WO1994002058A1

WO1994002058A1 - Carpet having improved appearance retention

Info

Publication number: WO1994002058A1
Application number: PCT/US1993/005991
Authority: WO
Inventors: Christopher E. Osuch
Original assignee: Allied-Signal Inc.
Priority date: 1992-07-20
Filing date: 1993-06-22
Publication date: 1994-02-03
Also published as: EP0651620A1

Abstract

A carpet having improved appearance retention characteristics having a primary backing and heat set pile fiber formed of a polymeric material in which polymer chains are cross-linked.

Description

CARPET HAVING IMPROVED

APPEARANCE RETENTION

BACKGROUND OF THE INVENTION

1. Field of the invention

This invention relates to carpet having improved appearance retention characteristics. Another aspect of this invention relates to cross-linked fibers for use in the fabrication of the carpet of this invention and in processes for forming said cross-linked fibers.

2. Prior Art

Crosslinked polymer materials are known. See for example Khim Volokna pp. 20-32 (1965); U.S. Patent Nos. 3,801,347 and 3,286,322; DE 2,707,066; DE 1,444,076; BP 1 565 820 and Chem. Vlakna, 1971, 21 pp. 28-33.

A desirable characteristic of carpet is that the carpet retains its appearance when subjected to normal traffic. Unfortunately, most carpet made from

conventional carpet fibers lacks good appearance retention characteristics because the individual tufts of the carpet lose ply-twist when the carpet is

subjected to normal traffic. This loss of ply-twist causes tuft ends to open up or "bloom", lose tuft endpoint definition and become entangled with

neighboring tuft ends which gives the pile a matted appearance and causes the pile to develop "walkout" in traffic areas. The term "appearance retention" is used to describe the ability of carpet to retain its initial appearance with respect to tuft endpoint definition and lack of matting after being subjected to repeated traffics, where each "traffic" is the occurrence of an individual walking across the carpet.

Efforts in the past to improve the appearance retention characteristics of carpet have not proven entirely satisfactory. It is apparent, therefore, that carpets having improved appearance retention

characteristics and a pleasing appearance and hand would constitute a major contribution in the art.

SUMMARY OF THE INVENTION

The present invention is directed to an improved carpet of the type having a primary backing and heat set pile fiber (tuft) in the form of individual lengths of plied fiber, each of which projects upwardly form said backing terminating at a cut end, the improvement comprising pile fiber formed from a crosslinked

polymeric material having an effective cross-link density. The carpet of this invention has several advantages. For example, the carpet of this invention exhibits improved appearance retention. The carpet of this invention also has a pleasing initial appearance and hand.

This invention also relates to (an improved process of forming cross-linked fibers which provide carpets having improved appearance retention which comprises treating a twisted and heat set fiber formed from a polymeric material with an effective

crosslinking agent under conditions suitable for crosslinking an effective number of polymer chains to form a fiber comprised of a crosslinked polymeric material having an effective cross-link density) . Yet another embodiment of this invention relates to the crosslinked fiber formed by the process of this

invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The carpet of this invention comprises as an essential component fiber formed from a crosslinked polymeric material having an effective "cross-link density" in the amorphous or non-crystalline regions of the material. As used herein, the term "fiber" means multifilament fiber or monofilament fiber and includes individual staple fibers or continuous fiber; the term "crosslinked polymeric material" means a polymeric material in which two or more polymeric chains are crosslinked by a "crosslinking moiety; the term

"crosslinking moiety" means a multivalent moiety which links two or more polymer chains together by ionic bonds, covalent bonds or a combination thereof; and the term "crosslink density" means the number of cross-linking occurrences per chain, where cross-links exists between two linear or branched polymer chains to form a network ("See "Principles of Polymer Chemistry," P.J. Flory, Cornell U. Press, Ithaca, NY 1973).

The crosslink density in the amorphous regions of the polymeric material forming the fiber component of the carpet is critical. While we do not wish to be bound by any theory, it is believed that the appearance retention characteristics of the carpet of this

invention result from use of a crosslinked polymeric material having an effective crosslink density in the amorphous regions of the material. If the cross-link density is less than the effective cross-link density the carpet does not exhibit the desired appearance retention characteristics and where the cross-link density is greater than the effective cross-link density then the carpet does not exhibit the desired hand. In general, the polymeric material used to form the fiber has a crosslink density in its amorphous regions of from about 1 to about 20. In the preferred embodiments of the invention, cross-link density is from about 3 to about 15. The crosslink density is more preferably from about 4 to about 5 and is most preferably about 7.

The crosslinking moiety employed to crosslink the polymeric material may vary widely and may be a crosslinking moiety which crosslinks by way of covalent bonds, ionic bonds or a combination thereof. The crosslinking moiety employed in any situation will usually depend on the chemical structure and reactivity of the polymer chains of the polymeric material. For example, those polymeric materials having polymer chains containing anionic moieties or cationic moieties such as sulfonated aryl groups, as for example,

sulfonated styrene or sulfonated pyridine, carboxylate groups or neutralized forms thereof, as for example, methacrylate groups or acrylate groups and the like; tetra alkyl anmonium groups; protonated amine groups; and the like can be crosslinked by way of ionic

moieties such as metal cations as for example

monovalent cations such as alkali metal cations (e.g. sodium and potassium); multivalent cations such as alkaline earth metal cations (e.g. calcium and

magnesium), Group IVa and Group IIIb metal cations (e.g. zirconium and aluminum) and the like; and low molecular weight polyanionic molecules such as

polyphosphates, polysulfates, poly carboxylates, and the like. Those polymeric materials in which the polymer chains contain nucleophilic or electrophilic moieties such as pendant ester, carboxylic acid, sulfonic acid, urethane, hydroxy, mercapto or amino functions can be crosslinked by way of reaction with complementary covalent crosslinking moieties formed from displacement reactions, addition reactions and the like such as aliphatic or aromatic compounds having two or more moieties select from the group consisting of acids, esters, hydroxy, amino, isocyanate and the like. Examples of such polymeric materials include natural polymeric materials as for example celluloses (rayon), cellulose esters such as cellulose acetate and

cellulose triacetate; proteins such as casein,

groundnut protein, zein, soya bean protein and collagen; and synthetic polymeric materials such as polyamides as for example nylon 6, nylon 6,6, nylon 11 and nylon 6, 10; polyesters such as poly (ethylene terephthalate) or poly (1,4-cyclohexylene dimethylene terephthalate) which include or have been derivatized with a suitable nucleophilic or electrophilic group such as amino, hydroxy, ethenyl, ethynyl, isocyanate, ureido, dienyl, sulfhydryl, halo, carboxylic acid ester, cyano and the like; polyvinyls and polyolefins, such as poly(acrylonitrile), poly(vinyl chloride), poly (vinylidene chloride), poly(vinyl alcohol), poly(vinyl styrene), poly(vinylidene dinitrile), poly(ethylene) and poly (propylene) which have been derivatized with a suitable nucleophilic or electrophilic group such as amino, hydroxy, ethenyl, ethynyl, isocyanato, dienyl, sulfhydryl, ureido, halo, carboxyester, cyano or like groups and/or which includes one or more such

nucleophibic or electrophibic groups in the polymeric chain such as one or more double bonds, sulfone, amide, imide, ester, amine or like linkages; polyurethanes such as those made from polyisocyanates and polyols by methods known to those skilled in the art, (see for example "The Encyclopedia of Polymer Science and

Engineering", 2nd Ed, Vol 13 p. 2 & 3); and polyureas such as those described in "The Encyclopedia of Polymer Science and Engineering", 2nd Ed. Vol. 13, p. 212. In the preferred embodiments of the invention, the polymer is crosslinked covalently by a divalent organic moiety such as an alkylene, alkenylene, alkynylene or arylene group which may include various functional groups containing one or more heteroatoms such as -O-, -N(R)- (where R is hydrogen or alkyl) ,-S(O)₂-, -C(O)-, -C(O)O-,-N(H)C(O)-, -N(H)C(O)N(H), -, -S-, -S₂- and the like. In the more preferred embodiments of the invention, useful polymeric materials are those which include nitrogen in the polymeric backbone substituted with a displaceable group (e.g. hydrogen) as for example a polyamides (e.g. nylon 6, and nylon 6,6,) and polyurethanes, and the crosslinking moieties are alkylene or alkenylene groups which may optionally include a divalent oxygen group. In the most preferred embodiments of the invention, useful crosslinking moieties are divalent alkylene of from 1 to about 7 carbon atoms (preferably methylene or methylene substituted with one or more alkyl groups of from 1 to 4 carbon atoms), or such alkylene groups which include one or more divalent ether like oxygen groups (preferably divalent methyleneoxymethylene) or methyleneoxymethylene in which the methyleneoxy moiety, the methylene moiety or a combination thereof is substituted with alkyl having from 1 to about 4 carbon atoms); and the polymeric material is a polyamide

(preferably nylon 6, nylon 6,6, nylon 11, or nylon 6,10, more preferably nylon 6 or nylon 6,6 and most preferably nylon 6).

The fiber for use as a component of the carpet of this invention may have been subjected to various kinds of processing to which conventional carpet fibers are subjected. For example, the fibers may have been drawn, textured, twisted, caliled, heat set, tufted or dyed. Such carpet fiber treatment processes are well known in the art and will not be described herein in great detail. See for example "Carpets", by G.

Robinson, 1966, Pitman and Song or "Textile Floor

Covering" by 6.H Crawshow and J. Ince, and Textile Progress (1977), 9, issue No. 2 pp. 1-80.

The fibers may consist of continuous fibers or staple fibers. Because of a number of factors known to those of skill in the art including ease of manufacture and the like, the fibers are preferably continuous fibers. If desired, the carpet fibers may consist of a mixture (blend) of carpet fibers having, for example, different cross-sectional shapes and/or different deniers and/or different lengths and/or different polymer composition (e.g. nylon 6 or nylon 6,6) for the purpose of providing, for example, special dyeing effects or to improve the economics and/or luster and/or body of the carpet.

The crosslinked fibers for use in the carpet of this invention may be manufactured by any suitable conventional method for crosslinking a polymeric material. See for example "Chemical Fiber",

Encyclopedia of Chemical Technology 3rd Ed. (by Kirk Othmer), Vol. 10, page 148.

The fiber is preferably crosslinked by treating a twisted fiber with an appropriate crosslinking agent which is capable of crosslinking said fiber. Suitable crosslinking agents will depend on the chemical

reactivity of the polymer forming the fiber. Useful cross-linking agents and processes for use of such agents are well known in the art and will not be described herein in great detail. See for example, R. Ballo et al. Acta. Chim. Acad. Sci. Hung. (1963) 39 253-70 "Effect of formaldehyde on the stress and strain properties of polyamide", T.L. Cairns et al. J. Am. Chem. Soc. (1949) 71 655-7 "The reaction of N-methylol polyamides", J.G. Frick and R.J. Harper J. Appl. Poly. Sci. (1982) 27 293-8 "Cross-linking cotton cellulose with aldehydes", D.T. Grubb and F.R. Kearney J. Appl. Poly. Sci. (1990) 39 695-705 "Modification of gel-drawn poly(vinyl alcohol) fiber with formaldehyde", A.Kh.

Khakimova et al. Khim. Volokna (1965) 29-32 "Preparing cross-linked polyamide fibers", Y. Minoura and M.T. Sukara J. Appl. Poly. Sci. (1968) 12 2509-31 "Cross-linking of rubber with aldehydes", G. Oster J. Poly. Sci. B: Poly. Letters (1964) 2 1181-2 "Photochemical cross-linking of non-aqueous polymers", E. Perry and J. Savory J. Appl. Poly. Sci. (1967) 11 2473-83

Modification of nylon-66 with diisocyanates and di-acid chlorides I. Chemical Reaction", and I.K. Varma et al. J. Appl. Poly. Sci. (1973) 17 2097-108 "Modification of nylon-6 by organochlorosilanes. I. Chemical Reactions".

In the preferred embodiments of the invention where the fiber is a polyamide such as nylon 6,6 or nylon 6, the crosslinking agent is an aliphatic

aldehyde, preferably formaldehyde. In these preferred embodiments, the cross-linking process can be carried out employing a number of procedures using the twisted fiber, either as the fiber before incorporation in the carpet or after incorporation in the carpet. It has been discovered that cross-linking the fiber before the fiber is twisted causes the resulting carpet to wear more quickly than carpet where the fiber is not cross-linked. While we do not wish to be bound by any theory, it is believed that the cross-links must form or be re-formed after the yarn has been twisted if good wear is to be obtained. Otherwise, the yarn may untwist when walked on. The cross linked fiber can conveniently be prepared by treating the twisted fiber with the cross-linking agent, such as formaldehyde in the gaseous phase under conditions suitable for cross-linking the fiber. For example, in a representative procedure, the twisted nylon fiber, either as the fiber or as the carpet, is placed into a vacuum fiber

treating chamber for a time sufficient to remove all or substantially all of the moisture. The fiber treating chamber is evacuated and kept under live vacuum, and is vented with dry inert gas (e.g. argon or nitrogen) for a time necessary to remove the desired amount of water. The amount of cross-linking agent, (e.g.

paraformaldehyde) required to provide the desired cross-link density is put into the fiber treating chamber which is then re-evacuated. When formaldehyde is the cross-linking agent dry HCl gas is introduced into the fiber treating chamber. After exposure of the twisted polyamide (e.g. nylon 6,6 or nylon 6) fiber to the dry HCl for time sufficient for the fiber to absorb the desired amount of HCl, the still sealed and

evacuated fiber treating chamber is put into an oven at a temperature and for a time sufficient to obtain the desired crosslink density. The fiber treating chamber is vented with a suitable inert gas such as argon or nitrogen and the crosslinked fiber or carpet containing the crosslinked fiber is removed. Lastly, the cross-linked fibers are washed in suitable base, such as an aqueous 50:50 NaHCO₃-Na₂CO₃ solution, to neutralize and remove the remaining HCl, rinsed and air dried to provided cross-linked fibers having the desired cross-link density.

In another embodiment of the process of this invention, the cross-linked fibers can be prepared by treatment of the fibers, either as the fiber or in a carpet, in a solution process. For example, polyamide fiber such as nylon 6 or nylon 6,6 fiber may be crosslinked by treatment with formaldehyde in a solution process. For example, a treatment reactor can be charged with a suitable solvent for formaldehyde such as toluene and the like, and an amount of dry HCl and para formaldehyde sufficient to provide the desired crosslink density. To the solution is added the fiber in any suitable form i.e. fiber or carpet. The reactor is sealed and heated in an inert atmosphere such as nitrogen or argon optionally with stirring at a temperature and for a period of time sufficient to crosslink the fiber to the desired crosslink density. The fiber is removed from the reactor and is washed with a suitable base such as 50:50 aqueous NaHCO₃-Na₂CO₃ solution to neutralize and remove residual HCl. The crosslinked fiber is then rinsed two times with

deionized water and air dried to provide fiber having the desired crosslink density.

In the preferred embodiments of the invention, the fiber is crosslinked in a modified aqueous process. In a preferred embodiment of this procedure, a reactor is charged with a suitable cross-linking agent for

polyamides (e.g. nylon 6 and nylone 6,6) as for

example, paraformaldehyde. The mixture is heated to a suitable temperature preferably 70-80ºC. Then

concentrated HCl is added, and the mixture is stirred and heated until the solution becomes clear to form a cross-linking composition. The twisted polyamide fibers, or a carpet formed from the fibers is place in a suitable cross-linking reaction vessel. The

crosslinking composition is then continuously

circulated across the fibers using a suitable

circulating means such a peristaltic pump fitted with tubing, for a time and at a temperature sufficient to achieve the desired crosslinking density. The

crosslinking composition may be heated to the desired crosslinking temperature employing any conventional heating means as for example by passing through a heat exchanger made from a glass condenser set a temperature designed to provide a fiber treating solution of the desired temperature. For example, The heat exchanger can be heated with a recirculating water bath set at 75ºC, giving a stabilized temperature in the tank of about 45ºC. The fibers are exposed to recirculating crosslinking composition at a suitable temperature (preferably about 45ºC) for an effective period of time, as for example, for from about 0.5 hrs. to about 4 hrs. After treatment, the crosslinking composition is pumped away and water is recirculated across the fibers, without heating. The washing step is

preferably repeated at least one additional time and the fibers are suspended for time to allow the water to drain and to allow the fibers to dry. The fibers are heated in a "vacuum" oven for a time period and at a temperature sufficient to complete the crosslinking reaction. For example, in one preferred embodiment of the invention, the fibers are heated to a temperature of about 95°C for about 8 hrs. A brisk flow of dry inert gas, such as nitrogen, is passed through the oven using the vacuum port as inlet and the vent port as outlet. A glass tube is preferably fitted inside the oven to insure that the flow passes from front to back. The flow of inert gas purges water vapor, HCl and formaldehyde from the oven. After a suitable time, the heat is turned off, but the nitrogen flow is left on a lower flow rate, while the oven is cooled down. After the oven has cooled, the carpet or fiber is removed and soaked in a base such as NaHCO₃ solution to neutralize any remaining HCl, washed once with fresh H₂O and dried to form a crosslinked fiber having the desired

crosslink density.

The crosslinking density is directly proportional to the concentration of the crosslinking agents, the type and the reactivity of the cross-linking agent and the efficiency of the cross-linking reaction. In general, to prepare fiber having relatively high crosslinking density the concentration of the

crosslinking agent is relatively high and to prepare carpet with lower cross-link density the crosslinking agent concentration is relatively low. In general, the amount of crosslinking agent is at least about 1 mole % based on total number of reactive moieties in the polymer material. For example, in the case of the preferred aliphatic polyamides the reaction moiety is the recurring amide linkages. The amount of

crosslinking agent is preferably from about 1 to about 5000 mole %, more preferably from about 100 to about 5000 mole % and most preferably from about 1000 to about 4000 mole % on the aforementioned basis.

Process temperature may vary widely depending on the reactivity of the polymer forming the fiber and the crosslinking agent. In the preferred embodiments of this invention employing the preferred polymeric material (preferably nylon 6 or nylon 6,6) and

crosslinking agents (preferably formaldehyde), reaction temperatures are equal to or less than about 200ºC. Reaction temperatures are more preferably equal to or less than abut 100ºC and most preferably from about 50ºC to about 75°C.

Contact times may vary widely and usually depend on factors known to those of skill in the art such as reactivity of the polymer forming the fiber and the crosslinking agent, reaction temperature and the like. In the preferred embodiments of the invention reaction times can be as long as twenty-four hours or more or as short as one or two minutes. More preferred reaction times are from about 5 minutes to about 5 hours, and most preferred reaction times are from about 30 minutes to about 3 hours.

The carpets of this invention may be formed entirely of the crosslinked fibers of this invention. The carpet of this invention may also contain in addition to the crosslinked carpet fibers other fibers so long as the carpet exhibits the above-mentioned appearance retention characteristics. For example, carpet may contain such other fibers made from wool, cotton, metal, or carbon, or fibers that contain additives such as carbon black or titanium dioxide. It is also contemplated that the fibers may include conventional fiber additives such as delustering agents (e.g. titanium dioxide), dyes and colorants and fiber finishers, and that all or a portion of the fibers of the carpet of this invention may be coated with

materials such as fluorocarbons and/or stain blockers for the purpose of improving the soil and stain

resistance of the fibers.

Other components of the carpet of this invention such as the primary backing, secondary backing, latex for attaching the secondary backing, and the like are conventional and one or more of such conventional components can be used. Moreover, the carpets of this invention can be of any conventional style, as for example saxony carpets, greige carpets, or thin cut pile tufted carpet made in the conventional manner with crosslinked fibers of this invention instead of

conventional carpet fibers. Conventional carpet components, carpet styles and carpet manufacturing techniques are well known in the art and include those described in more detail in "Textile Floor Coverings" by G.H. Crawshaw and J. Ince, supra.

The carpet of this invention can be used for conventional purposes. For example, the carpet can be used as a floor covering, wall coverings and the like.

The following specific examples are presented to more particularly illustrate the invention and are not to be construed as limitations thereon.

EXAMPLES 1 - 19

Examples 1 through 19 describe the preparation of cross-linked nylon fiber, in the form of greige carpet, according to the aqueous method of the invention. A summary of these examples is set forth in the following Table I.

Example 1:

Aqueous, acidulated, formalin was prepared by warming a slurry of paraformaldehyde powder in aqueous hydrochloric acid. In the present example 560 g of paraformaldehyde, 70 ml of concentrated hydrochloric acid and enough water to make a total, final, volume of 1435 ml were slurred together and heated to 90°C until the paraformaldehyde had dissolved. The solution was cooled to room temperature.

A piece of "greige" carpet 9" by 12" (machine direction by transverse direction) was placed into a plastic container. The greige carpet, a tufted-cutpile carpet backed only with polypropylene primary backing, face weight 32 oz/sq. yard, had been

manufactured from 1189 denier doubled nylon-6 yarn twisted 3½ twists per inch and heat set at 270°F using the Superba process. The tufts were stitched 9 per inch and the needles were spaced 6% per inch. The carpet was acid mock dyed before the cross-linking treatment, although that step is not required by the invention.

The room temperature formalin solution was poured over the greige carpet, completely immersing it. This was allowed to stand at room temperature for 4 hr 5 min, after which time the formalin was poured off and the carpet washed 3 times with 2 liters of water each time. After being hung to drain for 15 min the carpet was left overnight flat on an absorbent surface, such as a sponge, to dry.

The following day the carpet was put into a vacuum oven which was evacuated and heated to 90°C for 14 hr. This is included in Table I as example number 1.

Examples 2 and 3:

The fibers of example 2 were prepared similarly to example 1 except that no formalin was used. In example 3 the fibers were not treated in any way. Examples 2 and 3 are included in Table I.

Examples 4 through 8:

The samples in examples 4 through 8 were prepared in a manner similar to example 1 except that a metal tray, rather than a plastic tray, was used as the reaction vessel. In addition, the sample prepared in example 4 was washed with methanol two times, after the three water washes, and then dried. Examples 4 through 8 are included in Table I.

Examples 9 through 19:

The fibers of examples 9 through 19 were prepared similarly to the fibers of example 1 except that the formalin solution was pumped through the reaction vessel during the formalin soaking step. This is indicated in Table I by "Flow" as opposed to "Static" under the heading "Soaking Conditions." Also, the baking step performed during examples 9 through 19 was not done under vacuum, but rather under a flowing stream of dry nitrogen gas to purge volatile products from the oven. The greige carpet was supported on a glass-rod frame so vapors could move freely around it. Finally, a bicarbonate washing step (15 g NaHCO₃ per 5 liters water) was added in examples 10 through 19. The purpose of this step is to remove residual acid from the fibers. The use of this wash step is indicated in Table I by "Yes" under the heading "Bicarbonate Wash" and the wash was done within 24 hours of the final baking step.

EXAMPLES 20-27

Examples 20 through 27 illustrate using a non-aqueous solvent during the treatment process. Note that using this method of the invention it is not necessary to bake the carpets after the treatment as they are already cross-linked at that time.

Example 20:

Example 20 depicts the cross-linking of nylon fibers in the form of greige carpet using the non-aqueous, toluene solvent, method of the invention. A piece of greige carpet 11" by 24" was submerged in a previously prepared solution consisting of 3.75 liters of 2.0 × 10^-2 molar HCl in toluene and 11.36 grams of suspended, finely powdered paraformaldehyde. The reactor vessel was a 4 liter resin kettle approximately 13 cm in diameter by 34 cm high and the carpet was rolled up, tufts toward the inside, so that it would fit into it.

After carpet immersion, the reactor was allowed to stand at room temperature for 5 minutes. Then it was placed into a preheated boiling water bath, a

previously fitted stirrer was started, and argon was slowly flushed over the surface of the toluene. The reactor was heated in the bath for 50 minutes and it was then removed, the toluene was poured out and the carpet was taken out, unrolled and allowed to air dry.

After air drying for 2 hours the carpet was washed with bicarbonate solution as in examples 11 to 19 above. Example 20 is included in Table II.

Examples 21 to 27:

The same procedure was followed as in example 20 except that the amount of paraformaldehyde used was varied. These examples are summarized in the following Table II.

EXAMPLES 28-29

Example 28 illustrates the treatment of nylon fibers in the form of greige carpet with gas phase formaldehyde. Example 29 is the control experiment for these fibers.

Example 28:

A 12" by 24" piece of greige carpet was loosely rolled up (tufts facing inward) and was placed into a large vacuum desiccator. The weight of the carpet was about 240 grams. The air was removed from the

desiccator and pumping was continued for 7 hours, to remove water from the fiber. The desiccator was then vented with dry nitrogen. 1.213 grams of finely powdered paraformaldehyde was placed into the

desiccator in a small beaker. The desiccator was reevacuated and then 5 millimoles of HCl gas were allowed to pass into the desiccator and it was sealed off.

(The HCl was generated by addition of 10 millimoles of NaCl to 15 ml concentrated H₂SO₄; a 50% yield and transfer efficiency was assumed.) The desiccator was put into a preheated oven at 115ºC for 10 hours. The desiccator was vented with dry argon and the carpet was allowed to cool. Finally the carpet was washed in bicarbonate solution as in example 10.

Example 29:

A 12" by 24" piece of greige carpet was cut. No other treatment was given to it and it served as a control for example 28.

EXAMPLE 30

Example 30 illustrates the treatment of nylon fiber in the form of knitted sleeve with the gas phase formaldehyde method of the invention.

Example 30:

The same procedure was used as in example 28 to cross-link singles yarn knitted into the form of a sleeve, except for the following changes: 1. A larger portion of paraformaldehyde, 3.40 grams, was used; 2. 14 millimoles of HCl were used (assuming 50% yield from 1.58 g NaCl and 15 ml H₂SO₄). These changes reflect the higher mass of the sleeve, 667 g, relative to the greige carpet of example 28. The singles yarn was of the same type as the yarn used to make the greige carpets described in examples 1 through 29.

EXAMPLE 31

Example 31 illustrates the treatment of nylon fiber in the form of yarn skeins with the gas phase formaldehyde method of the invention.

Example 31:

The same procedure was used as in example 30 except for the following changes: 1. 1.89 grams of paraformaldehyde were used, and; 2. 7.5 millimoles of HCl were used (assuming 50% yield from the reaction of 0.877 grams of NaCl with 15 ml H₂SO₄). These changes reflect the weight of the yarn skeins, 370 grams, relative to that of the sleeve. These skeins were made from doubled yarn which had been twisted from singles yarn and heat set in a manner similar to the yarn used to manufacture the greige carpets of examples 1 through 29.

EXAMPLE 32

Example 32 illustrates the treatment of nylon fiber in the form of yarn skeins using the aqueous formalin method of the invention.

Example 32:

Skeins of doubled yarn were treated using aqueous formalin in a manner similar to example 10, except that the skeins were placed into the cylindrical reactor described in example 20 and the formalin was pumped from bottom to top during the reaction period. In addition, the skeins were put into the oven without the glass-rod frame. These skeins were made from doubled yarn which had been twisted from singles yarn and heat set in a manner similar to the yarn used to manufacture the greige carpets of examples 1 through 29.

EXAMPLES 33-61

Examples 33 through 61 depict the preparation of test carpets from the fiber samples prepared in examples 1 through 32. A summary of these examples is shown in the following Table III.

Example 33:

The treated greige carpet of example 1 was prepared for wear testing by first coating its back with latex and applying a jute secondary backing. The latex was cured by baking in an oven following the directions of the latex supplier. The back-coated carpet was then lightly sheared to even the carpet's surface. This carpet sample was then ready for floor wear testing.

Examples 34 through 61:

Each of these examples followed the procedure of example 33, except as noted in Table III fibers described in examples 2 through 29 were used. EXAMPLES 62-64

Examples 62 through 64 depict the preparation of test carpets from the yarn samples prepared in examples 30, 31 and 32.

Example 62:

The yarn prepared in example 30 was de-knitted and wound onto two packages. These two packages were cabled together, twist at 3% turns per inch and heat set at 270°F using the Superba process. The doubled, heat set yarn was wound onto 65 cones and used to feed 65 needles in the center of a 24" wide carpet needlepunching unit. The remaining needles were fed with untreated, standard nylon yarn of the type used in preparing the greige carpets of examples 1 through 29. The needle punching machine was set up to manufacture fabric with the same characteristics as the greige carpet of examples l through 29. This resulted in the manufacture of a "banded," cut pile carpet where the center 10 inches were of treated yarn and the 7 inches on either side were of untreated control yarn.

The banded carpet was then further processed by coating the backside with latex and applying a jute secondary backing, curing the latex according to the directions of the latex supplier, dyeing the carpet using the "beck" process and an acid dye and, finally, lightly shearing the surface to assure that the top surface was level. At this point the control and treated parts of the carpet had the same appearance and the carpet was ready for weartesting. This carpet appears in Table III as example 62.

Examples 63 and 64:

The carpets of examples 63 and 64 were prepared by processing the skeins prepared in examples 31 and 32, respectively, in a manner similar to that of example 62 except that the twisting and heat setting steps were omitted since the yarn was already doubled. That is to say, the skeins were wound directly onto 65 cones, and the yarn on these cones was used to feed the needle punching machine. The rest of the process was

identical to example 62. EXAMPLES 65-100

Testing of the sample carpets prepared in examples 33 to 64 is described in examples 65 through 100 which are summarized in the following Table IV.

Example 65: The carpet prepared in Example 33 was placed directly on the floor with the machine direction parallel to the walking direction, secured with tape at the edge and walked on. The number of foot treads were recorded and the wear test stopped at 50,000

"equivalent" treads. An "equivalent" tread is equal to approximately one-half of an actual tread in all the examples described herein. After the wear test the carpet was removed from the floor and taken to a well lighted room where it was compared to standard carpets of various degrees of wear. From this comparison it was possible to assign a wear rating to the carpet. This wear rating can range from 1 (no wear) to 7

(severely worn). The wear rating in this case was 2 (slightly worn). The most worn part of the carpet is used for the rating.

Samples of tufts from this carpet were removed and subjected to swelling in 95% formic acid to determine the cross-link density. To do this about 20 mg of fibers were accurately weighed in a stoppered

Erlenmeyer flask. Enough 95% formic acid was added to just cover the fibers, which rapidly swell. After 60 seconds the excess formic acid is removed by blotting with tissue and the remaining fibers plus absorbed formic acid are weighed. The swelling ratio is

calculated as:

where Ψ represents the "swelling ratio", W_T is the total weight of fibers plus absorbed formic acid and W_F is the weight of the fibers alone.

The cross-link density is then calculated from the equation: χ = 7 . 396 e^{- .043} Ψ + 0 . 8 where χ is the cross-link density in cross-links per chain. This equation was previously established as a valid approximation for the region of interest by using solid-state ¹³C NMR on a series of ¹³CH₂O cross-linked nylon-6 fibers. In the present example there were found to be 3.3 cross-links per chain.

Examples 66 through 90:

The carpets prepared for test in examples 34 through 59 were tested in a fashion similar to example 65. The results are tabulated in Table IV. If the fibers dissolve in 95% formic acid the cross-link density is taken as "0."

Examples 91. 92 and 93:

The carpet prepared in example 60 was tested in a manner similar to examples 65 through 90 except that the wear rating was determined at 10,000 and 25,000 as well as 50,000 equivalent treads. The results from examples 91, 92 and 93 are tabulated in Table IV.

Examples 94. 95 and 96:

The carpet prepared in example 61 was tested in a manner similar to examples 91, 92 and 93. The results from examples 94, 95 and 96 are tabulated in Table IV.

Examples 98. 99 and 100:

The banded carpets prepared in examples 62, 63 and 64, respectively, were tested in a manner similar to example 65 except that the banded carpet was placed on the floor with the machine direction of the carpet turned 90° to the walking path. Also the control and treated sections of the carpet were not given a

numerical rating, but simply judged for relative wear. The results from examples 98, 99 and 100 are tabulated in Table IV. "Control « X-link" (Example 98) indicates the control wore less (had a lower wear rating) than the treated area. "Control » X-link" (Example 99) indicates the control and treated areas wear at the same rate. "Control » X-link" (Example 100) indicates that the control wore more (had a higher wear rating) than the treated area.

Table I: Preparation of cross-linked nylon-6 fibers using the aqueous material

Claims

WHAT IS CLAIMED IS:

1. An improved carpet of the type having a primary backing and twisted pile fiber in the form of individually lengths of plied fiber, each of which projects upwardly from said backing terminating at the cut end, the improvement comprising pile fiber formed from the crosslinked polymeric material having an effective cross-link density in which polymer chains are crosslinked by a divalent cross-linking moiety.

2. An improved carpet according to claim 1 wherein said crosslink density is from about 1 to about 20.

3. An improved carpet according to claim 2 wherein said polymeric material is selected from the group consisting of polymers having a moiety of the formula -N(H))- in the polymer chain.

4. An improved carpet according to claim 3 wherein said polymeric material is a polyamide.

5. An improved carpet according to claim 4 wherein said polyamide is nylon 6 or nylon 6,6.

6. An improved carpet according to claim 5 wherein said polyamide is nylon 6.

7. An improved carpet according to claim 3 wherein said divalent crosslinking moiety is an organic moiety which is covalently bonded to the polymeric chains by covalent bonds.

8. An improved carpet according to claim 7 wherein said crosslinking moiety is a divalent group of the formula:

-C(H)(R)- or -OC(H)(R)- wherein R is hydrogen or alkyl having from 1 to about 7 carbon atoms, or combination thereof.

9. An improved carpet according to claim 8 wherein R is hydrogen.

10. A process of forming crosslinked fibers which provide carpets having improved appearance retention which comprises treating a twisted fiber formed from a polymeric material with an effective cross-linking agent for a time and at a temperature sufficient to cross link chains of said polymeric material to form