Wet spinning of porous polyacrylonitrile fibers and affect on fiber oxidation
A spinning apparatus was built to investigate the wet spinning technique for production of porous polyacrylonitrile fibers. Dimethylformamide was used as the solvent and a 17% by weight dope was extruded through a spinneret having four 118 micron diameter holes.
It was found that porous fibers could be produced with reasonable physical properties. Fiber porosity was increased with lower solvent concentration in the precipitation bath and higher bath temperatures. The fibers were particularly porous when low stretching ratios were used and the yarn was not allowed to relax during exposure to elevated temperatures. PAN fibers are stretched to improve the molecular orientation along the fiber axis while relaxation is generally used to improve the elastic properties. It appears that processing conditions can be changed to yield fibers with adequate properties for handling but with greater pore volume.
Pore volume does not appear to be directly correlated with the oxidation rate of the fibers. Experimental fibers containing pores did show generally a faster initial weight loss rate but some inconsistencies were found. The sample with greatest measured pore volume had a substantially higher weight loss and percentage weight loss rate than other experimental fibers and a commercial dry spun fiber. The effect of operating conditions on fiber properties and porosity were found to be in agreement with the literature.
It was recommended that the precision of the Thermogravimetric Analysis, for fibrous sample, be determined to provide some explanation perhaps of the inconsistencies found during the oxidation experimentation.