This invention relates to a process for chemically modifying polyester fibers to produce polyester textile materials having soft, dry, and warm handle similar to that of wool.

BACKGROUND OF THE INVENTION

The production of synthetic textile materials with aesthetics and properties similar to those of natural fibers, in particular silk and wool, has always been the ultimate aim of the fiber polymer scientist and textile technologist. Silk, due to its popularity, scarcity, and high cost, also because comparatively speaking, it is not as complex in chemical structure as wool, which has scales on its surface and contains sulfur in variable amounts along its fiber axis, attracted more attention. Accordingly, numerous styles of fully synthetic textile materials with silk-like properties have been introduced on the market and are well established commercially. Most prominent among these fabrics, possibly due to economic factors and practicality of production, have been the polyester silky woven fabrics produced by the caustic treatment process which thins out the polyester filaments making them - iner, drapier, and softer. The caustic treatment process results in caustic hydrolysis of the ester groups on the outside surface of the polyester fiber. Concentration of the caustic alkali, time and temperature of treatment, the presence of small amounts of specified quaternary ammonium salts, and

the heat history of the fiber are all important factors which affect the hydrolysis reaction and consequently the percentage weight loss and thinning achieved. Wool, on the other hand, proved more difficult to imitate than silk, and the task of producing synthetic textile materials with wool-like handle was left to the textile technologist to accomplish in practice. This has been achieved by fabric construction, i.e., different spinning methods and texturlzing techniques, and fabric finishing processes such as sanding, brushing napping, cropping and decatizing. Accordingly, a variety of synthetic textile materials with wool-like handle which are comparatively cheaper than wool fabrics have been introduced on the market and are well established commercially. The main drawback in this case is the fact that all these specialty or extra operations are costly, hence not economically favorable. An object of the present invention is to provide a process for improving the aesthetics and properties of textile materials composed of polymeric polyesters. A further object is to produce textile materials composed of the same polyester possessing a natural dry and warm handle similar to that of wool. Another object of this invention is to provide a treatment process in which the resulting fiber •surface, when viewed microscopically, is provided with a series of scales or micro-craters resembling the appearance of the wool fiber surface when similarly viewed. Still another object is to produce polyester fabrics with a very soft handle. Other

objects will be apparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated by the attached drawings are scanning electron microscope photographs of fibers in which:

FIGURES 1 A, B and C are SEM photographs of the fiber υf Example 1 prepared according to the invention;

FIGURE 2 is a SEM photograph of the fiber of Example 2 prepared according to the invention;

FIGURE 3 is a SEM photograph of the fiber of Example 3 prepared according to the invention;

FIGURES 4 A and B are SEM photographs of the untreated polyester fiber used in Examples 1-7;

FIGURES 5 A and B are SEM photographs of the fiber of Example 5 (comparative) treated with caustic soda only and not according to the invention; and

FIGURE 6 is a SEM photograph of the product of Εxample 6 (comparative) treated with amine only and not according to the invention;

FIGURE 7 is a SEM photograph of the product of Example 7 (comparative) treated with amine only and not according to the invention; and

FIGURES 8 A, B and C are SEM photographs of a fiber treated according to Example 8 of the invention.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention, polyester textiles are treated to have a soft, dry and warm handle similar to that of wool by chemically modifying the surface of the polyester fiber and creating micro-craters on its surface.

It has now been found that the formation of micro-craters and scales on the surface of the polyester fiber, when viewed microscopically, can be achieved in practice by treating the polyester fiber with a solution comprising an amine and an alkali metal hydroxide. As a result of the treatment, a portion of the polyester fiber is hydrolized resulting in a loss in weight typically ranging in the area of about 17 to 50%. The formation of the micro-craters and scales on the surface of the polyester fiber can only be achieved when both the amine and the alkali metal hydroxide are present in the treatment solution. When the polyester fiber is treated only with the alkali metal hydroxide solution, the polyester fiber is hydrolized on the surface, and thinned becoming finer and silkier in handle. Treatment of the polyester fiber with the • -amine solution alone does not result in any weight loss or surface modification, thus a combination of the two components is essential.

The polyester fibers which may be treated according to the present invention have a terephthaloyl group in their molecular repeat unit

and are obtained by polycondensation of terephthalic acid, a low aliphatic ester of terephthalic acid or their derivatives with glycols having 2 - 10 carbon atoms in their aliphatic chain as well as from certain cylic glycols. Minor amounts of other divalent compounds copolymerisable with the terephthaloyl group may be incorporated'in amounts up to 15% by weight, such as isophthalic acid or its derivatives and sebasic acid. The polyester for which this invention is particularly suitable and which is referred to in the following examples is polyethylene terephthalate (PET) commercially available from several sources such as Dacron, a registered trademark of E.I duPont, Fortrel, a registered trademark of Celanese, or Kodel, a registered trademark of Eastman Kodak. Blends of polyester with natural fibers typically used to prepare fabrics may also be treated according to the present invention. Such blends include those composed of polyester and cellulosic fibers, e.g.,

65% polyester and 35% cotton; 50% polyester and 50% cotton. Fabric and fiber blends of polyester with polyamide fibers, e.g., 50% polyester and 50% nylon may also be treated according to the invenion. The polyester fibers are treated with the active materials in solution form. The fiber treatment solutions hereinafter referred to are aqueous ^• solutions, however it will be appreciated that other hydroxylated liquids, which are soluble or miscible with water, may be used. Examples of the amine which can be present in the solution, include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, n-propylamine,

di-n-propylamine, tri-n-propylamine, n-butylamine, n-amylamine, n-octylamine, n-hexylamine, nonylamine, laurylamine, ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, propylenediamine, butylenediamine, ethanolamine, diethanolamine, triethanolamine, diethylenetriamine, triethylenetetramine, tetraethylenetetramine, hexamethylenediamine, and N,N,N, 'N' -tetramethyl 1,3-butanedi mine. Aromatic amines, such as aniline, can also be present in the treatment solution. Suitable .amounts of the amine component range from about 0.05% to about 5% by weight with preferred amounts in the range of 0.05 to 1% by weight. Examples of the alkali metal hydroxides present in the solution include sodium, potassium and lithium hydroxides. Other alkaline agents such as sodium and potassium carbonates, alkali metal bicarbonates such as sodium bicarbonate, sodium trichloracetate, barium hydroxide, sodium silicate and trisodium phosphate can also be present in the solution. A suitable caustic alkali solution which is preferred is sodium hydroxide in water. The amount of the alkali metal hydroxide, typically sodium hydroxide, in the solution may be varied over a wide range, for example between about 0.1 and about 40% by weight. Preferred amounts of sodium hydroxide are between 1 and about ^• 5% by weight.

The concentrations of the alkali and the amine in the solution, to an extent, depend upon the duration of the treatment and the temperature thereof, with lower concentrations being particularly useful with elevated temperatures under pressure and

with longer treatment times. The temperature of the treatment may vary from about 50°C to about 200°C at atmospheric conditions or under pressure. The preferred temperature of the treatment may vary between about 100 to about 125°C, either at atmospheric conditions or under pressure.

The treatment may be applied to fibers in stock, tow or filament form, with or without tension, as well as in fabric form before or after dyeing. The treatment can also be carried out continuously on fabrics or yarns utilizing equipment such as high temperature steamers.

The following examples, in which all parts and percentages are by weight and temperatures reported in degrees centigrade, serve to further illustrate but not limit the invention.

EXAMPLE 1

A 100% polyethylene terephthalate (PET) polyester fabric weighing about 7.0 ounces per square yard and constructed from texturized continuous filament

2 ply/30 filaments per ply yarns of 150 denier was treated for a period of 30 minutes at 121°C with an aqueous solution containing 2.3% caustic soda and 0.8% N,N,N, ^* N' -tetramethyll,3-butanediamine using a 17.5:1 liquor to goods ratio. The fabric was then ^• cooled and washed thoroughly with hot and cold water, and finally dried. The resultant fabric lost approximately 34% of its original weight during the caustic/amine treatment.

The thus treated fabric exhibited a much more desirable natural soft, dry, and warm handle similar

to that of wool. Scanning electron microscope (SEM) examination of the treated fabric revealed that the fiber surface was modified from its previously smooth surface into one which had countless micro-craters. Figs. 1 A, B and C are various SEM views of a fiber treated according to this example which are to be compared with the untreated fiber of Figs. 4A and B.

EXAMPLE 2 The procedure of Example 1 was repeated using an aqueous solution containing 2.3% caustic soda and 0.6% 1,6-hexanediamine. The resultant fabric lost approximately 32% of its original weight and acquired the desirable natural soft, dry, and warm handle similar to that of wool. Scanning electron microscope (SEM) examination of the treated fabric indicates that the fiber surface was modified from a smooth surface into one which has countless micro-craters. See SEM photograph Fig. 2.

EXAMPLE 3

The procedure of Example 1 was repeated and the fabric was treated for a period of one hour at 121°C with an aqueous solution containing 2.3% caustic soda and 0.6% 1,6-hexanediamine using a 17.5:1 liquor to goods ratio. The resultant fabric ^• lost approximately 49% of its original weight and acquired a much superior natural soft, dry, and warm handle similar to that of wool. Scanning electron microscope (SEM) examination of the treated fabric indicated that the fiber surface had been modified from a smooth surface into one which has countless

micro-craters and scales. See SEM photograph of Fig. 3.

EXAMPLE 4

The procedure of Example 1 was repeated treating the fabric for a period of 30 minutes at 121°C with an aqueous solution containing 1.9% caustic soda and 0.25% n-octylamine. The resultant fabric lost approximately 16.9% of its original weight and acquired the desirable natural soft, dry and warm 0 handle similar to that of wool. Scanning electron microscope (SEM) examination of the treated fabric indicated that the fiber surface was modified from a smooth surface into one which had countless micro-craters.

5 EXAMPLE 5

The procedure of Example 1 was repeated treating the fabric for a period of 30 minutes at 121°C with an aqueous solution containing 2.3% caustic soda. No o amine was present in the treatment solution. The resultant fabric lost approximately 16% of its original weight and the fabric acquired a smoother handle. Scanning electron microscope (SEM) examination of the treated fabric revealed that the 5 fiber surface had only been very slightly etched and did not contain any scales characteristic of natural ^• wool fibers. See the SEM photographs of Figs. 5A and B.

EXAMPLE 6 (Comparative) 0 he procedure of Example 1 was repeated treating the fabric for a period of 30 minutes at 121°C with

an aqueous solution containing 0.6% 1, 6-hexanediamine. No alkali was present in the treatment solution. The treated fabric lost no weight and the fabric handle was not affected. Scanning electron microscope (SEM) examination of the treated fabric indicated that no surface modification had taken place and the fiber surface was smooth. See the SEM photograph of Fig. 6.

EXAMPLE 7 (Comparative) The procedure of Example 1 was repeated treating the fabric for a period of 30 minutes at 121°C with an aqueous solution containing 0.8% N,N,N, ^* N' -tetramethyl- 1,3-butanedi mine. The treated fabric lost no weight and the fabric handle was not affected. Scanning electron microscope (SEM) examination of the treated fabric indicated that no surface modification had taken place and the fiber surface was smooth. See the SEM photograph of Fig. 7.

EXAMPLE 8 A (PET) polyester lightweight fabric weighing about 2.3 ounces per square yard and constructed from texturized continuous filament (one ply/34 filament yarns of 70 denier) was treated for a period of 30 minutes at 121°C with an aqueous solution containing 2.3% caustic soda and 0.7% ethylamine

^• using 17.5 : 1 liquor to goods ratio. The fabric is then processed as described in Example 1. The treated fabric lost about 34% of its original weight during the caustic/amine treatment. The resultant fabric had a superior soft handle and scanning electron microscope examination indicated the

presence of countless micro-craters on the fiber surface. See the SEM photographs of Figs. 8 A, B and C.