US2563637A - Process for producing lustrous cellulosic products - Google Patents

Description

Patented Aug. 7, 1951 UNITED STATES PATENT OFFICE PROCESS FOR PRODUCING LUSTROUS CELLULOSIC PRODUCTS Joseph Hendrickson Balthis, Wilmington, DeL,

and Frank Kerr Signaigo, Kenmore, N. Y., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application August 22, 1946, Serial No. 692,386

9 Claims. (Cl. 117-102) This invention relates to cellulosic materials of reduced flammability, and more particularly to the production of improved films, fibers, and fabrics of cellulose and its derivatives which are lustrous yet contain substantial quantities of insoluble titanium compounds.

It is well-known that the flammability of cellulosic materials may be reduced by incorporating suitable organic or inorganic materials therein. Though water-soluble impregnants suffice for some purposes, insolubility in water is frequently required. Water-insoluble compounds are usually incorporated by impregnating the cellulosic material with a water-soluble compound of an element which is subsequently precipitated in the form of one of its insoluble compounds, for example, as an oxide, silicate, phosphate, or tungstate. Titanium compounds have been found useful for this purpose but their utility has been limited by attendant, undesired delustering of the impregnated material. This ability of titanium compounds to deluster is well known and it is possible at times to take advantage of it. Thus, many textile materials are delustered by introducing titanium compounds before or after spinning. For many purposes, however, the luster and transparency of cellulosic materials must be preserved. Brightness and luster are frequently required in textile materials and to an even greater extent in films and foils. Many titanium compounds are free from color, chemically inert, difficultly soluble, and non-flammable, all of which-make them attractive as flame-retarding agents provided they can be incorporated in substantial quantity without delustering the cellulosic material. One principal object of this invention therefore is to provide methods by which titanium may be incorporated in films, fibers, and fabrics of cellulose and its derivatives without incurring undesired delustering of such materials.

In accordance with this invention, lustrous films, fibers, and fabrics of regenerated cellulose and cellulose esters and others containing titanium are produced by suitably impregnating such cellulosic materials with a soluble titanium compound, removing superficial impregnant from the treated product under non-hydrolyzing conditions, and then precipitating a water-insoluble titanium compound within impregnated cellulosic material.

In a more specific and preferred embodiment, the invention comprises producing a lustrous regenerated cellulosic material of materially reduced flammability containing at least 3% by weight of titanium, by impregnating said material with a relatively concentrated solution of a water-soluble, inorganic compound of titanium such as titanyl sulfate, removing excess or superficial impregnant from the treated material by thoroughly rinsing under non-hydrolyzing conditions and in the presence of an alcohol, and then precipitating a water-insoluble titanium compound Within the rinsed cellulosic product.

Regenerated cellulose and its derivatives have an appreciable tendency to incorporate titanium when immersed in solutions of titanium compounds. The amount incorporated depends upon many factors, including the nature of the solvent, the activity of the titanium compound, the prevailing temperature, the time of impregnation, and the chemical composition and degree of swelling and orientation of the cellulosic material. The choice of impregnating conditions and the particular titanium compounds introduced and precipitated depend upon the type of cellulosic material and the use for which it is intended. The present invention is not limited to any particular method of impregnation or precipitation though, by Way of illustration, certain expeditious and more preferred procedures will be described.

In accordance with one adaptation of the invention, regenerated cellulosic yarn or fabric is suitably impregnated by immersion, preferably, in a titanyl sulfate solution containing from about 50 to 150 g./l. of T102 for a relatively short period of time and at room temperature or temperatures ranging from 0 C. to C., care being exercised not to utilize elevated temperatures at which hydrolysis would occur. After such impregnation, excess impregnant is removed as thoroughly as possible by conventional hydro-extraction, draining or wringing. These and similarmechanical operations are insufiicient in themselves, however, to prevent undesired delustering of the cellulosic material in the subsequent operations necessary to insolubilize or fix the titanium. When materials treated in this manner are immersed in aqueous alkali, phosphate solution, water at ordinary temperature, or other media for fixing the titanium, external precipitation occurs in the bath as well as internal precipitation within the cellulosic material. The cellulosic material becomes coated with a rough, adherent, delustering deposit of titanium compound. This deposit is relatively easy to remove from films but is exceedingly difficult, if not altogether impossible, to remove from textile materials by washing. Seemingly the deposition is due to incomplete removal of impregnating agent from the surface of the cellulosic material prior to fixation of the titanium. To overcome this and avoid such deposition, a thorough rinsing of the impregnated material in preferably an alcohol or an aqueous alcohol is resorted to. Ethyl alcohol is particularly preferred for use since it does not extract titanium yet appearsto be compatible with aqueous titanyl sulfate in all proportions, even though solid titanyl sulfate, TiOSO4.2I-IzO, is substantially insoluble therein. The rinsed product can then be washed with water torender it sulfate free, but preferably it is treated with a suitable neutralizing agent, such as a 3% solution of sodium carbonate, followed by'water washing.

To a clearer understanding of the invention, the following specific examples thereof. are given. These are merely illustrative and are not to be construed as in limitation of the invention:

Example I Five skeins of regenerated, freshly-spun, hightenacity gel rayon (275 denier, 120 filaments) yarn areimpregnatedby immersion at room temperature for one minute in a titanium solution obtained by dissolving 613 parts of essentially acid-freev titanyl sulfate: of the approximate. for-- mula, TiOSO42I-I2O, in. 625 parts of water,.filtering: and adding water' to adjust its titaniumconcentration to. 150grams/literof T102. The titanium-treated. skeins: are. hydro-extracted. and

then finished for comparative purposes by; the

following procedures inwhich (a) and. (b) com,- prise; orthodox. finishing and. (c), (d). and (e) areinaccordance with thisinvention:

(a) One. skein is. immersed in aqueous alkali. Even though the yarn. has beenhyro-extracted, hydrous titaniaprecipitates. on. the surface of the yarn andin the solution. The precipitatedtitania adheres. tenaciously'to the yarn as a. delustering' depositof titania. and is not completely removed; by; washing. The .dry'delustered yarn contains 1.9%. Ti byweight. Aggregates oftitaniumoxide adhering: to individual filaments can. be. detectedmicroscopically.

(b), Thesecond skeinissimply washed inpwater: at room temperature (about 25 C.) until free of.

sulfate. Titania precipitates in. the form. of a delustering deposit on the surface of theyarn, and. the final yarn, which contains about 1.3% Ti by weight, is .delustered and harsh.

(c) The third skein is thoroughly rinsed. in 95% alcohol to remove superficial titanylsulfate, hydro-extracted, immersed in l sodium hydroxide-and washed with water until alkali-free. In contrast to skeins (a') and (b) there is no: visible titania precipitation and the yarn, which contains about 1.6% titanium by weight; is bright and lustrous.

(d) The fourth skein is immersed for five minutes in water containing 1 sodiumhydroxideand 5% mannitol by Weight and is then washed with water until free of alkali. There is no external precipitation of, titania and the lustrous product contains about.l'.1% titanium by weight. (e) The fifthskein is cooled to 0-l0 C. and rinsed in water previously cooled to this'same temperature. The yarn is then neutralized at normal temperature by treatment with 3% sodium carbonate solution and is washed with water until neutral. As in the. instances of (c) and (11) above; no external precipitation of titania is evident and the yarn is a lustrous product.

Example II Freshly-spun rayon yarn is washed, desulfured, bleached, and. treated as. hereinafter described while still in the swollen gel state. Titanyl sulfate solution; is prepared in the manner described in Example I, but its titanium. content is adjusted to 134 grams/liter of T102 and 21.5% more Hz'SOrwater.. The titanated yarn is soft and lustrous in contrast to the material resulting from the orthodox treatment of (a) above.

(0) A third portion of the impregnated yarn is passed through a water solution containing 1% NaOH' and 10% glycerol by weight and is washed in water. The titanium-containing yarn is-alsosoft and lustrous.

Example III A skein of; a. cellulose derivative, hydroxyethyl cellulose, yarn is immersed: in titanyl' sulfate; solution (150 grams/liter-of T102). for fifteen minutes, removed, allowedto drain, thoroughly rinsed in. 95% aqueous ethyl alcohol, soaked in.3-%.aqueous= NazCOs. solution, and water washed. The. soft.

bright. lustrous product contains. 16.4%. titanium by weight.

Example IV Carboxyethyl. cellulose yarn. CHzCHzCOOH per glucose unit; preparedby the reaction of alkali cellulosewith acrylonitrile folilowedby hydrolysis) is treated asv in Example III-L The. treated. yarn. is. lustrous. and contains. about 9% titanium. by weight.

Example V" Cellulose yarn, modified with. by weight.

of a saponified copolymer. of allylidene. diacetate. and. vinyl. acetate, is treated in themanner described in Example III. The lustrous product containsabout. 7% titanium by weight.

Example VI A solution. of titanyl sulfate containing the. equivalent of 12 parts by weight. of 'IiOz is pre-- pared by dissolving 29.4- parts by weight of. TiOSOaZI-IzO in 70.6 parts. of. water. Freshly cast films of. regenerated cellulose are soaked: in the solution at room temperature. for. 15 min utes and finished asfollows: Thefilm is removed fromthe'titanyl sulfate and immersed in aqueous ammonia, av copious precipitate of hydrous titania formingin the ammoniacal solution and some of the'precipitate adhering to the. film. In contrast to results with fibers and. fabrics, the precipitate may be removed'by rubbing or washing in water. To. prevent precipitation altogether,

the impregnated film is'rinsed with alcohol prior to immersion in the aqueous ammonia. Following. such ammonia treatment, the. film is washed in water until free of sulfate. The films contain up to 18-20% by weight of titanium, are clear, transparent and lustrous, and can be softened with. glycerol. or. other known softening agents. The introduction of. titanium. reduces solubility in cuprammonium hydroxide and. imparts opacity to. ultra-violet light.

Although the invention has been. described above as applied to. certain. preferred. embodiments thereof, it will be obvious that due variance (0.5. mol of.

therefrom may be made without departing from its underlying principles and scope. Thus, although it is particularly applicable to the treatment of textile materials such as cellulosic threads, yarns, or fabrics, the invention is not limited thereto. It may, for example, be applied to films, foils, sheets and even to plastic compositions and molded objects. The materials treated may consist of or contain cellulose acetate or other derivatives of cellulose, for example, cellulose nitrate, cellulose nitro-acetate, cellulose formate, cellulose propionate, cellulose butyrate, hydroxyethyl cellulose, ethyl cellulose and other esters, ethers, and ester-ethers of cellulose. The titanium may be introduced during spinning or casting, as for example by incorporating titanyl sulfate in an acid regenerating bath, or at any suitable stage during subsequent processing or fabrication.

It is usually possible to introduce up to 20% by weight of titanium (calculated as TiOz) into films and up to 13% by weight into textile materials. The amount of titanium introduced may be relatively small, e. g., as low as .5% by weight. At least 3 by weight of titanium is required to materially reduce flammability. The reduction in flammability is directly related to the quantity of titanium introduced and larger quantities (preferably from 5-10% by Weight) are frequently desirable when the cellulosic material has a large surface area, as in the case of brushed rayon fabrics. Preferably, also, the titanium is precipitated within the cellulose structure as the oxide, phosphate, or phytate.

As noted above, titanyl sulfate is advantageously employed as the preferred impregnating agent by virtue of its high solubility in water, its relatively non-injurious effect on cellulose, and its ability to introduce large quantities of titanium. It is usually employed in aqueous solutions at a concentration equivalent to, say, from 50 to 150 gram/liter of TiOz, though higher concentrations (up to 200 or 300 g./l.) can also be used, i. e., from 5%-30% TiOz in solution. Excess sulfuric acid above that required for stoichiometric equivalence with titanyl ion sometimes facilitates introduction of the titanium though less than 100% excess is preferred.

The soluble titanium compound may be incorporated in a variety of ways, as for example by a bath treatment, by padding or by spraying. It is not always imperative that impregnation with titanium be the first step and such impregnation may be preceded by introduction of phosphate or other anion required to fix the titanium in insoluble form. Any soluble titanic, titanous, or titanyl salt may be used though the sulfates, chlorides, oxalates, and acetates are particularly suitable. The titanium may be precipitated within the fibers by a variety of agents, for example, phosphates, phytates, silicates, tannates, borates, etc. Though water is preferred as the impregnating and precipitating medium, all or part of the water may be replaced with alcohols, acetone, dioxane, and the like.

It is not essential to pre-swell the cellulosic structure but this is usually helpful and may be accomplished by soaking in Water or other swelling medium or, in the case of regenerated cellulose, by employing so-called gel cellulose which has not been dried after regeneration. The rate of incorporation of titanium may sometimes be increased by raising the temperature of the impregnating solution, but, as already noted, care must be exercised to avoid hydrolysis. The time of impregnation may vary from a few seconds to aminute or more in case of yarns, fabrics, and

films continuously passed through an impregnating bath up to 15 minutes or longer in batchwise impregnations.

The alcohol rinsing step may be carried out at any convenient temperature and pressure, though operation at or near room temperature is generally expedient. While ethyl alcohol comprises a preferred reagent for use in this step, other watersoluble monohydric or polyhydric alcohols, for example, methyl alcohol, propyl alcohol, ethylene glycol, glycerol, or glucose, may also be used or substituted for ethyl alcohol. It is usually possible to reduce the cost of the alcohol without seriously impairing its effectiveness by diluting it with water.

Optionally, an aqueous solution containing both an alkali and a polyhydric alcohol, for example, 1% sodium hydroxide and 10% glycerol by weight, may be substituted for the alcohol. There is no precipitation when a large volume of such solution is used through titanium oxide is immediately precipitated by alkali in the absence of glycerol. Aqueous sodium hydroxide-glycerol tends to extract titanium, hence time therein is held at a minimum, usually 15 minutes or less.

Water at low (ice-cold) temperature can be used in lieu of alcohol or polyhydric alcoholalkali. It is imperative, however, that the temperature of the water not exceed about 10 .C. If the temperature of the water is higher, hydrolysis occurs with ensuing undesired precipitation of titania and delustering of the cellulose. The rate of hydrolysis of titanyl sulfate is markedly dependent upon temperature. Under conditions at which precipitation (hydrolysis) is immediate at 25 0., it is inhibited for about two hours at 2 C. Like ethyl alcohol, water has little or no tendency to extract titanium from impregnated material, though both extract sulfate ion slowly. There is no precipitation of titania in adequately cooled water. Advantageously the cellulosic material may be precooled prior to treatment to a temperature ranging from 0 C.- 10 C.

When rinsing with polyhydric alcohol-alkali, temperature and pressure are not particularly critical. It is possible to use many polyhydric alcohols, for example, ethylene glycol, glycerol, mannitol or glucose, and even, at times, monohydric alcohols. Likewise, a variety of alkaline materials may be used including alkali (sodium, potassium, etc.) and alkaline earth metal (calcium, barium, strontium) hydroxides and carbonates and ammonium hydroxide. Both the absolute concentration and the relative pro-portions of polyhydric alcohol and alkali may be varied widely.

Processing subsequent to rinsing depends upon the particular titanium compound to be precipitated. If titanium oxide is to be precipitated, the especially rinsed materials are simply washed with water until sulfate-free or, since this is slow, neutralized with alkali, preferably 3% aqueous sodium carbonate, and washed with water. If it is desired to precipitate another insoluble titanium compound, the rinsed ma terial may be immersed in a dilute solution of the desired anion, as, for example, a water'solution containing a phosphate, a phytate, or the corresponding free acids. Acids which extract titanium, for example, hydrochloric and sulfuric, should be avoided.

It is usually advantageous to employ aqueous sodiumbarbonate asa neutralizing agent and to avoidan acid rinse in removing the carbonate. An acetic acid rinse subsequent to sodium carbonate; treatment, even though followed by thorough washing in water, frequently accelerates the; deterioration of titanium-containing cellulose materials at elevated temperature.

If; desired; the process may be used to reduce the flammability of previously delustered materials when it is desirable to avoid further reduction in luster, clarity, or surface deposition of inorganic material.

We claim as. our invention:

1. A. process for producing a lustrous regenera'tedcellulosic product which comprises impregnating" a regenerated cellulosic material with a water-soluble titanium compound, removing superficial impregnant therefrom by thoroughly rinsingwith a solution of astraight chain watersoluble aliphatic alcohol, and then precipitating a delustering concentration of a water-insoluble titaniumcompound ranging from 3% to 20% of titanium by weight within the rinsed cellulosic materialby reacting said first-mentioned titanium compound with an alkaline precipitating agent.

2. A process for producing a lustrous regen erated cellulosic product which comprises impregnating said cellulosic material-with a watersoluble titanium compound, removing superficial impregnant therefrom by thorough rinsing with water containing a straight chain, water-soluble aliphatic alcohol, and then precipitating a water-insoluble titanium compound in amount ranging from 3%-20% titanium by weight within the rinsed cellulosic material by treating said materialwith a solution of an alkaline precipitating agent. a

3. A process for producing a lustrous regenerated cellulosic product which comprises impregnating said cellulosic material with a watersoluble titanium compound, removing superficial impregnant therefrom by thoroughly rinsing with an aqueous alkali and water-soluble straight chain, aliphatic polyhydric-alcohol solution, and then precipitating a water-insoluble titanium compound in amount ranging from 3%-20% by Weight of titanium within the rinsed cellulosic material by treating said material with a solution of an alkaline precipitating agent.

4. A method for producing a lustrous regenerated cellulosic product, comprising impregnating a regenerated cellulosic material with a solution. of. titanyl sulfate, removing superficial impregnant from the surface of the resulting product by rinsing said product in aqueous ethyl alcohol, and then precipitating a delustering concentration of an insoluble titanium compound in amount ranging from 5%-10% by weight of titanium within the resulting alcohol-rinsed product by treatment with an alkaline precipitating solution.

. 5. A method for producing a lustrous regenerated cellulosic material which comprises initially impregnating said material with a solution of titanyl sulfate, removing superficial impregnant from the surface of the resulting product bythoroughly rinsing it with an aqueous solution of sodium hydroxide and glycerol, and then neutralizing the rinsed product with an alkaline solution to precipitate therein an insoluble titanium compound in amount ranging from 5l0% by'weightof titanium. v

6. A method for producing a lustrous regeneratedcellulosic product of reduced. flammability which corn-prises immersing the. regeneratedceb lulosic material in a concentrated titanyl sulfate solution to impregnate the same, following such.

titanium compound, ranging from 3%-20%- by weight of titanium within the rinsed cellulosic product by treating itwith an alkaline precipitating agent.

7. A method for producing a lustrous regen-- i erated cellulosic product'of reduced flammability which comprises impregnating the regenerated cellulosic material by immersion in a concentrated titanyl sulfate solution containing from -150 g./l. T102 at temperatures ranging from 0 C. to 80 (3., following such impregnation thoroughly rinsing the impregnated product with a solution of a water-soluble straight chain aliphatic alcohol to remove excess impregnant from its surfaces, and then precipitating a delustering, concentration of a Water-insoluble titanium compound ranging from 5% to 10% by weight of titanium within the rinsed cellulosic product by treating said product with a dilute solution of sodium carbonate.

8. A method for producing a lustrous regenerated cellulosic yarn of reduced flammability which comprises impregnating the regenerated cellulosic material by immersion in. a concentrated titanyl sulfate solution, following such impregnation'thoroughly rinsing said material with ethyl alcohol to remove superficial impregnant from its surfaces and-then precipitating a de1ustering concentration of a water insoluble titanium compound ranging from 5l0% by weight of titanium within the rinsed cellulosic product by treating said product. withan alkaline precipitating agent.

9. A process for producing a lustrous, regenerated cellulosic product which comprises impregnating said cellulosic material with an aqueous solution of a titanium compound, removing superficial impregnant from its surface by thoroughly rinsing it with a liquid reagent containing a straight chain, water-soluble, aliphatic alcohol and without hydrolysis of said titanium compound taking place, and thereafter precipitating a delustering concentration of a water-insoluble titanium compound ranging from 3% to 20% by weight of titanium within said impregnated cellulosic material by reacting the titanium compound impregnant with an alkaline precipitating agent.

JOSEPH HENDRICKSON BALTHIS. FRANK KERR SIGNAIGO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

Claims (1)

1. A PROCESS FOR PRODUCING A LUSTROUS REGENERATED CELLULOSIC PRODUCT WHICH COMPRISES IMPREGNATING A REGENERATED CELLULOSIC MATERIAL WITH A WATER-SOLUBLE TITANIUM COMPOUND, REMOVING SUPERFICIAL IMPREGNANT THEREFROM BY THOROUGHLY RINSING WITH A SOLUTION OF A STRAIGHT CHAIN WATERSOLUBLE ALIPHATIC ALCOHOL, AND THEN PRECIPITATING A DELUSTERING CONCENTRATION OF A WATER-INSOLUBLE TITANIUM COMPOUND RANGING FROM 3% TO 20% OF TITANIUM BY WEIGHT WITHIN THE RINSED CELLULOSIC MATERIAL BY REACTING SAID FIRST-MENTIONED TITANIUM COMPOUND WITH AN ALKALINE PRECIPITATING AGENT.