ASTM D4895-18(2023)
(Specification)Standard Specification for Polytetrafluoroethylene (PTFE) Resin Produced From Dispersion
Standard Specification for Polytetrafluoroethylene (PTFE) Resin Produced From Dispersion
ABSTRACT
This specification covers dry-powder resins of polytetrafluoroethylene (PTFE) resin produced from dispersion. PTFE mixtures with additives are not covered in this specification. This specification covers type I and type II PTFE. The resins shall be tested for bulk density, particle size, water content, melting peak temperature, tensile strength, elongation at break, standard specific gravity, extrusion pressure, thermal instability index, and stretching void index. Specimen preparation, testing, inspection, and packaging shall be in accordance to the procedures indicated in this specification.
SCOPE
1.1 This specification2 covers polytetrafluoroethylene (PTFE) prepared by coagulation of a dispersion. These PTFE resins are homopolymers of tetrafluoroethylene or modified homopolymers containing not more than 1 % by weight of other fluoromonomers. The materials covered herein do not include mixtures of PTFE with additives such as colors, fillers, or plasticizers; nor do they include reprocessed or reground resin or any fabricated articles because the properties of such materials have been irreversibly changed when they were fibrillated or sintered.
1.2 The values stated in SI units as detailed in IEEE/ASTM SI-10 are to be regarded as standard. The values given in parentheses are for information only.
1.3 The following safety hazards caveat pertains only to the Specimen Preparation Section, Section 9, and the Test Methods Section, Section 10, of this specification: 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. See Warning note in 9.1.1 for a specific hazards statement.
Note 1: Information in this specification is technically equivalent to related information in ISO 20568-1 and ISO 20568-2.
1.4 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
Relations
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: D4895 − 18 (Reapproved 2023)
Standard Specification for
Polytetrafluoroethylene (PTFE) Resin Produced From
Dispersion
This standard is issued under the fixed designation D4895; 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 2. Referenced Documents
2.1 ASTM Standards:
1.1 This specification covers polytetrafluoroethylene
D618 Practice for Conditioning Plastics for Testing
(PTFE) prepared by coagulation of a dispersion. These PTFE
D638 Test Method for Tensile Properties of Plastics
resins are homopolymers of tetrafluoroethylene or modified
D792 Test Methods for Density and Specific Gravity (Rela-
homopolymers containing not more than 1 % by weight of
tive Density) of Plastics by Displacement
other fluoromonomers. The materials covered herein do not
D883 Terminology Relating to Plastics
include mixtures of PTFE with additives such as colors, fillers,
D1708 Test Method for Tensile Properties of Plastics by Use
or plasticizers; nor do they include reprocessed or reground
of Microtensile Specimens
resin or any fabricated articles because the properties of such
D1895 Test Methods for Apparent Density, Bulk Factor, and
materials have been irreversibly changed when they were
Pourability of Plastic Materials
fibrillated or sintered.
D3892 Practice for Packaging/Packing of Plastics
1.2 The values stated in SI units as detailed in IEEE/ASTM
D4052 Test Method for Density, Relative Density, and API
SI-10 are to be regarded as standard. The values given in
Gravity of Liquids by Digital Density Meter
parentheses are for information only.
D4441 Specification for Aqueous Dispersions of Polytet-
1.3 The following safety hazards caveat pertains only to the
rafluoroethylene
Specimen Preparation Section, Section 9, and the Test Methods
D4591 Test Method for Determining Temperatures and
Section, Section 10, of this specification: This standard does
Heats of Transitions of Fluoropolymers by Differential
not purport to address all of the safety concerns, if any,
Scanning Calorimetry
associated with its use. It is the responsibility of the user of this
D4894 Specification for Polytetrafluoroethylene (PTFE)
standard to establish appropriate safety, health, and environ-
Granular Molding and Ram Extrusion Materials
mental practices and determine the applicability of regulatory
E11 Specification for Woven Wire Test Sieve Cloth and Test
limitations prior to use. See Warning note in 9.1.1 for a specific
Sieves
hazards statement.
E29 Practice for Using Significant Digits in Test Data to
Determine Conformance with Specifications
NOTE 1—Information in this specification is technically equivalent to
E177 Practice for Use of the Terms Precision and Bias in
related information in ISO 20568-1 and ISO 20568-2.
ASTM Test Methods
1.4 This international standard was developed in accor-
IEEE/ASTM SI-10 Use of the International System of Units
dance with internationally recognized principles on standard-
(SI): The Modern Metric System
ization established in the Decision on Principles for the
2.2 ISO Standards:
Development of International Standards, Guides and Recom-
ISO 20568-1 Plastics Fluoropolymer Dispersions and Mold-
mendations issued by the World Trade Organization Technical
ing and Extrusion Materials—Part 1: Designation and
Barriers to Trade (TBT) Committee.
Specification
ISO 20568-2 Plastics Fluoropolymer Dispersions and
Molding and Extrusion Materials—Part 2: Preparation of
This specification is under the jurisdiction of ASTM Committee D20 on
Plastics and is the direct responsibility of Subcommittee D20.15 on Thermoplastic
Materials. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved May 1, 2023. Published May 2023. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1989. Last previous edition approved in 2018 as D4895 – 18. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D4895-18R23. the ASTM website.
2 4
Specifications for other forms of polytetrafluoroethylene are found in Specifi- Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
cations D4441 and D4894. 4th Floor, New York, NY 10036, http://www.ansi.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4895 − 18 (2023)
Test Specimens and Determination of Properties 4. Classification
ISO 13322-2 Particle size analysis—Image analysis
4.1 This specification covers the following types of PTFE:
methods—Part 2: Dynamic image analysis methods
4.1.1 Type I and Type II—Resin produced from dispersion.
Each type of resin has the same requirements for bulk density,
3. Terminology
particle size, water content, melting peak temperature, tensile,
3.1 Definitions—The definitions given in Terminology
and elongation. Each type of resin is divided into grades in
D883 are applicable to this specification.
accordance with standard specific gravity (SSG), Thermal
3.2 Definitions of Terms Specific to This Standard:
Stability Index (TII), and Stretching Void Index (SVI). Grades
3.2.1 bulk density, n—the mass in grams per litre of resin
are divided into classes according to extrusion pressure.
measured under the conditions of the test.
NOTE 2—See Tables 1 and 2 for details about grades and classes.
3.2.2 extended specific gravity (ESG), n—the specific grav-
4.2 A line callout system is used to specify materials in this
ity of a specimen of PTFE material molded as described in this
specification. The system uses predefined cells to refer to
specification and sintered (see 3.2.7) for an extended period of
specific aspects of this specification, as illustrated as follows:
time, compared to the sintering time for the measurement of
SSG (see 3.2.8), using the appropriate sintering schedule given
in this specification.
3.2.3 lot, n—one production run or a uniform blend of two
Specification
or more production runs.
Standard Number Type Grade Class Special Notes
3.2.4 preforming, vb—compacting powdered PTFE material
Block
under pressure in a mold to produce a solid object, called a
| | | | |
preform, that is capable of being handled. Molding and
Example: Specification I 2 C
compaction are terms used interchangeably with preforming
D4895 - XX
for PTFE.
3.2.5 reground resin, n—resin produced by grinding PTFE
material that has been preformed but has never been sintered.
For this example, the line callout would be Specification
3.2.6 reprocessed resin, n—resin produced by grinding
D4895 - XX, I2C, and would specify a coagulated dispersion
PTFE material that has been preformed and sintered.
form of polytetrafluoroethylene that has all of the properties
listed for that type, grade, and class in the appropriate specified
3.2.7 sintering, n—as it applies to PTFE, a thermal treat-
properties or tables, or both, in the specification identified. A
ment during which the PTFE is melted and recrystallized by
comma is used as the separator between the standard number
cooling with coalescence occurring during the treatment.
and the type. Separators are not needed between the type,
3.2.8 standard specific gravity (SSG), n—the specific grav-
grade, and class.
ity of a specimen of PTFE material molded as described in this
specification and sintered using the appropriate sintering
5. Mechanical Properties
schedule given in this specification.
5.1 The resins covered by this specification shall be in
3.2.9 strained specific gravity (strained SG), n—the specific
accordance with the requirements prescribed in Tables 1 and 2,
gravity of a specimen of PTFE material molded, sintered, and
when tested by the procedures specified herein.
strained as described in this specification.
3.2.10 stretching void index (SVI), n—a measure of the
6. Other Requirements
change in specific gravity of PTFE material which has been
subjected to tensile strain as described in this specification. 6.1 The resin shall be uniform and shall contain no additives
or foreign material.
3.2.11 thermal instability index (TII), n—a measure of the
decrease in molecular weight of PTFE material which has been
6.2 The color of the material as shipped by the supplier shall
heated for a prolonged period of time.
be natural white.
3.2.12 unstrained specific gravity (USG), n—the specific
gravity, prior to straining, of a specimen of PTFE material used
in the Stretching Void Index Test (see 10.9) of this specifica- 5
See the Form and Style for ASTM Standards manual, available from ASTM
tion. Headquarters.
A
TABLE 1 Detail Requirements for all Types, Grades and Classes
Melting Peak
Particle Size
Bulk Density, Water Content, Tensile Strength, Elongation at Break,
Temperature, °C
Type Average
g/L max, % min, MPa min, %
Diameter, μm
Initial Second
B
I 550 ± 150 500 ± 200 0.04 327 ± 10 19 200
B
II 550 ± 150 1050 ± 350 0.04 327 ± 10 19 200
A
The types, grades, and classes are not the same as those in previous editions of Specification D4895.
B
Greater than 5.0°C above the second melting peak temperature.
D4895 − 18 (2023)
A
TABLE 2 Detail Requirements for All Types, Grades and Classes
Standard Specific Gravity
Thermal Instability Index, Stretching Void Index,
Type Grade Class Extrusion Pressure, MPa
max max
min max
B C
I 1 A 2.14 2.18 5 to <15 50 NA
D C
B 2.14 2.18 15 to <55 50 NA
E C
C 2.14 2.18 15 to <75 50 NA
B C
2 A 2.17 2.25 5 to <15 50 NA
D C
B 2.17 2.25 15 to <55 50 NA
E C
C 2.17 2.25 15 to <75 50 NA
E
3 C 2.15 2.19 15 to <75 15 200
E
D 2.15 2.19 15 to <65 15 100
E
E 2.15 2.19 15 to <65 50 200
D
4 B 2.14 2.16 15 to <55 15 50
B C
II 1 A 2.14 2.25 5 to <15 50 NA
A
The types, grades, and classes are not the same as those in previous editions of Specification D4895.
B
Tested at a reduction ratio of 100:1 (reduction ratio is the ratio of the cross-sectional area of the preform to the cross-sectional area of the die).
C
Not applicable.
D
Tested at a reduction ratio of 400:1.
E
Tested at a reduction ratio of 1600:1.
NOTE 3—For maximum precision, these weighing and preforming
6.3 For purposes of determining conformance, all specified
operations shall be carried out at 23 6 2°C (73.4 6 3.6°F) (the “near
limits for this classification system are absolute limits, as
ambient” temperature referred to herein). These operations shall not be
defined in Practice E29.
performed at temperatures below 21°C (70°F) due to the crystalline
6.3.1 With the absolute method, an observed value is not
transition that occurs in PTFE in this temperature region which leads to
rounded, but is to be compared directly with the limiting value.
possible cracks in sintered specimens and differences in specimen density
(as well as changes in other physical properties). Problems caused by the
Example: In Table 2 Type I, Grade 4, Class B, under Specific
effect of temperature on the specific gravity or density of PTFE shall be
Gravity, 2.14 shall be considered as 2.140000 and 2.16 shall be
minimized when the measurement is made using immersion procedures if
considered 2.160000.
a sensitive thermometer (for example, one reading 6 0.1°C) is used in the
liquid and the temperature is adjusted to be at least 22°C.
7. Sampling
9.1.2 Screen 14.5 g of PTFE resin through a No. 10 sieve
7.1 Sampling shall be statistically adequate to satisfy the
into the die. Adjust the lower plug height to allow the resin in
requirements in Section 11.
the die can be leveled by drawing a straightedge in contact with
the top of the die across the top of the die cavity. Insert the die
8. Number of Tests
in a suitable hydraulic press and apply pressure gradually (see
8.1 Lot inspection shall include tests for bulk density,
Note 4) until a pressure of 14 MPa (2030 psi) is attained. Hold
particle size, and extrusion pressure. Periodic tests shall consist
this pressure for 3 min. Remove the disk from the die. Write the
of all the tests specified in Tables 1 and 2 and shall be made at
sample identification number on the preform using an appro-
least once per year.
priate marker that will not affect the PTFE during sintering.
8.2 The tests listed in Tables 1 and 2, as they apply, are
NOTE 4—As a guide, increasing the pressure at a rate of 3.5 MPa (500
sufficient to establish conformity of a material to this specifi-
psi)/min is suggested until the desired maximum pressure is attained.
cation. One set of test specimens as prescribed in Section 9
9.1.3 Place the sintering oven in a laboratory hood (or equip
shall be considered sufficient for testing each sample. The
it with an adequate exhaust system) and sinter the preforms in
average of the results for the specimens tested shall conform to
accordance with Table 3, Procedure A (see Note 5).
the requirements of this specification.
NOTE 5—Although the rate of heat application is not critical, the
9. Specimen Preparation cooling cycle is most important and the conditions cited in this procedure
must be followed very closely. If they are not followed, the crystallinity of
9.1 Test Disks for Tensile Properties:
the disks and the resulting physical properties will be markedly changed.
9.1.1 Use the die shown in Fig. 1 for the molding of test
Therefore, the use of a programmed oven is recommended for the most
precise sintering cycle control and the hood window shall be left down
disks (see Note 2). Place flat aluminum disks, 0.1 to 0.4 mm
during the entire sintering procedure, the latter being an important safety
(0.004 in. to 0.016 in.) thick and 76 mm (3 in.) in diameter, on
consideration.
both sides of the resin. The test resin shall be near ambient
9.2 Test Specimens for Standard Specific Gravity and Ther-
temperature prior to molding (see Note 3). (Warning—PTFE
mal Instability Index:
resins can evolve small quantities of gaseous products when
heated above 204°C (400°F). Some of these gases are harmful. 9.2.1 A cylindrical preforming mold, 29-mm (1.14-in.) in-
Consequently, exhaust ventilation must be used whenever ternal diameter by at least 76 mm (3 in.) deep, is used to
these resins are heated above this temperature, as they are prepare the preforms. Clearance shall be sufficient to ensure
during the sintering operations that are a part of this specifi- escape of air during pressing. Place flat al
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