US 3053775 A
Description (OCR text may contain errors)
Sept. 115 1962 w, F. ABBOTT METHOD FOR CARBONIZING FIBERS Filed Nov. l2, 1959 l//LL//JM ,055077 INVENToR.
o-W 54X 706/145' VS United States Parent fornia i t Filed Nov.` 1 2', 1959, Ser. No. 852,580 8 Claims. (Cl. 252-421) This applicationisV a' continuation-impart of my prior, co-pending application Serial No. 569,391, filed March 5, 1956, entitled Method for Carbonizing Fibers, and Articles Produced Therefrom, now abandoned.
This' invention relates to Vfibrous materials and has particular reference to a process for carbonizing fibers and to articles produced therefrom.
One of the primary objects of this invention is to provide a process for the production of carbon in fibrous formv having a highV intrinsic liber density and good tensile strength. While fibers of carbon are not basically new, carbon fibers heretofore produced have been so weak in structure that they could not resist even slight mechanical forces without breakage or disintegration. The present invention provides for the first time bers substantially of car-bon which are su'fiiciently strong to retain theiriibrous form upon being subjected to mechanical forces.
Another object of this invention is to provide a hard, high density carbon in the form of tine fibers, the fibers being clean and' strong because of the high density, yet flexible and resilient due to the small diameter of the fibers.
Another object of this invention is to provide a process for the production of carbon fibers having a wide rangel ofiber diameter and other characteristics for use in varied specific applications.
Another object of this invention is to provide a carbon fiber which is capable of being activated to `a high level While -still .retaining 4a considerable part of its original strength, the activated fiber having adsorption characteristics equal on a weight basis to conventional activated carbon in granular form. Granular activated carbon is Well knownjin industrial applications, but is limited to use' applications' which provide means to contain the carbon granules. Activated carbonfibers of the present invention e'xtendthe use of carbon to clothing, masks, andiilters of fiber construction.
Other objects and advantages ofthe invention,` it is believed, will be readily apparent 4from the following detailed description o f preferred embodiments thereof when readin connection with the accompanying drawings.
In the drawings:
The single FlGURE is a diagrammatic view illustrating the apparatus required to carry out the process of this invention on a small scale.
Briefly, this invention comprehends within its scope the discovery that certain synthetic fibers may Ibe car-4 bonized by carefully controlled thermal decomposition to produce a dense, strong carbon fiber, The choice of rawmaten'als is limited to synthetic fibers of the nonthermoplastic type, which do nottend to melt or how on heating and hence retain the fibrous form when heated to the ldecomposition point.
Natural fibers, `such as cotton, for example, are not suitablefor the purpose of this invention. Although such fibers may be carbonized, they are weakand therefore are unsatisfactory for practical use in the form of carbon fibers.
lthas been found that a regenerated cellulose fiber, such as viscose rayon, cuprammnium rayon and'saponified acetate rayon, is a particularly suitable raw Amaterial foi accomplishing the endsofwthepresent invention.
The present process comprises heating' the raw fiber material in an inert, oxygenfree atmosphere to a temperature suiciently high to bring about substantially complete Vthermal decomposition of the non-carbon corrstituents ofthe material, great care being taken to confL trol the rate of temperature risesiohthat gasificaticn is slow to prevent fiber rupture by rapid dec'ompos'itiri.`
4It has been discovered that a critical temperature f angfel of from about 250 to about 5002" E ex'ists for thedej sired carbonization of the raw regenerated cellulose tibiA It is in this range that theV major part of the ca rbo-r'iiii-L tion takes place. It is extremely important' that the rate of temperature rise throngh this temperature range be controlled so that the weight yield of c'arbo 1 `1` fiber will be greater, preferably, than 45 percent' o\f the c bon content of the original raw regenerated cellulose, and so that the tensile strength ofthe resultant'carboniibei" will be at least 5,000 p. s.i. The temperature rise through thi-s range for a single fiber, for example, should take place uniformly in not less. than Srininuts and preferably over a period of one hour so as to preventexcessively fast gasification, s uch as would otherwisedamag'e the fiber. In actual practice, utilizinga mass .of fibersthe time required to raise the temperature o f 4the entire nia'ss of fibers through this range will exceed the timerequired for an individual fiber according .tothe heat, tran sfe r c har acteristics of the particular, equipment employed and the volume ofthe mass offibfers-v The gaseous decomposition products givemoffdu the heating, operation can themselvesprovide the inert, oxygen-free atmosphere if properly contained In` ,order; to avoid brittl eness in the product, theffiberddiameteri of the raw materials s'hould be'` less than abou;t 2 0 O microns. Preferably, the'ber diameter is lessl than 100 rnicrons.
The raw materials may, be` tijeateddnthefqrm offlco'n tinuous mono-filamentain ghyforrr'rv of shortflerigth .or staple fibers, the f orin oflyarn" of, woven webs; or. any other suitable fiber for '1r`1. Continuous mo'no-fila-, ments or yarns are preferredfsince they can be ,contin ously treatedj by passag e through a suitable furnace or other heating apparatn's. ,V ,i i
'l`l 1econtiui.i`o`usprocess` may `b 4 furnace having a p reheat sect1onf..fol lowed..b -pheric trap, .acarboniziing section aridaicool through, which the fiber, is drawn.,4` 'lghe roller .for the fiber shoulclfbe'ofi ceramic material, `an i aterial is preferably. suppo rit-edA andwguid A furnace onk a guide belt or beltsoi g1 1 a rtz.glassclcjthn Inasmuchas the fibers undergo. shrinkageofffrorn to 35% during carbonization, provision must, be, made for such shrinkage by providing for multiple-driver gf. quartzbelts in the carbonizatipn zjone f l`he cog l ing. s ec tioni may comprise water j acketedheat transfergplates,
The process may alsobe `carried out batchwiseyiu-. suitable furnace provided With adequate temperature controlrneans. ,y ff( Produtsrrodud by the abqvezdesribedthernial der composition processhave a .wide,se9pe ;of industria1 u s es., Thavbon .fibers are strong, yethighly iexible and man be readily fabricated into the desired form or assembled with other components foruse f-huS, Coritinuous carbon filaments may be.wover1 into ,yarn and/or clothgfor then, malinsulation, filtration applications nad., the .like..:i.Th.e. yarn, cloth, or staple carbon fiberstghaving sufficient strength to provide a sc lfzsupporting mass of fibers, may be formed into mats or padsforsimilar uses. Also, the carbon fibers in yarn, or staple form mayabemsedfas a catalyst 0r` Catalyst Carrier, and;L as a eaulkng mateal for; specialized applications. Other industrial` applications will readily present themselves to those skilled in the art.
If desired, the brous raw material may be formed before carbonization into mats, pads, orY continuous webs of low bulk density and having a high degree of shape retention by bonding the bers together with a suitable thermosetting resin such `as urea formaldehyde. The resin should be applied at a low viscosity such that cross-ber cementing occurs without the deposition of excessive or thick resin masses.v Any extensive thickening ofthe ber diameters or the formation of nodules of resin on the bers `is undesirable and produces brittle Vsections in the nished product. Preferably,the resin bond lm is of the sameorder ofmagnitude as the ber diameter. The cured,resinbonded ber mats or pads are carbonized in accordancewithV the above-described process to produce carbon-bonded, carbon ber mats or pads suitable forense in air lters, as thermal insulation and the like. e
V' It isjwithin the scopeofqthis invention to provide the carbon` bersV withV coatings of various types, applied either before or after carbonization. Such coatings may include oxides for various purposes,'i.e., MgO, ZnOg, etcQ, forimp'roved reproong, to minimize-the need to protect the material from-oxidizing atmospheres when used as la thermal insulation; Fe203, Cr2O3, A1203, as catalyst surfaces for catalytic reactions utilizing `the carbon ber as the carrier; CuO, CuzO, etc., for inversion of the selective adsorption characteristics to provide specic adsorption properties; andappropriate oxides to change the black color ofthe carbon bers.
The above and other surface coating materials may be introducedprior to or during regeneration and ber formation. This simplies the coating process and produces more thorough and-uniform coatings, more imperto the ber. It has been found that during the'carbonization process the raw material undergoes a change'from an elecnace on ceramic blocks 12 was a set of three rectangular iron pans 14, 15 and 16 of progressively increasing size.V The pan 14 measured 19" in length, 10 in width and 6 in depth; the pan 15 measured 20 X 11" x 61/2; and
can Viscose Co., 5.5 denier; length, 5"-7; qual., A;
type, var. reg.; lustre, brt.; sym., 1432) to prevent pack-` ing.V Pan 14 wasthen. covered with pan 15 and the two pans inverted and then covered with pan'16. 'Ihe furv Vnace was preheated to 300 F. for about l5 minutes and vious coatings, and coatings with a greater degree of bond the assembly of the three pans put into the center of the furnace on ceramic blocking to permit uniform movement of air. The furnaceand contents were then heated slowly through the gasication stage (300-500 F.) for 21A hours. The temperature was then allowed to rise to 1000 F. to drive o Vthe gases, the lfurnace then turned olf and the batch allowed to cool for 18% hours. v
The carbon bers producedV had a `tensile strength of l 10,000 p.s.i. and a weight yieldkof 52% of the carbon content of the raw regenerated cellulose bers. Y
The followingrexample vdescribes the production of activated kcarbon wool bers by the batch method:
f I ExampleVV vThe apparatus described in ,Example 1 was utilized with l the addition of a lengthY of 1i-inch steel tubing 30 welded through oneendV of thepan 15 andV to the bottom, the tubing being provided With a plurality (-about 6 in this case) of l 1zfinch holes 31 equally spaced inside the pan length. The tubing passed through the furnace'port- 11.`
uctrnay be made to exhibit variable specic resistance.
, SuehV materials are useful in electronic applications suchV asin making sensing elements, transducers, conductivity devices, andthe like.`
Carbon bers produced by the present carbonization method have verylow adsorption'capacity. These same bers jmay, however, befactivatedV to provide saturation adsorption capacities fori carbon tetrachloride, for exam! ple, of E10-50% by Weight of the activated carbon ber, whilestill retaining a higrhproportionjof the strength properties ofthe unactivated carbonized ber. It has Y been found that the vunactivated carbonized bers may be activated Vbyjreattion with steam at temperatures from Y 1Z00 to 1800 F. ThisV is( the well knownactivation process whichhas heretofore, been, applied to vgranular carbon materials'. 'Y The activation process may be carried out continuouslyon continuous laments by introducing a steam ret action? chamber immediately prior `to 'the cooling ,sectionV Y' carried out oni a small-scale batch operation, but itis to be understood that'theinvention-is not to be liimted to the details set forth: e
-Examplel j The apparatus is shown diagrammatically inthe drawingand includes a 4 bur`ner, gas-redbox kiln furnace 10 provided with a side port 11. Mounted inside the fur- A S-gallon bottle 39 of distilled water was positioned on top of the furnace'andprovided with a supply tube 40 conl nected to the tubing 50.V A stop-cock 45 was also provided in the tube 40.
The carbonization step vof this examplewas identical to that of Example 1, except that here, following the 2%- hour carbonization step, the temperature of the carbon bers was raised to 1450" F., and maintained there for about'2 hours, during which time about 5 gallons of distilled Water from the bottle 39 wasV- slowly fed by gravityk into the tubing 30. Steam was thus -forced out of the holes- 31 and through the carbonized bers to activate the same. Atgthe end ofthe two-hour period, Vthe batch was dried by lowering the temperature to about 500 F. for about l5V j minutes. The furnace was then allowed to cool for about 18% hours as in Example 1. The activated carbon bers yF. for 21/2 hours. The temperaturen/as then raised` to l l000 F. to drive oi gases from the furnace; The batch of ycarbonized bers was Vthen permitted to cool to room temperatures over a period of approximately 18 hours.
VThe carbon bers thus 'produced were tested and revealed a tensile strength of 8,000p.'s.i. and a Weight yield equal to 50.4% of the carbon content of the raw cupram? monium rayon bers. p
' Example 4 e Again, utilizing the apparatus described in connection with Example 1, a 1.5 pound batch of 1 denier saponied acetate rayon bers was carbonized yby slowly heating the same through a temperature range of 250". F. to 500 F.
for 21/2 hours. The temperature was then raised to 1000 F. and the batch allowed to cool to room temperature over an 18 hour period. The resultant carbonized bers were tested and revealed a tensile strength of 11,200 p.s.i. and a weight yield equal to 51.7% of the carbon content of the original saponied acetate rayon bers.
Further tests and experiments in connection with single bers or mono-laments of these materials reveal that the rate of increase in temperature through the critical range of -from about 250 F. to about 500 F. should be accurately controlled, so that the increase in temperature from 250I F. to 500 F. will consume a period of time of at least 8 minutes. If the temperature rise is attained in a time shorter than 8 minutes, the tensile strength and weight yield of the resultant carbonized ber will be materially reduced.
Having fully described my invention, `it is to be understood that I do not wish to be limited to the details set forth, but my invention is of the full scope of the appended claims.
Having thus described my invention, what I claim is:
l. A process for the production of a carbon ber comprising the steps of heating viscose rayon ber in an inert atmosphere through a temperature range of from about 300 F. to about 500 F., said heating requiring at least 30 minutes to attain said 500 F. temperature.
`2. A process for the production of a carbon ber comprising the steps of heating viscose rayon ber in an inert atmosphere through a temperature range of from about 300 F. to about 500 F., said heating requiring about two hours to attain said 500 F. temperature.
3. A process for the production of a carbon ber comprising the steps of heating viscose rayon ber in an inert atmosphere through a temperature range of from about 300 F. vto about 500 F., said heating requiring at least 30 minutes to attain said 500 F. temperature, and subjecting the ber thus produced to the action of steam at an elevated temperature to activa-te the same.
4. A process `for the production of a carbon ber comprising the steps of heating viscose rayon ber in an inert atmosphere through a temperature range of from about 300 F. to about 500 F., said heating requiring about two hours to attain said 500 F. temperature, and subjecting the ber thus produced to the action of steam at an elevated temperature to activate the same.
5. The method of making a carbon ber which cornprises heating a non-thermoplastic, regenerated cellulose ber in an inert atmosphere through a temperature range of `from approximately 250 F. to approximately 500 F., said heating requiring at least 8 minutes to attain said 500 F. temperature.
6. The method of making a carbon ber which comprises heating a non-thermoplastic, regenerated cellulose ber in an inert atmosphere through a temperature range of from approximately 250 F. to approximately 500 F. in a time period of not less than 8 minutes; and subjecting the ber thus produced to the action of steam at an elevated temperature to activate the same.
7. The method of making a carbon ber having a tensile strength of at least 5,000 p.s.i. which comprises heating in an inert atmosphere a regenerated cellulose ber selected from the class consisting of viscose rayon, cuprammonium rayon and saponied acetate rayon, through a temperature range of from about 250 F. to about 500 F., the increase n temperature yfrom about 250 F. to about 500 F. being accomplished in not less than 8 minutes.
8. 'I'he method dened in claim 7 including the further step of subjecting the thus heat-treated ber to the action of steam at a further elevated temperature to activate the same.
References Cited in the le of this patent UNITED STATES PATENTS 2,925,879 Costa et al Feb. 23, 1960 FOREIGN PATENTS 11,997 Great Britain 1886