【AS澳大利亞標(biāo)準(zhǔn)】AS 4828.2-2008 Degradability of plastics—Methods of test Method 2 Determination of brittle point in plastic film using a tensile elongation

as 4828.220081 as 4828.22008australian standarddegradability of plasticsmethods of testmethod 2: determination of brittle point in plastic film using a tensile elongation testprefacethis standard was prepared by standards australia committee ev-017, degradability ofplastics.this standard forms a part of a series of test methods and performance standards to enable certification bodies to validate and if appropriate, support claims. test methods in the series include:as4828degradability of plasticsmethods of test4828.1method 1: determination of level of prodegradant ions4828.2method 2: determination of brittle point in plastic film using a tensile elongation test4828.3method 3: test method for ultraviolet laboratory exposure of degradable plastics4828.4method 4: test method for heat aging of degradable plastics4828.5method 5: outdoor exposure testing of degradable plasticsthis standard is based on but not equivalent to astm d3826, standard practice for determining degradation end point in degradable polyethylene and polypropylene using a tensile .au5as 4828.22008forewordsome plastics contain chemical additives that, when exposed to sufficient levels of ultraviolet radiation, or heat, accelerate the oxidation of the polymer and thus promote the degradation of the physical properties of the plastic, ultimately leading to disintegration.the tensile elongation property determined by this test method is of value for the characterization of degradable plastics. the tensile elongation property may vary with specimen thickness, method of preparation, speed of testing, type of grips used, and manner of measuring test extension. consequently, where precise comparative results are desired, these factors must be carefully controlled.the tensile elongation property may be utilized to provide data for research and development and engineering design as well as quantity control specifications. however, data from such tests cannot be considered significant for application differing widely from the load-time scale of the test employed.materials that fail by tearing give anomalous data that cannot be compared with those from normal failure.before proceeding with this test method, reference should be made to the specifications of the material being tested. any test specimen preparation, conditioning, dimensions, or testing parameters or a combination thereof, covered in the material specifications should take precedence over those mentioned in this test method. if there are no material specifications, then the default conditions apply.method1 scopethis standard specifies a method for the determination of a brittle point for degradable plastic films and sheeting less than 1.0 mm thick. this practice is not intended for determination of the rate of degree of degradation of a plastic film or sheet, but rather, to assess when in the course of its degradation under some condition, a brittle point is reached.this standard employs a constant rate of separation of the grips holding the sample and a static load cell.this standard is based on the use of grip separation as a measure of extension; however, the desirability of using extension indicators accurate to 1.0% or better as specified in astm d638 is recognized, and a provision for the use of such instrumentation is incorporated in the procedure.the results of this test method may be used in conjunction with the results of other test methods in this series, in particular where the plastic specimens have been exposed to ultraviolet radiation, heat and outdoor exposures, prior to testing under this standard.the results of this test method are to be used for comparative ranking of test specimens and are not to be used as a performance standard. standards a.au2 referenced documentsthe following documents are referred to in this standard: astmd374test methods for thickness of solid electrical insulationd618practice for conditioning plastics and for testingd638mtest method for tensile properties of plastics (metric)3 definitionsfor the purpose of this standard the definitions in astm d638 and those below apply.3.1 brittle pointin degradable plastic film, that point in the history of a material when 75% of the specimens tested have a tensile elongation at break of 5% or less.3.2 filma piece of material not exceeding 1.0 mm in thickness.3.3 line gripsin tensile testing machines, grips having faces designed to concentrate the entire gripping force along single line perpendicular to the direction of testing stress.3.4 tear failurein tensile testing of films, a failure characterized by fracture initiating at one edge of the specimen and progressing across the specimen at a rate slow enough to produce an anomalous load-deformation curve.4 apparatus4.1 testing machinesa testing machine of the constant rate-of-jaw-separation type. there should be a device for recording the tensile load and the amount of separation of the grips; both of these measuring systems shall be accurate to 2%. the rate of separation of the grips shall be uniform and capable of adjustment from approximately 1.3 to 500 mm/min in increments necessary to produce the strain rates specified in clause 8.4.2 gripsa gripping system that minimizes both slippage and uneven stress distribution with the test specimen.note: grips lined with thin rubber, crocus-cloth, or pressure-sensitive tape as well as file-faced or serrated grips have been successfully used for many materials. the choice of grip surface depends on the material tested and thickness. more recently, line grips padded on the round face with 1.0 mm blotting paper have been found superior. air-actuated grips have been found advantageous, particularly in the case of materials that tend to neck into the grips, since pressure is maintained at 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 the edges where the grips come in contact with the test area of the specimen.4.3 thickness gaugea dead-weight dial micrometer as prescribed in method c of astm d374, reading to0.0025 mm or less.4.4 width-measuring devicessuitable test scales or other width-measuring devices capable of reading to 0.25 mm or less.4.5 specimen cutterfixtures incorporating razor blades, suitable paper cutters, or other devices capable of safely cutting the specimens to the proper width and producing straight, clean, parallel edges with no visible imperfections. a device consisting of two parallel knives mounted firmly against a precision-ground base shear-block (similar to a paper cutter) has proved satisfactory. the use of striking dies is not recommended because poor and inconsistent specimen edges may be produced. it is imperative that the cutting edges be kept sharp and free from visible scratches or nicks.4.6 extension indicatorsif employed, extension indicators shall conform to requirements specified in astm d638. in addition, such apparatus shall be so designed as to minimize stress on the specimen at the contact points of the specimen and the indicator.note: a high-response speed in the recording system is desirable, particularly when relatively high strain rates are employed for rigid materials. the speed of pen response for recorders is supplied by manufacturers of this equipment. take care to conduct tests at conditions such that response time (ability of recorder to follow actual load) produces less than 2% error.5 test specimenstest specimens shall be cut prior to exposure. take utmost care in cutting specimens to prevent nicks and tears that are likely to cause premature failures.the edges shall be parallel to within 5% of the width over the length of the specimen between the grips.prepare the test specimen with uniform width and length. examples of typical lengths and widths are:width, mm length, mm1310225152the test specimen thickness shall be the same or greater than used or intended to be used in the specific end-use application.wherever possible, select test specimens so that thickness is uniform to within 10% of the thickness over the length of the specimen between the grips in the case of materials0.25 mm, or less in thickness, and to within 5% in the case of materials greater than0.25 mm in thickness but less than 1.00 mm thickness.note: in cases where thickness variations are in excess of those recommended above, results may not be characteristic of the material under test.whenever possible, cut test specimens and test in the machine direction only.6 number of test specimenstake sufficient test specimens in the machine direction from each sample to ensure four acceptable measurements. samples that break during degradation exposure can be deemed to have absolute tensile elongations of less than 5% (see clause 9)note: when exposing samples (especially outdoors) they will sometimes break up, and tensile tests cannot be properly performed. for this reason, broken samples are deemed to have reached5% absolute elongation for the purpose of determining the brittle point.discard specimens that fail at some obvious flaw, or that fail outside the gauge length, unless such flaws or conditions constitute a variable whose effect is being studied. however, jaw breaks (failures at the grip contact point) are acceptable if it has been shown that results from such tests are in essential agreement with values obtained from breaks occurring within the gauge length.note: in the case of some materials, examination of specimens prior to and following testing under crossed optical polarizers (polarizing films) provides a useful means of detecting flaws which may be responsible for premature failure.7 conditioning7.1 conditioningcondition the test specimens at 23 2c and 50 5% relative humidity for not less than40 h prior to test in accordance with procedure a of astm d618.7.2 test conditionsconduct tests in the standard laboratory atmosphere of 23 2c and 50 5% relative humidity.8 procedurethe procedure shall be as follows:(a) set the initial grip separation that is appropriate for the dimensions of the test specimen.(b) set the rate of grip separation to provide an initial strain rate of 100 mm/min(unexposed) and 50 mm/min (exposed).(c) measure the thickness to an accuracy of 0.0025 mm or better for films less than0.25 mm, in thickness and to an accuracy of 1% or better for specimens greater than0.25 mm but less than 1.0 mm in thickness.(d) place the test specimen in the grips of the testing machine, taking care to align the long axis of the specimen with an imaginary line joining the points of attachment of the grips to the machine. tighten the grips evenly and firmly to the degree necessary to minimize slippage of the specimen during the test.9 calculationthe percentage elongation at break shall be calculated by dividing the elongation at the moment of rupture of the specimen by the initial gauge length of the specimen and multiplying by 100. when the gauge marks or extensometers are used to define a specific test section, use only this length. report the result in percent to two significant figures.the material is considered degraded to the brittle point when 75% or more of the test specimens have a tensile elongation of 5% or less.10 reportthe following information shall be reported:(a) complete identification of the material tested, including type, level of prodegradant master-batch and other additives or master-batches, source, manufacturers code number, form, principal dimensions, previous history, and orientation of samples with respect to anisotropy (if any).(b) method of preparing test specimens.(c) thickness, width and length of test specimens.(d) complete identification of exposure practice or procedure used to degrade test specimens.(e) grip separation (initial).(f) crosshead speed (rate of grip separation).(g)gauge length (if different from gauge separation). (h)type of grips used, including facing (if any).(i) conditioning procedure (test conditions, temperature, and relative humidity, if non- standard).(j) anomalous behaviour such as tear failure and failure at a grip.(k)percentage elongation at break of each sample and the number of samples that broke during exposure.(l) whether or not the specimens tested reached the brittle point and the exposure time required to do so.(m)indicate whether an extensometer is employed.public claims should not be made or implied that a material meets this standard.7as 4828.22008notesas 4828.22008this australian standard was prepared by committee ev-017, degradability of plastics. it was approved on behalf of the council ofstandards australia on 26 february 2008 and published on 28 april 2008.the following are represented on committee ev-017: australian chamber of commerce and industryaustralian conservation foundationaustralian retailers associationdepartment of the environment and heritage (federal)keep australian beautiful national associationnsw advisory council on recreational fishingnational association of testing authorities australiapackaging council of australiaplastics and chemicals industries associationswinburne uni