Monday, May 2, 2011
Grand Ballroom C-D, 2nd fl (Sheraton Seattle)
Untreated and ammonia - treated duckweed, cassava leaves and sugar cane bagasse, together with cane leaves, corn stubbles, plantain leaves and midribs, were subjected to drying at several conditions. The drying kinetics of the materials, their chemical characterization, crystallinity index and FTIR spectra, were determined. Kinetics was modeled and its relationship with the evaluated characteristics analyzed. Additionally, ammonia treatments were simulated and the effects of rehydration, grinding, cutting sizes and degreasing of the materials on the kinetics were observed. The drying curves showed, for all cases, a monotonic decrease of moisture fraction not eliminated with respect to time, with one falling rate period with internal control. The best model found was that of Hii, followed by Midilli. The diffusion type was anomalous, so that Fick's second law does not apply. Drying changed the original structure of plants, especially in very wet samples, transforming cellulose I into cellulose II without changes in their crystallinity index, increasing the proportion of cellulose II at higher drying temperatures. There was more anomalous diffusion (concentration factor) in samples with greater exposure of the fiber (grinding or cutting), higher proportion of cellulose I, higher crystallinity and less rigidity of the fiber. This factor was correlated with the initial moisture. Ammonia treatments increased the crystallinity without changing the ratio of cellulose I to II. FTIR spectra presented an overview of the presence of fiber and the effectiveness of the ammonia treatment.
Keywords: drying, biomass characterization, ammonia treatment, crystallinity index, FTIR spectra.