New useful ASTM test methods and standards now available internationally.

ASTM evolved from the American Section of the IATM (International Association of Testing Materials) which was formally organized in 1895 in Vienna. ASTM (American Society for Testing and Materials) was formally incorporated in 1902 (refs. 1 and 2). The IATM ceased to exist in 1915; however, ASTM has grown into a standards organization that publishes over 11,000 standards which are used throughout the world. In fact, ASTM formally changed its name in 2002 to ASTM International. ASTM Committee D11 has jurisdiction in developing rubber test methods and standards, with over 300 active standards used worldwide.

ASTM International is a private, non-government, not-for-profit organization. In total number of standards, staffing levels and organizational structure, it is somewhat similar to the International Organization for Standardization (ISO), which was founded after World War II in 1946. Just as ASTM, ISO is also a non-governmental organization whose standards have no legal force (ref. 3). (However, more than half of the official standards bodies that are members of ISO have incorporated ISO standards into public laws, just as some national and state governments have done with ASTM standards) (ref. 4).

There are over 340 members in the ASTM D11 committee from the rubber industry in the United States, as well as 12 other countries. There are two meetings a year (June and December) to advance new ASTM standards and update existing ones. All ASTM standards go through a balloting process. Voting is balanced between users and producers, and all negatives (disapprovals) in this balloting process must be reviewed by the technical subcommittee having jurisdiction for the specific standard. Therefore, all approved ASTM standards and test methods truly represent a consensus of the rubber industry.

ASTM D11 has recently developed new standards which will have a significant impact on the rubber industry. The purpose of this article is to review some of these recent standard test methods and standard practice advancements.

New, fast and effective processability test

A very important ASTM processability test, ASTM D6204, was first published in 1997. This standard was a result from the previous three years of work of the Task Group on Rotorless Shear Rheometry under Subcommittee D11.12, Processability Tests. This standard was based mainly on the use of the Alpha Technologies RPA 2000 rubber process analyzer (which will hereafter be referred to as simply the RPA). When this standard was first published, it specified the conditions for a three-point frequency sweep (0.1, 2 and 20 Hz, at 100[degrees]C and [+ or -] 7% strain) in order to quickly test processing differences in raw rubber (usually based on differences in average molecular weight, molecular weight distribution, long chain branching and gel concentration). This three-point frequency sweep is significantly faster than the traditional Mooney viscosity test (ASTM D1646); but more importantly, the three-point measurement is far more sensitive to processability differences among received shipments of raw polymer.

Not only is this three-point frequency sweep applied to raw rubber, it is also applied to mixed rubber batches as well. This procedure is used to determine the shear thinning profiles for different stocks, which is very important in predicting a mixed stock's performance in extrusion or injection molding, for example. Figure 1 gives an example of a typical output from this three-point frequency sweep. While this three-point frequency sweep method can also be used to

[FIGURE 1 OMITTED]

ASTM evolved from the American Section of the IATM (International Association of Testing Materials) which was formally organized in 1895 in Vienna. ASTM (American Society for Testing and Materials) was formally incorporated in 1902 (refs. 1 and 2). The IATM ceased to exist in 1915; however, ASTM has grown into a standards organization that publishes over 11,000 standards which are used throughout the world. In fact, ASTM formally changed its name in 2002 to ASTM International. ASTM Committee D11 has jurisdiction in developing rubber test methods and standards, with over 300 active standards used worldwide.

ASTM International is a private, non-government, not-for-profit organization. In total number of standards, staffing levels and organizational structure, it is somewhat similar to the International Organization for Standardization (ISO), which was founded after World War II in 1946. Just as ASTM, ISO is also a non-governmental organization whose standards have no legal force (ref. 3). (However, more than half of the official standards bodies that are members of ISO have incorporated ISO standards into public laws, just as some national and state governments have done with ASTM standards) (ref. 4).

There are over 340 members in the ASTM D11 committee from the rubber industry in the United States, as well as 12 other countries. There are two meetings a year (June and December) to advance new ASTM standards and update existing ones. All ASTM standards go through a balloting process. Voting is balanced between users and producers, and all negatives (disapprovals) in this balloting process must be reviewed by the technical subcommittee having jurisdiction for the specific standard. Therefore, all approved ASTM standards and test methods truly represent a consensus of the rubber industry.

ASTM D11 has recently developed new standards which will have a significant impact on the rubber industry. The purpose of this article is to review some of these recent standard test methods and standard practice advancements.

New, fast and effective processability test

A very important ASTM processability test, ASTM D6204, was first published in 1997. This standard was a result from the previous three years of work of the Task Group on Rotorless Shear Rheometry under Subcommittee D11.12, Processability Tests. This standard was based mainly on the use of the Alpha Technologies RPA 2000 rubber process analyzer (which will hereafter be referred to as simply the RPA). When this standard was first published, it specified the conditions for a three-point frequency sweep (0.1, 2 and 20 Hz, at 100[degrees]C and [+ or -] 7% strain) in order to quickly test processing differences in raw rubber (usually based on differences in average molecular weight, molecular weight distribution, long chain branching and gel concentration). This three-point frequency sweep is significantly faster than the traditional Mooney viscosity test (ASTM D1646); but more importantly, the three-point measurement is far more sensitive to processability differences among received shipments of raw polymer.

Not only is this three-point frequency sweep applied to raw rubber, it is also applied to mixed rubber batches as well. This procedure is used to determine the shear thinning profiles for different stocks, which is very important in predicting a mixed stock's performance in extrusion or injection molding, for example. Figure 1 gives an example of a typical output from this three-point frequency sweep. While this three-point frequency sweep method can also be used to measure the state-of-mix of batches, as well as predict downstream properties, such as extrusion die swell, later studies have shown that these properties are better measured with higher applied strains (refs. 5 and 6).

Because higher strain test conditions with the RPA were found to be more effective at measuring differences in batch to batch state-of-mix, die swell behavior, etc., a new Part B to ASTM D6204 was written and published in 2001. This new which use standard reference materials.

Twenty years ago, the ASTM D11 Committee and the rubber industry used standard reference materials provided by the National Bureau of Standards (NBS), which is now known as National Institute of Standards and Technology (NIST). However, about 15 years ago NIST decided to cancel their program that provided these standard reference materials to the rubber industry. In order to fulfill a critical rubber industry need, ASTM Committee D11 formed the IRM Ad Hoc Group, under Subcommittee D11.20, Compounding Materials, to establish IRM (Industry Reference Material) replacements for the various NIST SRM (Standard Reference Materials) that were being phased out. As can be seen from table 2, today almost all of the old SRMs have now been replaced with IRMs. Also, quite a few new IRMs have been added, as well.

ASTM D4678 was published in 1994 to describe the preparation, testing, acceptance and documentation of IRMs; while D5900 was published in 1998 to denote the exact chemical and physical specifications for IRMs. Also, several new IRMs were introduced this year. IRM 3 has just been established for TBBS accelerator for use in various ASTM test recipes. IRM 913 (protein) and IRM 914 (antisera) have just been established for use in the new ASTM Standard D6499, which is the determination of antigenic protein in natural rubber and its products. Specifications for all three of these IRMs are being added to ASTM D5900.

Also, currently the IRM Ad Hoc committee is working on establishing a new fluoroelastomer compound, with a very long shelf life, as a standard reference compound to verify that MDRs and RPAs (in ASTM D5289) are in a state of statistical control (ref. 10).

New computer classification system for compounding materials

Most rubber manufacturers have their raw materials (or compounding ingredients) entered into their computer material management systems by chemical names, trade names, manufacturers, CAS registry number and code numbers. Many companies can also classify their raw materials by functionality. However, these classification systems can differ greatly from plant to plant and company to company, and certainly are not universal or all-inclusive.

An effective, standardized classification system is desirable, because often times retrieving information by the other traditional fields is not effective. For example, "common" chemical names are not standardized. On the other hand, IUPAC nomenclature, while standardized, is very lengthy and does not lend itself to easy retrieval. In addition, one may not know such identifiers as the trade name, CAS registry number or the vendor name.

ASTM D5899, which provides a standardized classification system for rubber compounding ingredients, was first published in 1998. This classification system is a two-tier system in which the primary classification is based on functionality, while the secondary classification is based on chemical characteristics. By assigning the "functional use" to the primary and the "chemical characteristics" to the sub-classification, this system is much more effective.

Table 3 lists the 18 functional classification categories upon which this system is based. D5899 also lists 177 chemical classification designations.

New test methods for silica

In the 1990s, there was a significant increase in technical effort in the tire industry to reduce tire rolling resistance without the loss of traction, in order to improve energy efficiency and reduce carbon dioxide emissions. This resulted in a significant increase in the use of precipitated hydrated silica in tire tread formulations. However, in this time period, ASTM had only one standard method for testing silica. Through the efforts of the Silica Task Group (led by Jeff Melsom, Michelin), there are now ten new ASTM Standards, which involve the testing of silica or organosilanes (which are commonly used as coupling agents with silica in rubber compounding). These new standards are summarized in table 4.

Surface area (which relates inversely to particle size) is a very important property to measure when determining the quality of a rubber grade silica. There are now three different methods for measuring silica surface area; D1993 for multipoint BET nitrogen adsorption, D5604 for single point BET nitrogen adsorption, and D6845 for CTAB surface area. The multipoint BET method takes longer to perform than the single point BET method; however, the multipoint BET has greater accuracy in measuring silica surface area. On the other hand, the CTAB (cetyltrimethylammonium bromide) method uses an absorbing agent with much larger molecules (as compared to nitrogen), which more effectively measures the actual surface area available to rubber.

Structure, while harder to define with silica compared to carbon black, is still an important silica property that can partially predict the performance of silica in a rubber compound. The Silica Task Group is presently working on the exact test conditions for a new oil absorption test that is very much modeled after the ASTM DBP Absorption Test currently used to measure the structure of carbon black.

Also, ASTM D6738 has recently been approved for measuring the volatile content of rubber grade silica, and D6739 is now available for determining the pH value imparted to an aqueous slurry by these silica grades. Variation in measured pH values for silica can have a profound effect on their performance in a rubber compound.

In addition, other new test methods have been developed by the Task Group to measure the quality of organosilanes. Variation in the quality of these coupling agents can greatly affect the performance of a rubber grade silica in a commercial compound. ASTM D6740, Residue on Ignition, relates to the silicon content (before oxidation). D6741, Sulfur Content, relates to the amount of sulfur present, which certainly can relate to the coupling agent's performance in a rubber formulation. Also, D6844 was just approved to test organosilane by high performance liquid chromatography (HPLC).

This procedure can measure the polysulfide distribution for bis(triethoxysilylpropyl)sulfanes. Lastly, these organosilanes can be further characterized by gas chromatography (GC) in accordance with the new ASTM meth-od, D6843.

New stress relaxation method for vulcanizates

The rubber industry was in need of a good, reliable method for measuring the stress relaxation characteristics of a cured compound. An old method (ASTM D1390) was published in 1956, but this method did not meet the industry's needs and was withdrawn in 1986 because of lack of use. Around 1995, a new Task Force for Stress Relaxation Under Compression was established (led by Santosh Kaushal) to develop a new method. This task group under Subcommittee D11.14, Time and Temperature Dependent Tests, studied the effectiveness of the Shawbury-Wallace and the Wykeham Farrance Stress Relaxation Fixtures. In 1997, a new standard, ASTM D6147, was published. It is generally believed that compressive stress relaxation relates better to such properties as sealing pressure for seals, than traditional compression set methods.

New method for measuring green strength

Green strength measurements recently have gained even more importance, especially in the extrusion of EPDM compounds for industrial product applications. Previously, ASTM had no standard method to measure this important processing characteristic. However, three years ago a task group under Subcommittee D11.12, Processability Tests, was formed to meet this challenge (led by Denise Kotz). This effort resulted in a new ASTM Standard, D6746, being published in 2002. This standard calls for reporting such parameters as yield stress, maximum stress, yield elongation or stress at a defined elongation from the extensional deformation of a specially prepared uncured dumbbell test piece separated at 100 mm/min. Figure 5 gives an example of some of these reported parameters.

[FIGURE 5 OMITTED]

New test methods and classification for recycled rubber

In the last decade, a great deal of emphasis was placed on increasing the recycling of rubber. In 1995, Dr. Krishna Baranwal was appointed to head up the newly formed D11.26 Subcommittee on Recycled Rubber. After extensive discussions, ASTM D5603 was first published in 1996. This new standard provides a classification system for ground rubber based on mesh size. Perhaps more importantly, a new standard for measuring particle size and particle size distribution of ground rubber was established with the publishing of ASTM D 5644 in 1996, as well. Before this date, the recycled rubber industry did not have a well defined method. Therefore, a "30 mesh" ground rubber was not well defined and could differ greatly before this standard was published. In addition, ASTM D 5603 defines six different grades of crumb rubber based on parent compounds. These six grades are classified in table 5.

New standard practice for measuring statistical test sensitivity

It is a generally accepted practice to provide a precision statement (for measured repeatability and reproducibility) for a standard ASTM test method used in the rubber industry. This precision is in accordance with a long established statistical standard practice, ASTM D 4483. However, historically no attempt was made to measure and report statistical test sensitivity. Measurement of the test sensitivity of a new test method can be calculated statistically by measuring signal-to-noise ratio (ref. 11). The higher this S/N value means the greater the discernability of the test method relative to some other method with a lower S/N ratio. The Test Sensitivity Task Group under Subcommittee D 11.16, Application of Statistical Methods, was formed in 1996, which ultimately resulted in ASTM D6600, "Standard practice for evaluating test sensitivity for rubber test methods," being published for the first time in 2000. The principle author of D6600 was Alan Veith.

New, published ASTM guide to test selection

ASTM has published a new book titled Basic Rubber Testing: Selecting Methods for a Rubber Test Program. This book was published in September. It consists of ten chapters (230 pages), with written contributions by Alek Vare, Julia Zimmerman, Jeff Melsom, Krishna Baranwal, Alan Veith, and John Dick. The purpose of this book is to provide the reader with a guide for selecting from more than 300 ASTM rubber test standards in order to establish an efficient laboratory-testing program.

ASTM international and ISO standards

ASTM and ISO standards are both used worldwide. In many ways, ASTM International and ISO standards are complements in the worldwide rubber industry. Approximately one-third of all ASTM publication sales are outside the United States. ASTM D11 membership is from not only the U.S., but other countries as well. Unlike ISO, which uses countries as the participants, participation in ASTM is open directly to representatives from industry, government and academia which have a legitimate interest in participating in the standard writing process. The ASTM process for standard development is focused on the technical merits of the proposed standard and developing a consensus between both users and producers, so that there is industry acceptance. ASTM proceedings are very transparent and have been relatively free of international controversies. Also, the standards development process in ASTM International is well known to be fast and efficient. Many times a new standard may only require one-half or even one-third the time to be approved compared to an ISO standard, which can require as long as five years to gain approval. With technology changing rapidly throughout the world, the rapidity of the standard development process is very important. In addition, based on the principles outlined in Annex 4 of the 2nd triennial review of the World Trade Organization's Agreement on Technical Barriers to Trade, ASTM International is an international standards development organization that develops international standards. Therefore, in international commerce, there is definitely a place for both ASTM International and ISO standards to be used worldwide.

Conclusion

In the last five years, there has been a significant level of participation by the rubber industry in developing ASTM standards that are highly relevant to the industry's current needs.

Table 1--location of test recipes for synthetic rubbers

Synthetic rubber being tested               ASTM test
                                             method

SBR with or without oil                       D3185
SBR oil and black masterbatch                 D3196
Polybutadiene                                 D3189
Oil extended polybutadiene                    D3484
EPDM with or without oil                      D3568
IIR (butyl)                                   D3188
BIIR and CIIR                                 D3958
IR (synthetic polyisoprene)                   D3403
NBR                                           D3187
NBR mixed with carbon black (masterbatch)     D3848
CR                                            D3190

Table 2--established industry reference materials now available

No.        Identification                              Annual
                                                     consumption

SRMs
SRM 370    Zinc oxide                                     0
SRM 371    Sulfur                                     64 units
SRM 372    Stearic acid                               109 units
SRM 376    Magnesium oxide                                0
SRM 378    Carbon black, HAF                              0
SRM 382    Carbon black, SRF                              0
SRM 383    Mercaptobenzothiazole (MBT)                   10
RM 8384    N-tert-butyl-2-benzothiazolesulfenamide    56 units

IRMs
IRM 001a   Tetramethylthiuram disulfide (TMTD)            0
IRM 002b   Benzothiazyl disulfide (MBTS)               55 lb.
IRM 003    N-tert-butyl-2-benzothiazolesulfenamide
IRM 021a   Stearic acid                                  350
IRM 031a   Sulfur                                        300
IRM 43a    Naphthenic process oil                     160 gal.
IRM 91a    Zinc oxide                                  250 lb.
IRM 241b   Butyl rubber ML 1+8 @ 100[degrees]C 72     120 bales
IRM 902a   Petroleum oil                             1,127 gal.
IRM 903b   Petroleum oil                             41,427 gal.
IRM 341a   Magnesium oxide                             300 lb.
ASTM #5

No.         Est. date to depletion       Current source

SRMs
SRM 370    Out, replaced by IRM 91a   NIST
SRM 371              Out              NIST
SRM 372              Out              NIST
SRM 376              Out              NIST
SRM 378              out              NIST
SRM 382              Out              NIST
SRM 383             2000+             NIST
RM 8384              Out              NIST

IRMs
IRM 001a             Out
IRM 002b           Unknown            Ak. Rubber Dev. Lab.
IRM 003                               Not established yet
IRM 021a                              Ak. Rubber Dev. Lab.
IRM 031a                              Ak. Rubber Dev. Lab.
IRM 43a            May 2003           R.E. Carroll, Inc.
IRM 91a              2014             R.E. Carroll, Inc.
IRM 241b          Jan. 2001           Ak. Rubber Dev. Lab.
IRM 902a          Sept. 2001          R.E. Carroll, Inc.
IRM 903b          Sept. 2001          R.E. Carroll, Inc.
IRM 341a          July 2002           C.P. Hall
ASTM #5           June 2010           R.E. Carroll, Inc.

Table 3--primary functional classification
categories for ASTM D5899

1. Accelerators
2. Adhesion promoters
3. Antidegradants
4. Antistatic agents
5. Blowing agents
6. Colorants
7. Fillers, extenders and reinforcing agents
8. Flame retardants
9. Fungicides
10. Masterbatches
11. Odorants
12. Processing materials
13. Promotors and coupling agents for fillers and
    reinforcing agents
14. Rubbers
15. Retarders and inhibitors
16. Tackifiers
17. Thermostics
18. Vulcanizing agents and activators

Table 4--new ASTM silica and organosilane test methods

ASTM          ASTM title
designation

D1993         Test Method for Precipitated Silica - Surface
              Area by Multipoint BET Nitrogen Adsorption

D5604         Test Method for Precipitated Silica - Surface
              Area by Single Point BET Nitrogen Adsorption

D6738         Standard Test Methods for Precipitated Silica
              - Volatile Content

D6739         Standard Test Methods for Precipitated Silica
              - pH Value

D6740         Test Method for Silanes Used in Rubber
              Formulations (bis-(triethoxysilylpropyl)sul-
              fanes) - Residue on Ignition

D6741         Test Method for Silanes Used in Rubber
              Formulations (bis-(triethoxysilylpropyl)sul-
              fanes) - Sulfur Content

D6843         Test Method for Bis-Triethoxysilpropyl Sul-
              fanes - Characterization by GC

D6844         Test Method for Bis-Triethoxysilpropyl Sul-
              fanes - Characterization by HPLC

D6845         Test Method for Silica, Precipitated, Hydrat-
              ed - CTAB (Cetyltrimethylammonium Bromide)
              Surface Area

D68xx         Test Method for Precipitated Silica -
              n-Dibutyl Phthalate Absorption Number

Table 5--six different grades of crumb rubberbased on parent compounds

Grade number   Description

Grade 1        Crumb rubber from passenger, bus and
               truck tires in which metal and fibers are
               removed

Grade 2        Crumb rubber from passenger, truck
               and bus tires which are only from the
               treads

Grade 3        Crumb rubber from passenger, truck
               and bus tires which is from the tread
               and shoulder area buffing (in retread
               operations)

Grade 4        Crumb rubber from bus, truck and passenger
               tire retreading where buffings from these
               tires include sidewalls, shoulder area
               and treads.

Grade 5        Crumb rubber from OTR tires, large equipment
               tires and industrial tires, farm implement
               tires and forklift tires. This grade does
               not include truck, bus or passenger tires.

Grade 6        Crumb rubber from non-tire sources

References

(1.) R.D. Stiehler, "Committee D11 on Rubber and Rubberlike Materials, eightly years of standardization," ASTM Standardization News, August, 2002.

(2.) J. Dick, "ASTM in the globalization of rubber standards and specifications," Rubber and Plastics News, July 3, 1995.

(3.) "Guide for U.S. delegates to ISO meetings," American National Standards Institute, New York, NY p. 22.

(4.) Helen Davis, "Standardization in Europe, a success story," ASTM Standardization News, February, 1990, p. 36.

(5.) C.A. Stevens, J.S. Dick, "Factory testing and control of raw natural rubber and mixed batches using the rubber process analyzer," Rubber World, January, 2001 and KGK (Kautschuk Gummi Kunststoffe), Jan./Feb. 2001, 54, No. 1-2, p. 29.

(6.) J.S. Dick and H.A. Pawlowski, "Rubber characterization by applied strain variations using the rubber process analyzer," Rubber World, Jan. 1995.

(7.) John Dick, Chris Sumpter and Brian Ward, "New effective methods for measuring processing and dynamic property performance of silicone compounds," KGK (Kautschuk Gummi Kunststoffe) September, 1999 (52 600-607).

(8.) J.S. Dick and H. Pawlowski, "Applications for the rubber process analyzer," Rubber and Plastics News, April 26 and May 10, 1993.

(9.) J. Dick, "Dynamic aging of vulcanizates using RPA," Rubber and Plastics News, April 30, 2001, and GAK (Gummi Fasern Kunststoffe), 54, No. 8, August, 2001, p. 50.

(10.) John Dick and Allan Worm, "Storage stability of fluoro-elastomer compound based on a bisphenol AF/onium cure system and its potential use as a standard reference compound," Rubber World, January, 1999.

(11.) John Mandel, The Statistical Analysis of Experimental Data, Dover Publishers, NY, 1964, p. 369.