Biodegradable multi-layer film

Abstract

A multi-layer polymer film comprising at least one middle layer A, the polymeric constituents of which are soluble in aqueous solution, and in each case at least one substantially water-impermeable covering layer B, C arranged above and below the at least one middle layer A, wherein the layers A, B and C independently of each other in each case comprise at least one thermoplastic polymer and at least one of the covering layers B and C comprises at least one polyhydroxyalkanoate is presented and described. Processes for the production of the multi-layer polymer film according to the invention and its use for the production of molded parts, films or bags are furthermore presented and described.

Claims

1. A multi-layer polymer film comprising: at least one middle layer A, the polymeric constituents of which are soluble in aqueous solution; at least one covering layer B arranged above the at least one middle layer A and that is water-impermeable so as to withstand a column of water of at least 20 mm in accordance with DIN EN 20811:1992; and at least one covering layer C arranged below the at least one middle layer A and that water-impermeable so as to withstand a column of water of at least 20 mm in accordance with DIN EN 20811:1992, wherein the layers A, B and C independently of each other in each case comprise at least one thermoplastic polymer, wherein at least one of the covering layers B and C comprises at least one polyhydroxyalkanoate in an amount of 20 wt. % to 95 wt. % based on a total weight of the particular covering layer, at least one additional polymer, and less than 5 wt. % of starch polymer based on the total weight of the particular covering layer, and wherein the particular covering layer includes 95 wt. % to 100 wt. % by combined weight of the at least one polyhydroxyalkanoate and the at least one additional polymer based on the total weight of the particular covering layer, wherein the at least one polyhydroxyalkanoate is selected from the group consisting of poly(3-hydroxybutanoate), poly(3-hydroxyvalerate), poly(3-hydroxy-hexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), and mixtures thereof, wherein the at least one additional polymer is selected from the group consisting of polylactic acid in an amount of 30 wt. % to 69 wt. % based on the total weight of the particular covering layer, polycaprolactone in an amount of 5 wt. % to 15 wt. % based on the total weight of the particular covering layer, aromatic-aliphatic copolyesters in an amount of 5 wt. % to 70 wt. % based on the total weight of the particular covering layer, and mixtures thereof, wherein at least one of the covering layers B and C has a tensile strength in an extrusion direction (MD) of at least 10 MPa and a tensile strength transverse to the extrusion direction (TD) of at least 10 MPa, wherein the polyhydroxyalkanoate in the particular covering layer, through post-crystallization, causes or allows the particular covering layer to disintegrate in aqueous solution within at most 14 days into parts having (i) a surface area of at most 60% of the total surface area of the multi-layer polymer film and/or (ii) a surface area of at most 100 cm.sup.2.

2. The polymer film according to in claim 1, wherein at least one of the covering layers B and C comprises the at least one polyhydroxyalkanoate, at least one aliphatic-aromatic copolyester in an amount in a range of 5 to 70 wt. %, and 0% to less than 5 wt. % by combined weight of starch, starch derivative, destructured starch, and thermoplastic starch, based on the total weight of the particular covering layer.

3. The polymer film according to claim 1, wherein the at least one thermoplastic polymer of one of the covering layers B and C can be decomposed in water by hydrolysis.

4. The polymer film according to claim 1, wherein the covering layers B and C independently of each other comprise at least one thermoplastic polymer selected from the group consisting of thermoplastic starch, starch-containing thermoplastics, polyvinyl alcohol, thermoplastic polyvinyl alcohol, polyvinyl acetate, poly(3-hydroxybutanoate), poly(3-hydroxyvalerate), poly(3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxy-butyrate-co-3-hydroxyhexanoate), polylactic acid, polycaprolactone, polybutylene succinate, poly(butylene adipate-co-succinate), aromatic-aliphatic copolyester, poly(butylene adipate-co-terephthalate), poly(butylene sebacate-co-terephthalate), and mixtures thereof.

5. The polymer film according to claim 1, wherein the at least one polyhydroxyalkanoate in at least one of the covering layers B and C includes at least poly(3-hydroxybutyrate-co-3-hydroxy-hexanoate).

6. The polymer film according to claim 1, wherein the at least one polyhydroxyalkanoate in at least one of the covering layers B and C has been produced by microorganisms in a fermentation process and/or by chemical synthesis.

7. The polymer film according to claim 1, wherein each of the covering layers B and C comprises the at least one polyhydroxyalkanoate in an amount that, through post-crystallization, causes or allows the covering layers B and C to disintegrate in aqueous solution within at most 10 days into parts having (i) a surface area of at most 60% of the total surface area of the multi-layer polymer film and/or (ii) a surface area of at most 100 cm.sup.2.

8. The polymer film according to claim 1, wherein at least one of the covering layers B and C comprises the at least one polyhydroxyalkanoate, at least one aliphatic-aromatic copolyester in an amount in a range of 10 to 70 wt. %, and 0% to less than 5 wt. % by combined weight of starch, starch derivative, destructured starch, and thermoplastic starch.

9. The polymer film according to claim 1, wherein each of the covering layers B and C, in accordance with ASTM D6866, comprises at least 40 wt. % of biobased carbon, based on the total amount of carbon of the particular covering layer.

10. The polymer film according to claim 1, wherein each of the covering layers B and C, in accordance with ISO 15985 and/or in accordance with ISO 14855, is biodegradable to the extent of at least 40%.

11. The polymer film according to claim 1, wherein the middle layer A, in accordance with ISO 15985 and/or in accordance with ISO 14855, is biodegradable to the extent of at least 40%.

12. The polymer film according to claim 1, wherein the at least one thermoplastic polymer of the middle layer A is selected from the group consisting of thermoplastic starch, starch-containing thermoplastics, polyvinyl alcohol, thermoplastic polyvinyl alcohol, polyvinyl acetate, polyethylene glycol, cellulose acetate, ethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, poly(vinylpyrrolidone), poly(3-hydroxybutanoate), poly(3-hydroxyvalerate), poly(3-hydroxyhexanoate), poly(3-hydroxy-butyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), polylactic acid, polycaprolactone, polybutylene succinate, poly(butylene adipate-co-succinate), aromatic-aliphatic copolyester, poly(butylene adipate-co-terephthalate), poly(butylene sebacate-co-terephthalate) and mixtures thereof.

13. The polymer film according to claim 1, wherein the polymer film has in the dry state an elongation at break in the extrusion direction (MD) in accordance with EN ISO 527 of 100% or more.

14. The polymer film according to claim 1, wherein the polymer film has in the dry state an elongation at break transversely to the extrusion direction (TD) in accordance with EN ISO 527 of 100% or more.

15. The polymer film according to claim 1, wherein the polymer film has in the dry state a specific dart drop value in accordance with ASTM D1709 of at least 5 g/μm.

16. The polymer film according to claim 1, wherein the covering layers B and/or C independently of each other disintegrate in aqueous solution within at most 7 days, into parts having a surface area of in each case at most 60% of the total surface area of the multi-layer polymer film.

17. The polymer film according to claim 1, wherein the covering layers B and/or C independently of each other disintegrate in aqueous solution within at most 7 days, into parts having a surface area of in each case at most 100 cm.sup.2.

18. The polymer film according to claim 1, wherein the polymer film has a total thickness of from 10 μm to 80 μm.

19. The polymer film according to claim 1, wherein the middle layer A of the polymer film makes up 30% to 90% of the total thickness of the polymer film.

20. The polymer film according to claim 1, wherein the covering layers B and C of the polymer film together make up 10% to 70% of the total thickness of the polymer film.

21. The polymer film according to claim 1, wherein the covering layers B and/or C independently of each other have places with a lower resistance to mechanical influences and/or to aqueous solutions.

22. The polymer film according to claim 1, wherein the covering layers B and/or C independently of each other comprise a water-soluble polymer.

23. The polymer film according to claim 1, wherein the surfaces of the covering layers B and/or C independently of each other have a corrugated surface.

24. The polymer film according to claim 1, wherein the covering layers B and/or C have in the dry state in each case a specific dart drop value of at least 5 g/μm in accordance with ASTM D1709.

25. The polymer film according to claim 1, wherein the covering layers B and/or C independently of each other have a tensile strength in the extrusion direction (MD) of at least 20 MPa, in accordance with EN ISO 527.

26. The polymer film according to claim 1, wherein the covering layers B and/or C independently of each other have a tensile strength transversely to the extrusion direction (TD) of at least 20 MPa, in accordance with EN ISO 527.

27. The polymer film according to claim 1, wherein the covering layers B and/or C independently of each other have an elongation at break in the extrusion direction (MD) of at least 100%, in accordance with EN ISO 527.

28. The polymer film according to claim 1, wherein the covering layers B and/or C independently of each other have an elongation at break transversely to the extrusion direction (TD) of at least 100%, in accordance with EN ISO 527.

29. The polymer film according to claim 1, wherein the middle layer A has a tensile strength in the extrusion direction (MD) of at least 10 MPa in accordance with EN ISO 527.

30. The polymer film according to claim 1, wherein the middle layer A has a tensile strength transversely to the extrusion direction (TD) of at least 10 MPa in accordance with EN ISO 527.

31. The polymer film according to claim 1, wherein the middle layer A has an elongation at break in the extrusion direction (MD) of at least 100%, in accordance with EN ISO 527.

32. The polymer film according to claim 1, wherein the middle layer A has an elongation at break transversely to the extrusion direction (TD) of at least 100%, in accordance with EN ISO 527.

33. The polymer film according to claim 1, wherein the covering layers B and C are identical.

34. A molded part, film or bag produced from a multi-layer polymer film according to claim 1.

35. A multi-layer polymer film comprising: at least one middle layer A, the polymeric constituents of which are soluble in aqueous solution; at least one covering layer B arranged above the at least one middle layer A and that is water-impermeable so as to withstand a column of water of at least 20 mm in accordance with DIN EN 20811:1992; and at least one covering layer C arranged below the at least one middle layer A and that water-impermeable so as to withstand a column of water of at least 20 m in accordance with DIN EN 20811:1992, wherein the layers A, B and C independently of each other in each case comprise at least one thermoplastic polymer, wherein at least one of the covering layers B and C comprises at least one polyhydroxyalkanoate in an amount of 20 wt. % to 95 wt. % based on a total weight of the particular covering layer, at least one additional polymer is selected from the group consisting of polylactic acid in an amount of 30 wt. % to 69 wt. % based on the total weight of the particular covering layer, polycaprolactone in an amount of 5 wt. % to 15 wt. % based on the total weight of the particular covering layer, aromatic-aliphatic copolyesters in an amount of 5 wt. % to 70 wt. % based on the total weight of the particular covering layer, and mixtures thereof, and less than 5 wt. % of starch polymer based on the total weight of the particular covering layer, and wherein the particular covering layer includes 95 wt. % to 100 wt. % by combined weight of the at least one polyhydroxyalkanoate and the at least one additional polymer based on the total weight of the particular covering layer, wherein the layer A has a tensile strength in the extrusion direction (MD) and transversely to the extrusion direction (TD) in accordance with EN ISO 527 of at least 15 MPa, wherein each of layers B and C has a tensile strength in the extrusion direction (MD) of at least 20 MPa and a tensile strength transversely to the extrusion direction (TD) of at least 20 MPa in accordance with EN ISO 527, and wherein the at least one thermoplastic polymer of the covering layers B and C decomposes by hydrolysis in aqueous solution within at most 14 days.

36. A process for the production of a multi-layer polymer film at least comprising a middle layer A, the polymeric constituents of which dissolve in aqueous solution, at least one covering layer B arranged above the middle layer A, and at least one covering layer C arranged below the middle layer A, wherein layers B and C are water-impermeable so as to withstand a column of water of at least 20 mm in accordance with DIN EN 20811:1992, wherein the layers A, B and C independently of each other in each case comprise at least one thermoplastic polymer, the process comprising: (a) providing a polymer composition of a first covering layer which comprises at least one polyhydroxyalkanoate in an amount of 20 wt. % to 95 wt. % based on a total weight of the first covering layer, at least one additional polymer, and less than 5 wt. % of starch polymer based on the total weight of the first covering layer, wherein the at least one additional polymer is selected from the group consisting of polylactic acid in an amount of 30 wt. % to 69 wt. % based on the total weight of the particular covering layer, polycaprolactone in an amount of 5 wt. % to 15 wt. % based on the total weight of the particular covering layer, aromatic-aliphatic copolyesters in an amount of 5 wt. % to 70 wt. % based on the total weight of the particular covering layer, and mixtures thereof, and wherein the first covering layer includes 95 wt. % to 100 wt. % by combined weight of the at least one polyhydroxyalkanoate and the at least one additional polymer based on the total weight of the first covering layer, (b) forming the first covering layer from the polymer composition in (a), (c) providing at least one thermoplastic polymer of the middle layer A, (d) forming the middle layer A from the at least one thermoplastic polymer of (c), (e) providing a polymer composition of a second covering layer, and (f) forming the second covering layer from the polymer composition in (e), wherein at least one of the first or second covering layers has a tensile strength in an extrusion direction (MD) of at least 10 MPa and a tensile strength transverse to the extrusion direction (TD) of at least 10 MPa and decomposes by hydrolysis in aqueous solution within at most 14 days.

37. The process according to in claim 36, wherein steps (b), (d), and (f) are carried out simultaneously.

38. The process according to claim 36, wherein the process includes a coextrusion step.

39. The process according to claim 36, wherein the process comprises a laminating step.

40. The process according to claim 36, wherein at least one polyhydroxyalkanoate is included in the polymer composition in step e.

41. The process according to claim 36, further comprising forming the multi-layer polymer film into molded parts, films or bags.

Description

EXAMPLE 1 (COMPARATIVE EXAMPLE)

(1) Using a twin-screw extruder (co-rotating) of the Werner & Pfleiderer (COPERION) ZSK 70 type, screw diameter 70 mm, L/D=36, the following polymer blend A was compounded (metered contents in percent by weight):

(2) TABLE-US-00001 TABLE 1 Recipe A A PBAT 57.4 Starch 42.6

(3) The following compounding parameters were maintained here:

(4) TABLE-US-00002 TABLE 2 Temperature profile ZSK 70 Zone Zone Zone Zone Zone Zone Zone Zone Zone Zone Zone 1 2 3 4 5 6 7 8 9 10 11 Die 25° C. 190° C. 190° C. 190° C. 170° C. 170° C. 170° C. 170° C. 155° C. 100° C. 150° C. 140° C.

(5) Melt temperature at the die opening: 163° C.

(6) Speed of rotation: 205 min.sup.−1

(7) Throughput: 400 kg/h

(8) Degasification: active (vacuum, zone 9)

(9) Water content: less than 1 wt. %

(10) (measured after exit from the extruder)

(11) Using a single-screw extruder of the COLLIN 30 (DR. COLLIN) type, screw diameter 30 mm, L/D=33, thermoplastic starch (TPS) with the following recipe was furthermore compounded (metered contents in percent by weight):

(12) TABLE-US-00003 TABLE 3 TPS recipe TPS Glycerin 20 Sorbitol 10 Starch 70

(13) Granules A were then melted with a single-screw extruder of the COLLIN 30 (DR. COLLIN) type, screw diameter 30 mm, L/D=33 and processed together with the thermoplastic starch TPS, which was likewise melted in a single-screw extruder of the COLLIN 30 (DR. COLLIN) type, screw diameter 30 mm, L/D=33, in a coextrusion step to give a three-layer film, wherein the middle layer comprised TPS and the covering layers comprised composition A. The mechanical properties of the three-layer film as well as the decomposability of the covering layers into smaller parts and the solubility of the middle layer in water were investigated.

(14) For the investigation of the stability of the three-layer film in water, specimens of the film were clamped in slide frames and laid in natural sea water. The film was furthermore exposed to mechanical stress. The decomposition of the film was evaluated visually.

(15) The results of this investigation are summarized in the following table.

(16) TABLE-US-00004 TABLE 4 Mechanical properties of the three-layer film and decomposability/solubility in water Thickness Specific Tensile Elongation covering Thickness dart drop strength at break layers middle [g/μm] [MPa] [%] (each) layer ASTM D EN ISO 527 EN ISO 527 Decomposability Solubility [μm] [μm] 1709 MD TD MD TD covering layers middle layer 10 10 8 10.7 7.6 475 230 No Middle layer decomposition intact after after 14 days 14 days due to intact covering layers

(17) As can be seen from the table, the resulting film on the one hand has a tensile strength which are inadequate for the requirements of a bag. Furthermore, after 14 days no decomposition of the covering layers was to be seen, for which reason the film was still intact even after 14 days.

EXAMPLE 2

(18) Using a twin-screw extruder (co-rotating) of the Werner & Pfleiderer (COPERION) ZSK 40 type, screw diameter 40 mm, L/D=42, the following recipe B was compounded (metered contents in percent by weight):

(19) TABLE-US-00005 TABLE 5 Recipe B PBAT 44.6 PHBH 19.8 Starch 20.5 PVOH 10 PLA 5.1

(20) The following compounding parameters were maintained here:

(21) TABLE-US-00006 TABLE 6 Temperature profile ZSK 40 Zone Zone Zone Zone Zone Zone Zone Zone 1 2 3 4 5 6 7 8 Die 25° C. 150° C. 150° C. 140° C. 130° C. 130° C. 130° C. 130° C. 130° C.

(22) Melt temperature at the die opening: 133° C.

(23) Speed of rotation: 140 min.sup.−1

(24) Throughput: 40 kg/h

(25) Degasification: active (vacuum, zone 7)

(26) Water content: less than 1 wt. %

(27) (measured after exit from the extruder)

(28) Granules B were then melted with a single-screw extruder of the COLLIN 30 (DR. COLLIN) type, screw diameter 30 mm, L/D=33 and processed together with PVOH, which was likewise melted in a single-screw extruder of the COLLIN 30 (DR. COLLIN) type, screw diameter 30 mm, L/D=33, in a coextrusion step to give a three-layer film, wherein the middle layer comprised PVOH and the covering layers comprised composition B. The mechanical properties of the three-layer film as well as the decomposability of the covering layers into smaller parts and the solubility of the middle layer in water were investigated.

(29) For the investigation of the stability of the three-layer film in water, specimens of the film were clamped in slide frames and laid in natural sea water. Furthermore, the film was exposed to mechanical stress. The decomposition of the film was evaluated visually.

(30) The results of this investigation are summarized in the following table.

(31) TABLE-US-00007 TABLE 7 Mechanical properties of the three-layer film and decomposability/solubility in water Thickness Specific Tensile Elongation covering Thickness dart drop strength at break layers middle [g/μm] [MPa] [%] (each) layer ASTM D EN ISO 527 EN ISO 527 Decomposability Solubility [μm] [μm] 1709 MD TD MD TD covering layers middle layer 10 10 25.4 37.0 40.3 281 234 Smaller parts Completely after 7 days dissolved after 7 days

(32) The table shows for this film significantly increased values for the tensile strength and good values for the elongation at break, which render it suitable, for example, for a bag. It was furthermore observed that after a few days both covering layers started to disintegrate into smaller parts, which exposed the middle layer, the polymeric constituents of which dissolved in aqueous solution.

EXAMPLES 3 TO 15

(33) Using a 5-layer blown film line of the Biotem 10 15 (Dr. Collin) type with screw diameters of 20 mm, L/D=25, for the outer four layers and a screw diameter of 25 mm, L/D=25, for the inner layer, multi-layer films were produced. The following recipes were compounded in the extruders here for the covering layers (metered amounts in percent by weight):

(34) TABLE-US-00008 TABLE 8 Recipes for the covering layers C D E F G H J PHBH 84 72 63 26 30 58 75 PBAT 16 15 21 41 42 26 10 PBST — 13 — — — — — Starch — — 15 30 28 15 — PLA — —  1  3 —  1 — PCL — — — — — — 15 K L M N O PHBH 70 30 70 31 95 PBAT 17 42 — — — PBSA 13 — — — — Starch — 28 — — — PLA — — 30 69 — PCL — — — —  5

(35) For multi-layer films in which recipe L was used for the covering layers TPS (see Example 1) was used for the middle layer. For multi-layer films in which recipes C to K, M to O and pure PHBH were used for the covering layers PVOH was used for the middle layer. The following combinations thus resulted for the multi-layer films:

(36) TABLE-US-00009 TABLE 9 Combinations of the recipes of the covering layers with the various middle layers Multi-layer film no. Covering layers Middle layer I PHBH PVOH II Recipe C PVOH III Recipe D PVOH IV Recipe E PVOH V Recipe F PVOH VI Recipe G PVOH VII Recipe H PVOH VIII Recipe J PVOH IX Recipe K PVOH X Recipe L TPS XI Recipe M PVOH XII Recipe N PVOH XIII Recipe O PVOH

(37) The following processing parameters were maintained:

(38) TABLE-US-00010 TABLE 10 Temperature profile Biotem 1015 Covering Zone Zone Zone Zone Flange layer Extruder 1 2 3 4 1 Die PHBH, covering 25° C. 160° C. 165° C. 165° C. 165° C. 170° C. recipes layers C, D, G, middle 25° C. 185° C. 185° C. 185° C. 185° C. 175° C. J, K, O layer Recipes covering 25° C. 180° C. 180° C. 180° C. 180° C. 175° C. E, F, H layers middle 25° C. 185° C. 185° C. 185° C. 185° C. 175° C. layer Recipe L covering 25° C. 160° C. 165° C. 165° C. 165° C. 170° C. layers middle 25° C. 165° C. 165° C. 165° C. 165° C. 165° C. layer Recipes covering 25° C. 180° C. 185° C. 185° C. 185° C. 185° C. M, N layers middle 25° C. 185° C. 185° C. 185° C. 185° C. 175° C. layer

(39) Speed of rotation: 55-90 min.sup.−1

(40) Annular die: diameter 60 mm

(41) Annular gap: 1.20 mm

(42) Blow-up ratio: approx. 1:3.

(43) Films having a total thickness of from 20 to 35 μm were produced. The multi-layer films had the construction of covering layer-covering layer-middle layer-covering layer-covering layer. The individual layers here had a ratio of covering layer:covering layer:middle layer:covering layer:covering layer of 1:1:2-4:1:1.

(44) The films were then stored for at least 72 hours, before the mechanical properties were investigated.

(45) TABLE-US-00011 TABLE 11 Mechanical properties of the multi-layer films Tensile strength Elongation at break Specific dart drop [MPa] [%] [g/μm] EN ISO 527 EN ISO 527 Film ASTM D 1709 MD TD MD TD I 6 35 37 190 410 II 7 27 25 320 450 III 8 23 24 457 530 IV 8 24 26 418 491 V 11 37 40 281 234 VI 10 28 30 405 436 VII 5 37 28 216 228 VIII 9 22 24 480 562 IX 6 32 31 310 378 X 7 11 10 513 444 XI 5 47 49 209 220 XII 5 52 55 123 147 XIII 7 26 28 280 452

(46) The table shows that on the basis of their mechanical properties films I to IX and XI to XIII are suitable in particular for plastic carrier bags. It was likewise observed that films I to XIII, when clamped in slide frames, laid in natural sea water and exposed to mechanical stress, disintegrated into smaller parts after several days in water. The middle layer dissolved here and the covering layers disintegrated into smaller parts.