Processes in alkaline peroxide bleaching of pinus radiata tmp
thesisposted on 2023-05-26, 22:34 authored by Ginting, Yos Adiguna
The response of Pinus radiata thermomechanical pulp to alkaline peroxide has been studied. Factors influencing the maximum brightness attained for various bleaching conditions have also been examined and the concepts of 'reagent limited' and 'pulp limited' have been related to the observation of limiting brightness on repeated bleaching. Further observations were carried out on the kinetic behaviour during constant reagent concentration. Several previously reported kinetic models have been tested and found to be inadequate to describe the observed kinetic behaviour in terms of a minimum of chemically meaningful parameters. From the experimental evidence, a new kinetic model which is defined in terms of first order processes has been proposed. This model assumes the existence of a single class of chromophores which reacts to give colourless products and potential chromophores. The process of the elimination of chromophores is opposed by a colour formation process from the conversion of potential chromophores to chromophores in an equilibrium type reaction. The 'equilibrium' model was found not only to be able to describe the observed light absorption coefficients - time (K-t) relationship under constant reagent concentration, but also to explain the response of the pulp when reagent concentrations are changed part way through the bleaching process. Previously reported results on the reactions between alkaline peroxide and the model lignin chromophore cinnamaldehyde have been studied by means of computational methods. From these calculations, it was found that the epoxidation of cinnamaldehyde is exothermic with an overall activation energy close to zero. The experimental presence of two epoxide isomers with the trans isomer as the preferred product agrees with the results of our calculations. Good agreement between the results of the less sophisticated PM3 calculations and the more sophisticated ab initio calculations at RHF/6- 31G(d) suggest that PM3 can be used for further studies without sacrificing significant accuracy of the results. PM3 is also computationally preferred since it generally requires less computation time to perform. The research presented in this thesis is an extension of the work performed by the author during his study at an undergraduate level. As such, some of the results which were obtained from the previous study are included in parts of this thesis.
Rights statementCopyright 1996 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Studies the response of Pinus radiata thermomechanical pulp to alkaline peroxide. Several existing kinetic models were tested, and a new kinetic model proposed, which assumes the existence of a single class of chromophores. Thesis (Ph.D.)--University of Tasmania, 1997. Includes bibliographical references. Studies the response of Pinus radiata thermomechanical pulp to alkaline peroxide. Several existing kinetic models were tested, and a new kinetic model proposed, which assumes the existence of a single class of chromophores