Moisture and oil barrier

Abstract

Use of a cellulose ester film as a barrier to moisture and oil is provided. 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 ranging from 15% to 40 mol%. The film can be used as a barrier layer for food packaging. Also provided are compositions comprising the cellulose ester and an additional film-forming material, packaging materials comprising the film of the composition, and methods for making the packaging materials.

Description

BACKGROUND

[0001] Plastic packaging materials are commonly used for packaging food and beverages. Plastic is inexpensive to manufacture and transport and is an effective barrier to moisture and oil and grease. However, plastic has a significant environmental impact. For example, most plastic is produced from non-renewable resources and is not biodegradable. There is an increasing desire to reduce the amount of plastic waste.

[0002] Glass and metal packaging can be used as an alternative to plastic. These materials have good barrier properties and can be easily recycled. However, glass and metal have the disadvantage of being expensive to manufacture and transport.

[0003] Paperboard is an attractive material from an environmental point of view as it is manufactured from renewable materials and is biodegradable. However, paperboard is porous and absorbent and does not have sufficient moisture and oil and grease barrier properties.

[0004] There remains a need in the art for cost-effective packaging materials with a reduced environmental impact.

[0005] WO 2019 / 060694 Al discloses a substrate having a coating comprising a cellulose acetate film. The cellulose acetate film has a glass transition temperature of at least 140°. SUMMARY

[0006] 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 in a ratio ranging from 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 ranging from 15 mol% to 40 mol%. The further film-forming material is selected such that when the composition is dissolved in ethylene glycol diacetate, the resulting 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 with a spindle speed of 60 rpm. The spindle can be an LV4 spindle.

[0007] The composition can be in the form of a film. The film can be a continuous film disposed on a surface of a substrate.

[0008] A related aspect provides the use of the film as a barrier to moisture and oil.

[0009] In another aspect, there is provided the use of a cellulose ester film as a barrier to moisture and oil, the cellulose ester having free hydroxyl groups and ester substituents. The ester substituents are each independently selected from Ci to C6alkyl ester groups. The free hydroxyl groups are present in an amount in the range of 15 to 40 mol%. BRIEF DESCRIPTION OF DRAWINGS

[0010] To assist in understanding embodiments of the present application and to show how the embodiments can be implemented, reference is made by way of example only to the accompanying drawings in which:

[0011] Figure 1 is a schematic cross-section of a packaging material;

[0012] Figure 2 is a flow chart outlining a method of manufacturing a packaging material;

[0013] Figure 3 is a flow chart outlining a method of storing food or beverage;

[0014] Figure 4 is an indication of the exemplary cellulose ester discussed in Example 1 13 C NMR spectrum;

[0015] Figures 5A-5K are photographs of films of various cellulose esters taken after the films were contacted with olive oil as discussed in Example 4; and

[0016] Figures 6A-6B is a photograph of a film comprising a blend of cellulose esters taken after the film was contacted with olive oil as discussed in Example 6. DETAILED DESCRIPTION

[0017] As used herein, the verb "comprise" is used as an open-ended term that is intended to cover any and all aspects of the term "including" or "consist of." In other words, although the verb "comprise" is intended to be an open term, it is explicitly contemplated that the term "consist of" can be substituted for the term "comprise" where the context so requires, particularly when used in conjunction with chemical compositions.

[0018] Unless otherwise indicated, all molecular weights reported herein are number average molecular weights, Mwn.

[0019] "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).

[0020] "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.

[0021] Cellulose is a polymer consisting of D-glucose units linked by β(1→4). In the non-derivatized state, each D-glucose unit comprises three free hydroxyl groups. In cellulose derivatives, some or all of these hydroxyl groups are derivatized, e.g. esterified. The relative proportions of free and derivatized hydroxyl groups can 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 carries two free hydroxyl groups and one acetyl group can be described as having a free hydroxyl content of 66.66 mol% and an acetyl content of 33.33 mol%.

[0022] The amount of a given substituent present in a cellulose derivative can be determined by 13 C NMR spectroscopy, e.g. using the technique described in Example 1.

[0023] Viscosity is measured using a Brookfield viscometer operating at a spindle speed of 60 rpm. The viscometer can in particular be a Brookfield Model DV viscometer. The spindle can in particular be a Brookfield LV 4 spindle (which can also be indicated by its spindle code 64). Viscosity measurements are carried out at room temperature, i.e. 22 ± 1 °C. For the purpose of measuring viscosity, a sample of the composition can be dissolved in ethylene glycol diacetate. The resulting solution can comprise 30 wt% of the composition, based on the weight of the solution. While in actual use, the composition can of course be used under conditions different from those used to assess viscosity, it has been found that the conditions set for the present application are useful for assessing the operability of the composition.

[0024] The present application provides packaging materials comprising films comprising cellulose esters. It has surprisingly been found that certain cellulose esters provide an effective barrier against both moisture and oil and grease. Cellulose esters can be formulated into blends which have improved handling properties compared to the cellulose esters alone, while still maintaining advantageous moisture and oil and grease barrier properties.

[0025] Reference will first be made to Figure 1 The structure of the packaging material will be explained. Figure 1 A schematic cross-section of an exemplary packaging material 100 is shown.

[0026] The packaging material 100 comprises a substrate 110. The nature of the substrate is not particularly limited and can be suitably chosen. The substrate can comprise a cellulose material, e.g. paperboard. Paperboard is biodegradable and can be obtained from renewable resources. Other substrates can be used, e.g. aluminum.

[0027] A membrane 120 containing cellulose esters is disposed on the top surface of the substrate 110. The membrane 120 acts as a water and oil barrier layer to restrict the diffusion of water and oil / grease into and out of the substrate 110. For this purpose, the membrane 120 is a continuous, unbroken membrane.

[0028] Packaging material 100 can be used to package food or beverages. During use, film 120 will come into contact with the food or beverage.

[0029] Figure 1 Many variations of the structure shown are possible.

[0030] Substrate 110 in Figure 1 It is shown as a single layer, but may alternatively include multiple layers. For example, substrate 110 may include a boxboard.

[0031] Figure 1 A single membrane 120 is shown on the top surface of the substrate 110. In several variations, an additional membrane may be provided on the bottom surface of the substrate.

[0032] The cellulose ester used as a barrier layer against moisture and oil in membrane 120 will now be explained in detail.

[0033] Cellulose esters have free hydroxyl groups and ester substituents. These ester substituents are each independently selected from C1 to C6 alkyl ester groups. The free hydroxyl groups are present in an amount ranging from 15 mol% to 40 mol%. Surprisingly, it has been found that by providing cellulose esters containing free hydroxyl groups in an amount ranging from 15 mol% to 40 mol%, a film is obtained that is effective as a barrier layer against both water and oil, as well as fats and greases.

[0034] Optionally, free hydroxyl groups may be present in amounts ranging from 15 to 30 mol%, more preferably from 25% to 30 mol%. The following examples demonstrate that cellulose esters having amounts of free hydroxyl groups within these ranges exhibit particularly good oil and grease barrier properties.

[0035] The C1 to C6 alkyl ester groups are preferably each independently selected from acetate groups, propionate groups, and butyrate groups.

[0036] Cellulose esters may include one type of alkyl ester group, meaning that each alkyl ester group may include the same group. For example, a cellulose ester may be cellulose acetate. Alternatively, a cellulose ester may include two or more different types of alkyl ester groups. Examples of such cellulose esters include cellulose propionate acetate and cellulose acetate butyrate.

[0037] The cellulose ester can be substantially free of substituents other than ester groups and free hydroxyl groups. By "substantially free" it is meant that the cellulose ester does not contain any other substituents within ordinary manufacturing tolerances. For example, any other substituents can be present in a total amount less than or equal to 1 mol%, alternatively 0.1 mol%, further alternatively 0.01 mol%.

[0038] Alternatively, the cellulose ester can further comprise carboxyalkyl substituents. The carboxyalkyl substituents can be selected from carboxymethyl, carboxyethyl, and carboxypropyl. In particular, the cellulose ester can comprise carboxymethyl substituents.

[0039] The carboxyalkyl substituents can be present in an amount ranging from 1 to 25 mol%, alternatively 1 to 10 mol%, further alternatively 1 to 5 mol%. The cellulose ester can be substantially free of substituents other than alkyl ester groups, carboxyalkyl substituents, and free hydroxyl groups.

[0040] Particularly preferably, the cellulose ester can be cellulose acetate butyrate.

[0041] The cellulose acetate butyrate can comprise butyl groups in an amount up to 80 mol%, alternatively 40 to 60 mol%.

[0042] The cellulose acetate butyrate can comprise acetyl groups in an amount ranging from 0.5 to 10 mol%, alternatively 2 to 5 mol%.

[0043] For example, the cellulose acetate butyrate can comprise butyl groups in an amount ranging from 65 to 75 mol% and acetyl groups in an amount ranging from 2 to 5 mol%.

[0044] Particularly preferred cellulose acetate butyrates comprise butyl groups in an amount ranging from 65 to 75 mol%, acetyl groups in an amount ranging from 2 to 5 mol%, and free hydroxyl groups in an amount of 25 to 30 mol%. The cellulose acetate butyrates of this embodiment can be substantially free of other substituents. The cellulose acetate butyrates of this embodiment can have a molecular weight ranging from 18,000 to 35,000 g mol -1 .

[0045] The cellulose ester is not particularly limited in molecular weight, provided that the cellulose ester is capable of forming a film. It was found that the molecular weight has no significant influence 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 can have a molecular weight ranging from 15,000 to 80,000 g mol -1 , alternatively 18,000 to 35,000 g mol -1 , further alternatively 18,000 to 22,000 g mol -1 .

[0046] The film can 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. Hydrophilic plasticizers can increase the oil and grease resistance of the film. Dibutyl sebacate is a hydrophobic plasticizer. Hydrophobic plasticizers can increase the moisture barrier resistance of the film.

[0047] The amount of plasticizer, if present, is not particularly limited, and can be suitably selected. For example, the plasticizer can be present in the film in an amount ranging from 15 wt% to 25 wt%, based on the weight of the cellulose ester.

[0048] Related aspects provide a composition comprising a mixture of a cellulose ester and an additional film-forming material. The cellulose ester and the additional film-forming material are present in the composition in a ratio ranging from 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 ranging from 15% to 40 mol%.

[0049] The additional film-forming material can allow the composition to be more easily applied to a substrate. For example, the additional film-forming material can be used to adjust the viscosity of the composition. The additional film-forming material can be selected such that when the composition is dissolved in ethylene glycol diacetate, the resulting 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 operated with a spindle speed of 60 rpm. The spindle can be an LV4 spindle.

[0050] Various techniques can be used to manufacture the film. Examples include casting, rod coating, and spraying. It is desirable for the solution to have as high a dissolved solids content as possible in order to allow a relatively thick film to be formed in a single operation, for example a single casting step. However, increasing the amount of cellulose ester in the solution increases the viscosity of the solution. If the viscosity increases too much, then the solution becomes unmanageable.

[0051] Surprisingly, it has been found that films comprising a mixture of a cellulose ester and an additional film-forming material retain the advantageous barrier properties of the cellulose ester as described above. Thus, by adding an additional film-forming material to the composition, the solids content can be increased during processing without excessively increasing the viscosity and without significantly compromising the technical properties of the film.

[0052] The composition can be in the form of a film, for example as previously referred toFigure 1 The film 120 is described. In particular, the film can be disposed on a paperboard substrate, as previously described.

[0053] Alternatively, the composition can further include a solvent and can be in the form of a solution. Any appropriate solvent can be used. The solvent can be an organic solvent. Examples of useful organic solvents include acetone, ethanol, and ethylene glycol diacetate. The solution is used to make the film.

[0054] The solution can have a viscosity in the range of 250 mPa.s to 7500 mPa.s. The solution can have a viscosity of less than or equal to 4500 mPa.s, or in the range of 250 mPa.s to 4500 mPa.s. It has been found that compositions that can be dissolved to produce a solution having a viscosity in the range of 250 mPa.s to 4500 mPa.s have particularly advantageous handling properties.

[0055] The cellulose ester is as described above. It will be appreciated that the discussion of the cellulose ester above in relation to the film aspect equally applies to the composition aspect. Figure 1 The cellulose ester described above in relation to the film aspect equally applies to the composition aspect.

[0056] The cellulose ester can have a relatively high molecular weight, for example a molecular weight having in the range of 15,000 to 80,000 g mol -1 optionally in the range of 18,000 to 35,000 g mol -1 and further optionally in the range of 18,000 to 22,000 g mol -1 The cellulose ester can have a relatively high molecular weight, for example a molecular weight having in the range of 15,000 to 80,000 g mol

[0057] The properties of the additional film-forming material are not particularly limited, provided that the additional film-forming material is compatible with the cellulose ester and a solution having an acceptable viscosity can be obtained. The additional film-forming material can be a polymer. Compatibility of polymers can be identified by casting a film of a mixture comprising the cellulose ester and a candidate additional film-forming material onto a glass plate. If a transparent film is obtained, then the additional film-forming material is compatible.

[0058] The cellulose ester is 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 ; epoxy resins; polyvinyl acetates; and lignin.

[0059] The additional film-forming material can be a bioplastic, in other words a plastic produced from renewable biomass starting materials. Plastics from biological sources can be distinguished from plastics from fossil fuel sources by radiocarbon dating. Plastics produced from fossil fuels contain substantially no 14 C.

[0060] The additional film-forming material can be an additional cellulose ester, which is different from the cellulose ester having a quantity of free hydroxyl groups in the range of 15 mol% to 40 mol%. The cellulose ester having a quantity of free hydroxyl groups in the range of 15 mol% to 40 mol% is referred to herein as the "first cellulose ester".

[0061] The additional cellulose ester can comprise a quantity of free hydroxyl groups less than or equal to 14 mol%, for example less than or equal to 10 mol%.

[0062] The additional cellulose ester can have a molecular weight in the range of 1,000 to 14,000 g mol -1 , optionally 2,000 to 10,000 g mol -1 , and further optionally 3,000 to 4,000 g mol -1 . The molecular weight of the additional cellulose ester is typically lower than the molecular weight of the first cellulose ester. For example, the molecular weight of the additional cellulose ester can be at least 2,000 g mol -1 lower than the molecular weight of the first cellulose ester.

[0063] The ester substituents of the additional cellulose ester can each independently be selected from acetate groups, propionate groups, and butyrate groups.

[0064] The relative proportions of the first cellulose ester and the additional film-forming material can be suitably selected. For example, the cellulose ester and the additional film-forming material can be present in a ratio in the range of 0.5:1 to 1.5:1 by weight, and optionally in a ratio in the range of 0.8:1 to 1.2:1 by weight.

[0065] A method of manufacturing a packaging material using the composition will now be described with reference to Figure 2 Figure 2. Figure 2 is a flow chart outlining the steps of the method.

[0066] At block 201, a solution comprising the composition dissolved in a solvent is prepared. Any suitable technique can be used. For example, a solution of the cellulose ester and a solution of the additional film-forming material can be prepared, which can then be mixed together. Alternatively, the cellulose ester and the additional film-forming material can be provided in powder form and can be stirred into the solvent. Preferably, the solution is prepared without the use of heating.

[0067] At block 202, the composition is applied to a surface of a substrate to form a film comprising the cellulose ester and the additional film-forming material. For example, the film can be solution cast, or applied with a film applicator, such as a Bird-type film applicator.

[0068] Figure 3 A method of using a film as described herein as a barrier to moisture and oil is shown in FIG. 1. Figure 3 is a flow chart outlining the method.

[0069] At block 301, a food or beverage package is prepared in accordance with the Figure 1 type of package described herein. The packaged food or beverage is in contact with the film.

[0070] At block 302, the film limits the diffusion of moisture and oil from the food or beverage to the substrate. The films provided herein act as a barrier and can allow for the packaging of moist, perishable food products in packaging materials comprising a cellulose substrate, such as a paperboard substrate, a molded fiber substrate, or a fabric substrate.

[0071] After use, the package can be disposed of, for example, by composting. The cellulose substrate, such as paperboard, and the films provided herein are capable of breaking down in a composting environment. This can limit the environmental impact of the package. Composting conditions can be adjusted to achieve a desired level of breakdown of the cellulose ester film, for example as described in Puls et al, J Polym Environ (2011) 19: 152-165.

[0072] Example

[0073] Example 1: Characterization of cellulose esters by nuclear magnetic resonance spectroscopy

[0074] Using 13 C nuclear magnetic resonance spectroscopy was used to investigate the structure of a group of six cellulose esters (Materials A through F). Materials A through D are cellulose acetate butyrate. Material E is carboxymethylated cellulose acetate butyrate. Material F is cellulose acetate.

[0075] Approximately 120 mg of each cellulose ester was dissolved in 1 mL of deuterated dimethyl sulfoxide. The resulting samples were then analyzed 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.

[0076] The 13 C NMR spectrum of Material 1 is shown in FIG. 1. The spectrum is annotated with the identification of peaks in the spectrum. The results of the analysis are listed in Table 1 below. The integral value for one carbon of the glucose ring was calculated as the average of the six carbons at a shift of 100 ppm to 55 ppm. The integral value for one carbon of the butyryl substituent was calculated as the average of signals c and d, as shown in FIG. 1. Figure 4 The results of the analysis are listed in Table 1 below. The integral value for one carbon of the glucose ring was calculated as the average of the six carbons at a shift of 100 ppm to 55 ppm. The integral value for one carbon of the butyryl substituent was calculated as the average of signals c and d, as shown in FIG. 1.Figure 1 The integral of one carbon of the acetyl substituent was calculated to be 4.8 Figure 1 The integral of the signal f identified in the middle.

[0077] Table 1 : Results of NMR spectra

[0078]

[0079] 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.

[0080] Table 2: Amount of substituents determined by NMR

[0081]

[0082] Example 2: Preparation of thin films of single cellulose esters

[0083] A series of solutions were prepared, each containing a cellulose ester in acetone at a concentration of 10 wt% solution. Each solution further included a plasticizer selected from triethyl citrate or dibutyl sebacate, which was used in an amount of 20 wt% based on the weight of the cellulose ester. The solutions were then cast onto an aluminum substrate or an Avanta Prima substrate. Avanta Prima is a commercially available boxboard.

[0084] The physical properties of the cellulose esters studied are listed in Table 3 below. Material A, Material B, Material C and Material D are cellulose acetate butyrate. Material E is carboxymethylated cellulose acetate butyrate. Material F is cellulose acetate.

[0085] Table 3: Properties of the cellulose esters studied

[0086]

[0087] It was observed that Material F dissolved slowly in acetone and formed a more viscous solution than the other solutions.

[0088] Example 3: Moisture barrier performance

[0089] The water absorption of each of the films obtained in Example 2 was measured by the Cobb test, with a contact time of 300 seconds. The water vapor transmission rate, WVTR, was also determined for each of these films. Lower water absorption and lower WVTR indicate better moisture barrier performance.

[0090] Table 4: Moisture barrier performance of cellulose ester films

[0091]

[0092] The film of material B exhibited the best moisture barrier performance, and material D gave the worst moisture barrier performance.

[0093] A 30 minute (1800 seconds) Cobb test was also performed on a film comprising material B and dibutyl sebacate as plasticizer. This film absorbed 7 g.m -2 of water under these conditions. Less than or equal to 10 g.m -2 of water absorption after 30 minutes is desirable.

[0094] Example 4: Grease and oil barrier performance

[0095] The oil and grease barrier performance 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 after exposure to olive oil are shown in Figures 5A-5K respectively.

[0096] It was found that films comprising material B Figure 5C , Figure 5D , material E Figure 5I , Figure 5J , and material F Figure 5K had the greatest resistance to olive oil. These films were not visibly altered by the olive oil.

[0097] Films comprising material A Figure 5A , Figure 5B , material C Figure 5E , Figure 5F , and material D Figure 5G , Figure 5H had relatively poor resistance to olive oil.

[0098] The results indicate that oil and grease resistance is related to the relative amount of free -OH groups in the cellulose ester.

[0099] Material D is a very similar polymer to material A, except that it has a smaller number average molecular weight, and the two polymers performed similarly in the olive oil test. This indicates that molecular weight does not have a significant effect on olive oil resistance.

[0100] It is generally found that films comprising triethyl citrate as plasticizer have better olive oil resistance than films comprising dibutyl sebacate (see, for example Figure 5A and Figure 5B ). This indicates that oil and grease barrier performance can be adjusted to some extent with plasticizer chemistry.

[0101] Example 5: Moisture barrier performance of blended films

[0102] A solution of cellulose ester was prepared as described in Example 2. The pair of solutions was then mixed by adding the more viscous solution of the pair to the less viscous solution of the pair, by mixing with an effective magnetic stirrer. No heating was used. The ratio of the amount of polymer in each blend was 1 : 1 by weight, based on the weight of the polymer.

[0103] The films were then obtained by casting the blended solutions onto an aluminium and Avanta Prima boxboard substrate.

[0104] The water absorption of each blended film was measured by the Cobb test, with a contact time of 300 seconds. The water vapour transmission rate, WVTR, was also determined for each of these films.

[0105] Table 5: Moisture barrier properties of blended films

[0106]

[0107] It was found that the blends comprising material D and material B had advantageous moisture barrier properties.

[0108] Example 6: Grease and oil barrier properties of blended films

[0109] The olive oil resistance of two blends comprising material D and material B was investigated. Figure 6A and Figure 6B Photographs of the films are shown. It was found that both blends had good olive oil resistance.

[0110] It was found that the moisture and oil and grease barrier properties of the blended films were dominated by the relatively high molecular weight material B component.

[0111] Example 7: Viscosity measurements

[0112] The solutions shown in Table 6 were prepared in glass bottles. Where necessary, in order to fully dissolve the cellulose ester, the solutions were heated to 40-50 °C and mixed vigorously using a magnetic stirrer. Prior to viscosity measurements, the solutions were allowed to cool to room temperature (21-23 °C).

[0113] All viscosities were measured at room temperature (21-23 °C) using a Brookfield viscometer (DV type) using an LV04 spindle running at 60 rpm. Viscosity values are expressed in mPa.s (millipascal seconds). The viscosity values are summarised in Table 1.

[0114] The solutions were applied to a paperboard substrate to form films by using a film applicator TQC sheen VF1501 and a 120 micrometer cover. The applicability of each solution is described in Table 8.

[0115] Solution 1 was found to have the best applicability and levelling, despite having the highest solids content. Solution 9 was still applicable, despite the very high viscosity, but was difficult to handle.

[0116] More generally, solutions comprising a mixture of material B, which is an embodiment of a cellulose ester having 15 to 30 mol% free OH groups, combined with material D, which is an embodiment of a low molecular weight cellulose ester, have good applicability and are less viscous for a given solids content than compositions comprising only the corresponding amount of material B. This suggests that mixing cellulose esters having 15 to 30 mol% free OH groups with additional film-forming polymers can allow solutions to be prepared having high solids content and acceptable viscosity.

[0117] Table 6: Viscosity of various solutions of cellulose esters

[0118]

[0119] All amounts shown in Table 8 are in parts by weight.

[0120] The present disclosure provides the following items:

[0121] Item 1. A composition comprising a mixture of a cellulose ester and an additional film-forming material;

[0122] wherein the cellulose ester and the additional film-forming material are present in the composition in a ratio ranging from 0.1 : 1 to 10: 1 by weight;

[0123] wherein the cellulose ester has ester substituents and free hydroxyl groups;

[0124] wherein the ester substituents of the cellulose ester are each independently selected from C2 to C6 alkyl ester groups;

[0125] wherein the free hydroxyl groups of the cellulose ester are present in an amount ranging from 15% to 40 mol%;

[0126] and wherein the additional film-forming material is selected such that, when the composition is dissolved in ethylene glycol diacetate, the resulting 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 with a spindle speed of 60 rpm.

[0127] Item 2. The composition according to item 1, wherein the resulting solution has a viscosity ranging from 250 mPa.s to 7500 mPa.s.

[0128] Item 3. The composition according to item 1 or item 2, wherein the resulting solution has a viscosity of less than or equal to 4500 mPa.s.

[0129] Item 4. The composition of any one of items 1 to 3, wherein the cellulose ester and the additional film-forming material are present in a ratio ranging from 0.5: 1 to 1.5: 1 by weight.

[0130] Item 5. The composition of item 4, wherein the cellulose ester and the additional film-forming material are present in a ratio ranging from 0.8: 1 to 1.2: 1 by weight.

[0131] Item 6. The composition of any one of items 1 to 5, wherein the ester substituents of the cellulose ester are each independently selected from acetate groups, propionate groups, and butyrate groups.

[0132] Item 7. The composition of item 6, wherein the cellulose ester is cellulose acetate butyrate.

[0133] Item 8. The composition of item 7, wherein the cellulose ester comprises butyl substituents in an amount ranging from 65% to 75 mol%, and acetyl substituents in an amount ranging from 2 mol% to 5 mol%.

[0134] Item 9. The composition of any one of items 1 to 8, wherein the cellulose ester has a molecular weight ranging from 15,000 to 80,000 g mol -1 .

[0135] Item 10. The composition of item 9, wherein the cellulose ester has a molecular weight ranging from 18,000 g mol -1 to 35,000 g mol -1 .

[0136] Item 11. The composition of item 10, wherein the cellulose ester has a molecular weight ranging from 18,000 g mol -1 to 22,000 g mol -1 .

[0137] Item 12. The composition of any one of items 1 to 11, wherein the free hydroxyl groups of the cellulose ester are present in an amount ranging from 15 mol% to 30 mol%.

[0138] Item 13. The composition of item 12, wherein the free hydroxyl groups of the cellulose ester are present in an amount ranging from 20 mol% to 30 mol%.

[0139] Item 14. The composition of item 13, wherein the free hydroxyl groups of the cellulose ester are present in an amount ranging from 25 mol% to 30 mol%.

[0140] Item 15. The composition of any one of items 1 to 14, wherein the additional film- forming material is an additional cellulose ester, and has a molecular weight in the range of 1,000 g mol -1 to 14,000 g mol -1 .

[0141] Item 16. The composition of item 15, wherein the additional film-forming material is an additional cellulose ester, and has a molecular weight in the range of 2,000 to 10,000 g mol -1 .

[0142] Item 17. The composition of item 16, wherein the additional film-forming material has a molecular weight in the range of 3,000 g mol -1 to 4,000 g mol -1 .

[0143] Item 18. The composition of any one of items 15 to 17, wherein the ester substituents of the additional cellulose ester are each independently selected from the group consisting of acetate groups, propionate groups, and butyrate groups.

[0144] Item 19. The composition of any one of items 15 to 18, wherein the additional cellulose ester comprises free hydroxyl groups in an amount less than or equal to 14 mol %.

[0145] Item 20. The composition of any one of items 1 to 19, further comprising a plasticizer.

[0146] Item 21. The composition of item 20, wherein the plasticizer is present in an amount in the range of 15% to 25% by weight, based on the weight of the composition.

[0147] Item 22. The composition of item 20 or item 21, wherein the plasticizer is triethyl citrate.

[0148] Item 23. The composition of any one of items 1 to 22, in the form of a film.

[0149] Item 24. A packaging material comprising the composition of item 23, wherein the film is a continuous film disposed on a surface of a substrate.

[0150] Item 25. The packaging material of item 24, wherein the substrate is a cellulose substrate, optionally wherein the cellulose substrate is selected from the group consisting of a paperboard substrate, a fabric substrate, and a molded fiber substrate; further optionally wherein the substrate is a fabric substrate.

[0151] Item 26. The composition of any one of items 1 to 22, in the form of a solution further comprising a solvent.

[0152] Item 27. The composition of item 26, wherein the solvent is selected from the group consisting of acetone, ethanol, and ethylene glycol diacetate.

[0153] Item 28. A method of manufacturing a packaging material, the method comprising:

[0154] preparing a composition as defined in item 26 or item 27; and

[0155] applying the composition to a surface of a substrate so as to form a film comprising the cellulose ester and the additional film-forming material on the surface of the substrate.

[0156] Item 29. The method of item 28, wherein the substrate is a cellulose substrate, optionally wherein the cellulose substrate is selected from the group consisting of a paperboard substrate, a fabric substrate, and a molded fiber substrate; further optionally wherein the substrate is a fabric substrate.

[0157] Item 30. Use of the composition of item 23 as a barrier to moisture and oil.

[0158] Item 31. Use of a film of a cellulose ester having free hydroxyl groups and ester substituents,

[0159] wherein the ester substituents are each independently selected from the group consisting of Ci to C6 alkyl ester groups; and

[0160] wherein the free hydroxyl groups are present in an amount in the range of 15% to 40 mol%.

[0161] Item 32. The use of item 31, wherein the ester substituents are each independently selected from the group consisting of acetate groups, propionate groups, and butyrate groups.

[0162] Item 33. The use of item 32, wherein the cellulose ester is cellulose acetate butyrate.

[0163] Item 34. The use of item 33, wherein the cellulose ester comprises butyl substituents in an amount in the range of 65% to 75 mol% and acetyl substituents in an amount in the range of 2 mol% to 5 mol%.

[0164] Item 35. The use of any one of items 31 to 34, wherein the free hydroxyl groups of the cellulose ester are present in an amount in the range of 15 mol% to 30 mol%.

[0165] Item 36. The use of item 35, wherein the free hydroxyl groups of the cellulose ester are present in an amount in the range of 20% to 30 mol%.

[0166] Item 37. The use of any one of items 31 to 36, wherein the cellulose ester has a molecular weight in the range of 15,000 to 80,000 g mol -1 .

[0167] Item 38. The use of item 37, wherein the cellulose ester has a molecular weight in the range of 18,000 g mol -1 to 35,000 g mol -1 .

[0168] Item 39. The use of item 38, wherein the cellulose ester has a molecular weight in the range of 18,000 g mol -1 to 22,000 g mol -1 .

[0169] Item 40. The use of any one of items 31 to 39, wherein the film further comprises a plasticizer.

[0170] Item 41. The use of item 40, wherein the plasticizer is triethyl citrate.

[0171] Item 42. The use of item 40 or item 41, wherein the plasticizer is present in the film in an amount in the range of 15% to 25% by weight, based on the weight of the film.

[0172] Item 43. The use of any one of items 31 to 42, wherein the film is disposed on a surface of a cellulose substrate.

[0173] Item 44. The use of any one of items 31 to 43, wherein the film is in contact with a food or beverage.

Claims

1. A composition comprising a mixture of a first cellulose ester and a further film-forming material; The first cellulose ester and the additional film-forming material are present in the composition in a ratio ranging from 0.1:1 to 10:1 by weight; The first cellulose ester has ester substituents and free hydroxyl groups; The ester substituents of the first cellulose ester are each independently selected from C2 to C6 alkyl ester groups; The free hydroxyl groups of the first cellulose ester are present in an amount ranging from 15 mol% to 40 mol%. in, The additional film-forming material was selected such that when the composition is dissolved in ethylene glycol diacetate, the resulting solution has a viscosity of 22 ± 1 μL when measured using a Brookfield viscometer operated at a rotor speed of 60 rpm. o Viscosity less than or equal to 7500 mPa·s, measured at a temperature of C. The additional film-forming material has a molecular weight at least 2,000 g mol lower than that of the first cellulose ester. -1 Other cellulose esters with different molecular weights; and The additional cellulose ester contains less than or equal to 14 mol% of free hydroxyl groups.

2. The composition according to claim 1, wherein the ester substituents of the first cellulose ester are each independently selected from acetate groups, propionate groups, and butyrate groups.

3. The composition according to claim 2, wherein the first cellulose ester is cellulose acetate butyrate.

4. The composition according to claim 3, wherein, The first cellulose ester contains 65 mol% to 75 mol% of butyl substituents and 2 mol% to 5 mol% of acetyl substituents.

5. The composition according to any one of claims 1-4, wherein, The first cellulose ester has a content of 15,000 to 80,000 g mol. -1 Molecular weight within the specified range.

6. The composition according to claim 5, wherein the first cellulose ester has a content of 18,000 to 35,000 g mol. -1 Molecular weight within the specified range.

7. The composition according to claim 5, wherein the first cellulose ester has a content of 18,000 to 22,000 g / mol. -1 Molecular weight within the specified range.

8. The composition according to any one of claims 1-4, wherein, The free hydroxyl groups of the first cellulose ester are present in an amount ranging from 15 mol% to 30 mol%.

9. The composition according to claim 8, wherein, The free hydroxyl groups of the first cellulose ester are present in an amount ranging from 20 mol% to 30 mol%.

10. The composition according to any one of claims 1-4, wherein, The additional cellulose ester has a content of 1,000 to 14,000 g mol. -1 Molecular weight within the specified range.

11. The composition according to claim 10, wherein, The additional cellulose ester has a content of 2000 to 10,000 gmol. -1 Molecular weight within the specified range.

12. The composition according to claim 11, wherein, The additional cellulose ester has a content of 3,000 to 4,000 gmol. -1 Molecular weight within the specified range.

13. The composition according to any one of claims 1-4, wherein the ester substituents of the additional cellulose ester are each independently selected from acetate groups, propionate groups and butyrate groups.

14. The composition according to any one of claims 1-4, wherein the composition is in the form of a film.

15. Use of the composition according to claim 14 as a barrier layer against moisture and oil.

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