US3542503A - Process for imparting wrinkle resistance and recovery properties to cotton stretch fabrics - Google Patents

Description

"United States Patent Oifice 3,542,503 Patented Nov. 24, 1970 U.S. Cl. 8116.3 6 Claims ABSTRACT OF THE DISCLOSURE The process of this invention comprises the steps of treating cellulosic material with aqueous alkali and subsequently reacting the alkali treated material with an alkali catalyzed resin or crosslinking agent.

An non-exclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

This invention relates to a continuous process for the production of cellulosic textile materials having excellent stretch and wet-and-dry wrinkle recovery properties. More specifically, it deals with a continuous process comprising shrinking cellulosic fibrous textile materials with an alkaline solution, and subsequently without tension reacting the alkali-treated cellulose formed during the shrinking process with a thermosetting resin or (other) suitable crosslinking agent which may be catalyzed by the alkaline reagent.

The term cellulosic textile material or cellulosic fibrous materials, as used herein, relates to the natural cellulosic products such as cotton, linen, ramie, etc.; it also relates to the synthetic cellulosic fibers such as rayon, and the like. These products may be in the natural state, but better treatment is effected when the cellulosic material has been prepared by conventional procedures for removing natural waxes, and other noncellulosic impurities. The fibrous materials may be in the form of yarns; or they may be knitted or woven fabrics.

Processes for producing stretch cottons by slack mercerization or other alkali-contraction techniques are known in the art. Processes for the crosslinking, or chemical treatment of cotton using alkaline catalysts also are known. However, in the present-day art of producing wrinkle-resistant, cotton stretch-fabrics, each of the two processes is carried out as a separate entity; this is frequently referred to as a two-stage process. That is, the fabric is first slack mercerized, then washed completely free of alkali (or soured and rinsed) and dried. This is the first stage. The dry slack-mercerized cellulosic material is then chemically treated by resination, or crosslinking, in the second-stage treatment. Frequently, the equipment for these two stages of treatment are at separate places in the plant, or the slack-mercerized cellulosic material may be transported to another plant for the cross? linking treatment. In either case, since the chemical used for slack mercerization is completely removed from the cellulosic material in the first stage, additional caustic solution must be used when an alkali-type catalyst is to be used in the second stage. US. Pat. 3,145,132 teaches such a two-step batch finishing treatment in which complete removal of the reagent that effects shrinkage of the cellulosic fibers is required, followed by drying before the crosslinking reactant, or thermosetting resin can be applied to the cellulosic material.

It is an object of this invention to provide a process whereby cellulosic textile materials may be treated so as to produce excellent stretch properties and a high level of wet-and-dry wrinkle resistance in a continuous sequence of finishing steps.

It is a further object of this invention to eliminate certain steps which are necessary in the above-mentioned two-stage batch process for producing wrinkle-resistant, cotton stretch fabrics, thereby providing added economy of time and expense.

These objects of our invention are accomplished by processing woven or knit cellulosic fabrics as follows:

(a) Impregnating the cellulosic fa bric under minimum tension with an aqueous solution of an alkaline swelling agent to shrink or reduce the dimensions of the material in one, or both, direction; this makes the fabric stretchable;

(b) Maintaining a period of dwell from about 0.5 to 5.0 minutes in the alkaline solution to insure uniform swelling and shrinking of the fabric;

(0) Removing the excess alkaline solution by mechanical means such as padder rolls (squeeze rolls), centrifugation, and the like;

(d) Further increasing the swelling and shrinking of the fabric by reducing the concentration of the alkaline solution by rinsing in water and passing through padder rolls (squeeze rolls) to give about 0.1 to 10 weight percent residual alkali on the weight of the dry fabric;

(e) With minimum tension, passing the swollen, wet fabric of step (d) into, and through, a 2 to 20 weight percent solution of a crosslinking reagent whose reaction with the cellulose is catalyzed by the residual (0.1 to 10%) alkaline reagent;

(f) With minimum tension, reacting the crosslinking agent with the cellulose (curing);

(g) With minimum tension, washing the crosslinked fibrous material to remove all unreacted chemicals and unwanted byproducts; and thereafter (h) Drying with minimum tension the cellulosic fabrics having excellent stretch properties and improved wet-and-dry wrinkle resistance.

This sequence of steps permits continuous processing of the fabric, eliminates costly washing, souring (acid treatment), rinsing, and drying after the alkali-shrinking step. It also permits utilization of the alkali-swelling agent as a catalyst during the resin-finishing, or crosslinking step. The economy of this reduction in processing steps is apparent.

Two essential concentrations of the alkaline reagent are required in this invention. In the first place, a concentration capable of shrinking the cellulosic material must be employed in step (a) above. For example, when a sodium hydroxide solution is used, a concentration of at least 13 weight percent on the weight of the solution (OWS) at 32 F. is required. At ambient room temperatures (about to 86 P.) concentrations ranging from 3 about 23 to 30 weight percent (OWS) cause satisfactory shrinkage to be obtained.

For effective catalysts of certain reagents in the crosslinking step (step (f) above), a lower concentration of alkali is essential. With sodium hydroxide at ambient room temperatures (65 to 86 F.) 0.1 to weight percent, on the weight of the fiber (OWF), is suitable for catalyzing the reaction between the cellulose and the thermosetting resin, or crosslinking agent. Step ((1) above is achieved (without an intermediate drying step) by rising, and by adjusting the retention of water and alkali on, and in, the fabric. This may be done by squeezing (between padder rolls), centrifuging, or other available mechanical means.

We have found that, when a fabric is impregnated with a sodium hydroxide solution of about 23 weight percent at ambient temperatures (65 to 86 F.), soaking for about 5 minutes in -50 times the weight of the dry fabric in water reduces the amount of residual sodium hydroxide to about 4 to 8 weight percent alkali (OWF).

It is an advantage of the process of our invention that the application of sodium hydroxide solution of mercerizing strength to cotton material followed by rinsing, and washing to about 4 to 8 weight percent concentration (OWF) has the distinct advantage of producing a higher degree of swelling of the cellulose with resultant improvement in shrinkage than is obtained from caustic solutions containing at least 13 weight percent sodium hydroxide (OWS), at 32 F., or 23 to 30 weight percent sodium hydroxide (OWS) at ambient room temperatures. This unexpected phenomenon was discovered by determination of the water of imbibition which is recognized as an index of the state of swelling of the fibers. For example, the water of imbibition of a sample of cotton yarn treated by impregnation with 30 weight percent sodium hydroxide (OWS) was 105%. Portions of this yarn which had been impregnated with 30 weight percent sodium hydroxide (OWS), and then reduced to 4 to 8 percent sodium hydroxide (OWF) by rinsing and washing, had water-of-imbibition values of 122125%. (Water of imbibition was measured by the weight of water retained by the fiber after centrifugation at 1,000 times the force of gravity for minutes. The weight percent of pickup of water is based on the original weight of the dry cotton.) These higher water-of-imbibition values indicate correspondingly greater degrees of swelling. Swelling and shrinkage are, of course, directly related.

Alkaline swelling agents which may be used in the fabric contraction step include sodium hydroxide, potassium hydroxide, trimethyl benzyl ammonium hydroxide, and the like. Concentrations sufiicient to bring about mercerization and attendant shrinkage of the cellulose are used. In general, concentrations above about 13 Weight percent (OWS) are required. However, as noted above, the concentration of the shrinking (mercerizing) reagent is related to the temperature of the solution and may vary from about 13 to 30 weight percent (OWS).

The fabric-contraction step is carried out at a temperature of about to 86 F. or below, and for a time sufiicient to allow shrinkage to an extent which imparts stretchability to the fabric to occur. About 0.5 to 5.0 minutes at ambient room temperatures is a good practice.

After the fabric has shrunk, it is treated with an amount of water such that upon adjustment of pickup, preferably 90 to weight percent (OWF) the concentration of alakli calculated as solids remaining, is about 0.1 to 10 weight percent of the dry fabric. As noted above, residual alkali serves as a catalyst in the subsequent chemical reaction step.

A thermosetting resin, usually amide-formaldehyde condensates, such as methylolated urea, melamine, or other crosslinking reactants such as bis(Z-hydroxyethyl) sulfone, epichlorohydrin, dichloropropanol, the disodium salt of tris(sulfatoethyl)sulfonium inner salt, and the like, whose reaction with cellulose is catalyzed by alkaline agents, is then applied. Application of the resin, or reactant, to the fabric wet with alkali solution may be by dipping, soaking, padding, spraying, brushing, and the like. However, for continuous operation a pad box equipped with one or more pairs of squeeze (padder) rolls is a good practice. The fabric is passed into, and through, the alkaline solution prior to passage through the squeeze rolls. Concentrations of resin, or crosslinking reactant, ranging from about 2 to 20 weight percent (OWS) may be employed. When the pickup is properly adjusted, the treated fabric should also contain about 2 to 20 weight percent solid reagent (OWF). If one passage of the fabric into, and through, the crosslinking solution does not deposit the desired 2 to 20 weight percent solids on the fabric, the fabric is passed through again until the desired amount is deposited on the fabric. Extreme care must be maintained to reduce the tension on the fabric at all times to a minimum to obtain the best results.

After application of the resin, or crosslinking reactant, to the alkali-containing fabric, reaction with the cellulose is allowed to proceed. This reaction may be carried out under (1) dry-cure conditions, or (2) in the wet state.

In a dry-cure reaction, the fabric may be dried and cured in a single heat-treatment operation; or alterna tively it may be dried at a temperature sufficient to reduce its moisture content to about 10 weight percent (OWF), or less, and subsequently heat-treated at a higher temperature to bring about a reaction between the cellulose and the crosslinking agent. In this latter case, a delay period as much as six months, or more, between drying and curing can be used, if desired. Preferred practical conditions for curing are about one minute to about 10 minutes at temperatures from about 275 F. to about 365 F., the time and temperature of curing being inversely related. Heavier-weight fabrics require stronger curing conditions, that is, the higher temperatures and/ or longer times than the lighter fabrics.

When curing is to be accomplished in the wet state, and the reagent is applied to the alkali-containing fabric, the fabric is first rolled onto a tube, or core; it is then wrapped in a plastic sheeting to prevent evaporation of water, and allowed to stand at ambient room temperature or at elevated temperature for a period of time. The time necessary for completion of the reaction may vary from a few minutes to several hours. Usually a standing time of about 30 to minutes at 77 to 95 F. causes satisfactory curing to be obtained.

After the reaction between the cellulose and the reagent is completed, the fabric is thoroughly washed, or soured and washed, to remove all unused reactant, catalyst, and/or byproducts. During all the handling and final drying, it is essential that the fabric be processed with minimum tension to preserve the stretchability imparted by the shrinking or swelling treatment.

When treated by the process of this invention, cotton fabrics having excellent stretch properties and wet-anddry wrinkle resistance are obtained. The values of these improved properties in a woven or knitted fabric are obvious to those skilled in the art of textile finishing. Furthermore, their values are indicated by the continuing, increasing demands of the consumer for garments and other household items having both stretch properties, and wet-and-dry wrinkle resistance. These properties when imparted to cellulosic textile products, provide greater comfort and convenience to the consumer and at the present time are in great demand by the public.

The following examples are given to illustrate the invention and in no way are to be construed as restricting the obvious variations that may be used to achieve similar results. Percentages are listed by weight on the weight of the solution (OWS) or by weight on the weight of the dry fabric (OWF). The percentage of water of imbibition, although not so stated, relates to weight percent on the weight of the dry fabric. Sulfur is determined as described by I. Lysyj and J. E. Zarembo, Microchem. 1., 3, 173-80 (1959). Solubility is qualitatively observed microscopically by treating fibers from the sample with 0.5 M concentration of cupriethylenediamine solution. This test is. recognized by those skilled in the art as a means of observing crosslinking and is described by Tripp et al. in Textile Research 1., 31, 295-301 1961 Nitrogen content is determined by the Kjeldahl method. Dry Wrinkle recovery angles are determined by the Monsanto method, ASTM designation D1295-53T. Wet wrinkle recovery angles were determined by soaking the specimens 5 minutes at 150 F. in water containing 0.1% wetting agent, removing excess moisture by touching the edge of the specimens to a blotter, and then following the Monsanto procedure for dry recovery.

EXAMPLE 1 (1) A portion of desized, scoured, and bleached 80 x 80 woven cotton fabric measuring 9 inches by 9 inches, was marked into 9 squares, each 3 X 3 inches. From another portion of the same fabric 12 similar 3 X 3 in. squares were marked, cut, and weighed, and the average dry weight of each square calculated. A 9 X 9 in. portion was then soaked in an alkaline solution containing 23 weight percent sodium hydroxide for 5 minutes at ambient room temperature with no tension on the fabric. The sample was then passed through a pair of squeeze rolls to give a pickup of about 90 to 110 weight percent (OWF). One marked square was cut off, placed in 100 milliliters of distilled water containing a phenolphthalein indicator and titrated with'standard l N HCl to determine the amount of residual alkali in the fabric. The remainder of the original 9 X 9 in. sample was soaked in a volume of Water equal to 50* times its dry weight for 5 minutes, then squeezed through pad rolls after which another marked square was out 01f, and titrated to determine the amount of residual alkali in the fabric.

The remaining portions of the original 9 x 9 inch sample were again soaked in water equal in volume to 50 times their dry weight and the same sequence, described above. was followed until titration showed no residual alkali remained in the fabric. The data in the following'table illustrate the amount of residue] alkali in the fabric after each step outlined above.

Weight percent No. rinses: NaOH in fabric 43.6

It will be observed that one rinse in an amount of water equal to about 30 to 50 times the dry weight of the fabric before shrinking, followed by squeezing to about 90 to 110% pickup, reduces the strength of the alkali to about 4 weight percent alkali (OWF).

(2) A sample A of the same cotton printcloth used above was immersed tensionless in 23% sodium hydroxide solution at ambient roomtemperature to effect shrinkage, and thus impart stretchability, then passed through squeeze rolls, rinsed in a volume of water equal to 50 times its dry weight for 5 minutes, and again squeezed. Concentrations of sodium hydroxide remaining in the fabric Was about 4% of the weight of the fabric. This sample was then passed into, and through, an aqueous solution containing Weight percent (OWS) of bis(2- hydroxyethyl) sulfone, passed through squeeze rolls again, dried 7 minutes at 140 F., cured 3 minutes at 320 F., Washed thoroughly to remove unwanted chemicals, and dried.

(3) A second sample B was treated with 10 weight percent bis(2 hydroxyethyl) sulfone as in (A) above after first being similarly immersed in 23% sodium hydroxide but rinsed twice with 50 times its weight in water.

-(4) A third sample C was treated with 23% sodium hydroxide and rinsed free of alkali. This sample was not Wrinkle recovery angles in degrees Sulfur Solubility in warp plus fill content 0.5M weight, cupriethylenc- Sample Dry Wet percent diamine solution 231 257 0.75 Completely insoluble.

217 233 0.10 Partly soluble.

190 196 0.00 Soluble.

EXAMPLE 2 The procedures of Example 1 for samples A and B were repeated except that a concentration of 20% bis(2- hydroxyethyl)sulfone (OWS) was used. These samples are D and E, and correspond to A and B, respectively and had excellent stretch properties.

Wet wrinkle recovery angles (deg) Sulfur content weight, percent EXAMPLE 3 The procedures for samples A and B of Example 1 were repeated except the 10 weight percent solution of bis(2- hydroxyethyl)sulfone was applied to the samples by means of spraying. These samples are P and G corresponding to A and B, respectively and had excellent stretch properties.

Wrinkle recovery angles in degrees Sulfur warp plus fill content weight, Dry Wet percent EXAMPLE 4 The procedure of Example 3 was repeated except the concentration of bis(2 hydroxyethyl)sulfone was raised to 20%. These samples are H and I corresponding to F and G, respectively and had excellent stretch properties.

Wet Wrinkle recovery Surface content angles (deg) Weight, percent Sample H 253 0. 73 I 240 0. 58 Control 196 0. 0

EXAMPLE 5 (A) A portion of a sample of cotton printcloth was soaked in 25 weight percent sodium hydroxide solution without tension and allowed to shrink. It was then passed through squeeze rolls, rinsed with a volume of water equal to times its dry weight to give a sodium hydroxide content of about 4 weight percent (OWF), squeezed, and then passed into, and through, a solution containing 10% dimethylol urea. It was again passed through squeeze rolls, passed into, and through, the 10% solution of dimethylol urea a second time, and again passed through squeeze rolls. It was then dried Without tension at F. for 7 minutes, and dry cured at 320 F. for 3 minutes, after which it was thoroughly washed, and dried.

(B) Another portion of the same sample of cotton printcloth used in A above was treated as in part (A) of this example except that it was rinsed twice with water after the shrinkage treatment, to give a sodium hydroxide content of about 0.1 weight percent (OWF), and 20% dimethylol urea solution was used for the crosslinking treatment. It was then dried, cured, washed thoroughly, and again dried as in (A) above.

(C) A sample of cotton printcloth was soaked in 25% sodium hydroxide solution and allowed to shrink. It was Washed free of alkali, and dried.

All fabrics had excellent stretch properties.

Results of these treatments are shown as follows:

Wrinkle recovery angles in degrew Nitrogen Solubility Warp plus fill content in 0.5 M

weight, cupriethylene- Dry Wet percent diamino solution 258 250 1. 6 Insoluble. 273 258 2. 9 D0. 171 233 Soluble.

EXAMPLE 6 A portion of the same sample of cotton printcloth was soaked in 25 sodium hydroxide solution, squeezed, rinsed in 50 times its dry weight of water, passed through pad rolls, soaked in a 10 weight percent solution of the disodium salt of tris(sulfatoethyl)sulfonium inner salt, passed through squeeze rolls to remove excess solution, rolled on a glass tube, and wrapped with an impermeable plastic film. It was allowed to react in this wet state at 80 F. for one hour, then washed free of unused reactants and byproducts, and dried. The fabric contained 0.47% sulfur and was crosslinked, as is shown by its insolubility in 0.5 M cupriethylenediamine solution and had excellent stretch properties.

EXAMPLE 7 Another portion of the same cotton printcloth used in Example 6 was treated as in Example 6, except only bis(2 hydroxyethyDsulfone was used. The treated fabric contained 0.11% sulfur, was insoluble in cupriethylenediamine solution, and had excellent stretch properties.

We claim:

1. A continuous process for imparting excellent stretch properties and wet-and-dry wrinkle resistance to a cellulosic fabric selected from the group consisting of a woven cellulosic fabric and a knitted cellulosic fabric, comprising:

(a) impregnating the cellulosic fabric under minimum tension with an aqueous solution of an alkaline swelling agent selected from the group consisting of sodium hydroxide, potassium hydroxide, and trimethyl benzyl ammonium hydroxide, said solution 8 having a concentration ranging from about 13 percent at 32 F. to 30 weight percent at 86 F.;

(b) maintaining a period of dwell from about 0.5 to 5.0 minutes in the alkaline solution to reduce the dimensions of the fabric by shrinking;

(c) reducing the concentration of alkali in the impregnated fabric by rinsing the fabric in water and passing the rinsed fabric through squeeze rolls until the residual alkali concentration within the fabric is within the range of 0.1 to 10 weight percent based on the weight of the original dry fabric;

(d) with minimum tension, passing the resulting swollen, wet fabric of step (c) into and through a 2 to 20 weight percent solution of a crosslinking reagent whose reaction with the swollen cellulose is catalyzed by the residual alkaline agent;

(e) with minimum tension, reacting the crosslinking agent with the cellulose;

(f) with minimum tension, washing the crosslinked fabric to remove all unreacted chemicals and unwanted byproducts; and thereafter (g) with minimum tension drying the fabric having excellent stretch properties and wet-and-dry wrinkle resistance.

2. The process defined in claim 1 wherein the wet fabric of step (d) is dried and subsequently cured with minimum tension at an elevated temperature ranging from about 275 to 365 F. for about 1 to 10 minutes, the higher temperature requiring the shorter curing time.

3. The process defined in claim 1 wherein the wet fabric of step (d) is cured without tension at ambient room temperature for about 30 to minutes prior to washing and drying.

4. The process defined in claim 1 wherein the alkaline swelling agent is sodium hydroxide.

5. The process defined in claim 1 wherein the crosslinking agent is selected from the group consisting of dimethylol urea, methylolated melamine, bis(2-hydroxyethyl)sulfone, epichlorhydrin, dichloropropanol, and the disodium salt of tris(sulfatoethyl)sulfonium inner salt.

6. The process defined in claim 2 wherein the wet fabric is dried to a moisture content not greater than 10 weight percent and the heat treatment has a delay period not greater than six months.

References Cited UNITED STATES PATENTS 2,950,553 8/1960 Hurwitz 8l16.3 X 3,145,132 8/1964 Seltzer 2874 X 3,285,690 11/1966 Cooper et a1. 8116.3

OTHER REFERENCES Gardon: A Quantitative Study of Crosslinking Cotton With N-Methylol Acrylamide, Journal of Applied Polymer Science, vol. V, issue 18, pp. 734-739.

Ward: Chemistry and Chemical Technology of Cotton, Interscience Publishers, Inc., New York, 1955, p. 507.

LEON D. ROSDOL, Primary Examiner M. HALPERN, Assistant Examiner US. Cl. X.R. 8-116,