POLYOLEFIN COMPOSITIONS WITH IMPROVED OXYGEN SCAVENGING CAPABILITY

Abstract

Oxygen scavenging polymeric compositions that possess an improved oxygen scavenging capability and can be formed into transparent/translucent thin films are disclosed. A composition can include iron powder, ferrous sulfate heptahydrate (FeSO.sub.4.7H.sub.2O) and glycerol dispersed in polyethylene. Such compositions are useful for creating packaging films with improved oxygen scavenging capability.

Claims

1. A film composition comprising: a polymer matrix, iron; ferrous sulfate heptahydrate; glycerol; and optionally, an electrolyte.

2. The film composition according to claim 1, wherein the composition comprises, with regard to the total weight of the film composition: ≥0.5 and ≤10.0 wt %, of the iron; and/or ≥0.5 and ≤10.0 wt %, of the ferrous sulfate heptahydrate; and/or ≥0.5 and ≤10.0 wt %, of the glycerol.

3. The film composition according to claim 1, wherein the film comprises a quantity of the scavenging components of ≤20.0 wt %, with regard to the total weight of the film composition, wherein the quantity of the scavenging components is defined as the sum of the weight of the iron, the ferrous sulfate heptahydrate, the glycerol, and the electrolyte.

4. The film composition of claim 1, wherein: the polymer matrix comprises at least one of polyethylene, polypropylene; or a polyethylene grafted compound.

5. The film composition according to claim 1, comprising ≥80.0 wt % of the polyolefin, with regard to the total weight of the film composition.

6. The film composition of claim 1, wherein: the iron is iron powder with a particle size of 1-100 micron.

7. The film composition according to claim 1, wherein the film composition comprises up to 2.0 wt. % of the electrolyte.

8. A film for use in food packaging, wherein the film comprises the film composition according to claim 1.

9. The film according to claim 8, wherein the film is a single-layer film or a multi-layer film.

10. The film according to claim 8, wherein the film has a thickness of ≥≤and ≤200 μm.

11. The film according to claim 8, wherein the film has an oxygen scavenging performance of greater than 2 mg of oxygen per gram of film.

12. The film according to claim 8, wherein the film is a multi-layer film comprising the film composition in a layer of the multi-layer film that is adjacent to that an outer layer of the multi-layer film that is or is to be exposed to the environment wherein oxygen scavenging is to be taking place.

13. The film according to claim 12, wherein the layer of the multi-layer film that is adjacent to that outer layer of the multi-layer film that is or is to be exposed to the environment wherein oxygen scavenging is to be taking place consists of the film composition.

14. Package comprising the film according to claim 8.

15. (canceled)

16. The film according to claim 5, wherein the polyolefin is a linear low-density polyethylene having: a density of ≥900 and ≤925 kg/m.sup.3, as determined in accordance with ASTM D792 (2008); and/or a melt mass-flow rate of ≥0.1 and ≤20.0 g/10 min, as determined in accordance with ASTM D1238 (2013), at a temperature of 190° C. under a load of 2.16 kg.

17. The package according to claim 14, wherein the comprises an enclosed space for containing a product, wherein at least a section of the walls enclosing that space contains a film comprising the film composition.

18. The film composition of claim 1, wherein the composition comprises, with regard to the total weight of the film composition: ≥0.5 and ≤5.0 wt %, of the iron, ≥0.5 and ≤5.0 wt %, of the ferrous sulfate heptahydrate; and ≥0.5 and ≤10.0 wt %, of the glycerol.

19. The film composition according to claim 1, wherein the film composition comprises of ≥0.5 and ≤2.0 wt %, of the electrolyte.

20. The film according to claim 1, wherein the electrolyte is sodium chloride.

Description

[0116] Other objects, features and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.

[0117] In this invention, transparent/translucent thin films can be formed using novel oxygen scavenging polymeric compositions that possess an improved oxygen scavenging capability. A preferred composition of the film comprises iron powder, ferrous sulfate heptahydrate (FeSO.sub.4.7H.sub.2O) and glycerol dispersed in polyethylene. Such compositions are useful for packaging films.

[0118] The addition of glycerol can improve the oxygen scavenging ability of the oxygen scavenging components (Fe+auxiliary additives), especially with higher loading of oxygen scavenging components. Further, glycerol addition significantly improves the dispersion of the inorganic oxygen scavenging components and the overall processability of the formulation.

[0119] In general, films without glycerol experienced difficulty in melt processing and moulding. A preferred composition uses polyethylene as a base matrix for melt blending with oxygen scavenging additives. Such additives can include but are not limited to iron powder and FeSO.sub.4.7H.sub.2O. The preferred composition exhibits an improved oxidation of iron in the film, facilitated by glycerol, which also helps to disperse the iron powder and ferrous sulfate heptahydrate uniformly within the PE matrix. The further addition of an electrolyte, such as sodium chloride, can provide additional benefits.

[0120] The specific features/components of a preferred embodiment of the invention that can exemplified with the compositions outlined in the table below.

TABLE-US-00001 TABLE 1 Different components of the preferred embodiment. Percentage Component Option used in invention by weight Polymer (base matrix of Polyethylene (PE)- LDPE, 98-88%  Oxygen Scavenging film for LLDPE, Polyethylene-graft- active packaging) maleic anhydride (PE-g-MA) (0.1 mol % Maleic Anhydride) Oxygen Scavenger Iron powder 0.5-5% Oxygen Scavenger Ferrous Sulfate 0.5-5% Heptahydrate Oxidation Reaction medium Glycerol .sup. 1-2% and dispersing aid

[0121] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results.

[0122] The following materials were used in the examples:

TABLE-US-00002 PE-1 LLDPE 118NE, obtainable from SABIC PE-2 MA-g-LLDPE, an LLDPE grafted with maleic anhydride, comprising 0.1 mol % of maleic anhydride, obtainable from SABIC Fe Iron powder, 325 mesh, obtainable from Sigma Aldrich FeSO.sub.4 Ferrous sulfate heptahydrate GL Glycerol NaCl Sodium Chloride

[0123] As a first step, oxygen scavenger (OS) additive compositions are pre-blended. A mortar and pestle was used to crush a weighed amount of ferrous sulfate heptahydrate crystals. The required amount of iron powder, crushed ferrous sulfate heptahydrate and glycerol were weighed in separate vials. Iron powder and crushed ferrous sulfate heptahydrate powder were then thoroughly mixed in a beaker with a spatula. To this solid mixture, glycerol was added and mixed with the spatula for 1-2 min under a nitrogen blanket until a consistent dark colour pasty mass was obtained. To this pasty mixture, a portion of LLDPE pellets was added with vigorous stirring with the spatula, until the surface of the pellets are uniformly (mostly) coated/moistured with the pasty mass. This step was then repeated with the remaining lot of LLDPE. The pasty mass coated LLDPE was then thoroughly mixed in a plastic bag and kept under a nitrogen blanket until melt mixing.

Melt Mixing via HAAKE Mixer.

[0124] A number of polymer formulations were prepared by mixing of ingredients in a HAAKE mixer according to the procedure as herein below. These compositions are indicated in the table 2 below by “H” under mixing type. Desired amount of additives (iron powder, ferrous sulfate heptahydrate powder and glycerol) were weighed and physically blended with weighed amount of polyethylene (for example, LLDPE 118NE). Such physically blended components were further melt processed in a HAAKE mixer for obtaining melt mixed compositions. This material was subsequently compression moulded into thin films. In commercial applications, the moulding could be by various methods. Table 2 gives the details of the formulations along with their oxygen scavenging capabilities, as measured by a GC headspace analysis method.

Melt Mixing via Twin-Screw Extrusion

[0125] A number of polymer formulations were prepared by mixing of ingredients in a ZSK twin-screw extruder according to the procedure as herein below. These compositions are indicated in the table 2 below by “Z” under mixing type. This was accomplished with a 10-barrel twin-screw extruder set-up. In this instance, the extruder was made by Coperion, and was their ZSK 25 mm extruder fitted with co-rotating screws. The extruder set-up was purged with LLDPE for a time ranging from thirty minutes to one hour, until no (or minimal) black particles were seen in the strand. An inventive strand was then extruded using a temperature profile as follows: 100, 160, 185, 195, 200, 205, 205, 210, 210, 220° C. The extrusion was done at 250 rpm, with a feed rate of 5.6 Kg/hour. After over-night storage at room temperature, the strands were pelletized.

TABLE-US-00003 TABLE 2 Formulation of polymer compositions Example Mixing Type Polymer Type Polymer Qty Fe FeSO.sub.4 GL NaCl 1 — — — — — — — 2 Z PE-1 100.0  — — — — 3 Z PE-2 100.0  — — — — 4 — — — 100.0  — — — 5 Z PE-1 80.0 20.0  — — — 6 Z PE-1 95.0 — — 5.0 — 7 Z PE-1 90.0 3.0 5.0 2.0 — 8 Z PE-1 93.0 — 5.0 2.0 — 9 H PE-1 89.0 — 1.0 10.0  — 10 H PE-1 88.0 — 6.0 6.0 — 11 Z PE-1 93.0 — 5.0 2.0 — 12 Z PE-1 95.0 1.5 2.5 1.0 — 13 H PE-1 95.0 2.0 2.0 1.0 — 14 H PE-1 94.0 3.0 2.0 1.0 — 15 H PE-1 80.0 5.0 10.0 5.0 — 16 Z PE-1 75.0 10.0  10.0 5.0 — 17 Z PE-1 80.0 10.0  10.0 — — 18 Z PE-1 92.0 3.0 5.0 — — 19 Z PE-1 91.8 3.0 5.0 0.2 — 20 Z PE-1 94.5 2.0 3.0 0.5 — 21 H PE-1 88.0 5.0 5.0 2.0 — 22 Z PE-1 90.0 3.0 3.0 2.0 2.0 23 H PE-2 90.0 3.0 5.0 2.0 24 H PE-2 88.0 5.0 5.0 2.0 25 H PE-2 92.0 1.0 5.0 2.0

[0126] In the above table, the quantities of the ingredients indicate the wt % of each of the ingredients with regard to the total weight of the formulation.

[0127] The next step was to take the extruded pellets and subsequently compression mould them. This was accomplished using a SANTEC moulding machine, with a plate temperature of 200° C., and the following conditions:

[0128] Holding pressure: 110 bar

[0129] Pre-heating time: 2 min

[0130] Breathing time: 3 times each 1 sec

[0131] Holding/curing time: 5 min

[0132] Cooling time: 5 min

[0133] Supporting material: Teflon coated flexible Al-sheet (0.15 mm) on top and bottom

[0134] Thickness of the compression moulded film=140-180 microns

[0135] Size: 120×120 mm (Two films of each compositions are made)

[0136] The compression-moulded films were wrapped with Al-foil to prevent exposure to open atmosphere.

[0137] Using compression moulded samples as prepared above of sample formulations 2,3 and 5-22, and samples of a blank atmosphere (1) and pure iron powder (4), the oxygen absorbing capacity of the formulations was determined via gas chromatography (GC) headspace analysis.

[0138] For determination of oxygen absorption, a specimen of ca. 0.20 g, weighed to 3 digit accuracy, of each of the samples were each placed in a GC vial having a volume of 20 ml, which contained a 1 ml vial comprising water, in order to maintain 100% relative humidity in the vial. The vials were sealed with a Teflon cap, so as to form a closed container comprising an air atmosphere, the sample and water. The test vials were placed in an oven at 65° C. for 72 hours to simulate accelerated aging conditions.

[0139] After aging, the atmosphere in the test vials was analysed via gas chromatography using an Agilent 7890 B gas chromatographer and a 7697A headspace sampler. The GC was equipped with Carboxen ® (Sigma-Aldrich Co., USA) plot 1010 column of dimensions 30 m (length)×0.53 mm (internal diameter)×30 μm (film thickness) and a TCD detector. An isothermal oven temperature was set at 35° C. for 10 minutes. The inlet and detector temperature were maintained at 250° C. The sample vials were placed in the headspace samples while maintaining oven temperature at 50° C. for 1 min, and then samples of the atmosphere in each vial were subjected to GC analysis to determine the composition of the atmosphere in each vial. By comparing the oxygen content in the atmosphere of each sample as thus determined with the oxygen content of the blank sample 1, the absorbed oxygen quantity per g of the compression moulded film could be determined, providing the oxygen scavenging capacity of the polymer formulations of the present invention.

[0140] The results of the GC headspace oxygen analyses of the aged samples is presented in the table 3 below.

TABLE-US-00004 TABLE 3 Oxygen absorption Example 1 2 3 4 5 6 7 8 9 10 11 O.sub.2 absorption 0.0 0.0 0.0 0.0 0.0 0.0 10.8 2.1 0.0 3.0 2.1 Example 12 13 14 15 16 17 18 19 20 21 22 O.sub.2 absorption 2.6 2.9 4.7 9.9 19.6 14.0 6.5 5.5 3.8 10.0 13.7 Example 23 24 25 O.sub.2 absorption 6.4 1.8 0.7

[0141] In this table 3, the O.sub.2 absorption reflects the quantity of O.sub.2 absorbed from the atmosphere in the vial, in mg, related to 1.00 g of the sample material.

[0142] From the above results, the following may be observed.

[0143] The examples 2 and 3 show that pure polyethylene does not scavenge any oxygen, nor does pure iron powder (example 4), or iron powder in a PE film without any other scavenger additive (example 5). Also, glycerol used in PE film does not absorb any oxygen (example 6).

[0144] Example 7 shows that using a combination of Fe, FeSO.sub.4 and glycerol in a PE film, thus using a formulation according to the present invention, does provide a significant oxygen absorption. The examples 8, 10 and 11 show that a limited oxygen scavenging effect can be obtained by using a combination of FeSO.sub.4 with glycerol, however if the quantity of FeSO.sub.4 is too low, no absorption occurs, as shown by example 9.

[0145] The examples 12-15 and 7 show the optimal loading of iron powder for maximum efficiency. It indicates an improvement of oxygen scavenging performance from 2.9 mg/g to 4.7 mg/g by increasing the loading of iron powder from 2.0 wt % to 3.0 wt %. In general, it can be observed that as iron content is increased along with FeSO.sub.4 content, the oxygen scavenging performance increases up to 10.8 mg/g.

[0146] Based on the results, is can be observed that a particularly desirable oxygen scavenging performance of over 10.0 mg/g of film can be achieved with a relatively low quantity of loading, such as with a total loading of 10.0 wt % or less. Higher scavenging properties can also be achieved, however then the total loading is to exceed 10.0 wt %, which may result in a deterioration of visual appearance of the film.

[0147] A further advantageous effect may be observed from the addition of a fraction of an electrolyte such as NaCl, which further contributes to the oxygen scavenging performance of a film comprising a composition of Fe, FeSO.sub.4 and glycerol, as exemplified by example 22, reaching an oxygen absorption value of 13.7 mg/g film.

[0148] SEM studies of the samples were carried out using a ZEISS® (Carl Zeiss Corporation, Germany) EVO-18 scanning electron microscope. SEM images were taken under secondary electron mode with an operating voltage of 10 kV. All the samples were air cleaned and coated with 10nm gold prior to imaging. Imaging showed that the iron powder and Fe.sub.2SO.sub.4.7H.sub.2O was indeed uniformly dispersed in the sample.

[0149] The following aspects also present certain embodiments of the invention.

[0150] Aspect 1: A film composition comprising: [0151] a polymer matrix, preferably a polyolefin; [0152] iron; [0153] ferrous sulfate heptahydrate; and, [0154] glycerol.

[0155] Aspect 2: The film composition of aspect 1, wherein: [0156] the polymer matrix is selected from the group comprising: [0157] polyethylene; [0158] polypropylene; [0159] a polyethylene grafted compound; or, [0160] a mixture of these.

[0161] Aspect 3: The film composition of aspect 2, wherein: [0162] the polyethylene is selected from the group comprising: [0163] high density polyethylene; [0164] medium density polyethylene; [0165] low density polyethylene; [0166] very low density polyethylene; [0167] ultra-low density polyethylene; or, [0168] linear low density polyethylene.

[0169] Aspect 4: The film composition of aspect 2, wherein: [0170] the polyethylene grafted compound comprises maleic anhydride grafted polyethylene.

[0171] Aspect 5: The film composition of aspect 1, wherein: [0172] the polymer matrix comprises maleic anhydride grafted polyethylene mixed with polyethylene.

[0173] Aspect 6: The film composition of aspect 1, wherein: [0174] the iron comprises iron powder with a particle size of 1-100 micron, preferably 10-60 micron, more preferably 20-50 micron.

[0175] Aspect 7: The film composition of aspect 1, wherein: [0176] the polymer matrix comprises 90-95 wt. % of the film, and the remaining components comprise up to 5-10 wt. % of the film composition.

[0177] Aspect 8: The film composition of aspect 1, further comprising an electrolyte.

[0178] Aspect 9: The film composition of aspect 8, wherein the electrolyte comprises up to 2.0 wt. % of the film composition.

[0179] Aspect 10: The film composition of aspect 9, wherein the electrolyte is sodium chloride.

[0180] Aspect 11: The film composition of aspect 1, wherein: [0181] the polymer matrix comprises 20-50 wt. % of the film composition, and the remaining components comprise up to 50-80 wt. % of the film composition.

[0182] Aspect 12: The film composition of aspect 10, wherein: [0183] the polymer matrix comprises 20-50 wt. % of the film composition, and the remaining components comprise up to 50-80 wt. % of the film composition.

[0184] Aspect 13: The film composition of aspect 12, wherein the film composition comprises around 90 wt. % of polymer matrix, around 3 wt. % of iron powder, around 3 wt. % of ferrous sulfate heptahydrate, around 2 wt. % glycerol, and around 2 wt. % sodium chloride.

[0185] Aspect 14: A film for use in food packaging, the film having an oxygen scavenging performance of greater than 2 mg of oxygen per gram of film.

[0186] Aspect 15: The film of aspect 14, wherein the film has an oxygen scavenging performance of greater than 10 mg of oxygen per gram of film.

[0187] Aspect 16: The film of aspect 14, wherein the film comprises: [0188] a polymer matrix; [0189] iron powder; [0190] ferrous sulfate heptahydrate; and, [0191] glycerol.

[0192] Aspect 17: The film of aspect 16, further comprising sodium chloride.

[0193] Aspect 18: The film of aspect 16, wherein: [0194] the polymer matrix comprises 90-95 wt. % of the film, and the remaining components comprise up to 5-10 wt. % of the film.

[0195] Aspect 19: The film of aspect 17, wherein: [0196] the polymer matrix comprises 90-95 wt. % of the film, and the remaining components comprise up to 5-10 wt. % of the film.

[0197] Aspect 20: The film of aspect 19, wherein the film comprises: [0198] around 90 wt. % of polymer matrix; [0199] around 3 wt. % of iron powder; [0200] around 3 wt. % of ferrous sulfate heptahydrate; [0201] around 2 wt. % glycerol; and, [0202] around 2 wt. % sodium chloride.