Natural resin adhesive composition for water-resistant wood products

Abstract

The present development describes a natural resin adhesive composition for producing wood products, a method for obtaining the composition and a method for producing wood products using the adhesive composition. The development employs a plant extract characterised by the presence of metabolites with aldehyde or hydroxyl functional groups to replace formaldehyde or glyoxal in conventional resins. The wood products obtained using the natural resin adhesive composition of the present development have mechanical and antimicrobial properties comparable to commercial products, which makes them suitable for replacing conventional resins, providing a sustainable and biodegradable alternative.

Description

[0001] ADHESIVE COMPOSITION OF NATURAL RESIN FOR WOOD PRODUCTS

[0002] WATER RESISTANT

[0003] TECHNICAL FIELD

[0004] This development relates to compositions for bonding wood products. Specifically, it relates to natural resin adhesive compositions for water-resistant wood products.

[0005] DESCRIPTION OF THE STATE OF THE ART

[0006] According to the Food and Agriculture Organization of the United Nations (FAO), global production of plywood and particleboard in 2022 was estimated at 235 million cubic meters. Increased production of wood materials increases the demand for raw materials, which are generally wood and wood particles, and consequently, deforestation. Global wood consumption has been quantified by the FAO at 4 billion cubic meters.3 in 2022 and is expected to grow by 37% by 2050.

[0007] To produce wood products such as particleboard, three main components are required: water, biomass, and resin. The choice of resin plays a crucial role in determining the properties and performance of the particleboard. There are several types of resins commonly used in particleboard production, each with distinct characteristics. The most common types of resin include phenol-formaldehyde, melamine-urea-formaldehyde, methylene diphenyl diisocyanate (MDI), polymeric diphenyl methylene diisocyanate (PMDI), and urea-formaldehyde. Most industrially used wood adhesives contain formaldehyde, a reactive compound, making it well-suited for its intended use.Formaldehyde is a volatile organic compound found in pressed wood products, paper, and paints. It has been classified as a carcinogen by the International Agency for Research on Cancer (IARC 2004, EPA 2017). Because of its small molecular weight and high volatility, it can be released into the air over time, posing potential health and environmental concerns. In particular, the World Health Organization notes that exposure to this compound should be considered for workers who produce formaldehyde-based resins in the manufacture of composite wood panels, as well as for indoor air pollution. Particleboard for indoor use emits formaldehyde, which can have long-term health effects (LD50 rat 100 mg / kg; LD50 mouse 42 mg / kg) [Doi 10.1016 / JJTICE.2014.02].007], Additionally, formaldehyde resin particleboard waste can pose environmental problems, especially if not properly managed.

[0008] Efforts have been made to replace formaldehyde in resin synthesis, as the production of wood adhesives relies heavily on this non-renewable petroleum derivative. Other aldehydes have been studied as alternatives; however, some present problems such as low reactivity or some toxicity (L. Cao et al., "Preparation and characterization of a novel environment-friendly urea-glyoxal resin of improved bonding performance," Eur Polym J, vol. 162, p. 110915, Jan. 2022) [Doi. 10.1016 / J.ENVPOL.2024.123419 and 10.1016 / J.EUROPOLYMJ.2021.110915]. Therefore, replacing formaldehyde is the biggest obstacle in the production of wood products. Glyoxal has been found to be a promising substitute because it has high reactivity, low toxicity, and can react with urea to form urea-glyoxal resins, similar to urea-formaldehyde resins.However, industrial production of glyoxal typically involves synthetic processes, and obtaining glyoxal directly from natural sources on a large scale is not easy due to the yields obtained. For example, US patent 10125295 discloses protein adhesive compositions and methods for manufacturing and using such adhesives. This adhesive composition comprises a hydroxyaromatic compound, an aldehyde source selected from the group consisting of formaldehyde, acetaldehyde, glyoxal, methylglyoxal, and glutaraldehyde, a reactive prepolymer, and a polypeptide composition isolated from plant biomass.Furthermore, patent CA2392876 describes an adhesive system for use in bonding lignocellulosic materials comprising at least one powdered tannin, a liquid solution of polymeric isocyanate, and an aldehyde polymer selected from phenol-formaldehyde, urea-formaldehyde, melamine-urea-formaldehyde, melamine-formaldehyde, and phenol-formaldehyde polymers modified with at least one member selected from urea, melamine-formaldehyde polymers, urea-formaldehyde polymers, proteins, and tannins.

[0009] Using plant extracts as resins for wood particleboard can offer several benefits. Plant extracts are derived from renewable resources, contributing to sustainability by reducing reliance on finite, fossil-based materials. The production of plant-based resins emits fewer pollutants and is generally more biodegradable compared to the manufacture of synthetic resins. Plant-based resins are typically more biocompatible and pose fewer health risks during manufacturing, handling, and final applications. Therefore, replacing synthetic aldehydes with natural aldehydes for wood resins, obtained from plant-derived compounds, offers environmentally friendly alternatives that can improve the sustainability and biodegradability of wood-based products.

[0010] Among the technical and structural differences identified between the aldehydes in this development and synthetic aldehydes is that the former are naturally sourced from plant waste and are non-toxic. Furthermore, the differences between the aldehydes in this development and glyoxal include: i) increased water resistance in wood products, ii) a high number of adhesive functional groups, and iii) the combination of adhesive functional groups, resulting in more than one adhesion mechanism.

[0011] Responding to this opportunity, the inventors have developed adhesives that include natural aldehydes that are non-toxic and present in extracts of agricultural waste, which, among other things, increase water resistance.

[0012] BRIEF DESCRIPTION

[0013] This development relates to a natural resin adhesive composition for the manufacture of wood products. The composition comprises at least one plant extract, urea, and water. The plant extract is selected from beetroot (Beta vulgaris), barley (Hordeum vulgare), honeysuckle (Lonicera spp.), green tea (Camellia sinensis), spinach (Spinacia oleracea), or mixtures thereof.

[0014] Additionally, a method for obtaining a natural resin adhesive composition is described. The method comprises preparing a dried plant extract, obtaining an aqueous solution of the powdered plant extract, and mixing it with an aqueous urea solution to obtain a natural resin adhesive composition.

[0015] Thirdly, this development relates to obtaining a wood-based composite product with a natural resin adhesive. The method involves applying the natural resin adhesive to wood particles using mechanical pressure to create a wood-based composite product.

[0016] BRIEF DESCRIPTION OF THE FIGURES

[0017] FIG. 1A shows the Fourier transform infrared (FTIR) spectra in the 1500 to 1800 cm region 1 of the plant extracts extracted from Honeysuckle (Ms), Spinach (Es), Beetroot (Re), Barley (Cb) and Green Tea (Tv) compared to the 40% Glyoxal solution (Gly).

[0018] FIG. IB shows the DTG (% / °C) curves for the dry plant extracts, Honeysuckle (Ms), Spinach (Es), Beetroot (Re), Barley (Cb) and Green Tea (Tv).

[0019] FIG. 2 shows the water absorption and swelling of samples with resins based on plant extracts, Honeysuckle (Ms), Spinach (Es), Beetroot (Re), Barley (Cb) and Green Tea (Tv) at 20% concentration, control resin Urea-Glyoxal (UG) at 20% concentration, samples without resin (AC), commercial particle board (Com) and HempWood (CCon) after 48 hours of immersion in water.

[0020] FIG. 3 shows the modulus of elasticity of the samples with resins based on extracts at 20% concentration, Honeysuckle (20Ms), Spinach (20Es), Beetroot (20Re), Barley (20Cb) and Green Tea (20Tv), control resin Urea-Glyoxal at 1% (1UG) and 20% concentration (20UG), samples without resin (Ac), commercial particle board (Com) and HempWood (CCOn).

[0021] FIG 4 shows the results of the flexural strength test of samples with resins based on extracts at 20% concentration of Honeysuckle (20Ms), Spinach (20Es), Beetroot (20Re), Barley (20Cb), and Green Tea (20Tv), samples without resin (AC), and control resin Urea-Glyoxal at 20% concentration (20UG) as a function of density.

[0022] FIG. 5 shows the indentation strength of samples with extract-based resins, Honeysuckle (Ms), Spinach (Es), Beetroot (Re), Barley (Cb), and Green Tea (Tv) at 20% concentration, control Urea-Glyoxal (UG) resin at 15% and 20% concentration, commercial particle board (Com), and HempWood (Ccon).

[0023] Figure 6 shows the results of the fire resistance test, measuring the flame height reached after direct exposure to a small flame of samples containing resins based on extracts at 20% concentration: Honeysuckle (20Ms), Beetroot (20Re), Barley (20Cb), and Green Tea (20Tv), a control resin of Urea-Glyoxal at 20% concentration (20UG.1), and Hempwood (Ccon). The figures also indicate which resins produced ash and / or sparks.

[0024] FIG. 7 shows the FTIR spectra of glyoxal (Gly) and samples extracted from natural sources: Barley (Cb), Green Tea (Tv), Honeysuckle (Ms), Spinach (Es) and Beetroot (Re).

[0025] DETAILED DESCRIPTION

[0026] For the purposes of this document, all percentages below are in p / p, unless expressly stated otherwise. "Around" means a difference of at least ±5% from the defined value.

[0027] The present development refers to adhesives prepared from plant extracts of agricultural waste in which the presence of aldehydes has been identified that can be efficient in the bonding performance, agglomeration, mechanical properties, thermal resistance and water resistance.

[0028] Regarding the potential implementation of the present invention, the preparation of prototypes of wood agglomerates using natural adhesives is being considered. The preparation of pellets that could be used for any wood product is also being considered.

[0029] Adhesive composition of natural resin

[0030] In its first aspect, the development refers to a natural resin adhesive composition. A “natural resin adhesive composition” is defined as a composition for the manufacture of wood products, where the composition functions as both an adhesive and a binder for the wood particles. Additionally, “natural resin” is defined as a composition comprising a plant extract, urea, and water. For the purposes of this development, “wood product” is defined as any product manufactured from wood, biomass, or their derivatives, including but not limited to plywood, particleboard, composite board, engineered wood, multi-layered wood, chipboard, recycled wood board, particleboard, and medium- or low-density fiberboard.

[0031] Additionally, for the purposes of this document, "plant extract" means an extract obtained from selected plant material, including leaves, seeds, stems, roots, flowers, or combinations thereof. In one instance, the plant extract is obtained from waste plant material. In another instance, the plant extract is selected from extracts of beetroot (Beta vulgaris), barley (Hordeum vulgare), honeysuckle (Lonicera spp.), green tea (Camellia sinensis), spinach (Spinacia oleracea), or mixtures thereof.

[0032] In a preferred embodiment, the plant extract is an aqueous, hydroalcoholic, or alcoholic extract. In a preferred embodiment, the plant extract is obtained by a particular aqueous extraction process, considering that alcohols can be more expensive and that, when the inventors conducted tests, they found little difference in extraction between water and alcohol.

[0033] Additionally, the plant extract used in this development is characterized by the presence of metabolites with aldehyde or hydroxyl functional groups, preferably containing between 1 and 2 aldehyde groups and between 2 and 23 hydroxyl groups. Specifically, the plant extract is characterized by the presence of these functional groups in metabolites such as terpenoids, simple aromatics, benzopyranoids, benzofuranoids, amino acids, peptides, miscellaneous compounds, and lignans. In a preferred embodiment, the plant extract is characterized by the presence of saponins, benzaldehydes, monoterpenes, diterpenes, triterpenes, glycosides, and mixtures thereof. The metabolites present in the plant extract have a molecular weight between 100 and 1600 g / mol, between 138 and 1250 g / mol, or preferably between 130 and 900 g / mol.

[0034] In a preferred embodiment, the metabolites present in the plant extract comprise: 3,4-dihydroxybenzaldehyde, Gypsophila saponin,

[0035] Protocatechualdehyde, Amaranth Saponin IV, Oleragenoside, Assam Saponin A, Secolaganinoleragenoside, and secologanin.

[0036] 3,4-dihydroxybenzaldehyde

[0037] For the purposes of this development, the selection of the natural extract is related to the presence of the metabolites mentioned above. Furthermore, the selected extracts must have adhesive properties when prepared in a wood resin, resulting in greater water resistance and thermal resistance, among other benefits.

[0038] Additionally, the adhesive composition of the natural resin development may include variations in the concentration and proportion of metabolites present in the plant extract, as well as the combination of different extracts from different plant sources to optimize the mechanical properties and water resistance of the final resin.

[0039] The composition comprises at least one plant extract, urea, and water. Each of the components of the composition is required for the reaction to form a polymeric resin with an amide linkage resulting from a condensation between urea and aldehyde functional groups in water.

[0040] For the purposes of this development, the natural resin adhesive composition comprises between 1 and 70% w / w of plant extract, between 1 and 60% w / w of plant extract, between 2 and 60% w / w of plant extract, more than 5% w / w of plant extract, more than 15% w / w of plant extract, up to 60% w / w of plant extract, preferably between 2 and 50% w / w of plant extract, more preferably between 20 and 30% w / w of plant extract. The natural resin adhesive composition further comprises urea between 1 and 60% w / w, between 2 and 55% w / w, greater than 3% w / w, greater than 5% w / w, greater than 10% w / w, between 5 and 50% w / w, up to 50% w / w, less than 20% w / w, between 10 and 30% w / w, preferably between 5 and 40% w / w, more preferably between 10 and 20% w / w of urea, or the amount necessary to prepare a wood adhesive resin with urea and water.Additionally, the natural resin adhesive composition comprises water between 5 and 90% w / w, up to 90% w / w, greater than 10% w / w, greater than 20% w / w, greater than 50% w / w, less than 70% w / w, between 15 and 85% w / w, between 30 and 70% w / w, preferably between 20 and 80% w / w, more preferably between 50 and 70% w / w of water, or the amount necessary to prepare a wood adhesive resin with urea and plant extract. In one embodiment, the natural resin adhesive composition comprises between 2 and 50% w / w of a plant extract, urea, and water. The plant extract is beetroot, barley, honeysuckle, green tea, spinach, or mixtures thereof.

[0041] In one embodiment, the natural resin adhesive composition comprises between 2 and 50% w / w of a plant extract, between 5 and 40% w / w of urea, and between 20 and 80% w / w of water. Where the plant extract is an aqueous extract of beetroot, barley, honeysuckle, green tea, spinach, or mixtures thereof.

[0042] In one embodiment, the natural resin adhesive composition comprises a plant extract between 20 and 30% w / w, urea between 10 and 20% w / w and water between 50 and 70% w / w.

[0043] In a preferred embodiment, the natural resin adhesive composition comprises a plant extract which is barley extract.

[0044] In a preferred embodiment, the natural resin adhesive composition comprises a plant extract which is spinach extract.

[0045] In a preferred embodiment, the natural resin adhesive composition comprises a plant extract which is honeysuckle extract.

[0046] In a preferred embodiment, the natural resin adhesive composition comprises the plant extract which is barley extract with 3,4-dihydroxybenzaldehyde from 0.05 to 15%, preferably from 0.1 to 10% w / w.

[0047] The natural resin adhesive composition of this development can be found in a particleboard product. The wood is selected from the group comprising, but not limited to, hemp, pine, fir, cedar, larch, redwood, birch, poplar, beech, oak, mahogany, chestnut, eucalyptus, wood chips, sawdust, shavings, bark remnants, recycled wood pellets, and others. In a preferred embodiment, the natural resin adhesive composition is found in a hemp-based particleboard product.

[0048] In a preferred embodiment, the natural resin adhesive composition is incorporated into a hemp-bonded wood product in the quantity necessary to ensure particle adhesion. For example, a concentration between 2 and 40%, preferably between 5 and 30% of the natural resin adhesive composition.

[0049] Method for obtaining an adhesive composition of natural resin

[0050] Secondly, this development focuses on a method for obtaining a natural resin adhesive composition. The method involves preparing a dry plant extract, obtaining an aqueous solution of the powdered plant extract, and mixing it with an aqueous urea solution to obtain a natural resin adhesive composition.

[0051] Preparation of the dry plant extract:

[0052] First, a plant extract is prepared from plant material selected from leaves, seeds, stems, roots, flowers, or combinations thereof. For the purposes of this development, the plant material is selected from the group comprising beetroot (Beta vulgaris), barley (Hordeum vulgare), honeysuckle (Lonicera spp.), green tea (Camellia sinensis), spinach (Spinacia oleracea), or mixtures thereof.

[0053] In one embodiment, the plant extract is obtained as an aqueous, hydroalcoholic, or alcoholic extract. In a preferred embodiment, the plant extract is obtained through an aqueous extraction process. Useful methods for obtaining the plant extract include maceration, decoction, infusion, or a combination of these techniques, combined with filtration and concentration steps of the resulting plant extract.

[0054] The preparation of the leaf plant extract is carried out in water at a plant material-to-water ratio of 0.5:20 to 2:5, at a temperature between 1 and 50 °C, preferably between 1 and 3 °C, for a period of more than 30 hours, preferably between 45 and 50 hours, without stirring. The preparation of the granule plant extract is carried out in water at a plant material-to-water ratio of 0.5:20 to 2:5, at a temperature between 1 and 50 °C, preferably between 40 and 50 °C, for a period of more than 2 hours, preferably between 45 and 50 hours, with constant stirring at 10 to 250 rpm, preferably between 40 and 50 rpm, to obtain an aqueous plant extract.

[0055] The plant extract obtained is dried using any known method to produce a powdered plant extract, allowing for control of the powder concentration in the adhesive resin formulation. Preferably, the plant extract is dried by freeze-drying. This is particularly useful considering that each plant may have varying concentrations in the aqueous extract, but when the extract is in powder form, the water volume can be adjusted to control the final concentrations in the resin.

[0056] Preparation of the aqueous solution of the powdered plant extract

[0057] Secondly, an aqueous solution of the powdered plant extract is prepared. The aqueous solution has a concentration of between 30 and 50% by weight of plant extract, preferably a concentration of 40% plant extract relative to 100% of the natural resin adhesive composition. Simultaneously, an aqueous urea solution is prepared with a concentration of between 20 and 40% urea, preferably a concentration of 30%.

[0058] Mixing of solutions: Subsequently, an aqueous solution of plant extract and an aqueous solution of urea are mixed. The mixture is prepared to obtain a solution with a volume or weight ratio (plant extract to urea) or (aqueous solution of plant extract: aqueous solution of urea) between 1:1 and 2:1. The resulting mixture is allowed to react for a time between 1 and 10 hours at a temperature between 25 and 150 °C, preferably for a time between 2 and 8 hours, at a temperature between 50 and 100 °C.

[0059] In one method, the mixing of the aqueous plant extract solution and the aqueous urea solution is carried out in two stages. In the first stage, two-thirds of the total volume of the urea solution is added to the aqueous plant extract solution and allowed to react for 1 to 4 hours at a temperature between 50 and 100 °C. Subsequently, the remaining volume of the urea solution is added and allowed to react for another 1 to 3 hours at the same temperature. The addition of the aqueous urea solution in two steps is performed to control resin formation.

[0060] Drying

[0061] Finally, the resulting product is dried into a highly viscous solid or liquid that, when mixed with water, becomes the adhesive composition of the natural resin. The drying stage is carried out using any known method, preferably at a temperature above 90 °C, and more preferably at 120 °C. The resulting solid is characterized as a dark-colored, viscous solid or liquid.

[0062] Method for obtaining a particleboard product

[0063] Thirdly, this development relates to obtaining a wood-based composite product with a natural resin adhesive. The method involves applying the natural resin adhesive to wood particles using mechanical pressure to create a wood-based composite product.

[0064] In particular, the method for obtaining a particleboard product comprises mixing between 5 and 50% w / w of the natural resin adhesive composition with water in an amount between 30 and 50% w / w and wood fiber between 30 and 50% w / w in relation to 100% w / w of the weight of the particleboard product. For the purposes of this development, "wood fiber" is understood to mean the material composed of elongated, thin plant cells, extracted from the wood of different species or biomass, selected from the group comprising hemp, pine, fir, cedar, larch, redwood, birch, poplar, beech, oak, mahogany, chestnut, eucalyptus, wood chips, sawdust, wood shavings, bark residue, and recycled wood pellets.

[0065] For the purposes of this development, the mixture of natural resin adhesive compound, wood fiber, and water is prepared until a homogeneous mixture is obtained, or for a period of 6 to 18 hours. Among the parameters that can be considered to identify that the mixture is ready is that the biomass fibers change color and absorb all the liquid. Subsequently, the resulting mixture undergoes a drying process. The drying of the mixture is carried out using any method known in the prior art.

[0066] Subsequently, the mixture obtained after drying is placed in a mold, where a temperature above 90 °C, preferably between 100 and 160 °C, is applied at a pressure between 1 and 5 MPa for a period exceeding 5 minutes, preferably between 5 and 30 minutes. Finally, a wood-based product with the natural resin adhesive composition of this formulation is removed from the mold.

[0067] In a preferred embodiment, the agglomerated wood product obtained by the developed method has a density ranging from 0.10 to 1.0 g / cm³ 3 between 0.20 and 0.8 g / cm 3 , preferably between 0.35 and 0.60 g / cm 3 which identifies the samples as low-density particleboard.

[0068] The adhesive composition of natural resin gives the particleboard product characteristics such as: better water resistance; bond strength comparable to that of commercial samples; low probability of deformation under stress; higher strength resistance values, indicating that its surface is less prone to deformation under applied pressure; antifungal properties by slowing the growth of fungi.

[0069] Examples

[0070] Example 1. Selection of plant species by computational screening

[0071] Compounds from the Analyticon MEGx database were used for screening, and two datasets were downloaded from the website: MEGx_l and MEGx_2. MEGx_l contains 6348 compounds, and MEGx_2 contains 414 compounds. The 3D structure of each compound was generated using OpenBabel version 2.4.1 and the Universal Force Field (UFF) molecular mechanics theory level. Then, using the PaDEL-descriptor software, substructure fragment analysis was performed with the SubFPC48 fingerprint, which is associated with the presence of aldehyde groups in the examined molecules. Furthermore, the toxicity of the molecules was assessed using the SiliS-PTOXRA software, considering the Environmental Protection Agency (EPA) and Globally Harmonized System (GHS) classifications.

[0072] Computational screening was performed for MEGx_1 and MEGx_2, and several filters were applied to select potential candidates for detailed evaluation. First, the number of aldehyde groups was set to 1 or 2. Then, only non-toxic compounds classified as EPA Class III and IV and GSH Class IV and V were considered. Subsequently, the chemical classes of terpenoids, simple aromatics, benzopyranoids, benzofuranoids, amino acids, peptides, miscellaneous compounds, and lignans were considered, while alkaloids were excluded. Compounds with molecular weights in the range of 138–1250 g / mol were selected. Finally, a total of 67 compounds were identified in MEGx_1 and 10 compounds in MEGx_2. Following this process, the molecules were thoroughly explored to determine natural sources for their extraction and subsequent use. The sources were selected based on their availability, restrictions, and cost.With this, 6 molecules were selected which are presented in Table 1.

[0073] Table 1. Compounds containing aldehydes selected from the MEGx_l and MEGx_2 groups. (Terp. = Terpenoids, PM = Molecular Weight; TX = Toxicity)

[0074] Six natural sources were selected based on computational screening as described in the previous section. Table 2 shows these molecules and the natural sources that are likely to contain them.

[0075] Table 2. Selected compounds and plant material containing them

[0076] Example 2. Obtaining the plant extract and synthesis of the adhesive composition of natural resin

[0077] The honeysuckle plant (Lonicera japonica) (Ms) was purchased from a local garden center in Nayón, Ecuador. Spinach leaves (Spinacia oleracea) (Es), beetroot samples (Beta vulgaris) (Re), green tea leaves (Camellia sinensis) (Tv), and barley seeds (Hordeum vulgare) (Cb) were purchased from a local supermarket (Quito, Ecuador). All sources are free of use restrictions, meaning there are no environmental, social, or economic controls on their use and harvesting.

[0078] For species where the material of interest is powdered dried leaves, these were immersed in distilled water at a ratio of 1:10 weight / volume (plant material: water) for 48 hours at 1°C. For species where the plant material of interest is grains, the powdered seeds were immersed in water at the same 1:10 weight / volume ratio, with constant stirring for 2 hours at 45°C; and then allowed to concentrate at 1°C for 48 hours.

[0079] Subsequently, the liquid phase of the extraction was recovered and dried by lyophilization for further characterization and use. The dried extract was weighed and the percent extraction yield was calculated; the results are shown in Table 3.

[0080] Table 3. Yield of aqueous extraction of plant material

[0081] Once the powdered plant extract was obtained, the synthesis of the natural resin adhesive compound continued. For this, the dried extract was weighed and diluted to a concentration of 40% w / w to obtain an aqueous solution of the powdered plant extract. Simultaneously, a 30% w / w aqueous urea solution was prepared and added in a two-stage reaction. The total amount of urea to be added was divided into U1 and U2 in a weight ratio of 2:1 U1 / U2. The diluted plant extract and solution U1 were added to a beaker, and the reaction took place for 2 hours at 75°C. Then, solution U2 was added to the beaker. This second stage of the reaction took place for 1 hour at 75°C. The reaction mixture was dried at 120°C until the natural resin adhesive composition was obtained as a solid.

[0082] Example 3. Characterization of plant extracts

[0083] To use plant extracts as a replacement for glyoxal in the reaction for the synthesis of adhesive resin with urea, it was necessary to determine the presence of aldehyde groups in them. The dried extracts were characterized to determine if molecules with an aldehyde group were present in each plant extract.

[0084] Fourier Transform Infrared Spectroscopy (FTIR)

[0085] This analysis was performed on both the original dry extracts and the 40% glyoxal solution (Gly) (control), using the Agilent Technologies Cary 630 FTIR spectrometer. Measurements were recorded in the 400–4000 cm⁻¹ range. 1 in absorbance mode with a resolution of 4 cm 1 after 8 continuous scans with a threshold of 0.002. FIG. 1A shows the FTIR spectra of the sources extracted in the 1500 to 1800 cm region 1as well as glyoxal as a commercial control for the aldehyde used in wood resins. Since the extracts are expected to have complex compositions, the main purpose of these spectra is to identify the presence of aldehyde groups in the samples. The bands that suggest the presence of aldehyde groups are primarily a peak at 1660–1750 cm⁻¹ 1 and a double band at 2700-2900 cm 1 caused by a CH stretching of the aldehyde. As a control, glyoxal has a strong peak at 1637 cm⁻¹ x but not a double band. The spinach extract spectrum shows a small double band at 2900-2860 cm⁻¹ 1 and an intense peak at 1585 cm 1 Both suggest the presence of aldehyde groups in the extract. The spectrum of the beetroot extract also shows a small double band at 2920–2880 cm⁻¹ 1 and a peak at 1600 cm' 1 In addition, green tea extract has an intense peak at 1608 cm⁻¹ 1On the other hand, the barley extract has a small peak at 1645 cm' 1 and a small broadband at 2900 cm' 1 The honeysuckle extract shows a small peak at 1610 cm' 1 and a small double peak at 2920 - 2887 cm' 1 Of the six extracts characterized by FTIR, all samples showed the presence of peaks corresponding to aldehydes, suggesting that they contain natural aldehydes in the mixture.

[0086] FTIR alone typically cannot reveal all the functional groups of molecules due to the potential overlap of different peaks from functional groups present in the complex composition of the material. For this reason, these results were complemented by thermogravimetric analysis (TGA) of the dried extracts in an effort to identify the number of components present in each and their relative abundance.

[0087] Thermogravimetric Analysis (TGA)

[0088] When combined with infrared techniques, TGA can be used to determine identification and chemical composition. Thermogravimetric analysis was performed on the extracted materials to further investigate their composition. Tests were programmed to run from 25 °C to 900 °C at a heating rate of 10 °C / min on the Pelkin Elmer STA 8000 simultaneous thermal analyzer. Figure 1B shows the respective thermogravimetric curves for the dried extracted materials. These curves suggest that the extracted materials have complex compositions, as they exhibit two or more degradation peaks, as expected in aqueous extractions. Extracts Re, Ms, and Cb have a strong degradation peak around 200 °C, which could be attributed to the presence of organic acids, lipids, and proteins. Extract Re shows a second peak at 318 °C, attributed to the source pigments.Extracts Ms and Cb also exhibit a notable degradation point at 280°C, which could be associated with phenolic compounds, the molecules expected to be extracted. The DTG curve of extract Am points to the presence of carbohydrates, lipids, and proteins. For extract Es, the degradation peaks occur around 150°C, 170°C, and 260°C, suggesting the presence of proteins, lipids, and triterpenes. Finally, extract Tv shows peaks in the DTG curve at 130°C, 150°C, and a broad peak between 210°C and 300°C. This could be interpreted as the extract being composed of small volatile compounds, polyphenols, alkaloids, lipids, and proteins.

[0089] Thin Layer Chromatography

[0090] Samples were detected at a concentration of 2% w / w on glass-backed silica gel 60 plates (5.5 x 2.5 cm) along with commercial saponin. Four mL of acetic acid-water-n-butanol (2:3:5 v / v / v) was used as the developing solvent. An iodine chamber, 254 nm UV light, and 365 nm UV light were used as visualization devices. Additionally, 10% sulfuric acid in ethanol was used as a visualization agent. The developed and dried plates were immersed in the acid solution until saturation, followed by heating on a hot plate at 110 °C for 3 minutes. The developed plates were also silver-plated using 0.15 M silver nitrate for visualization of aldehydes.

[0091] Phytochemical Tests. The extracted materials were tested using various phytochemical tests based on Harbome's guide to phytochemical methods (JB, Harbome, Phytochemical methods: a guide to modern techniques of plant analysis. Chapman and Hall, 1998). Among the most relevant tests, the extracts were tested for steroidal triterpenoids using the Salkowski test, for phenols and tannins using the FeCh test, for diterpenes using the copper acetate test, for saponins using the saponin foam test, and for free aldehydes using the Tollens' test. These tests allow for the identification of the molecules intended for extraction from the sources.

[0092] The phytochemical tests consisted of a total of 16 tests that qualitatively confirmed the presence or absence of 12 metabolites. Of the six extracts characterized by phytochemical analysis and TLC, the samples showed the presence of the corresponding chemical class, suggesting that they contain the molecules of interest. A summary of these findings is presented in Table 4.

[0093] Table 4. Summary of phytochemical test results for natural dry extracts of Honeysuckle (Ms), Spinach (Es), Beetroot (Re), Barley (Cb), and Green Tea (Tv), and commercial Quillaja saponin (SQ).

[0094] For the aqueous extract of spinach, the target molecule was oleragenocid, a triterpenoid saponin. The sample tested positive for aldehyde, saponin, diterpene, and triterpenoid groups, and along with the FTIR and TGA results, it is highly likely that the molecule is present in the extract. Furthermore, additional confirmation of the molecule's presence was obtained from TLC analysis, where the band revealed with the acid visualizer had an Rf value of 0.629, similar to the commercial saponin standard visualized on the same plate.

[0095] For the aqueous extract of beetroot root, the molecules sought were gypsophyllasaponin, a terpenoid saponin, and protocatechualdehyde, a simple aromatic compound. Although the extract tested negative for saponins in the phytochemical assay, TLC revealed the presence of a saponin in the extract. A band with an Rf value of 0.425 was revealed using the sulfuric acid visualizer, which differs from the saponin standard that had an Rf value of 0.549 on the same plate. Therefore, it is likely that both molecules are present in the extract, and the difference in Rf values ​​could be due to differences in molecular weight and polarity between the standard and the molecule present in the extract.

[0096] For the aqueous extract of green tea leaves, the target molecule was Assam saponin A, a triterpenoid saponin. The extract tested positive for the presence of triterpenoids. TLC analysis revealed a complex composition in the extract, with several bands in the chromatogram, some of which had Rf values ​​similar to the saponin standard. This indicates the possible presence of the compound, although it was masked by the presence of other molecules.

[0097] Finally, for the aqueous extract of barley seeds, the target molecule was protocatechualdehyde, a simple aromatic compound. The extract tested positive for the presence of aldehydes, with a distinctly high presence of proteins and saponins. The Cb resin composition showed performance close to that of the UG control resin in water resistance and mechanical tests, demonstrating its viability and competitiveness as a material for particleboard production. Therefore, the presence of protocatechualdehyde in the extract was quantified using a TLC method where the developed spot area of ​​the molecule present in the extract was compared to the developed spot area of ​​commercially available protocatechualdehyde. This method confirmed a presence of 0.9 wt% of the molecule in the extract.

[0098] Example 4. Obtaining a particleboard product with the adhesive composition of natural resin

[0099] Laboratory plywood prototypes were prepared from mixtures of hemp (fiber) and resin at various resin concentrations, and were made for the tests described below.

[0100] For the fabrication of the prototype samples, fiber-resin blends were prepared with a 1:1 g / mL composite / resin ratio. Resin dilutions of 20% w / w in water were studied. The blend was allowed to stand overnight before use. The samples used for water resistance and compression tests were prepared as rod-shaped samples with a diameter of 1 cm and a height of 1 cm, using a mold of the specified dimensions. The blend was packed into the mold and then pressed at 140°C and 2.5 MPa for 10 minutes. The samples were conditioned for 48 hours before any testing. The density of these samples ranged from 0.38 to 0.55 g / cm³. 3This identifies the samples as low-density particleboard. Additionally, samples for flexural and durometer tests were prepared as flat samples approximately 4.0 x 12 x 0.30 cm, using release paper to apply the mixture in thin layers until the desired width of 3 mm was reached. Between each layer, the sample was cured for 10 seconds at 140 °C without pressure. After the final layer, the sample was pressed at 140 °C and 2.5 MPa for 5 minutes and allowed to condition for 48 hours. The density of these samples ranges from 0.39 to 0.68 g / cm³. 3 , which identifies the samples as low and medium density particle boards (MDP).

[0101] Finally, for fire resistance testing, flat samples measuring 5 x 10 x 1 cm were prepared using a mold with the specified dimensions. The mixture was packed into the mold and then pressed at 20 °C and 2.5 MPa for 10 minutes. The heat was then applied to 140 °C, and pressing continued for another 5 minutes at 2.5 MPa. The samples were removed from the mold and pressed for a further 15 minutes at 140 °C and 2.5 MPa. The samples were allowed to dry for 48 hours before any testing. The density of these samples ranged from 0.60 to 0.72 g / cm³. 3 , which identifies the samples as medium density particle boards (MDP).

[0102] Example 5. Comparative water resistance tests

[0103] Water absorption and swelling of particleboard are problematic because they can lead to dimensional instability and structural damage. When particleboard absorbs water, the wood fibers swell, causing the board to expand. This swelling can result in warping, delamination, and loss of structural integrity, compromising the particleboard's performance and durability. Furthermore, increased moisture content can promote mold and mildew growth, further deteriorating the board and affecting indoor air quality. Controlling water absorption and swelling is crucial for maintaining the quality and longevity of particleboard in a variety of applications.Water absorption, according to ASTM D-1037, indicates the water retention of samples as a percentage change by weight, and volumetric swelling shows the increase in sample volume as a result of water absorption. By studying both properties, it is possible to determine which sample has more efficient water resistance.

[0104] The same samples were used as those obtained in the test performed in the previous example.

[0105] The results show that most of the samples were prepared as flat 5 x 10 x 1 cm specimens using a mold with the specified dimensions. Packing the mixture into the mold was followed by pressing at 20 °C and 2.5 MPa for 10 minutes. These specimens exhibited volume swelling values ​​between 10 and 50%, and water absorption ranging from 100 to 250%. Volume swelling is the determining factor in whether a specimen is water-resistant, as it causes visual and structural problems and is the most important variable considered in national manufacturing standards.

[0106] Figure 2 shows the behavior of selected samples after 48 hours of immersion in water. The three controls used in our studies included the Urea-Glyoxal (UG) control resin at 20% concentration, resin-free samples (AC), commercial particleboard (Com), and HempWood (CCon). The control samples with UG resin at different concentrations in Figure 7 illustrate the influence of resin content on sample water resistance. The UG samples with resin concentrations of 15% and 20% exhibited the least volume swelling and water absorption compared to other UG resin formulations. Lower UG resin concentrations (1%, 2.5%, and 5%) proved ineffective in improving the water resistance of the samples, as they showed high water absorption and volume swelling.A higher resin concentration (25% UG) showed worse water resistance than 20% UG, suggesting that a continuous increase in resin content does not necessarily improve the water resistance of the samples. This could be due to oversaturation of the particles with resin, which might prevent the fibers from bonding together through the resin by occupying too much space.

[0107] The control sample AC (resin-free hemp) had the lowest water resistance, confirming that the use of resin reduces volume swelling and water absorption. On the other hand, the control sample CCon (commercial HempWood) showed high volume swelling (83.7%) but low water absorption (81.8%). The commercial particleboard sample Com showed very high volume swelling (approximately 84%) and low water absorption (approximately 90%) after 48 hours in contact with water.

[0108] Overall, samples with resins based on Cb, Es, and Ms extracts produced with 20% resin showed the best water resistance compared to concentrations of 5% and 30%, commercial controls, and UG resins. Increasing or decreasing the resin concentration from 20% did not improve water resistance. Three of the samples produced (20Cb, 20Ms, and 20Es) had low volume swelling (12.5%, 16.2%, and 16.4%, respectively) and relatively low water absorption (171.7%, 171.2%, and 164.0%) compared to samples 20Re, 20Tv, and 20Am. For the Tv resin, increasing the resin concentration improved water resistance, but it still performed worse than the other resins. Water absorption and volume swelling of Es resin improve when less resin is used, suggesting that the fibers are saturated with less Es resin than with UG resin.

[0109] Based on the data presented, the samples using the adhesive composition of natural resins from extracts appear to be promising as substitutes for UG resin in the production of particle boards.

[0110] Example 6. Comparative tests of mechanical properties

[0111] The mechanical properties of particleboard are crucial because they determine the material's strength, stiffness, durability, and overall performance in various applications. These properties, which include tensile strength, compressive strength, flexural strength, and shear strength, influence the structural integrity and load-bearing capacity of particleboard in construction, furniture manufacturing, and other uses. Understanding and optimizing these mechanical properties is fundamental to ensuring that particleboard meets the required standards for specific applications, providing stability, longevity, and reliability in a wide range of structural and non-structural uses. The modulus of elasticity (MOE), indentation strength, and flexural strength were obtained and calculated for samples with 20% resin, as this resin-to-fiber ratio exhibited the best water resistance.

[0112] Figure 3 shows the Modulus of Elasticity (MOE) obtained from the linear region of the load-deformation curve for each sample. The commercial samples CCon and Com show the lowest MOE values ​​(1100 MPa and 3000 MPa, respectively), indicating that they are less resistant to compression. Importantly, the commercial samples exhibited clear moments of rupture under compression, while the laboratory samples did not show clear rupture but were compressed into shapes similar to small discs. The samples with natural resins had higher MOE values ​​than the UG and Ac samples, indicating that they are less likely to deform under stress. This could be due to the shape of the laboratory samples and other factors such as fiber origin and size, density, moisture content, and manufacturing conditions, which determine this property of particleboard.

[0113] Based on this, the collected data suggest that the origin of the resin does not influence the MOE values. However, the results show that the resin composition does not affect the modulus of elasticity of the samples.

[0114] The modulus of elasticity for particleboard is generally in the range of 1500 to 4000 MPa. The results suggest that the adhesive composition of natural resin can affect the bond strength of the samples. In this respect, the commercial samples fall within this range, as expected. Some laboratory samples, however, have higher MOEs, indicating that they may be prone to fracture or cracking rather than undergoing significant plastic deformation and resisting stress.

[0115] Although the samples with the natural resin adhesive composition of this development exhibit improved water resistance, they are more brittle than commercially available materials. This could be due to the shape of the laboratory samples and other factors such as fiber origin and size, density, moisture content, and manufacturing conditions, all of which determine this property of particleboard. However, some compositions have bond strength similar to that of commercially available samples. Specific applications of both types of particleboard could benefit from one of these characteristics, so further testing was conducted, including static bending and hardness tests.

[0116] Figure 4 shows the Modulus of Rupture (MOR) of the samples as a function of their density. Since the density of the samples did not vary considerably, the differences in MOR values ​​could be attributed to the origin of the binder and the manufacturing process. Failure in the samples after the flexural tests frequently occurred off-center. This indicates poor material distribution throughout the samples, which could be attributed to the manufacturing process.

[0117] Previous studies exploring hemp particleboard, with a sample thickness similar to that presented in this study, report comparable flexural strength values ​​of around 5 MPa. Commercially available particleboards with a thickness greater than 1 inch report values ​​of 20–30 MPa. However, Rb values ​​are dependent on sample thickness. Consequently, increasing sample thickness is likely to increase the maximum stress that can be applied to the materials before they fracture. Despite limitations in sample thickness due to the equipment used, the results in Figure 4 were used to evaluate resin-based formulations and determine that natural resins could successfully replace formaldehyde-based resins.It is noteworthy that the resins synthesized from Green Tea (Tv), and Honeysuckle (Ms) presented Rb values ​​similar to that of the control sample with urea-glyoxal resin (UG).

[0118] The indentation strength of a sample, as shown in Figure 5, indicates how resistant the material is to permanent indentation on its surface. The commercial particleboard samples had the highest strength values, indicating that their surface is less prone to deformation under applied pressure. Among the laboratory samples, AC had the lowest indentation strength and 15UG the highest. The extract resin samples had similar values ​​to each other, indicating that other factors, such as density, manufacturing process, and fiber origin, are more important determinants of this property.

[0119] Example 7. Comparative antifungal activity assays

[0120] Visual fungal growth in the samples was assessed by placing control and laboratory samples in a dark, high-humidity environment. An additional set of samples was prepared by pre-sterilizing the extract with methanol and filtering it to remove potential contaminants from the final sample. Environmental conditions were monitored using a Preshwous® 5-in-1 air quality monitor.

[0121] The resistance of particleboard to fungal activity allows for the determination of potential product uses. Samples were placed in a dark, high-humidity environment, and visual assessment of fungal growth was performed on laboratory samples for 5 weeks, collecting qualitative data at 4-day intervals. Table 5 details the progression of fungal growth in the samples. Table 5. Fungal activity in samples after exposure to a high-humidity environment After 32 days of exposure to the established environment, fungal growth was observed in all samples studied. Laboratory samples 20Am and 20Tv showed fungal growth later, after 32 days from the start of the test. In contrast, the control sample AC and the filtered sample 20Am.F showed the first signs of fungal growth only after 15 and 18 days from the start of the test, respectively. This indicates that the use of a suitable resin in plywood manufacturing provides antifungal properties by slowing fungal growth.

[0122] The commercial samples CCon and Com, and the laboratory samples 20Tv, 20Am, 20Ms, 20Cb, 20Re, and 20Cb.F showed similar behavior, with the first signs of fungal growth observed on day 29. This means that fungal growth was delayed by approximately 10 days when these resins were used, in both the commercial and laboratory samples. However, the commercial samples have additional treatments against fungal growth besides the resin, while our laboratory samples do not. Including these treatments could improve the antifungal activity of the laboratory samples. Nevertheless, the laboratory resins perform as well as the commercial particleboard samples without additional treatments, further demonstrating their viability as manufacturing materials.

[0123] Example 8. Comparative fire resistance tests

[0124] A sample is considered fire-resistant if the flame height is less than 150 mm after direct exposure to a small flame. Figure 6 shows the flame height reached after the samples were exposed directly to a small flame for 15 seconds.

[0125] As shown in Figure 6, all samples had flame heights below 150 mm. In this respect, all the tested materials can be considered flame retardant. However, the ash development and the presence of flaming droplets indicate different combustion behaviors that could affect the use of the materials. In particular, flaming droplets were observed when no resin was used (sample AC), indicating that adding a natural resin adhesive composition changes the combustion behavior and minimizes flaming droplets. Ash development is an indicator of sample degradation when burned. The absence of resin in the sample allowed the particleboard to degrade considerably when exposed to the flame. By adding UG and Cb resins, ash development decreased, indicating greater resistance of the material to combustion.

Claims

CLAIMS 1. A natural resin adhesive composition, comprising between 2 and 50% w / w of a plant extract, urea and water; wherein the plant extract is beetroot, barley, honeysuckle, green tea, spinach extract, or mixtures thereof.

2. The natural resin adhesive composition of Claim 1, comprising urea between 5 and 40% w / w and water between 20 and 80% w / w.

3. The natural resin adhesive composition of Claim 1, wherein the plant extract comprises metabolites selected from: saponins, benzaldehydes, monoterpenes, diterpenes, triterpenes, and glycosides.

4. The natural resin adhesive composition of Claim 1, wherein the plant extract comprises metabolites with aldehyde and hydroxyl functional groups.

5. The natural resin adhesive composition of Claim 1, wherein the plant extract is an aqueous extract.

6. The natural resin adhesive composition of Claim 1, wherein the plant extract is barley, spinach or honeysuckle extract.

7. The natural resin adhesive composition of Claim 1, wherein the plant extract comprises 3,4-dihydroxybenzaldehyde, oleragenoside, secologanin or a mixture thereof.

8. The natural resin adhesive composition of Claim 1, wherein the plant extract is barley extract with 0.1 to 10% w / w of 3,4-dihydroxybenzaldehyde.

9. The natural resin adhesive composition of Claim 1 comprising a plant extract between 20 and 30% w / w, urea between 10 and 20% w / w and water between 50 and 70% w / w.

10. A wood composite product with the adhesive composition of natural resin containing plant extract of Claim 1.

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