MODIFIED AMINOPLASTIC ADHESIVE RESIN, PROCEDURE OF ITS PREPARATION, AND COMPOSITE MATERIALS PREPARED USING THE MODIFIED AMINOPLASTIC ADHESIVE RESIN

Abstract

A temperature-curable aminoplastic adhesive resin that is a (poly)-condensate of: (i) at least one aminoplast-forming chemical; (ii) 5-hydroxymethylfurfural (5-HMF), its oligomers and/or its isomers; and, (iii) at the least one second (poly-)condensable chemical. Composite boards, such as wood-based panels, can be produced using this adhesive resin. The production of the aminoplastic adhesive resin includes the reaction of urea with 5-hydroxymethylfurfural (5-HMF) and glyoxal. The adhesive resin can be used in the production of wood-based panels such as particleboards, fiberboards and products usually called, among others, plywood and/or blockboards.

Claims

1. A temperature-curable resin preparable by the (poly)-condensation of: at least one aminoplast-forming chemical, with 5-hydroxymethylfurfural (5-HMF), its oligomers and/or its isomers, and at the least one second (poly-)condensable chemical, under reaction conditions under which said at least one aminoplast-forming chemical, 5-hydroxymethylfurfural (5-HMF), its oligomers and/or its isomers, and the at least one second (poly-)condensable chemical (poly-)condensate to the temperature-curable resin.

2. The temperature-curable resin according to claim 1, wherein the at least one second (poly-)condensable chemical is at least one aldehyde different from 5-hydroxymethylfurfural, its oligomers or its isomers.

3. The temperature-curable resin according to claim 1, wherein the at least one second (poly-) condensable chemical is glyoxal.

4. The temperature-curable resin according to claim 1, wherein the at least one aminoplast-forming chemical is selected from the group of consisting of: urea, melamine, substituted melamine, substituted urea, acetylenediurea, guanidine, thiourea, thiourea derivatives, diaminoalkane, or diamidoalkane, or mixtures thereof.

5. The temperature-curable resin according to claim 1, wherein in the (poly)-condensation, a molar ratio (a:b:c) of (a) the totality of the at least one aminoplast-forming chemical, to (b) the totality of 5-hydroxymethylfurfural (5-HMF), its oligomers and/or its isomers, to (c) the totality of the least one second (poly-)condensable chemical, is adapted to 1:0.1 to 1.0:0.05 to 0.5, preferably 1:0.2 to 0.4:0.1 to 0.3, particularly preferably 1:0.3 to 0.4:0.15 to 0.25.

6. The temperature-curable resin according to claim 1, comprising a solid content of 60-85 mass %, all solid contents determined by evaporating the water content of the reaction solution after its preparation under vacuum until a constant mass has been achieved.

7. The temperature-curable resin according to claim 1, comprising a viscosity of 150-1,000 mPa*s, all viscosities measured using a rotational viscosimeter at 20? ? C. according to ISO 3219:1994.

8. A method for the production of a temperature-curable resin, the method comprising (poly)-condensation of at least one aminoplast-forming chemical with 5-hydroxymethylfurfural (5-HMF), its oligomers and/or its isomers, and at the least one second (poly-)condensable chemical, under reaction conditions under which said at least one aminoplast-forming chemical, 5-hydroxymethylfurfural (5-HMF), its oligomers and/or its isomers, and the at least one second (poly-)condensable chemical (poly-)condensate to the temperature-curable resin.

9. The method according to claim 8, wherein the (poly-)condensation is performed at temperatures in the range from 10 to 90? C.

10. The method according to claim 8, wherein the (poly-)condensation is carried out in a solution until the solution has reached a predetermined viscosity or the reaction is complete.

11. A method for the production of composite materials, comprising: providing a temperature-curable resin according to claim 1, bringing into contact the temperature-curable resin with lignocellulose containing or non-lignocellulose containing material, or a mixture thereof, preparing a curable mass, and curing of the curable mass under formation of the composite material, said curing being carried out by means of elevated temperature and pressure.

12. The method according to claim 11, wherein the lignocellulose-containing materials or the non-lignocellulose containing materials is selected from the group consisting of: wood chips, wood fibers, plant fibers, wood flakes, wood strands, wood particles, wood stripes, mixtures of various lignocellulosic materials, inorganic fibres, inorganic fibre mats, and mixtures of these thereof.

13. The method according to claim 11, wherein the lignocellulose-containing or the non-lignocelluose containing material is mixed with an amount of 2% by weight to 20% by weight of the temperature-curable resin, based on the weight of the dry lignocellulose-containing or non-lignocellulose containing material.

14. The method according to claim 11, wherein the step of preparing the curable mass is carried out in a flat press, continuous press, or molding press.

15. The method according to claim 11, wherein the curing of the resin is carried out in a press at a temperature of 160 to 250? C.

16. A composite material formed by the method according to claim 11, wherein the composite material comprises a composite boards based on wood or inorganic materials in a form of a wooden particleboard, fiberboard, OSB panel, HDF- or MDF panel, plywood and/or blockboard.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0018] FIG. 1 illustrates the development of the bond strengths with the press time for two resins described herein.

DETAILED DESCRIPTION

[0019] The present disclosure discloses a temperature-curable resin preparable by the (poly)-condensation of [0020] at least one aminoplast-forming chemical, with [0021] 5-hydroxymethylfurfural (5-HMF), its oligomers and/or its isomers, and [0022] at the least one second (poly-)condensable chemical, under reaction conditions under which said at least one aminoplast-forming chemical, 5-hydroxymethylfurfural (5-HMF), its oligomers and/or its isomers, and the at least one second (poly-)condensable chemical (poly-)condensate to the temperature-curable resin.

[0023] According to the present disclosure, 5-hydroxymethylfurfural, its oligomers and/or its isomers, are capable to react with the at least one aminoplast-forming chemical via polycondensation. Furthermore, the at the least one second (poly-)condensable chemical is capable to react with the at least one aminoplast-forming chemical and/or 5-hydroxymethylfurfural (5-HMF), its oligomers and/or its isomers via polycondensation.

[0024] The temperature-curable resin according to the present disclosure accordingly is a polycondensate. Preferably the aminoplast forming chemical comprises NH.sub.2 or NH groups and the at least one second (poly-)condensable chemical comprises one or more aldehyde functions.

[0025] It has now been experienced by coincidence, and not yet reported in literature, that the (poly-)condensation of at least one aminoplast-forming chemical, 5-hydroxymethylfurfural (5-HMF), its oligomers and/or its isomers, and at the least one second (poly-)condensable chemical, can overcome the short-comings as they are described above in details.

[0026] Especially, it turned out in experiments, that precipitation and phase separation can be avoided, rendering the process suitable for industrial application of resin production.

[0027] Analysis of this practical experiences point to the fact, that the increase in hydro-philic behavior in the resin keeps the bigger molecules, as they are formed with the polycondensation reaction during the resin production, still in solution, hence avoiding the effects of precipitation and phase separation.

[0028] According to a specific embodiment, the at least one second (poly-)condensable chemical is at least one aldehyde different from 5-hydroxymethylfurfural, its oligomers or its isomers.

[0029] Preferably, the at least one second (poly-)condensable chemical is glyoxal.

[0030] Furthermore, the at least one aminoplast-forming chemical can be selected from the group of consisting of urea, melamine, substituted melamine, substituted urea, acetylenediurea, guanidine, thiourea, thiourea derivatives, diaminoalkane, or diamidoalkane or mixtures thereof.

[0031] According to an advantageous embodiment, the (poly)-condensation a molar ratio (a:b:c) of (a) the totality of the at least one aminoplast-forming chemical, to (b) the totality of 5-hydroxymethylfurfural (5-HMF), its oligomers and/or its isomers, to (c) the totality of the least one second (poly-)condensable chemical, is adapted to 1:0.1 to 1.0:0.05 to 0.5, preferably 1:0.2 to 0.4:0.1 to 0.3, particularly preferably 1:0.3 to 0.4:0.15 to 0.25.

[0032] The temperature-curable resin according to the present disclosure may have a solid content of 60-85 mass %, preferably 65-80 mass %. All solid contents were determined by evaporating the water content of the reaction solution after its preparation under vacuum until a constant mass has been achieved.

[0033] According to an additional advantageous aspect, the temperature-curable resin has a viscosity of 150-1,000 mPa*s, preferably 200-600 mPa*s, particularly preferably 200-400 mPa*s. The viscosity here is measured directly at the given liquid resin without any modification, only the temperature of the liquid resin is adjusted to 20? C. The measurement is done in the usual way as known to skilled artisans by a rotational viscosimeter (such as Brookfield viscosimeter), also described in EN ISO 3219:1994 Annex B.

[0034] According to the another aspect, the present disclosure relates to a method for the production of a temperature-curable resin by (poly)-condensation of [0035] at least one aminoplast-forming chemical with [0036] 5-hydroxymethylfurfural (5-HMF), its oligomers and/or its isomers, and [0037] at the least one second (poly-)condensable chemical,
under reaction conditions under which said at least one aminoplast-forming chemical, 5-hydroxymethylfurfural (5-HMF), its oligomers and/or its isomers, and the at least one second (poly-)condensable chemical (poly-)condensate to the temperature-curable resin.

[0038] A specific embodiment of the method foresees that the (poly-)condensation is performed at temperatures in the range from 10 to 90? C., preferably in the range from 20 to 60? C., particularly preferably in the range from 20 to 50? C.

[0039] The (poly-)condensation can be carried out in a solution until the solution has reached a predetermined viscosity or the reaction is complete.

[0040] Another aspect of the present disclosure relates to a method for the production of composite materials, comprising the following steps: [0041] provision of a temperature-curable resin according to the present disclosure, [0042] bringing into contact the temperature-curable resin with lignocellulose containing or non-lignocellulose containing material, or a mixture thereof, [0043] preparation of a curable mass, and [0044] curing of the curable mass under formation of the composite material, said curing being carried out by means of elevated temperature and pressure.

[0045] In a specific embodiment of this method, the lignocellulose-containing materials or the non-lignocellulose containing materials is selected from the group consisting of wood chips, wood fibers, plant fibers, wood flakes, wood strands, wood particles, wood stripes, mixtures of various lignocellulosic materials, inorganic fibres, inorganic fibre mats, and mixtures of these.

[0046] Moreover, the lignocellulose-containing or the non-lignocelluose containing material is mixed with an amount of 2% by weight to 20% by weight, preferably with an amount of 5% by weight to 15% by weight, of the temperature-curable resin, based on the weight of the dry lignocellulose-containing or non-lignocellulose containing material.

[0047] The step of preparing of a curable mass can be carried out in a flat press, continuous press, or molding press.

[0048] Advantageously, the curing of the resin is carried out in a press at temperatures of 160 to 250? C.

[0049] Finally, the present disclosure relates to a composite material, obtained by a method according to the present disclosure, as described in the foregoing, preferably composite boards based on wood or inorganic materials, especially in form of wooden particleboards, fiberboards, OSB panels, HDF- or MDF panels, plywood, and/or blockboards, which can be used among other applications as e.g. flooring-, wall-, or ceiling panels.

[0050] The present disclosure will be described in greater detail in the following, without limiting the disclosure to the specific details given.

[0051] That is, the preparation of the composite materials preferably follows the usual and well-known procedures, as they are described in literature, such as in the case of wood-based panels, by Dunky and Niemz (Dunky, M. and Niemz, P. (2002). Wood-Based Panels and Adhesive Resins: Technology and Influential Parameters (German). Springer, Heidelberg, pp. 986). The procedure of the production of composite materials includes: (i) the preparation and provision of the cellulosic or inorganic materials, such as particles, strands, or fibers, to give only few examples of many examples suitable within the procedure of the production of composite materials; (ii) the preparation and provision of the suitable and necessary adhesive and adhesive mix, including not only the adhesive, but also other components, such as hardeners or crosslinkers; (iii) the provision of other additives or components, such as paraffin, in various form as hydrophobic agent; (iv) mixing according the well-known technologies of the various components, as mentioned under (i) to (iii); (v) preparation of a mass with certain structures and sizes under various sequences of one or several layers; (vi) pressing of this mass under impact of temperature and various pressures for a certain time, whereby the temperature can vary in a broad range, and where the pressures are selected accordingly in order to achieve the formation of the intended composite materials; and finally, (vii) cooling of the composite materials. The relevant conditions and details in the various steps (i) to (vi) depend on many parameters, such as the types of the wooden or inorganic raw materials, the types of a chemical components added, and the types, size, and shape of the composite materials as they shall be produced, to just mention here the most important parameters. Skilled artisans in the field of the production of composite materials know a large number of influential parameters to be considered and followed in order to achieve the intended results.

[0052] The following examples shall only act as exemplary and more detailed description of the disclosure without restriction on scope of the disclosure.

Example 1

[0053] The following example describes the formation of an adhesive resin based on urea, 5-HMF, and glyoxal. The raw materials and the used amounts in the recipe are summarized in the following Table 1.

TABLE-US-00001 TABLE 1 Raw materials and their used amounts in the recipe concerning Example 1 Molar Mol Mass of mass equiva- raw materials Reagents (Da) *) lents used (g) urea 60 3.0 180 5-HMF (50 mass %) 126 1.0 252 Glyoxal (40 58 0.45 65 mass %) *) rounded to full digit numbers

[0054] Contrary to the 5-HMF-modified melamine-glyoxal resin mentioned above, here the urea-5-HMF-resin was modified by glyoxal, whereby the proportion of glyoxal on the total amount of used aldehydes in Example 1 is only 17 mass %. The amount of glyoxal was adjusted, after finding that the addition of a second aldehyde can solve the problems with inhomogeneities as encountered above, to the necessary number to keep these positive effects remaining.

[0055] For the preparation of the raw materials 548 g of a 23 mass % 5-HMF solution were concentrated in a rotary evaporator (rotavapor) under vacuum at p=<32 mbar and a temperature T of 42? C. until a solid content of 50 mass % was reached. With this step, the amount of 5-HMF solution was decreased from 548 g to 252 g. Same results can be achieved when directly using a 50% solution of 5-HMF. Another possibility is the use of mixtures of various types of 5-HMF with different concentrations or the mix of an 5-HMF solution of lower concentration with solid 5-HMF. Also the dissolution of the relevant mass of solid 5-HMF in water in order to get an aqueous 5-HMF solution with the desired concentration is a possible way for the preparation of the 5-HMF solution. The upconcentration of the 5-HMF solution starting with a lower concentration and yielding a higher concentrated 5-HMF solution after the upconcentration is no defined and necessary step in the procedure.

[0056] If such an upconcentration step is performed, no special procedure conditions for this step are requested and no special treatment of and changes in the chemical structure and behavior of the 5-HMF are requested when preparing aminoplastic resins based on this 5-HMF. The same is the case with any special composition of the upconcentrated 5-HMF concerning a certain proportion of oligomers. Oligomers have not been detected as well as they are neither intended nor necessary for the design of the resin preparation, as it is described here.

[0057] To those 252 g of the 50 mass % 5-HMF solution, 180 g of urea and 65 g of a 40 mass % glyoxal solution were added. The mixture was stirred at room temperature without heating until complete dissolution of the urea was achieved. Once the urea was dissolved, the pH of the mixture was measured and adjusted to pH=3 using an aqueous 10% solution of H.sub.2SO.sub.4. The necessary amount of the sulphuric acid is not specified and depends on the pH of the solution after the urea has dissolved. It is well-known to skilled artisans that urea can affect the pH in certain ways due to different proportions of residual ammonia in the urea. Tests with different types of urea did not show any special and unexpected effects.

[0058] The mixture after the urea was dissolved and after adjustment of the pH was then heated up to 40? C. and stirred at 500 rpm for 1 h, followed by cooling and additional 4 h of stirring at room temperature again at 500 rpm. After this period, the solution was liquid and can be stored as it is. Preferably, the pH is adjusted to pH=7.

[0059] In order to increase further the viscosity, depending on the intended application, the resin, as it was obtained after the two condensation steps at 40? C. and at room temperature, can be distilled in order to increase the resin solid content. For the determination of the resin solid content, a small amount of the resin (approx. 0.4-0.5 g) was treated at 50? C. and p<32 mbar for 10 minutes, followed by another 10 minutes at p<10 mbar, in order to remove all water. Once the solid content is determined, the necessary amount of water to be removed from the resin can be determined by calculation and the resin can be upconcentrated to the intended resin solid content. This resin solid content can be as an example 80 mass %, without restricting the intended resin solid content to other values, depending on the application mode.

[0060] To optimize the storage stability, it has found out by experiments that the longest possible storage stability was achieved at a starting pH after resin production of pH=9.5, under consideration of the decrease of the pH with time during storage, independent on the temperature during storage. Additionally it has proven to be an advantage, to stabilize the pH of the resin during the storage by adding small amounts (up to maximum 0.5 mass %) of sodiumbicarbonate to the final resin after its preparation.

Example 2

[0061] Example 2 is similar to Example 1, but with an increased amount of glyoxal. When changing the amount of glyoxal, no compensation was neither intended nor implemented to keep the equivalents of aldehyde groups to urea constant. In both examples, the total aldehyde equivalent increased by adding the equivalent for the glyoxal on top of the already given equivalent of the aldehyde group of the 5-HMF.

[0062] In Example 2, the amount of glyoxal was increased in comparison with Example 1, from an equivalent of 0.45 to 0.65. The raw materials and the used amounts in the recipe of Example 2 are summarized in the following Table 2. The proportion of glyoxal on the total amount of used aldehydes in Example 2 is 23 mass %.

TABLE-US-00002 TABLE 2 Raw materials and their used amounts in the recipe concerning Example 1 Molar Mol Mass of mass equiva- raw materials Reagents (Da) *) lents used (g) *) urea 60 3.0 180 5-HMF (50 mass %) 126 1.0 252 Glyoxal (40 mass %) 58 0.65 94 *) rounded to full digit numbers

[0063] The preparation procedure for the resin in Example 2 is identical to the described procedure in Example 1.

Example 3

[0064] The curing reaction of the 5-HMF based resins as described in the two Examples 1 and 2, and the formation of durable bond lines using the two 5-HMF-based resins as examples for all mentioned types of 5-HMF resins, was investigated using the so-called Automatic Bonding Evaluation System (ABES; P. E. Humphrey, Device for testing adhesive bonds, U.S. Pat. No. 5,176,028; ASTM D7998-2015) method. The resins as described in Example 1 and Example 2 (6 droplets) were applied onto veneers and distributed properly over an area of 100 mm.sup.2 (20 mm*5 mm). The ABES tests were performed at a press temperature of 120? C. for various press times of 30, 60, 120, and 300 seconds. According to the procedure of the ABES test, the overlap-ping part of the bonded sample was cooled with an air stream for 30 seconds, with subsequent determination of the bond strength by the tensile shear strength test mode. For each press time, the tests were repeated at least 3 times. Average tensile shear strength (MPa) and standard deviation for each of the hot-press times were determined and evaluated. FIG. 1 shows the development of the bond strengths with the press time for the two resins as described in Example 1 and Example 2. For the ABES tests, 5% of wheat flour was added to the two 5-HMF-based resins.

[0065] The occurrence of wood failure showed that curing of the resins was achieved. Wood failure means that the shear strength of the bond line is higher than the strength of the used wood veneers themselves. Skilled artisans will confirm that occurrence of wood failure is the strongest indication and evidence for a proper bonding result.