ASTM C613-23

Standard Test Method for Constituent Content of Composite Prepreg by Soxhlet Extraction

SIGNIFICANCE AND USE
5.1 The prepreg volatiles content, matrix content, reinforcement content, and filler content of composite prepreg materials are used to control material manufacture and subsequent fabrication processes, and are key parameters in the specification and production of such materials, as well as in the fabrication of products made with such materials.  
5.2 The extraction products resulting from this test method (the extract, the residue, or both) can be analyzed to assess chemical composition and degree of purity.
SCOPE
1.1 This test method covers a Soxhlet extraction procedure to determine the matrix content, reinforcement content, and filler content of composite material prepreg. Volatiles content, if appropriate, and required, is determined by means of Test Method D3530.  
1.1.1 The reinforcement and filler must be substantially insoluble in the selected extraction reagent and any filler must be capable of being separated from the reinforcement by filtering the extraction residue.  
1.1.2 Reinforcement and filler content test results are total reinforcement content and total filler content; hybrid material systems with more than one type of either reinforcement or filler cannot be distinguished.  
1.2 This test method focuses on thermosetting matrix material systems for which the matrix may be extracted by an organic solvent. However, other, unspecified, reagents may be used with this test method to extract other matrix material types for the same purposes.  
1.3 Alternate techniques for determining matrix and reinforcement content include Test Methods D3171 (matrix digestion), D2584 (matrix burn-off/ignition), and D3529 (matrix dissolution and ignition loss). Test Method D2584 is preferred for reinforcement materials, such as glass, quartz, or silica, that are unaffected by high-temperature environments.  
1.4 The technical content of this standard has been stable since 1997 without significant objection from its stakeholders. As there is limited technical support for the maintenance of this standard, changes since that date have been limited to items required to retain consistency with other ASTM D30 Committee standards. The standard therefore should not be considered to include any significant changes in approach and practice since 1997. Future maintenance of the standard will only be in response to specific requests and performed only as technical support allows.  
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in Section 9 and 7.2.3 and 8.2.1.  
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 14-Nov-2023
• ICS: 83.120 - Reinforced plastics
• Technical Committee: D30 - Composite Materials
• Drafting Committee: D30.03 - Constituent/Precursor Properties

Relations

• Replaces: ASTM C613-19 - Standard Test Method for Constituent Content of Composite Prepreg by Soxhlet Extraction
• Effective Date: 15-Nov-2023
• Refers: ASTM D883-24 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2024
• Refers: ASTM D883-23 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2023
• Refers: ASTM E456-13a(2022)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• Refers: ASTM E456-13a(2022) - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• Referred By: ASTM D3529-16(2021) - Standard Test Methods for Constituent Content of Composite Prepreg
• Effective Date: 15-Nov-2023
• Referred By: ASTM D4762-23 - Standard Guide for Testing Polymer Matrix Composite Materials
• Effective Date: 15-Nov-2023

Overview

ASTM C613-23: Standard Test Method for Constituent Content of Composite Prepreg by Soxhlet Extraction provides a comprehensive procedure to determine the matrix, reinforcement, and filler content of composite prepreg materials. Utilizing a Soxhlet extraction approach, this standard enables accurate measurement and quality control of composite material constituents, essential in material specification, manufacturing processes, and end-product performance evaluation. The method is primarily designed for thermosetting matrix systems where the matrix can be extracted by suitable organic solvents, but it can be adapted for other matrix types with appropriate reagents. This standard is recognized internationally and has been approved for use by agencies such as the U.S. Department of Defense.

Key Topics

• Application of Soxhlet Extraction: The method describes the use of Soxhlet extraction apparatus to separate and quantify matrix, reinforcement, and filler in a composite prepreg sample.
• Volatile Content Determination: For thermosetting materials, volatile content is assessed using a referenced ASTM method (D3530), as these volatiles influence material properties.
• Sample Preparation and Mass Measurement: Accurate sample preparation, mass determination, and control of environmental factors are emphasized to ensure precise and repeatable results.
• Separation of Constituents: Reinforcement and filler, if both are present, must be substantially insoluble in the extraction reagent and capable of separation by filtering the residue.
• Correction Factors: The standard includes procedures to account for changes in reinforcement or filler mass caused by exposure to extraction reagents, ensuring reliable constituent quantification.
• Statistical Analysis: Guidelines are provided for calculating averages, standard deviations, and coefficients of variation to assess data reliability and process control.

Applications

Adhering to ASTM C613-23 is critical for organizations involved in the production and quality assurance of composite prepreg materials and finished composite products. The practical value of this standard includes:

• Quality Control: Enables precise measurement of constituent content, supporting batch-to-batch consistency during prepreg manufacture and fabrication.
• Material Development: Supports evaluation of new formulations and material systems by providing reliable methods for comparing constituent proportions.
• Process Optimization: Informs necessary adjustments in fabrication and curing processes based on accurate knowledge of resin, reinforcement, and filler content.
• Compliance and Specification: Serves as a definitive reference in material specifications and contract documents, helping suppliers and manufacturers demonstrate compliance with technical requirements.
• Purity Assessment: Extraction residues or solutions can be further analyzed to determine chemical composition and assess raw material purity.

Related Standards

ASTM C613-23 references and aligns with several other ASTM standards and international guidelines critical to composite materials testing:

• ASTM D3530 - Test Method for Volatiles Content of Composite Material Prepreg
• ASTM D3171 - Test Methods for Constituent Content of Composite Materials (matrix digestion)
• ASTM D2584 - Test Method for Ignition Loss of Cured Reinforced Resins (burn-off/ignition)
• ASTM D3529 - Test Methods for Constituent Content of Composite Prepreg (dissolution, ignition loss)
• ASTM D883/D3878/E456/E177 - Terminologies and statistical concepts relevant to plastics and composite materials
• NFPA 86 - Standard for Ovens and Furnaces (safety considerations)
• International Principles: Developed in accordance with WTO’s Technical Barriers to Trade (TBT) Committee principles, ensuring global acceptance.

Conclusion

ASTM C613-23 is an essential standard for accurately determining the constituent content of composite prepreg materials using Soxhlet extraction. Its use supports quality control, material development, and specification compliance within the composites industry-delivering precise data on matrix, reinforcement, and filler content that are vital to process optimization and product performance. For maximum utility, practitioners should reference related ASTM standards and adhere to all safety and environmental best practices.

Keywords: ASTM C613-23, composite prepreg, Soxhlet extraction, matrix content, reinforcement content, filler content, resin content, volatile content, composite materials, ASTM standards, material testing, quality control, thermosetting composites.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C613 − 23
Standard Test Method for
Constituent Content of Composite Prepreg by Soxhlet
Extraction
This standard is issued under the fixed designation C613; 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 (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope since 1997. Future maintenance of the standard will only be in
response to specific requests and performed only as technical
1.1 This test method covers a Soxhlet extraction procedure
support allows.
to determine the matrix content, reinforcement content, and
1.5 The values stated in SI units are to be regarded as
filler content of composite material prepreg. Volatiles content,
standard. No other units of measurement are included in this
if appropriate, and required, is determined by means of Test
standard.
Method D3530.
1.1.1 The reinforcement and filler must be substantially 1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
insoluble in the selected extraction reagent and any filler must
be capable of being separated from the reinforcement by responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
filtering the extraction residue.
mine the applicability of regulatory limitations prior to use.
1.1.2 Reinforcement and filler content test results are total
Specific precautionary statements are given in Section 9 and
reinforcement content and total filler content; hybrid material
7.2.3 and 8.2.1.
systems with more than one type of either reinforcement or
1.7 This international standard was developed in accor-
filler cannot be distinguished.
dance with internationally recognized principles on standard-
1.2 This test method focuses on thermosetting matrix ma-
ization established in the Decision on Principles for the
terial systems for which the matrix may be extracted by an
Development of International Standards, Guides and Recom-
organic solvent. However, other, unspecified, reagents may be
mendations issued by the World Trade Organization Technical
used with this test method to extract other matrix material types
Barriers to Trade (TBT) Committee.
for the same purposes.
2. Referenced Documents
1.3 Alternate techniques for determining matrix and rein-
forcement content include Test Methods D3171 (matrix
2.1 ASTM Standards:
digestion), D2584 (matrix burn-off/ignition), and D3529 (ma-
D883 Terminology Relating to Plastics
trix dissolution and ignition loss). Test Method D2584 is
D2584 Test Method for Ignition Loss of Cured Reinforced
preferred for reinforcement materials, such as glass, quartz, or
Resins
silica, that are unaffected by high-temperature environments.
D3171 Test Methods for Constituent Content of Composite
Materials
1.4 The technical content of this standard has been stable
D3529 Test Methods for Constituent Content of Composite
since 1997 without significant objection from its stakeholders.
Prepreg
As there is limited technical support for the maintenance of this
D3530 Test Method for Volatiles Content of Composite
standard, changes since that date have been limited to items
Material Prepreg
required to retain consistency with other ASTM D30 Commit-
D3878 Terminology for Composite Materials
tee standards. The standard therefore should not be considered
E122 Practice for Calculating Sample Size to Estimate, With
to include any significant changes in approach and practice
Specified Precision, the Average for a Characteristic of a
Lot or Process
This test method is under the jurisdiction of ASTM Committee D30 on
Composite Materials and is the direct responsibility of Subcommittee D30.03 on
Constituent/Precursor Properties. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Nov. 15, 2023. Published November 2023. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1967. Last previous edition approved in 2019 as C613 – 19. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/C0613-23. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C613 − 23
E177 Practice for Use of the Terms Precision and Bias in c—percent reinforcement mass change due to reagent expo-
ASTM Test Methods sure
E456 Terminology Relating to Quality and Statistics CV—coefficient of variation statistic of a sample population
for a given property
2.2 NFPA Standard:
M —additional mass of filler in the test specimen
a
NFPA 86 Standard for Ovens and Furnaces
M —mass of the test specimen extraction residue
e
M —initial mass of the test specimen
i
3. Terminology
M —mass of reinforcement in the test specimen
r
3.1 Definitions—Terminology D3878 defines terms relating
n—number of replicates in the sample population
to composite materials. Terminology D883 defines terms
s —standard deviation statistic of a sample population for
n−1
relating to plastics. Terminology E456 and Practice E177
a given property
define terms relating to statistics. In the event of a conflict
W —weight percent of filler in prepreg
f
between terms, Terminology D3878 shall have precedence
W —weight percent of matrix in prepreg
m
over the other documents.
W —weight percent of reinforcement in prepreg
r
3.2 Definitions of Terms Specific to This Standard:
x —test result for an individual test specimen from the
i
3.2.1 dry resin content, n—prepreg resin content calculated
sample population for a given property
by subtracting the average mass loss due to volatiles from the
x¯—average value of a sample population for a given
initial test specimen mass.
property
3.2.2 filler content, n—the amount of filler present in a
4. Summary of Test Method
prepreg or composite expressed either as percent by weight or
percent by volume.
4.1 The exposed surface area of the prepreg material test
3.2.2.1 Discussion—In this test method the reinforcement is
specimen is increased by cutting the test specimen into smaller
separated from the remainder of the material, which includes
pieces. The test specimen is weighed and the matrix material
the matrix and the filler. If the filler is not then separated from
removed by means of Soxhlet extraction. The extracted residue
the matrix to determine the proportion of each, then the filler
is dried and weighed. If a filler is present in the residue, in
content is included in the matrix content.
addition to reinforcement, the two components are separated
by filtering the residue. From mass measurements of the initial
3.2.3 replicate, n—a test specimen tested under nominally
test specimen, and of the residue taken at various stages in the
identical conditions as other test specimens from the same
process, the matrix content, reinforcement content, and filler
sample.
content are calculated and reported in weight percent.
3.2.4 test result, n—the value obtained for a given property
4.1.1 Soxhlet Process—While described in detail in com-
from one test unit.
mon quantitative chemical analysis textbooks, the Soxhlet
3.2.4.1 Discussion—A test result may be a single observa-
process is summarized as follows. The test specimen is loaded
tion or a combination of a number of observations when two or
into a filtering extraction thimble, which is placed into the
more test specimens are measured for each test.
extraction chamber of a Soxhlet extraction assembly (see Fig.
3.2.5 test specimen, n—a test unit or portion of a test unit
1) containing an appropriate extraction reagent. The porous
upon which a single or multiple observation is to be made.
thimble allows the liquid extraction reagent to pass while
3.2.6 test unit, n—a unit or portion of a material that is
retaining the test specimen. Freshly distilled liquid reagent
sufficient to obtain a test result(s) for the property or properties enters from the top of the extraction chamber, filling it until the
to be measured.
liquid reaches the highest level of the reagent-return tube. At
3.2.6.1 Discussion—A test unit may be a subunit of a this moment the tube operates as a siphon, draining the
primary (first stage) sampling unit or it may be a subunit of a
extraction chamber completely as it returns the liquid reagent
composite of primary sampling units or of increments from
these primary sampling units.
3.2.7 volatiles content, n—the amount of volatiles present in
a prepreg expressed as percent by weight.
3.2.8 wet resin content, n—prepreg resin content determined
by considering volatiles as part of the resin mass.
3.3 Symbols:
A—initial mass of dry reinforcement during a reagent expo-
sure evaluation
B—final mass of dry reinforcement during a reagent expo-
sure evaluation
Available from National Fire Protection Association (NFPA), 1 Batterymarch
Park, Quincy, MA 02169-7471, http://www.nfpa.org.
See Form and Style for ASTM Standards. FIG. 1 Schematic of Soxhlet Extraction Apparatus
C613 − 23
and any extracted material to a reservoir beneath the extraction ible under the conditions of the test, and if this change has the
chamber. The heated reservoir boils the reagent, the vapor of same value for the reinforcement alone as for the reinforcement
which is led to a condenser placed above the extraction in the matrix. Otherwise, a different reagent, or another test
chamber. The distilled condensate then drips down into the method, must be selected.
thimble, starting once again the process of filling the extraction
chamber. The Soxhlet operation is not a continuous operation, 7. Apparatus
but rather a sequence of fillings and siphonings, each cycle of
7.1 General Requirements:
which is called a reflux change. The heat input and reagent
7.1.1 Container Volume—A suggested volume is shown for
volume are adjusted to cause the boiling reagent to return to the
each container. However, other sizes may be required depend-
extraction flask from the condenser at 3 to 10 reflux changes
ing upon the test specimen size, the amount of reagent needed
per hour, with the extraction continuing for a minimum of 4 h
to complete the extraction process, and the relative sizes of
or 20 reflux changes, whichever comes first.
related equipment.
4.1.2 Volatiles Content—Volatiles content is primarily ap-
7.1.2 Thermal Shock—Laboratory equipment that is sub-
plicable to thermosetting materials, and, if required, is deter-
jected to non-ambient temperatures (hot or cold) shall be of
mined by Test Method D3530. Volatiles content determination
tempered-glass or PTFE materials.
requires different test specimens than those used in the extrac-
7.1.3 Post-Test Elemental Analysis—If a post-test elemental
tion process, since the process of determining volatiles content
analysis of the extract or residue is to be performed, laboratory
renders thermosetting material specimens unsuitable for sub-
equipment contacting the test specimen shall be constructed of
sequent organic solvent extraction.
PTFE and test specimen cutting shall be limited to tools that do
not leave an elemental trace.
5. Significance and Use
7.2 General Equipment:
5.1 The prepreg volatiles content, matrix content, reinforce-
7.2.1 Analytical Balance—The analytical balance shall be
ment content, and filler content of composite prepreg materials
capable of reading to within 60.1 mg.
are used to control material manufacture and subsequent
7.2.2 Muffle Furnace—The muffle furnace used to condition
fabrication processes, and are key parameters in the specifica-
glass extraction thimbles shall be capable of maintaining a
tion and production of such materials, as well as in the
temperature of 510 °C 6 15 °C.
fabrication of products made with such materials.
7.2.3 Air-Circulating Drying Oven—The drying oven shall
5.2 The extraction products resulting from this test method
be capable of maintaining a temperature of 163 °C 6 3 °C.
(the extract, the residue, or both) can be analyzed to assess
(Warning—For safety purposes listed in NFPA 86, take care to
chemical composition and degree of purity.
limit volatile concentration in the oven by controlling sample
quantity, temperature, and ventilation.)
6. Interferences
7.2.4 Desiccator—The desiccator shall be capable of con-
6.1 Extent of Cure in Thermosetting Systems—The effi-
taining the required test specimens.
ciency of extraction for thermosetting matrix materials is
7.3 Extraction Assembly:
directly related to the extent of cure of the resin system. Resins
7.3.1 Extraction Thimbles—The extraction thimbles shall be
that have started to cross-link (such as B-staged resins) will be
increasingly more difficult to extract as the cure advances. This deep, narrow filtering cups, of either borosilicate glass in an
appropriate pore size, or fat-extracted cellulose paper, suitable
test method may not be appropriate for such materials; Test
Methods D3171 or D2584 may be better test method choices. for use in the extraction chamber.
7.3.2 Hot Plate—The hot plate shall have adjustable con-
6.2 Reagent Selection—The proper reagent, in a suitable
trols suitable for heating the reagent within the reservoir flask
quantity, must be selected for the constituents under test. The
to 260 °C and shall be capable of controlling the required
reagents listed in Section 8 are provided for consideration,
reagent temperature within 615 °C.
particularly with regard to thermosetting materials, but cannot
7.3.3 Reservoir Flask—The reservoir flask shall be of boro-
be assured to perform well on all material systems within the
silicate glass, of suitable volume (125 mL is suggested) for the
scope of this test method.
reagent quantity and extraction chamber volume, and shall
6.3 Thimble Contamination—If the extract is to undergo
have a ground tapered joint capable of connection with the
further analysis, the thimble must be clean to avoid a signifi-
remainder of the assembly.
cant source of contamination.
7.3.4 Soxhlet Extraction Chamber—The extraction chamber
6.4 Reinforcement Mass Change as a Result of Reagent— shall be of borosilicate glass, with an automatic recycling
siphon that recycles at a suitable liquid volume (50 mL is
The calculations of this test method assume that the reinforce-
ment mass (or filler, if filler content is being determined) is not suggested), and with a ground tapered joint at each end capable
of connecting with the remainder of the assembly.
significantly affected (whether mass increase or mass loss) by
exposure to the reagent. Small, consistent changes in the 7.3.5 Condensing Chamber—The condensing chamber shall
reinforcement mass caused by exposure to the reagent can be
be of borosilicate glass, shall be water cooled, and shall have
corrected by the process described in 14.4.5. The resulting a ground tapered joint capable of connecting with the remain-
correction may be used if this change is sufficiently reproduc- der of the assembly.
C613 − 23
7.4 For Determining Filler Content: 8.2.2 Ethanol (Ethyl Alcohol), C H OH.
2 5
7.4.1 Vacuum Filter System—The vacuum filter system shall
8.3 Washing Reagents—A suitable washing reagent(s) shall
be suitable for filtering material from the filtering crucible and
be selected that is compatible with the material system under
holder.
test and the apparatus. Read and understand the precautions
7.4.2 Filtering Crucible—The filtering crucible shall be of
listed in Section 9 before selecting a washing reagent. Washing
fritted glass and of suitable pore size and of appropriate volume
reagents that have been found effective include the following:
(30 mL is suggested).
8.3.1 Acetone (2-Propanone), CH COCH .
8 8
8.3.2 Water, Distilled or Demineralized.
NOTE 1—Filter porosity should be sized to filter the smallest expected
filler size from the reinforcement. If there is any doubt about the filter
pore-size selection, evaluate, with the material under test, filters of
9. Hazards
successively different porosity size until confidence is established in the
filter size selected. While the glass fiber filter is used in concert with the 9.1 This test method should be used only by laboratory
fritted filter to reduce any tendency to clog, note that certain materials,
workers with general training in the safe handling of chemi-
particularly those containing filler of a broad range of particle size and 7
cals. A source of useful information is given in Footnote 7.
shape, may nevertheless clog the filter pores without visible sign. The
(Precaution—In addition to other precautions, consult the
filter tare mass should be monitored for change as a result of the test. A
appropriate material safety data sheet for each material used,
change in the filter tare mass indicates a potentially incorrect determina-
tion of reinforcement to filler proportion, and therefore, incorrect rein-
including reagent materials and test specimen materials, for
forcement and filler content test results.
specific recommendations on safety and handling.)
7.4.3 Crucible Holder—The crucible holder shall be ca- (Precaution—In addition to other precautions, the extraction
pable of holding the filtering crucible. and filtering processes should be performed under a suitable
7.4.4 Glass Fiber Filter—A glass fiber filter of suitable vented chemical fume hood.) (Precaution—In addition to
porosity and of appropriate diameter to fit in the filtering other precautions, materials that have been exposed to poten-
crucible. tially toxic or flammable reagents must be air-dried under a
hood before being subsequently oven-dried, to eliminate
7.5 Miscellaneous Common Laboratory Items—Other com-
build-up of a potentially dangerous concentration of vapor in
monly available laboratory items may be needed including:
the drying oven. Useful guidelines for estimating the safe
scissors or knife, beakers or flasks, flexible tubing, equipment
volatiles mass for a given oven size are given in NFPA
connectors, wash bottles, aluminum foil, and lint-free wipes.
Standard 86.)
8. Reagents and Materials
9.2 Use of mixed extraction reagents with different boiling
points is not covered by this test method. (Precaution—In
8.1 Purity of Reagents—As a minimum, a technical-grade
addition to other precautions, do not use mixed extraction
reagent is required to provide accurate results. However, when
reagents with different boiling points. Use of mixed extraction
resolving disputes or performing subsequent analysis of
...

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. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C613 − 19 C613 − 23
Standard Test Method for
Constituent Content of Composite Prepreg by Soxhlet
Extraction
This standard is issued under the fixed designation C613; 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 (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope
1.1 This test method covers a Soxhlet extraction procedure to determine the matrix content, reinforcement content, and filler
content of composite material prepreg. Volatiles content, if appropriate, and required, is determined by means of Test Method
D3530.
1.1.1 The reinforcement and filler must be substantially insoluble in the selected extraction reagent and any filler must be capable
of being separated from the reinforcement by filtering the extraction residue.
1.1.2 Reinforcement and filler content test results are total reinforcement content and total filler content; hybrid material systems
with more than one type of either reinforcement or filler cannot be distinguished.
1.2 This test method focuses on thermosetting matrix material systems for which the matrix may be extracted by an organic
solvent. However, other, unspecified, reagents may be used with this test method to extract other matrix material types for the same
purposes.
1.3 Alternate techniques for determining matrix and reinforcement content include Test Methods D3171 (matrix digestion), D2584
(matrix burn-off/ignition), and D3529 (matrix dissolution and ignition loss). Test Method D2584 is preferred for reinforcement
materials, such as glass, quartz, or silica, that are unaffected by high-temperature environments.
1.4 The technical content of this standard has been stable since 1997 without significant objection from its stakeholders. As there
is limited technical support for the maintenance of this standard, changes since that date have been limited to items required to
retain consistency with other ASTM D30 Committee standards. The standard therefore should not be considered to include any
significant changes in approach and practice since 1997. Future maintenance of the standard will only be in response to specific
requests and performed only as technical support allows.
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use. Specific precautionary statements are given in Section 9 and 7.2.3 and 8.2.1.
This test method is under the jurisdiction of ASTM Committee D30 on Composite Materials and is the direct responsibility of Subcommittee D30.03 on
Constituent/Precursor Properties.
Current edition approved April 15, 2019Nov. 15, 2023. Published May 2019November 2023. Originally approved in 1967. Last previous edition approved in 20142019
as C613 – 14.C613 – 19. DOI: 10.1520/C0613-19.10.1520/C0613-23.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C613 − 23
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D883 Terminology Relating to Plastics
D2584 Test Method for Ignition Loss of Cured Reinforced Resins
D3171 Test Methods for Constituent Content of Composite Materials
D3529 Test Methods for Constituent Content of Composite Prepreg
D3530 Test Method for Volatiles Content of Composite Material Prepreg
D3878 Terminology for Composite Materials
E122 Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or
Process
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E456 Terminology Relating to Quality and Statistics
2.2 NFPA Standard:
NFPA 86 Standard for Ovens and Furnaces
3. Terminology
3.1 Definitions—Terminology D3878 defines terms relating to composite materials. Terminology D883 defines terms relating
to plastics. Terminology E456 and Practice E177 define terms relating to statistics. In the event of a conflict between terms,
Terminology D3878 shall have precedence over the other documents.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 dry resin content, n—prepreg resin content calculated by subtracting the average mass loss due to volatiles from the initial
test specimen mass.
3.2.2 filler content, n—the amount of filler present in a prepreg or composite expressed either as percent by weight or percent by
volume.
3.2.2.1 Discussion—
In this test method the reinforcement is separated from the remainder of the material, which includes the matrix and the filler. If
the filler is not then separated from the matrix to determine the proportion of each, then the filler content is included in the matrix
content.
3.2.3 matrix content, n—the amount of matrix present in a composite or prepreg expressed either as percent by weight or percent
by volume; for polymer matrix composites this is resin content.
3.2.4 reinforcement content, n—the amount of reinforcement present in a composite or prepreg expressed either as percent by
weight or percent by volume; this is sometimes stated as a fraction, that is, reinforcement volume fraction.
3.2.3 replicate, n—a test specimen tested under nominally identical conditions as other test specimens from the same sample.
3.2.4 test result, n—the value obtained for a given property from one test unit.
3.2.4.1 Discussion—
A test result may be a single observation or a combination of a number of observations when two or more test specimens are
measured for each test.
3.2.5 test specimen, n—a test unit or portion of a test unit upon which a single or multiple observation is to be made.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from National Fire Protection Association (NFPA), 1 Batterymarch Park, Quincy, MA 02169-7471, http://www.nfpa.org.
See Form and Style for ASTM Standards.
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3.2.6 test unit, n—a unit or portion of a material that is sufficient to obtain a test result(s) for the property or properties to be
measured.
3.2.6.1 Discussion—
A test unit may be a subunit of a primary (first stage) sampling unit or it may be a subunit of a composite of primary sampling
units or of increments from these primary sampling units.
3.2.7 volatiles content, n—the amount of volatiles present in a prepreg expressed as percent by weight.
3.2.8 wet resin content, n—prepreg resin content determined by considering volatiles as part of the resin mass.
3.3 Symbols:
A—initial mass of dry reinforcement during a reagent exposure evaluation
B—final mass of dry reinforcement during a reagent exposure evaluation
c—percent reinforcement mass change due to reagent exposure
CV—coefficient of variation statistic of a sample population for a given property
M —additional mass of filler in the test specimen
a
M —mass of the test specimen extraction residue
e
M —initial mass of the test specimen
i
M —mass of reinforcement in the test specimen
r
n—number of replicates in the sample population
s —standard deviation statistic of a sample population for a given property
n−1
W —weight percent of filler in prepreg
f
W —weight percent of matrix in prepreg
m
W —weight percent of reinforcement in prepreg
r
x —test result for an individual test specimen from the sample population for a given property
i
x¯—average value of a sample population for a given property
4. Summary of Test Method
4.1 The exposed surface area of the prepreg material test specimen is increased by cutting the test specimen into smaller pieces.
The test specimen is weighed and the matrix material removed by means of Soxhlet extraction. The extracted residue is dried and
weighed. If a filler is present in the residue, in addition to reinforcement, the two components are separated by filtering the residue.
From mass measurements of the initial test specimen, and of the residue taken at various stages in the process, the matrix content,
reinforcement content, and filler content are calculated and reported in weight percent.
4.1.1 Soxhlet Process—While described in detail in common quantitative chemical analysis textbooks, the Soxhlet process is
summarized as follows. The test specimen is loaded into a filtering extraction thimble, which is placed into the extraction chamber
of a Soxhlet extraction assembly (see Fig. 1) containing an appropriate extraction reagent. The porous thimble allows the liquid
extraction reagent to pass while retaining the test specimen. Freshly distilled liquid reagent enters from the top of the extraction
chamber, filling it until the liquid reaches the highest level of the reagent-return tube. At this moment the tube operates as a siphon,
FIG. 1 Schematic of Soxhlet Extraction Apparatus
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draining the extraction chamber completely as it returns the liquid reagent and any extracted material to a reservoir beneath the
extraction chamber. The heated reservoir boils the reagent, the vapor of which is led to a condenser placed above the extraction
chamber. The distilled condensate then drips down into the thimble, starting once again the process of filling the extraction
chamber. The Soxhlet operation is not a continuous operation, but rather a sequence of fillings and siphonings, each cycle of which
is called a reflux change. The heat input and reagent volume are adjusted to cause the boiling reagent to return to the extraction
flask from the condenser at 3 to 10 reflux changes per hour, with the extraction continuing for a minimum of 4 h or 20 reflux
changes, whichever comes first.
4.1.2 Volatiles Content—Volatiles content is primarily applicable to thermosetting materials, and, if required, is determined by Test
Method D3530. Volatiles content determination requires different test specimens than those used in the extraction process, since
the process of determining volatiles content renders thermosetting material specimens unsuitable for subsequent organic solvent
extraction.
5. Significance and Use
5.1 The prepreg volatiles content, matrix content, reinforcement content, and filler content of composite prepreg materials are used
to control material manufacture and subsequent fabrication processes, and are key parameters in the specification and production
of such materials, as well as in the fabrication of products made with such materials.
5.2 The extraction products resulting from this test method (the extract, the residue, or both) can be analyzed to assess chemical
composition and degree of purity.
6. Interferences
6.1 Extent of Cure in Thermosetting Systems—The efficiency of extraction for thermosetting matrix materials is directly related
to the extent of cure of the resin system. Resins that have started to cross-link (such as B-staged resins) will be increasingly more
difficult to extract as the cure advances. This test method may not be appropriate for such materials; Test Methods D3171 or D2584
may be better test method choices.
6.2 Reagent Selection—The proper reagent, in a suitable quantity, must be selected for the constituents under test. The reagents
listed in Section 8 are provided for consideration, particularly with regard to thermosetting materials, but cannot be assured to
perform well on all material systems within the scope of this test method.
6.3 Thimble Contamination—If the extract is to undergo further analysis, the thimble must be clean to avoid a significant source
of contamination.
6.4 Reinforcement Mass Change as a Result of Reagent—The calculations of this test method assume that the reinforcement mass
(or filler, if filler content is being determined) is not significantly affected (whether mass increase or mass loss) by exposure to the
reagent. Small, consistent changes in the reinforcement mass caused by exposure to the reagent can be corrected by the process
described in 14.4.5. The resulting correction may be used if this change is sufficiently reproducible under the conditions of the test,
and if this change has the same value for the reinforcement alone as for the reinforcement in the matrix. Otherwise, a different
reagent, or another test method, must be selected.
7. Apparatus
7.1 General Requirements:
7.1.1 Container Volume—A suggested volume is shown for each container. However, other sizes may be required depending upon
the test specimen size, the amount of reagent needed to complete the extraction process, and the relative sizes of related equipment.
7.1.2 Thermal Shock—Laboratory equipment that is subjected to non-ambient temperatures (hot or cold) shall be of
tempered-glass or PTFE materials.
7.1.3 Post-Test Elemental Analysis—If a post-test elemental analysis of the extract or residue is to be performed, laboratory
equipment contacting the test specimen shall be constructed of PTFE and test specimen cutting shall be limited to tools that do
not leave an elemental trace.
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7.2 General Equipment:
7.2.1 Analytical Balance—The analytical balance shall be capable of reading to within 60.1 mg.
7.2.2 Muffle Furnace—The muffle furnace used to condition glass extraction thimbles shall be capable of maintaining a
temperature of 510 6 15 °C.510 °C 6 15 °C.
7.2.3 Air-Circulating Drying Oven—The drying oven shall be capable of maintaining a temperature of 163 6 3 °C.163 °C 6 3 °C.
(Warning—For safety purposes listed in NFPA 86, take care to limit volatile concentration in the oven by controlling sample
quantity, temperature, and ventilation.)
7.2.4 Desiccator—The desiccator shall be capable of containing the required test specimens.
7.3 Extraction Assembly:
7.3.1 Extraction Thimbles—The extraction thimbles shall be deep, narrow filtering cups, of either borosilicate glass in an
appropriate pore size, or fat-extracted cellulose paper, suitable for use in the extraction chamber.
7.3.2 Hot Plate—The hot plate shall have adjustable controls suitable for heating the reagent within the reservoir flask to 260 °C
and shall be capable of controlling the required reagent temperature within 615 °C.
7.3.3 Reservoir Flask—The reservoir flask shall be of borosilicate glass, of suitable volume (125 mL is suggested) for the reagent
quantity and extraction chamber volume, and shall have a ground tapered joint capable of connection with the remainder of the
assembly.
7.3.4 Soxhlet Extraction Chamber—The extraction chamber shall be of borosilicate glass, with an automatic recycling siphon that
recycles at a suitable liquid volume (50 mL is suggested), and with a ground tapered joint at each end capable of connecting with
the remainder of the assembly.
7.3.5 Condensing Chamber—The condensing chamber shall be of borosilicate glass, shall be water cooled, and shall have a
ground tapered joint capable of connecting with the remainder of the assembly.
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7.4 For Determining Filler Content:
7.4.1 Vacuum Filter System—The vacuum filter system shall be suitable for filtering material from the filtering crucible and holder.
7.4.2 Filtering Crucible—The filtering crucible shall be of fritted glass and of suitable pore size and of appropriate volume (30
mL is suggested).
NOTE 1—Filter porosity should be sized to filter the smallest expected filler size from the reinforcement. If there is any doubt about the filter pore-size
selection, evaluate, with the material under test, filters of successively different porosity size until confidence is established in the filter size selected. While
the glass fiber filter is used in concert with the fritted filter to reduce any tendency to clog, note that certain materials, particularly those containing filler
of a broad range of particle size and shape, may nevertheless clog the filter pores without visible sign. The filter tare mass should be monitored for change
as a result of the test. A change in the filter tare mass indicates a potentially incorrect determination of reinforcement to filler proportion, and therefore,
incorrect reinforcement and filler content test results.
7.4.3 Crucible Holder—The crucible holder shall be capable of holding the filtering crucible.
7.4.4 Glass Fiber Filter—A glass fiber filter of suitable porosity and of appropriate diameter to fit in the filtering crucible.
7.5 Miscellaneous Common Laboratory Items—Other commonly available laboratory items may be needed including: scissors or
knife, beakers or flasks, flexible tubing, equipment connectors, wash bottles, aluminum foil, and lint-free wipes.
8. Reagents and Materials
8.1 Purity of Reagents—As a minimum, a technical-grade reagent is required to provide accurate results. However, when resolving
disputes or performing subsequent analysis of extract or residue, a reagent-grade reagent shall be used. Unless otherwise indicated,
it is intended that the reagent conform to the specifications of the Committee on Analytical Reagents of the American Chemical
Society, where such specifications are available. Other equivalent grades may be used, provided the reagent is of sufficiently high
purity to permit its use without lessening the accuracy of the determination.
8.2 Extraction Reagents—A suitable extraction reagent shall be selected that is compatible with the material system under test and
the apparatus. Read and understand the precautions listed in Section 9 before selecting an extraction reagent. Extraction reagents
that have been found effective for many thermosetting matrices include the following:
8.2.1 Dimethylformamide (DMF), (CH ) NCHO. (Warning—As of the approval date of this standard, DMF was listed by the
5 2
International Agency for Research on Cancer in Group 3 as a “possible human carcinogen” and is considered a reproductive toxin
by the National Toxicology Program. See a recent DMF material safety data sheet for more information.)
8.2.2 Ethanol (Ethyl Alcohol), C H OH.
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8.3 Washing Reagents—A suitable washing reagent(s) shall be selected that is compatible with the material system under test and
the apparatus. Read and understand the precautions listed in Section 9 before selecting a washing reagent. Washing reagents that
have bee
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