Enzymatic and chemical treatments to obtain pulps with high-cellulose content
- Autores: Elisabet Quintana Vilajuana
- Directores de la Tesis: Cristina Valls Vidal (dir. tes.), María Blanca Roncero Vivero (codir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2016
- Idioma: español
- Tribunal Calificador de la Tesis: Teresa Vidal Llucia (presid.), David Ibarra Trejo (secret.), Pilar Díaz Lucea (voc.)
- Materias:
- Enlaces
- Resumen
Cellulose is the most abundant polymer in the Earth and recently has gained wide interest as a source for new products with distinct processing and quality requirements compared to conwntional processes for obtaining pulp and paper. The restrictions on cotton cultivation and the increase ofdissolving pulp manufacturing provide new opportunities to cellulose polymer.ln addition,compared topetroleum based chemicals, cellulose enables sustainable approaches and environmentally friendly products. This is the context that framed the present doctoral thesis. The work focused on two different research lines, namely: conwrsion of sulfite pulp to dissolving-grade with the aid of enZ'ymatic and chemical treatments, and the (bio)modification of high-cellulose content pulps. The approach of two research lines, justifies the use of two pulps with different characteristics, as a feedstock.
The first part ofthe thesis ini.Qiwd the use of enZ'ymes to bleach softwood sulfite pulp.The aim was to explore the potential of natural and synthetic compounds for lignin removal and provide an improwment in the bleaching process. The effluents resulting from each stage in the sequence were analyzed with a view to assessing the environmental impact ofthe lacease treatment. Afterwards, the mediatorwith bestefficiencyto promete delignification and enhance the bleaching effect, was used to de-.elop a totallychlorine free (TCF) sequence composed oflaccase-mediator system (LMS),a chelating (Q) stage anda hydrogen peroxide stage reinforced with pressurized oxygen (PO). The resulting pulp exhibited an ISO brightness of90% and a satisfactory degree of polymerization. In orderto understand the effects of enZ'ymatic treatments caused in crystallinity and the surtace of the cellulose ehain, samples were analyzed by thermogravimetry and X-ray diffraction techniques.
The second part ofthe thesis was based on the conwrsion ofthese biobleached sulfite pulps to dissolving-grade.
Purification was carried outwith the aid ofchemical and enZ'ymatic treatments, specificallyemploying strong alkaline extractions and hydrolytic enZ'ymes (endoglucanases). The combination of both procedures led to reduce the amount of hem icelluloses and increase the solubility behavior of cellulose,desired aspects for its final application.Moreo-.er, pure cellulose modification (commercial dissolving-grade pulp) by means of enZ'ymatic systems, but with the interest to bring and de-.elop new properties to the final products was also studied.With the purpose of improving reactivity and accessibility, the studygains knowledge on understanding the role ofendoglucanases in combination with strong alkaline extraction to cellulose structure. On the other side, laccase-TEMPO system was used to evaluate the im pro-.ement of strength properties through oxidati-.e m odification of cellulose. Asignificant impro-.ement in wet strength attributed to the formation of aldehyde groups in cellulose chains that facilitated inter-fiber bonding through hemiacetallinkages was obser-.ed. The ability of laccase-TEMPO system was impro-.ed by introducing a pre-refining step.
The last part of the thesis in-.estigates the suitability of dissolving grade-pulp obtained by chemo-enZ'ymatic processes for heterogeneous- and homogeneous-phase acetylation reactions (chemical modification). The results were compared with those from a commercially-available dissolving fiber grade,obtained bytraditional chemical methods, which was used as reference. Surface acetytated handsheets and transparent cellulose acetate films were achie-.ed.
To conclude,"biocon-.ersion" was explored from the initial stages, with the need to bleach pulp resulted from a sulfite cooking; to the transformation stages, where dissolving pulps characteristics were achie-.ed; until the preparation of acetate films as a final product.
