Thermal Insulation Properties of Microfibrillated Cellulose Aerogel

Microfibrillated cellulose(MFC)aerogels are bio-based materials with high thermal resistance.In this study,MFC aerogels and MFC-kapok composite aerogels were prepared.A series of experiments were carried out in a climate chamber to study the influence of MFC concentration,the temperature gradient,testing methods and introduction of kapok fibers on the thermal insulation properties of aerogels.The results suggested that the density of MFC aerogels was less than 10 mg/cm3 and the porosity was higher than 99%.Besides,the minimum thermal conductivity of MFC aerogels was 0.0357 W·m-1·K-1 observed at 0.8%MFC aerogels.The minimum thermal conductivity of MFC-kapok composite aerogels was 0.0382 W·m-1·K-1 when the ratio of MFC to kapok was 2∶6.

Highly Porous Yet Transparent Mechanically Flexible Aerogels Realizing Solar-Thermal Regulatory Cooling

The demand for highly porous yet transparent aerogels with mechanical flexibility and solar-thermal dual-regulation for energy-saving windows is significant but challenging.Herein,a delaminated aerogel film(DAF)is fabricated through filtration-induced delaminated gelation and ambient drying.The delaminated gelation process involves the assembly of fluorinated cellulose nanofiber(FCNF)at the solid-liquid interface between the filter and the filtrate during filtration,resulting in the formation of lamellar FCNF hydrogels with strong intra-plane and weak interlayer hydrogen bonding.By exchanging the solvents from water to hexane,the hydrogen bonding in the FCNF hydrogel is further enhanced,enabling the formation of the DAF with intra-layer mesopores upon ambient drying.The resulting aerogel film is lightweight and ultra-flexible,which pos-sesses desirable properties of high visible-light transmittance(91.0%),low thermal conductivity(33 mW m^(-1) K^(-1)),and high atmospheric-window emissivity(90.1%).Furthermore,the DAF exhibits reduced surface energy and exceptional hydrophobicity due to the presence of fluorine-containing groups,enhancing its durability and UV resistance.Consequently,the DAF has demonstrated its potential as solar-thermal regulatory cooling window materials capable of simultaneously providing indoor lighting,thermal insulation,and daytime radiative cooling under direct sunlight.Significantly,the enclosed space protected by the DAF exhibits a temperature reduction of 2.6℃ compared to that shielded by conventional architectural glass.

Fabrication of cellulose aerogel from wheat straw with strong absorptive capacity

An effectively mild solvent solution containing NaOH/PEG was employed to dissolve the cellulose extracted from the wheat straw.With further combined regeneration process and freeze-drying,the cellulose aerogel was successfully obtained.Scanning electron microscope,X-ray diffraction technique,Fourier transform infrared spectroscopy,and Brunauer-Emmett-Teller were used to characterize this cellulose aerogel of low density(about 40 mg·cm^(–3))and three-dimensional network with large specific surface area(about 101 m2·g^(–1)).Additionally,with a hydrophobic modification by trimethylchlorosilane,the cellulose aerogel showed a strong absorptive capacity for oil and dye solutions.

Cellulose aerogels decorated with multi-walled carbon nanotubes:preparation,characterization,and application for electromagnetic interference shielding

Electromagnetic wave pollution has attracted extensive attention because of its ability to affect the operation of electronic machinery and endanger human health.In this work,the environmentally-friendly hybrid aerogels consisting of cellulose and multi-walled carbon nanotubes(MWCNTs)were fabricated.The aerogels have a low bulk density of 58.17 mg·cm^(–3).The incorporation of MWCNTs leads to an improvement in the thermal stability.In addition,the aerogels show a high electromagnetic interference(EMI)SEtotal value of 19.4 dB.Meanwhile,the absorption-dominant shielding mechanism helps a lot to reduce secondary radiation,which is beneficial to develop novel eco-friendly EMI shielding materials.

Synthesis of Mn Fe_2O_4/cellulose aerogel nanocomposite with strong magnetic responsiveness

Cellulose aerogel, with abundant three-dimensional architecture, has been considered as a class of ideal eco-friendly matrix materials to encapsulate various nanoparticles for synthesis of miscellaneous functional materials. In the present paper, hexagonal single-crystalline MnFe_2O_4 was fabricated and inserted into the cellulose aerogel using an in situ chemical precipitation method. The as-prepared MnFe_2O_4 nanoparticles were well dispersed and immobilized in the micro/nanoscale pore structure of the aerogel, and exhibited superparamagnetic behavior. In addition, the nanocomposite was easily actuated under the effect of an external magnetic field, revealing its strong magnetic responsiveness.Combined with the advantages of environmental benefits,facile synthesis method, strong magnetic responsiveness,and unique structural feature, this class of MnFe_2O_4/cellulose aerogel nanocomposite has possible uses for applications such as magnetically actuated adsorbents.

Fibrous Aerogels with Tunable Superwettability for High-Performance Solar-Driven Interfacial Evaporation

Solar-driven interfacial evaporation is an emerging technology for water desalination.Generally,double-layered structure with separate surface wettability properties is usually employed for evaporator construction.However,creating materials with tunable properties is a great challenge because the wettability of existing materials is usually monotonous.Herein,we report vinyltrimethoxysilane as a single molecular unit to hybrid with bacterial cellulose(BC)fibrous network,which can be built into robust aerogel with entirely distinct wettability through controlling assembly pathways.Siloxane groups or carbon atoms are exposed on the surface of BC nanofibers,resulting in either superhydrophilic or superhydrophobic aerogels.With this special property,single component-modified aerogels could be integrated into a double-layered evaporator for water desalination.Under 1 sun,our evaporator achieves high water evaporation rates of 1.91 and 4.20 kg m^(-2)h^(-1)under laboratory and outdoor solar conditions,respectively.Moreover,this aerogel evaporator shows unprecedented lightweight,structural robustness,long-term stability under extreme conditions,and excellent salt-resistance,highlighting the advantages in synthesis of aerogel materials from the single molecular unit.

Lightweight,Flexible Cellulose-Derived Carbon Aerogel@Reduced Graphene Oxide/PDMS Composites with Outstanding EMI Shielding Performances and Excellent Thermal Conductivities

In order to ensure the operational reliability and infor-mation security of sophisticated electronic components and to protect human health,efficient electromagnetic interference(EMI)shielding materials are required to attenuate electromagnetic wave energy.In this work,the cellulose solution is obtained by dissolving cotton through hydrogen bond driving self-assembly using sodium hydroxide(NaOH)/urea solution,and cellulose aerogels(CA)are prepared by gelation and freeze-drying.Then,the cellulose carbon aerogel@reduced graphene oxide aerogels(CCA@rGO)are prepared by vacuum impregnation,freeze-drying followed by thermal annealing,and finally,the CCA@rGO/polydimethylsiloxane(PDMS)EMI shielding composites are prepared by backfilling with PDMS.Owing to skin-core structure of CCA@rGO,the complete three-dimensional(3D)double-layer con-ductive network can be successfully constructed.When the loading of CCA@rGO is 3.05 wt%,CCA@rGO/PDMS EMI shielding composites have an excellent EMI shielding effectiveness(EMI SE)of 51 dB,which is 3.9 times higher than that of the co-blended CCA/rGO/PDMS EMI shielding composites(13 dB)with the same loading of fillers.At this time,the CCA@rGO/PDMS EMI shielding composites have excellent thermal stability(T_(HRI) of 178.3℃)and good thermal conductivity coefficient(λ of 0.65 W m^(-1) K^(-1)).Excellent comprehensive performance makes CCA@rGO/PDMS EMI shielding composites great prospect for applications in lightweight,flexible EMI shielding composites.

Utilization of discarded crop straw to produce cellulose nanofibrils and their assemblies

A tremendous amount of wheat straw(WS)has been generated by wheat crops every year,while only a small percentage is being used in applications,and most get burned on the field,causing a large amount of the exhaust gas that pollutes the environment.Herein,we report on the extraction of cellulose nanofibrils(CNF)from the alkali treated WS by a combination of 2,2,6,6-tetramethylpyperidine-1-oxyl(TEMPO)-oxidation and mechanical disintegration method.The crystalline structures,thermal properties,natural charge of the CNF were examined.The re-sultant nano-building blocks of the CNF was assembled into macroscopic cellulose materials,i.e.,film,aerogel,and filament in this work.Furthermore,the morphologies and microstructues as well as other properties of these three kinds of the CNF assemblies were investigated.The ob-tained CNF and its assemblies showed a potential application in new materials areas.This work explored a new way to utilize the discarded WS instead of being burned.

Preparation,Properties,and Applications of Natural Cellulosic Aerogels:A Review

With the depletion of fossil fuel and increasing environmental concerns,the modernized era of technology is urgently in need for sustainable and eco-friendly materials.The industrial sector certainly possesses enough resources for the production of available cost-effective,renewable,reusable,and sustainable raw materials.Ul-tralight,eco-friendly and renewable cellulosic aerogels are one of the most accentuated materials in the polymer research field due to their highly abundant and inexpensive raw material,biocompatibility,high specific surface area and other feasible properties.This review summarizes the recent progress in cellulosic aerogels,their main processing route,including a detailed description of versatile new solvents along with some essential properties of cellulosic aerogels and illustrate how their variety of chemical functionalities can be adjusted for applications in the fields of thermal insulation,fire retardant,antibacterial,CO 2 capture and energy storage systems.A de-tailed morphological analysis has been elaborated and effect of processing route,solvent medium and drying procedure on the morphology of cellulosic aerogels is also decribed.Finally,we propose some suggestions to the functionalization such as silanized cellulosic aerogels and their applications in antibacterial activity yet they are still in progress and need further study for future research.