Method for improving wood properties based on furfuryl alcohol / hyperbranched polymer synergy

Abstract

The application discloses a method for improving wood performance based on furfuryl alcohol / hyperbranched polymer synergistic effect, which comprises the following steps: step 1, construction of a modified system, glycerol, diisopropyl alcohol amine and carboxylic acid are mixed, the molar ratio of hydroxyl and carboxyl is controlled to be 1:1-1:1.2, and sufficient reaction is carried out at 150 DEG C for 4h to obtain a uniform yellow viscous liquid, i.e. a hyperbranched polyester amide prepolymer; a furfuryl alcohol modified solution is configured, and the furfuryl alcohol modified solution comprises furfuryl alcohol, maleic anhydride as a catalyst and sodium tetraborate as a buffer agent according to mass percentage, and the pH of the system is adjusted to about 4. The application can simultaneously improve the impact toughness, hardness, bending strength, dimensional stability and moisture resistance of wood, solves the problem of toughness reduction of furfuryl alcohol modified materials, and through the regulation of the impregnation process, most of the modifiers are introduced into the cell wall region, so that the problems of large amount of modifiers and excessive concentration of the modifiers in the cell cavity region are avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wood processing, and particularly relates to a method for improving wood performance based on synergistic effect of furfuryl alcohol / hyperbranched polymer. BACKGROUND

[0002] Wood is an environmentally friendly natural polymer material, which is widely used in many fields of national economic development such as building, furniture and decoration. However, with the promulgation of policies such as banning or limiting logging in natural forests in various countries around the world, fast-growing wood has attracted attention due to its fast growth rate and short rotation period. However, fast-growing wood has poor quality, small density and soft texture, and is prone to cracking and deformation, which limits its application range and value. Therefore, improving the physical and mechanical properties of low-quality fast-growing wood and realizing the optimal use of inferior wood are the needs of green and sustainable development of the wood industry, and are also the key to alleviating the contradiction between supply and demand of wood and ensuring the safety of national wood resources.

[0003] Furfuryl alcohol modification uses furfuryl alcohol derived from abundant agricultural residues (such as sugarcane residue, corn cob, straw, etc.) as a modifier, which greatly improves the dimensional stability, hydrophobicity, compressive strength and biological degradation resistance of modified wood. In addition, the modified wood has low toxicity and less impact on the environment, which has attracted attention in the industry and has been industrialized in some European countries and the United States.

[0004] However, furfuryl alcohol modification has no obvious effect on the bending strength and elastic modulus of wood. In addition, the impact toughness of furfuryl alcohol modified wood decreases significantly, and the toughness of Betula pubescens Ehrh. and Fagus sylvatica L. modified by 48% furfuryl alcohol decreases by more than 70%. The decrease in toughness increases the risk coefficient of wood as a structural material, limiting the application range of furfuryl alcohol modified wood.

[0005] Previous researchers used nanoparticles and flexible polymers such as polyvinyl alcohol to synergize furfuryl alcohol for wood impregnation modification. However, nanoparticles are prone to aggregation and difficult to disperse well, which may cause aggregation in cell cavities, resulting in high weight gain and large amount of modifier. Due to the limitations of its molecular structure and size, polyvinyl alcohol is difficult to enter the cell wall in large quantities (the cell wall of wood has multi-scale pores with a diameter usually less than 100 nm, and the inter-microfibril gap is less than 5 nm), which may affect the entry of furfuryl alcohol into the cell wall and affect the improvement effect of wood performance.

[0006] Hyperbranched polymers are a class of macromolecular polymers that gradually grow into highly branched, three-dimensional spherical structures through the polymerization of small monomer molecules. Their synthesis process is relatively simple, facilitating large-scale production and providing a solid industrial foundation. Hyperbranched polymers have smaller particle sizes than linear polymers of the same molecular weight, and their outer surfaces typically contain functional groups that can participate in molecular modification. This facilitates the regulation of interactions between hyperbranched polymers and other chemical components, allowing for timely changes in compatibility with other chemical substances. Internally, they possess a unique microporous structure, which is beneficial for regulating stress distribution. Furthermore, the molecular weight of hyperbranched polymers is easily controllable, with less molecular chain entanglement, less crystallization, good solubility, and low viscosity that does not change with increasing molecular weight. They can also be used as toughening modifiers to improve the toughness of thermosetting resins and other polymers. However, there is limited research on their application in wood modification and performance enhancement. Summary of the Invention:

[0007] The technical problem to be solved by the present invention is to provide a method for improving wood performance based on the synergistic effect of furfuryl alcohol / hyperbranched polymer. This method can simultaneously improve the impact toughness, hardness, bending strength, dimensional stability and moisture barrier properties of wood, solve the problem of decreased toughness of furfuryl alcohol modified wood, and through the control of the impregnation process, direct most of the modifier into the cell wall region, avoiding problems such as large amount of modifier and excessive concentration of modifier in the cell cavity region.

[0008] The technical solution of this invention is to provide a method for improving wood properties based on the synergistic effect of furfuryl alcohol / hyperbranched polymers, comprising the following steps:

[0009] Step 1: Construction of the modified system. Glycerol, diisopropanolamine, and carboxylic acid are mixed, controlling the molar ratio of hydroxyl to carboxyl groups to be 1:1-1:1.2. The mixture is reacted at 150℃ for 4 hours to obtain a homogeneous yellow viscous liquid, i.e., the hyperbranched polyesteramide prepolymer. A furfuryl alcohol modification solution is prepared, comprising furfuryl alcohol (25%), maleic anhydride (1-2%) as a catalyst, and sodium tetraborate (2-4%) as a buffer, adjusted to a pH of approximately 4 by mass percentage. Then, the hyperbranched prepolymer (2-10%) is mixed with the furfuryl alcohol modification solution using ethanol as a solvent and magnetically stirred until a homogeneous pale yellow clear solution is obtained, thus obtaining the furfuryl alcohol / hyperbranched polymer modified system.

[0010] Step 2, Wood processing and characterization: Select sapwood from fast-growing timber and process the wood into test materials with dimensions of 4mm (axial) × 20mm (tangential) × 20mm (radial), 80mm (axial) × 10mm (tangential) × 4mm (radial), and 120mm (axial) × 10mm (tangential) × 4mm (radial).

[0011] Step 3, Intermittent Vacuum Impregnation and Post-Vacuum Modification of Wood: The furfuryl alcohol / hyperbranched polymer modified system was treated with intermittent vacuum impregnation (each interval was 1 hour, and the impregnation time was 2 hours). Post-vacuum treatment was then performed to remove most of the modifier from the cell cavities. The sample was then removed and the surface was wiped clean of excess reagent. To avoid monomer volatilization loss during high-temperature curing and to promote the diffusion of the modifier into the cell wall, the sample was wrapped in aluminum foil and kept at room temperature and atmospheric pressure for 48 hours to promote uniform distribution of the modifier. Then, the sample was placed in a vacuum drying oven, and a wood gradient drying program was set (60(±2)℃, 2 hours, -0.1MPa; 80(±2)℃, 2 hours, -0.1MPa; remove the foil, adjust the temperature to 103(±2)℃, 24 hours). This achieved in-situ curing of the polymer within the wood cell wall and oven-drying of the sample, thereby obtaining furfuryl alcohol / hyperbranched polymer synergistically modified wood. This results in the synergistic modification of wood by furfuryl alcohol and hyperbranched polymers, which improves the physical and mechanical properties of the modified wood, including impact toughness, hardness, bending strength, dimensional stability, and moisture barrier properties.

[0012] The fast-growing timber of this invention includes broad-leaved timber, such as poplar, white poplar, eucalyptus, etc., and also includes coniferous timber, such as fir, larch, Masson pine, etc.

[0013] Compared with the prior art, the present invention has the following advantages after adopting the above solution:

[0014] This invention can simultaneously improve the impact toughness, hardness, bending strength, dimensional stability, and moisture barrier properties of wood, solving the problem of decreased toughness in furfuryl alcohol-modified wood. Furthermore, by controlling the impregnation process, most of the modifier is directed into the cell wall region, avoiding problems such as excessive modifier dosage and excessive concentration of modifier in the cell cavity region. This invention is of great significance for realizing the high-value application of furfuryl alcohol-modified fast-growing wood and the sustainable development of the industry. Detailed implementation method:

[0015] The present invention will be further described below with reference to specific embodiments:

[0016] Example 1

[0017] Glycerol, diisopropanolamine, and carboxylic acid were mixed, with the molar ratio of hydroxyl to carboxyl groups controlled at 1:1. The mixture was reacted at 150°C for 4 hours to obtain a homogeneous yellow viscous liquid, i.e., hyperbranched polyesteramide prepolymer. A furfuryl alcohol modification solution was prepared, with furfuryl alcohol (25%), maleic anhydride (1%) as catalyst, and sodium tetraborate (2%) as buffer, adjusting the pH of the system to approximately 4 by mass percentage. Then, the hyperbranched prepolymer (5%) was mixed with the furfuryl alcohol modification solution, using ethanol as solvent, and magnetically stirred until a homogeneous pale yellow clear solution was obtained, yielding the furfuryl alcohol / hyperbranched polymer modified system.

[0018] Wood processing and characterization: Eucalyptus wood was selected and processed into test materials with dimensions of 4mm (axial) × 20mm (tangential) × 20mm (radial), 80mm (axial) × 10mm (tangential) × 4mm (radial), and 120mm (axial) × 10mm (tangential) × 4mm (radial).

[0019] Intermittent vacuum impregnation followed by vacuum modification of wood involved treating wood with a furfuryl alcohol / hyperbranched polymer modified system through intermittent vacuum impregnation (each interval was 1 hour, and the impregnation time was 2 hours). A post-vacuum treatment was then performed to remove most of the modifier from the cell cavities. The specimens were then removed and the surface was wiped clean of excess reagent. To avoid monomer volatilization loss during high-temperature curing and to promote the diffusion of the modifier into the cell walls, the specimens were wrapped in aluminum foil and kept at room temperature and atmospheric pressure for 48 hours to promote uniform distribution of the modifier. Then, the specimens were placed in a vacuum drying oven, and a gradient drying program was set (60℃, 2 hours, -0.1 MPa; 80℃, 2 hours, -0.1 MPa; remove the foil, adjust the temperature to 103℃, 24 hours). This achieved in-situ curing of the polymer within the wood cell walls and oven-drying of the specimens, thereby obtaining furfuryl alcohol / hyperbranched polymer synergistically modified wood.

[0020] Example 2

[0021] Unlike Example 1, glycerol, diisopropanolamine, and carboxylic acid were mixed, with the molar ratio of hydroxyl to carboxyl groups controlled at 1:1.1. The mixture was reacted at 150°C for 4 hours to obtain a homogeneous yellow viscous liquid, i.e., the hyperbranched polyesteramide prepolymer. A furfuryl alcohol modification solution was prepared, comprising furfuryl alcohol (25%), maleic anhydride (1%) as a catalyst, and sodium tetraborate (2%) as a buffer, adjusting the pH of the system to approximately 4. Then, the hyperbranched prepolymer (8%) was mixed with the furfuryl alcohol modification solution using ethanol as a solvent and magnetically stirred until a homogeneous pale yellow clear solution was obtained, yielding the furfuryl alcohol / hyperbranched polymer modified system. This system was then subjected to intermittent vacuum impregnation and post-vacuum modification of wood as described in Example 1.

[0022] Comparative Example 1

[0023] Untreated wood was dried to absolute dryness at 103 (±2)℃ to prepare physical and mechanical test specimens of various sizes.

[0024] Comparative Example 2

[0025] A modified impregnation solution containing 25% furfuryl alcohol, 1% maleic anhydride, and 2% sodium tetraborate was prepared and magnetically stirred until a homogeneous, pale yellow, clear solution with a pH of 4-5 was obtained. Furfuryl alcohol served as the main modifier, maleic anhydride as the catalyst, and sodium tetraborate as the buffer. The wood was then subjected to intermittent vacuum impregnation followed by vacuum modification.

[0026] The impact toughness of wood was tested according to national standards GB / T1843-2008 and GB / T1940-2009, with axial and tangential lengths of 80 mm and 10 mm, respectively. Consistent with previous studies, furfuryl alcohol modification alone in Comparative Example 2 had a certain negative effect on the impact toughness of the wood. After synergistic modification, the impact toughness of the wood in Examples 1 and 2 was significantly improved compared to the furfuryl alcohol-modified wood in Comparative Example 1. Example 2 showed the best modification effect, with the highest impact toughness, exceeding 45% compared to the furfuryl alcohol-modified wood.

[0027] The bending resistance of the test material was tested using a three-point bending test according to standard ASTM D4761-19, with a speed of 1 mm / min and axial and tangential lengths of 120 mm and 10 mm, respectively. In Example 2, the bending strength and modulus of elasticity of the synergistically modified wood were both improved. This is mainly attributed to the increased wood density after synergistic modification, which causes the furfuryl alcohol resin molecules to cross-link within the wood, reducing the free volume of the molecules and restricting the slippage of the wood macromolecular chains.

[0028] The hardness of the test materials was tested according to ASTM D2240. The hardness of Examples 1 and 2 was improved compared with Comparative Example 1, with the hardness of Example 1 being improved by more than 15%.

[0029] Different saturated salt solutions (including K₂CO₃, NaBr, and NaCl) were prepared at 25°C to obtain environments with relative humidity of 49.3%, 62.8%, and 77.8% at 25°C, respectively. The moisture absorption process of the wood started from the environment with the lowest relative humidity and reached equilibrium states sequentially. The mass and dimensions at each equilibrium state were measured, and the equilibrium moisture content and dimensional change rate were calculated. Compared with Comparative Example 1, Comparative Example 2 showed a decrease in both moisture content and dimensional change rate of the wood modified with furfuryl alcohol. Examples 1 and 2 showed even lower moisture content and dimensional change rates, with Example 2 showing a reduction of more than 40% in both moisture content and dimensional change rate compared to Comparative Example 1.

[0030] The above description only illustrates preferred embodiments of the present invention and should not be construed as limiting the scope of the claims. Any equivalent structural or procedural modifications made using this specification are included within the patent protection scope of the present invention.

Claims

1. A method for improving wood properties based on the synergistic effect of furfuryl alcohol / hyperbranched polymers, characterized in that: Step 1: Construction of the modified system. Glycerol, diisopropanolamine, and carboxylic acid are mixed, and the molar ratio of hydroxyl to carboxyl groups is controlled at 1:1-1:1.

2. The mixture is reacted at 145-155℃ for 3-5 hours to obtain a hyperbranched polyester amide prepolymer. A furfuryl alcohol modification solution is prepared, consisting of 20-30% furfuryl alcohol, 1-2% maleic anhydride, and 2-4% sodium tetraborate by mass percentage. The pH of the system is adjusted to 3.8-4.

2. Then, 2-10% of the hyperbranched prepolymer is mixed with the furfuryl alcohol modification solution, using ethanol as a solvent, and magnetically stirred until a homogeneous pale yellow clear solution is obtained, thus obtaining the furfuryl alcohol / hyperbranched polymer modified system. Step 2, wood processing and characterization: Select fast-growing wood and process it into test materials of the required size; Step 3: Intermittent vacuum impregnation and post-vacuum modification of wood. The furfuryl alcohol / hyperbranched polymer modified system is intermittently vacuum impregnated with wood, followed by post-vacuum treatment to remove more than 90% of the modifier from the cell cavities. The sample is then removed and the surface is wiped clean of excess reagent. The sample is wrapped in aluminum foil and kept at room temperature and normal pressure for 40-55 hours to promote uniform distribution of the modifier. Then, the sample is placed in a vacuum drying oven and a wood gradient drying program is set. The foil is removed, the temperature is adjusted to 101-105℃, and kept for 20-28 hours to achieve in-situ curing of the polymer in the wood cell wall and oven-drying of the sample, thereby obtaining furfuryl alcohol / hyperbranched polymer synergistic modified wood.

2. The method for improving wood properties based on the synergistic effect of furfuryl alcohol / hyperbranched polymer according to claim 1, characterized in that: In step 1, glycerol, diisopropanolamine and carboxylic acid are mixed, and the molar ratio of hydroxyl to carboxyl groups is controlled to be 1:1-1:1.

2. The mixture is reacted at 150°C for 4 hours to obtain hyperbranched polyester amide prepolymer. A furfuryl alcohol modification solution is prepared, including 25% furfuryl alcohol, 1-2% maleic anhydride and 2-4% sodium tetraborate, and the pH of the system is adjusted to 4.

3. The method for improving wood properties based on the synergistic effect of furfuryl alcohol / hyperbranched polymer according to claim 1, characterized in that: In step 2, the sapwood of fast-growing timber is selected and processed into test materials with dimensions of 4mm×20mm×20mm, 80mm×10mm×4mm, and 120mm×10mm×4mm, respectively, according to the axial × tangential × radial direction.

4. The method for improving wood properties based on the synergistic effect of furfuryl alcohol / hyperbranched polymer according to claim 1, characterized in that: In step 3, the furfuryl alcohol / hyperbranched polymer modified system is subjected to intermittent vacuum impregnation of wood, with each intermittent period lasting 1 hour and the impregnation time lasting 2 hours.

5. The method for improving wood properties based on the synergistic effect of furfuryl alcohol / hyperbranched polymer according to claim 1, characterized in that: In step 3, the sample is wrapped with aluminum foil and kept at room temperature and normal pressure for 48 hours to promote uniform distribution of the modifier; then, the sample is placed in a vacuum drying oven.

6. The method for improving wood properties based on the synergistic effect of furfuryl alcohol / hyperbranched polymer according to claim 5, characterized in that: The wood gradient drying program is set as follows: 58-62℃, 2h, -0.1MPa; 78-82℃, 2h, -0.1MPa.