High-efficiency heat insulation composite aerogel for fresh chilled meat preservation and preparation method and application thereof

Abstract

The present application relates to the technical field of food preservation packaging materials, and discloses a high-efficiency heat-insulating composite aerogel for fresh-keeping of chilled meat, a preparation method and application thereof.The high-efficiency heat-insulating composite aerogel takes carboxylated nanocellulose CCNFs and polyvinyl alcohol PVA as a matrix, takes ultrathin montmorillonite nanosheets as a heat-insulating filler, takes citric acid as a chemical crosslinking agent, and introduces hydrophobic silica nanoparticle-stabilized cyclooctane Pickering emulsion as a microporous template to construct a composite nanosystem, so as to obtain the high-efficiency heat-insulating composite aerogel.The high-efficiency heat-insulating composite aerogel for fresh-keeping of chilled meat has an extremely low thermal conductivity under high-temperature conditions, significantly delays temperature fluctuation of a cold chain, has good mechanical properties, and effectively prolongs the fresh-keeping period of chilled meat.

Description

Technical Field

[0001] This invention relates to the field of food preservation packaging materials technology, and in particular to a high-efficiency heat-insulating composite aerogel for the preservation of chilled meat, its preparation method and application. Background Technology

[0002] Fresh chilled meat, due to its rich nutrients and high water content, is susceptible to temperature fluctuations during cold chain transportation and retail, leading to microbial growth, fat oxidation, juice loss, and color deterioration, ultimately resulting in spoilage and a significantly shortened shelf life. Currently, the mainstream packaging methods for chilled meat include low-temperature refrigeration, which relies on a complete cold chain, resulting in high operating costs and a high risk of chain disruption; and polyurethane foam, while possessing some insulation properties, has a high thermal conductivity, insufficient cold storage capacity, and is non-biodegradable, posing a significant environmental burden. As consumers increasingly demand higher quality and safety from chilled meat consumers, the market urgently needs to develop safe, efficient, and low-cost new packaging materials to meet the insulation and temperature control requirements of the entire cold chain, extend shelf life, and ensure meat quality.

[0003] Aerogels, with their excellent properties such as ultra-low thermal conductivity, high porosity, and low density, are ideal high-efficiency thermal insulation materials with potential applications in cold chain insulation and food preservation. However, existing aerogel packaging materials are mostly prepared with a single matrix (such as pure cellulose or pure silicon), which generally suffers from poor mechanical properties, easy structural collapse, and poor formability, making it difficult to meet practical application requirements. Composite aerogels can optimize their performance by introducing functional fillers and chemical crosslinking agents, but how to synergistically control the interfacial compatibility of multiple components and the porous structure design during aerogel preparation remains to be explored. Therefore, developing a green, safe, biodegradable, and highly efficient thermal insulation bio-based aerogel material has become a key issue that urgently needs to be addressed in the field of food preservation packaging. Summary of the Invention

[0004] The purpose of this invention is to provide a high-efficiency thermal insulation composite aerogel for the preservation of chilled fresh meat, its preparation method and application. This high-efficiency thermal insulation composite aerogel exhibits an extremely low thermal conductivity under high temperature conditions, significantly delaying temperature fluctuations in the cold chain, while also possessing good mechanical properties, effectively extending the shelf life of chilled fresh meat.

[0005] To achieve the above objectives, on the one hand, the present invention provides a method for preparing a high-efficiency thermal insulation composite aerogel for the preservation of chilled fresh meat. The high-efficiency thermal insulation composite aerogel uses carboxylated cellulose nanofibers (CCNFs) and polyvinyl alcohol (PVA) as the matrix, ultrathin montmorillonite nanosheets as the thermal insulation filler, citric acid as the chemical crosslinking agent, and introduces cyclooctane-pickerlin emulsion stabilized by hydrophobic silica nanoparticles as a microporous template to construct a composite nanosystem, thereby obtaining the high-efficiency thermal insulation composite aerogel.

[0006] Furthermore, the preparation method of the high-efficiency thermal insulation composite aerogel for preserving chilled meat includes the following steps: Step 1: Dissolve polyvinyl alcohol and carboxylated nanocellulose in deionized water separately and stir until completely dissolved to obtain polyvinyl alcohol solution and carboxylated nanocellulose solution. Homogenize the carboxylated nanocellulose solution under high shear and then subject the homogenized carboxylated nanocellulose solution to ultrasonic disruption. Step 2: The homogeneous dispersed carboxylated nanocellulose solution, polyvinyl alcohol solution, ultrathin montmorillonite nanosheets, citric acid and hydrophobic silica nanoparticle-stabilized cyclooctane-pickerlin emulsion were stirred and mixed overnight. The stirred mixture was then allowed to stand at 4°C for 12-15 h to obtain the composite nanohydrogel. Step 3: Pour the composite nano-hydrogel into a mold, directionally freeze the composite nano-hydrogel with liquid nitrogen, freeze-dry at -80 ℃ for 1 to 2 days, and then dry at 50 to 60 ℃ for 6 hours to obtain a high-efficiency thermal insulation composite aerogel.

[0007] Further, in step 1, the concentration of the polyvinyl alcohol solution is 1%, the concentration of the carboxylated nanocellulose solution is 1%; the stirring temperature is 60~70℃; the high shear homogenization time is 10~15 min, the rotation speed is 1000~1500 rpm; the ultrasonic crushing time is 25~35 min, the power is 350 W, and the frequency is 40 kHz.

[0008] Furthermore, in step 2, the volume ratio of the carboxylated nanocellulose solution to the polyvinyl alcohol solution is 0:10 to 8:2; In the composite nanohydrogel, the amount of ultrathin montmorillonite nanosheets added is 0.3~1.5g / 100mL; In the composite nanohydrogel, the amount of citric acid added is 0.5~2.5g / 100mL; In the composite nanohydrogel, the volume fraction of cyclooctane-pickerlin emulsion is 2-12%.

[0009] Furthermore, the preparation method of ultrathin montmorillonite nanosheets is as follows: ① Weigh out montmorillonite and sodium carbonate and disperse them in deionized water. Stir the mixture at 60-80 °C for 12 h. After the reaction is complete, the mixture is dispersed and centrifuged repeatedly 2-4 times. Discard the supernatant and wash the precipitate with deionized water to remove residual salt. Vacuum dry the washed product for 6 h to obtain sodium-based montmorillonite raw material for subsequent stripping. ② Disperse sodium-based montmorillonite raw material in deionized water and stir at 40-60 ℃ for 6 h to form a uniform suspension. Place the suspension in an environment of -50 ℃ for 24 h and then thaw the frozen sample naturally at room temperature. The thawed suspension is ultrasonically treated at 330 W for 15 min and then the light yellow supernatant is collected by high-speed centrifugation. ③ The collected supernatant was freeze-dried to obtain fluffy powdery ultrathin montmorillonite nanosheets.

[0010] Furthermore, in step ①, the mass ratio of montmorillonite to sodium carbonate is 5–10:1; the ratio of the total mass of montmorillonite and sodium carbonate to deionized water is 0.4–1 g: 20 mL.

[0011] Furthermore, the preparation method of cyclooctane-pickerlin emulsion is as follows: 1) Weigh maltodextrin and dissolve it in deionized water, and stir at 20-40 °C for 2 h; then weigh hydrophobic silica nanoparticles and disperse them in the maltodextrin solution, and use high shear homogenization and ultrasonic crushing alternately to obtain an aqueous phase in which hydrophobic silica nanoparticles are uniformly dispersed. 2) Weigh out hydrophobic silica nanoparticles and dissolve them in cyclooctane oil phase; 3) The aqueous and oil phases were uniformly mixed using a high-shear homogenizer to obtain a hydrophobic silica nanoparticle-stabilized cyclooctane Pickering emulsion.

[0012] Further, in step 1), the concentration of maltodextrin is 15-20%; in step 3), the volume ratio of oil phase to water phase is 0.1-0.3:1; and the amount of hydrophobic silica nanoparticles added is 0.5%-1.5% of the solid content of cyclooctane-pickerlin emulsion.

[0013] Secondly, the present invention provides a high-efficiency thermal insulation composite aerogel for the preservation of chilled fresh meat, which is prepared by the above-mentioned preparation method.

[0014] Thirdly, the present invention provides the application of the above-mentioned high-efficiency thermal insulation composite aerogel for the preservation of chilled meat in the preparation of high-efficiency thermal insulation composite aerogel materials.

[0015] The advantages and positive effects of the high-efficiency thermal insulation composite aerogel for chilled fresh meat preservation, its preparation method, and its application described in this invention are as follows: 1. The bio-based composite aerogel prepared by this invention forms a three-dimensional interconnected porous structure with a density of 40.46±0.28 mg / cm³. 3 The porosity is as high as 98.94±0.59%, and the compressive strength reaches 243.76 kPa. Fourier transform infrared spectroscopy analysis shows that CCNFs and PVA in this composite aerogel form electrostatic interactions (1603 cm⁻¹). -1 ).

[0016] 2. This invention uses carboxylated cellulose nanofibers (CCNFs) and polyvinyl alcohol (PVA) as a green and biodegradable framework, combined with citric acid (CA) chemical crosslinking and ultrathin montmorillonite nanosheet fillers (MMTNS), to significantly improve the mechanical strength and structural stability of aerogels, solving problems such as easy collapse and difficulty in forming. Furthermore, it innovatively introduces Pickering emulsion templates and directional freeze-drying technology to construct an isotropic porous structure, giving the material an extremely low thermal conductivity, significantly delaying cold chain temperature fluctuations, and meeting the needs of chilled fresh meat preservation packaging.

[0017] 3. The preparation process of this invention is green and environmentally friendly. The resulting composite aerogel can effectively extend the shelf life of chilled meat, reduce the loss rate of cold chain transportation, and reduce economic losses. At the same time, the material is completely degradable, avoiding the environmental burden caused by traditional insulation materials such as polyurethane, and has both significant economic benefits and good social benefits.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1 These are scanning electron microscope (SEM) images of cross-sectional structures of CCNFs / PVA aerogels with different ratios in Example 1 of this invention; where a represents CCNFs. 10 / PVA0, b is CCNFs8 / PVA2, c is CCNFs7 / PVA3, d is CCNFs5 / PVA5, e is CCNFs3 / PVA7, f is CCNFs2 / PVA8; Figure 2 The graph shows the density and porosity results of CCNFs / PVA aerogels with different CCNFs / PVA contents in Example 1 of the present invention. Figure 3 The FTIR spectra of CCNFs / PVA aerogels with different ratios in Example 1 of this invention; Figure 4 The graph shows the density and porosity results of CCNFs / PVA@MMTNS aerogels with different MMTNS contents in Example 2 of the present invention. Figure 5 The graph shows the textural properties of CCNFs7 / PVA3@MMTNS aerogels with different MMTNS contents in Example 2 of the present invention, where a represents hardness, b represents elasticity, c represents cohesion, and d represents resilience. Figure 6 The graph shows the density and porosity results of CCNFs / PVA@MMTNS / CA aerogels with different CA contents in Example 3 of the present invention. Figure 7CCNFs7 / PVA3@MMTNS with different CA contents in Example 3 of this invention 0.9 Stress-strain curve of CA aerogel; Figure 8 CCNFs7 / PVA3@MMTNS with different Pickering emulsion contents in Example 4 of this invention 0.9 / CA 1.5 - Scanning electron microscope (SEM) images of the cross-sectional structure of Pickering aerogels; where a is Pickering 2, b is Pickering 4, c is Pickering 6, d is Pickering 8, and e is Pickering 9. 10 f stands for Pickering 12 ; Figure 9 The graph shows the density and porosity results of CCNFs / PVA@MMTNS / CA-Pickering aerogels with different Pickering contents in Example 4 of this invention. Figure 10 The graph shows the thermal conductivity test results of 9 groups of aerogel samples obtained by orthogonal experimental design in Example 5 of the present invention. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0022] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. Experimental instruments, equipment, and reagents in the following embodiments that do not specify their sources are all commercially available materials.

[0023] Unless otherwise defined or stated, all technical and scientific terms used in this invention have the same meaning as those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention.

[0024] This invention provides a method for preparing a highly efficient thermally insulating composite aerogel for preserving chilled meat. The method uses carboxylated cellulose nanofibers (CCNFs) and polyvinyl alcohol (PVA) as the matrix, ultrathin montmorillonite nanosheets as the thermally insulating filler, citric acid as the chemical crosslinking agent, and introduces a cyclooctane-pickerlin emulsion stabilized with hydrophobic silica nanoparticles as a microporous template to construct a composite nanosystem, thereby obtaining a highly efficient thermally insulating composite aerogel. The specific steps are as follows: Step 1: Dissolve polyvinyl alcohol and carboxylated nanocellulose in deionized water separately and stir until completely dissolved to obtain polyvinyl alcohol solution and carboxylated nanocellulose solution. Homogenize the carboxylated nanocellulose solution under high shear and then subject the homogenized carboxylated nanocellulose solution to ultrasonic disruption. Step 2: The homogeneously dispersed carboxylated nanocellulose solution, polyvinyl alcohol solution, ultrathin montmorillonite nanosheets, citric acid and hydrophobic silica nanoparticle-stabilized cyclooctane-pickering emulsion were stirred and mixed overnight. The stirred mixture was then allowed to stand at 4°C for 12-15 h to obtain the composite nanohydrogel. Step 3: Pour the composite nano-hydrogel into a mold, directionally freeze the composite nano-hydrogel with liquid nitrogen, freeze-dry at -80 ℃ for 1 to 2 days, and then dry at 50 to 60 ℃ for 6 hours to obtain a high-efficiency thermal insulation composite aerogel.

[0025] It should be noted that in step 1, the concentration of the polyvinyl alcohol solution is 1%, and the concentration of the carboxylated nanocellulose solution is 1%; the stirring temperature is 60-70 ℃, which can be 60 ℃, 65 ℃, or 70 ℃; the high-shear homogenization time is 10-15 min, and the rotation speed is 1000-1500 rpm; the ultrasonic crushing time is 25-35 min, the power is 350 W, and the frequency is 40 kHz.

[0026] It should be noted that in step 2, the volume ratio of the carboxylated nanocellulose solution to the polyvinyl alcohol solution is 0:10 to 8:2. In the composite nanohydrogel, the amount of ultrathin montmorillonite nanosheets added is 0.3-1.5 g / 100 mL; preferably 0.3 g / 100 mL, 0.6 g / 100 mL, 0.9 g / 100 mL, 1.2 g / 100 mL, or 1.5 g / 100 mL. In the composite nanohydrogel, the amount of citric acid added is 0.5-2.5 g / 100 mL; preferably 0.5 g / 100 mL, 1 g / 100 mL, 1.5 g / 100 mL, 2 g / 100 mL, or 2.5 g / 100 mL. In the composite nanohydrogel, the volume fraction of cyclooctane-pickerlin emulsion is 2-12%; preferably 2%, 4%, 6%, 8%, 10%, or 12%.

[0027] The preparation method of ultrathin montmorillonite nanosheets is as follows: ① Weigh out montmorillonite and sodium carbonate and disperse them in deionized water. Stir the mixture at 60-80 °C for 12 h. After the reaction is complete, the mixture is dispersed and centrifuged repeatedly 2-4 times. Discard the supernatant and wash the precipitate with deionized water to remove residual salt. Vacuum dry the washed product for 6 h to obtain sodium-based montmorillonite raw material for subsequent stripping. The mass ratio of montmorillonite to sodium carbonate is 5 to 10:1; preferably 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1. The ratio of the total mass of montmorillonite and sodium carbonate to deionized water is 0.4–1 g: 20 mL; preferably 0.4 g: 20 mL, 0.5 g: 20 mL, 0.6 g: 20 mL, 0.7 g: 20 mL, 0.8 g: 20 mL, 0.9 g: 20 mL, or 1 g: 20 mL. ② Disperse sodium-based montmorillonite raw material in deionized water and stir at 40-60 ℃ for 6 h to form a uniform suspension. Place the suspension in an environment of -50 ℃ for 24 h and then thaw the frozen sample naturally at room temperature. The thawed suspension is ultrasonically treated at 330 W for 15 min and then the light yellow supernatant is collected by high-speed centrifugation. ③ The collected supernatant was freeze-dried to obtain fluffy powdery ultrathin montmorillonite nanosheets.

[0028] The preparation method of cyclooctane-pickerlin emulsion is as follows: 1) Weigh maltodextrin and dissolve it in deionized water, and stir at 20-40 °C for 2 h; then weigh hydrophobic silica nanoparticles and disperse them in the maltodextrin solution, and use high shear homogenization and ultrasonic crushing alternately to obtain an aqueous phase in which hydrophobic silica nanoparticles are uniformly dispersed. The concentration of maltodextrin is 15-20%, preferably 15%, 16%, 17%, 18%, 19%, or 20%. 2) Weigh out hydrophobic silica nanoparticles and dissolve them in cyclooctane oil phase; 3) The aqueous phase and oil phase are uniformly mixed using a high-shear homogenizer to obtain a hydrophobic silica nanoparticle-stabilized cyclooctane Pickering emulsion; the volume ratio of the oil phase to the aqueous phase is 0.1 to 0.3:1, preferably 0.1:1, 0.2:1, or 0.3:1; the amount of hydrophobic silica nanoparticles added accounts for 0.5% to 1.5% of the solid content of the cyclooctane Pickering emulsion.

[0029] The following examples provide a detailed explanation.

[0030] Example 1 A method for preparing a high-efficiency thermal insulation composite aerogel for preserving chilled fresh meat includes the following steps: (1) Weigh out polyvinyl alcohol (PVA) and carboxylated cellulose nanoparticles (CCNFs) and dissolve them separately in deionized water at a solid-liquid ratio of 1 g: 100 mL. Stir magnetically at 600 rpm at 60 ℃ until completely dissolved to obtain a 1 wt% polyvinyl alcohol solution and a 1 wt% carboxylated cellulose nanoparticle suspension. Homogenize the 1 wt% carboxylated cellulose nanoparticle suspension at 1500 rpm for 15 min using high shear, maintaining the suspension temperature ≤10 ℃ during homogenization. Then, ultrasonically break down the homogenized suspension at 350 W and 40 kHz for 30 min to destroy the aggregates in the carboxylated cellulose nanoparticles and disperse them uniformly in the system.

[0031] (2) A uniformly dispersed 1wt% carboxylated nanocellulose solution and a 1wt% polyvinyl alcohol solution were magnetically stirred overnight at 600 rpm at 4 ℃. After mixing, the mixture was allowed to stand at room temperature for 12 h to obtain a composite nanohydrogel. Six groups were set up with volume ratios of 1wt% carboxylated nanocellulose solution to 1wt% polyvinyl alcohol solution of 10:0, 8:2, 7:3, 5:5, 3:7, and 2:8. Each composite nanohydrogel was poured into a mold, directionally frozen with liquid nitrogen, freeze-dried at -80 ℃ for 2 days, and then dried at 60 ℃ for 6 h to obtain a high-efficiency thermal insulation composite aerogel.

[0032] Surface morphology analysis, density and porosity determination of high-efficiency thermal insulation composite aerogel: The prepared composite aerogel was cooled with liquid nitrogen and then fractured into a brittle fragment. A cross-section was then cut and fixed onto conductive adhesive on the sample stage. The composite aerogel was then subjected to vacuum gold sputtering, and the cross-sectional morphology of the composite aerogel was observed using a scanning electron microscope. Specific results are as follows: Figure 1 As shown.

[0033] The porosity of the composite aerogel was determined using the liquid displacement method. The composite aerogel sample was dried in a 60 °C oven for 6 h, and then immersed in anhydrous ethanol for 24 h. Subsequently, the saturated sample was removed and weighed. The porosity P of the aerogel was calculated according to formula (1), and the results are as follows: Figure 2 As shown.

[0034] (1); in, m 0, m 1 represents the mass of the composite aerogel before and after soaking, in g; ρ Anhydrous ethanol has a density of 0.785 g / cm³. 3 ; V 0 represents the volume of the composite aerogel sample, in cm³. 3 .

[0035] Depend on Figure 1 It is evident that CCNFs / PVA aerogels prepared by directional freeze-drying all possess a three-dimensional porous network structure, with the pore structure formed jointly by ice crystal growth and polymer molecular chain aggregation during the freezing process. As the proportion of CCNFs increases, the aerogel pores gradually transform from large-sized, irregularly perforated pores to honeycomb-like, uniform micropores; pure PVA aerogel, due to excessive molecular chain entanglement, exhibits pore wall collapse and a dense structure. Figure 2 It can be seen that as the proportion of CCNFs increases, the aerogel density increases from 14.6 mg / cm³. 3 Gradually decreased to 12.3 mg / cm 3 The porosity increased from 31.2% to 85.5%, indicating a negative correlation between density and porosity for aerogels with different CCNFs / PVA ratios. When the CCNFs to PVA ratio was 7:3, the resulting aerogel possessed both a uniform porous structure and suitable density and porosity, providing a good skeletal foundation for the subsequent introduction of functional fillers.

[0036] FTIR spectroscopy determination of high-efficiency thermal insulation composite aerogel: The chemical structure and intercomponent interactions of the composite aerogel were characterized by FTIR spectroscopy. The aerogel samples were cooled with liquid nitrogen, ground into powder, mixed with KBr, compressed into pellets, and then tested. The test range was 500–4000 cm⁻¹. -1 4 cm resolution -1 The average of 32 scans was taken, and the result is as follows: Figure 3 As shown.

[0037] Depend on Figure 3 It can be seen that CCNFs / PVA aerogels with different ratios all retained the typical characteristic absorption peaks of carboxylated nanocellulose and polyvinyl alcohol. (3420 cm⁻¹) -1 The peak at 2922 cm⁻¹ represents the stretching vibration of the hydroxyl group (-OH). -1 The peak at 1737 cm⁻¹ represents the saturated CH stretching vibration peak. -1 The corresponding C=O stretching vibration of the carboxyl group (-COOH) in CCNFs is 1061 cm⁻¹. -1 The peak at 1603 cm⁻¹ is a characteristic absorption peak of the cellulose backbone (COC). As the proportion of CCNFs increases, the peak at 1603 cm⁻¹ increases. -1 carboxylate ions (-COO) - The characteristic peak gradually increases, and at the same time, the 3420 cm⁻¹ peak... -1The significant shift in the hydroxyl peak indicates a strong hydrogen bond and electrostatic interaction between the carboxyl groups of CCNFs and the hydroxyl groups of PVA, resulting in a stable composite at the molecular level. No new impurity peaks appeared in CCNFs / PVA aerogels of different ratios, and the matrix characteristic peaks were fully preserved, indicating that the composite process of CCNFs and PVA is a physical blending and intermolecular interaction, without disrupting the skeletal structure of CCNFs and PVA.

[0038] Example 2 The effect of different amounts of ultrathin montmorillonite nanosheets on the performance of bio-based composite aerogels.

[0039] A method for preparing bio-based composite aerogels with different amounts of ultrathin montmorillonite nanosheets includes the following steps: (1) The preparation method of polyvinyl alcohol and carboxylated nanocellulose solution is the same as step (1) in Example 1.

[0040] (2) A uniformly dispersed 1 wt% carboxylated nanocellulose solution and a 1 wt% polyvinyl alcohol solution were magnetically stirred overnight at 600 rpm at 4 °C, wherein the volume ratio of the 1 wt% carboxylated nanocellulose solution to the 1 wt% polyvinyl alcohol solution was 7:3. During the mixing process, ultrathin montmorillonite nanosheets were added at solid-liquid ratios of 0.3 g / 100 mL, 0.6 g / 100 mL, 0.9 g / 100 mL, 1.2 g / 100 mL, and 1.5 g / 100 mL, respectively. After mixing, the mixture was allowed to stand at room temperature for 12 h to obtain composite nanohydrogels. Each composite nanohydrogel was poured into a mold, and the composite nanohydrogels were directionally frozen with liquid nitrogen, freeze-dried at -80 °C for 2 days, and then dried at 60 °C for 6 h to obtain bio-based composite aerogels with different contents of ultrathin montmorillonite nanosheets.

[0041] Determination of density and porosity of bio-based composite aerogels with different amounts of ultrathin montmorillonite nanosheets: The specific methods for determining the density and porosity of the composite aerogel are the same as in Example 1, and the results are as follows: Figure 4 As shown.

[0042] Depend on Figure 4 It can be seen that with the increase of MMTNS content, the density and porosity of the composite aerogel show a significant synergistic change. When the MMTNS content increases from 0.0% to 0.9%, the aerogel density increases from 12.8 mg / cm³. 3 It continued to rise to 30.0 mg / cm³ 3The porosity simultaneously increased from around 70% to a peak of approximately 88.6%; this indicates that an appropriate amount of MMTNS filling the gaps in the CCNFs / PVA framework effectively densified the pore wall structure and increased the solid packing density. When the content exceeded 0.9%, the density continued to increase to 30.0 mg / cm³. 3 The porosity rapidly decreased to approximately 69.2%, attributed to the agglomeration effect caused by excessive filler content, which disrupted the uniformity of the aerogel porous network. This result confirms that 0.9% is the optimal addition amount of MMTNS, at which point the aerogel possesses both suitable density and high porosity, providing a structural basis for subsequent optimization of thermal insulation performance.

[0043] Texture properties of bio-based composite aerogels with different amounts of ultrathin montmorillonite nanosheets: The hardness, elasticity, cohesion, and resilience of the aerogel were tested using a physical property analyzer. A 5 mm diameter P / 5 cylindrical probe was selected, and the measurements were performed in TPA mode. The pre-compression speed was set to 1 mm / s, the compression ratio to 50% of the sample height, and the interval was 5 s. The results are as follows: Figure 5 As shown.

[0044] Depend on Figure 5 It can be seen that the introduction of different contents of MMTNS has a regulatory effect on the textural properties of CCNFs7 / PVA3 aerogel, showing an initial increase followed by a decrease. When the MMTNS content is 0.9%, the aerogel hardness reaches a peak of 2554 g, and the cohesion and resilience also climb to 58% and 28%, respectively, with the resilience consistently maintaining a high plateau above 90%. This is attributed to the uniform dispersion of MMTNS in the gaps of the CCNFs / PVA three-dimensional network, which densifies the pore walls through lamellar overlap and interfacial adsorption effects, significantly enhancing the material's load-bearing capacity and structural integrity. When the MMTNS content exceeds 0.9%, the hardness, cohesion, and resilience all decrease to varying degrees. The 1.5% group shows a decrease in hardness to 1571 g and a drop in resilience to below 15%. This is because excessive nanosheets agglomerate, disrupting the uniformity and continuity of the aerogel's porous structure, leading to uneven densification and susceptibility to local defects under stress. Considering the changes in overall texture index, the optimal addition amount of MMTNS is about 0.9%. The composite aerogel prepared under this condition has both excellent hardness and elasticity, which can effectively meet the mechanical support and cushioning requirements of cold meat preservation packaging in practical applications.

[0045] Example 3 The effect of different amounts of citric acid added on the performance of bio-based composite aerogels.

[0046] A method for preparing bio-based composite aerogels with different amounts of citric acid, comprising the following steps: (1) The preparation method of polyvinyl alcohol and carboxylated nanocellulose solution is the same as step (1) in Example 1.

[0047] (2) A uniformly dispersed 1 wt% carboxylated nanocellulose solution and a 1 wt% polyvinyl alcohol solution were magnetically stirred overnight at 600 rpm at 4 °C, wherein the volume ratio of the 1 wt% carboxylated nanocellulose solution to the 1 wt% polyvinyl alcohol solution was 7:3. During the mixing process, ultrathin montmorillonite nanosheets were added at a solid-liquid ratio of 0.6 g / 100 mL, and citric acid was added at solid-liquid ratios of 0.5 g / 100 mL, 1 g / 100 mL, 1.5 g / 100 mL, 2 g / 100 mL, and 2.5 g / 100 mL, respectively. After mixing, the mixture was allowed to stand at room temperature for 12 h to obtain composite nanohydrogels. Each composite nanohydrogel was poured into a mold, and the composite nanohydrogels were directionally frozen with liquid nitrogen, freeze-dried at -80 °C for 2 days, and then dried at 60 °C for 6 h to obtain bio-based composite aerogels with different contents of ultrathin montmorillonite nanosheets.

[0048] Determination of density and porosity of bio-based composite aerogels with different citric acid additions: The specific methods for determining the density and porosity of the composite aerogel are the same as in Example 1, and the results are as follows: Figure 6 As shown.

[0049] Depend on Figure 6 It can be seen that the density of the composite aerogel increases continuously with increasing CA content, while the porosity first increases and then decreases. When the CA content increases from 0.0% to 1.5%, the aerogel density increases from 21.6 mg / cm³. 3 Rising to 34.1 mg / cm 3 The porosity increased from 83.2% to a peak of 94.2% because CA, as a chemical crosslinking agent, enhanced the network bonding between CCNFs and PVA through esterification, thereby improving the density of the framework and optimizing the porous structure. When the CA content exceeded 1.5%, the porosity rapidly decreased, dropping to 88.1% at 2.5%, attributed to network shrinkage and pore collapse caused by excessive crosslinking. In summary, the optimal CA addition is 1.5%, at which point the aerogel possesses both high porosity and suitable density, providing a structural basis for efficient thermal insulation.

[0050] Stress-strain properties of bio-based composite aerogels with different citric acid additions: Stress-strain tests were performed on bio-based composite aerogels using an electronic universal testing machine. The test sample was a cylindrical aerogel with a diameter of 34 mm and a height of 14.5 mm. The test conditions were room temperature, a compression rate of 2 mm / min, and a maximum compressive strain of 70%. Specific results are as follows: Figure 7 As shown.

[0051] Depend on Figure 7 It can be seen that the addition of CA affects CCNFs7 / PVA3@MMTNS0.9 The stress-strain properties of the aerogel exhibit a significant pattern of initial enhancement followed by a decrease. The blank aerogel without added CA showed a stress of only 35.9 kPa at 50% strain. With increasing CA content to 1%, the mechanical strength of the aerogel increased significantly, reaching a peak stress of 46.2 kPa at 50% strain. Furthermore, the stress-strain curve displayed typical compression characteristics of porous materials, indicating that CA enhanced the three-dimensional network structure of CCNFs and PVA through esterification crosslinking, significantly improving the material's load-bearing capacity and structural stability. When the CA content exceeded 1%, the mechanical properties gradually decreased. At a CA content of 2.5%, the stress at 50% strain was only 16.9 kPa, attributed to excessive network shrinkage and pore collapse caused by excessive crosslinking, which disrupted the porous structure and mechanical continuity of the aerogel. In summary, the optimal CA addition level is 1%, at which point the aerogel possesses both excellent mechanical strength and structural integrity, meeting the practical application requirements for chilled meat preservation packaging.

[0052] Example 4 The effect of different amounts of Pickering emulsion added on the structure of bio-based composite aerogels.

[0053] A method for preparing bio-based composite aerogels with different amounts of Pickering emulsion, comprising the following steps: (1) The preparation method of polyvinyl alcohol and carboxylated nanocellulose solution is the same as step (1) in Example 1.

[0054] (2) A uniformly dispersed 1 wt% carboxylated nanocellulose solution and a 1 wt% polyvinyl alcohol solution were magnetically stirred overnight at 600 rpm at 4 ℃, wherein the volume ratio of the 1 wt% carboxylated nanocellulose solution to the 1 wt% polyvinyl alcohol solution was 7:3. During the mixing process, ultrathin montmorillonite nanosheets were added at a solid-liquid ratio of 0.6 g / 100 mL, citric acid was added at a solid-liquid ratio of 1 g / 100 mL, and Pickering emulsions with volume fractions of 2%, 4%, 6%, 8%, 10%, and 12% were added respectively. After mixing, the mixture was allowed to stand at room temperature for 12 h to obtain composite nanohydrogels. Each composite nanohydrogel was poured into a mold, and the composite nanohydrogels were directionally frozen with liquid nitrogen, freeze-dried at -80 ℃ for 2 days, and then dried at 60 ℃ for 6 h to obtain bio-based composite aerogels with different contents of ultrathin montmorillonite nanosheets.

[0055] Surface morphology analysis, density and porosity determination of bio-based composite aerogels with different amounts of Pickering emulsion: The surface morphology analysis method for the composite aerogel is the same as in Example 1, and the results are as follows: Figure 8 As shown.

[0056] The density and porosity of the composite aerogel were determined using the same methods as in Example 1, and the results are as follows: Figure 9As shown.

[0057] Depend on Figure 8 It can be seen that the composite aerogels with different Pickering emulsion contents all exhibit a three-dimensional porous network structure, and their pore morphology varies significantly with the amount of emulsion added. The composite aerogel with a Pickering emulsion content of 2% has large, uneven pores. As the emulsion content increases to 6%, the aerogel forms a uniform, interconnected honeycomb-like microporous structure with complete and continuous pore walls. When the emulsion content exceeds 8%, the pores gradually become denser and local agglomeration defects appear. Combined with… Figure 9 It can be seen that as the Pickering emulsion content increases from 0% to 6%, the aerogel density increases from 32.1 mg / cm³. 3 Increased to 40.5 mg / cm 3 The porosity increased from 94.2% to a peak of 98.9%. When the content exceeded 6%, the porosity slowly decreased while the density continued to rise, attributed to the pore compression and structural densification caused by excessive emulsion. This result confirms that the optimal addition amount of Pickering emulsion is 6%, at which point the aerogel possesses a uniform porous structure, high porosity, and suitable density, providing a structural basis for efficient thermal insulation performance.

[0058] Example 5 Orthogonal experiments were used to optimize the preparation conditions of bio-based composite aerogels.

[0059] The orthogonal experimental design of bio-based composite aerogels includes the following steps: Based on the results of the above single-factor experiments, the suitable dosage ranges of carboxylated nanocellulose:polyvinyl alcohol ratio, ultrathin montmorillonite nanosheets, citric acid, and hydrophobic silica nanoparticle-stabilized cyclooctane-pickerlin emulsion were screened (the suitable ratios of carboxylated nanocellulose:polyvinyl alcohol were selected as 8:2, 7:3, and 5:5; the suitable contents of ultrathin montmorillonite nanosheets were selected as 0.6%, 0.9%, and 1.2%; the suitable contents of citric acid were selected as 1%, 1.5%, and 2%; and the suitable contents of pickerlin emulsion were selected as 4%, 6%, and 8%). An L9 (3) design was then established. 4 An orthogonal experiment was conducted, repeated three times. Based on the experimental results, a multi-index (density, porosity, and compressibility, etc.) comprehensive scoring method was used to optimize the optimal composition ratio of the composite aerogel. The orthogonal experimental design was carried out with reference to the orthogonal experimental table (Table 1).

[0060] Table 1. Orthogonal Experiment of Formulation L9(3) 4 )

[0061] Thermal conductivity testing of bio-based composite aerogels prepared by orthogonal experiments: The thermal conductivity of polystyrene foam and various composite aerogel samples was tested using a Hotdisk thermal conductivity meter according to the ISO 22007-2 international standard, employing the transient planar heat source method. Polystyrene foam served as a control group. Before testing, samples were cut to standard dimensions and smoothed. Measurements were performed at room temperature. Three different locations were selected for each test, and the average value was taken. The results are shown below. Figure 10 As shown.

[0062] Depend on Figure 10 It was found that the thermal conductivity of all composite aerogel samples was significantly lower than that of the control group polystyrene foam (0.040 W / mK), with the A2B1C2D3 group exhibiting the lowest thermal conductivity at 0.0275 W / mK, a 31.25% reduction compared to the control group, demonstrating excellent thermal insulation performance. Significant differences in thermal conductivity were observed among the different orthogonal groups, indicating that the ratio of CCNFs to PVA, the content of MMTNS, the content of CA, and the content of Pickering emulsion significantly modulate the thermal insulation performance. The optimal thermal insulation performance of the A2B1C2D3 group is attributed to the formation of a uniform, interconnected three-dimensional porous structure in the composite aerogel at this ratio. Combined with the "maze effect" of MMTNS and the microporous structure constructed by the Pickering emulsion, this effectively extended the heat conduction path and suppressed gas convection and solid-state heat conduction. The other groups, due to imbalanced component ratios, exhibited problems such as uneven pore structure and denser structure, leading to increased thermal conductivity. These results confirm that CCNFs7 / PVA3@MMTNS 0.6 / CA 1.5 -Pickering8 is the optimal formulation for composite aerogels, which can meet the high-efficiency heat insulation requirements of chilled meat preservation packaging.

[0063] Therefore, the high-efficiency thermal insulation composite aerogel for chilled meat preservation described in this invention uses carboxylated cellulose nanofibers (CCNFs) and polyvinyl alcohol (PVA) as a green, biodegradable bio-based framework. Ultrathin montmorillonite nanosheets (MMTNS) are added as thermal insulation fillers, and a uniform and stable microporous structure is constructed using Pickering emulsion template technology. Simultaneously, citric acid (CA) is introduced as a chemical crosslinking agent to enhance the mechanical properties and molding effect of the three-dimensional network structure. Directional freeze-drying technology is employed to form an isotropic porous structure, thereby effectively reducing the thermal conductivity of the composite aerogel and obtaining a composite aerogel with high-efficiency thermal insulation properties, possessing significant economic and social benefits.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a high-efficiency thermal insulation composite aerogel for preserving chilled fresh meat, characterized in that: The high-efficiency thermal insulation composite aerogel uses carboxylated cellulose nanofibers (CCNFs) and polyvinyl alcohol (PVA) as the matrix, ultrathin montmorillonite nanosheets as the thermal insulation filler, citric acid as the chemical crosslinking agent, and introduces cyclooctane-pickerlin emulsion stabilized by hydrophobic silica nanoparticles as a microporous template to construct a composite nano system, thus obtaining the high-efficiency thermal insulation composite aerogel.

2. The preparation method of the high-efficiency thermal insulation composite aerogel for preserving chilled meat according to claim 1, characterized in that, Includes the following steps: Step 1: Dissolve polyvinyl alcohol and carboxylated nanocellulose in deionized water separately and stir until completely dissolved to obtain polyvinyl alcohol solution and carboxylated nanocellulose solution. Homogenize the carboxylated nanocellulose solution under high shear and then subject the homogenized carboxylated nanocellulose solution to ultrasonic disruption. Step 2: The homogeneous dispersed carboxylated nanocellulose solution, polyvinyl alcohol solution, ultrathin montmorillonite nanosheets, citric acid and hydrophobic silica nanoparticle-stabilized cyclooctane-pickerlin emulsion were stirred and mixed overnight. The stirred mixture was then allowed to stand at 4°C for 12-15 h to obtain the composite nanohydrogel. Step 3: Pour the composite nano-hydrogel into a mold, directionally freeze the composite nano-hydrogel with liquid nitrogen, freeze-dry at -80℃ for 1 to 2 days, and then dry at 50 to 60℃ for 6 hours to obtain a high-efficiency thermal insulation composite aerogel.

3. The preparation method of the high-efficiency thermal insulation composite aerogel for preserving chilled meat according to claim 2, characterized in that: In step 1, the concentration of the polyvinyl alcohol solution is 1%, and the concentration of the carboxylated nanocellulose solution is 1%; the stirring temperature is 60~70℃; the high-shear homogenization time is 10~15 min, and the rotation speed is 1000~1500 rpm; the ultrasonic crushing time is 25~35 min, the power is 350 W, and the frequency is 40 kHz.

4. The preparation method of the high-efficiency thermal insulation composite aerogel for preserving chilled meat according to claim 1, characterized in that: In step 2, the volume ratio of the carboxylated nanocellulose solution to the polyvinyl alcohol solution is 0:10 to 8:2; In the composite nanohydrogel, the amount of ultrathin montmorillonite nanosheets added is 0.3~1.5g / 100mL; In the composite nanohydrogel, the amount of citric acid added is 0.5~2.5g / 100mL; In the composite nanohydrogel, the volume fraction of cyclooctane-pickerlin emulsion is 2-12%.

5. The preparation method of the high-efficiency thermal insulation composite aerogel for preserving chilled meat according to claim 4, characterized in that, The preparation method of ultrathin montmorillonite nanosheets is as follows: ① Weigh out montmorillonite and sodium carbonate and disperse them in deionized water. Stir the mixture at 60-80 °C for 12 h. After the reaction is complete, the mixture is dispersed and centrifuged repeatedly 2-4 times. Discard the supernatant and wash the precipitate with deionized water to remove residual salt. Vacuum dry the washed product for 6 h to obtain sodium-based montmorillonite raw material for subsequent stripping. ② Disperse sodium-based montmorillonite raw material in deionized water and stir at 40-60 ℃ for 6 h to form a uniform suspension. Place the suspension in an environment of -50 ℃ for 24 h and then thaw the frozen sample naturally at room temperature. The thawed suspension was ultrasonically treated at 330 W for 15 min, and then the light yellow supernatant was collected by high-speed centrifugation. ③ The collected supernatant was freeze-dried to obtain fluffy powdery ultrathin montmorillonite nanosheets.

6. The preparation method of the high-efficiency thermal insulation composite aerogel for preserving chilled meat according to claim 5, characterized in that: In step ①, the mass ratio of montmorillonite to sodium carbonate is 5–10:1; the ratio of the total mass of montmorillonite and sodium carbonate to deionized water is 0.4–1 g: 20 mL.

7. The preparation method of the high-efficiency thermal insulation composite aerogel for preserving chilled meat according to claim 4, characterized in that, The preparation method of cyclooctane-pickerlin emulsion is as follows: 1) Weigh maltodextrin and dissolve it in deionized water, and stir at 20-40 °C for 2 h; then weigh hydrophobic silica nanoparticles and disperse them in the maltodextrin solution, and use high shear homogenization and ultrasonic crushing alternately to obtain an aqueous phase in which hydrophobic silica nanoparticles are uniformly dispersed. 2) Weigh out hydrophobic silica nanoparticles and dissolve them in cyclooctane oil phase; 3) The aqueous and oil phases were uniformly mixed using a high-shear homogenizer to obtain a hydrophobic silica nanoparticle-stabilized cyclooctane Pickering emulsion.

8. The preparation method of the high-efficiency thermal insulation composite aerogel for preserving chilled meat according to claim 7, characterized in that: In step 1), the concentration of maltodextrin is 15-20%; in step 3), the volume ratio of oil phase to water phase is 0.1-0.3:1; the amount of hydrophobic silica nanoparticles added is 0.5%-1.5% of the solid content of cyclooctane-pickerlin emulsion.

9. A high-efficiency thermal insulation composite aerogel for preserving chilled fresh meat, characterized in that: It is prepared by the preparation method according to any one of claims 1-8.

10. The application of the high-efficiency thermal insulation composite aerogel for preserving chilled meat as described in claim 9 in the preparation of high-efficiency thermal insulation composite aerogel materials.

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