Preparation method of flexibility-adjustable rosin-based photo-thermal gel

Abstract

The invention discloses a preparation method of flexibility-adjustable rosin-based photo-thermal gel, which comprises the following steps: jointly attacking epoxidized soybean oil by using epoxy rosin and citric acid as nucleophilic reagents, and introducing lignin rich in phenolic hydroxyl groups to enhance the crosslinking degree and photo-thermal conversion capacity of the gel during ring opening polymerization of the epoxidized soybean oil. Finally, the covalent bond network and hydrogen bond network interpenetrating double-network rosin-based photo-thermal gel is formed. The formed rosin-based photo-thermal gel shows adjustable mechanical properties, and the crosslinking density of a gel network can be controlled by adjusting the ratio of epoxy rosin to citric acid, so that the controllable conversion of the gel from strong and soft to rigid and hard is realized. The light-heat-electricity conversion device assembled by taking the rosin-based photo-thermal gel as the photo-thermal layer is high in heating rate, large in temperature difference amplitude and high in conversion efficiency.

Description

Technical Field

[0001] This invention relates to the field of natural polymer materials, specifically to a method for preparing a flexible and tunable rosin-based photothermal gel. Background Technology

[0002] Gels, with their tunable mechanical properties, excellent extensibility, and good environmental responsiveness, show broad application prospects in biomedicine, flexible electronics, and emerging energy fields. Biomass materials offer significant advantages as gel substrates due to their wide availability and renewability, good biodegradability, and ease of functionalization. Rosin, a unique natural resin composed of diterpenoid resin acids secreted by pine trees, possesses a rigid hydrophobic property due to its tricyclic phenanthrene skeleton, while its carboxyl groups provide active sites for chemical modification, making it a promising substrate for preparing high-performance biomass-based gels. However, the application of rosin-based materials in gel materials is limited by its own molecular structure. The highly rigid phenanthrene ring structure of rosin molecules restricts the free movement of polymer chain segments, affecting the mechanical strength and extensibility of rosin gels. Therefore, it is urgent to overcome the rigidity bottleneck of rosin through collaborative innovation in molecular structure design and advanced preparation processes, achieving precise control of the mechanical properties and functional integration of rosin-based gels. Summary of the Invention

[0003] The purpose of this invention is to address the problem that the high-value-added applications of rosin-based materials are limited due to their excessive rigidity and brittleness, and to provide a method for preparing flexible and adjustable rosin-based photothermal gels.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a flexible and tunable rosin-based photothermal gel includes the following steps: (1) Disperse lignin in preheated epoxidized soybean oil solvent. While heating and stirring in an oil bath, add epoxidized rosin and citric acid to form a mixed solution. After reacting in the oil bath for a certain time, pour into a mold to form a rosin-based gel precursor.

[0005] (2) The rosin-based gel precursor obtained in step (1) is placed in a forced-air drying oven and further cross-linked in a high-temperature environment to form a rosin-based photothermal gel.

[0006] Furthermore, the preheating temperature of the epoxidized soybean oil in step (1) is 80-150 ℃.

[0007] Further, in the rosin-based gel precursor of step (1), the mass fractions of epoxy rosin, lignin and citric acid in the epoxy soybean oil solvent are 20-50 wt%, 1-50 wt% and 5-20 wt%, respectively.

[0008] Furthermore, the oil bath reaction temperature in step (1) is 80-150 ℃, and the oil bath reaction time is 1-3 h.

[0009] Further, the injection diameter of the rosin-based gel precursor in step (1) is 10-25 cm and the injection thickness is 5-20 mm.

[0010] Furthermore, the temperature of the blower drying oven in step (2) is 90-105 ℃, and the drying time is 1-6 h.

[0011] Furthermore, in step (1), the epoxy rosin is formed by the ring-opening reaction of rosin acid and epichlorohydrin. Specifically, it includes the following steps: 1. Esterification ring opening ① Add 100 g of polymerized rosin to a three-necked flask, along with 98 g of ECH and 1.0 g of tetramethylammonium bromide; ② Heat the oil bath to 95-120 ℃, purge with N2, reflux the reaction and stir continuously; ③ Take a sample every 30 minutes to measure the acid value until the acid value is ≤ 0.2 mg KOH / g (usually 2-3 h).

[0012] 2. Closed-loop (epoxidation) ① Cool the system to 75 ℃; ② Add 14 g of NaOH solid in batches slowly (to be completed in about 15 minutes), while controlling the temperature at 70-80 ℃; ③ Continue the reaction for 3.5 h, monitoring the pH with pH test paper during this period, and maintaining the pH of the system ≥ 12; ④ After the reaction is complete, the system becomes an emulsion with a large amount of NaCl precipitating out.

[0013] 3. Post-processing ① Remove NaCl by vacuum filtration while the liquid is still hot; ② Dilute the filtrate with 50 mL of toluene and transfer it to a separatory funnel; ③ Wash sequentially with 40 ℃ hot water (3×50 mL) until the pH of the aqueous phase is approximately 7; ④ The separated organic phase was dried with anhydrous Na2SO4 for 30 min and then filtered; ⑤ Recover toluene and excess ECH by rotary evaporation at 50 ℃ (vacuum ≤ 10 mmHg, time ≤ 30 min); ⑥ A yellow to brownish-yellow viscous liquid or semi-solid is obtained, namely epoxy rosin.

[0014] This invention uses epoxy rosin and citric acid as nucleophiles to jointly attack epoxidized soybean oil. While the epoxidized soybean oil undergoes ring-opening polymerization, lignin rich in phenolic hydroxyl groups is introduced to enhance the crosslinking degree and photothermal conversion capability of the gel, ultimately forming a double-network rosin-based photothermal gel with interpenetrating covalent and hydrogen bond networks. The resulting rosin-based photothermal gel exhibits adjustable mechanical properties. By adjusting the ratio of epoxy rosin to citric acid, the crosslinking density of the gel network can be controlled, thereby achieving a controllable transformation of the gel from "strong and flexible" to "rigid and hard."

[0015] Significant advantages of this invention: (1) This invention uses biomass as the main raw material, which is green and environmentally friendly. The production process is simple, and the mechanical properties of the prepared rosin-based photothermal gel are adjustable, the solvent tolerance is good, and it is biodegradable.

[0016] (2) When the rosin-based photothermal gel prepared by the present invention is used for photothermal applications, the heating rate is fast, the temperature difference range is large, and the working range is wide. Attached Figure Description

[0017] Figure 1 Digital photographs of the rosin-based photothermal gels prepared in Examples 1-4.

[0018] Figure 2 Stress-strain curves of rosin-based photothermal gels prepared in Examples 1-4.

[0019] Figure 3 SEM images of the rosin-based photothermal gel prepared in Example 1; (a) gel surface, (b) gel cross section.

[0020] Figure 4 Photothermal effect diagrams of the rosin-based photothermal gel prepared in Example 1; (a) before simulated sunlight exposure, (b) after simulated sunlight exposure.

[0021] Figure 5 Temperature-time curves of the rosin-based photothermal gel prepared in Example 1 at different light power densities. Detailed Implementation

[0022] To make the content of this invention easier to understand, the technical solutions of this invention will be further explained in conjunction with specific embodiments, but this invention is not limited thereto.

[0023] The preparation method of the epoxy rosin used in the following examples includes the following steps: (1) Esterification ring opening: 100 g of polymerized rosin was put into a three-necked flask, and 98 g of ECH and 1.0 g of tetramethylammonium bromide were added. The oil bath was heated to 95°C, N2 was passed through, the reaction was refluxed and stirred continuously. A sample was taken every 30 min to measure the acid value until the acid value was ≤ 0.2 mg KOH / g (usually 2-3 h).

[0024] (2) Ring closure (epoxidation): Cool the system to 75 °C; slowly add 14 g of solid NaOH in batches (about 15 min to complete the addition), and control the temperature at 70 °C; continue the reaction for 3.5 h, during which pH paper is used to monitor and maintain the pH of the system ≥ 12; after the reaction is completed, the system is an emulsion with a large amount of NaCl precipitated.

[0025] (3) Post-treatment: Remove NaCl by hot filtration; dilute the filtrate with 50 mL toluene and transfer it to a separatory funnel; wash the aqueous phase with 40 ℃ hot water (3×50 mL) until the pH of the aqueous phase is ≈ 7; dry the separated organic phase with anhydrous Na2SO4 for 30 min and filter; recover toluene and excess ECH by rotary evaporation at 50 ℃ (vacuum ≤ 10 mmHg, time ≤ 30 min); and obtain epoxy rosin.

[0026] Example 1 7.5 g of lignin was dispersed in 15 g of epoxidized soybean oil solvent at 80 ℃. While heating and stirring in an oil bath at 80 ℃, 7.5 g of epoxidized rosin and 1.5 g of citric acid were added to form a mixed solution. After reacting in the oil bath for 1 hour, the solution was poured into a mold to form a rosin-based gel precursor. The precursor was then placed in a 100 ℃ forced-air drying oven and reacted for another 3 hours before being removed from the mold to obtain the rosin-based photothermal gel.

[0027] Example 2 7.5 g of lignin was dispersed in 15 g of epoxidized soybean oil solvent at 120 ℃. While heating and stirring in an oil bath at 120 ℃, 4 g of epoxidized rosin and 2.25 g of citric acid were added to form a mixed solution. After reacting in the oil bath for 1 hour, the solution was poured into a mold to form a rosin-based gel precursor. The precursor was then placed in a 105 ℃ forced-air drying oven and reacted for another 4 hours before being removed from the mold to obtain the rosin-based photothermal gel.

[0028] Example 3 5 g of lignin was dispersed in 15 g of epoxidized soybean oil solvent at 150 ℃. While heating and stirring in an oil bath at 150 ℃, 3 g of epoxidized rosin and 3 g of citric acid were added to form a mixed solution. After reacting in the oil bath for 1 hour, the solution was poured into a mold to form a rosin-based gel precursor. The precursor was then placed in a 100 ℃ forced-air drying oven and reacted for another 1 hour before being removed from the mold to obtain the rosin-based photothermal gel.

[0029] Example 4 0.5 g of lignin was dispersed in 15 g of epoxidized soybean oil solvent at 80 ℃. While heating and stirring in an oil bath at 80 ℃, 7.5 g of epoxidized rosin and 2.5 g of citric acid were added to form a mixed solution. After reacting in the oil bath for 1 hour, the mixture was poured into a mold to form a rosin-based gel precursor. The precursor was then placed in a 90 ℃ forced-air drying oven and reacted for another 6 hours before being removed from the mold to obtain the rosin-based photothermal gel.

[0030] Depend on Figure 1 It is known that all embodiments of the present invention can prepare rosin-based photothermal gels with stable structure and uniform bulk phase. When the lignin content is low, the gel exhibits a light yellow and translucent state, while when the lignin content is increased, due to the conjugated system acting as a chromophore, the gel exhibits a black color that is beneficial to the photothermal effect. Figure 2 As shown, in Example 1, the carboxyl group content of epoxy rosin is higher than that of citric acid. At this time, epoxy rosin acts as the main nucleophile, and its nucleophilic ability is relatively weak and it is easy to form hydrogen bonds. The hydrogen bond network inside the gel is dominant, and the gel is "strong and flexible". When the citric acid content is high, a large amount of citric acid forms a dense covalent bond network with epoxy soybean oil and lignin, resulting in the gel obtained in Example 3 exhibiting the characteristics of "rigid and hard". Figure 3 The SEM image of the gel in Example 1 shows that the gel surface is smooth, the internal structure is dense and non-porous, and it exhibits a uniform condensed state structure. Figure 4 The photothermal effect diagram of the gel under one solar intensity in Example 1 shows that the core temperature of the rosin-based photothermal gel is close to 150°C, and the average temperature can reach 132°C. Figure 5 The temperature-time curves of the gel under different light power densities in Example 1 show that the gel has a large temperature difference range and heating rate, exhibiting a wide working range and excellent photothermal performance.

[0031] The above description is only a typical embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing a flexible and tunable rosin-based photothermal gel, characterized in that: Includes the following steps: (1) Disperse lignin in preheated epoxidized soybean oil solvent. While heating and stirring in an oil bath, add epoxidized rosin and citric acid to form a mixed solution. After reacting in the oil bath for a certain time, pour into a mold to form a rosin-based gel precursor. (2) The rosin-based gel precursor obtained in step (1) is placed in a forced-air drying oven and further cross-linked in a high-temperature environment to form a rosin-based photothermal gel.

2. The method for preparing a flexible and tunable rosin-based photothermal gel according to claim 1, characterized in that: The preheating temperature of the epoxidized soybean oil in step (1) is 80-150 ℃.

3. The method for preparing a flexible and tunable rosin-based photothermal gel according to claim 1, characterized in that: In step (1), the rosin-based gel precursor contains epoxy rosin, lignin, and citric acid in 20-50 wt%, 1-50 wt%, and 5-20 wt% of the epoxidized soybean oil solvent, respectively.

4. The method for preparing a flexible and tunable rosin-based photothermal gel according to claim 1, characterized in that: The oil bath reaction temperature in step (1) is 80-150 ℃, and the oil bath reaction time is 1-3 h.

5. The method for preparing a flexible and tunable rosin-based photothermal gel according to claim 1, characterized in that: The injection diameter of the rosin-based gel precursor in step (1) is 10-25 cm and the injection thickness is 5-20 mm.

6. The method for preparing a flexible and tunable rosin-based photothermal gel according to claim 1, characterized in that: The temperature of the forced-air drying oven in step (2) is 90-105 ℃, and the drying time is 1-6 h.

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