A bamboo lignin-based polymer material, a preparation method thereof and application thereof in thermal management

Abstract

A bamboo lignin-based polymer material, a preparation method thereof and application thereof in thermal management. The material is prepared from arginine-modified polyphenol bamboo lignin, thioctic acid and elemental sulfur as raw materials, and is prepared through thioctic acid ring-opening polymerization, mercapto radical-polyphenol Michael addition reaction and Fe 3+ coordination crosslinking. The material has a "fast-slow" dual dynamic network structure, and has high tensile property, high softness, excellent room temperature self-repairing efficiency, high strain sensitivity and 40-60 DEG C wide temperature range thermal management performance. The present application breaks through the limitations of poor ductility and difficulty in balancing strength and self-repairing of dynamic network caused by rigid skeleton of lignin, realizes the synergy of mechanical robustness and multifunctionality, has wide application prospect in the fields of flexible sensor, electronic skin and personal thermal regulation, and provides a green and sustainable new way for high value utilization of lignin.

Description

Technical Field

[0001] This invention belongs to the field of lignin functionalized materials, specifically relating to a bamboo lignin-based polymer material, its preparation method, and its application in thermal management. Background Technology

[0002] Lignin is the most abundant aromatic natural polymer in nature. Its molecular skeleton is composed of phenylpropane units linked by ether bonds and carbon-carbon bonds. It contains modifiable groups such as phenolic hydroxyl groups and methoxy groups, exhibiting good biocompatibility and renewability. In recent years, the construction of sustainable functional materials based on lignin has become a research hotspot. Among them, introducing dynamic covalent or non-covalent bonds into lignin cross-linking networks to endow materials with self-healing, reprocessable, and recyclable properties is an important direction for promoting the high-value utilization of lignin. However, existing technologies face the following common challenges: on the one hand, lignin itself has a low content of phenolic hydroxyl groups (usually less than 5 mmol / g), resulting in a scarcity of modifiable sites and low efficiency in chemical modification, making it difficult to form a high-density dynamic cross-linking network; on the other hand, in the reported lignin-based dynamic polymers, the exchange reactions of dynamic bonds (such as ester bonds, imine bonds, disulfide bonds, etc.) usually require high temperatures (>100 ℃), long reaction times, or external catalysts, making repeated processing conditions harsh, and the mechanical properties decay significantly after multiple cycles. More importantly, the inherent rigid aromatic ring structure of lignin greatly restricts the mobility of polymer chain segments, making it difficult for materials to simultaneously achieve high ductility (e.g., elongation at break >500%) and rapid room temperature self-healing ability. Therefore, how to overcome the inherent contradiction of lignin's "high rigidity-low ductility" and achieve efficient and non-destructive recycling under mild conditions is a technical bottleneck that urgently needs to be overcome in this field.

[0003] To address the aforementioned bottlenecks, researchers both domestically and internationally have undertaken various attempts. Regarding improving lignin reactivity, strategies such as demethylation and phenolation can effectively increase the content of phenolic hydroxyl groups. For example, treatment with acidic ionic liquids or Lewis acid systems can convert methoxy groups into phenolic hydroxyl groups, thereby providing more grafting sites. In terms of dynamic network construction, the introduction of supramolecular interactions such as hydrogen bonds and metal coordination bonds, or reversible covalent bonds such as disulfide bonds and urethane bonds, has been used to prepare lignin-based self-healing elastomers or glass-like polymers. Some studies have reported lignin-based polyurethanes with tensile strengths exceeding 30 MPa and elongation at break exceeding 1000%, but their self-healing or reprocessing still requires heating to 80–120 °C and applying pressure. Furthermore, after 3–4 repeated hot-pressing cycles, the retention rate of mechanical properties typically drops to 70%–85%. In addition, existing lignin-based conductive or sensing materials often require the addition of conductive fillers such as carbon nanotubes and metal nanoparticles, which increases costs and may affect the material's flexibility and self-healing efficiency. In summary, existing technologies still struggle to simultaneously achieve high ductility, complete self-healing, highly sensitive strain sensing, and excellent thermal management performance of lignin-based materials at room temperature without irritation, necessitating a novel molecular design strategy.

[0004] Therefore, it is urgent to start from the molecular level of lignin and expand its modifiable site density through structural optimization, thereby improving its reactivity. At the same time, functional units that can be reversibly processed under mild conditions should be introduced into the lignin-based polymer network to effectively reconcile the inherent contradiction between the material's recyclability and practical application performance. Summary of the Invention

[0005] Technical problem to be solved: The invention aims to overcome the technical defects of existing lignin-based materials, such as poor ductility due to rigid skeleton, difficulty in balancing mechanical strength and room temperature self-healing efficiency of dynamic cross-linked networks, and difficulty in functional integration. It provides a bamboo lignin-based polymer material with a "fast-slow" dual dynamic network structure, its preparation method and its application in thermal management, so as to realize the rapid self-healing and repeated processing of lignin-based materials under mild conditions (room temperature, no external stimulation), while taking into account high ductility, mechanical strength and multiple functional integration.

[0006] Technical solution: A method for preparing a bamboo lignin-based polymer material, comprising the following steps: (1) mixing bamboo lignin and pyrogallol in a lithium chloride aqueous solution containing hydrochloric acid, and performing a demethylation and phenolation reaction at 100℃-120℃, followed by purification to obtain pyrogallol-modified bamboo lignin; the mass ratio of bamboo lignin to pyrogallol is 1:(0.2-0.5); (2) under alkaline conditions, performing a grafting reaction between the pyrogallol-modified bamboo lignin obtained in step (1) and arginine in the presence of glyoxal, followed by purification to obtain arginine-grafted bamboo lignin; the mass ratio of pyrogallol-modified bamboo lignin to arginine is 5:4; (3) heating and melting lipoic acid, adding elemental sulfur S8 and the arginine-grafted bamboo lignin obtained in step (2) for copolymerization to obtain a copolymer; then adding FeCl3 for coordination crosslinking reaction to form a polymer network, thereby obtaining the bamboo lignin-based polymer material.

[0007] In step (1), the lithium chloride aqueous solution containing hydrochloric acid is a 50wt.%-70wt.% lithium chloride aqueous solution containing 1.0 mol / L-3.0 mol / L hydrochloric acid.

[0008] In step (1), the concentration of hydrochloric acid in the lithium chloride aqueous solution is 2.4 mol / L and the concentration of lithium chloride is 63 wt.%.

[0009] In step (1), the temperature of the demethylation reaction is 110°C and the reaction time is 1-3 hours.

[0010] In step (2), the grafting reaction is carried out in an aqueous sodium hydroxide solution with a pH of 10 to 12, at a temperature of 50°C to 70°C, for a reaction time of 2 to 6 hours.

[0011] In step (3), the mass ratio of lipoic acid to elemental sulfur S8 and arginine-grafted bamboo lignin is 21:9:(0.2-1.2), and the proportion of FeCl3 added is 10wt.%.

[0012] In step (3), the temperature of the copolymerization reaction is 150°C and the time is 1.5 hours; the temperature of the coordination crosslinking reaction is 100°C and the time is 10 minutes.

[0013] The bamboo lignin-based polymer material prepared by the above method.

[0014] The aforementioned material comprises a reversible cross-linked network structure consisting of dynamic disulfide bonds, dynamic polysulfide bonds, and iron-carboxylate coordination bonds.

[0015] The application of the above-mentioned bamboo lignin-based polymer materials in the preparation of personal thermal management products.

[0016] Beneficial Effects: This invention employs a strategy of demethylation and arginine grafting to directionally increase the types and density of active sites in lignin that can participate in dynamic cross-linking, breaking through the efficiency bottleneck of traditional methods that rely solely on phenolic hydroxyl modification. Based on this, utilizing the low-energy-barrier ring-opening characteristics of the disulfide bonds in the five-membered ring of lipoic acid, a dynamic covalent framework rich in disulfide and polysulfide bonds is synergistically constructed with elemental sulfur, and Fe is introduced. 3+ By forming coordination nodes, a "fast-slow" dual dynamic network capable of spontaneous exchange at room temperature is constructed. This design endows the material with both rapid self-healing capabilities under mild conditions and stable mechanical support properties, while also endowing it with intrinsic strain-sensitive conductivity and wide-temperature-range thermal buffering function. This invention elucidates the depolymerization-recombination mechanism of lignin-based dynamic networks without external stimulation, solving the problem of mutual constraints between ductility, recyclability, and functionality in traditional lignin-based materials. The modification strategy and dynamic cross-linking structure described are universal and can be extended to the functionalization design of other biomass aromatic polymers, providing a new path for the efficient, closed-loop utilization of lignin resources and their application in flexible electronics, personal thermal management wearables, and other fields. Attached Figure Description

[0017] Figure 1 The GF index of the bamboo lignin-based polymer material prepared in this invention under different strains.

[0018] Figure 2 The softness of the polymer materials prepared for this invention and common fabric materials.

[0019] Figure 3 The heating-cooling curves of the bamboo lignin-based polymer material prepared according to the present invention are shown. Detailed Implementation

[0020] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0021] Example 1

[0022] 3.0 g of bamboo lignin and 1.0 g of pyrogallol were suspended in a 63 wt.% LiCl aqueous solution containing 2.4 mol / L HCl and reacted with stirring at 110 °C for 2 h. After the reaction was completed, the mixture was cooled to room temperature, filtered to collect the solid, and washed three times with a 5 vol.% ethanol aqueous solution to remove unreacted pyrogallol. The solid was then dried under vacuum at 40 °C for 48 h to obtain demethylated phenolic bamboo lignin (PAL). 1.5 g of PAL and 1.2 g of arginine were dispersed in a NaOH aqueous solution, the pH was adjusted to 11, and the mixture was heated to 60 °C under a N2 atmosphere. 10 wt.% glyoxal aqueous solution was added dropwise, and the reaction was allowed to proceed for 4 h. After cooling, the reaction solution was neutralized to pH 7.0-7.5, centrifuged, and the supernatant was dialyzed using a 1000 Da dialysis bag for 3 days. The supernatant was then freeze-dried to obtain arginine-grafted bamboo lignin (PAL-Arg). 21.0 g of lipoic acid was heated to 150 °C to melt, and 9.0 g of S8 and 0.2 g of PAL-Arg were added. After stirring for 1.5 h, 5 g of 60 wt.% FeCl3 aqueous solution was added dropwise, and stirring was continued for 1 h. The reaction mixture was transferred to a mold, allowed to cool naturally to room temperature, and allowed to stand for 1 h to obtain bamboo lignin-based supramolecular ionic gel, denoted as Sample 1.

[0023] Example 2

[0024] 3.0 g of bamboo lignin and 1.0 g of pyrogallol were suspended in a 63 wt.% LiCl aqueous solution containing 2.4 mol / L HCl and reacted at 110 °C for 2 h with stirring. After the reaction was completed, the mixture was cooled to room temperature, filtered to collect the solid, and washed three times with a 5 vol.% ethanol aqueous solution to remove unreacted pyrogallol. The solid was then dried under vacuum at 40 °C for 48 h to obtain demethylated phenolic bamboo lignin (PAL). 1.5 g of PAL and 1.2 g of arginine were dispersed in a NaOH aqueous solution, the pH was adjusted to 11, and the mixture was heated to 60 °C under a N2 atmosphere. 10 wt.% glyoxal aqueous solution was added dropwise, and the reaction was allowed to proceed for 4 h. After cooling, the reaction solution was neutralized to pH 7.0-7.5, centrifuged, and the supernatant was dialyzed against a 1000 Da dialysis bag for 3 days. The supernatant was then freeze-dried to obtain arginine-grafted bamboo lignin (PAL-Arg). 21.0 g of lipoic acid was heated to 150 °C to melt, and 9.0 g of S8 and 0.4 g of PAL-Arg were added. After stirring for 1.5 h, 5 g of 60 wt.% FeCl3 aqueous solution was added dropwise, and stirring was continued for 1 h. The reaction mixture was transferred to a mold, allowed to cool naturally to room temperature, and allowed to stand for 1 h to obtain bamboo lignin-based supramolecular ionic gel, denoted as sample 2.

[0025] Example 3

[0026] 3.0 g of bamboo lignin and 1.0 g of pyrogallol were suspended in a 63 wt.% LiCl aqueous solution containing 2.4 mol / L HCl and reacted at 110 °C for 2 h with stirring. After the reaction was completed, the mixture was cooled to room temperature, filtered to collect the solid, and washed three times with a 5 vol.% ethanol aqueous solution to remove unreacted pyrogallol. The solid was then dried under vacuum at 40 °C for 48 h to obtain demethylated phenolic bamboo lignin (PAL). 1.5 g of PAL and 1.2 g of arginine were dispersed in a NaOH aqueous solution, the pH was adjusted to 11, and the mixture was heated to 60 °C under a N2 atmosphere. 10 wt.% glyoxal aqueous solution was added dropwise, and the reaction was allowed to proceed for 4 h. After cooling, the reaction solution was neutralized to pH 7.0-7.5, centrifuged, and the supernatant was dialyzed against a 1000 Da dialysis bag for 3 days. The supernatant was then freeze-dried to obtain arginine-grafted bamboo lignin (PAL-Arg). 21.0 g of lipoic acid was heated to 150 °C to melt, and 9.0 g of S8 and 0.6 g of PAL-Arg were added. After stirring for 1.5 h, 5 g of 60 wt.% FeCl3 aqueous solution was added dropwise, and stirring was continued for 1 h. The reaction mixture was transferred to a mold, allowed to cool naturally to room temperature, and allowed to stand for 1 h to obtain bamboo lignin-based supramolecular ionic gel, denoted as sample 3.

[0027] Example 4

[0028] 3.0 g of bamboo lignin and 1.0 g of pyrogallol were suspended in a 63 wt.% LiCl aqueous solution containing 2.4 mol / L HCl and reacted at 110 °C for 2 h with stirring. After the reaction was completed, the mixture was cooled to room temperature, filtered to collect the solid, and washed three times with a 5 vol.% ethanol aqueous solution to remove unreacted pyrogallol. The solid was then dried under vacuum at 40 °C for 48 h to obtain demethylated phenolic bamboo lignin (PAL). 1.5 g of PAL and 1.2 g of arginine were dispersed in a NaOH aqueous solution, the pH was adjusted to 11, and the mixture was heated to 60 °C under a N2 atmosphere. 10 wt.% glyoxal aqueous solution was added dropwise, and the reaction was allowed to proceed for 4 h. After cooling, the reaction solution was neutralized to pH 7.0-7.5, centrifuged, and the supernatant was dialyzed against a 1000 Da dialysis bag for 3 days. The supernatant was then freeze-dried to obtain arginine-grafted bamboo lignin (PAL-Arg). 21.0 g of lipoic acid was heated to 150 °C to melt, and 9.0 g of S8 and 0.8 g of PAL-Arg were added. After stirring for 1.5 h, 5 g of 60 wt.% FeCl3 aqueous solution was added dropwise, and stirring was continued for 1 h. The reaction mixture was transferred to a mold, allowed to cool naturally to room temperature, and allowed to stand for 1 h to obtain bamboo lignin-based supramolecular ionic gel, denoted as sample 4.

[0029] Example 5

[0030] 3.0 g of bamboo lignin and 1.0 g of pyrogallol were suspended in a 63 wt.% LiCl aqueous solution containing 2.4 mol / L HCl and reacted at 110 °C for 2 h with stirring. After the reaction was completed, the mixture was cooled to room temperature, filtered to collect the solid, and washed three times with a 5 vol.% ethanol aqueous solution to remove unreacted pyrogallol. The solid was then dried under vacuum at 40 °C for 48 h to obtain demethylated phenolic bamboo lignin (PAL). 1.5 g of PAL and 1.2 g of arginine were dispersed in a NaOH aqueous solution, the pH was adjusted to 11, and the mixture was heated to 60 °C under a N2 atmosphere. 10 wt.% glyoxal aqueous solution was added dropwise, and the reaction was allowed to proceed for 4 h. After cooling, the reaction solution was neutralized to pH 7.0-7.5, centrifuged, and the supernatant was dialyzed against a 1000 Da dialysis bag for 3 days. The supernatant was then freeze-dried to obtain arginine-grafted bamboo lignin (PAL-Arg). 21.0 g of lipoic acid was heated to 150 °C to melt, and 9.0 g of S8 and 1.0 g of PAL-Arg were added. After stirring for 1.5 h, 5 g of 60 wt.% FeCl3 aqueous solution was added dropwise, and stirring was continued for 1 h. The reaction mixture was transferred to a mold, allowed to cool naturally to room temperature, and allowed to stand for 1 h to obtain bamboo lignin-based supramolecular ionic gel, denoted as sample 5.

[0031] Example 6

[0032] 3.0 g of bamboo lignin and 1.0 g of pyrogallol were suspended in a 63 wt.% LiCl aqueous solution containing 2.4 mol / L HCl and reacted at 110 °C for 2 h with stirring. After the reaction was completed, the mixture was cooled to room temperature, filtered to collect the solid, and washed three times with a 5 vol.% ethanol aqueous solution to remove unreacted pyrogallol. The solid was then dried under vacuum at 40 °C for 48 h to obtain demethylated phenolic bamboo lignin (PAL). 1.5 g of PAL and 1.2 g of arginine were dispersed in a NaOH aqueous solution, the pH was adjusted to 11, and the mixture was heated to 60 °C under a N2 atmosphere. 10 wt.% glyoxal aqueous solution was added dropwise, and the reaction was allowed to proceed for 4 h. After cooling, the reaction solution was neutralized to pH 7.0-7.5, centrifuged, and the supernatant was dialyzed against a 1000 Da dialysis bag for 3 days. The supernatant was then freeze-dried to obtain arginine-grafted bamboo lignin (PAL-Arg). 21.0 g of lipoic acid was heated to 150 °C to melt, and 9.0 g of S8 and 1.2 g of PAL-Arg were added. After stirring for 1.5 h, 5 g of 60 wt.% FeCl3 aqueous solution was added dropwise, and stirring was continued for 1 h. The reaction mixture was transferred to a mold, allowed to cool naturally to room temperature, and allowed to stand for 1 h to obtain bamboo lignin-based supramolecular ionic gel, denoted as sample 6.

[0033] Example 7

[0034] 3.0 g of bamboo lignin and 1.0 g of pyrogallol were suspended in a 63 wt.% LiCl aqueous solution containing 2.4 mol / L HCl and reacted with stirring at 110 °C for 2 h. After the reaction was completed, the mixture was cooled to room temperature, filtered to collect the solid, and washed three times with a 5 vol.% ethanol aqueous solution to remove unreacted pyrogallol. The solid was then dried under vacuum at 40 °C for 48 h to obtain demethylated phenolic bamboo lignin (PAL). 1.5 g of PAL and 1.2 g of arginine were dispersed in a NaOH aqueous solution, the pH was adjusted to 11, and the mixture was heated to 60 °C under a N2 atmosphere. 10 wt.% glyoxal aqueous solution was added dropwise, and the reaction was allowed to proceed for 4 h. After cooling, the reaction solution was neutralized to pH 7.0-7.5, centrifuged, and the supernatant was dialyzed using a 1000 Da dialysis bag for 3 days. The supernatant was then freeze-dried to obtain arginine-grafted bamboo lignin (PAL-Arg). 21.0 g of lipoic acid was heated to 150 °C to melt, and 1.4 g of PAL-Arg was added. After stirring for 1.5 h, 5 g of 60 wt.% FeCl3 aqueous solution was added dropwise, and stirring was continued for 1 h. The reaction mixture was transferred to a mold, allowed to cool naturally to room temperature, and allowed to stand for 1 h to obtain bamboo lignin-based supramolecular ionic gel, which was designated as sample 7.

[0035] Example 8

[0036] 3.0 g of bamboo lignin and 1.0 g of pyrogallol were suspended in a 63 wt.% LiCl aqueous solution containing 2.4 mol / L HCl and reacted at 110 °C for 2 h with stirring. After the reaction was completed, the mixture was cooled to room temperature, filtered to collect the solid, and washed three times with a 5 vol.% ethanol aqueous solution to remove unreacted pyrogallol. The solid was then dried under vacuum at 40 °C for 48 h to obtain demethylated phenolic bamboo lignin (PAL). 1.5 g of PAL and 1.2 g of arginine were dispersed in a NaOH aqueous solution, the pH was adjusted to 11, and the mixture was heated to 60 °C under a N2 atmosphere. 10 wt.% glyoxal aqueous solution was added dropwise, and the reaction was allowed to proceed for 4 h. After cooling, the reaction solution was neutralized to pH 7.0-7.5, centrifuged, and the supernatant was dialyzed against a 1000 Da dialysis bag for 3 days. The supernatant was then freeze-dried to obtain arginine-grafted bamboo lignin (PAL-Arg). 21.0 g of lipoic acid was heated to 150 °C to melt, 1.4 g of PAL-Arg was added, and the mixture was stirred for 1.5 h. The reaction mixture was then transferred to a mold, allowed to cool naturally to room temperature, and allowed to stand for 1 h to obtain bamboo lignin-based supramolecular ionic gel, which was designated as sample 8.

[0037] The bamboo lignin-based polymer material prepared in this invention performs well as a flexible sensor. Figure 1 As shown, it not only has an excellent GF index, but can also sensitively detect changes in resistance caused by the movement of objects, and also has high conductivity. Figure 2-3It demonstrates excellent softness as a personal thermal management material and exhibits superior thermal cushioning over a wide temperature range.

[0038] Table 1. GF index of each sample under different tensile deformations

[0039]

[0040] Table 2. Softness of polymer materials and common fabric materials

[0041]

Claims

1. A method for preparing a bamboo lignin-based polymer material, characterized in that, The process includes the following steps: (1) Bamboo lignin and pyrogallol are mixed in a lithium chloride aqueous solution containing hydrochloric acid and subjected to a demethylation and phenolation reaction at 100℃-120℃. After the reaction, the mixture is purified to obtain pyrogallol-modified bamboo lignin. The mass ratio of bamboo lignin to pyrogallol is 1:(0.2-0.5); (2) Under alkaline conditions, the pyrogallol-modified bamboo lignin obtained in step (1) is grafted with arginine in the presence of glyoxal. After the reaction, the mixture is purified to obtain arginine-grafted bamboo lignin. The mass ratio of pyrogallol-modified bamboo lignin to arginine is 5:4; (3) After heating and melting lipoic acid, elemental sulfur S8 and the arginine-grafted bamboo lignin obtained in step (2) are added to perform a copolymerization reaction to obtain a copolymer. FeCl3 is then added to perform a coordination crosslinking reaction to form a polymer network, thereby obtaining the bamboo lignin-based polymer material.

2. The method according to claim 1, characterized in that, In step (1), the lithium chloride aqueous solution containing hydrochloric acid is a 50 wt.%-70 wt.% lithium chloride aqueous solution containing 1.0 mol / L-3.0 mol / L hydrochloric acid.

3. The method according to claim 2, characterized in that, In step (1), the concentration of hydrochloric acid in the lithium chloride aqueous solution is 2.4 mol / L, and the concentration of lithium chloride is 63 wt.%.

4. The method according to claim 1, characterized in that, In step (1), the temperature of the demethylation reaction is 110°C and the reaction time is 1-3 hours.

5. The method according to claim 1, characterized in that, In step (2), the grafting reaction is carried out in an aqueous sodium hydroxide solution with a pH of 10 to 12, at a temperature of 50°C to 70°C, for a reaction time of 2 to 6 hours.

6. The method according to claim 1, characterized in that, In step (3), the mass ratio of lipoic acid to elemental sulfur S8 and arginine-grafted bamboo lignin is 21:9:(0.2-1.2), and the proportion of FeCl3 added is 10wt.%.

7. The method according to claim 1, characterized in that, In step (3), the temperature of the copolymerization reaction is 150°C and the time is 1.5 hours; the temperature of the coordination crosslinking reaction is 100°C and the time is 10 minutes.

8. Bamboo lignin-based polymer materials prepared by the method according to any one of claims 1-7.

9. The bamboo-lignin-based polymer material according to claim 8, characterized in that, The material comprises a reversible cross-linked network structure consisting of dynamic disulfide bonds, dynamic polysulfide bonds, and iron-carboxylate coordination bonds.

10. The use of the bamboo lignin-based polymer material of claim 8 in the preparation of personal thermal management products.

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