US2372561A - Process of treating low rank textile fibers - Google Patents

Description

OFFICE PROCESS. OF TREATING LOW RANK TEXTILE FIBERS Joseph C. Elgin, Princeton, N. J.

No Drawing. Application June 19, 1941,

Serial No. 398,851

Claims.

This invention relates to an improved and novel method of treating relatively highly lignified low rank textile fibers such as jute, pita, and

caroa fibers and to the greatly improved products for textile use obtained thereby, and more particularly it relates to the production from such low rank lignified fibers of a white and purified, strong first rank textile fiber greatly improved in resistance to discoloration upon aging and to the chemicals with which it may come into contact in normal usage. The application is filed as a continuation-in-part of my copending application Serial No. 310,659, filed December 22, 1939.-

The highly lignified low rank fibers, e. g., jute, pita, and caroa, to which this invention pertains, in contrast to the well known first rank textile fibers such as linen, ramie, and cotton, contain in addition to normal cellulose, appreciably higher quantities of hemicelluloses and pentosans, and in particular, larger quantities of lignin intimately associated with the physical construction of the fiber itself. In addition, such lignified fibers contain relatively larger proportions of gums, resins, waxes, and natural color or color forming bodies more or less associated with the lignin and the construction of the fiber itself. Inconsequence, these lignified fibers are medium to very dark brown in color, very harsh and brittle, so that in their natural state or when treated by previously known methods, they are suitable only as low rank fibers for coarser uses.

Because of the differences in chemical compositions, methods of treating and bleaching suitable for first rank fibers such as ramie, linen,

and cotton are entirely unsuited to the lignified fibers such as jute, pita, and caroa. In fact the latter fibers are not susceptible to worthwhile improvement by hitherto known bleaching methods'except by serious alteration in the strength and character of such fibers, and indeed their the entirely unsatisfactory results and properties of the lignified fibers obtained from such processes are well known. The composition of linen versus jute and the bleaching of the two types of fibers above mentioned are discussed, for example, by Matthews, Bleaching and Related Processes, Chemical Catalog Company, New York, pages 490-528, 1921. If properly boiled out with alkalies, linen can be satisfactorily bleached by known methods. Ramie is so white naturally that it requires about the same bleaching methods as cotton. On the other hand, previously known methods do not yield satisfactory results on highly lignified fibers such as jute. In consequence, in spite of the well developed bleaching art, jute is relatively little subjected to bleaching and continues to be regarded as a low rank textile fiber employed for rough and crude gabrics and not frequently dyed in delicate colors. Previous methods of treating and bleaching fibers (known in the art) have failed, either to do more than partially decolorize, or if-satisfactory bleaching was efiected, the strength of the fibre was greatly reduced and the fibre disintegrated. Further, the product of these methods, unless resulting from such drastic treatment as to simultaneously substantially disintegrate the fiber, has a marked susceptibility to deterioration on aging.

The difficulties in chemically treating lignified fibers such as jute, pita, and caroa to remove their objectionable properties, and in obtaining even a half bleach by the hitherto known complicated methods without simultaneously seriously altering and weakening the fiber, as well as the impossibility hitherto of obtaining a perfect white on such fibers, arise because of their high lignin content which carries associated intimately with it certain types of natural color or colorforming bodies and which form an inherent part of the chemical and physical composition .of such fibers. It has previously commonly been thought that the lignin itself was the constituent mainly responsible for the objectionable properties of such lignified fibers, their resistance to bleaching, and the light sensitivity of the bleached product. I have, howeyer, now found that it is the relatively small quantity of natural color and/or color-forming bodies associated with the lignin that is primarily responsible for the great resistance of such fibers t decolorization and, if allowed to remain in the fiber, for the major part of the sensitivity, of the bleached product to discoloration upon aging. Previously known methods of treating-and bleaching such fibers have either intentionally or'unavoidably t lltt search Room they are cementing constituents, or have been unable t overcome satisfactorily the great resistance of the fibers to deooloration, or its subsequent sensitivity to deterioration on aging. Furthermore, no previously known process which does not simultaneously destroy the fiber has permitted bleaching to a perfect white. Inaddi= tion, such treatments have failed to remove certain types of color bodies which, although decolorized to a large extent by the treatment, are reconverted to colored bodies by the action of light and/or of certain chemical agents such as alkalies. Still further, such previous methods have been unable to remove sufficiently the Waxes, gums, resins, etc., responsible for brittle-- ness and harshness in the fiber without simultaneously substantially weakening and disintegrating it.

As stated above, I have found that it is the relatively small quantity of-waterand alkaliinsoluble color bodies or natural dyes associated with such high lignin content fibers that is primarily responsible for the great resistance of such fibers to decolorization and to a major extent.

for the sensitivity of the bleached product to discoloration on aging. By aging as used herein, normal exposure to light and heat and time isv included. I have furthermore developed a process by which these color and color-forming bodies'may be extracted and removed from the lignified jute, pita, and caroa fibers by extracting and treating them with organic solvent in which the said color and color-forming bodies are soluble. In this way I dissociate such 'organic-solvent-extractable color bodies from the fiber and their associated lignin content without simultaneously substantially removing or altering the lignin and/or hemicellulose content of the fiber. The term organic solvent-extractable color body includes any such constituent inherent to the lignified fiber imparting color to it, or capable of being converted into a material imparting color to the fiber upon aging and upon contact with the chemicals with which it may come in contact in normal usage. I have further found that the natural color =bodies associated with the lignin content of such fibers as jute, pita, and caroa are apparently of more than one kind. Certain of these are soluble in water and aqueous solutions of inorganic compounds, such as alkalies, and can accordingly be removed by leaching with aqueous solutions. Leaching with aqueous solutions is, however, unable to effect substantial removal of those organic solvent-exbodies since in thepresence of'alkali, these are '5 converted to new color bodies more deeply brown, red, and yellow which fix themselves tenaciously to the fiber. Hence, not only are these color bodies not removable substantially. by leaching with aqueous alkaline solution, but such solution tends to prevent or diminish their extraction by organic solvents. In carrying my invention into practice, therefore, I prefer to solvent-extract prior to treatment with such solutions.

I have further found that after extraction of the organic solvent-extractable color bodies and without any other preliminary treatment the fiber is readily and quickly bleached in a single step. For example, a perfect white fiber is obtained by use of a percompound, preferably hydrogen peroxide. The fiber thus organic solventextracted and bleached is greatly improved in its resistance to discoloration and deterioration on aging. So far as I am aware these results are unattainable by any other hitherto known method or process known to the art. Another advantage of my invention is that by use of the solvents which I have found. to be usable. for the extraction of theobjectionable natural color bodies from the fiber, the natural waxes, gums, and resins are simultaneouslyremoved substantially from the fiber so that the resultant extracted fiber is greatly improved in harshness and brittleness. Hence, in practicing my invention, I prefer to use a solvent of such nature and. solvent power as hereinafter disclosed that both results are simultaneously achieved in a single extraction step. While manysolvents, e. g. fat and wax solvents such as naphtha, benzene, and other hydrocarbons, are able to remove wax and oily matters from the fibers, they possess little or no solvent power for the natural color bodies associated with the lignin.

In carrying out my invention, I'have found the rapidity and completeness of extraction of the color bodies together with the waxes, gllms, and resins to be greatly assisted and improved by subjecting the raw fiber prior to the solvent extraction to a dehydration-degassing treatment, preferably at a temperature of 27,5F. to 350 F., and preferably in the absence ,of oxygen and water vapor or under vacuum for about thirty to ninety minutes. The solvent extraction is thereby rendered more rapid and complete, the subsequent bleaching takes :place still 'rngre rapidly and easily, and the properties of the final product are very-substantially furtherirnproved.

The process of my present invention, therefore, contemplates the treatment of such highly lignified low rank textile fibersas jute, pita, and caroa to remove the effect of the color bodies gf the type described and produce a decolorized product Without removing or altering the lignin and hemicellulose content to anextentsufiicient to afiect materially the strength of the fiber. It further contemplates the simultaneous removal of waxes, gums, and resins from thefiber,

The principal object of thepresent invention, therefore, is to provide asirnple and economic process for thetreatmentof highly lignifiedlow rank textile fiberbyxwhich.a product of whiteness and resistance to aging'not hitherto-availa ay be obtained wi hout mat ia ly Weakening or disintegrating thefiber,

Another object is to provide aprocess for the decolorizing of the aforesaid fibers which resnits not only in a brilliant white fiber, but also in-a fiber resistant to discoloration upon aging,

still another object is topmduce.f oma natural highly lignified-low rank textilevfibenga white fiber essentially stable against discoloration by ordinary exposure to sunlight and chemicals, such as alkalies, and being of substantially undiminished strength, due to the retention in the fiber of a major and important part of the lignin content thereof. 1

Another object is to provide from the aforesaid types of fibers a soft pliable fiber of the type described suitable for spinning from which substantially all the harshness and brittleness, due to resins, waxes, and the like, inherent in the raw fibers and those treated by hitherto known processes have been removed.

- Other objects will be apparent from a consideration of the specification and claims.

While the process of the present invention is applicable for the treatment of the highly lignifiedtextile fibers in general, such as jute, pita, caroa, and the like, in fibrous form or in the form of yarn or fabric, the invention is particularly advantageously applied to the treatment of jute, and, due to the availability of this fiber, will be described in conjunction therewith. Where the term fiber is used herein, it includes the fiber in the form of yarn and fabric, as well as loose In order to bleach and otherwise improve their properties for textile and similar uses, it has been well known in the art to treat vegetable fibers such as cotton, flax, linen, ramie, and 1:

others with aqueous solutions of inorganic substances such as acids, alkalies, and salts, and of oxidizing and reducing agents such'as chloride of lime; hypochlorite; potassium permanganate; oxalic acid, percompounds, e. g., hydrogen peroxide; and hydrosulphite, and the like. The hitherto known processes employ various combinations of such agents and treatments under various conditions. For example, the fibers may be given a preliminary leachingor boil-off treatment with water or a water solution of some alkali such as caustic soda, soda ash, sodium silicate,.etc., to which may be, added various detergents and wetting-out agents such as soap, sulphonated oils, higher alcohol'sulphates and sulphonates, etc. This step is then followed by treatment with an aqueous oxidizing agent such as hypochlorite or a percom'pound, and the liquor may also contain various wetting-out agents and/or detergents. A complicated series of such agents may be used, such as treatment with a series of different. oxidizing agents or alternate treatments with oxidizing'and reducing agents. The latter has usually been employed in attempts to apply such methods to highly lignified low rank fibers such as jute. While the first rank high cellulosic content textile fibers are relatively easily treated by such methods with excellent results, the extreme difiiculty and unsatisfactory results of such previously known processes when applied to the low rank highly lignified textile fibers such as jute are well known to those skilled in the art. Even a partial or half bleach requires a' prolonged and complicated treatment under drastic conditions with rigorous and exacting control and is accompanied by a serious reduction in the strength andcharacter of the fiber and no improvement in its susceptibility to deterioration on aging and little in its harshness and brittleness. A full or perfect white is not obtainable by such processes except by such drastic treatment that the fiber is so seriously altered and weakened as to render it unfit for most textile uses. I

- The difilculties in decolorizlng and treating jute flifialt'iii ii & CHEMlCAL Mom-Ft. Callltii Qt l'EXl'iLES & FIBERS.

it ii. 2,872,561

brown or bright yellow even by drastic oxidizing treatment such as with hydrogen peroxide, or by alternate oxidizing and reducing treatment with agents such as permanganate and hydrosulphite.

Hence, such color bodies prevent decolorization of the fiber, except by means which simultaneously disintegrates the fiber, removing them along with lignin and hemicellulosic constituents by rendering these soluble in the aqueous treating solution. As is well known the lignin content of such highly lignified fibers as jute is'un usually readily susceptible to attack by chemical agents, the lignin being attacked and apparently destroyed or rendered water-soluble by many inorganic agents resulting in the disintegration or serious weakening of the fiber. Itis well known, for example, that jute is readily and quickly attacked by even weakly acid solutions, the result being the disintegration of the fiber in very prolonged treatments or with moderate acid concentrations. such as jute in alkaline aqueous solutions or even in pure water also leads to a serious weakening of the fiber. Such prolonged boiling in water or aqueous solutions furthermore acts simultaneously to attack, hydrolyze, and render soluble hemicellulosic constituents of the fiber, an additiona1 cause of weakening and disintegration thereof. Chlorine and aqueous solutions of chlorine-containing compounds, such as hypochlorites tend to attack the lignin component of jute apparently chlorinating it and rendering it soluble. Anything but the mildest treatment of lignified fibers such as jute with such agents seriously weakens and disintegrates them and the drastic treatment with such agentsnecessary to obtain even a partial decolorization so seriously weakens them as to render them unfit for the majority of textile uses. Hence, if the types of color bodies and. natural dyes before described are allowed to remain in the fiber, the prolonged and drastic treatment required to even partially decolorize some of them results in serious weakening of the fiber and furthermore certain of them are not decolorized beyond a yellow by even drastic treatment with known bleaching agents. Still further, these partially decolorized color bodies remaining in the fiber are especially susceptible to colorization by light and aging. In any case, the more prolonged the treatment with any aqueous agent, the greater will be the weakening of the fiber.

It has been ascertained that, while treatment with water and aqueous solutions of inorganic compounds effects the removal of some portiono-f the resins, waxes, gums, and certain of the color bodies of jute fibers, it is unable to eifect substantial removal of those color bodies responsible for the great resistance to decolorization on bleaching and for the light sensitivity of the bleached product. Thus, I have found that if unextracted just bleached to a light yellow by hydrogen peroxide is subsequently extracted with solvents of the type hereinafter described, .the

Prolonged boiling of fibers yellow oxidized color bodies; remaining; in. theand responsible for: its color are removed by; the solvent leaving a perfectly white: fiber; In contrast: with. my solvent extractionprocess I have further been unable to find any substantial change in the ease of bleaching. of. jutefiberby preliminary treatment with various aqueous agents known in-v theart. Thus, previously known methods. of; treating with. aqueous. alkaline: or acid solutions prior to: bleaching unable to effect substantial improvement. in these respects; and it, has been found that. they may actually be detrimental since, as previously pointed out, if. the raw fiber prior tobleaching is treated with, an appreciably alkaline solution such as. caustic sodaor sodium carbonate, the color bodies. not removable therebya-reconvertedby thealkali into more deeply brown, reddish. color bodies or dyes tenaciously heldI by: the fiber and extremely diflicult, if notv impossible, to remove by any method short of. disintegrating the fiber. On. subjecting the product to' bleaching by oxidation or reduction. with, agents such: as peroxide or hydro-sub phite,- the product is. very difiicult to decolorize and usually there remainsa brownishor brilliant yellow tint, which it. is impossible to furtherremove or reduce by known: methods which do: not substantially destroy the fiber. Further-more, such product, even if a. bleaching is. obtained, is very sensitive to discoloration upon aging and by moderately strong alkalies.

In: accordance with the present invention, the color and color-forming. bodies of lignified low rank textile fibers, such. as. jute, which are re.- sponsible for the objectionable properties. described above and not removable.- by. bleaching withwater or aqueoussolutions of inorganic com.-

poundsare. removed, and their subsequent (301011] zation efiects, substantially eliminated, by treatnrent with. an organic liquid solvent inwhich said, color bodies arescluble. As will. hereinafter. appear, the raw jute, prior to the solvent treat.- ment, is. preferably subjected to a. dehydration treatment; The treatment with the solvent is preferably carried out on the raw jute prior toits subjection tov aqueous solutions or toanybleaching treatment. A. mild washing. stepwith cold or warmed Water which may contain. a mild detergent or wetting: agent to-removeadhering dirt and the. like may occasionally be desirable, but; is usually unnecessary and is. always-to: beayoidedpossible. Thus, in. carrying out my invention, rawjute fiber is first extracted with an organic solvent of the type hereinafter disclosed; JPhe objectionable organic solvent-extractable color or-color-forming bodies together with the'waxes, resins, and gums are thereby substantially removed. No other preliminary treatment or. preliminary SllbjC-JCtiUI'lztO an aqueoussolution is re.- quired, but if the extraction is preceded by the dehydration step hereinafter described the results are still further improved. The objectionable jute odor is removed, the hand is improved;

and especially with certain solvents and if the dehydration step is employed, an appreciable lightening in the color of thejute is obtained. The. extracted fiber is next advantageously subaerator used, the product is a pure brilliant whi-tesuperior to, that obtainable by any other known bleach.- ing; process on unextracted fiber. Furthermore, th decolorized; product is essentially resistant to discolorationupon. aging and is very littleif; any reduced in strength. If peroxide concentra.- tions of 2% to 4% andtemperature of, for-example, 208 F. to 212 F. are employed. on the extracted fiber, decolorization to a full brilliant white; is. obtained inas little as fifteen to sixty minutes time. If desired, a removal of; the yellow oxidized colorbodies by the organic solvent may be carried out on previously bleached fibers, in which case the color of the. bleached product and its stability to colorization .by light are: greatly improved, but the" ease of bleaching gained by prior extraction. is lost and the general results are-not as satisfactory. If bleached fibers are to be: treated by the dehydration. treatment, the bleaching should be conducted in a bath which contains no material tending. to fill the pores or the-fibers, since, otherwise, the advantages of the dehydration treatment will not-be obtained.

It: is well known in the art to employ percompounds and, hydrogen peroxide for the general bleaching of vegetable fibers. It is likewise known to employ such agents on-unextracted jute and analogous fibers. Hydrogen peroxide gives the-best results obtainable-oniuteby any or the hitherto. known methods. However, its use ac.- cording to the normal methods and: conditions known to the art on unextracted jute requires prolonged and drastic treatment to produceeven apartial bleach and: so far as I am aware a full, perfect and brilliant White is unobtainable. Furthermore, the fiberv is seriously reduced in strength and not improved in its. susceptibility to discoloration by light. In contrast, there is obtained by my process of solvent extraction. with low concentrations of peroxide, shorter times, greatlyreduced volumes of liquor and quantities of peroxide, and without any other. preliminary aqueous treatment, a perfect brilliant white prod.- uct of essentially undiminished strength and greatly improved in susceptibility to discoloration by light.

While any known bleaching agent may beused in the oxidizing. step of; my process, I prefer'to jected to an oxidizing treatment with a percomperoxide concentration of 1% to 2% or'higheris.

employ a ercompound, such as hydrogen per.- oxide since the best results are thereby obtained; and; substantial attack on the lignin. content of. the; fibers thereby avoided. I have ascertained that, while hypochloritesmay. be applied with better. results. than on unextract-edfiber, they do not produce a perfect. white product of substantially undiminished strength nor do they, produce the. results described above which are obtained when. a percompound is employed in the oxidizing-:step. of; my process. Other types of oxidizing agents commonly employedin the art-for bleaching: likewise do not produce equivalent results and; require very-muchmore-drastic and complicated'. treatment. of: the extracted fiber to produce even.partialdecolorization. This is also thecase with.- reduoing, agents such as hydrosulphite.

Such, agents do, however; provide apartial dee coljorizationi on, my solvent extracted fiberwith an ease. and: to an extent notgiven. by similar application on unextracted fiber, andthey-yield-a superior product to thatwhich is obtained. without the organic. solvent extraction step of. my process. If a partial d'ecolorization. alone isdesired,.such agents maybe appliedinthe second step of my process to the extractedl-fiberand in such case it'issnot. intendedto limit my solvent a w. uvuavuj TLUHJ a cannon Mount .ene; lower molecular weight alcohols, e. g.,

methyl, ethyl, and butyl alcohols, diacetone alcohols; ethers, e. g., ethyl ether, isopropyl ether, dioxane, butyl'ether, dichlorethyl ether, propylene oxide; ethyl alcohol containing a small percentage of acetic acid, say 3%; furfural and its derivatives; furfuryl alcohol and its derivatives; certain cyclic amines, e. g., morpholine; esters, e. g.,

methyl, ethyl, and isopropyl acetates; alcoholethers, e. g., ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether diethylene glycol monoethyl ether. It will be understood that while solvents of the types mention d may in general be employed, that such solvents vary in their specific solvent power for the described natural color bodies associated with the lignin of the fiber, and that those possessing the higher specific solvent power will yield the most satisfactory results. For ease of application and recovery, and for economy, the organic solvent employed will preferably have a relatively low boilin point, for example, a boiling point below 150 C., and generally a boiling point below- 75 C.-100 C. The solvents preferably should be anhydrous and, in any event, as free from water as it is economically and practically possible to have them. Of the solvents available, those ofyelatively low molecular weight are desirable for use because of better penetration of the minute interstices of the fiber, and unless the dehydration step is employed best results are obtained by the use of water-miscible solvents. acetone being perhaps the best. While any of the solvents designated are applicable for use, preferred solvents when the fibers are sub- "jected to the dehydration step are acetone, di-

oxane, morpholine, and a mixture of anhydrous ethyl alcohol (50%)and ethyl ether (50%). Of the various groups of solvents'mentioned above, the ketones are preferred. While the chlorinated solvents such as ethylene dichloride and chloroform possess 'sufiicient specific solvent power for the color bodies of lignified fibers to be usable,

they produce less satisfactory results and require prolonged extraction and they are less desirable for use than others designated since on continued use at elevated temperatures and especially in the presence of water they tend to decompose and hydrolyz with the formation of chlorine and hydrochloric acid which attacks and weakens the jute fiber and prevents satisfactory decolorization in the subsequent oxidizing step. Hydrocarbon solvents, such as naphtha and benzene ndium 513' ll LHLIIL tentionally added to the yarn in the course of its spinning or weaving, with types of fat and grease solvents such as benzene, petroleum ether, carbon disulphide, carbon tetrachloride, chloride of ethylene, and similar solvents in order to facilitate bleaching and other ordinary textile processing. Prior to the present invention, however,

no process has involved the extraction and removal of the natural color bodies from the highly lignified low rank textile fibers such as jute, pita, and caroa by the use of specific solvents for such color bodies and the dissociation of the color bodies responsible for the resistance to bleaching and objection-able properties of such fibers from the lignin in order to obtain the results and, products of my invention as herein set forth. It has not been known hitherto. to use the solvents disclosed for the extraction of jute, pita and caroa fibers, nor to bleach jute, caroa, and pita fibers so extracted with oxidizing agents, such as percoinpounds, whereby the product and results of my invention are obtained. The known art has hitherto been to extract fats, oils, and waxes from first rank relatively non-lignified (high normal cellulosic content) fibers by specific solvents therefor. The results and advantages of -my invention do not obtain nor is it necessary to treat such fibers by my process since they contain relatively little if any of the lignin and natural color bodies of the type which it is the object of my invention to remove from the low rank lignified textile fibers.

The solvent extraction may be performed with any one of theindividual solvents, may consist of successive treatments in series with one or more such solvents, or'may consist of treatment with mixtures of such solvents. In general, if

extraction with a specific solvent of high solvent power for the color bodies described such as acetone, dioxane, or morpholine be used, only one such solvent need be employed to obtain excellentresults on the majority of commercial grade of such fibers, especially if the dehydration step be employed. The solvent treatment may be performed hot or cold, preferably hot. It may be performed i any type of equipment, or by any method known to be efficient for conducting such treatments. For example, the fiber may simply be immersed in the solvent for a suitable length of time, or the fresh solvent maybe circulated continuously countercurrent to the fiber; or the co-current Soxhlet method by which fresh solvent is continuously contacted with the material, or a countercurrent cell method similar to the Well-known beet sugar diffusion battery may be employed. .The treatment may be conducted at or below the boiling point of the solvent or above the boiling point and under elevated pressure. These are all well known methods of efficient solvent treatment, and are designated herein by the term organic solvent extraction.

The organic solvent liquid treatment may be continued as long as desired, and preferably until nothing further is removed or acted upon by the solvent or solvents. The ease and rapidity of decclorization and the stability of the product upon aging arev inproportion to the extent and efficiency of the removal of the solvent-soluble constituents, although very marked improvement is obtained by comparatively short and ineflicient treatment. The ease of removal of the solventsoluble color bodies varies to some degree with the grade of jute and as between specimens and the treatment to which it has been subjected Search Room.

fiber as normally obtained in commerce, and

while it is preferable that the solvent treatment be performed on the raw jute prior to treatment with aqueous and bleaching solutions, it is, however, to some degree efiicacious at any stage in the chemical treatment of jute, provided that it has not been previously subjected to sufiiciently strong alkalies to stabilize and render the color bodies very diificult or impossible to remove by the action of the solvent. As previously' pointed out, the advantages of the dehydration step will not be obtained if the prior treatment has involved the use of a material tending to fill the pores of the fiber. Thus, jute may be leached in hot water with or without peroxide prior to the solvent treatment; or water-leaching and then bleaching with a 3% peroxide solution at 190 to 250''F. may be carried out and the solvent treatment then performed on the bleached jute to improve substantially its color and its stability to sunlight by removal of the color-forming bodies remaining in the fibers after aqueous treatment with the oxidizing agent. The important advantages of ease of bleaching with small or no loss in strength provided by my preferred process are, however, thus 10st and the resulting product is inferior in properties to that obtainable by my preferred method of applying solvent extraction prior to any aqueous treatment. When raw jute (especially if this be of a dark brown lower grade) is subjected c;

to the dehydration step to be described followed by the solvent extraction treatment, a product of substantially lighter color as compared to the raw jute is obtained which will be applicable for certain uses without further treatment.

As previously stated, if the jute is subjected even to moderately strong or concentrated alkalies prior to the solvent treatment, the organic solvent-soluble color bodies are converted to a form tenaciously retained by the fiber and difficult if not impossible to remove by treatment with the organic solvent, with the result that the jute is almost impossible to decolorize beyond a straw yellow. It has been found that, subsequent to eflicient treatment with organic solvents, the treated jute may be subjected to aqueous alkalies with no effect on its subsequent ease of bleaching or stability to discoloration upon aging, the color bodies initially contained in the untreated jute and converted to bleach-resistant bodies having been removed by the prior solvent treatment. treatment, the jute is no longer sensitive to the production of non-bleaching bodies by alkalies.

As previously indicated, the jute, prior to solvent extraction and preferably before any other treatment or contact with any other agent or aqueous solution, is advantageously dehydrated. This may be accomplished by subjecting the fiber to a temperature above 212 F., preferably between 275" F. and 350 F., and below the tem perature' at which thermal disintegration of the cellulose and lignin commences, for a sufficient time, for example, for thirty minutes to one hour, to liberate the water from the fiber. Preferably, the fiber is dehydrated under conditions also resulting in the degassing thereof, and this In other words, after the solvent Iii . solvent.

sible, say 26" to 28 of mercury or even higher and at a temperature of 295 152-310" F. is employed. In this manner, not only is the deteriorating efiect of oxygen at higher temperatures substantially avoided, permitting the use of higher dehydration temperatures, but at the same time a degassing and removal of adsorbed gases and gas from the pores and interstices of the fiber is effected. The dehydration, however, may be carried out in the presence of a dry inert gas, such as nitrogen, carbon dioxide, etc., but the degassing effect is thus substantially lost. A partially satisfactory dehydration may, if desired, be obtained by prolonged treatment at 250-300 in the presence of dry air, but care must be taken to avoid deterioration of the fiber by oxidation. Much better results are obtained under vacuum and the dehydration and degassing is preferably carried outv in this manner. If this step is carried out in the presence of gas, means must be provided for removing the liberated moisture, preferably by circulating dried air or gas through the fiber, and the final stages of the dehydration must be carried out in the presence of dried air or gas containing substantially no Water vapor.

The jute fiber suitably dehydrated in the above manner and withoutv intermediate contact with water vapor (i. e. air), is then subjected to sol-- vent extraction with a suitable organic solvent of the types previously disclosed possessing specific solvent action for the natural color bodies contained in jute fiber in the natural state. The

solvent is brought into contact with the dehydrated fiber without letting the latter comeinto contact, or at least for any appreciable period, with water or air. If a dehydrated, degassed fiber is obtained, the fiber is also kept out of con tact with gas. In carrying out the process, it is convenient to use the same vessel for the dehydration step and for the solvent extraction step. In this Way, as soon as the dehydration is complete, the vesseland fiber may be brought to the extracting temperature without contact With water vapor or air and the solvent then run immediately upon it. Once the fiber is covered and saturated with solvent, contact with Water vapor and air makes little or no difference subsequently in the treatment. i

In the dehydrated state, and even more so in the degassed condition, the fiber is particularly susceptible to extraction and penetration by the The solvent is able to penetrate into all the pores, channels, and interstices of the fiber and cells and between the walls and through the cells of the fiber. Substantially complete extraction not only of those color and color-forming bodies-responsible for the objectionable properties previously described but of waxes, gums, and resins is very rapidly obtained by the circulation of relatively small quantities of the solvent through the fiber. The extraction is effected'as rapidly as solvent can be brought into contact with the fiber and prolonged contact is-unnecessary. The fiber thus treated and extracted is lightened in color, and that from a dark brown jute approximates substantially in color a light shade of tan. It is very soft and its harshness and brittleness have been substantially completely removed. The extracted fiber is rapidly and easily decolorized in very short times and with relatively low concentrations of a solution of a percompound, preferably hydrogen peroxide, to a pure brilliant white. The product obtained from ordinary raw jute in this manner is TREATMEM 6r canteen triQDlFL other material are removed.

lUli TEX;

cotton or wool. It has lost completely all the brittleness and harshness of normal treated or untreated jutes and is readily spinnable. It is further believed that an advantageous change in the chemical nature of certain of the constituents of jute fibers is brought about'by heat at temperatures of about 275 F. and above in the absence of oxygen possibly but not solely concerned with the elimination of chemically combined water from certain constituents of the fiber under these conditions and resulting in a very great improvement in the final product not due to the complete extraction of the color bod-- ies, waxes, gums, and resins alone.

Substantially complete removal of brittleness and harshness by completely dewaxing, degumming, and deresinifying jute has been obtained by the present process without disintegrating the fiber and is not obtainable by any other hitherto disclosed process, or by solvent-extraction per se, or is it closely approached by these. Jutes treated by hitherto known methods retain the large majority of their harshness and brittleness due to the fact that complete dewaxing, degumming, and deresinifying' without destroying th fiber have never hitherto been approached. This is due to the fact that these substances together with natural color bodies and dyes normally contained by jute are held not only on the surface but uniformly throughout the cells, between the cells, and within the ultimate cells of the fibers, and are intimately associated with the major building components of the fibers. Aqueous solutions, alkalies, oxidizing agents, etc., are not only unable to remove and destroy much of these materials, but they are unable to penetrate the fibers and cells unless large proportions of cementing and It has also been found by microscopic examination and other methods that solvent extraction of jute in its normal condition with organic solvents results largely only in the removal of color bodies, waxes. etc, from the outer surface layers of the fibers and cells, leaving the center parts of fiber and cells largely untouched. While this partial removal thus effected gives aproduct and fiber greatly improved in properties, bleaching susceptibility, and in the color andresistance to deterioration by aging, and other properties, it does not give a product approaching that of the dehydrated solvent-extracted product.

In its normal condition, raw jute contains both, in chemically bound and unbound condition, large amounts of Water amounting to say 25% to 50% or more of its own Weight, only 10% to of such Water representing hygroscopic moisture being normally removable by ordinary air drying at temperatures of 212 F. to 220 F. This water together with gas and adsorbed gases fills the pores and channels of fiber and cells and prevents the penetration of solvent. Further, the cells within themselves contain large amounts of water. As long as this is present, the solvent is unable to penetrate into these cells except by diffusion which is an infinitesimally slow process. Dehydration of these cells permits the solvent to penetrate them and forms pores and channels through which it can flow. Further, as long as Water is present the solvent which reaches the cells is greatly diluted and unable to dissolve thecolor bodies, resins, etc. In order for solvent to get in, water must diffuse out counter to the incoming solvent, and furthermore the solvent in the cells can never be pure solvent since all of the water 2,872,661- scit, pliable, and pleasing to touch, resembling would have to diffuse out which is impossible theoretically. In support of these facts, I have found that with jute in the normal state, water immiscible solvents are much less effective in extraction than water-miscible solvents, whereas, with dehydrated jute, water-immiscibility appears to have little effect. Furthermore, normal jute is less satisfactorily extracted by solvents of high molecular weight which diffuse more slowly and are less able to penetrate the microscopic pores in jute than are the lower molecular weight solvents. On the other hand, the molecular weight of the solvent is less important in the case of dehydrated jute, although the use of lower molecular weight solvents is preferable. The result of my dehydration-solvent-extraction-treating process is that the cells and the spaces between the cells of the fiber and fiber walls are completely, quickly, and thoroughly penetrated by strong solvent with the result that all solvent-soluble natural organic color and color-forming bodies, resins, Waxes, gums are substantially completely removed. The result on bleaching is a new product never before obtained. It is not physically or chemically identifiable with normal or ordinarily treated jutes and possesses properties of its own.

An important result of my process and propert of the fiber is its increased tensile strength as compared to that of the normal raw jute fiber from which it is made. This enhanced tensile strength is believed to be due in part to a shrinkage cf the cellulosic and lignin constituents by virtue of the removal of extending materials from the cells, thus giving a more compact and stronger fiber; in part to the removal of harshness and brittleness which in natural fiber make'it easily broken by bending or twisting; and in part to the fact that in my process only a slight loss in weight (for example, 10%), which is primarily due to the relatively small percentage of color bodies, waxes, etc., occurs, since in my process the fiber is subjected to' aqueous solutions at elevated temperatures for relatively brief periods of time, say at the most usually two hours and most frequently ten to thirty minutes. An alkali or aqueous treatment other than a mild bleach 'with a percompound is unnecessary and thus the cementing constituents destroyed by hydrolysis in the drastic and manifold treatments hitherto known for treating jute are largely retained.

Another important property of fiber prepared from. jute by my process is resistance to rot. This fiber is highly rot-resistant by ordinary rotting agencies relative to that shown by normal jute. This is believed to be due to the fact that waxes, resins, gums, etc., and brittleness are those agencies which support and deteriorate under rotting.

The product has an excellent white color and is characterized by its resistance to deterioration by aging, by light and heat. The product produced by the process is much superior in this respect to that obtained by solvent extraction alone. The product, for example, when exposed to astrong ultra-violet are at a distance of two inches for sixty hours, turned just off white to 1 very light yellow color. Jute treated and bleached by known methods under the same conditions is'turned to a dark brown in about two to six hours time, ultimately regaining its natural color under similar conditions on longer exposures.

A further advantage of the dehydration-extraction process for treating jute is the relatively mild treatment and few steps required. Five to itiiiilllit ten minutes or even less with a hydrogen peroxide solution of about-2% to 4% at 200 F. suffices to give a substantially perfect White color on the dehydrated, solvent-extracted fiber. Using longer times at lower temperatures, practically equal whiteness can be obtained with very low peroxide concentrations. In contrast, a yellow-white product results from treating normal jute with 4% peroxide even at 212 F. and even this yellow white cannot be obtained with lower concentrations and temperatures.

In carrying out the second decolorization step of my process on solvent extracted fiber, one or more percompounds will preferably be employed as the bleaching agent, such as hydrogen peroxide, alkali and alkaline earth peroxides, perborates, persulphates, percarbonates, and organic peroxides, including urea peroxide and benzoyl peroxide, and other materials liberating nascent oxygen. A relatively dilute solution of commercial hydrogen peroxide containing a customary stabilizer is preferred, although, of course, solutions containing no stabilizer may be used. The concentration of the percompound and the temperature employed in the oxidizing step may, if desired, correspond to those of known methods. The ease and rapidity of the decolorization of solvent-extracted jute depend on the strength of the bleaching agent, the temperature employed, and the nature of the jute treated, and whether or not the dehydration step has been employed prior to extraction. A longer time isrequired with a particular jute specimen to obtain the same result with lower concentrations and temperatures as is obtained in shorter times with higher concentrations and temperatures. The results are approximately equivalent so far as decolorization is concerned but shorter treatment with aqueous oxidizing agents are preferred from the viewpoint of strength of the treated fiber. In the case of bleaching unextraoted fiber with percompounds, time and concentration are not equivalent in yielding the same decolorization of the fiber. As previously stated, with some types of jute, successive treatment with more than one of the solvents disclosed may improve the results. Oxidation of a solvent-treated (but not dehydrated) jute fiber with 2% by weight of an aqueous solution of 100 volume commercial hydrogen peroxide containing an equal percentage of 40 Baum sodium silicate as astabilizer at 200 F.215 F. for forty minutes effected complete decolorization to a pure, brilliant, lustrous white, which could not be obtained by any other known method or treatment without disintegration of the fiber. The product was for all practical purposes not materially discolored upon aging or by the action of alkalies. Using .a 4% solution of hydrogen. peroxide at temperatures of 180 F. to 200 F. produced an excellent, pure white product in about twenty to thirty minutes with the same stability. Equal results are obtained in substantially longer times at 180 F. with low percentage of peroxide.

When the dehydration step is employed, a pure white product is obtained with greater ease, that is, with a, lower concentration of peroxide and in a shorter time. of the bleaching compound preferably follows the dehydration step (if employed) and the solvent-extraction process, but if desired, the treatment with the bleaching compound may precede the other treatment.

It will be clear that the fibers treated in accordance with this invention may also be proc- As previously stated, the use.

ble in the organic solvent used in the extractionof the natural color bodies, the oxidizing agent may be dissolved in the solvent.

In a. particular case, where the dehydration step was not used, raw jute fiber was extracted with acetone for two hours in a Soxhlet type extractor. The resulting product while lightened in color was still brown. The jute odor had been removed and the fiber had not decreased measurably in strength. A considerable amount of, yellowish-brown coloring matter was removed by the solvent. The light sensitive nature of this coloring matter was demonstrated by concentrating the extract, saturating a piece of white filter paper with it, and exposing to an ultraviolet light. The filter paper turned a dark brown whereas a control with pure acetone showed no change in color. The extracted jute was treated as follows:

Example 1 Bleached with 2% H2O2 (com. vol.) -2-% silicate solution for forty minutes at 200 F.-210 F., using about six to ten times the Weight of liquor to the weight of jute. Product is a pure brilliant white of great resistance to discoloration upon aging and not materially weakened.

Example 2 Bleached with peroxide-4% silicate for ten minutes at 212 F. Product same as Example 1.

Example 3 Bleached with 1% peroxide-1% silicate for one hour at 2l0-2l2 F. Product of excellent white but somewhat inferior to Example 1 in color; otherwise the same.

Example 4 Bleached with 0.5% peroxide-0.5% silicate for ten-twelve hours at 180 F. Good white but inferior to product of Examples 1 and 3 .and appreciably more weakened in strength but of same resistance to discoloration upon aging.

Example 5 Treated with 10% hydrosulphite at F. for twenty-thirty minutes. Product is a light straw color.

Example 6 Bleached with hypochlorite for five hours at room temperature. Product is alight gray-brown of reduced strength.

Analogous experiments were conducted using (1) dioxane, (2) ethylene dichloride, (3) ethyl ether, (4) morpholine, (5') chloroform, (6) etherill dross Rtttlititllt. Search Room withone orniore or the solvents disclosed and for various periods of time and then treating the extracted fiber with various aqueousinorganic solutions, with various oxidizing and reducing what less harsh and brittle than jute. The extracted fiber was then bleached for about one hour using 4% peroxide-4% silicate solution at "210 F's-212 F. The product was a full, perfect white undiminished in strength and highly reagents, and to bleaching with variousconcentra- 5 'sistant to discoloration upon aging. tions of peroxide in various weight ratios of liquor Example 8 to jute and at various temperatures for various times. The best results as previously described 7 A sample of caroa fiber was solvent extracted were'alw'ays obtained by extraction with one of with acetone as described for Examples 1 to"6. thepreferred solvents, 7 especially acetone and 10 The extracted fiber was then bleached for about dioxane, followed by oxidizing with-peroxide. fifty minutes using 2% peroxide-2% silicate solu- Essentially thesa'me results were obtained with tion at about 175 F. The product was white, solvents of the types disclosed except that'these resistant to discoloration upon aging, and of hi were inferior in decolorization and ease of bleachstrength. 1 ing to those obtained with the preferred solvents 7 Example and more prolonged extraction was required. 1 With low peroxide concentrations, about 0.5%, at rlhe e o le-illustrates the process 180" F. much longer bleaching times, about tenof e invention Where the hyd t o st p i sixteen hours, were required "to obtain a good e y A Sample f raw jute fi r dark b own white and this was inferior'tothat'obtained with 111 00101 Was Placed 111 3 S m j c eted vessel. higher concentrations of peroxide" and higher h Vessel was evacuated and the cuum mamtemperatures and the fiber was noticeably tamed of u y 1 a esteam.was weakened. This is to be compared 'with the same Placed on the Jacket a the n h mted nd treatment of unextracted "jute given various degassed at this p ature forone. hour. "The preliminary treatments with" aqueous" solutions heat was then h 'h the Ve$B1 11 which could not be decolorized beyond'a light deI VaC1111m b lrcul'atlng-water in the acket w under such cbnditions; Treatment' of t until the vessel was cooled-to the desired point. extracted jute with such agents as caustic soda Acetone then run n the sample and the subsequent to the extraction and prior to t Vacuum broken after'the fiber was saturated with peroxide bleaching g no i b g in t 30 acetone. Acetone was then circulated for 10 to 30 results and served to materially weaken the fiber. minutes through the Sample t t bo t m- Prolonged boiling with aqueous solutions always Derawre (SOXhlet et od) 11 1311 n0 morecolor tended to weaken the fiber materially andinm any was removed: e solvent wa t n ramed oh cases very seriously. No treatment with oxidizing and that retalhed 1n the fiber removed y S e mfand reducing agents other than' peroxide and n t ac to e was recovered fromthe conpercompoundsserved to producea-iull', perfect, densed steam by fractional distillation. At the brilliant white, usually 'a light brown,"'brownn of the extraction, t e sa ple had a consider gray gr ygllow even on th xtracted flbr being ably lighter tan shade, had lost all traces'of 1 10!- the result and the strength of the fiber in many mal jute odor. a w soft and p a e;w t "1 tt1e cases was seriously and drastically damaged; In race of its former harshness and brittleness. The all cases, the results are to be contrasted with Was bleached h aqueous yd og n pethose of similar experiments with unextracted roxme Solutloh cohtalmhg by Weight of P fiber which in no case produced a full, perfect, loxlde and an equal percentage of 136-8061111111 brilliant white (in many cases only a scarcely silicate at 180 F.-200 F. tor about 15 minutes. perceptible decolorization), and if anything ap- 4.5 It was thehweshed and The p o ct had proaching a decolorization to white was obtained, the propertles p w ly bed. The time of t fiber was seriously damaged by t t ttreatment with the peroxide solution can, if dement. and in all cases it was very markedly sensired, be extended to 40 minutes or more, and if a sitive to discoloration by light. In one experisolution of 3% per xi is used, the er y he ment, the raw jute prior to solvent extraction treated at about 200 F. for 5to 10 minutes. was boiled for one hour in a 0.2% soap solution, The description in this specification is illustraextracted with acetone, and then subjected to tive, and does not limit the invention, the essentreatmcnt consecutively with caustic soda, hydrotial feature of which is the removal, to the extent sulphite, and peroxide bleaching. The caustic desired, either with or without the dehydration soda boil-off removed reddish brown coloring treatment, of the ic fl v t-s lub Co r matter giving a deeper reddish brown fiber. The bodies existing in natural raw jute and other hydrosulphite treatment produced a slight straw similar lignified low rank textile fibers. As a recolor. and the fiber when bleached with 3% sult of the treatment, the fibers are rendered peroxide-3% silicate at 2l0-212 F. gave essenmore susceptible to bleaching and/or purifying. tially the same product as obtained in Example Fibers may be obtained which are a brilliant 1 except that the bleaching was more difficult and white, and are essentially stable to discoloration the fiber, considerably weakened, was not quite upon aging and the chemicals with which they so good in color and did not age as satisfactorily. may come in contact in normal usage. In addi- This result is to be contrasted with exactly the tion, the fibers contain the major portion of their same course of treatment of an unextracted jute lignin content and, in any event, contain sufiicient sample. In this case the hydrosulphite did not lignin so that they possess a strength comparable lighten the color, the product could not be to that of the natural fiber prior to treatment. bleached beyond a deep yellow, and it was highly Considerable modification is possible in the solsensitivc to further discoloration on aging. vent employed, in the methods of extraction, and in the dehydration step (if employed) as well as Example 7 in the treatment of the fibers before and after sol- A Sample Of D fiber Was solveht extracted vent-extraction, without departing from the eswith acetone as described for Examples 1 to 6. Sential featu of the invention The raw sample was light tan in color but some- 1 claim;

1. The steps in the process of decolorizing lignified. low rank textile fibre selected from the group consisting of jute, pita, and caroa which comprise heating said fibre in an atmosphere substantially free from water-vapor at a temperature above 212 F. and below that at which thermal disinte gration of the cellulose and lignin commences for at least about thirty minutes to liberate Water from the fiber; bringing a substantially anhydrous organic solvent chemically inert to the fibre and the constituents thereof and possessing specific solvent action for the natural color bodies con tained in said fibre into intimate contact with said heat-treated fibre prior to appreciable contact thereof with water-vapor; and extracting the said color bodies from said fibre by said solvent.

2. The steps in the process of decolorizing lignified low rank textile fibre selected from the group consisting of jute, pita, and caroa which comprise heating said fibre under a vacuum of at least 26 inches mercury at a temperature above 212 F.

and below that at which thermal disintegration of the cellulose and lignin commences for at least about thirty minutes to liberate water from the fibre and to free it substantially from gas; bringing a substantially anhydrous organic solvent chemically inert to the fibre and the constituents thereof and possessing specific solvent action for the natural color bodies contained in said fibre,'

into intimate contact with said heat-treated and degassed fibre prior to appreciable contact thereprise heating said fibre in an atmosphere substan-' tially free from water-vapor at a temperature between about 275 and about 350 F. for between about thirty minutes and about ninety minutes to liberate water from the fibre; bringing a substantially anhydrous organic solvent chemically inert to the fibre and the constituents thereof and possessing specific solvent action for the natural color bodies contained in said fibre into intimate contact with said heat-treated fibre prior to appreciable contact thereof with water-vapor; and ex tracting the said color bodies from said fibre by said solvent.

5. The steps in the process of decolorizing lignified low rank textile fibre selected from the group consisting of jute, pita, and caroa which comprise heating said fibre under a vacuum of at least26 inches mercury at a temperature between about 275 and about 350 F. for between about thirty minutes and about ninety minutes to liberate water from the fibre and to free it substantially from gas; bringing a substantially anhydrous organic solvent chemically inert to the fibre and the constituents thereof and possessing specific so1- vent action for the natural color bodies contained in said fibre into intimate contact with said heattreated and degassed fibre prior to appreciable contact thereof with gas and water-vapor; and extracting the said natural color bodies from said fibre by said solvent. o

JOSEPH C. ELGIN;