Background of the Invention

Field of the Invention

[0001] The present invention concerns a method for manufacturing lignocellulosic structures, suitable for use as interior construction elements, as well as the solid structures obtained using said method.

Description of Related Art

[0002] Layered structures for use as interior construction elements are typically formed of gypsum board or chip board, which provide both strength and durability, as well as an advantageously smooth surface. Typically, such interior elements are formed of mixtures or layers of several different types of materials, which hinder recycling and diminish the possibilities for reusing the elements. Such products also commonly use formaldehyde-containing glues, which are considered harmful.

[0003] Other layered glued structures include paper machine cores and glued plain structures used e.g. on children’s books. These are both hard structures, where no design features can be implemented, and they are both glued together using starch. [0004] Paper is commonly used for glued multilayer sheets, but its use in

manufacturing construction elements would not be advantageous, due to the high number of layers required to form a rigid structure.

[0005] JP 2012197544 A describes multilayer paper with good interlaminar strength.

[0006] US 20170072670 describes a paper laminate for use in e.g. packaging industry. In said laminate, paper layers are bonded together using cellulose nanofibrils. [0007] The product described in these publications would, however, not be useful in producing rigid structures that allow shaping, since the porosity of regular paper is low, while rigidity would require an unreasonably high number of paper sheets. [0008] US 20160194527 describes a laminated structure comprising paperboard or corrugated boxboard materials comprising at least two layers of substrate adhered to each other using a TEMPO-based CNF adhesive. Such an adhesive has a low consistency, causing a high amount of required drying energy, as well as a lower flexibility of the final structure, whereby its moulding is not possible.

[0009] Lehmonen et al. (2017) describes the effect of cellulose micro fibril (CMF) addition on the strength properties of middle ply of board, whereby the publication merely focuses on the common use of microfibrils that are added to the fibre in the wet end of the process, i.e. the microfibrils are used as reinforcement agents.

Summary of the Invention

[0010] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0011] According to a first aspect of the present invention, there is provided a method for manufacturing lignocellulosic structures.

[0012] According to a second aspect of the present invention, there is provided a method, wherein two or more layers of cellulosic sheets are combined using a cellulose- based bonding agent.

[0013] According to a third aspect of the invention, there is provided lignocellulosic structures containing, or consisting of, several layers of cellulose-based materials, pressed or moulded into layered sheets or 3-dimensional structures.

[0014] The present invention is thus based on the finding that it is possible to use cellulose-based bonding agents, particularly excluding plastic components, to glue together sheets of cellulose-based sheets, thus providing a recyclable and reusable all-cellulose composite material having the required strength for use as construction elements. [0015] The present invention concerns a method for manufacturing lignocellulosic structures, as well as the solid structures obtained using said method. [0016] The invention provides several advantages. Among others, the present method provides the possibility to mould or shape the structures before hardening into their final rigid shape. As a result, the final structures can be in the form of flat sheets, they can have a defined form, or they can include a surface pattern. [0017] The high-consistency bonding agent used in the method of the present invention results in lower amounts of water that need to be evaporated in the final steps of the method. Further, high amounts of water result in the loss of some of the bonding agent in the bonding step. High amounts of water also cause weakening of the final product. [0018] The resulting structure is also strong, light and contains only wood-based and biodegradable components.

Brief Description of the Drawings [0019] FIGURE 1 is a SEM image illustrating the typical cross-sectional structure of a product according to the present invention, showing the loose upper layer without the bonding agent and the more dense CNF impregnated layers beneath.

[0020] FIGURE 2 shows the bending strength of various structures based on either prior art (such as common chip board, gypsum board and MDF) in similar, i.e. comparable, thicknesses

Embodiments of the Invention

[0021] Definitions

In the present context, the term“cellulose nanofibrils” (CNF) comprises

nanocellulose with a high level of fibrillation. The term“HefCel”, in turn means cellulose nanofibrils produced by high-consistency enzymatic fibrillation, where the cellulose fibrils are produced at a consistency of 20- 40%, which consistency is maintained throughout the fibrillation process. The production takes place by gently agitating the raw material at high consistency (20- 40%) in the presence of a cellulase enzyme cocktail, resulting in fibrillation due to the high fibre-fibre friction in the low water content. The degree of fibrillation can be adjusted by the enzyme dosage and the treatment time.

The porous carton or paper that is a preferred alternative for use as the cellulose- based sheets of the present invention typically has a grammage of 30-200g/m ² , or a porosity of 200-2000ml/min measured by the Bendtsen method. Preferably the paper or carton does not contain glue, as that would have a negative effect on the adsorption of the nano fibrils.

Typically, this structure has a density of < 0.9 g/cm ³ .

[0022] The present invention relates to a method for manufacturing lignocellulosic structures, suitable for use as interior construction elements, as well as the solid structures obtained using said method.

[0023] The invention is based on the aim of providing formed and solid

lignocellulosic structures for interior design uses containing no formaldehyde.

[0024] Further, the invention provides formed and solid lignocellulosic structures, wherein two or more layers of cellulose-based sheets are bonded together using a bonding agent from which all plastic components have been excluded.

[0025] Thus, in the method of the invention, two or more layers of cellulose-based sheets are combined using a cellulose-based bonding agent.

[0026] According to a preferred embodiment of the invention, the cellulose-based sheets are formed of two or more layers of carton, or of different layers of paper and carton. Such sheet materials are preferred because of their cellulose-content, as well as their strength and rigidity, combined with the advantageous thickness and porosity of the carton. [0027] A high cellulose content is thus preferred. However, components typically present in cellulosic products, such as hemicellulose and lignin, are allowed to be present in minor amounts, i.e. in ratios of further component to cellulose of < 1 :1. [0028] Examples of highly suitable sheet materials of the invention are carton, porous kraft paper or sack paper, or various cellulose-based non- woven sheets without any surface sizing.

[0029] According to a preferred embodiment, the cellulose-based bonding agent is formed of cellulose nano fibrils (CNF), preferably of enzymatically fibrillated

nanocellulose, and most suitably high-consistency enzymatically fibrillated cellulose nanofibrils (HefCel CNF). The bonding agent can be mixed with various additives, such as sorbitol, carboxymethyl cellulose (CMC), or methyl cellulose, in order to improve the strength or flexibility (mouldability) of the product. Also surfactants can be added to improve the adsorption of the nano fibrils into the fibrous sheets.

[0030] A high cellulose content is thus preferred also for the bonding agent.

However, components typically present in cellulosic products, such as hemicellulose and lignin, are allowed to be present in minor amounts, i.e. in ratios of further component to cellulose of < 1 :1.

[0031] The cellulose-based bonding agent is typically added as a layer to a base sheet in the form of a suspension in water, whereby the water softens the cellulose-based sheet. When a top sheet is added onto the layer of bonding agent, also the cellulose of the top sheet is softened. This results in a sufficiently moist structure, having surface layers that can be moulded or patterned.

[0032] Preferably, said bonding agent has been diluted to a consistency of 8-15%, preferably about 10%, to be used at said consistency in the bonding step of the present method. Such consistencies typically result in contents of cellulose-based bonding agent, in the final structure, of up to 7 w-%.

[0033] A preferred bonding agent is also formed of short fibres, with average dimensions of 15-20nm (width), and 200~400nm (length). However, the bonding agent may contain also fibre bundles with widths of up to 100-200nm and lengths of several micrometers. [0034] After the layers have been applied, and the optional shapes or patterns have been formed, the method of the invention typically includes a step of evaporation, preferably by heating, whereby the bonding agent solidifies, and forms a hardened network of bonding agent, which has partly been impregnated into the cellulose-based sheets.

[0035] The resulting structure can be in the form of a flat sheet, it can have a defined form, or it can have a surface pattern.

[0036] The resulting structure is also strong, light and contains only wood-based and biodegradable components.

[0037] The structures manufactured according to the present invention can be utilized in a wide variety of elements, particularly interior construction elements, such as building blocks, elements of horizontal and vertical grids, square tubes, slab structures, honeycomb structures, and shell structures in 3D shaped stuffed elements, particularly aimed for dry areas.

[0038] It is, however, possible also to add polymer coatings to the structures manufactured according to the present invention, thus making them suitable for use in wet- rooms or even for use outdoors.

[0039] Other alternative uses of the manufactured structures are packaging intended for cosmetics or medicaments.

[0040] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0041] Reference throughout this specification to one embodiment or an

embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases“in one embodiment” or“in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0042] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and examples of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0043] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In this description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc.

[0044] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0045] The following non-limiting example is intended merely to illustrate the advantages obtained with the embodiments of the present invention. EXAMPLE 1

[0046] The bending strength of various structures based on either prior art (such as common chip board, gypsum board and MDF) in similar, i.e. comparable, thicknesses, was analyzed, and the results are shown in Figure 2.

Industrial Applicability [0047] The present material can be used in forming building blocks, elements of horizontal and vertical grids, square tubes, slab structures, honeycomb structures, and shell structures in 3D shaped stuffed elements, and generally for replacement of conventional interior construction elements. [0048] In particular, the present material is useful in providing all-cellulose sheets and panels, and completely biodegradable interior construction elements.

Citation List

Patent Literature

JP 2012197544

US 20160194527

US 20170072670

Non-Patent Literature

J. Lehmonen et ah,“Effect of cellulose micro fibril (CMF) addition on strength properties of middle ply of board”, Cellulose 24 (2017) 1041-1055