Moulded pulp article

Abstract

The present invention relates to a method of producing a moulded pulp article (1), the method comprising: a) applying a composite phase (2) to the pulp (3), the composite phase (2) comprising precursor particles (4); b) shaping the pulp (3); and c) converting the composite phase (2) to a ceramic coating (5) by heating the composite phase; and moulded pulp articles.

Description

[0001] MOULDED PULP ARTICLE

[0002] Field of the invention

[0003] The present invention relates to moulded pulp articles with improved barrier properties and methods for their production.

[0004] Background of the invention

[0005] Moulded pulp is a material that is used with increasing frequency for packaging, particularly of foodstuffs. A key benefit of these materials is that they are easily recycled and biodegrade, often being home compostable. Existing technologies of moulded pulp allow the production of rigid containers such as paper cans, paper bottles or capsules for beverages. Being made of cellulosic fibres, it is usually necessary to coat or laminate the moulded pulp in order to add sealing and barrier properties (e.g. to prevent ingress of oxygen).

[0006] The provision of moulded pulp with effective barriers to water vapour remains a challenge and significant additional processing is required to provide a suitable barrier. In particular, the provision of effective barriers that do not interfere with the recyclable and biodegradable nature of the mould pulp.

[0007] It is an object of the present invention to solve one or more of the foregoing problems.

[0008] Summary of the invention

[0009] A first aspect of the present invention relates to a method of producing a moulded pulp article (1), the method comprising: a) applying a composite phase (2) to the pulp (3), the composite phase (2) comprising precursor particles (4); b) shaping the pulp (3); and c) converting the composite phase (2) to a ceramic coating (5) by heating the composite phase. The composite phase (2) may comprise an aqueous dispersion of the precursor particles (4) or a dry powder comprising the precursor particles. In embodiments, applying the composite phase (2) comprises dip coating or spray coating the pulp (3) with the aqueous dispersion. In alternative embodiments, applying the composite phase (2) comprising spreading or screen printing the pulp (3) with the dry powder.

[0010] The precursor particles may be selected from the group comprising aluminium oxide, silicon dioxide, zinc oxide, calcium oxide, and combinations thereof.

[0011] In embodiments, steps a), b), and c) occur in order. Alternatively, or additionally, steps b) and c) occur simultaneously. In further embodiments, step b) occurs before step a), which occurs before step c).

[0012] The composite phase may further comprise a catalyst, the catalyst comprising an acid or a base, optionally in a concentration of 2 to 5% w / w.

[0013] The composite phase (2) may be heated at a temperature of between 100 and 250 °C. The composite phase (2) may be heated for a period of up to 1 minute.

[0014] Conversion of the composite phase (2) may further comprise compressing the composite phase (2), optionally at a pressure of 1 to 150 MPa. Optionally, step c) comprises compression moulding.

[0015] The composite phase (2) may further comprise a tetraalkyl orthosilicate, optionally wherein the tetraalkyl orthosilicate is selected from tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), and combinations thereof. A second aspect of the present invention relates to a moulded pulp article (1) comprising: a shaped pulp (3); and a ceramic coating (5).

[0016] In embodiments, the ceramic coating (5) comprises a continuous layer (5a) of fused precursor particles. Additionally, or alternatively, the ceramic coating (5) comprises precursor particles at least partially embedded within a network of silicon dioxide (5b).

[0017] The ceramic coating (5) may have a thickness of from 1 to 100 pm. The ceramic coating (5) may be covalently bonded to the pulp.

[0018] A third aspect of the present invention relates to the use of a moulded pulp article according to the second aspect of the present invention, for packing an edible product for human or animal consumption.

[0019] A fourth aspect of the present invention relates to a packaged edible product, comprising a moulded pulp article according to the second aspect of the present invention, at least partially filled with an edible product for human or animal consumption.

[0020] As used in this specification, the words "comprises", "comprising", and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean "including, but not limited to".

[0021] Brief description of the drawings Additional features and advantages of the present invention are described in, and will be apparent from, the description of the presently preferred embodiments which are set out below with reference to the drawings in which:

[0022] Figure 1 shows a schematic cross section of a moulded pulp article (1) according to the present invention. The moulded pulp article (1) includes a pulp (3) and a ceramic coating (5), the ceramic coating (5) comprising a continuous layer (5a) of fused precursor particles;

[0023] Figure 2 shows a schematic cross section of a precursor to a moulded pulp article (1) according to the present invention. The precursor to the moulded pulp article (1) includes a pulp (3) and a composite phase (2), the composite phase (2) comprising precursor particles (4);

[0024] Figure 3 shows a schematic cross section of a moulded pulp article (1) according to the present invention. The moulded pulp article (1) includes a pulp (3) and a ceramic coating (5), the ceramic coating (5) comprising precursor particles (4) at least partially embedded within a network of silicon dioxide (5b);

[0025] Figure 4 shows a schematic cross section of a precursor to a moulded pulp article (1) according to the present invention. The precursor to the moulded pulp article (1) includes a pulp (3) and a composite phase (2), the composite phase (2) comprising precursor particles (4) and a tetraalkyl orthosilicate.

[0026] Figure 5 shows a representative SEM image of a ZnO layer on a cellulose layer as formed by the method of the present invention in Example 1.

[0027] Figure 6 shows a representative SEM image of a ZnO layer on a cellulose layer as formed by the method of the present invention in Example 2.

[0028] Figure 7 shows a representative XRD trace of a ZnO layer on a cellulose layer as formed by the method of the present invention in Example 2.

[0029] Detailed description of the invention By "fibre", it is meant a cellulosic fibre, which is generally extracted from plants, seeds or trees; such fibres contain not only cellulose molecules, but also hemi-cellulose as well as lignin.

[0030] By "moulded pulp articles", also known as "moulded fibre articles", it is meant articles that are formed by the moulding of fibrous materials. The fibrous materials may be obtained by recycling processed fibre sources, such as paper or cardboard, or obtained directly from natural fibre sources, such as sugarcane bagasse, bamboo, and straw. Moulded pulp articles are commonly used for packaging and is widely considered to be sustainable.

[0031] Method of Providing a Moulded Pulp Article

[0032] A first aspect of the present invention relates to a method of producing a moulded pulp article, the method comprising: a) applying a composite phase to the pulp, the composite phase comprising precursor particles ; b) shaping the pulp; and c) converting the composite phase to a ceramic coating by heating the composite phase.

[0033] In embodiments, applying the composite phase comprises applying an aqueous dispersion of the precursor particles to the surface of the pulp. The aqueous dispersion may be in the form of a liquid or a paste. The aqueous dispersion in the form of a liquid may have a particle concentration of from 0.5 to 50 vol%, whereas the aqueous dispersion in the form of a paste may have a particle concentration of from 50 to 99 vol%. The aqueous dispersion may be applied by any suitable means, such as spray coating or dip coating. The aqueous dispersion may be dried prior to conversion to a ceramic coating. Alternatively, the aqueous dispersion is dried as it is converted to the ceramic coating. In an alternative embodiment, applying the composite phase comprises applying a dry powder of the precursor particles to the surface of the pulp. The dry powder can be compacted to the surface of the pulp. The dry powder may be applied by any suitable means, such as spreading or screen printing.

[0034] The precursor particles may be particles of metal oxide, metalloid oxide, ceramic, or combinations thereof. The precursor particles may be selected from aluminium oxide, silicon dioxide, zinc oxide, calcium oxide, or combinations thereof. Generally, combinations of particles (e.g. aluminium oxide and silicon dioxide) refers to a mixture of particles (e.g. particles of aluminium oxide and particles of silicon dioxide).

[0035] The precursor particles may have an average particle size of from 0.01 pm to 150 pm, preferably from 0.1 pm to 100 pm, more preferably from 0.5 pm to 80 pm, most preferably from 1 pm to 60 pm. The precursor particles may have an average particle size of from 1 nm to 1000 nm, preferably from 5 nm to 500 nm, more preferably from 10 to 200 nm, most preferably from 20 to 100 nm. Any suitable technique may be applied to measure the particle size, for example, scanning electron microscopy (SEM) as is described in ISO 19749:2021 or transmission electron microscopy (TEM) as is described in ISO 21363:2020.

[0036] Steps a), b), and c) may occur in order. In other words, the composite phase is applied to the pulp, then the pulp is shaped, and then the composite phase is converted to the ceramic coating.

[0037] Alternatively, step b) occurs before step a), which occurs before step c). In other words, the pulp is shaped, then the composite phase is applied, and then the composite phase is converted to the ceramic coating. Steps b) and c) may occur simultaneously after step a). In other words, the composite phase is applied to an unshaped pulp (for example, as a flat sheet) and the pulp is then formed into the shape of the moulded pulp article as the composite phase is converted to the ceramic coating.

[0038] The aqueous dispersion or dry powder may further comprise a catalyst. If present, the catalyst may be present in a concentration of from 1 to 10% w / w, preferably from 2 to 5% w / w. The catalyst may comprise an acid or a base, for example, a mineral acid, such as hydrochloric acid, or an organic acid, such as acetic acid.

[0039] Converting the composite phase to the ceramic coating comprises heating the composite phase. Heating the composite phase may comprise heating the composite phase at a temperature of between 100 and 250 °C. Preferably, the composite phase is heated at a temperature of between 120 and 200 °C, more preferably the composite phase is heated at a temperature of between 130 and 180 °C. The composite phase may be heated for a period of from 10 seconds to 120 seconds. Preferably the composite phase is heated for a period of from 30 to 90 seconds, more preferably the composite phase is heated for a period of around 60 seconds. The composite phase may also be compressed during conversion, preferably simultaneously with the heating. Compressing the composite phase may comprise applying a pressure of from 0.5 to 200 MPa to the composite phase. In embodiments, the pressure is from 1 to 10 MPa is applied, more preferably a pressure of from 3 to 7 MPa. In alternative embodiments, the pressure is from 75 to 175 MPa, preferably from 90 to 150 MPa. In an embodiment, the heating and / or compressing comprises compression moulding. In compression moulding, a flat substrate is pressed into a mould by a plug, at least one of the mould and the plug may be heated. The above effects cold sintering of the precursor particles to form the ceramic coating, which has a sufficient density for effective barrier properties, while avoiding degradation of the pulp due to exposure to excessive heat.

[0040] The composite phase may further comprise a tetraalkyl orthosilicate, for example, tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), or combinations thereof. The tetraalkyl orthosilicate is operable to covalently bond to itself to form a network of silicon dioxide and to the surface of the particles under the conversion conditions. The tetraalkyl orthosilicate may also covalently bond to the surface of the pulp fibres via hydroxyl groups present on the cellulose fibres.

[0041] Moulded Pulp Article

[0042] A second aspect of the present invention relates to a moulded pulp article comprising: a shaped pulp; and a ceramic coating. The ceramic coating is a continuous layer that comprises an inorganic polymer network.

[0043] The ceramic coating may comprise particles of aluminium oxide and / or silicon dioxide that have been fused together to form a continuous layer. The continuous layer substantially preventing the movement of gases (such as oxygen or water vapour) therethrough. Such coatings can be formed by the conversion of a composite phase comprising particles of aluminium oxide and / or silicon dioxide and a catalyst.

[0044] In embodiments, the ceramic coating may comprise particles of aluminium oxide and / or silicon dioxide at least partially embedded within a network of silicon dioxide, which together form a continuous layer. The continuous layer substantially preventing the movement of gases (such as oxygen or water vapour) therethrough. Such coatings can be formed by the conversion of a composite phase comprising particles of aluminium oxide and / or silicon dioxide, a tetraalkyl orthosilicate, and a catalyst. In embodiments, the network is covalently bonded to the particles and / or to hydroxyl groups of the cellulose fibres present in the pulp. In certain embodiments, at least a portion of the particles of aluminium oxide and / or silicon dioxide that are at least partially embedded within the network of silicon dioxide are fused.

[0045] The ceramic coating may have a thickness of from 1 to 100 pm. Preferably, the ceramic coating has a thickness of from 2 to 80 pm, more preferably a thickness of from 5 to 25 pm.

[0046] The moulded pulp article may be a can, a cup, a tray, a bottle, or a capsule.

[0047] The moulded pulp article may be produced by the method of the first aspect of the present invention.

[0048] Uses of the Moulded Pulp Article

[0049] Moulded pulp articles as described herein may be used for packing an edible product for human or animal consumption. Preferably, the moulded pulp article is in the form of a partially open vessel and the edible product is inserted via the opening. Once the moulded pulp article is filled, the opening is sealed, preferably with a polymeric film, a removable cap (e.g. a screw-cap), or a foil.

[0050] A further aspect of the present invention is a packaged edible product, comprising a moulded pulp article as described herein, at least partially filled with an edible product for human or animal consumption.

[0051] Preferably, said edible product is a powder, a gel, or kibbles and is selected within the list of: ground coffee, soluble coffee, nutrition compositions for infant, adult, or elderly consumption, soup, confectionery or candies, chocolate-based products, dry animal food, dairy products.

[0052] Examples

[0053] The following examples were analysed using SEM and XRD.

[0054] For SEM, samples were prepared by mounting in resin and then sequentially grinding and polishing with 800, 1200, and 2500 grit, followed by 3 pm and 1 pm diamond paste. The mounted and smoothed surface was then sputter coated with gold. SEM was performed in secondary electron mode with an FEI Inspect F 50 at 10 kV spot size of 3.0.

[0055] For XRD, the ZnO layer was removed and ground in a pestle and mortar. The powdered sample was then analysed in a PANalytical Aeris with CuK a radiation, 30 kV, divergence slit, a 0.15 mm Ni filter, 0.02 Rad seller slits, step size 0.02.

[0056] Example 1

[0057] ZnO particles with a size of 10 to 50 nm (obtained from US Research Nanomaterials, Inc.) were combined with 1.0 M acetic acid and pressed onto the surface of cellulose board at a temperature of 130 °C and a pressure of 150 MPa.

[0058] The resulting coating was analysed by SEM and was found to be a dense coating of ZnO in good contact with the underlying cellulose and having a thickness of approximately 500 pm. A representative image is shown in Fig. 5.

[0059] Example 2 ZnO particles with a size of 10 to 50 nm (obtained from US Research

[0060] Nanomaterials, Inc.) were combined with 1.0 M acetic acid and pressed onto the surface of cellulose board at a temperature of 130 °C and a pressure of 90 MPa. The resulting coating was analysed by SEM and was found to be a dense coating of ZnO in good contact with the underlying cellulose and having a thickness of approximately 200 pm. A representative image is shown in Fig. 6.

[0061] The coating was also analysed by XRD, which found that the coating adopted the expected Wurtzite ZnO structure, along with a secondary phase of zinc acetate. A representative trace is shown in Fig. 1, with # indicating peaks representative of ZnO, * indicating peaks representative of zinc acetate, and @ indicating anomalous peaks.

Claims

Claims1. A method of producing a moulded pulp article (1), the method comprising: a) applying a composite phase (2) to the pulp (3), the composite phase (2) comprising precursor particles (4); b) shaping the pulp (3); and c) converting the composite phase (2) to a ceramic coating (5) by heating the composite phase.

2. The method according to claim 1, wherein the composite phase (2) comprises an aqueous dispersion of the precursor particles (4) or a dry powder comprising the precursor particles.

3. The method according to claim 2, wherein applying the composite phase (2) comprises dip coating or spray coating the pulp (3) with the aqueous dispersion.

4. The method of claim 2, wherein applying the composite phase (2) comprising spreading or screen printing the pulp (3) with the dry powder.

5. The method according to any one of claims 1 to 4, wherein the precursor particles are selected from the group comprising aluminium oxide, silicon dioxide, zinc oxide, calcium oxide, and combinations thereof.

6. The method according to any one of claims 1 to 5, wherein: i. steps a), b), and c) occur in order; and / or ii. wherein steps b) and c) occur simultaneously.

7. The method according to any one of claims 1 to 5, wherein step b) occurs before step a), which occurs before step c).

8. The method according to any one of the preceding claims, wherein the composite phase further comprises a catalyst, the catalyst comprising an acid or a base, optionally in a concentration of 2 to 5% w / w.

9. The method according to any one of the preceding claims, wherein the composite phase (2) is: i. heated at a temperature of between 100 and 250 °C; and / or ii. heated for a period of up to 1 minute.

10. The method according to any one of the preceding claims, wherein conversion of the composite phase (2) further comprises compressing the composite phase (2), optionally at a pressure of 1 to 150 MPa.

11. The method according to claim 10, wherein step c) comprises compression moulding.

12. The method according to any one of the preceding claims, wherein the composite phase (2) further comprises a tetraalkyl orthosilicate, optionally wherein the tetraalkyl orthosilicate is selected from tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), and combinations thereof.

13. A moulded pulp article (1) comprising: a shaped pulp (3); and a ceramic coating (5).

14. The moulded pulp article according to claim 13, wherein the ceramic coating (5) comprises: i. a continuous layer (5a) of fused precursor particles; and / or ii. precursor particles at least partially embedded within a network of silicon dioxide (5b).

15. The moulded pulp article according to claim 13 or claim 14, wherein the ceramic coating (5) has a thickness of from 1 to 100 pm.

16. The moulded pulp article according to any one of claims 13 to 15, wherein the ceramic coating (5) is covalently bonded to the pulp.

17. Use of a moulded pulp article according to any one of claims 13 to 16, for packing an edible product for human or animal consumption.

18. A packaged edible product, comprising a moulded pulp article according to any one of claims 13 to 16, at least partially filled with an edible product for human or animal consumption.

Images