A cold storage agent for ice packs and a method for preparing the same

Abstract

The present application relates to the technical field of phase change materials, and particularly relates to a cold storage agent for ice bags and a preparation method thereof. The cold storage agent comprises deionized water, propylene glycol and modified sodium carboxymethyl cellulose. The core is that the sodium carboxymethyl cellulose is chemically modified: first, an aldehyde group is introduced by oxidation, then 6-amino-6-deoxy-beta-cyclodextrin pre-coated with 1-adamantane amine and dodecylamine are grafted onto the polymer chain to construct a hierarchical network with stable host-guest nodes and dynamic hydrophobic association. The structure significantly improves the freeze-thaw stability of the cold storage agent, the viscosity retention rate can reach more than 85% after 20 cycles, the water separation rate is less than 3.2%, and the cold storage agent has good shear thinning characteristics and excellent cold storage uniformity, effectively overcoming the problems of easy water separation, viscosity attenuation and uneven cold storage of conventional products.

Description

Technical Field

[0001] This invention relates to the field of phase change materials technology, and in particular to a cold storage agent for ice packs and its preparation method. Background Technology

[0002] Ice packs, as a convenient cold storage medium, are widely used in cold chain transportation, medical cold compresses, and food preservation. Their core function relies on the internal cold storage agent absorbing or releasing a large amount of latent heat during phase change. To improve user experience and safety, an ideal cold storage agent needs to have a certain viscosity in the liquid phase to prevent rapid liquid leakage should the packaging break, while maintaining a uniform state and not separating water during freezing and thawing to ensure uniform cold transfer and reusability.

[0003] Currently, water-based cold storage agents often use water-soluble polymeric thickeners, such as sodium carboxymethyl cellulose (CMC), to thicken the system, inhibit internal convection, and reduce its fluidity. CMC is widely used due to its good water solubility, thickening properties, and relatively low cost. However, conventional CMC primarily relies on the physical entanglement and hydration of molecular chains to construct its network structure. This structure exhibits significant limitations when facing drastic temperature cycling, especially repeated freeze-thaw cycles. During freezing, ice crystal growth compresses and destroys the polymeric network; during thawing, the damaged network structure may not fully recover, leading to localized aggregation of polymeric chains, resulting in insufficient swelling and the formation of visible colloidal particles or agglomerates. This irreversible damage to the structure directly leads to a decrease in the system's apparent viscosity and a weakened ability to bind water, resulting in severe water separation after freeze-thaw cycles. Water separation not only reduces the effective cold storage capacity but also causes an uneven state of water and ice shavings coexisting inside the ice pack, severely affecting the uniformity of the cold storage temperature.

[0004] Furthermore, the viscosity of conventional sodium carboxymethyl cellulose solutions is highly sensitive to temperature. Within the viscosity range required for room temperature filling, its low-temperature viscosity is often too high, potentially affecting filling efficiency; conversely, if a lower low-temperature viscosity is desired, its room-temperature viscosity may be too low, failing to meet the basic requirements for leak prevention. This characteristic of viscosity fluctuating excessively with temperature makes it difficult to strike a balance between ease of filling at room temperature and stability in effectively suppressing convection at low temperatures. A formulation that is easy to fill at room temperature may, at low temperatures, experience a sudden increase in viscosity, affecting the uniform nucleation and growth of ice crystals, or, when ice packs melt locally first, insufficient viscosity may trigger internal convection, accelerating overall melting and shortening the cold-keeping time.

[0005] Therefore, the core of developing a novel cold storage agent lies in the deep and effective structural modification of sodium carboxymethyl cellulose (CCMC), the basic material. This modification aims to fundamentally solve its bottleneck problems, such as poor structural stability under repeated freeze-thaw conditions, easy water separation, and viscosity-temperature mismatch. This is crucial for obtaining high-performance, reusable, and safe ice pack products. Current technologies lack solutions that can simultaneously achieve excellent freeze-thaw stability, suitable and stable processing viscosity, and effective low-temperature convection suppression within a single thickener system. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a cold storage agent for ice packs and its preparation method, so as to solve the problems of conventional ice pack cold storage agents with sodium carboxymethyl cellulose as thickener. During repeated freeze-thaw cycles and long-term storage, due to the uneven network structure and poor stability of the thickener, the ice packs are prone to problems such as insufficient swelling and clumping, viscosity decay and water separation after freeze-thaw cycles, and excessive viscosity fluctuations with temperature. These problems lead to uneven cold storage and leakage risks, making it difficult to meet the requirements of long-term morphological stability and temperature uniformity for reusable ice packs.

[0007] To achieve the above objectives, the present invention provides a cold storage agent for ice packs, comprising, by weight parts: 874-906 portions of deionized water; 88-120 parts propylene glycol; 3-6 parts of modified sodium carboxymethyl cellulose.

[0008] Preferably, it also includes 1 part sodium benzoate.

[0009] Preferably, it also includes 0.01 parts of brilliant blue FCF.

[0010] Preferably, the propylene glycol comprises 70-100 parts of propylene glycol for preparing the aqueous phase and 18-20 parts of propylene glycol for dispersing the modified sodium carboxymethyl cellulose.

[0011] Furthermore, the preparation steps of the modified sodium carboxymethyl cellulose are as follows: (1) Sodium carboxymethyl cellulose was oxidized with sodium periodate under light-shielding conditions to introduce aldehyde sites, and ethylene glycol was added to terminate the oxidation to obtain a sodium carboxymethyl cellulose reaction solution containing aldehydes. (2) 6-amino-6-deoxy-β-cyclodextrin was pre-encapsulated with 1-adamantaneamine to obtain a pre-encapsulated host-guest mixed solution; (3) The pre-encapsulated host-guest mixture solution was added to the sodium carboxymethyl cellulose reaction solution containing aldehyde group. After mixing for 20 min, 6-amino-6-deoxy-β-cyclodextrin was added and reacted for 120 min. Then, dodecylamine was added and reacted for 60 min. The mixture was then cooled to 3-8℃ and sodium borohydride was added in stages under alkaline conditions for reduction and locking. The precipitate was washed, vacuum dried, and passed through a 40-mesh sieve to obtain modified sodium carboxymethyl cellulose.

[0012] Preferably, based on 10 parts by weight of sodium carboxymethyl cellulose, the amounts of sodium periodate, 6-amino-6-deoxy-β-cyclodextrin, 1-adamantaneamine, dodecylamine, and sodium borohydride are 0.15-0.22 parts by weight, 0.22-0.34 parts by weight, 0.02-0.04 parts by weight, 0.06-0.12 parts by weight, and 0.2 parts by weight, respectively.

[0013] Preferably, the mass ratio of 6-amino-6-deoxy-β-cyclodextrin in step (2) to 6-amino-6-deoxy-β-cyclodextrin in step (3) is 0.08-0.12:0.14-0.22.

[0014] Preferably, in step (3), the sodium borohydride is added in stages: sodium borohydride is added in two stages, wherein the amount added in the first stage is 50wt%-70wt% of the total amount, and the two stages are added 30min apart.

[0015] Furthermore, the present invention also provides a method for preparing a cold storage agent for ice packs, comprising the following steps: dispersing modified sodium carboxymethyl cellulose in propylene glycol to form a modified sodium carboxymethyl cellulose slurry; then mixing deionized water with propylene glycol and adding the modified sodium carboxymethyl cellulose slurry and hydrating it, allowing it to stand to degas, and obtaining a cold storage agent for ice packs.

[0016] The beneficial effects of this invention are: Controlled, mild oxidation of sodium carboxymethyl cellulose with sodium periodate introduces uniformly distributed active aldehyde sites onto its molecular chain. These aldehyde groups serve as anchor points for subsequent reactions, laying the foundation for constructing a homogeneous and stable chemically modified network. This step prevents random aggregation of modification reaction sites from the outset, ensuring a high degree of homogeneity in the final three-dimensional network structure. This homogeneous network can more effectively resist the compression and destruction of ice crystals under repeated freeze-thaw stress, thereby significantly improving the freeze-thaw cycle stability of the colloidal system and effectively suppressing colloidal agglomeration and post-freeze-thaw water separation caused by local structural collapse or polymer chain aggregation.

[0017] Based on the introduced aldehyde sites, this scheme innovatively employs a "pre-inclusion" temporal strategy. First, a portion of 6-amino-6-deoxy-β-cyclodextrin and 1-adamantaneamine are pre-recognized and included in the host solution to form a host-guest complex. This complex is then introduced into aldehyde-modified sodium carboxymethyl cellulose for covalent grafting and fixation. This path of recognition-assembly followed by covalent locking ensures that the strongly interacting 1-adamantaneamine is precisely and uniformly fixed onto the polymer backbone, serving as robust nodes in the network. The uniform distribution of these stable nodes significantly enhances the mechanical strength and structural integrity of the entire network backbone, enabling the colloid to better maintain its network morphology and bind free water during phase transitions. This is crucial for achieving low water separation rate and high viscosity retention.

[0018] Furthermore, this scheme constructs a hierarchical network structure combining strong and weak interactions. While introducing the aforementioned strong host-guest stabilizing nodes, dodecylamine is added stepwise as a weakly interacting hydrophobic guest. The hydrophobic alkyl chains of dodecylamine can form dynamically reversible hydrophobic associations. This interaction is of moderate strength and can undergo reversible deassociation-reassociation under freeze-thaw stress, thereby dissipating energy and providing a dynamic buffering effect. The synergy of strong and weak interactions allows the resulting modified sodium carboxymethyl cellulose network to possess both the skeletal support provided by rigid nodes and the toughness brought by a flexible energy dissipation mechanism. Macroscopically, this manifests as significant shear-thinning behavior at room temperature (facilitating filling and stirring), while its viscosity is significantly less sensitive to temperature changes. It maintains sufficient structural strength at low temperatures to suppress internal convection and recovers after shearing or stress, thus achieving a balance between processing performance and application stability.

[0019] Ultimately, the cold storage agent prepared from this modified sodium carboxymethyl cellulose exhibits significantly improved overall performance. Its robust and resilient three-dimensional network maintains a uniform colloidal state for an extended period, greatly reducing the risk of flow after leakage. When applied to ice packs, this cold storage agent ensures a more uniform temperature field distribution during freezing and thawing, preventing premature local melting or freezing, thereby extending the effective cold-keeping time and improving the reliability and safety of ice pack use. This invention, through precise molecular design and process control, simultaneously overcomes multiple technical challenges, including freeze-thaw stability, viscosity suitability, and cold-keeping uniformity, within a single modified polymer system. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. Example 1

[0021] The sodium carboxymethyl cellulose used in this embodiment is a product of TCI (Shanghai) Chemical Industry Development Co., Ltd. (product code C0603); 6-amino-6-deoxy-β-cyclopaste is a product of TCI (Shanghai) Chemical Industry Development Co., Ltd. (product code A3453); 1-adamantaneamine is a product of TCI (Shanghai) Chemical Industry Development Co., Ltd. (product code A2318); dodecylamine is a product of TCI (Shanghai) Chemical Industry Development Co., Ltd. (product code D0980); and brilliant blue FCF is a product of TCI (Shanghai) Chemical Industry Development Co., Ltd. (product code B0790).

[0022] Step S1: Add 990g of deionized water to the reaction vessel, turn on the mechanical stirrer at 600r / min, sprinkle 10g of sodium carboxymethyl cellulose along the liquid surface, maintain 25℃ and stir for 60min, then add 200mg of sodium periodate in batches (100mg each time, 2min interval) under light-proof conditions, control the reaction temperature at 30℃ and stir at 500r / min for 90min; then add 300mg of ethylene glycol, maintain 30℃ and stir at 400r / min for 30min to obtain sodium carboxymethyl cellulose reaction solution containing aldehyde group; Step S2: Add 20g of deionized water to container A and dissolve 100mg of 6-amino-6-deoxy-β-cyclodextrin to obtain a cyclodextrin amine solution; add 20g of propylene glycol to container B and heat to 40℃ to dissolve 30mg of 1-adamantaneamine to obtain an adamantaneamine propylene glycol solution; add the solution from container B to container A and stir at 300r / min for 30min at 25℃ to obtain a pre-encapsulated host-guest mixture solution; add 20g of propylene glycol to container C and heat to 50℃ to dissolve 80mg of dodecylamine, then cool to 30℃ to obtain a dodecylamine propylene glycol solution; Step S3: The pre-encapsulated host-guest mixture obtained in step S2 was added to the sodium carboxymethyl cellulose reaction solution containing aldehydes obtained in step S1, and stirred at 25°C for 500 rpm for 20 min. Then, 40 g of deionized water was added, and 180 mg of 6-amino-6-deoxy-β-cyclodextrin was dissolved and added, followed by 2 g of acetic acid. Stirring continued at 300 rpm, and the pH of the system was adjusted to 6 using sodium bicarbonate. The reaction was then maintained at 25°C and stirred at 300 rpm for 120 min. Next, the dodecylamine propylene glycol solution obtained in step S2 was added dropwise over 20 min, with stirring at 500 rpm during the dropwise addition. After the dropwise addition was completed, the reaction was maintained at 30°C and stirred at 300 rpm for 60 min. The mixture was then cooled to 5°C and stirred at 300 rpm. Sodium carbonate was added to adjust the pH of the system to 9, and then 200 mg of sodium borohydride was added in two portions (120 mg initially, and 80 mg later, after 30 min of reaction). Add 0 mg of ethanol and continue stirring for 60 min. After the reaction is complete, add acetic acid to adjust the pH of the system to 7 to terminate the reduction reaction. Then add 3300 g of anhydrous ethanol to precipitate the modified sodium carboxymethyl cellulose. After standing for 20 min, filter and collect the precipitate. Wash the precipitate once with 1000 g of anhydrous ethanol. Add the precipitate to 1000 g of deionized water and stir at 600 r / min for 30 min to redissolve. Repeat the process of "adding 3300 g of anhydrous ethanol to precipitate - filtering - washing with 1000 g of anhydrous ethanol" twice. Finally, place the obtained precipitate in a vacuum drying oven at 45℃ and dry for 12 h to constant weight. Crush and pass through a 40 mesh sieve to obtain modified sodium carboxymethyl cellulose powder. Step S4: Take 5g of modified sodium carboxymethyl cellulose powder and add it to 20g of propylene glycol. Disperse at 200r / min for 5min to form a modified sodium carboxymethyl cellulose slurry. Step S5: Add 894g of deionized water and 80g of propylene glycol to a mixing container, stir at 400r / min for 10min, then add 1g of sodium benzoate and continue stirring for 10min until completely dissolved; then add 10mg of brilliant blue FCF and stir for 5min until the color is uniform; then add the modified sodium carboxymethyl cellulose slurry obtained in step S4 along the liquid surface while stirring at 800r / min for 10min, and continue stirring at 800r / min for 20min after the addition is complete, then reduce the stirring speed to 300r / min and stir for 60min to fully hydrate; then let the system stand for 30min to degas, and obtain the cold storage agent for ice packs. Example 2

[0023] The raw materials used in this embodiment are the same as those in Embodiment 1.

[0024] In step S1, the amount of sodium periodate added was adjusted to 150 mg, and it was added in 3 batches (50 mg each time, 2 min apart). The reaction temperature was controlled at 28°C and the mixture was stirred at 500 r / min for 80 min. After adding 300 mg of ethylene glycol, the mixture was stirred at 400 r / min at 28°C for 30 min. The rest was the same as in Example 1.

[0025] In step S2, the amount of 6-amino-6-deoxy-β-cyclodextrin in container A was adjusted to 120 mg; the amount of 1-adamantaneamine in container B was adjusted to 25 mg; after adding the solution from container B to container A, the mixture was stirred at 25°C at 300 r / min for 40 min; the amount of dodecylamine in container C was adjusted to 60 mg; the rest was the same as in Example 1.

[0026] In step S3, after adding 40g of deionized water, the amount of 6-amino-6-deoxy-β-cyclodextrin added was adjusted to 200mg; the pH of the system was adjusted to 6.2 with sodium bicarbonate; the sodium borohydride was still 200mg, but the addition method was adjusted to 100mg in the first addition and 100mg in the second addition; the rest was the same as in Example 1.

[0027] In step S4, the amount of modified sodium carboxymethyl cellulose powder was adjusted to 4g, and the amount of propylene glycol was adjusted to 18g; the rest was the same as in Example 1.

[0028] In step S5, the amount of deionized water is adjusted to 905g and the amount of propylene glycol is adjusted to 72g; the other conditions are the same as in Example 1. Example 3

[0029] The raw materials used in this embodiment are the same as those in Embodiment 1.

[0030] In step S1, the amount of sodium periodate added was adjusted to 220 mg, and it was added in three batches (100 mg, 100 mg, and 20 mg each time, with an interval of 2 min). The reaction temperature was controlled at 30°C and the mixture was stirred at 500 r / min for 90 min. The rest was the same as in Example 1.

[0031] In step S2, the amount of 6-amino-6-deoxy-β-cyclodextrin in container A is adjusted to 90 mg; the amount of 1-adamantaneamine in container B is adjusted to 35 mg; after adding the solution from container B to container A, the mixture is stirred at 25°C at 300 r / min for 30 min; the amount of dodecylamine in container C is adjusted to 100 mg; the rest is the same as in Example 1.

[0032] In step S3, after adding 40g of deionized water, the amount of 6-amino-6-deoxy-β-cyclodextrin added was adjusted to 160mg; the pH of the system was adjusted to 5.8 with sodium bicarbonate; the rest was the same as in Example 1.

[0033] In step S4, the amount of modified sodium carboxymethyl cellulose powder is adjusted to 6g, and the amount of propylene glycol is 20g; the rest is the same as in Example 1.

[0034] In step S5, the amount of deionized water is adjusted to 883g and the amount of propylene glycol is adjusted to 90g; the remaining conditions are the same as in Example 1. Example 4

[0035] The raw materials used in this embodiment are the same as those in Embodiment 1.

[0036] In step S1, the amount of sodium periodate added remains unchanged at 200 mg, but the reaction temperature is adjusted to 32°C and the mixture is stirred at 500 r / min for 100 min; after adding 300 mg of ethylene glycol, the mixture is stirred at 400 r / min at 32°C for 30 min; the rest is the same as in Example 1.

[0037] In step S2, the amount of 6-amino-6-deoxy-β-cyclodextrin in container A was adjusted to 110 mg; the amount of 1-adamantaneamine in container B was adjusted to 40 mg; after adding the solution from container B to container A, the mixture was stirred at 25°C at 300 r / min for 45 min; the amount of dodecylamine in container C was adjusted to 120 mg; the rest was the same as in Example 1.

[0038] In step S3, after adding 40g of deionized water, the amount of 6-amino-6-deoxy-β-cyclodextrin added was adjusted to 220mg; the pH of the system was adjusted to 6.0 with sodium bicarbonate; the cooling temperature was adjusted to 3℃ and stirring was maintained at 300r / min, and sodium carbonate was added to adjust the pH of the system to 9.5; the sodium borohydride was still 200mg, but the addition method was adjusted to 140mg in the first addition and 60mg in the second addition; the rest was the same as in Example 1.

[0039] In step S4, the amount of modified sodium carboxymethyl cellulose powder is 5g, and the amount of propylene glycol is 20g; the rest is the same as in Example 1.

[0040] In step S5, the amount of deionized water is adjusted to 874g and the amount of propylene glycol is adjusted to 100g; the other conditions are the same as in Example 1. Example 5

[0041] The raw materials used in this embodiment are the same as those in Embodiment 1.

[0042] In step S1, the amount of sodium periodate added was adjusted to 180 mg, and it was added in two batches (90 mg each time, with an interval of 2 min). The reaction temperature was controlled at 28°C and the mixture was stirred at 500 r / min for 70 min. After adding 300 mg of ethylene glycol, the mixture was stirred at 400 r / min at 28°C for 30 min. The rest was the same as in Example 1.

[0043] In step S2, the amount of 6-amino-6-deoxy-β-cyclodextrin in container A is adjusted to 80 mg; the amount of 1-adamantaneamine in container B is adjusted to 20 mg; after adding the solution from container B to container A, the mixture is stirred at 25°C at 300 r / min for 20 min; the amount of dodecylamine in container C is 80 mg; the rest is the same as in Example 1.

[0044] In step S3, after adding 40g of deionized water, the amount of 6-amino-6-deoxy-β-cyclodextrin added was adjusted to 140mg; the pH of the system was adjusted to 6.5 with sodium bicarbonate; the cooling temperature was adjusted to 8℃ and stirring was maintained at 300r / min; sodium carbonate was added to adjust the pH of the system to 8.5; sodium borohydride was still 200mg and added in two portions (120mg was added first, and 80mg was added after reacting for 30min); the rest was the same as in Example 1.

[0045] In step S4, the amount of modified sodium carboxymethyl cellulose powder is adjusted to 3g, and the amount of propylene glycol is 20g; the rest is the same as in Example 1.

[0046] In step S5, the amount of deionized water is adjusted to 906g and the amount of propylene glycol is adjusted to 70g; the remaining conditions are the same as in Example 1.

[0047] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that in step S2, the solution from container B is not added to container A and stirred at 25°C for 300 r / min for 30 min to obtain a pre-encapsulated host-guest mixture solution. Instead, the cyclodextrin amine solution obtained from container A and the adamantane amine propylene glycol solution obtained from container B are added to the reaction solution obtained in step S1 in step S3. The remaining conditions are the same as in Example 1.

[0048] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that the amount of dodecylamine used in container C in step S2 is 0 mg; the other conditions are the same as in Example 1.

[0049] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that sodium borohydride was added in step S3 in one go (200 mg), instead of being added in two separate doses; the other conditions were the same as in Example 1.

[0050] Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that the amount of 1-adamantaneamine used in container B in step S2 is 0 mg; the other conditions are the same as in Example 1.

[0051] Comparative Example 5: The difference between Comparative Example 5 and Example 1 is that in step S4, the modified sodium carboxymethyl cellulose powder is replaced with an equal mass of sodium carboxymethyl cellulose; the other conditions are the same as in Example 1.

[0052] Performance testing: Sample preparation: Ice pack refrigerants were prepared according to Examples 1-5 and Comparative Examples 1-5, and were allowed to stand at 25℃ for 30 minutes to degas before use. For the ice pack application test, 200.0g of the degassed refrigerant was filled into a polyethylene bag (120mm×180mm) with a thickness of 0.08mm and heat-sealed. The bag was then placed in a -18℃ freezer for 24 hours before use. All tests were conducted at (25.0±0.5)℃. Three copies of each sample were prepared and tested separately. The arithmetic mean of the results was taken.

[0053] Differential scanning calorimetry (DSC): DSC was performed according to GB / T 19466.1-2004 "Differential Scanning Calorimetry (DSC) for Plastics - Part 1: General Rules" and GB / T 19466.3-2004 "Differential Scanning Calorimetry (DSC) for Plastics - Part 3: Determination of Melting and Crystallization Temperatures and Enthalpy". 10.0 mg of ice pack refrigerant was placed in a sealed aluminum crucible for each sample. Using an empty crucible as a reference, the temperature was first maintained at 25℃ for 3 min under a nitrogen flow rate of 50 mL / min, then decreased to -30℃ at a rate of 5℃ / min and maintained at that temperature for 5 min. Subsequently, the temperature was increased to 25℃ at a rate of 5℃ / min. The solidification peak temperature Tf (℃), melting peak temperature Tm (℃), and enthalpy change ΔHm (J / g) were recorded.

[0054] Apparent viscosity and shear thinning characteristics: Apparent viscosity was measured using a rotational viscometer. Each refrigerant sample was placed in a 25.0℃ constant temperature water bath for 30 min. Using rotor No. 4, the stable viscosity values ​​were read after maintaining a speed of 6 r / min and 60 r / min for 60 s, respectively, and recorded as η6 (25℃) and η... 60 (25℃), and calculate the shear thinning index SI=η6 / η 60 .

[0055] Freeze-thaw stability and water separation rate: The freeze-thaw stability test was conducted in accordance with GB / T 9268-2008 "Determination of Freeze-Thaw Resistance of Latex Paints". The number of freeze-thaw cycles was set in combination with the scenario of repeated use of ice packs. 100.0g of each cold storage agent sample was placed in a 250mL polypropylene bottle with a cap, sealed and placed in a -18℃ freezer for 16h, and then transferred to a 25℃ constant temperature chamber for 8h as one freeze-thaw cycle. 20 cycles were carried out continuously. After the cycle, the sample was allowed to stand at 25℃ for 2h. The viscosity retention rate Rη after freeze-thaw was measured (η6 (after freeze-thaw) / η6 (before freeze-thaw)) was calculated as Rη = η6 (after freeze-thaw) / η6 (before freeze-thaw) × 100%. Then, 50.0g of the frozen-thaw sample was placed in a centrifuge tube and centrifuged at 25℃ and 3000r / min for 10min. The supernatant was collected and its mass m (supernatant) (g) was weighed. The water separation rate was calculated as W = m (supernatant) / 50.0 × 100%.

[0056] Post-leakage flowability: A post-leakage flowability test was established according to GB / T 13477.6-2002 "Test Methods for Building Sealing Materials Part 6: Determination of Flowability". After each refrigerant sample was allowed to stand at 25℃ for 30 minutes to degas, 20.0g of sample was weighed and placed in a rectangular mold (mold cavity dimensions 50mm × 10mm × 10mm) located in the center of a glass plate. The surface was leveled, and the mold was immediately removed. The glass plate was then fixed vertically at 90° to the horizontal plane and placed in a 25℃ constant temperature chamber for 24 hours. Subsequently, the drooping distance L of the lower edge of the sample relative to the initial leveled position was measured using vernier calipers. 25 (mm); then another sample prepared in the same way was placed in a 40℃ constant temperature oven for 24 hours and the droop distance L was measured. 40 (mm), with L 25 With L 40 As an indicator of liquidity after leakage.

[0057] Uniformity and Duration of Cold Retention: Following the usage conditions for cold retention applications in T / TJWL 004-2018 "Cold Storage Agents for Food Cold Chain," tests were conducted on the uniformity and duration of cold retention for ice packs. 200.0g of each cold storage agent sample was filled into 0.08mm thick polyethylene bags (120mm × 180mm) and heat-sealed. Three K-type thermocouples were pre-embedded on both sides of the heat-sealed opening (embedded at the geometric center of the bag, 30mm from the center at the edge, and 45mm from the center at the corner, respectively). The thermocouple leads were simultaneously sealed to ensure no leakage. After placing the ice pack samples in a -18℃ freezer for 24 hours, they were immediately removed and placed flat on a polystyrene plate in a 25℃ constant temperature chamber. Data was continuously recorded at 1-minute intervals until the center temperature reached 5℃. The time t0 (min) required for the center temperature to rise from -10℃ to 0℃ was used as the cold retention duration index, and the maximum temperature difference ΔT at the three measurement points during the recording process was used as the indicator. max (°C) is used as an indicator of cold insulation uniformity.

[0058] Table 1 Performance test results of the examples and comparative samples

[0059] Data Analysis: As can be seen from the data in Table 1, the cold storage agent for ice packs prepared by this invention falls within the suitable range for cold chain applications in terms of phase change temperature and latent heat of phase change. Furthermore, the phase change peak temperature and latent heat of phase change show controllable changes with adjustments in the amounts of propylene glycol and modified sodium carboxymethyl cellulose. Simultaneously, the apparent viscosity is higher at low rotational speeds and significantly decreases at high rotational speeds, exhibiting typical shear-thinning characteristics, accompanied by a low water separation rate and a high viscosity retention rate, indicating that the system can maintain a stable network structure after freeze-thaw cycles. In terms of ice pack applications, the shorter flow distance, longer cold-keeping duration, and lower uniform temperature difference in cold-keeping indicate that the system can achieve better shape retention and temperature field stability within the packaging bag. The reason is speculated to be that: the low-degree oxidation of sodium periodate provides sodium carboxymethyl cellulose with controllable and more uniformly distributed reaction sites. Subsequently, 6-amino-6-deoxy-β-cyclodextrin is introduced and forms a pre-encapsulated host-guest complex with 1-adamantaneamine. Combined with the hydrophobic association of dodecylamine, the network has both stable host-guest binding nodes and energy-consuming and buffering mechanisms that can be rearranged. At the same time, sodium borohydride is added in two batches after adjusting the alkali with sodium carbonate, which helps to fully fix the connection structure formed by the aldehyde and amine groups and reduce the subsequent structural drift caused by residual active groups. Thus, the system can suppress the migration of the aqueous phase and maintain its homogeneity during the phase transition.

[0060] As can be seen from the data in Example 1 and Comparative Example 1 in Table 1, when the cyclodextrin amine solution and the adamantane amine propylene glycol solution are added separately to the sodium carboxymethyl cellulose reaction solution containing aldehydes without pre-encapsulation, the apparent viscosity and shear thinning characteristics of the system are weakened, the water separation rate increases and the viscosity retention rate decreases, and a larger flow distance and poorer cold-keeping uniformity are observed. The main reason is that the host-guest recognition is not pre-assembled before entering the main reaction system, resulting in competition and local enrichment of 6-amino-6-deoxy-β-cyclodextrin and 1-adamantaneamine during grafting and compounding, leading to uneven distribution of network nodes and easier formation of aqueous migration channels during freeze-thaw cycles, thus resulting in a decline in overall performance.

[0061] As can be seen from the data in Table 1 for Example 1 and Comparative Example 3, when sodium borohydride is added all at once instead of in two stages, although the changes in phase transition temperature and latent heat of phase transition are not significant, the water separation rate and flow distance increase, the viscosity retention rate decreases, and the uniformity of cold preservation deteriorates. The presumed reason is that adding sodium borohydride all at once causes the reduction process to proceed too quickly in a short time, resulting in asynchronous local reaction rates and viscosity increases, which can easily lead to uneven fixation of the network structure. Simultaneously, residual active sites are more likely to trigger network rearrangement during subsequent storage or freeze-thaw cycles, manifesting as viscosity decay and increased water separation. Therefore, staged reduction is not only an optimization of process details but also directly related to the long-term stability of the network.

[0062] As can be seen from the data in Table 1 for Example 1 and Comparative Examples 2 and 4, when only one guest component is retained, the system exhibits increased water separation rate, decreased viscosity retention, increased flow distance, and accompanied by a shortened cooling time and decreased uniformity. In the absence of dodecylamine, the network energy consumption and rearrangement capacity are insufficient, making the freeze-thaw cycle more prone to structural fatigue. In the absence of 1-adamantaneamine, the number of stable host-guest nodes is insufficient, weakening the network framework support and making it more prone to flow. The main reason for this is that 1-adamantaneamine and 6-amino-6-deoxy-β-cyclodextrin provide strong host-guest bonding to construct the framework, while dodecylamine provides weaker hydrophobic association to achieve dynamic buffering. The combination of these two components can simultaneously meet the dual requirements of stable support and dynamic energy consumption.

[0063] As can be seen from the data in Table 1 for Example 1 and Comparative Example 5, when the modified sodium carboxymethyl cellulose was replaced with an equal mass of sodium carboxymethyl cellulose, the apparent viscosity decreased significantly and the shear thinning characteristics weakened. After freeze-thaw cycles, the water separation rate increased substantially, the viscosity retention rate decreased significantly, and this resulted in a longer flow distance and poorer cold-keeping uniformity. The main reason for this is the lack of introduction of 6-amino-6-deoxy-β-cyclodextrin and its host-guest complex network with 1-adamantaneamine and dodecylamine. The system can only rely on the thickening and physical entanglement of the sodium carboxymethyl cellulose bulk, making it difficult to effectively bind the aqueous phase and resist structural damage caused by cycling during phase transition. Therefore, the host-guest network constructed by the modified sodium carboxymethyl cellulose plays a crucial role in maintaining the shape and stabilizing the temperature of ice packs.

[0064] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A cold storage agent for ice packs, characterized in that, By weight, it includes: 874-906 parts deionized water; 88-120 parts propylene glycol; 3-6 parts modified sodium carboxymethyl cellulose; The preparation steps of the modified sodium carboxymethyl cellulose are as follows: (1) Sodium carboxymethyl cellulose was oxidized with sodium periodate under light-shielding conditions to introduce aldehyde sites, and ethylene glycol was added to terminate the oxidation to obtain a sodium carboxymethyl cellulose reaction solution containing aldehydes. (2) 6-amino-6-deoxy-β-cyclodextrin was pre-encapsulated with 1-adamantaneamine to obtain a pre-encapsulated host-guest mixed solution; (3) The pre-encapsulated host-guest mixture solution was added to the sodium carboxymethyl cellulose reaction solution containing aldehyde group. After mixing for 20 min, 6-amino-6-deoxy-β-cyclodextrin was added and reacted for 120 min. Then, dodecylamine was added and reacted for 60 min. The mixture was then cooled to 3-8℃ and sodium borohydride was added in stages under alkaline conditions for reduction and locking. The precipitate was washed, vacuum dried, and passed through a 40-mesh sieve to obtain modified sodium carboxymethyl cellulose.

2. The cold storage agent for ice packs according to claim 1, characterized in that, It also includes 1 part sodium benzoate.

3. The cold storage agent for ice packs according to claim 1, characterized in that, It also includes 0.01 parts of Brilliant Blue FCF.

4. The cold storage agent for ice packs according to claim 1, characterized in that, The propylene glycol comprises 70-100 parts of propylene glycol for preparing the aqueous phase and 18-20 parts of propylene glycol for dispersing the modified sodium carboxymethyl cellulose.

5. The cold storage agent for ice packs according to claim 1, characterized in that, Based on 10 parts by weight of sodium carboxymethyl cellulose, the amounts of sodium periodate, 6-amino-6-deoxy-β-cyclodextrin, 1-adamantaneamine, dodecylamine, and sodium borohydride are 0.15-0.22 parts by weight, 0.22-0.34 parts by weight, 0.02-0.04 parts by weight, 0.06-0.12 parts by weight, and 0.2 parts by weight, respectively.

6. The cold storage agent for ice packs according to claim 1, characterized in that, The mass ratio of 6-amino-6-deoxy-β-cyclodextrin in step (2) to that in step (3) is 0.08-0.12:0.14-0.

22.

7. The cold storage agent for ice packs according to claim 1, characterized in that, In step (3), the sodium borohydride is added in stages: sodium borohydride is added in two stages, wherein the amount added in the first stage is 50wt%-70wt% of the total amount, and the two stages are added 30min apart.

8. A method for preparing a cold storage agent for ice packs according to any one of claims 1-7, characterized in that, The process includes the following steps: dispersing modified sodium carboxymethyl cellulose in propylene glycol to form a modified sodium carboxymethyl cellulose slurry; then mixing deionized water with propylene glycol, adding the modified sodium carboxymethyl cellulose slurry and hydrating it, allowing it to stand to remove bubbles, and obtaining a cold storage agent for ice packs.

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