ASTM D4894-07(2012)
(Specification)Standard Specification for Polytetrafluoroethylene (PTFE) Granular Molding and Ram Extrusion Materials
Standard Specification for Polytetrafluoroethylene (PTFE) Granular Molding and Ram Extrusion Materials
ABSTRACT
This specification focuses on granular polytetrafluoroethylene (PTFE) resins that have never been preformed or molded, and are normally processed by methods similar to those used in powder metallurgy or ceramics, or by special extrusion processes. These PTFE resins are homopolymers of tetrafluoroethylene, or, in some cases, modified homopolymers containing not more than one percent by weight of other fluoromonomers. The materials included herein do not include mixtures of PTFE resin with additives such as colorants, fillers or plasticizers; nor do they include reprocessed or reground resin or any fabricated articles. Included are specimen preparation, test methods and requirements for materials, melting characteristics, bulk density, particle size, water content, standard specific gravity, thermal instability index, and mechanical (tensile) properties.
SCOPE
1.1 This specification covers granular resins and test methods for polytetrafluoroethylene (PTFE) that have never been preformed or molded and are normally processed by methods similar to those used in powder metallurgy or ceramics, or by special extrusion processes. These PTFE resins are homopolymers of tetrafluoroethylene, or, in some cases, modified homopolymers containing not more than one percent by weight of other fluoromonomers. The usual methods of processing thermoplastics generally are not applicable to these materials because of their viscoelastic properties at processing temperatures. The materials included herein do not include mixtures of PTFE resin with additives such as colorants, fillers or plasticizers; nor do they include reprocessed or reground resin or any fabricated articles. The methods and properties included are those required to identify the various types of resins. Additional procedures are provided in the Appendix for further characterization of the resins.
1.2 The values stated in SI units as detailed in are to be regarded as the standard, and the practices of are incorporated herein.
1.3 The following precautionary caveat pertains only to the Specimen Preparation section, Section 9, and the Test Methods section, Section 10, of this specification: This specification 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 and health practices and determine the applicability of regulatory limitations prior to use. See Notes 3 and 9 for specific cautionary statements.
Note 1—Information in this specification is technically equivalent to related information in ISO 12086-1 and ISO 12086-2.
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Standards Content (Sample)
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Designation:D4894 −07(Reapproved 2012)
Standard Specification for
Polytetrafluoroethylene (PTFE) Granular Molding and Ram
Extrusion Materials
This standard is issued under the fixed designation D4894; 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* 2. Referenced Documents
1.1 This specification covers granular resins and test meth- 2.1 ASTM Standards:
ods for polytetrafluoroethylene (PTFE) that have never been D618Practice for Conditioning Plastics for Testing
preformed or molded and are normally processed by methods D638Test Method for Tensile Properties of Plastics
similar to those used in powder metallurgy or ceramics, or by D792Test Methods for Density and Specific Gravity (Rela-
special extrusion processes. These PTFE resins are homopoly- tive Density) of Plastics by Displacement
mers of tetrafluoroethylene, or, in some cases, modified ho- D883Terminology Relating to Plastics
mopolymerscontainingnotmorethanonepercentbyweightof D1895Test Methods forApparent Density, Bulk Factor, and
other fluoromonomers. The usual methods of processing ther- Pourability of Plastic Materials
moplastics generally are not applicable to these materials D3295Specification for PTFE Tubing, Miniature Beading
because of their viscoelastic properties at processing tempera- and Spiral Cut Tubing
tures.Thematerialsincludedhereindonotincludemixturesof D3892Practice for Packaging/Packing of Plastics
PTFE resin with additives such as colorants, fillers or plasti- D4441Specification for Aqueous Dispersions of Polytetra-
cizers;nordotheyincludereprocessedorregroundresinorany fluoroethylene
fabricated articles. The methods and properties included are D4591Test Method for Determining Temperatures and
those required to identify the various types of resins. Addi- Heats of Transitions of Fluoropolymers by Differential
tional procedures are provided in the Appendix for further Scanning Calorimetry
characterization of the resins. D4745Classification System and Basis for Specification for
FilledPolytetrafluoroethlyene(PTFE)MoldingandExtru-
1.2 The values stated in SI units as detailed in IEEE/ASTM
sion Materials Using ASTM Methods
SI-10 are to be regarded as the standard, and the practices of
D4895 Specification for Polytetrafluoroethylene (PTFE)
IEEE/ASTM SI-10 are incorporated herein.
Resin Produced From Dispersion
1.3 The following precautionary caveat pertains only to the
E11Specification forWovenWireTest Sieve Cloth andTest
SpecimenPreparationsection,Section9,andtheTestMethods
Sieves
section, Section 10, of this specification: This specification
E177Practice for Use of the Terms Precision and Bias in
does not purport to address all of the safety concerns, if any,
ASTM Test Methods
associated with its use. It is the responsibility of the user of this
IEEE/ASTM SI-10Standard for Use of the International
standard to establish appropriate safety and health practices
System of Units (SI): The Modern Metric System
and determine the applicability of regulatory limitations prior
2.2 ISO Standards:
to use. See Notes 3 and 9 for specific cautionary statements.
ISO 12086-1 Plastics—Fluoropolymer Dispersions and
Moulding and Extrusion Materials—Part 1: Designation
NOTE 1—Information in this specification is technically equivalent to
related information in ISO12086-1 and ISO12086-2.
System and Basis for Specification
1 2
This specification is under the jurisdiction of ASTM Committee D20 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Plastics and is the direct responsibility of Subcommittee D20.15 on Thermoplastic contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Materials. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved April 1, 2012. Published June 2012. Originally the ASTM website.
approved in 1989. Last previous edition approved in 2007 as D4894-07. DOI: Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
10.1520/D4894-07R12. 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
D4894−07 (2012)
A
TABLE 1 Detail Requirements for Tests on Resins
Type Grade Bulk Density, g/L Particle Size, Average Diameter, µm Water Content, max, % Melting Peak Temperature
Initial °C Second °C
A
I 1 700 ± 100 500 ± 150 0.04 327±10
A
2 675±50 375±75 0.04 327±10
A
II . . . . . . <100 0.04 327±10
A
III 1 400 ± 125 <100 0.04 327±10
A
2 850 ± 100 500 ± 150 0.04 327±10
A
IV 1 650 ± 150 550 ± 225 0.04 327±10
A
2 >800 . . . 0.04 327±10
A
3 580±80 200±75 0.04 327±10
V . . . 635 ± 100 500 ± 250 0.04 327 ± 10 327 ± 10
A
VI . . . 650 ± 150 800 ± 250 0.04 327±10
A
>5°C above the second melting peak temperature.
ISO 12086-2Test Methods for Fluoropolymers 4.1.1 Type I—Resin used for general-purpose molding and
ram extrusion.
3. Terminology
4.1.2 Type II—Finely divided resin with an average particle
3.1 Definitions:
size less than 100 micrometres.
3.1.1 The terminology given in Terminology D883 is appli-
4.1.3 Type III—Modified resins, either finely divided or
cable to this specification.
free-flowing, typically used in applications requiring improved
3.2 Descriptions of Terms Specific to This Standard:
resistance to creep and stress-relaxation in end-use.
3.2.1 bulk density—the mass (in grams) per litre of resin
4.1.4 Type IV—Free-flowing resins. Generally made by
measured under the conditions of the test.
treatment of finely divided resin to produce free-flowing
agglomerates.
3.2.2 extended specific gravity (ESG)—the specific gravity
4.1.5 Type V—Presintered. Resin that has been treated
of a specimen of PTFE material molded as described in this
thermally at or above the melting point of the resin at
specificationandsintered(g.v.)foranextendedperiodoftime,
atmospheric pressure without having been previously pre-
comparedtothesinteringtimeforthemeasurementofstandard
formed.
specificgravity(SSG),usingtheappropriatesinteringschedule
4.1.6 Type VI—Resin, not presintered, but for ram extrusion
given in this specification.
only.
3.2.3 lot, n—one production run or a uniform blend of two
or more production runs. NOTE 2—See Tables 1 and 2 for division of Types by Grades, and
footnotes to Tables 1 and 2 (and Table X2.1 inAppendix X2.) for former
3.2.4 preforming—compacting powdered PTFE material
classifications.
under pressure in a mold to produce a solid object, called a
4.2 Aline callout system is used to specify materials in this
preform, that is capable of being handled. Molding and
standard. The system uses predefined cells to refer to specific
compaction are terms used interchangeably with preforming
aspects of this specification, illustrated as follows:
for PTFE.
3.2.5 reground resin—that produced by grinding PTFE
Specification
material that has been preformed but has never been sintered.
Standard Number
: Type : Grade : Class : Special notes
Block
3.2.6 reprocessed resin—that produced by grinding PTFE
:: : : :
material that has been both preformed and sintered.
Example: ASTM
III 2
D4894 – 04
3.2.7 sintering—as it applies to PTFE, a thermal treatment
during which the PTFE is melted and recrystallized by cooling
with coalescence occurring during the treatment.
For this example, the line callout would be ASTM
3.2.8 skiving—a machining operation during which a con-
D4894–04, III2, and would specify a granular polytetrafluo-
tinuousfilmofPTFEmaterialispeeledfromthelateralsurface
roethylene that has all of the properties listed for thatType and
of a cylindrical sintered molding.
Grade in the appropriate specified properties, Tables, or both,
3.2.9 standard specific gravity (SSG)—the specific gravity
in this specification. In this case there is no Class item so the
of a specimen of PTFE material molded as described in this
cell position for class is left blank. A comma is used as the
specification and sintered using the appropriate sintering
separator between Standard Number and Type. Separators are
schedule given in this specification.
not needed between Type, Grade, and Class. Provision for
3.2.10 thermal instability index (TII)—a measure of the
Special Notes is included so that other information will be
decreaseinmolecularweightofPTFEmaterialwhichhasbeen
providedwhenrequired.AnexamplewouldbeinSpecification
heated for a prolonged period of time.
D3295 where dimensions and tolerances are specified for each
AWG size within Type and Class. When Special Notes are
4. Classification
used, they shall be preceded by a comma.
4.1 This specification covers the following six types of
PTFE generally used for compression molding or ram
extrusion, or both: See the ASTM Form and Style Manual, available from ASTM Headquarters.
D4894−07 (2012)
TABLE 2 Detail Requirements for Tests on Molded Specimens
Type Grade Thermal Instability Index, max Standard Specific Gravity Tensile Strength, min Elongation at break min %
min max MPa psi
I 1 50 2.13 2.18 13.8 2000 140
2 50 2.13 2.18 17.2 2500 200
II . . . 50 2.13 2.19 27.6 4000 300
III 1 50 2.14 2.22 28.0 4060 450
2 50 2.14 2.18 20.7 3000 300
IV 1 50 2.13 2.19 25.5 3700 275
2 50 2.13 2.19 27.6 4000 300
3 50 2.15 2.18 27.6 4000 200
A A A A A A
V . NA NA NA NA NA NA
B A A A A A A
VI . NA NA NA NA NA NA
A
NA: Not Applicable by molding techniques included in this specification.
B
Extrusions of this resin show different degrees of clarity from the others.
5. Mechanical Properties 9.1.2 Screen 14.5 g (for tensile properties) or 7.25 g (for
electrical properties discussed in Appendix X1.7) of PTFE
5.1 Theresinscoveredbythisspecificationshallconformto
resinthroughaNo.10handsieveintothedie.Adjustthelower
the requirements prescribed in Tables 1 and 2 when tested by
plug height to allow the resin in the die can be leveled by
the procedures specified herein. Table 1 lists tests to be carried
drawing a straightedge in contact with the top of the die across
outonresins.Table2liststestsrequiringspecimensmoldedas
the top of the die cavity. Insert the die in a suitable hydraulic
described in Section 9.
pressandapplypressuregradually(Note3)untilatotalof34.5
MPa (5000 psi) is attained. Hold this pressure for 3 min.
6. Other Requirements
Remove the disk identification on the disk at this time.
6.1 Theresinshallbeuniformandshallcontainnoadditives
NOTE3—Asaguide,increasingthepressureatarateof3.45MPa(500
or foreign material.
psi)/min is suggested until the desired maximum pressure is attained.
6.2 The color of the material as shipped by the seller shall
9.1.3 Sinter the preforms in accordance with Table 3 (Note
be white.
4).
9.1.3.1 Use Procedure B for Types I, II and IV and Proce-
7. Sampling
dure C for Type III.
7.1 Sampling shall be statistically adequate to satisfy the
NOTE 4—Although the rate of heating application is not critical, the
requirements of 11.4
cooling cycle is most important and the conditions cited in these
procedures must be followed very closely. If they are not followed, the
8. Number of Tests
crystallinity of the disks and the resulting physical properties will be
markedly changed. Therefore, the use of a programmed oven is recom-
8.1 Lot inspection shall include tests for bulk density,
mended for the most precise sintering cycle control so that the hood
particle size and standard specific gravity. Periodic tests shall
window will be left down during the entire sintering procedure, the latter
consist of all the tests specified in Tables 1 and 2 and shall be
being an important safety consideration.
made at least one per year.
9.2 Test Specimens for Standard Specific Gravity (SSG) and
8.2 The tests listed in Tables 1 and 2, as they apply, are
Extended Specific Gravity (ESG):
sufficient to establish conformity of a material to this specifi-
9.2.1 A cylindrical preforming die, 28.6 mm (1 ⁄8 in.)
cation. One set of tests specimens as prescribed in Section 7
internal diameter by at least 76.2 mm (3 in.) deep, is used to
shall be considered sufficient for testing each sample. The
preparethepreforms.Endplugclearancesshallbesufficientto
averageoftheresultsforthespecimenstestedshallconformto
ensureescapeofairduringpressing.Thetestresinshallbenear
the requirements of this specification.
ambient temperature prior to molding (Note 5).
NOTE 5—For maximum precision, the weighing and preforming opera-
9. Specimen Preparation
tions shall be carried out at 23 62°C (73.4 63.6°F) (the “near ambient”
9.1 Test Disks:
temperaturereferredtoherein).Theseoperationsshallnotbepreformedat
temperatures below 21°C (70°F) due to the crystalline transition that
9.1.1 Use the die shown in Fig. 1 for the molding of test
occurs in PTFE in this temperature region which leads to possible cracks
disks.The test resin shall be near ambient temperature prior to
in sintered specimens and differences in specimen density (as well as
molding (Note 5). Warning—PTFE can evolve small quanti-
changes in other physical properties). Problems caused by the effects of
ties of gaseous products when heated above 204°C (400°F).
temperature on the specific gravity or density of PTFE will be minimized
Some of these gases are harmful. Consequently, exhaust when the measurement is made using immersion procedures if a sensitive
thermometer (for example, one reading 60.1°C) is used in the liquid and
ventilation must be used whenever the resins are heated above
the temperature is adjusted to be at least 22°C.
this temperature, as they are during the sintering operations
that are a part of this specification. Since the temperature of 9.2.2 Weighout12.0 60.1gofresinandplaceitinthedie.
burning tobacco exceeds 204°C (400°F), those working with Screen non-free-flowing resins through a No. 10 sieve. Break
PTFE resins should ensure that tobacco is not contaminated. upcompactedresinsbyhand-shakingcoldresininahalf-filled
D4894−07 (2012)
FIG. 1 Assembly and Details of Die for Molding Test Specimens
TABLE 3 Sintering Procedures
BC DE FG H I
Initial temperature, °C (°F) 290 (554) 290 (554) 238 (460) 238 (460) 290 (554) 238 (460) 238 (460) 238 (460)
Rate of heating, °C/h (°F/h) 120 ± 10 120 ± 10 60 ± 5 60 ± 5 120 ± 10 60 ± 5 60 ± 5 60 ± 5
(216 ± 18) (216 ± 18) (108 ± 9) (108 ± 9) (216 ± 18) (108 ± 9) (108 ± 9) (108 ± 9)
Hold temperature, °C (°F) 380 ± 6 357 ± 8 371 ± 6 360 ± 6 380 ± 6 357 ± 8 380 ± 6 371 ± 6
(716 ± 10) (675 ± 15) (700 ± 10) (685 ± 10) (716 ± 10) (675 ± 5) (716 ± 10) (700 ± 10)
H
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