A phosphated cellulose synergistically reinforced flame-retardant composite phase change material and a preparation method thereof

Abstract

The application discloses a kind of phosphated cellulose synergistically enhanced flame-retardant composite phase change materials and preparation method thereof, belong to thermal management material technical field.Preparation method includes steps: the eutectic phase change material CPCM of specific mass ratio of mannitol and galactitol is invented;Preparation MC@rGO skeleton, and with CPCM composite preparation CPCM / MC@rGO;Cellulose is modified in situ phosphated to obtain P-CSF, and rGO is polymerized to form P-CSF@rGO skeleton, then with above-mentioned CPCM composite obtains CPCM / P-CSF@rGO.The material prepared in the application retains up to 152.7 J / g latent heat of phase change and 1.039 W / (m•K) high thermal conductivity, while the limiting oxygen index LOI is improved to 30.64%, the material is endowed with high flame retardant properties, and it also has flexibility, realizes the synergistic enhancement of heat storage, heat conduction and flame retardant performance, and the material is especially suitable for advanced energy systems and electronic devices with strict requirements on thermal safety, energy storage density and thermal management efficiency.

Description

Technical Field

[0001] This invention relates to the field of thermal management materials technology, and in particular to a flame-retardant composite phase change material synergistically reinforced with phosphorylated cellulose and its preparation method. Background Technology

[0002] In recent years, phase change materials have shown great potential in the fields of thermal energy storage and temperature control due to their ability to absorb or release a large amount of latent heat during phase transition. Among them, organic phase change materials, especially sugar alcohols, have advantages such as high latent heat of phase change, small supercooling, and stable chemical properties.

[0003] However, organic phase change materials face three key technological bottlenecks in practical applications, severely restricting their industrialization. First, their intrinsic thermal conductivity is poor. The thermal conductivity of organic phase change materials is generally below 0.5 W / (m•K). This extremely low thermal conductivity leads to a significant lag in thermal response during heat absorption and release, resulting in low charge / release power and a tendency for large temperature gradients to form within the system. Existing technologies typically employ the strategy of adding high thermal conductivity fillers (such as metal powders, carbon nanotubes, and graphene) to improve thermal conductivity. However, simple physical blending often leads to uneven filler dispersion and high interfacial thermal resistance, which in turn causes new problems, significantly reducing the effective content of the phase change component per unit mass of material and causing a substantial decrease in the overall latent heat of phase change in the composite material. Therefore, how to significantly improve thermal conductivity while maximizing the maintenance of high latent heat of phase change is one of the core contradictions that current technologies have not yet effectively resolved.

[0004] Second, the inherent flammability poses a safety hazard. Most organic phase change materials are essentially carbohydrates, which are combustible. Their limiting oxygen index (LOI) is typically below 22%, making them highly flammable when exposed to open flames or high-temperature heat sources, posing a significant safety hazard. Traditional solutions involve the physical addition of flame retardants, such as halogenated, phosphorus-based, nitrogen-based, or inorganic hydroxide flame retardants. However, these methods also have significant drawbacks: the amount of flame retardant added usually needs to reach a high loading level to be effective, which inevitably leads to a severe loss of the latent heat of phase change; the flame retardant has poor compatibility with the organic matrix, easily migrating and precipitating, and its flame-retardant performance decays over time. Therefore, developing an efficient, durable, and inherently flame-retardant technology with minimal impact on the material's energy storage performance is an urgent technical need in this field. Third, synergistic performance optimization is difficult. Existing research mostly focuses on improving a single performance aspect. However, the actual application environment of phase change materials is complex, often requiring them to simultaneously possess high energy density, high thermal conductivity, high safety, and good physical stability. Currently, there are no publicly reported composite phase change material systems that can achieve efficient synergy of high latent heat of phase change, high thermal conductivity, and inherently high flame retardancy at the molecular and microstructure levels through a systematic material design and preparation method.

[0005] In summary, existing technologies struggle to synergistically address the issues of slow thermal conductivity, flammability, and low effective heat storage density in organic phase change materials within a single material system. In particular, there is a significant challenge in maximizing the retention of effective latent heat of phase change while simultaneously improving safety and thermal conductivity. Therefore, there is an urgent need to develop innovative material design strategies and preparation methods capable of synergistic regulation at the molecular and structural levels to fundamentally overcome these technological bottlenecks. Summary of the Invention

[0006] This invention provides a flame-retardant composite phase change material synergistically reinforced with phosphorylated cellulose and its preparation method, in order to overcome the core technical problems of poor thermal conductivity, low effective latent heat and flammability of existing organic phase change materials.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: A method for preparing a phosphorylated cellulose-synergistically reinforced flame-retardant composite phase change material includes the following steps: S1: Prepare eutectic phase change material CPCM by heating mannitol and galactitol in a specific mass ratio; S2: The eutectic phase change material CPCM was mixed with the composite framework MC@rGO formed by cellulose and reduced graphene oxide, and the mixture was heated to react to obtain CPCM / MC@rGO composite material. S3: Phosphorylated cellulose is modified in situ to obtain phosphorylated cellulose P-CSF. The phosphorylated cellulose P-CSF is then self-polymerized with reduced graphene oxide rGO to form a P-CSF@rGO framework. The P-CSF@rGO framework is then combined with the eutectic phase change material CPCM to obtain the flame-retardant composite phase change material CPCM / P-CSF@rGO.

[0008] Further, in step S1, the mass ratio of mannitol to galactitol is (7-8):(2-3).

[0009] Furthermore, in step S2, the method for preparing the composite framework MC@rGO is as follows: S2.1: Immerse 600-mesh corn stalk powder in a 5-10 wt.% NaOH solution and mix thoroughly. Heat and stir at 60 ℃ for 2-3 h to promote lignin dissolution and ensure uniform reaction. After the reaction, centrifuge to collect the solid product and wash repeatedly with deionized water until the washing liquid is neutral to obtain the treated corn stalk. Then, perform oxidative bleaching to further remove residual lignin. Immerse the treated corn stalk in a 3-5 wt.% H2O2 solution and react at 60 ℃ for 2-3 h. After the reaction, separate the solid and liquid components and wash the solid product with deionized water. Acid treat the treated corn stalk to remove insoluble lignin and hemicellulose and improve cellulose purity. The method is as follows: Immerse the treated solid product in a 2-5 wt.% HCl solution and stir at 100 r / min for 2-3 h at 60 ℃. After the reaction, centrifuge to separate the solid product and wash repeatedly with deionized water until the washing liquid is neutral. Then, dry in an oven at 100 ℃. Drying at ℃ yields cellulose MC; S2.2: Cellulose MC was prepared into an MC suspension with a concentration of 5-10 wt.%, and the MC suspension was mixed with a graphene oxide (GO) suspension with a concentration of 10 mg / mL. The mixture was ultrasonically dispersed for 1-3 h, and then a reducing agent was added. The mixture was subjected to a hydrothermal reaction at 90-150 °C for 2-4 h. The solid and liquid were separated, and the solid product was washed multiple times with deionized water. After drying, the composite framework MC@rGO was obtained. Furthermore, in step S3, the method for in-situ phosphorylation modification of cellulose is as follows: The phosphorylated cellulose P-CSF was prepared by soaking corn stalks in a phosphorylated solution formed by a mixture of diammonium hydrogen phosphate and urea at 100 °C for 3-5 h, followed by drying at 100-130 °C and curing at 150-200 °C for 1-3 h. The mass ratio of diammonium hydrogen phosphate to urea is (3-5):1.

[0010] Further, in step S3, the preparation method of P-CSF@rGO framework is as follows: dissolve phosphorylated cellulose P-CSF in deionized water to obtain a phosphorylated cellulose P-CSF suspension with a concentration of 0.1-2 wt.%; mix the phosphorylated cellulose P-CSF suspension with a GO suspension with a concentration of 10 mg / mL at a volume ratio of (5:1)-(15:1); ultrasonically disperse for 0.5-2 hours to obtain a mixed solution; then add ascorbic acid to the mixed solution according to the mass ratio of GO to ascorbic acid of (3-5):1 to obtain a mixed material; place the mixed material in a hydrothermal reactor and heat it at 90 ℃ for 3 h; after the reaction is completed, centrifuge the product and wash it with deionized water; then dry it in an oven at 60 ℃ for 4 h to obtain the P-CSF@rGO framework.

[0011] Furthermore, the preparation method of CPCM / P-CSF@rGO is as follows: the obtained P-CSF@rGO composite framework is immersed in the eutectic phase change material CPCM prepared in step S1, heated in an oil bath at 150 °C, and stirred for 2 h to obtain CPCM / P-CSF@rGO.

[0012] Further, in step S1, the method for preparing the eutectic phase change material is as follows: mannitol and galactitol are mixed in a mass ratio and melted in an oil bath at 150 °C, and then stirred at 450 r / min for 30 min to obtain the eutectic phase change material CPCM.

[0013] Further, in step S2.2, the volume ratio of MC suspension to graphene oxide (GO) suspension is (5:1)-(15:1), preferably 1:10.

[0014] Further, in step S2.2, the reducing agent is ascorbic acid, and the mass ratio of graphene oxide (GO) to ascorbic acid is 1:(3-5).

[0015] In another aspect, the present invention provides a flame-retardant composite phase change material synergistically reinforced with phosphorylated cellulose obtained by the aforementioned preparation method.

[0016] The beneficial effects of this invention are: I. This invention is the first to successfully achieve a synergistic improvement and perfect integration of high heat storage capacity, high thermal conductivity, and high flame retardant performance within the same material system. While retaining high latent heat of phase change, the thermal conductivity is increased to over 1.0 W / m•K, and the limiting oxygen index (LOI) reaches over 28%, achieving a high flame retardant rating. Second, this invention introduces active phosphate groups into the biomass cellulose skeleton through phosphorylation modification. These groups form a strong hydrogen bond network with the eutectic phase change molecules, fundamentally solving the leakage problem of phase change materials and endowing the material with good flexibility, enabling it to better conform to the curved inner walls of batteries and other materials.

[0017] Thirdly, regarding flame retardancy, the phosphorylated component of this invention exhibits highly efficient char-forming activity upon heating, promoting the rapid formation of a dense and stable carbon layer on the material surface, thus isolating heat and oxygen and achieving highly efficient condensed-phase flame retardancy. Regarding thermal conductivity, rGO and P-CSF construct a continuous three-dimensional hydrogen bond network, significantly improving heat transfer efficiency. These two mechanisms work synergistically through the same modified framework, enabling the resulting material to possess rapid thermal response and excellent fire-resistant properties.

[0018] Fourth, the gradient development path proposed in this invention, from eutectic design with specific mass ratios to unmodified framework composites, and then to phosphorylated modified framework composites, constitutes a complete and logically clear material system design method. This method is not only applicable to the specific components of this invention, but its core ideas can also be extended to other phase change materials and biomass composite systems, possessing significant methodological value.

[0019] V. This invention uses renewable biomass cellulose as the main structural raw material, which aligns with the concept of green and sustainable development. The prepared composite material combines flexibility, lightweight, high safety, and high efficiency, demonstrating enormous industrialization potential in cutting-edge fields such as flexible electronic thermal management and power battery thermal safety protection, which have extremely high requirements for the comprehensive performance of materials. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is the experimental flowchart. Figure 1 a is a flowchart of CPCM / MC@rGO preparation process; Figure 1 b is a flowchart of the CPCM / P-CSF@rGO preparation process; Figure 2 SEM images of the materials obtained in each step, where Figure 2 a is the SEM image of CPCM. Figure 2 b is the SEM image of MC@rGO. Figure 2 c is the SEM image of P-CSF. Figure 2 d represents the SEM image of P-CSF@rGO. Figure 2 e represents the SEM image of CPCM / MC@rGO. Figure 2 f is the SEM image of CPCM / P-CSF@rGO; Figure 3 The results of differential scanning calorimetry (DSC) tests for CPCM, CPCM / MC@rGO, and CPCM / P-CSF@rGO are shown in the figure. Figure 4 The graph shows the thermal conductivity test results for CPCM, CPCM / MC@rGO, and CPCM / P-CSF@rGO. Figure 5 The infrared thermal distribution temperature variation diagrams for CPCM and CPCM / P-CSF@rGO are shown. Figure 5 a is a graph showing the temperature changes during the heating process; Figure 5 b is the temperature distribution diagram of the cooling process; Figure 6 Thermal drying analysis (TGA) curves for CPCM, CPCM / MC@rGO, and CPCM / P-CSF@rGO; Figure 7 The image shows the results of the CPCM / P-CSF@rGO flame burn test. Figure 8 The limiting oxygen index test results for CPCM, CPCM / MC@rGO, and CPCM / P-CSF@rGO are shown in the figure. Figure 9 The results of cone calorimetry for CPCM / MC@rGO and CPCM / P-CSF@rGO are shown in the figure. Figure 9 a is the test curve of average thermal emissivity (ARHE). Figure 9 b is the heat release rate (HRR) test curve. Figure 9 c represents the total heat release (THR) test curve. Figure 9 d represents the total smoke production (TSP) test curve. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example: A method for preparing a phosphorylated cellulose-synergistically reinforced flame-retardant composite phase change material includes the following steps: S1: Preparation of eutectic phase change materials (CPCM) The phase change material of this invention is prepared by melt blending, using mannitol and galactitol as base materials, and proportioned according to the theoretical molar ratio calculated by the Gibbs free energy method. The final calculated mass ratio of mannitol to galactitol is 7.2:2.8. After mixing mannitol and galactitol according to this mass ratio, the mixture is placed in an oil bath at 150 °C and stirred at 450 r / min for 30 min to ensure thorough mixing of the reactants, resulting in a transparent and homogeneous eutectic phase change material (CPCM), providing high phase change performance for subsequent research. S2: Preparation of CPCM / MC@rGO composite material S2.1: Preparation of cellulose (MC) First, the corn stalk powder is pretreated to remove hemicellulose and lignin to expose the cellulose, thereby improving the effect of subsequent treatment. The specific steps are as follows: 4g of 600-mesh corn stalk powder was thoroughly mixed with 10 wt.% NaOH solution (the NaOH solution should completely cover the powder). The mixture was heated and stirred at 300 r / min for 2 hours at 60 ℃, and repeatedly washed with deionized water until the washing solution was neutral to obtain the treated corn stalk. Subsequently, an oxidative bleaching treatment was performed to further remove residual lignin. The treated corn stalk was soaked in 3-5 wt.% H2O2 solution and reacted at 60 ℃ for 2 hours. After the reaction was completed, solid-liquid separation was performed, and the solid product was washed with deionized water. The treated corn stalk was then acid-treated to remove insoluble lignin and hemicellulose and improve cellulose purity: the treated solid product was soaked in 2 wt.% HCl solution and stirred at 100 r / min for 1 hour at 60 ℃. After the reaction was completed, the solid product was separated by centrifugation and repeatedly washed with deionized water until the washing solution was neutral. Then, it was dried in an oven at 100 ℃ to obtain cellulose MC. S2.2: Preparation of the MC@rGO composite framework 100 mg of the MC prepared in S2.1 was dispersed in 50 mL of deionized water to prepare an MC suspension. The MC suspension was mixed with 500 mL of graphene oxide (GO) suspension with a concentration of 10 mg / mL and ultrasonically dispersed for 1 h. Ascorbic acid was added to the mixture at a mass ratio of GO to ascorbic acid of 3:1. The material was then placed in a hydrothermal reactor and heated at 90 °C for 3 h. After the reaction was completed, the solid product was centrifuged and washed multiple times with deionized water. Subsequently, it was dried in an oven at 60 °C for 4 h to finally obtain the MC@rGO composite framework. S2.3: Preparation of CPCM / MC@rGO composite material The MC@rGO composite framework prepared in step S2.2 was immersed in the CPCM prepared in step S1. The mixture was then placed in a 150 °C oil bath and stirred at 450 r / min for 2 h with heating and magnetic stirring to ensure full impregnation of the CPCM. After heating was stopped, the mixture was cooled to room temperature to obtain the CPCM / MC@rGO composite material. The preparation process of CPCM / MC@rGO is as follows: Figure 1 As shown in a; S3: Preparation of CPCM / P-CSF@rGO S3.1: The preparation of phosphorylated cellulose (P-CSF) is as follows: First, diammonium hydrogen phosphate and urea were mixed at a mass ratio of 4:1 to prepare a phosphorylation solution. Dried corn stalks were immersed in the phosphorylation solution and placed in a petri dish at 100 °C for 3 h, followed by drying at 105 °C for 1 h. Finally, the phosphorylated cellulose was cured at 150 °C for 1 h. After curing, the sample was thoroughly washed with deionized water to obtain P-CSF. S3.2: Preparation of P-CSF@rGO composite framework 100 mg of the P-CSF prepared in S3.1 was dispersed in 50 mL of deionized water to prepare a phosphorylated cellulose P-CSF suspension. The prepared phosphorylated cellulose P-CSF suspension was mixed evenly with 500 mL of graphene oxide (GO) suspension at a concentration of 10 mg / mL, and ultrasonically dispersed for 1 h to obtain a mixture. Then, ascorbic acid was added to the mixture at a mass ratio of graphene oxide (GO) to ascorbic acid of 3:1. The resulting material was placed in a hydrothermal reactor and heated at 90 °C for 3 h. After the reaction was completed, the solid product was centrifuged and washed several times with deionized water. Subsequently, it was dried in a 60 °C oven for 4 h to finally obtain the P-CSF@rGO composite framework. S3.3: Preparation of CPCM / P-CSF@rGO composite material Take 0.5 g of the P-CSF@rGO composite framework prepared in step S3.2 above, immerse it in the CPCM prepared in step S1, place the mixture in a 150 ℃ oil bath, and stir with a heating magnetic stirrer at 450 r / min for 2 h to ensure sufficient CPCM impregnation. After stopping heating, cool to room temperature to obtain the final flame-retardant composite phase change material CPCM / P-CSF@rGO. The preparation flow chart of CPCM / P-CSF@rGO is shown below. Figure 1 As shown in b.

[0024] The performance of the flame-retardant composite phase change material prepared above was tested: (1) SEM image analysis was performed on CPCM, P-CSF, MC@rGO, P-CSF@rGO, CPCM / MC@rGO, and CPCM / P-CSF@rGO materials respectively. This invention characterizes the microstructure of CPCM, P-CSF, MC@rGO, P-CSF@rGO, CPCM / MC@rGO, and CPCM / P-CSF@rGO using scanning electron microscopy (SEM). The results are as follows: Figure 2 As shown.

[0025] from Figure 2In image a, pure CPCM exhibits a layered crystal structure with complete crystal faces and a smooth surface, indicating its highly crystalline properties. This large-scale crystal structure is the direct cause of the material's fragile mechanical properties. Figure 2 b, The MC@rGO framework shows that rGO sheets are attached to the cellulose surface in a wrinkled manner, but the coverage is discontinuous, with obvious exposed areas; while from Figure 2 c. It was found that the surface of P-CSF became rough after phosphorylation treatment, with obvious nanoscale protrusions and grooves, which is proof of successful grafting of phosphate groups; Figure 2 As shown in d, the P-CSF@rGO framework exhibits a tighter and more continuous bonding between the rGO sheets and P-CSF fibers, forming a fiber-sheet interpenetrating network structure with a more uniform pore size distribution; as shown in d, Figure 2 e- Figure 2 As shown in f, CPCM / MC@rGO and CPCM / P-CSF@rGO exhibit a dense and uniform morphology. CPCM is evenly dispersed in the three-dimensional skeleton, achieving good interface bonding.

[0026] (2) Phase transition property test This experiment performed multiple differential scanning calorimetry (DSC) tests. The DSC test results for CPCM, CPCM / MC@rGO, and CPCM / P-CSF@rGO are shown in the figure below. Figure 3 As shown, from Figure 3 It can be observed that pure CPCM exhibits a sharp absorption peak at 153.6 °C, with a latent heat of phase transition of 301.2 J / g. When CPCM is combined with the MC@rGO framework, the crystallinity of CPCM molecules decreases due to the spatial constraint of the porous MC@rGO framework and the weak hydrogen bond interaction between the -OH groups on the MC surface and CPCM molecules. The phase transition temperature of CPCM / MC@rGO drops to 149.7 °C, and the latent heat decreases to 251.8 J / g. Finally, the phase transition temperature of the CPCM / P-CSF@rGO material decreases to 136.3 °C, with a latent heat of 152.0 J / g. The strong hydrogen bond network formed between the phosphate groups and rGO deeply confines the movement of CPCM molecules, not only inhibiting their regular crystallization and thus reducing the latent heat, but also triggering the phase transition at a lower temperature. However, CPCM has a relatively large latent heat, so even with the decrease in latent heat, CPCM / P-CSF@rGO still achieves a high heat storage density.

[0027] (3) Thermal conductivity test This test used a Hot Disk TPS 2500S thermal constant analyzer (Hot Disk AB, Sweden) to analyze the thermal conductivity of phase change materials. Samples CPCM, CPCM / MC@rGO, and CPCM / P-CSF@rGO were fabricated into 10 mm block specimens. During testing, a dedicated planar sensor was tightly clamped between two identical specimens to form a symmetrical structure, and measurements were then taken to verify the high-efficiency heat transfer capability of the composite materials. The results are as follows: Figure 4 As shown, the intrinsic thermal conductivity of pure CPCM is only 0.542 W / (m·K), with heat transfer mainly relying on slow molecular vibrations. The introduction of the MC@rGO and P-CSF@rGO frameworks is key to improving the material's thermal conductivity. After introducing the MC@rGO framework, the thermal conductivity of CPCM / MC@rGO increased by 91% to 1.035 W / (m·K), mainly attributed to the three-dimensional hydrogen bond network formed between rGO and MC.

[0028] The thermal conductivity values ​​of CPCM / P-CSF@rGO and CPCM / MC@rGO, using the P-CSF@rGO framework, are almost identical, reaching 1.039 W / (m·K). This indicates that the phosphorylation modification process did not affect the thermal conductivity of the composite material. The final material, CPCM / P-CSF@rGO, showed a 91.6% improvement in thermal conductivity compared to pure CPCM, achieving a significant improvement in thermal conductivity.

[0029] To further visualize the improvement in the thermal properties of the materials, the temperature changes of CPCM and CPCM / P-CSF@rGO during the heating and cooling processes were recorded using an infrared thermal imager, such as... Figure 5 As shown.

[0030] The temperature change during the heating process is as follows: Figure 5 As shown in Figure a, the CPCM temperature rises slowly within 50 s, only reaching 58.4 ℃, while CPCM / P-CSF@rGO reaches 69.4 ℃. This is consistent with the fact that the thermal conductivity of CPCM is significantly lower than that of CPCM / P-CSF@rGO. During heating times of 50-180 s, the rate of change for CPCM / P-CSF@rGO is faster than that for CPCM. The surface color of CPCM / P-CSF@rGO is also uniform, indicating uniform heat distribution. This is attributed to the effective heat transfer path provided by the P-CSF@rGO framework. The cooling process after removing the heat source is as follows... Figure 5 b. It can be observed that the temperature of the high-temperature area on the CPCM / P-CSF@rGO surface drops rapidly from 86.3℃ to room temperature, indicating that the material can quickly reach thermal equilibrium with the environment.

[0031] (4) Thermal stability test To investigate the thermal stability of the material, thermogravimetric analysis (TGA, DTG-60, Japan) was used to analyze the thermal stability of the material in the temperature range from room temperature to 750 °C in an air atmosphere, with a heating rate of 10 °C / min. Figure 6 Thermal drying analysis (TGA) curves for CPCM, CPCM / MC@rGO, and CPCM / P-CSF@rGO. Figure 6 The results showed that pure CPCM began to decompose at 315.6 °C and completely volatilized at 531.0 °C, with a residue close to zero. This is the decomposition and vaporization process of polyol-type small molecule organic compounds. CPCM / MC@rGO began to decompose at 291.1 °C and completed its main weight loss at 501.6 °C. Although the multi-stage decomposition of cellulose complicated the process, the final residual carbon content was still extremely low, indicating that the MC@rGO framework failed to effectively improve the char-forming ability and high-temperature stability of the material.

[0032] In contrast, the initial decomposition temperature of CPCM / P-CSF@rGO was lowered to 251.36 °C. This is due to the breaking of the P=O bonds in phosphorylated cellulose and the release of active substances such as phosphoric acid and polyphosphoric acid, which triggered the cross-linking reaction between P-CSF and CPCM, resulting in a significantly smoother main weight loss phase. After combustion, CPCM / P-CSF@rGO forms a dense and thermally stable carbon layer on the material surface. This carbon layer inhibits the escape of internal combustible gases (such as CO, CH4, and H2) and slows down the heat transfer process. Ultimately, CPCM / P-CSF@rGO achieved a residual carbon content of 1.5% at 800 °C, a stark contrast to the other two materials. CPCM / P-CSF@rGO exhibits excellent thermal stability under high-temperature conditions, making it an ideal choice for thermal management applications.

[0033] (5) Real flame burning test and results To evaluate the flame-retardant performance of CPCM / P-CSF@rGO under actual ignition conditions, a cyclic open flame test was conducted. CPCM / P-CSF@rGO was heated in the outer flame of an alcohol lamp for 10 seconds and then removed. The combustion behavior of the material was observed, and this process was repeated three times. The results are as follows: Figure 7 As shown.

[0034] During the initial ignition, a brief and weak flame appeared on the surface of the material in contact with the flame, but the flame failed to spread continuously, and the combustion area was strictly controlled near the directly exposed point. Within a very short time after the heat source was removed, any open flame completely ceased, and there was no continued combustion; the material exhibited rapid self-extinguishing properties. In the subsequent second and third ignition cycles, the material repeated the same flame-retardant behavior. After three cycles, the material did not experience drastic shrinkage or sudden combustion; only a dense, stable carbon layer formed in the directly heated area.

[0035] This is because, upon heating, P-CSF rapidly cross-links with the CPCM surface, forming a dense carbon layer. This carbon layer not only prevents external oxygen from penetrating the material but also blocks internal combustible products from leaking out and contacting the ignition source, forcing the flame to extinguish rapidly after the ignition source is removed. Real flame tests have confirmed that the CPCM / P-CSF@rGO material possesses resistance to ignition, spread, and self-extinguishing capabilities. The carbonization mechanism of CPCM / P-CSF@rGO maintains excellent fire resistance even under repeated open flame impacts, demonstrating its potential for safe application in real fire scenarios.

[0036] (6) Limiting oxygen index test To quantitatively analyze the flame-retardant behavior of CPCM / P-CSF@rGO, the limiting oxygen index (LOI) was used to evaluate the flame-retardant effect and fire resistance of the materials. Simultaneously, the LIO values ​​of CPCM and CPCM / MC@rGO were compared. The LIO test results for each material are shown below. Figure 8 As shown, CPCM's LOI value is only 18.26%, classifying it as a flammable material. CPCM / MC@rGO's LOI value is 21.3%, only reaching the flame-retardant level, indicating that the physical barrier effect of cellulose and rGO alone has limited impact on improving flame retardant performance. After phosphorylation modification, the LOI value of CPCM / P-CSF@rGO significantly increases to 30.64%, reaching a high flame-retardant level.

[0037] This fundamental improvement is attributed to the flame-retardant effect of phosphate groups in both the gas and condensed phases. In the condensed phase flame-retardant mechanism, P-CSF is the core component. Upon heating, the phosphorus-containing derivatives generated from the decomposition of P-CSF efficiently catalyze the dehydration and cross-linking reaction of the P-CSF@rGO framework and CPCM molecules, forming a dense carbon layer on the material surface. This carbon layer acts as a highly efficient physical barrier, isolating heat and oxygen transfer while inhibiting the escape of combustible gases generated by the internal CPCM combustion, fundamentally interrupting the combustion process. Regarding the gas-phase flame-retardant mechanism, the phosphorus-containing free radicals PO· and P· released by P-CSF during thermal decomposition enter the flame, effectively capturing the H· and OH· free radicals necessary for the combustion chain, interrupting flame combustion through chemical reactions, and effectively inhibiting the gas-phase combustion reaction.

[0038] (7) Cone calorimeter test To further verify the refractory performance of CPCM / P-CSF@rGO in application, a cone calorimeter was used to evaluate the refractory performance of the materials. Simultaneously, the refractory performance of CPCM / MC@rGO was measured. The cone calorimeter results for CPCM / MC@rGO and CPCM / P-CSF@rGO are as follows: Figure 9As shown, the combustion behavior of the material is analyzed by average thermal emissivity (ARHE), heat release rate (HRR), total smoke production (TSP), and total heat release (THR).

[0039] ARHE is defined as the ratio of cumulative radiant heat to time, and its peak value (PARHE) can be used as a parameter to assess the trend of fire occurrence. Figure 9 As shown in figure a, CPCM / MC@rGO reaches 266.7 kW / m 2 However, the PARHE of the phosphorylated CPCM / P-CSF@rGO decreased to 243.96 kW / m³. 2 This study revealed that phosphorylated modified cellulose can synergistically reduce the tendency of fires to occur. For example... Figure 9 b、 Figure 9 As shown in c, the PHRR of CPCM / MC@rGO reaches 442.3 kW / m. 2 The THR reached 44.1 MJ / m 2 This indicates a potential risk of thermal runaway when using unmodified materials in battery modules. However, after using the P-CSF@rGO framework, both PHRR and THR decreased significantly, and CPCM / P-CSF@rGO exhibited good fire resistance, with PHRR and THR reduced to 390.22 kW / m³. 2 and 40 MJ / m 2 These figures were reduced by 12% and 10% respectively, effectively limiting heat release.

[0040] Furthermore, the smoke generated during combustion poses a serious threat to life safety; therefore, a cone calorimeter was used to assess the smoke generation rate (TSP) of the two materials. Figure 9 As shown in d, the TSP of CPCM / MC@rGO reaches 9.16 m. 2 This indicates that CPCM / MC@rGO produces smoke during combustion. CPCM / P-CSF@rGO, made using modified P-CSF, exhibits a lower TSP of 6.7 m. 2 This indicates that the physical carbon layer formed after P-CSF combustion acts as a barrier and shielding layer, inhibiting the release of smoke.

[0041] In summary, based on the ARHE, HRR, SPR, TSP, and THR results above, we can conclude that CPCM / P-CSF@rGO exhibits superior fire resistance compared to CPCM / MC@rGO, effectively suppressing flame propagation. CPCM / P-CSF@rGO successfully overcomes the bottleneck of synergistic performance optimization in existing technologies, achieving a synergistic integrated material system that combines high thermal conductivity and high latent heat with high flame retardant performance.

[0042] 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 the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a phosphorylated cellulose-synergistically reinforced flame-retardant composite phase change material, characterized in that, Includes the following steps: S1: Prepare eutectic phase change material CPCM by heating mannitol and galactitol in a specific mass ratio; S2: The eutectic phase change material CPCM was mixed with the composite framework MC@rGO formed by cellulose and reduced graphene oxide, and the mixture was heated to react to obtain CPCM / MC@rGO composite material. S3: Phosphorylated cellulose is modified in situ to obtain phosphorylated cellulose P-CSF. The phosphorylated cellulose P-CSF is then self-polymerized with reduced graphene oxide rGO to form a P-CSF@rGO framework. The P-CSF@rGO framework is then combined with the eutectic phase change material CPCM to obtain the flame-retardant composite phase change material CPCM / P-CSF@rGO.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of mannitol to galactitol is 7-8:2-3.

3. The preparation method according to claim 1, characterized in that, In step S2, the method for preparing the composite framework MC@rGO is as follows: S2.1: The straw powder was immersed in a 5-10 wt.% NaOH solution and thoroughly mixed. The mixture was heated and stirred at 60 °C for 2-3 h. After the reaction was completed, the solid product was collected by centrifugation and washed with deionized water until the washing liquid was neutral to obtain the treated corn straw. Subsequently, an oxidative bleaching treatment was performed by immersing the treated corn straw in a 3-5 wt.% H2O2 solution and reacting at 60 °C for 2-3 h. After the reaction was completed, solid-liquid separation was performed, and the solid product was washed with deionized water. The treated solid product was then immersed in a 2-5 wt.% HCl solution and stirred at 60 °C for 2-3 h. After the reaction was completed, the solid product was separated by centrifugation and repeatedly washed with deionized water until the washing liquid was neutral and then dried to obtain cellulose MC. S2.2: Prepare a 5-10 wt.% MC suspension with cellulose MC, mix the MC suspension with a 10 mg / mL GO suspension, add a reducing agent, and carry out a hydrothermal reaction at 90-150℃ for 2-4 h. Separate the solid and liquid to obtain the composite framework MC@rGO.

4. The preparation method according to claim 3, characterized in that, In step S3, the method for in-situ phosphorylation modification of cellulose is as follows: The phosphorylated cellulose P-CSF was prepared by soaking straw in a phosphorylated solution formed by a mixture of diammonium hydrogen phosphate and urea at 100 °C for 3-5 h, followed by drying at 100-130 °C and curing at 150-200 °C for 1-3 h. The mass ratio of diammonium hydrogen phosphate to urea is (3-5):

1.

5. The preparation method according to claim 1, characterized in that, In step S3, the preparation method of P-CSF@rGO framework is as follows: dissolve phosphorylated cellulose P-CSF in deionized water to obtain a phosphorylated cellulose P-CSF suspension with a concentration of 0.1-2 wt.% and mix the phosphorylated cellulose P-CSF suspension with a GO suspension with a concentration of 10 mg / mL at a volume ratio of (5:1)-(15:1). Disperse the mixture by ultrasonication for 0.5-2 hours to obtain a mixed solution. Then, add ascorbic acid to the mixed solution at a mass ratio of GO to ascorbic acid of (3-5):1 to obtain a mixed material. Place the mixed material in a hydrothermal reactor and heat it at 90 ℃ for 3 h. After the reaction is completed, centrifuge the product, wash it with deionized water, and dry it to obtain the P-CSF@rGO framework.

6. The preparation method according to claim 5, characterized in that, The preparation method of CPCM / P-CSF@rGO is as follows: The obtained P-CSF@rGO composite framework is immersed in the eutectic phase change material CPCM prepared in step S1, heated in an oil bath at 150 ℃, and stirred for 2 h to obtain CPCM / P-CSF@rGO.

7. The preparation method according to claim 2, characterized in that, In step S1, the method for preparing the eutectic phase change material is as follows: mannitol and galactitol are mixed in a mass ratio and melted in an oil bath at 150 °C. Then, the mixture is stirred at 450 r / min for 30 min to obtain the eutectic phase change material CPCM.

8. The preparation method according to claim 3, characterized in that, In step S2.2, the volume ratio of MC suspension to graphene oxide (GO) suspension is (5:1)-(15:1).

9. The preparation method according to claim 3, characterized in that, In step S2.2, the reducing agent is ascorbic acid, and the mass ratio of graphene oxide (GO) to ascorbic acid is 1:(3-5).

10. A phosphorylated cellulose-synergistically reinforced flame-retardant composite phase change material prepared by the preparation method of claim 1.

Images