Carbon nanocellulose aerogel based on gas phase adsorption as well as preparation method and application of carbon nanocellulose aerogel

Abstract

The invention provides carbon nanocellulose aerogel based on gas phase adsorption as well as a preparation method and application of the carbon nanocellulose aerogel, and belongs to the technical field of slow release of tobacco flavor. The preparation method comprises the following steps: preparing a nanocellulose suspension through 2, 2, 6, 6-tetramethylpiperidine oxide mediated oxidation reaction and homogenization treatment; sequentially performing freezing and vacuum freeze drying to obtain nano cellulose aerogel; the nano cellulose aerogel is carbonized, and carbon nano cellulose aerogel is obtained; the carbon nanocellulose aerogel and alpha-ionone, 3-acetylpyridine or citral are subjected to gas phase adsorption, and the carbon nanocellulose aerogel based on gas phase adsorption is obtained. The aerogel material prepared by utilizing a gas phase adsorption method has a good controlled release function, can realize accurate release of perfume under a high-temperature condition, meets the requirements of temperature and controlled release of perfume during cigarette combustion, and is simple and feasible in preparation process and suitable for industrial large-scale production.

Description

Technical Field

[0001] This invention relates to the field of sustained-release technology of tobacco flavorings, and in particular to a carbon nanofiber cellulose aerogel based on gas-phase adsorption, its preparation method, and its application. Background Technology

[0002] Cigarette aroma is a crucial indicator of cigarette quality. However, many flavorings and fragrances suffer from drawbacks such as volatility, high heat sensitivity, and susceptibility to oxidative degradation, resulting in short-lasting aroma and poor stability, severely limiting their application in the cigarette industry. Currently, mainstream flavoring sustained-release technologies primarily rely on physical adsorption methods in solution environments (such as porous material impregnation adsorption) or chemical surface modification methods (such as grafting functional groups onto a carrier). However, both methods have significant drawbacks: the adsorption efficiency of physical adsorption is highly dependent on the solution environment; pH changes alter the surface charge state of the carrier, leading to fluctuations in adsorption or even desorption; temperature changes easily damage the flavoring molecule structure or accelerate the decomposition of the carrier-flavoring complex; and solvent molecules in the solution compete with flavorings for binding sites, further reducing the effective loading capacity. After drying, flavoring molecules are also prone to detaching from the carrier surface. While surface modification can partially increase the loading capacity, it requires complex chemical modification of the carrier, with harsh reaction conditions and potential residual byproducts. The modified carrier exhibits a singular release behavior, making it difficult to meet the dual requirements of long-term sustained release during cigarette storage and instantaneous release during combustion.

[0003] Aerogels are promising flavor adsorbents, but their application still faces bottlenecks: their pore structure has a low degree of matching with the size of flavor molecules, resulting in an adsorption capacity far lower than the theoretical value and low flavor loading; traditional aerogels lack mechanical strength, are prone to collapse and flavor leakage during cigarette processing or transportation, and rely on complex processes such as supercritical drying, which are energy-intensive, costly, and difficult to mass-produce. Therefore, developing a nanocellulose aerogel material that combines high loading capacity, controlled release characteristics, and low cost for mass production, to overcome the limitations of solution environments and achieve precise control of cigarette aroma, has become a key breakthrough for improving cigarette quality. Summary of the Invention

[0004] The purpose of this invention is to provide a carbon nanofiber cellulose aerogel based on gas phase adsorption, its preparation method and application, so as to solve the problems of low fragrance loading and uneven fragrance release in existing aerogel materials.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing carbon nanofiber cellulose aerogel based on gas phase adsorption, comprising the following steps:

[0007] Cellulose, 2,2,6,6-tetramethylpiperidine oxide, sodium bromide, sodium hypochlorite and water were mixed, an alkaline solution was added, and an oxidation reaction was carried out. After homogenization, a nanocellulose suspension was obtained.

[0008] The nanocellulose suspension was sequentially frozen and then freeze-dried under vacuum to obtain nanocellulose aerogel.

[0009] The nanocellulose aerogel was carbonized to obtain carbon nanocellulose aerogel.

[0010] The carbon nanocellulose aerogel was subjected to gas-phase adsorption with fragrance to obtain a carbon nanocellulose aerogel based on gas-phase adsorption.

[0011] Preferably, the mass ratio of cellulose, 2,2,6,6-tetramethylpiperidine oxide, sodium bromide, and sodium hypochlorite is 1:(0.01-0.02):(0.05-0.20):(1.20-1.30).

[0012] The alkaline solution includes a sodium hydroxide solution with a concentration of 0.5–2 mol / L.

[0013] Preferably, the pH of the oxidation reaction is 9.5 to 10.5, the rotation speed is preferably 200 to 400 r / min, the temperature of the oxidation reaction is 25 to 30°C, and the time is 2 to 6 h.

[0014] Preferably, the homogenization process is carried out at a rotation speed of 5000–20000 r / min for a duration of 5–20 min.

[0015] The concentration of the nanocellulose suspension is 1.0–4.0 wt%.

[0016] Preferably, the freezing temperature is -80°C and the freezing time is 8 to 16 hours;

[0017] The vacuum freeze-drying temperature is -50℃, and the time is 24 to 48 hours.

[0018] Preferably, the carbonization is carried out under a protective atmosphere, the heating rate of the carbonization is 1-5℃ / min, the temperature is 500-700℃, and the time is 1-2h.

[0019] Preferably, the mass ratio of the carbon nanocellulose aerogel to the fragrance is 1:0.5 to 2;

[0020] The fragrance includes α-ionone, 3-acetylpyridine, or citral.

[0021] Preferably, the temperature of the gas-phase adsorption reaction is 70–90°C, and the time is 7–9 hours.

[0022] This invention provides carbon nanofiber cellulose aerogels based on gas-phase adsorption prepared by the above preparation method.

[0023] This invention provides the application of the above-mentioned carbon nanocellulose aerogel based on gas phase adsorption in the field of cigarettes or slow-release flavorings.

[0024] The beneficial effects of this invention are:

[0025] This invention produces nanocellulose through TEMPO-mediated oxidation and mechanical decomposition. After chemical and physical treatment, negatively charged CNFs are obtained, which enable good dispersibility in water and ensure sufficient mechanical strength through hydrogen bonding formed by abundant functional groups. Subsequently, during cryogenic freezing, the dispersed nanocellulose is compressed by randomly growing ice crystals. Intermolecular and intramolecular hydrogen bonds promote cellulose aggregation, random entanglement, and extensive assembly into a dense film. Finally, the nanocellulose is converted into aerogel (CA) using freeze-drying. The sublimation of ice crystals establishes open channels between CNF layers, forming a porous structure. After calcination in an N2 atmosphere, the smooth surface of the CA sheets becomes rough, and the carbon nanocellulose aerogel (C / CA) forms a wavy sheet structure, increasing the specific surface area and generating some macroporous structures, providing more abundant adsorption sites. The carbon nanocellulose aerogel provided by this invention has a high specific surface area and porous structure, enabling efficient loading of fragrances and achieving uniform fragrance release, solving the problems of low fragrance loading and uneven release in traditional physical adsorption methods.

[0026] This invention employs a gas-phase adsorption method to load α-ionone, 3-acetylpyridine, or citral into an aerogel, thus preparing a carbon nanofiber aerogel based on gas-phase adsorption. This invention avoids the influence of the solution environment on the fragrance addition efficiency in traditional solution adsorption methods, thereby improving the fragrance addition efficiency. The fragrance is uniformly distributed on the surface and inside the aerogel, significantly increasing the fragrance loading capacity and release stability.

[0027] The preparation process of this invention is simple and easy to scale up, and the carbonization treatment further improves the structural stability and adsorption performance of the aerogel. The carbon nanofiber cellulose aerogel based on gas phase adsorption prepared can be widely used in the fields of cigarettes or slow-release flavorings, and has broad market prospects. Attached Figure Description

[0028] Figure 1 A schematic diagram of the mechanism of oxidation reaction mediated by 2,2,6,6-tetramethylpiperidine oxide;

[0029] Figure 2 This is a schematic diagram of the preparation of aerogels in Example 1 and Comparative Example 1, wherein... Figure 2 (a) and Figure 2 (c) is a schematic diagram of the preparation of C / CA-αL in Example 1. Figure 2 The process of preparing nanocellulose aerogel (CA) in (a) and Figure 2 (b) is a schematic diagram of the preparation of CA-αL in Comparative Example 1;

[0030] Figure 3 (a) is the SEM image of CA obtained in Comparative Example 1. Figure 3 (b) is the SEM image of C / CA obtained in Example 1. Figure 3 (c) is a comparison diagram of the physical samples of C / CA obtained in Example 1 and CA obtained in Comparative Example 1;

[0031] Figure 4 In the middle (a), the CT results of CA obtained in Comparative Example 1 are shown. Figure 4 (b) shows the CT results of C / CA obtained in Example 1;

[0032] Figure 5 The adsorption capacity of CA and C / CA prepared in Example 1 for α-ionone is shown in the figure.

[0033] Figure 6 The cumulative release percentage of fragrance from C-CA-αL prepared in Example 1 and CA-αL prepared in Comparative Example 1 at 20°C, 60°C and 80°C are shown. Detailed Implementation

[0034] This invention provides a method for preparing carbon nanofiber cellulose aerogel based on gas phase adsorption, comprising the following steps:

[0035] Cellulose, 2,2,6,6-tetramethylpiperidine oxide, sodium bromide, sodium hypochlorite and water were mixed, an alkaline solution was added, and an oxidation reaction was carried out. After homogenization, a nanocellulose suspension was obtained.

[0036] The nanocellulose suspension was sequentially frozen and then freeze-dried under vacuum to obtain nanocellulose aerogel.

[0037] The nanocellulose aerogel was carbonized to obtain carbon nanocellulose aerogel.

[0038] The carbon nanocellulose aerogel was subjected to gas-phase adsorption with fragrance to obtain a carbon nanocellulose aerogel based on gas-phase adsorption.

[0039] In this invention, unless otherwise specified, all raw materials required for preparation are commercially available products well known to those skilled in the art.

[0040] In this invention, cellulose is preferably added to water containing 2,2,6,6-tetramethylpiperidine oxide (TEMPO), sodium bromide, and sodium hypochlorite. An alkaline solution is added dropwise during stirring. After oxidation under alkaline conditions, ethanol is added to terminate the reaction. The product is then washed with water by centrifugation and homogenized using a high-pressure homogenizer to obtain a nanocellulose (CNF) suspension. Figure 1 As shown, during the catalytic oxidation process, the TEMPO / NaBr / NaCIO system selectively oxidizes the primary hydroxyl group at the C6 position of cellulose to a carboxyl group without affecting other carbon sites, thereby improving the dispersibility and reactivity of cellulose.

[0041] In this invention, the preferred mass ratio of cellulose, 2,2,6,6-tetramethylpiperidine oxide, sodium bromide, and sodium hypochlorite is 1:(0.01-0.02):(0.05-0.20):(1.20-1.30), more preferably 1:0.016:0.1:1.24; the preferred mass ratio of cellulose to water is 1:50.

[0042] In this invention, the alkaline solution includes a sodium hydroxide solution, and the concentration of the sodium hydroxide solution is preferably 0.5 to 2 mol / L, more preferably 1 mol / L.

[0043] The present invention does not impose any special limitation on the amount of ethanol used, as long as the reaction is terminated. In the examples, the volume of ethanol is preferably 10 mL.

[0044] In this invention, the pH of the oxidation reaction is preferably 9.5 to 10.5, more preferably 10; the rotation speed is preferably 200 to 400 r / min, more preferably 300 r / min; the temperature of the oxidation reaction is preferably 25 to 30°C, more preferably 25°C; and the time is preferably 2 to 6 h, more preferably 4 h.

[0045] In this invention, the rotation speed of the homogenization process is preferably 5000-20000 r / min, more preferably 15000 r / min, and the time is preferably 5-20 min, more preferably 5 min.

[0046] In this invention, the concentration of the nanocellulose suspension is preferably 1.0 to 4.0 wt%, more preferably 2.5 wt%.

[0047] In this invention, the above-mentioned nanocellulose suspension is preferably poured into a mold, placed in a refrigerator for freezing, and then transferred to a freeze dryer for vacuum freeze drying to obtain nanocellulose aerogel (CA).

[0048] In this invention, the freezing temperature is preferably -80°C, and the freezing time is preferably 8 to 16 hours, more preferably 12 hours.

[0049] In this invention, the vacuum freeze-drying temperature is preferably -50°C, and the time is preferably 24 to 48 hours, more preferably 48 hours.

[0050] In this invention, the above-mentioned nanofiber aerogel is preferably carbonized to obtain carbon nanofiber cellulose aerogel (C / CA). This invention uses freeze-drying to prepare nanofiber cellulose aerogel (CA) and high-temperature carbonization to prepare carbon nanofiber cellulose aerogel (C / CA), thereby improving the structural stability and adsorption performance of the material.

[0051] In this invention, the carbonization is preferably carried out under a protective atmosphere, preferably nitrogen, the heating rate of the carbonization is preferably 1-5°C / min, more preferably 3°C / min, the temperature is preferably 500-700°C, more preferably 700°C, and the time is preferably 1-2h, more preferably 2h.

[0052] In this invention, the carbon nanofiber cellulose aerogel is dried and placed in a sealed container containing fragrance. It is then allowed to stand at a high temperature to perform gas phase adsorption, thereby obtaining carbon nanofiber cellulose aerogel (C / CA-αL) based on gas phase adsorption. The fragrance is loaded into the aerogel by gas phase adsorption, thereby achieving efficient loading and uniform release of the fragrance.

[0053] In this invention, the mass ratio of the carbon fiber aerogel to the fragrance is preferably 1:0.5 to 2, and more preferably 1:1.

[0054] In this invention, the fragrance preferably includes α-ionone, 3-acetylpyridine or citral, and more preferably α-ionone.

[0055] In this invention, the temperature of the gas phase adsorption is preferably 70-90°C, more preferably 80°C, and the time is preferably 7-9 hours, more preferably 8 hours.

[0056] The present invention also provides carbon nanofiber cellulose aerogels based on gas phase adsorption prepared by the above preparation method.

[0057] The present invention also provides the application of the above-mentioned carbon nanocellulose aerogel based on gas phase adsorption in the field of cigarettes or slow-release flavorings.

[0058] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0059] Example 1

[0060] like Figure 2As shown in (a), 1 g of cellulose was weighed and added to water containing 0.016 g TE MPO, 0.1 g NaBr and 1.24 g NaClO. During stirring, 1 mol / L NaOH solution was continuously added dropwise to make the pH 10 ± 0.2. The mixture was stirred at 300 r / min for 4 h at room temperature to carry out the oxidation reaction. After the reaction was completed, 10 mL of ethanol was added to terminate the reaction. The product was washed by centrifugation with water and then homogenized at 15000 r / min for 5 min using a high-pressure homogenizer to obtain a 2.5 wt% nanocellulose (CNF) suspension. The CNF suspension was poured into a mold and frozen at -80 °C for 12 h. After freezing, the sample was quickly transferred to a freeze dryer and freeze-dried under vacuum at -50 °C for 48 h to obtain nanocellulose aerogel (CA). The CA was calcined at 700 °C in a N2 atmosphere at a heating rate of 3 °C / min for 2 h to obtain carbon nanocellulose aerogel (C / CA).

[0061] like Figure 2 As shown in (c), the above C / CA aerogel material was dried at 60°C and then placed in a sealed container containing α-ionone. The mass ratio of α-ionone to C / CA aerogel material was 1:1. The container was placed at 80°C for 8 hours to carry out a gas phase adsorption reaction, thereby obtaining carbon nanofiber cellulose aerogel (C / CA-αL) based on gas phase adsorption.

[0062] Comparative Example 1

[0063] like Figure 2 As shown in Figure (a), the process for preparing nanocellulose aerogel (CA) in Comparative Example 1 is the same as in Example 1;

[0064] The only difference from Example 1 is:

[0065] No carbonization step is performed after the preparation of nanocellulose aerogel (CA), such as Figure 2 As shown in (b), the above-mentioned nanocellulose aerogel (CA) was directly dried and placed in a sealed container containing α-ionone to carry out a gas phase adsorption reaction, thereby obtaining nanocellulose aerogel (CA-αL) based on gas phase adsorption.

[0066] Characterization and performance determination

[0067] 1. The surface morphology of the prepared cellulose material was characterized using SEM, and the results are as follows: Figure 3 As shown, Figure 3 (a) is the SEM image of CA obtained in Comparative Example 1. Figure 3 (b) is the SEM image of C / CA obtained in Example 1. Figure 3 (c) is a comparison diagram of the physical samples of C / CA obtained in Example 1 and CA obtained in Comparative Example 1;

[0068] like Figure 3 As shown in (a), the SEM image reveals a tightly interwoven, laterally ordered CA microstructure; while... Figure 3 As shown in (b), after calcination at 700℃, the CA aerogel undergoes significant volume shrinkage, forming a C / CA carbon material. Figure 3 Image (c) also shows images of two samples. The calcination process roughens the smooth surface of the CA sheets and creates a wavy sheet microstructure, which is beneficial for providing more abundant adsorption sites for C / CA.

[0069] 2. Figure 4 In the middle (a), the CT results of CA obtained in Comparative Example 1 are shown. Figure 4 Image (b) shows the CT results of C / CA obtained in Example 1, clearly demonstrating the differences in pore structure between the two materials. The first row of images shows the distribution of pores in the three materials, while the second row reflects the forming characteristics of the nanofiber materials: CA aerogel exhibits a uniform and dense pore structure; while C / CA aerogel calcined at 700℃ has an increased number of pores, but the arrangement is disordered, resulting in significant voids and defects inside and outside the aerogel.

[0070] 3. The adsorption capacity of CA and C / CA prepared in Example 1 for α-ionone was determined, and the results are as follows: Figure 5 As shown, the adsorption capacity of CA prepared in Example 1 for αL was 48.14 mg / g, and the adsorption capacity of C / CA for αL was 332.64 mg / g, indicating that C / CA has abundant adsorption sites and obvious pore structure, and exhibits strong adsorption capacity for αL.

[0071] 4. To simulate temperature changes during cigarette storage and combustion, the flavor release behavior of C-CA-αL prepared in Example 1 and CA-αL prepared in Comparative Example 1 was tested at 20℃, 60℃, and 80℃. Equal amounts of C-CA-αL and CA-αL were exposed to the above three temperatures. 5 mg samples were taken every 5 minutes for the next 30 minutes, and α-L was extracted with ethanol. The results are shown in […]. Figure 6 ;

[0072] like Figure 6As shown, with the extension of release time, the amount of fragrance released gradually decreases and tends to reach equilibrium. This phenomenon mainly occurs because, over time, the difference in fragrance concentration inside and outside the aerogel gradually decreases, leading to a continuous slowdown in the fragrance release rate. C / CA-αL has a higher specific surface area and a more developed pore structure, providing more adsorption sites for fragrance molecules, thereby increasing the adsorption amount and delaying the fragrance release time. Furthermore, temperature regulation has a significant impact on the fragrance release rate. Temperature-controlled release experiments show that increasing temperature accelerates the fragrance release rate. Therefore, suitable flavored aerogel materials can be selected according to different usage requirements to achieve intelligent controlled release. The aerogel material prepared in this invention can achieve precise fragrance release under high-temperature conditions, meeting the temperature-controlled fragrance release requirements during cigarette combustion.

[0073] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing carbon nanofiber cellulose aerogel based on gas-phase adsorption, characterized in that, Includes the following steps: Cellulose, 2,2,6,6-tetramethylpiperidine oxide, sodium bromide, sodium hypochlorite and water were mixed, an alkaline solution was added, and an oxidation reaction was carried out. After homogenization, a nanocellulose suspension was obtained. The nanocellulose suspension was sequentially frozen and then freeze-dried under vacuum to obtain nanocellulose aerogel. The nanocellulose aerogel was carbonized to obtain carbon nanocellulose aerogel. The carbon nanocellulose aerogel was subjected to gas-phase adsorption with fragrance to obtain a carbon nanocellulose aerogel based on gas-phase adsorption.

2. The preparation method according to claim 1, characterized in that, The mass ratio of cellulose, 2,2,6,6-tetramethylpiperidine oxide, sodium bromide, and sodium hypochlorite is 1:(0.01~0.02):(0.05~0.20):(1.20~1.30); The alkaline solution includes a sodium hydroxide solution with a concentration of 0.5–2 mol / L.

3. The preparation method according to claim 2, characterized in that, The oxidation reaction is carried out at a pH of 9.5–10.5, with a preferred rotation speed of 200–400 r / min, a temperature of 25–30°C, and a duration of 2–6 h.

4. The preparation method according to claim 1 or 3, characterized in that, The homogenization process is carried out at a rotation speed of 5000–20000 r / min for 5–20 min. The concentration of the nanocellulose suspension is 1.0–4.0 wt%.

5. The preparation method according to claim 1, characterized in that, The freezing temperature is -80℃, and the time is 8 to 16 hours; The vacuum freeze-drying temperature is -50℃, and the time is 24 to 48 hours.

6. The preparation method according to claim 1, characterized in that, The carbonization is carried out under a protective atmosphere, with a heating rate of 1–5 °C / min, a temperature of 500–700 °C, and a time of 1–2 h.

7. The preparation method according to claim 1, characterized in that, The mass ratio of the carbon nanofiber cellulose aerogel to the fragrance is 1:0.5-2; The fragrance includes α-ionone, 3-acetylpyridine, or citral.

8. The preparation method according to claim 7, characterized in that, The temperature for gas-phase adsorption is 70–90°C, and the time is 7–9 hours.

9. Carbon nanofiber cellulose aerogel based on gas phase adsorption prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the carbon nanofiber cellulose aerogel based on gas phase adsorption as described in claim 9 in the field of cigarettes or sustained-release flavorings.

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