1、Designation: D7444 18D7444 18aStandard Practice forHeat and Humidity Aging of Oxidatively DegradablePlastics1This standard is issued under the fixed designation D7444; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of las
2、t revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice indicates how to test the oxidative degradation characteristics of plastics that degrade in the environmen
3、t underatmospheric pressure and thermal and humidity simulations, only, in the absence of any selected disposal environment such as soil,landfill, or compost. This practice does not by any extension or extrapolation of data or results generated indicate that such plasticsare suitable for or will deg
4、rade on disposal in these said environments. It is particularly noted that in real world environments suchas soil, compost and landfill oxidations, if they occur, will predominantly be under conditions where other interfering ingredientsare present and, in the case of landfill, at sub-atmospheric ox
5、ygen concentrations. This practice, therefore, can only result in arelative ordering of the potential for oxidation of plastic materials under the conditions tested, which are not always reflective oftheir behavior in a particular real world disposal systems. Prediction of the oxidation of a plastic
6、 under real world disposalconditions is an essential further testing in appropriate methodologies, such as Test Method D5338 for composting. No claims canbe made for real world behavior based on this practice.1.2 This practice is only intended to define the exposure conditions of plastics at various
7、 temperatures in air at atmosphericpressure under controlled humidity levels for extended periods of time. The humidity levels and temperature ranges are selectedto be within the variable recorded seasonal ranges (upper and lower levels) generally observed in disposal sites where such plasticsare di
8、scarded. For example: soil (15 to 40 percent moisture); landfill (35 to 60 percent moisture), and compost (45 to 70 percentmoisture). It is optional to expose the plastic at zero humidity, if comparison with specified humidity ranges is of interest. Onlythe procedures for heat and humidity exposures
9、 are specified, not the test method or specimen, necessary for the evaluation of theheat and humidity exposure effects. The effect of heat and humidity on any particular property is determined by selection of theappropriate test method and specimen; however, it is recommended that Practice D3826 be
10、used to determine the embrittlementendpoint, which is defined as that point in the history of a material when 75 % of the specimens tested have a tensile elongationat break of 5 % or less at an initial strain rate of 0.1 mm/mm min.1.3 This practice is used to compare the effects of heat and humidity
11、 at any selected temperature, such as those found in thementioned disposal environments, on the degradation of a particular plastic by selection of an appropriate test method andspecimen.1.4 This practice is to be used in order to apply selected exposure conditions when comparing the thermal-aging c
12、haracteristicsat controlled humidity levels of plastic materials as measured by the change in some property of interest (that is, embrittlementby means of loss of elongation, molecular weight, disintegration, etc.). It is very similar to Practice D3045 but is intended for usein evaluating plastics d
13、esigned to be oxidized easily after use. The exposure times used for this practice will be significantly shorterthan those used for Practice D30451.5 The type of oven used can affect the results obtained from this practice. The user can use one of two methods for ovenexposure. Do not mix the results
14、 based on one method with those based on the other one.1.6 Procedure A: Gravity-Convection OvenRecommended for film specimens having a nominal thickness not greater than0.25 mm (0.010 in.).1.7 Procedure B: Forced-Ventilation OvenRecommended for specimens having a nominal thickness greater than 0.25
15、mm(0.010 in.).1.8 This practice recommends procedures for comparing the thermal and humidity aging characteristics of materials at a singletemperature under dry or selected humidity conditions. Recommended procedures for determining the thermal aging characteristics1 This practice is under the juris
16、diction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.96 on Environmentally DegradablePlastics and Biobased Products.Current edition approved July 1, 2018Sept. 15, 2018. Published August 2018October 2018. Originally approved in 2011. Last previous edition app
17、roved in 20112018 asD744411. DOI:10.1520/D7444-18.18. DOI:10.1520/D7444-18A.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately
18、 depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM Intern
19、ational, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1of a material at a series of temperatures and humidity conditions for the purpose of estimating time to a defined property changeat some lower temperature are also described. This practice does not predict t
20、hermal aging characteristics where interactionsbetween stress, environment, temperature, and time control failure.1.9 The values stated in SI units are to be regarded as the standard.1.10 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathem
21、aticalconversions to SI units that are provided for information only and are not considered standard.NOTE 1There is no known ISO equivalent to this standard.1.11 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the De
22、cision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D618 Practice for Conditioning Plastics for TestingD883 Terminology Relating to
23、 PlasticsD3045 Practice for Heat Aging of Plastics Without LoadD3593 Test Method for Molecular Weight Averages/ Distribution of Certain Polymers by Liquid Size-Exclusion Chromatog-raphy (Gel Permeation Chromatography GPC) Using Universal Calibration (Withdrawn 1993)3D3826 Practice for Determining De
24、gradation End Point in Degradable Polyethylene and Polypropylene Using a Tensile TestD5032 Practice for Maintaining Constant Relative Humidity by Means of Aqueous Glycerin SolutionsD5338 Test Method for Determining Aerobic Biodegradation of Plastic Materials Under Controlled Composting Conditions,In
25、corporating Thermophilic TemperaturesD6954 Guide for Exposing and Testing Plastics that Degrade in the Environment by a Combination of Oxidation andBiodegradationE104 Practice for Maintaining Constant Relative Humidity by Means of Aqueous SolutionsE145 Specification for Gravity-Convection and Forced
26、-Ventilation Ovens3. Terminology3.1 DefinitionsThe definitions used in this practice are in accordance with Terminology D883.4. Significance and Use4.1 Since the correlation between the conditions specified in this practice and actual disposal environments (for example,composting, soil or landfill)
27、has not been determined or established, the test results are to be used only for comparative and rankingpurposes in the laboratory. No extrapolation to real world disposal expectations or predictions are to be made from results obtainedby this procedure. Real world evaluations and correlations are n
28、eeded for such claims.4.2 Degradable plastics exposed to heat and humidity are subject to many types of physical and chemical changes. The severityof the exposures in both time, temperature and humidity level, determines the extent and type of change that occurs. For example,short exposure times at
29、elevated temperatures generally serve to shorten the induction period of oxidatively degradable plasticsduring which the depletion of antioxidants and stabilizers occurs. Physical properties, such as tensile and impact strength andelongation and modulus, sometimes change during this induction period
30、; however, these changes are generally not due tomolecular-weight degradation, but are merely a temperature-dependent response, such as increased crystallinity or loss of volatilematerial, or both. The effects of humidity are less well understood and are more difficult to predict and depend on the d
31、egradableplastics characteristics such as hydrophilicity, polarity and composition.4.3 Generally, short exposures at elevated temperatures drive out volatiles such as moisture, solvents, or plasticizers; relievemolding stresses; advance the cure of thermosets; increase crystallinity; and cause some
32、change in color of the plastic or coloringagent, or both. Normally, additional shrinkage is expected with a loss of volatiles or advance in polymerization.4.4 Some plastic materials such as PVC become brittle due to loss of plasticizers or to molecular breakdown of the polymer.Polypropylene and its
33、copolymers tend to become very brittle as molecular degradation occurs, whereas polyethylene tends tobecome soft and weak before it embrittles with resultant loss in tensile strength and elongation.4.5 Embrittlement of a material is not necessarily commensurate with a decrease in molecular weight. T
34、est Method D3593 isused to characterize any molecular-weight changes that are suspected to have occurred during thermal exposure.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume informatio
35、n, refer to the standards Document Summary page on the ASTM website.D7444 18a24.6 The degree of change observed will depend on the property measured. Different properties do not change at the same rate.In most cases, ultimate properties, such as break strength or break elongation, are more sensitive
36、 to degradation than bulkproperties such as modulus.4.7 Effects of exposure can be quite variable, especially when samples are exposed for long intervals of time. Factors that affectthe reproducibility of data are the degree of temperature control of the enclosure, humidity level of the oven, air ve
37、locity over thespecimen, and exposure period which are evaluated by this practice. Errors in exposure are cumulative with time; for examplecertain materials have the potential to be degraded due to the influence of humidity rather than oxidation in long-term tests andthus give misleading results. Ma
38、terials susceptible to hydrolysis (that is, hydrolytically degradable plastics) undergo degradationwhen subjected to long-term thermal tests due to the presence of moisture rather than oxidation.4.8 Do not infer that comparative material ranking is undesirable or unworkable. On the contrary, this pr
39、actice is designed toprovide information that can be used for such comparative purposes after appropriate physical property tests are performedfollowing exposure. However, since it does not account for the influence of stress or environment that is involved in most real lifeapplications, the informa
40、tion obtained from this practice must be used cautiously by the designer, who must inevitably makematerial choices using additional information, such as moisture, soil-type and composition, and mechanical-action effects that areconsistent with the requirements of the particular application.4.9 It is
41、 possible for many temperature indices to exist, in fact, one for each failure criterion (time to reach failure is dependenton the exposure temperature and humidity). Therefore, for any application of the temperature index to be valid, the thermal-agingprogram must duplicate the intended exposure co
42、nditions of the end product. If the plastic material is exposed in the end use ina manner not evaluated in the aging program, the temperature index thus derived is not applicable to the use of the plastic material.4.10 In some situations, a material can be exposed to one temperature and humidity, fo
43、r a particular period of time, followedby exposure to another temperature at the same humidity, for a particular period of time. This practice can be used for suchapplications. The heat-aging curve of the first temperature and humidity is derived, followed by derivation of the heat-aging curvefor th
44、e second temperature at the same humidity, after exposure of samples to the first temperature and humidity.4.11 There can be very large errors when Arrhenius plots or equations based on data from experiments at a series oftemperatures and humidity are used to estimate time to produce a defined prope
45、rty change at some lower temperature.This estimateof time to produce the property change or failure must always be accompanied by a 95 % confidence interval for the range of timespossible based on the calculation or estimate.5. Apparatus5.1 Provisions for Conditioning, at specified standard conditio
46、ns.5.2 Oven Type:5.2.1 Gravity-Convection OvenRecommended for film specimens having a nominal thickness not greater than 0.25 mm(0.010 in.).5.2.2 Forced-Ventilation OvenRecommended for specimens having a nominal thickness greater than 0.25 mm (0.010 in.).When it is necessary to avoid contamination a
47、mong specimens or materials, it is desirable to use a tubular-oven procedure, suchas described in Specification E145, in accordance with Type 1A and Type IIB, with 50 6 10 air changes/h and the requirementsfor uniformity extended to include the range of test temperatures. Recording instrumentation t
48、o monitor the temperature andhumidity of exposure is recommended.5.3 Specimen RackA specimen rack or frame of suitable design to allow ready air circulation around the specimens.5.4 Relative Humidity Control:5.4.1 The chamber shall be able to control relative humidity to within 65 % when the set poi
49、nt temperature has an operationaltolerance of 61C.5.4.2 Relative humidity at different temperatures can be controlled within a narrow range by using saturated aqueous solutionsin accordance with Practice E104 or Practice D5032.6. Test Specimen6.1 The number and type of test specimens required shall be in accordance with theASTM test method for the specific propertyto be determined; this requirement must be met at each time and temperature and humidity selected. Unless otherwise specifiedor agreed upon by all interested parties, expose a minimum of three replicates of each
