Changes in light absorption coefficient spectra as a result of TCF bleaching
1999 (English)In: Paperi ja puu, ISSN 0031-1243, Vol. 81, no 2, 130-137 p.Article in journal (Refereed) Published
Light absorption coefficient, k, spectra in the wavelength range from 200 to 700 nm have been determined for a number of modified kraft and alkaline sulfite pulps after O, OAZ and OAZQP* bleaching (O=oxygen, A=acid treatment, Z=ozone, Q=complexing agent, P*=peroxide stage with Mg addition). The different pulp types have earlier shown differences in bleachability and selectivity when bleached in an OAZQP* sequence and also in other sequences. However, the reason for the differences in bleachability are not fully understood. In this paper, the changes in k spectra after the different bleaching stages for the different pulp types are shown, and the differences are discussed, The accuracy in the determination of k is also discussed and why it is preferable to measure k rather than brightness. There were no significant differences between the shape of the k spectra for the different pulp types that could explain the known differences in bleachability between the pulp types. However, the levels of the k spectra after the oxygen stage could be correlated to the known differences in bleachability between the pulps, The k spectra for the ASAM pulp, the pulp that has shown best bleachability, was significantly lower compared to the other investigated pulps. Ozone and peroxide bleached pulps showed k spectra of approximately the same shape as the oxygen-delignified pulps. In this study, k values as high as about 10 m(2)/kg were correctly measured. At higher k values, the light scattering coefficient (s) began to deviate due to too high a light absorption. Dilution, i.e. mixing the pulp with a brighter pulp of lower and known k value so that the k value of the mixture does not exceed 10 m2/kg is a way of circumventing the problem. However, there are also some limitations with the pulp mixing method, which are discussed.
Place, publisher, year, edition, pages
1999. Vol. 81, no 2, 130-137 p.
Kubelka-Munk equation, light absorption, light scattering, softwood, kraft pulps, alkaline sulfite pulps, oxygen, azone, hydrogen peroxide, DIFFUSE-REFLECTANCE, PULPS, SPECTROSCOPY
Paper, Pulp and Fiber Technology Materials Engineering
IdentifiersURN: urn:nbn:se:kth:diva-13901ISI: 000079200500010OAI: oai:DiVA.org:kth-13901DiVA: diva2:328082
QC 201007012010-07-012010-07-012010-07-01Bibliographically approved