Compostable cellulosic paper for gas barrier in packaging materials

Abstract

The present invention provides a 10 cm 3 / (m 2 The present invention relates to a compostable cellulosic paper having an oxygen permeability of less than 1000 kJ / day, wherein the compostable cellulosic paper comprises a continuous cellulosic fiber matrix containing natural cellulosic fibers and non-fibrous cellulosic material, and the content of the non-fibrous cellulosic material in the continuous cellulosic fiber matrix is ​​15 to 50% by weight.

Description

[Technical Field]

[0001] The present invention relates to compostable cellulosic paper that can be used as a gas barrier layer in food packaging. A further aspect of the present invention includes packaging for oxygen-sensitive products comprising the compostable cellulosic paper described herein. [Background technology]

[0002] Packaging materials are a source of large amounts of waste, and many countries are currently trying to reduce this by replacing fuel-based plastic packaging with fully biodegradable, compostable, and biologically-sourced packaging materials. Cellulose fibers are known as biodegradable packaging materials. Such biodegradable packaging materials must meet various requirements when used as food packaging that comes into contact with food. In particular, when used as packaging materials for oxygen-sensitive products, the packaging materials must have sufficient gas barrier properties.

[0003] To achieve the desired gas barrier properties, biodegradable packaging materials made from cellulose fibers are typically laminated with additional gas barrier layers.

[0004] EP2841263A1 describes a multilayer article comprising a biodegradable polymer layer and a cellulose fiber support, which are bonded together by an adhesive.However, the dissolution of the adhesive may lead to delamination, in which the multilayer structure is separated into individual layers.In this case, the desired gas barrier properties and mechanical properties of the packaging material cannot be maintained.

[0005] WO2017 / 187024A1 and WO2018 / 197676A1 both relate to compostable lids for sealing beverages, which are composed of a multilayer structure including a nonwoven layer containing at least 50% by weight of biodegradable fibers and a support layer made of vegetable parchment. WO2008 / 084139A1 describes a multilayer product that can be used as a sausage casing, which is a reinforced composite parchment sheet including a first nonwoven support layer of precipitated cellulose material and a second nonwoven layer of thermoplastic fibers intertwined with the cellulose fibers. The layers in the multilayer product are bonded by treating the cellulose-containing layer with a gelling agent to partially dissolve the cellulose material (parchmentation process) and form a gelled cellulose material that acts as an adhesive between the layers.

[0006] However, these prior art approaches remain unsatisfactory because the gas barrier properties of these products are achieved only by including an additional layer in the biodegradable cellulose support layer, which provides the desired mechanical reinforcement properties of the packaging material. Thus, the production of prior art materials involves multiple process steps that consume energy, generate waste, and require significant amounts of time and cost.

[0007] Furthermore, since the multi-layer products described in the prior art contain synthetic fibers, it is difficult to obtain 100% biodegradability. Another problem occurs in these products because the synthetic fibers contained in the multi-layer structures of the prior art do not dissolve in the parchmentation process, presenting an additional interface between the composite and the fibers that reduces the gas barrier properties.

[0008] Two approaches are known for impregnating fibrous webs with viscose to achieve sufficient gas barrier properties and desirable mechanical strength. One approach involves adding a polymer film made from regenerated cellulose (e.g., viscose film), obtained by extrusion or coating and serving as a good gas barrier, to a biodegradable cellulose support (base paper). However, this approach has the problem that the laminate may not have sufficient strength under humid conditions, and exposure to steam or moisture can cause delamination of the gas barrier film. Another approach involves adding or using regenerated or nanocellulose in wet-laid cellulose base paper. However, with this other approach, it is difficult to add enough nanocellulose to the structure by coating or impregnation, and sufficient gas barrier properties cannot be achieved. Furthermore, the energy consumption for nanocellulose production is high, and its low consistency makes it difficult to impregnate the base paper with sufficient nanocellulose.

[0009] Known products, such as fibrous meat casings made from regenerated cellulose, are unable to provide sufficient gas barrier properties, particularly against oxygen, because the structure of these products remains porous. Although it is possible to form gas barrier films from regenerated cellulose, these barrier films are unable to provide the desired enhanced mechanical properties due to the absence of fibers in the material.

[0010] It is therefore an object of the present invention to provide an improved biodegradable packaging material with sufficient gas barrier properties and enhanced mechanical properties that is easy to manufacture in an energy and waste efficient manner.A further object of the present invention is to provide a biodegradable packaging material with excellent mechanical properties, for example, with respect to wet strength, wet burst strength, and dry burst strength.

[0011] Compared to regenerated cellulose films, the present invention has better mechanical properties due to the presence of fibers in the material. Compared to existing wet-laid products containing regenerated cellulose, the present invention provides better gas barrier properties due to its continuous, non-porous structure. Regarding nanocellulose, it is not yet possible to develop nanocellulose-based materials with sufficient barrier properties on an industrial scale that is economically viable in terms of energy consumption. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] EP2841263A1 [Patent Document 2] WO2017 / 187024A1 [Patent Document 3] WO2018 / 197676A1 [Patent Document 4] WO2008 / 084139A1 Summary of the Invention

[0013] The present invention solves the problems of the prior art by the following means.

[0014] In a first aspect, the present invention provides a method for producing a 10 cm 3 / (m 2 Compostable cellulose-based paper having an oxygen permeability of less than 10 ... The compostable cellulosic paper comprises a continuous cellulosic fiber matrix that includes natural cellulosic fibers and non-fibrous cellulosic materials; The content of non-fibrous cellulosic material in the continuous cellulosic fiber matrix is 15 to 50% by weight.

[0015] Compostable cellulosic paper containing 15-50 wt.% non-fibrous cellulosic material in a continuous cellulosic fiber matrix has been found to provide excellent gas barrier properties while simultaneously enhancing mechanical properties in a single layer, thereby solving the problems of the prior art. Moreover, a further advantage lies in the fact that preparing compostable cellulosic paper as described herein helps to save energy and minimize waste compared to prior art procedures.

[0016] In a second aspect, the present invention relates to packaging materials for oxygen-sensitive products comprising the compostable cellulosic paper described herein. [Brief explanation of the drawings]

[0017] [Figure 1a] FIG. 1 shows the continuous cellulosic fiber matrix of a compostable cellulose-based paper according to an exemplary embodiment of the present invention as measured by transmission electron microscopy (Transmission Electron Microscopy (TEM), Philips EM 400T, 3000x magnification). [Figure 1b] FIG. 1 shows the continuous cellulosic fiber matrix of a compostable cellulose-based paper according to another exemplary embodiment of the present invention as measured by transmission electron microscopy (Transmission Electron Microscopy (TEM), Philips EM 400T, 3000x magnification). DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention provides a 10 cm 3 / (m 2 Compostable cellulose-based paper having an oxygen permeability of less than 10 ... The compostable cellulosic paper comprises a continuous cellulosic fiber matrix that includes natural cellulosic fibers and non-fibrous cellulosic materials; The content of non-fibrous cellulosic material in the continuous cellulosic fiber matrix is 15 to 50% by weight.

[0019] In the context of the present invention, the following definitions and test methods apply.

[0020] The term "compostable" is generally defined in accordance with the EN 13432 standard, as defined in the version published in 2000, and therefore corresponds to the EN 13432:2000 standard. The term "compostable cellulosic paper" refers to cellulosic paper containing up to 5% by weight of non-compostable components, thereby meeting EN 13432:2000. When applied to a material or product, "compostable" means that the entire material or product will biodegrade and break down. "Biodegrading" means that the chemical structure or material is broken down under the action of microorganisms, while "breaking down" means that at the end of a typical composting cycle, the material or product made from it will physically break down into small, visually indistinguishable fragments. To be considered a compostable polymeric material, the polymer chains must break down under the action of microorganisms so that total mineralization (i.e., the conversion of the material into CO2, water, inorganic compounds, and biomass under aerobic conditions) is achieved at a rate compatible with the normal composting process of plant waste.

[0021] As used herein, the term "fiber" refers to a material form characterized by an extremely high length-to-diameter ratio. Cellulose fibers generally have a wide range of diameters and lengths, depending on the fiber type and fiber source. The average length of wood pulp fibers suitable for use in the present invention typically ranges from 0.3 mm to 3.5 mm, preferably from 0.3 mm to 3.0 mm, more preferably from 0.8 mm to 2.5 mm, and even more preferably from 1.0 mm to 2.0 mm. The diameter of wood pulp fibers typically ranges from 10 μm to 40 μm, preferably from 15 μm to 35 μm, and even more preferably from 20 μm to 30 μm. Therefore, the aspect ratio (ratio of fiber length to fiber diameter) of wood pulp fibers typically ranges from 7.5 to 350, preferably from 7.5 to 300, more preferably from 10 to 200, and even more preferably from 20 to 150. The terms "fiber" and "filament" can be used interchangeably for purposes of the present invention, unless otherwise specifically indicated.

[0022] The term "cellulosic fibrous base sheet" refers to a nonwoven fibrous base sheet that has a structure of individual fibers interleaved but not identifiable as in woven or knitted fabrics, and that is derived from or prepared from cellulose fibers. Cellulosic fibers are fibers that are substantially composed of cellulose. Nonwoven materials can be formed from many processes, such as spin-laying, carding, air-laying, and water-laying processes. The basis weight of a nonwoven material, such as a cellulosic fibrous base sheet, is typically measured as weight per unit area, e.g., grams per square meter (gsm = g / m 2The cellulose fiber base sheet used in the present invention is preferably a wet-laid paper sheet. The cellulose fiber base sheet that can be used in embodiments of the present invention includes artificial sources (e.g., regenerated cellulose fibers or lyocell fibers) or natural sources, such as cellulose fibers or cellulose pulp from woody and non-woody plants. Woody plants include, for example, deciduous and coniferous trees. Non-woody plants include, for example, cotton, flax, esparto grass, kenaf, sisal, abaca, milkweed, straw, jute, hemp, and bagasse. Preferably, the cellulose fiber base sheet is a waterleaf sheet or vegetable parchment, which is a wood pulp paper sheet with a porosity that favors access of the gelling agent to the fibers during the parchmentation process. The cellulose fiber base sheet used in the present invention preferably contains at least 10%, and preferably more than 50%, of hardwood fibers, more preferably eucalyptus fibers, relative to the total amount of fibers in the cellulose fiber base sheet.

[0023] The term "cellulosic material" refers to a material that is substantially composed of cellulose. The material may be a fiber or a film. Cellulosic materials may be derived from artificial sources, such as regenerated cellulose fibers or films, or from natural sources, such as fibers or pulp from woody or non-woody plants.

[0024] The term "continuous cellulosic fiber matrix" refers to a cellulosic material comprising natural cellulosic fibers and non-fibrous cellulosic materials, where the natural cellulosic fibers are embedded in the non-fibrous cellulosic materials, thereby blocking the pores of the fibrous framework. Thus, the continuous cellulosic fiber matrix represents a high-density material that provides a cellulose continuum between the natural cellulosic fibers and the non-fibrous cellulosic materials, avoiding any voids at the interface between the natural cellulosic fibers and the non-fibrous cellulosic materials. Thus, the continuous cellulosic fiber matrix is a continuous, non-porous material with high gas barrier properties, particularly against oxygen. Preferably, the continuous cellulosic fiber matrix can be composed of natural cellulosic fibers, destructured cellulosic fibers, and non-fibrous cellulosic materials.

[0025] The term "natural cellulosic fiber" refers to cellulose fibers from natural sources, such as woody plants, including deciduous and coniferous trees, or non-woody plants, including cotton, flax, esparto grass, kenaf, sisal, abaca, milkweed, straw, jute, hemp, and bagasse. Preferably, the natural cellulosic fiber is suitable for dissolution by a gelling agent in the parchmentation process. Fibers suitable for dissolution include, for example, eucalyptus fiber, birch fiber, or other annual plant fibers. Natural cellulosic fiber forms a crystalline material containing a crystallized fraction with the crystalline morphology of cellulose I, which contains all parallel-oriented cellulose chains.

[0026] The term "non-fibrous cellulosic material" identifies a material obtained by dissolving or partially dissolving natural cellulosic fibers with a gelling agent (the parchmentation process), thereby splitting the natural cellulosic fibers and forming a gel-like viscous material, followed by washing with water to remove the gelling agent, thereby precipitating the gel-like material and forming a solid material. This solid material, referred to herein as non-fibrous cellulosic material, is mostly amorphous and may contain crystallized fractions of other forms, such as a crystallized fraction having the cellulose II crystalline form, which contains antiparallel cellulose chains. The non-fibrous cellulosic material is preferably a re-precipitated gelled cellulosic material.

[0027] The term "destructured cellulosic fibers" refers to the periphery of native cellulosic fibers that have been partially dissolved with a gelling agent during the parchmentation process, thereby causing a gradual structural change from native cellulose to precipitated cellulose. Such a gradual structural change means that the structure of the continuous cellulosic fiber matrix contains a structural gradient, and the crystalline structure of the native cellulosic fibers slowly changes to the amorphous structure of the majority of the non-fibrous cellulosic material with the formation of destructured cellulosic fibers on the surface of the native cellulosic fibers. Thus, the destructured cellulosic fibers surround the native cellulosic fibers and are intercalated between the native cellulosic fibers and the non-fibrous cellulosic material.

[0028] The term "regenerated cellulose" refers to man-made cellulose with a fibrous structure obtained by chemical treatment of natural cellulose to form soluble chemical derivatives or intermediate compounds, and subsequent splitting of the derivatives to regenerate cellulose with a fibrous structure. Regenerated cellulose includes spun rayon and cellophane film. Processes for preparing regenerated cellulose include the viscose process, the cuprammonium process, and saponification of cellulose acetate.

[0029] The term "synthetic fibers" refers to fibers formed from man-made materials such as glass, polymers, combinations of polymers, metals, carbon, regenerated cellulose, lyocell, and the like.

[0030] The "oxygen transmission rate (OTR)" of a material is the rate at which oxygen permeates a specified area (m ) of the material over the course of a day at an atmospheric pressure of 1.013 bar (1 atm), a temperature of 23°C, and a relative humidity of 50%. 2 The amount of oxygen (cm) that permeates through 3 ) refers to the oxygen transmission rate (OTR) (cm 3 / m 2 The OTR (Optical Torrency Rate) is measured according to ASTM D 3985 and ASTM F 1927. The OTR of a material is an indicator of the gas barrier properties of the material and indicates its gas barrier level. In other words, the lower the OTR of a material, the less gas will permeate through the material, and as a result, the material provides a high barrier to gases, especially oxygen.

[0031] The term "vegetable parchment" refers to paper made by treating cellulose paper sheets with a gelling agent, such as sulfuric acid, under conditions that limit the reaction time between the gelling agent and the cellulose to control cellulose dissolution, hydrolysis, and degradation. The treated paper is then thoroughly washed to remove the gelling agent and then dried. The bath chemicals partially dissolve or gelatinize the cellulose in the paper sheet. The dissolved cellulose is then precipitated when the bath chemicals are diluted by washing the treated paper. This process, called parchment or parchmentation, produces very strong, stiff, and smooth paper that has a certain appearance similar to that of authentic parchment. Because paper treated in this way tends to become brittle and wrinkle upon drying, it is sometimes treated with plasticizers, such as glycerin, glucose, or sorbitol. Vulcanized fiber is a related product made by treating cellulose paper sheets with a gelling agent, such as zinc chloride.

[0032] As mentioned above, the first aspect of the present invention is a 10 cm 3 / (m2 The present invention relates to a compostable cellulosic paper having a low oxygen permeability (oxygen permeability of less than 1000 kJ / day), wherein the compostable cellulosic paper comprises a continuous cellulosic fiber matrix containing natural cellulosic fibers and non-fibrous cellulosic material in an amount of 15 to 50% by weight. The present inventors have surprisingly found that when the non-fibrous cellulosic material is contained in the continuous cellulosic fiber matrix in an amount of 15 to 50% by weight, preferably 15 to 40% by weight, more preferably 18 to 35% by weight, and even more preferably 20 to 30% by weight, compostable cellulosic paper having high oxygen barrier properties and excellent gas barrier properties, particularly excellent mechanical properties, is provided.

[0033] One important aspect of the present invention is that dissolution of natural cellulosic fibers with a gelling agent results in the formation of non-fibrous cellulosic materials that further strengthen the continuous cellulosic fiber matrix thus formed, thereby providing compostable cellulosic paper with higher breaking strength.

[0034] A further key aspect of the present invention is the discovery that the non-fibrous cellulosic material also serves to occlude substantially all of the pores of the fibrous framework by filling the voids between the native cellulosic fibers and providing a continuous, dense structure (a continuous cellulosic fiber matrix), leading to a compostable cellulosic paper that has excellent gas barrier properties, particularly to oxygen, and provides excellent protection from moisture.

[0035] Therefore, the compostable cellulosic paper described herein can be advantageously used as a barrier layer for the construction of highly gas- and moisture-impermeable packaging materials, particularly for packaging oxygen-sensitive foods. Furthermore, because the compostable cellulosic paper described herein has excellent mechanical properties in terms of wet strength, wet burst strength, and dry burst strength, it can also be used as a reinforcing layer for the construction of packaging materials, particularly for packaging of non-solid foods that require food packaging with a predetermined shape.

[0036] The wet burst strength of compostable cellulosic paper is typically in the range of 100 kPa or greater, and preferably 150 kPa or greater. The dry burst strength of compostable cellulosic paper is typically in the range of 200 kPa or greater, and preferably 250 kPa or greater. Wet burst strength is measured according to ISO 3689, and dry burst strength is measured according to ISO 2758.

[0037] The present invention provides a completely biodegradable, compostable, and biologically-sourced product that consists essentially of cellulose and acts as a gas barrier layer and a reinforcing layer. The continuous cellulosic fiber matrix contained in the compostable cellulosic paper can be generated in situ directly during the parchmentation process, thereby saving energy required for production and reducing waste generated during production. Thus, the compostable cellulosic paper of the present invention is easily and efficiently produced.

[0038] continuous cellulosic fiber matrix The continuous cellulosic fiber matrix contained in the compostable cellulosic paper of the present invention includes natural cellulosic fibers and non-fibrous cellulosic materials. Preferably, the continuous cellulosic fiber matrix is composed of natural cellulosic fibers, destructured cellulosic fibers, and non-fibrous cellulosic materials. In the continuous cellulosic fiber matrix, the natural cellulosic fibers are essentially completely embedded in the non-fibrous cellulosic materials, thereby preventing any fiber release from the continuous cellulosic fiber matrix. The term "essentially completely embedded" means that the natural cellulosic fibers are ideally completely embedded in, i.e., completely surrounded by, the non-fibrous cellulosic materials. However, "essentially completely embedded" does not exclude that some of the natural cellulosic fibers are not covered by or embedded in the non-fibrous cellulosic materials, as long as the natural cellulosic fibers are firmly attached to the non-fibrous cellulosic materials in the continuous cellulosic fiber matrix so as to prevent any fiber release therefrom. Therefore, when the compostable cellulosic paper of the present invention is used as a packaging material for food, potential contamination of the packaged food, particularly coffee during brewing, with cellulose fibers is avoided.

[0039] Figure 1a shows an exemplary continuous cellulosic fiber matrix according to an embodiment of the present invention. Figure 1b shows another preferred exemplary continuous cellulosic fiber matrix according to an embodiment of the present invention. As can be seen from Figures 1a and 1b, the present invention provides a seamless, continuous cellulose construction because all of the pores or voids in the fibrous material are filled with non-fibrous cellulosic material, resulting in a very dense material that provides good gas barrier properties and excellent mechanical strength. Therefore, both gas and moisture barrier properties and mechanical strength can be achieved by the compostable cellulosic paper of the present invention without requiring the presence of additional layers.

[0040] The continuous cellulosic fiber matrix is preferably generated in situ during the parchmentation process of a cellulose fiber base sheet containing natural cellulosic fibers with a gelling agent, thereby obtaining a non-porous, more continuous structure than that obtained by impregnating the cellulose fiber base sheet with regenerated cellulose. This is due to the absence of an interface between the natural cellulosic fibers and the non-fibrous cellulosic material. Even when the cellulose fiber base sheet is impregnated with a large amount of regenerated cellulose, i.e., twice as much regenerated cellulose, compared to the amount of non-fibrous cellulosic material contained in the compostable cellulosic paper of the present invention, the paper obtained after such an impregnation process remains porous and requires an additional coating layer to achieve sufficient barrier properties against gases and moisture.

[0041] Cellulose fiber based sheet The cellulose fiber base sheet comprises natural cellulosic fibers and, optionally, additional non-cellulose fibers, which are synthetic fibers. In a preferred embodiment of the present invention, at least 50 percent, preferably at least 60 percent, and even more preferably at least 80 percent of the fibers in the nonwoven base sheet are cellulose fibers. In a more preferred embodiment, at least 90 percent, preferably at least 95 percent, and more preferably 100 percent of the fibers in the nonwoven base sheet are cellulose fibers. Therefore, the cellulose fiber base sheet advantageously consists essentially of cellulose fibers from the viewpoint of biodegradability. Most preferably, the cellulose fiber base sheet is 100% biodegradable. Therefore, the cellulose fiber base sheet preferably contains no more than 5% by weight of non-compostable or undetermined compostable materials to meet the requirements of the EN 13432 standard. Most preferably, any additives added to the cellulose fiber base sheet are compostable.

[0042] Preferably, the cellulose fiber base sheet has sufficient porosity to facilitate penetration of the gelling agent used in the parchmentation process into the fibrous structure of the cellulose fiber base sheet. The porosity of the sheet can be measured using a Bendtsen porosity tester according to the ISO 5636-3 standard, which calculates the porosity by forcing air through the sheet and measuring the flow rate. The cellulose fiber base sheet preferably has a Bendtsen porosity in the range of 1000 mL / min to 3000 mL / min, more preferably 1500 mL / min to 2500 mL / min, and most preferably 1800 mL / min to 2200 mL / min.

[0043] When the Bendsten porosity of the cellulose fiber base sheet is lower than 1000 mL / min, the gelling agent cannot reach the core of the fibrous structure of the cellulose fiber base sheet and cannot sufficiently form a continuous cellulosic fiber matrix, which may result in a decrease in the gas barrier properties of the compostable cellulose-based paper.On the other hand, when the Bendsten porosity of the cellulose fiber base sheet is higher than 3000 mL / min, the cellulose fiber base sheet may be more easily broken, and therefore the cellulose fiber base sheet may not have sufficient mechanical strength to perform the parchmentation process.

[0044] However, by adjusting the process parameters during the preparation of the base sheet and during the parchmentation step in the acid bath, it is still possible to use a cellulose fiber base sheet with a porosity lower than 1000 mL / min.For example, those skilled in the art will adapt process parameters such as machine speed to find a balance between sufficient migration of gelling agent to the core of the fibrous structure of cellulose fibers and excessive gelling of the fibrous structure, which will lead to the loss of structural integrity.A lower basis weight or thinner sheet can also be used to improve the penetration of gelling agent.

[0045] Preferably, the cellulose fiber base sheet contains wood pulp fibers with a specified degree of polymerization (DP) of less than 500, preferably 200-400, more preferably 300, to simplify dissolution with a gelling agent during the parchmentation process. If the DP is too high, dissolution of the cellulose will take too long, resulting in less gelatinous material forming non-fibrous cellulosic material within the specified time period. If the DP is too low, excessive hydrolysis will occur compared to dissolution, leading to poor mechanical properties of the non-fibrous cellulosic material in the final product.

[0046] In a preferred embodiment, the cellulose fiber base sheet is a waterleaf sheet or vegetable parchment. In a more preferred embodiment, the cellulose fiber base sheet is made of eucalyptus pulp.

[0047] The basis weight of the cellulose fiber base sheet can be selected according to the fiber and / or filament composition and the intended end use. In some embodiments, the basis weight of the cellulose fiber base sheet on a dry basis can be 200 gsm or less, preferably 30 gsm to 130 gsm. When the basis weight of the cellulose fiber base sheet is within these ranges, the resulting compostable cellulose-based paper has excellent mechanical properties and provides excellent barrier properties. That is, a cellulose fiber base sheet having a base weight within the above range advantageously exhibits a wet burst strength of greater than 150 kPa and a dry burst strength of greater than 250 kPa, with a wet burst to dry burst ratio of at least 50%.

[0048] The cellulose fiber base sheet typically has an average thickness of 30 μm to 150 μm, preferably 50 μm to 130 μm, even more preferably 80 μm to 120 μm, and most preferably about 100 μm, in order to achieve excellent mechanical reinforcement properties.

[0049] Typically, cellulose fiber base sheets will be free of binders and other additives. However, additives can be used to achieve specific desired results. For example, thermosetting resins such as KYMENE, available from Hercules Incorporated of Wilmington, Delaware, USA, can be added to modify the reactivity of the fibers in the cellulose fiber base sheet for subsequent processing operations, such as gelation. Wet strength additives can be beneficial in providing a wet base sheet with strength that ensures subsequent operations without fracture. Fillers such as TiO2 can be added to modify the opacity of the cellulose fiber base sheet. Preferably, the base sheet contains no more than 5% by weight of non-compostable or undetermined compostable materials to meet the requirements of the EN 13432 standard. Most preferably, any additives added are biodegradable and / or compostable.

[0050] natural cellulosic fibers The natural cellulose fiber is derived from natural or artificial sources. Preferably, the natural cellulose fiber is selected from wood pulp fiber, non-wood plant fiber, and regenerated cellulose fiber. The natural cellulose fiber is preferably eucalyptus fiber, birch fiber, or other annual plant fiber, such as cotton fiber, hemp fiber, or flax fiber (preferably cotton fiber), preferably hardwood fiber, in view of the solubility by the gelling agent in the parchmentation process of the cellulose fiber base sheet. The natural cellulose fiber is typically cellulose I. α and / or Cellulose I β The crystalline material forms in a continuous cellulosic fiber matrix containing crystalline morphology of cellulose, with the cellulose chains oriented parallel.

[0051] The natural cellulose fibers can be applied to the cellulose fibrous base sheet as a preformed web or tissue, for example, using a wet-lay or air-lay process. The choice of cellulose application process will typically depend on the available processing equipment. The natural cellulose fibers will generally be applied in amounts of about 10 gsm to about 200 gsm, advantageously less than 200 gsm, and typically about 30 gsm to about 130 gsm.

[0052] The natural cellulosic fibers may be included in the continuous cellulosic fiber matrix in an amount of 60 to 85% by weight, preferably 65 to 82% by weight, and more preferably 70 to 80% by weight. When a lower amount of natural cellulosic fibers is included, the reinforcing strength provided by the fibers may be insufficient, and the compostable cellulosic paper may be more easily broken. Furthermore, the three-dimensional stability of the compostable cellulosic paper may be insufficient for packaging non-solid foods that require packaging materials with a predetermined shape. On the other hand, when the amount of natural cellulosic fibers is too high, the gelling agent may not penetrate the fibrous material easily, and a continuous cellulosic fiber matrix may not be sufficiently formed. In this case, the compostable cellulosic paper may remain porous, resulting in reduced gas and moisture barrier properties. In a preferred embodiment, when the continuous cellulosic fiber matrix further includes destructured cellulosic fibers in addition to the natural cellulosic fibers and non-fibrous cellulosic materials, the amount of natural cellulosic fibers may be 65 to 80% by weight.

[0053] The diameter of the cellulose fibers is preferably 10 μm to 40 μm, more preferably 15 μm to 35 μm, and even more preferably 20 μm to 30 μm. The length of the cellulose fibers is preferably 0.3 mm to 3.5 mm, more preferably 0.3 mm to 3.0 mm, even more preferably 0.8 mm to 2.5 mm, and most preferably 1.0 mm to 2.0 mm. Therefore, the average aspect ratio (ratio of length to diameter of cellulose fibers) is preferably 7.5 to 350, more preferably 7.5 to 300, even more preferably 10 to 200, and most preferably 20 to 150.

[0054] Non-fibrous cellulosic materials Non-fibrous cellulosic materials typically form mostly amorphous material in a continuous cellulosic fiber matrix surrounding the native cellulosic fibers. A small portion of the non-fibrous cellulosic material may contain the crystalline form of cellulose II, in which the cellulose chains are oriented antiparallel.

[0055] The non-fibrous cellulosic material is contained in the continuous cellulosic fiber matrix in an amount of 15 to 50% by weight. When the content of the non-fibrous cellulosic material is less than 15% by weight, the pores of the cellulosic fiber base sheet cannot be sufficiently blocked, and the compostable cellulosic paper remains porous. Therefore, sufficient gas and moisture barrier properties, especially oxygen barrier properties, may not be achieved. Furthermore, when the amount of non-fibrous cellulosic material is too low, the mechanical strength of the continuous cellulosic fiber matrix may decrease. On the other hand, when the content of the non-fibrous cellulosic material exceeds 50% by weight, the natural cellulosic fibers contained in the continuous cellulosic fiber matrix may spread more widely, thereby preventing the desired reinforcing properties provided by the fibers. It may then be difficult to use the compostable cellulosic paper as a packaging material having a predetermined shape, for example, to package non-solid foods.

[0056] In a preferred embodiment, the content of non-fibrous cellulosic material in the continuous cellulosic fiber matrix is 15 to 40 wt. %. In another more preferred embodiment, the content of non-fibrous cellulosic material in the continuous cellulosic fiber matrix is 18 to 35 wt. %. In another even more preferred embodiment, the content of non-fibrous cellulosic material in the continuous cellulosic fiber matrix is 20 to 30 wt. %.

[0057] To achieve the content of non-fibrous cellulosic material in the continuous cellulosic fiber matrix of the present invention, the parchmentation conditions, such as reaction time, must be set appropriately. Suitable parchmentation conditions are described below.

[0058] The non-fibrous cellulosic material is obtained by partially dissolving natural cellulosic fibers with a gelling agent in a parchmentation process that produces a gel-like material, followed by re-precipitation of the gel-like material to form a solid material. The non-fibrous cellulosic material thus formed serves to fill the pores and voids within the fibrous structure of the cellulosic fiber base sheet, thus producing a dense, non-porous material that inhibits oxygen flow through the material. The non-fibrous cellulosic material forms around each of the natural cellulosic fibers and serves to attach the fibers together, thereby forming a continuous cellulosic fiber matrix.

[0059] By incorporating 15-50% by weight of non-fibrous cellulosic material in a continuous cellulosic fiber matrix, compostable cellulosic paper can be made to a thickness of 10 cm. 3 / (m 2 It has a low oxygen permeability of less than 1000kJ / day.

[0060] Preparation of compostable cellulosic paper The compostable cellulose-based paper of the present invention can be prepared by any commonly employed parchmentation process known in the art. That is, a cellulose fiber base sheet can be treated with a gelling agent by passing it through a bath containing the gelling agent under predetermined conditions of time and temperature. Suitable conditions for treating a cellulose fiber base sheet with a gelling agent can be easily determined by one skilled in the art.

[0061] The continuous cellulosic fiber matrix of compostable cellulosic paper is (i) providing a cellulose fiber base sheet comprising cellulose fibers; (ii) treating a cellulose fibrous base sheet with a gelling agent to obtain a treated base sheet comprising non-fibrous cellulosic material; (iii) washing the treated base sheet comprising non-fibrous cellulosic material to obtain a precursor cellulosic fiber matrix; (iv) drying the precursor cellulosic fiber matrix to obtain a continuous cellulosic fiber matrix.

[0062] In step (ii), when the cellulose fiber base sheet is contacted with a gelling agent, for example, by immersing the cellulose fiber base sheet in a bath of the gelling agent or passing the cellulose fiber base sheet through the gelling agent, the natural cellulosic fibers are partially dissolved and form a gel-like viscous material that fills the pores and voids in the fibrous material, resulting in a treated base sheet (parchmentation process). The treated base sheet is then washed with a detergent in step (iii) to remove the gelling agent therefrom. Preferably, the treated base sheet is washed with water in step (iii). Thus, a precursor cellulosic fiber matrix containing natural cellulosic fibers and a gel-like material is obtained. The precursor cellulosic fiber matrix is then dried in step (iv) to remove any residual detergent and / or moisture, resulting in a continuous cellulosic fiber matrix.

[0063] The gelling agent can be appropriately selected according to the cellulose-based paper sheet. The gelling agent can include at least one cellulose solvent selected from the group consisting of inorganic acids including sulfuric acid and phosphoric acid, Lewis acids including ZnCl2 and Ca(SCN)2, inorganic bases including NaOH, organic bases including N-methylmorpholine N-oxide, and ionic liquids including tetraalkylammonium salts. In a preferred embodiment, the gelling agent includes sulfuric acid.

[0064] Under typical parchmentation conditions, the gelling agent is a mineral acid, preferably sulfuric acid, in an aqueous solution at a concentration of 55 to 85 weight percent, preferably 63 to 75 weight percent, with a view to forming a continuous cellulosic fiber matrix having a desired content of non-fibrous cellulosic material.

[0065] The duration of treatment in step (ii) is preferably at least 60 seconds, so that the non-fibrous cellulosic material is formed in an amount of 15 to 50% by weight in the continuous cellulosic fiber matrix. Advantageously, the cellulosic fiber base sheet is contacted with the gelling agent in step (ii) for at least 90 seconds to ensure that all pores and voids in the fibrous material are blocked, thereby improving the barrier properties of the compostable cellulosic paper.

[0066] Mineral acids used as gelling agents are typically at temperatures between -10°C and 25°C, and preferably between -5°C and 20°C. The gelling agent acts to partially dissolve or gel the portion of the cellulose fibers that come into contact with the agent. Typically, 30 percent or less of the cellulose in the treated base sheet is dissolved by the gelling agent.

[0067] As the treated base sheet is transported into, through, and out of the gelling agent bath, it passes over and under material handling rolls. Passing the treated base sheet over the rolls serves to coat or spread the non-fibrous cellulosic material across the surface of the sheet and between the other fibers of the sheet.

[0068] In a preferred embodiment of the present invention, the compostable cellulosic paper is prepared by a process comprising steps (i) to (iv) above, the cellulosic fiber base sheet provided in step (i) has a Bendsten porosity of 1000 mL / min to 3000 mL / min and a thickness of 30 μm to 150 μm, and the cellulosic fibers contained in the cellulosic fiber base sheet have a fiber diameter of 10 μm to 40 μm and a fiber length of 0.3 mm to 3.5 mm; Sulfuric acid having a concentration of 55 to 85 weight percent is used as a gelling agent, The cellulosic fibrous base sheet is treated in step (ii) with a gelling agent at a temperature of between -10°C and 25°C for at least 60 seconds.

[0069] When preparing compostable cellulosic paper according to this preferred embodiment, the compostable cellulosic paper comprises: 10 cm when determined at 23°C and 50% relative humidity 3 / (m 2 Oxygen permeability of less than 1000kJ / day A wet burst strength of 150 kPa or greater, and It has excellent mechanical properties with a dry burst strength of over 200 kPa and excellent barrier properties.

[0070] Compostable cellulosic paper Compostable cellulose paper may comprise a continuous cellulosic fiber matrix and additional optional components. Such optional components include synthetic fibers, preferably synthetic fibers that are also biodegradable. However, the total amount of non-biodegradable fibers or fibers of undetermined biodegradability should preferably be less than 5% by weight of the total components of the compostable cellulose paper to maintain its biodegradability. Preferably, the compostable cellulose paper may consist essentially of a continuous cellulosic fiber matrix.

[0071] Compostable cellulose-based paper is suitable for use in 10cm² rooms, providing sufficient barrier properties against gases and moisture, especially oxygen. 3 / (m 2 Advantageously, the oxygen permeability is less than 2 cm 3 / (m 2 days), preferably less than 1 cm 3 / (m 2 Oxygen transmission rate is determined at atmospheric pressure (1 atm), 23°C and 50% relative humidity, and is measured according to ASTM D 3985 and ASTM F 1927.

[0072] The basis weight and thickness of the compostable cellulosic paper can be selected according to the intended end use. In some embodiments, the basis weight of the compostable cellulosic paper can be 200 gsm or less, preferably 30 gsm to 130 gsm, on a dry basis. The thickness of the compostable cellulosic paper can be 30 μm to 250 μm, preferably 30 μm to 150 μm, more preferably 80 to 120 μm, and most preferably about 100 μm.

[0073] Compostable cellulosic paper containing 15 to 50% by weight, preferably 20 to 30% by weight, of non-fibrous cellulosic material, 10 cm when determined at 23°C and 50% relative humidity 3 / (m 2 · days) less than 2 cm, preferably 3 / (m2 Oxygen permeability of less than 1000kJ / day a wet burst strength of 100 kPa or more, preferably 150 kPa or more, and It has excellent mechanical properties, such as a dry burst strength of 200 kPa or more, preferably 250 kPa or more, and excellent barrier properties.

[0074] The compostable cellulosic paper of the present invention can be used as a packaging material for gas- and / or moisture-sensitive products, particularly as a packaging material for oxygen-sensitive foods. Preferably, the compostable cellulosic paper can be used in the construction of coffee capsules or coffee pads due to its excellent barrier properties and mechanical strength.

[0075] packaging material In a second aspect, the present invention relates to packaging materials for oxygen-sensitive products comprising the compostable cellulosic paper described herein.

[0076] The packaging material is not particularly limited and can be used to preserve food, such as oxygen-sensitive food. The packaging material can be selected from the group consisting of butter wrapping, beverage containers, coffee capsules, coffee pads, chocolate packaging, and biscuit packaging. Preferably, the packaging material is used to construct coffee capsules or coffee pads.

[0077] The packaging material includes cellulose paper and, optionally, an additional layer. That is, the packaging material may be a multi-layer product including compostable cellulose paper as a first material layer and at least one additional material layer laminated on the surface of the compostable cellulose paper. The additional layer is not particularly limited and can be appropriately selected depending on the desired additional properties that need to be added to the packaging material. The additional layer is preferably selected from the group consisting of a water vapor barrier layer, an aroma barrier layer, a water-resistant layer, a heat-sealable layer, an oil-resistant layer, and a printable layer. [Example]

[0078] In this example, the following raw materials are used:

[0079] Cellulose fiber based sheet The waterleaf sheet contains eucalyptus fibers with an average fiber length of 1.0 to 3.0 mm, an average fiber diameter of 15 μm to 20 μm, and an aspect ratio (fiber length / fiber diameter) of 50 to 200; the cellulose fiber base sheet has a basis weight of 61 gsm and is based on 100% cellulose with a beating level of 30°SR (Schopper-Riegler); the average thickness of the cellulose fiber base sheet is 102 μm.

[0080] Gelling agent :Sulfuric acid with a concentration of 70% to 75%.

[0081] The properties of the compostable cellulosic papers prepared in the examples of the present invention are measured according to the following methods.

[0082] Oxygen transmission rate (OTR) is measured according to ASTM D 3985 and ASTM F 1927. Wet burst strength is measured according to ISO 3689 and dry burst strength is measured according to ISO 2758.

[0083] Method for determining the content of non-fibrous cellulosic material in compostable cellulosic paper Before the test begins, the weight of the compostable cellulose paper is measured. The compostable cellulose paper is then softened in an enzyme solution containing cellulase at room temperature and 1 atm atmospheric pressure. The cellulase begins to digest the paper, initiating cellulose degradation in the most accessible material, which is the low-crystalline material that represents the non-fibrous cellulosic material present between the cellulose fibers in the compostable cellulose paper. As the non-fibrous cellulosic material disappears from the structure due to digestion by cellulase, fewer and fewer cellulose fibers are bonded together, dramatically reducing the mechanical strength of the compostable cellulose paper. Following the decomposition of the compostable cellulose paper, the mechanical strength properties of the compostable cellulose paper, such as tensile strength, wet burst strength, and dry burst strength, are measured.

[0084] The mechanical strength of the compostable cellulosic paper decreases over time due to the progression of decomposition until a plateau is reached. At this point, the weight of the compostable cellulosic paper is measured again. The weight loss of the compostable cellulosic paper after reaching a plateau of reduced mechanical strength, compared to its initially measured weight, corresponds to the total loss of non-fibrous cellulosic material digested by cellulase. The weight loss between the initial sample and the decomposed compostable cellulosic paper (when the plateau is reached) corresponds to the amount of non-fibrous cellulosic material in the compostable cellulosic paper.

[0085] Example 1 and Comparative Examples 1 to 3 The cellulose fiber base sheet was immersed in a bath of gelling agent, which was maintained at a temperature of -6°C to -2°C for a specified duration as shown in Table 1 below. The treated base sheet was then washed with fresh water for at least 1 minute to neutralize the reaction and obtain a precursor cellulosic fiber matrix. The precursor cellulosic fiber matrix was then dried at 90°C for at least 1 minute to obtain a compostable cellulosic paper comprising a continuous cellulosic fiber matrix. [Table 1]

[0086] Comparative Examples 4 and 5 In a typical industrial process for preparing compostable cellulosic paper, the reaction time (contact time with the gelling agent) during parchmentation is approximately 10 seconds, leading to a resulting product with lower barrier properties. This is shown for two exemplary industrial compostable cellulosic papers in Table 2. [Table 2]

[0087] Example 2 and Comparative Examples 6 and 7 Furthermore, the compostable cellulosic papers of Example 2 and Comparative Examples 6 and 7 below were prepared using the same industrial method as Comparative Examples 4 and 5, i.e., by contacting a cellulose fiber base sheet with a gelling agent for about 10 seconds. For Example 2, the contact time with the gelling agent was increased to about 20 seconds, resulting in a higher content of non-fibrous cellulosic material and therefore providing superior gas barrier and mechanical properties compared to Comparative Examples 6 and 7, which have lower amounts of non-fibrous cellulosic material, as shown in Table 3. [Table 3]

Claims

1. An oxygen transmission rate of 10 cm as measured in accordance with ASTM D 3985 and ASTM F 1927 and determined at 23°C and 50% relative humidity. ３ / (m ２ compostable cellulosic paper with a shelf life of less than 10 years, the compostable cellulosic paper comprises a continuous cellulosic fiber matrix comprising natural cellulosic fibers and non-fibrous cellulosic materials; the content of the non-fibrous cellulosic material in the continuous cellulosic fiber matrix is 15 to 50 wt. %; The compostable cellulose paper meets compostability standard EN13432.

2. the continuous cellulosic fiber matrix comprising: (i) providing a cellulose fiber base sheet comprising cellulose fibers; (ii) treating the cellulosic fibrous base sheet with a gelling agent to obtain a treated base sheet comprising non-fibrous cellulosic material; (iii) washing the treated base sheet including the non-fibrous cellulosic material to obtain a precursor cellulosic fiber matrix; (iv) drying the precursor cellulosic fiber matrix to obtain the continuous cellulosic fiber matrix.

3. The gelling agent is an inorganic acid, including sulfuric acid and phosphoric acid, ZnCl ２ and Ca(SCN) ２ 3. The compostable cellulose-based paper of claim 2, comprising at least one cellulose solvent selected from the group consisting of a Lewis acid comprising: an inorganic base comprising: NaOH; an organic base comprising: N-methylmorpholine N-oxide; and an ionic liquid comprising: a tetraalkylammonium salt.

4. The compostable cellulosic paper of claim 3, wherein the gelling agent is sulfuric acid and / or the sulfuric acid has a concentration of 63-75%.

5. The compostable cellulosic paper of any one of claims 2 to 4, wherein step (ii) involves contacting the cellulose fiber base sheet with the gelling agent for at least 60 seconds.

6. Compostable cellulose-based paper described in any one of claims 2 to 5, wherein the washing in step (iii) is carried out with water.

7. The compostable cellulosic paper of any one of claims 2 to 6, wherein the cellulose fibers are selected from wood pulp fibers, non-wood plant fibers, and regenerated cellulose fibers.

8. The compostable cellulosic paper is A wet burst strength of 150 kPa or more; The compostable cellulose-based paper of any one of claims 1 to 7, having a dry burst strength of 200 kPa or more.

9. The compostable cellulose-based paper has a thickness of 200 g / m ２ The compostable cellulosic paper of any one of claims 1 to 8, having a basis weight of 30 μm to 250 μm and / or a thickness of 30 μm to 250 μm.

10. The compostable cellulosic paper of any one of claims 1 to 9, wherein the continuous cellulosic fiber matrix comprises 15 to 40% by weight of the non-fibrous cellulosic material.

11. The oxygen transmission rate of the compostable cellulosic paper is greater than 2 cm when determined at 23° C. and 50% relative humidity. ３ / (m ２ The compostable cellulose-based paper of any one of claims 1 to 10, wherein the compostability is less than 100% (days).

12. A packaging material for oxygen-sensitive products comprising the compostable cellulosic paper of any one of claims 1 to 11.

13. 13. The packaging material of claim 12, selected from the group consisting of butter wrapping, beverage containers, coffee capsules, coffee pads, chocolate packaging, and biscuit packaging.

14. 14. The packaging material of claim 12 or 13, wherein the packaging material is a multi-layer product comprising the compostable cellulosic paper as a first material layer and at least one additional material layer, the at least one additional material layer being laminated on a surface of the compostable cellulosic paper.

15. 15. The packaging material of claim 14, wherein the at least one additional layer of material is selected from the group consisting of a water vapor barrier layer, an aroma barrier layer, a water resistant layer, a heat sealable layer, an oil resistant layer, and a printable layer.

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