Ozone depolymerization of polysaccharides in different materials

• Autor(a) principal: Simões, Rogério
• Data de Publicação: 2001
• Outros Autores: Castro, José Almiro A. M.
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.6/580
• topic: Polysaccharides; Depolymerization; Ozone; Cellulose; Bleached pulps; Unbleached pulps; Holocellulose; Microcrystalline cellulose; Temperature; pH; Radicals

The behaviour of polysaccharides contained in different cellulosic materiais is studied with respect to depolymerization by ozone in an aqueous medium. The ejJect of concentration in the liquid phase, temperature and time upon the depolymerization of holocellulose, bleached and unbleached pulps, microcrystalline and native celluloses is investigated. The viscosimetric degree of polymerization and lhe molecular weighl dislribulion are used to monitor the processo The resulls show that, allow values of temperature and pH, which inhibit the produclion ofradicals, the depolymerization rate is moderalefor lignin-free materiais. However, Ihis rale and its maximum exlent increase markedly with temperature. Moreover; the experiments suggest that the reactivity of ozone and the amounl of radicais in the system and its physical accessibility are the key factors to explain the observed depolymerization pro files. Finally, the results for lignin-free materiais are compared with those obtained with similar materiais but containing residuallignin, and this study confirms that lhe presence of lignin in the fibre matrix increases the depolymerization of the carbohydrates.