In the family of polyimide(PI)materials,Upilex-S^(■) film has been a shining star through the research PI materials due to its appealing merits.Unfortunately,the wholly rigid-rod backbone and easily formed skin-core ...In the family of polyimide(PI)materials,Upilex-S^(■) film has been a shining star through the research PI materials due to its appealing merits.Unfortunately,the wholly rigid-rod backbone and easily formed skin-core micromorphology and microvoids of Upilex-S~type PI lead to the high difficulty in melt-and wet-spinning fabrication.Herein,we propose a facile and scalable method,reaction-spinning,to fabricate the Upilex-S^(■) type PI fiber,in which the rapid solidification of spinning dope and partial imidization take place simultaneously.Thus,the stability and mechanical strength of as-spun fibers can be improved,and the microvoids in fibers can be greatly reduced in relative to the wet-spun fibers.The resultant Upilex-S^(■) type PI fiber shows higher tensile strength and modulus than most commercial thermal-oxidative polymeric fibers with an ultrahigh glass transition temperature T_(g) of 478℃.Moreover,the WAXS and SAXS results indicate that orthorhombic crystals are formed for Upilex-S^(■) type PI fiber in the post hot-drawing process.Increasing the hot-drawing temperature results in a continuous crystallization and high orientation of PI chains in amorphous phase and perfects the existing lamellar structure,which make a great contribution to the improved mechanical property.展开更多
In this study, polyimide fibers at different stages of imidization were characterized by TGA, DSC, and FTIR. The imidization degree （ID） calculated by TGA was based on the weight loss of each sample, which was cause...In this study, polyimide fibers at different stages of imidization were characterized by TGA, DSC, and FTIR. The imidization degree （ID） calculated by TGA was based on the weight loss of each sample, which was caused by the imidization of residual amic acid groups. The results of TGA showed good regularity with the thermal treatment temperature of the PI fibers. For DSC, the ID was calculated based on the area of endothermal peak of each sample. Compared with TGA, DSC showed a relatively higher value because the endothermal peak was reduced by the exothermic re-formation of polyamic acid which may be partially degraded during thermal treatment. The IDs obtained by the FTIR spectra generally showed poorer regularities than those obtained by both TGA and DSC, especially for the results calculated using the 730 cm^-1 band. Based on the 1350 cm^-1 band, the obtained IDs showed better agreement with the TGA or DSC results. The results obtained by these three methods were compared and analyzed. The ID obtained by TGA showed much more reliability among these three methods.展开更多
In this work, a fully rigid coplanar symmetric heterocyclic unit was introduced into the rigid polyimide macromolecular backbone structure to prepare high-performance polyimide fibers. The novel co-polyimide(co-PI) fi...In this work, a fully rigid coplanar symmetric heterocyclic unit was introduced into the rigid polyimide macromolecular backbone structure to prepare high-performance polyimide fibers. The novel co-polyimide(co-PI) fibers based on 3,3',4,4'-biphenyltetracarboxylic anhydride(BPDA), p-phenylenediamine(PDA) and 2,6-(4,4'-diaminodiphenyl) benzo[1,2-d:5,4-d'] bisoxazole(PBOA) were fabricated via a twostep wet-spinning method. The effects of benzobisoxazole moiety on spinnability, aggregation structure, and mechanical properties of fibers were systematically discussed. The detailed structural analysis revealed that the well-defined aggregation structures of co-PI fibers were obtained from initial amorphous structure when post hot-drawing temperature was higher than 460 ℃ under proper drawing ratio, and the incorporation PBOA into BPDA-PDA structures produced more compact structural co-PI fiber than homo BPDA-PDA fiber. The BPDA-PDA/PBOA co-PI fibers exhibited optimum tensile strength and modulus of 2.65 and 103 GPa, which increased by 182% and 84% compared to the homo BPDA-PDA fiber, respectively.展开更多
A series of polyamic acid copolymers(co-PAAs) with para-hydroxyl groups was synthesized using two diamine monomers,namely p-phenylenediamine(p-PDA) and 5-amino-2-(2-hydroxy-5-aminobenzene)-benzoxazole(m-pHBOA), of dif...A series of polyamic acid copolymers(co-PAAs) with para-hydroxyl groups was synthesized using two diamine monomers,namely p-phenylenediamine(p-PDA) and 5-amino-2-(2-hydroxy-5-aminobenzene)-benzoxazole(m-pHBOA), of different molar ratios through copolymerization with 3,3′,4,4′-biphenyltetracarboxylic dianhydride(BPDA) in N,N-dimethyacetamine(DMAc). The co-PAA solutions were used to fabricate fibers by dry-jet wet spinning, and thermal imidization was conducted to obtain polyimide copolymer(coPI) fibers. The effects of the m-pHBOA moiety on molecular packing and physical properties of the prepared fibers were investigated.Fourier transform infrared(FTIR) spectroscopic results confirmed that intra/intermolecular hydrogen bonds originated from the hydroxyl group and the nitrogen atom of the benzoxazole group and/or the hydroxyl group and the oxygen atom of the carbonyl group of cyclic imide. As-prepared PI fibers displayed homogenous and smooth surface and uniform diameter. The glass transition temperatures(Tgs) of PI fibers were within 311-337 °C. The polyimide fibers showed 5% weight loss temperature(T5%) at above 510 °C in air. Twodimensional wide-angle X-ray diffraction(WXRD) patterns indicated that the homo-PI and co-PI fibers presented regularly arranged polymer chains along the fiber axial direction. The ordered molecular packing along the transversal direction was destroyed by introducing the m-pHBOA moiety. Moreover, the crystallinity and orientation factors increased with increasing draw ratio. Small-angle X-ray scattering(SAXS) results showed that it is beneficial to reduce defects in the fibers by increasing the draw ratio. The resultant PI fibers exhibited excellent mechanical properties with fracture strength and initial modulus of 2.48 and 89.73 GPa, respectively, when the molar ratio of p-PDA/m-pHBOA was 5/5 and the draw ratio was 3.0.展开更多
A series of polyimide fibers containing phosphorus element derived from （3-aminophenyl） methyl phosphine oxide （DAMPO） diamine was exposed to an artificial atomic oxygen environment which simulated the space envir...A series of polyimide fibers containing phosphorus element derived from （3-aminophenyl） methyl phosphine oxide （DAMPO） diamine was exposed to an artificial atomic oxygen environment which simulated the space environment in low earth orbit （LEO）. The mass loss, surface morphology, chemical composition, and mechanical properties of the fibers before and after atomic oxygen （AO） exposure were compared in detail with a blank sample. Results showed that the phosphor-containing fibers demonstrated lower mass change and less tensile strength reduction. SEM results showed that the fibers with phosphorous element had relatively dense surface after AO exposure. Meanwhile, XPS results indicated that a passivated phosphate layer, which could protect the following under-layer from attacking by AO, was formed on the surface of the fibers. These results indicated that the incorporation of diamine （DAMPO） into the main chains could protect the fibers for avoiding further erosion from AO exposure. Hence, the phosphor-containing PI fibers exhibits potential application in space fields.展开更多
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
A series of co-polyimide(PI)fibers containing phenylphosphine oxide(PPO)group were synthesized by incorporating the bis(4-aminophenoxy)phenyl phosphine oxide(DAPOPPO)monomer into the PI molecular chain followed by dry...A series of co-polyimide(PI)fibers containing phenylphosphine oxide(PPO)group were synthesized by incorporating the bis(4-aminophenoxy)phenyl phosphine oxide(DAPOPPO)monomer into the PI molecular chain followed by dry-jet wet spinning.The effects of DAPOPPO molar content on the atomic oxygen(AO)resistance of the fibers were investigated systematically.When the AO fluence increased from 0to 3.2×1020the mass loss of the fibers showed the dependence on DAPOPPO molar content in co-PI fibers.The PI fiber containing 40%DAPOPPO showed lower mass loss compared to those containing 0%and 20%DAPOPPO.At higher AO fluence,the higher DAPOPPO content gave rise to dense carpet-like surface of fibers.XPS results indicated that the passivated phosphate layer was deposited on the fiber surface when exposed to AO,which effectively prevented fiber from AO erosion.With the DAPOPPO content increasing from 0%to 40%,the retentions of tensile strength and initial modulus for the fibers exhibited obvious growth from 44%to 68%,and 59%to 70%,after AO exposure with the fluence of 3.2×1020The excellent AO resistance benefits the fibers for application in low Earth orbit as flexible construction components.展开更多
A series of polyamic acid copolymers(co-PAAs) containing phosphorous groups in the side chains were synthesized from [2,5-bis(4-aminophenoxy) phenyl] diphenylphosphine oxide(DATPPO) and 4,4′-oxydianiline(ODA) with 3,...A series of polyamic acid copolymers(co-PAAs) containing phosphorous groups in the side chains were synthesized from [2,5-bis(4-aminophenoxy) phenyl] diphenylphosphine oxide(DATPPO) and 4,4′-oxydianiline(ODA) with 3,3′,4,4′-biphenyltetracarboxylic dianhydride(s-BPDA) through the polycondensation in N,N′-dimethyacetamide(DMAc). The co-PAA solutions were spun into fibers by a dry-jet wet spinning process followed by thermal imidization to obtain co-polyimide(co-PI) fibers. FTIR spectra and elemental analysis confirmed the chemical structure of PI fibers. SEM results indicated that the resulting PI fibers had a smooth and dense surface, a uniform and circle-shape diameter. The thermogravimetric measurements showed that with the increase of DATPPO content, the resulting PI fibers possessed high decomposition temperature and residual char yield, indicating that the PI fibers had good thermal stability. The corresponding limiting oxygen index(LOI) values from the experiment results showed that the co-PI fibers possessed good flame-retardant property. Furthermore, the mechanical properties of the co-PI fibers were investigated systematically. When the DATPPO content increased, the tensile strength and initial modulus of the co-PI fibers decreased. However, the mechanical properties were improved by increasing the draw ratio of the fibers. When the draw ratio was up to 2.5, the tensile strength and initial modulus of the co-PI fibers reached up to 0.64 and 10.02 GPa, respectively. The WAXD results showed that the order degree of amorphous matter increased with increased stretching. In addition, the SAXS results displayed that valuably drawing the fibers could eliminate the voids inside and lead to better mechanical property. WAXD revealed that the orientation of the amorphous polymer influenced the mechanical properties of the fibers.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 modify t...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
Polymer fiber with an ultrahigh thermal stability,superior flame retardancy and low smoke release during combustion is urgently needed and a crucial challenge for developing advanced fireproof textiles.In this study,a...Polymer fiber with an ultrahigh thermal stability,superior flame retardancy and low smoke release during combustion is urgently needed and a crucial challenge for developing advanced fireproof textiles.In this study,a series of high-performance polyimide fibers are synthesized by copolymerizing 4,4'-diaminodiphenylmethane(MDA)into the pyromellitic dianhydride-p-phenylenediamine(PMDA-PDA)backbone for synergistically solving the technical challenge of poor fiber processing ability of these polyimides with a high inherent molecular rigidity.The glass transition temperature(Tg)of resultant fibers with the PDA molar ratio over 50 mol%reaches above 420℃ and their 10 wt%weight loss temperature(T10%)is within 543-633℃.For the typical fiber containing 80 mol%of PDA,the limiting oxygen index(LOI)reaches 39%and exhibits a rapid self-extinguishing performance after deviating from the flame.Meanwhile,this fiber exhibits the minimum heat release rate of 14.1 kW/m^(2) in a long ignition time of 813 s during combustion,revealing its better flame retardancy than the well-known Nomex fiber with a heat release rate of 140.6 kW/m^(2) during the 120 s ignition.Meanwhile,the total smoke production of this polyimide fiber is only 1/9 of the Nomex fiber.Accordingly,the excellent flame retardancy of polyimide fibers indicating them more attractive as the fireproof materials in the field of emergency protection.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
High performance is always the research objective in developing triboelectric nanogenerators(TENGs)for future versatile applications.In this study,flexible triboelectric membranes were prepared based on polyimide(PI)m...High performance is always the research objective in developing triboelectric nanogenerators(TENGs)for future versatile applications.In this study,flexible triboelectric membranes were prepared based on polyimide(PI)membranes doped with barium titanate(BTO)nanoparticles and multi-walled carbon nanotubes(MWCNTs).The piezoelectric BTO nanoparticles were incorporated to boost the electric outputs by the synergistic effect of piezoelectricity and triboelectricity and MWCNTs were incorporated to provide a microcapacitor structure for enhancing the performance of TENGs.When the mass fraction of the BTO nanoparticle was 10%and the mass fraction of the MWCNT was 0.1%,the corresponding TENG achieved optimum electric outputs(an open-circuit voltage of around 65 V,a short-circuit current of about 20.0μA and a transferred charge of about 25.0 nC),much higher than those of the TENG with a single PI membrane.The TENG is potentially used to supply energy for commercial light-emitting diodes and as self-powered sensors to monitor human physical training conditions.This research provides a guideline for developing TENGs with high performance,which is crucial for their long-term use.展开更多
基金supported by the National Natural Science Foundation of China(Nos.51903038,21774019,21975040)the Program of Shanghai Academic Research Leader(No.18XD1400100)the Scientific Research Innovation Plan of Shanghai Education Commission(No.2019-01-07-00-03-E00001).
文摘In the family of polyimide(PI)materials,Upilex-S^(■) film has been a shining star through the research PI materials due to its appealing merits.Unfortunately,the wholly rigid-rod backbone and easily formed skin-core micromorphology and microvoids of Upilex-S~type PI lead to the high difficulty in melt-and wet-spinning fabrication.Herein,we propose a facile and scalable method,reaction-spinning,to fabricate the Upilex-S^(■) type PI fiber,in which the rapid solidification of spinning dope and partial imidization take place simultaneously.Thus,the stability and mechanical strength of as-spun fibers can be improved,and the microvoids in fibers can be greatly reduced in relative to the wet-spun fibers.The resultant Upilex-S^(■) type PI fiber shows higher tensile strength and modulus than most commercial thermal-oxidative polymeric fibers with an ultrahigh glass transition temperature T_(g) of 478℃.Moreover,the WAXS and SAXS results indicate that orthorhombic crystals are formed for Upilex-S^(■) type PI fiber in the post hot-drawing process.Increasing the hot-drawing temperature results in a continuous crystallization and high orientation of PI chains in amorphous phase and perfects the existing lamellar structure,which make a great contribution to the improved mechanical property.
基金financially supported by the National Basic Research Program of China(No.2014CB643603)the National Natural Science Foundation of China(No.51173178)
文摘In this study, polyimide fibers at different stages of imidization were characterized by TGA, DSC, and FTIR. The imidization degree （ID） calculated by TGA was based on the weight loss of each sample, which was caused by the imidization of residual amic acid groups. The results of TGA showed good regularity with the thermal treatment temperature of the PI fibers. For DSC, the ID was calculated based on the area of endothermal peak of each sample. Compared with TGA, DSC showed a relatively higher value because the endothermal peak was reduced by the exothermic re-formation of polyamic acid which may be partially degraded during thermal treatment. The IDs obtained by the FTIR spectra generally showed poorer regularities than those obtained by both TGA and DSC, especially for the results calculated using the 730 cm^-1 band. Based on the 1350 cm^-1 band, the obtained IDs showed better agreement with the TGA or DSC results. The results obtained by these three methods were compared and analyzed. The ID obtained by TGA showed much more reliability among these three methods.
基金financially supported by the National Natural Science Foundation of China (Nos. 51903038 and 21975040)Guangdong Basic and Applied Basic Research Foundation (No. 2020A1515110897)。
文摘In this work, a fully rigid coplanar symmetric heterocyclic unit was introduced into the rigid polyimide macromolecular backbone structure to prepare high-performance polyimide fibers. The novel co-polyimide(co-PI) fibers based on 3,3',4,4'-biphenyltetracarboxylic anhydride(BPDA), p-phenylenediamine(PDA) and 2,6-(4,4'-diaminodiphenyl) benzo[1,2-d:5,4-d'] bisoxazole(PBOA) were fabricated via a twostep wet-spinning method. The effects of benzobisoxazole moiety on spinnability, aggregation structure, and mechanical properties of fibers were systematically discussed. The detailed structural analysis revealed that the well-defined aggregation structures of co-PI fibers were obtained from initial amorphous structure when post hot-drawing temperature was higher than 460 ℃ under proper drawing ratio, and the incorporation PBOA into BPDA-PDA structures produced more compact structural co-PI fiber than homo BPDA-PDA fiber. The BPDA-PDA/PBOA co-PI fibers exhibited optimum tensile strength and modulus of 2.65 and 103 GPa, which increased by 182% and 84% compared to the homo BPDA-PDA fiber, respectively.
基金financially supported by the National Key R&D Program of China(No.2017YFB0308300)the National Basic Research Program of China(No.2014CB643603)
文摘A series of polyamic acid copolymers(co-PAAs) with para-hydroxyl groups was synthesized using two diamine monomers,namely p-phenylenediamine(p-PDA) and 5-amino-2-(2-hydroxy-5-aminobenzene)-benzoxazole(m-pHBOA), of different molar ratios through copolymerization with 3,3′,4,4′-biphenyltetracarboxylic dianhydride(BPDA) in N,N-dimethyacetamine(DMAc). The co-PAA solutions were used to fabricate fibers by dry-jet wet spinning, and thermal imidization was conducted to obtain polyimide copolymer(coPI) fibers. The effects of the m-pHBOA moiety on molecular packing and physical properties of the prepared fibers were investigated.Fourier transform infrared(FTIR) spectroscopic results confirmed that intra/intermolecular hydrogen bonds originated from the hydroxyl group and the nitrogen atom of the benzoxazole group and/or the hydroxyl group and the oxygen atom of the carbonyl group of cyclic imide. As-prepared PI fibers displayed homogenous and smooth surface and uniform diameter. The glass transition temperatures(Tgs) of PI fibers were within 311-337 °C. The polyimide fibers showed 5% weight loss temperature(T5%) at above 510 °C in air. Twodimensional wide-angle X-ray diffraction(WXRD) patterns indicated that the homo-PI and co-PI fibers presented regularly arranged polymer chains along the fiber axial direction. The ordered molecular packing along the transversal direction was destroyed by introducing the m-pHBOA moiety. Moreover, the crystallinity and orientation factors increased with increasing draw ratio. Small-angle X-ray scattering(SAXS) results showed that it is beneficial to reduce defects in the fibers by increasing the draw ratio. The resultant PI fibers exhibited excellent mechanical properties with fracture strength and initial modulus of 2.48 and 89.73 GPa, respectively, when the molar ratio of p-PDA/m-pHBOA was 5/5 and the draw ratio was 3.0.
基金financially supported by National Basic Research Program of China(973 Program,No.2014CB643604)the National Natural Science Foundation of China(No.51373164)
文摘A series of polyimide fibers containing phosphorus element derived from （3-aminophenyl） methyl phosphine oxide （DAMPO） diamine was exposed to an artificial atomic oxygen environment which simulated the space environment in low earth orbit （LEO）. The mass loss, surface morphology, chemical composition, and mechanical properties of the fibers before and after atomic oxygen （AO） exposure were compared in detail with a blank sample. Results showed that the phosphor-containing fibers demonstrated lower mass change and less tensile strength reduction. SEM results showed that the fibers with phosphorous element had relatively dense surface after AO exposure. Meanwhile, XPS results indicated that a passivated phosphate layer, which could protect the following under-layer from attacking by AO, was formed on the surface of the fibers. These results indicated that the incorporation of diamine （DAMPO） into the main chains could protect the fibers for avoiding further erosion from AO exposure. Hence, the phosphor-containing PI fibers exhibits potential application in space fields.
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financially supported by the National Basic Research Program of China (973 Program, Key Project: No. 2014CB643604)
文摘A series of co-polyimide(PI)fibers containing phenylphosphine oxide(PPO)group were synthesized by incorporating the bis(4-aminophenoxy)phenyl phosphine oxide(DAPOPPO)monomer into the PI molecular chain followed by dry-jet wet spinning.The effects of DAPOPPO molar content on the atomic oxygen(AO)resistance of the fibers were investigated systematically.When the AO fluence increased from 0to 3.2×1020the mass loss of the fibers showed the dependence on DAPOPPO molar content in co-PI fibers.The PI fiber containing 40%DAPOPPO showed lower mass loss compared to those containing 0%and 20%DAPOPPO.At higher AO fluence,the higher DAPOPPO content gave rise to dense carpet-like surface of fibers.XPS results indicated that the passivated phosphate layer was deposited on the fiber surface when exposed to AO,which effectively prevented fiber from AO erosion.With the DAPOPPO content increasing from 0%to 40%,the retentions of tensile strength and initial modulus for the fibers exhibited obvious growth from 44%to 68%,and 59%to 70%,after AO exposure with the fluence of 3.2×1020The excellent AO resistance benefits the fibers for application in low Earth orbit as flexible construction components.
基金financially supported by the National Basic Research Program of China(973 Program,Key Project:2014CB643604)the National Natural Science Foundation of China(No.51373164)
文摘A series of polyamic acid copolymers(co-PAAs) containing phosphorous groups in the side chains were synthesized from [2,5-bis(4-aminophenoxy) phenyl] diphenylphosphine oxide(DATPPO) and 4,4′-oxydianiline(ODA) with 3,3′,4,4′-biphenyltetracarboxylic dianhydride(s-BPDA) through the polycondensation in N,N′-dimethyacetamide(DMAc). The co-PAA solutions were spun into fibers by a dry-jet wet spinning process followed by thermal imidization to obtain co-polyimide(co-PI) fibers. FTIR spectra and elemental analysis confirmed the chemical structure of PI fibers. SEM results indicated that the resulting PI fibers had a smooth and dense surface, a uniform and circle-shape diameter. The thermogravimetric measurements showed that with the increase of DATPPO content, the resulting PI fibers possessed high decomposition temperature and residual char yield, indicating that the PI fibers had good thermal stability. The corresponding limiting oxygen index(LOI) values from the experiment results showed that the co-PI fibers possessed good flame-retardant property. Furthermore, the mechanical properties of the co-PI fibers were investigated systematically. When the DATPPO content increased, the tensile strength and initial modulus of the co-PI fibers decreased. However, the mechanical properties were improved by increasing the draw ratio of the fibers. When the draw ratio was up to 2.5, the tensile strength and initial modulus of the co-PI fibers reached up to 0.64 and 10.02 GPa, respectively. The WAXD results showed that the order degree of amorphous matter increased with increased stretching. In addition, the SAXS results displayed that valuably drawing the fibers could eliminate the voids inside and lead to better mechanical property. WAXD revealed that the orientation of the amorphous polymer influenced the mechanical properties of the fibers.
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.
基金financially supported by the National Natural Science Foundation of China(Nos.51903038 and 21975040)the Scientific Research Innovation Plan of Shanghai Education Commission(No.2019-01-07-00-03-E00001)+1 种基金the Natural Science Foundation of Shanghai(No.21ZR1400200)the Project“Fiber materials and products for emergency support and public safety”from Jiangsu New Vision Advanced Functional Fiber Innovation Center Co.,Ltd.(No.2021fx020204)。
文摘Polymer fiber with an ultrahigh thermal stability,superior flame retardancy and low smoke release during combustion is urgently needed and a crucial challenge for developing advanced fireproof textiles.In this study,a series of high-performance polyimide fibers are synthesized by copolymerizing 4,4'-diaminodiphenylmethane(MDA)into the pyromellitic dianhydride-p-phenylenediamine(PMDA-PDA)backbone for synergistically solving the technical challenge of poor fiber processing ability of these polyimides with a high inherent molecular rigidity.The glass transition temperature(Tg)of resultant fibers with the PDA molar ratio over 50 mol%reaches above 420℃ and their 10 wt%weight loss temperature(T10%)is within 543-633℃.For the typical fiber containing 80 mol%of PDA,the limiting oxygen index(LOI)reaches 39%and exhibits a rapid self-extinguishing performance after deviating from the flame.Meanwhile,this fiber exhibits the minimum heat release rate of 14.1 kW/m^(2) in a long ignition time of 813 s during combustion,revealing its better flame retardancy than the well-known Nomex fiber with a heat release rate of 140.6 kW/m^(2) during the 120 s ignition.Meanwhile,the total smoke production of this polyimide fiber is only 1/9 of the Nomex fiber.Accordingly,the excellent flame retardancy of polyimide fibers indicating them more attractive as the fireproof materials in the field of emergency protection.
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.
基金National Natural Science Foundation of China(No.52103267)。
文摘High performance is always the research objective in developing triboelectric nanogenerators(TENGs)for future versatile applications.In this study,flexible triboelectric membranes were prepared based on polyimide(PI)membranes doped with barium titanate(BTO)nanoparticles and multi-walled carbon nanotubes(MWCNTs).The piezoelectric BTO nanoparticles were incorporated to boost the electric outputs by the synergistic effect of piezoelectricity and triboelectricity and MWCNTs were incorporated to provide a microcapacitor structure for enhancing the performance of TENGs.When the mass fraction of the BTO nanoparticle was 10%and the mass fraction of the MWCNT was 0.1%,the corresponding TENG achieved optimum electric outputs(an open-circuit voltage of around 65 V,a short-circuit current of about 20.0μA and a transferred charge of about 25.0 nC),much higher than those of the TENG with a single PI membrane.The TENG is potentially used to supply energy for commercial light-emitting diodes and as self-powered sensors to monitor human physical training conditions.This research provides a guideline for developing TENGs with high performance,which is crucial for their long-term use.
