Modification method for improving size stability of rubber wood and modified material and application thereof

Abstract

The invention provides a modification method for improving the size stability of rubber wood and a modified material and application thereof, and relates to the field of rubber wood processing. The modification method comprises the following steps: 1, mixing choline chloride with a hydrogen bond donor compound containing carboxyl to obtain a DES solvent, and adding water to obtain a DES solution; secondly, the rubber wood plate is put into the DES solution in the first step, pressurized dipping treatment is carried out, and then the rubber wood plate is taken out and aired; and thirdly, the rubber wood treated in the second step is placed at the temperature of 150-160 DEG C to be subjected to heat treatment for 1-2 h, and the rubber wood DES modified material is obtained and placed under the room temperature condition to be balanced. The modification method is simple and easy to operate, the hygroscopicity of the rubber wood is remarkably reduced, the dimensional stability of the rubber wood is improved, the modification liquid can be repeatedly used, and cost saving and efficiency increasing are achieved. The environment-friendly and performance bottlenecks of a traditional method are solved, a new way is opened up for efficient value-added utilization of rubber wood, and the strategic requirement of sustainable material development is met.

Description

Technical Field

[0001] The present invention relates to the field of rubber wood processing, and in particular to a modification method for improving the dimensional stability of rubber wood, a modified material thereof, and applications thereof. Background Art

[0002] Rubber trees are a major plantation species in tropical regions, providing not only raw materials for the rubber industry but also abundant timber resources. Their high-quality wood, beautiful texture, and high market demand have made them the largest imported tropical sawn timber species in my country. However, rubber wood's inherent porous structure and hydrophilic chemical components (such as cellulose and hemicellulose) make it susceptible to changes in humidity and temperature, resulting in significant hygroscopic expansion and drying shrinkage, and poor dimensional stability, severely restricting its application in high-value-added wood products.

[0003] Currently, conventional methods for improving the dimensional stability of wood primarily include chemical modification, heat treatment, and physical filling. For example, phenolic resin impregnation reduces hygroscopicity by filling cellular cavities or cross-linking hydroxyl groups, but carries the risk of formaldehyde release and is not environmentally friendly. High-temperature heat treatment can reduce wood's hydrophilicity, but can lead to deterioration in mechanical properties (such as decreased flexural strength) and high energy consumption. While filling with inorganic salts or nanomaterials can partially improve stability, they often face challenges such as high cost, complex processes, or weak interfacial bonding with the wood. These methods have limitations in terms of environmental protection, cost-effectiveness, and functionality, necessitating the development of new, green modification technologies. Summary of the Invention

[0004] In view of this, the present invention proposes a modification method for improving the dimensional stability of rubber wood to solve the above problems.

[0005] Deep eutectic solvents (DES), with their environmentally friendly, highly designable, and low-cost advantages, have recently demonstrated unique advantages in the biomass refining sector. Research has demonstrated that DES can effectively disrupt the hydrogen bond network in lignocellulose, selectively dissolving hemicellulose or lignin while preserving the cellulose backbone structure. This property offers new insights into wood modification: by manipulating DES composition and treatment conditions, it is possible to modify wood cell wall components in a targeted manner, reducing the number of hydrophilic groups and inducing optimized microfibril alignment, thereby improving dimensional stability at the molecular level. Furthermore, some DES systems possess antimicrobial and antiseptic properties, potentially providing additional protection for rubberwood and extending its service life.

[0006] Existing research has primarily focused on the use of DES in biomass pretreatment or component extraction, but its use as a wood modifier for the modification of solid rubberwood has yet to be reported. The compatibility of traditional DES formulations with respect to wood permeability, reactivity, and post-treatment mechanical property retention requires further exploration. Therefore, developing a green rubberwood modification process based on deep eutectic solvents, which precisely regulates DES composition and processing parameters, while improving dimensional stability while balancing environmental and economic considerations, holds significant technological innovation value and promising application prospects.

[0007] The technical solution of the present invention is achieved as follows: A modification method for improving the dimensional stability of rubber wood comprises the following steps: Step 1: Mix choline chloride and a carboxyl-containing hydrogen bond donor compound to obtain a DES solvent, and add water to obtain a DES solution; Step 2: Place the rubber wood board into the DES solution prepared in step 1, perform pressure impregnation treatment, and then take it out and air dry; Step 3: heat-treat the material treated in step 2 at 150-160°C for 1-2 hours to obtain the rubber wood DES modified material, and then allow it to equilibrate at room temperature. A further technical solution is that in step 1, the carboxyl-containing hydrogen bond donor compound is at least one of lactic acid, oxalic acid, and propionic acid.

[0008] A further technical solution is that in step 1, the mass ratio of choline chloride to the carboxyl-containing hydrogen bond donor compound is 1:2-3, preferably 1:2.

[0009] A further technical solution is that in step 1, the volume ratio of the DES solvent to water is 100:40-70, preferably 100:50-65, and more preferably 100:55-60.

[0010] A further technical solution is that in step 2, the pressure of the immersion treatment is 0.2-10 MPa, the time is 1-2 hours, and the preferred pressure is 5-10 MPa.

[0011] A further technical solution is that in step three, the solid content of the modified material is increased by 12-20% compared to the rubber wood board before modification.

[0012] A rubber wood DES modified material is prepared by any modification method described in the present invention.

[0013] The rubber wood DES modified material of the present invention is used in the preparation of high-humidity resistant wood products.

[0014] Furthermore, the high humidity environment humidity is RH80%~95%.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a method for modifying rubber wood based on a low eutectic solvent. By optimizing the DES system and treatment process, the controllable modification of wood cell wall components is achieved, which significantly reduces the hygroscopicity of rubber wood and improves its dimensional stability.

[0016] (2) The solution prepared by the modification method of the present invention maintains the integrity of the hydrogen bond network at a specific concentration and significantly reduces the viscosity, thereby achieving low-pressure penetration into rubber wood.

[0017] (3) The modification method adopted in the present invention is simple and easy to operate, and the modified liquid can be reused, thereby achieving cost savings and efficiency improvement.

[0018] (4) The present invention not only solves the environmental protection and performance bottlenecks of traditional methods, but also opens up a new way for the efficient value-added utilization of rubber wood, which meets the strategic needs of sustainable material development. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Cross-sectional microstructure of rubber wood treated with DES and the control group. a. Untreated control group, b. DES treated rubber wood.

[0020] Figure 2 Comparison of swelling rates between rubber wood DES modified materials and the control group at 90% RH.

[0021] Figure 3 The moisture absorption rate and swelling rate of rubber wood DES modified material and the control group were compared at 75% RH.

[0022] Figure 4 The moisture absorption rate and swelling rate of rubber wood DES modified material and the control group were compared at 65% RH.

[0023] Figure 5 Comparison of weight gain and dimensional stability of rubber wood modified with different concentrations of DES. DETAILED DESCRIPTION

[0024] In order to better understand the technical content of the present invention, specific examples are provided below to further illustrate the present invention.

[0025] Unless otherwise specified, the experimental methods used in the examples of the present invention are all conventional methods.

[0026] Unless otherwise specified, the materials, reagents, etc. used in the examples of the present invention can be obtained from commercial sources.

[0027] Example 1 A modification method for improving the dimensional stability of rubber wood comprises the following steps: Step 1: Mix choline chloride and lactic acid in a ratio of 1:2 (m / m) to obtain a DES solvent, then add water so that the volume ratio of DES solvent to water is 100:55, and stir until a uniform phase is obtained to obtain a DES solution; Step 2: Place the rubber wood board into the DES solution prepared in step 1, immerse and react at room temperature and pressure of 5 MPa for 1 hour, then take it out and air dry; Step 3: Heat treatment was performed at 155°C for 1.5 hours to obtain the rubber wood DES modified material. The solid content of the modified material increased by 13.4%, and the material was allowed to equilibrate at room temperature.

[0028] Control group: Take rubber wood material and put it into the same volume of water, pressurize and immerse it for 1 hour, take it out and place it at 155℃ for 1.5 hours to obtain the rubber wood control group material, and let it stand at room temperature for equilibrium. Figure 1 The rubber wood control group and rubber wood DES modified materials were placed in a 90% constant temperature and humidity chamber to adjust the humidity balance, and the changes in their dimensional stability were tested. Figure 2 .

[0029] The results showed that the vessels and intercellular spaces of the DES-modified rubberwood were filled with a light yellow film-forming substance. The swelling rate of the untreated rubberwood control group under a 90% high humidity environment was 6.69%, while the swelling rate of the DES-modified rubberwood changed by 3.04%. This indicates that the DES solvent compound fills the vessels and intercellular spaces of the rubberwood, reducing its water absorption, effectively improving its dimensional stability, and significantly reducing the change in swelling rate under high humidity.

[0030] Example 2 A modification method for improving the dimensional stability of rubber wood comprises the following steps: Step 1: Mix choline chloride and lactic acid in a ratio of 1:2 (m / m) to obtain a DES solvent, then add water so that the volume ratio of DES solvent to water is 100:60, and stir until a uniform phase is obtained to obtain a DES solution; Step 2: Place the rubber wood board into the DES solution prepared in step 1, immerse and react at room temperature and pressure of 10 MPa for 1.5 hours, then take it out and air dry; Step 3: Heat treatment was performed at 160°C for 1 hour to obtain the rubber wood DES modified material. The solid content of the modified material increased by 15.2%, and the material was allowed to equilibrate at room temperature.

[0031] Control group (control material): Take the rubber wood material and put it into the same volume of water, pressurize it at 10MPa and immerse it for 1.5 hours. Take it out and place it at 160℃ for 1 hour to obtain the rubber wood control group material. Let it stand at room temperature for equilibrium. The rubber wood control group and the rubber wood DES modified material were placed in a 75% constant temperature and humidity chamber for humidity balance. The changes in their dimensional stability are tested as shown in the attached figure. Figure 3 .

[0032] The results showed that the moisture absorption rate of the untreated rubber wood control group was 16.70% and the swelling rate was 5.42% under a 75% RH environment, while the moisture absorption rate of the rubber wood modified with DES solvent was 1.78% and the swelling rate change was 1.67%, indicating that the hygroscopicity of rubber wood modified with choline chloride-lactic acid DES solution in this concentration range decreased, and the dimensional stability was significantly improved, which expanded the application scenarios of rubber wood.

[0033] Example 3 A modification method for improving the dimensional stability of rubber wood comprises the following steps: Step 1: Mix choline chloride and oxalic acid in a ratio of 1:2 (m / m) to obtain a DES solvent, then add water so that the volume ratio of DES solvent to water is 100:55, and stir until a uniform phase is obtained to obtain a DES solution; Step 2: Place the rubber wood board into the DES solution prepared in step 1, immerse and react at room temperature and pressure of 8 MPa for 2 hours, then take it out and air dry; Step 3: Heat treatment at 150°C for 1 hour to obtain rubber wood DES modified material. The solid content of the modified material increased by 13%, and the material was allowed to equilibrate at room temperature.

[0034] Control group (control material): Take the rubber wood material and put it into the same volume of water, pressurize it at 8MPa and immerse it for 2 hours, then take it out and place it at 150℃ for 1 hour to obtain the rubber wood control group material, and let it balance at room temperature. The rubber wood control group and the rubber wood DES modified material were placed in a 65% constant temperature and humidity chamber to adjust the humidity balance, and the changes in their dimensional stability were tested. See the attached Figure 4 .

[0035] The results showed that the moisture absorption rate of the untreated rubber wood control group was 15.05% and the swelling rate was 5.06% under a 65% RH environment, while the moisture absorption rate of the rubber wood modified with DES solvent was 0.31% and the swelling rate change was 1.64%. This shows that the modification of rubber wood with the choline chloride-oxalic acid DES solvent system can also significantly improve the dimensional stability of rubber wood and realize the high value-added application of rubber wood.

[0036] Comparative Study 1 A modification method for improving the dimensional stability of rubber wood comprises the following steps: Step 1: Choline chloride and lactic acid were mixed in a ratio of 1:2 (m / m) to obtain a DES solvent, and then water was added to prepare solution systems with different volume ratios. The volume ratios of DES solvent to water were 100:80, 100:55, and 100:30 (groups a, b, and c, respectively), and stirred until a uniform phase was obtained to obtain a DES solution. Step 2: Place the rubber wood board into the DES solution prepared in step 1, immerse and react at room temperature and pressure of 5 MPa for 1 h, then take it out and air dry; Step 3: Heat-treat at 160°C for 1 hour to obtain rubber wood DES modified materials a, b, and c. Test the solid content of each modified material. The solid content of modified material a increased by 8.1%, the solid content of b increased by 12.9%, and the solid content of c increased by 6.3%. Then, place it at room temperature for equilibrium.

[0037] Step 4: Place the three groups of modified materials in a 65% constant temperature and humidity chamber to adjust the humidity balance and test their dimensional stability changes. Figure 5 .

[0038] The analysis results show that compared with the modification liquid concentration of group b, the weight gain rate of rubber wood boards modified with DES solution systems with too high or too low concentrations is significantly lower than that of the rubber wood boards obtained in group b, and the dimensional stability modification effect is also poor. Therefore, the concentration of the DES solution system formed by choline chloride and carboxyl-containing hydrogen bond donor compounds is crucial to the modification effect of rubber wood.

[0039] Comparative Study 2 A modification method for improving the dimensional stability of rubber wood, based on Example 1, wherein in step 1, the mass ratio of choline chloride to lactic acid is 1:1.5. Specifically, the method comprises the following steps: Step 1: Mix choline chloride and lactic acid in a ratio of 1:1.5 (m / m) to obtain a DES solvent, then add water so that the volume ratio of DES solvent to water is 100:55, and stir until a uniform phase is obtained to obtain a DES solution; Step 2: Place the rubber wood board into the DES solution prepared in step 1, immerse and react at room temperature and pressure of 5 MPa for 1 hour, then take it out and air dry; Step 3: Heat treatment was performed at 155°C for 1.5 hours to obtain the rubber wood DES modified material. The solid content of the modified material increased by 10.5%, and the material was allowed to equilibrate at room temperature.

[0040] The results showed that the solid content of the modified material increased by 10.5%, indicating that when the mass ratio of choline chloride to carboxyl-containing hydrogen bond donor compound was 1:1.5 for modifying rubber wood, the solid content of the modified material was lower than that of the modification system with a mass ratio of 1:2. Therefore, the mass ratio of choline chloride to carboxyl-containing hydrogen bond donor compound has an important influence on the modification effect.

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the scope of the present invention should be included in the scope of protection of the present invention.

Claims

1. A modification method for improving the dimensional stability of rubber wood, characterized in that: The following steps are involved: Step 1: Mix choline chloride and a carboxyl-containing hydrogen bond donor compound to obtain a DES solvent, and add water to obtain a DES solution; Step 2: Place the rubber wood board into the DES solution prepared in step 1, perform pressure impregnation treatment, and then take it out and air dry; Step 3: heat-treat the material after step 2 at 150-160°C for 1-2 hours to obtain rubber wood DES modified material, and then allow it to equilibrate at room temperature.

2. The method for improving the dimensional stability of rubber wood according to claim 1, wherein In step 1, the carboxyl-containing hydrogen bond donor compound is at least one of lactic acid, oxalic acid, and propionic acid.

3. The method for improving the dimensional stability of rubber wood according to claim 1, wherein In step 1, the mass ratio of the choline chloride to the carboxyl-containing hydrogen bond donor compound is 1:2-3.

4. The method for improving the dimensional stability of rubber wood according to claim 3, wherein In step 1, the mass ratio of the choline chloride to the carboxyl-containing hydrogen bond donor compound is 1:

2.

5. The method for improving the dimensional stability of rubber wood according to any one of claims 1 to 4, wherein: In step 1, the volume ratio of the DES solvent to water is 100:40-70.

6. The method for improving the dimensional stability of rubber wood according to claim 1, wherein: In step 2, the immersion treatment pressure is 0.2-10 MPa and the time is 1-2 hours.

7. The method for improving the dimensional stability of rubber wood according to claim 1, wherein: In step 3, compared with the rubber wood board before modification, the solid content of the modified material is increased by 12-20%.

8. A rubber wood DES modified material, characterized in that: The invention is prepared by the modification method according to any one of claims 1 to 7.

9. Use of the rubber wood DES modified material according to claim 8 in the preparation of high-humidity resistant wood products.

10. The use according to claim 9, characterized in that The high humidity environment humidity is RH80%~95%.

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