Preparation And Properties Of Cellulose-based Composites For Radiation Regulation And Energy Saving

Efficient regulation of solar and thermal radiation is a new energy-saving strategy that requires no power input and has no greenhouse gas emissions.It provides a new way for improving energy efficiency,alleviating energy consumption and global climate change,and shows huge energy-saving potential in buildings,automobiles,and other fields.For the radiation regulation requirements in different application scenarios,materials need to have spectral properties that match the requirements to achieve synergistic modulation of multi-band lights（visible（VIS）,near-infrared（NIR）,mid-infrared（MIR））.Based on the concept of green development,eco-friendly and sustainable cellulose and its derivatives are widely used in the field of radiation regulation and energy-saving because of their excellent optical properties.However,single-component cellulose and its derivative materials have limited spectral modulation range and cannot directly meet the needs of different applications.Therefore,based on cellulose and its derivatives,this thesis develops cellulose-based composites with multi-band radiation regulation properties through micro-nano structure design and combination of materials with different optical properties,and explores their radiation regulation strategies in the VIS-NIR-MIR bands and their potential in energy-saving applications.The main contents are as follows:（1）In the VIS-NIR bands,cellulose-based dual-band electrochromic materials capable of the spectrally selective modulation of VIS light and NIR light are developed for selective regulation of solar radiation.Nb-Ti O2 nanocrystals with VIS-NIR dual-band independent modulation properties were synthesized by a simple hydrothermal method.Ethyl cellulose（EC）was selected as the polymer binder to enhance the adhesion to the conductive substrate.Uniform and compact EC/Nb-Ti O2 composite films were prepared by a room temperature spraying process.The composite film has wide optical modulation range in the full solar spectrum with 92.9%VIS light modulation and 95.0%NIR light modulation,showing an impressive dual-band electrochromic performance.A prototype dual-band electrochromic assembled device based on the composite film has three operating modes of bright,cool,and dark by controlling the applied potentials.And the temperature difference of the light absorbing material between the bright and cool,cool and dark operating modes is about12°C and 18°C,respectively,which realizes intelligent management of solar light and solar heat.（2）Extending the spectrum to the MIR thermal radiation band,cellulose-based radiative cooling materials with ultra-high solar reflectance and infrared emittance are prepared for synergistic modulation of solar-thermal radiation.EC/Ba SO4 radiative cooling coating with ultra-high solar reflectance（98.6%）and thermal emittance（98.1%）were constructed by simple processes such as brushing and rolling,using eco-friendly EC as the polymer matrix,Ba SO4 NPs with large electronic band gaps as the optical scatterer,and green solvents（ethanol and water）to construct porous structures.Field test showed that the EC/Ba SO4 composite achieved a sub-ambient temperature drop of over 2.5°C under a solar intensity of～920 W m^-2,and the theoretical simulation results showed that the composite materials can save 6%～23%of the energy for cooling.（3）In the VIS-NIR-MIR bands,cellulose-based composite films with adaptive switching of radiation regulation on/off state are further explored for adaptive modulation of solar-thermal radiation.Cellulose-based composite films with a three-layer architecture,including cellulose nanofiber（CNF）/carbon nanotube（CNT）layer,EC/CNT layer and silver infrared-reflecting layer,were prepared by a traditional liquid casting method and magnetron sputtering techniques.The films are capable of adaptively regulating solar-thermal radiation due to the synergistic effect of the light-adaptive self-folding motion of the films and the radiation dissipation suppression of the silver layer.In addition,light-adaptive shutters（LAS）were designed based on the cellulose-based composite films,and the theoretical power calculation results showed that LAS suppressed the radiative heat dissipation by 20 times,and achieved a near-zero net radiative heat dissipation.Furthermore,a LAS was demonstrated to enhance the temperature by～23℃in a 3-day field test,showing high-efficiency photothermal storage performance.