Utilization of waste PAN fibers as adsorbents by chemical and thermal modification
(EN)
Mladenov, I
(EN)
Simitzis, J
(EN)
Terlemesian, E
(EN)
Polyacrylonitrile (PAN) polymers obtained from industrial waste fibers (i.e. ''Bulana'') were modified with ethylene diamine (EDA) at low and high concentration. The structural changes after the chemical treatment were determined by IR-spectroscopy following dissolution in concentrated sulfuric acid. The cross-linking formation as well as the formation of various groups (such as amine, imine, amide, carbonyl) were observed. The unmodified and EDA-modified polymers were pyrolyzed in a nitrogen stream at temperatures up to 600 degrees C. The weight losses measured by weighing the sample before and after pyrolysis and thermogravimetric analysis revealed three regions (up to 300 and 500 degrees C having very high weight losses and above 500 degrees C having lower weight losses), while associated changes of the various groups of the polymers were determined by IR-spectroscopy, The adsorption (discoloring) ability of the polymers was examined by using aqueous solution of methylene blue or alizarin yellow. The experimental results were correlated with those of model polymers based on polyacrylonitrile, having known structure, and interpreted on the basis of electron donor-acceptor (EDA) interaction concept between the main groups of the polymers and the dyes. The adsorption ability of the pyrolyzed polymers up to 300 degrees C (especially for the unmodified and low amine modified forms) for both dyes were improved in comparison with the corresponding unmodified polymer. The pyrolyzed polymers treated above 400 degrees C showed no discoloring ability because of the absence of nitrile groups (completely lost through cyclization reactions) and other groups.
(EN)
