Cellulose-based films and methods of manufacture thereof

Abstract

In various embodiments, the present invention provides: methods of manufacturing a cellulose-based film comprising electrophoretically depositing cellulose nanofibrils onto a deposition interface to form a cellulose nanofibril film layer, wherein the cellulose nanofibrils comprise holocellulose nanofibrils (hCNFs); cellulose-based films comprising a cellulose nanofibril film layer comprising holocellulose nanofibrils (hCNFs), wherein the cellulose nanofibril film layer is formed by electrophoretic deposition of hCNFs onto a deposition interface; methods of manufacturing a composite cellulose-based film comprising electrophoretically depositing cellulose nanofibrils and ethyl cellulose onto a deposition interface to form the composite cellulose-based film; and composite cellulose-based films comprising cellulose nanofibrils and ethyl cellulose, wherein the film is formed by electrophoretic deposition of cellulose nanofibrils and ethyl cellulose onto a deposition interface. The invention also includes composite structures and food packaging incorporating such films, or films produced by such methods.

Description

[0001] 8568552

[0002] 1

[0003] Cellulose-based films and methods of manufacture thereof

[0004] Funding

[0005] Elements of the work leading to this invention have received funding from NERC grant NE / V010565 / 1.

[0006] Field of the Invention

[0007] The present invention relates to methods of manufacturing cellulose-based films, and particularly, although not exclusively, to methods including electrophoretically depositing cellulose nanofibrils (CNFs) onto a deposition interface, optionally in combination with other cellulose derivatives including ethyl cellulose. It also relates to cellulose-based films produced by such methods, and products incorporating said films.

[0008] Background

[0009] Escalating environmental issues associated with the quantity of waste packaging and a legacy of poor materials selection has led to significant environmental and health concerns around the end-of-life disposal of plastics. In particular, plastic packaging accounts for over 2.2 Mt per annum of plastic waste in the UK, the majority of which is not effectively recycled or composted. The escalating global environmental challenge posed by non-biodegradable packaging plastics, with an overall market size of $265 billion which is forecast to double over next five years, calls for large-scale, sustainable solutions. The unmet need lies in developing an innovative, mass-production method that balances sustainability, functionality, and economic viability.

[0010] Food packaging is ubiquitous in modern society, and a necessary part of our ‘just-in-time’ supply chain, but there are growing concerns that plastics used for packaging are contributing significantly to problematic, non-biodegradable waste, with one study finding that 63% of US solid waste generated purely from food packaging. The breakdown of these plastic packaging materials can release microplastics, injure wildlife, and disrupt ecosystems.

[0011] Furthermore, due to increasing regulations around plastic production, and disposal, companies are looking to reduce their carbon footprints and move to biodegradable polymers from biological sources. Currently, the European biodegradable food packaging market was valued at over $2.76B in 2021, and is predicted to grow to at a CAGR of 6.47% to $5.5B USD by 2032.

[0012] Some of these problems may be address by use of compostable materials for food packaging. Before the widespread take-up of fossil-based plastics, cellulose has been used historically as a packaging material for food. However, it presents issues in obtaining the required moisture barrier, and mechanical properties (Cellulose 26, 3271-3284, (2019)), as well as requiring environmentally unfriendly chemical treatments such as viscose process (for regenerated cellulose) and TEMPO oxidation (for dispersal of native cellulose nanocrystals or nanofibrils) in order to process the raw cellulose into films or fibres (Adv. Mater. 33, 2001118, (2021 )).

[0013] The present invention has been devised in light of the above considerations. 8568552

[0014] 2

[0015] Summary of the Invention

[0016] The present inventors have realised the importance of development of alternative compostable materials which can be broken down naturally in the environment without significant environmental impact while still providing the necessary moisture and oxygen barrier properties to ensure food safety and lifetime, and which preferably do not require the use of environmentally unfriendly chemical treatments such as the viscose process (for regenerated cellulose) and TEMPO oxidation (for dispersal of native cellulose nanocrystals or nanofibrils) in order to process the raw cellulose into films or fibres. Furthermore, it would be desirable to provide materials which are formed by processes that are easily scalable, to allow for mass-manufacture of the material for use in food packaging.

[0017] The present inventors have realised that some or all of the above problems can be addressed by provision of cellulose-based films comprising cellulose nanofibrils, wherein the cellulose nanofibrils comprise holocellulose nanofibrils (hCNFs). The term “cellulose nanofibril” is used herein to refer to nanoscale cellulose assemblies having at least one dimension in the nanoscale range. In some embodiments, the cellulose nanofibrils may comprise or consist of fibrils with widths in a range of from 5- 20 nanometres. The length of the fibrils may be in the micrometre range.

[0018] The present inventors have realised that some or all of the above problems can alternatively or additionally be addressed by provision of composite cellulose-based films comprising cellulose nanofibrils & ethyl cellulose.

[0019] Further, the inventors have realised that some or all of the above problems may be addressed by the use of electrophoretic deposition (EPD) to form those films, as EPD provides a fast, flexible and controllable process.

[0020] Accordingly, in a first aspect, the present invention provides a method of manufacturing a cellulose-based film, the method comprising: electrophoretically depositing cellulose nanofibrils onto a deposition interface to form a cellulose nanofibril film layer, wherein the cellulose nanofibrils comprise holocellulose nanofibrils (hCNFs).

[0021] In a second aspect, the present invention provides a method of manufacturing a composite cellulose- based film, the method comprising: electrophoretically depositing cellulose nanofibrils and ethyl cellulose onto a deposition interface to form the composite cellulose-based film.

[0022] In a third aspect, the present invention provides a cellulose-based film comprising a cellulose nanofibril film layer comprising holocellulose nanofibrils (hCNFs), wherein the cellulose nanofibril film layer is formed by electrophoretic deposition of hCNFs onto a deposition interface.

[0023] In a fourth aspect, the present invention provides composite cellulose-based film comprising: cellulose nanofibrils; and ethyl cellulose; wherein the film is formed by electrophoretic deposition of cellulose nanofibrils and ethyl cellulose onto a deposition interface. 8568552

[0024] 3

[0025] The present inventors have found that by electrophoretically depositing holocellulose nanofibrils, or by depositing cellulose nanofibrils and ethyl cellulose, the resulting cellulose-based films have suitable oxygen barrier and water barrier properties that make them appropriate for use as a sustainable food packaging material. The resulting films may be biocompostable. Biocompostable in this context means that the waste is suitable for industrial composting.

[0026] Furthermore, EPD is a low energy alternative to other known methods of film formation (for example, casting). Formation of films via EPD offers significant benefits in comparison to methods which involve casting of films, as it can reduce the need to undertake lengthy drying processes which are essential for casting-based processes. The drying processes required to form films via casting methods are time consuming, energy intensive and costly. The use of EPD can mitigate these factors by concentrating very dilute suspension onto an electrode, resulting in relatively low-moisture films that can be dried relatively easily and quickly with low energy input.

[0027] The term “cellulose-based film” is used herein to describe a film wherein the major components of the film are cellulose-based materials (i.e. materials comprising cellulose). That is, the film may be at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% or substantially 100% formed from cellulose-based materials. The remaining proportion of the film may comprise optional additives and / or unavoidable impurities.

[0028] The cellulose-based film is in some embodiments a substantially homogeneous film formed from a single material (e.g. hCNFs). The cellulose-based film is in some other embodiments a composite film formed from multiple cellulose-based materials (e.g. formed from a combination of hCNF and another cellulose- based material such as ethyl cellulose)

[0029] Whilst the present disclosure relates to (i) films comprising or formed of holocellulose nanofibrils and (ii) films comprising or formed of cellulose nanofibrils and ethyl cellulose, as noted above, it is also contemplated that methods as discussed herein may be more broadly applicable for production of other cellulose-based composite films having different compositions. In this case, the method may more generally comprise steps of deposition of one or more different cellulose-based materials onto a deposition interface to form a cellulose-based film. Some methods may comprise deposition of two or more different cellulose-based materials onto a deposition interface to form a composite cellulose-based film. Furthermore, it will be understood that ethyl cellulose has similar properties to a number of other polymeric cellulose derivatives, and as such, other polymeric cellulose derivatives may be suitable for use in place of ethyl cellulose.

[0030] The method may include applying an electric field across a suspension comprising a material to be deposited, to cause electrophoretic deposition of said material at the deposition interface. The material to be deposited may alternatively be referred to as a dispersed phase. The dispersed phase may comprise or consist of cellulose-based materials. In some methods, the dispersed phase comprises or consists of cellulose nanofibrils, for example holocellulose nanofibrils (hCNFs). In some methods, the dispersed phase may comprise ethyl cellulose.

[0031] For example, where the method is a method of manufacturing a cellulose-based film which includes electrophoretically depositing holocellulose nanofibrils (hCNFs) onto a deposition interface to form a 8568552

[0032] 4 cellulose-based film, the method may include applying an electric field across a suspension comprising hCNFs to cause electrophoretic deposition of the hCNFs at the deposition interface.

[0033] Where the method is a method of manufacturing a composite cellulose-based film comprising electrophoretically depositing cellulose nanofibrils and ethyl cellulose onto a deposition interface to form the composite cellulose-based film, the method may include steps of:

[0034] (a) applying an electric field across a suspension comprising cellulose nanofibrils to cause electrophoretic deposition of the cellulose nanofibrils at the deposition interface; and

[0035] (b) applying an electric field across a suspension comprising ethyl cellulose to cause electrophoretic deposition of ethyl cellulose at the deposition interface; wherein steps (a) and (b) are performed simultaneously or sequentially, in any order.

[0036] In some methods, the cellulose nanofibrils and ethyl cellulose may be deposited sequentially. That is, steps (a) and (b) may be performed one after the other, in either order. That is, in some examples, the cellulose nanofibrils may be deposited first, with the ethyl cellulose being deposited subsequently (i.e. step (a) followed by step (b)). In other examples, the ethyl cellulose may be deposited first, with the cellulose nanofibrils being deposited subsequently (i.e. step (b) followed by step (a)). Such methods may result in a bilayer composite film including a layer comprising cellulose nanofibrils and a layer comprising ethyl cellulose.

[0037] In some methods steps (a) and / or (b) may be performed multiple times. For example, the method may include sequences of steps as follows:

[0038] (a), (b), (a);

[0039] (b), (a), (b);

[0040] (a), (b), (a), (b);

[0041] (b), (a), (b), (a); etc.

[0042] Such methods may result in a multilayer composite film including multiple layers of cellulose nanofibrils and / or ethyl cellulose.

[0043] In some methods, multiple steps of depositing the same cellulose-based material may be performed. For example, the method may include performing multiple cycles of applying an electric field across a suspension comprising cellulose nanofibrils (e.g. hCNFs) to cause electrophoretic deposition of the cellulose nanofibrils (e.g. hCNFs) at the deposition interface. The suspension may be changed or refreshed each cycle - for example, the deposition interface may remain in place, but the suspension surrounding the deposition interface may be replaced with a new suspension. Performing such multideposition methods can provide for methods in which comparatively thick films can be produced via an electrophoretic deposition process.

[0044] Where the method comprises multiple deposition steps, the method may be a ‘wet-on-wet’ multilayer deposition process, where deposition of a subsequent layer is performed directly onto a wet deposited layer, i.e. a deposited layer than has not been subject to a drying step. Alternatively, the method may be a ‘wet-on-dry’ multilayer deposition process, where deposition of a subsequent layer is performed directly onto a dry deposited layer, i.e. a deposited layer than has been subject to a drying step. 8568552

[0045] 5

[0046] In some methods, cellulose nanofibrils and ethyl cellulose are deposited simultaneously. In such arrangements, the suspension comprising cellulose nanofibrils and the suspension comprising ethyl cellulose may be a mixed suspension comprising both cellulose nanofibrils and ethyl cellulose, and steps (a) and (b) may be performed as a single step ((a)+(b)) of applying an electric field across the mixed suspension to cause co-deposition of both cellulose nanofibrils and ethyl cellulose at the deposition interface. The mixed suspension may be a continuously titrated mixture. Where the mixed suspension is a continuously titrated mixture, the relative proportions of each suspension within the mixture may be varied over time. Such methods may result in a single layer composite film comprising both cellulose nanofibrils and ethyl cellulose.

[0047] It is also contemplated that in yet further methods, the methods may include both simultaneous and sequential deposition of cellulose nanofibrils and ethyl cellulose. For example, the method may comprise a first step of depositing one of cellulose nanofibrils and ethyl cellulose, a second step of simultaneously depositing cellulose nanofibrils and ethyl cellulose, and a third step of depositing one of cellulose nanofibrils and ethyl cellulose. In other words, the method may include sequences of steps as follows:

[0048] (a), (a)+(b), (b);

[0049] (a), (a)+(b), (a);

[0050] (b), (a)+(b), (b);

[0051] (b), (a)+(b), (a); etc.

[0052] Such methods may result in a multilayer composite film including multiple layers of cellulose nanofibrils and / or ethyl cellulose. Such methods may be achieved in practice by providing a deposition suspension, the composition of which changes over time during the deposition process, in order to produce a film which has a changing composition across the thickness of the film. For example, the deposition suspension may initially be a suspension comprising cellulose nanofibrils and substantially no ethyl cellulose. After a first predetermined time, the composition of the deposition suspension may be changed to increase the amount of ethyl cellulose present in the suspension (e.g. from zero to a predetermined amount). The amount of cellulose present in the deposition suspension may be decreased in a manner that corresponds with the increase in the amount of ethyl cellulose in suspension. After a second predetermined time, the deposition suspension may be a suspension comprising ethyl cellulose and substantially no cellulose nanofibrils. In this way, a film having a graded composition through the film can be formed.

[0053] In preferred methods, the composite cellulose-based film may be formed by: (i) sequential deposition of CNFs and EC in separate baths containing different suspensions; or (ii) flowing separate suspensions of CNFs and EC respectively into a single bath, and adjusting the relative flow rates of the separate suspensions to thereby sequentially deposit CNFs and EC. Such methods may result in bi-layer films having suitable properties. Bi-layer composite films may be preferred over single layer composite films in view of their improved oxygen and / or water barrier properties.

[0054] As noted above, the EPD may be performed by applying an electric field across a suspension comprising a material to be deposited (e.g. a cellulose based material), to cause electrophoretic deposition of said material at the deposition interface. 8568552

[0055] 6

[0056] Where the suspension comprises cellulose nanofibrils, the suspension comprising cellulose nanofibrils may comprise cellulose nanofibrils in amounts of from 0.05 wt% to 2 wt%, 0.1 wt% to 2 wt%, or 0.1 wt% to 1 wt%, e.g. in amounts of 0.2 wt% or more, 0.3 wt % or more, 0.4 wt % or more, 0.5 wt% or more, or in amounts of 0.9 wt% or less, 0.8 wt% or less, 0.7 wt% or less, or 0.6 wt% or less, based on total weight of the suspension. In some methods, the suspension may comprise cellulose nanofibrils (for example may comprise hCNFs) in an amount of from 0.062 wt% to 0.248 wt%. In general, the suspension may comprise cellulose nanofibrils (for example may comprise hCNFs) in an amount of less than 0.25 wt%. It has been found that providing concentrations of cellulose nanofibrils of less than 0.25 wt% in the suspension can provide for suspensions having a greater magnitude of zeta potential and faster deposition.

[0057] As discussed above, the cellulose nanofibrils may comprise or consist of holocellulose nanofibrils (hCNFs). The hCNFs may be derived from natural plant sources. The use of hCNFs may be particularly preferred as holocellulose does not require TEMPO oxidation in order to be processed: accordingly, preferably the holocellulose nanofibrils are manufactured by a method not involving the TEMPO oxidation process. The hCNFs may be manufactured by enzymatic treatment of cellulose nanofibrils. The enzymatic treatment of cellulose nanofibrils may change the surface charge of the hCNF as a result of enzymatic cleavage of selected bonds on the bound hemicelluloses. The enzymatic treatment of cellulose nanofibrils may be performed as described in e.g. Koskela et al, “Lytic polysaccharide monooxygenase (LPMO) mediated production of ultra-fine cellulose nanofibres from delignified softwood fibres” (2019); or Rogowski et al, “Evidence That GH115 a-Glucuronidase Activity, Which Is Required to Degrade Plant Biomass, Is Dependent on Conformational Flexibility” (2014). In addition to the advantages described above (that the use of hCNFs does not require the use of environmentally unfriendly chemical treatments such as the use of TEMPO oxidation in order to process the raw cellulose into films or fibres), it has been advantageously found that films formed using hCNFs can display unexpectedly good oxygen and / or water barrier properties, making them particularly suitable for use as a sustainable food packaging materials.

[0058] The cellulose nanofibrils (e.g. hCNFs) may have a zeta potential greater than or less than zero, when in suspension. The zeta potential measures the electrochemical equilibrium at the particle-liquid interface. The zeta potential may be in a range of from ±1 to ±200 mV. Preferably the zeta potential has a magnitude of ±10 mV or more, ±20 mV or more, or ±30 mV or more. The greater the magnitude of the zeta potential of the suspended particles, the faster it may be possible to deposit the particles from suspension via EPD. In some methods, the method may include a step of modifying the cellulose nanofibrils or one or more other properties of the suspension of cellulose nanofibrils in order to increase the magnitude of the zeta potential of the nanofibrils. For example, holocellulose nanofibrils (hCNFs) may have a zeta potential of approximately -30mV, but this can be modified by surface functionalisation of the hCNFs, or by changing the solvent ratios, or pH of the suspension, or by adding one or more salts to the suspension.

[0059] As discussed above the method may include applying an electric field across a suspension comprising a material to be deposited (dispersed phase). The dispersed phase is typically dispersed in a carrier liquid. For example, where the suspension comprises cellulose nanofibrils, the suspension comprising cellulose 8568552

[0060] 7 nanofibrils may comprise cellulose nanofibrils suspended in a carrier liquid. The suspension comprising cellulose nanofibrils may comprise one or more solvents in which the cellulose nanofibrils are suspended. That is, the carrier liquid may comprise the one or more solvents. The solvents may comprise one or more solvents selected from: water, ethanol, methanol, benzyl alcohol or 2-propanol. Preferably the suspension comprises water and at least one other relatively non-polar solvent (i.e. at least one other solvent having a polarity less than water) - e.g. preferably the suspension comprises water and at least one of ethanol, methanol, benzyl alcohol or 2-propanol. The addition of relatively non-polar solvents such as ethanol to an otherwise aqueous suspension may provide a technical advantage of suppressing bubble formation at the film surface during the electrophoretic deposition process, thereby improving the barrier properties of the resultant film. Preferably the solvent(s) are non-toxic, to ensure that the resultant films are suitable for use in food packaging. Further details on suitable compositions for the suspension are set out below. However, in general, the solvent(s) may provide the balance of the suspension, once cellulose nanofibrils and any other optional additives have been accounted for.

[0061] The inclusion of ethanol in the suspension may be particularly preferred as ethanol is cheap and readily available - accordingly, one particularly preferred form for the suspension is an aqueous suspension comprising water and ethanol. In some methods, the suspension is an aqueous suspension comprising water and ethanol, wherein ethanol is present in the suspension in amounts of from 15 wt% to 35 wt%, preferably in amount of from 20 wt% to 30 wt%, relative to the total weight of the suspension. It has been found that providing suspensions where the carrier liquid comprises ethanol in such amounts may have a greater magnitude of zeta potential and thereby allow for faster deposition of the dispersed phase from the suspension. The use of ethanol in the suspension may also be particularly effective in suppressing bubble formation during EPD processes.

[0062] The suspension comprising cellulose nanofibrils may comprise a plasticising agent. Addition of a plasticising agent can improve the mechanical properties of the resultant film. The plasticising agent may be a bio-derived plasticising agent. The plasticising agent may comprise one or more of: a cellulose- based plasticising agent, pectin, sorbitol, or lignin, alone or in combination. Where the plasticising agent comprises a cellulose-based plasticising agent, the cellulose-based plasticising agent may comprise one or more of: hydroxypropylcellulose (HPC) and hydroxypropylmethylcellulose (HPMC). The use of cellulose-based plasticising agents may be preferred, as it may provide suitable enhancement to the mechanical properties of the film whilst maintaining excellent biocompostability in view of the use of all cellulose-based materials in the film. The plasticising agent(s) may be present in the suspension in amounts of from 0.1 v / v% to 5 v / v%, based on total volume of the suspension, more preferably in amount of from 0.5 v / v% to 2 v / v% . The plasticising agent(s) may be present in the suspension in a weight ratio with respect to the amount of cellulose nanofibril of from 1 :2 to 1 :1 weight of CNF to weight of plasticiser, more preferably in a ratio of from 1 :1 weight of CNF to weight of plasticiser.

[0063] The suspension comprising cellulose nanofibrils may comprise an indicator compound which changes colour in response to changes in pH. Incorporation of such indicator compounds can give an indication of food freshness, when the film is used as a food packaging material. The indicator compound may be a bio-derived indicator. For example, the film may comprise curcumin. The indicator compound(s) may be present in the suspension in amounts of from 0.5 wt % to 10 wt% based on the weight of cellulose 8568552

[0064] 8 nanofibrils, more preferably in amounts of from 1 wt % to 5 wt%, e.g. about 1 wt%, about 2 wt% or about 3 wt%, based on the weight of cellulose nanofibrils.

[0065] The suspension comprising cellulose nanofibrils may comprise one or more further optional additives, selected from, but not limited to: one or more pH adjustment additives (e.g one or more acids or bases); one or more dispersants; one or more stabilisers (steric / electrostatic); one or more binders; one or more buffering additives (e.g. one or more salts); and combinations thereof. The amount of such additives to be incorporated in the suspension may depend on the intended final properties of the suspension. In some arrangements, such optional additives may be present in amounts of 10 wt% or less, 5 wt% or less, 3 wt% or less, 2 wt% or less, 1 wt% or less, 0.5 wt% or less or 0,1 wt% or less based on the total weight of the suspension. In some arrangements, the suspension may comprise substantially no other optional additives. In some arrangements, the suspension may comprise unavoidable impurities.

[0066] The pH of the suspension may be alkaline. That is, the pH of the suspension may be greater than 7, for example in a range of from 7 to 10. It has been found that providing an alkaline suspension may provide a greater magnitude of zeta potential and thereby allow for faster deposition of the dispersed phase from the suspension.

[0067] In some methods, the suspension comprising cellulose nanofibrils (e.g. hCNF) is obtained from the supernatant of a centrifuged slurry of cellulose nanofibrils. In other words, such methods may include steps of centrifuging a slurry of cellulose nanofibrils, extracting the supernatant of the centrifuged slurry, and applying an electric field across a suspension comprising the extracted supernatant.

[0068] Advantageously, it is theorised that when a slurry of cellulose nanofibrils undergoes centrifugation, large micro-scale cellulose fibres settle into a sedimentary layer, whilst finer nanofibrils remain in suspension in the supernatant. Given the fine nature of the dispersed phase in the supernatant, it is found that films produced using a supernatant of a centrifuged slurry of cellulose nanofibrils may exhibit better than expected water and / or oxygen barrier properties than films formed from EPD of bulk slurries.

[0069] It is contemplated that this development may find broader applicability than either the first or second aspects discussed above, in that it may be compositionally independent. Accordingly, in a further aspect, the present disclosure provides a method of manufacturing a film by electrophoretic deposition, wherein the method comprises applying an electric field across a suspension including a dispersed phase such that the dispersed phase is electrophoretically deposited onto a deposition interface to form the film, wherein the suspension comprises, consists of, or is otherwise obtained from, the supernatant of a centrifuged slurry. In other words, such method may include steps of centrifuging a slurry, extracting the supernatant of the centrifuged slurry, and applying an electric field across a suspension comprising the extracted supernatant.

[0070] It is hypothesized that such methods may find applicability in electrophoretic deposition of many materials, in particular materials where a distribution in particles sizes is expected to be present in the bulk slurry - in such cases, centrifuging the slurry and using the supernatant of the centrifuged slurry can ensure that the suspension used for the EPD process only has small particles remaining in the dispersed phase.

[0071] A preferred example composition for the suspension comprising cellulose nanofibrils may be as follows: 8568552

[0072] 9

[0073] CNF suspension (comprising CNF, optionally hCNF, in water at a defined w / w% of from 0.1 to 2 w / w%) in an amount of from 33 to 50 v / v%

[0074] Water in an amount of from 0 to 50 v / v%

[0075] Ethanol in an amount of from 33 to 50 v / v%

[0076] Unavoidable impurities.

[0077] The suspension comprising ethyl cellulose may comprise ethyl cellulose in amounts of from 0.1 wt% to 5 wt%, or 0.6 wt% to 1.5 wt% based on total weight of the suspension, e.g. in amounts of 0.2 wt% or more, 0.3 wt % or more, 0.4 wt % or more, 0.5 wt% or more, 1 wt% or more, 1 .5 wt% or more, 2 wt% or more, or in amounts of 4 wt% or less, 3 wt% or less, 2.5 wt% or less, 2 wt% or less, or 1 .5 wt% or less, based on total weight of the suspension.

[0078] The suspension comprising ethyl cellulose may comprise ethyl cellulose suspended in a carrier liquid. The suspension comprising ethyl cellulose may comprise one or more solvents in which the ethyl cellulose is suspended. That is, the carrier liquid may comprise the one or more solvents. The solvents may comprise one or more solvents selected from: water, ethanol, methanol, benzyl alcohol or 2- propanol. Preferably the suspension comprises water and at least one other relatively non-polar solvent (i.e. at least one other solvent having a polarity less than water) - e.g. preferably the suspension comprises water and at least one of ethanol, methanol, benzyl alcohol or 2-propanol. The addition of relatively non-polar solvents such as ethanol to an otherwise aqueous suspension may provide a technical advantage of suppressing bubble formation at the film surface during the electrophoretic deposition process, thereby improving the barrier properties of the resultant film. The inclusion of ethanol may be particularly preferred as ethanol is cheap and readily available. Further details on suitable compositions for the suspension are set out below. However, in general, the solvent(s) may provide the balance of the suspension, once ethyl cellulose and any other optional additives have been accounted for.

[0079] The suspension comprising ethyl cellulose may comprise a plasticising agent. Addition of a plasticising agent can improve the mechanical properties of the resultant film. The plasticising agent may be a bioderived plasticising agent. The plasticising agent may comprise one or more of: a cellulose-based plasticising agent, pectin, sorbitol, or lignin, alone or in combination. Where the plasticising agent comprises a cellulose-based plasticising agent, the cellulose-based plasticising agent may comprise one or more of: hydroxypropylcellulose (HPC) and hydroxypropylmethylcellulose (HPMC). The use of cellulose-based plasticising agents may be preferred, as it may provide suitable enhancement to the mechanical properties of the film whilst maintaining excellent biocompostability in view of the use of all cellulose-based materials in the film. The plasticising agent(s) may be present in the suspension in amounts of from 0.1 v / v% to 5 v / v%, based on total volume of the suspension, more preferably in amounts of from 0.5 v / v% to 2 v / v% . The plasticising agent(s) may be present in the suspension in a weight ratio with respect to the amount of ethyl cellulose of from 1 :2 to 1 : 1 weight of ethyl cellulose to weight of plasticiser, more preferably in a ratio of from 1 : 1 weight of ethyl cellulose to weight of plasticiser.

[0080] The suspension comprising ethyl cellulose may comprise an indicator compound which changes colour in response to changes in pH. Incorporation of such indicator compounds can give an indication of food 8568552

[0081] 10 freshness, when the film is used as a food packaging material. The indicator compound may be a bioderived indicator. For example, the film may comprise curcumin. The indicator compound(s) may be present in the suspension in amounts of from 0.5 wt % to 10 wt% based on the weight of ethyl cellulose, more preferably in amounts of from 1 wt % to 5 wt%, e.g. about 1 wt%, about 2 wt% or about 3 wt%, based on the weight of ethyl cellulose.

[0082] The suspension comprising ethyl cellulose may comprise one or more further optional additives, selected from, but not limited to: one or more pH adjustment additives (e.g one or more acids or bases); one or more dispersants; one or more stabilisers (steric / electrostatic); one or more binders; one or more buffering additives (e.g. one or more salts); and combinations thereof. The amount of such additives to be incorporated in the suspension may depend on the intended final properties of the suspension. In some arrangements, such optional additives may be present in amounts of 10 wt% or less, 5 wt% or less, 3 wt% or less, 2 wt% or less, 1 wt% or less, 0.5 wt% or less or 0,1 wt% or less based on the total weight of the suspension. In some arrangements, the suspension may comprise substantially no other optional additives. In some arrangements, the suspension may comprise unavoidable impurities.

[0083] A preferred example composition for the suspension comprising ethyl cellulose may be as follows:

[0084] Ethanol in an amount of from 96 to 99.9 w / w%

[0085] Ethyl cellulose in an amount of from 0.1 to 4 w / w%

[0086] Unavoidable impurities.

[0087] The step of electrophoretically depositing cellulose nanofibrils / ethyl cellulose may comprise a step of applying an electric field across a suspension comprising cellulose nanofibrils / ethyl cellulose respectively, to cause electrophoretic deposition of the cellulose nanofibrils / ethyl cellulose. The electric field may be applied between opposing electrodes.

[0088] Where the electric field is applied between opposing electrodes, the distance between the electrodes may be in a range of from 1 mm to 100 mm, preferably 1 mm to 50mm, e.g. 5 mm or more, 10 mm or more, 20 mm or more, 25 mm or more or 30 mm or more, 90 mm or less, 80 mm or less, 70 mm or less, or 60 mm or less.

[0089] The electrophoretic deposition may be performed at an applied voltage in a range of from 1 to 100V. Different sub-ranges within this broader range of applied voltages may lead to different technical advantages. For example, in some methods, it may be preferred to operate at a lower applied voltage, e.g. in order to reduce or minimise bubble formation at the layer deposition interface. In such methods, the applied voltage may more preferably be in a range of from 1 to 40 V, more preferably from 2 to 25 V, more preferably 10V or less. In other methods, it may be preferred for the voltage to selected to be in a range that optimises the deposition speed during the EPD processes. In such methods, the applied voltage may more preferably be in a range of from e.g. 20 V to 50 V, more preferably in a range of from 30 V to 40 V.

[0090] In some methods, the applied voltage may be varied throughout the deposition process. The applied voltage may be varied in response to one or changes in deposition rate and / or in response to changes in one or more indicators of film quality (for example, in response to measured deposited film thickness). 8568552

[0091] 11

[0092] This may be particularly relevant for continuous deposition processes, as discussed in greater detail below.

[0093] The electrophoretic deposition may be DC-EPD. The electrophoretic deposition may be AC-EPD.

[0094] The electric field strength of the electric field applied across the suspension(s) to be deposited may be in the range 10 to 5000 volts / m, preferably 100-2000 volts / m.

[0095] The electric field may be pulsed in order to perform pulsed EPD. The average pulse length may be in the range 10-100ms. The duty cycle may be in a range of from 20-70%.

[0096] The electrophoretic deposition may be performed for a time of from 2 minutes to 2 hours, e.g. 5 minutes or more, 10 minutes or more, 1 hour or less, 30 minutes or less.

[0097] At least one of the electrodes may be in contact with the suspension. In some arrangements, both of the electrodes may be in contact with the suspension. Where at least one of the electrodes is in contact with the suspension, the deposition interface may be provided by the surface of an electrode.

[0098] However, the nature of the deposition interface is not particularly limited. In some arrangements, the deposition interface is provided by:

[0099] (i) an electrode;

[0100] (ii) a release layer provided at a surface of an electrode, to permit separation of the deposited layer from the electrode;

[0101] (Hi) a raft of bubbles generated at a surface of an electrode; or

[0102] (iv) a suspended deposition membrane.

[0103] Each of these different deposition interfaces may offer different technical advantages: Deposition onto a release layer, a raft of bubbles generated at a surface of an electrode or a suspended deposition membrane may be preferable to deposition onto an electrode in some ways, as it may increase ease of removal of the film from the deposition interface, and may additionally reduce the risk of gas nucleation / individual bubble formation at the deposition interface surface disrupting film formation.

[0104] However, it is also contemplated that deposition directly onto an electrode may provide other advantages in terms of providing a simple and convenient manufacturing method.

[0105] Where the deposition interface is provided by an electrode, the electrode may comprise polytetrafluoroethylene (PTFE). Using an electrode which comprises PTFE can assist in removing the deposited film from the electrode.

[0106] It is contemplated that this development may find broader applicability than either the first or second aspects discussed above, in that such electrodes may be used in a variety of EPD processes regardless of the material to be deposited. Accordingly, in a further aspect, the present disclosure provides a method of manufacturing a film by electrophoretic deposition, wherein the method comprises applying an electric field across a suspension including a dispersed phase such that the dispersed phase is electrophoretically deposited onto a deposition interface to form the film, wherein the deposition interface is provided by an electrode, the electrode comprising PTFE.

[0107] Preferably the electrode is a carbon-based electrode which comprises PTFE. Conveniently, the electrode may comprise at least 10 wt% carbon, based on total weight of the electrode, more preferably at least 15 8568552

[0108] 12 wt% carbon, or at least 20 wt% carbon. This can help to ensure that the electrode has suitable conductivity for use in EPD processes. The form of the carbon is not particularly limited: for example, the electrode may comprise one or more of: amorphous carbon, carbon fibre, carbon nanotubes and / or graphite. The balance of the electrode may comprise PTFE and optionally one or more binder materials.

[0109] The release layer or the suspended deposition membrane, where used, may comprise a sacrificial layer. The method may include a step of selectively removing the sacrificial layer, after formation of the cellulose-based film. In the case of a release layer, this may allow for easier separation of the deposited film from the electrode.

[0110] In some methods, the deposition interface may be provided by a fiber-based sheet material. The fiberbased sheet material may be selected from: paperboard, carboard, or a cellulosic composite material. The use of a fiber-based sheet material as the deposition interface may allow for particularly convenient production of sustainable food packaging materials.

[0111] The raft of bubbles, where present, may be generated by suitable selection of parameters for the EPD process. The term “raft of bubbles” is used herein to refer to a substantially continuous layer of bubbles. The raft of bubbles may be generated at a surface of an electrode in contact with the suspension, the deposition interface thereby being spatially separated from the surface of the electrode. In this case, the bubbles are generated due to electrolysis of a carrier liquid comprised in the suspension (e.g. water). The electric field may be applied between opposing electrodes with the potential difference between the electrodes being, for example at least 20 V, at least 30V or at least 40V. The potential difference between the electrodes may be, for example at most 200 V.

[0112] In some methods where an electrode is used as the deposition interface, the electrode may be a static electrode. In some alternative methods, the deposition interface may be provided by an electrode that is configured to move during the deposition process- this may be referred to as a dynamic electrode arrangement.

[0113] In some methods, the deposition interface may be provided by a moving substrate (e.g. by a moving electrode where the deposition interface is provided by an electrode). Deposition onto a moving deposition interface (e.g. moving electrode) may allow for continuous film formation at the deposition interface. For example, where the EPD is performed by applying a voltage between two electrodes, the two electrodes may move past each other in a linear fashion during the deposition process. The method may include a step of continuously removing the formed composite cellulose-based film from the moving deposition interface. This may be performed as cellulose nanofibrils and ethyl cellulose are continuously deposited onto the moving deposition interface.

[0114] In some methods, the deposition interface may be provided by an electrode that is configured to rotate during the deposition process. Deposition onto a rotating electrode may allow for continuous film formation at the electrode. The method may include a step of continuously removing the formed cellulose-based film from the rotating electrode. This may be performed as cellulose nanofibrils (and optionally ethyl cellulose) are continuously deposited onto the rotating electrode. It is contemplated that the use of a moving (e.g. a linearly moving or rotating) deposition interface may find application in EPD methods that are composition independent. In other words, it is contemplated that such methods may 8568552

[0115] 13 have applicability in forming other types of film using EPD in addition to forming cellulose-based films as discussed herein.

[0116] Accordingly, a further aspect of the present disclosure provides a method of performing electrophoretic deposition including steps of: applying an electric field across a suspension comprising suspended particles in a carrier liquid to thereby deposit the suspended particles onto a deposition interface to form a film; wherein the deposition interface is configured to move during the deposition.

[0117] The phrase “suspension comparing suspended particles” is considered to be equivalent to the phrase “a suspension including a dispersed phase”, and these phrases are used interchangeably in the present disclosure.

[0118] A yet further aspect of the present disclosure provides apparatus configured for use in such method.

[0119] In such methods, the electric field may be provided between two electrodes, and the deposition interface may be provided by one of the two electrodes.

[0120] The movement of the deposition interface may be substantially linear. Alternatively, the movement of the deposition interface may be rotational. Alternatively, the movement of the deposition interface may follow a predefined movement path. In some such methods, the deposition interface may be provided by a conductive conveyor belt which is configured to move through the deposition suspension during the deposition. The conveyor belt may be configured to move along a predefined movement path. Where the deposition interface is provided by a conductive conveyor belt, this may be connected to one or more rotating drums, e.g. may be connected to two or more co-rotating drums which are configured to cause the conveyor belt to move as a result of rotation of the drums.

[0121] The conductive conveyor belt may provide a first electrode, and one or more counter-electrodes may be provided adjacent the conductive conveyor belt, to allow application of an electric field between the conductive conveyor belt and the respective counter electrode(s).

[0122] The speed of the movement of the deposition interface, the applied voltage at which the EPD is performed, the zeta potential of the particles to be deposited, and / or the viscosity of the deposition suspension may be selected as appropriate in order to achieve the desired deposition results.

[0123] The method may further comprise a step of removing the film from the deposition interface. The step of removing the film from the deposition interface may be performed continuously. For example, a peeling mechanism may be provided to lift the film from the deposition interface (e.g. conveyor belt). The peeling mechanism may comprise a doctor blade or an automated roller system designed to separate the film from the deposition interface, preferably without causing damage or deformation.

[0124] The method may include a step of monitoring the resultant film thickness. A film thickness measurement module may be provided in order to provide this monitoring. Where the apparatus comprises a peeling mechanism for removal of the film from the deposition interface, the film thickness measurement module may be provided near or adjacent to the peeling mechanism. The thickness measurement module may conveniently be provided as a laser micrometre or optical thickness gauge. It may conveniently be 8568552

[0125] 14 configured to monitor the film thickness in real-time, e.g. as the film is removed from the deposition substrate, or shortly afterwards.

[0126] In some methods, information on film thickness output by the film thickness measurement module may be used to dynamically adjust one or more parameters of the EPD process. For example, information on film thickness output by the film thickness measurement module may be used to dynamically adjust one or more of conveyor speed, solution flow rate, and deposition time. This can allow for optimisation of the process for consistent film output.

[0127] Whilst such methods are composition independent, they may find particular applicability in combination with methods according to the first aspect, including one or more optional features thereof, as discussed above. As discussed above, the methods of the first and second aspects of the present disclosure result in formation of cellulose-based films. Such films may be films according to the third and fourth aspects of the present disclosure, respectively. In other words, films according to the third aspect may be formed by methods according to the first aspect, including one or more optional features thereof, as discussed above. Similarly, films according to the fourth aspect may be formed by methods according to the second aspect, including one or more optional features thereof, as discussed above

[0128] As noted above, such films are found to have suitable oxygen barrier and water barrier properties that make them appropriate for use as a sustainable food packaging material, and may be biocompostable. Films formed by electrophoretic deposition are distinguishable from films formed by other methods (e.g. by casting) as a result of their differing microstructure. Typically films formed by EPD are denser than films formed by casting. Providing films with increased density would be expected to improve the water and oxygen barrier properties of the film, as well as improve the mechanical properties by providing increased stiffness and / or strength of the film. Typically films formed by EPD may display a degree of fibre alignment that is not present in films formed by casting.

[0129] In some methods, an additional step of depositing a layer of a polymeric cellulose derivative may be performed. The layer of polymeric cellulose derivative may be deposited: (i) onto the cellulose nanofibril film layer after formation of said layer, or (ii) prior to deposition of the cellulose nanofibril film layer. The step of depositing a layer of polymeric cellulose derivative may be performed by a method selected from e.g. EPD, wire-bar coating, doctor blade coating, or any other suitable deposition method. Preferably, the polymeric cellulose derivative comprises or consists of ethyl cellulose.

[0130] The Young’s modulus (calculated using the initial linear region of the stress strain curve) of the cellulose- based film may be at least around 0.5 GPa, at least around 0.6 GPa, or at least around 0.7 GPa. In some examples, the Young’s modulus may be about 0.84 GPa.

[0131] The yield stress of the cellulose-based film may be at least about 8 MPa, at least around 9 MPa, or at least around 10 MPa. In some examples, the yield stress may be about 11.47 MPa.

[0132] The UTS of the cellulose-based film may be at least about 35 MPa, at least around 40 MPa, or at least around 42 MPa. In some examples, the UTS may be about 43.27 MPa.

[0133] The failure strain of the cellulose-based film may be at least about 10%, at least about 12%, or at least about 15%. In some examples, the failure strain may be about 16.32 %. 8568552

[0134] 15

[0135] The cellulose-based films may have a water vapour transport rate (WVTR) as measured at 23 °C and 50% relative humidity of less than 250 g / m2per day, less than 180 g / m2per day, less than 160 g / m2per day, less than 150 g / m2per day, less than 140 g / m2per day, or less than 130 g / m2per day. The WVTR may be measured according to ASTM F1249-20.

[0136] The cellulose-based films may have a water vapour transport rate (WVTR) as measured at 37.8 °C and 90% relative humidity of less than 850 g / m2per day, less than 830 g / m2per day, less than 820 g / m2per day, or less than 810 g / m2per day. The WVTR may be measured according to the ASTM F3299-18 test method.

[0137] The cellulose-based films may have an oxygen transport rate (OTR) as measured at 23 °C and 0% relative humidity of less than 14 cm3 / m2per day, less than 10 cm3 / m2per day, or less than 6 cm3 / m2per day.

[0138] Where the film is a composite cellulose-based film, it may be a bilayer composite film including a layer comprising cellulose nanofibrils and a layer comprising ethyl cellulose.

[0139] Where the film is a composite cellulose-based film, it may be a multilayer composite film including multiple layers of cellulose nanofibrils and / or ethyl cellulose.

[0140] The composition of the composite cellulose-based film may vary in a graduated manner through the film thickness. Alternatively, the composition of the composite cellulose-based film may vary in a step-wise manner through the film thickness.

[0141] The thickness of the cellulose-based film may be at least 5pm, at least 7.5 pm, at least 10 pm, at least 50 pm, at least 60 pm, or at least 80 pm. The thickness of the cellulose-based film may be up to 50 pm, or up to 100 pm or more. In some examples, the thickness of the cellulose-based film may be in a range of from 7.5 pm to 50 pm. In other examples, the thickness of the cellulose-based film may be in a range of from 50 pm to 200 pm, e.g. in a range of from 60 pm to 100 pm. For certain technical applications, a film thickness of at least 60 pm may be preferred. In particular, providing a thicker film may improve the oxygen and / or water barrier properties of the film, which is typically thickness-dependent.

[0142] The area of the resultant film is not particularly limited and will depend on the specific processing set-up. For example, for batch-wise deposition using a static electrode system, the area of the resulting film may be relatively small, e.g. less than 1 cm2, although it is contemplated that sizes of up to e.g. around 1 m2, or perhaps greater, may be achievable using such systems.

[0143] Significantly larger film areas may be achievable by use of continuous deposition processes. For such processes, the area of the resultant film may be greater than 1 m2, 2m2or more, 5m2or more, or 10m2or more. The width of a film produced by continuous processing may be in a range of from 0.8m - 2 m, and the length of the film may be 1 m or more, 5 m or more, 10 m or more, 20m or more, or 50 m or more.

[0144] The cellulose-based film may be hydrophobic. Hydrophobic films may provide improved water barrier properties. The hydrophobicity of the film may be selected so as to balance the water barrier properties of the film whilst ensuring that the film is compostable.

[0145] The cellulose-based film may comprise an indicator compound which changes colour in response to changes in pH. Incorporation of such indicator compounds can give an indication of food freshness, when 8568552

[0146] 16 the film is used as a food packaging material. The indicator compound may be a bio-derived indicator. For example, the film may comprise curcumin.

[0147] In a fifth aspect, the present invention provides a composite structure comprising a first layer provided by the cellulose-based film of the third or fourth aspects, and at least a second layer having a different composition.

[0148] The further layers in the composite structure may not be formed using EPD. For example, in some embodiments, the cellulose-based film of the third or fourth aspects may be deposited directly onto a substrate material to form said composite structure. Alternatively, or additionally, one or more additional layers may be applied to the cellulose-based film of the third or fourth aspects after formation, by non- EPD techniques such as doctor-blading, to form said composite structure.

[0149] The nature of the further layers in the composite structure is not particularly limited. In some examples, the composite structure may comprise a fiber-based sheet material, such as paperboard, carboard, or a cellulosic composite material.

[0150] In some examples, the composite structure may comprise a polymeric layer, e.g. a layer comprising a polymeric cellulose derivative such as ethyl cellulose. Polymeric layers may conveniently be applied to the cellulose-based film by any suitable means, e.g. using EPD, using a wire-bar coating method, or using a doctor-blade coating method.

[0151] In a sixth aspect, the present invention provides a food packaging comprising a cellulose-based film according to either the third or fourth aspects. The food packaging of this aspect may in some arrangements be a composite structure according to the fifth aspect.

[0152] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0153] Summary of the Figures

[0154] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0155] Figure 1 shows a schematic of one suitable system used for electrophoretic deposition (‘EPD cell’).

[0156] Figure 2 shows a schematic of electrophoretic deposition of charged particles onto electrodes during EPD.

[0157] Figure 3 shows the electrophoretic deposition of a wet-on-dry process for production of a multi-layered membrane; (a) a suspension is placed in the EPD cell and an electric field applied, the suspended particles within the suspension move towards the cathode where they form a solid or semi-solid structure, such as a membrane or gel. (b) The electrode is removed and allowed to air dry, significantly reducing the thickness of the deposit (c) The EPD cell is reassembled with the dry film still attached, a further deposition suspension is placed in the EPD cell and an electric field is applied. A new layer deposits on top of the previous film, which acts as a deposition interface, (d) The electrode is removed and allowed to 8568552

[0158] 17 air dry, the deposited film reduces significantly in thickness, (e) Steps (a)-(d) are repeated and, after a desired number of cycles, a multilayer film is produced.

[0159] Figure 4 shows a graph of apparent zeta potential for an hCNF suspension diluted to 0.125%(w / v) in 50% ethanol.

[0160] Figure 5 is a graph showing zeta potential (mV) of an aqueous hCNF deposition suspension with respect to ethanol concentration (wt%), for an hCNF concentration of 0.124 wt%.

[0161] Figure 6 is a graph showing the zeta potential (mV) of various aqueous hCNF deposition suspensions (each having different composition of carrier liquid), with respect to hCNF concentration (wt%).

[0162] Figure 7 is a graph showing the zeta potential (mV) of two different hCNF suspensions (0.124 wt% hCNF aqueous suspension, and 0.093 wt% hCNF in 30 wt% EtOh) against pH of the suspension.

[0163] Figures 8 (a)-(f) show: (a) wet film mass against voltage; (b) wet film concentration against voltage; (c) dry film mass against voltage; (d) measured thickness of the dry film against voltage; (e) % mass deposited against voltage; and (f) zeta potential against voltage; each for a single deposition of 0.124wt% hCNF slurry (aqueous suspension, 30wt% EtOH), for times of 5 and 10 minutes.

[0164] Figures 9 (a)-(f) show: (a) wet film mass against deposition time; (b) wet film concentration against deposition time; (c) dry film mass against deposition time; (d) measured thickness of the dry film against deposition time; (e) % mass deposited against deposition time; and (f) zeta potential against deposition time; each for a single deposition of 0.124wt% hCNF slurry (aqueous suspension, 30wt% EtOH), at an applied voltage of 5 V.

[0165] Figure 10 shows a free-standing hCNF film produced using EPD.

[0166] Figure 11 shows an EC-hCNF film produced via EPD deposited on electrode from 0.5wt% hCNF slurry and 0.3wt% EC slurry.

[0167] Figures 12 (a)-(e) show: (a) wet film mass against no. of depositions; (b) wet film concentration against no. of depositions; (c) dry film mass against no. of depositions; (d) measured thickness of the dry film against no. of depositions; (e) % mass deposited against no. of depositions.

[0168] Figure 13 is a graph showing various mechanical properties of hCNF films electrophoretically deposited from 0.124 wt% hCNF in aqueous + 30 wt% EtOH suspension.

[0169] Figure 14 is a graph showing Oxygen Transport rate (OTR) against thickness of various films.

[0170] Figure 15 is a graph showing water vapour transport rate (WVTR) of various film samples, measured at 37.8 °C and 90% relative humidity.

[0171] Figure 16 is a graph showing water vapour transport rate (WVTR) of various film samples, measured at 23.0 °C and 50% relative humidity.

[0172] Figure 17 is an image showing hCNF coated onto a cardboard substrate via EPD.

[0173] Figure 18 is a series of images showing the ability of the EPD deposited hCNF film to provide an effective water barrier for cardboard over time. 8568552

[0174] 18

[0175] Figure 19 is an image showing a sample of hCNF suspension that has undergone centrifugation for 5 min at 4000 rpm.

[0176] Figure 20 shows data from a feasibility study based on cast films useful for understanding advantages of the present invention. It demonstrates (a) the transparency of the hCNFs / hydroxypropyl cellulose (HPC) films on the logos of the University of Cambridge and Macromolecular Materials Lab (MML), (b) Folding, rolling, and twisting test for hCNFs-based films, and (c) Tensile mechanical properties of C-CNF, T- CNF / HPC and hCNF / HPC films (Young’s modulus, strength).

[0177] Figure 21 shows data from a feasibility study based on cast films useful for understanding the advantages of the present invention. It demonstrates oxygen transmission rates for cast hCNF films at 23 °C and 0%, 50%, 90% RH (bottom line = 0% RH, middle line = 50% RH, top line = 90% RH).

[0178] Figure 22 shows cellulose-based packaging bags with curcuma longa-derived curcumin to monitor the freshness of packaged shrimp at 25 °C for 24 h, from a feasibility study based on cast films useful for understanding advantages of the present invention.

[0179] Figure 23 shows a schematic diagram of one possible configuration for an apparatus for continuous EPD deposition of films.

[0180] Figure 24 shows a schematic diagram of one possible configuration for an apparatus for drying of films produced by a continuous EPD process (e.g. of films produced using an apparatus as shown in Fig. 23).

[0181] Detailed Description of the Invention

[0182] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0183] The discussion below includes description of suitable methodologies for production of deposition slurries suitable for use in the present invention, as well as suitable methodologies for deposition of CNF and EC to form films via EPD.

[0184] Procedure for preparation of holo-cellulose (hCNF) and ethyl-cellulose (EC) nanofiber slurry for the EPD process

[0185] Preparation of hCNF suspension

[0186] Industrial rapeseed fibers were washed to remove dirt and soaked in distilled water for at least 24 hours. The soaked fibers were delignified by treating with 3% aqueous peracetic acid solution (mass of dry fibers / mass of pure acid — 3 : 1 ). Before the solution was added to the fibers, the pH was adjusted to 4.8 by adding a small amount of 10M NaOH. After 45 minutes of reaction at 85 °C, the delignifying solution was decanted and the treatment was repeated twice until white fibers were obtained. After delignification, the fibers were washed three times with 0.1 M NaOH and several times with water until the conductance of the washing solution was close to that of distilled water. The delignified fibers were fibrillated using a kitchen blender for 20 minutes to obtain a suspension of holocellulose nanofibers in water at a defined w / w%. 8568552

[0187] 19

[0188] To assess the feasibility of depositing hCNF by EPD, the hCNF suspension was diluted to 0.125%(w / v) in 50% ethanol. The zeta potential for the hCNF was found to be negative, with results of -37.2, -35.5, -37.9 mV across three samples, indicating feasibility for EPD. A graph showing apparent zeta potential of the diluted hCNF suspension is shown in Fig. 4. On further feasibility testing, it was found to be possible to make suspensions having Zeta potentials with a magnitude as large as -80 mV, again indicating excellent feasibility for deposition of hCNF via EPD.

[0189] Preparation of hCNF slurry (deposition suspension) for EPD processes hCNF-water-ethanol slurry for the EPD process was prepared by mixing volumes of hCNF suspension (0.1 to 2 w / w%) and pure ethanol. The hCNF may also be diluted with water as required and the mixture homogenized by stirring.

[0190] Example final composition ranges of the slurry (deposition suspension): hCNF suspension: 33 to 50 v / v%

[0191] Water: 0 to 33 v / v%

[0192] Ethanol: 33 to 50 v / v%

[0193] Some work was done to investigate optimal composition for the hCNF slurry.

[0194] Fig. 5 is a graph showing the zeta potential of an aqueous hCNF deposition suspension with respect to ethanol concentration (wt%) at 0.124 wt% hCNF. 1.24 wt% hCNF aqueous slurry was diluted to 0.124 wt% using deionised water and ethanol (EtOH) (99.9%) to obtain 10 mL of hCNF suspensions with 10 to 50 wt% EtOH each (with 10 wt% increments) as suspension media. After dilution, the suspensions were mixed thoroughly with a vortex machine to obtain a homogenous suspension. Approximately 1 mL of suspension was drawn from each suspension with different EtOH contents and added to a folded capillary cell, which was then placed inside the Zetasizer. Zeta potential measurements were carried out using laser Doppler electrophoresis with a Zetasizer Nano-ZS (Malvern Instruments). For each sample, 3 data sets were taken, with multiple measurements of the zeta potential used to produce a single data point after the value had stabilised. This data was then averaged and the standard deviation calculated. It can be seen from this figure that the greatest magnitude of zeta potential was observed at EtOh concentrations of between 20 and 30 wt%. The magnitude of the zeta potential is an important factor in EPD kinetics, since it determines whether the suspended particles are stabilised, the direction and velocity of particle migration during EPD, and the density of the deposit. For faster deposition, all other things being equal, the greater the magnitude of the zeta potential the better. Accordingly, from this data, it can be concluded that EtOh concentrations of around 20 to 30 wt% would be expected to provide the best performance.

[0195] Fig. 6 is a graph showing the zeta potential of various aqueous hCNF deposition suspensions (each having different composition of carrier liquid), with respect to hCNF concentration. Similarly to the method described in relation to Fig. 5, a 1.24 wt% hCNF aqueous slurry was diluted to the respective hCNF concentration as shown on the x-axis with suspension media as indicated in the legend, and the zeta potential of the resulting suspensions was measured with the Zetasizer. Based on the graph, for optimum EPD performance in aqueous hCNF suspension, the range of hCNF concentration was 8568552

[0196] 20 observed to be between 0.062 and 0.248 wt%. In 30 wt% EtOH suspension media, the optimum hCNF concentration range was observed to be between 0.031 and 0.217 wt%. In 50 wt% EtOH suspension media, the optimum hCNF concentration range was observed to be between 0.062 and 0.124 wt%. For all of the suspension media tested, it was seen that the largest magnitude of zeta potential was achieved at hCNF compositions of less than about 0.25 wt% hCNF, e.g. less than 0.2 wt% hCNF, indicating that more generally, independent of the composition of the suspension media (carrier liquid), a suspension having an hCNF composition of 0.25 wt% hCNF or less than 0.2 wt% hCNF may provide the best performance.

[0197] Fig. 7 is a graph showing the zeta potential of two different hCNF deposition suspensions (0.124 wt% hCNF aqueous suspension, and 0.093 wt% hCNF in 30 wt% EtOh) against pH of the suspension. Similarly to the method described in relation to Fig. 5, a 1.24 wt% hCNF aqueous slurry was diluted to the respective hCNF concentration with suspension media as indicated in the legend. The pH of the suspensions was adjusted using 0.01 M HCI and 0.1 M NaOH solutions respectively and was measured with a pH meter (Thermo Orion 3 Star). The zeta potential of the resulting suspensions was measured with the Zetasizer. Based on the data, the optimum suspension pH for best EPD performance was observed to be between 7 and 10 for both aqueous suspension media and 30 wt% EtOH. In general, a trend of increasing (negative) magnitude of zeta potential was seen as the pH increased, indicating that an alkaline suspension media is preferred for better / faster EPD of hCNF.

[0198] Preparation of EC slurry (deposition suspension) for EPD processes

[0199] EC-ethanol slurry for EPD was prepared by dissolving commercial EC powders in pure ethanol and stirring to obtain a clear solution.

[0200] Example final composition of slurry (deposition suspension):

[0201] EC: 0.1 to 4 w / w%

[0202] Example process for deposition of hCNF films

[0203] The deposition of hCNF films was carried out in a custom-built EPD rig, a schematic representation of which is provided as Fig. 1. The EPD cell consisted of two parallel 316 L stainless steel electrodes, separated by 4 silicone spacers (Fig. 1 showing 5 spacers as it is a schematic drawing) providing a deposition area of 5x2.5cm with a distance between electrodes of 0.75cm. The two electrodes were connected to an EA-PS 2042-10 B DC power supply and clamped with cardboard on either side.

[0204] Before deposition, a 1wt% cellulose acetate solution in acetone was cast on the anode to form a release layer and the rest of the rig was assembled while the release layer was still damp.

[0205] A 0.5w / w% of hCNF suspension in water was prepared according to step 1. Equal volumes of this suspension, ethanol and water were mixed together to form a new suspension as described above in the section ‘Preparation of hCNF slurry (deposition suspension) for EPD processes’.

[0206] Precisely 5ml of the prepared new suspension of hCNF was then carefully pipetted into the rig. The deposition was carried out at voltage and time of 10 V and 10 minutes, respectively, whilst the acetate 8568552

[0207] 21 release layer was still damp. Following deposition, the power supply was turned off, the electrodes were disconnected, and the remaining liquid was gently poured out keeping the anode faced up. After no liquid remained, the rest of the rig was dismantled keeping the anode faced up to prevent the film from sliding. The wet acetate layer, along with the hCNF film, was then gently peeled off the anode and placed on top of a petri dish. The film was then air-dried in a fume hood overnight and once dry submerged in acetone to dissolve the acetate layer, releasing the hCNF film. The film was then left to dry for 30 minutes and then carefully collected and weighed. An image of the film can be seen in Fig. 10.

[0208] The weight of the film in Fig. 10 was recorded as 0.0075g. Knowing this, as well as approximating the density of hCNF as 1.5g / cm3, and knowing the surface area of the film, one can estimate the thickness of the film produced using the following equations:

[0209] Volume = area x thickness mass P=- volume mass thickness = - p x area

[0210] This means that the above film is approximately 8.33 microns thick.

[0211] Whilst this film was not subsequently deposited on to form a composite cellulose based film according to the invention, it will be understood that the resultant freestanding CNF layer could be used (before or after drying) as a deposition interface for subsequent deposition of EC by EPD to form a composite cellulose film, e.g. as described below, or as shown schematically in Fig. 3.

[0212] Further work was also undertaken to investigate optimisation of various parameters for the EPD deposition process.

[0213] Fig. 8 (a)-(f) show: (a) wet film mass against voltage; (b) wet film concentration against voltage; (c) dry film mass against voltage; (d) measured thickness of the dry film against voltage; (e) % mass deposited against voltage; and (f) Zeta potential against voltage; each for a single deposition of 0.124wt% hCNF slurry (aqueous suspension, 30wt% EtOH), for times of 5 and 10 minutes. In obtaining this data, a setup similar to that shown in Fig. 1 was used. The electrodes used were made using a mixture of PTFE and graphite (25%), and were purchased from WKH Group. The separation between the electrodes was 6 mm. Since the hCNF particle has a negative zeta potential, it was deposited to the positive electrode during EPD. The mass of the positive electrode ( ME) was measured prior to EPD. 10 mL of 0. 124wt% hCNF slurry (aqueous suspension, 30wt% EtOH) was poured into the EPD cell and a voltage between 5 to 40 V (5 V increments) was applied between the electrodes with a DC power supply (Tenma 72-10480 and EA-PS 2042-10 B) for either 5 or 10 min. After EPD, the mass of the positive electrode with the wet deposited film ( ME+W) was measured. The hCNF film was then left air dry on the bench. After drying, the mass of the positive electrode with the dry film (ME+D) was measured.

[0214] The wet film mass (Mw) was calculated by using ME+W - ME 8568552

[0215] 22

[0216] The dry film mass (MD) was calculated by using ME+D - ME

[0217] The wet film concentration was calculated by using MD / MW

[0218] The percentage mass deposited was calculated by using MD / (0.124% x 9.26). The denominator is the theoretically total mass of hCNF in 10 ml_ of the suspension.

[0219] The thickness of the resultant dry film was measured with a micrometre at 6 different locations and the values were averaged and standard deviation reported with respect to the applied voltage and time.

[0220] The zeta potential of the slurry after the deposition was measured with the Zetasizer following the methods described under Slide 2.

[0221] Based on the data, for faster and more completed hCNF deposition, the optimum applied voltage was observed to be between 30 and 40 V.

[0222] Fig. 9 (a)-(f) show: (a) wet film mass against deposition time; (b) wet film concentration against deposition time; (c) dry film mass against deposition time; (d) measured thickness of the dry film against deposition time; (e) % mass deposited against deposition time; and (f) Zeta potential against deposition time; each for a single deposition of 0. 124wt% hCNF slurry (aqueous suspension, 30wt% EtOH), at an applied voltage of 5 V. The data was obtained from similar experiments as those described in relation to Fig. 8, except the EPD voltage was kept constant at 5 V and the deposition time was varied between 5 to 40 min with a 5 min interval. By comparison with the data in Fig. 8, it can be seen that EPD is possible at lower voltages such as 5V, but where the applied voltage is lower, the deposition time will need to be increased significantly to achieve comparable level of deposition. Hence, for faster deposition, the applied voltage should be above 30 V. However, if the applied voltage is required to be below a certain threshold, e.g. for safety reasons or to avoid significant water electrolysis, the deposition time can be increased accordingly to achieve complete deposition.

[0223] Example process for deposition of EC-hCNF composite films

[0224] The deposition of EC-hCNF composite films was carried out in a custom-built EPD rig described above in relation to the method for forming the hCNF film: The EPD cell consisted of two parallel 316 L stainless steel electrodes, separated by 4 silicone spacers providing a deposition area of 5x2.5cm with a distance between electrodes of 0.75cm. The two electrodes were connected to an EA-PS 2042-10 B DC power supply and clamped with cardboard on either side. No release layer was used in this case and deposition took place directly onto the electrode.

[0225] Precisely 5ml of 0.3wt% slurry in ethanol of EC was then carefully pipetted into the rig. The deposition of EC was carried out at voltage and time of 40 V and 30 minutes, respectively. After 30 minutes, the power supply was turned off, the electrodes were disconnected, and the remaining liquid was gently poured out. After no liquid remained, the electrode polarity was switched and reconnected i.e. , the anode became the cathode and vice versa.

[0226] Whilst the EC and electrodes remained wet, precisely 5ml of 0.5wt% suspension of hCNF was then carefully pipetted into the rig. The deposition of hCNF was carried out at voltage and time of 10 V and 10 minutes, respectively. Following deposition, the power supply was turned off, the electrodes were disconnected, and the remaining liquid was gently poured out keeping the anode faced up. After no liquid 8568552

[0227] 23 remained, the rest of the rig was dismantled keeping the anode faced up to prevent the film from sliding. The film was then air-dried in a fume hood overnight. An image of the film on the electrode can be seen in Fig. 11.

[0228] The total film weight was 0.0079g.

[0229] Because the film was produced as a ‘wet-on-wet’ process, it was not possible to obtain the mass of EC solely and thus determine the film thickness. However, if one assumes the mass of hCNF produced is the same as before (i.e., 0.0075g) we can back-calculate EC mass from the total film weight as 0.0004g. This and knowing that the total area is 3.8cm x 2cm and the density of ethyl cellulose is 1.32g / cm3 it is possible to approximate the thickness using the equation previously used. hCNF:

[0230] 0.0075#

[0231] 0.000658cm

[0232] 1.5g / cm3x 2 cm x 3.8cm

[0233] EC:

[0234] 0.0004#

[0235] , , = 0.00004cm

[0236] 1.32g / cm 'x 2 cm x 3.8cm

[0237] In this case, the hCNF thickness was approximately 6.58 microns thick whilst the EC was 0.4 microns thick, i.e. the total film thickness of the bilayer composite cellulose-based film was estimated to be around 7 microns thick.

[0238] Further studies relating to multi-cycle deposition of cellulose-based films

[0239] In order to assess the feasibility of continuous deposition processes, multi-cycle deposition processes were performed, and the results are shown in Fig. 12(a)-(e). Fig. 12 (a)-(e) show: (a) wet film mass against no. of depositions; (b) wet film concentration against no. of depositions; (c) dry film mass against no. of depositions; (d) measured thickness of the dry film against no. of depositions; (e) % mass deposited against no. of depositions. The EPD setup was the same as described in relation to Fig. 8.

[0240] For single deposition, 10 ml_ of the 0.124 wt% hCNF slurry (aqueous solution, 30 wt% EtOH) was poured into the EPD cell and respective voltage (20, 30 and 40 V) was applied for 10 min. The deposited slurry was then poured away for zeta potential measurements. The various masses were measured and calculated following the methods described above.

[0241] For double depositions, similar to the methods described above, after the 1st deposition and pouring away the used slurry, a fresh 10 mL of the 0.124 wt% hCNF slurry (aqueous solution, 30 wt% EtOH) was poured into the same EPD cell to further deposit more hCNF onto the existing wet hCNF film. The masses ME+W and ME+D were only measured after the 2nd deposition.

[0242] For triple depositions, similar to the methods described above, the masses ME+W and ME+D were only measured after the 3rd deposition.

[0243] The zeta potential of all the slurries were measured after deposition.

[0244] The data in this figure provide basis for continuous deposition as it shows hCNF can be electrophoretically deposited multiple times under wet conditions. The film mass and thickness increase 8568552

[0245] 24 with the number of depositions. In practice for continuous production, hCNF can be regularly or continuously added into the suspension to achieve continuous deposition or to control the thickness of the deposited film. The data also shows that the magnitude of the zeta potential of the post-deposition slurry decreases with applied voltage, suggesting a more complete deposition with use of higher applied voltages. It is theorised that this is because use of a higher voltage (higher E field) depletes more of hCNF in the slurry, and this is reflected in a decrease in the magnitude of the zeta potential observed.

[0246] Characterisation of EPD-deposited hCNF films: investigation of mechanical properties

[0247] In order to investigate mechanical properties of films according to the invention, hCNF films were electrophoretically deposited from 0.124 wt% hCNF in aqueous + 30 wt% EtOH suspension. The voltage applied was 30 V. The distance between the electrodes was 6 mm. The deposition time was 10 min per each deposition. 10 ml_ of the slurry was used per each deposition. The number of depositions was 2 for the films used for mechanical testing.

[0248] The film was cut into small strips with a width of approximately 3 mm. The exact width of each strip was measured at three different positions using a vernier calliper and averaged. The thickness of each strip was measured using a micrometre at three different positions and averaged. The cross-sectional area of each strip was calculated using the averaged width and thickness of the strip.

[0249] The tensile tests were performed using a Tinius Olsen 5 kN load frame universal test machine under ambient conditions. The load cell used was 1 kN and the strain rate was 0.1 mm min1. The film strip was sandwiched between two pieces of paper and sticked together with double-sided tape at the grips to ensure better grip between the machine and the film strip. Seven film strips were tested. The mean and standard deviation of the various mechanical properties were reported as shown in Fig. 13 - the Young’s modulus of the films (calculated using the initial linear region of the stress strain curve) was observed to be about 0.84 GPa. The Yield stress of the films was observed to be about 11.47 MPa. The UTS of the films was observed to be about 43.27 MPa, and the Failure strain of the films was observed to be about 16.32 %.

[0250] Characterisation of EPD-deposited hCNF films: investigation of oxygen transport rate

[0251] Fig. 14 is a graph showing Oxygen Transport rate (OTR) against thickness of various films made via multiple depositions as described above in relation to Fig. 12 (10 ml_ and 10 min per deposition).

[0252] The 20 V and 30 V samples were made using normal 0.124wt% hCNF slurry (aqueous, 30 wt% EtOH) and deposited 2 times.

[0253] For the centrifuged supernatant samples, they were deposited at 30 V for 3 times using the supernatant of a centrifuged 0.124wt% hCNF slurry (aqueous, 30 wt% EtOH). The normal slurry was centrifuged for 5 min at 4000 rpm and the supernatant was taken for EPD.

[0254] The thickness of the films was measured with a micrometre following the methods described above.

[0255] The oxygen transport rate of the films was measured using OTR analyser Systech Illinois 8101 which conforms to ASTM D3985-17, ASTM F1927-20, DIN 53380-3, JIS 7126, ASTM F1307, and ISO 15105-2 standards. The measurements were carried out at 23 °C and 0% relative humidity. 8568552

[0256] 25

[0257] Based on the data, it was observed that films formed using an applied voltage of 30 V displayed better oxygen barrier properties than films produced using an applied voltage of 20 V, indicating that higher applied voltage may lead to improved oxygen barrier performance of the resulting films. It was also observed that in general, thicker films displayed better oxygen barrier properties.

[0258] It was also observed that films formed from the supernatant of centrifuged hCNF slurry exhibited excellent oxygen barrier properties, even with lower film thicknesses - without wishing to be bound by theory, the inventors suggest that this is because centrifuging the slurry removes large micro-scale cellulose fibres leaving mainly finer hCNF particles, and that forming a film from these remaining fine particles results in films with improved properties.

[0259] Characterisation of EP D-d e posited hCNF films: investigation of water vapour transport rates

[0260] In order to investigate water barrier properties of films according to the invention, 45 g of pre-made hCNF slurry was diluted with 135 g of EtOH (99.9%) and 270 g of deionised water so that EtOH made up exactly 30 wt% of the final suspension. After dilution, the volume was mixed thoroughly with a vortex machine to obtain a homogenous suspension. The concentration of hCNF in the suspension was determined by taking 10 ml_ of the 450 ml_ suspension, allowing it to evaporate overnight, and then weighing the remaining solid. This was repeated three times and averaged; in this case, the final concentration was determined to be 0.15 wt% respectively. The suspension was then decanted into separate centrifuge tubes, each containing 10 ml_.

[0261] To obtain a supernatant, the diluted slurry (the suspension as described in the above paragraph) was centrifuged for 5 min at 4000 rpm, and the transparent supernatant was separated from the dense opaque pellet by carefully pipetting off the top. The supernatant was thoroughly mixed via a vortex before EPD.

[0262] Films were formed from both the suspension and the supernatant using an EPD process. The EPD rig consisted of two 6x6 cm PTFE (25% amorphous carbon) composite electrodes separated by a 6mm gap with 4 white nitrile spacers in between. The deposition area was approximately 4x4 cm. The rig was held together with cardboard and clamped. Each electrode was connected to a DC power supply (T enma 72- 10480 or EA-PS 2042-10 B). A centrifuge tube of 10 mL of hCNF suspension was vortexed, and the contents were poured into the EPD cell. A voltage of 30V was applied for 10 min. After 10 min, the power supply was turned off, and the remaining undeposited suspension was poured out of the rig and stored for further reference. The deposit and electrode were then left to air dry on the bench under a plastic cover with small ventilation holes.

[0263] For a multi-deposition, instead of drying, an additional 10 mL was added to the emptied rig still containing the wet deposit and the same EPD process was repeated the desired number of times. Deposits were then left to dry in the same manner.

[0264] Once sufficiently dried, films were either carefully removed from the electrode or left attached for further coating. Films were approximately 4x4 cm in size.

[0265] Films were tested for their Water Vapour Transmission Rate using a Systech AquaSense 7101 Water

[0266] Vapor Permeation (Industrial Physics). The machine uses the ASTM F3299-18 test method and conforms 8568552

[0267] 26 to International ISO 15106-3 and ISO 15105-2 standards. The measurements were carried out at 37.8 °C and 90% relative humidity.

[0268] Before testing, the attached nitrogen gas valve was checked to be at the correct pressure. The water reservoir was also checked to reach above the fill line.

[0269] Films were prepared for testing by first assembling the mask, which fits onto the testing stage. A ring of grease was applied to the inner ring of the metal disk, to which the film was carefully stuck and ensured that no gaps were present. A gasket was placed on top of this, and another small metal ring on top, forming the mask. This was all carefully screwed together, with the screws fastened parallel to each other to apply even pressure and prevent the film from becoming creased. As the machine has two cells, this was repeated for another film.

[0270] The top cover of the machine was lifted and set aside. The central lever was pulled, revealing the testing stage. The aluminium foils covering the testing cells were set aside, and any leftover grease was cleaned. New grease was applied to the outer ring, with any that entered the chamber being cleaned up. Each mask with film was then placed on top of the testing cell A and B with the screws facing up, and the mask was pushed lightly to ensure a tight seal. The top part of the testing stage was then pulled back on top, and the lever was securely fastened. The top cover was then placed back on top, and the test started.

[0271] The machine begins each test with a flash stage, followed by a gas purge stage, taking approximately 45 minutes. It then measured the WVTR of each cell individually every 15 minutes until it obtained 5 consecutive values within a 1% difference or stopped manually. In this case, after the initial ramp and settle-in values, the machine was manually stopped after having recorded at least 5 data points.

[0272] After this, the machine was opened, masks removed, and films detached in the reverse steps to the above. Aluminium foil protectors were reapplied to the testing cells until the next test. The data of each film was obtained, averaged, and the deviation was calculated. hCNF film samples were made according to the EPD methods given above and WVTR data from these films are shown in table 1 , below, and in Fig. 15. Data was also obtained from a commercial viscose sample (more specifically, a commercial sample manufactured using cellulose that has gone through the viscose process).

[0273] Table 1 : WVTR readings measured at 90% humidity at 37.8 C, for hCNF films formed via the EPD process as described above and a commercial viscose film (comparative).

[0274] The data show that through the EPD process, WVTR transmission at 90% relative humidity comparable with commercial viscose film can be obtained from hCNF films. Samples made via EPD using the same parameters (using either a supernatant slurry or an as prepared slurry) achieve a similar WVTR 8568552

[0275] 27 performance. Furthermore, the EPD film formed using the supernatant was observed to be more optically transparent (i.e. have greater optical clarity) than the other films: this is an indication that films having both good WVTR and good optical clarity can be achieved by EPD processes as discussed herein.

[0276] Some further analysis of the WVTR of films according to the invention was carried out at a commercial test facility using MOCON Permatran-W 3 / 34 Water Vapor Permeability Instrument. The machine uses test methods which conform to ASTM F1249-20, TAPPI T557 and JIS K7129 standards. The measurements were carried out at 23 °C and 50% relative humidity.

[0277] A 1.24 wt% hCNF aqueous slurry was diluted to 0.25 wt% hCNF with deionised water and EtOH (99.9%) to obtain a 44.1 wt% EtOH suspension, and film samples were produced by triple depositions. A electrode separation of 6mm was used in each case.

[0278] The following results were obtained:

[0279] Table 2: WVTR readings measured at 50% humidity at 23 °C, for hCNF films formed via the EPD process described above.

[0280] This data demonstrates measured WVTR values for a range of films produced using a range of different voltages and deposition times. This means that systematic comparison across samples is not possible. However, the data nevertheless demonstrates that WVTR values of less than 6 g / m2 / day can be achieved for conditions of 50% relative humidity and 23 °C for films according to the invention. The measured values show some variation - the inventors hypothesize, without wishing to be bound by theory, that this variation may be due to defects in some of the films tested. The lower values are considered to represent more accurate lower bounds for defect-free films.

[0281] Characterisation of composite EC-hCNF films: investigation of water vapour transport rates

[0282] In order to investigate water barrier properties of composite EC-hCNF films, an hCNF film was prepared via EPD as described above in the section ‘Characterisation of EPD-deposited hCNF films: investigation of water vapour transport rates’. The hCNF film was prepared using a voltage of 30V with 5 min per 8568552

[0283] 28 deposition, 50 ml of slurry for each deposition and with 3 depositions. The film was dried and then wirebar coated with ethyl cellulose according to the following method:

[0284] A 5 wt% solution of ethyl cellulose (EC) was prepared by diluting 2.5g in 47.5 g of EtOH, which was then thoroughly mixed in a vortex.

[0285] The dry hCNF film was placed on a flat glass panel and taped to the glass panel on all sides. 1 ml_ of EC solution was then poured above the top-most taped section of the film. The solution was poured with the same width as the film so that the entire width of the film would be evenly coated. A wire bar with a gap of 300 pm was then placed above the wet solution and film. The wire bar was then slowly and translationally moved downwards by hand, with no rotation of the bar as it evenly coated the EC solution on the film.

[0286] The coated film was then left to air dry for approximately ten minutes. Once dry, the taped film was carefully removed from the glass panel. The tape was either carefully peeled off the film, or the tape with the edge of the film still attached was cut off the rest of the film with scissors.

[0287] The thickness of the resultant dry film was measured with a micrometre at 6 different locations, once at each corner and twice at the centre, the values were averaged, and the standard deviation was calculated.

[0288] The coated film was then weighed, and the thickness was measured similarly to the prior method. The EC coating thickness was determined by calculating the difference in thickness before and after coating.

[0289] The film was tested for its WVTR using protocols as discussed above, at 50% humidity at 23.0 °C. The results are set out in table 3, below, and in Fig. 16. For comparison, data from non-EC-coated hCNF films is also included:

[0290] Table 3: WVTR readings measured at 50% humidity at 23.0 °C, for hCNF film formed via the EPD process and wire bar coating methods as described above.

[0291] From this data, it is observed that lower WVTR values are obtained from EC-coated films, than were obtained from uncoated hCNF films. This data demonstrates that for EC-coated hCNF films, WVTR values less than 130 g / m2 / day (e.g. about 124.5 g / m2 / day) can be achieved.

[0292] Further studies relating to nature of deposition interface 8568552

[0293] 29

[0294] In order to assess the feasibility of various different materials for deposition interfaces, a number of experiments were conducted.

[0295] Firstly, an experiment was done to assess the feasibility of deposition onto PTFE-based electrodes. A number of different electrode compositions were tested, as noted in the table below (base material for the electrode = PTFE, remaining additive content listed):

[0296] Table 4: Investigation of EPD capability of electrodes having different compositions.

[0297] It was found that PTFE-based electrode that had carbon compositions of at least 20 wt% were effective for use in EPD methods.

[0298] Secondly, an experiment was done to assess the feasibility of deposition onto fiber-based sheet material (e.g. paperboard, carboard, or a cellulosic composite material). Cardboard was selected as an example material.

[0299] For coating carboard with hCNF via EPD, the procedures were very similar to the EPD methods described earlier. Corrugated cardboard insulators were cut from a box into rectangles of approximately 6 x 7.5 cm. A piece of cardboard was placed adjacent to the positive electrode when assembling the EPD setup. The cardboard piece was sandwiched between the positive electrode and the spacers. 10 ml_ of the 0.124 wt% hCNF in aqueous 30 wt% EtOH slurry was used. A single deposition was carried out electrophoretically at 40 V for 5 min (this could also be performed at 30 V for 10 min). After deposition, the used slurry was poured away and the coated cardboard carefully removed from the setup and allowed to air dry. After drying, the resulting hCNF film coating was as shown in Fig. 17 - the deposited film is seen as a pale square shape in the centre of the cardboard.

[0300] The ability of the deposited hCNF film to provide an effective water barrier for the cardboard was then tested: Using a dropper, a drop of deionised water was dropped onto the hCNF coated cardboard surface and the adjacent uncoated carboard surface simultaneously. A photo was taken right after dropping water onto the cardboard and subsequently every 10 minutes to capture the appearance changes of the hCNF coated and uncoated cardboard surface. The results are shown in Fig. 18. It can be seen from this figure that the water droplet placed on the hCNF coated cardboard surface took significantly longer to absorb 8568552

[0301] 30 into the cardboard than the water droplet placed on the adjacent uncoated carboard surface, indicating that the films can provide a suitable water barrier for cardboard.

[0302] Further studies relating to use of supernatant of centrifuged slurry as the deposition suspension

[0303] In order to assess the feasibility & effect of use of supernatant of centrifuged slurry as the deposition suspension, a 0.124 wt% hCNF in aqueous, 30 wt% EtOH slurry was centrifuged for 5 min at 4000 rpm - the resultant slurry is shown in Fig. 19. As indicated in the figure, sedimented large fibres were observed near the bottom, and a concentration gradient of hCNF fibres of different sizes can be seen moving up into the supernatant layer.

[0304] The supernatant layer was then extracted and used to form films using EPD processes as described previously. The EPD film formed using the supernatant appeared to be clearer than the film of similar thickness (and EPD conditions) made using normal slurry, suggesting smaller fibre size increases optical transparency of the resultant films. As discussed earlier in relation to Fig. 13, the oxygen barrier properties were also assessed, and it was found that use of the supernatant as the EPD suspension provided excellent oxygen barrier properties. Furthermore, as discussed in relation to Fig. 15, the water barrier properties of the film were also assessed, and were observed to be at least comparable to commercial samples produced via the viscose process.

[0305] Further feasibility studies relating to cellulose-based films

[0306] In order to assess the feasibility of use of cellulose-based films including composite cellulose nanofibrils and ethyl cellulose based films as a packaging material (in particular for food packaging), a number of additional studies were performed. hCNF films, as well as composite hCNF and hydroxypropyl cellulose based (HPC) films were formed by casting, and the films were then characterised.

[0307] Fig. 20 shows (a) the transparency of the hCNFs / hydroxypropyl cellulose (HPC) films on the logos of the University of Cambridge and Macromolecular Materials Lab (MML), (b) Folding, rolling, and twisting test for hCNFs-based films, and (c) Tensile mechanical properties of C-CNF, T-CNF / HPC and hCNF / HPC films (Young’s modulus, strength).

[0308] Fig. 21 shows oxygen transmission rates for cast hCNF films at 23 °C and 0%, 50%, 90% RH (bottom line = 0% RH, middle line = 50% RH, top line = 90% RH).

[0309] It is hypothesised that films formed by processes according to the present invention (i.e. via EPD) would display similar or better mechanical, optical and / or water barrier and oxygen transmission rate properties than these comparative cast films, giving a strong indication of suitability of films according to the present invention for use in as a packaging material (in particular for food packaging).

[0310] Fig. 22 shows cellulose-based packaging bags with curcuma longa-derived curcumin to monitor the freshness of packaged shrimp at 25 °C for 24 h. It is hypothesised that composite cellulose nanofibrils and ethyl cellulose based films formed by processes according to the present invention (i.e. via EPD) could incorporate curcumin or other indicator compounds in a similar manner in order to provide an indication of freshness of food contained within packaging formed from the film, giving a further indication 8568552

[0311] 31 of suitability of films according to the present invention for use in as a ‘smart’ packaging material (in particular for food packaging).

[0312] Example procedure for preparation of composite cellulose-based films via continuous production

[0313] Whilst the above examples use static deposition set-ups for EPD deposition, composite cellulose-based films according to the present invention (and more generally, other films formable via EPD independent of their composition) can also be produced via continuous production process employing a dynamic electrode arrangement.

[0314] Fig. 23 shows a schematic diagram of one possible configuration for an apparatus 100 for continuous EPD deposition of films (e.g. of composite cellulose-based films according to the present invention). A deposition suspension 1 is provided in a suitable first container 3 (also referred to as a ‘mixing container’). The deposition suspension may optionally be stirred (e.g. using magnetic stirrer 4). The deposition suspension 1 is pumped into a suitable second container 5 (also referred to as a ‘deposition container’ or ‘deposition chamber’) in which film formation will occur, via a pump 7. The arrangement shown here, where the deposition chamber 5 is fed from the mixing container 3 allows for easy replenishment of the deposition suspension 1 in the deposition chamber to maintain consistent concentration and volume throughout the process. A continuous flow system is recommended to keep the solution fresh, remove byproducts, and prevent contamination, ensuring the integrity of the deposition process.

[0315] Within the deposition chamber 5, at least two co-rotating, electrified cylinders (drums) 7a, b are provided, the drums being immersed in the deposition suspension 1 . A conductive conveyor belt 9, serving as the deposition electrode, is stretched over the drums 7a, b under modest tension. Whilst the arrangement of Fig. 23 shows only 2 drums, it is contemplated that suitable arrangement could employ multiple subsidiary drums distributed along the length of belt, to avoid sagging of the belt and maintain a constant potential difference between the electrodes.

[0316] Counter electrodes 11a, b are located both above and below the conveyor belt 9, with a vertical separation of 0.5 to 1 cm, while remaining fully immersed in the deposition suspension 1. The voltage at each electrode may be monitored using voltmeters as shown: a feedback loop may be integrated into the system to adjust the applied voltage in response to changes in deposition rate and film quality. This ensures consistent electrostatic forces and uniform film properties across the entire production process.

[0317] During operation of the apparatus, an electric field is applied across the deposition suspension 1, between the conveyor belt 9 and the counter electrodes 11a and 11 b to cause electrophoretic deposition of particles suspended in the deposition suspension at the deposition interface, which is here provided by the conveyor belt 9. This particle deposition results in film formation on the conveyor belt 9 - the film 10 being represented by a dashed line in this schematic figure.

[0318] As the film begins to form on the conveyor belt 9, the slow rotation of the drum moves the belt along the deposition suspension bath. This movement allows the film to continue stabilizing and thickening as it progresses along the conveying line. With an assumed deposition rate of 1 micron per minute, and a desired film thickness of 10 microns, the film at the initial deposition point should take approximately 10 minutes to reach the point of removal from the conveyor, ensuring adequate time for mechanical stability to develop before it is lifted out of the solution. 8568552

[0319] 32

[0320] This means that the production rate will be determined primarily by the length of conveyor belt that can be used, all other things being equal. For example, if the conveyor belt is 10 m long, then it will need to travel at 1 m / min = 1.67 cm / s.

[0321] A more general calculation process is as follows: let minimum film thickness be Tmin [microns], deposition rate r [micron / min], conveyor belt length L [metres]. Then production speed V = Lr / Tmin [metres / min].

[0322] At the secondary drum, a peeling mechanism 13 is provided to lift the film from the conveyor belt. This can be achieved in practice using a doctor blade or an automated roller system designed to gently separate the film from the belt without causing damage or deformation.

[0323] The apparatus can also comprise a film thickness measurement module 15 near or adjacent to the peeling mechanism. The thickness measurement module is here conveniently provided as a laser micrometre or optical thickness gauge, and is configured to monitor the film thickness in real-time. The data from this sensor can be used to dynamically adjust parameters such as drum speed, solution flow rate, and deposition time, optimizing the process for consistent output.

[0324] After the film 10 is separated from the conveyor belt by peeling mechanism 13, it may be transported for onwards processing. Onward processing may include e.g. movement of the film to a secondary deposition bath, similar to that shown in Fig. 23, where a second layer of film may be deposited on the existing film layer in order to produce a bi-layer composite film (e.g. a CNF / EC composite film).

[0325] Onwards processing may alternatively or additionally include movement of the film to a drying section. The drying method can be selected based on the specific solvent and material properties, with options including infrared heaters, forced air, or vacuum drying. This ensures the film is fully dried and ready for subsequent processing or use.

[0326] Fig. 24 shows a schematic diagram of one possible configuration for a drying apparatus 200 for drying of films produced by a continuous EPD process (e.g. for drying of films produced using an apparatus as shown in Fig. 23). The apparatus comprises a plurality of rotating cylinders (drums) 17 configured to move the film 10 along a drying path, and a plurality of heaters 19 configured to dry the film. As the film 10 moves along the drying path, the heat output by heaters 19 causes evaporative loss of solvent from the film, thereby leading to drying of the film.

[0327] Throughout both film forming and drying processes, humidity and temperature control may be performed to ensure stable humidity and temperature conditions. This can prevent variability in the film formation process, particularly when dealing with volatile solvents. Environmental control systems may be implemented to maintain these conditions within the desired range.

[0328] The use of continuous film production processes may offer advantages over batch-based processes in terms of their suitability for scaling.

[0329] ***

[0330] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof. 8568552

[0331] 33

[0332] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0333] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0334] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0335] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0336] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / - 10%.

[0337] References

[0338] A number of publications are cited above in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Full citations for these references are provided below. The entirety of each of these references is incorporated herein.

[0339] Koskela et al, “Lytic polysaccharide monooxygenase (LPMO) mediated production of ultra-fine cellulose nanofibres from delignified softwood fibres” (2019)

[0340] Rogowski et al, “Evidence That GH115 a-Glucuronidase Activity, Which Is Required to Degrade Plant Biomass, Is Dependent on Conformational Flexibility” (2014)

[0341] Li et al, “Facile preparation of reactive hydrophobic cellulose nanofibril film for reducing water vapor permeability (WVP) in packaging applications” Cellulose. 26:3271-3284 (2019)

[0342] Yang et al, “Structural and Ecofriendly Holocellulose Materials from Wood: Microscale Fibers and Nanoscale Fibrils”, Adv. Mater. 33, 2001118, (2021 )

Claims

856855234Claims:

1. A method of manufacturing a cellulose-based film, the method comprising: electrophoretically depositing cellulose nanofibrils onto a deposition interface to form a cellulose nanofibril film layer, wherein the cellulose nanofibrils comprise holocellulose nanofibrils (hCNFs).

2. The method according to claim 1 wherein the method includes applying an electric field across a suspension comprising hCNFs to cause electrophoretic deposition of the hCNFs at the deposition interface.

3. The method according to claim 2 wherein the suspension comprising hCNFs further comprises water and at least one of ethanol, methanol, benzyl alcohol or 2-propanol.

4. The method according to claim 3 wherein the suspension comprises ethanol in an amount of from 20 to 30 wt%.

5. The method according to any one of claims 2 to 4 wherein the suspension comprising hCNFs comprises hCNF in an amount of from 0.062 and 0.248 wt%.

6. The method according to any one of claims 2 to 5 wherein the pH of the suspension comprising hCNFs is between 7 and 10.

7. The method according to any one of claims 2 to 6 wherein the suspension comprising hCNFs further comprises a plasticising agent, optionally wherein the plasticising agent is a bio-derived plasticising agent, further optionally wherein the plasticising agent is a cellulose-based plasticising agent, optionally wherein the plasticising agent is hydroxypropyl cellulose.

8. The method according to any one of claims 2 to 7 wherein the suspension comprising hCNFs further comprises an indicator compound which changes colour in response to changes in pH.

9. The method according to any one of claims 2 to 8 wherein the suspension comprising hCNF is obtained from the supernatant of a centrifuged slurry of cellulose nanofibrils.

10. The method according to any one of the preceding claims wherein the deposition interface is provided by:(i) an electrode;(ii) a release layer provided at a surface of an electrode, to permit separation of the deposited layer from the electrode;(iii) a raft of bubbles generated at a surface of an electrode;(iv) a suspended deposition membrane.

11. The method according to claim 10, wherein the deposition interface is provided by an electrode, wherein the electrode comprises polytetrafluoroethylene (PTFE), optionally wherein the electrode further comprises at least 15 wt% carbon, based on total weight of the electrode.

12. The method according to any one of the preceding claims wherein the deposition interface is provided by a fiber-based sheet material, optionally wherein the fiber-based sheet material is selected from: paperboard, carboard, or a cellulosic composite material.85685523513. The method according to any one of the preceding claims, wherein the deposition interface is provided by an electrode that is configured to move during the deposition process, optionally wherein the electrode is provided by a conductive conveyor belt.

14. The method according to any one of the preceding claims wherein the electrophoretic deposition is performed at an applied voltage in a range of from 1 to 100V; optionally wherein the electrophoretic deposition is performed at an applied voltage in a range of from 30 and 40 V.15 The method according to any one of the preceding claims wherein the electrophoretic deposition is performed for a time of from 2 minutes to 2 hours.

16. A method of manufacturing a cellulose-based film according to any one of the preceding claims, wherein the method comprises a substantially continuous deposition process.

17. A method of manufacturing a cellulose-based film according to any one of the preceding claims, wherein the method comprises a further step of depositing a layer of a polymeric cellulose derivative; optionally wherein the layer of polymeric cellulose derivative is deposited: (i) onto the cellulose nanofibril film layer after formation of said layer, or (ii) prior to deposition of the cellulose nanofibril film layer; optionally wherein the step of depositing a layer of polymeric cellulose derivative is performed by a method selected from EPD, wire-bar coating or doctor blade coating; optionally wherein the polymeric cellulose derivative comprises or consists of ethyl cellulose.

18. A cellulose-based film comprising a cellulose nanofibril film layer comprising holocellulose nanofibrils (hCNFs), wherein the cellulose nanofibril film layer is formed by electrophoretic deposition of hCNFs onto a deposition interface.

19. The cellulose-based film according to claim 18 wherein the thickness of the film is greater than 5 pm, optionally greater than 60 pm.

20. The cellulose-based film according to any one of claims 18 to 19 wherein the film has an area in a range of from less than 1 cm2to 1 m2or more.

21. The cellulose-based film according to any one of claims 18 to 20 wherein the film is hydrophobic.

22. The cellulose-based film according to any one of claims 18 to 21 wherein the film comprises an indicator compound which changes colour in response to changes in pH.

23. The cellulose-based film according to any one of claims 18 to 22 wherein the film comprises a polymeric cellulose derivative layer, optionally wherein the polymeric cellulose derivative layer comprises or consists of ethyl cellulose.

24. A method of manufacturing a composite cellulose-based film, the method comprising: electrophoretically depositing cellulose nanofibrils and ethyl cellulose onto a deposition interface to form the composite cellulose-based film.

25. The method according to claim 24 wherein the method includes steps of:(a) applying an electric field across a suspension comprising cellulose nanofibrils to cause856855236 electrophoretic deposition of the cellulose nanofibrils at the deposition interface; and(b) applying an electric field across a suspension comprising ethyl cellulose to cause electrophoretic deposition of ethyl cellulose at the deposition interface; wherein steps (a) and (b) are performed simultaneously or sequentially, in any order.

26. The method according to claim 25, wherein the cellulose nanofibrils and ethyl cellulose are deposited sequentially.

27. The method according to claim 25 wherein the cellulose nanofibrils and ethyl cellulose are deposited simultaneously.

28. The method according to claim 25 wherein the method includes both simultaneous and sequential deposition of cellulose nanofibrils and ethyl cellulose.

29. The method according to any one of claims 25 to 28 wherein one or both of: (i) the suspension comprising cellulose nanofibrils; and (ii) the suspension comprising ethyl cellulose; comprise water and at least one of ethanol, methanol, benzyl alcohol or 2-propanol.

30. The method according to any one of claims 25 to 29 wherein one or both of: (i) the suspension comprising cellulose nanofibrils; and (ii) the suspension comprising ethyl cellulose; comprise a plasticising agent.

31. The method according to claim 30 wherein the plasticising agent is a bio-derived plasticising agent, optionally a cellulose-based plasticising agent, optionally wherein the plasticising agent is hydroxypropyl cellulose.

32. The method according to any one of claims 25 to 31 wherein one or both of the suspension comprising cellulose nanofibrils and the suspension comprising ethyl cellulose comprises an indicator compound which changes colour in response to changes in pH.

33. The method according to any one of claims 24 to 32 wherein the cellulose nanofibrils comprise or consist of holocellulose nanofibrils (hCNFs).

34. The method according to any one claims 24 to 33, wherein the deposition interface is provided by:(i) an electrode;(ii) a release layer provided at a surface of an electrode, to permit separation of the deposited layer from the electrode;(Hi) a raft of bubbles generated at a surface of an electrode; or (iv) a suspended deposition membrane.

35. The method according to claim 34, wherein the deposition interface is provided by an electrode, where the electrode comprises polytetrafluoroethylene (PTFE).

36. The method according to any one of claims 24 to 35 wherein the deposition interface is provided by a fiber-based sheet material, optionally wherein the fiber-based sheet material is selected from: paperboard, carboard, or a cellulosic composite material.85685523737. The method according to any one of claims 24 to 36, wherein the deposition interface is provided by an electrode that is configured to move during the process of deposition to form the composite cellulose-based film, optionally wherein the electrode is provided by a conductive conveyor belt.

38. The method according to any one of claims 24 to 32 wherein the electrophoretic deposition is performed at an applied voltage in a range of from 1 to 100V.

39. The method according to any one of claims 24 to 38 wherein the electrophoretic deposition is performed for a time of from 2 minutes to 2 hours.

40. A composite cellulose-based film comprising: cellulose nanofibrils; and ethyl cellulose; wherein the film is formed by electrophoretic deposition of cellulose nanofibrils and ethyl cellulose onto a deposition interface.

41. The composite cellulose-based film according to claim 40 wherein the film is a bilayer composite film including a layer comprising cellulose nanofibrils and a layer comprising ethyl cellulose.

42. The composite cellulose-based film according to claim 40 wherein the film is a multilayer composite film including multiple layers of cellulose nanofibrils and / or ethyl cellulose.

43. The composite cellulose-based film according to any one of claims 40 to 42 wherein the composition of the film varies in a step-wise manner through the film thickness.

44. The composite cellulose-based film according to any one of claims 40 to 42 wherein the composition of the film varies in a graduated manner through the film thickness.

45. The composite cellulose-based film according to any one of claims 40 to 44 wherein the thickness of the film is in a range of from 5 pm to 50 pm.

46. The composite cellulose-based film according to any one of claims 40 to 45 wherein the film has an area in a range of from less than 1 cm2to 1 m2or more.

47. The composite cellulose-based film according to any one of claims 40 to 46 wherein the film is hydrophobic.

48. The composite cellulose-based film according to any one of claims 40 to 47 wherein the film comprises an indicator compound which changes colour in response to changes in pH.

49. A composite structure comprising a first layer provided by the cellulose-based film of any one of claims 18 to 23, and at least a second layer having a different composition.

50. A food packaging comprising a cellulose-based film according to any one of claims 18 to 23 and / or comprising a composite cellulose-based film according to any one of claims 40 to 48.

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