It tests the exposure conditions to which plastics should be exposed to test their resistance to oxidation or other types of degradation occurring over time. Exposure to higher temperatures than the intended use temperature for extended periods of time causes polymers to age prematurely. This aging procedure can be helpful in predicting how materials will age with time. This practice plays a guiding role in comparing thermal weathering characteristics of materials as measured by the fluctuation in specific properties of interest at a single temperature.
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All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon e indicates an editorial change since the last revision or reapproval. Scope 1. Referenced Documents 2. Terminology 3.
A plastic material isnot necessarily degraded by exposure to elevated temperatures,but may be unchanged or improved. However, extendedperiods of exposure of plastics to elevated temperatures willgenerally cause some degradation, with progressive change inphysical properties. Normally, additional shrinkage should beexpected with loss of volatiles or advance in polymerization. Othertypes of plastics may become soft and sticky, either due tosorption of volatilized plasticizer or due to breakdown of thepolymer.
Different properties, mechanical or electri-cal, may not change at the same rate. Current edition approved March 10, Published April Originallyapproved in Last previous edition approved in as D — 92 Ultimate properties suchas strength or elongation are more sensitive to degradation thanbulk properties such as modulus, in most cases.
Errors inexposure are cumulative with time. Materials susceptible to hy-drolysis may undergo degradation when subjected to long-termheat resistance tests. On the contrary, this practice isdesigned to provide data which can be used for such compara-tive purposes. If the material is stressed in the end product ina manner not evaluated in the aging program, the temperatureindex thus derived is not applicable to the use of the materialin that product.
Apparatus 5. When it is necessary to avoidcontamination among specimens or materials, a tubular ovenmethod such as Practice D may be desirable. For higher temperature,Type IIA is required. Provision should be made for suspendingspecimens without touching each other or the side of thechamber. Recording instrumentation to monitor the tempera-ture of exposure is recommended.
Sampling 6. Test Specimens 7. Conditioning 8. Procedure 9. Use asufficient number of replicates of each material for eachexposure time so that results of tests used to characterize thematerial property can be compared by analysis of variance orsimilar statistical data analysis procedure.
The following procedures are recommended for selectingexposure temperatures The next higher temperature shouldproduce the same level of property change or product failure atapproximately six months.
If the suggested heat aging times in 9. In practice it is oftendifficult to estimate the effect of heat aging before obtainingtest data. Therefore, it is usually necessary to start only theshort-term heat aging at one or two temperatures until data areobtained to be used as a basis for selecting the remainder of theheat aging temperatures. Following expo-sure, condition these specimens in accordance with establishedprocedure, and then test.
If an effect of aging without heat isanticipated, likewise condition and test a parallel set or agedunexposed specimens. If necessary, establish a procedure forcooling after oven exposure. Calculation Use theresults from each replicate of each material being compared forthe analysis of variance. This time can be used forgeneral ranking of materials for temperature stability or as anestimate of the maximum expected service life at the tempera-ture selected.
Plots should beprepared in accordance with Fig. Use the regression equation to determine the exposuretime necessary to produce a predetermined level of propertychange. A plot of the residuals value of propertyretention predicted by regression equation minus actual value versus aging time must show a random distribution.
A typical plot of this type known as an Arrhenius plot isshown in Fig. An acceptable regression equation must meet the require-ments described in This is readily available from mostsoftware packages that do regression analysis. This may be based on prior knowledge of similarmaterials, and may subsequently be amended on the basis of the described short term data, as in 9.
Suggested Exposure Times: A—3, 6, 12, 24, 48 weeks; B—1, 3, 6, 12, 24 weeks; C—6, 12, 24, 48, 96 days; D—2, 4, 8, 16, 32 days. Report
More D The severity of the exposures in both time and temperature determines the extent and type of change that takes place. A plastic material is not necessarily degraded by exposure to elevated temperatures. However, extended periods of exposure of plastics to elevated temperatures will generally cause some degradation, with progressive changes in physical properties. Specific properties and failure or lifetime criteria for these properties are typically chosen for the evaluation of thermal endurance. Normally, additional shrinkage should be expected with loss of volatiles or advance in polymerization. Other types of plastics become soft and sticky, either due to sorption of volatilized plasticizer or due to breakdown of the polymer.
ASTM D3045-92 - Standard Practice for Heat Aging of Plastics Without Load