COATING METHOD AND PRODUCT THEREOF

Abstract

A process for the preparation of a coated substrate is described, in which a substrate is coated with a coating mixture containing a polymer and an amino acid-modified layered double hydroxide. The process of the invention is markedly simpler than conventional techniques for affording coated substrates having reduced permeability to degradative gases. The coated substrates obtainable by the process are particularly useful in packaging applications, notably in the food industry.

Claims

1. A process for the preparation of a coated first substrate, the process comprising the steps of: a) providing a coating mixture comprising: i. an amino acid-modified layered double hydroxide, ii. a polymer, and iii. a solvent for the polymer; b) applying a layer of the coating mixture to a first substrate to provide a coated first substrate; and c) drying the coated first substrate.

2. The process of claim 1, wherein the total solids content of the coating mixture is 2.0-20.0% by weight relative to the total weight of the coating mixture.

3. The process of claim 1, wherein the total solids content of the coating mixture is 8.0-12.0% by weight relative to the total weight of the coating mixture.

4. The process of claim 1, wherein of the total solids present in the coating mixture, 10-90 wt % is the amino acid-modified LDH.

5. The process of claim 1, wherein of the total solids present in the coating mixture, 50-75 wt % is the amino acid-modified LDH.

6. The process of any preceding claim, wherein the polymer is a water-soluble polymer.

7. The process of any preceding claim, wherein the polymer is one or more water-soluble polymers selected from the group consisting of poly(vinyl alcohol) (PVOH), poly(vinyl acetate) (PVAc), copolymers comprising vinyl alcohol (e.g. polyethylene vinyl alcohol (EVOH)), polylactic acid (PLA), and polyacrylic acid (PAA), or one or more water-based polymers selected from the group consisting of water-based polyurethane and water-based polyacrylate.

8. The process of any preceding claim, wherein the polymer is PVOH or crosslinked PVOH and the solvent is >95 wt % water.

9. The process of any preceding claim, wherein the first substrate is selected from the group consisting of polyethylene terephthalate (PET), polyethylene (PE), biaxiaily oriented polypropylene film (BOPP), polypropylene (PP), and polyvinyl dichloride (PVDC).

10. The process of any preceding claim, wherein the first substrate is sheet-like, having a thickness of 1-30 μm.

11. The process of any preceding claim, wherein the first substrate is polyethylene terephthalate (PET).

12. The process of any preceding claim, wherein the aspect ratio of the amino acid-modified layered double hydroxide is greater than 85, wherein aspect ratio is the average diameter of the layered double hydroxide platelet divided by the average thickness of the layered double hydroxide platelet.

13. The process of any preceding claim, wherein the aspect ratio of the amino acid-modified layered double hydroxide is >150.

14. The process of any preceding claim, wherein the amino acid-modified layered double hydroxide is a layered double hydroxide comprising 1-25 wt % of an amino acid.

15. The process of any preceding claim, wherein step a) comprises the steps of: a-i) providing a layered double oxide; a-ii) providing a mixture of an amino acid and a solvent for the amino acid (e.g. water); a-iii) providing a mixture of the polymer and the solvent for the polymer; a-iv) contacting the layered double oxide with the mixture of step a-ii) to yield an amino acid-modified layered double hydroxide; and a-v) contacting the amino acid-modified layered double hydroxide with the mixture of step a-iii) to yield the coating mixture.

16. The process of claim 15, wherein during step a-iv), the amino acid is in an excess with respect to the layered double oxide.

17. The process of claim 15, wherein the weight ratio of amino acid (e.g. glycine) to layered double hydroxide in step a-iv) is 1.1:1 to 2:1.

18. The process of claim 15, 16 or 17, wherein step a-iv) is conducted at a temperature of 50-150° C., and/or step a-iv) is conducted for >1 minute, preferably >10 minutes, more preferably >1 hour.

19. The process of any one of claims 15 to 18, wherein the solvent for the amino acid is water.

20. The process of any one of claims 15 to 19, wherein the mixture of step a-ii) and/or step a-iii) further comprises either or both of a) a source of an inorganic oxyanion (e.g. a salt), and b) a polymer crosslinking agent (e.g. a crosslinking agent suitable for crosslinking PVOH, such as trisodium trimetaphosphate).

21. The process of any one of claims 15 to 20, wherein the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide at a temperature of 260-550° C.

22. The process of any one of claims 15 to 21, wherein the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide at a temperature of 325-475° C.

23. The process of any one of claims 15 to 22, wherein the layered double oxide is obtainable by thermally treating a precursor layered double hydroxide for a period of 6-18 hours.

24. The process of any one of claims 15 to 23, wherein prior to step a-v), a base (e.g. NaOH) is added to the mixture resulting from step a-iv) to precipitate the amino acid-modified LDH.

25. The process of any one of claims 21 to 24, wherein either or both of the precursor layered double hydroxide and the amino acid-modified layered double hydroxide contained within the coating mixture is a Zn/Al, Mg/Al, ZnMg/Al or Ca/Al layered double hydroxide.

26. The process of any one of claims 21 to 25, wherein either or both of the precursor layered double hydroxide and the amino acid-modified layered double hydroxide contained within the coating mixture is a Mg/Al LDH.

27. The process of any one of claims 21 to 26, wherein either or both of the precursor layered double hydroxide and the amino acid-modified layered double hydroxide contained within the coating mixture is a Mg/Al LDH in which the molar ratio of Mg:Al is (1.9-2.5):1.

28. The process of any one of claims 21 to 27, wherein either or both of the precursor layered double hydroxide and the amino acid-modified layered double hydroxide contained within the coating mixture is a carbonate-containing layered double hydroxide.

29. The process of any preceding claim, wherein the amino acid is non-aromatic.

30. The process of any preceding claim, wherein the amino acid is β-aminobutyric acid or glycine.

31. The process of any preceding claim, wherein the amino acid is glycine.

32. The process of any preceding claim, wherein the coating mixture is applied to the substrate in step b) at a thickness of 0.5 μm-100 μm.

33. The process of any one of claims 15 to 32, wherein step a-i) comprises thermally treating a precursor layered double hydroxide at a temperature of 325-475° C.; during step a-iv), the amino acid (e.g. glycine) is in an excess with respect to the layered double oxide; and step a-iv) is conducted at a temperature of 50-150° C.

34. The process of any one of claims 15 to 33, wherein step a-i) comprises thermally treating a precursor layered double hydroxide at a temperature of 325-475° C.; the weight ratio of amino acid (e.g. glycine) to layered double hydroxide in step a-iv) is 1.1:1 to 2:1; step a-iv) is conducted at a temperature of 70-120° C., optionally under hydrothermal conditions; and prior to step a-v), a base (e.g. NaOH) is added to the mixture resulting from step a-iv) to precipitate the amino acid-modified LDH.

35. The process of any one of claims 15 to 34, wherein either or both of the precursor layered double hydroxide and the amino acid-modified layered double hydroxide contained within the coating mixture is a magnesium aluminium carbonate LDH in which the molar ratio of Mg:Al is (1.9-2.5):1; the amino acid-modified layered double hydroxide is a layered double hydroxide comprising 1-25 wt % of an amino acid; and the aspect ratio of the amino acid-modified layered double hydroxide is >120.

36. The process of any one of claims 15 to 35, wherein either or both of the precursor layered double hydroxide and the amino acid-modified layered double hydroxide contained within the coating mixture is a magnesium aluminium carbonate LDH in which the molar ratio of Mg:Al is (1.9-2.5):1; the amino acid-modified layered double hydroxide is a layered double hydroxide comprising 1-25 wt % of glycine; and the aspect ratio of the amino acid-modified layered double hydroxide is >175.

37. A coated substrate comprising: a) a first substrate; and b) a coating layer provided on at least one surface of the first substrate, wherein the coating layer comprises 20-90 wt % of an amino acid-modified layered double hydroxide dispersed throughout a polymeric matrix.

38. The coated substrate of claim 37, wherein the amino acid-modified layered double hydroxide is randomly dispersed throughout the polymeric matrix.

39. The coated substrate of claim 37 or 38, wherein the coated substrate is free from urea.

40. The coated substrate of any one of claims 37, 38 and 39, wherein the coating layer comprises 35-75 wt % of amino acid-modified layered double hydroxide.

41. The coated substrate of one of claims 37 to 40, wherein the amino acid-modified layered double hydroxide, the amino acid, the polymer and the first substrate are as defined in any preceding claim.

42. The coated substrate of any one of claims 37 to 41, wherein the coating layer has a thickness of 20 nm-5.0 μm

43. The coated substrate of any one of claims 37 to 42, wherein the coating layer comprises 30-85 wt % of amino acid-modified layered double hydroxide; the aspect ratio of the amino acid-modified layered double hydroxide is >120; the polymer is PVOH; and the first substrate is PET.

44. The coated substrate of any one of claims 37 to 43, wherein the coating layer comprises 50-75 wt % of amino acid-modified layered double hydroxide; the aspect ratio of the amino acid-modified layered double hydroxide is >150; the polymer is PVOH; the coating layer has a thickness of 50 nm-2.5 μm; and the first substrate is PET.

45. The coated substrate of any one of claims 37 to 44, wherein the coating layer comprises 50-75 wt % of glycine-modified layered double hydroxide; the aspect ratio of the glycine-modified layered double hydroxide is >175; the polymer is PVOH or crosslinked PVOH; the coating layer has a thickness of 50 nm-2.5 μm; and the first substrate is PET having a thickness of 5-20 μm.

46. The coated substrate of any one of claims 37 to 45, wherein the coated substrate has an OTR of <7.0 cc/m.sup.2/day/atm.

47. The coated substrate of any one of claims 37 to 46, wherein the coated substrate has an OTR of <1.5 cc/m.sup.2/day/atm.

48. The coated substrate of any one of claims 37 to 47, wherein the coated substrate has a WVTR of <7.0 g/m.sup.2/day.

49. The coated substrate of any one of claims 37 to 48, wherein the coated substrate has a WVTR of <1.5 g/m.sup.2/day.

50. Use of a coated substrate as claimed in any one of claims 37 to 49 in packaging.

51. The use of claim 50, wherein the packaging is food packaging.

52. Packaging comprising a coated substrate as claimed in any one of claims 37 to 49.

53. The packaging of claim 52, wherein the packaging is food packaging.

Description

EXAMPLES

[0572] One or more examples of the invention will now be described, for the purpose of illustration only, with reference to the accompanying figures, in which:

[0573] FIG. 1 shows a flow diagram illustrating the various steps involved in the formation of the coating mixtures of the invention according to Procedure 2.

[0574] FIG. 2 shows TEM images of precursor LDHs used this study: (a) Mg.sub.4Al—CO.sub.3-AMO LDH from co-precipitation (Cop-AMO LDH); (b) Mg.sub.4Al—CO.sub.3-AMO LDH from urea-hydrothermal method (UHT-AMO LDH); and (c) a commercial 7 μm diameter Mg.sub.4Al—CO.sub.3 LDH obtained from SCG Chemicals.

[0575] FIG. 3 shows (a) the XRD patterns of a commercial 7 μm diameter Mg.sub.4Al—CO.sub.3 LDH obtained from SCG Chemicals (FIG. 2(c)) thermally treated at 450 and 550° C. affording LDO; (b) the XRD pattern of a coprecipitated precursor LDH, as well as the XRD pattern of the corresponding LDO, and various amino acid-modified LDHs (i.e. LDHs reconstructed (“RC”) from various amino acids).

[0576] FIG. 4 shows XRD patterns of LDHs modified with glycine for various periods of time following Procedure 2.

[0577] FIG. 5 shows the FTIR spectrum of a coprecipitated LDH, as well as the FTIR spectra of the corresponding LDO, and various amino acid-modified LDHs (i.e. LDHs reconstructed (“RC”) from various amino acids) prepared in a round bottom flask following Procedure 1.

[0578] FIG. 6 shows an FTIR spectrum of a coprecipitated LDH reconstructed with glycine for 24 hours following Procedure 2.

[0579] FIG. 7 shows TEM images of LDHs reconstructed with different amino acids in round bottom flask vs autoclave with hydrothermal treatment using coprecipitated Mg.sub.4Al—CO.sub.3-AMO precursor LDHs (Cop-AMO LDH)) following procedure 1; (a), (e) R-Alanine, (b), (f) @-aminobutyric acid, (c), (g) S-Leucine, (d), (h) β-Phenylalanine reconstructed LDHs in round bottom flask and in autoclave hydrothermal treatment, respectively and (i) Aspartic acid, (j) Glutamic acid, (k) Asparagine and (I) Serine reconstructed LDHs in round bottom flask.

[0580] FIG. 8 shows TEM images of LDHs reconstructed with different amino acids in round bottom flask vs autoclave with hydrothermal treatment using urea-hydrothermally treated Mg.sub.4Al—CO.sub.3-precursor AMO LDH (UHT-AMO LDH) following procedure 1; (a), (e) β-Alanine, (b), (f) β-aminobutyric acid, (c), (g) β-Leucine, (d), (h) β-Phenylalanine reconstructed LDHs in round bottom flask and in autoclave hydrothermal treatment, respectively.

[0581] FIG. 9 shows TEM images of an LDH reconstructed with glycine following Procedure 2.

[0582] FIG. 10 shows Atomic Force Microscopy image of an LDH reconstructed with glycine following Procedure 2.

[0583] FIG. 11 shows a cross-sectional TEM image of a PET substrate coated with a coating mixture containing an LDH reconstructed with glycine following Procedure 2.

[0584] FIG. 12 shows oxygen transmission rate results for various coated and uncoated PET substrates, demonstrating the effect the presence of amino acid (without LDH) on the OTR properties. PET substrate was 23 μm thick and PVA was Mowiol 4-88 (M.sub.w˜31000 g/mol).

[0585] FIG. 13 shows oxygen transmission rate results for various coated and uncoated PET substrates, demonstrating the effect of the LDH synthesis method (coprecipitated vs urea hydrothermal) and reconstruction conditions (round bottom flask vs hydrothermal treating in autoclave) on the OTR properties. PET substrate was 23 μm thick and PVA was Mowiol 4-88 (M.sub.w˜31000 g/mol).

[0586] FIG. 14 shows oxygen transmission rate results for various coated and uncoated PET substrates, demonstrating the effect of single vs double layer coating on the OTR properties. PET substrate was 23 μm thick and PVA was Mowiol 4-88 (M.sub.w˜31000 g/mol).

[0587] FIG. 15 shows oxygen transmission rate results for various coated and uncoated PET substrates, demonstrating the effect of washing the amino acid-modified LDH on the OTR properties. PET substrate was 23 μm thick and PVA was Mowiol 4-88 (M.sub.w˜31000 g/mol).

[0588] FIG. 16 shows oxygen transmission rate results for various coated and uncoated PET substrates, demonstrating the effect of different amino acid-modified LDHs on the OTR properties. PET substrate was 23 μm thick and PVA was Mowiol 4-88 (M.sub.w˜31000 g/mol).

[0589] FIG. 17 shows optical properties of various coated and uncoated PET substrates; (a) transmittance, (b) haze and (c) clarity. PET substrate was 23 μm thick and PVA was Mowiol 4-88 (M.sub.w˜31000 g/mol).

[0590] FIG. 18 shows optical properties (transmittance, haze and clarity) of various coated and uncoated PET substrates. PET substrate was 23 μm thick and PVA was Mowiol 4-88 (M.sub.w˜31000 g/mol).

[0591] FIG. 19 shows the transparency and haze of uncoated films, and films coated with only PVA or a coating mixture containing glycine modified LDH and PVA at a 5% solid content. The PET film was 12 μm thick and LDH used was 7 um LDH (FIG. 2(c)) calcined at 550° C. and reconstructed with glycine according to Procedure 2 for 48 h at 100° C. Within the coating mixture, LDH was 3 wt % and PVA (M.sub.w 67,000) was 2 wt % (total 5% solids). Left columns—10 wt % PVA (no LDH). middle columns—5 wt % LDH+PVA (3% wt LDH+2 wt % PVA). Right column—uncoated 12 μm thick PET film.

[0592] FIG. 20 shows the BET (N.sub.2) traces for the LDH depicted in FIG. 2(c) as well as the same LDH thermally treated at 450 and 550° C., affording LDO. The 7 μm LDH has a surface area of 4 m.sup.2/g and the LDO of 130 and 202 m.sup.2/g for temperature of calcination at 450 and 550° C. respectively.

[0593] FIG. 21 shows the variation on aspect ratio, thickness and diameter over reconstruction time for two different thermal treatment temperatures using the precursor LDH depicted in FIG. 2(c) that has been modified with glycine according to Procedure 2. It shows that the aspect ratio increases with increasing time of reconstruction.

[0594] FIG. 22 shows FTIR spectrum of a coprecipitated LDH, as well as the FTIR spectra of the corresponding LDO, and various amino acid-modified LDHs (i.e. LDHs reconstructed from various amino acid solutions) prepared in under hydrothermal (“HT”) conditions in an autoclave according to Procedure 1.

[0595] FIG. 23 shows the XRD pattern of a coprecipitated precursor LDH, as well as the XRD pattern of the corresponding LDO, and various amino acid-modified LDHs (i.e. LDHs reconstructed from various amino acids) prepared by heating in a round bottom flask (“RC”) or under hydrothermal (“HT”) conditions in an autoclave according to Procedure 1. o and x denote the Bragg reflections of impurities from phenylalanine (o) and leucine (x). (*Bragg reflections due to the sample holder were observed at 26=43-44 and 500 and reflections from the silicon wafer were located at 26=330 and 62.)

[0596] FIG. 24 shows TEM images with particle size distributions of reconstructed products from co-precipitation LDHs (Cop) with different nonpolar amino acids. “RC” and “HT” were denoted as product from round bottom flask using oil bath heating and hydrothermal reactors, respectively, according to Procedure 1. Black lines indicate the best fit of a Gaussian distribution, showing approximately a normal distribution. Mean values and standard deviation were obtained from measurement of 300 particles. ‘*’ indicates that only small size particles were used for size distribution curves.

[0597] FIG. 25 shows the Zeta potential of a coprecipitated precursor LDH and various reconstructed amino acid-modified LDHs.

[0598] FIG. 26 shows TGA curves of coprecipitated precursor LDHs (water-washed and AMO solvent treated), a LDH reconstructed from an LDO in water, and various reconstructed amino acid-modified LDHs prepared by round bottom flask heating according to Procedure 1.

[0599] FIG. 27 shows differential thermogravimetric curves (DTG) of coprecipitated precursor LDHs (water-washed and AMO solvent treated), a LDH reconstructed from an LDO in water, and various reconstructed amino acid-modified LDHs prepared by round bottom flask heating according to Procedure 1.

[0600] FIG. 28 shows XRD pattern of reconstructed LDHs (originated from UHT-AMO LDHs) by nonpolar amino acids by round bottom flask heating according to Procedure 1. o and x denote the Bragg reflections of impurities from phenylalanine (o) and leucine (x). (*Bragg reflections due to the sample holder were observed at 2θ=43-44° and 50° and reflections from the silicon wafer were located at 2θ=330 and 62°.)

[0601] FIG. 29 shows TEM images with particle size distributions of reconstructed products from urea-hydrothermal LDHs (UHT) with different nonpolar amino acids. ‘RC’ and ‘HT’ were denoted as product from round bottom flask using oil bath heating and hydrothermal reactors, respectively, according to Procedure 1. Black lines indicate the best fit of a Gaussian distribution, showing approximately a normal distribution. Mean values and standard deviation were obtained from measurement of 300 particles. ‘*’ indicates that only small size particles were plotted the size distribution curves.

[0602] FIG. 30 shows FTIR spectra of reconstructed LDHs (originated from UHT-AMO LDHs) by nonpolar amino acids using round bottom flask using oil bath heating (“RC”) or hydrothermal conditions (“HT”) according to Procedure 1.

[0603] FIG. 31 shows (a) XRD patterns and (b) FTIR of reconstructed LDHs (originated from Cop-AMO LDHs) using polar side chain amino acids. (*Bragg reflections due to the sample holder were observed at 2θ=43-44° and 50° and reflections from the silicon wafer were located at 2θ=33° and 62°).

[0604] FIG. 32 shows TEM images of reconstructed LDHs using different polar amino acids.

[0605] FIG. 33 shows optical properties of coated films: (a) % transmission, (b) % clarity, (c) % haze and (d) film thickness.

[0606] FIG. 34 shows high aspect ratio LDH NS. (a), Schematic showing (I) calcination (interlayer water and anions are removed by calcination) and (II) reconstruction process and the preferential growth inhibition in a high dielectric constant solution: thickness growth is much slower than the diameter growth, giving high aspect ratio NS. TEM (b) and AFM images (c) of the MgAl-LDH reconstructed in glycine solution (inset in TEM image represents the diameters measured by TEM). (d), Mean diameter and mean thickness measured by AFM measurements and the calculated mean aspect ratio of original LDH, LDH reconstructed in glycine and in water (Mean aspect ratio is taken the mean value of the aspect ratio of individual particles). (e), Estimation of crystallite sizes calculated from Scherrer equation confirming the growth inhibition in the c direction. (f), IR spectra: formation of hydrogen bonding evidenced by the red shift of asymmetry vibration of COO.sup.− group and that part of the group is shifted to orthogonal position (v.sub.as(COO.sup.−)=1557 cm.sup.−1) during reconstruction in glycine solution.

[0607] FIG. 35 shows a digital image of the reconstructed LDH gel.

[0608] FIG. 36 shows thermal analysis of LDO, LDO reconstructed in glycine and in water.

[0609] FIG. 37 shows mean aspect ratio, thickness, and diameter of LDHs. The original LDH (a, b and c), LDH reconstructed in glycine solution (d, e, and f), and LDH reconstructed in water (g, h, and i). Thickness and diameter are obtained from AFM measurements of samples at more than three different spots. Aspect ratio was calculated by diameter divided by thickness of individual particles.

[0610] FIG. 38 shows particle size of LDHs: TEM and AFM images of the original LDH (a and b) and the control LDH reconstructed in water (c and d) (inset in TEM images represents the diameters measured by TEM).

[0611] FIG. 39 shows XRD patterns of MgAl-LDH NS at reconstruction time varied from 1 minute to 48 hours: diameter growth monitored by (110) peak (f) (48 hrs-W, W represent washed sample) compared with the original LDH, calcined LDO and washed 48 hours sample.

[0612] FIG. 40 shows XRD patterns of MgAl-LDH NS at reconstruction time varied from 1 minute to 48 hours: thickness growth monitored by (003) (48 hrs-W, W represent washed sample) compared with the original LDH, calcined LDO and washed 48 hours sample.

[0613] FIG. 41 shows IR spectra of LDH reconstructed in glycine solution for various periods of time.

[0614] FIG. 42 shows reconstruction of other LDHs containing various metal cations. TEM images of reconstructed NiAl (a), Mgln (b), MgGa (c), and ZnAl-LDH NS (d); XRD patterns of the reconstructed LDHs NS (e) and original LDHs (f).

[0615] FIG. 43 shows digital images of LDH NS dispersion in water (a) and stable LDH/PVA coating solution (b).

[0616] FIG. 44 shows the structure of LDHs barrier films. (a), Schematic of coating process and tortuous pathway. (b), Coating layer thickness plotted as a function of coating gap (inset shows the coating layer thickness of film coated with 24 μm coating gap measured by AFM). (c), Transparency and haze of the barrier films. (d), Cross-sectional TEM image of the barrier film containing 60% LDH showing ordered structure where LDH NS are aligned parallel to each other. Pole figure measurements of intercalation phase and bulk phase in the barrier films containing 20% (e and f), 60% (g and h) and 90% LDHs (i and j) in the coating layer. (k), Summary of degree of orientation of LDH NS calculated by equation (3). The total solid content of all the coating solutions are 5 wt % for all the coated film samples discussed in this figure.

[0617] FIG. 45 shows the thickness of coating layers measured by AFM. Coating layer thickness of film coated with 6 (a), 12 (b), and 40 μm (c) coating gap and films coated twice with 12 μm (d) coating gap which is very close to the thickness of film coated with 24 μm coating gap (Coating solution is 5 wt %-60% LDH).

[0618] FIG. 46 shows the thickness of coating layers measured by AFM. Coating layer thickness of film coated with 80% LDH in 5 wt % total solid content solution (a) and with 60% LDH in 10 wt % total solid content solution (b). The coating gap of the rod is 24 μm.

[0619] FIG. 47 shows XRD measurements of barrier films containing 10-90% LDH in the coating layer (* indicates diffractions from PET substrates).

[0620] FIG. 48 shows the orientation of LDH NS in barrier films. The φ averaged intensity plotted against the ψ angle for coating film containing 20 wt % (a), 60 wt % (b) and 90 wt % LDH (c). Data measured at a 26 of 8.5° are marked by the black circles and fitted with a Gaussian coloured red and data measured at a 2θ of 11.5° are marked by black squares and fitted with a blue Gaussian. d, FWHMs in degrees plotted against LDH wt % in coating layer.

[0621] FIG. 49 shows the gas barrier properties of coated films. (a), OTR plot against LDHs % in the coating layer and total solid content of the coating solutions. (b), OTR plot against coating gap and the inset shows that the OTR values are very similar by coating a substrate with the same coating layer thickness (a single and double coating process). (c), WVTR of the crosslinked barrier film at 10 wt % total solid content (C indicates that PVA is crosslinked). (d), Barrier improvement factor plot against barrier film thickness: Comparison of this work and other works with LDH.sup.9, clay.sup.14, and graphite oxide.sup.16 as filler and commercial metallized film.sup.17.

[0622] FIG. 50 shows that dynamic viscosity of the coating solution with LDH percentage varied from 10 to 90% compared with control PVA solution which, unlike the rest of the samples, the 90% LDH sample showed significant shear thinning effect (the total solid content of each sample is 5 wt %).

[0623] FIG. 51 shows OTR properties of films before and after 50, 100, and 200 flexes.

[0624] FIG. 52 shows SEM and AFM images of film surface before (a and b) and after 200 flex (c and d) showing smooth surface.

[0625] FIG. 53 shows SEM images of film surface coated with PVA (a) and original LDH/PVA (b) showing rough surface compared to the reconstructed LDH coated films (b inset shows that the film is opaque).

[0626] FIG. 54 shows WVTR plot against LDH weight percentage in the coating layer. All the coating solution used to prepare the coated films has a total solid content of 5 wt %, same as the films in FIG. 44.

PART A

Example 1—Formation of Coating Mixtures

Procedure 1

[0627] Scheme 1 below is a flow diagram illustrating the various steps involved in the formation of the coating mixtures of the invention according to Procedure 1.

##STR00001##

Procedure 2

[0628] FIG. 1 is a flow diagram illustrating the various steps involved in the formation of the coating mixtures of the invention according to Procedure 2.

Example 1a—Preparation of Precursor LDHs

[0629] The precursor Mg.sub.3Al—CO.sub.3 LDHs used in the preparation of coated substrates were prepared either by a co-precipitation (Cop) technique (to yield flower-like LDHs) or a urea-hydrothermal (UHT) technique (to yield platelet-like LDHs). The general synthetic approach for each technique is outlined below.

[0630] General co-precipitation technique: Aqueous solution (50 mL) of 0.80 M Mg(NO.sub.3).sub.2.6H.sub.2O and 0.20 M of Al(NO.sub.3).sub.3.9H.sub.2O was added drop-wise into the 50 mL of 0.5 M Na.sub.2CO.sub.3 solution with stirring and the pH was controlled at 10 using 4.0 M NaOH solution. After stirring at room temperature for 24 hours, the product was filtered and washed with DI water until the pH was close to 7.

[0631] General urea-hydrothermal technique: An aqueous solution (100 mL) of 0.40 M Mg(NO.sub.3).sub.2.6H.sub.2O, 0.10 M of Al(NO.sub.3).sub.3.9H.sub.2O, and 0.80 M urea was prepared. The mixed solution were transferred to a Teflon-lined autoclave and heated in an oven at the 100° C. for 24 hours. After the reactions were cooled to room temperature, the precipitate products were washed several times with deionised water by filtration.

[0632] Prior to drying, the as-prepared LDHs were subjected to one of two washing techniques. LDHs denoted “water” or “W” were washed with DI water and then subsequently dried. LDHs denoted “AMO” or “A” were washed with acetone (an Aqueous Miscible Organic solvent) and then subsequently dried.

[0633] FIG. 2 shows TEM images of (a) Mg.sub.4Al—CO.sub.3-AMO LDH from co-precipitation (Cop-AMO LDH) and (b) Mg.sub.4Al—CO.sub.3-AMO LDH from urea-hydrothermal method (UHT-AMO LDH). The difference in morphology (flower vs platelet) arising from the different preparation techniques is readily apparent.

[0634] FIG. 2(c) depicts a commercial 7 μm diameter Mg.sub.4Al—CO.sub.3 LDH obtained from SCG Chemicals, which was used as received. FIG. 20 shows the BET (N.sub.2) traces for the LDH depicted in FIG. 2(c) as well as the same LDH thermally treated at 450 and 550° C., affording LDO. The 7 μm LDH has a surface area of 4 m.sup.2/g and the LDO of 130 and 202 m.sup.2/g for temperature of calcination at 450 and 550° C. respectively.

Example 1b—Formation of LDOs and Amino Acid-Modified LDHs

[0635] LDHs prepared in Example 1a were then calcined in air at 450° C. (Procedure 1) or 550° C. (Procedure 2) for 12 hours to yield the corresponding LDOs. The LDOs were then used in the preparation of various amino acid-modified LDHs.

[0636] The amino acid-modified LDHs were prepared by mixing quantities of the LDO and an amino acid in DI water at 80° C. (in a round bottom flask or an autoclave, Procedure 1) or at 100° C. (in an autoclave, Procedure 2). Contacting the LDO with the amino acid and DI water resulted in reconstruction of the LDH structure. Without wishing to be bound by theory, it is believed that the presence of an amino acid during this reconstruction step resulting in LDH platelets having improved morphology (e.g. aspect ratio, uniformity, etc).

[0637] Some of the resulting amino acid-modified LDHs (i.e. reconstructed LDHs) were then subjected to washing by centrifugation in DI water.

[0638] The terms “amino acid-modified LDH” and “reconstructed LDH” are synonymously used herein. The term “RC” may be used to denote a reconstructed LDH.

[0639] FIG. 3(a) shows the XRD patterns of a commercial 7 μm diameter Mg.sub.4Al—CO.sub.3 LDH obtained from SCG Chemicals thermally treated at 450 and 550° C. affording LDO. FIG. 3(b) shows XRD patterns of various coprecipitated (“Cop”) precursor LDHs, as well as various LDHs that have been reconstructed (“RC”) using various different amino acids in a round bottom flask according to Procedure 1.

[0640] FIG. 4 shows XRD patterns of LDHs reconstructed with glycine for various period of time following Procedure 2.

[0641] FIG. 5 shows FTIR spectra of coprecipitated LDHs reconstructed with various different amino acids in a round bottom flask following Procedure 1. FIG. 6 is an FTIR spectrum of a coprecipitated LDH reconstructed with glycine for 24 hours following Procedure 2, which clearly shows signals at −1540 cm.sup.−1 and −1400 cm.sup.−1 indicating the presence of glycine within the LDH structure.

[0642] FIG. 7 shows TEM images of coprecipitated AMO-LDHs reconstructed with various different amino acids in a round bottom flask or in an autoclave at 80° C. following Procedure 1.

[0643] FIG. 8 shows TEM images of urea-hydrothermal AMO-LDHs reconstructed with various different amino acids in a round bottom flask or in an autoclave at 80° C. following Procedure 1.

[0644] FIG. 9 shows TEM images of an LDH reconstructed with glycine following Procedure 2 using the precursor LDH depicted in FIG. 2(c).

[0645] FIG. 10 is an Atomic Force Microscopy image an LDH reconstructed with glycine following Procedure 2, indicating that the thickness of the platelets ranges from 0.8 to 2.2 nm.

[0646] FIG. 21 shows the variation on aspect ratio, thickness and diameter over reconstruction time for two different thermal treatment temperatures using the precursor LDH depicted in FIG. 2(c) that has been modified with glycine according to Procedure 2. It shows that the aspect ratio increases with increasing time of reconstruction.

Example 1c—Preparation of Coating Mixtures

[0647] As depicted in Scheme 1 and FIG. 1, the amino acid-modified LDHs prepared in Example 1b were mixed with an aqueous solution of poly(vinyl alcohol) to yield a coating mixture of 5 wt % solids. The ratio of amino acid-modified LDH to poly(vinyl alcohol) within the coating mixture was 70:30, 50:50 or 40:60.

Example 2—Formation of Coated Substrates

[0648] The various coating mixtures prepared in Example 1c were coated onto a PET substrate using an automated coater (K101 Control Coater). The coated substrates were then dried at room temperature for 5-30 minutes.

[0649] FIG. 11 is a cross-sectional TEM image of a PET substrate coated with a coating mixture containing an LDH reconstructed with glycine following Procedure 2. FIG. 11 shows that the amino acid-modified platelets present in the coating mixture are well aligned with the substrate onto which they have been coated.

[0650] The OTR properties of the coated and uncoated substrates were assessed. As a control, the OTR properties of an uncoated PET substrate were assessed, as were a PET substrate that had been coated with i) PVA, and ii) PVA+β-aminobutyric acid. The results are shown in FIG. 12.

[0651] FIG. 13 demonstrates the OTR properties of various coated and uncoated PET substrates. The results show that PET substrates that have been coated with a coating mixture comprising β-aminobutyric acid-modified LDH (i.e. LDH reconstructed (“RC”) with β-aminobutyric acid) gave substantially lower OTR values.

[0652] FIG. 14 demonstrates the OTR properties of various coated and uncoated PET substrates. The results show that PET substrates that have been coated with a coating mixture comprising β-aminobutyric acid-modified LDH (i.e. LDH reconstructed (“RC”) with s-aminobutyric acid) gave substantially lower OTR values. Particularly good results were observed in respect of samples that had been double coated with a coating mixture comprising β-aminobutyric acid-modified LDH that was derived from coprecipitated precursor LDHs, and which had been modified with the amino acid in a round bottom flask (i.e. at 80° C.).

[0653] FIG. 15 demonstrates the OTR properties of various coated and uncoated PET substrates. The results show that washing the amino acid-modified LDH with DI water prior to formation of the coating mixture leads to a decrease in OTR.

[0654] FIG. 16 demonstrates the OTR properties of various coated and uncoated PET substrates. The results show that reduced OTR (when compared with uncoated substrates and non-LDH containing coated substrates) was observed using coating mixtures containing LDHs modified with glycine, β-alanine, β-aminobutyric acid and β-leucine.

[0655] Table 1 below compares the OTR properties of an uncoated PET substrate, with those of a PET substrate coated solely with PVA and a PET substrate coated with a PVA coating mixture containing 3 wt % of a glycine-modified LDH. The glycine-modified LDH was prepared from the precursor LDH depicted in FIG. 2(c).

TABLE-US-00001 TABLE 1 OTR properties of uncoated, PVA-coated and PVA/glycine-modified LDH-coated PET substrates Total solid content LDH Average Samples (wt %) (wt %) OTR.sup.a OTR.sup.a OTR.sup.a 12 μm PET 0 0 133.5 134.5 132.5 10 wt % PVA 10 0 10.5 10.5 10.4 22.6 23.0 22.2 5 wt %-3 wt % LDH- 5 3 0.36 0.27 0.45 2 wt % PVA .sup.aCC m.sup.−2 day.sup.−1 atm.sup.−1

[0656] The results shown in Table 1 illustrate that the inclusion of glycine-modified LDH within the coating mixture gives rise to a significant decrease in OTR properties.

[0657] The optical properties of the coated and uncoated substrates were also assessed.

[0658] The transmittance of the coated and uncoated substrates was assessed by a haze meter (The haze-gard I, BYK-Gardner GmbH Inc) according to ASTM D 1003. It is the ratio of transmitted light to the incident light, which is influenced by the absorption and reflection properties of the materials. The specimen is placed at the film holder at the entrance port of the haze meter in order to measure the transmittance. Average of ten measurements is reported in units of percent.

[0659] The haze of the coated and uncoated substrates was assessed by a haze meter (The haze-gard I, BYK-Gardner GmbH Inc) according to ASTM D 1003. It is the percent of transmitted light which in passing through deviates from the incident beam greater than 2.5 degrees in the average. The specimen is placed at the film holder at the entrance port of the haze meter in order to measure the haze. Average of ten measurements is reported in units of percent.

[0660] The clarity of the coated and uncoated substrates was assessed by a haze meter (The haze-gard I, BYK-Gardner GmbH Inc). This measurement describes how well very fine details can be seen through the specimen. It needs to be determined in an angle range smaller than 2.5 degrees. The specimen is placed at the film holder at the entrance port of the haze meter in order to measure the clarity. Average of ten measurements is reported in units of percent.

[0661] FIGS. 17, 18 and 19 demonstrate the optical properties of various uncoated and coated substrates. The results show that, when compared with uncoated PET substrates and non-LDH containing coated PET substrates, the coated substrates of the invention exhibited comparable—and in some cases better—optical properties.

PART B

Example 3—Extended Characterisation of Amino Acid-Modified LDHs

[0662] Further characterisation of amino acid-modified LDHs prepared according to Procedure 1 (Example 1) was conducted. In Example 3:

Cop-W denotes a precursor LDH prepared by co-precipitation technique and then washed with water
Cop-AMO denotes a precursor LDH prepared by co-precipitation technique and then washed with acetone
UHT denotes a precursor LDH prepared by urea hydrothermal synthesis
HT denotes an LDH that has been reconstructed from an LDO under hydrothermal conditions in an autoclave
RC denotes an LDH that has been reconstructed from an LDO by heating in a round bottom flask.

Example 3a—Use of Nonpolar Amino Acids and Coprecipitated LDHs (“Cop-AMO LDH”)

[0663] Fourier transform infrared (FTIR) spectra of obtained products after reconstruction of calcined Cop-AMO LDHs in different nonpolar amino acids in the closed hydrothermal reaction are shown in FIG. 22. The characteristic bands of amino acid are present in FTIR spectra which suggests the presence of amino acid molecules in the product. The carbonate band at 1370 cm.sup.−1 was observed in all reconstruction LDHs indicating the co-intercalated carbonate ion in the samples.

[0664] Powder X-ray diffraction (XRD) data of the LDH products obtained from LDH reconstruction are shown in FIG. 23. All LDHs appear to be phase pure by XRD, except for the ones that are reconstructed with β-leucine and β-phenylalanine due to low water solubility of these amino acids making them difficult to remove by washing process. No expansion of the interlayer spacing was observed in most amino acids reconstructed LDHs. Those molecules may horizontally align parallel to the LDH layers, resulting in no expansion of the interlayer. On the other hand, enlargement of the interlayer spacing was observed in products reconstructed with β-leucine and β-phenylalanine. The larger interlayer expansion might be due to the bilayer arrangement of the amino acids in the interlayer region as well as the larger molecular size. The reaction under hydrothermal conditions may favour the introduction of this hydrophobic amino acid into the LDH interlayer regions which enlarges the basal spacing expanding to 15.43 Å. The thickness of smaller amino acids such as glycine and alanine is comparable to that of carbonate and nitrate. Those molecules may horizontally align parallel to the LDH layers, resulting in no expansion of the interlayer. d-spacing values of obtained products are summarised in Table 2.

TABLE-US-00002 TABLE 2 Summary of d-spacing of reconstructed LDHs using different nonpolar amino acids. ‘RC’ and ‘HT’ were denoted as product from round bottom flask heated and hydrothermal conditions in an autoclave, respectively, according to Procedure 1. Sample d-spacing (Å) Cop-AMO LDHs 7.93 RC Glycine 7.78 β-Alanine 7.8 β-Aminobutyric acid 7.83 γ-Aminobutyric acid 7.8 β-Leucine 7.83, 12.05, 13.41 β-Phenylalanine 7.9 HT Glycine 7.71 β-Alanine 7.76 β-Aminobutyric acid 7.82 γ-Aminobutyric acid 7.83 β-Leucine 7.76, 12.02 β-Phenylalanine 7.79, 13.91, 15.43

[0665] TEM was used to determine the particle sizes and size distribution. TEM images and particle size distribution curves of LDHs are shown in FIG. 24 and summarised in Table 3.

TABLE-US-00003 TABLE 3 Summary of average particle size of reconstructed LDHs using different nonpolar amino acids. ‘RC’ and ‘HT’ were denoted as product from round bottom flask heated and hydrothermal conditions in an autoclave, respectively, according to Procedure 1. The TEM images were used to determine the mean values and standard deviation by measurement of 300 particles. Sample Particle size Cop-AMO LDHs 1131 ± 504 nm* RC Glycine  42 ± 12 nm β-Alanine  55 ± 10 nm β-Aminobutyric acid  55 ± 13 nm γ-Aminobutyric acid  52 ± 15 nm β-Leucine  61 ± 16 nm β-Pheny1alanine  181 ± 78 nm HT β-Alanine  62 ± 17 nm β-Aminobutyric acid  76 ± 29 nm γ-Aminobutyric acid  63 ± 15 nm β-Leucine  47 ± 12 nm β-Phenylalanine  61 ± 25 nm, 0.5-1 μm *measured from the secondary particles of LDHs.

[0666] The average particle sizes decreased drastically to 40-60 nm after reconstruction and formed uniform LDH platelets, indicating original structure was not retained. However, it is difficult to find a direct relationship between the chain length of the amino acids and the particle size of the final reconstructed LDHs. It is believed that hydrogen bonding should play a role in directing morphology transformation of the LDHs.

[0667] FIG. 25 shows Zeta potential of reconstructed LDHs by different amino acids by round bottom flask heating (RC) according to Procedure 1. Zeta potential is significantly increased to 32-40 mV after reconstruction with amino acids, suggesting a stable colloid dispersion in water.

[0668] Thermal properties of Cop-AMO LDH, LDOs and reconstructed LDHs by different amino acids were determined by thermogravimetric analysis (TGA) and the differential thermogravimetric curves (DTG), as shown in FIGS. 26 and 27. For amino acid reconstructed LDHs, the total mass loss increased with increasing molecular weight of the amino acid, 50 to 60 wt % for glycine and phenylalanine, respectively. Three steps of a major weight losses were observed for all amino acid reconstructed LDHs as shown in the differential thermogravimetric curves (DTG). The first step occurs below 200° C. due to the removal of adsorbed water and interlayer water. The second step, corresponding to the dehydroxylation of LDH layers and the decomposition of the intercalated amino acids, occurs between 250-400° C. The last step corresponds to the combustion of the intercalated amino acids and formation of a carbonaceous residue produced from the decomposition of the amino acid.

[0669] The amino acid content in all reconstructed products was determined by elemental analysis (EA), the results are summarised in Table 4.

TABLE-US-00004 TABLE 4 Elemental analysis (EA) and TGA studies. % C % H % Mass % Mass apart apart different different % from from from from Amino amino amino ‘original ‘controlled Sample acid* acid* acid* LDH’** sample’** Cop-AMO LDH — 3.50 4.35 — −4.50 Cop-W LDH — 2.01 3.54 0.61 −3.89 Cop-LDO in water — 1.46 4.29 4.50 — Cop-RC-Glycine 16.67 0.06 2.33 −2.24 −6.74 Cop-RC-β-Alanine 27.56 0.53 4.43 −3.97 −8.47 Cop-RC-β- 22.46 0.00 2.81 −6.73 −11.23 Aminobutyric acid Cop-RC-β-Leucine 32.43 0.01 2.99 −12.54 −17.04 Cop-RC-β- 38.82 3.98 2.28 −13.10 −17.60 Phenylalanine *calculated on the basis of Elemental analysis results and ** from TGA results.

[0670] Amino acid content in the LDH was assumed to be the sole source of nitrogen in the samples. In addition, it was also used to determine the carbon and hydrogen content which do not originate from the amino acid. These carbon and hydrogen contents indicate the amount of carbonate and hydroxide intercalated anions and structural water molecules in the reconstructed LDHs.

[0671] Table 5 and 6 present the raw data for ICP results and formula of LDHs before and after reconstruction.

TABLE-US-00005 TABLE 5 ICP results of LDHs before and after reconstruction. % Weight from Total % Mole ICP results % Mole mole fraction Mg Al Mg Al fraction in total Mg/Al Sample (avg.) sd (avg.) sd % % Mg + Al Mg Al ratio Cop-AMO 20.95 0.21 5.73 0.10 0.86 0.21 1.07 0.80 0.20 4.06 LDH Cop-LDO in 27.50 0.25 8.01 0.16 1.13 0.30 1.43 0.79 0.21 3.81 water Cop-RC- 22.22 0.24 7.29 0.13 0.91 0.27 1.18 0.77 0.23 3.38 Glycine Cop-RC-β- 23.16 0.19 7.13 0.10 0.95 0.26 1.22 0.78 0.22 3.60 Alanine Cop-RC-β- 22.86 0.06 7.03 0.04 0.94 0.26 1.20 0.78 0.22 3.61 Aminobutyric acid Cop-RC-β- 19.81 0.06 6.39 0.07 0.82 0.24 1.05 0.77 0.23 3.44 Leucine Cop-RC-β- 17.56 0.10 6.87 0.07 0.72 0.25 0.98 0.74 0.26 2.84 Phenylalanine

TABLE-US-00006 TABLE 6 Compositional formula of LDHs before and after reconstruction. Sample Formula of LDHs Cop-AMO LDH [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.10]•0.245H.sub.2O•0.215(Ethanol) Cop-W LDH [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.10]•0.634H.sub.2O Cop-LDO in water [Mg.sub.0.79Al.sub.0.21(OH).sub.2(HCO.sub.3).sub.0.031(CO.sub.3).sub.0.095]•1.194H.sub.2O Cop-RC-Glycine [Mg.sub.0.77Al.sub.0.23(OH).sub.2(HCO.sub.3).sub.0.031(CO.sub.3).sub.0.100]•0.053H.sub.2O•0.111(Glycine) Cop-RC-β-Alanine [Mg.sub.0.78Al.sub.0.22(OH).sub.2(HCO.sub.3).sub.0.031(CO.sub.3).sub.0.095]•2.212H.sub.2O•0.420(β-Alanine) Cop-RC-β- [Mg.sub.0.78Al.sub.0.22(OH).sub.2(HCO.sub.3).sub.0.031(CO.sub.3).sub.0.095]•2.465H.sub.2O•0.206 Aminobutyric acid (β-Aminobutyric acid) Cop-RC-β-Leucine [Mg.sub.0.77Al.sub.0.23(OH).sub.2(HCO.sub.3).sub.0.031(CO.sub.3)0.100]•0.033H.sub.2O•0.195(β-Leucine) Cop-RC-β- [Mg.sub.0.74Al.sub.0.26(OH).sub.2(HCO.sub.3).sub.0.031(CO.sub.3).sub.0.115]•0.281H.sub.2O•0.308 Phenylalanine (β-Phenylalanine)

[0672] XRD patterns of reconstruction products prepared from urea hydrothermal treatment (UHT) precursor LDHs according to Procedure 1 are presented in FIG. 28 and d-spacing values are summarised in Table 7. No layer spacing expansion was obtained using small size amino acids. An increase of the basal spacing was observed in products produced from leucine (12 Å) but it was not found in the case of phenylalanine. This is probably due to several factors such as: the large particle size of the original LDHs, the contact area and accessibility of the amino acid. In addition, the hydrophobicity of the phenylalanine may suppress the interaction with the LDH surface.

[0673] TEM images and particle size distributions are shown in FIG. 29 and Table 7 for all samples. The obtained products from the UHT-AMO LDH produce a mixture of small and large particles particularly in air, the large platelets were almost all transformed into small particles under hydrothermal conditions. Normally hydrothermal conditions favour larger particle size formation of LDHs.

TABLE-US-00007 TABLE 7 Summary of d-spacing and average particle size of reconstructed LDHs using different nonpolar amino acids. ‘RC’ and ‘HT’ were denoted as product from round bottom flask heated and hydrothermal conditions in an autoclave, respectively, according to Procedure 1. The TEM images were used to determine the mean values and standard deviation by measurement of 300 particles. Bragg reflections of excess amino acids in samples were excluded in this table. Sample d-spacing (Å) Particle size UHT-AMO LDHs 7.62  3-4 μm RC Glycine 7.58  87 ± 22 nm, 3 ± 1 μm β-Alanine 7.36 132 ± 40 nm, 3 ± 1 μm β-Aminobutyric acid 7.61 105 ± 32 nm, 3 ± 1 μm γ-Aminobutyric acid 7.51 101 ± 41 nm β-Leucine 7.65, 12.08 131 ± 42 nm, 3 ± 1 μm β-Phenylalanine 8.12 352 ± 176 nm, 3 ± 1 μm HT Glycine 7.52 109 ± 25 nm, 3 ± 1 μm β-Alanine 7.6 135 ± 41nm β-Aminobutyric acid 7.63  89 ± 28 nm γ-Aminobutyric acid 7.56 100 ± 37 nm β-Leucine 7.55, 11.99 135 ± 31 nm, 3 ± 1 μm β-Phenylalanine 8.08 125 ± 88 nm

[0674] The characteristic bands for phenylalanine (as well as the other amino acids) are present in FTIR spectra shown in FIG. 30. The spectra suggest the presence of amino acid molecules in the product. The carbonate band at 1370 cm.sup.−1 was observed in all reconstruction LDHs indicating the co-intercalated carbonate ion in the samples.

Example 3c—Use of Polar Amino Acids

[0675] FIG. 31 shows XRD data and FTIR spectra of the reconstructed LDHs using polar side-chain amino acids by round bottom flask heating according to Procedure 1. Their interlayer distances are summarised in Table 8, the intercalation occurred with no expansion of the interlayer spacing, peak shift from the original parent LDH was observed in all cases.

TABLE-US-00008 TABLE 8 Summary of d-spacing and average particle size of reconstructed LDHs using polar amino acids. The TEM images were used to determine the mean values and standard deviations by measurement of 300 particles. d-spacing Particle size Sample (Å) (nm) Aspartic acid 7.60 46 ± 13 Glutamic acid 7.60 59 ± 25 Asparagine 7.74 63 ± 27 Serine 7.74 25 ± 5 

[0676] FIG. 32 displays the TEM images of the reconstruction products by round bottom flask heating according to Procedure 1, their size distribution is summarised in Table 8. Well-dispersed LDH hexagonal platelets (with lateral size <100 nm) were formed after reconstruction with asparagine (63 nm), serine (25 nm), glutamic acid (59 nm) and aspartic acid (46 nm). In the case of aspartic acid, a flower like shape was observed. The formation of this morphology is still unclear.

Example 4—Coating Applications

[0677] A variety of PVA-based coating mixtures were prepared according to the procedure outlined in Scheme 1 and were then coated onto PET films according to the procedure described in Example 2.

[0678] FIG. 33 presents the optical properties and film thickness of coated films. All samples show similar film transparency, clarity and haze values as the PET substrate, except in the coated film containing phenylalanine reconstructed LDHs. The present of large particles from TEM images of this sample leads to increases of light scattering and a broad particle size distribution, reduces film transparency and clarity values and considerably increase haze value of the coated film. No difference in the thickness of the coated and uncoated films could be measured using a micrometer.

PART C

Example 5—Use of Glycine-Modified LDHs in Coating Applications

Materials and Methods

[0679] Materials. The MgAl—CO.sub.3.sup.2--LDH (Mg:Al 2:1 ratio) is commercially available LDHs (Alcamizer 1) and was used as purchased from Kisuma Chemicals, Netherlands. Polyvinyl alcohol (PVA) 8-88 (MW: 67,000), Poval 56-98 PVA (MW: 195,000), glycine (≥98%), and sodium hydroxide pellets (≥98%) were purchased from Sigma Aldrich. Polyethylene terephthalate (PET) film (12 μm thick) was sent from SCG chemicals.

[0680] Calcination of LDHs. LDH was calcined at 450° C. for 12 hr at a heating rate of 5° C./min. The calcined LDO was taken out of furnace at ca. 80° C. and stored in a desiccator to avoid slow rehydration in air.

[0681] Reconstruction of LDOs in amino acid solution. Typically, glycine was mixed with 0.1 g calcined LDO at 1.5:1 weight ratio in 1 mL water and the mixture was placed in an autoclave and reacted at 100° C. for 48 hr to obtain a semi-transparent gel. The obtained gel was then dispersed and stirred in water (usually 100 mL) overnight. The dispersion is very stable and thus LDH NS can be difficult to collect by centrifuge. Thus, to improve the yield, LDHs suspension is intentionally precipitated by adding NaOH solutions. The LDHs was then collected by centrifuge at 35954 g force for 10 minutes and washed with D.I. water for three times. After centrifuge, the collected LDH gel was partially dried at 100° C. in oven for 2 hours to determine the solid content (the average solid content of three measurements was used in all cases).

[0682] Reconstruction of LDOs in water. The LDOs were reconstructed under the same conditions as in amino acid solution, except without adding amino acid as a control experiment.

[0683] Coating solution preparation. PVA solution was prepared by dissolving PVA resin in water at ca. 90° C. under reflux for an hour. 10 wt % PVA stock solution was used to prepare coating solution. Reconstructed LDHs gel was mixed and stirred overnight with 10 wt % PVA solution and water to make coating solution with different total solid contents and LDHs loadings. The coating solutions typically contain 95 wt % water and 5 wt % solid where LDHs is 3 wt % and PVA is 2 wt %.

[0684] Coating process. PET substrate was coated with the coating solutions by a semiautomatic coater (K control coater, RK PrintCoat instruments Ltd, UK) at a coating speed equivalent to 9.8 m/min. After coating, the PET films are dried at room temperature for about 1 hr before testing.

[0685] Crosslinking of PVA for WVTR. PVA with molecular weight of 195,000 was only used to improve water vapor barrier of the coated film. Trisodium trimetaphosphate (TSMP) was used to crosslink PVA following a previous report.sup.1. Typically, 5 g of 10 wt % PVA solution (Or LDH/PVA mixture) was mixed with 0.08 ml of 0.16 M TSMP and 0.03 ml of 2.5 M NaOH right before coating. After coating, the coated film was dried and cured at 100 C for 5 hours in oven.

[0686] OTR testing. The OTR of the barrier films were tested on M8001 oxygen permeation analyser (Systech Instruments, UK) at zero relative humidity. The instrument testing limit is 0.005 cc/m.sup.2/day. The testing complies with ASTM D-3985.

[0687] WVTR testing. The WVTR of the barrier films were tested on M7001 water vapour permeation analyser (Systech Instruments, UK) at 23° C. and 50% relative humidity. The testing complies with ASTM standard F-1249.

[0688] XRD measurements. The samples for XRD measurements of LDOs reconstructed in glycine were prepared by quench the reaction by liquid nitrogen after certain periods of time (from 1 minute to 48 hours) to rapidly cool down the temperature. After the reaction mixture temperature rose back to room temperature, the mixture was put into an aluminium holder and covered with Mylar® film (0.25 mil, XRF Window Film, Fisher Scientific) to avoid drying of the samples. The samples were scanned at a canning speed of 0.04°/min. The barrier films were taped on to an aluminium holder to make XRD measurements with the coated side facing the incident X-ray beam. All XRD measurements were recorded on Bruker D8 diffractometer (40 kV and 30 mA) with Cu Kα radiation (λ.sub.1=1.544 Å and λ.sub.2=1.541 Å).

[0689] Estimation of crystallite sizes. Scherrer equation is used to estimate the size of crystallites which correlates to the peak broadening in an X-ray diffraction pattern.

[00001]$\begin{array}{cc}D=\frac{k}{\beta }& \left(1\right)\end{array}$

where D is the mean size of crystallites perpendicular to the diffraction plane; k is a dimensionless shape factor (usually is 0.89 for LDHs); λ is the wavelength of the X-ray (λ=0.15406 nm); β is the peak broadening at half maximum intensity (FWHM) after subtracting the instrument line broadening in radian; θ is the Bragg angle.

[0690] FT-IR measurements. IR spectra were recorded on a Varian FTS-7000 Fourier transform infrared spectrometer fitted with a DuraSamplIR Diamond ATR. The samples were prepared as described in XRD measurements and tested as it is.

[0691] TEM measurements of LDHs and cross-sectional TEM sample preparation. All TEM images were obtained on a JEOL JEM-2100 transmission electron microscope with an accelerating voltage of 200 kV. The coated PET films were first embedded into epoxy, and slices of ca. 80-100 nm thickness were cut on a Reichert-Jung Ultracut E ultramicrotome from the embedded epoxy sample. The slices were deposited on 75-mesh copper grids for imaging.

[0692] Viscosity measurements. Dynamic viscosity is measured on HR-2 discovery hybrid rheometer (TA instruments) using 60 mm aluminium cone plate with an angle of 1.010 and a truncation gap of 30 μm at 25° C.

[0693] SEM imaging. SEM images were taken on a Zeiss Merlin-EBSD scanning electron microscope with an operating voltage of 5 kV. The films were first coated with ca. 10 nm gold before imaging.

[0694] AFM measurements. The coating layer thickness and thickness of LDHs were measured by a NanoScope MultiMode atomic force microscope using tapping mode with a silicon tip coated with aluminium with a force constant of 40 N/m. LDHs samples were diluted into ca. 0.01 mM and spin coated on freshly cleaved mica wafer for AFM imaging.

[0695] Mechanical flex of the films. The films were conditioned at 23±2° C. and 50±5% RH for 48 hours before the flex. All films were flexed by a Gelbo flex tester (IDM instruments) following ASTM F392-93 standard.

[0696] Optical measurements of the barrier films. Haze and transparency of the films were tested by a haze-gard I haze meter (BYK instruments) following ASTM D1003-00 Standard test method. The film samples were conditioned at 23±2° C. and 50±5% RH for 48 hours before testing.

[0697] Pole figure measurements. For Pole figure measurements a Panalytical X'Pert Pro MRD was used. This is equipped with a 4-bounce Ge Hybrid Monochromator giving pure Cu Kai radiation and a Pixcel detector as a point detector with an 8.5 mm active length. This provides each pole figure with a 2θ range of 1.5°, allowing us to isolate the scattering from the intercalated and bulk phase scattering. The samples containing 20%, 60%, and 90% LDH in the coating layer were mounted on a glass slide using double-sided tape and oriented so that at φ=0° the top of the sample. The pole figure measurement consists of a series of p scans (rotation of the sample about the surface normal) made at a number of different ψ angles (sample tilt angle). Each φ scan was from 0 to 360° with a 2° step size and a counting time of 0.88 s per position. A phi scan was made every 2° from 0 to 26 in ψ giving a total collection time per pole figure of 45 minutes. For each sample a measurement was made with the detector fixed at 8.5° and 11.5° in 26 to ensure the diffracted intensity was from the intercalated LDHs and bulk LDHs, respectively.

[0698] Degree of Orientation.

[00002]$\begin{array}{cc}\partial =\frac{1-F}{1}*100& \left(3\right)\end{array}$

where FWHM is the full width at half maximum obtained by pole figure measurements.

[0699] Barrier improvement factor. Barrier improvement factor (BIF) is defined as Ps/Pt, where Ps is the permeability of the substrate and Pt is the permeability of the coated substrate.

RESULTS AND DISCUSSION

[0700] MgAl—CO.sub.3.sup.2-LDH was first calcined and then reconstructed in an amino acid solution (FIG. 34a and Materials and methods) to obtain a translucent gel (FIG. 35). Further agitating the gel in water gave green high aspect ratio LDH NS (FIGS. 34b and c) that contained both water and amino acids (Table 9 and 10 and FIG. 36).

TABLE-US-00009 TABLE 9 Mg/Al ratios of original LDH, LDH reconstructed in glycine and control LDH reconstructed in water: the metal ratios stay very close to each other indicating that the reconstruction process does not change the metal ratio. Mg/Al Mg Al molar Average Samples (wt %) (wt %) ratio ratio Original LDH 18.1 9.51 2.12 2.11 18.2 9.63 2.10 18.3 9.64 2.10 LDH-gly 18.3 9.54 2.13 2.13 18.2 9.48 2.13 18.2 9.52 2.12 LDH-water 18.8 9.94 2.10 2.10 18.8 9.95 2.10 18.7 9.94 2.09

TABLE-US-00010 TABLE 10 Glycine content in reconstructed LDH calculated from TGA. Total Glycine content Weight weight (wt %) loss at loss at (weight loss 200° C. 800° C. difference Samples (wt %) (wt %) at 800° C.) A1C-450° C. LDO 3.32 9.33 7.44 A1C-450° C.-Gly 10.5 50.94 A1C-450° C.-water 7.63 43.5

[0701] The aspect ratio was calculated by dividing the diameter by thickness of individual particles. The LDH NS have a mean aspect ratio of 204.5±75.4 (FIG. 34d, FIG. 37d-f), ca. 64 times and 17 times higher than that of the pristine LDH (FIG. 37a-c; FIGS. 38a and b) and the control LDH reconstructed in water respectively (FIG. 37g-1; FIGS. 38c and d).

[0702] The majority of the LDH NS comprise 2 LDH layers (FIG. 37e) (0.48 nm for each metal hydroxides layer) and glycine (0.3 nm from ChemDraw) and water molecules with refined shape rather than fragments that are usually obtained by exfoliation of LDHs.sup.2. Calcination at high temperature removes interlayer water and anions (ca.<600° C.).sup.3,4 that screened the interlayer interactions, thus, molecules/ions can interact freely with newly grown LDH NS during reconstruction process in solution (FIG. 34a).

[0703] In concentrated glycine solution, LDOs dissolve rapidly at an elevated temperature in the acidic amino acid solution (pH=5.6 of 2M glycine solution) followed by almost instantaneous reconstruction of LDHs structure (FIG. 39). During the reconstruction process, whilst the LDO peak disappears at the fourth minute, the LDH crystallites evolve at the third minute and grow larger in diameter as the (110) peak grows and becomes sharper with reaction time (FIG. 39). On the other hand, the LDH growth along c axis is much slower where only a broad hump was observable centred at around 2=11.60° (corresponds to diffraction from (003) crystal plane) after 15 hours of reaction (FIG. 40). LDHs growth is inherently faster in the in-plan direction due to the formation of stronger covalent bonds in contrast to the weaker electrostatic interactions dominating interlayer growth. Thus, in an environment lack of large amounts of anions, the presence of amino acid decreased the electrostatic interactions between the positively charge LDH NS and counter anions, slowing down the interlayer growth. The thickness growth of the LDH NS is monitored by the (003) peak positioned around 26=11.6° (FIG. 40) where the thickness remained very stable with only a slight increase from 0.5 nm to 1.6 nm (FIG. 34e). This is in sharp contrast to the rapid growth of the diameter from 17.6 nm to 43.0 nm (FIG. 34e) monitored by the (110) peak positioned around 26=60.6° in 48 hours of reconstruction (FIG. 39). The values are estimations.sup.5, but the growth trends are representative. The preferential growth suppression in the c direction is ascribed to the high dielectric constant of the amino acid solution (125 of 2M glycine aqueous solution is comparable to that of 111 of formamide, a known exfoliation agent for LDHs).sup.6 where the carbonyl group interacts with surface hydroxyl groups of the reconstructed LDH through hydrogen bonding (FIG. 34f and FIG. 41), weakening interlayer electrostatic interactions which in turn inhibits interlayer growth.

[0704] A range of LDH NS other than MgAl—CO.sub.3.sup.2-LDH with various metal cations were successfully obtained, including NiAl, Mgln, MgGa, and ZnAl-LDH NS, through the calcination and reconstruction method (FIG. 42).

[0705] After reaction, the gel was dispersed in water by homogenizer and a semi-transparent dispersion was formed (FIG. 43a). The LDH NS were precipitated by adding NaOH solution and collected by centrifuge; the precipitate was subsequently washed with water to remove the excess glycine and NaOH. The precipitation led to the stacking of LDH NS proven by the much resolved hump at (003) peak position (FIG. 40).

[0706] 2D-NS are impermeable to gas molecules due to the dense packing of ions in the crystal structure, thus, they are natural barriers to gas molecules. Theoretical predictions.sup.7 and experiments.sup.8 have shown that well-aligned high aspect ratio NS are highly effective in diminishing gas diffusion through polymer films due to the extra diffusion path (FIG. 44a) the gas molecules are forced to migrate around the barrier NS. The structure of tortuous pathway is an universal barrier to gas.sup.9, moisture.sup.10, heat.sup.10, chemical molecules.sup.11 and electricity.sup.12 that is widely adopted in packaging materials, insulation materials and flame retardant materials. The gas barrier properties of the tortuous pathway derive from the alignment of the NS in the polymer matrix indicating.sup.7 that a higher degree of alignment is more efficient in resisting gas diffusion through the film.

[0707] It was then demonstrated that the high aspect ratio green LDH NS can be mixed with polyvinyl alcohol (PVA) to make a coating solution (FIG. 43b). A substrate polymer film, polyethylene terephthalate (PET), was coated with a single coating process using industrialized bar coater with the LDH/PVA coating solution (FIG. 44a). The coating layer thickness can be easily tuned by changing coating rod with different coating gap (FIG. 44b and FIGS. 45-46) where the thickness can be tuned from ca. 100 nm to 1.8 μm. The coating layer does not decrease the transparency of the PET substrate and the haze of the coated film is very similar to that of the substrate film (FIG. 44c). The coating solution was labelled as X wt %-Y % LDH where X wt % (ranging from 3-13 wt %) refers to the total solid content (LDH and PVA) in water solution and Y % (ranging from 10-90%) refers to the weight ratio of LDH over PVA. When referring to the coated films, Y % is the weight ratio of LDH over PVA; C means that the PVA is crosslinked.

[0708] The reconstructed LDH NS are well aligned parallel to each other in PVA matrix (FIG. 44d) indicating the formation of a high barrier film. In the XRD patterns (FIG. 47) of the coated films, two phases were identified: an LDH/PVA intercalation phase and a second LDH/glycine bulk phase (d-spacing is ca. 7.7 Å). The interlayer distance of the intercalation phase decreased from 11.3 Å to 10.1 Å and finally merged with the bulk phase when the weight percentage of LDH NS increases from 10 to 90% in the coating layer. The decreased interlayer distance is ascribed to less PVA present in between LDH NS layers when the LDH percentage is increased in the coating layer.

[0709] The degree of alignment of LDH NS was statistically examined by pole figure measurements that show graphical representations of the orientation distribution of the NS in PVA matrix (FIG. 44e-j). Two sets of measurements were carried out with 26 degrees fixed at 8.5° (the intercalated phase) and 11.5° (the bulk phase) where three samples (containing 20%, 60%, and 90% LDH) were scanned at a sample tilting angle (L) and a rotation angle (p) (FIG. 44e). Visually, the pole figures show some anisotropic scattering but are all centred around 0° in ψ indicating that LDH layers are well aligned around (003) crystal plane (parallel to PET substrate, where scattering intensity at high ψ angle indicates the presence of LDH layers aligned ψ angle away from (003) crystal plane). It can also be clearly observed that the orientation distribution of the doped layers is very similar to that of the bulk layers. The orientation distribution is compared by the averaged full width at half maximum height (FWHM) of their scattering from all φ angles. To estimate the FWHM of the LDH NS orientation distribution the scattering from all φ angles was averaged. This allowed a single set of scattering intensities as a function of sample tilt ψ to be produced. These could then be fitted with a Gaussian distribution as shown below: where y.sub.0 is the background intensity, A is the area, w is the FWHM and x.sub.c is the peak centre.

[00003]$\begin{array}{cc}y=y_0+\frac{{\mathrm{Ae}}^{\frac{-4.Math..Math.\ln \left(2\right).Math.{\left(x-x_c\right)}^2}{w^2}}}{w.Math.\sqrt{\frac{\pi }{4.Math..Math.\ln \left(2\right)}}}& \left(2\right)\end{array}$

The fitting gave FWHM (FIG. 48a-c) of the bulk phase and intercalated phase of 19.5±0.3° and 19.3°±0.6°, 17.0°±0.2° and 17.4±0.2°, 20.1°±0.1° and 21.8°±0.8° for the coating films containing 20%, 60%, and 90% LDH NS respectively (FIG. 48d), suggesting that coating film containing 60% LDH has the highest degree of orientation of 90.3%, while the 90% LDH film has the lowest degree of orientation of 87.9% (FIG. 44k) (The calculation method can be found in Materials and methods). The anisotropy effect on FWHM is also considered for 60% LDH coating film. The pole figure measured at 26=8.5° was analysed by averaging the data into 45 sectors (Table 11) where the average FWHM is 16±1.8°, consistent with the value of 17.0°±0.2° determined when averaging all p angles. Both analysis methods suggest that the 60% LDH coating film has the highest level of alignment.

TABLE-US-00011 TABLE 11 FWHM and peak centres of Gaussian fits for φ sector data measured on coating film with 60 wt % LDH at 2θ = 8.5°. φ Sector (°) 45- 90- 135- 180- 215- 270- 315- Average STD 0-45 90 135 180 215 270 315 360 (°) (°) FWHM (°) 14.9 17.0 18.7 13.1 16.4 17.6 16.7 13.7 16.0 1.8 Uncertainty 1.1 0.7 0.3 0.4 0.8 0.8 1.1 0.5 (°) Xc (°) −0.5 0.0 4.0 1.3 −3.6 −2.5 3.0 2.4 0.5 Uncertainty 0.7 0.4 0.1 0.2 0.7 0.6 0.4 0.2 (°)

[0710] The oxygen transmission rate (OTR) of the coated films can be efficiently reduced to below the testing limit of the instrument (<0.005 cc/m.sup.2/day/atm) (FIG. 49a). The OTR decreased significantly with LDH loading and the lowest value was obtained when the LDH NS loading was in between 60-80% (FIG. 49a). In sharp contrast, the OTR increased when LDH concentration reached 90%. This is probably due to the viscosity change of the coating solution. Unlike the rest of the samples, at 90% LDH, the coating solution showed significant shear thinning behaviour (FIG. 50). At such a high LDH concentration (90%), due to the high viscosity the LDH NS are difficult to rotate to be aligned as perfectly, thus giving a poor overall LDH alignment. Another reason would be that the coating layer turned so rigid after the majority of the flexible polymer is replaced by LDH that the film became fragile and susceptible to cracking. The OTR of the coated film decreases with increasing total solid content of the solution and coating gap of the coating rod. The OTR decreased from 0.124 to below 0.005 cc/m.sup.2/day/atm when the total solid content is increased from 3 to 7 wt % (OTR stayed below detection at total solid content larger than 7 wt %) (FIG. 49a). The OTR decreased from 1.92 to 0.036 cc/m.sup.2/day/atm when the coating gap is increased from 6 to 40 μm when the coating solution contains 60% LDH and 5 wt % total solid content (FIG. 49b). It was also confirmed that a single coating process is efficient enough to decrease the OTR of the coated film (FIG. 49b inset). The OTR value is very similar (FIG. 49b inset) between the two films coated once with a 24 μm rod and twice with a 12 μm rod which have almost the same coating thickness (FIG. 45d and Table 12).

TABLE-US-00012 TABLE 12 Barrier properties of the coated films. STP, standard temperature and pressure. Coating O.sub.2 permeability of coated thickness OTR barrier film Samples.sup.a (nm) [cc/(m.sup.2 .Math. day)] [10.sup.−16cm.sup.3(STP) .Math. cm/cm.sup.2 .Math. s .Math. Pa] BIF.sup.b PET(12) — 133.5 18.3 — PVA-5 wt %-24.sup.c 890 ± 32  18.25 2.6 7  5 wt %-60% LDHs-24.sup.c 665 ± 33  0.044 0.00629 2908  5 wt %-80% LDH-24.sup.c 891 ± 42  0.042 0.00618 2959  7 wt %-60% LDH-24.sup.c 1000 ± 47  <0.005 0.000742 24640 10 wt %-60% LDH-24.sup.c 1103 ± 21  <0.005 0.000748 24452  5 wt %-60% LDH-6.sup.d 92 ± 10 1.92 0.26519 69  5 wt %-60% LDH-12.sup.e 295 ± 14  0.21 0.029774 615  5 wt %-60% LDH-12-T.sup.f 690 ± 20  0.041 0.005943 3079  5 wt %-60% LDH-40.sup.g 1845 ± 33  0.036 0.005695 3213 PET(180)-LDHs.sup.9 149 <0.005 0.01029 1685 PET(180)-LDHs.sup.10 360 <0.005 0.010301 1683 PET(179)-MMT.sup.11 82.6 <0.005 0.0102281 1719 PET(125)-GO.sup.12 1 × 10.sup.4 <0.005 0.00771034 2120 Commercial metallized 42 0.25 0.0348524 678 PET(12).sup.20 .sup.aThe value inside the parentheses is the thickness of substrate PET films in μm; .sup.bBarrier improvement factor (BIF) (which is defined as Ps/Pt, where Ps is the permeability of the substrate and Pt is the permeability of the coated substrate); .sup.c24 denotes the coating gap is 24 μm. .sup.c,d,e,g24, 6, 12, and 40 denotes the coating gap in μm. .sup.fThe sample is coated twice with 12 μm coating gap rod.

[0711] The flexibility of the barrier films was then tested, where the films were flexed 50, 100, and 200 times, and the OTR value of the coated films remain almost the same compared to that of the film before flex (FIG. 51). The surface of the coated film is smooth (FIGS. 52a and b) compared to the film coated with control LDH (FIG. 53). Even after 200 cycles flex, the surface of the coated film does not show defects (FIGS. 52c and d).

[0712] The water vapour transmission rate (WVTR) of the coated film showed significant decrease as well. Similarly, the WVTR decreased when increasing LDH NS loading and the lowest WVTR decreased from 8.99 of bare PET film to 1.04 g/m.sup.2/day after coating with LDH/PVA (FIG. 54). To further improve water vapour barrier, a high molecular weight PVA was used and the PVA was crosslinked with trisodium trimetaphosphate (TSMP).sup.113, a previously reported food grade cross-linker. After crosslinking, PVA becomes insoluble in water, maximizing the possibility of preserving the ordered structure during the test. By adding 60% LDH NS into the coating layer, the WVTR of the coated film decreased to 0.04 g/m.sup.2/day (FIG. 49c). The improvement is significant considering its thin coating thickness and hydrophilic nature of LDH which in return, supports the theory of tortuous pathway formed by the good alignment of high aspect ratio LDH NS.

[0713] The highest oxygen barrier films based on LDHs can reduce the OTR to below instrument detection limit by LBL assembling LDHs with polymer binders.sup.9. However, the barrier films of the invention are far more effective when taking the coating thickness into account and calculating the permeability of the barrier films (Table 12). This is also true when comparing the permeability of the barrier films containing other 2D materials, such as Montmorillonite (MMT).sup.14,15, graphene oxide (GO).sup.16 and commercial metallized PET film.sup.17 (The permeability of the barrier films are calculated by a previously described method.sup.18) (FIG. 49d). The advantage of the barrier films of the invention is more obvious when comparing the barrier improvement factor (BIF) which is the permeability of the bare substrate divided by the permeability of the barrier film.sup.19. The BIF reached 24452 when the coating layer contains 60% LDHs and the coating solution contains 10 wt % total solid contents as shown in Table 12. It is more than 14 times higher than the existing best LDHs based barrier films and ca. 11 times higher than other 2D materials filled barrier films. More impressively, it is more than 36 times higher than the commercial metalized PET film.sup.17.

[0714] It has been demonstrated that by reconstructing LDOs in amino acid solution, high aspect ratio LDH NS can be obtained and the NS can be stably dispersed in water. A possible explanation for this is that in the amino acid solution, LDHs particle growth in the c direction is significantly inhibited compared to that of the in-plane growth due to the lack of appreciated amount of anions (other than amino acid ions) present (CO.sub.3.sup.2− and OH.sup.− for example) in the solution. Amino acid can efficiently decrease the electrostatic interactions and inhibit interlayer growth of LDHs due to their high dielectric constant. The obtained LDH NS are high aspect platelets and when incorporated into PVA matrix, they can effectively decrease both the OTR and WVTR of the PET film. The barrier film is thin, transparent, and flexible, most importantly; the high aspect ratio MgAl-LDH NS used to enhance the barrier properties does not contain any toxic substances, making it an ideal candidate for food packaging.

[0715] While specific embodiments of the invention have been described herein for the purpose of reference and illustration, various modifications will be apparent to a person skilled in the art without departing from the scope of the invention as defined by the appended claims.

REFERENCES

[0716] 1 Chaouat, M. et al. A novel cross-linked poly (vinyl alcohol)(PVA) for vascular grafts. Adv. Funct. Mater. 18, 2855-2861 (2008). [0717] 2 Liu, Z. et al. Synthesis, anion exchange, and delamination of Co— Al layered double hydroxide: assembly of the exfoliated nanosheet/polyanion composite films and magneto-optical studies. J. Am. Chem. Soc. 128, 4872-4880 (2006). [0718] 3 Millange, F., Walton, R. I. & O'Hare, D. Time-resolved in situ X-ray diffraction study of the liquid-phase reconstruction of Mg—Al-carbonate hydrotalcite-like compounds. J. Mater. Chem. 10, 1713-1720 (2000). [0719] 4 Rocha, J., del Arco, M., Rives, V. & A. Ulibarri, M. Reconstruction of layered double hydroxides from calcined precursors: a powder XRD and 27Al MAS NMR study. J. Mater. Chem. 9, 2499-2503, doi:10.1039/A903231B (1999). [0720] 5 Langford, J. I. & Wilson, A. Scherrer after sixty years: a survey and some new results in the determination of crystallite size. J. Appl. Crystallogr. 11, 102-113 (1978). [0721] 6 Wyman, J. The Dielectric Constant of Solutions of Dipolar Ions. Chem. Rev. 19, 213-239 (1936). [0722] 7 Cussler, E., Hughes, S. E., Ward, W. J. & Aris, R. Barrier membranes. Journal of Membrane Science 38, 161-174 (1988). [0723] 8 Dou, Y. et al. Transparent, flexible films based on layered double hydroxide/cellulose acetate with excellent oxygen barrier property. Adv. Funct. Mater. 24, 514-521 (2014). [0724] 9 Dou, Y. et al. Transparent, Ultrahigh-Gas-Barrier Films with a Brick-Mortar-Sand Structure. Angew. Chem. Int. Ed. 54, 9673-9678 (2015). [0725] 10 Ding, F. et al. Biomimetic nanocoatings with exceptional mechanical, barrier, and flame-retardant properties from large-scale one-step coassembly. Science Advances 3, e1701212 (2017). [0726] 11 Li, P. et al. Highly effective anti-corrosion epoxy spray coatings containing self-assembled clay in smectic order. Journal of Materials Chemistry A 3, 2669-2676, doi:10.1039/C4TA06221C (2015). [0727] 12 Cao, Y., Irwin, P. C. & Younsi, K. The future of nanodielectrics in the electrical power industry. IEEE Transactions on Dielectrics and Electrical Insulation 11, 797-807 (2004). [0728] 13 Lack, S., Dulong, V., Picton, L., Le Cerf, D. & Condamine, E. High-resolution nuclear magnetic resonance spectroscopy studies of polysaccharides crosslinked by sodium trimetaphosphate: a proposal for the reaction mechanism. Carbohydr. Res. 342, 943-953 (2007). [0729] 14 Priolo, M. A., Gamboa, D., Holder, K. M. & Grunlan, J. C. Super gas barrier of transparent polymer-clay multilayer ultrathin films. Nano Lett. 10, 4970-4974 (2010). [0730] 15 Das, P. et al. Nacre-mimetics with synthetic nanoclays up to ultrahigh aspect ratios. Nature communications 6, 5967 (2015). [0731] 16 Chen, J.-T. et al. Enhancing polymer/graphene oxide gas barrier film properties by introducing new crystals. Carbon 75, 443-451 (2014). [0732] 17 Jamieson, E. & Windle, A. Structure and oxygen-barrier properties of metallized polymer film. Journal of Materials Science 18, 64-80 (1983). [0733] 18 Roberts, A. et al. Gas permeation in silicon-oxide/polymer (SiOx/PET) barrier films: role of the oxide lattice, nano-defects and macro-defects. Journal of Membrane Science 208, 75-88 (2002). [0734] 19 Priolo, M. A., Holder, K. M., Gamboa, D. & Grunlan, J. C. Influence of Clay Concentration on the Gas Barrier of Clay-Polymer Nanobrick Wall Thin Film Assemblies. Langmuir 27, 12106-12114, doi:10.1021/la201584r (2011).