Microencapsulated Phase Change Materials Via Regenerated Chitin-Stabilized Pickering Emulsion And Its Application In Textile

Thermo-regulating textile are functional textile which developed by combining phase change materials（PCM）with fiber and textile manufacturing technology.They can absorb or release heat depending on the ambient temperature to ensure that the human body is always at a comfortable temperature range.However,PCM have disadvantages such as low thermal conductivity,combustibility,and poor stability when absorbing or releasing heat,which are not conducive to the practical application in textiles.In order to overcome these defects,microencapsulation technology is an effective and common method to obtain a core-shell microcapsule by encapsulating PCM in organic（or inorganic）shells（micro PCM）.Micro PCM can not only prevent leakage of PCM,increase heat transfer areas,but also reduce PCM reactivity with the outside environment.Emulsion templating is a common method to fabricate micro PCM.However,the abuse of surfactant has caused many environmental issues.Pickering emulsion is an emulsion,in which solid particles are used as a stabilizer.Compared to traditional emulsion,Pickering emulsion is more sustainable,biocompatible,and stable.Therefore,Pickering emulsion template method is considered to be an ideal approach to prepare micro PCM.Regenerated chitin（RCh）obtained from shrimp shells or crab shells via hydrolyzed-regenerated,has been widely used to prepare Pickering emulsions due to its sustainable,biodegradable,biocompatible properties and excellent ability to stabilize the oil-water interface.Therefore,in order to prepare thermo-regulating textiles as well as to solve the problems of leakage and low thermal conductivity of PCM,this paper will use RCh as stabilizer to fabricate micro PCM via Pickering emulsion template method and apply them to textiles.Using RCh as Pickering stabilizer to prepare micro PCM can not only reduce the use of surfactants and improve the mechanical strength and thermal stability of micro PCM,but also endow additional functionality to micro PCM by introducing other nanoparticles.The main research contents and concludes are as follows:（1）The shrimp shells were completely dissolved with phosphoric acid and poured into D.I.water to allow the reassembly of chitin.Then,the RCh suspension was obtained and RCh has a fibrillar structure.The Pickering emulsions were prepared under the Rotor stator with RCh suspension as the aqueous phase and the solution of n-octadecane and isophorone diisocyanate（IPDI）as the oil phase.After the ethylenediamine（EDA）was added into the Pickering emulsion,the IPDI and EDA were polymerized at the oil-water interface to fabricate micro PCM with polyurea shell.The parameters such as mass fraction of RCh suspension,oil/water mass ratio（O/W）and core/shell ratio were studied,and then the optimal experimental conditions for the preparation of micro PCM can be obtained:the mass fraction of RCh suspension was 0.2 wt%,the O/W was 1:9,and the core/shell ratio was 4:1.The micro PCM had a high melting enthalpy of 214.2 J/g and the encapsulation rate was 82.1%.The results of FT-IR and X-ray diffraction（XRD）showed that IPDI reacted completely under the action of excessive EDA to form polyurea shell,and the shell material did not affect the crystal structure of n-ocadecane.The leakage and leakproofness tests displayed that polyurea shell can effectively prevent the leakage and volatilization of n-octadecane,showing a good sealing performance.After 200 heating/cooling cycles,the melting enthalpy retention rate was still 99%,which showed an excellent cycling stability.（2）The Layer-by-Layer（LBL）assembly technique as a facile,flexibility and cost-effective strategy can be used to construct multifunctional thin films.However,there is little research on the preparation of flame retardant/thermo-regulating film on cotton fabric by this technique.The LBL assembly was used for introducing Micro PCM and ammonium polyphosphate（APP）to cotton fabric via the electrostatic reaction,endowing cotton with thermo-regulating and flame retardant properties,which can not only reduce the fire hazard caused by the inflammable PCM,but also broaden the application range of cotton fabric and enhance its additional value.The surface morphology of LBL assembled cotton fabric was observed by scanning electron microscope（SEM）.The results showed that the cellulose fiber was gradually covered by thin film,and Micro PCM on the surface were also gradually increased.When the number of LBL self-assembled layers reaches20（Micro PCM/APP-20）,the weight gain rate of cotton is 45%,the areal density increased by 42%,and the water vapor transmittance（WVT）decreased from 67.55 g/（m²·h）to 50.57 g/（m²·h）.The results of thermogravimetry（TG）,differential scanning calorimetry（DSC）,limiting oxygen index（LOI）and infrared thermal imaging showed that the flame retardancy of Micro PCM/APP-20 is significantly improved with an increase of LOI value from 19.9%to 24.4%and residual carbon of34.53%.It also showed a melting enthalpy of 30.09 J/g and the temperature difference is 6.4°C comparing with pure cotton fabric.After 30 laundering cycles,the residual carbon is reduced to19.64%and the melting enthalpy reduced to17.69 J/g,showing a good durability.（3）In generally,the finishing method will reduce the moisture absorption and air permeability of the textile,and the thermo-regulating property is also not durable.The introduction of micro PCM into Lyocell fibers by spinning can not only solve these problems,but also be an effective way to enhance the application value of Lyocell fibers.Therefore,in order to combine microc PCM with Lyocell fibers,on the basis of the above preparation method,the micro PCM for spinning can be obtained by a tunable oil/water mass ratio（O/W）.When the O/W ratio was 1:25（M5）,the melting enthalpy of M5 was up to 189.92 J/g,the encapsulation rate was about 77%,and the average particle size was about 4μm.UV-vis and FT-IR were used to analysis the degradation between M5 and NMMO.The results displayed that M5 had no significant decomposition effect on NMMO and could be used for the preparation of Lyocell thermo-regulating fiber.M5 were blended with Lyocell spinning solution,and prepared thermo-regulating Lyocell fibers via dry-wet spinning method.When the M5 loading was 20 wt%（Lyocell-M5@20）,SEM and XRD results showed that the introduction of M5 reduced the smoothness of the fiber as well as the crystallinity of the fiber.The DSC results displayed that Lyocell-M5@20 exhibited melting enthalpy as high as 21.07 J/g.After20 laundering cycles,the melting enthalpy of thermo-regulating Lyocell fiber was still reduced by about 9%.They also demonstrate a good durability,where 95%of the original melting enthalpy were retained after 100 heating/cooling cycles.In addition,mechanical strength tests of the fibers showed that M5 resulted in a decrease of fibers in tensile strength,but within an acceptable range.（4）The preparation of thermally conductive microcapsules with organic/inorganic hybrid shells by the Pickering emulsion template method using various thermally conductive particles as stabilizers of Pickering emulsions is an efficient strategy.Therefore,in order to improve the thermal conductivity of micro PCM and expand their application scenarios,we proposed to combine graphene nanosheets（GNPs）with RCh under hydrophilic-hydrophobic and electrostatic gravitational forces to obtain GNPs/RCh suspensions.GNPs/RCh suspension was used to stabilize Pickering emulsion,and the micro PCM(GNPs10/PU@C₂₂)with inorganic/organic hybrid shell and n-docosane(C₂₂)as core material were fabricated via Pickering emulsion template strategy.GNPs10/PU@C₂₂ exhibited the melting enthalpy as high as 199.5 J/g and high thermal conductivity of 0.65 W/（m·K）,which is 138%higher than that of pure Micro PCM.The results of infrared thermal imager showed that the surface temperature of pure Micro PCM increases by about 10°C in 360 s,while GNPs10/PU@C22 can increase by about 10°C in 140 s,indicating an efficient energy transfer efficiency.In addition,after 200 heating/cooling cycles,the melting enthalpy of GNPs10/PU@C₂₂decreased from 199.5 J/g to 196.3 J/g,a reduction of 3.2 J/g.GNPs10/PU@C₂₂ was combined with polyurethane（PU）to prepare a thermal conductive thermo-regulating film,which can successfully realize the cooling of 5G mobile phone equipment.The micro PCM(GNPs10/PU@C₁₈)with n-ocadecane as core material can also be prepared via the same strategy.They can also combine with PU to prepare composite fibers by wet spinning.The fiber can be woven and regulate the temperature of the body surface,which has a potential application value.