ASTM D 4894-07

Designation: D 4894 – 07 Standard Specification for Polytetrafluoroethylene (PTFE) Granular Molding and Ram Extrusion Materials 1 This standard is issued under the fixed designation D 4894; 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* 1.1 This specification covers granular resins and test meth- ods 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 homopoly- mers of tetrafluoroethylene, or, in some cases, modified ho- mopolymers containing not more than one percent by weight of other fluoromonomers. The usual methods of processing ther- moplastics generally are not applicable to these materials because of their viscoelastic properties at processing tempera- tures. The materials included herein do not include mixtures of PTFE resin with additives such as colorants, fillers or plasti- cizers; 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. Addi- tional procedures are provided in the Appendix for further characterization of the resins. 1.2 The values stated in SI units as detailed in IEEE/ASTM SI-10 are to be regarded as the standard, and the practices of IEEE/ASTM SI-10 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. 2. Referenced Documents 2.1 ASTM Standards: 2 D 618 Practice for Conditioning Plastics for Testing D 638 Test Method for Tensile Properties of Plastics D 792 Test Methods for Density and Specific Gravity (Rela- tive Density) of Plastics by Displacement D 883 Terminology Relating to Plastics D 1895 Test Methods for Apparent Density, Bulk Factor, and Pourability of Plastic Materials D 3295 Specification for PTFE Tubing, Miniature Beading and Spiral Cut Tubing D 3892 Practice for Packaging/Packing of Plastics D 4441 Specification for Aqueous Dispersions of Polytet- rafluoroethylene D 4591 Test Method for Determining Temperatures and Heats of Transitions of Fluoropolymers by Differential Scanning Calorimetry D 4745 Specification for Filled Compounds of Polytet- rafluoroethylene (PTFE) Molding and Extrusion Materials D 4895 Specification for Polytetrafluoroethylene (PTFE) Resin Produced From Dispersion E 11 Specification for Wire Cloth and Sieves for Testing Purposes E 177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods IEEE/ASTM SI-10 Standard for Use of the International System of Units (SI): The Modern Metric System 2.2 ISO Standards: 3 ISO 12086-1 Plastics—Fluoropolymer Dispersions and Moulding and Extrusion Materials—Part 1: Designation System and Basis for Specification 1 This specification is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.15 on Thermoplastic Materials. Current edition approved Sept. 1, 2007. Published October 2007. Originally approved in 1989. Last previous edition approved in 2004 as D 4894 - 04. 2 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards volume information, refer to the standard’s Document Summary page on the ASTM website. 3 Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036. 1 *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. Copyright ASTM International Provided by IHS under license with ASTM Licensee=University of Texas Revised Sub Account/5620001114 Not for Resale, 12/04/2007 06:54:38 MSTNo reproduction or networking permitted without license from IHS - - ` , ` ` , ` ` , ` ` ` ` , , , ` , , , , , , ` , ` ` ` ` , ` - ` - ` , , ` , , ` , ` , , ` - - - ISO 12086-2 Test Methods for Fluoropolymers 3. Terminology 3.1 Definitions: 3.1.1 The terminology given in Terminology D 883 is ap- plicable to this specification. 3.2 Descriptions of Terms Specific to This Standard: 3.2.1 bulk density—the mass (in grams) per litre of resin measured under the conditions of the test. 3.2.2 extended specific gravity (ESG)—the specific gravity of a specimen of PTFE material molded as described in this specification and sintered (g.v.) for an extended period of time, compared to the sintering time for the measurement of standard specific gravity (SSG), using the appropriate sintering schedule given in this specification. 3.2.3 lot, n—one production run or a uniform blend of two or more production runs. 3.2.4 preforming—compacting powdered PTFE material under pressure in a mold to produce a solid object, called a preform, that is capable of being handled. Molding and compaction are terms used interchangeably with preforming for PTFE. 3.2.5 reground resin—that produced by grinding PTFE material that has been preformed but has never been sintered. 3.2.6 reprocessed resin—that produced by grinding PTFE material that has been both preformed and sintered. 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. 3.2.8 skiving—a machining operation during which a con- tinuous film of PTFE material is peeled from the lateral surface of a cylindrical sintered molding. 3.2.9 standard specific gravity (SSG)—the specific gravity of a specimen of PTFE material molded as described in this specification and sintered using the appropriate sintering schedule given in this specification. 3.2.10 thermal instability index (TII)—a measure of the decrease in molecular weight of PTFE material which has been heated for a prolonged period of time. 4. Classification 4.1 This specification covers the following six types of PTFE generally used for compression molding or ram extru- sion, or both: 4.1.1 Type I—Resin used for general-purpose molding and ram extrusion. 4.1.2 Type II—Finely divided resin with an average particle size less than 100 micrometres. 4.1.3 Type III—Modified resins, either finely divided or free-flowing, typically used in applications requiring improved resistance to creep and stress-relaxation in end-use. 4.1.4 Type IV—Free-flowing resins. Generally made by treatment of finely divided resin to produce free-flowing agglomerates. 4.1.5 Type V—Presintered. Resin that has been treated thermally at or above the melting point of the resin at atmospheric pressure without having been previously pre- formed. 4.1.6 Type VI—Resin, not presintered, but for ram extrusion only. NOTE 2—See Tables 1 and 2 for division of Types by Grades, and footnotes to Tables 1 and 2 (and Table X2.1 in Appendix X2.) for former classifications. 4.2 A line callout system is used to specify materials in this standard. The system uses predefined cells to refer to specific aspects of this specification, illustrated as follows: Specification Standard Number Block : Type : Grade : Class : Special notes : : : : : Example: ASTM D 4894 – 04 III 2 For this example, the line callout would be ASTM D 4894 – 04, III2, and would specify a granular polytetrafluo- roethylene that has all of the properties listed for that Type and Grade in the appropriate specified properties, Tables, or both, in this specification. In this case there is no Class item so the cell position for class is left blank. A comma is used as the separator between Standard Number and Type. Separators are not needed between Type, Grade, and Class.4 Provision for Special Notes is included so that other information will be provided when required. An example would be in Specification D 3295 where dimensions and tolerances are specified for each AWG size within Type and Class. When Special Notes are used, they shall be preceded by a comma. 4 See the ASTM Form and Style Manual, available from ASTM Headquarters. TABLE 1 Detail Requirements for Tests on ResinsA Type Grade Bulk Density, g/L Particle Size, Average Diameter,µm Water Content, max, % Melting Peak Temperature Initial °C Second °C I 1 700 6 100 500 6 150 0.04 A 327 6 10 2 675 6 50 375 6 75 0.04 A 327 6 10 II . . . . . . <100 0.04 A 327 6 10 III 1 400 6 125 <100 0.04 A 327 6 10 2 850 6 100 500 6 150 0.04 A 327 6 10 IV 1 650 6 150 550 6 225 0.04 A 327 6 10 2 >800 . . . 0.04 A 327 6 10 3 580 6 80 200 6 75 0.04 A 327 6 10 V . . . 635 6 100 500 6 250 0.04 327 6 10 327 6 10 VI . . . 650 6 150 800 6 250 0.04 A 327 6 10 A >5°C above the second melting peak temperature. D 4894 – 07 2Copyright ASTM International Provided by IHS under license with ASTM Licensee=University of Texas Revised Sub Account/5620001114 Not for Resale, 12/04/2007 06:54:38 MSTNo reproduction or networking permitted without license from IHS - - ` , ` ` , ` ` , ` ` ` ` , , , ` , , , , , , ` , ` ` ` ` , ` - ` - ` , , ` , , ` , ` , , ` - - - 5. Mechanical Properties 5.1 The resins covered by this specification shall conform to the requirements prescribed in Tables 1 and 2 when tested by the procedures specified herein. Table 1 lists tests to be carried out on resins. Table 2 lists tests requiring specimens molded as described in Section 9. 6. Other Requirements 6.1 The resin shall be uniform and shall contain no additives or foreign material. 6.2 The color of the material as shipped by the seller shall be white. 7. Sampling 7.1 Sampling shall be statistically adequate to satisfy the requirements of 11.4 8. Number of Tests 8.1 Lot inspection shall include tests for bulk density, particle size and standard specific gravity. Periodic tests shall consist of all the tests specified in Tables 1 and 2 and shall be made at least one per year. 8.2 The tests listed in Tables 1 and 2, as they apply, are sufficient to establish conformity of a material to this specifi- cation. One set of tests specimens as prescribed in Section 7 shall be considered sufficient for testing each sample. The average of the results for the specimens tested shall conform to the requirements of this specification. 9. Specimen Preparation 9.1 Test Disks: 9.1.1 Use the die shown in Fig. 1 for the molding of test disks. The test resin shall be near ambient temperature prior to molding (Note 5). Warning—PTFE can evolve small quanti- ties of gaseous products when heated above 204°C [400°F]. Some of these gases are harmful. Consequently, exhaust ventilation must be used whenever the resins are heated above this temperature, as they are during the sintering operations that are a part of this specification. Since the temperature of burning tobacco exceeds 204°C [400°F], those working with PTFE resins should ensure that tobacco is not contaminated. 9.1.2 Screen 14.5 g (for tensile properties) or 7.25 g (for electrical properties discussed in Appendix X1.7) of PTFE resin through a No. 10 hand sieve into the die. Adjust the lower plug height to allow the resin in 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 in a suitable hydraulic press and apply pressure gradually (Note 3) until a total of 34.5 MPa [5000 psi] is attained. Hold this pressure for 3 min. Remove the disk identification on the disk at this time. NOTE 3—As a guide, increasing the pressure at a rate of 3.45 MPa [500 psi]/min is suggested until the desired maximum pressure is attained. 9.1.3 Sinter the preforms in accordance with Table 3 (Note 4). 9.1.3.1 Use Procedure B for Types I, II and IV and Proce- dure C for Type III. NOTE 4—Although the rate of heating application is not critical, the cooling cycle is most important and the conditions cited in these procedures must be followed very closely. If they are not followed, the crystallinity of the disks and the resulting physical properties will be markedly changed. Therefore, the use of a programmed oven is recom- mended for the most precise sintering cycle control so that the hood window will be left down during the entire sintering procedure, the latter being an important safety consideration. 9.2 Test Specimens for Standard Specific Gravity (SSG) and Extended Specific Gravity (ESG): 9.2.1 A cylindrical preforming die, 28.6 mm [11⁄8 in.] internal diameter by at least 76.2 mm [3 in.] deep, is used to prepare the preforms. End plug clearances shall be sufficient to ensure escape of air during pressing. The test resin shall be near ambient temperature prior to molding (Note 5). NOTE 5—For maximum precision, the weighing and preforming opera- tions shall be carried out at 23 6 2°C [73.4 6 3.6°F] (the “near ambient” temperature referred to herein). These operations shall not be preformed at temperatures below 21°C [70°F] due to the crystalline transition that occurs in PTFE in this temperature region which leads to possible cracks in sintered specimens and differences in specimen density (as well as changes in other physical properties). Problems caused by the effects of temperature on the specific gravity or density of PTFE will be minimized 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 the temperature is adjusted to be at least 22°C. 9.2.2 Weigh out 12.0 6 0.1 g of resin and place it in the die. Screen non-free-flowing resins through a No. 10 sieve. Break up compacted resins by hand-shaking cold resin in a half-filled sealed glass container. Condition the resin in the sealed glass container in a freezer or dry-ice chest. After breaking up resin lumps, allow the sealed container to equilibrate to near ambient 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 V . . . NAA NAA NAA NAA NAA NAA VIB . . . NAA NAA NAA NAA NAA NAA A NA: Not Applicable by molding techniques included in this specification. B Extrusions of this resin show different degrees of clarity from the others. D 4894 – 07 3Copyright ASTM International Provided by IHS under license with ASTM Licensee=University of Texas Revised Sub Account/5620001114 Not for Resale, 12/04/2007 06:54:38 MSTNo reproduction or networking permitted without license from IHS - - ` , ` ` , ` ` , ` ` ` ` , , , ` , , , , , , ` , ` ` ` ` , ` - ` - ` , , ` , , ` , ` , , ` - - - temperature. Then screen and weigh the 12.0 6 0.1-g sample. Insert the die in a suitable hydraulic press and apply pressure gradually (Note 3) until a pressure of 34.5 MPa [5000 psi] is attained. Hold this pressure for 2 min. Remove the preform from the die. Write the sample identification number using an appropriate marker that will not effect the PTFE during sintering on the preform at this time. 9.2.3 Sinter the preforms in accordance with Table 3 (Note 4). 9.2.3.1 For SSG specimens use Procedure B for Types I, II and IV and Procedure C for Type III. 9.2.3.2 For ESG specimens use Procedure F for Types I, II and IV and Procedure G for Type III. NOTE 6—Improved precision in SSG and ESG test results has been obtained with the use of an upright, cylindrical oven and an aluminum sintering rack. The cylindrical oven has an inside diameter of 140 mm [5.5 in.] and an inside depth of 203 mm [8 in.] plus additional depth to accommodate a 50.8-mm [2-in.] thick cover, and is equipped with suitable heaters and controllers to sinter specimens in accordance with the Procedures in Table 3. The rack, as shown in Fig. 2, allows preforms to be placed symmetrically in the center region of the oven. Place six preforms on each of the middle oven rack shelves (if six or fewer preforms are to be sintered, place them on the middle rack, filling in with “dummies” as needed). Place “dummies” on the top and bottom shelves. Specimens must be spaced evenly in a circle on each shelf, with none of them touching. An FIG. 1 Assembly and Details of Die for Molding Test Specimens TABLE 3 Sintering Procedures B C D E F G 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 6 10 120 6 10 60 6 5 60 6 5 120 6 10 60 6 5 60 6 5 60 6 5 [216 6 18] [216 6 18] [108 6 9] [108 6 9] [216 6 18] [108 6 9] [108 6 9] [108 6 9] Hold temperature, °C [°F] 380 6 6 357 6 8 371 6 6 360 6 6 380 6 6 357 6 8 380 6 6 371 6 6 [716 6 10] [675 6 15] [700 6 10] [685 6 10] [716 6 10] [675 6 5] [716 6 10] [700 6 10] Hold time, min 30 + 2, −0 30 + 2, −0 240 6 15 240 6 15 360 6 5 240 6 15 960 6 15 120 6 5 Cooling rate, °C/h [°F/h] 60 6 5 60 6 5 60 6 5 60 6 5 60 6 5 60 6 5 60 6 5 60 6 5 [108 6 9] [108 6 9] [108 6 9] [108 6 9] [108 6 9] [108 6 9] [108 6 9] [108 6 9] Final or second hold temperature, °C [°F] 294 6 6 294 6 6 238 6 6 238 6 6 294 6 6 238 6 6 238 6 6 238 6 6 [561 6 10] [561 6 10] [460 6 10] [460 6 10] [561 6 10] [460 6 10] [460 6 10] [460 6 10] Second hold time, min 24 + 0.5, −0 24 + 0.5, −0 NAA NAA 24 + 0.5, −0 NAA NAA NAA Period to room temperature, min, h 1⁄2 1⁄2 6 6 1⁄2 6 6 6 A NA, Not applicable. FIG. 2 SSG Samples Sintering Rack D 4894 – 07 4Copyright ASTM International Provided by IHS under license with ASTM Licensee=University of Texas Revised Sub Account/5620001114 Not for Resale, 12/04/2007 06:54:38 MSTNo reproduction or networking permitted without license from IHS - - ` , ` ` , ` ` , ` ` ` ` , , , ` , , , , , , ` , ` ` ` ` , ` - ` - ` , , ` , , ` , ` , , ` - - - oven load must be no less than 18 pieces including “dummies.” “Dum- mies” are defined as normal 12-g specimens that have previously been through the sintering cycle. “Dummies” must only be used for an additional two or three thermal cycles, due to eventual loss of thermal stability and physical form. 9.2.4 Remove all flash from each specimen so that no air bubbles will cling to the edges when the specimen is immersed in the solution for weighing during the standard specific gravity and thermal instability index tests. It is recommended for this section and during testing that cotton gloves be worn while handling test specimens. 9.3 Test Billets: 9.3.1 Use test specimens cut or skived from billets may be used as alternatives to the test disks described in 9.1 and 9.2 for Types I, II, III and IV resins. 9.3.2 Mold test billets in a mold similar to Fig. 3, having an inside diameter of 57 mm [2.25 in.] and of sufficient height to contain the resin sample. Plug clearance shall be sufficient to ensure escape of air during pressing. A 254-mm [10-in.] mold cavity fill depth will produce a billet approximately 76 mm [3 in.] long from a resin charge of 400 6 50 g. Vary the billet length in accordance with the testing to be done. The test resin shall be near