Wood-based composite phase change material and preparation method thereof

Abstract

This invention discloses a wood-based composite phase change material and its preparation method, belonging to the field of phase change material technology. The preparation method of the wood-based composite phase change material is as follows: wood is cut and heated in a delignification solution, then removed and washed with water to obtain delignified wood; the delignified wood is added to a modification solution and heated, then removed, washed with water, and dried to obtain pretreated wood; polyethylene glycol, citric acid, and boric acid are mixed, heated, and stirred to obtain a phase change material; the pretreated wood is impregnated into the phase change material under vacuum, removed, and dried to obtain the final product; the modification solution is composed of an ethanol aqueous solution, a modified filler, 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane, and triethylamine. This invention uses delignification solution and modification solution to pretreat the wood, thereby enabling better bonding with the phase change material and preventing leakage. The resulting wood-based composite phase change material has excellent thermal management capabilities and stability.

Description

Technical Field

[0001] This invention belongs to the field of phase change materials technology, specifically relating to a wood-based composite phase change material and its preparation method. Background Technology

[0002] Phase change materials (PCMs), as materials capable of efficiently absorbing, storing, and releasing latent heat through phase transitions within a specific temperature range, exhibit unique advantages in the field of thermal energy management. These materials can store and release energy while maintaining a constant temperature during phase change, possessing characteristics such as high heat storage density and constant temperature. They show potential in solar thermal energy storage, building energy conservation, and intelligent temperature control, and are of great significance for efficient energy utilization. However, traditional PCMs face several technical bottlenecks in practical application. For example, liquid leakage during solid / liquid phase transitions can lead to material failure; low thermal conductivity often limits the thermal response rate; and a single phase change temperature is insufficient to adapt to dynamically changing environmental demands. With the deep integration of building energy conservation and smart home concepts, higher requirements are being placed on thermal management materials. These materials not only require efficient energy storage capacity but also need to be safe, non-toxic, morphologically stable, and compatible with building materials. Traditional PCMs struggle to meet these comprehensive requirements.

[0003] Chinese patent CN103468216A discloses a phosphate inorganic nano-phase change energy storage material and its preparation method. The phase change energy storage material consists of a wall material encapsulating a core material. The wall material is composed of tetraethyl orthosilicate, tetrabutyl zirconate, and silica gel (derived from manganese nitrate hydrolysis), zirconium oxide, and manganese dioxide powder. The core material is a nano-inorganic salt hydrate, disodium hydrogen phosphate dodecahydrate. This phase change material has a simple process and low cost, and can be used for home phase change energy storage. Chinese patent CN106916572A discloses a phase change energy storage plate and its manufacturing method. The phase change energy storage plate includes a honeycomb panel and an encapsulated composite phase change material. The composite phase change material is composed of emulsified paraffin wax, graphite powder, and expanded graphite. This phase change composite material has good thermal conductivity. The energy storage plate made from this material can be used as an indoor energy storage decorative material to prevent excessively low or high indoor temperatures and create a comfortable indoor temperature environment. However, the phase change materials disclosed above still need further improvement in terms of thermal management capabilities and moisture resistance and water stability. Natural wood possesses a unique multi-level porous structure and a controllable chemical composition, with its vertically arranged cellulose skeleton providing a natural pathway for heat transfer. By combining phase change materials (PCMs) with a wood substrate, composite energy storage systems that combine stability and thermal management capabilities can be constructed. Wood-based composite PCMs not only solve the leakage problems of traditional PCMs, but their natural and renewable characteristics also align with the principles of green and sustainable development, making them promising for applications in building energy conservation and smart home temperature control. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention provides a composite phase change material based on natural porous material "wood". By removing some lignin from the wood and performing pretreatment such as modification, while retaining its porous structure and support structure, its specific surface area and active sites are further improved, so that it can better bond firmly with the phase change material, prevent leakage, and has excellent thermal management capabilities and stability.

[0005] This invention aligns with the development trends of "green wood industry" and intelligent home furnishing, and can be widely applied to ceilings, floors, walls, and other parts in whole-house customization, helping to promote the upgrading of green wood industry from "single products" to green and energy-saving "whole-house" applications.

[0006] This invention provides a method for preparing a wood-based composite phase change material, comprising the following steps:

[0007] Step 1: After cutting the wood, heat it in a delignification solution, remove it and wash it with water to obtain delignified wood; add the delignified wood to a modification solution and heat it, remove it and wash it with water, and dry it to obtain pretreated wood.

[0008] Step 2: Mix polyethylene glycol, citric acid, and boric acid, and heat and stir under nitrogen protection to obtain a phase change material;

[0009] Step 3: Impregnate the pretreated wood with the phase change material under vacuum, remove it and dry it to obtain the wood-based composite phase change material.

[0010] Preferably, a method for preparing a wood-based composite phase change material includes the following steps:

[0011] Step 1: Cut the wood into the required size, then add it to the delignification solution and heat it at 75-85℃ for 6-8 hours. After removing it, wash it with water to obtain delignified wood. Add the delignified wood to the modification solution and heat it at 50-60℃ for 3-5 hours. After removing it, wash it with water and vacuum dry it to obtain pretreated wood.

[0012] Step 2: Mix polyethylene glycol, citric acid, and boric acid, and stir at 55-65℃ under nitrogen protection for 1.5-3 hours to obtain a phase change material;

[0013] Step 3: Impregnate the pretreated wood with the phase change material under vacuum, remove it and dry it under vacuum to obtain the wood-based composite phase change material.

[0014] Preferably, the modified liquid in step one is composed of an aqueous ethanol solution, a modified filler, 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane, and triethylamine; the weight ratio of the aqueous ethanol solution, the modified filler, 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane, and triethylamine is 100:(1-2):(2-3):(0.1-0.4).

[0015] Preferably, the concentration of the ethanol aqueous solution is 85-90 wt%.

[0016] Preferably, the modified filler is prepared by:

[0017] Boron nitride nanosheets were ultrasonically dispersed in a buffer solution, then dopamine hydrochloride was added and stirred. After filtration, the nanosheets were washed with water and dried to obtain modified boron nitride nanosheets. The modified boron nitride nanosheets were then added to a lauric acid-methanol solution, heated and stirred, filtered, and dried to obtain the modified filler.

[0018] In the first step of this invention, after the wood is treated with delignification, it is further modified with a modifying liquid of a specific composition. This can build a stable "three-dimensional cross-linking-thermal conduction-hydrophobicity" interface layer between the wood skeleton and the phase change material, thereby solving the problems of weak interface bonding, easy leakage and poor stability of traditional physical composite methods. Firstly, through the chemical bridging effect of 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane, its methoxy group condenses with the hydroxyl group of wood cellulose to form a strong Si-OC bond. Then, the active alicyclic epoxy groups undergo ring-opening esterification reactions with citric acid and polyethylene glycol in the phase change material during subsequent heat treatment, forming a three-dimensional cross-linked network of "wood skeleton-silane-phase change material" with covalent bonds as the core. This chemical anchoring effect is like locking the phase change material firmly within the wood pores with "molecular chains," fundamentally inhibiting its loss under high temperature and water washing conditions. This is the structural basis for improved thermal stability and water resistance. Moreover, the introduced rigid alicyclic structure can withstand higher temperatures and has stronger resistance to moisture attack; secondly, The modified filler is uniformly immobilized on the skeleton surface through the strong adhesion of polydopamine. Its core boron nitride nanosheets construct an efficient thermal conduction pathway, significantly improving the thermal response rate of the composite material. The grafted lauric acid molecules, on the one hand, can form a dense hydrophobic protective layer on the surface with their long alkyl chains, actively repelling the intrusion of water molecules. On the other hand, they play an auxiliary role in phase change, achieving synergy between thermal conduction and heat storage. In addition, the addition of triethylamine catalyst to the modification solution can promote the efficient and complete silanization and grafting reactions. The entire modification process takes place inside the inherent three-dimensional porous structure of wood. Through covalent cross-linking, enhanced thermal conductivity, and hydrophobic protection, the thermal stability and water resistance of the resulting wood-based composite phase change material are significantly improved, effectively preventing leakage.

[0019] Preferably, the molar ratio of polyethylene glycol, citric acid, and boric acid in step two is (4-5):1:(0.03-0.06).

[0020] In this system, polyethylene glycol serves as the thermal storage substrate, while citric acid acts as a multifunctional crosslinking agent. This system not only possesses a high phase change enthalpy, but the multiple carboxyl groups in citric acid also lay the foundation for subsequent esterification crosslinking. The small amount of boric acid added can react with the hydroxyl groups of polyethylene glycol and citric acid to form BOC bonds, upgrading the binary crosslinking network into a more compact three-dimensional hybrid crosslinking system. This effectively hinders the penetration path of water molecules, improves water resistance, and the high BO bond energy helps to enhance thermal stability.

[0021] Preferably, the delignification solution in step one is a 1-2 wt% sodium chlorite aqueous solution, and the pH is adjusted to 4.5-5.0 with glacial acetic acid.

[0022] Preferably, the weight ratio of wood to delignification solution in step one is 1-2:10.

[0023] Preferably, the weight ratio of wood to modified liquid in step one is 1-2:10.

[0024] Preferably, the weight ratio of the pretreated wood to the phase change material in step three is 1:2-3.

[0025] Preferably, the wood mentioned in step one is any one of balsa wood, poplar, linden, paulownia, and birch.

[0026] Preferably, the polyethylene glycol in step two is at least one of polyethylene glycol 1000, polyethylene glycol 2000, polyethylene glycol 3000, polyethylene glycol 600, and polyethylene glycol 1500.

[0027] Preferably, the dimensions of the wood after cutting in step one are: length 20-40mm, width 20-40mm, and thickness 1-5mm; the dimensions include, but are not limited to, 20mm×20mm×2mm, 20mm×20mm×4mm, 30mm×30mm×3mm, 40mm×40mm×3mm, and 40mm×40mm×4mm.

[0028] Preferably, the number of water washes in step one is 4-6.

[0029] Preferably, the stirring rate in step two is 200-300 r / min.

[0030] Preferably, the vacuum impregnation conditions in step three are: vacuum impregnation at 55-65℃ and 0.06-0.08MPa for 2-5 hours.

[0031] Preferably, the modified filler is prepared by:

[0032] Boron nitride nanosheets were added to a buffer solution and ultrasonically dispersed for 40-60 min. Then, dopamine hydrochloride was added, and the mixture was stirred at room temperature for 20-30 h. After filtration and washing with water, the mixture was freeze-dried to obtain modified boron nitride nanosheets. The modified boron nitride nanosheets were added to a lauric acid-methanol solution and stirred at 55-65℃ for 1-3 h. After filtration and vacuum drying, the modified filler was obtained.

[0033] Preferably, the buffer solution is a Tris-HCl buffer solution; the concentration of the Tris-HCl buffer solution is 0.5-1.5M and the pH is 8.0-9.0.

[0034] Preferably, the weight ratio of the boron nitride nanosheets, dopamine hydrochloride, and buffer solution is (2-4):(1-2):100.

[0035] Preferably, the weight ratio of the modified boron nitride nanosheets to the lauric acid methanol solution is 1-2:100.

[0036] Preferably, the boron nitride nanosheets have a thickness of 5-15 nm, a diameter of 1-2 μm, and a purity of ≥98.0%.

[0037] Preferably, the concentration of the lauric acid methanol solution is 3-5 wt%.

[0038] Preferably, the ultrasonic frequency is 30-50kHz and the ultrasonic power is 300-400W.

[0039] Preferably, the modified filler is washed 4-6 times in the preparation method.

[0040] Preferably, the stirring rate in the preparation method of the modified filler is 200-300 r / min.

[0041] The present invention also provides a wood-based composite phase change material, which is prepared by the above method.

[0042] The beneficial effects of this invention are:

[0043] The wood-based composite phase change material prepared by this invention possesses excellent heat storage and energy storage capabilities. By pretreating the wood with delignification and modification solutions, not only is a porous support structure with a high specific surface area obtained, but a stable "three-dimensional cross-linking-thermal conductivity-hydrophobicity" interface layer is also constructed between the wood skeleton and the phase change material. This enhances the interfacial bonding between the phase change material and the wood skeleton, improving heat and water resistance stability. This invention aligns with the development trends of "green wood industry" and intelligent home furnishings, and can be widely applied to ceilings, floors, walls, and other components in whole-house customization. Detailed Implementation

[0044] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Example 1

[0046] A method for preparing a wood-based composite phase change material includes the following steps:

[0047] Step 1: Cut the wood into the required size (20mm×20mm×4mm), then add it to the delignification solution and heat it at 80℃ for 7 hours. After removing it, wash it with water 5 times to obtain delignified wood. Add the delignified wood to the modification solution and heat it at 50℃ for 4 hours. After removing it, wash it with water 5 times and vacuum dry it to obtain pretreated wood. The wood is balsa wood. The weight ratio of the wood to the delignification solution is 1.5:10. The weight ratio of the wood to the modification solution is 1.5:10.

[0048] Step 2: Mix polyethylene glycol 1000, citric acid, and boric acid in a molar ratio of 4.5:1:0.05, and stir at 60°C under nitrogen protection for 2 hours to obtain a phase change material; the stirring rate is 300 r / min.

[0049] Step 3: Impregnate the pretreated wood with phase change material at a weight ratio of 1:2.5. Vacuum impregnate the wood at 60°C and 0.08 MPa for 3 hours, then remove and vacuum dry to obtain wood-based composite phase change material.

[0050] The delignification solution mentioned in step one is a 1.5wt% sodium chlorite aqueous solution, and the pH is adjusted to 4.6 with glacial acetic acid.

[0051] The modified solution described in step one is composed of 90wt% ethanol aqueous solution, modified filler, 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane (CAS: 3388-04-3), and triethylamine in a weight ratio of 100:1.5:2.5:0.25;

[0052] The modified filler is prepared by:

[0053] Boron nitride nanosheets were ultrasonically dispersed in a buffer solution for 50 min at a frequency of 40 kHz and a power of 350 W. Dopamine hydrochloride was then added, and the mixture was stirred at room temperature for 24 h. After filtration, the nanosheets were washed five times with water and freeze-dried to obtain modified boron nitride nanosheets. The modified boron nitride nanosheets were then added to a 5 wt% lauric acid-methanol solution and stirred at 60 °C for 2 h. After filtration and vacuum drying, the modified filler was obtained. The buffer solution was a Tris-HCl buffer solution (1 M concentration, pH 8.5); the weight ratio of boron nitride nanosheets, dopamine hydrochloride, and buffer solution was 3:1.5:100; the weight ratio of modified boron nitride nanosheets to lauric acid-methanol solution was 1.5:100; the boron nitride nanosheets were purchased from Suzhou Napo Materials Technology Co., Ltd., with a thickness of 10 nm, a diameter of 1-2 μm, and a purity ≥98.0%; the stirring rate was 200 r / min.

[0054] Example 2

[0055] A method for preparing a wood-based composite phase change material includes the following steps:

[0056] Step 1: Cut the wood into the required size (20mm×20mm×4mm), then add it to the delignification solution and heat it at 75℃ for 8 hours. After removing it, wash it with water 4 times to obtain delignified wood. Add the delignified wood to the modification solution and heat it at 50℃ for 5 hours. After removing it, wash it with water 4 times and vacuum dry it to obtain pretreated wood. The wood is balsa wood. The weight ratio of the wood to the delignification solution is 1:10. The weight ratio of the wood to the modification solution is 1:10.

[0057] Step 2: Mix polyethylene glycol 1000, citric acid, and boric acid in a molar ratio of 4:1:0.03, and stir at 55°C under nitrogen protection for 3 hours to obtain a phase change material; the stirring rate is 200 r / min.

[0058] Step 3: Impregnate the pretreated wood with phase change material at a weight ratio of 1:2. Vacuum impregnate the wood at 55°C and 0.06 MPa for 5 hours, then remove and vacuum dry to obtain wood-based composite phase change material.

[0059] The delignification solution mentioned in step one is a 1 wt% sodium chlorite aqueous solution, and the pH is adjusted to 4.5 with glacial acetic acid.

[0060] The modified solution in step one is composed of 85wt% ethanol aqueous solution, modified filler, 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane, and triethylamine in a weight ratio of 100:1:2:0.1; the modified filler is the same as in Example 1.

[0061] Example 3

[0062] A method for preparing a wood-based composite phase change material includes the following steps:

[0063] Step 1: Cut the wood into the required size (20mm×20mm×4mm), then add it to the delignification solution and heat it at 85℃ for 6 hours. After removing it, wash it with water 6 times to obtain delignified wood. Add the delignified wood to the modification solution and heat it at 60℃ for 3 hours. After removing it, wash it with water 6 times and vacuum dry it to obtain pretreated wood. The wood is balsa wood. The weight ratio of the wood to the delignification solution is 2:10. The weight ratio of the wood to the modification solution is 2:10.

[0064] Step 2: Mix polyethylene glycol 1000, citric acid, and boric acid in a molar ratio of 5:1:0.06, and stir at 65°C under nitrogen protection for 1.5 hours to obtain a phase change material; the stirring rate is 300 r / min.

[0065] Step 3: Impregnate the pretreated wood with phase change material at a weight ratio of 1:3. Vacuum impregnate the wood at 65°C and 0.08 MPa for 2 hours. After impregnation, vacuum dry the wood to obtain wood-based composite phase change material.

[0066] The delignification solution mentioned in step one is a 2wt% sodium chlorite aqueous solution, and the pH is adjusted to 5.0 with glacial acetic acid.

[0067] The modified solution in step one is composed of 90wt% ethanol aqueous solution, modified filler, 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane, and triethylamine in a weight ratio of 100:2:3:0.4; the modified filler is the same as in Example 1.

[0068] Example 4

[0069] A method for preparing a wood-based composite phase change material includes the following steps:

[0070] Step 1: Cut the wood into the required size (20mm×20mm×4mm), then add it to the delignification solution and heat it at 80℃ for 7 hours. After removing it, wash it with water 5 times to obtain delignified wood. The wood is balsa wood. The weight ratio of the wood to the delignification solution is 1.5:10.

[0071] Step 2: Mix polyethylene glycol 1000, citric acid, and boric acid in a molar ratio of 4.5:1:0.05, and stir at 60°C under nitrogen protection for 2 hours to obtain a phase change material; the stirring rate is 300 r / min.

[0072] Step 3: Impregnate the delignified wood with phase change material at a weight ratio of 1:2.5. Vacuum impregnate the wood at 60°C and 0.08 MPa for 3 hours, then remove and vacuum dry to obtain wood-based composite phase change material.

[0073] The delignification solution mentioned in step one is a 1.5wt% sodium chlorite aqueous solution, and the pH is adjusted to 4.6 with glacial acetic acid.

[0074] Example 5

[0075] A method for preparing a wood-based composite phase change material includes the following steps:

[0076] Step 1: Cut the wood into the required size (20mm×20mm×4mm), then add it to the delignification solution and heat it at 80℃ for 7 hours. After removing it, wash it with water 5 times to obtain delignified wood. Add the delignified wood to the modification solution and heat it at 50℃ for 4 hours. After removing it, wash it with water 5 times and vacuum dry it to obtain pretreated wood. The wood is balsa wood. The weight ratio of the wood to the delignification solution is 1.5:10. The weight ratio of the wood to the modification solution is 1.5:10.

[0077] Step 2: Mix polyethylene glycol 1000, citric acid, and boric acid in a molar ratio of 4.5:1:0.05, and stir at 60°C under nitrogen protection for 2 hours to obtain a phase change material; the stirring rate is 300 r / min.

[0078] Step 3: Impregnate the pretreated wood with phase change material at a weight ratio of 1:2.5. Vacuum impregnate the wood at 60°C and 0.08 MPa for 3 hours, then remove and vacuum dry to obtain wood-based composite phase change material.

[0079] The delignification solution mentioned in step one is a 1.5wt% sodium chlorite aqueous solution, and the pH is adjusted to 4.6 with glacial acetic acid.

[0080] The modified solution in step one is composed of 90wt% ethanol aqueous solution, modified filler, 3-glycidyl etheroxypropyltrimethoxysilane (CAS: 2530-83-8), and triethylamine in a weight ratio of 100:1.5:2.5:0.25; the modified filler is the same as in Example 1.

[0081] Example 6

[0082] A method for preparing a wood-based composite phase change material includes the following steps:

[0083] Step 1: Cut the wood into the required size (20mm×20mm×4mm), then add it to the delignification solution and heat it at 80℃ for 7 hours. After removing it, wash it with water 5 times to obtain delignified wood. Add the delignified wood to the modification solution and heat it at 50℃ for 4 hours. After removing it, wash it with water 5 times and vacuum dry it to obtain pretreated wood. The wood is balsa wood. The weight ratio of the wood to the delignification solution is 1.5:10. The weight ratio of the wood to the modification solution is 1.5:10.

[0084] Step 2: Mix polyethylene glycol 1000, citric acid, and boric acid in a molar ratio of 4.5:1:0.05, and stir at 60°C under nitrogen protection for 2 hours to obtain a phase change material; the stirring rate is 300 r / min.

[0085] Step 3: Impregnate the pretreated wood with phase change material at a weight ratio of 1:2.5. Vacuum impregnate the wood at 60°C and 0.08 MPa for 3 hours, then remove and vacuum dry to obtain wood-based composite phase change material.

[0086] The delignification solution mentioned in step one is a 1.5wt% sodium chlorite aqueous solution, and the pH is adjusted to 4.6 with glacial acetic acid.

[0087] The modification solution described in step one is composed of 90wt% ethanol aqueous solution, boron nitride nanosheets, 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane, and triethylamine in a weight ratio of 100:1.5:2.5:0.25. The boron nitride nanosheets were purchased from Suzhou Napo Materials Technology Co., Ltd., with a thickness of 10nm, a diameter of 1-2μm, and a purity of ≥98.0%.

[0088] Example 7

[0089] A method for preparing a wood-based composite phase change material includes the following steps:

[0090] Step 1: Cut the wood into the required size (20mm×20mm×4mm), then add it to the delignification solution and heat it at 80℃ for 7 hours. After removing it, wash it with water 5 times to obtain delignified wood. Add the delignified wood to the modification solution and heat it at 50℃ for 4 hours. After removing it, wash it with water 5 times and vacuum dry it to obtain pretreated wood. The wood is balsa wood. The weight ratio of the wood to the delignification solution is 1.5:10. The weight ratio of the wood to the modification solution is 1.5:10.

[0091] Step 2: Mix polyethylene glycol 1000, citric acid, and boric acid in a molar ratio of 4.5:1:0.05, and stir at 60°C under nitrogen protection for 2 hours to obtain a phase change material; the stirring rate is 300 r / min.

[0092] Step 3: Impregnate the pretreated wood with phase change material at a weight ratio of 1:2.5. Vacuum impregnate the wood at 60°C and 0.08 MPa for 3 hours, then remove and vacuum dry to obtain wood-based composite phase change material.

[0093] The delignification solution mentioned in step one is a 1.5wt% sodium chlorite aqueous solution, and the pH is adjusted to 4.6 with glacial acetic acid.

[0094] The modified solution described in step one is composed of 90wt% ethanol aqueous solution, modified filler, 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane, and triethylamine in a weight ratio of 100:1.5:2.5:0.25;

[0095] The modified filler is prepared by:

[0096] Boron nitride nanosheets were added to a buffer solution and ultrasonically dispersed for 50 min at a frequency of 40 kHz and a power of 350 W. Dopamine hydrochloride was then added, and the mixture was stirred at room temperature for 24 h. After filtration, the mixture was washed five times with water and freeze-dried to obtain the modified filler. The buffer solution was a Tris-HCl buffer (1 M, pH 8.5); the weight ratio of boron nitride nanosheets, dopamine hydrochloride, and buffer solution was 3:1.5:100; the boron nitride nanosheets were purchased from Suzhou Napo Materials Technology Co., Ltd., with a thickness of 10 nm, a diameter of 1-2 μm, and a purity ≥98.0%; the stirring rate was 200 r / min.

[0097] Example 8

[0098] A method for preparing a wood-based composite phase change material includes the following steps:

[0099] Step 1: Cut the wood into the required size (20mm×20mm×4mm), then add it to the delignification solution and heat it at 80℃ for 7 hours. After removing it, wash it with water 5 times to obtain delignified wood. Add the delignified wood to the modification solution and heat it at 50℃ for 4 hours. After removing it, wash it with water 5 times and vacuum dry it to obtain pretreated wood. The wood is balsa wood. The weight ratio of the wood to the delignification solution is 1.5:10. The weight ratio of the wood to the modification solution is 1.5:10.

[0100] Step 2: Mix polyethylene glycol 1000 and citric acid at a molar ratio of 4.5:1.05, and stir at 60°C under nitrogen protection for 2 hours to obtain a phase change material; the stirring rate is 300 r / min.

[0101] Step 3: Impregnate the pretreated wood with phase change material at a weight ratio of 1:2.5. Vacuum impregnate the wood at 60°C and 0.08 MPa for 3 hours, then remove and vacuum dry to obtain wood-based composite phase change material.

[0102] The delignification solution mentioned in step one is a 1.5wt% sodium chlorite aqueous solution, and the pH is adjusted to 4.6 with glacial acetic acid.

[0103] The modified solution in step one is composed of 90wt% ethanol aqueous solution, modified filler, 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane, and triethylamine in a weight ratio of 100:1.5:2.5:0.25; the modified filler is the same as in Example 1.

[0104] Test Example 1

[0105] The phase transition temperature and phase transition enthalpy (melting and solidification process) of the wood-based composite phase change materials obtained in the above embodiments were determined using a differential scanning calorimeter (model: DSC 300 Caliris Classic, Netzsch, Germany). The samples corresponding to each embodiment were heated from 0℃ to 100℃ and held at 100℃ for 5 min, then cooled from 100℃ to 0℃ and held at 0℃ for 5 min. The heating / cooling rate was 10℃ / min, and the atmosphere was N2 inert atmosphere. The phase transition temperature and phase transition enthalpy were recorded.

[0106] Table 1. Phase transition temperature and enthalpy of wood-based composite phase change materials

[0107]

[0108] Test Example 2

[0109] The thermal stability of the wood-based composite phase change materials obtained in the above embodiments was determined using a thermogravimetric analyzer (model: TG209F1, Netzsch, Germany). The test temperature range was 30-700℃, the heating rate was 10℃ / min, and the atmosphere was N2 inert atmosphere. The initial thermal weight loss of the sample (250℃) was recorded as the initial mass loss rate, used to evaluate thermal stability. The wood-based composite phase change materials obtained in the above embodiments were immersed in water at room temperature for 12 hours, then vacuum dried to constant weight to obtain water-washed samples. The thermal weight loss of the water-washed samples (250℃) was then measured according to the above method and recorded as the water-washed mass loss rate, used to evaluate water resistance.

[0110] Table 2. Thermal stability and water resistance of wood-based composite phase change materials

[0111]

[0112] As can be seen from the test results in Tables 1 and 2, the wood-based composite phase change materials obtained in Examples 1-3 of this invention have excellent heat storage and energy storage capabilities (enthalpy of fusion > 125 J·g). -1 Enthalpy of solidification > 117 J·g -1The thermal stability (weight loss at 250℃ <1%) and water resistance of the wood-based composite phase change material were significantly worse than those of Examples 1-3 because Examples 4-8 did not employ necessary technical solutions. Specifically, Example 4 did not use a modifying liquid to further modify the delignified wood in the preparation of the pretreated wood, Examples 5-7 did not use a modifying liquid with a specific composition, and Example 8 used an equal amount of citric acid instead of boric acid in the preparation of the phase change material. This is because Examples 1-3 of the present invention, after treatment with a specific modifying liquid, can construct a stable "three-dimensional cross-linking-thermal conductivity-hydrophobicity" interface layer between the wood skeleton and the phase change material, enhancing the interfacial bonding between the phase change material and the wood skeleton, and improving heat resistance and water resistance. In addition, the small amount of boric acid added to the phase change material can form BOC bonds with polyethylene glycol and citric acid, upgrading the binary cross-linking network into a denser three-dimensional hybrid cross-linking system, thereby improving water resistance and thermal stability.

[0113] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing a wood-based composite phase change material, characterized in that, Includes the following steps: Step 1: After cutting the wood, heat it in a delignification solution, remove it and wash it with water to obtain delignified wood; add the delignified wood to a modification solution and heat it, remove it and wash it with water, and dry it to obtain pretreated wood. Step 2: Mix polyethylene glycol, citric acid, and boric acid, and heat and stir under nitrogen protection to obtain a phase change material; Step 3: Impregnate the pretreated wood with the phase change material under vacuum, remove and dry to obtain the wood-based composite phase change material; The modified solution is composed of an aqueous ethanol solution, a modified filler, 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane, and triethylamine; the modified filler is prepared by: Boron nitride nanosheets were added to a buffer solution and ultrasonically dispersed. Then, dopamine hydrochloride was added and stirred. After filtration, the nanosheets were washed with water and dried to obtain modified boron nitride nanosheets. Modified boron nitride nanosheets were added to a lauric acid methanol solution, heated and stirred, filtered, and dried to obtain the modified filler.

2. The method for preparing the wood-based composite phase change material as described in claim 1, characterized in that, The weight ratio of the ethanol aqueous solution, modified filler, 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane, and triethylamine is 100:(1-2):(2-3):(0.1-0.4).

3. The method for preparing the wood-based composite phase change material as described in claim 1, characterized in that, The weight ratio of the boron nitride nanosheets, dopamine hydrochloride, and buffer solution is (2-4):(1-2):100; the weight ratio of the modified boron nitride nanosheets and lauric acid methanol solution is 1-2:

100.

4. The method for preparing the wood-based composite phase change material as described in claim 1, characterized in that, The buffer solution is Tris-HCl buffer solution; the boron nitride nanosheets have a thickness of 5-15 nm and a diameter of 1-2 μm.

5. The method for preparing the wood-based composite phase change material as described in claim 1, characterized in that, The delignification solution is a 1-2 wt% sodium chlorite aqueous solution, and the pH is adjusted to 4.5-5.0 with glacial acetic acid.

6. The method for preparing the wood-based composite phase change material as described in claim 1, characterized in that, The molar ratio of polyethylene glycol, citric acid, and boric acid is (4-5):1:(0.03-0.06).

7. The method for preparing the wood-based composite phase change material as described in claim 1, characterized in that, The wood is any one of balsa wood, poplar, linden, paulownia, and birch; the polyethylene glycol is at least one of polyethylene glycol 1000, polyethylene glycol 2000, polyethylene glycol 3000, polyethylene glycol 600, and polyethylene glycol 1500.

8. A wood-based composite phase change material, characterized in that, Prepared according to the method according to any one of claims 1-7.

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