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The deacetylation of beta-chitin assisted by high i ntensity ultrasound was studied and the effects of the irradiation amplitude and durati on and of the temperature on the reaction efficiency as well as on the chitosan characteristi cs were evaluated. The nuclear magnetic ressonance and infrared spectroscopies were employe d for the structural characterization while the X ray diffraction and the scanning electr on microscopy allowed the evaluation of morphological characteristics. The average degree o f acetylation was determined by titrimetry while the weight average molecular weight and the v iscosity average molecular weight were determined by size-exclusion chromatography and vis cometry, respectively. The chitosan samples pertaining to Group I were produced by carr ying out the experiments in which the irradiation amplitude (low, intermediate and high) and the time (30, 45 and 60 minutes) were varied, while those of Group II resulted from exper iments in which the temperature (50, 60, 70 e 80C) and the irradiation amplitude (low, intermediate and high) were varied, the irradiation time being fixed at 30 minutes. In Grou p I the values of average degree of acetylation and viscosity average molecular weight of the chitosans ranged as 7%<DA<25% and 1,0x10<Mv<6,5x10g/mol, respectively. These results evidenced a stro ng relationship between the irradiation amplitude and duration and the structural characteristics of chitosans, the values of DA and Mv being lower the higher the irradiaton amplitude and duration. The chitosans of Group II exhibited a DA range similar to that of the samples of Group I however the molecular weights of the chitosans were higher in Group II (4,5x10<Mv<7,1x10 g/mol). According to the results of such experiments, the t emperature effect is more important than the irradiation duration effect, mainly on the macr omolecular character of the chitosans. Regardless of the Group (Group I or II), the reacti on yields (Y) were high and they were inserted in the range 72%<Y<90%. However, the sizeexclusion chromatography analyses showed that the chitosans of Group II contained low molecular weight products. The results of this investigation showed that the h igh intensity ultrasound-assisted beta-chitin deacetylation is a novel process more e fficient than those commonly used to produce chitosan in industries and in research labo ratories. Thus, if the parameters process are adequately chosen, chitosans with high molecular we ights (5,0-7,0 x 10 5 g/mol) and low average degrees of acetylation (<10%) are produced in shorter times and at lower temperatures than those tipically of the commonly u sed processes.

Desacetilação de beta-quitina assistida por ultra-som de alta intensidade: estudo dos efeitos da amplitude e do tempo de irradiação e da temperatura da reação