US3706526A - Process for treating cellulosic material with formaldehyde and sulfur dioxide - Google Patents

Abstract

CELLULOSIC MATERIALS SUCH AS COTTON FABRICS ARE TREATED AT HIGH TEMPERATURES WITH FORMALDHYDE AND SULFUR DIOXIDE IN THE PRESENCE OF MOISTURE TO IMPROVE THEIR DIMENSIONAL STABILITY, CREASE RESISTANCE, AND SMOOTH DRYING CHARACTERISTICS.

Description

United States Patent U.S. Cl. 8115.7 13 Claims ABSTRACT OF THE DISCLOSURE Cellulosic materials such as cotton fabrics are treated at high temperatures with formaldehyde and sulfur dioxide in the presence of moisture to improve their dimensional stability, crease resistance, and smooth drying characteristics.

CROSS-REFERENCE This application is a continuation-in-part of Ser. No. 706,792 filed Feb. 20, 1968, and now abandoned,

BACKGROUND OF THE INVENTION In recent years various methods have been devised for treating cellulosic fiber-containing products, such as cloth made of cotton or cotton blends, in order to impart durable crease resistance and smooth drying characteristics thereto. For example, cellulosic materials have been crosslinked with formaldehyde, giving durable crosslinks having good resistance to repeated laundering and also to various acids and alkalis, and chlorine bleaches. These formaldehyde treated cellulosic materials are resistant to discoloration and yellowing.

However, while formaldehyde has made a significant contribution to the cotton finishing art, the results have been far from perfect. For instance, in some cases the formaldehyde crosslinking treatment has tended to lack reproducibility, since control of the formaldehyde crosslinking reaction heretofore has been difficult. When high curing temperatures were used with a strong acid or a potential acid catalyst, overreaction and degradation of the cotton often occurred which considerably impaired its strength. This has been notably true when hydrogen chloride is used as the catalyst, as disclosed for instance by Reinhardt et al. in U.S. Patent 3,264,054. When attempts were made to achieve reproducibility at temperatures of 50 C. or less, much longer reaction or finishing times were usually required, rendering the process economically relatively unattractive. This has been particularly true when sulfur dioxide was used as a catalyst in the previously known processes such as that disclosed in British Patent 980,980, In other cases, formaldehyde crosslinking has not been able to meet commercial standards with respect to dry wrinkle recovery. For these and similar reasons efforts have been continuing to develop new and better finishing processes for materials made of cellulose and particularly of cotton.

3,706,526 Patented Dec. 19, 1972 DESCRIPTION OF THE INVENTION Accordingly, a primary object of the present invention is to provide a practical process for treating cellulosic materials with formaldehyde which substantially prevents or alleviates the problems mentioned above. A more specific object has been to develop a process for crosslink ing cotton with the aid of formaldehyde, using a strong acid catalyst formed in the process and substantially in the amount needed, so as to keep fiber injury to a minimum.

These and other objects, as well as the scope, nature, and utilization of the invention will become more clearly apparent from the following more detailed description. Unless otherwise indicated, all proportions and percentages of materials or compounds are expressed on a weight basis throuhgout this specification and appended claims.

In accordance with the present invention, a process is provided for treating a cellulosic fiber-containing material to improve its dimensional stability, crease resistance, and smooth drying characteristics by treating the material with formaldehyde and gaseous sulfur dioxide in the presence of moisture at a temperature between about C. and 150 C.

The process requires relatively short reaction times and gives high wrinkle recoveries while at the same time producing satisfactory tensile and tear strengths.

In the claimed invention the cellulosic material is conditioned to give it a moisture content of between about 4 to 20 percent, preferably 5 to 12 percent, based on the dry weight of cellulose fiber, and then introduced into a gaseous atmosphere containing a cellulose crosslinking amount of formaldehyde and a catalytic amount of sulfur dioxide at a temperature between about 65 and about 150 C., preferably between about or C. and 150 C., most preferably between C. and C., for a time of between about 10 seconds and 2 hours, preferably 2 to 15 or 20 minutes. In small laboratoryscale treating chambers through which a flow of gaseous formaldehyde and sulfur dioxide is passed as described below it is desirable to have the treating atmosphere contain formaldehyde in a concentration of, for instance, from 15 to 60 volume percent and sulfur dioxide at least at the start of the process in a concentration of between, for instance, about 5 and 30 volume percent. However, obviously, very low concentrations of formaldehyde and sulfur dioxide are sufficient in equipment wherein the weight ratio of treating atmosphere to textile material being treated is relatively high.

The optimum reaction time under any given set of other reaction conditions is one which is just long enough to effect the desired degree of crosslinking without unnecessarily over-exposing the fabric to the reactive atmosphere. Increasing the reaction temperature or, surprisingly, increasing the moisture content of the reactive atmosphere or of the fabric permits reducing the reaction time under otherwise comparable conditions, and vice versa. For optimum control of the crosslinking reaction, the moisture content of the treating atmosphere is maintained between about 10 and 70 volume percent. For instance, steam may be injected at the appropriate rate into the reaction chamber for this purpose.

The moisture content of the fabric to be treated is very important in the process of this invention, because it is the limiting factor in the reaction between sulfur dioxide and formaldehyde to give a strong acid which in turn determines the extent of the crosslinking of the cellulose by reaction with formaldehyde. Initial moisture in the fabric has a relatively small effect on the amount of formaldehyde incorporated into the fabric but will have a much larger effect on wrinkle recovery and flex abrasion characteristics. Generally speaking, too little moisture will give low wrinkle recovery values while too much moisture causes excessive degradation of the fabric. The amount of strong acid catalyst formed in the presence of water affects the proportion of formaldehyde that actually forms crosslinks on the fabric as against that merely present as formaldehyde polymer, but too much exposure to acid tends to weaken the fabric by hydrolyzing the cellulose. The strong but unstable acid catalyst makes the process fast as well as easy to control in a reproducible fashion.

Because of its chemical function in this process, water plays an unusual role here in that the crosslinking reaction automatically tends to come to a stop when water evaporates from the fabric to a point where insufiicient acid catalyst is formed or present to promote the crosslinking reaction. Whereas previous formaldehyde crosslink processes were difiicult to control, this makes the present process self-limiting in a desirable manner and produces a dry, crosslinked fabric which is essentially neutral when removed from the high temperature crosslinking chamber, and dissipation of moisture from the hot fabric automatically results in the removal of any residual catalyst therefrom. Moreover, such formaldehyde polymer as is left on the treated fabric at the end of the curing or crosslinking step can be easily and permanently removed therefrom by simple heating, e.g., in air and/or steam at a temperature above 100 0., preferably between 110 C. and 150 C., whereby the formaldehyde polymer is depolymerized and liberation of irritating formaldehyde from the fabric during subsequent use is precluded. Instead of removal by heating, formaldehyde or polyformaldehyde which is not permanently bound to the fabric may be removed and the acid catalyst neutralized or extracted by washing in an otherwise conventional manner in hot water, preferably mildly alkaline water, e.g., water which contains 1% sodium carbonate and/or a detergent such as a sodium alkylbenzene sulfonate, whereupon the fabric is dried. Removal of residual reactants by heating is particularly advantageous in processing garments whereas removal by washing is suitable in the continuous processing of flat fabric.

The fabric can be conditioned by any suitable method to give the moisture content necessary for the crosslinking reaction, such as by padding the fabric with water and partially drying or by adjusting the fabric to an appropriate moisture content by holding it for a time at a suitable temperature and relative humidity.

Other, optional features of the invention include the addition of various monomeric or polymeric additives to alter various fabric characteristics such as wrinkle recovery or smooth drying properties. For instance, treatment of the cloth prior to the formaldehyde-S treatment with a compound having an active hydrogen, and particularly with a hydroxyl compound such as ethylene glycol, triethylene or tetraethylene glycol dimethyl ether, glycerine, glycidol and the like, surprisingly results in a substantially greater increase in wet wrinkle recovery than dry wrinkle recovery, and can be used for this purpose when such an effect is desired. Other useful additives having an active hydrogen compound include amides such as urea proper or other ureas, e.g., cyclic ethyleneurea, allylurea and thiourea, acetamide, malonamide and acrylamide as well as sulfonamides such as methanesulfonamide; carbamates such as ethylcarbamate or hydroxyethylcarbamate; and so on. When such monomers which contain an active hydrogen are treated with formaldehyde in accordance with the present invention, they become fixed on the fabric so that they do not wash out. At dry add-ons of above 5%, e.g., between 5% and 20% pretreatment with the amides, and especially with urea, they tend to lead to unusually high tensile and tear strength retentions. They also add crispness to the fabric after being fixed thereon by the formaldehyde.

Moreover, pretreatment of the cloth, prior to the formaldehyde-S0 treatment, with polymerici resinous additives that form soft films, such as conventional dispersions or latexes, can result in an unusually great incremental improvement in wrinkle recovery as compared with similar effects when such additives are used in conjunction with more conventional crosslinking treatments. Polymers can also improve the flex abrasion resistance and tear strength, or alter the ratio of dry wrinkle recovery to wet wrinkle recovery, or in some instances shorten the reaction time needed to produce an acceptable durable press fabric. Polymeric additives suitable for such purposes are, in most cases, available commercially in concentrated aqueous latex form, and it is desirable to dilute these to a concentration of 1 to 3 percent polymer before padding onto the fabric. Suitable polymeric additives include solid resinous or rubbery acrylonitrilebutadiene copolymers and mixtures containing the same with various vinyl resins; polyethylene; deacetylated copolymers of ethylene and vinyl acetate; polyurethanes; and various polymers of alkyl acrylates, other polyesters and polyamides. Coating of the fabrics with such polymers subsequent to the formaldehyde treatment may also be used to give similar results.

The present invention is useful for treating various natural or artificial cellulosic fibers alone or as mixtures with each other in various proportions or as mixtures with other fibers. Such natural cellulosic fibers include cotton, linen and hemp, and regenerated or artificial cellulosic fibers useful herein include, for example, viscose rayon and cuprammonium rayon. Other fibers which may be used in blends with one or more of the above mentioned cellulosic fibers are, for example, cellulose acetate, polyamides, polyesters, polyacrylonitrile, polyolefins, polyvinyl chloride, polyvinylidine chloride, and polyvinyl alcohol fibers. Such blends preferably include at least 15 or 20 percent by weight, and most preferably at least 35 or 40 percent by weight, of cotton or natural cellulose fibers.

The fabric may be knit, woven or non-woven, or be any otherwise constructed fabric. The fabric may be flat, creased, pleated, hemmed, or formed into virtually any desired shaped article or garment prior to contact with the sulfur dioxide-containing atmosphere. After processing, the formed crosslinked fabric will maintain substantially the original configuration for the life of the article, that is, a wash-wear or durable press fabric will be produced.

When practicing the present invention the conditioned fabric is passed into a reactive atmosphere containing sulfur dioxide and formaldehyde which may be generated in any convenient manner. For instance, formaldehyde vapor may be generated by heating a suspension of paraformaldehyde in mineral oil and the vaporized formaldehyde is then metered into the reaction zone along with the gaseous sulfur dioxide. In addition to the formaldehyde, sulfur dioxide and water vapor, the reactive atmosphere may contain inert gases such as air, nitrogen, carbon dioxide, helium, and the like. Since sulfur dioxide forms the required strong acid catalyst by reacting with formaldehyde and water in the process, sulfur dioxide as such need not be supplied to or present in the process over the entire duration of the crosslinking reaction, but its supply may be discontinued after the first minute or two or when an adequate supply of the needed catalyst has formed. Moreover, to take maximum advantage of the self-limiting feature of this process, it can be advantageous to pass the fabric being treated through zones of progressively lower humidity. Obviously, a comparable selflimiting effect is not obtainable when the more common catalysts such as HCl, ammonium chloride or zinc nitrate are used.

To contact the fabric with the gaseous formaldehyde and sulfur dioxide any suitable means may be employed. For example, a batch system utilizing a closed vessel or tube containing the gaseous formaldehyde and sulfur dioxide may be used in which the conditioned, moisturecontaining fabric may be placed for the appropriate time. In the alternative, a dynamic or continuous system can be used such as one wherein a stream of formaldehyde and sulfur dioxide, preferably adjusted to contain between 10 and 70 volume percent water vapor by injection of the required amount of steam, is passed through a closed elongated chamber through which one also passes at an appropriate rate, either concurrently or countercurrently relative to the gas, the fabric or garments made therefrom. It is also possible to use combinations of the above, that is, one can pass a stream of formaldehyde and sulfur dioxide gas over a stationary fabric.

DESCRIPTION OF SPECIFIC EMBODIMENTS The present invention is further illustrated by the following examples.

Example 1 A glass tubular reactor approximately 8 cm. in diameter and 40 cm. in length, wrapped with heating tape and mounted horizontally, was heated to 120 C. Forma1dchyde was then generated by heating a suspension of paraformaldehyde in mineral oil to between 126 C. to 132 C. and the resulting formaldehyde was fed at flow rates between 30 and 150 mL/min. into one end of the reactor. Exact measurement of the actual formaldehyde flow was difi'icult because some re-polymerization of formaldehyde took place. Sulfur dioxide was metered concurrently at aa flow rate of 24 mL/min. from a storage tank into the reactor through an inlet adjacent the formaldehyde inlet. The downstream end of the reactor was closed with a large rubber stopper containing an exit tube 5 mm. in diameter.

A x 7.5 inch piece of conditioned cotton printcloth wrapper around a small frame was introduced into the reactor at the downstream end of the reactor. The conditioned printcloth was bleached, unmercerized cotton printcloth having a weight of 3.7 oz./yd. which had been padded with water to approximately 100% wet pickup, and then partially dried at 75 C. and conditioned overnight at 65% relative humidity and 70 F. to give the fabric a moisture content of 6%. After 5 minutes in the reactor, the printcloth was taken out, removed from the frame, rinsed with hot running water, washed in a household washer to which 25 ml. of commercial alkylbenzene sulfonate household detergent (Vel) had been charged, and tumble dried in a household dryer.

Physical properties evaluated after one wash-dry cycle are shown in Table I.

TABLE I.VAPOR PHASE CH20/S0z TREATMENT OF COT- Formaldehyde content of the treated fabric was 0.8%. Formaldehyde analysis was made by weighing printcloth samples of approximately 10 mg. to the nearest 0.1 mg. The samples were then heated for 30 minutes with 25 ml. of 2 N sulfuric acid at C. The solution was allowed to cool and a 2.0 ml. aliquot was piped into a test tube. To this aliquot was added 1.0 ml. of 0.1% aqueous solution of chromotropic acid and 7.0 ml. of concentrated sulfuric acid. The contents of the test tube were mixed. allowed to cool, and the absorbance at 570 m was measured with a Beckman DK-2 spectrophotometer. The amount of formaldehyde present in the printcloth was then calculated from a suitable calibration curve.

It can be seen that the fabric treated according to this invention had excellent wrinkle recovery and crease retention when compared with the untreated fabric.

Example 2 The cotton printcloth was treated and tested as in Example 1 except that certain polymeric additives were padded onto the printcloth along with the water before conditioning and treatment. Data and results are given in Table II. As can be seen, the use of polymeric additives in general improves wrinkle recovery values significantly.

As is evident from a comparison of the formaldehyde analyses made after a single wash-dry cycle and after 13 such cycles, the amount of formaldehyde durably deposited in the cotton fabric in this series of runs ranges from 0.3% upward based on the weight of the cellulose fibers. Satisfactory durable wrinkle recovery and tear strengths were obtained in all cases.

Example 3 The printcloth was treated and tested as in Example 1 except that certain monomeric additives were padded onto the printcloth before conditioning. Data and results are shown in Table III.

As can be seen the use of monomeric additives is capable of altering the ratio of dry wrinkle recovery to wet wrinkle recovery, improving tear strength, modifying the hand of the fabric, and so on.

TABLE II.VAPOR PHASE CHgO/SO TREATMENT WITH POLYMER ADDITIVE Pad bath composition Formal- Wrinkle recovery Total Reaction Moisture dehyde W+F, degrees Tear Solids, add'on, time, regain, content, strength,

Additive percent percent min. percent percent Dry Wet grams Untreated printcloth (control) 6.0 180 810 Properties after one wash-dry cycle None (water only). 8.0 2 6. 3 0.5 278 302 410 Rhoplex K-14 3.2 3. 9 3 5.8 0 8 325 324 400 Hycar 1562 2 2. 9 3. 5 3 5. 7 0. 4 319 301 430 Urethane latex, E502..... 3. 5 4. 3 3 7. 1 0.3 308 316 450 Deacetylated Elvax 210 3 1. 0 2. 3 3 6. 2 0.6 307 309 440 Properties after 13 wash-dry cycles Deacetylated Elvax 210 0. 0 3 6 0 0. 4 327 311 350 1 Acrylic resin. 2 Poly(butadienelacrylonitrile). 3 Poly(ethylene-vinylacetate), deacetylated.

TABLE IIL-VAPOR PHASE CHzO/SOa TREATMENT WITH MONOMER ADDITIVES PRETREAT Pad bath composition Wrinkle recovery Total Reaction W-i-F, degrees Tear Solids, add-on, time, strength, Additive percent percent min. Dry Wet grams Untreated printcloth (control) 180 130 810 None (water only).. 1.0 3 289 274 390 Form amide 1. 4 264 281 460 Malonamide 7. 1 2 312 297 400 Ar-Atamida 10 4. 5 3 306 296 330 Acryl amide 10 4. 7 3 290 284 340 Sulfamilamide 5 6. 4 3 240 213 520 Math nnmiil fnnamide 10 5, 4 3 259 269 410 2% 3. 8 3 284 270 440 10 5. 3 3 213 221 480 10 5. 4 2 254 242 580 1O 6. 5 2 234 181 820 Ethylcarbamate 10 2. 3 3 289 263 360 Hydroxyethylcarbamate. 10 10. 5 2 300 261 440 Ethylene glycol 10 6.0 3 277 309 290 Glynerine 10 8. 9 3 280 306 300 Glyr-idnl 10 0. 8 3 215 244 480 Sorhitnl 10 7. 9 3 273 277 310 Triethylene glycol dimethyl ether 10 2. 5 3 24.4 290 300 Tetraethylene glycol dimethyl ether 5 2. 5 3 230 283 320 1 Formaldehyde plus additive after one laundering.

Example 4 The fabric was treated and tested as in Example 1, except that a 100-liter cylindrical aluminum reactor (16% in OD. x 22 /2 in. high, approximately 50 times larger than in the preceding examples) was used, the quantity of fabric heated in this set of runs was approximately double that treated in the preceding examples, and a 7% aqueous dispersion of a polyacrylate was padded onto the fabric before treatment. The reactor walls were heated with electrical band heaters and the reactor wall temperature was controlled by an adjustable bimetallic thermostat. Steam at a certain rate was injected into the reaction zone along with the formaldehyde and sulfur dioxide in some runs, and different reaction times were used in various runs conducted in the presence of steam.

Fabrics conditioned to an initial moisture content of between 1% and 71% were treated with the formaldehyde-SO vapor mixture in this series of runs. Fabrics having a moisture content of 6%7% prior to treatment dried almost instantly in this large reactor, preventing formation of the strong acid catalyst necessary for catalysing the formaldehyde crosslinking reaction. 7

In contrast, fabrics having a moisture content of 10% or more prior to treatment showed a high degree of crosslinking in the process, demonstrating that moisture content of the system dramatically affects the efiicacy of the crosslinking reaction and the general properties of the treated fabrics. Fabrics treated for 3 minutes or more at initial moisture contents of 12% or more showed excellent wrinkle recovery but relatively low tearing strength and abrasion resistance, indicating that the fabrics were maintained longer than necessary in the presence of the strong sulfonic acid catalyst formed in the process. Fabrics having 10% moisture content showed good wrinkle recovery and relatively little loss in tearing strength and abrasion resistance when treated for 2 minutes or less. Very good results were obtained with treating times of only seconds, and comparable results were obtained with longer treating times when the sulfur dioxide How was reduced to compensate for the longer exposure. The high rate of reaction obtainable in this process makes the latter attractive for continuous processing.

Fabrics with moisture contents of 6%7% were treated successfully in the large reactor when the humidity in the reactor was increased by injection of steam at a certain rate into the reactor, thereby avoiding rapid drying of the fabrics. Some representative data and results are shown in Table IV.

TABLE IV.-EFFECT OF HUMIDITY ON DEGREE OF CROSSLINKING Crease recovery As shown by Run 1 in Table IV, the formaldehydesulfur dioxide system has little effect when moisture in the system is low. On the other hand, when moisture of the system is increased by injection of steam a satisfactory degree of crosslinking, as indicated by the crease recovery angle measurements, can be obtained. Comparing the results of Run 2 with those of Run 3 it can be seen that increasing the residence time of the fabric under otherwise comparable conditions results in a higher degree of crosslinking. Instead of achieving this increase in crosslinking by increasing the residence time, a comparable elfect can be obtained by still further increasing the humidity of the system.

Example 5 In this example a cotton fabric was impregnated with various amounts of urea before exposure to formaldehyde and sulfur dioxide gases substantially as described earlier herein. The reactor used was similar to the one described in Example 4. The results are summarized in Table V and illustrate the progressive improvement in the balance of strength retained to wrinkle recovery and durable press rating gained as concentration of urea increases. They also illustrate the superiority of the process, at all concentrations of urea, over a conventional durable press process, in terms of the balance of abrasion resistance retained to recovery and durable press rating gained.

Cotton twill fabric samples (Twist 'I will, I. P. Stevens and Company) were padded to 70% wet pickup with aqueous solutions containing 2.5% to 10% urea and 2.5% (solids) Urethane Latex E-502 (Wyandotte Chemicals Corporation), dried for 5 to 7 minutes at to C., sewn into cuifs, pressed with a commercial garment press, conditioned for a few hours in an atmosphere of 65% relative humidity, and then exposed to formaldehyde and sulfur dioxide vapors at 1.15 C. for 5 and 6 minute TABLE V.-PROPERTIES OF COTTON TWILL FAB RIOS TREATED WITH F/SO: PROCESS IN THE PRESENCE OF VARYING AMOUNTS F UREA Wrinkle recovery angle (degrees) Tearing Tensile Urea in strength Stoll flex strength Ratings 1 Exposure pad bath 2 Dry Wet (grams) abrasion, (1b.) time 1 (percent Addbn warp Durable Crease (min.) solids) (percent) Warp Fill Warp Fill Warp Fill (cycles) Warp Fill press retention Properties after 1 washing Untreated N.A N.A. N.A 78 71 74 78 3, 800 2, 060 640 175 66 N.A N.A

Untreated washed N.A N.A. N.A. 70 68 69 72 2, 840 1,630 670 161 74 N.A. N.A.

Treated with permairesh 113 B l N.A. 150 134 144 127 1, 600 1, 080 270 97 39 4. 0 3.8

l Fabrics exposed to F/SOz (formaldehyde-sulfur dioxide) vapors at 115 C.

2 All pad bath solutions contained 2.5% solids Urethane Latex E-502.

3 Fabric specimens tore across filling yarns only. I Greased fabric specimens rated after tumble drying. 5 Conventional durable press procedure.

NoTE.-N.A.=Not applicable.

periods. For comparison, other fabric samples were padded with an aqueous solution containing 5% solids of Permafresh 113B (dimethyloldihydroxyethyleneurea, Sun Chemical Company) and 2.5 solids of Urethane Latex E- 502. Wet pickup, drying, sewing, and pressing conditions were the same as above. These samples were conventionally heat-cured for 7.5 minutes at 160 C.

Intermediate concentrations of urea enhanced the wrinkle recovery angles obtained, a trend which was reversed at the highest level of urea concentration. Although it is simplest to make comparisons between treatments when they result in identical levels of wrinkle recovery, the variations obtained were not great enough to invalidate the following conclusions.

Increasing the concentration of urea used progressively improved the balance of tensile and tear strength to wrinkle recovery and durable press rating. In round figures, use of urea in the bath improved the tear and tensile strength values of formaldehyde and sulfur dioxide treated fabric by 40%, or on the basis of untreated values, without sacrifice of wrinkle recovery or durable press rating. There was no significant change in Stoll flex abrasion resistance. The conventional durable press treatment gave lower Stoll flex abrasion resistance figures than any level of urea concentration, and comparable tensile and tear strength figures to the zero urea concentration level, all comparisons being made at comparable levels of wrinkle recovery and durable press rating.

In still other examples, which are not reported here in detail, the fabric samples were similarly treated using various concentrations of cyclic ethyleneurea and trimethylolmelamine, respectively, in the pad bath instead of urea proper. Similar results were obtained.

While all of the above examples were conducted at atmospheric pressure, subor superatmospheric pressures may be used but are not necessary.

The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected herein may be practiced otherwise than is described without departing from the scope of the appended claims.

What is claimed is:

1. A process for improving the dimensional stability, wrinkle resistance and smooth drying characteristics of a cellulose fiber-containing fabric which comprises:

(a) conditioning the fabric to give the cellulose fibers a moisture content of between about 4 and 20% based on dry weight of cellulose;

(b) thereafter heating the conditioned moisture-containing fabric in a reactive vapor atmosphere containing effective amounts of formaldehyde, water vapor and catalyst-forming sulfur dioxide to a temperature between about 65 and 150 C. for a time of between about 10 seconds and 2 hours until formaldehyde in an amount equal to at least 0.3% by weight of said cellulose fibers is durably deposited in the fabric and the cellulose fibers become effectively crosslinked, said heating being conducted while governing the amount of water vapor in said atmosphere to control the amount of moisture in said fabric and thereby regulate the amount of strong acid catalyst formed by the reaction of formaldehyde and sulfur dioxide, a reaction in which water is the limiting factor, to provide a self-limiting reaction system; and

(c) heating the thus crosslinked fabric to dissipate water vapor, residual catalyst and unbound formaldehyde therefrom, thereby directly producing a dry, crosslinked, essentially neutral fabric.

2. A process according to claim 1 wherein the fabric is one containing at least 35% of cotton fibers by weight.

3. A process according to claim 1 wherein the fabric is heated in the reactive atmosphere in step (b) to a temperature between about and 150 C. for a time of between about 2 and 20 minutes and is heated in step (c) to a temperature above C.

4. A process according to claim 3 wherein the fabric is introduced into the process after having been formed into an article of predetermined configuration.

5. A process according to claim 3 wherein the fabric is a cotton-polyester blend containing at least 35% cotton by weight and is introduced into the process after having been formed into an article of predetermined configuration.

6. A process according to claim 3 wherein the fabric is padded in an aqueous solution of urea and contains from 5 to 25% dry add-on of urea prior to exposure to formaldehyde and sulfur dioxide.

7. A process for improving the dimensional stability, crease retention and smooth drying characteristics of a cellulose fiber-containing fabric which comprises:

(a) conditioning the fabric to give the cellulose fibers a moisture content of between about 4 and 20% based on dry weight of cellulose;

(b) thereafter heating the conditioned moisture-containing fabric in a reactive vapor atmosphere containing an effective amount of formaldehyde, water vapor and catalyst-forming sulfur dioxide to a temperature between about 65 and 150 C. for a time of between about 10 seconds and 2 hours until formaldehyde in an amount equal to at least 0.3% by weight of said cellulose fibers is durably fixed in the fabric and the cellulose fibers become effectively crosslinked, said heating being conducted while governing the amount of water vapor in said atmosphere to control the amount of moisture in said fabric and thereby regulate the amount of strong acid catalyst formed by the reaction of formaldehyde and sulfur dioxide, 3. reaction in which water is the limiting factor, to provide a self-limiting reaction system;

(c) washing the thus crosslinked fabric in water to remove residual catalyst and impermanently bound formaldehyde therefrom; and

(d) drying the washed, crosslinked fabric.

8. A process according to claim 7 which process is continuous and wherein the fabric being treated is fiat fabric.

9. A process according to claim 7 wherein the fabric is a cotton-polyester blend containing at least 35% by weight of cotton.

10. A process for improving the dimensional stability, wrinkle resistance and smooth drying characteristics of cotton-containing fabrics which comprises:

(a) conditioning the fabric to give the cotton a moisture content of between about 4 to 20% based on dry weight of cotton;

(b) exposing the conditioned fabric to a reactive vapor phase containing water vapor, about 15 to 60 volume percent formaldehyde and at least initially from about 5 to 30 volume percent sulfur dioxide in a reaction zone maintained at a temperature between about 90 and 120 C. for a time of from about 2 to 20 minutes, thereby effecting the desired degree of crosslinking; and

(c) at the end of said crosslinking step (b) removing residual catalyst and unbound formaldehyde from the fabric by heating it in an inert gaseous atmosphere, thereby directly producing a dry, crosslinked, essentially neutral fabric.

11. A process according to claim 10 wherein steam is injected into the reaction zone in step (b) to adjust the water vapor concentration therein at between about 10 and percent and thereby to retard evaporation of moisture from the conditioned fabric and control the crosslinking reaction.

12. A process according to claim 10 wherein the fabric is treated prior to the formaldehyde crosslinking step with a compound containing an active hydrogen and selected from the groups consisting of polyhydric alcohols, ureas, amides and carbamates.

13. A process according to claim 10 wherein the fabric is introduced into the process after having been formed into an article having a predetermined configuration.

References Cited UNITED STATES PATENTS 2,441,859 5/1948 Weisberg et al 8116.4 3,264,054 8/1966 Reinhardt et a1. 8116.4 3,310,363 3/ 1967 Russell et al. 8-116.4 3,660,013 5/1972 Payet et a1. 8116.4

FOREIGN PATENTS 980,980 1/ 1965 Great Britain 8-1164 OTHER REFERENCES Guthrie: American Dyestulf Reporter, vol. 51, No. 14,

Gagliardi et al.: Textile Research Journal, vol. 36, pp. 168-177 (1966).

Mehta et al.: Journal of the Textile Institute, vol. 58, pp. 279-292 (1967).

GEORGE F. LESMES, Primary Examiner J. CANNON, Assistant Examiner US. Cl. X.R.

2243; 8-115.5, 115. 6, 116.2, 116.3, 116.4, 129, 149.1, 149.2, 149.3, DIG. 4, DIG. 9, DIG. 10, DIG. 21; 34-37; 38-144