ASTM D7444-11
(Practice)Standard Practice for Heat and Humidity Aging of Oxidatively Degradable Plastics
Standard Practice for Heat and Humidity Aging of Oxidatively Degradable Plastics
SIGNIFICANCE AND USE
Since the correlation between the conditions specified in this practice and actual disposal environments (for example, composting, soil or landfill) has not been determined or established, the test results are to be used only for comparative and ranking purposes in the laboratory. No extrapolation to real world disposal expectations or predictions are to be made from results obtained by this procedure. Real world evaluations and correlations are needed for such claims.
Degradable plastics exposed to heat and humidity are subject to many types of physical and chemical changes. The severity of the exposures in both time, temperature and humidity level, determines the extent and type of change that occurs. For example, short exposure times at elevated temperatures generally serve to shorten the induction period of oxidatively degradable plastics during which the depletion of antioxidants and stabilizers occurs. Physical properties, such as tensile and impact strength and elongation and modulus, sometimes change during this induction period; however, these changes are generally not due to molecular-weight degradation, but are merely a temperature-dependent response, such as increased crystallinity or loss of volatile material, or both. The effects of humidity are less well understood and are more difficult to predict and depend on the degradable plastics characteristics such as hydrophilicity, polarity and composition.
Generally, short exposures at elevated temperatures drive out volatiles such as moisture, solvents, or plasticizers; relieve molding stresses; advance the cure of thermosets; increase crystallinity; and cause some change in color of the plastic or coloring agent, or both. Normally, additional shrinkage is expected with a loss of volatiles or advance in polymerization.
Some plastic materials such as PVC become brittle due to loss of plasticizers or to molecular breakdown of the polymer. Polypropylene and its copolymers tend to become very brittle as ...
SCOPE
1.1 This practice indicates how to test the oxidative degradation characteristics of plastics that degrade in the environment under atmospheric 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 plastics are suitable for or will degrade on disposal in these said environments. It is particularly noted that in real world environments such as soil, compost and landfill oxidations, if they occur, will predominantly be under conditions where other interfering ingredients are present and, in the case of landfill, at sub-atmospheric oxygen concentrations. This practice, therefore, can only result in a relative ordering of the potential for oxidation of plastic materials under the conditions tested, which are not always reflective of their behavior in a particular real world disposal systems. Prediction of the oxidation of a plastic under real world disposal conditions is an essential further testing in appropriate methodologies, such as Test Method D5338 for composting. No claims can be 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 temperatures in air at atmospheric pressure under controlled humidity levels for extended periods of time. The humidity levels and temperature ranges are selected to be within the variable recorded seasonal ranges (upper and lower levels) generally observed in disposal sites where such plastics are discarded. For example: soil (15 to 40 percent moisture); landfill (35 to 60 percent moisture), and compost (45 to 70 percent moisture). It is optional to expose the plastic at zero humidity, if comparison with specified humidity ranges is of interest. Only the procedures for heat and humidity exposures are specifie...
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Designation: D7444 − 11
Standard Practice for
Heat and Humidity Aging of Oxidatively Degradable
1
Plastics
This standard is issued under the fixed designation D7444; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope particular property is determined by selection of the appropri-
atetestmethodandspecimen;however,itisrecommendedthat
1.1 This practice indicates how to test the oxidative degra-
Practice D3826 be used to determine the embrittlement
dation characteristics of plastics that degrade in the environ-
endpoint, which is defined as that point in the history of a
ment under atmospheric pressure and thermal and humidity
material when 75% of the specimens tested have a tensile
simulations, only, in the absence of any selected disposal
elongation at break of 5% or less at an initial strain rate of 0.1
environment such as soil, landfill, or compost. This practice
mm/mm min.
does not by any extension or extrapolation of data or results
generated indicate that such plastics are suitable for or will
1.3 This practice is used to compare the effects of heat and
degrade on disposal in these said environments. It is particu-
humidity at any selected temperature, such as those found in
larly noted that in real world environments such as soil,
the mentioned disposal environments, on the degradation of a
compost and landfill oxidations, if they occur, will predomi-
particularplasticbyselectionofanappropriatetestmethodand
nantly be under conditions where other interfering ingredients
specimen.
are present and, in the case of landfill, at sub-atmospheric
oxygenconcentrations.Thispractice,therefore,canonlyresult 1.4 This practice is to be used in order to apply selected
in a relative ordering of the potential for oxidation of plastic exposure conditions when comparing the thermal-aging char-
materials under the conditions tested, which are not always
acteristics at controlled humidity levels of plastic materials as
reflective of their behavior in a particular real world disposal
measured by the change in some property of interest (that is,
systems. Prediction of the oxidation of a plastic under real
embrittlement by means of loss of elongation, molecular
world disposal conditions is an essential further testing in
weight, disintegration, etc.). It is very similar to Practice
appropriate methodologies, such as Test Method D5338 for
D3045butisintendedforuseinevaluatingplasticsdesignedto
composting. No claims can be made for real world behavior
be oxidized easily after use. The exposure times used for this
based on this practice.
practice will be significantly shorter than those used for
Practice D3045
1.2 This practice is only intended to define the exposure
conditions of plastics at various temperatures in air at atmo-
1.5 The type of oven used can affect the results obtained
spheric pressure under controlled humidity levels for extended
from this practice. The user can use one of two methods for
periods of time. The humidity levels and temperature ranges
oven exposure. Do not mix the results based on one method
are selected to be within the variable recorded seasonal ranges
with those based on the other one.
(upper and lower levels) generally observed in disposal sites
where such plastics are discarded. For example: soil (15 to 40 1.6 Procedure A: Gravity-Convection Oven—
percent moisture); landfill (35 to 60 percent moisture), and Recommended for film specimens having a nominal thickness
compost (45 to 70 percent moisture). It is optional to expose not greater than 0.25 mm (0.010 in.).
the plastic at zero humidity, if comparison with specified
1.7 Procedure B: Forced-Ventilation Oven—Recommended
humidityrangesisofinterest.Onlytheproceduresforheatand
for specimens having a nominal thickness greater than 0.25
humidity exposures are specified, not the test method or
mm (0.010 in.).
specimen, necessary for the evaluation of the heat and humid-
ity exposure effects. The effect of heat and humidity on any
1.8 Thispracticerecommendsproceduresforcomparingthe
thermal and humidity aging characteristics of materials at a
single temperature under dry or selected humidity conditions.
1
ThispracticeisunderthejurisdictionofASTMCommitteeD20onPlasticsand
Recommended procedures for determining the thermal aging
isthedirectresponsibilityofSubcommitteeD20.96onEnvironmentallyDegradable
characteristics of a material at a series of temperatures and
Plastics and Biobased Products.
humidity conditions for the purpose of estimating time to a
Current edition approved March 15, 2011. Published March 2011. DOI:10.1520/
D7444-11. defined property c
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