The Preparation And Thermophysical Properties Of Kevlar Fiber Based Composite Phase Change Materials

Thermal energy storage technology based on shape stabilized phase change materials（ss PCMs）can solve the problems of easy leakage and low thermal conductivity of single-phase change materials（PCM）,but ss PCM still has some shortcomings,such as poor flexibility and passive energy storage.In order to solve the above problems,the project employing Kevlar nanofibers（KNFs）as the confinement carrier,polypyrrole and silver nanowires as the high absorbance filler,prepared the Kevlar nanofiber-based composite phase change material with active energy conversion and heat storage function,investigated the morphology,structure and photo/electro-thermal conversion properties of the composite PCM and explored the influence of KNF on the thermo-physical properties of composite PCMs.The KNF/PF aerogel was prepared by sol-gel method,employing KNFs as the confinement carrier,paraffin（PF）as PCM.Based on this,the polypyrrole（PPY）was deposited on KNF/PF aerogel by in-situ polymerization method,endowing KNF/PF aerogel with photothermal conversion performance,exploring the influence of KNF on the thermophysical properties of KNF/PF and investigating the effect of PF ratio on the phase transition behavior and photo/electro-thermal conversion properties of PPY-KNF/PF.The results showed that due to the excellent hydrogen bond self-assembly performance of KNF,PF in KNF/PF80 was embedded between nanofibers and maintained shape stability,and its leakage rate was less than 1%.The actual latent heat of KNF/PF were lower than the theoretical latent heat due to the non-melting layer formed by the interface interaction of PF and KNF matrix,and the proportion of non-melting layer enlarged with the increase of PF content.Although the introduction of PPY reduced the phase change enthalpy of KNF/PF,it endowed KNF/PF with photo/electro-thermal conversion performance.The PPY-KNF/PF60 and PPY-KNF/PF80 with the PPY loading rate of 16.3%performed excellent cycling stability,the melting enthalpy of PPY-KNF/PF60 and PPY-KNF/PF80 were 74.3 J·g^-1 and 101.9J·g^-1,the photothermal conversion efficiency were 85.2%and 74.9%(250 m W·cm^-2)and the electrothermal conversion efficiency were 82.9%and 75.7%（5.0 V）,respectively.In order to improve the flexibility of composite PCM,expand the application field of PCM in hyperthermia and medical dressings and explore the influence of carrier on the crystallization behavior of composite materials,a flexible and thin composite film（AKD）was prepared by using KNF as confinement carrier,docosane（DE）as PCM and introducing silver nanowires（Ag NWs）with antibacterial property and active photothermal conversion performance.The results showed that due to hydrogen bond interaction,DE and Ag NWs were bounded in the layered structure of AKD film and maintained shape stability.Compared with the theoretical latent heat,the latent heat of AKD film decreased due to the presence of non-melting layer.On the other hand,due to the strong interfacial interaction between KNF and DE,there were not only non-melting layer but also transitional confinement layer in the composites.Therefore,a hierarchical phase transition model of non-melting layer,transitional confinement layer and bulk layer was proposed.The pilot-scale film with the thickness of 1.54 mm could rapidly rise to 50°C in 402 s and maintained the temperature from 50°C to 37°C for about 18 min.The rapid photo-thermal response and stable heat release performance make AKD promising to be used as thermal compress therapy.In addition,the kinetic analysis results of non-isothermal crystallization showed that the introduction of KNF confinement carrier reduced the crystallization rate of composite PCM and inhibited the crystallization of PCM.This paper provides the basic research for further understanding of the influence of confinement effect on the thermophysical properties of PCM.In conclusion,the interfacial interaction between KNF limited carrier and PCM could lead to the appearance of non-melting layer or transitional confinement layer,thus reducing the latent heat of composite PCM.