COLOR PARAMETERS AND DIFFERENTIAL UV-VIS SPECTRA ANALYSIS OF EUCALYPTUS CTMP IN BLEACHING AND ACCELERATED AGING PROCESS

摘要

To investigate the chromophores in CTMP and provide a possible mechanism for their formation when subjected to sunlight and heat treatment, diffuse reflectance ultraviolet spectra (DRUV) and pulp brightness, as well as color parameters (L*, a*, b*) were obtained from bleached eucalyptus CTMP with hydrogen peroxide, sodium dithionite and sodium borohydride and from eucalyptus CTMP and BCTMP treated by exposing to heat and sunlight in different moisture contents (MC) respectively. The results showed the pulp brightness and L* change in the similar trend in the process of bleaching as well as color reversion. Both the chromaticity of a* and b* decreased after bleaching. O-quinonoid structures, double bonds, carbonyls as well as the conjugated unsaturated structures reduced through the bleaching process. The brightness and chromatic parameters (L*, a*, b*) of the bleached pulp decreased after they had been exposed to sunlight. An increased concentration of quinoid structures was found when the pulp was exposed to the sunlight. Water acted as the media for the pulp color reversion and made a contribution to the decrease of a* and b*. There is a fairly good linear correlation between the pulp moisture content and the absorption changes.