Populus alba L., an Autochthonous Species of Spain: A Source for Cellulose Nanofibers by Chemical Pretreatment

Abstract

In order to identify new sustainable sources for producing cellulose nanofibers (CNFs), fast-growing poplar (Populus alba L.) wood was evaluated herein. For that purpose, bleached poplar kraft pulp was produced and submitted to TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) mediated oxidation (TEMPO-ox) chemical pretreatment followed by microfluidization. The resulting CNFs were thoroughly characterized, including a rheological study at different pH values. Poplar CNFs showed properties comparable to eucalypt CNFs (reference material for CNFs production), showing high carboxylate content (1048 ± 128 µmol g−1), fibrillation yield (87.3% ± 8.1%), optical transmittance (83% at 700 nm) and thermal stability (up to more than 200 °C). Regarding the rheological study, whereas pH from 4 to 10 did not produce significant changes in rheological behavior, a reduction of pH down to 1 led to an order-of-magnitude increase on the viscoelastic functions. Therefore, poplar CNF shows potential in the pH-sensitive hydrogels application field. Finally, the possible ecotoxicity of poplar CNF was assessed. The decrease in cell viability was very low so that only concentrations causing a 10% cytotoxicity could be calculated for the assay detecting alterations in cell metabolism (10 µg mL−1) and plasma membrane integrity (60 µg mL−1).

Fungal Selectivity and Biodegradation Effects by White and Brown Rot Fungi for Wood Biomass Pretreatment

“…Both brown rot fungi exposures resulted in the continuous decrease in the crystallinities of wood samples during the conversion period. As only cellulose has a crystalline structure among the three main chemical compositions of wood, this trend obtained from crystallinities suggests that cellulose could be depolymerized and converted more severely compared with hemicellulose and lignin [48,49]. Notably, the crystallinities of Hevea brasiliensis and Populus yunnanensis exposed to R. placenta decreased from 30.26% and 22.97% to 28.25% and 18.49% at 4 weeks respectively, while the mass loss was only 0.08% and 0.38%.…”