Packaging film

Abstract

The present invention relates to a film comprising at least one biodegradable layer (i) having an elastic modulus of more than 450 MPa, consisting of a mixture of polyhydroxyalkanoate constituting the continuous phase and aliphatic and/or aliphatic-aromatic polyester constituting the discontinuous phase, and at least one coating layer (ii) preferably capable of having barrier effects against gases and liquids. The surface of said layer (i) will have a root mean square roughness Sq of more than 10 nm and less than 45 nm, measured by atomic force microscopy (AFM). The film is particularly suitable for use in food packaging.

Claims

1. A barrier film comprising at least one biodegradable layer (i) having an elastic modulus higher than 450 MPa, consisting of a mixture comprising a polyhydroxyalkanoate constituting the continuous phase and an aliphatic and/or aliphatic-aromatic polyester constituting the discontinuous phase, the said mixture further comprising from 0.01 to 5% wt. of a crosslinking agent and/or a chain extending agent having two or multiple functional groups, and at least one coating layer (ii), where the surface of layer (i) is characterised by a root mean square roughness Sq of more than 20 nm and less than 45 nm, measured by atomic force microscopy (AFM).

2. The barrier film according to claim 1, in which the said mixture comprises from 0.01 to 0.45% wt. of a crosslinking agent and/or a chain extending agent having two or multiple functional groups.

3. The barrier film according to claim 1 in which the said crosslinking agent and/or chain extending agent is selected from compounds having two or multiple functional groups including isocyanate, peroxide, carbodiimide, isocyanurate, oxazoline, epoxy, anhydride or divinyl ether groups and mixtures of these.

4. The barrier film according to claim 1 in which layer (i) has elongation at break (Eb) values of 150% or above and below 400% measured according to ASTM D882 (23 C., 50% relative humidity at Vo 50 mm/min).

5. The barrier film according to claim 1, in which said polyhydroxyalkanoate is selected from the group consisting of: polyesters of lactic acid, polyhydroxybutyrate, polyhydroxybutyrate-valerate, polyhydroxybutyrate-propanoate, polyhydroxybutyrate-hexanoate, polyhydroxybutyrate-decanoate, polyhydroxybutyrate-dodecanoate, polyhydroxybutyrate-hexadecanoate, polyhydroxybutyrate-octadecanoate, poly-3-hydroxybutyrate-4-hydroxybutyrate polyesters and mixtures thereof.

6. The barrier film according to claim 5, in which said polyhydroxyalkanoate comprises at least 70% by weight of one or more polyesters of lactic acid.

7. The barrier film according to claim 1, in which said aliphatic and/or aliphatic-aromatic polyester layer (i) is selected from the group consisting of poly(1,4-butylene succinate), poly(1,4-butylene succinate-co-adipate), poly(1,4-butylene succinato-co-1,4-butylene azelate), poly(1,4 butylene adipate-co-1,4-butylene terephthalate), poly(1,4-butylene succinate-co-1,4-butylene terephthalate), poly(1,4-butylene azelate-co-1,4-butylene terephthalate), poly(1,4-butylene brassylate-co-1,4-butylene terephthalate), poly(1,4-butylene sebacate-co-1,4-butylene terephthalate), poly(1,4-butylene adipate-co-1,4-butylene sebacate-co-1,4-butylene terephthalate), poly(1,4-butylene azelate-co-1,4-butylene sebacate-co-1,4-butylene terephthalate), poly(1,4-butylene adipate-co-1,4-butylene azelate-co-1,4-butylene terephthalate), poly(1,4-butylene succinate-co-1,4-butylene sebacate-co-1,4-butylene terephthalate), poly(1,4-butylene adipate-co-1,4-butylene succinate-co-1,4-butylene terephthalate), poly(1,4-butylene azelate-co-1,4-butylene succinate-co-1,4-butylene terephthalate).

8. The barrier film according to claim 1, in which said crosslinking agent and/or a chain extending agent having two or multiple functional groups bears peroxide groups and is contained in the film layer (i) in amounts from 0.01 to 0.1% by weight of the total mixture constituting layer (i).

9. The barrier film according to claim 1, in which said crosslinking agent and/or a chain extending agent having two or multiple functional groups bears epoxy groups and is contained in the film layer (i) in amounts from 0.05 to 0.3% by weight of the total mixture constituting layer (i).

10. The barrier film according to claim 1, in which said coating layer (ii) is capable of having barrier effects against gases and liquids.

11. The barrier film according to claim 1, in which said coating layer (ii) comprises a first layer of organic material, which may be natural and/or synthetic, in contact with said layer (i) and a second layer of metal material covering the first.

12. The barrier film according to claim 1, further including a polymer layer (iii) (multilayer film).

13. The barrier film according to claim 12, in which said layer (iii) comprises one or more polymers selected from: polyhydroxyalkanoate, aliphatic/aromatic polyester of the diacid-diol type which is the same as or different from those comprised in layer (i), aliphatic polyester, and mixtures thereof.

14. Food packaging comprising the barrier film according to claim 1.

15. Packaging having a barrier effect comprising a biodegradable film with a modulus of more than 450 MPa, consisting of a mixture comprising a polyhydroxyalkanoate as the continuous phase and at least one aliphatic and/or aliphatic-aromatic polyester as the discontinuous phase.

16. Packaging comprising a barrier film according to claim 1.

17. The barrier film according to claim 2 in which the said crosslinking agent and/or chain extending agent is selected from compounds having two or multiple functional groups including isocyanate, peroxide, carbodiimide, isocyanurate, oxazoline, epoxy, anhydride or divinyl ether groups and mixtures of these.

18. The barrier film according to claim 2 in which layer (i) has elongation at break (8b) values of 150% or above and below 400% measured according to ASTM D882 (23 C., 50% relative humidity at Vo 50 mm/min).

19. The barrier film according to claim 3 in which layer (i) has elongation at break (8b) values of 150% or above and below 400% measured according to ASTM D882 (23 C., 50% relative humidity at Vo 50 mm/min).

20. The barrier film according to claim 2, in which said polyhydroxyalkanoate is selected from the group consisting of: polyesters of lactic acid, polyhydroxybutyrate, polyhydroxybutyrate-valerate, polyhydroxybutyrate-propanoate, polyhydroxybutyrate-hexanoate, polyhydroxybutyrate-decanoate, polyhydroxybutyrate-dodecanoate, polyhydroxybutyrate-hexadecanoate, polyhydroxybutyrate-octadecanoate, poly-3-hydroxybutyrate-4-hydroxybutyrate polyesters and mixtures thereof.

21. The barrier film according to claim 1, wherein the root mean square roughness Sq is above 40 nm.

22. The barrier film according to claim 1, wherein the at least one biodegradable layer (i) having an elastic modulus higher than 450 MPa, consists of a mixture comprising from 90 to 51% by weight of a polyhydroxyalkanoate constituting the continuous phase and from 10 to 49% by weight of an aliphatic and/or aliphatic-aromatic polyester constituting the discontinuous phase.

23. The barrier film according to claim 22, wherein the root mean square roughness Sq is above 40 nm.

Description

EXAMPLES

Example 1

(1) Layer (i)

(2) 14.3 kg/h poly(butylene adipate-co-butylene terephthalate), MFR 4.2 g/10 min (190 C.; 2.16 kg) and acidity 42 meq/kg, 24.7 kg/h of Ingeo 3251D polylactic acid (PLA), MFR 40 g/10 min (190 C.; 2.16 kg), 1.0 kg/h masterbatch comprising 10% by weight of Joncryl ADR4368CS (styrene-glycidylether-methyl methacrylate copolymer) and Ingeo 4043D 90% polylactic acid (PLA) were fed to an OMC-type twin-screw extruder operating under the following conditions: Screw diameter (D)=58 mm; L/D=36; Rotation speed=140 rpm; Thermal profile=60-150-180-2104-1802 C.; Throughput=40 kg/h; Vacuum degassing in zone 8 out of 10.

(3) The granules thus obtained had an MFR value (190 C.; 2.16 kg according to ISO standard 1133-1 Plasticsdetermination of the melt mass-flow rate (MFR) and melt volume flow rate (MVR) of thermoplasticsPart 1: Standard method) of 11.4 g/10 minutes. The granules so obtained were fed to a Ghioldi model bubble film machine with a 40 mm diameter screw with an L/D 30 operating at 64 rpm with a 120-2003 thermal profile. The film-forming head with a 0.9 mm gap and L/D 12 was set at 200 C. Film-forming was performed with a blowing ratio of 3.2 and a stretch ratio of 11.7.

(4) The film thus obtained (total 24 microns) was then characterised in terms of mechanical properties, in particular tensile strength (.sub.b), elongation at break (.sub.b), elastic modulus (E), optical properties (transmittance, haze and clarity) and roughness.

(5) Roughness measurements were made on an area of 10 m10 m through AFM operating in tapping mode with a resolution of 256 points by 256 lines, using a monolithic silicon microlever (cantilever) of length 225 microns, with a natural frequency of 190 kHz, force constant 48 N/m, tip radius less than 10 nm.

(6) TABLE-US-00002 TABLE 1 Determination of the properties of layer (i) in Example 1 FILM TRACTION ASTM D882 OPTICAL PROPERTIES (23 C. 50% RH - Vo 50 mm/min) ASTM D1003 ROUGHNESS .sub.b .sub.b E TRANS. HAZE CLARITY Sq Sy (MPa) (%) (MPa) (%) (%) (%) (nm) (nm) Ex. 1 37 314 2045 81 22 98 20.6 235.9
Layer (ii)

(7) A complexed starch-based coating composition was prepared by feeding 19.8 kg/h native corn starch (containing 12% water), 12.9 kg/h polyvinyl alcohol with a degree of hydrolysis between 84.2% and 86.2%, 2.8 kg/h glycerine and 4.5 kg/h water to an OMC model twin-screw extruder operating under the following conditions: Screw diameter (D)=58 mm; L/D=36; Rotation speed=140 rpm; Thermal profile=145-170-2004-1502 C.; Throughput=40 kg/h; Vacuum degassing in zone 8 out of 10.

(8) 20 g of the product were added to 80 g of deionised water and dispersed by means of a rotor-stator disperser (Ika Ultra-Turrax T25) at 25000 rpm for 15 minutes. The suspension was allowed to cool to room temperature before being applied to the surface of layer (i) by airbrush with a 12 g/m.sup.2 coating.

(9) The film obtained visually appeared to demonstrate good adhesion between layer (i) and layer (ii).

(10) The barrier properties of the film obtained were determined by permeability measurements performed in an Extrasolution Multiperm permeability meter at 23 C.-50% relative humidity, performed according to ASTM F2622-08 for oxygen and ASTM standard F2476-05 for carbon dioxide and are shown in Table 2.

(11) TABLE-US-00003 TABLE 2 Determination of barrier properties of the film in Example 1 P (O2) P .sub.(CO2) Example 1 $\left[\frac{{\mathrm{cm}}^3\mathrm{mm}}{m^{2}24h\mathrm{bar}}\right]$ $\left[\frac{{\mathrm{cm}}^3\mathrm{mm}}{m^{2}24h\mathrm{bar}}\right]$ Layer (i) 30.0 86.2 Layer (i) + Layer (ii) 2.7 14.0

(12) It can be seen that the application of coating layer (ii) has resulted in a significant reduction in oxygen and CO.sub.2 permeability, assuming a barrier film is obtained. This effect confirms the good adhesion between the two layers (i) and (ii).

Comparative Example 2

(13) Layer (i)

(14) An Ingeo Biopolymer 4043D polylactic acid (MFR (190 C., 2.16 kg) equal to 3 g/10 min) in granules was fed to a Ghioldi model bubble film-firming machine with a 40 mm diameter screw with an L/D 30 operating at 64 rpm with a 120-1903 C. thermal profile. The film head had a 0.9 mm gap and the L/D 12 was set at 190 C. Film-forming was carried out with a blowing ratio of 3.2 and a stretch ratio of 8.1.

(15) The film thus obtained (total 35 microns) was therefore characterised in terms of mechanical properties, in particular tensile strength (.sub.b), elongation at break (.sub.b) and elastic modulus (E), optical properties (transmittance, haze and clarity) and roughness, determined as in Example 1.

(16) TABLE-US-00004 TABLE 3 Determination of the properties of layer (i) in comparative Example 2 FILM TRACTION ASTM D822 OPTICAL PROPERTIES (23 C. 55% RH - Vo 50 mm/min) ASTM D1003 ROUGHNESS .sub.b .sub.b E TRANS. HAZE CLARITY Sq Sy (MPa) (%) (MPa) (%) (%) (%) (nm) (nm) Comp. 56 30 2983 95 2 99 9.2 89.3 Ex. 2

(17) As may be seen from Table 3, layer (i) obtained in Example 1 according to the invention has comparable mechanical and optical properties to those of layer (i) in Comparative Example 2 based only on PLA, and is suitable for packaging. In particular, layer (i) according to the invention has an elongation at break of a higher order of magnitude, denoting greater toughness.

(18) At the same time layer (i) according to the invention has greater roughness in terms of both root mean square roughness Sq and the difference Sy between maximum peak and maximum trough with respect to the mean line.

(19) Because of the lower surface roughness of PLA-only layer (i) in comparative example 2, application of a coating layer (ii) resulted in poorer adhesion.

Comparative Example 3

(20) Layer (i)

(21) 16 kg/h poly(butylene sebacate-co-butylene-adipate-co-butylene terephthalate), MFR 5.7 g/10 min (190 C.; 2.16 kg) and acidity 25 meq/kg, 24 kg/h of Ingeo 4043D polylactic acid (PLA), MFR 3 g/10 min (190 C.; 2.16 kg), were fed to an OMC-type twin-screw extruder operating under the following conditions: Screw diameter (D)=58 mm; L/D=36; Rotation speed=140 rpm; Thermal profile=50-180-2005-1602 C.; Throughput=40 kg/h; Vacuum degassing in zone 8 out of 10.

(22) The granules thus obtained had an MFR value (190 C.; 2.16 kg according to ISO standard 1133-1 Plasticsdetermination of the melt mass-flow rate (MFR) and melt volume flow rate (MVR) of thermoplasticsPart 1: Standard method) of 5.9 g/10 minutes.

(23) The granules so obtained were fed to a Ghioldi model bubble film machine with a 40 mm diameter screw with an L/D 30 operating at 64 rpm with a 120-145-1802 thermal profile. The film-forming head with a 0.9 mm gap and L/D 12 was set at 180 C. Film-forming was performed with a blowing ratio of 3.2 and a stretch ratio of 12.5.

(24) The film thus obtained (total 24 microns) was therefore characterised in terms of mechanical properties, in particular tensile strength (.sub.b), elongation at break (.sub.b) and elastic modulus (E), optical properties (transmittance, haze and clarity) and roughness, determined as in Example 1.

(25) TABLE-US-00005 TABLE 4 Determination of the properties of layer (i) in comparative Example 3 FILM TRACTION ASTM D822 OPTICAL PROPERTIES (23 C. 55% RH - Vo 50 mm/min) ASTM D1003 ROUGHNESS .sub.b .sub.b E TRANS. HAZE CLARITY Sq Sy (MPa) (%) (MPa) (%) (%) (%) (nm) (nm) Comp. 34 251 1594 85 25 75 64.6 378.8 Ex. 3

(26) Data in Table 4 show that the film layer (i) according to example 3 comparative, having a aliphatic-aromatic polyester to PLA molar ratio similar to the mixture of the film layer (i) of example 1 according to the invention but prepared in the absence of styrene-glycidylether-methyl methacrylate copolymer, is also characterized by good mechanical properties but has a much higher roughness, in terms of both root mean square roughness Sq and the difference Sy between maximum peak and maximum trough with respect to the mean line (see Table 1).

(27) The excessive roughness value is to the detriment of the evenness of the coating layer, thus decreasing the barrier effect.