Mouldable thermoplastic composite and method of producing the composite

Abstract

The current invention relates to a foam- formed composite comprising a thermoplastic material in an amount of 30 wt.% of the total composite, long reinforcing fiber and ligneous fiber capable of forming hydrogen bonds. The thermoplastic material can be in the form of bicomponent fibers or in powder form. In addition, the invention relates to a method for manufacturing a foam-formed composite and a material comprising a foam-formed composite.

Description

[0001] MOULDABLE THERMOPLASTIC COMPOSITE AND METHOD OF PRODUCING THE COMPOSITE

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a composite comprising a thermoplastic material and reinforcing fibers. In particular, the invention relates to a thermoplastic composite formed by foam-forming technique and comprises various fibers. The invention also relates to a method for manufacturing the thermoplastic composite. In particular, the method relates to a foam-forming technique, where the fibers and thermoplastic material are formed to a foamed dispersion (fiberfoam mixture) and then formed to a porous web or a sheet of the thermoplastic composite. The invention further relates to a foam-formed material comprising the composite in form of at least two sheets stacked together to form the material.

[0004] BACKGROUND OF THE INVENTION

[0005] A composite material can be defined as a combination of two or more materials that result in better properties than those of the individual components used alone. Thermoformable composites are thermoplastic materials reinforced with a fiber or filler material. The polymer matrix is the substance that binds the reinforcing fibers together. Thermoplastic polymers can be made from renewable raw materials. If the polymer is biodegradable, the product can be composted when biodegradable fibers are used. Using natural fibers as reinforcement in composites has received much attention due to environmental issues. Environmental legislation and consumer demands have created a need to develop environmentally friendly and sustainable materials to replace synthetic fibers and lessen the demand for petroleum-based products. For example, the automotive industry aims to improve safety and reduce noise, manufacturing costs, and vehicle weight, which results in energy savings. Lightweight thermoplastics achieve better impact and acoustic performance as well as complex shaping capability and flexibility in manufacturing.

[0006] Thermoformable composites are materials, which are mouldable at a certain high temperature and after cooling the materials become solid and rigid.

[0007] A thermoplastic polymer is a high-viscosity resin that is processed by heating it above its melting temperature. A thermoplastic polymer solidifies upon cooling, and it can be reheated and remoulded. There is an increasing need to replace plastic polymers with biobased and biodegradable materials such as wood- based and cellulosic fibers. Wood-based and cellulosic fibers have been used to form mouldable fibrous materials.

[0008] Thermoformable composites comprising reinforcing wood-based and lignocellulosic fibers have been used in various applications, such as in packaging in the food industry and small goods. There are several criteria for thermoplastic material and composites, mainly depending on the final application of the material. The thermoplastic material needs to be easily mouldable, provide strength, durability and sufficient rigidity to when moulded. Therefore, the physical properties of the thermoplastic composite and material are crucial and should in many applications be superior to or at least equal to thermoplastics formed from plastic polymers.

[0009] The thermoplastic material should also be adoptable to include various properties depending on the final application. Different applications require different material properties such as durability, flexibility, impact resistance, lightness and tear-resistance etc. In addition, it is important to introduce various additional properties to the thermoplastic material, such as hydrophobicity, hydrophilicity, other surface properties such as possibility to print or attach layers on the surface of the material. Also, it is important that other specific properties such as flame resistance, anti-microbial properties or conductivity, can be implied to the thermoplastic material, especially without losing material properties or at high costs.

[0010] Various methods to produce thermoplastic fibrous composites and materials have been presented. The manufacturing process, together with the components of the composite, have a great impact on the material properties of the composite and material. The properties and quality of the composite is highly dependent on the combination of the components used and the manufacturing process. Many thermoplastic materials still suffer poor material properties and lack of possibility to include other properties to the materials. There is therefore still a need to improve the fibrous thermoplastic composites and materials, which include both thermoplastic and fibrous materials.

[0011] BRIEF DESCRIPTION OF THE INVENTION

[0012] An object of the present invention is to provide a composite, which is produced with foam-forming technique. The composite has improved material properties especially regarding strength and impact resistance without compromising the density of the composite. In addition, the mouldability of the composite to form products for various applications should be high. The composites hereby provided can also be used together with various additives providing specific properties.

[0013] Another object of the present invention is to provide a method for manufacturing a foam-formed composite according to the invention. The method in combination with the components of the composite provides a composite with unique properties and adoptability. Especially, the method according to the present invention provides a light composite with low density but having high strength and impact resistance and still excellent mouldability properties.

[0014] Still another object is to provide a foam-formed material comprising a foam-formed composite according to the invention, wherein the composite is in the form of sheets stacked together to form the thermoplastic material. Stacking two or more sheets of foam-formed composites together forms a layered material, which can be moulded into the final product. The unique properties of the composite in combination with the manufacturing process produces sheets of the composite, which can easily be pressed together. The sheets of the composite forming the layers of the material are attached or adhered together, which makes it possible to mould products of the layered material.

[0015] Specifically, it is provided a foam-formed composite comprising

[0016] - a thermoplastic material,

[0017] - long reinforcing fiber having a fiber length of at least 10 mm, and

[0018] - ligneous fiber capable of forming hydrogen bonds having a fiber length of at most 5 mm, wherein the thermoplastic material forms at least 30 wt.% of total foam-formed composite.

[0019] The benefits of foam forming compared to traditional extrusion and injection molding methods are: (a) Fiber length is maintained during the composite manufacturing process, (b) The possibility to increase the amount and length of fibers, and [c] The possibility to disperse the fibers and other raw materials evenly in the matrix.

[0020] Thermoforming uses heat and pressure to transform a sheet into almost any shape. It is beneficial that the layers can be connected by thermoforming without the use of a separate adhesive layer. Layering also enables the production of end products with a high grammage. Manufacturing a web with a high grammage in one step would significantly limit the production speed of the foam-forming pro- cess. BRIEF DESCRIPTION OF THE FIGURES

[0021] Figure 1 presents composite tensile strength (MPa) as a function of density (kg / m3) of two different composites.

[0022] Figure 2 presents composite tensile strengths (MPa) of PLA and PLA / PLA samples as a function of density (kg / m3).

[0023] Figure 3 presents composite tensile strengths (MPa) of PE / PET samples as a function of density (kg / m3) for two different fiber lengths.

[0024] DETAILED DESCRIPTION OF THE INVENTION

[0025] The current invention presents a composite comprising thermoplastic material and different reinforcing fibers, long reinforcing fibers and ligneous fibers capable of forming hydrogen bonds. Particularly, the composite is a foam-formed composite. The term "foam-formed" means that the composite is formed in a foam forming process or using a foam forming technique. Generally, a foam forming technique means the components of the composite are mixed to a foamed dispersion in an aqueous liquid. The foamed dispersion contains a high amount of air, and comparatively low amount of water compared to wet-laid processes. The foamed dispersion is conveyed onto a support to form a web or sheet of the composite.

[0026] The basic idea behind the foam-forming method is to bind distinct fibers to foam bubbles. Following this, the fibers are practically immobile with each other until the foam collapses on the paper machine’s wire, under the influence of the suction boxes. Under relatively low straining rates, liquid foams behave as viscoelastic solids, beyond which they can flow and deform like a liquid. The web or sheet can subsequently be dried. Foam forming techniques as such are well known in art, and an example of foam forming can be found in publication US3,716,449. The foam-forming process provides a composite with unique properties since the fibers and thermoplastic material are evenly distributed. A relatively light fibrous composite, which is highly porous, can thus be obtained.

[0027] The current invention presents a foam-formed composite comprising a thermoplastic material and reinforcing fibers. With the term "thermoplastic" is here meant any material which possesses thermoplastic properties, meaning that the material becomes plastic and mouldable at high temperature, and solidifies again after cooling. Thermoplastic materials are also sometimes called thermosoftening materials, meaning the material will be soft and thereby mouldable at certain temperature. Thermoplastic materials are readily used to form products with various 3D-forms by moulding processes.

[0028] Thermoplastic fibers soften with heat. Thermoplastic fibers can be divided into two main categories: single component (or monocomponent) and bicomponent fibers. The major advantages of a bicomponent fibers, compared to monocomponent fibers, is that they have a broader temperature range needed to form thermal bonding. If the temperature needed to form thermal bonding is too low can cause inadequate bong strength. If the temperature is too high, the web will melt excessively and lose it identity as a web. When thermal bonding bicomponent fibers, the core of the fiber maintains the integrity of the web, while the sheats melts and bonds with other fibers at the fiber crossover points. When bicomponent fibers are used, the typical temperature range for thermal bonding may be as broad as 25 °C, or even broader such as 35 °C or even 85 °C.

[0029] In one embodiment of the current invention the thermoplastic material is a monocomponent fiber, a bicomponent fiber, a powder or any combination thereof. Monocomponent fibers are fibers of a thermoplastic material, where the fiber contains only one specific material, such as a polymer having a single melting temperature. Compared to monocomponent fibers, bicomponent fibers contain two different thermoplastic materials. The two thermoplastic materials in a bicomponent fiber have different properties, in particular they have different melting temperatures. There is a range of various bicomponent fibers. The bicomponent fibers are generally classified according to the shape of the various materials used to form the fiber. Bicomponent fibers can be so called side-by-side, segmented or core-sheath fibers. Core / sheath (C / S) fibers means that the fiber has a core in one material, and the core is surrounded completely or partially by another material forming the sheath of the fiber.

[0030] In one embodiment of the invention the thermoplastic material is bicomponent fiber of core / sheath type. In core / sheath type bicomponent fibers the core material has a higher melting point compared to the sheath material of the bicomponent material. When the sheath material has a lower melting point than the core material, the sheath of the bicomponent fiber melts before the core. The melted sheath can then attach to other fibers of the composite, while the core remains solid (not melted) and provides rigidness to the composite.

[0031] According to one embodiment of the invention the thermoplastic material is a bicomponent fiber of core / sheath type, where the material of the bicomponent fiber is selected from the group consisting of PE / PP, PP / PP, PE / PET, PLA / PLA bicomponent fibers and any combination thereof. Here PE stands for polyethylene, PP for polypropylene, PET for polyethylene therephthalate, and PLA for polylactic acid also called polylactide.

[0032] In one embodiment the thermoplastic material is a bicomponent poly- ethylene / polypropylene (PE / PP) bicomponent fiber, where the melting point of the PE and PP were 130 °C and 161 °C, respectively.

[0033] In one embodiment the thermoplastic material is a bicomponent poly- ethylene / polyethylene terephthalate (PE / PET) bicomponent fiber, where the melting point of the PE and PET were 127 °C and 256 °C, respectively.

[0034] In one embodiment the thermoplastic material is a bicomponent pol- ylactide / polylactide (PLA / PLA) bicomponent fiber, where the melting point of the PLA in sheath and PLA in core were 130 °C and 175 °C, respectively.

[0035] In one embodiment the thermoplastic material is a monocomponent fiber, meaning the fiber consists of one polymer, or alternatively in one embodiment the thermoplastic material is in powder form. The monocomponent fibers and the thermoplastic powder is typically selected from polymeric materials such as polyethylene (PE), polypropylene (PP), polylactic acid (or polylactide; PLA), polybutylene succinate (PBS), polybutylene adipate terephthalate (PBAT), cellulose acetate phthalate (CAP), polyhydroxyalkanoates (PHA), polyamines (PA) or any combination thereof.

[0036] The thermoplastic material forms at least 30 wt.% of the total foam- formed composite. In one embodiment of the invention the thermoplastic material forms at least 32 wt.%, at least 35 wt.%, at least 37 wt.% or at least 40 wt.% of the total foam-formed composite. The relative high amount of the thermoplastic material in the complete foam-formed composite provides unique properties to the fibrous composite. Especially good mouldability of the composite during the thermoforming stage is achieved with the relatively high among of thermoplastic material.

[0037] The foam-formed composite is formed by a foam forming technique, which ensures an even distribution of the thermoplastic material among the long reinforcing fibers and ligneous fibers, thereby providing a homogeneous composite, with evenly distributed thermoplastic composite.

[0038] The foam-formed composite according to the invention comprises in addition to the thermoplastic material also reinforcing fibers. The foam-formed composite comprises at least two types of fibers, namely long reinforcing fiber and ligneous fiber capable of forming hydrogen bonds. In one embodiment of the current invention the long reinforcing fibers are natural fiber or regenerated fiber, such as lignocellulosic or cellulosic fibers. The long reinforcing fibers provide rigidness and reinforcement to the composite. The long reinforcing fibers have a fiber length of at least 10 mm and fiber length of the long reinforcing fibers can be up to 30 mm or up to 50 mm.

[0039] In one embodiment the amount of long reinforcing fiber in the total foam-formed composite is at least 15 wt.%, at least 20 wt.% or at least 25 wt.%.

[0040] In one embodiment of the present invention the long reinforcing fiber is selected from the group consisting of regenerated fiber, such as viscose or Ten- cel, flax, jute, hemp, silk, kenaf, bamboo, bagasse, cotton, coconut fibers and any combination thereof.

[0041] The foam-formed composite also comprises ligneous fiber (or woodbased fiber) capable of forming hydrogen bonds. With the term "ligneous fiber" is herein meant natural fibers derived from plants including trees, and are composed mainly of cellulose, hemicellulose and / or lignin, individually or in any combination. Ligneous fibers can also be called lignocellulosic fibers. The ligneous fibers are capable of forming hydrogen bonds and the hydrogen bonds are formed in the drying phase of the web. The ligneous fiber can form hydrogen bonds and thereby forms an entanglement within the composite. Typically, the ligneous fibers forms hydrogen bonds with ligneous fiber, either as intra-fiber or inter-fiber hydrogen bonds. However, the hydrogen bonds can also be formed with other components of the composite. The hydrogen bonded ligneous fibers forms an entangled web of fibers providing both flexibility and porousness to the composite.

[0042] The ligneous fiber capable of forming hydrogen bonds is short ligneous fiber having a fiber length of at most 5 mm. In one embodiment the ligneous fiber capable of forming hydrogen bonds have a fiber length of at most 3 mm or at most 1 mm. The short ligneous fibers have a fiber length of at least 0.005 mm.

[0043] In one embodiment the amount of ligneous fibers in the foam-formed composite is at least 10 wt.%, such as at least 15 wt.%, at least 20 wt.% or at least 25 wt.% of the total composite.

[0044] In one embodiment of the present invention the ligneous fiber capable of forming hydrogen bonds is selected from the group consisting of pulp, sulphite pulp, sulphate pulp, organosolv pulp, chemical pulp, thermomechanical pulp (TMP), chemimechanical pulp (CMP), chemithermo mechanical pulp (CTMP), recycled fibers and any combination thereof. The pulp can be bleached or non- bleachded.

[0045] In one embodiment of the present invention the foam-formed composite comprises a thermoplastic material comprising polyethylene in powder form and a bicomponent polyethylene / polypropylene fiber.

[0046] In one embodiment of the present invention the foam-formed composite comprises

[0047] - a thermoplastic material, which is a biocomponent fiber of polyethylene / polypropylene,

[0048] - a long reinforced fiber, which is regenerated cellulose fiber (Tencel) with a fiber length of about 10 mm, and

[0049] - a ligneous fiber capable of forming hydrogen bonds having a fiber length of at most 5 mm, which is pulp.

[0050] The foam-formed composites can be formed to sheets or webs with various thickness. Thereby sheets can be formed with a various grammage, as defined by mass per unit area (g / m2). Composite sheets with a grammage of from 200 g / m2to 1500 g / m2can be manufactured.

[0051] The manufacturing process of a thermoformed product consists of two main steps 1) the production of a reeled porous web or sheet in which the different raw materials are evenly distributed and 2) the thermoforming of the dry web / sheet into the desired shape. The production of the porous web can take place in a separate production facility from the actual production facility of the final product. Whether the manufacturing occurs in one or two production plants, the process restricts the optimal raw material composition. To enable the best possible mouldability, the use of thermoplastic in fiber form is recommended. Preferred is to use a bi-component fiber (core / sheath type). Using long reinforcing fibers (natural or regenerated) increases the strength of the thermoformed composite, especially the impact strength. The foam-forming process enables the use of long reinforcing fibers, and the gentleness of the foam-forming process maintains the fibers' length throughout the manufacturing process up to the final composite product. Long fibers are beneficial when making sharp corners in the thermoforming stage. However, when only thermoplastic and long fibers are used, the dry / wet strength of the web is too weak. Therefore, the optimal recipe also contains shorter fibers (< 3 - 5 mm) that form strong hydrogen bonds and give sufficient strength to rolls or sheets before the thermoforming step. Such a combination of raw materials allows for the fast production of a uniform web and good formability during the thermoforming phase. The invention further relates to a method for manufacturing the foam- formed composite according to the invention. In particular, the method comprises the steps of

[0052] - providing an aqueous liquid and a foaming agent to form a foamed liquid,

[0053] - dispersing at least long reinforced fibers and ligneous fibers capable of forming hydrogen bonds in said foamed liquid forming a dispersion,

[0054] - mixing the dispersion with a thermoplastic material, which thermoplastic material is a foamable liquid or a dispersion forming a foamed dispersion, and

[0055] - conveying the foamed dispersion to a foraminous support and draining liquid through the foraminous support to form a web or a sheet, and thus forming the foam-formed composite, and wherein the thermoplastic material forms at least 30 wt.% of total foam-formed composite.

[0056] In one embodiment of the invention, the method further comprises a step of drying the formed web or sheet.

[0057] The invention further relates to a foam-formed material comprising foam-foam composite according to the present invention. In foam-formed material the foam-foam composite is in the form of sheets and the foam-formed material comprises two or more foam-formed composite sheets stacked together forming the foam-formed material. The foam-formed material is thereby layered with two or more sheets of composite according to the invention.

[0058] The benefit of making layered material with two or more composite sheets is that the individual sheets can then be thinner (with lower grammage), which makes them dry faster in the manufacturing process. One benefit is also that the material can comprise composite sheets with different compositions, and thereby different properties. For example a material can comprise three or more sheets, where the outer sheets have one composition and the inner sheet(s) have another composition. The foam-formed composite sheets according to the invention can be stacked together without the need of using adhesive between the sheets.

[0059] In one embodiment of the present invention the foam-formed material comprises foam-formed composites with identical or different compositions.

[0060] In another embodiment the foam-formed material is a layered material with at least three foam-formed composite sheets arranged such that outer sheets of the layered foam-formed material have specific properties and the inner sheet(s) has / have another specific property.

[0061] In yet another embodiment the foam-formed material comprises foam- formed composites sheet of the outer sheets, which comprises additives given the composite hydrophobic, hydrophilic, anti-microbial, conductive or similar properties.

[0062] EXAMPLES

[0063] Example 1

[0064] Composite-making procedure on a laboratory scale: The production of thermoformable composites begins by adding all the raw materials to tap water. After adding the surfactant, the suspension was foamed with a mechanical mixer. Foaming took place in a transparent container, which enabled the analysis of the foaming phase with a camera. The target air content was about 60 %. The fiber consistency was about 3 %. Foam-formed sheets were made using a hand sheet mould shown in Fig. XI. The sheet size was 35 cm x 22 cm. When making a hand sheet, the fiber-foam mixture was poured onto the top of the mould, where a funnel directed it to one side. Then, the fiber-foam mixture spread from one end of the mould to the other. This flow was enough to orient fibers in the flow direction. The funnel was then removed, and a plastic cover was placed on top of the foam to create a seal for the vacuum. Samples were wet pressed using an L&W wet press (Lorentz & Wetre) to remove water and consolidate the wet sheet. Then samples were dried using a drum dryer. The samples were thermo-formed with a dynamic press device in the final processing step. Dynamic press device has a hydraulic cylinder that clamps the plate attached above to the stationary plate. Users can select the compression pressure, pressing time, and plate temperatures. The maximum pressure in the hydraulic cylinder is 100 bar, and the maximum temperature of pressing plates is 250 °C. The pressure in the hydraulic cylinder 95 bar corresponds to about 6.2 bar pressure in the sample.

[0065] Composite-making procedure in pilot scale: The experiments were carried out in a pilot line with the closed vertical headbox configuration. The pilot line consists of an approach system, forming section, drying section, and reeler. Raw materials, including the surfactant, were dosed and mixed in a pulper (foam generator), generating a fiber-foam mixture. Then, the fiber-foam mixture was pumped into the closed vertical headbox. The foamed fiber suspension was fed into the top of the closed vertical head box between two wires. The formed web was partly dried by impingement drying units and finally reeled. The forming speed was 25 m / min. The foam density in the headbox was about 360 kg / m3. In headbox feeding, volumetric flow (1 atm) varied between 15-221 / s. Consistency ranged between 1.3 - 4.3 %, and the slice (headbox opening) opening was about 6.7 mm. At the pilot, the web was dried with air impingement dryers. After reeling, rectangular sheets were cut from the web. Those sheets were dried in the laboratory with KRK dryers. Dry samples were thermoformed with a dynamic press device in the final processing step.

[0066] 3D samples were made using a thermoforming device: Thermoforming of samples was made using two-step method where the sample is at first heated in a heat oven to a temperature which enables to melt the thermoplastic material in the foam formed sheet. The heating time depends on the sample bulk thickness, but is typically between 2 to 20 min. Then the sample is transferred to heat press between moulds those are able give the moulded 3D shape for the sheet. Mould temperature can be between room temperature to a temperature that is below thermoplastic material crystallization temperature. For PE / PP fibres was used mould temperature of 50-70°C. Pressing temperature, time and pressure has effect on the end product strength properties and surface quality. Typical pressing time of four minutes and cylinder pressures 25 to 130 bar were used. The press was MSK Vekomet hydraulic press.

[0067] Example 2

[0068] A mixture of SDS and Tween 20 was used for foaming. SDS (sodium dodecyl sulphate) is a small anionic surfactant with a negatively charged sulphate headgroup and carbon chain (C-12). SDS was purchased from Sigma-Aldrich and was used without further purification. Tween 20 (polysorbate-20) is a large nonionic surfactant of ethoxylated sorbitan molecules with 20 units of polyethylene glycol and a 12-carbon long fatty acid chain. Tween 20 was purchased from Sigma- Aldrich. Non-ionic surfactant (Tween 20) can function as a dispersion aid and increase the fiber surface’s hydrophobicity. Usually, the SDS dose was 0.3 g / 1, and the Tween 20 dose was also 0.3 g / L

[0069] Two thermoplastic materials were tested in this study. Polyethylene was used as a thermoplastic material in powder form (LDPE) and bi-component fiber (PE / PP 12 mm). The average particle size of LDPE powder was 350 gm, and the max particle size was 600 gm. The melting point was 108 °C, and the melt flow index at 190 °C was 8 g / 10 min. For the bi-component fiber, the PE and PP melting points were 129-130 °C and 161 °C, respectively. Short wood fiber was bleached softwood kraft pulp (BSKP) from Metsa Fibre Aanekoski. The long fiber was 10 mm Tencel fiber (1.7 dtex) (Lyocell by Lenzing), which is a regenerated cellulose fiber.

[0070] When using LDPE powder, the thermoforming temperature setting was 130° C, the pressing time was 2 x 180 s, and the set value for the pressure was 95 bar. The sample was turned 180 degrees between pressings, as the temperature distribution of the plates used for heating was not completely uniform. By turning the sample, we tried to ensure even heating.

[0071] When using bi-component (PE / PP) fiber, the pressing temperature was 150 °C. The pressure and time were the same as when using LDPE powder. Pressing times were relatively long, as the sample was at room temperature before being placed in the dynamic press device. The pressing time could be shortened by preheating the sample in an oven. However, in this study, no preheating was used. The target grammage was set at 1200 g / m2, as fiber-reinforced composites with this grammage are commercially available.

[0072] Tensile strength properties were determined according to the standard for isotropic and orthotropic fiber-reinforced composites (ISO 527-4:2021). The samples were kept in standard conditions (23 °C and 50 % relative humidity) for at least five days before testing. At each trial point, the tensile properties of five strips were measured in both the MD and CD directions. The results are presented in Table 1 below as geometric means of the properties measured in the MD and CD directions. We focused mainly on the tensile strength properties of the final product, as it is thought to describe the adhesion between the fiber and the polymer on a macroscopic scale.

[0073] When the amount of thermoplastic is low (10 %), the tensile strength and elongation at break are low. With a 30% amount of bi-component fiber, the tensile strength and elongation at break are significantly better. When comparing bi-component PE / PP fiber with LDPE powder, it was found that to reach the same tensile strength level, the dosage of LDPE powder had to be 50 % when the dosage of bi-component fiber was 30 %. By dosing long fiber (20 mass-%), the tensile strength of the composite and especially its impact strength can be increased. The notched impact strengths of the samples were generally over 100 kj / m2and, in some cases, even over 200 kj / m2.

[0074] Table 1, Compositions and properties of the various composites (trial points, TP)

[0075] The tensile strength of the pilot-produced sample, according to trial point (TP) 4, was 32 MPa, and the elongation at break was 11.2 %. The tensile strength of the pilot sample TP 6 was 24 MPa, and the elongation at break was 10.5 %.

[0076] Samples with a higher grammage (2000 g / m2) were also produced. There were no problems making high grammage sheets using foam forming hand sheet mould. The consistency of fiber suspension was 4.8 %. The air content of foamed fiber suspension was about 57 %. Samples with a high grammage allowed samples to be thermoformed to several different thicknesses. In practice, pressing to different thicknesses was carried out by using metallic spacers of different thicknesses. Figure 1 shows the tensile strength of the samples as a function of the density. LDPE dosage was 50 mass-%, and PE / PP bi-component dosage was 30 mass- %. The dependence between tensile strength and density differs when using different shapes of thermoplastic particles. Using bi-component fiber as the thermoplastic material, a high-strength porous structure is easier to achieve. The proportion of plastic in the composite can also be significantly lower (30% vs. 50 %).

[0077] Example 3

[0078] Layering enables the production of composites with a high grammage. It is beneficial that the low-grammage layers can be connected by thermoforming without using a separate adhesive layer. Manufacturing a web with a high grammage in one step would significantly limit the production speed of the foam-forming process. The production of composites by layering was investigated by producing a sample of about 1200 g / m2on a laboratory scale and a web of about 340 g / m2on the pilot. The raw material composition was the same in all trial points, i.e., 50% bleached softwood kraft pulp (BSKP), 20% viscose fiber (10 mm, 1.7 dtex), and 30% 12 mm PE / PP bi-component fiber. A mixture of SDS and Tween 20 was used for foaming. The forming speed at the pilot was 25 m / min. At the pilot, the web was pre-dried with air impingement dryers. After reeling, rectangular sheets were cut from the web. Those sheets were dried in the laboratory with KRK dryers. The single-layer structure (TP A) was thermoformed at a temperature of 150 °C and pressure of 6.2 bar. When stacking several layers (2 or 3) on top of each other, the same temperature and pressure settings were used in thermoforming. The tensile strength, strain at break, and z-directional strength of thermoformed samples (TP A- TP C) were determined. Tensile strength properties were determined according to the standard for isotropic and orthotropic fiber-reinforced composites (ISO 527- 4:2021). The Z-direction tensile strength was determined with a Zwick tester based on the standard TAPP1 T 541 (internal bond strength of paperboard). The thermoformed samples were kept in standard conditions (23 °C and 50 % relative humidity) for at least five days before testing. The tensile strength and strain at break of the composites made by stacking 2 or 3 layers were at the same level as the composite made from one 1200 g / m2sheet. A significant observation was that the z- strength of samples made by stacking several layers was also at the same level as the strength of the 1-layer structure.

[0079] Table 2; Properties of single layer and multilayer composites

[0080] It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

[0081] Example 4

[0082] Use of polylactic acid (PLA) fibers as a thermoplastic material

[0083] Polylactic acid (PLA) fibers were used as the thermoplastic material in this sample set. One of the PLA fibers was a mono-component PLA fiber, and the other was a bi-component PLA / PLA fiber. PLA fibers were purchased from Trevira GmbH. The length of the mono-component PLA fiber was 4 mm, and the linear density (~diameter) was 1.7 dtex. Mono-component PLA fiber (Trevira 400) was uncrimped and intended for water-laid applications. The melting point of mono-component PLA fiber was 160 °C. The bi-component PLA / PLA (Trevira 458) fiber length was 6 mm, and the linear density (~diameter) was 2.2 dtex. PLA / PLA fiber was crimped (4.8 crimps / cm) and intended for air-laid applications. The melting point of the core was 175 °C, and the melting point of the sheath was 130 °C. The mass fraction of PLA fiber was 30% (see Table 3). Either BSKP fibers (AK1 pulp) or CTMP fibers by Rottneros (CSF 650) were used as short fibers, and 10 mm long Tencel fiber (1.7 dtex) were used as long, reinforcing, fibers.

[0084] The raw material composition of the samples and the thickness of the samples after thermoforming are shown in Table 3. Thermoforming was done at 6.2 and 12.4 bar pressures. In practice, this was realized by changing the sample size. A mixture of sodium dodecyl sulphate (SDS) and Tween 20 (0.3 g / 1 + 0.3 g / 1) was used as a foaming aid. The consistency of the fiber suspension was about 3.1 %, and the air content of the foamed fiber suspension was about 60%. The target grammage of the samples was 1200 g / m2. The thermoforming time was 2 x 180 s at all trial points. The thermoforming temperature was 170 °C when using monocomponent PLA fiber as a thermoplastic material. When using bi-component PLA / PLA fiber, the thermoforming temperature was 150 °C. In Table 3, it can be observed that as the thermoforming pressure increases, the samples become thinner. The phenomenon is noticeable at all test points. When part of the wood (AK1 or CTMP) fibers is replaced with regenerated 10 mm Tencel fiber, the samples become thicker (for example, A7_l vs. A8_l).

[0085] Table 3; The raw materials of trial points A7-A14 and the sample's thickness (pm) after thermoforming are presented. The table shows the mass-% of the raw materials.

[0086] Apparent differences were observed in the densities of the composites when different pressures were used in thermoforming. Densities were up to 20% higher when a higher (12.4 bar) thermoforming pressure was used. In six trial points, the tensile strengths were over 30 MPa. In three cases, the tensile strength was even over 40 MPa (A9_2, A13_2 and A14_2). In all test points where the tensile strength exceeds 40 MPa, CTMP fiber was used, and the thermoforming pressure was 12.4 bar. When comparing PLA mono-component fibers to PLA / PLA bi- component fibers, it was observed that higher strengths were achieved when using a mono-component PLA fiber (see Figure 2). It should be noted that mono-component PLA fiber is intended for use in the wet-laid process, while the bi-component PLA / PLA fiber is designed for air-laid processes. Therefore, it could be assumed that the mono-component fiber would work better in the foam-forming process. In many cases, the notched impact strengths were higher when a higher pressure (12.4 bar) was used in thermoforming. The notched impact strengths of several samples (A7_l, A7_2, A8_l, All_2, A12_l, and A12_2) were over 100 kj / m2.

[0087] Example 5

[0088] Use of PE / PET fibers as a thermoplastic material

[0089] Using PE / PET (polyethylene / polyester) bi-component fiber as a thermoplastic material was investigated in this sample set. Both investigated PE / PET fibers were 1.3 dtex fibers. The melting temperature of the sheath (PE) was 127 °C and the melting temperature of the core (PET) was 256 °C. The investigated PE / PET fibers differed from each other based on the length of the fiber. The shorter PET fiber was 6 mm long, and the longer one was 12 mm. Fibers were purchased from Trevira GmbH. The PE / PET fiber mass fraction was 30 % (see Table 4). BSKP pulp (AK1), CTMP pulp (by Rottneros, CSF 650), and 10 mm Tencel fiber (1.7 dtex) were used as reinforcing fibers. The raw material composition of the samples and the thickness of the samples after thermoforming are shown in Table 4. Thermoforming was done at 6.2 and 12.4 bar pressures. In practice, this was realized by changing the sample size. A mixture of sodium dodecyl sulphate (SDS) and Tween 20 (0.3 g / 1 + 0.3 g / 1) was used as a foaming aid. The consistency of the fiber suspension was about 3 %, and the air content of the foamed fiber suspension was about 60%. The target grammage of the samples was 1200 g / m2. The thermoforming temperature was 150 °C, and the thermoforming time was 2 x 180 s at all trial points. Table 4 shows that the samples become thinner as the thermoforming pressure increases (12.4 bar vs. 6.2 bar). The phenomenon is noticeable at all test points, and differences in thickness are more than 20 % in some cases.

[0090] The densities of samples prepared at higher thermoforming pressure (12.4 bar) are, at a minimum, about 10% higher and, at a maximum, almost 40% higher than the densities of samples prepared at lower thermoforming pressure. Figure 3 shows that in four trial points, the tensile strengths are over 30 MPa; in one case, the tensile strength is even over 40 MPa. In all test points where the tensile strength exceeds 30 MPa, CTMP fiber was used, and the thermoforming pressure was 12.4 bar. When comparing samples made with PE / PET fibers of different lengths, it can be observed that slightly better tensile strengths are achieved with 12 mm fibers than with 6 mm fibers (see Figure 3).

[0091] Table 4; The raw materials of trial points A15-A22 and the sample's thickness (pm) after thermoforming are presented. The table shows the mass-% of the raw materials.

[0092] The impact strengths (notched samples) were higher when using bleached softwood kraft pulp than when using CTMP fiber. The impact strength improvement effect of the long 10 mm Tencel fiber was seen in almost all trial points. Notched impact strengths of eleven trial points (A15_l-A18_2, A20_l, A22_l and A22_2) were over 100 kj / m2.

Claims

CLAIMS1. A foam-formed composite comprising- a thermoplastic material,- long reinforcing fiber having a fiber length of at least 10 mm, and- ligneous fiber capable of forming hydrogen bonds having a fiber length of at most 5 mm, wherein the thermoplastic material forms at least 30 wt.% of total foam-formed composite.

2. The foam-formed composite of claim 1, wherein the thermoplastic material is a monocomponent fiber, a bicomponent fiber, a powder or any combination thereof.

3. The foam-formed composite of claim 1 or 2, wherein the thermoplastic material is a bicomponent fiber of core / sheath type.

4. The foam-formed composite of claim 3, wherein the bicomponent fiber of core / sheath type is selected from the group consisting of PE / PP, PP / PP, PE / PET, PLA / PLA bicomponent fibers and any combination thereof.

5. The foam-formed composite according to any previous claim, wherein the long reinforcing fiber has a fiber length of at least 10 mm, and up to 30 mm or 50 mm.

6. The foam-forming composite according to any previous claim, wherein the long reinforcing fiber is a natural fiber or a regenerated fiber, such as lignocellulosic or cellulosic fiber.

7. The foam-forming composite according to any previous claim, wherein the long reinforcing fiber is selected from regenerated fiber, such as viscose or Tencel, flax, jute, hemp, silk, kenaf, bamboo, bagasse, cotton, coconut fibers and any combination thereof.

8. The foam-formed composite according to any previous claim, wherein the ligneous fiber is short ligneous fiber having a fiber length of at most 3 mm.

9. The foam-formed composite according to any previous claim, wherein the ligneous fiber capable of forming hydrogen bonds forms at least 10 wt.% of total foam-formed composite.

10. The foam-formed composite according to any previous claim, wherein the ligneous fiber capable of forming hydrogen bonds is selected from the group consisting of pulp, sulphite pulp, sulphate pulp, organosolv pulp, chemicalpulp, thermomechanical pulp (TMP), chemimechanical pulp (CMP), chemithermo mechanical pulp (CTMP), recycled fibers and any combination thereof.

11. The foam-formed composite according to any previous claim, wherein the foam-formed composite comprises- a thermoplastic material, which is a biocomponent fiber of polyethylene / polypropylene,- a long reinforced fiber, which is regenerated cellulose fiber with a fiber length of about 10 mm, and- a ligneous fiber capable of forming hydrogen bonds having a fiber length of at most 5 mm, which is pulp.

12. A method for manufacturing a foam-formed composite according to any of claims 1 to 11, wherein the method comprises- providing an aqueous liquid and a foaming agent to form a foamed liquid,- dispersing at least long reinforcing fibers and ligneous fibers capable of forming hydrogen bonds in said foamed liquid forming a dispersion,- mixing the dispersion with a thermoplastic material, which thermoplastic material is a foamable liquid or a dispersion forming a foamed dispersion, and- conveying the foamed dispersion to a foraminous support and draining liquid through the foraminous support to form a web or a sheet, and thus forming the foam-formed composite, and wherein the thermoplastic material forms at least 30 wt.% of total foam-formed composite.

13. The method according to claim 12, wherein the formed web or sheet is subsequently dried.

14. A foam-formed material comprising foam-formed composite according to any one of claims 1 to 11, wherein the foam-formed composite is in the form of a sheet and the foam-formed material comprises two or more foam-formed composite sheets stacked together to form the foam-formed material.

15. The foam-formed material according to claim 14, wherein the foam- formed material comprises foam-formed composite sheets with identical or different compositions.

16. The foam-formed material according to any one of claims 14 or 15, wherein the foam-formed material is a layered material with at least three foam- formed composite sheets arranged such that outer sheets of the layered foam- formed material have a specific property and the inner sheet(s) has / have anotherspecific property.

17. The foam-formed material according to any one of claim 14 - 16, wherein the foam-formed composite sheets are pressed together, and no adhesive is used between the foam-formed composite sheets.

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