Structural modifications of residual lignins from sisal and flax pulps during soda-AQ pulping and TCF/ECF bleaching
2013
Rencoret, Jorge | Marques, Gisela | Gutiérrez Suárez, Ana | Martínez, Ángel T. | Jiménez-Barbero, Jesús | Río Andrade, José Carlos del
We have studied the structural modifications of lignins from sisal and flax during their soda-anthraquinone (AQ) pulping and subsequent totally chlorine-free (TCF) and elementary chlorine-free (ECF) bleaching. For this purpose, residual lignins were isolated from pulps, analyzed by Py-GC/MS, 2D-NMR, and GPC, and their characteristics compared to the “milled-wood” lignin of the raw materials. Soda-AQ pulping caused a preferential removal of S-lignin and cleavage of β–O–4′ linkages but the structure of the residual lignin remained relatively similar to native lignin. TCF bleaching barely affected the lignin structure, and noticeable amounts of β–O–4′ linkages still occurs in these pulps. In contrast, ECF bleaching caused strong modifications in the lignin structure with the complete removal of lignin markers in ECF-bleached sisal pulp. However, residual lignin was still present in ECF-bleached flax pulp, with a predominance of G- and H-lignin units and the presence of β–O–4′ linkages.
Show more [+] Less [-]This study has been funded by the Spanish project AGL2011-25379, the CSIC project 201040E075 and the EU-project LIGNODECO (KBBE-244362). JR thanks the CSIC for a JAE-DOC contract from the program “Junta para la Ampliación de Estudios” co-financed by Fondo Social Europeo (FSE).
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