Patent Application
20240301628
Plastic packaging materials are commonly used to package foods and beverages. Plastics are inexpensive to manufacture and to transport, and are effective barriers against moisture and oil and grease. However, plastics have a significant environmental impact. For example, most plastics are produced from non-renewable resources and are not biodegradable. There is an increasing desire to reduce the amount of plastic waste.
Glass and metal packaging may be used as alternatives to plastics. These materials have good barrier properties, and can readily be recycled. However, glass and metal suffer from the drawbacks that they are expensive to manufacture and to transport.
Paperboard is an attractive material from an environmental standpoint, because it is manufactured from renewable materials and is biodegradable. However, paperboard is porous and absorbent, and does not have adequate moisture and oil and grease barrier properties.
There remains a need in the art for cost-effective packaging materials with less environmental impact.
WO 2019/060694 A1 discloses a substrate having a coating comprising a cellulose acetate film. The cellulose acetate film has a glass transition temperature of at least 140°.
In one aspect, there is provided a composition comprising a mixture of a cellulose ester and a further film-forming material. The cellulose ester and the further film-forming material are present in the composition at a ratio in the range 0.1:1 to 10:1 by weight. The cellulose ester has ester substituents and free hydroxyl groups. The ester substituents of the cellulose ester are each independently selected from C2 to C6 alkyl ester groups. The free hydroxyl groups of the cellulose ester are present in an amount in the range 15 to 40 mol %. The further film-forming material is selected such that, when the composition is dissolved in ethylene glycol diacetate, the resultant solution has a viscosity of less than or equal to 7500 mPa·s as measured at a temperature of 22±1° C. using a Brookfield viscometer operating at a spindle speed of 60 rpm. The spindle may be an LV 4 spindle.
The composition may be in the form of a film. The film may be a continuous film arranged on a surface of a substrate.
A related aspect provides the use of the film as a barrier against moisture and oil.
In another aspect, there is provided the use of a film of a cellulose ester as a barrier against moisture and oil, the cellulose ester having free hydroxyl groups and ester substituents. The ester substituents are each individually selected from C1 to C6 alkyl ester groups. The free hydroxyl groups are present in an amount in the range 15 to 40 mol %.
To assist understanding of embodiments of the present invention and to show how such embodiments may be put into effect, reference is made, by way of example only, to the accompanying drawings in which:
As used herein, the verb ‘to comprise’ is used as shorthand for ‘to include or to consist of’. In other words, although the verb ‘to comprise’ is intended to be an open term, the replacement of this term with the closed term ‘to consist of’ is explicitly contemplated, particularly where used in connection with chemical compositions.
All molecular weights reported herein are number average molecular weights, MWn, unless otherwise stated.
“Tg” refers to the glass transition temperature. All glass transition temperatures reported herein were measured at a pressure of 101 kPa (i.e., 1 atm).
“CA” stands for cellulose acetate. “CAB” stands for cellulose acetate butyrate. “NMR” stands for nuclear magnetic resonance. “EGDA” stands for ethylene glycol diacetate. “PEG” stands for polyethylene glycol.
Cellulose is a polymer made up of β(1→4) linked D-glucose units. In an underivatized state, each D-glucose unit includes three free hydroxyl groups. In a cellulose derivative, some or all of these hydroxyl groups are derivatised, e.g. esterified. The relative proportions of free- and derivatized-hydroxyl groups may be expressed in mol %, based on the number of D-glucose units in the cellulose backbone divided by three. By way of illustration, a cellulose derivative in which each D-glucose unit bears two free hydroxyl groups and one acetyl group may be described as having a free hydroxyl content of 66.66 mol % and an acetyl content of 33.33 mol %.
The amount of a given substituent present in a cellulose derivative may be measured by 13C NMR spectroscopy, for example using the technique described in Example 1.
Viscosity is measured using a Brookfield viscometer operating at a spindle speed of 60 rpm. The viscometer may in particular be a Brookfield model DV viscometer. The spindle may in particular be a Brookfield LV 4 spindle (which may also referred to by its spindle code, 64).
Viscosity measurements are performed at room temperature, i.e. 22±1° C. For the purposes of measuring viscosity, a sample of the composition may be dissolved in ethylene glycol diacetate. The resulting solution may comprise 30 wt % of the composition, based on the weight of the solution. Although in practical use the composition may of course be used under conditions which differ from those used for assessing viscosity, the present set of conditions has been found to be useful for assessing the handleability of the composition.
Provided herein are packaging materials which include a film comprising a cellulose ester. It has surprisingly been found that certain cellulose esters provide an effective barrier against both moisture and oil and grease. The cellulose esters may be formulated into blends which have improved handling characteristics compared to the cellulose ester alone, while still retaining the favourable moisture and oil and grease barrier properties.
The structure of a packaging material will first be explained with reference to
Packaging material 100 includes a substrate 110. The nature of the substrate is not particularly limited and may be selected as appropriate. The substrate may comprise a cellulosic material, such as paperboard. Paperboard is biodegradable and obtainable from renewable resources. Other substrates, such as aluminium, may be used.
A film 120 comprising a cellulose ester is arranged on a top surface of substrate 110. Film 120 acts as a moisture and oil and grease barrier for restricting the diffusion of water and oil/grease to and from the substrate 110. To this end, film 120 is a continuous, unbroken film.
Packaging material 100 may be used to package a food or beverage. In use, film 120 will be in contact with the food or beverage.
Many variants of the structure illustrated in
Substrate 110 is illustrated as a single layer in
Cellulose esters useful as barriers against moisture and oil, e.g. in film 120, will now be explained in detail.
The cellulose ester has free hydroxyl groups and ester substituents. The ester substituents are each individually selected from C1 to C6 alkyl ester groups. The free hydroxyl groups are present in an amount in the range 15 to 40 mol %. It has surprisingly been found that by providing a cellulose ester comprising free hydroxyl groups are present in an amount in the range 15 to 40 mol %, a film which is effective as a barrier against both moisture and oil and grease is obtained.
Optionally, the free hydroxyl groups may be present in an amount in the range 15 to 30 mol %, further optionally 25% to 30 mol %. The Examples below demonstrate that cellulose esters having amounts of free hydroxyl groups within these ranges have particularly good oil and grease barrier properties.
The C1 to C6 alkyl ester groups are preferably each individually selected from acetate ester groups, propionate ester groups, and butyrate ester groups.
The cellulose ester may comprise one type of alkyl ester group, i.e. each of the alkyl ester groups may comprise the same group. For example, the cellulose ester may be cellulose acetate. Alternatively, the cellulose ester may comprise two or more different types of alkyl ester group. Examples of such cellulose esters include cellulose acetate propionate and cellulose acetate butyrate.
The cellulose ester may be substantially free of substituents other than the ester groups and the free hydroxyl groups. By “substantially free” it is meant that the cellulose ester does not comprise any other substituents to within ordinary manufacturing tolerances. For example, any other substituents may be present in a total amount of less than or equal to 1 mol %, optionally 0.1 mol %, further optionally 0.01 mol %.
Alternatively, the cellulose ester may further comprise carboxyalkyl substituents. The carboxyalkyl substituents may be selected from carboxymethyl, carboxyethyl, and carboxypropyl groups. In particular, the cellulose ester may include carboxymethyl substituents.
The carboxyalkyl substituents may be present in an amount in the range 1 to 25 mol %, optionally 1 to 10 mol %, further optionally 1 to 5 mol %. The cellulose ester may be substantially free of substituents other than the alkyl ester groups, the carboxyalkyl substituents, and the free hydroxyl groups.
Particularly preferably, the cellulose ester may be a cellulose acetate butyrate.
The cellulose acetate butyrate may comprise butyl groups in an amount of up to 80 mol %, optionally 40 to 60 mol %.
The cellulose acetate butyrate may comprise acetyl groups in an amount in the range 0.5 to 10 mol %, optionally 2 to 5 mol %.
For example, the cellulose acetate butyrate may comprise butyl groups in an amount in the range 65 to 75 mol %, and acetyl groups in an amount in the range 2 to 5 mol %.
A particularly preferred cellulose acetate butyrate comprises butyl groups in an amount in the range 65 to 75 mol %, acetyl groups in an amount in the range 2 to 5 mol %, and free hydroxyl groups in an amount of 25 to 30 mol %. The cellulose acetate butyrate of this example may be substantially free of other substituents. The cellulose acetate butyrate of this example may have a molecular weight in the range 18,000 to 35,000 g mol−1.
The molecular weight of the cellulose ester is not particularly limited, provided that the cellulose ester is capable of forming a film. It has been found that molecular weight does not have a significant impact on the barrier properties of the film. Typically, the cellulose ester has a molecular weight of at least 2,000 g mol−1. In particular, the cellulose ester may have a molecular weight in the range 15,000 to 80,000 g mol−1, optionally 18,000 to 35,000 g mol−1, further optionally 18,000 to 22,000 g mol−1.
The film may optionally further comprise one or more additives, such as a plasticizer. The nature of the plasticizer, if present, is not particularly limited provided that the plasticizer is compatible with the cellulose ester. Illustrative examples of plasticizers include triethyl citrate and dibutyl sebacate. Triethyl citrate is an example of a hydrophilic plasticizer. A hydrophilic plasticizer may increase the oil and grease resistance of the film. Tributyl sebacate is a hydrophobic plasticizer. A hydrophobic plasticizer may increase the moisture barrier resistance of the film.
The amount of plasticizer, if present, is not particularly limited and may be selected as appropriate. For example, the plasticizer may be present in the film in an amount in the range 15 to 25% by weight, based on the weight of the based on the weight of the cellulose ester.
A related aspect provides a composition comprising a mixture of a cellulose ester and a further film-forming material. The cellulose ester and the further film-forming material are present in the composition at a ratio in the range 0.1:1 to 10:1 by weight. The cellulose ester has ester substituents and free hydroxyl groups. The ester substituents of the cellulose ester are each independently selected from C2 to C6 alkyl ester groups. The free hydroxyl groups of the cellulose ester are present in an amount in the range 15% to 40 mol %.
The further film-forming material may allow the composition to be applied to a substrate more easily. For example, the further film-forming material may be used to adjust the viscosity of the composition. The further film-forming material may be selected such that, when the composition is dissolved in ethylene glycol diacetate, the resultant solution has a viscosity of less than or equal to 7500 mPa·s as measured at a temperature of 22±1° C. using a Brookfield viscometer operating at a spindle speed of 60 rpm. The spindle may be an LV 4 spindle.
Films may be manufactured using various techniques. Examples include casting, rod coating, and spraying. It is desirable for the solution to have a content of dissolved solids which is as high as possible, in order to allow a relatively thick film to be formed in a single operation, e.g. a single casting step. However, increasing the amount of cellulose ester in the solution increases the viscosity of the solution. If viscosity increases too much, then the solution becomes impractical to handle.
It has surprisingly been found that films comprising a mixture of the cellulose ester and a further film forming material retain the favourable barrier properties of the cellulose ester, as described above. Therefore, by adding the further film-forming material to the composition, solids content during processing may be increased without excessively increasing viscosity and without significantly impairing the technical performance of the film.
The composition may be in the form of a film, e.g. a film 120 as previously described with reference to
Alternatively, the composition may further comprise a solvent and may be in the form of a solution. Any appropriate solvent may be used. The solvent may be an organic solvent. Examples of useful organic solvents include acetone, ethanol, and ethylene glycol diacetate. The solution is useful for manufacturing the film.
The solution may have a viscosity in the range 250 mPa·s to 7500 mPa·s. The solution may have a viscosity of less than or equal to 4500 mPa·s, or in the range 250 mPa·s to 4500 mPa·s. It has been found that compositions which can be dissolved to yield a solution having a viscosity in the range 250 mPa·s to 4500 mPa·s have particularly favourable handling properties.
The cellulose ester is a cellulose ester as described above. It is to be appreciated that the discussion of the cellulose ester set out above with reference to the
The cellulose ester may have a relatively high molecular weight, for example a molecular weight has a molecular weight in the range 15,000 to 80,000 g mol−1, optionally in the range 18,000 to 35,000 g mol−1, and further optionally in the range 18,000 to 22,000 g mol−1.
The nature of the further film-forming material is not particularly limited, provided that the further film-forming material is compatible with the cellulose ester and that a solution having an acceptable viscosity can be obtained. The further film-forming material may be a polymer. Compatible polymers may be identified by casting a film comprising a mixture of the cellulose ester and the candidate further film-forming material onto a glass plate. If a clear film is obtained, then the further film-forming material is compatible.
Cellulose esters are compatible with most acrylics; polyesters such as polyhydroxyalkanoates; polyphenols; polyureas; and polyisocyanates. Other examples of compatible polymers include polyolefins such as polyethylene or polypropylene; poly(lactic acid); cellulose esters such as cellulose acetate; regenerated cellulose (“Cellophane”); polyamides such as polyamide 11; epoxies; polyvinyl acetates; and lignin.
The further film-forming material may be a bioplastic, in other words, a plastic produced from a renewable biomass starting material. Plastics from biological sources may be distinguished from plastics from fossil fuel sources by radiocarbon dating. Plastics produced from fossil fuel comprise substantially no 14C.
The further film-forming material may be a further cellulose ester, different from the cellulose ester having the free hydroxyl groups in an amount in the range 15 to 40 mol %. The cellulose ester having the free hydroxyl groups in an amount in the range 15 to 40 mol % is referred to herein as the “first cellulose ester”.
The further cellulose ester may comprise free hydroxyl groups in an amount of less than or equal to 14 mol %, for example, less than or equal to 10 mol %.
The further cellulose ester may have a molecular weight in the range 1,000 to 14,000 g mol−1, optionally in the range 2000 to 10000 g mol−1, and further optionally a molecular weight in the range 3000 to 4000 g mol−1. The further cellulose ester typically has a molecular weight which is lower than that of the first cellulose ester. For example, the molecular weight of the further cellulose ester may be at least 2,000 g mol−1 lower than the molecular weight of the first cellulose ester.
The ester substituents of the further cellulose ester may each be independently selected from acetate ester groups, propionate ester groups, and butyrate ester groups.
The relative proportions of the first cellulose ester and the further film-forming material may be selected as appropriate. For example, the cellulose ester and the further film-forming material may be present in a ratio in the range 0.5:1 to 1.5:1 by weight, and optionally at a ratio in the range 0.8:1 to 1.2:1 by weight.
A method of manufacturing a packaging material using the composition will now be described with reference to
At block 201, a solution comprising the composition dissolved in a solvent is prepared. Any appropriate technique may be used. For example, a solution of the cellulose ester and a solution of the further film-forming material may be prepared, and the two solutions may then be mixed together. Alternatively, the cellulose ester and further-film forming materials may be provided in the form of powders and may be stirred into the solvent. Preferably, the solution is prepared without the use of heating.
At block 202, the composition is applied to a surface of a substrate so as to form a film comprising the cellulose ester and the further film-forming material. For example, a film may be casted from the solution, or applied with a film applicator such as a Bird-type film applicator.
A method of using the films as described herein as barriers against moisture and oil is illustrated in
At block 301, a food or beverage is packaged in packaging of the type described with reference to
At block 302, the film restricts diffusion of moisture and oil from the food or beverage to the substrate. The films provided herein act as barriers and may allow moist, perishable foods to be packaged in packaging materials comprising cellulosic substrates, such as paperboard substrates, moulded fibre substrates, or textile substrates.
After use, the packaging may be disposed of, e.g. by composting. Cellulosic substrates such as paperboard and the films provided herein are capable of disintegrating in a composting environment. This may limit the environmental impact of the packaging. The composting conditions may be adjusted to achieve a desired level of disintegration of the cellulose ester film, for example as described in Puls et al, J Polym Environ (2011) 19:152-165.
The structures of a set of six cellulose esters, Materials A to F, were investigated using 13C nuclear magnetic resonance spectroscopy. Materials A to D were cellulose acetate butyrates. Material E was a carboxymethylated cellulose acetate butyrate. Material F was a cellulose acetate.
Approximately 120 mg of each cellulose ester was dissolved in 1 ml of deuterated dimethyl sulfoxide. The resultant samples were then analysed using a Bruker 400 Avance NMR instrument with a 5 mm BBO probe. The pulse program used was zgig30 and D1=20 s. The number of scans was 10,000 for each spectrum.
A 13C NMR spectrum for Material 1 is shown in
The degree of substitution (“DS”) and the amount of each substituent present in each material was calculated from the NMR data. The results are shown in Table 2.
A series of solutions each comprising a cellulose ester at a concentration of 10% by weight of the solution in acetone were prepared. Each solution further included a plasticizer selected from triethyl citrate or dibutyl sebacate, in an amount of 20% by weight based on the weight of the cellulose ester. The solutions were then casted onto either an aluminium substrate or an Avanta Prima substrate. Avanta Prima is a commercially available boxboard.
The physical properties of the cellulose esters investigated are set out in Table 3, below. Material A, Material B, Material C, and Material D are cellulose acetate butyrates. Material E is a carboxymethylated cellulose acetate butyrate. Material F is a cellulose acetate.
It was observed that Material F dissolved slowly in acetone, and formed a solution which was more viscous than the other solutions.
The water absorbance of each of the films obtained in Example 2 was measured by Cobb testing, with a contact time of 300 seconds. The water vapour transmission rate, WVTR, of each of the films was also determined. Lower water absorbance and lower WVTR are indicative of better moisture barrier properties.
Material B films showed the best moisture barrier performance, and Material D gave the worst moisture barrier performance.
A 30-minute (1800 second) Cobb test was also carried out for a film comprising Material B and dibutyl sebacate as a plasticizer. The film absorbed 7 g·m−2 of water under these conditions. A water absorbance of less than or equal to 10 g·m−2 after 30 minutes is desirable.
The oil and grease barrier properties of the films obtained in Example 2 were qualitatively assessed by visual inspection after contacting the films with olive oil. Photographs of films 1 to 11 following exposure to olive oil are shown in
Films comprising Material B (
Films comprising Material A (
The results suggest that oil and grease resistance is related to the relative amount of free-OH groups in the cellulose ester.
Material D is a very similar polymer to Material A, aside from having a smaller number-average molecular weight, and both polymers performed similarly in the olive oil test. This suggests that molecular weight does not have a significant impact on olive oil resistance.
Films comprising triethyl citrate as the plasticizer were generally found to have better olive resistance than films comprising dibutyl sebacate (see, e.g.,
Solutions of cellulose esters were prepared as described in Example 2. Pairs of solutions were then mixed, by adding the more viscous solution of the pair to the less viscous solution of the pair, with efficient magnetic stirrer mixing. No heating was used. The ratio of the amounts of the polymers in each blend was 1:1 by weight, based on the weight of the polymers.
Films were then obtained by casting the blended solution onto aluminium and Avanta Prima boxboard substrates.
The water absorbance of each of the blended films was measured by Cobb testing, with a contact time of 300 seconds. The water vapour transmission rate, WVTR, of each of the films was also determined.
The blends comprising Material D and Material B were found to have favourable moisture barrier properties.
The olive oil resistance of the two blends comprising Material D and Material B was investigated. Photographs of the films are shown in
The moisture and oil and grease barrier properties of the blended films were found to be dominated by the relatively higher molecular weight Material B component.
The solutions shown in Table 6 were prepared in glass bottles. Where necessary in order to dissolve fully the cellulose esters, solutions were heated to 40-50° C. and mixed vigorously using a magnetic stirrer. The solutions were allowed to cool to room temperature (21-23° C.) prior to the viscosity measurements.
All viscosities were measured at room temperature (21-23° C.) using a Brookfield viscometer (model DV) using an LV 04 spindle operating at 60 rpm. The viscosity values are expressed in mPa·s (millipascal second). The numeric values of the viscosities are summarized in table 1.
Films were formed by applying the solutions onto paperboard substrates using a film applicator TQC sheen VF1501 and a 120 micrometer lid. The applicability of each solution is described in table 8.
It was found that solution 1 had the best applicability and levelling, despite having the highest solid content. Solution 9 was still applicable despite of very high viscosity, but was quite difficult to handle.
More generally, solutions which comprised a mixture Material B (which is an example of a cellulose ester having 15 to 30 mol % free OH groups) in combination with Material D (which is an example of a low molecular weight cellulose ester) had good applicability and, for a given solids content, were less viscous than a composition comprising a corresponding amount of Material B alone. This illustrates that mixing a cellulose ester having 15 to 30 mol % free OH groups with a further film-forming polymer may allow preparation of a solution having a high solids content and an acceptable viscosity.
All amounts shown in Table 8 are in parts by weight.
The present disclosure provides the following clauses:
| Number | Date | Country | Kind |
|---|---|---|---|
| 2107574.2 | May 2021 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/064314 | 5/25/2022 | WO |
