US 3322489 A
Description (OCR text may contain errors)
May 30, 1967 G. M. MOUTAUD ETAL PROCESS OF GRAPHITIZING "POLYNOSIC" REGENERATED CELLULOSE FIBROUS TEXTILE AND RESULTING FIBROUS GRAPHITE TEXTILE Filed July 28, 1964 19x "/7552 45 weaoM/z60 l AMP dffi w/rvzfa fiw iw S e) it) 59 FIG. 2
INVENTORS GILBERTE M. MOUTAUD BY JACQUES L.DUFLOS United States Patent 3,322,489 PROCESS OF GRAPHITIZING POLYNOSIC RE- GENERATED CELLULOSE FIBROUS TEXTILE #RD RESULTING FIBROUS GRAPHITE TEX- E Gilberte Michelline Moutaud, Neuilly-sur-Seine, and Jacques L. Duflos, Paris, France, assignors of one-half to Societe le Carbone-Lorraine, Paris, France, and Etablissements Pierre Genin, Villeurhanne, France, both French companies Filed July 28, 1964, Ser. No. 385,726 4 Claims. (Cl. 8-116) This invention relates to novel carbon fabrics, and in particular graphite fabrics and to a process for manufacture thereof.
Carbon fabrics generally obtained by carbonization of cellulose or of cotton fabrics, have already found numerous applications, either in the activated or unactivated states. They have been used as materials for the construction of filters, evaporation and desiccation systems, apparatus for protection against polluted air or toxic gases, as bandages and objects for medical uses, etc.
Processes have heretofore been proposed for the production of such materials by carbonization and/or graphitization of fibers, batting, fleeces, fabrics and knitted articles of cotton, either rnercerized or not, of viscose or synthetic fiber and, in general all carbonizable fibers, natural or artificial.
Diverse processes have been proposed and described for the preparation of active carbons, electrically-conductive carbons, or fibrous graphite by carbonization of cellulose, regenerated or otherwise. Allthese processes more or less openly contemplate critical zones intervening in the course of carbonization of the materials used. In the thermal transformation of the cellulosic material to graphite, there are troublesome stages corresponding to the dehydration of the material, and to the disengagement of gases which may be deleterious to the good properties of the final product. To resolve these problems, there has been proposed a graphitization process in several steps including:
(1) Drying in an oven for 15 hours at 100 C., under rigorous protection against any danger of rehydration,
(2) Carbonization in the oven at 700 C. after having covered the dry material with coke, and while sweeping with a non-oxidizing gas,
(3) Graphitization of the carbonized material in an electric furnace at 2,500 C.
An object of the present invention is to provide an industrial process for fabrication of graphite fabrics, which overcomes the difficulties of prior processes.
Another object of the invention is to provide a direct process for carbonization and graphitization.
The invention is characterized by the use of a starting material having a particular structure, as more precisely described hereinfater.
In one particular embodiment of the invention, the novel graphite fabrics obtained according to the process retain after carbonization and graphitization the particular structure of the initial material and are endowed With remark-able elasticity and durability. Essentially, the invention concerns graphite fabrics obtained by carbonization and graphitization of fabrics composed of fibers characterized by a round cross section and a homogeneous internal structure, preferably fibers of the BX type (sometimes called polynosic).
BX-type filaments patented by the Comptoir des Textiles Artificielles, are distinguished from ordinary filaments of regenerated cellulose by a fibrillary structure near to that of natural fibers, such as cotton for example, and a homogeneous internal structure which confers 3,322,489 Patented May 30, 1967 upon them very great resistance to moisture as well as an extremely reduced swelling in water. The degree of polymerization of the regenerated cellulose in BX fibers is very high, above 40%. These fibers have ultrafine filaments and very high strength in the wet state.
According to the invention, it is preferred to use as starting materials BX fibers, sometimes called Polynosic fibers. These fibers are more fully described, and processes for their manufacture are described in the following French patents, in the name of Comptoir de Textiles Artificiels, Viscose Francaise & Givet Izieux: French Patent 943,103 and its addition 56,757, French Patent 1,006,078 and its addition 69,990, French Patent 1,106,- 707 and its addition 69,674, French Patent 1,111,579, French Patent 1,111,580, French Patent 1,121,007, and French Patent 1,128,006.
U.S. Patents 2,586,796 and 2,699,983, assigned to Textile and Chemical Research Co. Ltd. also describe methods for making BX fibers.
In general, production of BX fibers forming the preferred starting materials for use in the present invention comprises the steps of extruding into a bath of sulfuric acid at room temperature a viscose prepared from cellulose containing less than 25% by weight of molecular chains with a degree of polymerization below 500 and less than 4% by weight of molecular chains with a degree of polymerization below 250. This viscose is prepared from alkali-cellulose of which the minimum degree of polymerization after ripening is greater than 450. This viscose has a degree of xanthogenation ('y) (as described below) between 40 and 50. The concentration of sulfuric acid in the said bath is between 57.5 and 73% and is defined by the expression:
Percentage concentration by weight of sulfuric acid:
The extruded filaments are then subjected to a stretching operation to increase their length by to 280% while they are still wet from the spinning bath, the filaments are washed and then allowed to relax, and they are then subjected to winding and twisting.
U.S. Patent 2,586,796 describes this process, and in particular a mode of operation which can be carried out at room temperature. U.S. Patent 2,699,983 adds modifications to the basic process, which enable it to be carried out at higher temperatures, in this process the formula giving the concentration of sulfuric acid in the spinning bath is given by the following expression:
C=concentration (wt. percent) of H SO v=degree of xanthogenation T=Temperature C.)
In the modified process, the sulfuric acid concentration may range from 5 8 to 72% and the 7 value is between 40 and 53. The temperature is of the order of 20 to 40 C.
The filaments so obtained have a tenacity in dry air higher than 4.8 gm. per denier and an elongation at the breaking point greater than 8%.
U.S. Patent 2,591,243, of Textile and Chemical Research Co., Ltd, describes a method of making viscose rayon filaments, which can be preferably combined with the basic process above described. According to this method, the viscose is spun into a coagulating bath before being stretched, then removed from the bath, it is stretched, then held under non-stretching conditions for at least 3 seconds to allow relaxation of internal stresses, and fiinally spooled in a centrifugal cup. Other techniques are described in the above-cited patents, and may be advantageously adapted to the over-all process.
The degree of xanthogenation (y) referred to above, is the number of hydroxyl groups substituted by CSS groups per 100 glucose units.
BX fibers have a homogeneous structure and because of this homogeneous structure, are characterized by a round or nearly round cross-section, which is retained after carbonization or graphitization. This round or nearly round cross section in the finished product is believed to be responsible for the remarkably improved properties observed in the products of this invention, as compared with carbonized or graphitized products heretofore proposed.
Polynosic viscose cellulose textile fibers have been. defined as: A manufactured cellulosic fiber with a fine and stable microfibrillar structure which is resistant to the action of 8 percent sodium hydroxide solution down to C., which structure results in a minimum wet strength of 2.2 grams per denier and a wet elongation of less than 3.5 percent at a stress of 0.5 gram per denier.; see Man- Made Fibres, Fourth Edition, by R. W. Moncrieff, 1963, page 256, John Wiley and Sons Inc., New York City, New York for the aforesaid definition.
Certain regenerated cellulose fibers having the requisite properties of a round cross-section and a homogeneous internal structure may of course be employed with good results. In practive, the BX type of fiber has been found to give particularly good results and is therefore employed as the starting material in preference to any other.
Referring now to the figures:
FIGURE 1 is a cross section, enlarged 600 times, of graphitized BX fiber, according to the present invention.
FIGURE 2 is a cross section, enlarged 600 times, of graphitized 300-denier conventional viscose fiber.
Comparing the two figures, it may be readily observed that the cross section of the graphitized BX fiber according to the invention is perfectly circular, whereas the cross section of graphitized conventional viscose fiber is noncircular, and in fact is highly irregular and deeply indented..
This irregularity and indentation is attributable to the non-circular cross section of the original fiber or to heterogeneities in the structure thereof, which cause nonuniform shrinkage and consequent distortion. When a fiber having a circular cross section and a homogeneous structure, such as BX fiber, is used as the starting material, the cross section of the product is also circular in cross section, and the corresponding properties are definitely enhanced.
According to the invention, the novel graphite fabrics are made by carbonization and graphitization of a fabric of round, homogeneous threads, such as BX threads in a non-oxidizing atmosphere, in a controllable heating apparatus such as an industrial furnace. The non-oxidizing atmosphere may consist of an inert gas, or may be achieved simply by sealing the furnace so that atmosphere becomes non-oxidizing as its initial oxygen content is consumed.
The fabric to be carbonized is preferably wound on mandrels or the like, in order to be introduced into the furnace.
The heating of the fabric to be carbonized is accomplished by a slow and uniform increase in the temperature of the furnace, which should rise from room temperature to a temperature between about 2,500 and about 2,900 C., over a period of from about 230 to about 250 hours.
The following example, given as indicative but not limitative, illustrates the invention:
Example.Manufacture of a graphite fabric by direct carbonization at 2,800 C., 0] BX fiber fabric A finished fabric of 840 denier BX fiber is chosen, having 16 threads per centimeter in the direction of the warp as well as in the direction of the fill, or a fabric made starting with 1,650 denier BX thread having a thread count of 7.5 threads per centimeter in the direction of the fill and in the direction of the warp. About 20 meters of this 4t fabric, weighing 315 grams per square meter, having a width of 0.90 meter, is wound, on a mandrel of graphite for example, the dimensions of which are a function of the dimensions of the furnace.
The mandrels bearing the fabric of BX thread are placed in an industrial electric furnace in which the atmosphere is confined or reducing.
A very slow heating is then begun, according to a rigorously controlled progression, up to 2,800 C. over a period of 230 to 250 hours.
The charge is removed from the furnace after cooling. The fabrics thus obtained have a brillant black appearance, silky and supple.
The linear shrinkage of the graphite fabric compared to the BX thread fabric is approximately 27%. Its characteristics are as follows:
Weight per square meter g to Diameter of elementary fiber mm 0.005 Carbon content ..percent (wt.) 99.8 to 100 Materials volatile in the crucible, percent less than 1 Tensile Elongation strength In the direction of- The warp 5.5 kg./em. 10.6 mm. The fill. 5.5 kg
The following table permits comparison of the raw fabric and the graphitized fabric:
Warp Fill In the raw state 7.5 threads/ 75. threads] cm. cm. After graphitization 10.4 threads/ 10.4 threads/ cm. cm.
Graphite fabrics according to the present invention,
characterized by remarkable mechanical resistance and suppleness, give entire satisfaction in all of the applications of such fabrics.
The example mentions only graphitization of fabrics of BX threads in wound form, but the process is obviously not limited to this mode of realization and extends to the graphitization of circular cross section, homogeneous structured fibers and fabrics, such as BX fibers and fabrics, in all forms.
1. A process for the manufacture of fibrous graphite textile comprising graphitizing viscose regenerated cellulose textile fibers having a substantially round cross-section, a smooth surface, a homogeneous internal structure, with a fine and stable microfibrillar structure which is resistant to the action of 8% sodium hydroxide solution down to 0 C., minimum wet strength of 2.2 grams per denier and a wet elongation of less than 3.5% at :1 stress of 0.5 gram per denier, by heating said viscose regenerated cellulose textile fibers in an inert gas atmosphere contained in an electric furnace by a slow and uniform increase in the temperature of the furnace from room temperature to a maximum temperature between about 2,500 C. to about 2,900 C. for a total heating period of from about 230 to about 250 hours.
2. A process for the manufacture of graphite fabrics comprising graphitizing viscose regenerated cellulose fabric composed of viscose fibers having a substantially round cross-section, a smooth surface, a homogeneous internal structure, with a fine and stable microfibrillar structure which is resistant to the action of 8% sodium hydroxide solution down to C., a minimum wet strength of 2.2 grams per denier and a wet elongation of less than 3.5% at a stress of 0.5 gram per denier, by rolling said fabric on graphite mandrels, placing said rolled fabric in an electric furnace, sealing the electric furnace so that the atmosphere therein becomes non-oxidizing during the heating produced by said furnace, and heating said fabric by a slow and uniform increase in the temperature of the furnace from room temperature to a maximum temperature between about 2,500 C. and about 2,900" C. for a total heating period of from about 230 to about 250* hours.
3. A process for the manufacture of graphite fabrics comprising graphitizing viscose regenerated cellulose fabric composed of viscose fibers having a substantially round cross-section, a smooth surface, a homogeneous internal structure, with a fine and stable microfibrillar structure which is resistant to the action of 8% sodium hydroxide solution down to 0 C., a minimum wet strength of 2.2 grams per denier and a wet elongation of less than 3.5% at a stress of 0.5 gram per denier, by placing said fabric in an inert gas atmosphere contained in an electric furnace and heating said fabric by a slow and uniform increase in the temperature of the furnace from room temperature to a maximum temperature between about 2,500 C. and about 2,900 C. for a total heating period of from about 230 to about 250 hours.
4. Fibrous graphite textile whose fibers have a substantially round cross-section produced by the process of claim 1.
References Cited UNITED STATES PATENTS 3,053,775 9/ 1962 Abbott 252-421 3,107,152 10/1963 Ford et a1 8-116 X 3,116,975 1/ 1964 Cross et a1. 23-2092 3,179,605 4/ 1965 Ohsol 23-2092 X 3,242,000 3/1966 Lynch 8-116 X FOREIGN PATENTS 1,269,274 7/ 1961 France.
942,186 11/ 1963 Great Britain.
NORMAN G. TORCHIN, Primary Examiner. H. WOLMAN, Assistant Examiner.