Preparation And Performance Study Of Solid-Solid Phase Change Material Of Oil-Based Resin

Fatty acids as phase change materials have the advantages of suitable melt-crystallization temperature range,high heat capacity,low subcooling,low vapor pressure,non-toxicity,non-corrosive to metal containers,excellent chemical and thermal stability,low cost,small volume change and wide source.However,the preparation of phase change materials using vegetable oil fatty acids such as stearic acid（SA）as the phase change matrix suffers from the leakage problem of solid-liquid phase change materials,which severely limits their applications.Currently,most of them are prepared as solid-solid phase change materials by encapsulation in microcapsule shells and porous scaffolds to solve the leakage problem,but the leakage problem only can be fundamentally solved by connecting the phase change components through polymer networks with chemical bonds.Nevertheless,the preparation of solid-solid phase change materials by polymer networks also has the disadvantage of low actual enthalpy,which greatly limits its application.The domestic and international researches for the above problems have generally focused on the inter-binding interaction between their chain segments.Therefore,there is an urgent need to investigate the influencing factors limiting the phase change process by in situ characterization,which can be used to guide the molecular design and synthesis of polymeric solid-solid phase change materials,and provide new pathways and ideas to solve the problem of low enthalpy,so as to broaden the scope of their applications.In this paper,the sustainable vegetable oil,SA and tung oil acid,were selected as raw materials and polymerized into oleyl resin solid-solid phase change materials through polyol modification.Firstly,in order to study the effect of the interplay between the phase change elements and the resin network at the small molecular scale on the enthalpy of the solid-solid phase change materials of oleaginous resins,the material ratio of SA was changed to obtain three kinds of solid-solid phase change materials of oleaginous resins modified with different SA contents;Secondly,in order to fabricate oleoresin solid-solid phase change materials with higher phase change enthalpy,stable morphology and no melt leakage above the phase change temperature,sorbitol was introduced to replace pentaerythritol as the skeleton support material,and the effect of sorbitol on the phase change enthalpy of oleoresin solid-solid phase change materials was analyzed;Finally,to further expand the application scope of oleoresin solid-solid phase change materials,styrene was selected to copolymerize with the monomer of phase change materials to obtain oleoresin solid-solid phase change materials with shape memory function.The main research results are as follows:（1）Shape-stable,leak-free,thermally cyclically stable and heat-insulating oleoresin-based resin solid-solid phase change materials were prepared with SA as the phase change matrix and a cross-linked network of pentaerythritol-modified oleoresin-based resin as the support material.The phase transition temperatures of the three pentaerythritol-modified oleoresin solid-solid phase change materials（PSSPCMs）were 13.3,25.6 and 25.3℃,and the enthalpies of phase transition were 35.53,48.63 and 49.82 J/g,respectively,but the actual enthalpies were lower than the corresponding theoretical enthalpies（43.82,83.35 and 119.20 J/g）.XRD and non-isothermal kinetic analyses exhibited that the crystallinity and activation energy of PSSPCMs were lower compared to pure SA,indicating that the polymer network restricted the crystallization of SA fragments,which resulted in lower enthalpy of phase transition.The results of second-order derivative IR spectra and two-dimensional correlation IR spectra showed thatν_asCH₃,ν_asCH₂,νCH,ν_sCH₃ andν_sCH₂ of SA changed significantly during the phase transition,while onlyν_asCH₂ andν_sCH₂ changed notably in the PSSPCMs.From the above results,it could be seen that the vibrations ofν_asCH₃,νCH andν_sCH₃ were limited due to the highly cross-linked polymer network,which leaded to incomplete crystallization of SA and reduced the phase transition enthalpy of PSSPCMs contributed by SA.（2）The sorbitol-modified oleoresin cross-linked network was used as the support material,while the material ratio of the phase change substrate SA in the synthesis of monomers was increased to prepare oleoresin solid-solid phase change materials with stable shape,no leakage and good thermal insulation and heat storage properties.The theoretical enthalpy values of the sorbitol-modified oleoresin solid-solid phase change material（PSSPCM4）and PSSPCM3 which had the highest enthalpy of phase change among PSSPCMs,were basically the same,while the actual enthalpy value of PSSPCM4 was 33.57 J/g higher than that of PSSPCM3,which was 67.74%higher and had better thermal cycling stability.XRD patterns,non-isothermal kinetics and C-H evolution analysis revealed that when polyols vacate more hydroxyl groups while connecting SA,it was not only facilitates the esterification reaction,but also facilitates the melting and crystallization of SA fragments.In addition,the activation energy and the vibrational sensitivity of the C-H group were improved,which resulted in excellent crystallization properties of the solid-solid phase change material of the oil-based resin,thus improving its actual phase change enthalpy.In conclusion,the method in this study can provide a theoretical basis for solving the molecular design of high enthalpy solid-solid phase change materials.（3）On the basis of improving the phase change enthalpy value of the oil-based resin solid-solid phase change material,the monomer of PSSPCM4 was used to copolymerize with styrene to prepare the oil-based resin solid-solid phase change material（PSSPCM4-PS）with stable shape,no leakage,good thermal insulation and heat storage properties,and shape memory function.Due to the introduction of styrene,the relative molecular mass fraction of SA in PSSPCM4-PS was reduced,resulting in a lower actual phase change enthalpy of 7.65 J/g for PSSPCM4 than PSSPCM4,but it also had the same good thermal cycling stability as PSSPCM4.PSSPCM4-PS could recover to its original shape when heated at 100℃for 80 s This indicated that PSSPCM4-PS had good controllable shape fixation and recovery behavior.Combining the above advantages,PSSPCM4-PS could not only be better used in daily thermal insulation and thermal storage coatings,but also could be treated as a flexible matrix material,so the oil-based resin solid-solid phase change material could be further expanded to the field of intelligent materials.