The integration of electronic components and the popularity of flexible devices have come up with higher expectations for the heat dissipation capability and comprehensive mechanical performance of thermal management ...The integration of electronic components and the popularity of flexible devices have come up with higher expectations for the heat dissipation capability and comprehensive mechanical performance of thermal management materials.In this work,after the modification of polyimide(PI)fibers through oxidation and amination,the obtained PDA@OPI fibers(polydopamine(PDA)-modified pre-oxidized PI fibers)with abundant amino groups were mixed into graphene oxide(GO)to form uniform GO-PDA@OPI composites.Followed by evaporation,carbonization,graphitization and mechanical compaction,the G-gPDA@OPI films with a stable three-dimensional(3D)long-range interconnected covalent structure were built.In particular,due to the rich covalent bonds between GO layers and PDI@OPI fibers,the enhanced synergistic graphitization promotes an ordered graphitized structure with less interlayer distance between adjacent graphene sheets in composite film.As a result,the optimized G-gPDA@OPI film displays an improved tensile strength of 78.5 MPa,tensile strain of 19.4%and thermal conductivity of 1028 W/(m·K).Simultaneously,it also shows superior flexibility and high resilience.This work provides an easily-controlled and relatively low-cost route for fabricating multifunctional graphene heat dissipation films.展开更多
Structure characteristics about activated carbon fibers (ACF) and polyimide (P84) doped ACF modified by HNO3 solution were studied to apply in mercury removal in coal-fired flue gases. The P84, which was always used i...Structure characteristics about activated carbon fibers (ACF) and polyimide (P84) doped ACF modified by HNO3 solution were studied to apply in mercury removal in coal-fired flue gases. The P84, which was always used in the non-woven fabric for bag filter, was intermingled with polyacrylonitrile-based ACF (PAN-ACF) in the weight ratio of 1∶1 in order to make the doped ACF with P84 (doped-ACF-P84). Then the doped-ACF-P84 fibers were modified by HNO3 solution. The structure and morphology of doped-ACF-P84 were characterized and compared with those of ACF and doped-ACF-P84 modified by HNO3solution. The results show that the modified doped-ACF-P84 fibers have almost the same pore structure and specific surface area comparing with the original one. However, contrasted with the original PAN-ACF, the doped-ACF-P84 fibers modified by HNO3 solution have more oxygen-containing groups used for mercury removal. In particular, they have more lactone and carboxyl groups.展开更多
The mechanical properties of fibers were notably improved by incorporating 2,2＇-bis（trifluoromethyl）benzidine（TFMB） into 3,3＇,4,4＇-biphenyltetracarboxylic dianhydride（s-BPDA） and p-phenylenediamine（PPD） bac...The mechanical properties of fibers were notably improved by incorporating 2,2＇-bis（trifluoromethyl）benzidine（TFMB） into 3,3＇,4,4＇-biphenyltetracarboxylic dianhydride（s-BPDA） and p-phenylenediamine（PPD） backbone.The best strength and modulus of BPDA/PPD/TFMB polyimide（PI） fiber（diamine molar ratio of PPD/TFMB= 90/10） were 1.60 and 90 GPa,respectively,which was over two times that of BPDA/PPD PI fiber.SEM image showed that the cross-section of fibers at each stage was round and voids free.Besides,the ＂skin-core＂ and microfibrillar structure were not observed.The thermal properties of PI fibers were also investigated.The results showed that the fibers owned excellent thermal stability,moreover,the structural homogeneity of fibers were significantly improved by heat-drawn stage.The T g values were found to be around 300 °C by dynamic mechanical analysis（DMA）.Wide angle X-ray diffraction（WAXD） and small angle X-ray scattering（SAXS） experiments indicated that the order degree of longitudinal and lateral stacks,the molecular orientation and the structural homogeneity of fibers were improved in the preparation process of fibers.展开更多
The laser-induced porous graphene(LIG)prepared in a straightforward fabrication method is presented,and its applications in stretchable strain sensors to detect the applied strain are also explored.The LIGformed on th...The laser-induced porous graphene(LIG)prepared in a straightforward fabrication method is presented,and its applications in stretchable strain sensors to detect the applied strain are also explored.The LIGformed on the polyimide/polydimethylsiloxane(PI/PDMS)composite exhibits a naturally high stretchabil-ity(over 30%),bypassing the transfer printing process compared to the one prepared by laser scribing onPI films.The PI/PDMS composite with LIG shows tunable mechanical and electronic performances withdifferent PI particle concentrations in PDMS.The good cyclic stability and almost linear response of theprepared LIG’s resistance with respect to tensile strain provide its access to wearable electronics.To im-prove the PDMS/PI composite stretchability,we designed and optimized a kirigami-inspired strain sensorwith LIG on the top surface,dramatically increasing the maximum strain value that in linear response toapplied strain from 3%to 79%.展开更多
As a high-performance material for preparing composite materials, polyimide fibers suffer from many potential drawbacks, including poor bonding with other substrates, which results in composite materials with poor mec...As a high-performance material for preparing composite materials, polyimide fibers suffer from many potential drawbacks, including poor bonding with other substrates, which results in composite materials with poor mechanical properties. Therefore, this study proposed a simple and rapid technique for obtaining loose, porous polyimide fiber papers by implementing a wet method using equal amounts of polyimide fiber and polyimide fiber paper as reinforcements, respectively. The polyimide resin-based composite materials were prepared by hand lay-up and hot pressing. The results showed that the paper-based reinforcement exhibited high porosity and the fibers were arranged with a uniform pore size distribution. The tensile properties, bending performance, and interlaminar shear performance of the paper-based composite improved by 130%, 108%, and 34.5%, respectively, compared to those of the fiberbased counterpart. The factors affecting the mechanical properties of the composites were analyzed based on the fiber length, fiber beating or lack thereof, and the basis weight of the paper. The increased uniformity of the polyimide fiber paper changed the ordering of the fibers and resolved drawbacks such as difficult dispersion, uneven pore size distribution, and poor mechanical properties related to single fibers in the resin-based composite material.展开更多
Well-dispersed fiber suspension is the precondition of good paper formation. Compared with cellulosic fibers, synthetic fibers are prone to flocculate because of their long length and hydrophobic nature, resulting in ...Well-dispersed fiber suspension is the precondition of good paper formation. Compared with cellulosic fibers, synthetic fibers are prone to flocculate because of their long length and hydrophobic nature, resulting in poor paper formation. To solve this problem, dispersants and extremely low forming consistency are typically adopted during the traditional wet-forming process, which cause a large amount of water consumption and treatment cost. Therefore, increasing forming consistency without compromising paper formation remains a challenge for papermakers. In this work, foam forming was adopted to disperse polyimide fibers (PI) with high forming consistency. The results showed that the formation index of handsheets increased when the bubble size and distribution became small and narrow. Compared with traditional wet-forming process with the same consistency (0.4%), the formation index of handsheets by foam forming increased by approximately 100% when C8 alkyl glucoside (APG08) concentration reached 16 g/L. Notably, forming consistency could increase by eight times while keeping the same level of paper formation. Overall, foam forming exhibits great advantages in dispersing long fiber and reducing water consumption and environmental pressure, and has potential applications in specialty paper made of long fibers.展开更多
The application of polyimide( PI) fibers in the field of composite materials has been limited because of their smooth surface and chemical inertness. In order to overcome these problems,oxygen plasma was used to modif...The application of polyimide( PI) fibers in the field of composite materials has been limited because of their smooth surface and chemical inertness. In order to overcome these problems,oxygen plasma was used to modify the surface of fibers. The single fiber fragmentation test( SFFT) was used to characterize the interfacial adhesion performance of PI fiber as a simple and accurate analysis method. It was found that the interfacial shear strength between the fiber and resin after oxygen plasma modification was increased by 54% compared to the untreated fiber. Meanwhile, the surface micromorphology,chemical composition, wettability of fibers and the interface morphology at the fiber fracture were analyzed by field emission scanning electron microscope( FESEM), X-ray photoelectron spectroscopy( XPS),contact angle measurement and polarizing microscope,respectively. All of these results demonstrated that the single fiber fragmentation test for analyzing the interfacial adhesion of PI fibers was effective.展开更多
Recently, graphene and carbon fibers have enticed extensive consideration in many scientific fields, they are considered by many scientists to be one of the most promising materials in the 21<sup>st</sup> ...Recently, graphene and carbon fibers have enticed extensive consideration in many scientific fields, they are considered by many scientists to be one of the most promising materials in the 21<sup>st</sup> century. Due to the uniqueness of their properties w<span><span><span style="font-family:;" "="">as</span></span></span><span><span><span style="font-family:;" "=""> attracted to be used to reinforce polyimide. Impressive graphene properties coupled with those excellent of polyimide composites produced composites materials with good tribological properties, different contents of graphene and its derivatives tend to improve polyimide composites properties particularly friction and wear. Furthermore, nanofillers decorated graphene derivatives showed also an effect on the tribological properties of composites. Carbon fibers coupled with polyimide composites also reviewed and showed a significance in the improvement of the properties of composites materials. The results nanofillers reinforced carbon fibers/polyimide exhibit enhanced tribological properties, which can be applied in various fields. <span>Therefore, this survey article gives an enormous review study of the tribological properties under various conditions of graphene/polyimide and car</span></span></span></span><span><span><span style="font-family:;" "="">- </span></span></span><span><span><span style="font-family:;" "="">bon fibers/polyimide composites. Besides the effects of nanofillers size on tribological properties, preparation, and research challenges were also reviewed.</span></span></span>展开更多
A 4,4＇-（ hexafluoroisopropylidene ） diphthalic anhydride- bis [ 4-（ 4-aminophenoxy ） phenyl J sulfone （ 6FDA-BAPS） polyamic acid （PAA） was synthesized by using 6FDA and BAPS as reactive monomers and N-methyl-...A 4,4＇-（ hexafluoroisopropylidene ） diphthalic anhydride- bis [ 4-（ 4-aminophenoxy ） phenyl J sulfone （ 6FDA-BAPS） polyamic acid （PAA） was synthesized by using 6FDA and BAPS as reactive monomers and N-methyl-2-pyrrolidone（NMP） as a solvent. The PAA solution was prepared into membranes by casting technology and was also prepared into PAAhollow fiber membranes by dry wet spinning process. The PAA membranes and PAA hollow fiber membranes were exposed tothe high-temperature thermal cyclization at about 300 ℃ to produce a 6FDA-BAPS polyimide （PI） membranes and hollow fibermembranes. The structure and properties of 6FDA-BAPS PI products were studied. The results showed that the obtained 6FDA-BAPS PI was the target product which was of fairly good solubility in NMP, dimethylaeetamide and tetrahydrofuran ;the 6FDA-BAPS PI possessed the dense outer layer and the loose and porous support layer;the hollow fiber membranes had the 5 % weightloss temperature of 511 ℃ and breaking strength 26.5 MPa, indicating relatively high thermal and mechanical properties.展开更多
基金Projects(51971089, 51872087) supported by the National Natural Science Foundation of ChinaProject(2020JJ5021)supported by the Natural Science Foundation of Hunan Province,ChinaProject(kq1804010) supported by the Major Science and Technology Program of Changsha,China。
文摘The integration of electronic components and the popularity of flexible devices have come up with higher expectations for the heat dissipation capability and comprehensive mechanical performance of thermal management materials.In this work,after the modification of polyimide(PI)fibers through oxidation and amination,the obtained PDA@OPI fibers(polydopamine(PDA)-modified pre-oxidized PI fibers)with abundant amino groups were mixed into graphene oxide(GO)to form uniform GO-PDA@OPI composites.Followed by evaporation,carbonization,graphitization and mechanical compaction,the G-gPDA@OPI films with a stable three-dimensional(3D)long-range interconnected covalent structure were built.In particular,due to the rich covalent bonds between GO layers and PDI@OPI fibers,the enhanced synergistic graphitization promotes an ordered graphitized structure with less interlayer distance between adjacent graphene sheets in composite film.As a result,the optimized G-gPDA@OPI film displays an improved tensile strength of 78.5 MPa,tensile strain of 19.4%and thermal conductivity of 1028 W/(m·K).Simultaneously,it also shows superior flexibility and high resilience.This work provides an easily-controlled and relatively low-cost route for fabricating multifunctional graphene heat dissipation films.
基金National High Technology Research and Development Program,China(No.2008AA05Z305)
文摘Structure characteristics about activated carbon fibers (ACF) and polyimide (P84) doped ACF modified by HNO3 solution were studied to apply in mercury removal in coal-fired flue gases. The P84, which was always used in the non-woven fabric for bag filter, was intermingled with polyacrylonitrile-based ACF (PAN-ACF) in the weight ratio of 1∶1 in order to make the doped ACF with P84 (doped-ACF-P84). Then the doped-ACF-P84 fibers were modified by HNO3 solution. The structure and morphology of doped-ACF-P84 were characterized and compared with those of ACF and doped-ACF-P84 modified by HNO3solution. The results show that the modified doped-ACF-P84 fibers have almost the same pore structure and specific surface area comparing with the original one. However, contrasted with the original PAN-ACF, the doped-ACF-P84 fibers modified by HNO3 solution have more oxygen-containing groups used for mercury removal. In particular, they have more lactone and carboxyl groups.
基金Supported by the Science & Technology Development Program of Jilin Province,China(No.20100537)
文摘The mechanical properties of fibers were notably improved by incorporating 2,2＇-bis（trifluoromethyl）benzidine（TFMB） into 3,3＇,4,4＇-biphenyltetracarboxylic dianhydride（s-BPDA） and p-phenylenediamine（PPD） backbone.The best strength and modulus of BPDA/PPD/TFMB polyimide（PI） fiber（diamine molar ratio of PPD/TFMB= 90/10） were 1.60 and 90 GPa,respectively,which was over two times that of BPDA/PPD PI fiber.SEM image showed that the cross-section of fibers at each stage was round and voids free.Besides,the ＂skin-core＂ and microfibrillar structure were not observed.The thermal properties of PI fibers were also investigated.The results showed that the fibers owned excellent thermal stability,moreover,the structural homogeneity of fibers were significantly improved by heat-drawn stage.The T g values were found to be around 300 °C by dynamic mechanical analysis（DMA）.Wide angle X-ray diffraction（WAXD） and small angle X-ray scattering（SAXS） experiments indicated that the order degree of longitudinal and lateral stacks,the molecular orientation and the structural homogeneity of fibers were improved in the preparation process of fibers.
基金from the National Natural ScienceFoundation of China(Grant No.12072030).
文摘The laser-induced porous graphene(LIG)prepared in a straightforward fabrication method is presented,and its applications in stretchable strain sensors to detect the applied strain are also explored.The LIGformed on the polyimide/polydimethylsiloxane(PI/PDMS)composite exhibits a naturally high stretchabil-ity(over 30%),bypassing the transfer printing process compared to the one prepared by laser scribing onPI films.The PI/PDMS composite with LIG shows tunable mechanical and electronic performances withdifferent PI particle concentrations in PDMS.The good cyclic stability and almost linear response of theprepared LIG’s resistance with respect to tensile strain provide its access to wearable electronics.To im-prove the PDMS/PI composite stretchability,we designed and optimized a kirigami-inspired strain sensorwith LIG on the top surface,dramatically increasing the maximum strain value that in linear response toapplied strain from 3%to 79%.
基金financial support from the Lianyungang 555 Talents Project Program of China (2015-13)
文摘As a high-performance material for preparing composite materials, polyimide fibers suffer from many potential drawbacks, including poor bonding with other substrates, which results in composite materials with poor mechanical properties. Therefore, this study proposed a simple and rapid technique for obtaining loose, porous polyimide fiber papers by implementing a wet method using equal amounts of polyimide fiber and polyimide fiber paper as reinforcements, respectively. The polyimide resin-based composite materials were prepared by hand lay-up and hot pressing. The results showed that the paper-based reinforcement exhibited high porosity and the fibers were arranged with a uniform pore size distribution. The tensile properties, bending performance, and interlaminar shear performance of the paper-based composite improved by 130%, 108%, and 34.5%, respectively, compared to those of the fiberbased counterpart. The factors affecting the mechanical properties of the composites were analyzed based on the fiber length, fiber beating or lack thereof, and the basis weight of the paper. The increased uniformity of the polyimide fiber paper changed the ordering of the fibers and resolved drawbacks such as difficult dispersion, uneven pore size distribution, and poor mechanical properties related to single fibers in the resin-based composite material.
基金funded by National Key R&D Program of China (2017YFB0308300)Shaanxi Provincial Key R&D Program (2017GY-140)Doctoral Scientific Research Foundation of Shaanxi University of Science & Technology (BJ15-12, 2018BJ-22)
文摘Well-dispersed fiber suspension is the precondition of good paper formation. Compared with cellulosic fibers, synthetic fibers are prone to flocculate because of their long length and hydrophobic nature, resulting in poor paper formation. To solve this problem, dispersants and extremely low forming consistency are typically adopted during the traditional wet-forming process, which cause a large amount of water consumption and treatment cost. Therefore, increasing forming consistency without compromising paper formation remains a challenge for papermakers. In this work, foam forming was adopted to disperse polyimide fibers (PI) with high forming consistency. The results showed that the formation index of handsheets increased when the bubble size and distribution became small and narrow. Compared with traditional wet-forming process with the same consistency (0.4%), the formation index of handsheets by foam forming increased by approximately 100% when C8 alkyl glucoside (APG08) concentration reached 16 g/L. Notably, forming consistency could increase by eight times while keeping the same level of paper formation. Overall, foam forming exhibits great advantages in dispersing long fiber and reducing water consumption and environmental pressure, and has potential applications in specialty paper made of long fibers.
基金National Key R&D Program of China(No.2016YFB0303300)National Natural Science Foundation of China(No.11472077)Fundamental Research Funds for the Central Universities,China(No.2232018G-06)
文摘The application of polyimide( PI) fibers in the field of composite materials has been limited because of their smooth surface and chemical inertness. In order to overcome these problems,oxygen plasma was used to modify the surface of fibers. The single fiber fragmentation test( SFFT) was used to characterize the interfacial adhesion performance of PI fiber as a simple and accurate analysis method. It was found that the interfacial shear strength between the fiber and resin after oxygen plasma modification was increased by 54% compared to the untreated fiber. Meanwhile, the surface micromorphology,chemical composition, wettability of fibers and the interface morphology at the fiber fracture were analyzed by field emission scanning electron microscope( FESEM), X-ray photoelectron spectroscopy( XPS),contact angle measurement and polarizing microscope,respectively. All of these results demonstrated that the single fiber fragmentation test for analyzing the interfacial adhesion of PI fibers was effective.
文摘Recently, graphene and carbon fibers have enticed extensive consideration in many scientific fields, they are considered by many scientists to be one of the most promising materials in the 21<sup>st</sup> century. Due to the uniqueness of their properties w<span><span><span style="font-family:;" "="">as</span></span></span><span><span><span style="font-family:;" "=""> attracted to be used to reinforce polyimide. Impressive graphene properties coupled with those excellent of polyimide composites produced composites materials with good tribological properties, different contents of graphene and its derivatives tend to improve polyimide composites properties particularly friction and wear. Furthermore, nanofillers decorated graphene derivatives showed also an effect on the tribological properties of composites. Carbon fibers coupled with polyimide composites also reviewed and showed a significance in the improvement of the properties of composites materials. The results nanofillers reinforced carbon fibers/polyimide exhibit enhanced tribological properties, which can be applied in various fields. <span>Therefore, this survey article gives an enormous review study of the tribological properties under various conditions of graphene/polyimide and car</span></span></span></span><span><span><span style="font-family:;" "="">- </span></span></span><span><span><span style="font-family:;" "="">bon fibers/polyimide composites. Besides the effects of nanofillers size on tribological properties, preparation, and research challenges were also reviewed.</span></span></span>
文摘A 4,4＇-（ hexafluoroisopropylidene ） diphthalic anhydride- bis [ 4-（ 4-aminophenoxy ） phenyl J sulfone （ 6FDA-BAPS） polyamic acid （PAA） was synthesized by using 6FDA and BAPS as reactive monomers and N-methyl-2-pyrrolidone（NMP） as a solvent. The PAA solution was prepared into membranes by casting technology and was also prepared into PAAhollow fiber membranes by dry wet spinning process. The PAA membranes and PAA hollow fiber membranes were exposed tothe high-temperature thermal cyclization at about 300 ℃ to produce a 6FDA-BAPS polyimide （PI） membranes and hollow fibermembranes. The structure and properties of 6FDA-BAPS PI products were studied. The results showed that the obtained 6FDA-BAPS PI was the target product which was of fairly good solubility in NMP, dimethylaeetamide and tetrahydrofuran ;the 6FDA-BAPS PI possessed the dense outer layer and the loose and porous support layer;the hollow fiber membranes had the 5 % weightloss temperature of 511 ℃ and breaking strength 26.5 MPa, indicating relatively high thermal and mechanical properties.
