Empleo de mezclas de oxidantes en etapas tcf del blanqueo de pastas celulósicas de materias primas alternativas a las convencionales

Resumen

The overall objective of the doctoral dissertation was to study the feasibility and synergy of different oxidant mixtures usage in the one-stage TCF bleaching of abaca soda pulp, as well as olive wood-trimmings ethanolamine pulp. The analysis of physic-chemical properties of olive wood trimmings and abaca crops, as a potential alternative to non-wood material for the pulp production was set as a starting point, confirming their suitability for pulp and paper manufacturing. The factorial experimental design of central composition was used in order to asses the influence of the operating variables, used in the different bleaching processes of abaca soda pulp and olive wood trimmings ethanolamine pulp, on the properties of bleached pulps and the resulting paper sheets. The single-stage TCF bleaching of abaca soda pulps and the ethanolamine olive wood trimmings pulp with the different mixtures of oxidizing reagents were studied (firstly a mixture of peracetic acid and sodium perborate, secondly a mixture of peracetic acid and hydrogen peroxide, and finally a mixture of sodium perborate and hydrogen peroxide). Beginning with the abaca pulp bleaching, the range of independent variables was set with the purpose of comparing the results obtained: temperature (55-85¿C), time (30-120 min) pH (9-11), hydrogen peroxide concentration (0.5-1.5% o.d.p.), sodium perborate concentration (1-5% o.d.p.), and peracetic acid concentration (0.5-3, 5% o.d.p.). Similarly, the operating conditions of the ethanolamine olive trimmings pulp bleaching were established: temperature (55-85¿C), time (30-150 min), pH (9-11), hydrogen peroxide concentration (1-4% o.d.p.), sodium perborate concentration (2-8% o.d.p.), and peracetic acid concentration (2-6% o.d.p.). The experimental data were adjusted to the second order polynomial model, resulting in the equations that showed both the dependent and independent variables, capable of reproducing the experimental results of the former. Along the same lines, we performed a comparison of the results obtained in the bleaching of abaca and olive trimmings pulps. Last but not least, we examined the influence of different pulp beating¿s experimental designs on the properties of olive trimmings ethanolamine pulps, previously bleached with aforementioned mixtures of oxidants, as well as on the resulting paper sheets. We studied: Design 0 (not-refined pulp), Design I (500 PFI beating in all cases), Design II (beating 0, 500, 1000 PFI), Design III (beating 500, 750, 1000 PFI), and Design IV (beating 0, 500, 750, 1000 PFI). Subsequently, the comparison of the results obtained was assessed; type of pulp bleaching and applied refining design were taken into consideration. The lowest pulp brightness, for both abaca soda and olive wood trimmings ethanolamine pulps, was achieved in the one-stage bleaching with the mixture of hydrogen peroxide and sodium perborate (78,86, 72,84%, respectively), compared to that of the hydrogen peroxide and peracetic acid bleaching (85,86%, 75,28%, respectively), and those made with peracetic acid and sodium perborate (84,66, 75,12%, respectively). The kappa index of abaca and olive trimmings pulp, 5,55 and 10,31, decreases by 76 and 61,23%, respectively, when referenced against corresponding unbleached pulps. In both cases, the highest reduction of the kappa index value was observed for pulp bleached with a mixture of peracetic acid and sodium perborate in a single step operation. The best chemical characteristics in terms of the lignin, alpha-cellulose and holocellulose contents, were obtained in the single-step bleaching with a mixture of hydrogen peroxide and sodium perborate. The abaca pulp bleaching with the mixture of hydrogen peroxide and sodium perborate resulted in the best optimal value in the tear index (20.85 mNm2/g), and the worst in the stretch index (4.58%). The highest optimal breaking length value was obtained when the pulp was bleached with a mixture of peracetic acid and hydrogen peroxide (4781 m), whereas for the burst index (4.12 kN/g) when bleached with a mixture of peracetic acid and sodium perborate. The bleached olive wood trimmings pulps showed a good aptitude for the beating process, which resulted in a significant improvement in the quality of the obtained paper sheets. Consequently, the optimal results of the breaking length (5072.00 m), and the burst index (3.45 kN/g), were found in the case of the olive trimmings beaten pulp bleached with a mixture of hydrogen peroxide and sodium perborate, and finally the beaten pulp treated with a mixture of peracetic acid and hydrogen peroxide was characterized by the greatest values of tear index (4.88 mNm2/g) and stretch index (4.69%).