Crack formation in mesophase pitch-based carbon fibres: Part II Detailed structure of pitch-based carbon fibres with some types of open cracks

Several mesophase pitch-based carbon fibres showing radial textures in their transverse alignments were observed by high resolution scanning electron microscope (HR-SEM) to elucidate the principal factor that induces the open crack in the transverse sections of the fibre along its fibre axis. The HR-SEM images of transverse sections exhibited various features in the alignment and shapes of the domains, although they were approximately arranged in the radial direction. The alignment of the domains was often variable in the locations from the outer part to the centre. Linear domains radially oriented in the outer part of the transverse section, that induce the circumferential shrinkage at the spinning and further heat-treatment steps, were essential for the development of open cracks with the PAC-man shaped fibre. Non-radial alignment or non-linear, bent or loop domains in the outer parts prohibited the development of the crack; these are observed in the fibres with the radial skin-random core and the onion skin-radial core alignments. Fibres without cracks in their as-spun or stabilized states usually showed shallow cracks even after the graphitization because the bent and loop domains in the intermediate and centre parts prohibited cracks from propagating into the centre part because the graphitic shrinkage along the domain shapes cannot be linear. This revised version was published online in November 2006 with corrections to the Cover Date.     

Crack formation in mesophase pitch-basedcarbon fibres: Part I Some influential factors for crack formation

The crack observable in the transverse section of mesophase pitch-based graphitized fibres was studied to clarify its development on spinning, stabilization, carbonization and graphitization, and to find the factors influential on the development on spinning. The crack was already observed as an embryo in the as-spun fibre of radial texture, which increased the opening angle according to the extent of shrinkage due to carbonization and graphitization. The spinning temperature, length/diameter, diameter and wall material of the spinning nozzle and the kind of mesophase pitch were found influential in crack development, defining the transverse texture and the extent of longitudinal alignment along the fibre axis. Although the radial texture defined under an optical microscope tends to give a crack, not all of such textures carried the crack, suggesting the necessity of more detailed classification of the texture in terms of alignment, shape and size of domains observed under high resolution scanning electron microscopy (HR-SEM). The factors revealed as being influential on the textures appear to be related to the apparent viscosity, the perfectness of the radial orientation and die-swelling at the outlet of the nozzle to modify the texture defined through the nozzle. The interaction of the mesophase pitch with the nozzle wall and flow properties should be emphasized as factors controlling the texture on spinning. This revised version was published online in November 2006 with corrections to the Cover Date.     

COMPARISON OF PHYSICAL PROPERTIES OF AGAR, LOW GEL STRENGTH AGAR AND GELATIN, AS SUPPLEMENTARY FOOD FOR PEOPLE WITH SWALLOWING DIFFICULTY

Low gel strength agar (LGSA), recently developed as a supplementary food for swallowing was compared with ordinary agar and gelatin. LGSA was developed to have physical properties close to that of gelatin, while keeping one property of agar, i. e. its setting temperature which can be controlled comparatively easier than gelatin. Each specimen was prepared with and without orange flavor. After determination of their basic properties, i. e. hardness, adhesiveness, cohesiveness and gumminess, three samples of two flavors, six in all, were studied for ease of swallowing using electromyography and sensory evaluation, on middle age (40 to 60 years old) and senior age (60 to 70 years old) subjects. Those experiments revealed nearly the same results with all samples, except for a slight difference in gumminess in LGSA and gelatin. No significant difference in electromyograms were noted in six samples or with age of subjects. It is feasible to employ agar materials together with gelatin in institutions whose members have swallowing disorders.