US3573133A - Surface modifications of organic synthetic polyamides using sulfur trioxide - Google Patents

Abstract

DELUSTERED AND IMPROVED SOIL RESISTANT POLYAMIDE FIBERS AND SELF-BONDED WEBS COMPOSED OF POLYAMIDE FIBERS MAY BE PREPARED BY A PROCESS WHICH INCLUDES EXPOSING THE POLYAMIDE FIBERS TO A SULFUR TRIOXIDE ENVIROMENT AND THEN SUBSEQUENTLY REMOVING THE SULFUR TRIOXIDE THERE FROM.

Description

u H- E. HARRIS SURFACE MODIFICATIONS OF ORGANIC SYNTHETIC POLYAMIDES USING SULFUR TRIOXIDE Filed July 7, 1969 2 Sheets-Sheet 1 TAKE-UP WINDER CARR/ER GAS (N2) CONC H2804 FIG. I.

WASHING BATHS (I) a: gjx Z3 9 7 INVENTOR.

HENRY E. HARRIS ywg f ATTORNEY HARRIS INVENTOR. HENRY E ATTORNEY 3,, SURFACE MODIFICATIONS OF ORGANIC SYNTHETIC POLYAMIDES 2 Sheets-Sheet Z H. E. HARRIS USING SULFUR TRIOXIDE March 30, 171

Filed July 7, 1969 United States Patent O U.S. Cl. 156-307 9 Claims ABSTRACT OF THE DISCLOSURE Delustered and improved soil resistant polyamide fibers and self-bonded webs composed of polyamide fibers may be prepared by a process which includes exposing the polyamide fibers to a sulfur trioxide environment and then subsequently removing the sulfur trioxide therefrom.

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a contiriuation-in-part of US. application, Ser. No. 587,506, filed Oct. 18, 1966 and Ser. No. 587,421, filed Oct. 18, 1966, now abandoned.

BACKGROUND OF THE INVENTION (1) Field of invention This invention relates to a method of treating shaped structures containing organic synthetic polyamides and particularly to the preparation of self-bonded webs of polyamide fibers to produce non-woven fabrics and to the delustering of polyamide filaments.

(2) Description of the prior art Heretofore, non-woven structures have been bonded by use of external binders or by softening the fibers with heat, solvent, or plasticizer and subjecting them to pressure while in the softened state. The external binder may be an adhesive substance which is cured after application. mit mav be rendered adhesive after annlication by use of heat, solvent or plasticizer. External binders may be applied as powder, solutions, emulsions, or even in the form of fibers. These methods suffer several disadvantages. The use of an outside binder presents problems in uniform application and limits the properties of the entire web to those of the binder. Thus, for example, if a fiber with a relatively low melting point is used as a bonding material, the temperature conditions to which the Web or resulting fabric may be subjected are limited by the melting point of the binder material.

Autogenous bonding by the previous methods is not easily controlled and frequently tends to alter the aesthetic properties of the web. For example, in solvent bonding, achieveing adequate adhesiveness in the fibers without dissolving the entire web or at least impairing the physical properties thereof is dilficult.

It has been recognized that filaments, films, and other shaped forms of organic synthetic polyamide polymers have extremely smooth surfaces which are too lustrous and transparent for many end uses. In addition, such smooth surfaces lead to undesirable physical processing characteristics in many cases. In commercial practice, pigments such as titanium dioxide (TiO have been added to the polymers before shaping to overcome some of these problems. However, the presence of TiO is detrimental, particularly in ultraviolet radiation where TiO appears to act as a sensitizer for the degradation of many organic polymeric materials. Furthermore, in the case of fibers, the abrasive nature of the pigments contributes to rapid Patented Mar. 30, 1971 'ice wear of guides and other surfaces over which fibers are processed.

Roughening of fiber surfaces by erosion with solvents has been proposed, but control of solvent action is difficult and may cause undesired deterioration of the physical properties of the fibers. Uniformity is also difficult to achieve in methods involving mechanical abrasion of the surfaces, and deterioration of physical strength can prove to be a problem.

With the foregoing problems in mind, the primary objectives of the present invention are to provide bonded and delustered polyamide structures which are free from external bonding agents.

SUMMARY OF THE INVENTION A process for modifying the surface characteristics of organic synthetic shaped polyamide articles by subjecting the shaped articles to an environment of sulfur trioxide (S0 and thereafter removing the sulfur trioxide from the article. While the invention is intended to be extended to any surface modification, the embodiments disclosed are the delustering of nylon filaments and the bonding of touching filaments to form a self-bonded non-woven web.

The bonding of two polyamide structures crossed and under tension at their intersection is accomplished by exposure to sulfur trioxide gas per se or in a carrier medium such as an inert gas or liquid followed by removal of the sulfur trioxide. The sulfur trioxide can be removed either by washing with water or by neutralization with an aqueous solution of a base or with a base such as ammonia in the gaseous state. Preferably, the sulfur trioxide should be maintained at about 20 to 25 C. for uniform treating conditions and handling convenience although bonding can be accomplished at substantially higher and lower temperatures. The reaction rate is a function of the temperature with faster reaction occurring at elevated temperatures.

While aqueous solutions of sulfur trioxide (sulfuric acid) are known solvents for many polyamides, the process of this invention can be carried out under substantially anhydrous conditions, indicating that the bonding process is not dependent upon the formation of sulfuric acid.

To obtain this bonding reaction, the structures must be in very close contact. In the case of two intersecting fibers, this condition may be achieved by holding the fibers crossed under tension. In a web of fibers, it may be accomplished by shrinking entangled filaments after the web has been formed, or by subjecting the web to pressure. Pressing of the web can precede or follow exposure to the sulfur trioxide gas. In practice, the pre-pressing has the advantage that the pressing equipment need not be exposed to the activating gas.

While the mechanism of the bonding is not completely understood, it is believed that it is based on disruption of hydrogen bonds between the polymer chains by for mation of a complex with the amide group of the polyamide. In the polymer art it is well known that many of the physical properties of polyamides depend to a great extent on the intermolecular hydrogen bonds between the CO- and -NH groups in adjacent polymer chains. The intermolecular hydrogen bonds increase properties such as melting point and tensile strength. When these bonds are disrupted by the action of the sulfur trioxide, the polymer chains within the structure become more flexible and tend to shift to relieve the stress caused by tension or pressure on the structure. The complex formation is reversible, and when the sulfur trioxide is removed, the hydrogen bonds reform. In the shifted position of the polymer chains, many of the new bonds are between chains in two different structures. Photomicrographs of cross-sections of filaments bonded by this process show a homogeneous structure at the site of the bond with no indication of a boundary between the two filaments. Further support for this theory lies in the fact that self-bonding polyamide polymers cannot be bonded to polymers which are not self-bonding, such as polyesters and polyolefins, under the conditions of this process. However, two different polyamides which are self-bonding can be bonded to one another.

In order to undergo bonding by this process the polymer needs an adequate concentration of NHCO- (amide) groups which are accessible and attached to groups which do not alter basicity unfavorably. It has been found that polyamides containing some aromatic groups will undergo a bonding reaction, but certain wholly aromatic polyamides do not undergo the reaction despite concentrations of NHCO groups comparable to that in polyhexamethylene adipamide (nylon 66) which bonds very easily. This may result from the rigidity of the structure, from the effect of the aromatic rings on the basicity of the amide group, or from a combination of these effects.

Bonding and/or delustering is accomplished with exposure times which may vary from 0.5 second to several minutes, depending on composition and structure of the materials to be bonded. By regulation of exposure time, depth of penetration of the gas into the individual filaments can easily be controlled and limited to that necessary to obtain the desired result. Optimum time of exposure varies with the polymer composition, the concentration of the activating gas, the filament diameter, and the previous physical treatment of the filaments. In general, finer filaments, because of greater surface area per unit weight, will require a shorter time of exposure than will heavier denier filaments from the same polymer composition. Also, it has been observed that freshly spun filaments which have not been drawn generally require shorter exposure time than drawn filaments.

Removal of the activating gas may be achieved by washing with water or by neutralization with a solution of base or with a gaseous base such as ammonia. Washing may be accomplished by a number of known methods such as passing the treated filaments through a bath or subject ing them to a spray.

The bonded webs produced by this process are characterized by retention of a high percentage of the flexibility of an unbonded web while having a greatly increased tensile strength. The overall orientation of the filaments in the Webs is not significantly altered by the bonding process, and dyeability remains uniform throughout the web.

In its preferred form, the process comprises passing a running threadline or sheet of film through a chamber containing vapors of sulfur trioxide and then into a wash bath or spray to remove all of the absorbed sulfur trioxide.

The sulfur trioxide will not require neutralization if the water washing is sufficient to remove all of this corrosive chemical. When necessary neutralization can be accom plished with any suitable base of sufficient strength. Sodium hydroxide, sodium bicarbonate, and various amines are examples of suitable bases. When it is desirable to avoid passing the threadline through a bath, the neutralizing agent can be an amine of sufficient volatility such as ammonia, to be used in the gaseous or vaporous state.

Large variations in experimental conditions are possible depending on the degree of treatment desired at any particular fiber take-up speed. The denier and compositon of the fiber to be treated will also determine the range of experimental conditions that can be used. Concentrations of sulfur trioxide vapors in the reaction chamber for practical purposes can be varied from a low value of about one mole percent to 100% by variations in the temperature of the liquid sulfur trioxide and the temperature and flow rate of the carrier gas. For low denier filaments treated at slower speed the lower range of the concentration can be use, whereas very high speeds can be used with concentrated sulfur trioxide vapors.

In the examples given, the filament entered the treatment chamber at room temperature. In order to increase the rate of reaction, the filament could enter the treatment chamber at a higher temperature. The desirable temperature will depend on the nature and denier of the filament, the take-up speed, the concentration sulfur trioxide and the degree of treatment desired. Obviously, the melting point of the filamentary material sets an upper limit to the temperature. Conversely, the rate of reaction can be slowed by cooling the filament prior to treatment. In the preferred process, sulfur trioxide vapors are used because of ease of control, but liquid sulfur trioxide can be used.

Delustering is believed to be the result of formation of a complex of the S0 with the amide groups causing a disruption of the hydrogen bonds and a break-down of this complex upon quenching with water causing a surface roughness upon shifting of the polymer chains.

Therefore, it is an object of this invention to provide a method of delustering surfaces of shaped structures of polyamide polymers without adding pigments and without degrading the polymer.

It is a further object to modify the frictional properties of the surface nylon of fibers in an easily controlled process at a rate which is of practical value.

Another object is to provide a method for imparting to certain synthetic polyamide materials a general microscale roughing of the surface thereof which is characterized by micron-sized pits and crevices.

It is another object of this invention to bond shaped polyamide structures free of external bonding agents in the final product, without altering the geometry of the structures.

It is a further object to prepare drapable self-bonded, non-woven fabric structures suitable for use in textile applications.

It is a further object to provide an improved process for preparing self-bonded, non-woven polyamide fabrics in which the bondin is activated by a gaseous material which is subsequently removed.

A still further object is to use polyamide fibers as binder fibers in blends with other classes of fibers, using a gaseous material to activate the bonding properties of the polyamide.

DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a typical arrangement of apparatus having a chamber for treating materials in accordance with the present invention;

FIG. 2 represents an electron photomicrograph at 10,000 which illustrates the pits and crevices imparted to the surface of a polyamide (nylon 66) filament by the sulfur trioxide treatment;

FIG. 3 represents a reflected-light photomicrograph at 200x which illustrates the light scattering ability of a polyamide filament treated with sulfur trioxide compared with a similar untreated filament (left);

FIG. 4 represents a reflected-light photomicrograph showing a polyamide filament delustered by hydrogen chloride treatment (left) and a similar filament treated with sulfur trioxide (right); and

FIG. 5 represents an electron photomicrograph at 10,000 which illustrates the pits and crevices imparted to the surface of a polycaprolactam (nylon 66) filament by the sulfur trioxide treatment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In a preferred embodiment of this invention, bonding of webs is carried out in a continuous process. Freshly spun filaments are attenuated by an air-jet and formed into a random web on a moving foraminous belt. The web is then passed through pressure rolls and into a chamber through which the activating gas is passed. After exposure to the gas the web is passed into a second chamber where the activating gas is desorbed by washing or by neutralization with a gaseous base. If desorption is accomplished by washing, the web is then passed to a drying chamber.

It is not essential that the webs of this invention be composed of polyamide filaments only. Other fibers which are chemically inert to sulfur trioxide may be blended with polyamide filaments to provide fabrics having different physical properties. Webs can be prepared from continuous filaments of polyamide and at least one other filament-forming material. These filament forming materials include synthetics such as the polyesters, acrylics, polyolefins; elastomeric filaments such as spandex; and natural filaments such as rayon and acetate. If desired, the webs may be prepared by known methods of blending staple fibers from staple fiber blends which include the above materials and also natural fibers such as cotton and wool. Web formation of staple fibers may be accomplished on the Rando-Webber or conventional carding machines to form single-layered webs, or multi-layered and cross'laid webs can be formed by known methods. Entanglement of the fibers comprising the web can be achieved by needle punching to cause densification thereof if desired. When these webs which contain a component of polyamide fibers are exposed to the activating gas, the polyamide fibers bond to one another so that the other fibers are held together by physical entrapment. The entrapment, however, permits limited movement of the unbonded fibers which produces better flexibility. As would be expected, the strength of the bonded webs or fabrics decrease in percentage of the polyamide fiber content in the blend.

Referring to the apparatus shown in FIG. 1, there is shown an elongated tubular chamber having access ports for purging a portion of the chamber with an inert gas such as nitrogen. The chamber 10 is further provided with access ports for establishing an atmosphere of sulfur trioxide within the chamber. The vapors were generated by bubbling dry nitrogen through liquid sulfur trioxide as illustrated in FIG. 1. The sulfur trioxide vapors are forced through chamber 10 exit to an aqueous wash bath.

A nylon filament or ribbon 14 is drawn through the gaseous atmosphere in chamber 10 continuously where exposure time is controlled by the take-up rate of the filament. After leaving chamber 10 the filament travels through one or more wash baths to remove the absorbed sulfur trioxide. The wash bath may consist of water, but preferably a Water bath containing a neutralizing agent such as sodium bicarbonate.

The bulk physical properties of the treated filament are affected only slightly when treated in accordance with this invention. Preferably, only the outer surface layers are penetrated in accomplishing the objectives set forth herein. For example, when treating a 15 denier filament having a diameter of about 50 microns the sulfur trioxide penetrates the surface only to the extent of about 2 microns. This slight penetration is suflicient to deluster the filament without materially affecting the physical properties thereof.

The following specific examples illustrate bonding, roughening, and delustering of the surface of fibers by this process, but are not intended to limit the scope of this invention.

EXAMPLE 1 Polyhexamethylene adipamide (nylon 66) which contained no additives such as stabilizers or titanium dioxide was spun into a monofilament of approximately 70 denier and subsequently drawn without finish to about 15 denier.

A portion of this yarn was wound onto a small card, and subjected to gloss measurements. These measurements were carried out using a Hunter Development Laboratory D-16 Gloss Meter. Specular gloss was determined by an adaptation of ASTM Method D52362T using a 45 angle of incidence. The specular gloss is the light reflected at 45 from the sample versus the light reflected from a standard black reflector, and is expressed as a percentage of the latter. Contrast gloss is ratio of specular gloss to the percent of light reflected at 90 from the sample. In both cases, low values express a greater scattering of reflected light, indicating delustering. Values obtained from various samples treated under different conditions are shown in Table I.

TABLE I.GLOSS MEASUREMENTS OF VARIOUS NYLON SAMPLES Several hundred yards of the nylon filament prepared as in Example 1 and in equilibrium with ambient conditions (relative humidity 40-60%; temperature 2326) were exposed to sulfur trioxide vapors for about 1 second by pulling the filament at 90 ft./ min. as a threadline through the treatment chamber containing vapors of sulfur trioxide at room temperature, and subsequently through a neutralizing water bath containing sodium bicarbonate and then through a second bath to rinse the filament. The apparatus is illustrated in FIG. 1.

The vapors were generated by bubbling dry nitrogen at the rate of about 1 liter per minute through liquid sulfur trioxide contained in a gas wash bottle. Assuming that the nitrogen stream is saturated with sulfur trioxide, the concentration of the sulfur trioxide at 20 C. is about 1.1 g. of sulfur trioxide per liter of nitrogen.

The surface characteristics of the treated filament are illustrated in the electron photomicrograph shown in FIG. 2. This surface appears quite tough, without any pattern but is characterized by many pits .and crevices and a general surface roughness on a microscale of around one micron. This surface roughness is responsible for the scattering of incident light and, hence, for the delustered and opaque appearance of the treated filament.

EXAMPLE 3 A sample of 15 denier drawn nylon 6 filament was treated with sulfur trioxide vapors according to the experimental details described in Example 2. The treated filament had a contrast gloss value of 40.4 which is recorded in Table I. The electron photomicrograph shown in FIG. 5 illustrates the roughness imparted to the surface by the treatment.

The reflected-light photomicrograph shown in FIG. 3 gives an additional illustration of the light scattering ability of the treated filament as compared to untreated samples. The filament samples were illuminated using a Leitz Ortholux microscope at a high angle of incidence so that only light scattered by the sample was observed. The untreated filament on the left scattered little light and appears darkest in the photomicrograph. The treated sample on the right scattered much more incident light than the untreated or the semi-dull filaments and therefore appears brightest in the photomicrograph.

A portion of this SO treated filament and of the untreated filament of Example 1 were subjected to a soiling test. Samples of each in knit tubing form were treated with screened local carpet dirt on the basis of 2 g. per 30 sq. in. of tubing. After a standard vacuuming, each sample was tested for brightness on a General Electric West Lynn Spectrophotometer according to ASTM E 308-66. The untreated control lost 33% of its original brightnes as a result of the soil treatment, whereas, the

S treated sample lost only 24% of its original brightness. The brightness values are listed in Table II Physical properties of a sample of this yarn are compared with those of the untreated filament of Example 1 in Table III and show acceptable physical properties after sulfur trioxide treatment.

TABLE III A sample of the 15 denier drawn nylon prepared in Example 1 was exposed to vapors of S0 according to the procedure described in Example 2.

The coefiicient of fiber-to-fiber static friction of the fiber was determined by the following procedure:

One sample of the filament to be tested was mounted to form an inclined plane and a second sample was placed over the inclined element as a weighted loop to act as a slider. The inclined element was tilted until the slider first began to move. The inclined angle 0, is related theoretically to the static coeflicient of friction, ,u between the two filaments by the equation,

tan 19:11.

From this measurement, a value of 0.16 was obtained for the treated filament while a value of 0.08 was obtained for untreated filament. The higher coefficient of static friction of the treated filament can be attributed to its rougher surface.

EXAMPLE 5 A sample of the denier drawn nylon prepared in Example 1 was exposed to vapors of sulfur trioxide according to the procedures of Example 2 with the exception that the container of liquid sulfur trioxide was heated using an infrared bulb to keep the liquid at room temperature C.) or slightly above. The concentration of sulfur trioxide vapors was therefore increased over that present during the treatment of Example 2.

The treated filament had a very highly delustered and opaque appearance and retained its original strength. Gloss measurements showed that the sample was indeed highly delustered having a contrast gloss value of only 20.5. The significance of this number can be realized by examination of the data in Table I. Electron photomicrographs indicated in FIG. 2 an extreme degree of roughness imparted to the filament surface by this treatment.

EXAMPLE 6 A sample of the 15 denier drawn nylon filament of Example 1 was exposed to sulfur trioxide vapors according to the procedure of Example 2 with the exception that the filament was passed through a glass tube containing an atmosphere of gaseous ammonia, obtained from a pressurized cylinder, instead of through the water bath containing sodium bicarbonate. The resulting filament was comparable in appearance to the treated filament of Example 2.

EXAMPLE 7 A small sample of experimental nylon 66 film, about 0.5 mil in thickness was exposed to vapors of sulfur trioxide for about 1 second. The film lost its original clarity and became opaque upon exposure to water. The vapors were generated by bubbling dry nitrogen at the rate of about one liter per minute through liquid sulfur trioxide at room temperature.

EXAMPLE 8 A sample of knit tubing prepared from the 15 denier drawn nylon 66 filament of Example 1 was placed in a vessel which was subsequently partially evacuated and refilled with nitrogen containing about 25 mole percent S0 vapors. The tubing was immediately removed from the vessel after about /2 second exposure and washed in water. The filaments of the tubing were delustered and opaque in appearance after the water washing.

EXAMPLE 9 Two short lengths of drawn 15 denier filaments of polyhexamethylene adipamide (nylon 66) without finish were mounted on a glass frame so that pressure was developed at the cross-over point. The glass frame was placed in a resin flask into which nitrogen containing approximately 50 percent by weight of sulfur trioxide was subsequently passed. The gaseous sulfur trioxide was introduced into the nitrogen stream by bubbling dry nitrogen through the liquid at room temperature at a rate of about one-half liter per minute. After an exposure time of one second, the glass frame was removed, and the filament was washed immediately in water to remove all traces of sulfur trioxide.

The filaments were bonded together by the treatment to form a strong, flexible bond. Also, the filaments were delustered by the treatment.

EXAMPLE 10 Small strips of experimental nylon 66 film about 0.5 mil in thickness were mounted on a glass frame so that pressure was developed at the cross-over area. As in Example 9, the frame was placed in a resin flask into which nitrogen containing about 50 percent by weight of sulfur trioxide vapors was subsequently passed. After an exposure time of about one second the frame was removed and immediately washed in water to remove sulfur trioxide from the nylon film. The strips of film were bonded together and had lost their original clarity, becoming white and opaque.

EXAMPLE 1 l Strips of nylon 66 film were mounted as described in Example 10. The frame was placed in a resin flask that was subsequently heated with an infrared lamp while dry N was passed through the system. The apparatus and the nylon film were dried in this manner before nitrogen containing sulfur trioxide vapor was passed into the flask. After an exposure time of two seconds, the frame was removed and washed in water to remove all traces of sulfur trioxide. The film strips were bonded together and were made opaque by the treatment.

EXAMPLE 12 A web of continuous filament nylon 66 was made by rapidly attenuating filaments directly from a melt spinning jet and forming a non-woven layer of continuous filaments on a screen. The filaments which were 2 denier per filament, had a tenacity of 3.8 grams per denier with 134 percent elongation at break. A sample of the web was pressed at C. and 220 p.s.i.g. between flat plates for 10 seconds to obtain contiguity of the filaments. A 4" x 8" sample of the web was then placed on a screen mounted in a resin flask. The sample was held in place on the screen face by the partial vacuum created by an attached water aspirator. A stream of nitrogen containing about 50 percent by Weight of sulfur trioxide was then passed into the flask, where it penetrated the sample and exited through a water aspirator. After an exposure time of 10 seconds, the sample was quickly removed from the flask and immediately washed in water to remove all traces of S The resulting web was strongly bonded. Results obtained from a test sample cut from the diagonal are listed in Table I below.

TABLE I Web Wt.-3.2 oz./ sq. yd.

Bending length1.15 inches Breaking strength--27.9 lbs/inch Elongation at break-114% The breaking strength of the pressed Web before bonding was approximately 3 pounds/ inch. Breaking strengths of samples one inch in Width were determined on a standard tensile tester using a -inch jaw separation and a cross-head speed of cfive inches per minute. The bending length was determined according to the standard procedure of ASTM Test D-138855T.

EXAMPLE 13 A web consisting of equal weights of polyester (Dacron) and nylon 66 staple fibers was prepared by a Shirley Miniature Card. The nylon and polyester fibers were both 3 denier per filament and 1 /2 inches in length. The web was subjected to one pass through a Hunter Laboratory Needleloom to give it some integrity. The web was then extracted to remove finish, dried, and pressed between fiat plates at 200 C. and 220 p.s.i.g. in order to press the filaments into close contact. The web had a breaking strength in the machine direction of 3 lbs./in.

A sample of the web was then exposed to vapors of sulfur trioxide and subsequently washed in Water in the manner described in Example 12.

The resulting bonded web was found to have properties in the machine direction as shown in the Table II below:

TABLE 11 Wet wt.2.6 0z./sq. yd. Bending length0.86 inch Breaking strengthl3.4 lbs./in. Elongation at break88% What is claimed is:

.1. A process for preparing self-bonded structures which comprises:

(a) forming shaped articles from an organic synthetic polyamide polymer,

(b) exposing the shaped articles to an atmosphere of sulfur trioxide to allow surface absorption of said sulfur trioxide,

(c) compressing said shaped articles to cause contact between said articles,

(d) washing the shaped articles to remove the sulfur trioxide whereby bonds are formed between the contiguous surfaces of the article and (e) maintaining contact between said articles during the removal of said sulfur trioxide from said articles.

2. The process of claim 1 in which the polyamide articles are in the film form.

3. The process of claim 1 in which the polyamide articles are in the fiber form.

4. A process for producing a self-bonded non-woven web which comprises:

(a) forming said web, said web being comprised of at least 10 percent by weight of organic synthetic polyamide fibers,

(b) consolidating the web to cause contact between closely spaced fibers,

(c) exposing the compacted non-woven web to an atmosphere of sulfur trioxide to allow penetration of the surface of said nylon fibers with said sulfur trioxide,

(d) removing the sulfur trioxide from said nylon fibers by immersing the web in an aqueous solution of a base and (e) maintaining contact between touching nylon fibers during the removal of the sulfur trioxide therefrom to cause bonding between said touching nylon fibers.

5. The process of claim 4 in which the exposure time is at least one second.

6. The process of claim 4 in which the atmosphere is comprised of a mixture of an inert gas and sulfur trioxide gas.

7. The process of claim 4 in which the fibrous batt is compressed after exposure to the gaseous atmosphere.

8. The process of claim 4 in which the fibrous web is composed of nylon fibers and at least one other type fiber.

9. The process of claim 7 in which the fibrous batt is composed of from 10 to percent nylon fibers and 90 to 10 percent polyester fibers.

References Cited UNITED STATES PATENTS 3,102,323 9/1963 Adams 26040 3,216,965 11/1965 Cipriani 260-37 3,253,880 5/1966 Lawson et al 8-1l5.5

REUBEN EPSTEIN, Primary Examiner US. Cl. X.R.

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