Junya Yamashita

Organic and carbon aerogels derived from poly(vinyl chloride)

Organic aerogels were derived from dimethylformamide solution of poly(vinyl chloride) (PVC) via dehydrochlorination using a strong base, 1,8-diazabicyclo[5,4,0]undec-7-ene, and supercritical drying using carbon dioxide. From these organic aerogels, carbon aerogels were yielded via stabilization and carbonization. Changes in the porous structure of the aerogels during the preparation process and influences of the preparation conditions on the porous structure were investigated. The framework of the aerogels composed the walls of the meso- and macropores. The volume and the size of these pores were reduced during stabilization and carbonization due to the shrinkage of the framework caused by the release of decomposition gases and densification of the material. Simultaneously, the release of decomposition gases produced additional micropores. The extent of dehydrochlorination, the concentration of PVC in the starting solution and the molecular weight of PVC were the factors with which the porous structure of the aerogels could be controlled over a wide range. In addition, the stabilization conditions notably influenced the carbonization behavior of the organic aerogels and the porous structure of the carbon aerogels. The optimum stabilization conditions that minimized the loss of mass and maximized the pore volume of the carbon aerogels were determined.

Activation energy of structural development for phenol formaldehyde resin-based carbon fibers

Abstract Activation energy of the structural development for phenol formaldehyde resin-based glass-like carbon fibers has been investigated in comparison with those for the pitch- and polyacrylonitrile (PAN)-based carbon fibers. The fibers were isothermally heat-treated using the internal resistance heating, and the resistivity change during heat-treatment and the variation of the structural parameters of the fibers heat-treated with various conditions were measured. The activation energy was determined from the shift factors for superimposing resistivity curves. The PAN-based carbon fibers showed a lower activation energy in the lower temperature region due to the effects of the external and the internal stresses. The phenol formaldehyde resin-based carbon fibers showed a higher activation energy in the lower temperature region. For the phenol formaldehyde resin-based carbon fibers, the temperature dependence of the activation energy was an apparent phenomenon and resulted from successive structural change with two different activation energies. The activation energies for the pitch-, PAN- and phenol formaldehyde resin-based carbon fibers observed in the higher temperature region were about 1000 kJ mol −1 , which was close to the values reported for various graphitizing carbons. This suggested that although the crystallite sizes and the perfection of the structure are quite different between graphitizing and non-graphitizing carbons, the rate-determining, fundamental thermally activated processes are similar.

Development of mesopores during activation of poly(vinylidene fluoride)-based carbon

Mesoporous carbon films were prepared from poly(vinylidene fluoride) through liquid-phase dehydrofluorination (DHF)-treatment, carbonization at a high temperature and activation in carbon dioxide gas. The adsorption capacity of the resultant carbon was investigated by using nitrogen and methylene blue as adsorbates. The maximum adsorption capacity was obtained for the activated carbon prepared by applying a slight extent of DHF-treatment. The growing process of the pores in this carbon during activation was considered based on the changes of mass, pore volume and surface area. In order to increase the pore size in the activated carbon, it was essential to increase the pore size in the carbon before activation. The application of a slight extent of DHF-treatment was effective to increase the pore size in the carbon before activation.