Preparation method and application of biomass-based low-temperature freeze-thaw resistant material

Abstract

The invention discloses a preparation method and application of a biomass-based low-temperature freeze-thaw resistant material, and belongs to the technical field of green packaging materials.The preparation method comprises the steps that a deep eutectic solvent (DES) is added into sodium alginate (SA) film forming liquid, and blended film forming liquid is obtained; and drying, crosslinking with an ethanol-calcium chloride crosslinking agent, spraying a beewax emulsion on the outer side layer after crosslinking, and volatilizing ethanol to obtain the biomass-based low-temperature freeze-thaw resistant material (SA-DES-WAX). The SA-DES-WAX prepared by the invention can reduce the entering of water molecules in the freezing and thawing cycle process, and meanwhile, an internal strong hydrogen bond system can inhibit the phase change crystallization of the water molecules, so that a biomass-based material capable of keeping the structural stability under the fluctuation of freezing and thawing temperature is obtained.

Description

Technical Field

[0001] This invention belongs to the field of green packaging materials technology, and in particular relates to a method for preparing and applying a biomass-based low-temperature freeze-thaw resistant material. Background Technology

[0002] The development and application of green packaging materials is a crucial part of the current global wave of sustainable development. With increasing environmental awareness and the growing prominence of plastic pollution, the environmental pressure from traditional packaging materials has spurred the rise of green packaging. Historically, green packaging has evolved from early simple paper products and glass recycling to the research and commercialization of biodegradable materials. However, the drawbacks of biomass materials are also becoming apparent, especially for products used in freeze-thaw environments. Due to their hygroscopic nature, biomass materials struggle to maintain structural integrity under freeze-thaw conditions. Improving the freeze-thaw resistance of biomass materials to achieve large-scale commercial application remains a significant challenge.

[0003] In existing research, the structural adjustment and modification of traditional biomass materials is often overlooked, but this is a potential strategy for further expanding the applications of biomass materials. The key lies in how to improve the water storage capacity of biomass materials and inhibit the crystallization phase transition of water to protect their structural integrity. Some researchers have blended photothermal conversion materials such as carbon nanotubes (CNTs) into traditional biomass gelatin to self-heat and clean internal water molecules, alleviating the problem of crystallization phase transition caused by water molecules entering during freeze-thaw cycles. However, the preparation process is complex, and it utilizes a combination of biomass and other inorganic materials, which does not fully align with the concept of green environmental protection. Another approach is to dope antifreeze proteins, creating a thermal hysteresis effect between the phase transition and melting of internal water molecules, giving the material sufficient buffer time to resist the phase transition; however, this method is expensive and its performance is not stable enough. To ensure a certain water storage capacity within biomass materials while reducing excessive water molecule intrusion, new structures must be developed. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a method for preparing and applying a biomass-based low-temperature freeze-thaw resistant material.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing a biomass-based low-temperature freeze-thaw resistant material, comprising the following steps: The hydrogen bond acceptor and hydrogen bond donor were mixed, ground, dried, and water was added to obtain a eutectic solvent (DES). Sodium alginate (SA) is mixed with water and stirred until homogeneous to obtain sodium alginate film-forming solution; The sodium alginate film-forming solution was mixed with the eutectic solvent, stirred, vacuumed, dried, and then dried to obtain a sodium alginate-eutectic solvent (SA-DES) antifreeze film. The sodium alginate-eutectic solvent antifreeze film is immersed in a crosslinking agent to obtain a crosslinked sodium alginate-eutectic solvent antifreeze film. Beeswax (WAX) is coated onto the surface of the cross-linked sodium alginate-eutectic solvent antifreeze film, and after drying, the biomass-based low-temperature antifreeze-thaw material (SA-DES-WAX) is obtained.

[0006] This invention adds a eutectic solvent (DES) to a sodium alginate (SA) film-forming solution to obtain a blended film-forming liquid. After drying, a beeswax emulsion is sprayed onto the outer layer, and after the ethanol evaporates, a biomass-based low-temperature freeze-thaw resistant material (SA-DES-WAX) is obtained. The SA-DES-WAX prepared by this invention can reduce the intrusion of water molecules during freeze-thaw cycles, while the strong hydrogen bonding system inside can inhibit the phase transition crystallization of water molecules, thus obtaining a biomass-based material that can maintain structural stability under freeze-thaw temperature fluctuations.

[0007] The biomass-based freeze-thaw resistant material of this invention has a dual structure consisting of internal water retention and external water repellency. Internally, the SA (superoxide dismutase) layer carries DES (hydrophobic esters), which contains numerous hydrophilic groups (-OH, -COOH). The strong hydrogen bonding system within the DES layer allows it to combine with externally introduced water molecules to form bound water. Simultaneously, the hydrogen bond network between the DES components inhibits the directional alignment of water molecules during freezing, thus enabling it to retain water molecules absorbed by the environment during freeze-thaw cycles. Meanwhile, the external beeswax hydrophobic coating effectively prevents the absorption of airborne water molecules after liquefaction. This internal water retention and external water repellency structure effectively prevents structural damage caused by the crystallization phase transition of water.

[0008] Further, the hydrogen bond acceptor is L-proline; the hydrogen bond donor is selected from D-trehalose (Tre), sucrose (Suc), D-glucose (Glu), or D-fructose (Fru); preferably, the hydrogen bond donor is D-trehalose. For example, when the hydrogen bond acceptor is L-proline and the hydrogen bond donor is D-trehalose (Tre), the prepared sodium alginate-eutectic solvent antifreeze film is designated as SA-Pro-Tre antifreeze film.

[0009] SA-Pro-Tre's components contain trehalose molecules within their DES molecules. Trehalose molecules themselves have a highly symmetrical structure; in their lowest energy conformation, all hydrophilic hydroxyl groups on the two glucose rings face outwards. This allows it to exist in an "inert" and stable manner, with a very low chemical potential and a lack of the "driving force" to actively and violently interact with water molecules. Therefore, it maintains a very low moisture absorption rate even in environments with humidity up to 99% RH. Crucially, when trehalose absorbs a small amount of water, it does not first turn into a viscous syrup (supersaturated liquid) like sucrose, glucose, or fructose, but rather tends to directly form an amorphous, solid, glassy state. In the glassy state formed by trehalose, the water activity is reduced to an extremely low level, and it has no ability to adsorb more water molecules. The addition of a beeswax hydrophobic coating further reduces the opportunity for its internal components to come into contact with water molecules. Therefore, compared to the component without beeswax, it exhibits less stress-strain loss under 30 freeze-thaw cycles.

[0010] Frozen seafood and pre-prepared foods undergo extreme temperature fluctuations (from -25°C to 25°C) and high humidity (RH > 80%) within a short period (e.g., 2-8 hours) during their transfer from cold storage to refrigerated trucks and then to another cold storage facility. This is a long-standing pain point for existing packaging technologies: condensation buildup and repeated frost-freezing lead to packaging damage and a sharp decline in food quality. This invention solves the technical problem of existing bio-based packaging materials being easily damaged and causing rapid deterioration in food quality under these special conditions.

[0011] Furthermore, when the hydrogen bond donor is selected from D-trehalose or sucrose, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 3:1; When the hydrogen bond donor is selected from D-glucose or D-fructose, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:1.

[0012] Furthermore, the concentration of the sodium alginate film-forming solution is 2 wt%.

[0013] Furthermore, the crosslinking agent is prepared by mixing 1 wt% calcium chloride solution with anhydrous ethanol at a volume ratio of 1:1 to obtain the crosslinking agent.

[0014] Furthermore, the ratio of the sodium alginate film-forming solution to the eutectic solvent is 25 mL: 2 g.

[0015] Furthermore, the process of coating beeswax onto the surface of the cross-linked sodium alginate-eutectic solvent antifreeze film is as follows: beeswax and ethanol are mixed, stirred evenly under heating conditions, and cooled to obtain an ethanol-beeswax emulsion; the ultrasonically treated ethanol-beeswax emulsion is sprayed onto the surface of the cross-linked sodium alginate-eutectic solvent antifreeze film and dried.

[0016] The present invention also provides a biomass-based low-temperature freeze-thaw resistant material prepared by the above method.

[0017] The present invention also provides the application of the above-mentioned biomass-based low-temperature freeze-thaw resistant material in the preparation of materials for use in low-temperature fields, wherein the low temperature is below -25°C.

[0018] For example, the biomass-based low-temperature freeze-thaw resistant material of the present invention can be used as a preservation material for quick-frozen seafood and pre-prepared foods.

[0019] Compared with the prior art, the present invention has the following advantages and technical effects: (1) The SA-DES-WAX membrane material prepared by the present invention can form a water-retaining structure inside, which works in conjunction with the external hydrophobic structure to resist the problem of structural damage caused by the absorption of water vapor in the air during the freeze-thaw cycle and crystallization inside the material, and can be used for the preparation of low-temperature packaging materials.

[0020] (2) This invention utilizes the excellent film-forming properties and material compatibility of SA by blending and casting, adding DES into the blend, and then using a spraying method to allow beeswax to form a continuous hydrophobic coating on the outer surface of the film. A novel biomass antifreeze-thaw material is prepared, realizing the expansion of the application of biomass packaging materials in the field of low-temperature packaging materials.

[0021] Performance tests show that the introduction of DES endows SA with low-temperature freeze resistance. In low-temperature environments, the glass transition temperatures (Tg) of all four SA-DES materials are below -60℃, with the SA-DES(Tre) component exhibiting the lowest Tg at -68.7℃. This is because the hydrogen bond network within the trehalose-based DES is more sensitive to temperature, effectively inhibiting the directional alignment of water molecules. In a high-humidity environment (90% RH), SA-DES(Tre) is the least hygroscopic due to the structural stability of trehalose, meaning that water vapor is least likely to penetrate the material during freeze-thaw cycles. After absorbing moisture for 24 hours in an environment with extreme humidity of 99%RH, the water binding state at -30℃ can also be observed. It can be seen that SA-DES(Tre) has the shortest T2 time of 1.339ms, while SA-DES(Fru) has the longest T2 time of 7.663ms. This means that the water molecule activity in SA-DES(Tre) is the lowest in low-temperature environments. Therefore, SA-DES(Tre) is most suitable for use in low-temperature freeze-thaw cycles.

[0022] After adding a surface coating to SA-DES, its hydrophilic surface is modified into a hydrophobic layer. Compared with SA-DES, the water contact angle of SA-DES-WAX is as high as 133.7°, which has completely changed from a hydrophilic contact angle of less than 50° to a hydrophobic contact angle.

[0023] (3) The present invention compares the freeze-thaw resistance of four DES systems, selects the best DES component, enhances the freeze-thaw resistance of SA, and verifies the stability of biomass-based freeze-thaw resistance materials. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 The DSC heat flow curves of four different DES systems prepared in Examples 2, 4, 6 and 8 at a mass fraction of 20% characterize the low-temperature thermodynamic state of DES from high to low concentration.

[0025] Figure 2 DSC heat flow curves of four different DES systems prepared in Examples 1, 3, 5 and 7 at 80% mass fraction.

[0026] Figure 3 The viscosity of four different DES systems prepared in Examples 1, 3, 5 and 7 is shown as a function of temperature. (a) shows the viscosity as a function of temperature, and (b) shows the viscosity activation energy of the four different DES components.

[0027] Figure 4 The viscosity of DES systems with different concentrations (20%, 30%, 40%, 50%, 60%, 70%, 80%, all by mass percentage) and the viscosity of deionized water are shown.

[0028] Figure 5 The images show physical pictures of the crosslinked SA-DES antifreeze films prepared in Examples 1, 3, 5 and 7, where (a) is SA-Pro-Tre, (b) is SA-Pro-Fru, (c) is SA-Pro-Suc and (d) is SA-Pro-Glu.

[0029] Figure 6 The DES heat flow curve of the crosslinked SA film prepared for Comparative Example 1 is shown.

[0030] Figure 7The Tg curves are shown in the heat flow curves of SA-DES materials prepared in Examples 1, 3, 5 and 7, where (a) is the Tg curve of SA-Pro-Tre, (b) is the Tg curve of SA-Pro-Suc, (c) is the Tg curve of SA-Pro-Fru and (d) is the Tg curve of SA-Pro-Glu.

[0031] Figure 8 The curves of moisture absorption for 65 hours in an extreme humidity 90%RH environment for the crosslinked SA-DES antifreeze films prepared in Examples 1, 3, 5 and 7.

[0032] Figure 9 The SA-DES materials prepared in Examples 1, 3, 5, and 7 were subjected to moisture absorption for 24 hours in an extreme humidity environment of 99%RH, and the moisture binding state at -30℃ is shown in (a) for SA-Pro-Tre, (b) for SA-Pro-Suc, (c) for SA-Pro-Fru, and (d) for SA-Pro-Glu.

[0033] Figure 10 The images show the room temperature and low temperature moisture binding states of SA-DES prepared in Example 1, where (a) is a comparison of the room temperature and low temperature moisture binding states, and (b) is a comparison of the hydrogen bond strength at room temperature and low temperature.

[0034] Figure 11 The results are the low-temperature bendability test results of the SA-DES prepared in Example 1.

[0035] Figure 12 The water contact angle test results are for the biomass-based low-temperature antifreeze-thaw material (SA-DES-WAX) prepared in Example 1 and the cross-linked SA-DES antifreeze film (SA-DES) without beeswax coating prepared in Comparative Example 2. Among them, (a) is SA-Pro-Glu, with a water contact angle of 31.1°; (b) is SA-Pro-Fru, with a water contact angle of 34.6°; (c) is SA-Pro-Tre, with a contact angle of 48.7°; (d) is SA-Pro-Suc, with a contact angle of 44.1°; and (e) is SA-DES-WAX, with a contact angle of 133.7°.

[0036] Figure 13 The self-cleaning ability test results of the biomass-based low-temperature freeze-thaw resistant material (SA-DES-WAX) prepared in Example 1 are shown. The self-cleaning samples are methyl red dye and toner. (a) is SA-DES after being stained with toner, (b) is the effect after cleaning with toner, (c) is SA-DES after being stained with methyl red dye, and (d) is the effect after cleaning with methyl red dye.

[0037] Figure 14 The contact angles of the biomass-based low-temperature freeze-thaw resistant material (SA-DES-WAX) prepared in Example 1 with various liquids are shown. The test liquids, from left to right, are cola, plum juice, coffee, orange juice, and water.

[0038] Figure 15 The degree of loss of material mechanical properties after 15 and 30 freeze-thaw cycles before and after the addition of the waterproof coating is shown, where (a) represents stress and (b) represents strain. Detailed Implementation

[0039] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0040] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0041] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0042] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0043] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0044] An embodiment of the present invention provides a method for preparing a biomass-based low-temperature freeze-thaw resistant material, comprising the following steps: The hydrogen bond acceptor and hydrogen bond donor were mixed, ground, dried, and then water was added to obtain a eutectic solvent. Sodium alginate (SA) is mixed with water and stirred until homogeneous to obtain sodium alginate film-forming solution; Sodium alginate film-forming solution was mixed with a eutectic solvent, stirred, vacuumed, dried, and then dried to obtain a sodium alginate-eutectic solvent antifreeze film. Sodium alginate-eutectic solvent antifreeze film is immersed in crosslinking agent to obtain crosslinked sodium alginate-eutectic solvent antifreeze film; Beeswax (WAX) was coated onto the surface of the cross-linked sodium alginate-eutectic solvent antifreeze film, and then dried to obtain a biomass-based low-temperature antifreeze material.

[0045] In a preferred embodiment of the present invention, the hydrogen bond acceptor is L-proline; the hydrogen bond donor is selected from D-trehalose (Tre), sucrose (Suc), D-glucose (Glu) or D-fructose (Fru); preferably, the hydrogen bond donor is D-trehalose.

[0046] In a preferred embodiment of the present invention, when the hydrogen bond donor is selected from D-trehalose or sucrose, the molar ratio of hydrogen bond acceptor to hydrogen bond donor is 3:1; When the hydrogen bond donor is selected from D-glucose or D-fructose, the molar ratio of hydrogen bond acceptor to hydrogen bond donor is 1:1.

[0047] In a preferred embodiment of the present invention, the grinding time is 20 minutes; after grinding, it is dried at 60°C for 2 hours.

[0048] In a preferred embodiment of the present invention, after mixing, grinding and drying the hydrogen bond acceptor and the hydrogen bond donor, water is added to make the concentration of the eutectic solvent 20-80 wt%, preferably 50-80 wt%, and more preferably 80 wt%.

[0049] In a preferred embodiment of the present invention, the concentration of sodium alginate film-forming solution is 2 wt%.

[0050] For example, the preparation method of sodium alginate film-forming solution is as follows: take 1g of sodium alginate and put it into a beaker, add 50mL of distilled water, and mix until uniform under the conditions of 90℃ and 1500r / min to obtain sodium alginate film-forming solution.

[0051] In a preferred embodiment of the present invention, the crosslinking agent is prepared by mixing 1 wt% calcium chloride solution with anhydrous ethanol at a volume ratio of 1:1 to obtain the crosslinking agent.

[0052] In a preferred embodiment of the present invention, the sodium alginate-eutectic solvent antifreeze film is immersed in the crosslinking agent for 20 minutes.

[0053] In a preferred embodiment of the present invention, the ratio of sodium alginate film-forming solution to eutectic solvent is 25 mL: 2 g.

[0054] In a preferred embodiment of the present invention, the process of coating beeswax onto the surface of the cross-linked sodium alginate-eutectic solvent antifreeze film is as follows: beeswax and ethanol are mixed, stirred evenly under heating conditions, and cooled to obtain an ethanol-beeswax emulsion; the ultrasonically treated ethanol-beeswax emulsion is sprayed onto the surface of the cross-linked sodium alginate-eutectic solvent antifreeze film and dried (preferably dried in an oven at 75°C for 2 minutes).

[0055] In a preferred embodiment of the present invention, the ultrasonic time of the ethanol-beeswax emulsion is 2 hours, in order to ensure uniform dispersion.

[0056] In a preferred embodiment of the present invention, the process of spraying the ultrasonicated ethanol-beeswax emulsion onto the surface of the cross-linked sodium alginate-eutectic solvent antifreeze film is as follows: the ethanol-beeswax emulsion is loaded into a spray gun, the spray gun pressure is set to 20 psi, the distance from the film is 20 cm, and after spraying for 50 seconds, it is allowed to stand to allow the ethanol to evaporate completely.

[0057] An embodiment of the present invention also provides a biomass-based low-temperature freeze-thaw resistant material prepared by the above method.

[0058] Embodiments of the present invention also provide the application of the above-mentioned biomass-based low-temperature freeze-thaw resistant material in the preparation of materials for use in low-temperature fields, wherein the low temperature is below -25°C.

[0059] In a preferred embodiment of the present invention, the biomass-based low-temperature freeze-thaw resistant material of the present invention can be used to prepare preservation materials for quick-frozen seafood and pre-prepared foods.

[0060] Unless otherwise specified, the room temperature in this invention is 25±2℃.

[0061] All raw materials used in the embodiments of the present invention were obtained through commercial purchase.

[0062] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0063] The technical solution of the present invention will be further illustrated by the following embodiments.

[0064] Example 1 This embodiment provides a method for preparing a biomass-based low-temperature freeze-thaw resistant material, the steps of which are as follows: (1) Preparation of eutectic solvent (DES): L-proline, a hydrogen bond acceptor, and D-trehalose, a hydrogen bond donor, were mixed in a molar ratio of 3:1. The resulting mixture was placed in a mortar and ground for 20 min. After grinding, it was dried at 60 °C for 2 h. 20% (w / w) of distilled water (i.e., the dried solid accounted for 80% of the total mass of the dried solid and distilled water) was added to the dried solid to prepare an 80% (w / w) concentration eutectic solvent (DES), denoted as Pro-Tre. (2) Preparation of sodium alginate (SA) film-forming solution: Weigh 1g of sodium alginate and put it into a beaker, add 50mL of distilled water, and mix until uniform at 90℃ and 1500r / min to obtain SA film-forming solution; (3) Add 4g of 80% (w / w) DES to the SA film-forming solution in step (2), stir for 30min, remove air bubbles under vacuum, pour into a mold, and dry at 60℃ for 12h. After complete drying, SA-DES antifreeze film is obtained. (4) Mix 1 wt% calcium chloride solution with anhydrous ethanol at a volume ratio of 1:1 to prepare a crosslinking agent. Soak the SA-DES antifreeze film in the crosslinking agent for 20 min to obtain the crosslinked SA-DES antifreeze film, denoted as SA-Pro-Tre. (5) Preparation of biomass-based low-temperature freeze-thaw resistance material (SA-DES-WAX): Weigh 2g of beeswax (WAX) into a beaker, add 200mL of food-grade ethanol, mix at 80℃ and 550r / min for 2h, and cool to room temperature to obtain ethanol-beeswax emulsion; sonicate the ethanol-beeswax emulsion in an ultrasonic machine for 2h to disperse it evenly; then take 10mL of the evenly dispersed ethanol-beeswax emulsion into a spray gun, set the spray gun pressure to 20psi, and spray it evenly onto the surface of the cross-linked SA-DES antifreeze film at a distance of 20cm. After spraying and standing for 50s, wait for the ethanol to evaporate completely, put it in an oven at 75℃ for 2min and take it out to obtain biomass-based low-temperature freeze-thaw resistance material (SA-DES-WAX).

[0065] Example 2 This embodiment provides a method for preparing a biomass-based low-temperature freeze-thaw resistant material. The preparation method is the same as in Embodiment 1, except that in step (1), 80% (w / w) of distilled water (i.e., the dried solid accounts for 20% of the total mass of the dried solid and distilled water) is added to the dried solid to prepare a 20% (w / w) concentration eutectic solvent.

[0066] Example 3 This embodiment provides a method for preparing a biomass-based low-temperature freeze-thaw resistant material. The preparation method is the same as in Example 1, except that in step (1), the hydrogen bond donor is replaced with sucrose to ensure that the molar ratio of hydrogen bond acceptor L-proline to hydrogen bond donor sucrose is 3:1. The resulting eutectic solvent is denoted as Pro-Suc. The cross-linked SA-DES antifreeze film obtained in step (4) is denoted as SA-Pro-Suc.

[0067] Example 4 This embodiment provides a method for preparing a biomass-based low-temperature freeze-thaw resistant material. The preparation method is the same as in embodiment 3, except that in step (1), 80% (w / w) of distilled water is added to the dried solid to prepare a 20% (w / w) concentration eutectic solvent.

[0068] Example 5 This embodiment provides a method for preparing a biomass-based low-temperature freeze-thaw resistant material. The preparation method is the same as in Example 1, except that in step (1), the hydrogen bond donor is replaced with D-glucose to ensure that the molar ratio of hydrogen bond acceptor L-proline to hydrogen bond donor D-glucose is 1:1. The resulting eutectic solvent is denoted as Pro-Glu. The cross-linked SA-DES antifreeze film obtained in step (4) is denoted as SA-Pro-Glu.

[0069] Example 6 This embodiment provides a method for preparing a biomass-based low-temperature freeze-thaw resistant material. The preparation method is the same as in embodiment 5, except that in step (1), 80% (w / w) of distilled water is added to the dried solid to prepare a 20% (w / w) concentration eutectic solvent.

[0070] Example 7 This embodiment provides a method for preparing a biomass-based low-temperature freeze-thaw resistant material. The preparation method is the same as in Example 1, except that in step (1), the hydrogen bond donor is replaced with D-fructose to ensure that the molar ratio of hydrogen bond acceptor L-proline to hydrogen bond donor D-fructose is 1:1. The resulting eutectic solvent is denoted as Pro-Fru; the cross-linked SA-DES antifreeze film obtained in step (4) is denoted as SA-Pro-Fru.

[0071] Example 8 This embodiment provides a method for preparing a biomass-based low-temperature freeze-thaw resistant material. The preparation method is the same as in embodiment 7, except that in step (1), 80% (w / w) of distilled water is added to the dried solid to prepare a 20% (w / w) concentration eutectic solvent.

[0072] Comparative Example 1: Preparation of sodium alginate membrane (SA membrane) Weigh 1g of sodium alginate and place it in a beaker. Add 50mL of distilled water and mix until homogeneous at 90℃ and 1500r / min to obtain an SA film-forming solution. Stir for 30min, remove air bubbles under vacuum, pour into a mold, and dry at 60℃ for 12h. After complete drying, obtain an SA film. Mix 1wt% calcium chloride solution with anhydrous ethanol at a volume ratio of 1:1 to prepare a crosslinking agent. Immerse the SA film in the crosslinking agent for 20min to obtain a crosslinked SA film.

[0073] Comparative Example 2 Same as Example 1, except that step (5) is not performed, that is, this comparative example is a cross-linked SA-DES antifreeze film without beeswax coating.

[0074] Example 1 I. Performance Testing Methods (1) The thermodynamic properties of DES were measured using a differential scanning calorimeter (TA25, USA). 6 mg of DES was packaged in a standard aluminum crucible, and the temperature was measured at 10 °C for 1 min under nitrogen protection. -1 The change in heat flow of DES between 25 and -80℃ under cooling rate.

[0075] (2) The thermodynamic properties of SA (sodium alginate membrane) and SA-DES (referring to cross-linked SA-DES antifreeze membrane) were measured using a differential scanning calorimeter (TA25, USA). 8 mg of SA or SA-DES was placed in a standard aluminum crucible, and nitrogen was used as the protective gas. The temperature was increased to 10 °C and the temperature was increased to 10 °C. -1 The sample temperature was lowered from 20°C to -80°C by a heating rate, and then raised back to 20°C. The thermodynamic behavior, including crystallization, melting, and glass transition, was analyzed.

[0076] (3) The moisture binding state of the material was measured using a nuclear magnetic resonance imaging analyzer (MacroMR12-60). The instrument main frequency was set to 12MHz, the probe coil diameter was 40mm, and the sample temperature was -30℃.

[0077] (4) The viscosity of DES was measured using a rapid viscosity analyzer (RVA-TecMaster, Australia). The apparent viscosity (η) of DES was measured in the range of 30-80℃, with a sampling temperature interval of 5.0℃. After the instrument was automatically zeroed under no-load conditions, the DES was transferred to an aluminum drum and immersed up to the rotor markings. After the reading stabilized, the viscosity measurement was completed and the corresponding value was recorded.

[0078] (5) The hydrophilicity and hydrophobicity of the sample are characterized by a contact angle tester to analyze the variation law of the hydrophilicity and hydrophobicity of the material surface. Before the test, the sample is fixed flat on the sample stage to ensure that the surface is free of contamination and obvious defects.

[0079] (6) Water absorption test: The water absorption rate of the sample was tested using the gravimetric method. The sample was cut into pieces with a size of 2×2 cm. 2 The square was placed in a vacuum drying oven at 50°C and dried to constant weight. The initial mass was recorded. Subsequently, the sample was placed in a humidity chamber with extreme humidity of 90%RH or 99%RH and a room temperature of 25±2℃ and allowed to stand. After the set time of 8 hours, the sample was removed and its wet weight was immediately measured. Three parallel samples were tested in each group, and the average value was taken. Water absorption rate ( ) is calculated using the following formula: By comparing the water absorption rates of different samples, the hydrophilicity and water adsorption capacity of the materials were analyzed.

[0080] DES contains abundant hydrophilic groups that can bind with water molecules to form bound water, while its extensive hydrogen bond network also inhibits the directional crystallization of free water. High concentrations of DES can completely suppress water crystallization, allowing the sample to remain in a glassy state. Figure 2 As shown in the DSC heat flux curve at 80% (w / w), at high concentrations, the DES sample is in a state of "water-soluble in DES". However, at low concentrations, it can also be understood that excessive water absorption causes the DES's water storage capacity to reach its limit, such as... Figure 1 The DSC heat flow curves for 20% (w / w) DES samples show that the low-concentration DES sample is in a state of "DES dissolved in water". The presence of crystallization peaks in all four DES types indicates that water molecules in the DES system are oriented and crystallizing. When DES is blended with SA, DES exists within the SA gel network, providing stronger water binding capacity. However, due to the limited water storage capacity of DES, when the water content exceeds the upper limit of DES storage, the material will still freeze internally under low-temperature conditions, leading to structural damage. Therefore, screening for the DES component with the strongest water storage capacity and adding an external hydrophobic coating are two strategies that are of great significance for improving the freeze-thaw resistance of the material. Specific results are as follows: II. Characterization Results of DES and SA-DES (1) The viscosity of the four DES types was characterized, and the results are shown in the figure. Figure 3 and Figure 4 .

[0081] from Figure 3 As shown in (a), the viscosity of all four DES components decreases with increasing temperature. This is because higher temperatures provide the system with more energy to break hydrogen bonds and overcome intermolecular cohesion, thus DES exhibits better molecular fluidity at higher temperatures. Meanwhile, from... Figure 3As can be seen in (b), Figure 3 Substituting the average value of the data measured in the three parallel experiments in (a) into ,in The apparent viscosity (cP) is... It is a constant. Let R be the activation energy for viscous flow (kJ / mol), and R represent the molar gas constant (≈ 8.314 J / mol). -1 ·K -1 T represents the absolute temperature (K), and the viscous flow activation energy of each component of the DES is calculated using the formula. Pro-Glu): 56.02 kJ / mol; (Pro-Suc): 63.57kJ / mol; (Pro-Fru): 44.46 kJ / mol; (Pro-Tre): 64.73 kJ / mol; It can be seen that the Pro-Tre component has the highest viscous flow activation energy, indicating that the hydrogen bonds of the system are most sensitive to temperature. Therefore, under low temperature conditions, the hydrogen bonds of this component respond most strongly to temperature changes and can better suppress the crystallization of water molecules.

[0082] Different concentrations of DES were prepared according to the methods in Examples 1, 3, 5, and 7, and their viscosities were tested. Figure 4 As can be seen, as the concentration of DES decreases, the viscosity of each component decreases as the concentration increases, eventually becoming similar to the viscosity of water. At this point, the system is in a state of "DES dissolves in water", and the system can no longer store water.

[0083] Figure 5 The images show the cross-linked SA-DES antifreeze films prepared in Examples 1, 3, 5, and 7. (a) is SA-Pro-Tre, (b) is SA-Pro-Fru, (c) is SA-Pro-Suc, and (d) is SA-Pro-Glu. It can be seen that SA-DES is a transparent gel film, and the addition of DES will not affect the transparency of SA.

[0084] (2) The DSC heat flow curve of the crosslinked SA film prepared in Comparative Example 1 was measured to simulate the low-temperature thermodynamic properties of the material under low-temperature freeze-thaw conditions. The results are shown in the figure. Figure 6 The thermodynamic properties of the crosslinked SA film were characterized.

[0085] from Figure 6As can be seen, when the cross-linked SA membrane was not mixed with DES, crystallization peaks and melting peaks appeared on the DSC heat flow curve, indicating that the cross-linked SA membrane did not have water storage capacity at low temperatures.

[0086] Figure 7 The Tg curves are shown in the heat flow curves of the SA-DES materials prepared in Examples 1, 3, 5, and 7. From... Figure 7 As can be seen, all four SA-DES materials exhibited glass transition at low temperatures without crystallization. Specifically, the Tg of SA-Pro-Tre was -68.7℃, SA-Pro-Suc was -66.7℃, SA-Pro-Fru was -64.31℃, and SA-Pro-Glu was -66.3℃.

[0087] (3) The moisture absorption capacity of SA-DES in Examples 1, 3, 5 and 7 was measured. The better the moisture absorption effect, the easier it is to absorb water molecules during the freeze-thaw cycle.

[0088] from Figure 8 As can be seen, SA-Pro-Tre exhibits the smallest mass change rate after 65 hours of moisture absorption. This is because trehalose is a stable, non-reducing disaccharide formed by two glucose molecules, and the tight bond between trehalose molecules reduces the permeation and adsorption of water molecules. Therefore, materials containing trehalose molecules have the worst hygroscopicity.

[0089] (4) The changes in the low-temperature and room-temperature moisture binding state and hydrogen bond strength of SA-DES in Examples 1, 3, 5, and 7 were measured, and the results are shown in the figure. Figure 9 and Figure 10 .from Figure 9 As can be seen from the low-temperature moisture binding states of each component, SA-Pro-Tre has the shortest T2 time, at 1.339 ms. This indicates a greater restriction on moisture movement within the system and also demonstrates that the Pro-Tre component exhibits the best antifreeze performance at low temperatures. Figure 10 As can be seen, there is a significant change in peak intensity of the material's water-binding state from room temperature to low temperature, representing an increase in hydrogen bond strength. This further proves that the material can maintain its structural stability in a freeze-thaw cycle environment.

[0090] (5) Determine the bending properties of SA-DES in Example 1 under low temperature conditions.

[0091] from Figure 11 As can be seen, the material can still maintain good bending properties in an environment of -25℃.

[0092] Example 2 SA-DES-WAX's hydrophobic self-cleaning properties: (1) Although SA-DES can store water to a certain extent and keep it from freezing at low temperatures, Example 1 also verified that DES cannot withstand the water content when it exceeds a certain limit. In order to further enhance the freeze-thaw resistance of the material, a hydrophobic coating was added to reduce the entry of water molecules, and the hydrophobic effect was verified. The results are shown in Figure 12 As can be seen, compared with the cross-linked SA-DES antifreeze film without beeswax coating in Comparative Example 2, the water contact angle of SA-DES-WAX in Example 1 changed from a hydrophilic contact angle to a hydrophobic contact angle. This indicates that the surface hydrophobic modification of the material was successful and can reduce the entry of water molecules.

[0093] (2) The self-cleaning ability of the material was tested using methyl red hydrophilic dye and toner, and its hydrophobic effect was verified using different liquids. The results are shown in […]. Figure 13 and Figure 14 As can be seen, the methyl red dye on the material surface dissolves in water upon contact and flows into the glass dish with the water flow, while the carbon powder is also washed into the glass dish by the water flow. Furthermore, drops of cola, plum juice, coffee, and orange juice onto the material surface also exhibit the same water-repellent effect. Therefore, the addition of a hydrophobic coating creates a good water-repellent effect on the material surface. Even at low temperatures, water molecules are less likely to freeze on the material surface, and after freeze-thaw cycles, they are less likely to penetrate the material's interior. This verifies the superior freeze-thaw resistance of SA-DES-WAX (materials that easily become wet offer opportunities for water to penetrate; a good hydrophobic coating reduces these opportunities). Figure 13 The results demonstrate the stability of the material of this invention in freeze-thaw cycles.

[0094] Example 3 The mechanical properties of SA-DES after undergoing freeze-thaw cycles were tested using the following specific test method: The mechanical strength of the eutectic gel was determined using a universal testing machine, with three parallel tests performed on each sample. The gel film was fixed at both ends to the upper and lower clamps of the testing machine. The sample was cut into a dumbbell shape according to GB / T528-2009 Type 4 standard. A tensile test was performed, with the upper clamp raised at a speed of 30 mm / min until the material fractured. Based on the effective dimensions of the material, the stress-strain curve of the gel film was plotted. The formulas for calculating stress and strain are as follows: ; ; Where F is the force (N) measured in real time by the tension sensor, and A0 is the effective cross-sectional area of ​​the eutectic gel before stretching (m²). 2L0 and L represent the initial and maximum tensile lengths (mm) of the eutectic gel, respectively.

[0095] See results Figure 15 It can be seen that before the beeswax coating was applied, after 15 freeze-thaw cycles, the stress retained 84.91% and the strain retained 88.83%. After 30 freeze-thaw cycles, the stress retained only 71.8% and the strain only 75.38%. However, after adding a beeswax coating to the material surface, after 15 freeze-thaw cycles, the stress retained 94.40% and the strain retained 92.66%. After 30 freeze-thaw cycles, the stress retained 91.03% and the strain retained 88.58%. This is because the excellent water-repellent effect of the beeswax coating reduces the decrease in mechanical properties caused by phase transformation and crystallization after excessive moisture intrusion in the extreme environment of freeze-thaw cycles.

[0096] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a biomass-based low-temperature freeze-thaw resistant material, characterized in that, Includes the following steps: The hydrogen bond acceptor and hydrogen bond donor were mixed, ground, dried, and then water was added to obtain a eutectic solvent. Sodium alginate was mixed with water and stirred until homogeneous to obtain a sodium alginate film-forming solution. The sodium alginate film-forming solution was mixed with the eutectic solvent, stirred, vacuumed, dried, and then dried to obtain a sodium alginate-eutectic solvent antifreeze film. The sodium alginate-eutectic solvent antifreeze film is immersed in a crosslinking agent to obtain a crosslinked sodium alginate-eutectic solvent antifreeze film. Beeswax is coated on the surface of the cross-linked sodium alginate-eutectic solvent antifreeze film, and the biomass-based low-temperature antifreeze material is obtained after drying.

2. The method for preparing biomass-based low-temperature freeze-thaw resistant material according to claim 1, characterized in that, The hydrogen bond acceptor is L-proline; the hydrogen bond donor is selected from D-trehalose, sucrose, D-glucose or D-fructose.

3. The method for preparing biomass-based low-temperature freeze-thaw resistant materials according to claim 2, characterized in that, The hydrogen bond donor is D-trehalose.

4. The method for preparing biomass-based low-temperature freeze-thaw resistant materials according to claim 2, characterized in that, When the hydrogen bond donor is selected from D-trehalose or sucrose, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 3:1; When the hydrogen bond donor is selected from D-glucose or D-fructose, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:

1.

5. The method for preparing biomass-based low-temperature freeze-thaw resistant material according to claim 1, characterized in that, The concentration of the sodium alginate film-forming solution is 2 wt%.

6. The method for preparing biomass-based low-temperature freeze-thaw resistant material according to claim 1, characterized in that, The crosslinking agent is prepared by mixing 1 wt% calcium chloride solution with anhydrous ethanol at a volume ratio of 1:1 to obtain the crosslinking agent.

7. The method for preparing biomass-based low-temperature freeze-thaw resistant material according to claim 1, characterized in that, The ratio of sodium alginate film-forming solution to eutectic solvent is 25 mL: 2 g.

8. The method for preparing biomass-based low-temperature freeze-thaw resistant material according to claim 1, characterized in that, The process of coating beeswax onto the surface of the cross-linked sodium alginate-eutectic solvent antifreeze film is as follows: beeswax and ethanol are mixed, stirred evenly under heating conditions, and cooled to obtain an ethanol-beeswax emulsion; the ultrasonically treated ethanol-beeswax emulsion is sprayed onto the surface of the cross-linked sodium alginate-eutectic solvent antifreeze film and dried.

9. A biomass-based low-temperature freeze-thaw resistant material, characterized in that, It is prepared according to any one of claims 1-8.

10. The application of the biomass-based cryogenic antifreeze material as described in claim 9 in the preparation of materials for cryogenic applications, characterized in that, The low temperature is below -25°C.

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