure Source) Using the Sharp Cut-On Filter or Spectrographi.pdf

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1、Designation: G 178 09Standard Practice forDetermining the Activation Spectrum of a Material(Wavelength Sensitivity to an Exposure Source) Using theSharp Cut-On Filter or Spectrographic Technique1This standard is issued under the fixed designation G 178; the number immediately following the designati

2、on indicates the year oforiginal 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 practice describes the determi

3、nation of the relativeactinic effects of individual spectral bands of an exposuresource on a material. The activation spectrum is specific to thelight source to which the material is exposed to obtain theactivation spectrum. A light source with a different spectralpower distribution will produce a d

4、ifferent activation spectrum.1.2 This practice describes two procedures for determiningan activation spectrum. One uses sharp cut-on UV/visibletransmitting filters and the other uses a spectrograph todetermine the relative degradation caused by individual spec-tral regions.NOTE 1Other techniques can

5、 be used to isolate the effects ofindividual spectral bands of a light source, for example, interferencefilters.1.3 The techniques are applicable to determination of thespectral effects of solar radiation and laboratory acceleratedtest devices on a material. They are described for the UVregion, but

6、can be extended into the visible region usingdifferent cut-on filters and appropriate spectrographs.1.4 The techniques are applicable to a variety of materials,both transparent and opaque, including plastics, paints, inks,textiles and others.1.5 The optical and/or physical property changes in amater

7、ial can be determined by various appropriate methods.The methods of evaluation are beyond the scope of thispractice.1.6 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 appro-priate

8、 safety and health practices and determine the applica-bility of regulatory limitations prior to use.NOTE 2There is no ISO standard that is equivalent to this standard.2. Referenced Documents2.1 ASTM Standards:2D 256 Test Methods for Determining the Izod PendulumImpact Resistance of PlasticsD 638 Te

9、st Method for Tensile Properties of PlasticsD 822 Practice for Filtered Open-Flame Carbon-Arc Expo-sures of Paint and Related CoatingsD 1435 Practice for Outdoor Weathering of PlasticsD 1499 Practice for Filtered Open-Flame Carbon-Arc Ex-posures of PlasticsD 2244 Practice for Calculation of Color To

10、lerances andColor Differences from Instrumentally Measured ColorCoordinatesD 2565 Practice for Xenon-Arc Exposure of Plastics In-tended for Outdoor ApplicationsD 4141 Practice for Conducting Black Box and Solar Con-centrating Exposures of CoatingsD 4329 Practice for Fluorescent UV Exposure of Plasti

11、csD 4364 Practice for Performing Outdoor AcceleratedWeathering Tests of Plastics Using Concentrated SunlightD 4459 Practice for Xenon-Arc Exposure of Plastics In-tended for Indoor ApplicationsD 4508 Test Method for Chip Impact Strength of PlasticsD 4587 Practice for Fluorescent UV-Condensation Expo-

12、sures of Paint and Related CoatingsD 5031 Practice for Enclosed Carbon-Arc Exposure Testsof Paint and Related CoatingsD 6360 Practice for Enclosed Carbon-Arc Exposures ofPlasticsD 6695 Practice for Xenon-Arc Exposures of Paint andRelated CoatingsE 275 Practice for Describing and Measuring Performanc

13、eof Ultraviolet and Visible SpectrophotometersE 313 Practice for Calculating Yellowness and WhitenessIndices from Instrumentally Measured Color Coordinates1This practice is under the jurisdiction of ASTM Committee G03 on Weatheringand Durability and is the direct responsibility of Subcommittee G03.0

14、1 on JointWeathering Projects.Current edition approved April 15, 2009. Published June 2009. Originallyapproved in 2003. Last previous edition approved in 2003 as G 17803.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annu

15、al Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.E 925 Practice for Monitoring the Calibration ofUltraviolet-Visible Spectrop

16、hotometers whose SpectralSlit Width does not Exceed 2 nmG7 Practice for Atmospheric Environmental ExposureTesting of Nonmetallic MaterialsG24 Practice for Conducting Exposures to Daylight Fil-tered Through GlassG90 Practice for Performing Accelerated Outdoor Weath-ering of Nonmetallic Materials Usin

17、g Concentrated Natu-ral SunlightG113 Terminology Relating to Natural and ArtificialWeathering Tests of Nonmetallic MaterialsG 147 Practice for Conditioning and Handling of Nonme-tallic Materials for Natural and Artificial Weathering TestsG 152 Practice for Operating Open Flame CarbonArc LightApparat

18、us for Exposure of Nonmetallic MaterialsG 153 Practice for Operating Enclosed Carbon Arc LightApparatus for Exposure of Nonmetallic MaterialsG 154 Practice for Operating Fluorescent Light Apparatusfor UV Exposure of Nonmetallic MaterialsG 155 Practice for Operating Xenon Arc Light Apparatusfor Expos

19、ure of Non-Metallic Materials3. Terminology3.1 Definitions given in Terminology G113are applicableto this practice.3.2 Definitions of Terms Specific to This Standard:3.2.1 incremental degradation, n the increase in degrada-tion in the specimen exposed behind the shorter wavelengthcut-on filter of th

20、e pair due to the addition of short UVwavelengths transmitted by the filter.3.2.2 incremental ultraviolet, nthe additional short wave-length ultraviolet transmitted by the shorter wavelength cut-onfilter of the pair of sharp cut-on UV/VIS transmitting glassfilters. It is represented by the spectral

21、band (see 3.2.4).3.2.3 sharp cut-on UV/VIS transmitting glass filters,nfilters that screen out the short wavelengths and transmitradiation longer than the cut-on wavelength. The transmittanceincreases sharply from 5 %, the cut-on wavelength, to 72 %within a spectral range of about 20 nm. They are al

22、so referredto as longpass filters.3.2.4 spectral band, nthe spectral region defined by thedifference in transmittance of a pair of the sharp cut-onUV/VIS transmitting glass filters. It is also referred to as theincremental ultraviolet.3.2.5 spectral band pass, nthe spectral range of thespectral band

23、 at the delta 20 % transmittance level. It is thespectral range of the incremental ultraviolet mainly responsiblefor the incremental degradation.3.2.5.1 DiscussionThe definition of this term differs fromthat commonly applied to the spectral bandpass, also referredto as the spectral bandwidth, of a n

24、arrow band filter or theradiant energy leaving the exit slit of a monochromator. Theseterms are defined as the full width at half-maximum, FWHM,that is, the wavelength range at one half the peak height of thespectral band.3.2.6 cumulative spectral sensitivity curve, na plot of thecumulative effect o

25、n the optical or physical properties of amaterial of addition of progressively shorter wavelengths of thesource to the longer wavelength exposure with progressivedecrease in wavelength of the sharp cut-on UV/visible trans-mitting filter.4. Significance and Use4.1 The activation spectrum identifies t

26、he spectral region(s)of the specific exposure source used that may be primarilyresponsible for changes in appearance and/or physical proper-ties of the material.4.2 The spectrographic technique uses a prism or gratingspectrograph to determine the effect on the material of isolatednarrow spectral ban

27、ds of the light source, each in the absenceof other wavelengths.4.3 The sharp cut-on filter technique uses a specially de-signed set of sharp cut-on UV/visible transmitting glass filtersto determine the relative actinic effects of individual spectralbands of the light source during simultaneous expo

28、sure towavelengths longer than the spectral band of interest.4.4 Both the spectrographic and filter techniques provideactivation spectra, but they differ in several respects:4.4.1 The spectrographic technique generally provides bet-ter resolution since it determines the effects of narrowerspectral p

29、ortions of the light source than the filter technique.4.4.2 The filter technique is more representative of thepolychromatic radiation to which samples are normally ex-posed with different, and sometimes antagonistic, photochemi-cal processes often occurring simultaneously. However, sincethe filters

30、only transmit wavelengths longer than the cut-onwavelength of each filter, antagonistic processes by wave-lengths shorter than the cut-on are eliminated.4.4.3 In the filter technique, separate specimens are used todetermine the effect of the spectral bands and the specimens aresufficiently large for

31、 measurement of both mechanical andoptical changes. In the spectrographic technique, except in thecase of spectrographs as large as the Okazaki type (1),3a singlesmall specimen is used to determine the relative effects of allthe spectral bands. Thus, property changes are limited to thosethat can be

32、measured on very small sections of the specimen.4.5 The information provided by activation spectra on thespectral region of the light source responsible for the degrada-tion in theory has application to stabilization as well as tostability testing of polymeric materials (2).4.5.1 Activation spectra

33、based on exposure of the unstabi-lized material to solar radiation identify the light screeningrequirements and thus the type of ultraviolet absorber to use foroptimum screening protection. The closer the match of theabsorption spectrum of a UV absorber to the activationspectrum of the material, the

34、 more effective the screening.However, a good match of the UV absorption spectrum of theUV absorber to the activation spectrum does not necessarilyassure adequate protection since it is not the only criteria forselecting an effective UV absorber. Factors such as dispersion,compatibility, migration a

35、nd others can have a significantinfluence on the effectiveness of a UV absorber (see Note 3).The activation spectrum must be determined using a light3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.G178092source that simulates the spectral power distrib

36、ution of the oneto which the material will be exposed under use conditions.NOTE 3In a study by ASTM G03.01, the activation spectrum of acopolyester based on exposure to borosilicate glass-filtered xenon arcradiation predicted that UV absorber A would be superior to UV absorberB in outdoor use becaus

37、e of stronger absorption of the harmful wave-lengths of solar simulated radiation. However, both additives protected thecopolyester to the same extent when exposed either to xenon arc radiationor outdoors.4.5.2 Comparison of the activation spectrum of the stabi-lized with that of the unstabilized ma

38、terial provides informa-tion on the completeness of screening and identifies anyspectral regions that are not adequately screened.4.5.3 Comparison of the activation spectrum of a materialbased on solar radiation with those based on exposure to othertypes of light sources provides information useful

39、in selectionof the appropriate artificial test source. An adequate match ofthe harmful wavelengths of solar radiation by the latter isrequired to simulate the effects of outdoor exposure. Differ-ences between the natural and artificial source in the wave-lengths that cause degradation can result in

40、different mecha-nisms and type of degradation.4.5.4 Published data have shown that better correlations canbe obtained between natural weathering tests under differentseasonal conditions when exposures are timed in terms of solarUV radiant exposure only rather than total solar radiantexposure. Timing

41、 exposures based on only the portion of theUV identified by the activation spectrum to be harmful to thematerial can further improve correlations. However, while it isan improvement over the way exposures are currently timed, itdoes not take into consideration the effect of moisture andtemperature.4

42、.6 Over a long test period, the activation spectrum willregister the effect of the different spectral power distributionscaused by lamp or filter aging or daily or seasonal variation insolar radiation.4.7 In theory, activation spectra may vary with differencesin sample temperature. However, similar

43、activation spectrahave been obtained at ambient temperature (by the spectro-graphic technique) and at about 65C (by the filter technique)using the same type of radiation source.5. Activation Spectrum Procedure Using Sharp Cut-OnFilter Technique5.1 Spectral Bands of Irradiation:5.1.1 Select glass typ

44、es for the sharp cut-on UV/visibletransmitting glass filters which provide a spectral shift ofapproximately 10 nm at 40 % transmittance between filter pairswhen ground to appropriate thicknesses. It may be necessary touse filters from more than one source. The exact thickness towhich each filter is

45、ground is governed by the incrementalultraviolet transmitted by the shorter wavelength filter of thepair. Adjust the thicknesses so that the incremental ultravioletis within 10 % of the average of the incremental ultraviolet ofall filter pairs. The method for determining the incrementalultraviolet i

46、s described in 5.1.3.NOTE 4Typically, 12 or 13 filters with cut-on wavelengths rangingfrom 265 to 375 nm are used to determine the effects of 10 spectral bands,each approximately 20 nm wide, in the solar UV region. A larger set offilters can be used to reduce the width of each spectral band, but it

47、wouldextend the time required to produce degradation by each of the spectralregions. The filter size is normally 2 by 2 in., but other sizes up to 6 by 6in. can be used.NOTE 5The spectral transmittance curves of a typical set of filters areshown in Figs. X1.1 and X1.2 in the Appendix.NOTE 6Due to va

48、riations in the melt of each glass type, the filter typesand thicknesses used for one filter set may not be applicable to other sets.5.1.2 Spectral Transmittance Data:5.1.2.1 Use a UV/visible spectrophotometer that produceseither digital data or an analog curve to measure the spectraltransmittance o

49、f each filter from the spectral region of com-plete blocking at the short wavelength end to maximumtransmittance at the long wavelength end.5.1.2.2 Determine the wavelength calibration and linearityof the spectrophotometer as described in either Practice E 275or E 925. Check the 0 % and 100 % baselines and adjust, ifnecessary, according to manufacturers recommendations. Ifthe 100 % baseline is not flat in the spectral region in which thefilters are measured, correct the data. In the case of analogcurves, use sufficient chart expansion to allow accurate trans-mittance va