CN-121975173-A - Method for improving intrinsic enthalpy value of cross-linked polyurethane solid-solid phase change material through thermo-mechanical programming

Abstract

The invention discloses a method for improving intrinsic enthalpy value of a cross-linked polyurethane solid-solid phase change material through thermo-mechanical programming, and belongs to the technical field of thermal energy management. Aiming at the problem that the intrinsic latent enthalpy value of the existing crosslinking polyurethane solid-solid phase change material is low, so that the energy storage density is far lower than the theoretical level, the dynamic covalent bond characteristic of a carbamate bond in polyurethane is utilized to carry out thermomechanical programming, and the molecular chain segments are driven to rearrange under an activated state by external mechanical stress, so that the originally disordered isotropic topological state is converted into a highly oriented ordered state, thereby obviously reducing the potential barrier of crystallization nucleation on the premise of not changing the chemical components of the material, realizing the endogenous enhancement of the intrinsic latent heat of the material, and still maintaining the stable high energy storage density in long-time thermal circulation. The method expands the application potential of the polyurethane solid-solid phase change material in high-power heat dissipation scenes such as power battery heat management and the like.

Inventors

• ZOU RUQIANG
• HAN HAIWEI
• HAN SHENGHUI
• YAN HANG
• SHEN ZHENGHUI

Assignees

• 北京大学

Dates

Publication Date

20260505

Application Date

20260407

Claims (10)

1. 1. A method for increasing intrinsic enthalpy value of cross-linked polyurethane solid-solid phase change material is characterized by that the dynamic covalent bond characteristic of urethane bond in polyurethane is used to make thermomechanical programming, and specifically the cross-linked polyurethane solid-solid phase change material is heated to above the dynamic exchange activation temperature of urethane bond and kept at constant temperature to make it reach thermal equilibrium, then thermomechanical programming is carried out, i.e. the polyurethane solid-solid phase change material is applied with tensile stress until reaching preset programming strain, the stress treatment is continued for a period of time under constant temperature, then cooled to room temperature under the condition of keeping stress loading, and the programmed polyurethane solid-solid phase change material with increased intrinsic enthalpy value is obtained.
2. 2. The method of claim 1, wherein the cross-linked polyurethane solid-solid phase change material is warmed to greater than 130 ℃ and then thermomechanically programmed.
3. 3. The method of claim 1, wherein the predetermined programmed strain is stretching the material to a strain state of 50% to 150%.
4. 4. The method of claim 1, wherein after heat equilibration, the polyurethane solid-solid phase change material is uniaxially stretched at a constant rate of less than 5 mm/min until a predetermined programmed strain is reached, and the sample is continuously subjected to a holding stress treatment at constant temperature for 10 minutes or more, and then allowed to stand at room temperature.
5. 5. The method of claim 1, wherein the cross-linked polyurethane solid-solid phase change material is a composite material made from semi-crystalline polyether and hard segment linking agent through in situ cross-linking polymerization under the action of cross-linking agent, wherein crystalline soft segment domains are uniformly distributed in a cross-linked network composed of dynamic urethane bonds.
6. 6. The method of claim 5, wherein the cross-linked polyurethane solid-solid phase change material has a degree of cross-linking of 60% to 85%.
7. 7. The method of claim 5, wherein the semi-crystalline polyether is polyethylene glycol, the hard segment linking agent is a polyisocyanate, and the crosslinking agent is a hydroxyl-containing branched monomer.
8. 8. The method of claim 7, wherein the semi-crystalline polyether is PEG 6000, the hard segment linking agent is selected from one or more of hexamethylene diisocyanate, isophorone diisocyanate, and toluene diisocyanate, and the crosslinking agent is glycerol and/or triethanolamine.
9. 9. The method of claim 7, wherein the cross-linked polyurethane solid-solid phase change material is prepared by a two-step solution polymerization method, and comprises the steps of drying polyethylene glycol in a vacuum oven to remove water, dissolving in anhydrous acetone under the protection of nitrogen atmosphere, stirring to form a homogeneous transparent solution, slowly dripping polyisocyanate and cross-linking agent into the solution according to a preset stoichiometric ratio, stirring at constant temperature to perform a prepolymerization reaction, adding a catalyst after the prepolymerization is completed, stirring to uniformly mix a reaction system, pouring into a mold, performing thermal curing in a blast drying oven, and vacuum drying the film after demolding to obtain the elastomer film.
10. 10. The programmed polyurethane solid-solid phase change material obtained by the method according to any one of claims 1 to 9.

Description

Method for improving intrinsic enthalpy value of cross-linked polyurethane solid-solid phase change material through thermo-mechanical programming Technical Field The invention belongs to the technical field of thermal energy management, and particularly relates to a crosslinked polyurethane phase change material for realizing intrinsic enthalpy enhancement by utilizing thermo-mechanical programming and a preparation method thereof. Background Phase Change Materials (PCMs) are widely used in the fields of thermal energy storage, battery thermal management, building energy conservation, and the like, because they can absorb and release a large amount of latent heat during the phase change process. In various phase change materials, the solid-solid phase change material can maintain solid characteristics in the phase change process, so that the common problems of liquid leakage and structural failure of the solid-liquid phase change material are overcome, and the solid-solid phase change material has extremely high application prospect. The Polyurethane (PU) based solid-solid phase change material is an important platform for researching high-performance thermal management materials by virtue of the adjustable phase change behavior, excellent mechanical flexibility and various molecular designs. However, the latent heat enthalpy value is used as a key index for measuring the performance of the phase change material, and directly determines the energy storage capacity of the phase change material. For polyurethane-based solid-solid phase change materials, the intrinsic latent enthalpy value is relatively low, which becomes a major bottleneck limiting their large-scale application. The core reason for this problem is that the covalent cross-linked network inside the polyurethane greatly limits the molecular chain mobility of the phase change soft segment, preventing it from forming a highly ordered crystalline structure, thus resulting in a material with limited crystallinity and reduced latent heat performance. In order to raise the enthalpy value, the prior art generally employs a method of chemically modifying or introducing an external component. For example, the phase change component is nanoconfined by grafting polar monomers onto the polymer chains to enhance intermolecular forces, or by utilizing silica nanoshells. While these methods increase energy storage density to some extent, they often rely on complex, time consuming and costly chemical synthesis processes and must incorporate exogenous components, which not only alter the original components of the material, but can also result in increased processing difficulties and reduced mechanical properties. In addition, conventional physical treatments, such as annealing or mechanical stretching above the transformation temperature, while producing a transient orientation enhancing effect, are reversible, and once the material is reheated, the entropy elasticity of the molecules dominates the relaxation of the oriented chains, allowing them to quickly revert to the original low enthalpy state. Therefore, how to realize the stable improvement of the intrinsic enthalpy value of the cross-linked polyurethane solid-solid phase change material by a simple and efficient means without introducing complex exogenous components and ensure the performance stability of the cross-linked polyurethane solid-solid phase change material in the thermal cycle process is a technical problem to be solved in the field at present. Disclosure of Invention The invention aims to solve the technical problems of limited migration of a phase change chain segment and insufficient crystallinity caused by internal covalent network constraint of the conventional cross-linked polyurethane solid-solid phase change material, and further the low intrinsic latent enthalpy value is caused. In the existing polyurethane solid-solid phase change material design, although the cross-linking points ensure the non-leakage and dimensional stability of the material, the formed microscopic physical confinement effect greatly inhibits the ordered and compact crystal domain formed by the phase change soft segment (such as polyethylene glycol chain segment), so that the energy storage density is far lower than the theoretical level, and the application potential of the polyurethane solid-solid phase change material in high-power heat dissipation scenes such as power battery thermal management is limited. The core of the invention is to use the dynamic covalent bond characteristics of the urethane bonds in polyurethane to perform a thermo-mechanical programming strategy. Through urethane bonds formed in the polymerization process of the polyurethane solid-solid phase change material, the invention utilizes the bond exchange reaction at high temperature to endow the material with topological adaptability. The strategy aims at converting an originally disordered isotropic topological state into a highly orie