M. Shiraishi

The mechanism of polyimide pyrolysis in the early stage

Abstract Pyrolysis mechanism of Kapton-type polyimide was investigated with special attention to the early stage. Two approaches were employed to reveal the pyrolysis reactions: one is an analysis of evolved compounds, the other is a hydrolysis method that selectively converts polyimide char into low-molecular-weight compounds. In the initial step of pyrolysis, bond cleavage around imide ring and following hydrogen transfer generates various intermediates on aromatic segments in polymer chains. It was derived from the quantitative analysis by the hydrolysis method that new linkages between the intermediates are formed efficiently instead of the cleaved bonds. Solid 13 C-NMR study showed that the packing structure of polyimide molecules is little changed by heat-treatment at the starting temperature of pyrolysis, though the structure is gradually disintegrated by reconstruction reactions at higher temperatures. It was also found that the thickness of sample films affects the weight loss and amounts of evolved compounds, while the difference of graphitizability has no appreciable effect.

Mesoporous carbon membranes from polyimide blended with poly(ethylene glycol)

The control of the mesoporous structure in a carbon membrane from a poly(ethylene glycol)/polyimide-blended polymer was investigated. The size of the pores tends to become large with increase of the content of poly(ethylene glycol) against polyimide, that is, the mesoporous structure could be controlled by the composition of the blended polymers. On the other hand, the average molecular weight of poly(ethylene glycol) has little effect from the viewpoint of the control of the pore structure.

In-plane orientation and graphitizability of polyimide films

Abstract The relationship between in-plane orientation of polyimide film and the graphitizability was obtained. In-plane oriented films in which the molecular chains are aligned parallel to the film plane give graphitic carbons, whereas isotropic ones afford non-graphitic carbons. A thin region of graphitized carbon can be observed even on the non-graphitic film, the skin-core structure of which is derived from the non-uniform orientation of the polyimide film in the thickness direction.

In-plane orientation and graphitizability of polyimide films: II. Film thickness dependence

Abstract The relation between the in-plane orientation of polyimide film and graphitizability was investigated. The degree of in-plane orientation was estimated by means of optical birefringence and ESR technique. The polyimide film was found to have non-uniform orientation in the thickness direction because the thinner the film was, the greater the orientation. The inhomogeneity of orientation caused multiphase graphitization in a film with a composite profile of the X-ray diffraction peak.

Characterization of unordered carbon using Warren–Bodenstein’s equation

Abstract A new method is presented for characterizing the microstructure of unordered carbon, in which the observed X-ray diffraction pattern is assumed to be the superposition of the patterns of component crystallites of differing heights L c and widths L a but fixed interlayer spacing d 002 , calculated using Warren–Bodenstein’s equation. The weights of the components are obtained from a least squares analysis and used to calculate mean values 〈 L a 〉 and 〈 L c 〉. Results obtained from analysis of X-ray measurements of mesocarbon microbeads heat-treated in the range 700 to 1400°C are compared with those obtained from analyses by Diamond’s method for single layer plane distributions and Hirsch’s method for layer plane distributions.

Carbonization and graphitization of polyimide coated on carbon fiber

On examine par microscopie electronique a balayage et diffraction RX la couche de polyimide carbonisee et graphitisee a la surface de monofilaments de carbone a base de polyacrylonitrile

X-ray Diffraction Methods to Study Crystallite Size and Lattice Constants of Carbon Materials

The measurement of crystallite sizes ( L a and L c ) and lattice constants ( a o and c o )is described using X-ray diffraction profiles for graphitizable carbons during graphitization. The method is called the JSPS method and is based on the use of an internal standard of silicon crystal and thin sample (0.2 mm) with several corrections of observed intensity being applied. Crystallite size distributions are obtained from diffraction profiles for carbons heat-treated to relatively low temperatures.

Formation of a Seaweed Bed Using Carbon Fibers

Micro-organisms rapidly fix onto carbon fiber surfaces when the fibers are placed in the sea. The objective is to create an artificial bed of seaweed so establishing a food chain of bacteria, algae, zoo-plankton, small animals, and fish. Initial studies in fresh water indicated that this approach had considerable potential and should therefore be extended to seawater.