Cellulose nanocrystals （CNCs） of rod-like shape were prepared from degreased cotton using sulfuric acid hydrolysis. The obtained CNC suspension was neutralized using a sodium hydroxide solution to remove the...Cellulose nanocrystals （CNCs） of rod-like shape were prepared from degreased cotton using sulfuric acid hydrolysis. The obtained CNC suspension was neutralized using a sodium hydroxide solution to remove the residual sulfuric acid and improve the thermal stability of the CNC particles. Then, poly（ethylene oxide） （PEO） was employed to modify the nanocrystals through entanglement and physical adsorption. The goal was to further improve the thermal stability and weaken the hydrophilicity of CNCs. Original and modifed CNCs were dosed into a polylactic acid （PLA） matrix to prepare nanocomposites using a hot compression process. Results of the thermogravimetric analysis showed that the initial thermal decomposition temperature of the modifed CNCs showed a 120℃ improvement compared to the original CNCs. That is, the thermal stability of the modified CNCs improved because of their shielding and wrapping by a PEO layer on their surface. Results from scanning electron microscopy and ultraviolet-visible spectrophotometry showed that the compatibility of the modifed CNCs with organic PLA improved, which was attributed to the compatibility of the PEO chains adsorbed on the surface of the CNCs. Finally, the results of tensile tests indicated a significant improvement in terms of breaking strength and elongation at the break point.展开更多
As candidate thermal/environmental barrier coatings(T/EBCs),the structure characteristics and comprehensive properties of monoclinic-prime(m')RETaO4(RE=Yb,Lu,Sc)with excellent Al2O3/SiO2 chemical compatibility are...As candidate thermal/environmental barrier coatings(T/EBCs),the structure characteristics and comprehensive properties of monoclinic-prime(m')RETaO4(RE=Yb,Lu,Sc)with excellent Al2O3/SiO2 chemical compatibility are studied.Excellent thermal insulation protection will be provided by m'RETaO4 due to their low thermal conductivity(~1.6 Wm^-1 K^-1,900℃)and prominent thermal radiation resistance,which is much better than those of YSZ(~2.5 Wm^-1 K^-1,1000℃)and La-12 Zr2O7(~2.0 Wm^-1 K,900℃).The thermal expansion coefficients(TECs)are 3.0–8.0×10^-6 K^-1(200-1200℃),which is suitable for T/EBCs applications.Furthermore,absence of phase transition and extraordinary chemical compatibility with Al2O3/SiO2 up to 1500℃indicate the potential application prospect.The documented governing mechanisms of m'RETaO4 properties will enable researchers to promote their application in the future investigation.展开更多
Polyimide-based composite films with high thermal conductivity,good mechanical property and electrical insulating performance are urgently needed in the electronics and microelectronics fields.As one of the key techni...Polyimide-based composite films with high thermal conductivity,good mechanical property and electrical insulating performance are urgently needed in the electronics and microelectronics fields.As one of the key technical challenges to be solved,interfacial compatibility between filler and matrix plays an important role for composite film.Herein,boron nitride was modified by grafting polyimide brushes via a twostep method,and a series of thermally conductive polyimide/boron nitride composite films were prepared.Both characterization and performance results proved that the interfacial interaction and compatibility was greatly enhanced,resulting in a significant reduction in defects and interfacial thermal resistance.The interphase width of transition zone between two phases was also efficiently enlarged due to polyimide brushes grafted on filler surface.As a result,composite films based on polyimide-grafted boron nitride exhibited significantly improved properties compared with those based on pristine filler.Tensile strength can reach up to 80 MPa even if the filler content is as high as 50 wt%.The out-of-plane and in-plane thermal conductivity of composite film increased to 0.841 and 0.850 W·m^(-1)·K^(-1),respectively.In addition,thermal and dielectric properties of composite films were also enhanced to some extent.The above results indicate that surface modification by chemically grafting polymer brushes is an effective method to improve two-phase interfacial compatibility so as to prepare composite film with enhanced properties.展开更多
基金the National Natural Science Foundation of China (grant Nos. 31570578 and 31270632)the Fundamental Research Funds for the Central Universities (grant No. JUSRP51622A)the State Key Laboratory of Pulp and Paper Engineering (grant No. 201809)
文摘Cellulose nanocrystals （CNCs） of rod-like shape were prepared from degreased cotton using sulfuric acid hydrolysis. The obtained CNC suspension was neutralized using a sodium hydroxide solution to remove the residual sulfuric acid and improve the thermal stability of the CNC particles. Then, poly（ethylene oxide） （PEO） was employed to modify the nanocrystals through entanglement and physical adsorption. The goal was to further improve the thermal stability and weaken the hydrophilicity of CNCs. Original and modifed CNCs were dosed into a polylactic acid （PLA） matrix to prepare nanocomposites using a hot compression process. Results of the thermogravimetric analysis showed that the initial thermal decomposition temperature of the modifed CNCs showed a 120℃ improvement compared to the original CNCs. That is, the thermal stability of the modified CNCs improved because of their shielding and wrapping by a PEO layer on their surface. Results from scanning electron microscopy and ultraviolet-visible spectrophotometry showed that the compatibility of the modifed CNCs with organic PLA improved, which was attributed to the compatibility of the PEO chains adsorbed on the surface of the CNCs. Finally, the results of tensile tests indicated a significant improvement in terms of breaking strength and elongation at the break point.
基金under the support of the Natural Science Foundation of China(No.51762028,No.91960103)Materials Genome Engineering of Rare and Precious Metal of Yunnan Province(No.2018ZE019)。
文摘As candidate thermal/environmental barrier coatings(T/EBCs),the structure characteristics and comprehensive properties of monoclinic-prime(m')RETaO4(RE=Yb,Lu,Sc)with excellent Al2O3/SiO2 chemical compatibility are studied.Excellent thermal insulation protection will be provided by m'RETaO4 due to their low thermal conductivity(~1.6 Wm^-1 K^-1,900℃)and prominent thermal radiation resistance,which is much better than those of YSZ(~2.5 Wm^-1 K^-1,1000℃)and La-12 Zr2O7(~2.0 Wm^-1 K,900℃).The thermal expansion coefficients(TECs)are 3.0–8.0×10^-6 K^-1(200-1200℃),which is suitable for T/EBCs applications.Furthermore,absence of phase transition and extraordinary chemical compatibility with Al2O3/SiO2 up to 1500℃indicate the potential application prospect.The documented governing mechanisms of m'RETaO4 properties will enable researchers to promote their application in the future investigation.
基金financially supported by the Natural Science Foundation of Beijing(No.2202068)the National Natural Science Foundation of China(No.51803221)National Key Research and Development Program(No.2022YFB3603105).
文摘Polyimide-based composite films with high thermal conductivity,good mechanical property and electrical insulating performance are urgently needed in the electronics and microelectronics fields.As one of the key technical challenges to be solved,interfacial compatibility between filler and matrix plays an important role for composite film.Herein,boron nitride was modified by grafting polyimide brushes via a twostep method,and a series of thermally conductive polyimide/boron nitride composite films were prepared.Both characterization and performance results proved that the interfacial interaction and compatibility was greatly enhanced,resulting in a significant reduction in defects and interfacial thermal resistance.The interphase width of transition zone between two phases was also efficiently enlarged due to polyimide brushes grafted on filler surface.As a result,composite films based on polyimide-grafted boron nitride exhibited significantly improved properties compared with those based on pristine filler.Tensile strength can reach up to 80 MPa even if the filler content is as high as 50 wt%.The out-of-plane and in-plane thermal conductivity of composite film increased to 0.841 and 0.850 W·m^(-1)·K^(-1),respectively.In addition,thermal and dielectric properties of composite films were also enhanced to some extent.The above results indicate that surface modification by chemically grafting polymer brushes is an effective method to improve two-phase interfacial compatibility so as to prepare composite film with enhanced properties.
