Preparation And Multifunctional Innovation Of Wood-based Form-stable Composite Phase Change Materials

Phase change materials（PCMs）serve the efficient utilization of thermal energy,whose key problem lies in the morphological instability:PCMs are prone to leaking when the phase change process occurs,which will not only cause the decline of heat storage but also affect the appearance and security of surroundings.Fortunately,the natural porous structure and superb chemical reactivity of wood resources make them have potentials for application in preparing composite PCMs as form-stable package substrates.Meanwhile,the excellent compatibility of BRs also give them more chances to be functionalized for advanced applications.Therefore,in this study,natural wood was selected as the starting material to prepare the 3D scaffold with open bionic pore structure for the encapsulation of PCMs against leakage.Through a comprehensive analysis of the effects of size,space,and interface effects on the crystallization behavior of organic phase change materials with different molecular weights and functional group structures,the confinement mechanism of wood-based composite phase change energy storage materials is revealed.At the same time,a facile,efficient,and green surface modification method was introduced to make wood surpass itself with multifunctional properties for solar thermal energy storage and conversion.The specific research contents are as follows:（1）Selection of an optimal porous substrates for encapsulation of PCM according to the application requires,such as packaging capabilities,thermophysical properties,materials sources,processing properties,production costs,and environmental sustainability,is a crucial and tedious task.Therefore,Analytic Hierarchy Process（AHP）and Vlse Kriterijumska Optimisacija IKompromisno Resenje（VIKOR）technique,are introduced for substrates selection.Based on the above acquires of substrates,the valuation system of three level and six different attributes was constructed and then thoroughly evaluation was conducted by AHP and VIKOR models.The results show that the aforementioned two methods are practical and correct for selecting substrates and wood derived substrate is the optimal substrate for the encapsulation of PCMs.（2）Nanowood with the oriented microcapillary structure was prepared via selective removal of lignin in wood cell wall for encapsulation of PEG.The expansion of the pore structure on the macro and micro scales results in the packaging efficiency as high as 83.5%.The retention of hemicellulose gives the encapsulation substrate a certain mechanical strength,which can resist small external interference and ensure the stable shape of the composite material.Meanwhile,the influence of the cellulose based scaffold on the phase change performance of PEG is weakened.The as-prepared wood based composite phase change material exhibits ideal phase change temperature,ideal compression resistance,excellent dimensional stability,excellent thermal reliability and temperature regulation ability,which are very suitable for outdoor temperature in summer.（3）The interaction between the small molecule organic phase change heat storage material and the microporous/mesoporous wood-based packaging substrate was studied.Through calculation of relative crystallinity and density functional simulation,the limited phase change behavior of small molecule organic phase change heat storage materials in modified balsa wood powder is mainly caused by the influence of their free movement.This is mainly caused by the spatial size of the pore structure of the wood-based material and the hydrogen bond strength of the surface functional groups at the interface.It provides a comprehensive development of wood-based phase-change composites and obtains theoretical basis of the optimization of the encapsulant substrates and the PCMs.（4）With the positive surface charge of PEI,h-BN and PPy hybrid layer was established on the surface of delignified balsa wood scaffold via layer-by-layer assembly method.This modification process introduced the enhanced thermal conductivity and superior light to heat conversion.The optimal synthesis process was regulated,and the mechanism of h-BN and PPy synergistically enhanced heat conduction was clarified.The confinement mechanism of the embedded functional layer for the phase change behavior of the PEG in the wood substrate was explored,and the synergistic enhancement of the composite phase change material for solar thermal conversion,storage and release was realized.In addition,its superior thermal stability and thermal cycle stability make it exhibit broad prospects in the utilization of low-temperature solar heat,and expand the application fields of wood-based composite materials.（5）Natural polyphenols with rich reactivity were introduced into the functional modification of Nanowood scaffold.Tannic acid,a typical natural polyphenol that is rich in wood,are coated on the surface of nanowood via Fe³⁺coordination.Nanowood is activated by the rich catechol group of Tannic acid,so that it can serve as a platform to introduce Ag nanoparticles and octadecyl structures on wood surface through secondary reaction.While achieving enhanced packaging performance,the composite phase change material has excellent water resistance,superior solar light-to-heat conversion performance,efficient heat storage capacity,super interface compatibility,enhanced heat transfer performance,and excellent antibacterial properties.Due to the reliable environmental stability of functional wood-based energy storage composite materials,it can cope with various harsh outdoor environments,while always maintaining efficient solar energy conversion,storage and application capabilities.The material also has the potential for applications in biomedicine,medical and other aspects.At the same time,this one-step high-efficiency and multifunctional synergistic modification strategy also provides an innovative direction for the development of new advanced multifunctional composite phase change materials.