Oxidative afterwash treatment for crease resisting fabrics

The level of released formaldehyde in a durable press treated fabric is significantly reduced or eliminated altogether by an oxidative aftertreatment process in which the fabric, after treatment with a formaldehyde-based durable press finishing agent and curing to impart durable press properties, is contacted with an oxidizing agent to destroy formaldehyde-releasing moieties present in the fabric. Preferably, the treatment of the durable press fabric with the oxidizing agent is carried out by impregnating the fabric with a solution containing the oxidizing agent and then providing the fabric a residence time in contact with the oxidizing agent to allow for reaction of the oxidizing agent with the formaldehyde-releasing moieties.

Field and Background of the Invention 
This invention relates to a finishing process for textile fabrics and more 
particularly to a durable press treatment process for textile fabrics 
containing cellulosic fibers. 
In conventional finishing processes for imparting durable press properties 
to cellulose fiber-containing fabrics, the fabric is treated with a 
finishing agent, followed by heating to elevated temperature to ffect 
curing or crosslinking of the finishing agent and thereby impart crease 
resisting properties to the fabric. Many of the durable press treatment 
processes used commercially employ as the finishing agent a reactive resin 
based on formaldehyde. Perhaps the most commonly used reactive resin 
durable press finishing agent is dimethyloldihydroxyethyleneurea (DMDHEU), 
a formaldehyde-based resin formed from formaldehyde, glyoxal and urea. 
DMDHEU is commonly referred to in the industry as "glyoxal resin." There 
has also been a great deal of interest shown in durable press treatment 
processes which utilize formaldehyde itself as a reactive crosslinking 
agent for obtaining durable press properties. Generally, in these durable 
press treatment processes, the fabric is treated either with formaldehyde 
in the vapor phase or with an aqueous solution of formaldehyde. For 
example, commonly owned U.S. application Ser. No. 299,477, filed Sept. 4, 
1981, and entitled Aqueous Formaldehyde Textile Finishing Process 
describes a process in which durable press properties are obtained by 
treating the fabric with aqueous formaldehyde. 
Textile fabrics which have been treated with a formaldehyde-based finishing 
agent, such as those noted above, necessarily contain residual finishing 
agent from which formaldehyde can be released under conditions of storage 
and use. Released formaldehyde values in such fabrics typically range from 
500 to 2000 ppm. Recent concern over the safety of human exposure to 
formaldehyde has prompted increasing interest in reducing the levels of 
released formaldehyde from durable press treated fabrics, and various 
approaches to the reduction of formaldehyde release have been proposed, 
including the use of formaldehyde scavengers such as amides, urea and 
ethyleneurea; pad bath additives such as polyols; and the use of various 
inorganic additives or aftertreatments, such as sodium bisulfite or sodium 
borohydride. See for example Andrews et al Textile Chemist and Colorist, 
Vol. 12, No. 11 (November 1980) pp. 287-291. 
While these prior approaches have been successful to varying degrees in 
lowering the level of released formaldehyde, other accompanying problems, 
including reduction in crease-resistance, discoloration, chlorine 
retention, lack of durability, etc. have made these approaches less than 
fully satisfactory. 
SUMMARY OF THE INVENTION 
The present invention is based on the discovery that for fabrics that have 
been treated with a formaldehyde-based durable press finishing agent to 
achieve durable press properties, the level of released formaldehyde can 
be significantly reduced or eliminated altogether by subjecting the 
durable press finished fabric to an oxidative afterwash treatment in which 
a solution of an oxidizing agent is applied to the fabric and allowed to 
react with the formaldehyde-releasing moieties present in the fabric after 
durable press treatment. After this treatment the fabric may be optionally 
washed and thereafter dried. The oxidative afterwash treatment effectively 
destroys potential sources for released formaldehyde present in the fabric 
without adversely affecting the durable press performance or other fabric 
properties. The fabric shows a very significant reduction in the level of 
released formaldehyde after the oxidative afterwash treatment and, quite 
significantly, retains this reduced level of released formaldehyde over a 
long period of time. 
The oxidative afterwash treatment of the present invention is especially 
suited for durable press fabrics which have been treated with formaldehyde 
as the finishing agent. Released formaldehyde values for such fabrics have 
been reduced from in excess of 1000 ppm to well below 100 ppm by this 
treatment. The present invention has also been shown to provide 
significant reduction in released formaldehyde for fabrics treated with 
formaldehyde-based resin finishing agents, such as glyoxal resin. 
We have also determined that reduction in released formaldehyde to even 
further levels-essentially zero-is possible by a combination of the 
oxidative aftertreatment together with the addition of polyhydric alcohols 
as additives to the finishing agent bath. Suitable polyhydric alcohol 
finishing bath additives include ethylene glycol, diethylene glycol, 
glycerol, pentaerythritol, and low molecular weight carbohydrates. 
It has been observed that fabrics which have been treated with a 
formaldehyde-based finishing agent tend initially to lose some of the 
releasable formaldehyde fairly easily, e.g. by washing. However while the 
released formaldehyde level is reduced initially, the washing is not fully 
effective in removing the releasable formaldehyde, and the fabric 
continues to release formaldehyde over a period of time. 
In achieving effective long-term reduction of released formaldehyde, the 
present invention recognizes that the formaldehyde-based finishing agent 
present in the fabric following the durable press treatment process 
contains releasable formaldehyde in two forms: free and bound. The free 
releasable formaldehyde is not chemically bound to the fabric, and simple 
aftertreatments such as washing are fairly effective in removing it from 
the fabric. The term "bound" releasable formaldehyde refers to the 
formaldehyde releasing moieties present in formaldehyde-based finishing 
agent which is chemically bound to the cellulose, although the 
formaldehyde-releasing moiety may or may not be bound. Where the 
formaldehyde-releasing moiety is not itself chemically bound, such as by 
being tied up in a crosslink, it can split off from the finishing agent 
and be released as free formaldehyde at some later point in time. By 
contacting the durable press treated fabric with an oxidizing agent, these 
potential sources for long-term formaldehyde release are destroyed. This 
is accomplished without significantly affecting the level of crosslinking, 
which provides crease resistance to the fabric. This same treatment 
effectively removes residual free finishing agent from the treated fabric. 
Preferably, the treatment of the durable press fabric with the oxidizing 
agent is carried out by impregnating the fabric with a solution containing 
the oxidizing agent and then providing the fabric a residence time in 
contact with the oxidizing agent to allow for reaction of the oxidizing 
agent with the residual finishing agent. This may be conveniently 
accomplished, for example, in a continuous operation by padding the fabric 
with a solution of the oxidizing agent, and then directing the fabric into 
a scray or J-box to provide a holding time prior to further processing. 
The fabric is preferably heated during the holding period to promote 
reaction of the oxidizing agent with the residual finishing agent. A 
particularly suitable and effective method for heating of the fabric is by 
steaming, which may be suitably accomplished by directing live steam into 
an enclosed scray or J-box. After treatment with the oxidizing agent, the 
fabric may be further processed, e.g. by drying or by washing and drying. 
Any oxidant which will oxidize the formaldehyde-releasing moieties of the 
formaldehyde-based finishing agent can be employed as the oxidizing agent. 
Concentration levels can be suitably controlled so as to avoid 
overtreatment and loss of durable press and other fabric properties. A 
preferred class of oxidizing agents for use in the present invention are 
those selected from the group consisting of sodium perborate, hydrogen 
peroxide, and sodium hypochlorite. The oxidant is most conveniently 
applied as an aqueous solution, the concentration of oxidant preferably 
being up to about 5%, and most desirably on the order of about 1/2 to 3 
percent. Auxiliaries such as oxidant stabilizer, buffer salts, swelling 
agents, fabric softeners and the like may be added to the oxidative 
treatment solution. 
The oxidative afterwash treatment process of the present invention is 
especially useful and valuable with fabrics treated with formalin or 
formaldehyde as the finishing agent. However, the invention is also very 
useful with fabrics treated with formaldehyde-based resin-type finishing 
agents, such as glyoxal resin for example. In addition to glyoxal resin 
and formalin, other well known formaldehyde-based durable press finishing 
agents include ureaformaldehyde resin, dimethylolurea, dimethyl ether of 
ureaformaldehyde, melamine formaldehyde resins, cyclic ethylene urea 
formaldehyde resins, e.g. dimethylol ethylene urea, uron-formaldehyde 
resins, e.g. dimethylol uron, triazine-formaldehyde resins, and 
triazone-formaldehyde resins. This listing is not exhaustive (as there are 
many other known formaldehyde-based finishing agents) but is intended 
simply to illustrate the wide range of applicability of the treatment 
process of this invention. 
The treatment process of this invention is applicable to any cellulose 
fiber-containing fabric. As the cellulosic fiber-containing fabric, there 
can be employed various natural or regenerated cellulose fibers and 
mixtures thereof, such as cotton, linen, ramie, and rayon, for example. 
These may be used alone or in blends with one or more other types of fiber 
such as polyesters, polyamides, acrylics, and polyolefins for example. 
A further understanding of the present invention and its features and 
advantages will become apparent from the detailed description given 
hereinafter. It should be understood at the outset however, that the 
detailed description and specific example which follow are given by way of 
illustration only. They are intended to be understood as a broad, enabling 
teaching directed to persons skilled in the applicable art, and are not to 
be understood as restrictive, since various changes and modifications 
within the spirit and scope of the invention will become apparent to those 
skilled in the art.

DESCRIPTION OF ILLUSTRATED EMBODIMENT 
As illustrated in the drawing, a woven textile fabric 10 containing a blend 
of cotton and polyester fibers is directed continuously from a supply roll 
11 through a conventional pad apparatus generally indicated by the 
reference character 12, where it is immersed in and thoroughly impregnated 
with a formaldehyde-based durable press finishing agent 13. In the 
specific embodiment illustrated the finishing agent 13 is a conventional 
glyoxal resin-type finishing agent system, and includes an aqueous 
solution of glyoxal resin, together with a suitable curing catalyst, as is 
well known in the art. The pad bath may also contain conventional 
finishing bath auxiliary agents such as surfactants, softeners, 
penetrants, leveling agents, antifoam agents and the like which are well 
known to the finishing trade. 
From the pad bath 12 the fabric 10 is directed into and through a curing 
oven 14 where it is heated to dry and cure the fabric, thereby imparting 
crease resisting properties to the fabric. Processing conditions for 
effecting drying and curing are well known in the art and need not be 
described in detail here. 
Upon leaving the curing oven 14, the durable press treated fabric is 
directed into and through a second pad bath, generally indicated at 15, 
where the fabric is thoroughly impregnated with an impregnation solution 
16. The impregnation solution 16 is an aqueous solution containing an 
oxidant, preferably one selected from the group consisting of sodium 
perborate, hydrogen peroxide and sodium hypochlorite. 
Upon leaving the pad apparatus 15, the fabric is directed continuously into 
a holding zone formed by a scray apparatus or J-box 17. In the scray the 
fabric is deposited in loose folds to provide a residence time preferably 
of at least about a minute, and desirably longer. Increased holding time 
provides further reduction of released formaldehyde values, and the upper 
limit on holding time is essentially one of practicality. The oxidizing 
agent thus has an opportunity to thoroughly react with the 
formaldehyde-releasing moieties present in the fabric. 
Preferably, the holding of the fabric in the scray 17 is accompanied by 
heating of the fabric so as to promote the reaction of the oxidizing agent 
with the finishing agent. In the specific embodiment illustrated, the 
heating is accomplished by steaming. In this regard, it will be noted that 
the scray 17 includes both a lower wall 17a and an upper wall 17b 
cooperating to form an enclosed chamber. A steam line 18 communicates with 
the enclosed scray for directing live steam into the enclosed chamber. 
Upon leaving the scray 17, the fabric may be further processed as desired. 
In the embodiment illustrated, the fabric is directed through a 
conventional continuous washing range 20, and then into and through a 
continuous dryer apparatus 21, after which the fabric is formed into a 
roll 22 for convenience in storage and shipment. 
It is to be understood that while the use of a heated scray 17 is 
illustrated as being preferred, it is not essential. In many instances, 
adequate destruction of the formaldehyde-releasing moieties can be 
accomplished simply by impregnation without the necessity of an additional 
holding period or further heating. It should also be understood that the 
washing of the fabric following the oxidative treatment is optional, and 
if desired the fabric could be directly subjected to further finishing 
operations without washing, or could be dried. 
It should also be understood that while the drawings have illustrated an 
in-line continuous process, the invention is not limited thereto. For 
example, the oxidative afterwash treatment of the invention is equally 
applicable to batch processing where the fabric is accumulated in batches 
following the durable press curing step, and thereafter subjected to the 
oxidative afterwash. The afterwash treatment may be carried out, for 
example, by placing the durable press treated fabric in a batch dyeing 
machine or beck, for example, into which the oxidant solution is 
introduced. After heating or steaming for a suitable period of time in 
contact with the oxidant solution, the fabric may be washed and further 
processed in a conventional manner. 
A further understanding of this invention can be obtained by reference to 
the following specific example, which is provided herein for purposes of 
illustration only and is not intended to be limiting. 
EXAMPLE 
Samples of a 65 percent polyester/35 percent cotton blend woven fabric were 
treated with an aqueous formaldehyde finish at a wet pick up of 70 
percent, dried at 250 degrees F for 30 seconds and cured at 400 degrees F 
for 20 seconds. Finish bath formulation is shown in Table 1. 
TABLE 1 
______________________________________ 
Aqueous Formaldehyde Finish 
______________________________________ 
Formalin 66 g/l 
Wetting agent 1 g/l 
Softener 20 g/l 
Catalyst 16.5 g/l 
______________________________________ 
Samples were then after-treated with one each of the following: 
water 
2 percent hydrogen peroxide, 1 percent soda ash 
1 percent sodium hypochlorite 
2 percent sodium hypochlorite 
1 percent sodium perborate 
2 percent sodium perborate Treatment of the samples with the oxidizing 
agents used the following procedures: 
1. Impregnated with chemical solution on padder, held at room temperature 
for 15 minutes by hanging vertically, then dried at 250 degrees F for one 
minute. 
2. As Procedure #1, followed by rinsing in warm running water for one 
minute, extracted on padder and then dried at 250 degrees F for one 
minute. 
3. Impregnated with chemical solution on padder, held at 180 degrees F in 
oven for 15 minutes and then dried. 
4. As Procedure #3, except followed by rinsing in warm running water for 
one minute, extracted on padder and then dried at 250 degrees F for one 
minute. 
5. Impregnated with chemical solution on padder, dried at 250 degrees F for 
30 seconds and cured at 400 degrees F for 20 seconds. 
6. Treated in beaker with chemical solution at the boil for 15 minutes, 
then extracted on padder and dried at 250 degrees F for one minute. 
7. Treated in beaker at th boil for 15 minutes, rinsed in running warm 
water for one minute, extracted on padder and then dried a 250 degrees F 
for one minute. 
8. Treated in beaker at 160 degrees F for 15 minutes, extracted on padder 
and dried at 250 degrees F for one minute. 
9. Treated in beaker at 160 degrees F for 15 minutes, rinsed in running 
warm water for one minute, extracted on padder and then dried at 250 
degrees F for one minute. 
Immediately after drying, samples were sealed in bags for subsequent 
analysis of formaldehyde release by AATCC Test Method 112-1975 (Nash 
Reagent Option). The formaldehyde release test results are set forth in 
Table 2. 
TABLE 2 
______________________________________ 
RELEASED FORMALDEHYDE VALUES 
AATCC Test Method 112-1975 
Nash Reagent 
Parts Per Million 
1% 2% 
Per- Per- 
Treatment H.sub.2 O.sub.2 
1% 2% bo- bo- 
Method Water Na.sub.2 CO.sub.3 
NaOCl NaOCl rate rate 
______________________________________ 
1. Open Scray 
1018 177 1131 565 190 117 
15 Minutes 
2. Same + 874 322 824 768 380 286 
Rinsed 
3. 180.degree. Scray 
1565 678 1230 1341 1451 104 
15 Minutes 
4. Same + 1099 574 902 810 454 552 
Rinsed 
5. Pad-Dry- 909 283 666 661 217 24 
Cure 
6. Beaker at 109 0 154 94 64 0 
212.degree. F./15 
Min. 
7. Same + 92 0 116 60 62 0 
Rinsed 
8. Beaker at 161 72 210 227 63 0 
160.degree. F./15 
Min. 
9. Same + 197 73 174 166 92 0 
Rinsed 
______________________________________ 
Control (No Aftertreatment) = 1113 ppm 
From the above tests, the following observations were made: 
1. For the formalin finished samples, after-treatments of hydrogen peroxide 
or 2 percent sodium perborate gave the best results. 
2. Of the procedures tested, boiling for 15 minutes was the most effective, 
followed by heating at 160 degrees F for 15 minutes. 
3. Zero levels of liberated formaldehyde are attainable by oxidative 
aftertreatments. 
In the drawing and specification, there have been set forth preferred 
embodiments of the invention, and although specific terms are employed, 
they are used in a generic and descriptive sense only and not for purposes 
of limitation.