Claims:We Claim:

1. A composition redispersible in polar and non-polar solvents comprising :
zinc oxide nanoparticles having a coating of an alkali metal salt of an acid and an ester of carboxylic acid, such that the alkali metal salt of an acid is coated on the zinc oxide nanoparticles and the ester of carboxylic acid is coated on the alkali metal salt of an acid.

2. A composition as claimed in claim 1, wherein the alkali metal salt of an acid is a sodium or potassium salt of an acid.

3. A composition as claimed in claim 1 or 2, wherein the alkali metal salt of an acid is an alkali metal salt of any one of C1 – C22 carboxylic acid, chloride, nitrate or sulphate.
4. A composition as claimed in claim 1 or 2, wherein the alkali metal salt of an acid is any one of sodium acetate, sodium chloride, sodium nitrate or sodium sulphate.

5. A composition as claimed in claim 1, wherein the ester of carboxylic acid is C4 to C18 ester of carboxylic acid, sodium dioctyl sulfosuccinate, or sodium bistridecyl sulfosuccinate.

6. A composition as claimed in claim 1, wherein the concentration of zinc oxide in the composition is in a range of 15 to 30 weight percent.

7. A composition as claimed in claim 1, wherein the concentration of alkali metal salt of an acid in the composition is 50 to 75 weight percent.
8. A composition as claimed in claim 1, wherein the concentration of ester of carboxylic acid in the composition is in a range of 10 to 22 weight percent.

9. A composition as claimed in claim 1, wherein at least 70 percent of zinc oxide nanoparticles have a size in the range of 20 to 200nm.

10. A method of preparing a composition redispersible in polar and non-polar solvents comprising:
hydrolyzing a zinc metal precursor dissolved in a solvent to precipitated zinc oxide nanoparticles in a dispersion;
separating and drying the precipitated zinc oxide nanoparticles to obtain zinc oxide nanoparticles having a coating of alkali metal salt of an acid;
dissolving an ester of carboxylic acid in toluene to obtain a solution of the ester of carboxylic acid;
adding the zinc oxide nanoparticles having a coating of alkali metal salt of an acid to the solution of ester of carboxylic acid to obtain a slurry; and
drying the slurry to obtain zinc oxide nanoparticles having a coating of alkali metal salt of an acid and an ester of carboxylic acid, such that the alkali metal salt of an acid is coated on the zinc oxide nanoparticles and the ester of carboxylic acid is coated on the alkali metal salt of an acid.

11. A method as claimed in claim 10, wherein the zinc metal precursor is any one of zinc acetate, zinc chloride, zinc nitrate or zinc sulphate.

12. A method as claimed in claim 10, wherein the zinc metal precursor is hydrolysed by sodium hydroxide or potassium hydroxide.

13. A composition as claimed in claim 10, wherein the ester of carboxylic acid is C4 to C18 ester of carboxylic acid, sodium dioctyl sulfosuccinate or sodium bistridecyl sulfosuccinate.

14. A process as claimed in claim 10, wherein the solvent is N, N dimethyl formamide.

Dated this 7th day of October, 2015

Aparna Kareer
Of Obhan & Associates
Agent for the Applicant
Patent Agent No. 1359 , Description:The disclosure relates to zinc oxide nanoparticles. Specifically, the disclosure relates to zinc oxide nanoparticles redispersible in polar and non-polar solvents.
BACKGROUND
Zinc oxide nanoparticles find application in white pigment, as a catalyst, as a constituent of anti-bacterial skin protection ointment, in sunscreens, in adhesives for acid scavenging to increase stability and shelf life of products and in wood varnishes. Materials used for blocking UV radiation are required to be transparent to the visible part of the solar radiation while blocking the harmful UV radiation and zinc oxide nanoparticles are considered favorable in this regard.
For easy storage and transportation, it is preferred that zinc oxide nanoparticles are in the form of a dry powder. However, such dry powder should be dispersible in various mediums. The medium in which the zinc oxide nanoparticles are required to be dispersed depends upon the particular application. Cosmetics such as sun blocking creams and lotions, UV blocking paints, and adhesives for example require zinc oxide nanoparticles to be dispersible in water. Dispersion of zinc oxide nanoparticles in organic solvent is required for example when zinc oxide nanoparticles are required to be added to various polymers such as polyolefins, polyesters, polyamides, polyalcohols, and polysiloxanes for making them anti-microbial and protecting them from UV degradation.
Therefore, there is a need for zinc oxide nanoparticles that are dispersible in various solvents such as polar/non-polar aqueous solvents and non aqueous solvents, polymer and resins etc.
SUMMARY
The present disclosure relates to a composition redispersible in polar and non-polar solvents. The composition comprises of zinc oxide nanoparticles having a coating of an alkali metal salt of an acid and an ester of carboxylic acid, such that the alkali metal salt of an acid is coated on the zinc oxide nanoparticles and the ester of carboxylic acid is coated on the alkali metal salt of an acid.
The present disclosure also relates to a method of preparing a composition redispersible in polar and non-polar solvents. The method comprises of hydrolyzing a zinc metal precursor dissolved in a solvent to precipitated zinc oxide nanoparticles in a dispersion, separating and drying the precipitated zinc oxide nanoparticles to obtain zinc oxide nanoparticles having a coating of alkali metal salt of an acid, dissolving an ester of carboxylic acid in toluene to obtain a solution of the ester of carboxylic acid, adding the zinc oxide nanoparticles having a coating of alkali metal salt of an acid to the solution of ester of carboxylic acid to obtain a slurry, and drying the slurry to obtain zinc oxide nanoparticles having a coating of alkali metal salt of an acid and an ester of carboxylic acid, such that the alkali metal salt of an acid is coated on the zinc oxide nanoparticles and the ester of carboxylic acid is coated on the alkali metal salt of an acid.
BRIEF DESCRIPTION OF FIGURES
The accompanying figures illustrate the preferred embodiments and together with the following detailed description serves to explain the principles of the invention.
Figure 1 illustrates the particle size distribution of 1 % dispersion of an embodiment of a composition in water.
Figure 2 illustrates the zeta-potential of the 1 % dispersion of an embodiment of the composition.
Figure 3 illustrates the UV-Visible Spectrum of an embodiment of the composition.
Figure 4 illustrates the particle size distribution of 4 % dispersion of an embodiment of the composition in xylene.
Figure 5 illustrates the particle size distribution of 1 % dispersion of an embodiment of a composition in water.
Figure 6 illustrates the particle size distribution of 1 % dispersion of an embodiment of a composition in water.
Figure 7 illustrates the particle size distribution of 1 % dispersion of an embodiment of a composition in solvent comprising 70% weight/weight ethylene glycol and 30 % weight/weight water.
Figure 8 illustrates the particle size distribution of 1 % dispersion of an embodiment of a composition in solvent comprising 70% weight/weight ethylene glycol and 30 % weight/weight water.
DETAILED DESCRIPTION
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the disclosed invention, and such further applications of the principles of the invention therein being contemplated as would normally occur to one skilled in the art to which the invention relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.
Reference throughout this specification to “one embodiment” “an embodiment” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase “in one embodiment”, “in an embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
A composition redispersible in polar and non-polar solvents is disclosed. The composition comprises zinc oxide nanoparticles that have a coating of an alkali metal salt of an acid; and an ester of carboxylic acid, such that the alkali metal salt of an acid is coated on the zinc oxide nanoparticles and the ester of carboxylic acid is coated on the alkali metal salt of an acid.
In accordance with an aspect, the alkali metal salt of an acid is sodium or a potassium salt of an acid. The alkali metal salt of an acid is an alkali metal salt of any one of C1 – C22 carboxylic acid, chloride, nitrate or sulphate. By way of a specific example the alkali metal salt of an acid is sodium acetate, sodium chloride, sodium nitrate or sodium sulphate.
The concentration of the alkali metal salt of an acid in the composition is in a range of 10 to 22 weight percent.
In accordance with an aspect, the ester of carboxylic acid is selected from C4 to C18 ester of carboxylic acid, sodium dioctyl sulfosuccinate and sodium bistridecyl sulfosuccinate. The ester of carboxylic acid coated on the zinc oxide nanoparticles determines the solvent in which the composition is dispersible. Composition wherein the zinc oxide nanoparticles are coated with sodium dioctyl sufosuccinate is redispersible in water. Composition wherein the zinc oxide nanoparticles are coated with sodium bistridecyl sulfosuccinate is redispersible in organic based systems such as resins.
The concentration of ester of carboxylic acid is in a range of 10 to 22 weight percent.
In accordance with an aspect, at least 70 percent of the zinc oxide nanoparticles in the composition have a size in the range of 20 to 200nm. The concentration of zinc oxide nanoparticle in the composition is in a range of 15 to 30 weight percent.
A method for preparing a composition redispersible in polar and non-polar solvents is also disclosed. The method comprises of hydrolyzing a zinc metal precursor dissolved in a solvent to precipitate zinc oxide nanoparticles in dispersion; separating and drying the precipitated zinc oxide nanoparticles to obtain zinc oxide nanoparticles having a coating of alkali metal salt of an acid. An ester of carboxylic acid is dissolved in toluene to obtain a solution of ester of carboxylic acid. The zinc oxide nanoparticles having a coating of alkali metal salt of an acid is added to the solution of carboxylic acid to obtain a slurry. The slurry is dried to obtain zinc oxide nanoparticles having a coating of alkali metal salt of an acid and an ester of carboxylic acid, such that the alkali metal salt of an acid is coated on the zinc oxide nanoparticles and the ester of carboxylic acid is coated on the alkali metal salt of an acid.
The zinc metal precursor may be hydrolyzed by sodium hydroxide or potassium hydroxide.
The zinc metal precursor is selected from any one of zinc acetate, zinc chloride, zinc nitrate and zinc sulphate.
In accordance with an aspect, zinc acetate is dissolved in the solvent N, N dimethyl formamide.
In accordance with an aspect, the ester of carboxylic acid is C4 to C18 ester of carboxylic acid, sodium dioctyl sulfosuccinate or sodium bistridecyl sulfosuccinate.

EXAMPLES
The following example(s) of are exemplary and should not be understood to be in any way limiting.
Example 1: Composition comprising zinc oxide nanoparticles coated with sodium acetate and sodium dioctyl sulfosuccinate is prepared. The concentration of zinc oxide nanoparticles is 27%, sodium acetate is 53 % and sodium dioctyl sulfosuccinate is 20 % in the composition. This composition is used in any aqueous based system for UV blocking and anti-microbial protection.
The particle size distribution of 1% composition was determined. Figure 1 illustrates the particle size distribution of 1 % dispersion of the composition in water.
The zeta-potential of 1% composition was also measured. Figure 2 shows the zeta-potential of the 1 % composition.
The UV-visible spectrum of the composition is measured. Figure 3 shows the UV-Visible Spectrum of the composition.
The anti-bacterial activity of the composition as tested. Tests were carried out at various concentrations from 0.1 % to 1% of composition. Table 1 tabulates the results obtained using 0.3 % composition on various bacteria.

Table 1: Minimum Inhibitory Concentration Data with Input Bacteria Count 106 colony forming units/millilitre (cfu/ml) for composition dosage of 0.3 %

Bacteria Log Reduction after 24 hours
Escherichia coli ATCC 8739 5.25
Staphylococcus aureus ATCC 6538 5.20
Bacillus subtilis ATCC 6633 2.42
Salmonella typhi ATCC 10749 5.21
Klebsiella pneumoniae ATCC 4352 5.27
Pseudomonas aeruginosa ATCC 9027 4.25
Pseudomonas ovate (M. ovate ATCC 46744) 5.19
Streptococcus faecalis ATCC 9790 5.08
Propionibacter acene (Hospital strain) 3.97
Salmonella enteritidia ATCC 13076 2.31
Proteus mirabilis ATCC 14153 0.93
Serratia marcescens MTCC 97 1.82
Pseudomonas aeruginosa ATCC 9027 0.99
Proteus vulgaris ATCC 13315 1.89
Enterobacter cloacae NCIM 2015 0.12
Streptococcus pyogenes (Hospital strain) 1.67

Example 2: Solvent/resin dispersible zinc oxide
Composition comprising zinc oxide nanoparticles coated with sodium acetate and sodium bistridecyl sulfosuccinate is prepared. The concentration of zinc oxide nanoparticles is 28%, sodium acetate is 53% and sodium bistridecyl sulfosuccinate is 20%. This composition is used in an organic based system for UV blocking and anti-microbial protection. The particle size distribution of 4% composition dispersed in xylene was determined. Figure 4 shows the particle size distribution of 4% composition dispersed in xylene. The zeta-potential of the composition is also determined.
The composition is added to polyethylene films and said films are tested for anti-microbial activity. Tables 2 and 3 tabulates the results of the the anti-microbial activity of the composition in polyethylene films.
Table 2: Anti-microbical activity of the composition in polyethylene (PE) film against Staphylococcus aureus ATCC 6538

Table 3: Anti-microbical activity of the composition in polyethylene (PE) film against Escherichia coli ATCC 9739

Example 3. Composition comprising zinc oxide nanoparticles coated with sodium chloride and sodium dioctyl sulfosuccinate is prepared. The composition has 33.28% of zinc oxide nanoparticles, 46.72% of sodium chloride and 20% of sodium dioctyl sulfosuccinate. This composition may be used in any aqueous based system for UV blocking and anti-microbial protection. The particle size distribution of 1% composition was determined. Figure 5 illustrates the particle size distribution of 1 % dispersion of the composition in water.
Example 4. Composition comprising zinc oxide nanoparticles coated with sodium nitrate and sodium dioctyl sulfosuccinate is prepared. The composition comprises 35.80% of zinc oxide nanoparticles, 44.20% sodium nitrate and 20% sodium dioctyl sulfosuccinate. This composition is used in any aqueous based system for UV blocking and anti-microbial protection. The particle size distribution of 1% composition was determined. Figure 6 illustrates the particle size distribution of 1 % dispersion of the composition in water.
Example 5. Composition comprising zinc oxide nanoparticles coated with sodium chloride and sodium bistridecyl sulfosuccinate is prepared. The composition comprises 35.39% of zinc oxide nanoparticles, 44.61% of sodium chloride and 20% of sodium bistridecyl sulfosuccinate. The particle size distribution of 1% composition was determined. Figure 7 illustrates the particle size distribution of 1 % dispersion of the composition in solvent comprising 70% weight/weight ethylene glycol and 30 % weight/weight water.
Example 6. Composition comprising zinc oxide nanoparticles coated with sodium nitrate and sodium bistridecyl sulfosuccinate is prepared. The composition comprises 40.68% of zinc oxide, 39.32% of sodium nitrate and 20% of sodium bistridecyl sulfosuccinate. Figure 8 illustrates the particle size distribution of 1 % dispersion of the composition in solvent comprising 70% weight/weight ethylene glycol and 30 % weight/weight water.
SPECIFIC EMBODIMENTS ARE DESCRIBED BELOW:
A composition redispersible in polar and non-polar solvents comprising zinc oxide nanoparticles having a coating of an alkali metal salt of an acid and an ester of carboxylic acid, such that the alkali metal salt of an acid is coated on the zinc oxide nanoparticles and the ester of carboxylic acid is coated on the alkali metal salt of an acid.
Such composition(s), wherein the alkali metal salt of an acid is a sodium or potassium salt of an acid.
Such composition(s), wherein the alkali metal salt of an acid is an alkali metal salt of any one of C1 – C22 carboxylic acid, chloride, nitrate or sulphate.
Such composition(s), wherein the alkali metal salt of an acid is any one of sodium acetate, sodium chloride, sodium nitrate or sodium sulphate.
Such composition(s), wherein the ester of carboxylic acid is C4 to C18 ester of carboxylic acid, sodium dioctyl sulfosuccinate, or sodium bistridecyl sulfosuccinate.
Such composition(s), wherein the concentration of zinc oxide in the composition is in a range of 15 to 30 weight percent.
Such composition(s), wherein the concentration of alkali metal salt of an acid in the composition is 50 to 75 weight percent.
Such composition(s), wherein the concentration of ester of carboxylic acid in the composition is in a range of 10 to 22 weight percent.
Such composition(s), wherein at least 70 percent of zinc oxide nanoparticles have a size in the range of 20 to 200nm.
FURTHER SPECIFIC EMBODIMENTS ARE DESCRIBED BELOW:
A method of preparing a composition redispersible in polar and non-polar solvents comprising hydrolyzing a zinc metal precursor dissolved in a solvent to precipitated zinc oxide nanoparticles in a dispersion, separating and drying the precipitated zinc oxide nanoparticles to obtain zinc oxide nanoparticles having a coating of alkali metal salt of an acid, dissolving an ester of carboxylic acid in toluene to obtain a solution of the ester of carboxylic acid, adding the zinc oxide nanoparticles having a coating of alkali metal salt of an acid to the solution of ester of carboxylic acid to obtain a slurry, and drying the slurry to obtain zinc oxide nanoparticles having a coating of alkali metal salt of an acid and an ester of carboxylic acid, such that the alkali metal salt of an acid is coated on the zinc oxide nanoparticles and the ester of carboxylic acid is coated on the alkali metal salt of an acid.
Such method(s), wherein the zinc metal precursor is any one of zinc acetate, zinc chloride, zinc nitrate or zinc sulphate.
Such method(s), wherein the zinc metal precursor is hydrolysed by sodium hydroxide or potassium hydroxide.
Such method(s), wherein the ester of carboxylic acid is C4 to C18 ester of carboxylic acid, sodium dioctyl sulfosuccinate or sodium bistridecyl sulfosuccinate.
Such method(s), wherein the solvent is N, N dimethyl formamide.

INDUSTRIAL APPLICATION
The composition of zinc oxide nanoparticles as disclosed is redispersible in various solvents such as polar/non-polar aqueous solvents and non-aqueous solvents, polymer and resins etc. As the composition is in a power form it is easy to store and transport. Moreover the process of preparing the composition is also easy to perform and is economical.