EP2150555A1

EP2150555A1 - A zinc complex, process for preparing thereof and a method for treating fabric therewith

Info

Publication number: EP2150555A1
Application number: EP08749775A
Authority: EP
Inventors: Nitesh Omprakash Bhalla; Amitava Pramanik
Original assignee: Unilever PLC; Unilever NV
Current assignee: Unilever PLC; Unilever NV
Priority date: 2007-06-04
Filing date: 2008-04-28
Publication date: 2010-02-10
Also published as: CN101687888B; WO2008148610A1; BRPI0810352A2; CN101687888A

Abstract

The present invention relates to a Zinc complex, a process for making the Zinc complex and to method of fabric treatment, particularly to a method of increasing the stain repellence by increasing the hydrophobicity of fabrics using complexes of Zinc.

Description

A ZINC COMPLEX, PROCESS FOR PREPARING THEREOF AND A METHOD FOR TREATING FABRIC THEREWITH

FIELD OF INVENTION

The present invention relates to a method of fabric treatment, particularly to a method of increasing the stain repellence by increasing hydrophobicity of fabrics using complexes of Zinc.

The invention has been developed primarily for use in fabric treatment and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to this particular field of use .

BACKGROUND AND RELEVANT ART

Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.

Fabric or textile fibres easily stain upon contact with aqueous stains. These stains include inks, dyes, tea, coffee and other beverages. Repellence refers to the ability of a textile to repel aqueous or oil based liquids.

Thus, a material which has good repellence will not readily absorb liquids, but instead liquids will tend to "roll-up" or be repelled from the surface of such a textile. Achieving relatively high degree of repellence is generally desirable. This is especially the case for stains caused by products containing persistent dyestuffs or pigments for instance present in coffee, tea, wine, fruit juices, and inks. One approach is to coat or impregnate the fabrics such that subsequent removal of stains during washing becomes relatively easy. Thus hydrophobically treated fabrics are able to repel stains.

To this end, stain repellant agents have been reported in literature. Zinc based compounds, such as Zinc oxide and Silicones have been reported for this purpose.

Zinc-amine complexes have also been reported in the art.

GB 1198060 (British Petroleum) describes complexes of Zinc having the following structure : (RCOO) ZnO (R1NH2) n wherein R represents an alkyl, cycloalkyl, aryl, aralkyl or alkaryl group, having not more than 24 carbon atoms, Rl represents an alkyl group having from 1 to 30 carbon atoms, and which can be saturated or unsaturated, branched or straight-chain, and n is an integer from 1 to 8. The zinc atoms in the complex are arranged tetrahedrally around a central oxygen atom.

Complexes of Zinc have also been used to impart antibacterial and/or bacteriostatic properties to textiles.

US4172841 (US Commerce, 1981) describes the preparation of bacteriostatic, water-insoluble peroxide-containing complexes of zinc acetate, by reaction of zinc acetate with hydrogen peroxide in the presence of acetic acid, is disclosed. A process for in situ formation and deposition of these complexes on cellulosic and polyester textiles is described. The textile finishes so produced inhibit the growth and spreading of odor and infection producing gram- positive and gram-negative bacteria on the treated textiles. The antibacterial activity of the finished textiles is durable to repeated launderings.

Hydrophobic polymers, particularly fluorocarbons and silicones have been reported to render fabric surface stain repellent .

However, there is a continuing need for newer and better products .

OBJECT OF THE INVENTION

It is an object of the invention to provide a method for increasing the hydrophobicity of fabrics.

The present inventors have found a new class of compounds of Zinc that surprisingly give superior benefits when used in fabric treatment. It has been observed by the present inventors that these compounds impart high degree of hydrophobicity to surfaces, particularly fabrics. SUMMARY OF THE INVENTION

According to an aspect, the present invention relates to a complex of Zinc having the empirical formula Zn_x (AA) _y (BB) _z, where; "AA" represents neutral or deprotonated mono-, di- or tri-alkanolamines; "BB" represents carboxylate groups of the formula H(CH2)_pCθ2^~, where p = 1-5, which are bonded to Zinc either by terminal or bridged oxygen atoms; and, x, y and z are integers that satisfy the bivalency of zinc.

Preferably the complex has the following structure:

where, p=l-5

According to another aspect the present invention relates to a process for preparing a complex comprising the step of:

(i) contacting a Zinc salt of a carboxylic acid represented by the formula H(CH₂)_pCθ2H , where p =1-5, with an alkanolamine in the presence of an alcoholic solvent, which is substantially free of moisture; and,

(ii) separating the solvent to obtain said complex. According to another aspect the present invention relates to a method for treating fabric comprising the steps of:

(i) contacting fabric with an alcoholic solution of the complex according to the invention;

(ii) contacting the fabric with an aqueous medium having pH between 5 and 9; and (iii) drying the fabric.

Preferably the method includes an additional step of contacting the fabric with a solution of a fatty acid.

According to another aspect the present invention relates to use of a complex according to the invention for treatment of fabrics. The invention will now be explained in detail.

DETAILED DESCRIPTION

The present invention relates to a complex of Zinc having the empirical formula Zn_x (AA) _y (BB) _z, where;

"AA" represents neutral or deprotonated mono-, di- or tri- alkanolamines; "BB" represents carboxylate groups of the formula H(CH2)_pCθ2^~, where p = 1-5, which are bonded to Zinc either by terminal or bridged oxygen atoms; and, x, y and z are integers that satisfy the bivalency of zinc.

It is preferred that the alkanolamine is selected from methanolamine, monoethanolamine, diethanolamine or triethanolamine, more preferably it is triethanolamine . In a preferred form, the carboxylate groups are represented by the formula, H(CH₂)_pCθ2^~, where p = 1-5. This includes Acetic acid, Propionic acid, Butyric acid, Valeric acid and Caproic acid. It is preferred that the acid is Acetic acid.

A particularly preferred complex has the following structure :

where p = 1-5.

Complexes in accordance with the present invention can be prepared by a process that includes the step of:

(i) contacting a Zinc salt of a carboxylic acid represented by the formula H(CH₂)_pCθ2H , where p = 1-5, with an alkanolamine in the presence of an alcoholic solvent, which is substantially free of moisture; and,

(ii) separating the solvent to obtain the complex.

It was observed that the presence of moisture lead to the formation of some particles, instead of the complex, probably due to the hydrolysis of the complex. By substantially free it is meant that up to 5 wt % of moisture can be there in the alcoholic solvent. Any known method of separating the complex from the liquor may be employed, although it is preferred that the solvent is evaporated to get the complex. Alternatively, the liquor along with the complex, dissolved therein may be cooled to about 0°C to get the complex, and the solvent may be decanted off.

Amongst other salts of Zinc, which are suitable for the present invention, Zinc acetate is the most preferred salt.

Preferred solvents are alcoholic solvents selected from Methanol, Ethanol or Isopropanol, Ethanol being the most preferred solvent for low toxicity as compared to Methanol, low viscosity as compared to Isopropanol and relatively low boiling point.

It is preferred that the molar ratio of Zinc salt to alkanolamine is from 3:1 to 1:3, more preferably from 2:1 to 1:2 and most preferably 1:1.

The present invention also provides a method for treating fabric comprising the steps:

(i) Contacting, in any order, the fabric with an alcoholic solution of the complex according to the invention with an aqueous medium having pH between 5 and 12, and (ii) drying the fabric.

It is particularly preferred that the pH is between 6 and 8. Preferred concentration of the alcoholic solution is from 0.05% to 2.0%, and more preferably between 0.1% and 0.5%, the % being by weight.

In the method, the fabric, after contacting with the alcoholic solution, is removed from the solution and thereafter contacted with an aqueous medium. On the other hand, the alcohol from the alcoholic solution may be removed and thereafter the fabric may be contacted with the aqueous solution. The aqueous solution may be water or an aqueous solution containing detergents or electrolytes. The order of contact can be reversed, i.e. the fabric can be first contacted with an aqueous medium e.g. detergent solution, followed by contacting with an alcoholic solution of the complex according to the invention. Drying is preferably by air drying, although forced air drying and drying by blowing hot air is also possible. The treated fabric may be ironed, which helps in fixing the particles, which are believed to be formed due to the hydrolysis of the complex.

Preferably, the process includes an additional step of contacting the fabric with a solution of a fatty acid, selected from Cio to Cis straight or branched chain carboxylic acids. Preferred fatty acids are Laurie acid and Stearic acid.

The solution of fatty acid is prepared in a non-aqueous solvent selected from primary alcohols, alkanes or ketones, preferably primary alcohols, more preferably Ethanol. It is preferred that the concentration of this solution is between 0.25% wt and 2 %wt, more preferably between 0.5 %wt and 1.0 %wt .

Without wishing to be limited by theory, the increased hydrophobicity of fabric treated in accordance of the invention may be attributed to the deposition of particles, which generally are in size range of 100-1000 nm and more particularly between 200 nm and 500 nm. The particles could be a dough-nut shaped or a dimpled hemispherical shaped.

Any suitable fabric may be chosen for the invention, but is preferred that it is cotton, polycotton, polyester, silk, wool or other synthetics used for applications like making garments, shoes, upholstery, curtains, carpets and paintings .

The hydrophobicity is measured by contact angle measurement of water droplet in air. It is preferably in the range of 90° to 140°. On treatment with a fatty acid a contact angle of water droplet in air in the range of 145° to 170° could be achieved. Increased contact angles imply higher hydrophobicity which can be equated to repellence of aqueous stains .

The contact angle is the angle at which a liquid/vapor (or two immiscible liquids) interface meets the solid surface. The contact angle is specific for any given system and is determined by the interactions across the three interfaces. Most often the concept is illustrated with a small liquid droplet resting on a flat horizontal solid surface. The shape of the droplet is determined by Young-Laplace equation. One of the ways to measure contact angle is using a contact angle goniometer on a sessile drop of the liquid. This method is used to estimate wetting properties of a localized region on a solid surface. Angle between the baseline of the drop and the tangent at the drop boundary is the contact angle as shown in figure-1.

Here the angle θ (=ZABC) is the contact angle of the spherical drop on the base surface. It can be shown that the angle θ = 2 tan^"1 (h/r) where h = AD and r = AB .

On extremely hydrophilic surfaces, a water droplet completely spreads (an effective contact angle of 0°).

This occurs for surfaces that have a large affinity for water (including materials that absorb water, like cotton fabric) . On hydrophobic surfaces, one observes a large contact angle (70° to 90°). Higher the hydrophobicity, larger is the contact angle. Some surfaces may have water contact angles 140° or even higher.

On these surfaces, water droplets simply rest on the surface, without actually wetting to any significant extent. These surfaces are termed superhydrophobic . In the present invention, highly hydrophobic to superhydrophobic effects have been achieved by treatment of fabrics that are otherwise hydrophilic (contact angle 0 to 20°) . In addition to increased stain repellence, it was observed that the treated fabrics also showed anti-microbial and malodour control benefits.

The invention will now be described with the help of the following non-limiting examples.

Example 1

Synthesis of Zinc triethanolamine complex (Compound-1A) (ratio 1:1)

11 g (0.05M) Zinc acetate 2H₂O AR (Ex Merck) was taken in a round bottom flask and 500 ml Ethanol (HPLC grade absolute alcohol) was added to it. The alcohol was evaporated on rotavapour till about 250 ml alcohol was evaporated. The flask was then cooled in ice bath to 0°C.

In a 250ml beaker, 7.45g Triethanolmine AR (ex. SD Fine Chem) was dissolved in 100ml absolute alcohol. This solution was added dropwise to the round bottom flask containing alcoholic solution of Zinc acetate with constant stirring. A transparent sol was obtained. The alcohol was then evaporated to get the Compound-1A in the form of a white powder.

Characterization of the above white powder

The above powder (complex) was characterised by Powder XRD analysis, NMR spectroscopy, IR spectroscopy and Single Crystal XRD. IR spectrum

The spectrum was recorded on Perkin Elmer instrument by making a mixture with KBR.

The spectrum shows a broad band around 3500 cm^"1 corresponding to the hydroxyl groups (OH) , a peak at 1580 cm^" ¹, that corresponds to the carbonyl moeity of the acetate group. The spectrum has been included as figure-2.

NMR spectrum

The spectrum was recorded on a Perkin Elmer model by dissolving the sample in deuterated Methanol. The spectrum shows 4 peaks, represented by figure-3 (excluding solvent peak) .

A portion of the spectrum has been enlarged to show the peaks more clearly and this has been included as figure-4. A sharp singlet at 1.95 ppm appears due to the presence of methyl groups of the acetate groups. A triplet at 2.88 ppm can be attributed to the N-CH2- groups in the structure of the complex. Another triplet at around 3.76 ppm can be attributed to the presence of N-CH2-CH2-OH group. Two other peaks at 3.3 and 4.87 ppm may be ignored as they come from solvent impurities (methanol and water respectively) . As will be shown later, the molecule contains a complex structure with two different acetate environments, as terminal as well as bridged ligands in the same molecule. In solution, both of them appear to be rapidly inter-exchanging as characterized by a single peak in the NMR. Powder XRD

The analysis was preformed on Siemens D-500 instrument, using Copper K alpha 1.54 A wavelength units on a scale of 2-theta. The spectrum shows additional peaks over that of the corresponding spectrum for Zinc acetate, thus confirming that the complex was not Zinc acetate.

Single crystal structure elucidation

The transparent sol obtained in example-1 was taken in glass vial and the solvent was allowed to evaporate for about 30 days. The individual crystals were then collected and observed under optical microscope. A suitable single crystal of size 0.40 mm x 0.15 mm x 0.10 mm was chosen for the structure elucidation. Diffraction data were collected using Enraf-Nonius CAD-4 (MACH-3) single crystal X-ray diffractometer at ambient temperature, and the structure was solved and refined by full-matrix least-square technique using SHELX-97 and SHELXTL program packages [G. M. Sheldrick, SHELX-97, Program for crystal structure solution and refinement, University of Gottingen, Gottingen, Germany, 1997]. The solved structure is given as figure-5.

Crystal structure confirmed the molecule to be a tetranuclear zinc complex having centrosymmetric structure with two different zinc environments, one tetracoordinated and the other, pentacoordinated. Two of the OH groups of the triethanolamine moiety are deprotonated (02, 03 and their symmetry equivalents in the figure) and act as bridging groups between two zinc atoms. The third OH (Ol and its symmetry equivalent) remains protonated (not shown in the figure for clarity) , and coordinated to only one Zinc .

There are both bridging (through 04, 05 and their symmetry equivalents) and terminal (through 06 and its symmetry equivalent) acetate groups in the complex molecule. There is also a water molecule (shown as 0111 with 2 hydrogens) .

Example 2

Synthesis of Zinc Triethanolamine Acetate complex in powder form (Compound-IB)

11 g of zinc acetate dehydrate crystals was crushed to fine powder in a pestle and mortar. To this was slowly added about 6 g of triethanolamine. The mixture was mixed thoroughly under stirring to get compound-IB. It was pulverised in a kitchen mixer.

Example 3

Synthesis of zinc diethanolamine acetate complex in alcoholic solution (Compound-lC)

Anhydrous zinc acetate (0.05 M) and diethanolamine (0.1 M) was added to ethanol in a round bottom flask, and stirred for 30 min, to get compound-lC. Example 4

Synthesis of zinc monoethanolamine propionate complex in alcoholic solution (Compound-ID)

Zinc propionate (0.1 M) and monoethanolamine (0.05 M) was added to isopropanol in a round bottom flask and refluxed for 30 min. Solvent was slowly removed from the system in a rotavapor, leaving behind a gummy mass. The mass was then dissolved in methanol, to get a methanolic solution of Compound-ID .

Example 5

Treatment of fabric and contact angle measurement of treated fabrics :

A 50cm X 50cm piece of cotton cloth (100% cotton, commercially available) was soaked in 500 ml of a 0.5 wt% solution of compound-lA for 30 minutes.

The swatch was then dipped in distilled water, soaked for 15 minutes, removed from it and was allowed to dry in open sun. Thereafter, the swatches were ironed.

A 10cm x 10cm strip of the treated fabric was cut and pasted on a smooth glass slide by applying adhesive to the corners of the fabric.

The slide was then placed on the platform of a goniometer fitted with a camera. A drop of water was placed on the fabric by using a syringe and photographed. By a standard drop shape analysis the contact angle of the drop of water in air on the fabric surface was determined. In this case, the contact angle of water on the untreated and treated fabric swatch was 0° and 145° respectively.

Example 6

Study of contact angles of fabrics treated with compound-lA during washing process.

10cm X 10cm swatches of commercially available cotton (100%) and polycotton (67% polyester : 33% cotton) fabric, both with an initial water contact angle of 0° (i.e., highly hydrophilic) were soaked in 3% aqueous detergent solution for 30 minutes. Thereafter, the swatches were immediately soaked in 1 %wt solution of compound-lA for 30 minutes. The swatches were then rinsed twice with deionised water and were allowed to air dry. Thereafter, the swatches were ironed. The same experiment was repeated with commercially available Polycot (67:33) fabric. In another set of experiments, the swatches were soaked in detergent solution, rinsed twice with deionised water and thereafter were soaked in solution of compound-lA for 30 minutes.

The swatches were dried and ironed. In yet another set of experiments, the swatches were first soaked in a solution of compound-lA for 30 minutes, followed by soaking in 3% detergent solution. The swatches were then rinsed twice with deionised water and thereafter dried and ironed. The contact angles of water droplets on fabrics treated by these, as determined by the technique mentioned in Example 5 are summarised in table -1 below.

Table 1

Note: Samples 1-5 were cotton swatches while samples 6-9 were polycotton swatches.

Det: means 3% detergent solution - I i

It will be appreciated that illustrated compound-lA provides superior water repellence benefits as demonstrated by the contact angles. It will also be appreciated that there is flexibility in the sequence of treatment as the treatment with compound-lA can be done prior to or after the step of rinsing, without any major difference in the contact angle.

Example 7

Enhancement of hydrophobicity by additional treatment with fatty acid

A polycotton (67% polyester: 33% cotton) fabric swatch was treated by the process as mentioned in Example 5. It showed a contact angle of water in air of 142°. The treated fabric was soaked in a 0.5% ethanolic solution of stearic acid for 30 min, taken out, washed 3 times with water and dried in air. After this treatment, the contact angle of water in air for the fabric went up to 165°, which can be equated to uniform hydrophobic surface.

Example 8

Antibacterial and malodour control benefit

Testosterone and isobutyrin breakdown assays (as given below) were performed on control cotton and treated cotton samples followed by evaluation of malodour on the fabrics by experts on a scale of 0-5 (0 = least odourous; 5=most malodourous) . While the control samples gave malodour scores of 1.5 to 2, the treated samples gave scores of 0 to 0.5. This clearly demonstrates the malodour control benefit of the treated fabrics.

Testosterone and Isobutyrin Breakdown Assay

S. epidermidis or Corynebacterium sp was cultured on Tryptone Soy Broth for 24 hrs at 37°C in presence of the control or treated cotton swatches. This was centrifuged and the pellet was suspended in Phosphate Buffered Saline (PBS) containing 0.1% Tributyrin for S. epidermidis and in

IX PBS and 0.05% Testosterone for Corynebacterium sp . Tubes were sealed and on incubation at 37°C for 6 hours. These were then smelled by expert assessors and scored on a scale of 0-5.

Thus the illustrated examples provide for a complex that can be used to impart superior hydrophobicity to fabrics and a method for increasing the hydrophobicity of fabrics, thereby the stain repellence.

It will also be appreciated that the illustrated examples provide for a method for treating fabrics which gives malodour control benefits.

Although the invention has been described with reference to specific embodiments, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms .

Claims

A complex of Zinc having the empirical formula

Zn_x (AA) _y (BB) _z, where;

"AA" represents neutral or deprotonated mono-, di- or tri-alkanolamine (s) ;

"BB" represents carboxylate groups of the formula

H(CH₂)_pCθ2^~, where p = 1-5, which are bonded to Zinc either by terminal or bridged oxygen atoms; and, x, y and z are integers that satisfy the bivalency of

Zinc .

A complex as claimed in claim 1 wherein said alkanolamine is selected from methanolamine, monoethanolamine, diethanolamine or triethanolamine .

A complex as claimed in any one of the preceding claims having the following structure:

where p=l-5.

A process for preparing a complex, as claimed in any one of the preceding claims, comprising the step of: (i) contacting a Zinc salt of a carboxylic acid represented by the formula H(CH₂)_pCθ2H, where p = 1-5, with an alkanolamine in the presence of an alcoholic solvent, which is substantially free of moisture; and,

(ii) separating said solvent to obtain said complex.

5. A process as claimed in claim 4 wherein said carboxylic acid is selected from Acetic acid, Propionic acid, Butyric acid, Valeric acid or Caproic acid.

6. A process as claimed in claim 4 or claim 5, wherein said alkanolamine is Methanolamine, Monoethanolamine, Diethanolamine or Triethanolamine .

7. A process as claimed in any one of claims 4 to 6, wherein said alcoholic solvent is selected from Methanol, Ethanol or Isopropanol.

8. A process as claimed in any one of claims 4 to 7 wherein the molar ratio of said Zinc salt to said alkanolamine is from 3:1 to 1:3.

9. A process as claimed in claim 8 wherein said ratio is from 2:1 to 1:2.

10. A process as claimed in claim 9 wherein said ratio is 1:1.

11. A method for treating fabric comprising the steps: (ii) contacting, in any order, said fabric with an alcoholic solution of the complex as claimed in any one of the preceding claims 1 to 3 and an aqueous medium having pH between 5 and 12, and (iϋ) drying said fabric.

12. A method as claimed in claim 11 wherein said pH is between 6 and 8.

13. A method as claimed in claim 11 or 12 wherein concentration of said alcoholic solution is from 0.05 %wt to 2.0 %wt.

14. A method as claimed in claim 13 wherein concentration of said alcoholic solution is from 0.1 %wt to 0.5 %wt .

15. A method as claimed in any one of claims 11 to 14, comprising the step of contacting said fabric with a solution of a fatty acid.

16. A method as claimed in claim 15 wherein said fatty acid is a Cio to Ci8 straight or branched chain carboxylic acid.

17. A method as claimed in claim 15 or 16, wherein said solution of a fatty acid is prepared in a non-aqueous solvent selected from primary alcohols, alkanes or ketones .

18. Use of a complex as claimed in any one of the preceding claims 1 to 3 for fabric treatment.