Birch bark product obtained after a layering process and a granulation process

Abstract

Birch bark product obtained after a layering process comprising the steps: (a) providing a birch cane bark, preferably as flat-pressed birch cane bark; b) optional pre-sorting and / or pre-formatting of said birch bark; c) brushing off the predominantly white side of the birch bark; d) formatting the birch bark obtained after step c) to a uniform width and / or length, preferably in the range of 30 to 70 cm, more preferably in the range of 40 to 60 cm width, even more preferably to a width of 50 cm, in order to obtain one or more bark panels; e) optionally sorting the bark panels after step d) to obtain a randomised or a specifically selected slice pattern according to bark quality, bark thickness, colour and / or pattern; f) aligning and cutting the bark panels according to step d) or e) to obtain uniform layers of bark panels, preferably with a length of 140 to 160 cm and a width of 40 to 60 cm, more preferably with a length of 150 cm and a width of 50 cm; g) coating each layer of bark board according to step f) with an epoxy resin, preferably an epoxy resin with an open time of about 1 to 3 hours, preferably about 2 hours, preferably such a one-sided coating of each layer of bark board according to step f); h) followed by curing the bark panels according to step g) so that the Shore hardness of the epoxy resin is approximately equal to the Shore hardness of the bark panels, preferably both Shore hardnesses are in the range of 55 to 65 A, more preferably about 60 A, even more preferably 60 A; i) transferring the coated bark panels after steps g) and h) into a device for gluing and pressing layer by layer, preferably about 10 to 15 layers per gluing and pressing step, and wherein the device comprises a wood-based material board, preferably comprising a knot-free solid wood or a medium-density fiberboard (MDF); j) followed by pressing the bark panel layers according to step i) with a pressing pressure in the range of 270 to 290 bar, preferably 275 to 285 bar, more preferably about 280 bar, even more preferably 280 bar, calculated on an area of ​​150 cm length and 50 cm width; k) curing the pressed bark panels after step j) for at least 18 hours, preferably at least 24 hours, more preferably at least 48 hours, followed by opening the bonding and pressing device for a further build-up of layers of the pressed bark panels; I) Repeating steps a) to k) until a minimum number of 100 glued and pressed bark panels is obtained, preferably at least 120 glued and pressed bark panels, more preferably at least 140 glued and pressed bark panels, in order to obtain a bark block.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of materials engineering, in particular to birch bark products obtained from the production and processing of multilayer natural fiber composite materials. It relates to the provision of composite materials made of birch bark and curable resin systems, as well as to the semi-finished products produced therefrom, such as solid bark blocks, veneer sheets, handles, walls, surface materials, and components manufactured therefrom. The invention thus lies in the technical field of natural fiber materials, in particular to birch bark products obtained from the production of multilayer materials, as well as their use in furniture construction, interior design, and decorative surface applications, especially for wet areas in bathrooms, toilets, and on ships and boats, especially yachts.

[0002] Any reference to a manufacturing process in this disclosure serves to describe and characterize the obtained and claimed birch bark products by way of product-by-process claims only. No methods or manufacturing processes are expressly claimed per se or described herein solely for this purpose. BACKGROUND

[0003] Birch occupies a prominent position in the history of non-wood products.

[0004] Birch has been used worldwide for centuries, even beyond its wood. Its branches are still used today in Finnish saunas and as brooms, for example. Leaves and birch sap can be used to make teas, salads, birch wine, and birch sugar. The medicinal significance of birch should not be underestimated. The tea, in particular, is still considered an effective remedy against infections, fever, and other ailments.

[0005] Particularly noteworthy is the diverse uses of birch bark. Due to its special properties, it has historically been used as a writing material, a base for food preparation, a container for food storage, material for tent walls and canoes, as well as roof shingles, shoes, bags, and clothing. The bark could even serve as food in times of need. When processed, birch tar and birch pitch could be obtained, which were used as waterproofing and sealing agents, as well as tanning agents, dyes, firelighters, and leather preservatives.

[0006] An underlying problem of the present inventions is that over time, many natural products, including birch bark, have been replaced by synthetic materials. Plastics, in particular, have excelled in this process.

[0007] In addition to their ease of processing, they offered the possibility of shaping components as desired with little energy expenditure thanks to a low melting temperature and the ability to specifically influence their properties by adding additives. However, the use of plastics also has some disadvantages. For example, a large proportion of the material is made from petroleum and natural gas – both finite and CO2-intensive raw materials. Furthermore, while the material is theoretically highly recyclable, in practice only 9% of plastic waste worldwide is actually recycled. While approximately one-fifth of the waste is at least used for energy, half ends up in landfills, and a further 22% enters the environment uncontrolled. There, they are either openly burned or pollute land and water. In the wake of climate change, this issue is now particularly in the public spotlight.

[0008] Consumer awareness of environmentally friendly consumption behavior is increasing, and together with a new political direction, this is increasing pressure on the market to integrate sustainability into their business models. A look at the changes in product ranges and, above all, current marketing campaigns shows that this development is being taken seriously; many new companies even consider sustainability to be the core of their business model.

[0009] The latter is also impacting the plastics market. While plastics currently dominate the market for the production of molded parts and everyday objects, the trend is developing toward natural, renewable, and easily recyclable or compostable materials. The increased use of wood and wood-based materials is particularly emblematic of this. However, other natural products such as annual plants are also receiving increased attention.

[0010] The use of these materials brings the market a step closer to sustainability, but the processing of the material makes it difficult to establish an effective circular economy. To better influence the shape and properties of these natural materials, they are usually crushed and then bound with the addition of binding agents. This makes it difficult to later separate and return the material to the production cycle. Furthermore, industrial binding agents are not very environmentally friendly due to their formaldehyde content and are also harmful to health.

[0011] To overcome these disadvantages, the present inventors have obtained surprising birch bark products from layering and granulation processes for the production of birch bark products. Particularly noteworthy among the inventive products are veneers, panels, surface materials, handles, wall coverings, and, in particular, an innovative birch bark granulate.

[0012] One advantage of the innovative birch bark products is their inherent, natural adhesive, which, among other things, allows birch bark granules to be formed and provided as a solid composite by applying specially selected heat and pressure parameters and without the addition of an external binder. Thus, in one aspect, the invention offers a granulate base material that, in the long term, contributes to the replacement of binders and plastics with natural, sustainable, and recyclable materials.

[0013] There are approximately 35-60 birch species worldwide. These birch species are widespread throughout the globe, but only in the Northern Hemisphere. Birches have very low habitat requirements and are extremely hardy. Therefore, they are prime examples of pioneer tree species. Due to their hardiness, their distribution extends beyond the Arctic Circle, but a particularly high level of species diversity is found in the somewhat more temperate regions of East Asia.

[0014] Birches reach heights of 0.2 to 40 m. Their external appearance makes this species group one of the most striking among trees. The bark colors range from white to gray, dark brown, and pink to blood red. The most well-known, however, is the white color of birches, which is why they also got their name. The name "birch" is derived from the Indo-European word "bhereg," meaning "bright shimmering one." (

[13] , according to Laudert, 1998)

[0015] Particularly in Europe and northern Asia, the areas from which the birch bark used for this work is sourced, two birch species stand out as representatives of their species group: the silver birch (Betula pendula) and the downy birch (Betula pubescens).

[0016] With this background, within the scope of the invention, the silver birch (Betula pendula) and the downy birch (Betula pubescens) are particularly preferred starting materials for the preservation and provision of the birch cane bark.

[0017] The bark makes up approximately 6-22% of the trunk volume of a birch tree. Bark is defined as the tissue outside the secondary cambium. The secondary cambium is a narrow ring of living cells that is responsible for the (secondary) thickness growth of the tree. It releases xylem (the wood) on the inside and phloem (the bast) on the outside. The bast thus forms the innermost layer of the bark. It consists of living cells and is responsible for transporting the metabolic products of photosynthesis. However, it is not the outermost tissue of the tree. When the tree is young, another meristematic (dividing) tissue, the phellogen, also called cork cambium, differentiates from the bast cells. The phellogen begins to produce cells both outwards and inwards, similar to the secondary cambium. On the inside, it releases phelloderm, the cork skin.This is a living cell layer that separates the phellogen from the bast. It secretes phellem, better known as cork, on the outside. This then forms the outermost layer of the bark and thus the covering tissue. Phelloderm, phellogen, and phellem together are called periderm.

[0018] The use of birch bark has a long tradition, both as a raw material for handicrafts and for medicinal purposes.

[0019] Birch bark products made from a binder-free pressing of birch bark, in particular birch bark granules, into panels or other products are not pre-published in practice or in the literature as described herein. DESCRIPTION OF THE INVENTIONBirch bark starting material

[0020] To obtain the birch bark products according to the invention, the birch is harvested from the tree in a complex manual process without destroying the cambium – this layer is essential for the tree's continued growth. Harvesting the bark by hand is gentle and takes place without the use of heavy equipment that could compact the soil. This avoids skid trails and preserves the forest ecosystem.

[0021] Preferably up to 150 layers of birch bark form the basis for the surfaces according to the invention. Birch bark products / Product-by-Process / Birch bark granules

[0022] Given the context of the invention, each birch bark product is unique, with its own visual, chemical, and biological character.

[0023] The birch bark granulate according to the invention and birch bark granulate products obtained therefrom (such as boards) are characterized, for example, in that they remain adequately compressed without the addition of a binder and have advantageous material properties which are disclosed herein for the first time.

[0024] In one embodiment, the birch bark product according to the invention is a covering of a surface, e.g., a surface exposed to splash water on yacht interiors, bathroom cabinets, bathroom walls, toilet lids, washbasins, etc.

[0025] In one embodiment, the birch bark product according to the invention is a veneer. A veneer is a thin layer of wood that is cut from a tree trunk and then glued onto substrates such as chipboard, MDF, or multiplex boards as a decorative surface. The thickness of the veneer is preferably between 0.3 and 6 mm, more preferably between 0.7 and 2.5 mm; however, it is not limited thereto. The veneer according to the invention can be used, for example, for the surface of furniture, doors, walls, and floors, such as panels or parquet.

[0026] In one embodiment, the birch bark product according to the invention is a handle, for example a handle for doors, a handle for a shaving brush, a handle for a safety razor, a knife handle, a fork handle, a tool handle, a tap handle, a bicycle handlebar grip.

[0027] In one embodiment, the birch bark product according to the invention is a flooring material.

[0028] In one embodiment, the birch bark product according to the invention is a wall material.

[0029] In one embodiment, the birch bark product according to the invention is a wall panel. Technical advantages

[0030] Birch bark is a renewable, natural material that differs from conventional wood in several key properties and therefore offers particular advantages for a wide range of applications.

[0031] Unlike wood, birch bark exhibits pronounced resistance to moisture and humidity due to its natural function as the tree's protective layer. The material does not swell when it comes into contact with water, allowing for the production of dimensionally stable and durable products.

[0032] In addition, birch bark has a unique combination of mechanical and haptic properties compared to wood: on the one hand, it is velvety soft and offers a pleasant surface, and on the other hand, it can be deformed three-dimensionally without losing its structural integrity.

[0033] Through this combination of features, birch bark combines the advantageous properties of wood, stone and textiles in a natural, sustainable raw material and enables the production of components and surfaces with high functionality and design flexibility.

[0034] Surfaces made from Nordic birch bark exhibit a unique combination of functional and aesthetic properties that make them ideal for use in high-quality products. The material's characteristic natural color and texture lend it a visually appealing appearance with warm, wood-like tones, conveying a modern and sophisticated feel.

[0035] In addition to their visual appeal, the surfaces offer a high level of technical robustness. The natural surface structure of birch bark is resistant to mechanical stress, ensuring the surfaces retain their integrity even over long periods of use. A further advantage is that the material develops a uniform, aesthetically pleasing patina over time, further enhancing the appearance and providing exceptional longevity.

[0036] The combination of a dimensionally stable, resilient surface structure and an appearance that improves over time enables the use of birch bark surfaces in both highly functional and design-oriented application areas, thus creating an optimal balance between technical functionality and visual value.

[0037] A three-dimensionally deformable material made from birch bark has particular advantages in terms of its resistance to moisture and its anti-slip properties.

[0038] Due to its natural material structure, birch bark does not swell upon contact with water and retains its geometric shape and dimensional stability. This fundamentally distinguishes the material from conventional wood materials and makes it particularly suitable for use in environments with direct water exposure, such as bathrooms, spa areas, or yacht interiors.

[0039] The element that plays a crucial role in yacht interior design is water. Unlike wood, birch bark does not naturally swell upon contact with water; it quickly releases any absorbed moisture. The natural material also withstands salt water—and precisely these (salt) water-resistant qualities are also characteristic of the birch bark products described in this article.

[0040] Furthermore, the material's characteristic surface texture provides increased grip, effectively reducing slipping even on wet surfaces. This allows for applications that offer comparable or even better slip resistance than ceramic tiles.

[0041] The birch bark material according to the invention is non-slip, extremely easy to care for, and the oils contained in the bark with antimicrobial effects effectively prevent the formation of mold and the absorption of bacteria.

[0042] The combination of moisture resistance, dimensional stability, deformability and slip resistance opens up a wide range of possible applications in areas where both high optical requirements and special technical functionality are required.

[0043] The natural fibers contained in birch bark have a pronounced thermal insulation effect. This reduces heat loss and thus supports the creation of an energy-efficient and stable indoor climate. Furthermore, the material's even temperature distribution can contribute to a healthy indoor climate.

[0044] Furthermore, the material has antimicrobial properties, which reduce the growth of microorganisms on the surface. This increases hygiene safety, especially in damp rooms or other areas with increased microbiological contamination potential.

[0045] Additionally, the surface of birch bark has a pH value similar to that of human skin. This contributes to the material's skin compatibility and, combined with the velvety, warm feel of the surface, ensures a pleasant tactile sensation.

[0046] The combination of insulating effect, antimicrobial properties, skin-friendly pH value and pleasant feel opens up a wide range of application fields, particularly in interior design, furniture construction and in hygienically sensitive areas.

[0047] Consequently, the birch bark products according to the invention are particularly advantageously used where water, moisture, wind and / or the weather in general affect surfaces - such as in the furnishing and / or equipment of toilets, bathrooms, wet rooms, spas or on boats and ships, such as yachts.

[0048] In particular, the surface materials according to the invention are water-resistant directly from the manufacturing processes - without the need for surface coating.

[0049] The birch bark products of the invention are further characterized by being suitable for series production.

[0050] Birch bark is a renewable material and therefore meets the requirements of sustainability and environmental friendliness in the applications according to the invention.

[0051] The production and supply of birch bark surfaces takes place under ecological and resource-efficient conditions. The predominantly regional extraction and processing of raw materials within Germany minimizes overland transport routes, thus reducing emissions.

[0052] The material serves as an environmentally friendly alternative to plastic products, thus contributing to reducing the burden on marine ecosystems caused by plastic waste. Furthermore, the use of birch bark, as a renewable natural product, contributes to the preservation of natural forests, as it is a sustainable byproduct of timber harvesting and does not require additional tree felling.

[0053] Production is carried out according to high quality standards, which ensures long-lasting and environmentally friendly product use. EXAMPLESBirch bark granules

[0054] Selection of only suitable birch trees and pre-selection of suitable bark pieces. Bark pieces with the appropriate size, thickness, and visual surface quality (e.g., minimal unevenness) are selected. The bark pieces are stored under cover, preferably for two to four months. The selected pieces are then cut to the desired width and length, and any remaining adhesions / unevenness are removed, preferably manually.

[0055] The resulting birch bark is then optionally brushed.

[0056] This is followed by shredding the birch cane bark, preferably in two stages. In the first step, the birch cane bark is shredded using a single-shaft shredder, for example, at 90 rpm and with an 11 mm grate. The resulting material is then further mechanically broken down, for example, in a cutting mill. The cutting process preferably takes place at around 1500 rpm and with a sieve insert with a hole size of approximately 1 mm.

[0057] If the resulting material does not meet all the grain sizes required for the board production process due to excessive fineness, a certain portion of the birch bark material is additionally digested using a sieve insert of approximately 6 mm. This digestion preferably takes place at temperatures of approximately 31°C - 60°C. Sieve fractionation of birch bark granules

[0058] For the classification of the resulting granulate according to grain size, a vibrating screen is used. In this example, it is equipped with six screen inserts: 63 µm, 400 µm, 630 µm, 900 µm, 1000 µm and 2000 µm. This results in, for example, the

[0059] Table 1 shows the grain size classes of a birch bark granulate obtained according to the invention. Also shown are the quantities classified from the granulated material, broken down by quality and use of the cutting mill's screen insert. The resulting grain size distribution is also shown in Table 1, divided into purified and unpurified; this is to be understood as exemplary and not exhaustive. Table 1: Granules produced (in g) classified according to quality and sieve insert of the cutting mill Grain size (µm) <63 63 to <400 400 to <630 630 to <900 900 to <1000 1000 to <2000 ≥2000 cleaned Sieve insert 1mm 197,7 904,3 674,3 1051,5 74,1 355,0 0,2 Sieve insert 6 mm 26,0 125,1 81,3 136,9 39,4 970,7 1627,0 in total 223,7 1029,4 755,6 1188,4 113,5 1325,7 1627,2 uncleaned Sieve insert 1mm 194,3 1429,7 782,0 682,0 42,6 42,3 4,1 Sieve insert 6 mm 88,2 328,9 193,9 327,6 82,6 1768,8 2704,0 in total 282,5 1758,6 975,9 1009,6 125,2 1811,1 2708,1 microscopy

[0060] The particle shapes of the birch bark granules according to the invention resulting from comminution are shown as examples as purified and unpurified materials in the microscopic images of the Fig. 1 and Fig. 2. Only the 6 mm sieve used in the cutting mill was examined.

[0061] The Fig. 1 and Fig. 2 show that the particle shape is not round, but tends towards angular and elongated. Some selected particle sizes are shown in the Fig. 1 and Fig. 2. The Fig. 1 and Fig. 2 were taken with a Keyence microscope, type VHx500F.

[0062] Fig. 1: Micrographs of birch bark granules classes < 63 µm, 630-900 µm, > 2000 µm (from left to right), scale: 250 µm, 1000 µm, 1000 µm (from left to right), quality: cleaned.

[0063] Fig.2: Micrographs of birch bark granules classes < 63 µm, 630-900 µm, > 2000 µm (from left to right), scale: 250 µm, 250 µm, 1000 µm (from left to right), quality: uncleaned. Plates

[0064] To characterize the birch bark granulate according to the invention, several different grain size distributions were pressed into sheets and then technically characterized. A mixture in which the majority of the mass came from the medium grain sizes was to be used as a baseline. Based on this, two "boundary mixtures" were created, focusing on investigating the influence of the fines content on material strength. Therefore, the fines content was significantly increased for one mixture and completely omitted for the second.

[0065] The medium mixture was based on previously conducted studies. Pressing tests were conducted with a specific grain size distribution with the aim of developing an optimized manufacturing process for pressed boards made of birch bark granules. The grain size distribution used in these tests is shown in Table 2. Table 2: Grain size distribution of a medium mixture of birch bark granules Grain size (µm) <200 200 to <500 500 to <800 800 to <1000 1000 to <1250 1250 to <2000 ≥2000 Sieve (µm) Sieve bottom 200 500 800 1000 1250 2000 Mass fraction (%) 9,29 31,28 32,55 15,74 9,19 1,93 0 Screen pass rate (%) 0 9,29 40,57 73,12 88,86 98,05 99,98

[0066] This mixture is referred to below as the “Fraunhofer Ideal.” In order to benefit from the Fraunhofer’s findings on the manufacturing process of the panels, this mixture was to be reproduced. To obtain a comparable result, the distribution of the Fraunhofer Ideal was interpolated as follows: For each sieve insert used by the Fraunhofer, the quantity fraction not captured by the respective sieve (sieve pass) was calculated, and from this, a sieve characteristic curve was created, which is shown in Fig. 3. To replicate this distribution, the proportional sieve pass rates of the sieves used by Fraunhofer had to be embedded in this curve. For this purpose, the sieve pass rates of the sieves at the Zittau / Görlitz University of Applied Sciences (HSZG) were linearly interpolated starting from the next larger Fraunhofer sieve size, as shown in the following example: Sieve pass quantity 63 μm=63μm200μm∗9.29% (sieve pass quantity 200 μm) Sieve pass rate 63 μm=2.926%

[0067] This calculation was performed for all screen sizes of the HSZG. This resulted in the screen throughput rates shown in Table 3. Table 3: HSZG particle size distribution calculated from the Fraunhofer Ideal Grain size (µm) <63 63 to <400 400 to <630 630 to <900 900 to <1000 1000 to <2000 ≥2000 Sieve (µm) Sieve bottom 63 400 630 900 1000 2000 Screen pass rate (%) 0,00 2,93 32,46 57,58 79,97 88,86 99,98 Mass fraction (%) 2,93 29,53 25,13 22,39 8,89 11,12 0,00 rounded 3,00 30,00 25,00 22,00 9,00 11,00 0,00

[0068] In Fig. Figure 3 shows the interpolated points along with the sieve characteristic curve of the Fraunhofer Ideal. The newly calculated mixing ratio is referred to below as the "HSZG Ideal" (HSZG = Zittau / Görlitz University of Applied Sciences). To simplify weighing during the manufacturing process, the proportions were rounded to whole numbers. The resulting rounding error, as well as the rounding error of the Fraunhofer Ideal, were then corrected so that the total mass amounted to exactly 100%. The correction was placed in such a way that its influence on the distribution was minimal.

[0069] Fig.3: Fraunhofer Ideal sieve characteristic curve with interpolated sieve aperture for the HSZG sieve sizes.

[0070] From the calculated percentage grain size distribution, a mass distribution for the grain size classes could be calculated. The target production target was a board thickness of 4 mm. Since the Fraunhofer Institute used 100 g of granulate to produce a board thickness of 5 mm, 80 g (four-fifths of 100 g) were estimated for the production of a board with a thickness of 4 mm. Distributed across the grain size classes of the HSZG Ideal mixture, the mass distribution shown in Table 4 results, hereinafter referred to as "HSZG Ideal 4 mm." Table 4: Mass distribution HSZG Ideal 4 mm Grain size (µm) <63 63 to <400 400 to <630 630 to <900 900 to <1000 1000 to <2000 ≥2000 Mass (g) 2,4 24,0 20,0 17,6 7,2 8,8 0,0

[0071] 26.4 g of water (one-third of the granule mass) were added to this mixture. This was also done according to the Fraunhofer Institute's model.

[0072] Based on this mixture, the two boundary mixtures were then created. To shed light on the influence of fine material on the production and strength of the material, the proportion of fine material was significantly increased compared to the HSZG ideal for one boundary mixture and omitted for the other.

[0073] For the boundary mix with increased fines content, the proportion of the grain size class < 63 µm was increased to 30%. To deduct the 27% added for this from the other grain size classes, their percentage distribution (excluding the class < 63 µm) was determined, and the 27% was deducted proportionally according to this distribution. From now on, the mix will be called "GM with FA" (boundary mix with fines content).

[0074] A similar procedure was used to create the mixture without fines. Since the < 63 µm class only accounted for three percent of the Fraunhofer Ideal mixture, the 63 µm to < 400 µm class was also omitted to achieve clearer results. To compensate for this deficit, the proportion of the other grain size classes was increased following the procedure for the GM with FA mixture. However, since the resulting mixture was too strongly distributed in the center, the proportion of the 1000 µm to < 2000 µm class was subsequently increased to 25% following the same procedure. This resulted in the distribution shown in Table 5, which will be referred to below as "GM without FA" (boundary mixture without fines). Table 5: Mass fractions (in %) of the two boundary mixtures compared to the HSZG ideal Grain size (µm) <63 63 to <400 400 to <630 630 to <900 900 to <1000 1000 to <2000 ≥2000 HSZG Ideal 3,0 30,0 25,0 22,0 9,0 11,0 0,0 GM with FA 30,0 21,7 18,0 15,9 6,5 7,9 0,0 GM without FA 0,0 0,0 33,5 29,5 12,0 25,0 0,0

[0075] The limit mixes were also rounded to one decimal place and then corrected to a total of 100%. As with HSZG Ideal, the mixing ratios to achieve a 4-millimeter board thickness were applied to a granulate quantity of 80 g, with the added water amounting to 26.4 g.

[0076] In addition to these three standard mixtures, a small number of special mixtures were also produced. These were not intended for strength testing but rather served as a feasibility study. These mixtures are shown in Table 6. Table 6: Mass distribution (in g) of the manufactured special mixtures Grain size (µm) <63 63 to <400 400 to <630 630 to <900 900 to <1000 1000 to <2000 ≥2000 HSZG Ideal 5 mm unrounded 2,93 29,53 25,13 22,39 8,89 11,12 0,00 >2000 0 0 0 0 0 0 100 HSZG Ideal without 900 -1000 µm 4mm 2,4 24 20 24,8 0 8,8 0 >2000 4 mm 0 0 0 0 0 0 80 <63.4 mm 80 0 0 0 0 0 0

[0077] Finally, Table 7 shows how many panels were produced per mix and grade. The panels were distributed between the preliminary tests, which served to adjust the process parameters, and the main tests, from which the test specimens were subsequently produced. protocol

[0078] In the first step, the granules required for each mix to be produced were weighed and poured into a measuring jug. This was done starting with the largest grain size class and working downwards. Finally, the required amount of water was added. In the next step, the mixture was mixed thoroughly using an electric stirrer at the lowest speed. Due to the shape of the stirrer, the granules collected at the edge of the measuring jug after a while. This required manual loosening, after which the stirrer was turned on again.

[0079] After two manual loosenings, the mixture was removed from the stirrer and stirred 20 times by hand using a smaller mixing paddle. Thorough mixing ensured that the hydrophobic material bonded sufficiently with the water and that the particle size classes were evenly distributed. The material was then poured into a mold. This mold was first lined with release paper, and a temperature sensor was embedded through a hole in the side wall.

[0080] To achieve the most even distribution of the material, a top cap was attached to the mold. Since the pouring height of the material was higher than the mold rim, the top cap enabled loss-free and even pouring, especially in the edge areas. After pouring the granules, they were first stirred with a stirrer to compensate for any irregularities during pouring, and then the surface was smoothed with a brush.

[0081] Before removing the cap, the granules were pre-compacted manually using a wooden lid so that another release paper and the mold lid could then be placed on top.

[0082] Before the pressing process, the granulate residue was brushed off the edge of the mold, and spacers were placed between the lid and mold edges to maintain a constant distance during pressing and prevent measurement inaccuracies in the press. The spacers consisted of four parts: a 4 mm thick spacer bar and three thin spacer strips, each 0.1 mm thick, resulting in a total thickness of 4.3 mm. Both spacer bars were measured at regular intervals at 10 points each using a caliper. To simulate the thickness during the pressing process, the layers were compressed as tightly as possible using the caliper. This resulted in average thicknesses of 4.323 mm and 4.308 mm.

[0083] Since the tool was designed so that the gap between the lid and the mold edge reflects the pressing thickness, the resulting sheets had a thickness of 4.3 mm. This ensured that the sheets maintained the thickness of 4 ± 0.2 mm required by the standard for the test specimens produced later, even after the shrinkage process.

[0084] A hot press from Siempelkamp was used for the pressing process.

[0085] The upper and lower platens of the press were each preheated to 90°C and maintained at this temperature throughout the pressing process. The pressing pressure was also kept constant; in this case, 35 bar was set. However, this value does not reflect the pressure applied to the workpiece being pressed, as it is a system setting and not a value measured on the object. Furthermore, not all of the pressure acted on the birch bark granulate, but was presumably largely absorbed by the spacer bars used. In three preliminary tests without spacer bars, the press only required an average of 8–11 bar to achieve a plate thickness of 4–5 mm. This would correspond to a specific pressure of approximately 100–140 bar, related to the plate size. After placing the cold mold in the press, the aforementioned settings (90°C, 35 bar) were maintained for a pressing time of 20 minutes, of which 135 seconds were spent on the closing process.The closing time of 135 seconds was chosen to ensure a gentle closing process for both the tool and the material. To achieve this, the press was set so that the (movable) upper platen slowed down a few millimeters before touching the tool cover. Thus, only approximately 60 seconds of the 135 seconds were spent on the actual compaction process (from touching the cover to moving onto the spacers).

[0086] After the pressing time had elapsed, the press tool and spacer were removed from the hot press and placed in a Rucks cold press for 10 minutes to cool. There, too, a system pressure of 35 bar was set and maintained throughout the entire cooling phase.

[0087] At the end of the cooling phase, the mold was removed from the cold press and the sheet inside was demolded. This was possible thanks to the release paper inserted into the mold, eliminating the need for the threaded holes and screws provided for opening the mold. After initial measurement data were recorded, the sheets were placed in a drying rack to dry. The finished sheets had a length and width of 150 mm, corresponding to their shape. The rounded corners had a radius of 10 mm. Test specimen

[0088] The test specimens were cut from the previously described and obtained birch granulate panels using a CO2 laser cutter. This allowed cutting without the need to fix the panels or rework the test specimens. The laser cutter's narrow kerf allowed for a close distribution of the test specimens on the panels. Two tensile, four flexural, and seven compression test specimens were produced for each panel. To later identify the effects of the test specimen position within the panel on the strength properties, the test specimens were numbered and these numbers were transferred to the panels using a template.

[0089] The molds were distributed so that a minimum distance of 5 mm was maintained both from the edge and between the contours. Furthermore, the temperature sensor channel protruding from the lower edge into the plate (between compression test specimen 7 and flexure test specimen 3) was generously recessed. To compensate for the material loss caused by the laser cutter's kerf, all test specimens in the drawing were enlarged by 0.15 mm, deviating from the standard specifications.

[0090] For the cutting process, the laser was operated at a laser frequency of 19,500 Hz, a laser power of 60%, and a minimum laser power of 58%. The processing speed was 30 mm / s. After the cutting process, the test specimens were demolded and packaged.

[0091] A total of 554 test specimens were produced, including 86 tensile test specimens, 296 compression test specimens and 172 flexural test specimens.

[0092] Table 8 shows the number of test specimens produced per configuration. No test specimens were produced from the preliminary test panels or from special compound panels, which is why they are not included in the table. For simplification, also for the later part of this work, the individual configurations were reindexed as follows: HSZG Ideal 4 mm = HI; GM with FA 4 mm = GmF; GM without FA 4 mm = GoF.

[0093] The distinction between purified and unpurified mixtures is made by a hyphenated g (purified) or u (unpurified). Table 8: Manufactured test specimens per configuration with specifications configuration HI-g HI-u GmF-g GmF-u GoF-g GoF-u Train 14 14 14 14 14 14 Pressure 46 47 49 49 49 49 bend 28 28 28 28 28 28 Test specimen type 1B I3 Total length ≥ 150 I1 Length of the narrow parallel part 60,0 ± 0,5 r radius 60 ± 0,5 I2 Distance between the wide parallel sides 108 ± 1,6 b2 Width at the ends 20,0 ± 0,2 b1 Width of the narrow part 10,0 ± 0,2 h Preferred thickness 4,0 ± 0,2 L0 Gauge length (preferred) Gauge length (permitted upon request for quality control or if specified) 50,0 ± 0,5 L Initial distance between terminals 115 ± 1 FIGURE 5: Technical drawing and dimensions of the tensile test specimen 1B used

[0094] Before, during, and after the pressing process, various data and images were recorded for process monitoring. The procedure for documenting the process parameters is explained below.

[0095] The following were documented: temperature, plate thickness, side lengths, weight, condition during demolding and plate appearance, moisture content of the granulate and the plates.

[0096] The temperature was measured during the pressing process in the hot press using a temperature sensor and displayed as a temperature curve in the internal actual value window of the press software. The sensor was embedded in the granulate so that it protruded 55 mm into the sheet at a right angle from the bottom. The tip, and thus the measurement point, was positioned so that it was approximately in the middle of the sheet thickness. The temperature was no longer measured during the cooling phase.

[0097] Weight measurements were taken at various times. Before pressing, the mass of the granulate mixture in the closed press tool was measured. For this purpose, the filled press tool, including the temperature sensor, was placed on the scale, and the weight of the tool, temperature sensor, and release paper was subtracted.

[0098] Next, the sheet was weighed immediately after the cooling process. Instead of weighing the entire mold, each sheet was demolded and, after labeling, placed individually on the scale.

[0099] Subsequently, the panels were weighed once during each visit to the pilot plant to monitor the drying process. For some panels, drying data was also recorded over several days as an example. The panels were weighed at regular intervals depending on their degree of dryness. On the day of production, measurements were taken every 15 minutes, the following day every hour, and on the third day every two hours. Since the pilot plant was available a maximum of three days a week, longer, continuous monitoring was not feasible. To prevent interference from the moisture release of other panels, the panels to be measured were stored separately during the recording period.

[0100] The mass was measured in grams with an accuracy of one decimal place.

[0101] The side lengths, like the mass, were measured once during each visit to the technical center, but not on the day the panels were manufactured, as the mold dimensions provided a starting value. Exceptions to this were a few sample panels, whose side lengths were recorded over several days in parallel with the weight measurements. The time intervals were the same as for the weight measurements.

[0102] The upper and right side lengths were measured using a caliper to an accuracy of 0.01 mm.

[0103] Nine regularly spaced measuring points were created to measure the panel thickness. The points were recorded using a template after demolding the pressed panels and measured for the first time after the panels were weighed. Thereafter, measurements were taken once on each test day.

[0104] The measurement was performed using a mechanical thickness gauge with hemispherical measuring probes. The thickness was rounded to an accuracy of 0.1 mm according to standard rounding rules, as the thickness gauge did not have a scale in the hundredths of a millimeter range. The thickness measurement after reaching equilibrium moisture content in the physics laboratory was performed using an electronic thickness gauge with an accuracy of 0.001 mm.

[0105] During demolding, the board's condition was documented using two criteria: temperature, humidity, and appearance. The condition was not measured, but rather qualitatively estimated. It was classified into "cold" (room temperature to slightly elevated) and "warm" (noticeably elevated board temperature), as well as "moist" (slightly noticeable surface moisture) and "wet" (very noticeable surface moisture). Visual documentation was done using photographs. Photos were taken after demolding, following labeling and the initial measurements, and the boards were also photographed in their dry state. The front and back sides were photographed. A visual assessment was also carried out in the dry state to determine suitability for test specimen production. The examination included board warpage and visible damage (cracks, chipping, etc.). Moisture measurement of the birch granulate boards

[0106] In order to determine the equilibrium moisture content of the manufactured birch granulate boards in a controlled climate, the moisture content of the main test boards was measured.

[0107] The measurement was conducted in the HFT physics laboratory, as the room is climate-controlled. A piece of pressed bark granulate weighing approximately 4 g was taken from the cutting residues of each plate from the same location. The plate residues had already been stored in the laboratory for several weeks at this time and had therefore reached their equilibrium moisture content. The climate prevailing at the start of the test was documented, and the removed plate pieces were then weighed. A Mettler Toledo scale, model XA503S, was used. After weighing, the plate pieces were placed in a drying oven (Memmert GmbH + Co.KG, model 500). There they were dried for approximately 3 days at 105°C. After the drying time, the samples were weighed again. Microscopy images

[0108] Microscopic images were taken of the fracture points in the strength tests and of the plate surfaces, which vary due to different grain size distributions. A digital microscope camera from dnt, specifically the DigiMicro 2.0 Scale model, was used for this purpose. The test setup can be seen in [Error! Reference source could not be found]. Two specimens were selected from the fracture images for each grain size and quality configuration, and both sides of the fracture were photographed. For many test specimens, it was necessary to cut them by hand because, although the specimens had a fracture point, they still held together. This was especially true for the pressure hulls.

[0109] For the plate surfaces, only one plate of each grain size and quality configuration was photographed. Strength testsGeneral

[0110] Before the strength tests, the test specimens were left in open bags at a standard climate (20°C, 60% relative humidity) for at least 5 days. This ensured that equilibrium moisture content was reached. The tests took place from April 24 to 27, 2023. Table 9 shows the tests conducted on the respective days, including the numbers of the tested panels and the climate conditions prevailing at the start of the test. Table 9: Overview of test times and test conditions Date time tested property tested plates climate T in °C rel. running temperature in % 24.04.2023 14:04 Tensile strength H3 - H24 22,6 63,7 25.04.2023 09:54 Tensile strength H27 - H45 23,7 61,9 15:15 Flexural strength H3 - H24 23,3 63,8 26.04.2023 09:42 Flexural strength H27 - H45 22,4 63,2 27.04.2023 09:57 Compressive strength H3 - H45 21,7 62,8

[0111] All test specimens were tested using the "inspekt 10" universal testing machine from Hegewald and Peschke. The various fixtures required for the specific tests were installed on the machine as required. The "LabMaster" software, also distributed by Hegewald and Peschke, was used as the recording program.

[0112] The dimensional accuracy of all test specimens was checked using a Mitutoyo caliper (Absolute Digimatic model).

[0113] Table 10 shows the specimens tested per configuration. Table 10: Number of tested specimens per configuration configuration HI-g HI-u GmF-g GmF-u GoF-g GoF-u Train 8 14 14 12 10 12 Pressure 11 14 14 14 14 14 bend 14 14 14 14 14 15 ImplementationTrain

[0114] A total of 72 tensile test specimens were tested. The testing process was conducted according to DIN EN ISO 527-2:2012-06

[52] . The test specimens were based on specimen type 1B in terms of shape and dimensions. A technical drawing of the tensile test specimens can be found in the appendix (Error! Reference source could not be found.)

[0115] Before each test procedure, the respective test specimen was checked for its suitability for testing. This included checking its dimensional and shape accuracy. To determine dimensional accuracy, the thickness and width of the test specimen were measured at three evenly distributed points as far apart as possible within the center 50 mm of the test specimen. An arithmetic mean was calculated from these three values. Test specimens whose mean values ​​were outside the standard specifications were rejected. Shape accuracy was visually inspected. Test specimens with damaged edges or uneven surfaces were rejected. Some test specimens had laser cutting residue on their edges. These were carefully trimmed off with a knife to ensure smooth edges.

[0116] After testing, the test specimens were clamped into the testing machine. The distance between the clamping jaws was 108 mm, in accordance with the standard.

[0117] The specimens were clamped with the front side facing forward and the top side facing upward. During clamping, care was taken to position the specimen centrally and vertically in the fixture. The test process then began. The strain was measured using a camera and two adhesive strips applied to the specimen. The test speed of the testing machine was set to 1 mm / s. The test was terminated as soon as the software considered one of the following two criteria to be met: force ≥ 9.9 kN, force drop ≥ 40%.

[0118] The following data were collected during the test: Young's modulus (E(b), maximum force (Fmax), tensile strength (Rm), total longitudinal strain at Fmax (eps L Fmax), total transverse strain at Fmax (eps_Q_Fmax), manual elongation at break (A*), Rp0.2 yield strength (Rp0.2), travel (s). Pressure

[0119] 81 compression tests were conducted. The process parameters were based on DIN EN ISO 604

[53] . The test specimen used was Type B. This was a cuboid with dimensions of 10 ± 0.2 mm x 10 ± 0.2 mm x 4 ± 0.2 mm. Only two of the seven available test specimens were to be tested per plate. These were randomly selected.

[0120] Before testing, the test specimens were checked for dimensional and shape accuracy. To determine dimensional accuracy, the length, width, and thickness were simply measured. Any deviation from the standard specifications was discarded. Shape accuracy was visually inspected. Test specimens with uneven edges and / or surface irregularities were rejected. Any excess material on the edges was carefully removed with a knife.

[0121] The test specimen was then placed in the test system. This can be seen in Error! Reference source could not be found. To maintain the position of the test specimen on the compression plate, a slider was used, which, with the aid of stops, positioned it precisely in the center. As with the tensile test, the test specimen was positioned with the top side facing up and the front side facing forward.

[0122] The test was then started. The test speed was 1 mm / s. The test was terminated when one of the following three termination criteria was met: traveled distance ≥ 5 mm, compression ≥ 50%, force drop ≥ 30%.

[0123] The following data were recorded during the test: Young's modulus (E(b), maximum global force (Fmax), compressive strength (Rm), displacement at Fmax (s), force at 1mm displacement (F[1mm]), force at 2mm displacement (F[2mm]), force at 3mm displacement (F[3mm]), compression (eps St), displacement at end of test (End). bend

[0124] A total of 87 flexural strength tests were conducted. The standard applied for the process was DIN EN ISO 178

[54] . The test specimen had a cuboid shape with dimensions of 80 ± 2 mm x 10 ± 0.2 mm x 4 ± 0.2 mm. To maintain uniformity throughout the process, flexural test specimens numbered 2 and 3 were selected from the four available for each plate (for the indexing of the test specimen numbers, see "Error! Reference source could not be found.").

[0125] Before testing, the test specimens were checked for dimensional and shape accuracy. To verify dimensional accuracy, the width and thickness were measured in the center of the test specimen. If at least one of these values ​​deviated from the standard specification, the test specimen was rejected. Shape accuracy was visually inspected. Test specimens with uneven edges and / or uneven surfaces were rejected. Any excess material on the edges was carefully removed with a knife.

[0126] After inspection, the test specimen was placed on the bending jig, ensuring it was centered and straight. Each specimen was placed with the front facing up and the top facing left. A 3-point bending test was performed.

[0127] The radius of the compression fin and the supports was 5 mm, in accordance with the standard, and the distance between the supports was 64 mm. The test speed was 2 mm / s. The test ended when one of the following three criteria was met: traveled distance ≥ 10 mm, force ≥ 9.9 kN, force drop ≥ 30%.

[0128] The following data were recorded during the test: Young's modulus (E(b), maximum global force (Fmax), flexural strength (Rm), max. strain (strain fm), deflection fm (fm), displacement (w), force at 1mm displacement (F[1mm]), force at 2mm displacement (F[2mm]), force at 3mm displacement (F[3mm]), section modulus (W). Results, test evaluation of birch bark granulate and preserved plates thereof

[0129] The following parameters were evaluated: • Moisture of the birch bark granules • Temperature measured in the granulate / plate during the pressing process • Demoulding behaviour and condition during demoulding • Drying behavior (during and after pressing), including the associated dimensional change • Appearance of the dried plates • tested strengths (tensile, compressive, bending)

[0130] All parameters examined should be considered in their entirety, but in particular the differences between a) the two different granulate qualities (cleaned / uncleaned) b) the three different granulate mixtures (HSZG Ideal 4 mm, boundary mixture with fines 4 mm, boundary mixture without fines 4 mm) be brought into focus.

[0131] The following indexing is used (Table 11): Table 11: Indexing of the different mixtures and qualities HSZGmm Ideal 4 Border mixture with fine content 4mm Border mixture without fines 4mm both qualities cleaned / high quality HI HI-g GmF GmF-g GoF GoF-g uncleaned / low quality HI-u GmF-u GoF-u Granule moisture

[0132] Table 12 shows the results of the moisture measurements of the birch bark granules. Table 12: Granule moisture content according to grain size class and quality (abbreviations: x̅ - arithmetic mean) Grain size (µm) <63 63 to <400 400 to <630 630 to <900 900 to <1000 1000 to <2000 >=2000 x̅ low quality 2,89 2,67 2,73 2,77 2,65 3,00 2,83 2,79 high quality 2,40 2,59 2,41 2,43 2,48 2,63 2,65 2,51

[0133] The measured granule moisture levels ranged between 2.40 and 3.0%. This is significantly lower than the values ​​determined by Suryawanshi for Himalayan birch cork. However, Suryawanshi's measurements were taken on unprocessed cork. Therefore, the discrepancy could possibly be explained by water loss due to the heat generated during the milling process.

[0134] Although the moisture content of the low-quality granules is systematically somewhat higher than that of the high-quality granules, no significant difference can be observed between the two qualities or between the grain size classes. Temperature in the granules

[0135] During the pressing process, the following process variables were monitored: pressure, time, temperature of the heating plates, pressing distance and temperature in the granulate.

[0136] Since time, pressing distance, pressing pressure and the heating plates were adjusted so that they remained constant regardless of the material in the press, the temperature measured in the granulate will be the focus of the following.

[0137] The temperature shows a clear curve. This depends significantly on the pressure exerted on the granules. The curve begins at room temperature, as the mold and granules were placed in the press without preheating, and initially rises only slowly. With the onset of compression (from approximately 60 s), the temperature rose sharply in parallel, reaching approximately 90°C within the next 200 s. As the compression progressed, only a slow rise in the curve can be observed. Towards the end, the temperature was just under 100°C. This curve is representative of all produced boards. Nevertheless, slight differences were observed. Many of the boards reached their maximum temperature early in the process and then remained constant there until the end. Slight, but not significant, differences in the steepness of the temperature rise when the press closed were also observed.

[0138] The arithmetic mean of the measured temperature of all plates was 90.01°C. This value includes the warm-up phase and is therefore systematically lower than the actual temperature in the plates. Excluding the first third of the pressing phase, the average pressing temperature during the hot phase is 99.06°C. The minimum measured temperature during the hot phase was 83.70°C, and the maximum 119.00°C, resulting in a fluctuation of 35.30°C. On average, the manufacturing process fluctuated within a range of only 10°C. Fig. Figure 4 shows the arithmetic mean of some temperature parameters broken down into the three main mixtures HI, GmF and GoF.

[0139] Fig. 4: Arithmetic mean values ​​of various temperature parameters broken down by grain size mixture.

[0140] As already mentioned, the temperature during the warm-up phase is systematically lower than that during the hot phase (excluding the first third (400 s) of the pressing phase). For both values, no significant differences can be observed between HI, GmF, and GoF. The same applies to the average maximum and minimum measured temperatures. For this value, the maximum measured temperatures of the hot phase of each plate were determined, and then an arithmetic mean was calculated for each mixture from the values ​​of the corresponding plates. Here, too, no significant differences can be observed.

[0141] The evaluation of the differences between the two qualities (uncleaned / cleaned) looks similar.

[0142] No significant differences were observed between the qualities. However, it is noticeable that the parameters of the low-quality plates are systematically higher than those of the high-quality plates. This may be explained by the slightly higher temperature of the lower heating plate in these plates. Although the plate was mechanically set to 90°C, a software error caused the heating plate to regularly reach higher temperatures than the 90°C. Therefore, it had to be maintained at 90°C by manually switching it on and off, resulting in a slightly different average temperature.

[0143] Interestingly, the temperature inside the plate was systematically higher than the 90°C set on the press. The sharp and rapid rise in temperature during compression of the granules indicates that both the temperature rise and the increased temperature are pressure-induced. Although the mold had three holes in the bottom, inserting the base plate and pressing it firmly against the bottom of the mold, as well as pressing the mold against the press plate, created a nearly pressure-tight container from which only a small amount of the water and possibly steam contained in the granules escaped. The high pressure could therefore have caused a slightly higher temperature than that of the heating plates due to internal friction processes and compression of the water and granules. Demolding

[0144] Immediately after demoulding the panels, their haptic moisture and warmth as well as their appearance were determined.

[0145] The boards demolded well thanks to the paper inserted. However, it was evident at the edges of the boards that the granulate would likely have baked onto the metal without the paper. The temperature of the boards during demolding varied. Many of the boards had already cooled down to room temperature. Many were slightly warm, and a few were warm. All of the boards were noticeably moist, and some were classified as wet. The properties "warm" and "wet" usually occurred together. They occurred more frequently after the base on which the mold was placed on the jerk press (for cooling) was changed. The previous base had many indentations and slight bumps, while the new one was a smooth steel sheet. This presumably achieved a new level of pressure resistance, which made it difficult for water to escape and kept the temperature at a high level.This would support the theory of high temperatures during the hot pressing process. Drying process

[0146] The drying process of the boards to equilibrium moisture content took place in three steps. In the first step, the boards lost some of the water added to the granulate mixture during the pressing process. The boards were then placed in the Hainsberg pilot plant and dried completely.

[0147] However, since there was no controlled climate on site, the panels were finally taken to the physics laboratory, where they reached their equilibrium moisture content in a measurable climate.

[0148] In the course of the evaluation, attention should be paid to the following parameters: water loss during the pressing process, drying time of the boards in the pilot plant, final weight, shrinkage of the board dimensions, board thickness and equilibrium moisture content of the boards.

[0149] As already mentioned, the mold turned out to be relatively dense. This also meant that only a small portion of the water added to the granules evaporated during pressing. On average, 5.97 g were lost during the press (including the cooling phase), although there was a fairly large variation, ranging from a minimum of 3.7 g to a maximum of 8.2 g.

[0150] Although a difference of one gram in the mean values ​​can be seen between the two grades, the high standard deviation of approximately one gram in each case suggests that this difference is not particularly significant. The differences between the three blends, GmF, HI, and GoF, are more interesting. However, these are likely due to the manufacturing process rather than directly to the material properties.

[0151] As already described above, the base plate of the cooling press (Rucks) was replaced during the manufacturing process, which led to a higher density of the mold due to the smoother surface. This also appears to be reflected in the water loss. All of the plates pressed before the replacement belonged to the HI mixture, which is why they possibly lost more water than the plates of the other mixtures. Furthermore, it was found that the granulate without fines (GoF) absorbed the added water less well during mixing than the mixtures with fines. Thus, more water remained on the wall of the mixing cup, resulting in a water loss of approximately 1 g. This could be the reason for the lower water loss during pressing.Nevertheless, it is difficult to draw any conclusive conclusions from the data, since the water loss also depended significantly on the surface of the press plate and the tightness of the hole drilled for the temperature sensor.

[0152] After pressing, the boards were placed in drying racks. Since the drying process was closely monitored for only a few of the boards, only exemplary statements can be made regarding the drying time. Comparisons between the blends and qualities are not possible.

[0153] It is apparent that the drying process followed the usual hyperbolic shape of most materials. Initially, the board lost moisture rapidly due to the high humidity gradient between the board and the ambient air, particularly in the first three days. This was noticeable both in the weight and the side lengths of the board. As the humidity gradient decreased, a significant reduction in the drying rate was evident. The drying process took a total of 23 days. Interestingly, the two sides S1 and S2 approached the same length again, despite a relatively large difference in the drying process during the first few days. This phenomenon was observed frequently.The drying process shown here is reflected in other panels, especially in the first few days; the time until complete drying, especially for the last few percent of escaping water, showed considerable differences, probably due to changing conditions. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited non-patent literature

[0000] Bright-shimmering ones.” (

[13] , according to Laudert, 1998

[0014]

Claims

[1] Birch bark product obtained by a layering process comprising the steps: (a) providing a birch cane bark, preferably as flat-pressed birch cane bark; b) optional pre-sorting and / or pre-formatting of said birch bark; c) brushing off the predominantly white side of the birch bark; d) formatting the birch bark obtained after step c) to a uniform width and / or length, preferably in the range of 30 to 70 cm, more preferably in the range of 40 to 60 cm width, even more preferably to a width of 50 cm, in order to obtain one or more bark panels; e) optionally sorting the bark panels after step d) to obtain a randomised or a specifically selected slice pattern according to bark quality, bark thickness, colour and / or pattern; f) aligning and cutting the bark panels according to step d) or e) to obtain uniform layers of bark panels, preferably with a length of 140 to 160 cm and a width of 40 to 60 cm, more preferably with a length of 150 cm and a width of 50 cm; g) coating each layer of bark board according to step f) with an epoxy resin, preferably an epoxy resin with an open time of about 1 to 3 hours, preferably about 2 hours, preferably such a one-sided coating of each layer of bark board according to step f); h) followed by curing the bark panels according to step g) so that the Shore hardness of the epoxy resin is approximately equal to the Shore hardness of the bark panels, preferably both Shore hardnesses are in the range of 55 to 65 A, more preferably about 60 A, even more preferably 60 A; i) transferring the coated bark panels after steps g) and h) into a device for gluing and pressing layer by layer, preferably about 10 to 15 layers per gluing and pressing step, and wherein the device comprises a wood-based material board, preferably comprising a knot-free solid wood or a medium-density fiberboard (MDF); j) followed by pressing the bark panel layers according to step i) with a pressing pressure in the range of 270 to 290 bar, preferably 275 to 285 bar, more preferably about 280 bar, even more preferably 280 bar, calculated on an area of ​​150 cm length and 50 cm width; k) curing the pressed bark panels after step j) for at least 18 hours, preferably at least 24 hours, more preferably at least 48 hours, followed by opening the bonding and pressing device for a further build-up of layers of the pressed bark panels; I) Repeating steps a) to k) until a minimum number of 100 glued and pressed bark panels is obtained, preferably at least 120 glued and pressed bark panels, more preferably at least 140 glued and pressed bark panels, in order to obtain a bark block. [2] Birch bark product obtained by a layering process according to claim 1, further comprising the steps: m) applying an MDF board as a covering layer of the bark block obtained after step I); n) cutting the bark block smooth at the front after step m); o) applying reinforcement to the smoothly cut end faces of the bark block after step n); p) applying an MDF board to the reinforcement according to step o). [3] Birch bark product obtained by a layering process according to claim 1 or 2, wherein the birch bark has dimensions in the range of approximately 50 x 40 to 180 x 50 cm, preferably dimensions in the range of 50 x 40 to 180 x 50 cm. [4] Birch bark product obtained by a layering process according to one of claims 1 to 3, wherein the brushing according to step c) is carried out by means of a braided brush and / or by means of a mechanical cleaning process. [5] Birch bark product obtained by a layering process according to one of claims 1 to 4, wherein the epoxy resin is colored with a brown color paste according to step g). [6] Birch bark product obtained by a layering process according to one of claims 1 to 5, wherein birch bark dust is added to the epoxy resin according to step g) as a thixotropic agent with a grain size of ≤ 80 µm and / or to influence the coloring of the bark panels. [7] Birch bark product obtained by a layering process according to one of claims 1 to 6, wherein optionally, before step h), unevennesses in the bark panels are additionally filled with a suitable resin. [8] Birch bark product obtained by the layering process according to one of claims 1 to 7, wherein the birch bark product is a starting material for a group of products consisting of a floor covering, a panel, a veneer, a wall, a wall covering, and a handle. [9] Handle obtained by the layering method according to one of claims 1 to 7, the layering method further comprising the steps of: q) planing and optionally calibrating a handle blank from the bark block obtained according to claim 1 or 2; r) machining the handle blank obtained after step q); s) inserting a wooden or aluminum core into the handle blank, preferably into a milled opening in the handle blank; t) final surface treatment of the handle blank obtained after step s). [10] Veneer obtained by the layering process according to one of claims 1 to 7, wherein the layering process further comprises the steps: u) planing a long side of the bark block obtained according to claim 2; v) attaching the bark block according to step q) to a vacuum fastening device; w) slicing the bark block according to step r) to a veneer thickness between 0.7 and 2.5 mm; x) final surface treatment of the veneer obtained after step w) by lamination and / or trimming and / or filling of defects and / or surface sanding, preferably with a grain size of 120, and / or application of a surface care solution of hard oil, optionally combined with bleaching and / or staining and / or coloring of the hard oil. [11] Birch bark granules are obtained by a process comprising the following steps: i. Providing a birch cane bark, preferably as flat-pressed birch cane bark; ii. optional pre-sorting and / or pre-formatting of said birch bark; iii. optional brushing of the predominantly white side of the birch bark; iv. Comminution of the birch cane bark, preferably in two stages, wherein in a first step the birch cane bark is preferably comminuted by means of a single-shaft comminutor at approximately 70 to 100 rpm, more preferably 90 rpm, and with an 8 to 13 mm grate, more preferably an 11 mm grate, followed by further mechanical disruption, preferably by means of a cutting mill, more preferably at approximately 1100 to 1800 rpm, more preferably 1400 to 1600 rpm, even more preferably at 1500 rpm and with a sieve insert of 0.7 to 1.5 mm, more preferably 0.9 to 1.2 mm, even more preferably 1 mm hole size, and wherein the disruption takes place at a temperature of 22 to 80 °C, preferably 30 to 70 °C, more preferably 31 °C to 60 °C; v. optionally, the birch cane bark is additionally digested with a sieve insert of 4 to 8 mm, preferably 5 to 6 mm, even more preferably with a 6 mm sieve insert, and the digestion is carried out at a temperature of 22 to 80 °C, preferably 30 to 70 °C, more preferably 31 °C to 60 °C; vi. sieving the crushed and broken down birch bark granules to classify them according to grain size, preferably using a vibrating machine, more preferably said vibrating machine is provided with six sieve inserts: 63 µm, 400 µm, 630 µm, 900 µm, 1000 µm and 2000 µm; vii. optionally followed by purification of the birch bark granules obtained according to steps v. or vi. [12] Birch bark granules obtained by the manufacturing process according to claim 11, wherein the granule moisture is in the range of 2.40 to 3.0%. [13] Birch bark plate obtained from birch bark granules according to steps i. to vii. according to claim 11, further comprising the steps: viii. pressing the resulting birch bark granulate according to claim 1 in a suitable pressing device at a temperature in the range of 80 to 100 °C, preferably 85 to 95 °C, more preferably at 90 °C, with a specific pressure calculated on the birch bark plate size in the range of 90 to 160 bar, preferably in the range of 100 to 140 bar, for a suitable pressing time, preferably a pressing time of at least 100 s, preferably at least 120 s, more preferably at least 135 s, most preferably for 135 s; ix. followed by cooling the birch bark granulate plates for a period of at least 5 minutes, preferably at least 7 minutes, even more preferably at least 10 minutes, at a suitable pressure, e.g. in a cold press, in the range of 20 to 40 bar, preferably 25 to 35 bar, even more preferably at 35 bar.

Images