Properties of PAN Fibers Solution Spun into a Chilled Coagulation Bath at High Solvent Compositions
In this work, multifilament, continuous polyacrylonitrile (PAN) fiber tow was solution spun mimicking industrial processing at the small pilot scale (0.5 k tow), while carefully altering the composition of the coagulation bath, in order to determine the effect on the resulting fiber shape, density, orientation, and tensile properties at varying points in the spinning process. Novel here are the abnormally high coagulation bath solvent compositions investigated, which surpass those often reported in the literature. In addition, the coagulation bath was maintained at a slightly chilled temperature, contrary to reported methods to produce round fibers. Further, by altering the composition of the bath in a step-wise fashion during a single spinning run, variations in all other process parameters were minimized. We found that with increasing solvent composition in the coagulation bath, the fibers not only became round in cross section, but also became smaller in diameter, which persisted down the spin line. With this decrease in diameter, all else equal, came an accompanying increase in apparent fiber density via a reduction in microvoid content. In addition, molecular orientation and tensile properties also increased. Therefore, it was found that inadequate understanding of the coagulation bath effects, and spinning at low coagulation bath solvent compositions, can hinder the ability of the fiber to reach optimum properties.
Analyses of closed porosity of carbon fiber precursors using a robust thermoporosimetric method
Abstract We investigated a major fiber spinning process parameter, the coagulation bath concentration, which has a critical effect on the porosity of the polyacrylonitrile (PAN) fibers. Utilizing thermoporosimetry, a calorimetric method based on the Gibbs–Thomson effect, this work details the correlation between coagulation bath concentration, porosity and pore size distribution. Pore size, as well as the pore size distribution, of the fibers throughout the wet spinning process were determined in detail. Moreover, the changes in the number of porous zones, pore size and fiber morphology during the wet spinning process were also examined by changing the coagulation bath composition. Two coagulation bath compositions, 77.5 wt% and 80 wt% DMAc/deionized water were considered. The fibers spun at 80 wt% coagulation bath solvent concentration displayed skinless rough surfaces with high porosity values compared to the fibers spun at 77.5 wt%. Attempts to spin into slightly more concentrated DMAc baths were unstable due to reduced tow tenacity, leading to fiber failure. The study showed that even minor changes in the coagulation bath composition can have a pronounced effect on the fiber properties such as cross-sectional shape, the integrity of the external skin, and the number and size of pores.
The Prevalence of Dietary Supplement Use among College Students: A Nationwide Survey in Japan
To clarify the prevalence of dietary supplement use among college students, we conducted Internet-based nationwide questionnaire surveys with 157,595 Japanese college students aged between 18 to 24 years old who were registrants of Macromill Inc. (Tokyo, Japan). Among the 9066 respondents (response rate 5.8%), 16.8% were currently using dietary supplements. The prevalence of dietary supplement use did not differ significantly between males (17.1%) and females (16.7%). However, it increased according to their grade (13.1% to 20.5%), and it was higher in medical and pharmaceutical college students (22.0%) compared to others (16.7%). The main purpose of dietary supplement use was for the health benefits in both males and females. Other reasons were to build muscle in males, and as a beauty supplement and for weight loss in females. According to the purpose of dietary supplement use, the most commonly-used dietary supplements were vitamin/mineral supplements in both males and females, then protein and weight loss supplements in males and females, respectively. Although most students obtained information about dietary supplements via the Internet, they typically purchased the supplements from drug stores. Of the students surveyed, 7.5% who were currently using or used to use dietary supplements experienced adverse effects, with no significant difference between genders (8.8% in male, 7.0% in female). In conclusion, the prevalence of dietary supplement use increased with grade among college students in Japan. Some of them experienced adverse effects. Education may be important to prevent adverse effects resulting from supplement use in college.