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High-performance co-polyimide (co-PI) fibers derived from 3,3'4,4'-biphenyldianhydride (BPDA), p-phenylenediamine (p-PDA) and 2-(4-aminophenyl)-5-amino-benzimidazole (BIA) were prepared via the wet spinning and dry-jet wet spinning method, respectively. The distinctions between wet spinning and dry-jet wet spinning processes on the structures and properties of co-PI fibers were systematically investigated. The co-PI fibers prepared by dry-jet wet spinning exhibited smoother surface morphology and higher mechanical properties than those of co-PI prepared by wet spinning. Wide-angle X-ray diffraction (WAXD) results showed that the co-PI fibers prepared by dry-jet wet spinning exhibited highly oriented structure along the fiber direction along with a low degree of lateral packing order in the transverse direction. Small-angle X-ray scattering (SAXS) revealed that the radius, length, misorientation and internal surface roughness of the microvoids in the co-PI fibers prepared by the dry-jet wet spinning are lower than those in co-PI fibers prepared by wet spinning. Moreover, the effect of air layer height, as well as the heat treatment on the structure and properties of fibers during the dry-jet wet spinning process, was also studied. The tensile strength and modulus of co-PI fibers prepared by dry-jet wet spinning reached 2.72 GPa and 114.29 GPa, respectively, with an air layer height of 10 mm and a heat stretching temperature of 440°C. [ABSTRACT FROM AUTHOR]

Polyimide/graphene (PI/G) composite fibers containing p -phenylenediamine (p -PDA), 3,3′,4,4′-Biphenyl tetracarboxylic diandhydride (BPDA) and graphene (G) were prepared by wet spinning and thermal imidization. The mechanical properties, thermal stability, orientation factor and morphology of PI/G composite fibers were characterized and studied. Within the scope of the study, the tensile strength and tensile modulus of the fibers increased first and then decreased with the increase of the graphene content. Moreover, the glass transition temperature and thermal decomposition temperature of the PI/G composite fibers increased with the increased of the graphene content. X-ray diffraction (XRD) showed that the degree of orientation of the of prepared fibers increase firstly and then decrease with the content of graphene increasing. SEM indicated that graphene was dispersed evenly in the PI/G composite fibers and graphene had satisfactory compatibility with PI matrix. [ABSTRACT FROM AUTHOR]

The novel copolymerization polyimide (PI) hollow fibers (HFs) of 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) containing –CF3 groups were prepared and investigated through both simulation and experiment. To demonstrate the alteration attributable to the introduction of fluoromonomers, the condensed states of pyromellitic dianhydride (PMDA)/4,4′-oxybisbenzenamine (ODA), PMDA/6FDA/ODA, and 6FDA/ODA PI were constructed by Material Studio, and we simulated the mobility of molecular chain, free volume fraction, and O2/N2 dissolution–diffusion process. The molecular dynamics simulation results demonstrated that the properties of the copolymerized PI system with 6FDA were significantly improved, while the selectivity remained almost unchanged. Then, the films of copolymerized PI and HFs were prepared by the two-step method, and O2/N2 permeability of the PI copolymer films was characterized, indicating that although the gas permeation performance was greatly improved, the selectivity was not so satisfactory. However, the selection factor increased heavily after polydimethylsiloxane coating. [ABSTRACT FROM AUTHOR]

A series of polyimide/polyacrylonitrile (PI/PAN) blend fibers with different PAN weight ratios were prepared through a two-step wet-spinning method and stabilization process and then were carbonized at 1500°C under high-purity nitrogen atmosphere, yielding in PI/PAN-derived carbon fibers. The effects of PAN content on the structures of the PI/PAN blend fibers were systematically investigated. The elemental composition, aggregation structure, carbon yields, and electrical properties of the PI/PAN-derived carbon fibers were also analyzed. The imidization degree and molecular orientation of the PI/PAN blend fibers increased first and then decreased with increasing PAN content, which directly affect the aggregation structures and properties of the corresponding PI/PAN-derived carbon fibers. As a consequence, the carbon fibers derived from PI/PAN-35% exhibited perfect graphite structure with a planar spacing d002 of 0.349 nm, high carbon content of 97.14%, and low electrical resistivity of 1.89 × 10−5 Ω·m, attributing to the high degree of orientation along the fiber axis and low value of φa/φc in the PI/PAN blend fibers. [ABSTRACT FROM AUTHOR]

High-performance polyimide/polyacrylonitrile (PI/PAN) blend fibers were prepared through wet-spinning of the polymer blends of polyamide acid (PAA) and PAN solutions followed by a thermal treatment in air. During the heat treatment process, PAA was imidized into its final heteroaromatic PI form with the concomitant evolution of PAN into its ladder-like preoxidized form, thus yielding PI/PAN blend fibers with desirable properties. The structure evolution was traced by fourier transform infrared radiation spectrometer, differential scanning calorimetry and thermogravimetry, implying that the PAA moiety in the blend fibers played a role as initiator for the cyclization of PAN. The final PI/PAN blend fibers exhibited a single glass-transition peak at 326 °C and a smooth surface without any pores. Moreover, the PI/PAN blend fibers possessed the tensile strength of 1.06 GPa and modulus of 59.9 GPa. [ABSTRACT FROM AUTHOR]

Herein, a novel core@sheath nanofibrous membrane with ultrahigh strength, superior fire resistance and high wettability is prepared for lithium-ion batteries separator via self-bonding and self-compression technique, using the polyimide nanofiber as the core material and polybenzimidazole as the reinforced sheath material. The self-bonding and self-compression make the polyimide@polybenzimidazole-reinforced nanofibrous membrane possess ultrahigh strength up to 59 MPa and more compact porous structure, which is an exciting finding. The as-synthesized nanofibrous membrane exhibits super high thermal dimensional stability up to 300 °C and satisfying wettability. Furthermore the good thermal stability of as-synthesized membrane enables it to preserve the integrity of backbone at temperatures as high as 540 °C. More significantly, the unique fire resistance of polybenzimidazole also ensures the high security of batteries. Notably, the battery using the as-synthesized separator displays much higher capability (130.2 mAh g−1, 5 C) than that with Celgard separator (95.4 mAh g−1, 5 C), and it can work steadily at 120 °C. Therefore, we believe that this work is really a significant breakthrough for the polyimide nonwoven separators, especially the ultrahigh mechanical strength, indicating the promising applications for the next generation high-safety and high-performance lithium-ion batteries. Image 1 • A novel PI@PBI nanofibrous membrane was obtained. • The as-prepared membrane exhibits ultrahigh mechanical strength. • The membrane displays high security and good electrochemical performances. • The separator possesses better rate capability and can work steadily at 120 °C. [ABSTRACT FROM AUTHOR]