Preparation And Temperature-sensitive Response Of PLA/PEG Phase-change Energy Storage Conductive Composites

Phase change energy storage materials（PCMs）are typical latent heat and thermal energy storage forms in the process of phase transformation caused by external temperature environment,which is widely used in the direction of energy storage.Conductive polymer composites（CPCs）can relieve energy pressure,is a low cost,light weight,easy to process,corrosion resistance,easy to carry,environmental friendly with excellent electrical properties of the composite material;In this paper,the combination of PCMs material and CPCs material aims to give the material excellent energy storage characteristics under the condition of high conductivity.Using polyethylene glycol（PEG）and polylactic acid（PLA）two-phase biodegradable polymer as the research object,adding carbon nanotubes（MWCNTs）filler,through the characterization of its temperature-sensitive response and photosensitive response,The energy storage effect of the material was deeply explored,and thermal conductivity filler boron nitride（BN）,aluminum oxide（Al₂O₃）and copper（Cu）were introduced to improve the thermal conductivity of the material,and the change of its energy storage effect was observed.Firstly,PLA/MWCNTs/PEG composites were prepared by solution-melt blending method.When 30 wt%PEG was added,the initial crystallization temperature of the composites increased from 109.2℃to 126.5℃,and the maximum relative crystallinity reached 65.6%.The analysis of mechanical properties showed that the addition of PEG could improve the toughness of the composites,and the elongation at break increased from 11.2%to 160.6%.The results of isothermal resistance test show that PLA/MWCNTs/PEG composites have high electrical conductivity stability.With the increase of isothermal temperature,PLA/MWCNTs/PEG composites realized the transition from PTC to NTC effect.In addition,the cyclic resistance test at different temperatures showed that the maximum resistance value increased with the increase of heat treatment temperature,and the sensitivity of the composite was improved.When the heat treatment temperature of the composite T_end to be 140℃～150℃,the energy storage effect of PEG becomes particularly significant in the cooling process,which can release energy to maintain the stability of the resistance properties of the composite.Secondly,PEG/PLA/MWCNTs composites were prepared by solution method using PEG as matrix and PLA and MWCNTs as supporting structures.The microstructure of MWCNTs in PEG matrix composites was found to be similar to"isolated"structure,forming a uniform and continuous conductive network.Therefore,the conductivity of PEG matrix composites is significantly improved compared with that of PLA matrix composites,and the percolation threshold is as low as 0.13wt%.In addition,theΔR/R₀ values of PEG/PLA/CNTs composites increase with the increase of temperature,showing the PTC effect.When the circulating temperature reaches100℃,theΔR/R₀ values of PEG/PLA/CNTS composites decrease at high temperature,showing the NTC effect.In addition,during the cooling process,the composite material shows a good energy release platform,and with the circulation temperature increasing from 100℃to 140℃,the width of the energy release platform becomes wider,up to37.2min,and the energy storage effect is significantly improved.It is found in the simulation light source test that the composite can show the energy storage effect under different light intensity,and theηof the composite with 0.6wt%MWCNTs reaches 42.9%under 150m W/cm2 light intensity,and increases with the increase of light intensity.The endothermic and exothermic behaviors of the energy storage effect under light were further verified by thermal infrared imaging characterization.Compared with 0.1wt%and 2.0wt%,the composite material with 0.6wt%MWCNTs is more sensitive to light under the condition of good current stability,and can produce an energy storage platform earlier after the light is turned off.In addition,it was found that the composite with 0.6wt%MWCNTs maintained good thermal cycle stability and chemical structure by DSC and infrared tests before and after 100 cycles.In the shape stability test of the same sample,no leakage occurred at 160℃.Finally,in order to improve the thermal conductivity of composites to further improve its phase-change energy storage effect,the heat transfer performance of composites was improved by the physical hybridization of MWCNTs with ceramic thermal conductivity filler BN,metal oxide Al₂O₃ and metal thermal conductivity filler Cu,and the influence of the addition of thermal conductivity particles on the energy storage effect of composites was further explored.The presence of the three fillers all reduces the electrical conductivity of the composites.However,the electrical conductivity of the composites can be improved with the increase of the content of Al₂O₃ and Cu,while the increase of the content of BN significantly reduces the electrical conductivity of the composites.By observing the EDS spectrum,it is found that the distribution of Al₂O₃ in the composite is the most uniform,and the improvement of the thermal conductivity of the composite is the most obvious.When the content of Al₂O₃ is 40wt%,the thermal conductivity andΦvalue are up to 5.81 W/m·K and363.6%,respectively.Cu is a large area of agglomeration,unable to form a continuous heat conduction network.According to the cyclic temperature-resistance characterization,energy storage release effect occurred only after Al₂O₃ was added to the composite,and the composite with Al₂O₃ added still showed obvious energy storage phenomenon in all test temperature intervals after the temperature interval increased.It is found that under the same illumination intensity,Al₂O₃ can greatly improve the photothermal conversion efficiency of the composites compared with BN and Cu,ηincreases from 42.9%to 72.9%.Similarly,the presence of Al₂O₃ plays a positive role in improving the photosensitive response rate and current stability of the composites.According to the stability test,the stability of composite materials can still maintain excellent level after the addition of Al₂O₃.