Shaohua Jiang

Highly strong and highly tough electrospun polyimide/polyimide composite nanofibers from binary blend of polyamic acids

Electrospun blend-polyimide (blend-PI) nanofibers with high tensile strength and toughness are highlighted in this article. The blend-PI nanofibers were prepared by electrospinning the binary blend of rigid and flexible polyamic acids, followed by thermal imidization. The method is simple and can be extended to other kinds of polyamic acids. The morphologies and structures of the blend-PI nanofibers were investigated by scanning electron microscopy (SEM) and wide-angle X-ray diffraction (XRD). The mechanical properties, thermal properties and miscibility of the blend-PI nanofibers were studied by a tensile test, thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The mechanical properties of the blend-PI nanofibers, including tensile strength, modulus, elongation at break and toughness, could be well-tuned by modifying the molar ratio of the rigid component (B-PI) and the flexible component (O-PI). The blend-PI nanofibers with B-PI/O-PI molar ratio of 4/6 had an ultra-high strength of 1.3 GPa with an excellent toughness of 82 J g−1. All the blend-PI nanofibers showed thermal stability to above 500 °C. The presence of only one glass transition temperature (Tg) suggested the good miscibility of the binary PIs in the blend-PI nanofibers. This study would provide completely new opportunities for modifying the properties of electrospun PI nanofibers.

Natural source derived carbon paper supported conducting polymer nanowire arrays for high performance supercapacitors

Free-standing electrode materials have shown important application in supercapacitors. In this paper, a low cost and large scale producible carbon paper (CP) was prepared by the carbonization of cellulose paper. Self-supported conducting polymer composites were fabricated by in situ polymerization of aniline on the resulting CP substrate. The morphology and structure of the as-prepared polyaniline/carbon paper (PANI/CP) composites were characterized by scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy and an automatic N2 adsorption instrument. PANI/CP hybrids could be directly built into electrodes without adding polymer binders and conductive agents. The capacitance performance of PANI/CP electrodes was systematically studied with cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. PANI/CP hybrids showed a high specific capacitance of 1090.8 F g−1 along with low resistance and good stability. All the results indicated the prepared PANI/CP hybrids were promising electrode materials for supercapacitors.

Single electrospun nanofiber and aligned nanofiber belts from copolyimide containing pyrimidine units

Single electrospun copolyimide nanofiber and aligned co-PI nanofiber belts with high strength and high modulus were prepared from copolyamic acid containing pyrimidine units. The chemical structures of copolyamic acid and copolyimide were characterized by 1H-NMR and FT-IR spectra. The morphology of the electrospun nanofibers was investigated by SEM and AFM. The mechanical properties of the single electrospun nanofiber and aligned nanofiber belts were measured by the single fiber micro-tensile test and the uniaxial tensile test, respectively. The thermal properties of the co-PI nanofiber belts were evaluated on TGA and DMA machines. The results indicated that the incorporation of rigid pyrimidine units, the molar ratio of pyrimidine/4,4′-oxydianiline and the imidization temperature played an important role in the mechanical properties of electrospun copolyamic acid and copolyimide nanofibers while the thermal properties were influenced by the molar ratio of rigid and soft components in the copolyimide main chains.

Thermal, mechanical and thermomechanical properties of tough electrospun poly(imide-co-benzoxazole) nanofiber belts

Mechanically strong electrospun nanofibers at high temperature are highly desired in the aerospace industry, high temperature filtration and fire protection clothing. In the present work, highly tough poly(imide-co-benzoxazole) (PI-co-PBO) nanofiber belts with excellent thermal stability, mechanical properties and thermomechanical properties were produced from the highly viscous methoxy-containing polyamic acid (MeO-PAA) solution by electrospinning followed by thermal rearrangement. The chemical structures of the polymer nanofibers and the corresponding thermal rearrangement were confirmed by 1H-NMR, FT-IR and TGA. The mechanical properties and thermomechanical properties were characterized by a tensile test and thermomechanical analysis (TMA). The aligned nanofiber belts heat-treated at 450 °C (ANF-450) had the highest tensile strength of 559 MPa, a modulus of 11.2 GPa and a toughness of 12.0 J g−1, respectively, which were much higher than those of the pure PBO films made by thermal rearrangement. The TMA test showed that the ANF-450 exhibited a high tensile strength retention of 90% and a modulus retention of 94% at a high temperature of 200 °C. These excellent thermomechanical properties make electrospun PI-co-PBO nanofibers promising candidates in high temperature areas.

Heat and solvent resistant electrospun polybenzoxazole nanofibers from methoxy-containing polyaramide

Polybenzoxazole (PBO) nanofibers were prepared via electrospinning and thermal conversion from its precursor, methoxycontaining polyaramide (MeO-PA). The MeO-PA was synthesized from low-cost monomers. The structures and properties of polymers (MeO-PA and PBO) were characterized by FT-IR, TGA, DSC, OPM, SEM, and so forth. It was found that the PBO nanofibers had a diameter ranging from 300nm to 350 nm. The PBO nanofiber mats with high porosity provided a promising prospect in high-temperature filter materials, heat insulation materials, and high-temperature protection materials for its outstanding heat and solvent resistance and in preparing carbon nanofibers for its high char yield percentage.

Mechanical properties and chemical resistance of electrospun polyterafluoroethylene fibres

Porous fibrous polyterafluoroethylene (PTFE) membranes are widely used as high-temperature filters. However, high quality PTFE membranes with excellent mechanical properties and chemical resistance by electrospinning are still required. In this work, pure PTFE fibrous membranes were prepared by electrospinning PTFE emulsion with addition of a very small amount of polyethylene oxide (PEO) followed by a sintering process. The characterization of SEM and TEM indicated that after sintering, the PTFE particles in the fibres melted together and formed smooth fibres with uniform density. Tensile test showed that the membranes sintered at 380 °C possessed the best mechanical properties, much better than those electrospun from a blend of polyvinyl alcohol (PVA) and PTFE emulsion in previous reports. Chemical resistance test indicated that the PTFE membrane had excellent chemical resistance even on immersing in strong base and strong acid at 100 °C for 12 h. These electrospun fibrous PTFE membranes could be promising candidates as high-temperature and chemical resistance filters.

Facile synthesis, characterization and application of highly active palladium nano-network structures supported on electrospun carbon nanofibers

Palladium nano-network structures supported on electrospun carbon nanofibers (Pd-NNSs-ECNFs) were successfully prepared through a novel K2PdIICl4/K4FeII(CN)6 cyanogel method. The Pd-NNSs have the features and properties of small particle size, low dimensionality, quantum effects and high stability. SEM, TEM and XPS were used to characterize the Pd-NNSs-ECNFs. The Pd-NNSs-ECNFs were used as a catalyst in different types of Suzuki coupling reactions to evaluate the catalytic abilities. The results showed that the heterogeneous catalyst (Pd-NNSs-ECNFs) had a high catalytic activity (high yields to the products) to the Suzuki coupling reactions in an environmentally friendly solvent system (ethanol/H2O). The catalyst can be recycled by filtration, and reused seven times without losing the catalytic activity. This research opens new applications of Pd-NNSs-ECNFs in the area of green chemistry.

Molecular orientation in aligned electrospun polyimide nanofibers by polarized FT-IR spectroscopy

Quantitative explanation on the improved mechanical properties of aligned electrospun polyimide (PI) nanofibers as the increased imidization temperatures is highly required. In this work, polarized FT-IR spectroscopy is applied to solve this problem. Based on the polarized FT-IR spectroscopy and the molecular model in the fibers, the length of the repeat unit of PI molecule, the angle between the fiber axis and the symmetric stretching direction of carbonyl group on the imide ring, and the angle between the PI molecular axis and fiber axis are all investigated. The Mark-Howink equation is used to calculate the number-average molar mass of PI molecules. The orientation states of PI molecules in the electrospun nanofibers are studied from the number-average molar mass of PI molecules and the average fiber diameter. Quantitative analysis of the orientation factor of PI molecules in the electrospun nanofibers is performed by polarized FT-IR spectroscopy.