Modificações da Celulose Kraft Branqueada de Eucalipto por Tratamento Térmico e de Radiação Ultravioleta

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

Cellulose is used like raw material on many products, it may be found in native form (cellulose I) or on its modified forms (cellulose II, III1, III2, IV1, and IV2). Cellulose is obtained by many processes and raw materials being, alkaline pulping of woods (hardwood/softwood) is most frequent. In time function cellulose products are modified since hydrolysis, heating, light exposure, bacterial or mix of all. These degradation mechanisms may be catalyzed for transition metals and changing its optical and mechanical properties leading failures and depreciation. Optical properties behavior of cellulose and derivatives during degradation was fairly studded, however the effects on mechanical properties did not receive same attention. The role of pulp constituents on degraded processes was intensively investigated but still some questions. For most authors the degradation mechanisms are concentrated in free radicals action with important contribution of transition metals. Metals may also be direct source of pulp color. The chromofores contribution on optical properties changes is discussed and attributed to oxidized carbohydrates, Hexas and carbohydrate-lignin complexes the main yellowness of bleached pulp. In work bleached Eucalyptus fiber samples were exposed to thermal energy at 60C to 100C and ultraviolet radiation at 360 nm in many times. Optical, mechanical and thermal properties were evaluated after exposures showing important changes. It also experienced magnesium and xylanase treatments aiming to reduce unwanted effects of heat and ultraviolet exposure extending life cycle of products. The heat exposure caused more yellowness analyzed by whiteness CIELab and opacity rise. There was also observed acetone soluble compounds removal and no changing in pentoses content. The appearance of oxidized structures was monitored by ultraviolet analysis observing carbonyl and carboxyl increasing, the rise o carboxyl content led to pulp pH and conductivity changes. Viscosimetric polymerization degree was changed in time and temperature function with bigger reduction on higher time and temperature. The FTIR spectra showed important changes on hydrogen bonds that combined to tensile, elastic modulus and tenacity increase led to assumption of strengthening on cellulose chains and fiber interaction. Thermal analysis (TGA and DTA) showed changes indicating reduction on thermal stability. The ultraviolet exposure caused more brightness reduction than heat exposure. There was also observed acetone soluble compounds removal indicating it structure change making them insoluble. Like on heat exposure no change on pentoses content was observed. The appearance of oxidized structures was monitored by ultraviolet analysis observing carbonyl and carboxyl increasing. In unexpected way the viscosimetric polymerization degree did not change with ultraviolet exposure. Were also observed on FTIR spectra changes on hydrogen bonds but. It was observed tensile, elastic modulus and tenacity reduction ant thermal analysis (TGA and DTA) showed either thermal stability reduction. The samples treatment with magnesium (MgSO4.7H2O) showed none benefit on optical, mechanical and thermal properties preservation of fibers. Moreover xylanase treatment shown to be efficient on reduction of brightness lost, yellowness and mechanical properties. Thermal analysis showed no change after xylanase treatment in N2 atmosphere, while the results on Air showed thermal stability rise on first decomposition step and reduction on final step.

ASSUNTO(S)

cellulose, thermal treatment, ultraviolet radiation, optical properties, mechanical properties, thermal stability. polimeros, aplicacoes celulose, tratamento térmico, radiação ultravioleta, propriedades ópticas, propriedades mecânicas, estabilidade térmica.

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