Biopolymer composition and its use as a powder coating

Abstract

The present invention concerns a packaging material having a coating made of a biopolymer composition. In addition, the invention concerns a method for providing barrier properties for a packaging material by using the above mention composition. In particular, the present invention concerns coating of a porous material with a composition comprising a biopolymer formed by the reaction product of biodegradable polyester and siloxane precursor.

Claims

1. A packaging material comprising a coated porous substrate, wherein the coated porous substrate comprises a porous substrate and a coating on the porous substrate, the coating comprising a molten layer comprising a biopolymer formed by a reaction product of a biodegradable polyester and a metalloxane precursor.

2. The packaging material according to claim 1, wherein the coated porous substrate comprises a single-layer coating of the coating.

3. The packaging material according to claim 1, wherein the coating provides barrier properties for the packaging material selected from the group consisting of a liquid barrier, gas barrier, oil barrier, grease barrier, and combinations thereof.

4. The packaging material according to claim 1, wherein the coating has an arithmetic mean surface roughness value (Ra) below 20 μm, measured with an optical profilometer.

5. The packaging material according to claim 1, wherein the metalloxane precursor comprises a siloxane precursor selected from the group consisting of a siloxane monomer, oligomer and polymer, and combinations thereof, and wherein the biodegradable polyester comprises a thermoplastic biopolymer selected from the group consisting of polybuthylene succinate, polyglycolic acid, a polyhydroalkanoate, polycaprolactone, polylactid acid, polybutylene adipate terephthalate, and polybuthylene succinate.

6. The packaging material according to claim 1, wherein the metalloxane precursor is reacted with a monomeric or polymeric polyol comprising two or more hydroxyl groups, prior to mixing with the biodegradable polyester.

7. The packaging material according to claim 1, wherein the formed biopolymer is a random polymer containing repeating siloxane units in a hydrocarbyl backbone, and wherein the biopolymer comprises polyester that is grafted with siloxane precursor.

8. The packaging material according to claim 1, wherein the reaction product forming the biopolymer is formed by an esterification reaction between the biodegradable polyester and the metalloxane precursor, wherein the reaction product has a number average molecular weight of 2,000 to 1,500,000 g/mol.

9. The packaging material according to claim 1, wherein the coating is obtained by melting a powder coating composition comprising the biopolymer onto a surface of the porous substrate.

10. The packaging material according to claim 9, wherein the powder composition has an average particle size of 5 to 150 μm.

11. The packaging material according to claim 9, wherein the powder composition comprises at least 50 weight-% of the biodegradable polyester, and wherein the powder composition contains hydrocarbyl residues and siloxane residues at a molar ratio in the range of 99:1 to 50:50.

12. The packaging material according to claim 1, wherein the powder composition has a glass transition temperature, T.sub.g, between −50° C. and 79° C.

13. The packaging material according to claim 9, wherein the powder composition further comprises inorganic and/or organic fillers selected from the group consisting of talc, geo, starch, wheat gluten, natural polysaccharides, wood derivatives, cellulose, lignin and their derivatives, and combinations thereof.

14. The packaging material according to claim 1, wherein the substrate comprises paper, cardboard, or plastic.

15. A method for producing a packaging material comprising the steps of providing a porous substrate, providing a biodegradable polyester, providing a metalloxane precursor, reacting the biodegradable polyester with the metalloxane precursor to form a biopolymer composition, pulverizing the biopolymer composition to form a powder, applying the powder on the porous substrate, and curing the applied powder to form a packaging material.

16. The method according to claim 15, wherein the metalloxane precursor comprises a siloxane precursor, and wherein the siloxane precursor is obtained by mixing two or more siloxanes at room temperature, and wherein optionally a solvent is removed from the biopolymer composition prior to pulverization, and/or wherein the biodegradable polyester and the siloxane precursor are reacted under nitrogen, air or any protective atmosphere at elevated temperature of at least 60° C.

17. The method according to claim 16, wherein the biodegradable polyester and the metalloxane precursor are reacted in the presence of a monomeric, oligomeric or polymeric polyol comprising two or more hydroxyl groups.

18. The method according to claim 15, wherein the biopolymer composition is pulverized to form a powder having an average particle size of 1 to 150 μm, and wherein the pulverizing is done by grinding, cryogenic grinding, or solvent precipitation method, and wherein the powder is applied to the porous substrate using electrostatic spray coating after which the curing is performed at an elevated temperature of 100 to 250° C.

19. The method according to claim 15, wherein the biodegradable polyester and the metalloxane precursor are mixed using a melt compounding.

Description

EXAMPLES

Example 1

[0101] Mixture 1—Preparation of Siloxane Precursor Solution

[0102] 25 g (0.1058 mol) of 1,2-bis(triethoxysilyl)ethane, 25 g (0.0705 mol) of (3-glycidoxypropyl) trimethoxysilane, 50 g of ethanol and 5 g of water were mixed in a round bottom flask equipped with a magnetic stirrer. The solution was mixed for 1 hour at room temperature.

[0103] Preparation of biopolymer powder composition 23.4 g of commercial grade polybutylene succinate, 2.6 g of polyethylene glycol having an average molecular weight of 400 g/mol (M.sub.n), 2.6 g of Mixture 1 (Example 1), and 0.26 g of BYK333 (polyether-modified polydimethylsiloxane) as additive and 75 g of technical grade ethyl acetate was weighed into a 500 ml round bottom flask. The mixture was heated to 78° C. using reflux condenser and mixing under nitrogen atmosphere for 30 minutes. Then the formed biopolymer suspension was cooled to room temperature and the solvent was removed using solvent evaporation. After removal of the solvent, the obtained powder was sieved to median particle size between 30 and 70 μm.

[0104] Coating of the Substrate

[0105] The powder composition was used in powder coating of a cardboard substrate using electrostatic charging. The coating was applied using electrostatic spray gun on the charged substrate using 50 cm distance. Next, the substrate coated with the powder composition was heated in an air convection oven at 150° C. for 10 minutes to form an even coating layer on the substrate.

Example 2

[0106] Mixture 1—Preparation of Siloxane Precursor Solution

[0107] 50 g (0.141 mol) of 1,2-bis(triethoxysilyl)ethane, 100 g of ethanol and 5 g of water were mixed in a round bottom flask equipped with a magnetic stirrer. Solution was mixed for 1 hour at room temperature.

[0108] Mixture 2—Reacting Siloxane Precursor with Polyol

[0109] 60 g (0.150 mol) of polyethylene glycol having an average molecular weight of 400 g/mol (M.sub.n), 17.7 g (0.150 mol) of bio-succinic acid and 23.31 g of Mixture 1 (Example 2) were weighed into 500 ml round bottom flask. The mixture was heated to 160° C. using reflux condenser and mixing under nitrogen atmosphere for 1 hour 45 minutes. Then the mixture was cooled to room temperature.

[0110] Preparation of Biopolymer Powder Composition

[0111] 17.3 g of commercial grade polybutylene succinate and 2.7 grams of Mixture 2 (Example 2) as additive and 50 g of technical grade ethyl acetate was weighed into a 500 ml round bottom flask. The mixture was heated to 78° C. using reflux condenser and mixing under nitrogen atmosphere for 30 minutes. Then the formed biopolymer suspension was cooled to room temperature and the solvent was removed using solvent evaporation. After removal of the solvent, the obtained powder was sieved to median particle size between 30 and 70 μm.

[0112] Coating of the Substrate

[0113] The powder composition was used in powder coating of a cardboard substrate using electrostatic charging. The coating was applied using electrostatic spray gun on the charged substrate using 50 cm distance. Next, the substrate coated with the powder composition was heated in an air convection oven at 150° C. for 10 minutes to form an even coating layer on the substrate.

Example 3

[0114] Preparation of Biopolymer Powder Composition

[0115] 18 g of commercial grade polybutylene succinate and 0.16 g of BYK333 (polyether-modified polydimethylsiloxane) as additive and 50 g of technical grade ethyl acetate was weighed into a 500 ml round bottom flask. The mixture was heated to 78° C. using reflux condenser and mixing under nitrogen atmosphere for 30 minutes. Then the biopolymer suspension was cooled to room temperature and the solvent was removed using solvent evaporation. After removal of the solvent, the obtained powder composition was sieved to median particle size between 30 and 70 μm.

[0116] Coating of the Substrate

[0117] The powder composition was used in powder coating of a cardboard substrate using electrostatic charging. The coating was applied using electrostatic spray gun on the charged substrate using 50 cm distance. Next, the substrate coated with a powder composition was heated in an air convection oven at 150° C. for 10 minutes to form an even coating layer on the substrate.

Example 4

[0118] Preparation of Biopolymer Powder Composition

[0119] 18 g of commercial grade polybutylene succinate, 2 g of polyethylene glycol having average molecular weight of 400 g/mol (M.sub.n) and 0.2 grams of BYK333 (polyether-modified polydimethylsiloxane) as additive and 50 g of technical grade ethyl acetate was weighed into a 500 ml round bottom flask. The mixture was heated to 78° C. using reflux condenser and mixing under nitrogen atmosphere for 30 minutes. Then the biopolymer suspension was cooled to room temperature and the solvent was removed using solvent evaporation. After removal of the solvent, the obtained powder was sieved to median particle size between 30 and 70 μm.

[0120] Coating of the Substrate

[0121] The powder composition was used in powder coating of a cardboard substrate using electrostatic charging. The coating was applied using electrostatic spray gun on the charged substrate using 50 cm distance. Next, the substrate coated with the powder composition was heated in an air convection oven at 150° C. for 10 minutes to form an even coating layer on the substrate.

Example 5

[0122] Polyester Synthesis

[0123] Poly(butylene succinate) was synthetized using 1,4-butanediol (BDO) and succinic acid (SA) in molar ratios of 1.1:1. Firstly, esterification of SA and BDO was conducted in a temperature of 160 to 190° C. under nitrogen atmosphere while removing water and/or methanol from the reaction mixture. When no more water/methanol could be removed using atmospheric pressure, the polycondensation reaction was started in the presence of a organometallic catalyst, namely stannous octoate, at a temperature of 200 to 240° C. under vacuum for 4 to 6 hours. After obtaining desired viscosity of the polymer, it was collected from the reaction vessel and pelletized.

[0124] Preparation of Biopolymer Powder Composition

[0125] 18 g of prepared polybutylene succinate and 0.16 g of BYK333 (polyether-modified polydimethylsiloxane) as additive and 50 g of technical grade ethyl acetate was weighed into a 500 ml round bottom flask. The mixture was heated to 78° C. using reflux condenser and mixing under nitrogen atmosphere for 30 minutes. Then the biopolymer suspension was cooled to room temperature and the solvent was removed using solvent evaporation. After removal of the solvent, the obtained powder was sieved to median particle size between 30 and 70 μm.

[0126] Coating of the Substrate

[0127] The powder composition was used in powder coating of a cardboard substrate using electrostatic charging. The coating was applied using electrostatic spray gun on the charged substrate using 50 cm distance. Next, the substrate coated with the powder composition was heated in an air convection oven at 150° C. for 10 minutes to form an even coating layer on the substrate.

Example 6

[0128] Barrier properties of the compositions presented in the above examples were investigated by an overnight liquid absorption test and the results were compared to a substrate without any coating. The substrate used in the test was a cardboard. Oil, ethanol and water were used as absorbents. The results of the measurements are presented in Table 1.

[0129] Table 1. Oil, ethanol and water overnight liquid absorption test results for different powder coating compositions on a cardboard substrate compared to substrate without any coating. No=no absorption and/or penetration to the substrate, yes=absorbed through the coating to the substrate.

TABLE-US-00001 Coating Colored Coating thickness (μm) Oil Ethanol DI-water No coating 0.00 Yes Yes Yes Example 3 0.18 No No No Example 4 0.25 No No  No* *some colouring on the coating layer, not on substrate.

Example 7

[0130] Preparation of PLA

[0131] L-lactic acid (1000 g, 11.10 mol) were weighed into a round bottom flask and stirred at 175° C. for 4 hours. Then 0.1 wt-% of solid tin oxide catalyst was added and the temperature was raised to 230° C. L-lactide formed was separated from the mixture by vacuum of 5 mbar. Prepared L-lactide was heated in a round bottom flask at 170° C. on oil bath. Then 0.1 wt-% of tin octoate catalyst was added and the reaction was continued from 15 minutes to 4 hours until molecular weight of 180 000 g/mol was reached.

[0132] Preparation of Biopolymer Powder Composition

[0133] 900 g of previously prepared polylactic acid (PLA) was melt compounded using twin-screw extrusion with 100 g of polyethylene glycol having average molecular weight of 400 g/mol (M.sub.n) and 10 g of BYK333 at 180° C. extrusion temperature and 150 rpm screw speed. The compounded material was extruded into strands and pelletized into granules.

[0134] Powder Preparation

[0135] The biopolymer powder was manufactured using cryogenic grinding. Prior grinding, the compounded biopolymer granules were first precooled using liquid nitrogen. The precooled biopolymer granules were then grinded into a powder using and impact type cryogenic mill. Liquid nitrogen was used as cooling medium in the cryogenic grinding and it was continuously fed to keep temperatures inside the mill below 0° C. Rotational speed used in the milling was 15 000 rpm and the speed of the materials dosing screw was 20 rpm. 90 μm screen plate was used to obtain finely ground powder for powder coating. The obtained biopolymer powder was dried in vacuum oven before used as coating material.

[0136] Coating of the Substrate

[0137] The powder composition was used in powder coating of a cardboard substrate using electrostatic charging. The coating was applied using electrostatic spray gun on the charged substrate using 50 cm distance. Next, the substrate coated with the powder composition was heated in an air convection oven at 180° C. for 10 minutes to form an even coating layer on the substrate.

Example 8

[0138] Preparation of Biopolymer Powder Composition

[0139] 23 g of commercial grade poly(lactic acid), 2.6 g of trimethylene glycol having an average molecular weight between 900-1100 g/mol (M.sub.n), 2.6 g of Mixture 1 (Example 1), and 0.26 g of BYK359 as additive and 100 g of technical grade acetone was weighed into a 500 ml round bottom flask. The mixture was heated to 55° C. using reflux condenser and mixing under nitrogen atmosphere for 60 minutes. Then the formed biopolymer suspension was cooled to room temperature and the solvent was removed using solvent evaporation. After removal of the solvent, the obtained powder was sieved to median particle size between 30 and 70 μm.

[0140] Coating of the Substrate

[0141] The powder composition was used in powder coating of a cardboard substrate using electrostatic charging. The coating was applied using electrostatic spray gun on the charged substrate using 50 cm distance. Next, the substrate coated with the powder composition was heated in an air convection oven at 180° C. for 10 minutes to form an even coating layer on the substrate.

Example 9

[0142] Preparation of Biopolymer Powder Composition

[0143] 45 g of commercial grade polybutylene succinate, 5.0 g of trimethylene glycol having an average molecular weight between 900-1100 g/mol (M.sub.n), 0.5 g of BYK333 (polyether-modified polydimethylsiloxane) as additive and 100 g of technical grade ethyl acetate was weighed into a 500 ml round bottom flask. The mixture was heated to 78° C. using reflux condenser and mixing under nitrogen atmosphere for 30 minutes. Then the biopolymer suspension was cooled to room temperature and the solvent was removed using solvent evaporation. After removal of the solvent, the obtained powder composition was sieved to particle size below 100 μm.

[0144] Coating of the Substrate

[0145] The powder composition was used in powder coating of a cardboard substrate using electrostatic charging. The coating was applied using electrostatic spray gun on the charged substrate using 50 cm distance. Next, the substrate coated with a powder composition was heated in an air convection oven at 150° C. for 10 minutes to form an even coating layer on the substrate.

Example 10

[0146] Mixture 1—Preparation of Siloxane Precursor Solution

[0147] 50 g (0.201 mol) of methacryloxypropyltrimethoxysilane, 100 g of isopropanol and 2.1 g of 0.1M acetic acid were mixed in a round bottom flask equipped with a magnetic stirrer. Solution was mixed for 1 hour at room temperature.

[0148] Mixture 2—Reacting the Siloxane Precursor with Polyol

[0149] 60 g (0.150 mol) of polyethylene glycol having an average molecular weight of 400 g/mol (M.sub.n), 17.7 g (0.150 mol) of bio-succinic acid and 23.31 g of Mixture 1 (Example 10) were weighed into 500 ml round bottom flask. The mixture was heated to 160° C. using reflux condenser and mixing under nitrogen atmosphere for 1 hour 45 minutes. Then the mixture was cooled to room temperature.

[0150] Preparation of Biopolymer Powder Composition

[0151] 17.3 g of commercial grade polybutylene succinate and 2.7 grams of Mixture 2 (Example 10) as additive and 50 g of technical grade ethyl acetate was weighed into a 500 ml round bottom flask. The mixture was heated to 78° C. using reflux condenser and mixing under nitrogen atmosphere for 30 minutes. Then the formed biopolymer suspension was cooled to room temperature and the solvent was removed using solvent evaporation. After removal of the solvent, the obtained powder was sieved to median particle size between 30 and 70 μm.

[0152] Coating of the Substrate

[0153] The powder composition was used in powder coating of a cardboard substrate using electrostatic charging. The coating was applied using electrostatic spray gun on the charged substrate using 50 cm distance. Next, the substrate coated with the powder composition was heated in an air convection oven at 150° C. for 10 minutes to form an even coating layer on the substrate.

Example 11

[0154] Preparation of PLA

[0155] L-lactic acid (1000 g, 11.10 mol) were weighed into a round bottom flask and stirred at 175° C. for 4 hours. Then 0.1 wt-% of solid tin oxide catalyst was added and the temperature was raised to 230° C. L-lactide formed was separated from the mixture by vacuum of 5 mbar. Prepared L-lactide was heated in a round bottom flask at 170° C. on oil bath. Then 0.1 wt.-% of tin octoate catalyst was added and the reaction was continued from 15 minutes to 4 hours until molecular weight of 180 000 g/mol was reached.

[0156] Preparation of Biopolymer Powder Composition

[0157] 900 g of previously prepared polylactic acid (PLA) was melt compounded using twin-screw extrusion with 100 g of polyethylene glycol having average molecular weight of 400 g/mol (M.sub.n) and 10 g of BYK332 at 180° C. extrusion temperature and 150 rpm screw speed. The compounded material was extruded into strands and pelletized into granules.

[0158] Powder Preparation

[0159] The biopolymer powder was manufactured using cryogenic grinding. Prior grinding, the compounded biopolymer granules were first precooled using liquid nitrogen. The precooled biopolymer granules were then grinded into a powder using and impact type cryogenic mill. Liquid nitrogen was used as cooling medium in the cryogenic grinding and it was continuously fed to keep temperatures inside the mill below 0° C. Rotational speed used in the milling was 15 000 rpm and the speed of the materials dosing screw was 20 rpm. 90 μm screen plate was used to obtain finely ground powder for powder coating. The obtained biopolymer powder was dried in vacuum oven before used as coating material.

[0160] Coating of the Substrate

[0161] The powder composition was used in powder coating of a cardboard substrate using electrostatic charging. The coating was applied using electrostatic spray gun on the charged substrate using 50 cm distance. Next, the substrate coated with the powder composition was heated in an air convection oven at 200° C. for 10 minutes to form an even coating layer on the substrate.

Example 12

[0162] Preparation of Biopolymer Powder Composition

[0163] 980 g of commercial grade polybutylene succinate, 980 g of commercial grade poly(3-hydroxybutyrate-co-3-hydroxyvalerate), 20 g of Mixture 1 (Example 1) and 20 g of BYK360P (polyacrylate) were mixed and melt compounded into granules in a twin screw extruder at 170° C. using 100 rpm screw speed.

[0164] Powder Preparation

[0165] The biopolymer powder was manufactured using cryogenic grinding. Prior grinding, the compounded biopolymer granules were first precooled using liquid nitrogen. The precooled biopolymer granules were then grinded into a powder using and impact type cryogenic mill. Liquid nitrogen was used as cooling medium in the cryogenic grinding and it was continuously fed to keep temperatures inside the mill below 0° C. Rotational speed used in the milling was 15 000 rpm and the speed of the materials dosing screw was 20 rpm. 90 μm screen plate was used to obtain finely ground powder for powder coating. The obtained biopolymer powder was dried in vacuum oven before used as coating material.

[0166] Coating of the Substrate

[0167] The powder composition was used in powder coating of a cardboard substrate using electrostatic charging. The coating was applied using electrostatic spray gun on the charged substrate using 50 cm distance. Next, the substrate coated with the powder composition was heated in an air convection oven at 170° C. for 10 minutes to form an even coating layer on the substrate.

Example 13

[0168] Preparation of Biopolymer Powder Composition

[0169] 15 g of commercial grade polylactic acid, 32 g of commercial grade polybutylene succinate, 2.5 g of polyethylene glycol having average molecular weight of 200 g/mol (M.sub.n) and 0.5 g of commercial polyether-modified polydimethylsiloxane (BYK332) and 50 g of technical grade acetone was weighed into a 500 ml round bottom flask. The mixture was heated to 55° C. using reflux condenser and mixing under nitrogen atmosphere for 30 minutes. Then the formed biopolymer suspension was cooled to room temperature and the solvent was removed using solvent evaporation. After removal of the solvent, the obtained powder was sieved to median particle size between 30 and 70 μm.

[0170] Coating of the Substrate

[0171] The powder composition was used in powder coating of a cardboard substrate using electrostatic charging. The coating was applied using electrostatic spray gun on the charged substrate using 50 cm distance. Next, the substrate coated with the powder composition was heated in an air convection oven at 180° C. for 10 minutes to form an even coating layer on the substrate.

Example 14

[0172] Surface Modification of Talc

[0173] 30 g of talc powder (median particle size 1 μm) was mixed with 200 g of ethanol and 10 g of 3-aminopropyltriethoxysilane and mixed 3 h in room temperature under magnetic stirring. Talc was filtered from the solution, washed with 200 ml of ethanol and with 500 ml of deionized water, then dried in an air convection oven at 60° C. overnight.

[0174] Preparation of Biopolymer Powder Composition

[0175] 490 g of commercial grade polylactic acid, 480 g of commercial grade polybutylene succinate, 20 g of surface modified talc and 10 g of commercial polyether-modified polydimethylsiloxane (BYK307) was melt compounded in a twin screw extruder at 190° C. using 100 rpm screw speed. Then, 25 grams of the melt compounded biopolymer composition and 100 g of technical grade acetone was weighed into a 500 ml round bottom flask and heated to 55° C. using reflux condenser and mixed under nitrogen atmosphere for 30 minutes. Then the formed biopolymer suspension was cooled to room temperature and the solvent was removed using solvent evaporation. After removal of the solvent, the obtained powder was sieved to median particle size between 30 and 70 μm.

[0176] Coating of the Substrate

[0177] The powder composition was used in powder coating of a cardboard substrate using electrostatic charging. The coating was applied using electrostatic spray gun on the charged substrate using 50 cm distance. Next, the substrate coated with the powder composition was heated in an air convection oven at 180° C. for 10 minutes to form an even coating layer on the substrate.

Example 15

[0178] Mixture 1—Preparation of Siloxane Precursor Solution

[0179] 22.3 g of aqueous biosuccinic acid solution (1.3 wt.-% of biosuccinic acid diluted in deionized water) was gradually added to 191.7 g of methyltriethoxysilane. The solution was mixed 12 hours at room temperature prior to use.

[0180] Preparation of biopolymer powder composition 470 g of commercial grade polybutylene succinate, 25 g of polyethylene glycol having average molecular weight of 200 g/mol (M.sub.n) and 5 g of Mixture 1 (Example 15) was melt compounded using twin screw extrusion at 140° C. using 100 rpm screw speed. 50 g of the compounded biopolymer composition and 100 g of technical grade ethyl acetate was weighed into a 500 ml round bottom flask. The mixture was heated to 78° C. using reflux condenser and mixing under nitrogen atmosphere for 30 minutes. Then the formed biopolymer suspension was cooled to room temperature and the solvent was removed using solvent evaporation. After removal of the solvent, the obtained powder was sieved to median particle size between 30 and 70 μm.

[0181] Coating of the Substrate

[0182] The powder composition was used in powder coating of a cardboard substrate using electrostatic charging. The coating was applied using electrostatic spray gun on the charged substrate using 50 cm distance. Next, the substrate coated with the powder composition was heated in an air convection oven at 160° C. for 10 minutes to form an even coating layer on the substrate.

Example 16

[0183] Mixture 1—Preparation of Siloxane Precursor Solution 40 g (0.29 mol) of methyltrimethoxysilane, 80 g of ethanol and 5 g of water were mixed in a round bottom flask equipped with a magnetic stirrer. Solution was mixed for 1 hour at room temperature.

[0184] Preparation of Biopolymer Powder Composition

[0185] 23 g of commercial grade polylactic acid, 2.6 g of trimethylene glycol having an average molecular weight between 900-1100 g/mol (M.sub.n), 2.6 g of Mixture 1 (Example 16) and 100 g of technical grade acetone was weighed into a 500 ml round bottom flask. The mixture was heated to 55° C. using reflux condenser and mixing under nitrogen atmosphere for 90 minutes. Then the formed biopolymer suspension was cooled to room temperature and the solvent was removed using solvent evaporation. After removal of the solvent, the obtained powder was sieved to median particle size between 30 and 70 μm.

[0186] Coating of the Substrate

[0187] The powder composition was used in powder coating of a cardboard substrate using electrostatic charging. The coating was applied using electrostatic spray gun on the charged substrate using 50 cm distance. Next, the substrate coated with the powder composition was heated in an air convection oven at 180° C. for 10 minutes to form an even coating layer on the substrate.

Example 17

[0188] Barrier properties of the compositions presented in the above examples were investigated by an overnight liquid absorption test and the results were compared to a substrate without any coating as well as PBS and PLA powders. The reference materials were made into powder form using the solvent method described in the previous examples. PBS reference was prepared using ethyl acetate, 78° C. temperature and reflux condenser, PLA reference was prepared using acetone, 55° C. temperature and reflux condenser. The biopolymer suspensions were cooled to room temperature and made into powder form by removal of the solvent by evaporation.

[0189] The substrate used in the test was a cardboard. Oil, ethanol (50% ethanol:water mixture), and water with blue dye were used as absorbents. The results of the measurements are presented in Table 1.

[0190] Table 1. Oil, ethanol, and water overnight liquid absorption test results for different powder coating compositions on a cardboard substrate compared to substrate without any coating. No=no absorption and/or penetration to the substrate, yes=absorbed through the coating to the substrate.

TABLE-US-00002 Coating thickness Coating Colored Coating (mm) quality Oil Ethanol DI-water No coating 0.00 — Yes Yes Yes PBS 0.15 Poor Yes No  No* PLA 0.12 Poor Yes No No Example 3  0.18 even No No  No* Example 4  0.25 even No No  No* Example 9  0.11 even No No No Example 15 0.12 even No No No *some colouring on the coating layer, not on substrate.

[0191] The results in Table 1 show that the powder coating compositions according to the present invention have better coating quality and barrier properties compared to the uncoated substrate as well as the reference PBS and PLA materials. The improved barrier properties of the powder coatings can be related to the combination of biopolyester and siloxane precursors in the material compositions according to the invention. Also, the levelling and smoothness of the coatings according to the invention were clearly improved in comparison with the reference materials.

[0192] In addition, the powder coating compositions according to the present invention have better oil resistance compared to the substrate without any coating as well as the reference PBS and PLA materials. The poor oil resistance of the reference PBS and PLA is also due to the poor coating quality of the materials.

[0193] The ethanol and water resistance of the coating compositions according to the present invention in comparison with the uncoated substrate were also greatly improved. There was no signs of absorption of ethanol or water in the substrate.

INDUSTRIAL APPLICABILITY

[0194] The present invention can be used to produce packaging materials having a biopolymer coating, and generally for replacement of conventional methods of producing packaging materials.

[0195] In particular, the powder coating composition of the present in invention is useful in packaging materials of foodstuff, cosmetics and pharmaceuticals. Especially, the invention enables a single layer coating on a porous substrates.

CITATION LIST

Patent Literature

[0196] U.S. Pat. No. 6,274,672 [0197] U.S. Pat. No. 5,227,435