CA1207931A - Oxidized carbonaceous materials and vulcanized and vulcanizable rubber compositions reinforced with such carbonaceous materials - Google Patents

Abstract

OXIDIZED CARBONACEOUS MATERIALS AND
VULCANIZED AND VULCANIZABLE RUBBER
COMPOSITIONS REINFORCED WITH SUCH
CARBONACEOUS MATERIALS

ABSTRACT OF THE DISCLOSURE
Oxidized carbonaceous materials suitable for reinforcing such diene rubbers as styrene-butadiene rubber and natural rubber include carbon, oxidized iron dispersed in, intimately associated with and at lease partially bonded to the carbon, and hydrogen.

Description

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OXIDIZED CARBONACEOUS MATERIALS AND
VULCANIZED AND VULCANIZABLE RUB~ER
COMPOSITIONS REINFORCED WITH SUCH
CARBONACEOUS MATERIALS

This invention relates to new oxidized carbonaceous materials that include carbon, iron dispersed in, intimately associated with and at least partially bonded to the carbon, oxygen and hydrogen; ^to new compositions comprising a mixture of sulfur-curable, rubbery polymers and such oxidized carbon-aceous materials; and to vulcanized and vulcanizable compositions that include such mixtures.
In one broad aspect the invention pertains to a composition comprising a major amount of diene rubber and a minor amount of oxidized carbonaceous material comprising carbon in an amount of about 80% to about 99%, oxidized iron dispersed in, intimately associated with, and at least partially bonded to the carbon in an amount of about 1% to about 15%, and hydrogen in an amount of about 0.1% to about 1.5%~by weight.
In another aspect the invention pertains to fibrous carbonaceous material comprising carbon in an amount of about 80% to about 99% by weight, oxides of iron in an amount of about 1% to about 15% bv weight, and hydrogen in an amount of about 0.1~ to about 1.5% by weight, the fibrous carbonaceous material comprising carbon fibers with nodules comprising oxides of iron intimately associated with and at least partially bonded to the carbon fibers.
A still further aspect of the invention pertains to a fibrous carbonaceous material suitabl~ for reinforcement rubber compositions prepared by forming a fibrous carbonaceous material comprising carbon in an amount of about 80% to about 99% by weight, non-oxidized iron in an amount of about 1% to about 15%
by weight, and hydrogen in an amount of about 0.1% to about 1.5% by weight, with the carbonaceous material comprising carbon fibers with nodules comprising non-oxidized iron intimately associated with and at least partially bonded to the carbon fibers, and oxidizing the iron in the fibrous carbonaceous material at a temperature up to about 400F to convert the non-oxidized iron to oxidized iron.

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The new carbonaceous materials include carbon in an amount in the ranye of about 80~ to about 99% by weight, pre-ferably about 90% to about 94% by weight; oxidized iron dispersed in, intimately associated with and at least partially bonded to the carbon in an amount in the range of about 1~ to about 15%
by weight, preferably about 3~ to about 9% by weight; and hy-drogen,in an amount in the range of about 0.1% to about 1.5% by weight, preferably about 0.5% to about 0.8% by weight.
We make our new carbonaceous materials by depositing carbon from a carbon monoxide/hydrogen gas mixture on an iron-based initiator at a temperature in the range of about 300C.
to about 700C., and at a pressure in the range of about one to about 100 atmospheres or more. Canadian Patent No. 1,136,413 granted November 30, 1982 and entitled "Novel Carbonaceous Material and Process for Producing a ~igh BTU Gas from this Material"
describes these processes fully.
Because this carbon deposition reaction takes place in a chemically reducing environment, rich in carbon monoxide and hydrogen, the carbonaceous material itself is produced in a re-duced form. The iron in this reduced carbonaceous material is dispersed in, intimately associated with and at least partially bonded to the carbon in the material. X-ray analysis of this material shows diffraction patterns for ~-iron (2.03 dA), Fe3C
(2.08 dA), or both, but not for such oxidized forms of iron as FeO (2-15 dA), Fe2O3 t2.69 dA), FeO(OH) (6.26 dA), and Fe3O4 (2.53 dA).
Oxidation of the reduced iron in these carbonaceous materials produces a new oxidized carbonaceous material with the iron dispersed in, intimately associated with and at least partially bonded to the carbon in the oxidized material. This material is surprisingly effective in reinforcing sulfur-curable rubbery polymers. Such rubbery polymers typically include at least about two mole percent of residual unsaturation.
Oxidation of the iron in our carbonaceous materials can be effected in several ways. For example, the carbon can be heat-ed in air, steam or hot water at temperatures in the range of about 200F. to about 400F. for a time in the range of about 0.5 to about 24 hours. Alternatively, we can oxidize this iron chemically, say with dilute nitric acid. These processes ',~

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oxidize the iron to such oxide forms as FeO, Fe2O3, FeO(OH), or Fe3O4.
In one case, during oxidation, we convert the carbonaceous materials to agglomerates, called pellets in the carbon black industry. To pelletize our materials, we mix them with water in about a 1:1 weight ratio, and roll this mixture in a rotating -cylinder, rotating tilting dish, pin mill or pug mill for a time in the range of about one minute to about 60 minutes, or until pellets of desired sizes form. Desirable pellet sizes are in ~he range of about 8 mesh to about 35 mesh. After forming these pellets, we dry them at a tempera~ure in the range of about 80 C. to about 200 C. for a time in the range of about 0Ol to about two hours. Prepared in this manner~ the carbonaceous materials contain oxidized iron, substantially all of which is FeO and Fe2O3.
Our new oxidized carbonaceous materials provide unexpectedly good reinforcement for vulcanizable and vulcaniæed diene rubber compositions, such as those made rom styrene-butadiene rubber (SBR), polyisoprene rubber, natural rubber (NR), polybutadiene rubber (BR), Guayule, and blends thereof. In such compositions, our new carbonaceous materials can constitute an amount in the range of about 5% to about 60% by weight.
We can incorporate our new carbonaceous material in such diene-containing rubber polymers by conventional techniques. Such techniques include Banbury mixing, two-roll mill mixing, solvent or latex master batching, or dry master batching. Our new rubber compositions may, but need not always, include compounding oil. Such oils can constitute an amount of up to about 25~ of these compositions.

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Carbon black fillers are commonly added to rubber compositions to increase their modulusr tensile strength and hardness upon vulcanization. ASTM Tests D412 and D2240 show that conventional carbon blacks, such as semi-reinforcing furnace (SRF) of Type ASTM N-762, perf~rm such functions. They also permit rubber compositions containing them to flow for a time when the compositions are heated to vulcanization temperatures.
Flow times and vulcanization properties are oft~n measured with an oscillating disc rheometer (ODR) of the kind available from the Monsanto Company. When an unvulcanized, vulcanizable rubber composition is heated to vulcanization temperature in the ODR according to the procedure outlined in ASTM Test D1546, which calls for monitoring the torque required to turn the disc in a 3 arc while in contact with the vulcanizing rubber composition, the device produces a curve which traces the increasing torque that the disc encounters from the rubber as vulcanization progresses. The time for torque to increa~e five units, denoted T5, is called the scorch period. This scorch period is des;gnated as the point at which vulcanization begins. The time required for the vulcanizing rubber composition in the rheometer to reach about 90% of its optimum cure, denoted Tgol is designated the optimum cure. Maximum viscosity of the vulcanized rubber composition is directly related to its modulus and is denoted r max.
Our new oxidized carbonaceous materials increase modulus, tensile strength and hardness of vulcanized diene-containing rubber polymers reinforced with these carbonaceous materials to nearly the same extent as semi-reinforcing furnace (SRF) carbon black does. However, ~21~3~

our carbonaceous materials produce a shorter scorch period in diene-containing, rubbery polymers reinforced with them than SRF does in the same rubbery polymers.
Oxidizing the iron in our carbonaceous materials lengthens the scorch period for diene-containing, rubbery polymers containing them. By contrast, oxidation of conventional, petroleum-derived carbon black such as SRF
shortens the scorch period of diene-containing, rubbery polymers reinforced with them. Moreover, oxidation of conventional carbon blacks reduces their reinforcing properties. Indeed, highly oxidized conventional carbon blacks are not good reinforcing agents for diene-containing, rubbery polymers. By contrast, our oxidized carbonaceous m~terials are more highly reinforcing than the unoxidized forms of the same carbonaceous materials.
The following examples illustrate the preparation and properties of our new carbonaceous materials, methods for incorporating them in diene-containing, rubbery polymers and the effects on the properties of vulcanizable and vulcanized rubber compositions reinforced with them.

Following the methods disclosed in Canadian Patent No. 1,136,413, identified above more fully, we prepared carbonaceous material comprising about 95~ carbon, about 3.4~ iron in the iron carbide fonm and about 0.6~ hydrogen. We heated thls carbonaceous material for 16 hours at about 300F. in air to conver~
the iron carbide in the material to oxidized iron.

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We then prepared two vulcanizable, SBR-based compositions, one containing 50 parts of the unoxidized carbonaceous material (sample l), the other containing 50 parts of the oxidized carbonaceous material (sample 2).
We prepared both samples in a Banbury mixer operated at 77 revolutions per minute over a seven-minute time period, using a water coolant on both the rotor and shell of the mixture. The mixing regime was as follows in both cases: A~ zero time, we placed the polymer in the Banbury mixer. At 0.5 minutes, we added the other ingredients except for the carbonaceous material. At one minute, we added half of the carbonaceous material, and at two minutes, we added the other half of the carbonaceous material. At five minutes, we swept the mixer for undispersed material. At seven minutes, we removed the samples from ~he Banbury mixer. We then added curatives on a two-roll mill.
We cured one portion from each sample in an hydraulic press for 50 minutes at 293F., and tested these samples for tensile strength, elongation at break and Shore A hardness. These results appear in Table I
below.
We cured a second portion of each sample in an oscillating disc rheometer at 321F., and obtained the results set ~orth in Table I. These data show that the sample reinforced with oxidized carbonaceous material had a 12~ longer scorch period than the sample reinforced with unoxidized carbonaceous material.

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TABLE I

Component 1 2 Unoxidized Carbonaceous 50 Material Oxidized Carbonaceous - 50 Material lQ Zinc Oxide 3 3 Stearic Acid Sulfur 1.75 1.75 TBBTS Acceleratorl 1 1 156.75 156.75 Properties Tensile Strength, psi2 1~105 1,527 20 Elongation at break, percent2 320 360 Shore A Hardness3 48 55 T5, Minutes4 2.5 2.8 T~ol Minutes4 9.9 10 25 ~ Max4 68.5 77 1. N-t-buty1-2-benzothiazylsulfenamide 2~ Results from procedures described in ASTM Test D412

3 Results from procedures described in A~TM Test D2240

4 Resul~s from procedures described in ASTM Test D1646, run at 320F. and 3 arc.

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8 ~2~7931 We pelletized a portion of the unoxidized carbonaceous material whose preparation is set forth in

- 5 Example 1 above on a Ferro-Tech 16-inch diameter disc ~ pelletizer using a water-to-carbonaceous material weight ratio of about 1:1. We dried the pellets for two hours at 150C. and analyzed them for oxygen content. We found tha~ the pelletizing process converted substantially all the iron in the carbonaoeous material to ferric oxide (Fe304~.
We then prepared two S~R-based compositions in a Banbury mixer following the procedures set forth in Example 1 above. The first of these compositions, denoted sample 3 in Table II below, included 50 parts of the unoxidized carbonaceous material. The other sample, denoted sample 4 in Table II below, contain 50 parts of the pelletized, oxidized carbonaceous material.
Wa cured a portion of each of samples 3 and 4 in an hydraulic press for 50 minutes at 2904F., and tested these samples for tensile strength, elongation at break and Shore A hardne~s. The results obtained appear in Table II below.
We cured separate portions of each s~mple in an oscillating disc rheometer at 320F. using a 3 arc for the disc. The results obtained also appear in Table II
below, and show substantial lengthening of ~he scorch period, and a significant improvement in tensile strength and elongation for the oxidized, pelletized materials over the results obtained with the unoxidized carbonaceous material.
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TABLE II

comDonent 3 4 Unoxidized Carbonaceous 50 Material Oxidi~ed, Pelletized - 50 Carbonaceous Material 10 Zinc Oxide 3 3 Stearic Acid Sulfur 0-9 0-9 TBBTS Acceleratorl 1 1 Phthalimide Retarder5 0.4 _ 0-4 156.3 .156.3 Properties Tensile Strength, psi2 1~478 lr850 Elongation at Break, Percent2475 595 Shore A Hardness3 55 57 T5, Minutes4 3. 5- 3 Tgo, Minutes4 8~5 8.8 ~ Max 4 50 49 Die B Tear, pounds/
linear inch6 223 249 1. See footnote-lr~in Table I.
2. See footnote 2 in Table I.
3. See footnote 3 in Table I.
4. See footnote 4 in Table I.
5. N-(cyclohexylthio)phthalimide.

6. Results from procedures described in ASTM Test D 624.

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--1 o--- We prepared two additional samples, samples 5 and 6, containing the same components as samples 3 and 4 except tha~ we added five parts of compounding oil per 100 parts of SBR to each composition. Samples 5 and 6 were prepared in a Banbury mixer using the mixing regime set forth in Example 1.
We vulcanized a portion of each of samples 5 and 6 in an hydraulic press at 293~F. for 50 minutes, and tested each sample for tensile strength, elongation at break and Shore A hardness. We vulcanized separate portions of samples 5 and 6 in the~oscillating disc rhoemeter to determine the scorch ~eriod for each~ The resulting data appear in Table III below. They show that the oiled, oxidized carbonaceous material improved the tensile strength of the vulcanized SBR samp'le 6 containing this material, and lengthened its scorch period, as compared to the vulcanized SBR sample S
containing unoxidized, oiled c~xbon~ceous material.
Following the method described in Example 1 above, we prepared an unoxidized, iron-based carbonaceous material comprising about 95~ carbon, about 4.2% iron, and about 0.8~ hydrogen. We Oxidized this carbonaceous ~5 material in air for four hours at 400F., converting substantially all the iron to Fe203.
We then prepared two separate SBR-based vulcanizable ru~ber samples, one comprising 54 parts of the unoxidlzed carbonaceous material described above, and the other 54 parts of the oxidized carbonaceous material described above. The~e two compositions, namely samples

7 and 8, are set forth in detail below in Table IV~

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TABLE III

Tensile Strength, psi2 1,000 1,468 Elongation at Break, Percent2 510 480 Shore A Hardness3 - 57 55 T5, Minutes4 4.5 7.2 1~
2. See footnote 2 in Table I.
3. See footnote 3 in Table I.
4. See footnote 4 in Table I.

7~31 We vulcanized portions of sample 7 and sample 8 in an hydraulic press for 50 minutes at 293F., and tested these samples for tensile strength, elongation at break and Shore A hardness. The results obtained are also set forth in Table IV below. Second portions of - samples 7 and 8 were vulcanized in an oscillating disc rheometer at 320F. using a 3 a~rc. The results obtained are also set forth in Table IV.
The data in Table IV sho~ that the oxidation of the carbonaceous material improves the tensile strength and elongation at break of SBR reinforced with this material, lengthens its scorch period, but does not decrease the maxlmum torque obtained in the ODR tests.

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TABLE IV
__ Component 7 8 Naphthenic Oil 7.5 7.5 Unoxidized Carbonaceous 54 Materials : Oxidized Carbonaceous - 54 10 Materials Zinc Oxide 2 2 Stearic Acid Sulfur 1.31.3 15 TBBTS Acceleratorl 1 1 Phthalimide Retarder5 0.430.43 167023167.23 20 Ten~ile Strength, psi2 1,0431,195 Elongation at Break, Percen~2 360 440 Shore A Hardness3 58 55 T5, Minutes4 3.53-9 25 Tgo, Mlnutes4 lOlO- 9 ~Max4 57 57 1. See footnote 1 in Table I.
2. See footnote 2 in Table I.
3. See footnote 3 in Table I.
4. See footnote 4 in Table I.
5. See footnote 5 in Table II.

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We subjected two portions of the unoxidized carbonaceous material described in Example 1 above to two different steaming processes to oxidize them. We oxidized one portion of the unoxidized carbonaceous material with steam at a pressure of 90 to 140 psig for 4O5 hours, and the second portion of the carbonaceous material at 500 psig with steam for 4.5 hours. X-ray diffraction analysis of the oxidized carbonaceous material formed at 90 to 140 psig shows that the iron was con~erted to Fe304. The carbonaceous material steamed at higher pressure contained both Fe304 and Fe203.
We then prepared three separate reinforced SBR-based vulcanizable rubber samples, one containing theunoxidized carbonaceous material, the second containing the carbonaceous material oxidized at lower pressure, and the third containing the carbonaceous material oxidized at higher pressure. These three samples, denoted, 9, 10 and 11, are described in detail in Table V below.
We vulcanized portions of each of these samples at 293F. for 50 minutes, and tested each vulcanized sample for tensile strength, elongation at break and Shore A hardness. The results obtained are set forth in Table V.
Finally, we vulcanized a portion of each of these three samples in the ODR at 320F. using a 3 arc~ The results obtained are set forth in Table V.
As before, oxidation of the carbonaceous material lengthened the scorch period, and increased tensile strength, elongation at break and Shore A
hardness of vulcanized SBR compositions containing them.

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TABLE V

Component 9 10 11 -Unoxidized Carbonaceous SD - -Materials Oxidized Carbonaceous - 50 Materials (Lower Pressure) 10 Oxidized Carbonaceous - - 50 Materials (Higher Pressure) Zinc Oxide 3 3 3 Stearic Acid Sulfur 0-9 0-9 0-9 TBBTS Acceleratorl 1 1 1 Phthalimide Retarder50-4 0-4 ~ 74 156~3 156.3 156.3 Properties Tensile Strength, psi21,4781,524 1,632 Elongation at Break, Percent2475 480 430 Shore A Hardness3 55 58 60 25 T5, MinuteS4 3 4 4-3 Tgol Minutes4 8.5 130216 ~ Max4 50 54 56 lo See footnote 1 in Table I.
2. See footnote 2 in Table I, 3. See footnote 3 in Table I.
4. See footnote 4 in Table I.
5. See footnote 5 ln Table II.

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Yollowing the methods set forth in Example 1 above, we prepared an unoxidized carbonaceous material comprising about 93.7~ carbon, about 5~7% iron and about - 0.6% hydrogen. We oxidized this carbonaceous material in air for four hours at 400F., converting substantially all the iron to Fe203.
We then prepared two rubber samples, each containing both natural rubber and SBR. ~e reinforced one of the samples, denoted 12, with the unoxidized carbonaceous material, and the other, denoted 13, with the oxidized carbonaceous material. The complete recipes for these two samples appear in Table VI.
We vulcanized a portion of each sample a~ 307F.
for 20 minutes in an hydraulic press~ and tested the vulcanized sæmples for ~ensile strength/ elongation at break and Shore A hardness. The resul~s obtained are in Table VI.
We vulcanized a second portion of each composition in the ODR at 300F. using a 3 arc for the disc. The resul s obtained are also in Table VI.
The results in Table VI show that oxidation of the carbonaceous material produces a longer scorch period in a natural rubber/SBR composition reinforced with such material and better tensile strength, elongation at break and Shore A hardness, than in such rubber compositions reinforced with unoxodized carbonaceous material.

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TABLE VI

Component 12 13 Natural Rubber No. 1 RSS 30 30 SBR 1708 96.3 96.3 Unoxidized Carbonaceous 70 Material Oxidized Carbonaceous - 70 10 Material Rosin Oil 10 10 Zinc Oxide 4 4 Stearic Acid Polybutylated Bisphenol A
(Antioxidant) N-Cyclohexyl-2 Benzo-Thiazol-i.0 1.0 sulfenamide Accelerator Tetramethylthiuram 0.2 .02 Monosulfide-Accelerator Sulfer 2.3 2.0_ 215.8 215.5 Properties 25 Tensile Strength, psi21,260 1,490 Elongation at Break, Percent2 340 350 Shore A Hardness3 59 63 T5, Minutes4 3.8 4.7 30 Tgo, Minutes4 7.2 10.1 ~ Max4 61.2 63.3 2. See footnote 2 in Table I.
3. See footnote 3 in Table I.
4. See footnote 4 in Table I.

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___ We compared certain proper~ies of an unpel-letized, unoxidized carbonaceous material comprising about 94% carbon, about 0.7~ hydrogen and about 5.3~ iron ~ to the steam-oxidized, pelle~ized form of the same carbonaceous material. As the data in Table VII show, these two forms had substantially the same values for these properties. And these are the properties used to determine whether or not a carbonaceous material is suitable for reinforcing diene rubber. Accordingly, the surprisingly better-reinforcing properties obtained using our oxidized carbonaceous materials must be attributed to the oxidized iron in our materials.

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TABLE VII

Unpelletized Pelletized Carbonaceous Carbonaceous Materials Materials Iodine Number, mg/g 234 23_ Tinting Strength, ~ IRB No. 4 59.3 60 10 Dibutyl Phthalate Absorption, cc/ 93 85 Effective Specific Gravity 2.03 2.04 Volatile Content, 15 Percent by Weight 2.8 2.5 Ash Content, Percent by Weight 4.88 4.96 325 Mesh Grit, Percent by Weight 0.007 0.005 ~ 3E3,.,

Claims (15)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A composition comprising a major amount of diene rubber and a minor amount of oxidized carbonaceous material comprising carbon in an amount of about 80% to about 99%;
oxidized iron dispersed in, intimately associated with, and at least partially bonded to the carbon in an amount of about 1% to about 15%; and hydrogen in an amount of about 0.1% to about 1.5% by weight.

2. The composition of Claim 1 wherein said diene rubber is styrene-butadiene rubber, said styrene-butadiene rubber comprising an amount of about 90% to about 45% by weight of the composition and the carbonaceous material comprising an amount from about 5% to about 40% by weight of said composition.

3. The composition of Claim 1 wherein said diene rubber is selected from the group consisting of styrene-butadiene rubber, natural rubber and mixtures thereof, said rubber comprising an amount of about 90% to about 45%
by weight of said composition and the carbonaceous material comprising an amount of about 5% to about 40% by weight of said composition.

4. Fibrous carbonaceous material comprising carbon in an amount of about 80% to about 99% by weight; oxides of iron in an amount of about 1% to about 15% by weight;
and hydrogen in an amount of about 0.1% to about 1.5% by weight, the fibrous carbonaceous material comprising carbon fibers with nodules comprising oxides of iron intimately associated with and at least partially bonded to the carbon fibers.

5. Pelletized fibrous carbonaceous material comprising carbon in an amount of about 80% to about 99% by weight;

Claim 5 - cont'd ...
oxides of iron in an amount of about 1% to about 15% by weight;
and hydrogen in an amount of about 0.1% to about 1.5% by weight, the fibrous carbonaceous material comprising carbon fibers with nodules comprising oxides of iron intimately associated with and at least partially bonded to the carbon fibers.

6. The pelletized carbonaceous material of Claim 5, wherein the pellets have a size in the range of about 8 mesh to about 35 mesh.

7. The fibrous carbonaceous material of Claim 4 comprising carbon in an amount of about 90% to about 94% by weight; oxides of iron in an amount of about 3% to about 9%
by weight; and hydrogen in an amount of about 0.5% to about 0.8% by weight.

8. The pelletized fibrous carbonaceous material of Claim 5 comprising carbon in an amount of about 90% to about 94% by weight; oxides of iron in an amount of about 3% to about 9% by weight; and hydrogen in an amount of about 0.5% to about 0.8% by weight.

9. The fibrous carbonaceous material of Claim 6 comprising carbon in an amount of about 90% to about 94%
by weight; oxides of iron in an amount of about 3% to about 9% by weight; and hydrogen in an amount of about 0.5% to about 0.8% by weight.

10. A fibrous carbonaceous material suitable for reinforcement rubber compositions prepared by:
(a) forming a fibrous carbonaceous material comprising carbon in an amount of about 80% to about 99%
by weight, non-oxidized iron in an amount of about 1% to about 15% by weight, and hydrogen in an amount of about 0.1%

Claim 10 - cont'd ...

to about 1.5% by weight, the carbonaceous material comprising carbon fibers with nodules comprising non-oxidized iron intimately associated with and at least partially bonded to the carbon fibers; and (b) oxidizing the iron in the fibrous carbonaceous material at a temperature up to about 400°F to convert the non-oxidized iron to oxidized iron.

11. The fibrous carbonaceous material of Claim 10 in the form of pellets having a size in the range of about 8 mesh to about 35 mesh.

12. The fibrous carbonaceous material of Claim 10 wherein the iron is oxidized by heating the carbonaceous material in air at a temperature of less than about 400°F
for about 0.5 to about 24 hours.

13. The fibrous carbonaceous material of Claim 10 wherein the iron is oxidized by heating the carbonaceous material in steam at a temperature of less than about 400°F
for about 0.5 to about 24 hours.

14. The fibrous carbonaceous material of Claim 10 wherein the iron is oxidized by heating the carbonaceous material in hot water at a temperature of less than about 400°F for about 0.5 to about 24 hours.

15. The carbonaceous material of Claim 11 in which the iron is oxidized with dilute nitric acid.