Hybrid aerogels have been prepared by freeze-drying technique after mixing water dispersions of cellulose microfibers or cellulose nanofibers and silica(SiO2)of type SBA-15(2D-hexagonal).The prepared composites were c...Hybrid aerogels have been prepared by freeze-drying technique after mixing water dispersions of cellulose microfibers or cellulose nanofibers and silica(SiO2)of type SBA-15(2D-hexagonal).The prepared composites were characterized by different analysis techniques such as SEM,hot-filament,DMA,etc.These composites are compared to those previously prepared using nanozeolites(NZs)as mineral charge.The morphology studied by SEM indicated that both systems have different structures,i.e.,individual fibers for cellulose microfibers WP-based aerogels and films for nanofibrillated cellulose NFC-based ones....These differences seem to be driven by the charge of the particles,their aspect ratio and concentrations.These hybrid materials exhibit tunable thermal conductivity and mechanical properties.The thermal conductivity values range between^18 to 28 mW.m^-1.K^-1 and confirm the superinsulation ability of these fibrous aerogels.Synergism on the thermal insulation properties and mechanical properties was shown by adjunction of mineral particles to both cellulose-based aerogels by reaching pore size lower than 100 nm.It significantly reduces the thermal conductivity of the hybrid aerogels as predicted by Knudsen et al.Furthermore,the addition of mineral fillers to aerogels based on cellulose microfibers induced a significant increase in stiffness.展开更多
This paper reports green nanocomposites made by blending polyvinyl alcohol(PVA)with cellulose nanofiber(CNF)isolated from recycled deinked copy/printing paper(DIP).The reinforcement effect of DIPCNF in the nanocomposi...This paper reports green nanocomposites made by blending polyvinyl alcohol(PVA)with cellulose nanofiber(CNF)isolated from recycled deinked copy/printing paper(DIP).The reinforcement effect of DIPCNF in the nanocomposites is compared with other CNFs isolated from native cotton and hardwood by means of TEMPO-oxidation.The prepared PVA-CNF nanocomposites are characterized in terms of morphology,chemical interaction,structural,thermal and mechanical properties.X-ray diffraction and Fourier transform infrared spectroscopy confirm the reinforcing ability of cellulose nanofibers into PVA.By blending CNFs into PVA matrix,the thermal stability of the nanocomposites is improved and DIPCNF shows similar enhancement effect with COCNF and HWCNF.The prepared nanocomposites exhibit 50%Young’s modulus improvement by adding 6%of CNF and DIPCNF exhibits similar enhancement of the mechanical properties to COCNF and HWCNF in the nanocomposites.This indicates that the use of DIPCNF is beneficial for environment protection,resource retaining and save energy in comparison with COCNF and HWCNF.展开更多
The intelligent electronic devices have urgent demands for electromagnetic interference(EMI)shielding films with excellent heat dissipation capability.However,it is challenging to obtain excellent EMI shielding and th...The intelligent electronic devices have urgent demands for electromagnetic interference(EMI)shielding films with excellent heat dissipation capability.However,it is challenging to obtain excellent EMI shielding and thermal conductivity performances simultaneously.Herein,inspired by mille-feuille structure,the multifunctional EMI shielding films developed by a layer-by-layer self-assembly and hot-pressing strategy.The ingenious introduction of silver nanoparticles(AgNPs)with large specific surface area and highly conductive into the network formed by TEMPO-oxidized cellulose nanofibrils(TOCNFs)with large aspect ratio to form the TOCNFs/AgNPs.And the graphene nanoplates(GNPs)with high conductivity loss distributed alternately with TOCNFs/AgNPs to construct mille-feuille structure,which had highly efficient conductive network,complete thermally conduction pathway and rich heterogeneous interfaces.Consequently,the designed films presented high electrical conductivity of 8520 S/cm,superb EMI effectiveness(SE)of 98.05 dB,and excellent thermal conductivity of 18.82 W/(m·K).Furthermore,the films possessed outstanding Joule heating performances with low voltages,including high heating temperature(100℃),fast response time(<20 s),and impressive heating stability and reliability.Thus,such high-performance EMI shielding films with fascinating thermal conductivity and Joule heating performances have substantial application in flexible electronics,electromagnetic waves shielding and thermal management.展开更多
Two different chemical methods, TEMPO-oxidation and nitro-oxidation, were used to extract carboxyl cellulose nanofibers(CNFs) from non-wood biomass sources(i.e., jute, soft and hard spinifex grasses). The combined TEM...Two different chemical methods, TEMPO-oxidation and nitro-oxidation, were used to extract carboxyl cellulose nanofibers(CNFs) from non-wood biomass sources(i.e., jute, soft and hard spinifex grasses). The combined TEMPO-oxidation and homogenization approach was very efficient to produce CNFs from the cellulose component of biomass;however, the nitrooxidation method was also found to be effective to extract CNFs directly from raw biomass even without mechanical treatment.The effect of these two methods on the resulting cross-section dimensions of CNFs was investigated by solution small-angle Xray scattering(SAXS), transmission electron microscopy(TEM) and atomic force microscopy(AFM). The UV-Vis spectroscopic data from 0.1 wt% TEMPO-oxidized nanofiber(TOCNF) and nitro-oxidized nanofiber(NOCNF) suspensions showed that TOCNF had the highest transparency(> 95%) because of better dispersion, resulted from the highest carboxylate content(1.2 mmol/g). The consistent scattering and microscopic results indicated that TOCNFs from jute and spinifex grasses possessed rectangular cross-sections, while NOCNFs exhibited near square cross-sections. This study revealed that different oxidation methods can result in different degrees of biomass exfoliation and different CNF morphology.展开更多
文摘Hybrid aerogels have been prepared by freeze-drying technique after mixing water dispersions of cellulose microfibers or cellulose nanofibers and silica(SiO2)of type SBA-15(2D-hexagonal).The prepared composites were characterized by different analysis techniques such as SEM,hot-filament,DMA,etc.These composites are compared to those previously prepared using nanozeolites(NZs)as mineral charge.The morphology studied by SEM indicated that both systems have different structures,i.e.,individual fibers for cellulose microfibers WP-based aerogels and films for nanofibrillated cellulose NFC-based ones....These differences seem to be driven by the charge of the particles,their aspect ratio and concentrations.These hybrid materials exhibit tunable thermal conductivity and mechanical properties.The thermal conductivity values range between^18 to 28 mW.m^-1.K^-1 and confirm the superinsulation ability of these fibrous aerogels.Synergism on the thermal insulation properties and mechanical properties was shown by adjunction of mineral particles to both cellulose-based aerogels by reaching pore size lower than 100 nm.It significantly reduces the thermal conductivity of the hybrid aerogels as predicted by Knudsen et al.Furthermore,the addition of mineral fillers to aerogels based on cellulose microfibers induced a significant increase in stiffness.
文摘This paper reports green nanocomposites made by blending polyvinyl alcohol(PVA)with cellulose nanofiber(CNF)isolated from recycled deinked copy/printing paper(DIP).The reinforcement effect of DIPCNF in the nanocomposites is compared with other CNFs isolated from native cotton and hardwood by means of TEMPO-oxidation.The prepared PVA-CNF nanocomposites are characterized in terms of morphology,chemical interaction,structural,thermal and mechanical properties.X-ray diffraction and Fourier transform infrared spectroscopy confirm the reinforcing ability of cellulose nanofibers into PVA.By blending CNFs into PVA matrix,the thermal stability of the nanocomposites is improved and DIPCNF shows similar enhancement effect with COCNF and HWCNF.The prepared nanocomposites exhibit 50%Young’s modulus improvement by adding 6%of CNF and DIPCNF exhibits similar enhancement of the mechanical properties to COCNF and HWCNF in the nanocomposites.This indicates that the use of DIPCNF is beneficial for environment protection,resource retaining and save energy in comparison with COCNF and HWCNF.
基金support of the National Natural Science Foundation of China(Nos.31901265,22178208)the Key Technology R&D Program of Longyou County(No.JHXM2019063).
文摘The intelligent electronic devices have urgent demands for electromagnetic interference(EMI)shielding films with excellent heat dissipation capability.However,it is challenging to obtain excellent EMI shielding and thermal conductivity performances simultaneously.Herein,inspired by mille-feuille structure,the multifunctional EMI shielding films developed by a layer-by-layer self-assembly and hot-pressing strategy.The ingenious introduction of silver nanoparticles(AgNPs)with large specific surface area and highly conductive into the network formed by TEMPO-oxidized cellulose nanofibrils(TOCNFs)with large aspect ratio to form the TOCNFs/AgNPs.And the graphene nanoplates(GNPs)with high conductivity loss distributed alternately with TOCNFs/AgNPs to construct mille-feuille structure,which had highly efficient conductive network,complete thermally conduction pathway and rich heterogeneous interfaces.Consequently,the designed films presented high electrical conductivity of 8520 S/cm,superb EMI effectiveness(SE)of 98.05 dB,and excellent thermal conductivity of 18.82 W/(m·K).Furthermore,the films possessed outstanding Joule heating performances with low voltages,including high heating temperature(100℃),fast response time(<20 s),and impressive heating stability and reliability.Thus,such high-performance EMI shielding films with fascinating thermal conductivity and Joule heating performances have substantial application in flexible electronics,electromagnetic waves shielding and thermal management.
基金supported by the Polymer Program from Division of Materials Science of the National Science Foundation of USA(Grant No.DMR-1808690)supported by an NIH-NIGMS(Grant No.P41GM111244)
文摘Two different chemical methods, TEMPO-oxidation and nitro-oxidation, were used to extract carboxyl cellulose nanofibers(CNFs) from non-wood biomass sources(i.e., jute, soft and hard spinifex grasses). The combined TEMPO-oxidation and homogenization approach was very efficient to produce CNFs from the cellulose component of biomass;however, the nitrooxidation method was also found to be effective to extract CNFs directly from raw biomass even without mechanical treatment.The effect of these two methods on the resulting cross-section dimensions of CNFs was investigated by solution small-angle Xray scattering(SAXS), transmission electron microscopy(TEM) and atomic force microscopy(AFM). The UV-Vis spectroscopic data from 0.1 wt% TEMPO-oxidized nanofiber(TOCNF) and nitro-oxidized nanofiber(NOCNF) suspensions showed that TOCNF had the highest transparency(> 95%) because of better dispersion, resulted from the highest carboxylate content(1.2 mmol/g). The consistent scattering and microscopic results indicated that TOCNFs from jute and spinifex grasses possessed rectangular cross-sections, while NOCNFs exhibited near square cross-sections. This study revealed that different oxidation methods can result in different degrees of biomass exfoliation and different CNF morphology.
