Preparation And Properties Of Phase Change Insulation Materials By Pickering Emulsification Method

With the rapid development of society and economy and the improvement of people’s living standard,energy and environment problems have been paid more and more attention.Phase change material（PCM）is a kind of functional material which can absorb and release a lot of energy in the form of latent heat during the phase change process.It has great application prospect in the fields of environmental protection,engineering protection,thermal management and so on.However,there are some problems such as high cost,easy leakage and undercooling.By Pickering emulsification process,phase change insulation materials with better environmental protection,good biocompatibility and high environmental stability can be obtained.Natural polysaccharide polymers（such as chitin and cellulose）have many advantages as Pickering’s emulsion,such as high emulsion stability,biosafety and renewable.The use of polysaccharide materials is of great significance to solve the problems of traditional surfactants,such as high pollution,high recovery cost and poor stability.In order to further improve the performance of heat insulation,it is necessary to reduce heat dissipation.Aerogel is a very light and highly porous insulation material that is an excellent choice for heat management applications.However,hydrophobic aerogel is difficult to be mixed in wet state,and the aerogel itself is low density and easy to float,resulting in poor dispersion effect and practical application effect of aerogel.By using the high viscosity of hydrophilic polymer solution and the hydrophilic and hydrophobic difference between the hydrophilic and aerogel,the aerogel can be coated with polymer molecular chains under the action of strong external stirring,so as to achieve good dispersion of aerogel while preserving its pore structure.Paraffin Wax microcapsules were prepared using biological polysaccharide nanomaterials as paraffin wax emulsion.The effects of p H value,ionic environment,solid content of nanocrystalline suspension,emulsification temperature and other factors on the stability of emulsion were investigated.Furthermore,the prepared phase change microcapsules were combined with silica aerogel material dispersed in PVA solution.The prepared composite material has good energy storage and temperature control performance,and can be used in the field of building insulation material.The main research contents and relevant conclusions are as follows:（1）The main research contents and relevant conclusions are as follows:Chitin and cellulose were nano-treated to obtain stable and dispersed amino-chitin nanocrystals and carboxyl cellulose nanocrystals suspensions.The effects of different p H conditions on emulsification performance of chitin nanocrystalline were investigated.Under acidic conditions,Ch NCs disperse stably in water phase,but the emulsification effect is poor.Under neutral conditions,Ch NCs had the highest emulsification ability,the Pickering emulsion was the most stable,the emulsion droplet size was the smallest（5μm）and the distribution was uniform.Under alkaline conditions,the emulsion showed the emulsification ability between acidic and neutral,and the size of the emulsion reached tens of microns.The influence of ionic environment on emulsification performance of cellulose nanocrystalline was also investigated.Emulsifying system with CNCs dispersion or 50 m M/L Fe Cl₃ aqueous solution alone,emulsification failure leads to paraffin stratified crystallization and loss of emulsion fluidity.When 50 m M/L Fe Cl₃was added into the emulsion system of CNCs dispersion,the emulsion was uniform milky white and had fluidity.The improvement of emulsifying effect by Fe Cl3 may be due to the coordination between Fe³⁺and the hydroxyl group on CNCs,which enlarged the aggregation size of CNCs and enabled it to cover the paraffin surface.（2）PW microcapsules with cellulose nanocrystals as shells（PW@CNC）were prepared by using cellulose nanocrystals as emulsifier of PW-Pickering emulsion.The influence of different concentrations of CNCs on emulsion stability was studied.When the concentration of CNC increased from 0.1 to 1wt%,the size of emulsion drops decreased significantly,and the emulsion stability improved.The influence of temperature on the interfacial tension was also studied.With the increase of temperature,the interfacial tension of oil and water decreased.The interfacial tension finally stabilized at 35 m N/m at 40℃and decreased below 25 m N/m at 60℃.In order to verify the universality and practicability of the emulsification method adopted in this work,paraffin wax with different melting points was selected as phase change material,and CNCs was used for Pickering emulsion encapsulation.The range of temperature control of phase change thermal insulation composites is expanded through the universality experiment,so that it has a wider application value.（3）Cellulose nanocrystalline phase change microcapsules and Si O₂aerogel were dispersed into PVA solution as dispersing phase,and the thermal insulation material with both thermal insulation and energy storage functions was prepared by freeze-drying process（PW@CNC/PVA@Si O₂）.The thermal diffusion coefficient of the prepared composite is only 0.18 mm²/s,which is much lower than common thermal insulation materials in the market.The material also has good temperature regulation performance,can be used as building insulation material.The preparation of double layer insulation material by the combination of phase change material and aerogel material is also a relatively novel work,which plays an important role in the development of insulation material application field.Based on the above research,this work successfully prepared paraffin phase change microcapsules by Pickering emulsification method,and realized the combination of phase change materials and aerogel materials to obtain a functional composite material with both thermal insulation and energy storage effects.This work promotes the research of emulsification properties and high value-added applications of Pickering emulsions,and expands the application range of Pickering emulsions and phase change materials.