Fang-xu Niu

Spinnability of Polyacrylonitrile Gel Dope in the Mixed Solvent of Dimethyl Sulfoxide/Dimethylacetamide and Characterization of the Nascent Fibers

In this work, acrylonitrile copolymers were prepared via precipitation polymerization. The copolymer solutions prepared at various ratio of dimethyl sulfoxide and dimethylacetamide were tested to prepare the nascent fibers by one-step wet-spun method. The effect of temperature, solvent ratio, molecular weight and the solid content on the rheological properties of polyacrylonitrile gel solution in different mixed solvent were studied. It was shown that the viscosity decreased with the increase of the temperature and fluctuated with the different solvent ratio reaching the minimal value at the ratio of dimethyl sulfoxide to dimethylacetamide equal to 1.25. The crystallinity of copolymers and the structure of the nascent fiber surface also depended from the solvent ratio in polymerization. The optimum conditions for spinnability of copolymers were determined. The high-quality polyacrylonitrile precursor was achieved with the controllable range of 0.5–0.8 dtex and the toughness of polyacrylonitrile precursor was greater than 6.0 cN/dtex after the wet spinning process, while the tensile strength of carbon fiber is up to 6.25 GPa after their pre-oxidation and carbonization process.

Preparation and characterization of t-BN coatings on the surface of carbon fibers

ABSTRACT Turbostratic boron nitride (t-BN) coatings were successfully synthesized on the surface of carbon fibers by dip-coating method. Boric acid and urea were used as boron source and nitrogen source separately and the nitridation process was carried out at 850°C for 4h under the protection of N2. Dipping times were considered as variables to find out optimum amounts. The structure, chemical composition, phase and properties of BN coated carbon fibers were characterized. Results showed that continuous and uniform coatings were prepared after three times dipping and adhered well with carbon fibers. The coatings were mainly composed of the phase of t-BN. The oxidation property and high temperature resistant performance of the BN modified carbon fibers were greatly improved.

Preparing of high-quality carbon film from polyimide films by gradient heat treatment process

A series of carbon-graphite films were prepared via the gradient heating based on polyimide films under nitrogen atmosphere. FTIR spectroscopy, X-ray diffraction, Raman spectrum were used to systemically investigate the evolutions of chemical structure, crystal structure, thermal stability, morphological microstructure and properties of the carbon-graphite films. The study shows that the segment fracture and thermal cross-linking reaction occur first during the low temperature pyrolysis process of PI films, and the thermal cross-linking reaction changes the structure of polyimide. Radicals start restructuring and the thermal condensation becomes sharp with the increase of heat treatment temperature, and the amorphous structure of film is transformed into the ordered graphite structure, at the same time the crystallinity and orientation of the films are improved. When it reaches a certain temperature, the crystal lattice is further improved, and the structure of film can be transformed into polycrystalline graphite structure. With the increase of the temperature, the carbon content of film is gradually increasing, and the surface resistivity is smaller and smaller. It is obvious that once the continuous conductive network of carbon formed, the conductivity of composite sheet films hardly changed.