CB's role in compound curing behavior.

Carbon black is a universal reinforcing filler used in rubber compounds. Indeed, the physical properties of the carbon black-rubber composite are improved when compared to unfilled rubber compound. However, it is not just the "strength" of the rubber that is affected when carbon black is added; many other properties are also modified. One of those is the curing characteristics whose modifications in the presence of filler constitute the object of this article.

Generalities

In order to produce an elastomeric composite featuring relevant physical properties, the polymer chains must be chemically crosslinked. In the rubber industry a sulfur crosslinking system is generally used. Since the vulcanization rate with sulfur alone is slow, chemical accelerators and activators are necessary. This vulcanization process may occur via different reaction mechanisms, depending in particular on the chemicals/fillers used.

It is the objective of this article to better define the role of carbon black in the vulcanization process. Several studies were undertaken and the role of carbon black is emphasized. Curing characteristics are determined using an oscillating disk rheometer (Monsanto R100) in which a biconical oscillating rotor, enclosed in a cavity filled initially with the uncured rubber compound, develops a torque Which increases with time under constant temperature and oscillating conditions This torque versus time response is said to be a vulcanization curve.

It is noted that the oscillating angle used for the rheometer (1 [degree] arc) confers to the curing specimen a cyclic (1.6 Hz) strain of approximately 16%. Referring to previous studies (ref. 1) it should be noted that at such a strain the carbon black network has been disrupted. Therefore, the composite is not necessarily at the same morphological state as cured compounds in normal service conditions would be.

Sulfur vulcanization

The exact mechanism under which accelerated sulfur vulcanization of unfilled rubber compounds occurs will change as the class of accelerators/activators changes. However, a generally accepted sequence of reactions is as follows (ref. 2):

* An interaction of the curatives occurs to form what is termed the active sulfurating agent;

* The polymer chains interact with the sulfurating agent to form polysulfidic pendant groups terminated by accelerator groups;

* Polysulfidic crosslinks are formed; and

* Numerous parallel reactions such as continuing crosslink formation, crosslink destruction by thermal degradation, formation of inefficient cyclic crosslinks (sulfides), and numerous other network modifying reactions .

Figure 1 graphically shows this sequence for typical benzothiazole and sulfenamide accelerators where zinc oxide is the activator and a fatty acid such as stearic acid is the co-activator. This sequence, it should be pointed out, does not show the role of carbon black.

Earlier studies concerning the role of carbon black on compound cure behavior (ref. 3) showed that it decreases the vulcanization induction time and decreases the cure rate as the amount of surface acid groups on the carbon black increases. This latter fact was more pertinent when using channel blacks which exhibit high amounts of surface groups (due to about 3.5% oxygen content) as opposed to present day furnace carbon blacks which have a very small amount of these surface groups.

Role of carbon black

Compound mixing and testing

All mixing of carbon black filled compounds was done on a Haake Rheocord 90 using an initial temperature of 50 [degrees] C and a mixer speed of 1.5 Hz unless otherwise noted. Curing characteristics were evaluated on the rheometer at a test temperature of 160 [degrees] C, a frequency of 1.6 Hz, and a 1 [degree] arc amplitude, which corresponds in the specimens to approximately 16% strain. Typical response parameters as described in ASTM D2084 were monitored as well as a measurement of the cure rate taken as the slope at the inflection point (ref. 4). The cure characteristics evaluated in most of the studies were:

* [t.sub.s]1 the induction time (the time required for a 1 dN-m rise in torque above the minimum torque, [M.sub.L];

* cure rate in Nm/sec measured as described above,

* t'90 (time to reach a torque value equal to 90% of the torque difference [M.sub.H]-[M.sub.L])

* [M.sub.H] the maximum torque which is related to the dynamic stiffness of the cured compounds at that temperature.

Study 1: Role of carbon black with and without curing agents

Objective - Understand the influence of carbon black on compound vulcanization by examining its cure behavior as the various chemicals in a typical curing package are present or absent.

Compound mixes - This study was conducted using three different polymers: emulsion SBR, solution SBR and natural rubber. For each of these, six compounds were mixed as shown in table 1.

Table 1 - compounds for study I
Mix  Polymer  Sulfur*  Carbon  Accelerator**  Activators***
                         black
 1       X        X
 2       X        X        X
 3       X        X                  X
 4       X        X        X         X
 5       X        X                  X              X
 6       X        X        X         X              X

* SBR: 1.75 phr NR : 2.50 phr
** SBR: 1 phr TBBS NR: 0.60 phr MBTS
*** SBR: 3 phr Zno, 1 phr stearic acid NR: 5 phr Zno, 3 phr
stearic acid
Polymers used for this and subsequent studies: Emulsion SBR
- NIST 1500 (23.5% styrene); solution SBR - Duradene 706
(23.5% styrene) Natural rubber - SMRL

Discussion - Pertinent data are shown in tables 2-4 for each polymer. Note that in the two compounds containing sulfur but no accelerator or activators that the rheometer curve continued to rise in torque up to 16 hrs. at which the test was discontinued. Concentrating on [t.sub.s]1 data for all three polymers it is quite clear that the addition of carbon black causes a significant decrease in the induction time for vulcanization in every case. It could be theorized that the carbon black surface is used to accelerate the initial chemical reactions of vulcanization, i.e., acting like a catalyst for the reaction. Once the vulcanization reactions are initiated it is evident that carbon black affects the cure rate, which also is dependent on the polymer type. Note the significantly larger increase in cure rate due to the presence of carbon black for solution SBR compared to emulsion SBR. Natural rubber also exhibited a much greater cure rate increase from carbon black incorporation than did emulsion SBR, but note the cure package was different. Viewing the [M.sub.H] data for the three systems it appears evident that the increase in stiffness from carbon black is about the same within each system regardless of the nature of the polymer network.

Conclusions - Carbon black acts as a catalyst for the initiation of vulcanization. Its subsequent influence on the rate of vulcanization appears to be polymer dependent given a constant cure system. The increase in compound stiffness during curing due to carbon black does not appear to depend on the type of polymer network.

[TABULAR DATA OMITTED]

Study 2: Effect of carbon black loading and type on curing characteristics

Objective - Determine how curing characteristics are affected by the loading and type of carbon black. Use the information to better elucidate the role of carbon black on compound curing behavior.

Compound mixes - The ASTM D3191 recipe emulsion SBR recipe) was used to study a wide range of carbon blacks from N110 to N762 at loadings of 1. 4, 8, 20, 25, 30, 35 and 45 phr. The physicochemical properties of the carbon black samples are shown in table 5. The main characteristics identifying the carbon black are the specific surface area (measured by nitrogen adsorption) and the "structure" (measured here by CDBP).

Table 5 - carbon blacks under evaluation
Grade       DBP,      CDBP,   [N.sub.2]SA
         cc/100g    cc/100g   [m.sub.2]/g
N110       113.2       98.8   138.8
N234       121.0      106.2   122.5
N299       123.5      103.9   104.8
N330        99.1       87.2    80.6
N358       151.5      110.4    83.5
N550       119.3       85.2    39.5
N660        90.5       75.4    34.3
N762        62.6       59.5    27.7

The same investigation was conducted using solution SBR employing only two carbon blacks, N299 and N762.

Discussion - The data for the emulsion SBR and the solution SBR results are available from the authors. The relationship between loading and curing characteristics within each polymer system is virtually the same regardless of the type of carbon black. In general, increasing the loading of carbon black causes [t.sub.s] 1 to decrease, cure rate to increase, and [M.sub.H] to increase in either polymer system. The only curing characteristic that can be related to the type of carbon black employed appears only to be the stiffness of the cured compound as measured by [M.sub.H]. Figure 2 shows that at the higher loadings there is a relationship between CDBP and [M.sub.H]. No relationships of curing characteristics to the specific surface area of the carbon black were evident. Carbon black loading has a significant impact on curing characteristics, as mentioned before, and the impact is different between emulsion and solution SBR. At low carbon black loadings the [t.sub.s] 1 is greater in solution SBR but as the loading increases the difference eventually becomes negligible. Cure rate shows an opposite effect: the two polymer systems are similar at low loading but the solution SBR increases in cure rate faster with increased loading than the emulsion SBR compound. The combination of the two effects just discussed leads to the difference in t'90 behavior between the two types of SBR. The long induction time at low carbon black loadings leads to a longer t'90 for solution SBR. At higher loading the induction times are similar for both polymers but the cure rate is much faster for the solution SBR. Solution SBR thus exhibits a shorter t'90. Actually, the t'90 of the emulsion SBR compound is essentially the same at all loadings. Carbon black loading increases [M.sub.H] in a similar fashion for both systems.

Conclusions - Carbon black type is not an important parameter for curing characteristics. Carbon black loading has a significant influence on curing behavior. Generally, increasing the compound's loading of carbon black decreases the [t.sub.s] 1, increases the cure rate and increases the [M.sub.H]. The magnitude of these effects is dependent on the polymer system.

Study 3: Effect of mixing time on curing properties

Objective - Ascertain if curing properties are affected by the amount of time used to incorporate carbon black into a rubber compound.

Compound mixes - An ASTM D3191 compound emulsion SBR) was prepared without carbon black and cooled. An N299 carbon black was then added at a 50 phr loading and mixed for 120 seconds at 90 rpm. Similarly, compounds with carbon black mixing times of 180, 240 and. 360 seconds were prepared. Each mix was replicated eight times. During mixing the temperature did not exceed 100 [degrees] C.

Discussion - Testing results are presented in table 6. The following observations are made in regard to increasing the carbon black mixing time: slight decrease in [t.sub.s] 1, cure rate and [M.sub.H]. In fact, these effects may be explainable from the stand-point of the dispersion of the carbon black. One would expect that if the carbon black acts as a catalyst (in vulcanization) due to its surface that the better it was dispersed (more mixing time), the more reduction in the induction time would be observed. The slightly higher [M.sub.H] at a low mixing time (and most likely lower state of dispersion) may be explainable in terms of the carbon black subnetworks not being as broken up at this state and thus causing a greater hydrodynamic effect leading to a greater stiffness ([M.sub.H]).

Conclusions - In these studies using an emulsion SBR compound, increasing the carbon black mixing time from 2-6 minutes caused a slight decrease in [t.sub.s] 1, cure rate and [M.sub.H].

[TABULAR DATA OMITTED]

Study 4: Compound heat history. studies Objective - Determine if a carbon black filled compound's heat history has an influence on its curing characteristics.

Compound mixes - An N299 carbon black was mixed into solution SBR at a 50 phr loading. Duradene 711 was used in these studies instead of Duradene 706. The non-productive compound (i.e., with no curatives) was subjected to various heat treatment conditions and then the curatives were added in a final step.

The same was done for another set of compounds except using N660 in place of N299. The treatment conditions represent a central composite designed experiment using temperature and time as the, independent variables. Next, N299 was mixed in solution SBR at a 50 phr level and the necessary curatives were added. This productive mix was then subjected to various conditions using a central composite design, before testing on the rheometer. A corresponding study was also done with N660. Figure 3 graphically illustrates the two experiments.

Discussion - The results of the rheometer testing were submitted for statistical analysis. The results of the analysis did not show a statistical difference for any of the sets of conditions for either the non-productive compound study or the productive compound study using either N299 or N660.

Conclusions - Using the ascribed set of conditions for this study, there appears to be no influence of carbon black filled compound heat history on curing characteristics.

Study 5: Role of carbon black as the curing package varies in content

Objective - Examine the role of carbon black on curing behavior as the amount of curatives is varied.

Compound mixes - The ASTM D3191 recipe (emulsion SBR, 50 phr carbon black, 1.7 phr sulfur, 3 phr ZnO, 1 phr TBBS and 1 phr stearic acid) was used as the basic recipe. All chemicals were held constant except the one being varied. Zinc oxide was varied from 0-6 phr, stearic acid from 0-5 phr, TBBS (accelerator) from 0-5 phr, and sulfur from 0.75 to 3 phr. Five different grades of carbon black were used, making the same variations in curatives as described above: N110 N330, N358, N660 and N762 (see table 5 for their physicochemical properties). The study was also done replacing the emulsion SBR with solution SBR for the ZnO and stearic, acid variations and using only the N330 and N762 carbon blacks.

Discussion - The data for variation of zinc oxide content is given in table 7. When no zinc oxide is in the recipe the compounds, in general, cure much slower slower cure rate, longer time to 90% cure state). The one exception was N762 in emulsion SBR, which appeared to cure in a similar behavior at 0 phr and a normal loading of 3 phr. At twice the normal loading of zinc oxide the compounds showed little or no effect (compared to the normal ZnO loading) except for the N762 emulsion SBR compound, which showed lower curing and decreased stiffness ([M.sub.H]). The N762 emulsion SBR study was mixed again and tested with the same results. Another 700 series carbon black, N774, was also tested in a similar fashion, but it behaved like the lower series carbon blacks. In other words, the N762 specific surface area or structure cannot be used to explain its unusual behavior with variable zinc oxide content - the phenomenon must be related to a property not presently being measured. In solution SBR N762 did not exhibit unusual behavior as ZnO was varied.

Table 7 - variation in zinc oxide content
          phr ZnO   [M.sub.H]  t'90   [t.sub.s]1  cure rate

Emulsion
SBR recipe   0      42.3        34.8   2.7              4.1
N110
N110         3      53.2        20.2   3.8              7.2
N110         6      53.3        20.1   4.1              6.9
N358         0      43.7        37.5   3.1              5.3
N358         3      56.4        17.5   3.9              9.5
N358         6      56.3        18.6   4.2              9.9
N330         0      44.0        14.7   4.5              4.2
N330         3      47.3        15.1   3.4             10.6
N330         6      37.3        24.3   4.1             10.3
N660         0      40.8        34.5   3.7              4.6
N660         3      50.7        16.6   3.7              8.2
N660         6      53.1        16.7   4.3             10.2
N762         0      40.3        38.4   3.8             10.4
N762         3      49.0        15.1   3.9             10.3
N762         6      49.2        15.4   4.1              5.4
Solution
SBR recipe
N330         0      46.2        41.7   3.8              4.0
N330         3      46.5        13.2   4.1             15.0
N330         6      49.9        13.3   4.0             17.7
N762         0      37.7        24.4   5.3              7.2
N762         3      42.2        16.4   6.4             14.0
N762         6      43.3        16.8   5.6             13.3
Units for the table above:
ts1, t'90 = min./cure rate = Nm/sec x [10.sup.3]/MH = dNm

The next study involved varying the stearic acid content. In the emulsion SBR recipe the absence of stearic acid had no effect when compared to the normal recipe (1 phr stearic acid). This is probably due to the fact that emulsion SBR (by virtue of its manufacturing process) already contains fatty acids, most likely in sufficient quantity for the reaction mechanism to proceed. Doubling the stearic acid content does not have much effect either, but increasing the amount to five times normal causes a lowered [M.sub.H] (possibly from a lubrication phenomenon from the excess fatty acids). An observation for the N110 sample was that the t'90 appeared to lengthen with increasing stearic acid content unlike any other sample. The higher specific surface area of N110 may have been partially covered with increasing stearic acid content causing a decreased participation in the curing process (also note the lower cure rate at 5x the normal content). Solution SBR, which should not contain fatty acids, exhibited significantly different behavior with addition of stearic acid. The cure rate was considerably faster 2-3x faster) for no stearic acid versus the normal 1 phr loading. This is contrary to what was expected and brings the question of why its presence would slow the cure rate. The induction time shortened with increasing stearic acid up to 2 phr, especially for N762. [M.sub.H] appeared to decrease in the solution SBR with increasing stearic acid for both blacks. The net effect on t'90 for the stearic acid in solution SBR was a shorter time with no stearic acid but about the same time at 1 to 3 phr.

Based on this data, one would conclude that the maximum cure rate can be obtained if there is no fatty acid present. A possible explanation for these results is that the fatty acid is reducing the available carbon black surface for the crosslinking reactions to be catalyzed by. Supporting data for this hypothesis was done by mixing solution SBR, N330 carbon black, sulfur, TBBS and ZnO without any stearic acid in the, ratios appropriate for comparison to table 3. In addition, the, same mix without carbon black was done. The cure rates for these samples are compared to data from table 3 in table 8.

Table 8
Sample                             Cure rate, Nm/sec
SSBR/sulfur/TBBS/carbon black        6.2 * [10.sup.-3]
SSBR/sulfur/TBBS/ZnO/carbon black   32.2 * [10.sup.-3]
SSBR/sulfur/TBBS/ZnO/stearic        15.0 * [10.sup.-3]
acid/carbon black
SSBR/sulfur/TBBS                     2.3 * [10.sup.-3]
SSBR/sulfur/TBBS/ZnO                 6.4 * [10.sup.-3]
SSBR/sulfur/TBBS/ZnO/stearic acid    5.5 * [10.sup.-3]

It appears quite evident that carbon black is important to maximize the cure rate, but ingredients which - over or make unavailable the surface only slow the crosslinking process. In order to verify this claim another compound was prepared without stearic acid but using 5 phr oil to see if the oil would be able to partially cover the carbon black surface and reduce the cure rate. This compound (SSBR/sulfur/TBBS/ZnO/carbon black/oil) gave a cure rate of 19.0 Nm/sec* [10.sup.-3] was, as expected, less than the 32.2 Nm/sec * [10.sup.-3] wit out oil. It is thus further hypothesized that crosslinking reaction intermediates involving zinc are promoted on the carbon black surface. The effects from increasing accelerator and sulfur respectively in the emulsion SBR recipe show that these are the dominant chemicals in the vulcanization process (which was ready well known) as evidenced by the increasing [M.sub.H] and cure rate with increasing contents of these chemicals.

Conclusions - The type of carbon black may influence the curing behavior as a curative chemical is varied in content. It is hypothesized that fatty acids may actually cause the carbon black surface to be made unavailable for catalyzing the reaction mechanism. It is further hypothesized that intermediate crosslinking reaction steps involving zinc are promoted on the carbon black surface.

Conclusions

Carbon black is highly involved in the vulcanization process of filled compouds. It early a catalyst of vulcanization enhancing the induction and cure rate of vulcanization. In regard to the influence on curing behavior, the loading of carbon black has a significant impact whereas the type of carbon black has little effect. The type of carbon black may, however, influence the curing behavior as a curative chemical is varied in content. It is hypothesized that intermediate crosslinking reaction steps involving zinc occur and are catalyzed by the carbon black surface. Furthermore, the presence of fatty acids may cause the carbon black surface to be unavailable, which inhibits its activity as a catalyst.

Rubber Division meets in Chicago

The 145th Spring Technical Meeting of the Rubber Division, American Chemical Society, will be held April 19-22 at the Palmer House Hilton in Chicago, IL.

Ten symposia, including an educational symposium, will be part of the technical program, with 56 papers scheduled for presentation.

Technical symposia will include: Frontiers in rubber science; Automotive elastomeric application expectations; SPC - 10 years later; Aging and stabilization of rubber products; Advances in silicone elastomers; New commercial developments; Agricultural tires; Rubber recycling topical group; University polymer science programs - overview; and Educational Symposium - Fatigue in rubber.

The 1994 Charles Goodyear Medalist Alan G. Thomas will present his lecture, "The development of fracture mechanics for elastomers," on Wednesday, April 20.

Other awards presented during the Science & Technology Awards Banquet will include the Melvin Mooney Award to Noboru Tokita and the George Stafford Whitby Award to Jack- L. Koenig.

The Suppliers Cooperative Reception will take place Tuesday. April 19. The 25 Year Club Reception and Luncheon will be held Wednesday, April 20. The Rubber Division Business and Awards Meeting will take place Thursday, April 21.

The newly formed Rubber Recycling Topical Group of the Rubber Division will make its public debut at the Chicago meeting. The group was formed in answer to a perceived need within the industry to promote through education and communication the use of recycled materials at all levels, pre- or post-consumer, pre- or post-manufacturing.

The group is concerned with all technical aspects of recycling, resource recovery and disposal of rubber polymer materials.

A working meeting of the group will be held in Chicago on Tuesday. April 19 at 2 p.m. in the Wabash Room of the Palmer House Hilton. On Wednesday, April 20, John Serumgard, chairman of the Scrap Tire Management Council, will give a progress report on "Scrap tire recycling." This address will be followed by the presentation of five technical papers under the general heading "Recycled rubber technology applications for the 90s."

Those interested in attending these sessions or joining the group should contact Jan Smith [phone].

A technical course on "Molding of elastomers" will be presented April 17-19 at the Palmer House Hilton. The course instructor is John G. Sommer, Elastech.

This course will provide a general overview of the molding of both thermosetting elastomers and thermoplastic elastomers. It will emphasize the molding behavior and the equipment used for high-viscosity TSEs, like natural rubber and acrylonitrile-butadiene rubber.

Viscosity is the basis for comparing diverse elastomers that range from pourable liquids (castable polyurethanes and liquid silicone rubbers) through millable (high-viscosity) elastomers.

Discussion will include interactions among materials, molds and molding methods. Methods include compression, transfer, injection, blow, casting, liquid injection molding and reaction injection molding.

Also discussed will be elastomer flow behavior, shrinkage, adhesion, flash, mold venting, fouling and cleaning, and mold design basics.

This course is limited to 35 students. The prerequisite for attendance is an interest in elastomer molding. Registration costs $350 for Rubber Division members and $400 for non-members.

Further information on this course and on the Rubber Division's 145th meeting in Chicago is available from the Division [phone].

The schedule of paper presentations for the 145th meeting of the Rubber Division, ACS, is as follows:

Tuesday, April 19 - Session A Colloquium - Automotive elastomeric application expectations Harry Robins, Miles, Polysar Rubber Division, chairman.

8:10 - Introduction, Harry Robins.

8:15 - (1) Automotive elastomers: An evolution of challenges. Robert A. Pett and Lawrence R. Gullen, Ford motor.

(II) Working together: A constructive partnership for the automotive and rubber industries. Ron Toth, Chrysler.

(III) Compatibility of seal and hose materials in current and future automotive air conditioning systems. Govinda Prativadi, General Motors.

Tuesday, April 19 - Session B Colloquium - Frontiers in rubber science Michel Gerspacher, Sid Richardson Carbon, chairman.

8:15 - (IV) The relation of Schallamach pattern to rubber properties wear conditions. James A. Donovan and J. Chen, University of Massachusetts, and A.I. Medalia, Medalia Associates.

(V) NMR imaging of polysiloxane elastomers. L. Garrido, Massachusetts General Hospital.

(VI) The effect of liquid extenders on the dynamic mechanical properties of rubbers under strain. Keizo Akutagawa C. Davies and A. Thomas. University of London, England.

(VII) Mechanical response and fatigue properties of double network systems. P.G. Santangelo. C.M. Roland, I.S. Choi and E.F. Wedam, Naval Research Laboratory.

(Vlll) Synthesis and elastomer applications of direct functionalized aminoethene-propene copolymers. Sudhin Datta, Exxon Chemical.

Tuesday, April 19 - Session C

Contributed Papers Todd H. Speece, Ricon Resins, moderator.

8:00 - (1) Rheological properties of rubber-carbon black and carbon black-oil compounds including measurement very low shear rates. James L. White, G.J. Osanaiye and A.I. Leonov, University of Akron.

(2) Measurement of elastomer's bull, modulus by a confined compression test. Shu H. Peng, T. Shimbori and A. Naderi, Parker Hannifin.

(3) A study of accelerated sulfur vulcanization; the study of the cure of 2-mercaptobenzothiazole sulfenamide accelerators by 13C NMR and semi-empirical quantum mechanical methods. Frederick Ignatz-Hoover and G. Kulhs, Monsanto.

(4) The application of Mooney relaxation to quality control of elastomers. C.B. Friedersdorf and 1. Duvdevani, Exon Chemical Polymers.

(5) Rubber characterization of applied strain variations using the rubber process analysis. John S. Dick and H. Pawlowski, Monsanto.

(6) Study on infrared spectrum analysis of carbon black reinforced vulcanized rubber. Zhou Cuiwei and D. Qingping, Nanjing University, China.

Tuesday, April 19 - Session A

Colloquium - Automotive elastomeric application expectations Harry Robins, Miles, Polysar Rubber Division, chairman.

1:30 - (IX) Future challenges for the rubber industry: Vehicle integration perspective. Jamal N. El-Hout, General Motors.

(X) Guidelines and criteria for development of the GM accessory drive belt performance standards. John T. Beckett, General Motors.

(XI) Engine mounts for the 1990s. Robert Salisbury, Chrysler.

(XII) Application expectations for the, automotive ignition wire systems. David M. Zedan, Chrysler.

Tuesday, April 19 - Session B

Colloquium - Frontiers in rubber science Michel Gerspacher, Sid Richardson Carbon, chairman.

1:30 - (XIII) Phase behavior and properties of block copolymer/homopolymer blends. Jeffren, T. Koberstein and J. Baetzold, University of Connecticut.

(XIV) Carbon black - conducting polymer composites. K. Rajeshwar, University of Texas at Arlington, and W. Wampler, Sid Richardson Carbon.

(XV) The microstructure and morphology of carbon black: A study using small-angle neutron scattering (SANS) and contrast variation. Rex Hjelm and P. Seeger, Los Alamos National Lab, and W. Wampler and M. Gerspacher, Sid Richardson Carbon.

(XVI) Segmental orientation in elastomeric networks by Fourier transform infrared dichroism. L. Bokobza, S. Besbes and L. Monnerie. Laborataire PCSM, France, and 1. Bahar and B. Erman, Bogazici University, Turkey.

(XVII) Polymer adsorption on filler surfaces. G. Heinrich, Continental AG.

Tuesday, April 19 - Session C

Contributed Papers Brian Howard, Struktol Company of America, moderator.

1:30 - (7) An approach to modern polymer development: Enhancement of the service temperature range for hydrogenated nitrile-butadiene rubber (HNBR). Gilles Arsenault, T. Brown and I Jobe, Miles, Polysar Div.

(8) Estimation of styrene emissions from a styrene/butadiene rubber dryer. G.N. Ghebremeskel, Ameripol Synpol.

(9) Evaluation of highly saturated nitrile rubber compounds for use in tank track pads. Joey L. Mead, R.A. Michaud, K.M. Gabriel and D.A. Bulpett, U.S. Army Research Lab, and R.W. Simoneau, Keene State College.

(10) Biomedical segmented polyurethanes as a thermoplastic elastomer. Shinzo Kohjiya, Kyoto University, and Y. Ikeda, Kyoto Institute of Technology , Japan.

(11) Stress relaxation data as processability indicators. Frank J. Male, Ameripol Synpol.

Wednesday, April 20 - Session A Colloquium - Automotive elastomeric application expectations