A method for producing a cellulose product and a cellulose product

Abstract

A cellulose three-dimensional cellulose High Density Moulded Fibre (HDMF) product (5) and a method for producing a three-dimensional cellulose High Density Moulded Fibre (HDMF) product (5) from a cellulose material (4), wherein the method comprises the steps of; heating a forming mould (3) to a forming temperature in the range of 100°C to 300°C; conditioning the cellulose material (4) to a water content in the range of 5% to 20%; arranging the cellulose material (4) in the forming mould (3); and forming the cellulose HDMF product (5) from the cellulose material (4) in the heated forming mould (3), by pressing the cellulose material (4) with a forming pressure, thereby exposing the cellulose material (4) to a compression force in a first direction, and simultaneously expose the cellulose material (4) to at least a shear force in a second direction to obtain densification and in-mould defibrillation of the cellulose material (4) for the cellulose product (5).

Description

[0001] A METHOD FOR PRODUCING A CELLULOSE PRODUCT AND A

[0002] CELLULOSE PRODUCT

[0003] TECHNICAL FIELD

[0004] The present disclosure relates to a method for producing a three-dimensional shaped cellulose high density moulded fibre (HDMF) product from a cellulose material.

[0005] BACKGROUND

[0006] Cellulose fibres are often used as raw material for producing or manufacturing various products. Products formed of cellulose fibres can be used in many different situations where there is a need for having sustainable products of essentially non-flat shapes. An essentially non-flat shapes may refer to any suitable three-dimensional object shape. There is a wide range of products that can be produced from cellulose fibres and a few examples are disposable plates and cups, blank structures, caps and closures and packaging materials. Packages produced from cellulose fibres may for example be used for packaging of liquids, dry materials and other types of goods, where the packaging may be made in a three-dimensional shape or formed into a three- dimensional shape from a two-dimensional sheet material. Such products are often laminated with different films in order for the product to withstand liquids, grease, heat etc.

[0007] One method commonly used for producing cellulose fibre products is wet moulded pulp. Wet moulded pulp has the advantage of being considered as a sustainable packaging material, since it is produced from biomaterials and can often be recycled or composted after use. Consequently, wet moulded pulp has been quickly increasing in popularity for different applications. Wet moulded pulp articles are generally formed by immersing a suction mould into a liquid or semi liquid pulp suspension or slurry, while suction is applied, whereby a body of pulp is formed with the shape of the desired product by fibre deposition. The suction mould is then withdrawn from the suspension and the suction is generally continued to compact the deposited fibres while exhausting residual liquid. With all wet-forming techniques there is a need for drying of the wet moulded product, where the drying is a very time and energy consuming part of the production, which is costly. Further, this method requires a large quantity of water. The demands on aesthetical, chemical and mechanical properties of products are increasing, and due to the properties of wet-formed cellulose products, the mechanical strength, flexibility, and chemical properties are limited. It is also difficult in the wet-forming process to control the mechanical properties of the products with high precision.

[0008] Another known method for producing products from cellulose material is by pressing loose cellulose fibres in a dry state, known as Dry Moulded Fibres (DMF). These products can be made in a cost-efficient way without using water as a cellulose fibre bearer and with a reduced energy need. Such products can be used to replace disposable plastic products but are somewhat limited when it comes to strength and the possibility to vary the thickness of a product to a great extent.

[0009] In a DMF process, cellulose fibres are formed with a forming pressure between 10-20 MPa in a regular compression mould. In such forming, the cellulose fibres arranged in a cellulose fluff blank are drawn apart somewhat when a non-flat shape is created. If the shape or height difference is too large, the cellulose blank may be torn, which is one reason why deep drawn dry moulded fibre products are difficult to produce. Since the cellulose blank does not float or stretch, it is also difficult to produce dry moulded cellulose products where the difference in thickness varies over the cellulose product. DMF products can be produced at the same cost as disposable plastic products.

[0010] Both wet- and dry moulded fibre typically produces fibre products with a density of 0.9 - 1 ,2 kg / dm3 comprising essentially compressed intact fibres. The width or diameter of cellulose fibres is typically in the range of 10-50 micrometres, depending on the plant origin. The fibre product density and the size of the fibres results in a scattered bulk material structure comprising several pin holes. The ability to withstand liquid and gas, e.g. water, grease, oxygen, is directly related to the size and numbers of pin holes. The inherent barrier properties of wet- and dry moulded fibres, e.g. hydrophobicity or lipophobicity, is therefore generally low. These manufacturing methods are therefore often supplemented with a process step where barrier chemicals or plastic films are added to impart improved barrier properties.

[0011] The strength of any moulded fibre originates, predominantly, from hydrogen bonds. When compressing cellulose fibres, hydrogen bonds can only occur in contact areas between individual fibres. I.e. the number of potential cross points influences the number of potential hydrogen bonds. Both wet- and dry moulded fibre products are normally regarded as somewhat soft and fragile and not suitable for applications with high demands on mechanical strength, e.g. caps and closures comprising threads. The limited number of potential hydrogen bonds also enables the material structure to spring-back to a lower density compared to the obtained density in the mould during compression.

[0012] Several attempts to increase the density, strength and barrier properties for moulded fibre products using higher forming pressure has been published. E.g. Pintiaux et. Al. “Cellulose consolidation under high-pressure and high- temperature uniaxial compression; (2019). However, applying axial compression force only, is claimed to only partially create high density within the bulk of fibres in the fibre product giving overall lower strength and uneven barrier properties over the surface of the product.

[0013] Moreover, both wet- and dry moulding manufacturing methods are based on shell forming where a pre-defined amount of fibres are applied to the non-flat tool surfaces. I.e. the wall thickness of the fibre material cannot intentionally be varied within the fibre product. In many applications this feature constitutes a limitation, e.g. when designing and making caps and closures where the threads preferably protrude out from the wall of the cap or neck. The friction between natural fibres, compressed with 20 MPa or less, restrain the material from flowing in mould cavities with uneven gap between the male and female tool. A parallel to thermoplastics can be that wet- and dry moulding methods can be compared to thermo- (or vacuum-) forming, while there is no equivalent to injection moulding using natural cellulose fibre yet disclosed, without the use of a high proportion of additive such as starch.

[0014] There is thus a need for improved sustainable cellulose products, where cellulose products exhibiting improved mechanical and chemical properties, can be manufactured with variable wall thickness at high precision, and where the production is cost-efficient and rational.

[0015] SUMMARY

[0016] An object of the present disclosure is to provide a method for producing a cellulose product where the previously mentioned problems are avoided. This object is at least partly achieved by the features of the independent claim. The dependent claims contain further developments of the method for producing a cellulose product. Another object of the present disclosure is to provide a three- dimensional shaped cellulose product.

[0017] The disclosure concerns a method for producing a three-dimensional cellulose High Density Moulded Fibre product from a cellulose material wherein the method comprises the steps of; heating a forming mould to a forming temperature in the range of 100°C to 300°C, conditioning the cellulose material to a water content in the range of 5% to 20%, arranging the cellulose material in the forming mould; and forming the HDMF cellulose product from the cellulose material in the heated forming mould, by pressing the cellulose material with a forming pressure, thereby exposing the cellulose material to a compressing force in a first direction, and simultaneously expose the cellulose material to at least a shearing force in a second direction to obtain densification and in-mould defibrillation of the cellulose material for the cellulose product. Advantages with these features are that the method provides an efficient manufacturing process for cellulose products with improved mechanical and chemical properties, where a cellulose product is a high density moulded fibre (HDMF) product with a density of 1 ,3 to 1 ,6 g / cm3The advantage with this method is that high density moulded fibre products are provided, having a higher strength than regular dry moulded fibre (DMF) products that are moulded with a one directional compression force giving a forming pressure of 10-20 MPa. The forming pressure, created by the compressing force, is greater than 50 MPa, preferably greater than 100 MPa, and preferably greater than 200 MPa or more.

[0018] By simultaneously exposing the cellulose fibres to a shear force in a direction differing from the compression force, a non-parallel relative movement between the cellulose fibres is created, that will break up the fibre shells through friction abrasion. The shear force can be applied by rotating one of the mould halves or by translating one of the mould halves in an oscillating or vibrating movement or utilizing the mould geometry, when applicable, to transform the compression force into non-parallel relative movements between the fibres. In one example, ultrasonic frequencies have been studied to generate translational vibrations with great in-mould defibrillation capacity as a result. In another example, the rotation of one mould half has been successful in introducing shear forces to the cellulose fibres.

[0019] Natural fibres under high compressive pressure and harsh shear forces releases its content of macro fibrils, micro fibrils and nano fibrils. The number of micro fibrils in a cross section of one fibre is measured in millions. The number of potential cross points i.e. places for potential hydrogen bonds is thereby increased by a huge factor. The strength of HDMF has in some cases proven to be 100 times stronger than regular DMF.

[0020] It is well known, from research reports, that pure isolated nano fibrils can be 5- 10 times stronger than steel, lighter than plastics and can be transparent. Some claim that nano cellulose will be the future material for the planet to replace single use plastics. So far, the isolation of nano cellulose has only been possible to obtain through small scale laboratory methods. No substantial method has so far been developed or commercially utilized for making products with cellulose material that utilizes the mechanical and chemical properties of fibrils.

[0021] One advantage of this novel in-mould defibrillation technology is that at least a portion of the inner strength in cellulose fibres can be utilized commercially for low-cost production of high-quality cellulose products. The final mixture of macro- micro- and nano fibrils in a cellulose HDMF product depends on many parameters such product geometry, induced shear energy, cycle time, etc., but using a microscope, preferably a SEM-microscope, it is obvious that a HDMF material is totally different from regular wet- and dry moulded fibres. The material surface appears homogeneous, smooth, glossy and hard without periodical voids or visible natural fibres.

[0022] Depending on the induced shear forces and the actual geometry of the cellulose product, fibrillation can be more or less effective. When using mould halves with relative movements, rotations or translations, the most effective defibrillation may occur at the surface of the cellulose material where the abrasive and grinding effect is likely most harsh. In some cases, the core of the product could have more intact natural fibres. This effect is called the skin effect.

[0023] The surface properties of the mould cavities have proven to be of importance for how deep, in the cellulose product walls, the defibrillation penetrates. Irregularities, like traces from the machining (milling or lathing) increases penetration. Intentionally introduced protruding elements, like rims, will act as stirrers of the flowing cellulose material under pressure, in the mould, and will significantly influence penetration and macro flow.

[0024] In some cases, the skin effect is preferred. Recycling through repulping is one such case where the designer of the cellulose product can optimize the water resistance for its time of usage at surfaces of the product (the skin) and at product end-of-life ease the repulpability by intentionally keep a material core of the product with non-fibrillated fibres. In other cases, such as non-single use items like toys etc., it is preferable to obtains as homogeneous HDMF structure as possible.

[0025] The average density of the cellulose product can also be measured e.g. using a precision scale to determine the weight and an industrial CT scanner to determine the volume. By dividing the weight with the volume, the average density can be determined and compared with existing cellulose fibre products. A cellulose HDMF product can easily be identified and differentiated from regular cellulose fibre products produced by state-of-the-art methods.

[0026] The shear forces should result in relative movements between the male and female mould which will result in relative movements between the cellulose fibres which results in friction abrasion on the wall or shell of the cellulose fibres. This harsh grinding of the natural intact fibres will tear or rupture the shell of the cellulose fibres whereby the content of the fibres macro-, micro- and nano fibrils, will be released in the bulk of the cellulose material. Any voids of the cellulose fibre matrix will be filled by fibrils contributing to the densification process. Experiments have shown that the flowability of released fibrils are higher than for intact natural fibres. The densification process in voids between cellulose fibres is called micro flow.

[0027] The bulk cellulose material structure is filled up with released fibrils, binding together with many hydrogen bonds under high compression force while structural spring-back is restrained, and very high product density can be obtained even after mould ejection.

[0028] This method enables commercial production of cellulose fibre products essentially without any structural pin holes. I.e. chemical properties such as hydrophobicity, lipophobicity and even gas permeability is drastically increased. In a closed mould where the applied blank of cellulose fibre material is not able to fill the entire geometry of the cavity, before compression, pressure gradients will occur in the bulk of the cellulose material when applying the compression force. With sufficient pressure gradients, cellulose fibres heated and conditioned with sufficient water to an appropriate level with respect to glass transition and fibrillation through shear, the cellulose material start to “flow”, i.e. the material moves from places with high pressure to places with low pressure (e.g. atmospheric) in the mould, referred to as macro flow. The flow can be described as Visco-elastic behaviour, at fibre level - micro flow or at product geometry level - macro flow, is in general called flow. This advantage enables the possibility to mould densified homogenous products with variable wall thickness, e.g. protruding threads on a cap.

[0029] In one example, the forming pressure is higher than 150 MPa and may be higher than 200 MPa, depending on the produced cellulose product. The forming pressure may be up to 500 MPa or even up to 1000 MPa or more, depending on the intended use and the actual cellulose product. If various additives are used in the cellulose material, this may also impact the most suitable forming pressure. The density of the moulded cellulose product is greater than 1 ,30 g / cm3and may be up to 1 ,40 g / cm3or even higher. Tests have shown that a density of a moulded cellulose product greater than 1 ,50 g / cm3is possible to achieve.

[0030] Even though a higher forming pressure will give a cellulose product with a higher strength and a higher density, the preferred forming pressure is a forming pressure where the desired parameters for the cellulose product are met, without exceeding these parameters. A higher forming force adds a cost to the cellulose product. This means that in the same press with the same rated force, fewer and / or smaller cellulose products can be made with the same forming force. There is thus a need to optimize the used forming pressure to the desired properties of the cellulose product. It has been shown that a forming pressure exceeding approximately 100 MPa will start to give the cellulose material pseudo-plastic properties, which allows for a cellulose HDMF product having a more complicated shape and a varying thickness.

[0031] The cellulose product is formed in a forming mould which in one example comprises a first positive mould (male) part and a second negative mould (female) part. The forming mould parts are non-flexible, preferably made from steel, and may be heated to the desired forming temperature. The forming mould is, in one example, heated with integrated heating elements, preferably electrical heating elements, but also liquid heating is possible. The forming mould is preferably closed, such that the cellulose material is completely enclosed in the mould during moulding of the cellulose HDMF product.

[0032] If high shear energy is induced, e.g. when using ultrasonics, the friction between cellulose fibres and fibrils might create heating of the cellulose material. The cellulose material starts to discolour at temperatures above 200 °C. It can then be necessary to cool the mould instead of actively heating it.

[0033] In one example, the starting cellulose material is an air-laid cellulose blank structure used for regular dry moulded fibre products. Here, the cellulose material may be pre-pressed in a pre-forming mould, e.g. to a puck, with a low pre-forming pressure in the range between 1 - 10 MPa. The purpose of the pre-forming is to compress the cellulose material to a smaller volume such that it will be easier to insert the pre-formed cellulose material into the forming mould. In order to provide a cellulose HDMF product, more cellulose material will be needed for a cellulose HDMF product having desired dimensions, e.g. a desired thickness. If e.g. an air-laid cellulose blank material is used as starting material, a weight of between 1000 - 3000 GSM may be required, as compared to 400 - 600 GSM for a regular DMF product. Such a starting material may be difficult to insert in a forming mould without pre-forming it.

[0034] In another example, the starting material is a cellulose fluff pulp sheet or a cardboard sheet or a paper containing substantially only cellulose fibres or cellulose fibres mixed with other substances, e.g. lignin and hemi-cellulose, or other additives. The fluff pulp sheet or the cardboard sheet or a paper may be stacked in several layers, e.g. by rolling the sheets into a tube-shaped format, in order to obtain a desired starting material. With such a material consisting of stacked fluff pulp or cardboard sheets or paper, a pre-forming may not be necessary, depending on how it is inserted into the forming mould. The starting material may also be cellulose particles or cellulose granules containing substantially only cellulose fibres or a cellulose fibre mixture. The granules or particles may be inserted directly into the forming mould.

[0035] During the moulding of a three-dimensional HDMF cellulose product, different forces will act on the cellulose material. When a flat two-dimensional cellulose product is moulded, all forming pressure forces acting on the cellulose material will be in the same direction as the forming force direction, i.e. perpendicular to the mould surfaces. When a three-dimensional cellulose product is moulded, some of the forces will not be parallel to the direction of the forming pressure but will be perpendicular to the mould surface. Since the cellulose material does not flow at lower pressures, the cellulose material will be pulled apart somewhat in order to correspond to the three-dimensional shape of the mould, and this small displacement of the cellulose material will, together with the high forming pressure, induce shear forces on the cellulose material, at least at some regions of the cellulose material. Together with the high forming pressure, these shear forces will not be neglectable and will create defibrillation and flow.

[0036] In one example, the cellulose material is an air-laid cellulose blank comprising loose cellulose fibres. When an air-laid cellulose blank is used, the weight of the cellulose blank is preferably higher than the cellulose blank used for a regular DMF product and may be in the region between 1000 - 6000 GSM. With such a material, a strong cellulose HDMF product with a density exceeding 1 ,30 g / cm3can be obtained when moulded with a sufficiently high forming pressure. In another example, the cellulose material is a granular cellulose material comprising cellulose fibres particles, where the cellulose fibre particles are more or less compacted. When a granular cellulose material is used, the density of the granules may be lower than the density of the formed cellulose product and may be in the region between 0,4-0, 8 g / cm3With such a material, a strong cellulose HDMF product with a density exceeding 1 ,30 g / cm3can be obtained when moulded with a sufficiently high forming pressure.

[0037] The cellulose material may consist substantially of only cellulose fibres without any additives, i.e. a material containing substantially only cellulose fibres, where much of the lignin is removed. The cellulose material may also contain lignin, hemi-cellulose or other additives.

[0038] The cellulose material may also include additives, where the additives are used to decrease the liquid and / or gas permeability of the cellulose product and to increase the resistance to e.g. hot and cold liquids, grease, oil etc. Such additives may also be applied to the surface of the cellulose product after the cellulose product is formed. In one example, the cellulose material comprises at least 95% cellulose fibres by dry weight. The additives used are additives adapted to alter the permeability of the cellulose material and should not function as a binder material to bind the cellulose material together. By using untreated cellulose fibres, the cellulose fibres are bound together by hydrogen bonds and Van der Vahls bonds. Additives may decrease the possibility for hydrogen bonds.

[0039] Compacting essentially dry fibres in steel moulds can impart significant friction between the material and surfaces of the mould. It has been found through experiments that spraying water to the raw cellulose material just before loading the cellulose material into the mould will lower the friction coefficient for fibre-steel contact. Also using some surfactants, like soap (1-20%) in the water to be sprayed, reduced the friction and increases the flowability of the cellulose in the mould significantly. It is also possible to spray undiluted soap. At elevated temperature, together with plasticizing components such as water, the glass transition of the cellulose can be exceeded, causing a reduction in stiffness of the cellulose fibre on a molecular level. This further enhances flexibility and movability, i.e. flow, of the fibre and fibre fragments. Amorphous parts of the semi-crystalline cellulose polymer show increased movement above the glass transition temperature.

[0040] One suitable product made from cellulose HDMF is a screw cap for a bottle. The screw cap is provided with a top section and a concentric side wall having an inner surface and an outer surface, where the inner surface is provided with at least one internal thread section and where the circumferential outer surface is substantially even. Such a cellulose HDMF screw cap will resemble a regular plastic screw cap used for e.g. PET plastic bottles. The internal thread section may be a single thread or may comprise several thread sections that constitutes a screw thread. With the inventive method, a cellulose HDMF product where the thickness of the product varies with at least 200% can be obtained. A thickness variation up to 300-400% is possible if desired. In this way, it is possible to provide an internal thread on the inner surface of the screw cap, while the outer surface can be substantially smooth and even. It is of course also possible to provide the outer surface of the screw cap with some kind of gripping surface, a gripping rim and / or a tamper proof fixation rim. Another suitable product is a flip-cap used on containers that are not provided with a thread.

[0041] Another suitable cellulose HDMF product is a neck of a dry moulded cellulose fibre bottle, where the neck is provided with an external thread and a smooth inner surface. The rest of the bottle can be produced with a regular forming pressure of 10-20 MPa in order to save cost. A cellulose HDMF neck can also be applied on folded cartoon packages for liquids.

[0042] The cellulose HDMF product is formed in the forming mould during a cycle time period in the range of 0,1 to 10 seconds, and preferably less than 5,0 seconds. A suitable holding time for the product in the forming mould is less than a second, and may be e.g. 0,3-0, 7 seconds. The holding time together with the forming temperature and the forming pressure are important parameters in the forming of the cellulose product.

[0043] Wet moulded fibres defibrates chemically in a water-based slurry. Dry moulded fibres defibrates in a mill with air flow. High Density Moulded Fibers (HDMF), or dry moulded fibrils, not only defibrates but also defibrillates in the mould itself using shear forces.

[0044] BRIEF DESCRIPTION OF DRAWINGS

[0045] The disclosure will be described in greater detail in the following, with reference to the attached drawings, in which

[0046] Fig. 1 show schematically a simplified cellulose fibre and its built-up of macro- micro- and nano fibrils,

[0047] Fig. 2 show a SEM (Scanning Electron Microscope) microscopic image at 400X enlargement of a compressed cellulose material with both defibrillated and non-defibrillated fibre regions in the same material sample,

[0048] Figs. 3a-d show schematically a simplified three-fibre structure compressed, sheared and defibrillated,

[0049] Fig. 4a-d show schematically a simplified two-fibre structure compressed, sheared and defibrillated,

[0050] Figs. 5a-c show schematically a theoretical model presenting physical requirements for obtaining HDMF together with a schematic cross section and a schematic enlargement of the in-mould defibrillation process, Fig. 6 shows schematically a cross section of a device for an in-mould defibrillation process in four steps (A-D) using a puck blank and a rotational female tool,

[0051] Fig. 7 shows schematically a cross section of a device for an in-mould defibrillation process in four steps (A-D) using a rolled paper blank and a rotational female tool,

[0052] Fig. 8 shows a perspective illustration of a device using transversal ultrasonic vibrations for in-mould defibrillation, and

[0053] Fig. 9 shows schematically a cross section of a device for an in-mould defibrillation process in four steps (A-D) where shear forces are achieved through shape defined fibre motions without applying rotational or translational movements.

[0054] DESCRIPTION OF EXAMPLE EMBODIMENTS

[0055] Various aspects of the disclosure will hereinafter be described in conjunction with the appended drawings to illustrate and not to limit the disclosure, wherein like designations denote like elements, and variations of the described aspects are not restricted to the specifically shown embodiments but are applicable on other variations of the disclosure.

[0056] A nano fibril is several thousand times smaller than a natural cellulose fibre and it is impossible to illustrate these different cellulose components in the same image at the same scale. Therefore, all figures and embodiments showing fibres, macro-, micro- and nano fibrils are to be regarded as illustrative infographics.

[0057] In the present detailed description, a method for producing a cellulose HDMF product from a cellulose material will be described. The method is suitable for different products that should exhibit a higher strength, higher barrier properties and a higher density than regular DMF products, and that may have a more complicated shape with varying wall thickness. Such products may be relatively small with a volume of e.g. a few cm3due to the required high forming pressure, which is costly. It would of course also be possible to produce larger cellulose HDMF products if desired. The cellulose HDMF products are disposable, but may be used several times, depending on the actual product and actual post treatment of the product. The cellulose HDMF products may be recyclable and / or compostable.

[0058] Examples of such cellulose HDMF products are e.g. screw caps, flip caps, coffee pods, toys, candy enclosures, medical devices and packaging, such as blister packs. In one shown example, a screw cap is used as an example of a cellulose HDMF product.

[0059] The cellulose material used to form the cellulose HDMF product may be a cellulose material containing substantially only natural cellulose fibres. The cellulose material may also comprise at least 50% cellulose fibres or more. The cellulose material may e.g. be wood fibres comprising some lignin and hemi-cellulose, or may comprise cellulose fibres and some additives. One additive might be a colorant or a pigment that enable the final fibre product to be in any colour.

[0060] Additives, e.g. AKD (alkyl ketene dimer), may also be added to the cellulose material, where the additives are used to decrease the liquid and / or gas permeability of the cellulose product and to increase the resistance to e.g. hot and cold liquids, grease, oil etc. In one example, the cellulose material comprises at least 95% cellulose fibres by dry weight and at the most 5% additives by weight.

[0061] Hard and crystalline additives to increase the abrasion between fibres, e.g. chalk, clay or silica, can also be added. Additives to reduce friction in the mould, e.g. pine soap diluted in water (1-20%) to be sprayed to the cellulose blank just before moulding could also be considered. The cellulose material will also comprise some water, e.g. between 6% to 20% by weight. Water is not seen as an additive; it is necessary to create hydrogen bonds between the cellulose fibres and to act as a plasticiser, but will evaporate when the cellulose product is heated in an oven.

[0062] Fig. 1 show schematically a natural cellulose fibre 1 a with a diameter or width of Wa. A cellulose fibre might not have cylindrical shape and internal structure, as shown in Fig 1., but is more likely to have organic non-symmetrical shape and inner structure.

[0063] The components of the cellulose fibre 1 a are; macro fibrils 1 c, sometimes called only fibrils, with a width of Wc; micro fibrils 1 d, sometimes called MFC (Micro F ibri I lated Cellulose), with a width of Wd; and nano fibrils 1 e, sometimes called NFC (Nano Fibrillated Cellulose) with a width of We (not shown). The cellulose fibre 1 a is surrounded by a fibre shell 1 b.

[0064] The table below shows typical sizes and numbers of each component within a cross section of soft wood cellulose fibre.

[0065] Due to its extreme strength per weight, most of the research in recent decades has focused on defibrillation and isolation of nanofibrils and its subcomponents from the rest of the fibre structure. Mechanical, chemical or biological processes can be used but the required energy to obtain pure nano cellulose has limits in its commercial usage so far. Moreover, the state-of-the-art defibrillation technologies requires unacceptable long cycle times in manufacturing.

[0066] The required defibrillation energy increases drastically for each deeper level in the fibre structure, i.e. the fibre shell 1 b is relatively easy to break while releasing the nano fibrils 1e from the micro fibrils 1 d is exponentially harder.

[0067] By accepting a coarsely fibrillated cellulose with a mixture of fibre shell 1 b, macro fibrils 1 c, micro fibrils 1 d and some nano fibrils 1 e, the material properties preferred in a cellulose products as increased strength, increased chemical barrier and good flowability can be reached. Present innovation enables a cost effective and fast method to utilize the material properties of fibrils in commercial production of e.g. caps and closures to replace thermoplastics in the beverage industry.

[0068] The fibre shell 1 b is the first component to be broken and grinded into smaller fragments since the lower levels in the structure requires more energy. The fibre shell 1 b particles and all the released fibrils participate in the formation of hydrogen bonds in HDMF and together creates a homogeneous new material.

[0069] Fig. 2 shows a SEM-microscopic image at 400 times magnification of a compressed soft wood cellulose material. In this specific sample, the in-mould defibrillation process has created HDMF in part of the material sample. In the lower right corner of the image, natural fibres 1 a with a width of Wa are intact and shows a regular wet- or dry moulded fibre structure (B) comprising a lot of pin holes.

[0070] In the upper left corner of the image a homogeneous HDMF material has been created through in-mould defibrillation (A). No natural fibres 1 a or pin holes are visible in the HDMF region (A). The material comprises released macro- 1 c, micro-id and nano fibrils 1e together with fine grinded residuals of the fibre shell 1 b. The number of hydrogen bonds in (A) is many times higher than in (B), per unit area, since the physical ability to expose the cellulose molecules to the possibility to create bonds is exponentially larger. Under strong compression force the structure is densified to densities above 1 ,3 g / cm3and in some cases above 1 ,5 g / cm3. Traditional literature often claims 1 ,5 g / cm3to be the ultimate and maximal density for cellulose. However, recent research has shown that the true density of nanocellulose can be 1 ,6 g / cm3or higher.

[0071] In one example of this innovation, a cap for a PET-bottle has been made to an average density of 1 ,45 g / cm3. If pigments have been used to avoid natural pulp colours, the look and feel of such a cellulose cap is hard for an average consumer to distinguish from a polypropylene cap. It is stronger, glossy and somewhat harder.

[0072] Figs. 3a-d and 4a-d both conceptually illustrate this densification process through defibrillation inside the mould cavity. Since any effort to illustrate defibrillation through friction abrasion will be misleading in respect to size of scale and number of involved fibrils, Figs. 3 and 4 complement each other in clarity of different aspects of this process. They both intend to show the same process in four steps and will therefore be described together in the following.

[0073] In Fig. 3a and Fig. 4a, three respectively two natural fibres 1 a, with their schematically fibrils 1 c, 1 d and 1 e visible at the fibre end, are shown interlinked with three respectively one crossing without any external forces.

[0074] Figs. 3b and 4b shows the fibres 1a compressed by a compression force Fc. If appropriate temperature and moisture content is present hydrogen bonds 2 in the crossings will be created. This represents the moulding technology of regular wet- and dry moulding of fibres, using a moulding pressure of less than 20 MPa created by the compression force Fc, and equals the fibre structure (B) shown in fig. 2. The number of hydrogen bonds is limited to the number of physical contacts between fibre shells 1 b. Figs. 3c and 4c illustrate the start of defibrillation by applying a shear force Fs in a direction differing from the direction of the compression force Fc. In the shown example, the shear force Fs is orthogonal. A, to the compression force Fc, non-parallel shear force Fs results in relative movements between individual cellulose fibre layers due to friction. By simultaneously applying a strong compression force Fc, equalling to a moulding pressure, in this example, higher than 100 MPa, an abrasion process starts to tear the fibre shells 1 b apart. This mechanical grinding like shearing starts to release fibrils 1 c, 1 d and 1 e from the fibres 1 a.

[0075] Figs. 3d and 4d illustrates, conceptually, a simplified in-mould defibrillation process. A mixture of macro- 1 c, micro- 1 d, nano fibrils 1 e and fractions of fibre shell 1 b residuals have been released from the original cellulose fibres 1 a. Fibrils have shown more flow like rheological behaviour compared to natural fibre structures. Due to a compression moulding pressure higher than 100 MPa, in this example, these billions of fibrils will spread out to equalize pressure gradients and fill any voids in the adjacent structure. This flow is called micro flow. Equally to Figs. 3b and 4b, the compression force Fc will enable the creation of hydrogen bonds 2 (not shown) at many physical contacts between fibrils provided the temperature and moisture content is appropriate. The amount of hydrogen bonds 2 is exponentially higher in Figs. 3d and 4d, compared to Figs. 3b and 4b and illustrates HDMF corresponding to the (A) region of the SEM image in Fig. 2.

[0076] Moreover, it has been found that a material comprising fibrils 1 c, 1 d and 1e under compression force Fc and shear force Fs acts like a fluid-like state with Visco-elastic behaviour filling up any voids in the mould cavity. Significant material movements, within the mould cavity, enables mould cavity geometries, with a product thickness variation of several hundred percent, to entirely be filled up with cellulose. This innovative feature of HDMF is called macro flow. Both micro- and macro flow contributes to the densification process together with the compression force Fc.

[0077] Figs. 5a-c shows a theoretical model for the required physical conditions for densification through micro- and macro flow to happened at in-mould defibrillation. The model is illustrated with a schematically enlargement of the defibrillation process at microscopic level.

[0078] As illustrated by the three overlapping rings of Fig. 5a, three essential features should simultaneously be present in the mould to obtain good flow, high densification and strong material in the cellulose product; Pressure gradient; Shear forces; and Amorphous behaviour.

[0079] Pressure gradient.

[0080] Mechanical defibrillation assumes relative movements between fibres 1 a. All natural fibre structures comprise voids at a micro scale, so called pin holes. So does moulding, where the fundamental intended effect comprises a feedstock to fill or flow into voids in the mould cavity, here referred to as the macro level.

[0081] Only cellulose material without voids, i.e. with a density at 1 .5 g / cm3or above, i.e. the fibrils, can transform the applied compression force Fc into a moulding pressure P1. All micro and macro voids in the mould cavity will hold atmospheric pressure or low pressure provided sufficient venting.

[0082] In one example, a moulding pressure P1 of 100 MPa is proposed. Extreme local pressure gradients dP / dx, shown in the diagram in Fig. 5b, occurs between the fibrils and air-filled voids, and causes strong local forces on fibrils to move into the voids and equalize the pressure. These movements are referred to as micro- and macro flow.

[0083] Shear forces.

[0084] If a fibrous material structure is compressed in only one direction, the fibres will withstand the pressure up to a certain limit until the weakest structural element breaks or cracks, i.e. the fibre shell 1 b. Fibre break is an instable and instant process since the force on adjacent intact fibres 1 a will increase when the resistance from the broken fibres 1 c, 1 d, 1 e drops off. A burst explosion, where the natural fibre structure collapses, is likely to happen.

[0085] Even if strong pressure gradients are present, the static friction between natural compressed fibres restrain any movement or flow. A sudden an unwanted burst explosion is inevitable.

[0086] A controlled flow in the direction of the pressure gradient is preferred. Any, to the compression force Fc direction, non-parallel movement between the fibres, change the friction to dynamic and initiate both micro- and macro flow. Such a movement can be induced by applying a shear force Fs to the fibres.

[0087] Laboratory experiments have shown that the direction of the shear force Fs is of less importance if the shear force Fs does not coincide, i.e. is parallel, with the direction of the compression force Fc. The fibre shell 1 b breaking process is still an instable process spreading in the feedstock, in the mould cavity, where the shear forces Fc could be compared with a stirring force in a liquid. The liquid is capable to flow in all direction into all reachable voids.

[0088] It has also been proven that as long the defibrillated 1c, 1 d, 1e bulk of cellulose material is under compression Fc and movement (stirring) under influence of the shear force Fs continues, the cellulose material will act as a fluid or pseudoplastic material. The movements created by the shear force Fs has however to stop before the compression force Fc is released.

[0089] Amorphous behaviour.

[0090] At elevated temperature, together with plasticizing components such as water, the glass transition of the cellulose can be exceeded, causing a reduction in stiffness of the cellulose on a molecular level. This further enhances flexibility and movability, i.e. flow, of the fibre and fibre fragments. Amorphous parts of the semi-crystalline cellulose polymer show increased movement above the glass transition temperature. The brittle structure of the glassy amorphous sections is softened as molecular segments start to move, which reduces the stiffness of the entire cellulose molecule. This softening of the cellulose facilitates plastic deformation, meaning that cellulose which has moved remains in place rather than retract to its original position elastically when the moulding pressure is released.

[0091] Crystalline parts in the cellulose molecule interfere with the softening and cause a broadening of the glass transition of the amorphous parts of the cellulose. To the extreme, full crystallinity means there are no amorphous material in the cellulose, and therefore no glass transition takes place. The glass transition occurs in the amorphous parts of the semi-crystalline cellulose. Therefore, the crystallinity of the cellulose plays a role in the plastic deformation and consequently in the flow.

[0092] The glass transition temperature is strongly affected by the content of plasticizers. These may be consciously added, or for hygroscopic polymers - naturally absorbed from ambient air. Plasticizers lower the glass transition temperature of polymers. They increase the free volume between the polymer molecules, facilitating motion of molecular segments. Thereby the glass transition temperature is lowered. For cellulose, water acts as a plasticizer which can reduce the glass transition temperature.

[0093] The interplay between cellulose molecules with water and temperature is here denoted amorphous behaviour. To form a cellulose HDMF product, pressure gradients and shear forces need to be supplemented by an elevated temperature for the flow to be efficient. However, too high temperatures risk causing local burning of the cellulose, not the least due to poor heat transfer in a fluffy fibrous material causing high temperature gradients vis-a-vis the heated mould. The addition of water can lower the glass transition temperature, and thereby the temperature needed to attain the desired flow. Additionally, the added water cools the cellulose, mitigating burning. Yet, the water content needs to be balanced. Under high pressure gradients a too high water content will lead to water being pressed out of the cellulose. Such water will act as a lubricant in-between the cellulose fibres and the mould, thus reducing the shear forces. This impedes the desired micro flow and inmould defibrillation.

[0094] For thorough plasticization of the cellulose molecules in the fibres, water must penetrate deep into the structure so that it can interact properly with the cellulose molecules. Therefore, time is required for the transfer of water into the fibres. An efficient addition of water is conditioning at elevated relative humidity. Other means of water addition, e.g. spraying, will cause an uneven moisture distribution within the fibres with a lot of water on the surface. This again risks lubricating the cellulose / mould interface. However, rolling a sprayed sheet of cellulose fibres, e.g. a paper or fibre web, with the water on the inside of the roll can overcome the lubrication issue to a certain extent.

[0095] At low levels of moisture, the water is adsorbed onto the cellulose surface. Increasing the moisture content in the cellulose, e.g. by conditioning at a higher relative humidity, will increasingly force water in between cellulose molecules to form multiple layers of water molecules, disrupting the hydrogen bond network. This facilitates movement of fibres and molecules as the intermolecular forces are reduced.

[0096] In one example, a rotational female mould 3b is used, where the shear force Fs is applied by a torque, schematically shown in cross section in Fig. 6. The preferred settings for reaching a homogenized, densified and strong cellulose HDMF product 5, here a cap, is: moulding pressure P1 = 150 MPa, shear torque Ms = 300 Nm, forming temperature T3 = 100°C, water content %H20 = 12%, pressure gradient dP / dx = 10 N / mm3If the cap 5 has a diameter of 20 mm, the compression force Fc = 47,1 kN.

[0097] Fig. 6 shows schematically the in-mould defibrillation forming process in four steps A-D. In step A, a puck of natural cellulose fibres 4, typically with a density of 0,7 g / cm3, and a dry weight of 4 g, preconditioned in a climate chamber to a water content of %H2O = 12% holding room temperature, is placed in the female mould 3b, pre heated to a temperature T1 = 120°C. The cellulose puck 4 may be sprayed with an additional water (90%) and pine soap (10%) mixture aerosol just before insertion into the female mould 3b.

[0098] Fig. 6, step B, shows how the male mould 3a, pre heated to a temperature T1 = 100°C, is pressed down in the female mould 3b and closes the cavity. The cellulose puck 4 is compressed to some extent but the cellulose fibres 1 a are still intact and the compression force is building up. No shear forces Fs / Ms is applied at this stage. When the cellulose fibre puck is sufficiently compressed, the thermal conductivity increases drastically, and the cellulose material gets heated to a temperature T3 = 100°C through convection from the male mould 3a and the female mould 3b.

[0099] In step C, the fibrillation starts where the female mould 3b is rotated with a speed of 150 rpm and the compression force builds up the moulding pressure to P1 = 150 MPa. The fibrils 1 c, 1 d, and 1 e starts to flow f upwards in the cap rim of the mould cavity and fills up all voids, e.g. the threads.

[0100] Once the male mould 3a and the female mould 3b has been fully compressed, a cellulose product 5 corresponding to a cap is created, having a volume of 2,76 cm3and a density of 1 ,45 g / cm3. The cap can be ejected from the forming mould 3, shown in step D of Fig. 6.

[0101] This method produces a cellulose HDMF cap 5 with superior mechanical and chemical properties compared to conventional wet- and dry moulding of fibres.

[0102] By analysing the cellulose product 5 in a microscope, preferably a SEM- microscope, such a cellulose HDMF cap can easily be diversified from a non- defibrillated cellulose product, see Fig. 2. Also, the density can be measured using CT-scanner and a precision scale. In this way, high densities not possible to reach through regular fibre forming technologies can be obtained. An alternative example of a moulding device where a tubular cellulose material 4 is used, and where in-mould defibrillation of cellulose fibres is achieved, is schematically shown in cross section in Fig. 7.

[0103] One advantages of using a tubular cellulose material 4 is that a lowered compression force Fc is required while obtaining full mould pressure P1. It is further possible to use rolled paper or carton as the cellulose material 4.

[0104] The in-mould defibrillation process is shown in 4 steps A-D in Fig. 7. In step A, the tubular cellulose material 4 is applied to a mandrel 6, pre-heated to a temperature T1. The male mould 3a, pre-heated to a temperature T1 in this example, is also acting as a hollow piston scaping outside the mandrel 6. The mandrel 6 does not contribute to the generation of compression force and is held in a fixed distance from the bottom of the female mould 3b, i.e. defining the wall thickness of the top of the cap.

[0105] By closing the mould 3 in step B, the fibres start to compress by the force F and a moulding pressure builds up.

[0106] In-mould defibrillation starts in step C, when the moulding pressure, in this example, reaches P1 = 150 MPa and when the female tool 3b, pre-heated to a temperature T1 , is rotated back and forth with an amplitude of 30° and a frequency of 10 Hz.

[0107] This example is also used as an example in Fig. 5. The in-mould defibrillation process occurs between step C and D in Fig. 7.

[0108] In step D in Fig. 7, the cellulose HDMF product is ready and ejected.

[0109] In the previous example in Fig. 6, a cellulose HDMF cap having a diameter of 20mm was produced with a compression force Fc of 47,1 kN. In this example, an identical cap is produced with a compression force of only Fc = 9 kN. In this example, the rim of the cap is 1 mm in wall thickness and the tubular piston thickness of the male mould 3a is equal to the rim thickness. A piston area of 63 mm2and a compression force Fc of 9kN gives a mould pressure P1 = 150 MPa. When industrializing moulding machinery for cellulose HDMF products with multi cavity tools this feature allow more low-cost equipment with smaller press actuators to be used.

[0110] Rotating one of the mould parts requires mainly rotational symmetrical cellulose products. In case of square shaped cellulose products, small vibrations, e.g. rotational or transversal is a possibility. The moulding device in Fig. 7 also reveals a possibility to regard the compression cylinder portion of the female mould 3b as a separate fibril feeding device separated from the actual product shape and geometry. I.e. the piston cylinder arrangement can be applied in connection to a square shaped cavity.

[0111] Another embodiment of this innovation is to use small vibrations with high frequency. Fig. 8 shows, in perspective, a moulding device for in-mould defibrillation using ultrasonic vibrations Fs.

[0112] In this example the female mould 3b is pre-heated or cooled to a temperature T2 and vibrates with a typical amplitude of a = 15 - 50 pm and a frequency of [3 = 20 - 50 kHz. To enable these vibrations of the female cavity the entire component 3b, referred to as a sonotrode, must be designed to withstand high compression forces Fc.

[0113] The shear force Fs is generated by an ultrasonic converter or generator 7, typically 4kW, where the amplitude a is amplified by a booster 8. The male mould 3a pre-heated to a temperature T2, is mounted on a press actuator (not shown), enabling the male mould 3a to enter the female mould 3b with high precision without metal contact between the male mould 3a and the female mould 3b.

[0114] Since a lot of sonic energy is induced in the fibres and fibrils in a short time, less than a second, essential heating may require that the male mould 3a and the female mould 3b are cooled to a temperature T2 instead of being preheated. The advantage of ultrasonic generated shear forces is than any cellulose product shape, e.g. square shaped, can be in-mould defibrillated and formed with short cycle times.

[0115] In some cellulose product cases, no external shear force Fs is required to be applied. Fig. 9 shows schematically in cross section one such embodiment. Here, a one directional pressing force Fc induces shear forces Fs that are directed in a different direction than the pressing direction. This is due to geometrical conditions in the mould, such that a successful in-mould defibrillation can be obtained without applying external shear forces Fs. The fibres are simply forced to scape, flow f, non-parallel to the pressing direction.

[0116] Fig. 9. shows a method in four steps for producing a convex cellulose product 5, where a large amount of cellulose fibres 4, preferably lose fibres, are loaded into a female mould 3b, pre-heated to a temperature T1 in step A. Closing the mould 3 in step B will initiate fibre / fibril movement from the centre / top of the female mould 3b downwards to the sides.

[0117] In step C, when the compression force reaches the sufficient pressure in the mould 3, the shear forces Fs induce so much energy that the fibres defibrillate and starts to flow f in the entire bulk of cellulose material 1 b, 1 c, 1 d and 1 e.

[0118] Tests have shown that when forming a cellulose HDMF product, a suitable forming pressure level is at least 100 MPa and may be up to 200 MPa or more, depending on the desired properties of the actual cellulose HDMF product. A suitable moulding temperature level is in the range of 100°C to 300°C.

[0119] It will be appreciated that the above description is merely exemplary in nature and is not intended to limit the present disclosure, its application or uses. While specific examples have been described in the specification and illustrated in the drawings, it will be understood by those of ordinary skill in the art that various changes may be made, and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure as defined in the claims. Furthermore, modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure is not limited to the particular examples illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out the teachings of the present disclosure, but that the scope of the present disclosure will include any embodiments falling within the foregoing description and the appended claims. Reference signs mentioned in the claims should not be seen as limiting the extent of the matter protected by the claims, and their sole function is to make claims easier to understand.

[0120] REFERENCE SIGNS

[0121] 1 : Cellulose fibre system

[0122] 1a: Cellulose fibre

[0123] 1 b: Fiber shell

[0124] 1c: Macro fibril

[0125] 1d: Micro fibril

[0126] 1e: Nano fibril

[0127] 2: Hydrogen bond(s)

[0128] 3: Forming mould

[0129] 3a: Male mould

[0130] 3b: Female mould

[0131] 4: Cellulose material

[0132] 5: Cellulose product

[0133] 6: Mandrel

[0134] 7: Ultrasonic converter / generator

[0135] 8: Booster

[0136] A: Material region with HDMF

[0137] B: Material region with wet- or dry moulded fibres

[0138] F: Force

[0139] Fc: Compression force

[0140] Fs: Shear force f: Flow

[0141] Ms: Shear torque

[0142] T 1 : Preheated mould temperature

[0143] T2: Precooled or heated mould temperature

[0144] T3: Actual temperature of the fibres and fibrils

[0145] P: Pressure in the fibres and fibrils

[0146] P0: Atmospheric or low pressure

[0147] P1 : Moulding pressure

[0148] Px: The actual pressure at a distance x from the moulding pressure dP / dx: Pressure gradient %H2O: Amount of water content in weight percent a: Amplitude

[0149] [3: Frequency

[0150] W: Size measurement

Claims

CLAIMS1. A method for producing a three-dimensional cellulose High Density Moulded Fibre (HDMF) product (5) from a cellulose material (4) comprising cellulose fibres wherein the method comprises the steps of; heating a forming mould (3) to a forming temperature in the range of 100°C to 300°C, conditioning the cellulose material (4) to a water content in the range of 5% to 20%, arranging the cellulose material (4) in the forming mould (3); and forming the cellulose HDMF product (5) from the cellulose material(4) in the heated forming mould (3), by pressing the cellulose material (4) with a forming pressure, thereby exposing the cellulose material (4) to a compression force in a first direction, and simultaneously expose the cellulose material (4) to at least a shear force in a second direction to obtain densification and in-mould defibrillation of the cellulose material (4) for the cellulose product (5).

2. A method according to claim 1 , wherein the forming pressure is at least 100 MPa.

3. A method according to claim 1 or 2, wherein the shear force is provided by a rotational movement acting on the cellulose material4. A method according to claim 1 or 2, wherein the shear force is provided by a vibrating movement acting on the cellulose material.

5. A method according to any claims 1 to 4, wherein the cellulose material (4) is a dry-formed cellulose fibres blank formed in a dry-forming process where cellulose fibres are carriedand formed to the dry-formed cellulose fibres blank by air as carrying medium.

6. A method according to any of claims 1 to 4, wherein the cellulose material (4) is fluff pulp or cardboard.

7. A method according to any of claims 1 to 4, wherein the cellulose material (4) is a granular material comprising cellulose fibres.

8. A method according to any of the preceding claims, wherein the cellulose material comprises at least 95% cellulose fibres by dry weight.

9. A method according to any of claims 1 to 8, wherein the cellulose material (4) comprises a crystalline additive, such as chalk, clay or silica, that will increase the abrasion between cellulose fibres (1a).

10. A method according to any of claims 1 to 8, wherein the cellulose material (4) comprises a friction reducing additive, such as pine soap diluted in water, that will reduce the friction between cellulose fibres (1a) and the forming mould (3).11 . A method according to claim 10, wherein the friction reducing additive is sprayed onto the cellulose material before the forming of the cellulose HDMF product (5).

12. A method according to any of the preceding claims, wherein the cellulose product (5) has a density greater than 1 ,30 g / cm3.

13. A three-dimensional cellulose High Density Moulded Fibre (HDMF) product (5) formed from a cellulose material (4), characterized in that the cellulose product (5) has a density greater than 1,30 g / cm3and where at least some of the cellulose fibres has defibrillated in the forming mould (3) during the forming of the cellulose product (5).

14. A product according to claim 13, wherein the cellulose product (5) comprises macro fibrils and / or micro fibrils and / or nano fibrils created during the forming of the cellulose product (5).

15. A product according to claim 13 or 14 to, wherein the wall thickness of the cellulose product (5) varies with at least 200%.

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