ASTM D794-93

Practice for Determining Permanent Effect of Heat on Plastics (Withdrawn 1998)

General Information

• Status: Withdrawn
• Withdrawal Date: 09-Mar-1998
• ICS: 83.080.01 - Plastics in general
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.50 - Durability of Plastics

Relations

• Referred By: ASTM F1514-19 - Standard Test Method for Measuring Heat Stability of Resilient Flooring by Color Change
• Effective Date: 29-Sep-2023

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: D 794 – 93
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Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Practice for
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Determining Permanent Effect of Heat on Plastics
This standard is issued under the fixed designation D 794; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 4. Significance and Use
1.1 This practice is intended to define the conditions for 4.1 Plastic materials exposed to heat may be subject to
testing the resistance of plastic sheet, plastic laminated mate- many types of physical and chemical changes. The severity of
rials, and molded plastics to changes in properties due to the exposures in both time and temperature determines the
exposure at elevated temperatures. Only the procedure for heat extent and type of change that takes place. A plastic material is
exposure is specified, and not the test method or specimen. The not necessarily degraded by exposure to elevated temperatures,
effect of heat on any property may be determined by selection but may be unchanged or improved. However, extended
of an appropriate test method and specimen. periods of exposure of plastics to elevated temperatures will
1.2 This standard does not purport to address all of the generally cause some degradation, with progressive change in
safety problems, if any, associated with its use. It is the physical properties.
responsibility of the user of this standard to establish appro- 4.2 Generally, short exposures at elevated temperatures may
priate safety and health practices and determine the applica- drive out volatiles such as moisture, solvents, or plasticizers,
bility of regulatory limitations prior to use. relieve molding stresses, advance the cure of thermosets, and
may cause some change in color of the plastic or coloring
NOTE 1—There is no similar or comparable ISO standard.
agent, or both. Normally, additional shrinkage should be
expected with loss of volatiles or advance in polymerization.
2. Referenced Documents
4.3 Some plastic materials may become brittle due to loss of
2.1 ASTM Standards:
plasticizers after exposure at elevated temperatures. Other
D 495 Test Method for High-Voltage, Low-Current, Dry
2 types of plastics may become soft and sticky, either due to
Arc Resistance of Solid Electrical Insulation
sorption of volatilized plasticiser or due to breakdown of the
D 618 Practice for Conditioning Plastics and Electrical
3 polymer.
Insulating Materials for Testing
4.4 The degree of change observed will depend on the
D 756 Practice for Determination of Weight and Shape
property measured. Mechanical or electrical properties may not
Changes of Plastics Under Accelerated Service Condi-
3 change at the same rate. For instance, the arc resistance, see
tions
Test Method D 495, of thermosetting compounds improves up
D 790 Test Methods for Flexural Properties of Unreinforced
to the carbonization point of the material. Mechanical proper-
and Reinforced Plastics and Electrical Insulating Materi-
3 ties, such as flexural properties, see Test Methods D 790, are
als
3 sensitive to heat degradation and should be included in the test
D 883 Terminology Relating to Plastics
program.
D 1870 Practice for Elevated Temperature Aging Using a
4 4.5 Effects of exposure may be quite variable, especially
Tubular Oven
when specimens are exposed for long intervals of time. Factors
E 145 Specification for Gravity-Convection and Forced-
5 that affect the reproducibility of data are the degree of
Ventilation Ovens
temperature control of the enclosure, the type of molding, cure,
3. Terminology humidity of the oven room, air velocity over the specimen, and
period of exposure. Errors in exposure are cumulative with
3.1 Definitions: Definitions of terms applying to this prac-
time. Unless the effect of the molding procedure is a variable
tice appear in Terminology D 883.
under investigation, transfer or injection molding is recom-
mended as the trapped air and volatiles have a better chance to
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escape. Incompletely cured thermosets tend to blister or crack
This practice is under the jurisdiction of ASTM Committee D-20 on Plastics
and is the direct responsibility of Subcommittee D20.50 on Permanence Properties.
when exposed to high temperatures. Certain materials are
Current edition approved Feb. 15, 1993. Published April 1993. Originally
susceptible to degradation due to the influence of humidity in
published as D 794 – 44 T. Last previous edition D 794 – 82.
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long-term heat resistance tests. Materials susceptible to hy-
Annual Book of
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