Pergamon Carbon, Vol. 32, No. 7, pp. 1305-1310, 1994

Copyright 0 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved

0008.6223/94 1F6.M) + .OO

FIFTY YEARS OF RESEARCH AND PROGRESS ON CARBON BLACK

JEAN-BAPTISTE DONNET Laboratoire de Chimie Physique, Ecofe Nationale Superieure de Chimie de M&house and

Centre de Recherches sur la Physico-Chimie des Surfaces SolidesKNRS, Mulhouse, France

(Received 6 December 1993; accepted 7 December 1993)

Key Words-Carbon black, structure, surface properties, reinforcement, scanning tunneling microscopy.

It is certainly rewarding to look back at the last half century and try to summarize what concepts were con- sidered as established, and from there on discuss the progress and developments so as to assess the present state of knowledge.

I started my laboratory forty years ago (exactly, the 3rd of February 1953) when I was hired as Professor at the School of Chemistry in Mulhouse after six years devoted to my thesis (1947-1952), during which 1 al- ready worked with carbon black, which I chose as a physical mode1 for rigid “spherical particles”[ I].

Excelient review papers where published between 1949 and 196412-51 and it is quite clear that several points were already firmly established.

The electron transmission microscope discovered by Ruska in 1939 and made operative by Siemens in the forties was, from the very beginning, extensiveIy used to observe carbon black; extremely good pictures were already published by the late thirties and during the fifties when extensive studies were made[6,7]. Fig- ure 1 reproduces one of the these picture@]. From there on, the approximately spherical shape of more or less aggregated individual particles, whose dimen- sions where strongly dependent on the process param- eters, could not be doubted.

In the early forties, the X-ray diffraction diagram of carbon black was also observed[6,7] and in the fif- ties the “crystalline character” of carbon black was ev- idenced by Warren[9], Alexander et a/.[lO,l I] and Austin et a1.[12,13], by analytical treatment of the X-ray spectrograms. It was then possible to deduce the data published by Austin ef al. 112,131, and widely dis- cussed in the carbon black community. It was clearly shown that the crystalline parameters so obtained, and although representing average values which were tied to a simplified treatment of X-ray experimental data, nevertheless truly existed and were strongly dependent on the carbon black species (channel, thermal, furnace, acetylene , , . ) and on the process parameters as shown in Table 1, reproduced from Austin et a/.[12,13].

It is amazing also to read again the papers pub- lished more than forty years ago trying to relate oxygen and hydrogen content together or to pH, oil adsorp- tion, extrusion shrinkage[3]; the DBP concept was already there.

The surface chemistry was also largely started, hy- drogen and oxygen content were deeply studied, and Studebaker[3] already described carbon black as “be- ing somewhat like a series of degraded polycyclic ar- omatic hydrocarbons at various states of oxidation” and “to the extent that carbon black resembles these polycyclic hydrocarbons, we could expect a high or- der of reactivity.” This concept was useful when the theory concerning the nucleation and growth of car- bon black particles was established[l4].

Fig. 1. Electron micrograph of oil furnace blacks: (a) high- structure, (b) low-structure (from@]).

CAR 32:7-F 1305

1306 J.-B. DONNET

Table 1. X-ray analysis (from Austin[lS])

Trademark

Crystallite dimensions, A Carbon per cent Probability of number of

L, (breadth) (L, (height) In in parallel layers parallel single

(10) (ll) (002) Random layers layers 3 4 5

Rubber-grade blacks Thermax P-33 Pelletex Sterling V Kosmos 40 Shawinigan Statex B Philblack A Philblack 0 Philblack 1 Philblack E Vulcan SC Spheron 9 Spheron 6 Spheron 4 Spheron C CK-4

Color btacks Elf 0 Mogul A Mogul

30 20 17.3 9 78 13 .l .9 23 18 17.6 13 62 25 1.0 19 14 15.5 9 68 23 .6 .4 19 14 14.8 13 64 23 .8 .2 21 18 14.8 10 72 18 .8 .2 30 27 24.6 11 78 11 * 20 16 13.7 6 69 25 .l .9 16 15 14.4 18 60 22 .9 .l 18 18 12.7 23 58 19 .4 .6 18 18 12.3 23 54 23 .s .5 18 18 11.6 19 64 17 .7 .3 19 15 13.0 21 45 34 .3 .7 18 14 13.4 16 52 32 .2 .8 18 12 13.7 17 61 22 .l .9 18 13 12.7 13 60 27 .4 .6 19 17 12.0 9 67 24 .6 .4 14 11 12.7 26 55 19 .4 .6

15 1s 12.7 31 36 33 .4 .6 16 14 14.4 17 52 31 .9 .l 15.5 12 13.0 31 37 32 .3 .7

*Approx. mean number of layers equals 7.

The nature of the oxygen-containing groups was also the focus of intense activity and there were pa- pers on the possible existence of -COOH and -OH groups, by ViIlars in 1948[15]. Studebaker, et a!.[161 in 1956 showed that the presence of active hydrogen can be evidenced by the Grignard reagent, and the di- azomethane reaction with oxygen-containing groups on the carbon surface indicated the presence of labile hydrogen and carboxylic groups.

Study of the chemical surface functions of carbon black has been very active. It has been reviewed and was considered almost completed[~7-201 (however, re- cent signals indicate that this field should not be con- sidered exhausted). Anyway, Watson in 1956[21,22] postulated a radical acceptor character as did Garten and Sutherland[23,24] in 19.54-1957, and Szwarc[25], in 1956. These observations were the basis for one of the theories of reinforcement which were so deeply worked on and disputed during the next twenty years. Let us recall here the names of Blanchard and Parkinson (chemical reinforcement~26]), Payne (filler networking theory~27,28]), Medalia (rubber o~clusionI29]), Gess- ler (free radicals[30,31]), Smallwood (hydrodynamic effect[32]), Wolff et al. (filler effect and effective- ness factor[33,34]), Dannenberg (molecular slippage theory[35,36]) and Gerspacher (filler-filler interac- tion[37-391). This paragraph should be completed by the excellent analysis of the dynamic properties given by Medalia[40], and more recently in depth by several chapters of books about carbon black[41,42].

Concerning the modelling of the carbon black par- ticle internaf organization, the first step is undoubt-

Sweitzcr ct Heller (I 956) Dortnct et Bouland (1963)

DOMet et SChUltZ (1965) IIeekman et Ihrdling (19GG)

lless. Ban et Heidenreich (1968)

Fig. 2. Carbon black mod~llisation.

edly due to the X-ray data of Riley[43] as early as

1939. The systematic studies of oxidation followed by transmission electron microscopy gave results[44-481

that supported a clear improvement of this simplified

view. Heckman and Harling[49] confirmed our results and proposed a more elaborated model, which was further improved by the systematic use of high res- olution electron microscopy under the guidance of Hess[SO]. This model “saga” ended in 1968 as illus- trated by Figure 2.

Fifty years of research and progress on carbon black 1307

Table 2. Average value of adsorption energy (F) of and dispersive component (rf) of surface energy of carbon

blacks

N...x Area E, kJ/mol rz’, mJ/m’

NllOx 0.1127 27.2 87.6 N234x 0.0629 26.3 84.8 N330x 0.0432 25.4 82.0 N762x 0.0179 24.8 80.4

The most recent progress is due to new methods, namely Inverse Gas Chromatography (ICC) and Scan- ning Tunneling Microscopy (STM).

Inverse gas chromatography, introduced in our lab-

oratory by Saint-Flour and Papirer[S 11, is a very sim-

ple powerful adsorption method giving access to the thermodynamic data and the surface energy of a solid surface. Although application to carbon black encoun-

tered real difficulties at the very beginning[52,53], be- cause the method of infinite dilution (extremely small concentration of the probe) was used, it was rapidly evident that our hypothesis concerning the preferred detection of the most active sites was correct, and the

recent systematic use of the finite dilution method not only proved it, but enlarged the possibilities of IGC.

Systematic studies of carbon black by IGC were made by Wolff et a/. [54] in correlation with its rein-

forcing properties. We have shown in Mulhouse not only that ICC was extremely useful to study modifi-

cation of the surface, but also that by finite concen- tration studies we could reach data that fit perfectly

with the limiting values of the surface energy of pure graphite[55,56].

Table 2 reports the average value F (kJ/mol) of the adsorption energy and the surface energy r,* (mJ/m’)

NllOx - 15nmxl5nm N234x - 1 Onmxl Onm

N3!3Ox - 6nmx6nm N762x - lSnmxl5nm

Fig. 3. Scanning tunnelling microscopy of carbon blacks.

1308

Table 3. Compounding recipe

J.-B. DONNET

SBR (solution)* 100 Carbon Black 50 ZnO 3.0 Stearic acid 1.5 PPD (anti-oxidant)? 1.0 Sulfur 1.1 CBS$ 1.1

*SBR: Butadiene/Styrene 14/26 tPPD: N 1,3-dimethylbutyl N’-phenyl paraphenylene

diamine $CBS: Cyclohexylbenzothiazolsulphenamide

for representative carbon blacks. These values are quite close and the surface energy is not changed ap- preciably by chemical treatment (reduction, oxidation, grafting). The value of r,d is then in the range of 80

mJ/m2 f 5’70, almost independent of the density of active sites, which is related to the process parameters and carbon black grade. As observed at the beginning of our studies[52,53], IGC is instrumental for classifi- cation of carbon black by the infinite dilution method.

Fig. 4. Carbon black model.

Our recent results with STM gave access to the sur-

face organization of carbon black at the atomic range[55-611. These results are illustrated by Fig. 3; they are in good agreement with the recent findings of Schlogl[62].

Table 4. Mechanical properties of the green compound

Carbon black* Energy Trinatr “C

vsc., Bound Moony Rubber, %

N234 N234x N234xL N234XHh N234xHhNaOE,C1 N234xHhNaOEtCS N234G,,,.c N234G,,., N234Gzsc,,ac N234G,,,.,

N~~~X~K,S,O,

1460 1350 1350 1400 1420 1530

-

1630 1440 1460 1580

156 115 155 109 157 114 158 112 156 97 160 104 152 100 153 100 152 100 153 100 164 125

31 30 32 32 18 25

7 2 3 5

35

*N234: Original carbon black N234x: 48 hours toluene extracted N234 N234xL: 72 hours water extracted N234x N234xHh: Chemically reduced N234x by LiAlH, N234xHh,,,,,C,: Chemically reduced N234x by LiAlH, and Cl and C6 grafted N234G, SC: N234 Graphitized 30 min. at 1700, 2000, 2300, 2700°C N234xOKzszo,: N234x oxidized 12 hours by K&Os.

Table 5. Mechanical properties of the vulcanized compound

Carbon black ElO, ElOO, E300, loss at A r”pl %pt Energy MPa MPa MPa 10% % MPa J.rnm3

N234 5.13 4.04 9.20 31 170 244 N234x 5.47 3.78 8.62 30 790 248 N234xL 5.71 3.86 8.53 32 740 246 N234XHh 5.25 3.53 8.28 28 800 255 N234xHhNaoEtC, 4.51 2.92 6.27 27 870 265 N234xHhNaoEtC6 4.99 3.34 1.85 28 770 229 N234G,,cc.c 4.71 2.24 3.16 33 780 112 N234G,,., 5.08 2.24 2.96 33 750 96 N234G,,,., 4.88 2.14 2.84 34 750 88 N234G,,,.c 4.80 2.10 2.71 33 740 86

N~~~XOK~SZO~ 5.64 4.10 7.20 31 640 110

137 141 137 139 140 121

52 45 41 39 62

Fifty yean of research and progress on carbon black 13OY

t

MYPa

-d- reference 10

-Cl grafted

To elangatinn I I I +

0 so IW I50 200 250 ?Ofl

Fix. 5. Stress-strain curves of SDS rubber filled with initial and modified carbon black samples.

The quantochemical simulations by HOMO cal- culations supported the hypothesis that the surface organization could adequately be represented by quasi-

graphitic scales whose edges were characteristic of the

growth of aromatic systems. The deposition of these scales during the formation process results in approx-

imately spherical particles modelled in Fig. 4. Moreover, the condition of nucleation and growth

led us to propose a possible mechanism involving ful-

lerenes according to the Kroto[63] proposal for soot formation.

Macromolecular

ChGlS

Fig. 6. Schematic representation of the conformauon of macromolecular chains on the surface of a carbon black

particle.

The surface roughness due to the scale’s edges may

be involved in the aggregation’s primary mechanism. On the other hand we recently studied again, very

extensively, the influence of chemical modifications on

carbon black behavior in compounding[55,56]. Table 4

and 5 and Fig. 5 summarize our findings. We see again that chemical treatment, with the ex-

ception of oxidation for the low extensions, did not improve the reinforcing character of carbon black. (The compounding recipe is given in Table 3 nith the carbon black sample indexing.)

Finally, we think that our model permits a very

rational explanation of the reinforcing effect, as illus- trated by F‘ig. 6.

If an elastomeric chain is “wetting” the surface, and

is then submitted to any mechanical strain, the ele- ments of the chain which are (be it mechanicalIy or physicochemically “wetting”) in interact ion with the

edges of the scales will need energy to be removed, for “dewetting.” As soon as the strain is cut off, wetting and interaction at the edges may take place again. Such a mechanism, very similar to Dannenberg’s mo- lecular slippage, seems to be able to explain many physical properties of the filled compounds.

There remain, however, many unexplained aspects

of carbon black concerning its formation mechanism, physicochemistry, and behavior. Scientific knowledge has an ever-moving frontier, and every new acquisition starts new- questions. Let us make an appointment for

the next International Conference on Carbon Black!

REFERENCES

I. J.-B. Donnet, .J. Polym. Sci. 12, 53 (1954). 2. W. R. Smith, H~cycto~rdia of Chemical Tdtnolog), 2nd

Editmn, Vol. 3, page 48 (1949).

1310 J.-B. DONNET

3.

4.

5. 6.

I. 8.

9.

10.

11.

12.

13.

14.

15. 16.

17. 18. 19. 20.

21. 22. 23.

24.

25. 26.

21. 28.

29. 30

M. L. Studebaker, Rubber Chem. Technol. 30, 1400- 1483 (1957). A. A. Heckman, Rubber Chem. Technol. 37, 1245-1298 (1964). A. A. Heckman, Rubber Chem. Technol. 39, 1 (1968). J. Biscoe and B. E. Warren, J. Applied Phys. 13, 364 (1942). B. E. Warren, J. Chem. Phys. 2, 552 (1934). W. R. Smith, In Encyclopedia of Chemical Technology, Vol. 3, pages 34, 65 (1945). B. E. Warren, In Proceedings of the First and Second Conference on Carbon, page 49, The University of Buf- falo, Buffalo, NY (1956). L. Alexander and S. R. Darin, J. Chem. Phys. 23, 594 (1955). L. Alexander and E. C. Sommer, J. Phys. Chem. 60, 1646 (1956). A. E. Austin, W. A. Hedden, Ind. Eng. Chem. 46, 1520 (1954). A. E. Austin, In Crystal structuralproperties of Carbon Blacks Proceedings of the 3rd Carbon conference, Uni- versity of Buffalo, Buffalo, NY (1957). J. Lahaye and G. Prado, Chem. Phys. Carbon 14, 168 (1978). D. S. Villars, J.A.C.S. 70, 3655 (1948). M. L. Studebaker, M. C. Huffman, G. W. D. Wolfe, and L. G. Nabors, Ind. Eng. Chem. 48, 162 (1956). J.-B. Donnet, Bull. Sot. Chim. France 3353 (1970). J.-B. Donnet, Carbon 6, 161 (1968). J.-B. Donnet, Carbon 20, 266 (1982). H. P. Boehm, Advances in Catalysis, Vol. 26, page 179 Academic Press (1966). W. F. Watson, Ind. Eng. Chem. 47, 1281 (1955). W. F. Watson, Rubber Chem. Technol. 28, 1032 (1955). V. A. Garton and G. K. Sutherland, In Proceedings 3rd Rubber Technology Conference, London, page 536 (1954). V. A. Carton and G. K. Sutherland, Rubber Chem. Technoi. 30, 596 (1957). M. Szwarc, J. Polym. Sci. 19, 589 (1956). A. F. Blanchard and D. Parkinson, Ind. Eng. Chem. 44, 799 (1952). A. R. Payne, Rubber J. 146, 36 (1964). A. R. Payne, Rubber and Plastics Age 42, 963-967 (1961). A. I. Medalia, J. Colloid. Interf. Sci. 32, 115 (1970). A. M. Gessler, In 5th Rubber Chem. Technol. Conf. page 249 (1968).

35.

36.

31.

38.

39.

40. 41.

42.

43. 44. 45.

46.

47.

48.

49.

50.

51.

52.

53.

54.

55.

56.

51.

58.

59.

60. 31. A. M. Gessler, Rubber Chem. Technol. 42, 858 (1969). 32. H. M. Smallwood, J. Applied Phys. 45,758-766 (1944). 61. 33. S. Wolff and J.-B. Donnet, Rubber Chem. Technol. 63, 62.

32 (1990). 63. 34. S. Wolff and M.-J. Wang, In Carbon Black, 2nd Ed.,

p. 220, 290, M. Dekker, New York (1993).

E. M. Dannenberg, Trans. Int. Rubber Int. 42, T26-42 (1966). E. M. Dannenberg, PhD. Thesis, Mulhouse, France (1973). M. Gerspacher, In International Rubber Conference, Paris (1990). M. Gerspacher, H. H. Yang, and C. P. 0 Farrell, Rub- ber Division ACS, Washington D.C. 9-12 Oct. (1990). M. Gerspacher, In Carbon Black, 2nd Ed., p. 317, M. Dekker, New York (1993). A. I. Medalia, Rubber Chem. Technol. 5, 439 (1978). J.-B. Donnet and A. Voet, Carbon Black, 1st Ed., p. 212, M. Dekker (1975). J.-B. Donnet, R. C. Bansal, and M.-J. Wang, Carbon Black, 2nd Ed., p. 290, M. Dekker, New York (1993). H. L. Riley, Chem. Ind. 58, 391 (1939). J.-B. Donnet and J. C. Bouland, Carbon 4,201 (1966). J.-B. Donnet, J. C. Bouland, and J. Jaeger, C. R. Acad. Sci. 256, 5340 (1963). J.-B. Donnet and J. C. Bouland, Rev. Gen. Caoutchouc 47, 407 (1964). J.-B. Donnet and J. C. Bouland, Physicochimie du Noir de Carbone p. 43-50, CNRS Special Issue (1953). J.-B. Donnet, J. Schultz, and A. Eckardt, Carbon 6, 781 (1968). P. A. Heckman and D. E. Harling, Rubber Chem. Tech- nol. 39, 1 (1968). R. D. Heindenreich, W. M. Hess, and L. L. Ban, J. AppI. Cryst. 1, 1 (1968). C. Saint-Flour and E. Papirer, J. Colloid Interf. Sci. 91, 69 (1983). C. Lansinger, PhD. Thesis, Universite de Haute Alsace, Mulhouse, France (1990). J.-B. Donnet and C. Lansinger, Kaut. Gummi Kunst. 45, 459 (1992). S. Wolff, M.-J. Wang, and J.-B. Donnet, Rubber Chem. Technol. 64, 714 (1991). E. Custodero, PhD. Thesis, Universite de Haute Alsace, Mulhouse, France (1992). J.-B. Donnet and E. Custodero, In 2nd International Conference on Carbon Black, p. 222. J.-B. Donnet and E. Custodero, Carbon 30, 813-815 (1992). J.-B. Donnet and E. Custodero, C. R. AC. Sci. 314, 579- 584 (1992). J.-B. Donnet and E. Custodtro, Rubber Conf. IRC. New Dehli, Feb. (1993). J.-B. Donnet and E. Custodero, ACS meeting Rubber Div. Denver, May (1993). J.-B. Donnet and E. Custodero, Nature, to be published. R. Schogl, Carbon 30, 1123 (1992). H. W. Kroto, Angew Chem. Int. Ed. 31, 111-129 (1992).

This article is being published without the benefit of the author’s review of the proofs, which were not available at press time.