Plywood and wooden nail

Abstract

The present invention relates to a plywood (1) comprising at least three wood layers (2) disposed one on top of the other and joined to one another by means of a glue, in particular a water-resistant glue, characterized in that the glue comprises a bio-based resin, a curing agent and an additive, or consists of these components, and the additive preferably comprises or consists of high-molecular-weight aromatic substances which occur in nature or are technically produced and which have oxidized side groups.

Description

[0001] DESCRIPTION

[0002] Layered wood and wooden nail

[0003] The present invention relates to a laminated wood comprising at least three layers of wood arranged one above the other and bonded together with a particularly waterproof glue. Furthermore, the present invention relates to a wooden nail made from laminated wood.

[0004] Laminated wood is a wood-based material consisting of at least three layers of veneers or boards glued together. The grain directions of the individual layers can either be parallel to the grain, in which case it is referred to as laminated wood, or the grain directions can alternate by 90° from layer to layer, in which case it is referred to as plywood. Laminated wood is glued together under pressure, either at room temperature or at elevated temperatures. The pressure can be such that the individual layers of wood are pressed tightly together during gluing but not compressed. Alternatively, the individual layers of wood can be compressed under high pressure and heat during gluing. In this case, the wood layers can be impregnated with the resins if necessary. The highest levels of strength, chemical resistance, and swelling are achieved when veneers are compressed and glued with waterproof glues, such as:Melamine-formaldehyde resins (MF resins) or phenol-formaldehyde resins (PF resins) at high temperatures above 100 °C and high pressures, usually above 10 N / mm. 2 These materials are also referred to as synthetic resin pressed wood (KHP). Early patents that apply the principle of bonding with solid wood under high pressure and high temperature include US 1465383 from 1923 and GB299442 from 1927. Over the course of development, PF resin has emerged as the resin of choice, used in concentrations in the finished product of 20 to 30 weight percent (% (w / w)). Beech veneers are predominantly used as veneers, although other wood species, such as poplar, are also used. KHP made from beech veneers and PF resins have densities of 1.2 to 1.4 g / cm³. 3 , flexural strengths from 140 to 240 N / mm 2 and flexural elastic moduli of 14,000 to 22,000 N / mm 2(see Deutsche Holzveredelung Schmeing GmbH & Co. KG, 2023, according to the bibliography appended at the end of the description). In terms of mechanical strength, KHP has long been a mature product. With the emergence of a general discussion about the health risks of formaldehyde, which is classified as a carcinogen (see Pitcher, 2005), global warming, and the contribution of individual products to global warming, materials and their manufacturing processes must be scrutinized and, where possible, converted to more health- and climate-friendly production.

[0005] PF resin is produced from fossil raw materials, particularly petroleum, and requires a high level of energy, usually using natural gas. According to Bachmann (see Bachmann, Hidalgo, & Bricout, 2017), the greenhouse gas potential over a 100-year period (Global Warming Potential, GWP100) is 5.8 kg CO2eq / kg PF resin. Based on this prior art, it is an object of the present invention to create laminated wood of the type mentioned above with an improved structure while maintaining or improving the technical properties.

[0006] To achieve this object, the present invention provides a laminated wood comprising at least three layers of wood arranged one above the other and bonded to one another with a particularly water-resistant glue, characterized in that the glue comprises a bio-based resin, a hardener, for example in the form of an amino salt with 65% (w / w) dry matter content, and an additive or consists of these components, wherein the additive preferably comprises or consists of high-molecular, naturally occurring or technically produced aromatic substances with oxidized side groups.

[0007] Biobased resins, such as the furan resins preferred according to the invention, which are produced from hemicelluloses, have been known for some time. Furan resins consist of interconnected furan rings with four carbon atoms and one oxygen atom. They are used, for example, as polyfurfuryl alcohols (PFA) to bind sand molds in foundry technology. However, an attempt to use them as a replacement for polyester or epoxy resins in flax or glass fiber-synthetic resin composites failed because furan resins have lower mechanical properties (see Bachmann, Hidalgo, & Bricout, 2017). These lower mechanical properties are also known for wood-based material applications (see Wikipedia, 2023). However, the lower strength and higher brittleness of furan resins, such as PFA, can be overcome according to the invention by adding additives.Surprisingly, it has been shown that, particularly by adding small amounts of high-molecular-weight, naturally occurring or technically produced aromatic substances with oxidized side groups, such as humic substances or technical lignin, the strengths of PF resin-based KHP can not only be achieved but even exceeded. Humic acids are obtained by alkaline extraction (sodium or potassium hydroxide solution) from aromatic precursors with oxidized side groups, such as leonardite, biogas fermentation residues, hydrolysates from hydrothermal carbonization, or by oxidation of technical lignins.

[0008] Thanks to the glue composition according to the invention, PF, which is hazardous to health and harmful to the climate, can be replaced by formaldehyde-free and more environmentally friendly, bio-based resin in the production of laminated wood while maintaining or improving the technical properties.

[0009] According to one embodiment of the present invention, the wood layers are veneers.

[0010] Preferably the wood layers are compacted.

[0011] According to one embodiment of the present invention, the bio-based resin is furan resin, which is in particular a polyfurfuryl alcohol.

[0012] According to one embodiment of the present invention, the additive is a huminate.

[0013] The dry matter (DM) of the huminate preferably consists of more than 50% (w / w) humic acids.

[0014] According to one embodiment of the present invention, the additive is a technical lignin.

[0015] The additive is preferably a purified, desulfurized kraft lignin.

[0016] Advantageously, the additive content of the total resin, based on dry matter, is between 0.1% (w / w) and 10% (w / w), preferably between 0.5% (w / w) and 8% (w / w) and particularly preferably between 0.8% (w / w) and 5.5% (w / w).

[0017] The resin content in the laminated wood is preferably between 10% (w / w) and 30% (w / w), preferably between 15% (w / w) and 25% (w / w) and particularly preferably between 17% (w / w) and 23% (w / w).

[0018] The resin content and the type of bio-based resin are advantageously selected such that the global warming potential (GWP100) for the resin component is less than 0.5 kg CO2eq / kg of laminated wood. According to one embodiment of the present invention, the flexural strength determined according to ISO 16978:2003-07 is between 140 N / mm 2 and 350 N / mm 2 , preferably between 200 N / mm 2 and 310 N / mm 2 .

[0019] The flexural modulus of elasticity determined according to ISO 16978:2003-07 is preferably between 14,0000 N / mm2 and 30,000 N / mm 2 , preferably between 19,000 N / mm 2 and 25,000 N / mm 2 .

[0020] The shear strength determined in a test setup according to DIN EN 1380 and in a test according to EN 26 891:1991 is preferably at least 4650 N and particularly preferably at least 5100 N.

[0021] The characteristic pull-out parameter ^x,k determined according to DIN EN 14592:2012-08 is advantageously at least 7 N / mm 2 , preferably at least 8.6 N / mm 2 and particularly preferably at least 9.2 N / mm 2 .

[0022] According to one embodiment of the present invention, the impact energy applied to wooden nails with a diameter of 5.3 mm, because it is applied to round nails and therefore not standardized, is at least 0.3 J, preferably at least 0.4 J and particularly preferably at least 0.5 J using a pendulum impact device.

[0023] Furthermore, the present invention provides a wooden nail made of plywood according to the invention, preferably laminated wood. Further features and advantages of the present invention will become clear from the following description with reference to the accompanying drawing.

[0024] Figure 1 is a perspective view of individual wood layers during the production of a laminated wood according to an embodiment of the present invention;

[0025] Figure 2 is a perspective view of the finished laminated wood and

[0026] Figure 3 is a perspective view of a wooden nail made from the laminated wood shown in Figure 2.

[0027] The following describes the production of plywood 1 according to the invention, which in the present case each have at least three wood layers 2 arranged one above the other and formed from beech veneers, which are bonded to one another with a glue containing bio-based furan resin.

[0028] Polyfurfuryl alcohol with a water content of 10 to 15% (w / w) was used to produce the glue. An amino salt with a 65% (w / w) dry matter content (DS), similar to that used for urea-formaldehyde bonding, was used as a hardener. A potassium huminate with 18% (w / w) humic substance content and 22-23% (w / w) DS, as well as a purified, CO2-desulfurized, and oxidized technical kraft lignin powder with approximately 95% (w / w) DS, were used as additives. The lignin was dissolved 1:1 in dimethyl sulfoxide (DMSO). The individual glue mixtures were prepared according to the quantities specified in Table 1. Table 1: Glue compositions of the AD formulations in weight proportions, pressing conditions, and resin content in the finished laminated wood.

[0029] The wood layers 2 were glued on both sides with the recipes A, B, C and D and then dried. For recipes A and B, the wood layers 2 were used with 10% wood moisture content. For recipes C and D, the wood layers were first dried at 90 °C to less than 1% wood moisture content and then glued and dried. The dried wood layers 2 were laid parallel to the grain in the direction of the arrows 3 in

[0030] Figure 1 shows the laminated wood stacked on top of each other, with arrow 4 indicating the grain direction, and pressed in a hot press, then cooled under pressure, and removed from the press. Pressing conditions and resin content in weight percent are given in Table 1. Figure 2 shows the finished laminated wood 1.

[0031] Based on the dry matter content, the humic acid content in recipe B is 1.3% (w / w) or 1.4% (w / w) when assuming a dry matter content of 90% (w / w) or 85% (w / w) for PFA. For recipe C, the humic acid content is 0.95% (w / w) or 1.0% (w / w) when assuming a dry matter content of 90% (w / w) or 85% (w / w) for PFA. The lignin content in recipe D is 4.85% (w / w) or 5.1% (w / w) when assuming a dry matter content of 90% (w / w) or 85% (w / w) for PFA.

[0032] KHP with a PF resin content of 25% (w / w) or nails made from it were used as a reference.

[0033] Flexural strength and flexural modulus of elasticity were determined according to ISO 16978:2003-07, and shear strength according to DIN 52367:2017-02. Impact energy was determined using round nails of the same size. However, conversion to the fracture area (to determine the toughness J / area) is unusual for round cross-sections and not necessary for a direct comparison. The test setup for determining shear strength was according to DIN EN 1380, and the test procedure was according to EN 26 891:1991. Four nails with a diameter of 4.7 mm and a length of 65 mm were used per side. The characteristic pull-out parameter was determined according to DIN EN 14592:2012-08. The pull-out parameter describes the maximum pull-out force relative to the surface area of ​​the nail penetrating the specimen and the density of the specimen. The technical properties of the laminated wood produced according to the recipes in Table 1 are shown in

[0034] Table 2 summarizes the properties and compares them with a PF resin-bonded laminated wood as a reference material. Table 2: Technical properties of laminated wood. A to D are glue formulations according to Table 1. Ref. = Reference. How it turns out

[0035] As can be seen in Table 2, contrary to what is stated in the literature (Wikipedia, 2023), laminated wood or composites made with PFA can achieve and exceed the flexural strengths of commercial composites and almost match the flexural elastic moduli. However, composites made with PFA without additives (Formulation A) require resin contents of 28% (w / w) instead of 25% (w / w) as with PF-based composites.

[0036] By adding 7 parts of huminate solution as an additive to 100 parts of PFA (Formulation B), the flexural strength of 230 N / mm 2 to 305 N / mm 2, which corresponds to an increase of approximately 33%, while simultaneously reducing the resin content from 28% (w / w) to 23% (w / w). The reduction in the resin content corresponds to a reduction of 18%. The flexural modulus of elasticity is increased from 19 kN / mm 2 by 10.5% to 21 kN / mm 2 increased. The density is 1.35 g / cm 3 within the usual scope for KHP.

[0037] To make KHP more environmentally friendly, not only by switching to bio-based resin, the resin quantity can also be further reduced. Recipe C, with only 18% (w / w) resin and 5 parts huminate, still achieves strengths of 275 N / mm 2This is almost 20% higher than the value of the KHP with PFA without additives (Formulation A) or conventional high-quality KHP based on PF resin. The addition of 5 parts of lignin to PFA (Formulation D) also improves the KHP's flexural strength and flexural elastic modulus. With only 17% (w / w) resin content, the flexural strength of the reference sample produced with PF resin is achieved. Formulations A and D achieve the values ​​of high-quality, commercial KHP products based on PF resin. Formulations B and C are significantly higher.

[0038] The impact energy and pull-out strength of formulation A are both significantly below the reference values ​​at just under 60%. Formulation B, on the other hand, shows a slight increase of approximately 2 to 3% compared to the reference. Compared to formulation A, formulation B shows a 70% increase in impact energy. The shear strength of KHP according to formulation B, at 5,166 N, is approximately 20% higher than that of KHP according to formulation A at 4,284 N.

[0039] The characteristic pull-out parameter of KHP according to recipe B has a Zäx.k that is approximately 38% higher than KHP according to recipe A and a Zäx.k that is approximately 7% higher as the reference.

[0040] The production of furan resins, even if the raw material is bio-based, is not climate-neutral, as a large amount of fossil energy is required to convert the hemicelluloses to furfuryl alcohol and to polymerize it. According to Tumolva (see Tumolva, Kubouchi, Aoki, & Sakai, 2011), the GWP100 is 4.7 kg CO2 eq / kg furan resin. CO2 eq refers to the climate-relevant impact of any gas, such as methane, ammonia, nitrous oxide, etc., which corresponds to a GWP100 converted to CO2. The carbon content (C) in furan resin is 70% (w / w). 1 kg of furan resin therefore binds 2.57 kg CO2 (0.7 kg C * 3.667 (conversion factor C CO2). The net GWP 100 is therefore only 2.13 kg CO2 eq / kg furan resin. This still high GWP 100 can be significantly reduced in the future, or even reduced to negative values, if sustainable energy sources are used instead of fossil fuels.

[0041] Considering only the GWP100 for the resin, the GWP100 for KHP based on PF resin and a 25% (w / w) resin content for the resin component is 5.8 * 0.25 = 1.45 kg CO2eq / kg KHP. The GWP100 of the resin component of KHP based on furan resins with a 17% (w / w) resin content is 2.13 * 0.17 = 0.362 kg CO2eq / kg KHP. The GWP100 can thus be reduced to 25% using state-of-the-art technology (furan resins produced using fossil energy) while maintaining the technical properties.

[0042] From the plywood 1 according to the invention, wooden nails 5 in particular can be produced, as shown by way of example in Figure 3.

[0043] Bibliography

[0044] Bachmann, J., Hidalgo, C., & Bricout, S. (2017). Environmental analysis of innovative sustainable composites with potential use in aviation sector — A life cycle assessment review. Science China Technological Sciences, 1301-1317.

[0045] Deutsche Holzveredelung Schmeing GmbH & Co. KG. (9. 10 2023). Dehonit. Von Servicebereich-Downloads-dehonit Kunstharzpressholz Informationen: https: / / www.dehonit.de / servicebereich / abgerufen

[0046] Pitcher, M. (2005). LCA treatment of human health exemplified by formaldehyde within the furniture industry. 4th Australian LCA Conference, (S. 1-10). Sydney.

[0047] Tumolva, T., Kubouchi, M., Aoki, S., & Sakai, T. (2011). Evaluation the carbon storage potential of furan resin-based green composites. 18th International Conference on composite materials (S. 6). Jesu Island, South Korea: ICC.

[0048] Wikipedia entry "Furan resin" (last edited on November 21, 2020). Available at: https: / / de.wikipedia.org / wiki / Furanharz

Claims

CLAIMS 1. Plywood (1) comprising at least three layers of wood (2) arranged one above the other and bonded to one another with a particularly waterproof glue, characterized in that the glue comprises or consists of a bio-based resin, a hardener and an additive, wherein the additive preferably comprises or consists of high-molecular, naturally occurring or technically produced aromatic substances with oxidized side groups.

2. Plywood (1) according to claim 1, characterized in that the wood layers (2) are veneers.

3. Laminated wood (1) according to claim 1 or 2, characterized in that the wood layers (2) are compacted.

4. Laminated wood (1) according to one of the preceding claims, characterized in that the bio-based resin is furan resin, wherein the furan resin is in particular a polyfurfuryl alcohol.

5. Laminated wood (1) according to one of the preceding claims, characterized in that the additive is a huminate, wherein the dry sub- substance (TS) of the huminate consists in particular of more than 50% (w / w) humic acids.

6. Plywood (1) according to one of claims 1 to 4, characterized in that the additive is a technical lignin, wherein the additive is in particular a purified, desulfurized kraft lignin.

7. Laminated wood (1) according to one of the preceding claims, characterized in that the additive content of the total resin, based on dry matter, is between 0.1% (w / w) and 10% (w / w), preferably between 0.5% (w / w) and 8% (w / w) and particularly preferably between 0.8% (w / w) and 5.5% (w / w).

8. Laminated wood (1) according to one of the preceding claims, characterized in that the resin content is between 10% (w / w) and 30% (w / w), preferably between 15% (w / w) and 25% (w / w) and particularly preferably between 17% (w / w) and 23% (w / w).

9. Laminated wood (1) according to one of the preceding claims, characterized in that the resin content and the type of bio-based resin are selected such that the global warming potential (GWP100) for the resin component is less than 0.5 kg CO2eq / kg laminated wood.

10. Laminated wood (1) according to one of the preceding claims, characterized in that the bending strength determined according to ISO 16978:2003-07 is between 140 N / mm 2 and 350 N / mm 2 , preferably between 200 N / mm 2 and 310 N / mm 2 and / or that the flexural modulus of elasticity determined according to ISO 16978:2003-07 is between 14,0000 N / mm 2 and 30,000 N / mm 2 , preferably between 19,000 N / mm 2and 25,000 N / mm 2 and / or that the shear strength determined in a test setup according to DIN EN 1380 and in a test according to EN 26 891: 1991 is at least 4650 N and preferably at least 5100 N and / or that the characteristic pull-out parameter Zäx.k determined according to DIN EN 14592:2012-08 is at least 7 N / mm 2 , preferably at least 8.6 N / mm 2 and particularly preferably at least 9.2 N / mm 2 amounts.

11. Laminated wood (1) according to one of the preceding claims, characterized in that the impact energy for round wooden nails with a diameter of 5.3 mm is at least 0.3 J, preferably at least 0.4 J and particularly preferably at least 0.5 J.

12. Wooden nail (5), characterized in that it is made of plywood (1) according to one of the preceding claims.

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