resumo
The accessibility of glucuronoxylan from a refined, bleached Eucalyptus globulus industrial kraft pulp in 0-18% aqueous NaOH solution at room temperature (25 degrees C) was studied. The extraction profile revealed a maximum extraction of xylan in the pulp at about 10-12% NaOH concentration and was explained by the maximum swelling of the pulp according to the Gibbs-Donnan equilibrium. The kinetics of xylan removal and the monitoring of its structural features were performed at 5 and 10% NaOH concentrations. The maximum yields of xylans with 10% and 5% NaOH were as high as 90% and 60% for 2 h extraction, respectively. The structural features of xylan were assessed by acid methanolysis and one-dimensional (1D)/two-dimensional (2D) nuclear magnetic resonance (NMR), and the molecular weight by size exclusion chromatography (SEC). The xylan extracted with 10% NaOH had a slightly higher molecular weight and a lower branching with uronic moieties than the xylan extracted with 5% NaOH. The former was less pure (contained more beta-cellulose) than the latter. Structural studies by NMR resulted in the conclusion that there are at least two types of xylans removed from the pulp: one xylan with relatively high 4-O-methyl-alpha-D-glucuronosyl [MeGlcA-(1 ->] and [-> 2)-MeGlcA-(1 ->] substituents and another xylan with a much lower substitution with uronic residues.
palavras-chave
STRUCTURAL-CHARACTERIZATION; ACETYLATED HETEROXYLAN; CELLULOSE; HARDWOOD; EXTRACTION; HEMICELLULOSES; TEMPERATURE; RETENTION; SOFTWOOD; FIBERS
categoria
Forestry; Materials Science
autores
Gomes, TMP; de Sousa, ARM; Belenkiy, YI; Evtuguin, DV
nossos autores
Dmitry Evtyugin
Professor Associado com Agregaçãoagradecimentos
This work was financially supported by the CICECO-Aveiro Institute of Materials, within the scope of the project POCI-01-0145-FEDER-007679 (FCT Ref. UID/CTM/50011/2013), financed by national funds through the FCT/MEC and co-financed by FEDER under the PT2020 Partnership Agreement and by ERDF Funds through the Operational Competitiveness Program -COMPETE, in the frame of the project NMC - New cellulosic materials - FCOMP-01-0202-FEDER-034169.