ASTM D2734-94

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
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Designation: D 2734 – 94
Standard Test Methods for
Void Content of Reinforced Plastics
This standard is issued under the fixed designation D 2734; 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 composites are measured separately. Then the resin content is
measured and a theoretical composite density calculated. This
1.1 These test methods cover the void content of reinforced
is compared to the measured composite density. The difference
plastics or “composites.” The test methods are applicable to
in densities indicates the void content. A good composite may
composites for which the effects of ignition on the materials are
have 1 % voids or less, while a poorly made composite can
known. Most plastics, glass, and asbestos reinforcements fall
have a much higher void content. Finite values under 1 %
into this class. These test methods are not applicable to
should be recognized as representing a laminate density
composites for which the effects of ignition on the plastics, the
quality, but true void content level must be established by
reinforcement, and any fillers are unknown. This class may
complementary tests or background experience, or both.
include silicone resins, which do not burn off completely,
reinforcements consisting of metals, organic materials, or
4. Significance and Use
inorganic materials which may gain or lose weight, and fillers
4.1 The void content of a composite may significantly affect
consisting of oxides, carbonates, etc., which may gain or lose
some of its mechanical properties. Higher void contents
weight. Note that separate weight loss tests of individual
usually mean lower fatigue resistance, greater susceptibility to
materials will usually, but not necessarily, give the same result
water penetration and weathering, and increased variation or
as when all the materials are combined.
scatter in strength properties. The knowledge of void content is
NOTE 1—There is no known ISO equivalent to these test methods.
desirable for estimation of quality of composites.
1.2 The values stated in SI units are to be regarded as the
5. Interferences
standard.
5.1 The density of the resin, in these test methods, is
1.3 This standard does not purport to address all of the
assumed to be the same in the composite as it is in a large cast
safety concerns, if any, associated with its use. It is the
mass. Although there is no realistic way to avoid this assump-
responsibility of the user of this standard to establish appro-
tion, it is nevertheless not strictly correct. Differences in
priate safety and health practices and determine the applica-
curing, heat and pressure, and molecular forces from the
bility of regulatory limitations prior to use.
reinforcement surface all change the composite resin density
2. Referenced Documents
from the bulk resin density. The usual change is that bulk
density is lower, making void content seem lower than it really
2.1 ASTM Standards:
D 618 Practice for Conditioning Plastics and Electrical is.
Insulating Materials for Testing 5.2 For composites with high void contents, this error will
lower the true value an insignificant amount, from a true 7 %
D 792 Test Methods for Density and Specific Gravity (Rela-
tive Density) of Plastics by Displacement down to a calculated 6.7 %, for example. For composites with
low and void contents, the value may be lowered from a true
D 1505 Test Method for Density of Plastics by the Density-
Gradient Technique 0.2 % to a calculated − 0.1 %. This would indicate an obvious
error, and illustrates that as the void content gets lower the
D 2584 Test Method for Ignition Loss of Cured Reinforced
Resins constant error in resin density gets progressively more impor-
tant. Note that these values are for example only, that different
3. Summary of Test Methods
resin systems can give different errors, and that it is left to the
3.1 The densities of the resin, the reinforcement, and the individual tester to determine the accuracy of the calculated
result in his particular measurement.
5.3 For the special case of semi-crystalline plastics, such as
These test methods are under the jurisdiction of ASTM Committee D-20 on
polyphenylene sulfide (PPS) and polyetheretherketone
Plastics and are the direct responsibility of Subcommittee D20.18 on Reinforced
Thermosetting Plastics.
(PEEK), an interference due to the level of crystallinity present
Current edition approved June 15, 1994. Published August 1994. Originally
in the composite can cause significant variation in the mea-
published as D 2734 – 68 T. Last previous edition D 2734 – 91.
2 surement of void content by this test method. The level of
Annual Book of ASTM Standards, Vol 08.01.
Annual Book of ASTM Standards, Vol 08.02. crystallinity can be affected by a variety of circumstances,
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NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 2734
including the molding conditions. For these polymers, the rectangular block). Use the averages for each dimension to
density used in the calculation must be the actual density of the calculate the volume.
resin in the composite. 7.1.3.3 The tolerance on the accuracy of the micrometer
measurements shall be 60.0013 cm (60.0005 in.). With
NOTE 2—The actual degree of crystallinity of the composite can be
maximum tolerance buildup on a small sample, this could
measured by techniques such as differential scanning calorimetry (DSC)
result in an error in the calculated volume of 0.6 %. For larger
or by X-ray difraction.
samples, and with some measurements being in error on the
6. Conditioning plus side and some on the minus side, the error in the
calculated volume should not exceed 0.2 %.
6.1 Conditioning—Condition the test specimens at 23 6
7.1.3.4 Calculate the density by dividing the weight by the
2°C (73.4 6 3.6°F) and 50 6 5 % relative humidity for not less
volume; express as grams per cubic centimetre.
than 40 h prior to test in accordance with Procedure A of
7.2 Density of the Glass or Other Reinforcement—Most
Practice D 618, for those tests where conditioning is required.
glass reinforcement is E glass, which typically has a density
In cases of disagreement, the tolerances shall be 1°C (1.8°F)
between 2.54 and 2.59 g/cm ; S glass density is 2.46 to 2.49
and 62 % relative humidity.
g/cm . However, if a density determination is necessary, use
6.2 Test Conditions—Conduct tests in the standard labora-
Test Methods D 792. Pay particular attention to Note 11 of that
tory atmosphere of 23 6 2°C (73.4 6 3.6°F) and 50 6 5%
test method, which discusses removal of
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