Design,Preparation And Functionality Of Phase Change Materials Based On Bio-based Magnolol Polymer Crosslinked Network

Phase change materials（PCMs）are considered to be the key material to solve heat energy storage and alleviate the energy crisis.Polymer-based PCMs have attracted much attention due to their advantages,such as,designability of polymer networks,low cost,degradability and large-scale preparation.In the preparation process,the renewable bio-based raw materials instead of non-renewable petroleum-based raw materials,as well as the ability to recycle and photo-cure are effective ways to achieve resource conservation,green manufacturing and sustainable energy storage.However,bio-based PCMs mainly face the following problems:first,lack of compatibility between the reported bio-based support materials（such as,cellulose）and bio-based PCMs（such as,beeswax）,so it is still a challenge to prepare form-stable phase change materials（FSPCMs）while taking into account their recyclability.In addition,the current recyclable PCMs usually require high temperature and high pressure conditions in the recycling process,so a simple and efficient recycling and reuse process is of great significance.Finally,the current multi-functional integrated PCMs are mainly prepared by blending and pre-constructing functional filler network methods,resulting in poor transparency,which is not suitable for efficient and low-energy photo-curing molding.Therefore,this paper aims to prepare bio-based recyclable FSPCM,and explore the composite PCM efficient preparation and molding process,so as to manufacture multi-functional integrated PCM with efficient and green method.Based on the above problems,the specific research content and results of this paper are as follows:1.The magnolol epoxy phase change crosslinked network containing long fatty chain structure was prepared,which improved the compatibility with bio-based PCM.The Diels-Alder（D-A）reversible chemical crosslinked point was introduced to the phase change crosslinked network for achieving the recyclability of FSPCM.Its application in the field of thermal management materials was also explored.Bio-based magnolol with easy modification was selected as raw material.Side chain crystalline difunctional epoxy monomer（DGEM-18）was prepared by hydroxyl epoxidation and the“thiol-ene”click reaction with 1-Octadecanethiol（ODT）.Then,DGEM-18 and 2-furanomethylamine（FA）were prepolymerized,and the obtained prepolymer continued to undergo Diels-Alder（D-A）reaction with bio-based bismaleimide（MA）,and finally a reversible phase change crosslinked network was prepared.The phase change crosslinked network can encapsulate beeswax,which is a bio-based phase change material with long alkyl chains,to prepare FSPCM by Van Der Waals force between ODT and MA non-polar long alkyl chain and beeswax.Its maximum phase change latent heat reaches 119.1 J/g（DGEM-18/FA/MA/1.1BW）.In addition to ODT,the raw materials are all bio-based sources in the preparation process.The thermal reversible D-A reaction endows FSPCM with recyclability,and phase change latent heat does not decrease significantly after recycling.Moreover,due to the flexible structure of MA,DGEM-18/FA/MA showed flexibility even after packaging a certain amount of beeswax.Taking DGEM-18/FA/MA/0.4BW as an example,we combined it with flexible fabric material and confirmed its potential application in the thermal management field.This is the first report about the bio-based recyclable FSPCM,which has important significance for the sustainable heat energy storage.2.In order to simplify the PCMs recovery and reuse process and improve its applicability in the thermal interface materials field,an epoxy resin-based gel PCM was prepared by chain extension/curing synergistic reaction.As a thermal interface material,PCMs are mainly faced with the contradiction between the plasticity and surface adhesion required to adapt to different microstructure surfaces and the stable packaging.Gel PCM has unique advantages to solve this problem.The DGEM-18 and 1-（3-aminopropyl）-imidazole（IM）were used as base compound and chain expansion/curing agent,respectively.IM contains primary amine and tertiary amine groups that can react with epoxy groups by two different mechanisms.Through regulating relative proportion between the DGEM-18 and IM and the curing process,the stable gel PCM was obtained.It has a stable covalent crosslinked structure,which can maintain the shape stability at high temperature;After heating to above 70℃,it shows excellent chain segment mobility and surface adhesion,and can be stably attached to a variety of substrates surface,until cooled and crystallized to form a strong adhesive force;Meanwhile,the gel PCM can be easily removed and recovered from the substrate and re-bond the substrates.The re-bonding strength has little change compared with the initial bonding.Even with high roughness surface,it can be tightly attached to the substrate,thus reducing interface thermal resistance.Because of the ODT side chain reversible crystallization,the PCM can help heat dissipation interface to control the temperature in a suitable range by absorbing heat.This research is of great significance to the preparation and application of recyclable PCMs.3.The traditional blending method cannot solve the contradiction between efficient photo-curing and multi-functional integration of PCMs.For the first time,we prepared photo-cured multi-functional composite PCM by constructing lamellar structure.The side chain crystalline difunctional allyl monomer（DGEM-18^*）was prepared by magnolol hydroxyl epoxidation and the further“epoxy-thiol”ring-opening reaction with ODT.The DGEM-18^*can undergo photo-induced“thiol-ene”click reaction to obtain phase change crosslinked networks.Using the crosslinked network as the supporting material,the phase change latent heat could reach 136.4 J/g(DGEM-18^*/2SH/3SH_BW-50)by blending with beeswax.By spraying carboxylated carbon nanotubes（CCNTs）suspension on its surface,A two-layered composite FSPCM with self-cleaning and photo-thermal conversion functions was obtained.Among them,the CCNTs,which has low surface energy and can formed micro-nano structure on the surface give the PCM surface hydrophobicity and self-cleaning functions.At the same time,the combination of CCNTs and PCM also enables PCM to have the photo-thermal conversion ability,and its efficiency can reach 75%.This is of great significance for heat energy storage,as well as the utilization of renewable and clean energy.4.On the basis of solving the contradiction between efficient photo-curing and multi-functional integration of PCMs,dynamic disulfide bond,which can cause segment rearrangement and promote the functional filler layer to be embedded in PCM surface,was introduced into the polymer phase change crosslinked network for stabilizing the interface bonding between the filler and PCM layer.The CCNTs and silver nanowires（Ag NWs）composite fillers enable PCM to integrate self-cleaning,photo-thermal conversion and electromagnetic shielding functions.The DGEM-18^*and diallyl disulfide（DADS）were mixed proportionally and then reacted with thiol curing agent to obtain phase change crosslinked networks containing disulfide bonds.Using the crosslinked network as the supporting material,the phase change latent heat could reach 113.3 J/g(DGEM-18^*/DADS/3SH₄/4SH_6-45%BW)by blending with beeswax.After successive spraying Ag NWs and CCNTs suspensions on its surface and hot pressing,the lamellar composite PCM with self-cleaning,photo-thermal conversion and electromagnetic shielding functions was finally obtained.Among them,the CCNTs,which has low surface energy and can formed micro-nano structure on the outer surface give the PCM surface hydrophobicity and self-cleaning functions.The conductive path formed by Ag NWs on the surface can give it high electromagnetic shielding performance.In addition,both Ag NWs and CCNTs have the photo-thermal conversion ability,which makes the photo-thermal conversion efficiency of the lamellar composite PCM reach 78.5%.The water contact angle,surface roughness and electromagnetic shielding property of the lamellar composite PCM before and after sandpaper abrasion experiments were quantitatively measured.It was found that the segment rearrangement effect induced by disulfide bond plays a positive role in improving the interface bonding force.For the first time,we have designed and prepared a kind of photo-curable lamellar composite PCM with photo-thermal conversion,self-cleaning and electromagnetic shielding functions.The research is of great significance for the efficient preparation of PCM,improving the energy utilization rate,adapting to the practical application environment and prolonging the service life.