1、Designation: D 3826 98 (Reapproved 2002)Standard Practice forDetermining Degradation End Point in DegradablePolyethylene and Polypropylene Using a Tensile Test1This standard is issued under the fixed designation D 3826; the number immediately following the designation indicates the year oforiginal a
2、doption or, in the case of revision, the year of last revision. A number 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 practice covers the determination of a degradation-end point (a
3、 brittle point) for degradable polyethylene/polypropylene films and sheeting less than 1.0 mm (0.04 in.)thick. This practice is not intended for determination of the rateof degree of degradation of a polyethylene/polypropylene filmor sheet, but rather, to assess when in the course of itsdegradation
4、under some condition, a brittle point is reached. Ifone wishes to monitor tensile elongation during the degrada-tion process (such as when the tensile elongation is signifi-cantly greater than 5 %), Test Method D 882 is recommended.This practice should not be considered the only way ofdetermining a
5、degradation-end point.1.2 Tensile properties of plastics 1.0 mm (0.04 in.) orgreater in thickness shall be determined in accordance withTest Method D 638.1.3 Use a static weighing-constant rate of grip separationtest. This procedure employs a constant rate of separation ofthe grips holding the sampl
6、e and a static load cell.NOTE 1This procedure is based on the use of grip separation as ameasure of extension; however, the desirability of using extensionindicators accurate to 61.0 % or better as specified in Test Method D 638is recognized, and a provision for the use of such instrumentation isinc
7、orporated in the procedure.1.4 This procedure has been successful for determining thedegradation end point of ethylene-carbon-monoxide copoly-mers and has screened successfully two other additive-typepolyethylenes in a round robin test.1.5 The values stated in SI units are to be regarded as thestand
8、ard. The values in parentheses are for information only.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 safety and health practices and determine the applica-bilit
9、y of regulatory limitations prior to use.1.7 There is no equivalent ISO standard.2. Referenced Documents2.1 ASTM Standards:D 374 Test Methods for Thickness of Solid Electrical Insu-lation2D 618 Practice for Conditioning Plastics and Electric Insu-lating Materials for Testing3D 638M Test Method for T
10、ensile Properties of PlasticsMetric3D 882 Test Methods for Tensile Properties of Thin PlasticSheeting3D 5208 Practice for Operating Fluorescent UV and Conden-sation Apparatus for Exposure of Photodegradable Plas-tics4E 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of
11、 a Test Method53. Terminology3.1 Definitions:3.1.1 Definitions of terms and symbols relating to tensiontesting of plastics appear in the Annex to Test Method D 638.3.1.2 line grips, nin tensile testing machines, grips havingfaces designed to concentrate the entire gripping force along asingle line p
12、erpendicular to the direction of testing stress.3.1.3 tear failure, nin tensile testing of films, a failurecharacterized by fracture initiating at one edge of the specimenand progressing across the specimen at a rate slow enough toproduce an anomalous load-deformation curve.3.2 Description of Terms
13、Specific to This Standard:3.2.1 film, nfor the purpose of this practice, a piece ofmaterial not exceeding 0.250 mm (0.01 in.) in thickness.3.2.2 brittle point, nin degradable polyethylene/polypropylene film, that point in the history of a material when75 % of the specimens tested have a tensile elon
14、gation at breakof 5 % or less.1This practice is under the jurisdiction of ASTM Committee D20 on Plastics andis the direct responsibility of Subcommittee D20.96 on Environmentally DegradablePlastics.Current edition approved April 10, 1998. Published January 1999. Originallypublished as D 3826 91. Las
15、t previous edition D 3826 91e1.2Annual Book of ASTM Standards, Vol 10.01.3Annual Book of ASTM Standards, Vol 08.01.4Annual Book of ASTM Standards, Vol 08.03.5Annual Book of ASTM Standards, Vol 14.02.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,
16、United States.4. Significance and Use4.1 The tensile elongation property determined by thispractice is of value for the characterization of degradablematerials. The tensile elongation property may vary withspecimen thickness, method of preparation, speed of testing,type of grips used, and manner of
17、measuring test extension.Consequently, where precise comparative results are desired,these factors must be carefully controlled.4.2 The tensile elongation property may be utilized toprovide data for research and development and engineeringdesign as well as quality control specifications. However, da
18、tafrom such tests cannot be considered significant for applica-tions differing widely from the load-time scale of the testemployed.4.3 Materials that fail by tearing give anomalous data thatcannot be compared with those from normal failure.4.4 Before proceeding with this test method, referenceshould
19、 be made to the specifications of the material beingtested. Any test specimen preparation, conditioning, dimen-sions, or testing parameters or a combination thereof, coveredin the material specifications shall take precedence over thosementioned in this test method. If there are no materialspecifica
20、tions, then the default conditions apply.5. Apparatus5.1 Testing Machines:5.1.1 Use a testing machine of the constant rate-of-jaw-separation type. The machine shall be equipped with a weigh-ing system that moves a maximum distance of 2 % of thespecimen extension within the range being measured. Also
21、,there should be a device for recording the tensile load and theamount of separation of the grips; both of these measuringsystems shall be accurate to 62 %. The rate of separation ofthe grips shall be uniform and capable of adjustment fromapproximately 1.3 to 500 mm/min (0.05 to 20 in./min) inincrem
22、ents necessary to produce the strain rates specified in9.2.5.2 GripsUse a gripping system that minimizes bothslippage and uneven stress distribution with the test specimen.NOTE 2Grips lined with thin rubber, crocus-cloth, or pressure-sensitive tape as well as file-faced or serrated grips have been s
23、uccessfullyused for many materials. The choice of grip surface depends on thematerial tested and thickness. More recently, line grips padded on theround face with 1.0 mm (40 mil) blotting paper have been found superior.Air-actuated grips have been found advantageous, particularly in the caseof mater
24、ials that tend to neck into the grips, since pressure is maintainedat all times. In cases where samples frequently fail at the edge of the grips,it may be advantageous to increase slightly the radius of curvature of theedges where the grips come in contact with the test area of the specimen.5.3 Thic
25、kness GageA dead-weight dial micrometer asprescribed in Method C of Test Methods D 374, reading to0.0025 mm (0.0001 in.) or less.5.4 Width-Measuring DevicesSuitable test scales or otherwidth-measuring devices capable of reading to 0.25 mm (0.010in.) or less.5.5 Specimen CutterFixtures incorporating
26、razor blades,suitable paper cutters, or other devices capable of safely cuttingthe specimens to the proper width and producing straight,clean, parallel edges with no visible imperfections. A deviceconsisting of two parallel knives mounted firmly against aprecision-ground base shear-block (similar to
27、 a paper cutter)has proved satisfactory. The use of striking dies is notrecommended because poor and inconsistent specimen edgesmay be produced. It is imperative that the cutting edges be keptsharp and free from visible scratches or nicks.5.6 Extension IndicatorsIf employed, extension indica-tors sh
28、all conform to requirements specified in Test Method D638. In addition, such apparatus shall be so designed as tominimize stress on the specimen at the contact points of thespecimen and the indicator.NOTE 3A high-response speed in the recording system is desirable,particularly when relatively high s
29、train rates are employed for rigidmaterials. The speed of pen response for recorders is supplied bymanufacturers of this equipment. Take care to conduct tests at conditionssuch that response time (ability of recorder to follow actual load) producesless than 2 % error.6. Test Specimen6.1 Cut test spe
30、cimens prior to exposure. Take utmost carein cutting specimens to prevent nicks and tears that are likelyto cause premature failures (see Note 4). The edges shall beparallel to within 5 % of the width over the length of thespecimen between the grips.NOTE 4A microscopic examination of the specimen ma
31、y be used todetect flaws due to sample or specimen preparation.6.2 Prepare the test specimen with uniform width andlength. Examples of typical lengths and widths are:Width, mm Length, mm13 (0.5 in.) 152 (6 in.)25 (1.0 in.) 102 (4 in.)6.2.1 The test specimen thickness is contingent upon thethickness
32、of the end-use application. The test specimen thick-ness should be the same as that for the specific end-useapplication.6.3 Wherever possible, select test specimen so that thick-ness is uniform to within 10 % of the thickness over the lengthof the specimen between the grips in the case of materials
33、0.25mm/in. (0.010 in.) or less in thickness, and to within 5 % in thecase of materials greater than 0.25 mm (0.010 in.) in thicknessbut less than 1.00 mm (0.040 in.) in thickness.NOTE 5In cases where thickness variations are in excess of thoserecommended in 6.3, results may not be characteristic of
34、the materialunder test.6.4 Whenever possible, cut test specimens and test in themachine direction only.7. Number of Test Specimens7.1 Take sufficient test specimens in the machine directionfrom each sample to ensure four acceptable measurements (see4.3, 7.2). Samples that break during degradation ex
35、posure canbe deemed to have absolute tensile elongations of less than 5 %(see 10.2).NOTE 6When exposing samples (especially outdoors) they will some-times break up, and tensile tests can not be properly performed. For thisreason, broken samples are deemed to have reached 5 % absoluteelongation for t
36、he purpose of determining the brittle point.D 3826 98 (2002)27.2 Discard specimens that fail at some obvious flaw, or thatfail outside the gage length, unless such flaws or conditionsconstitute a variable whose effect is being studied. However,jaw breaks (failures at the grip contact point) are acce
37、ptable ifit has been shown that results from such tests are in essentialagreement with values obtained from breaks occurring withinthe gage length.NOTE 7In the case of some materials, examination of specimens priorto and following testing under crossed optical polarizers (polarizing films)provides a
38、 useful means of detecting flaws which may be responsible forpremature failure.8. Conditioning8.1 ConditioningCondition the test specimens at23 6 2C (73.4 6 3.6F) and 50 6 5 % relative humidity fornot less than 40 h prior to test in accordance with Procedure Aof Practice D 618.8.2 Test ConditionsCon
39、duct tests in the standard labora-tory atmosphere of 23 6 2C (73.4 6 3.6F) and 50 6 5%relative humidity.9. Procedure9.1 Set the initial grip separation that is appropriate for thedimensions of the test specimen.9.2 Set the rate of grip separation to provide an initial strainrate of 0.1 mm/mm min.9.3
40、 Measure the thickness to an accuracy of 0.0025 mm(0.0001 in.) or better or films less than 0.25 mm (0.010 in.) inthickness and to an accuracy of 1 % or better for specimensgreater than 0.25 mm (0.010 in.) but less than 1.0 mm (0.040in.) in thickness.9.4 Place the test specimen in the grips of the t
41、estingmachine, taking care to align the long axis of the specimenwith an imaginary line joining the points of attachment of thegrips to the machine. Tighten the grips evenly and firmly to thedegree necessary to minimize slippage of the specimen duringthe test.10. Calculation10.1 Calculate the percen
42、tage elongation at break by divid-ing the elongation at the moment of rupture of the specimen bythe initial gage length of the specimen and multiplying by 100.When the gage marks or extensometers are used to define aspecific test section, use only this length. Report the result inpercent to two sign
43、ificant figures.10.2 The material is considered degraded to the brittle pointwhen 75 % or more of the test specimens have a tensileelongation of 5 % or less.11. Report11.1 Report the following information:11.1.1 Complete identification of the material tested, includ-ing type, source, manufacturers c
44、ode number, form, principaldimensions, previous history, and orientation of samples withrespect to anisotropy (if any),11.1.2 Method of preparing test specimens,11.1.3 Thickness, width and length of test specimens,11.1.4 Complete identification of exposure practice or pro-cedure used to degrade test
45、 specimens,11.1.5 Grip separation (initial),11.1.6 Crosshead speed (rate of grip separation),11.1.7 Gage length (if different from gage separation),11.1.8 Type of grips used, including facing (if any),11.1.9 Conditioning procedure (test conditions, tempera-ture, and relative humidity, if non-standar
46、d),11.1.10 Anomalous behavior such as tear failure and failureat a grip,11.1.11 Percentage elongation at break of each sample andthe number of samples that broke during exposure,11.1.12 Whether or not the specimens tested reached thebrittle point and the exposure time required to do so.11.1.13 Indic
47、ate whether an extensometer is employed.12. Precision and Bias12.1 A round robin conducted and analyzed according toPractice E 691 for three degradable polyolefin polymers pro-duced the repeatability and reproducibility results for tensileelongation shown in Table 1. Each laboratory tested specimens
48、that were unexposed and specimens that had been exposed for240 h according to Practice D 5208 (Cycle A).613. Keywords13.1 brittle point; degradable plastics; plastics;polyethylene/polypropylene films/sheeting; tensile elongation6Supporting data available at ASTM Headquarters. Request RR: D 20.TABLE
49、1 Tensile Elongation at Break Determined According to Practice D 3826Material Tested AverageRepeatability StandardDeviation, SrReproducibility StandardDeviation, SRRepeatability Limit,rReproducibility Limit,RECO,Aunexposed 282.4 41.6 138.8 166.8 388.7ECO, exposed 240 hB2.5 1.8 2.1 5.1 6.0clear LLDPE,Cunexposed 371.4 40.1 231.3 112.3 647.7clear LLDPE, exposed 240 hB6.5 5.1 5.8 14.2 16.3white LLDPE, unexposed 235.4 34.3 146.5 96.0 410.2white LLDPE, exposed 240 hB1.4 0.5 1.0 1.4 2.6AECO material is an ethylene/CO polymer that is known to degrade under UV expos
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