Alternative bleaching agents

Peracetic acid and other peracids are efficient bleaching agents. PAA can be used for bleaching of natural cellulose fibres. In contrast to hydrogen peroxide it acts at low temperatures and in neutral to slightly alkaline medium. For optimal exploitation of PAA, which would lead to high degree of whiteness without damaging of fibres, it is necessary to look into the mechanisms and kinetics of PAA consumption and decomposition during the bleaching process. The influence of temperature, pH, different activators, catalysts and stabilizers on the consumption and decomposition of equilibrium PAA in the presence of cotton fibres and in the PAA solution without fibres will be followed. As activators different alkalis, metallic complexes and cationic bleaching activators will be used, as catalyst different metallic salts and oxides, and as stabilizers buffering salts and complexing agents. Bleaching with equilibrium PAA will be compared to bleaching with PAA, produced in situ from hydrogen peroxide and peracid precursors like NOBS and TAED. The possibility of decomposition of residual oxidants with enzymes and other catalysts will be investigated. The feasibillity of combining the PAA with enzymes pectinases, amylases and cellulayses in the bleaching/scouring procedures will be studied and the effects of such treatments on the degree of whiteness, water absorbency and fibre damage of cotton fabrics will be investigated. The quantity of used water and energy and the waste water loading will be measured and compared to conventional one-bath treatments of cotton. The alterations of the surface of fibres treated in different procedures will be observed with scanning electron microscope (SEM), the alterations of functional groups will be determined by FTIR spectroscopy, the depolymerisation of cellulose will be measured with the viscosimetric method in cuoxam, the quantity of calcium, magnesium and iron on the fibres will be measured with the atomic absorption spectroscopy and titrimetric. Calcium, magnesium and iron are namely the indicators of pectins and other incrusts on the fibres. Iron and other metallic ions are the catalysts of the decomposition of PAA and hydrogen peroxide.