Ana F. Lourenço

On the morphology of cellulose nanofibrils obtained by TEMPO-mediated oxidation and mechanical treatment.

The morphological properties of cellulose nanofibrils obtained from eucalyptus pulp fibres were assessed. Two samples were produced with the same chemical treatment (NaClO/NaBr/TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) oxidation), but distinct mechanical treatment intensities during homogenization. It was shown that the nanofibrils production yield increases with the mechanical energy. The effect of mechanical treatment on the yield was confirmed by laser profilometry of air-dried nanocellulose films. However, no significant differences were detected regarding the nanofibrils width as measured by atomic force microscopy (AFM) of air-dried films. On the other hand, differences in size were found either by laser diffraction spectroscopy or by dynamic light scattering (DLS) of the cellulose nanofibrils suspensions as a consequence of the differences in the length distribution of both samples. The nanofibrils length of the more nanofibrillated sample was calculated based on the width measured by AFM and the hydrodynamic diameter obtained by DLS. A length value of ca. 600 nm was estimated. The DLS hydrodynamic diameter, as an equivalent spherical diameter, was used to estimate the nanofibrils length assuming a cylinder with the same volume and with the diameter (width) assessed by AFM. A simple method is thus proposed to evaluate the cellulose nanofibrils length combining microscopy and light scattering methods.

Relation between magnetic parameters and nematode abundance in agricultural soils of Portugal--a multidisciplinary study in the scope of environmental magnetism.

Soil is composed of different types of particles which are either natural or of anthropogenic origin. Anthropogenic particles are often related to the presence of heavy metals and thus provide information on soil quality. Magnetic parameters can detect the presence of such particles and may be used as a proxy for environmental pollution. This study explores the relationships between magnetic particles and the nematofauna of agricultural soils. Magnetic, pedological, microscopy and nematological analyses were conducted in soils collected from major regions of potato production in Portugal. The magnetic characterisation of soils identified regions with magnetic particles with possible anthropogenic origin. Microscopy analysis revealed the presence of spherical particles dominantly composed of Fe, O and C. A positive and significant relationship was found between saturation isothermal remanent magnetisation (SIRM) and mass-specific susceptibility (χ), confirming the importance the ferrimagnetic fraction to magnetic properties. The nematode communities were composed of nematodes belonging to four trophic groups (bacterial feeding, plant feeders, fungal feeders and omnivores/predators). The relationships between magnetic parameters and the nematodes showed that (1) S−25 has a linear correlation with number of nematodes per kilogram of soil and with plant feeders’ trophic group and (2) SIRM correlates with the bacterial feeders trophic group. This study reveals that magnetic proxies may provide means for detecting regions with higher levels of pollution, possibly related to heavy metals. Due to the large background variability found in magnetic parameters, the sampling spacial mesh should to be further refined and the input of magnetic minerals needs to be locally calibrated.

Cationic cellulosic derivatives as flocculants in papermaking

Water-soluble cationic cellulose derivatives were synthesized by three different procedures, cationizing bleached hardwood kraft pulp with (3-chloro-2-hydroxypropyl) trimethylammonium chloride. The first procedure involved a previous depolymerization step with orthophosphoric acid. The second one consisted on dissolving cellulose in NaOH/urea before cationization. For the third procedure, the reaction medium was heterogeneous since it was carried out with a part of cellulose with high degree of polymerization. Oppositely to the common methods, cationization occurred under mild conditions. Differences among the three derivatives are illustrated by X-ray diffraction patterns of pretreated samples, infrared spectra, and determinations of the degree of substitution, the zeta potential, the charge density and the molecular weight. The performance of these polyelectrolytes for the flocculation of mineral fillers used in papermaking was tested by laser diffraction spectrometry. The flocculant with the highest degree of polymerization and charge originated the best results, particularly when the filler used was kaolin, proving that water-soluble cationic cellulose derivatives can aid in the flocculation of fillers used in papermaking. On the contrary, the shortest-chained derivative was not effective. The results were interpreted in terms of the characteristics of the cellulose derivatives flocculants and of the fillers, and neutralization and patching were proposed as the dominant mechanisms.

Evaluating the genotoxicity of cellulose nanofibrils in a co-culture of human lung epithelial cells and monocyte-derived macrophages

Cellulose nanofibrils (CNF) are manufactured nanofibres that hold impressive expectations in forest, food, pharmaceutical, and biomedical industries. CNF production and applications are leading to an increased human exposure and thereby it is of utmost importance to assess its safety to health. In this study, we screened the cytotoxic, immunotoxic and genotoxic effects of a CNF produced by TEMPO-mediated oxidation of an industrial bleached Eucalyptus globulus kraft pulp on a co-culture of lung epithelial alveolar (A549) cells and monocyte-derived macrophages (THP-1 cells). The results indicated that low CNF concentrations can stimulate A549 cells proliferation, whereas higher concentrations are moderately toxic. Moreover, no proinflammatory cytokine IL-1β was detected in the co-culture medium suggesting no immunotoxicity. Although CNF treatment did not induce sizable levels of DNA damage in A549 cells, it leaded to micronuclei formation at 1.5 and 3 μg/cm2. These findings suggest that this type of CNF is genotoxic through aneugenic or clastogenic mechanisms. Noteworthy, cell overgrowth and genotoxicity, which are events relevant for cell malignant transformation, were observed at low CNF concentration levels, which are more realistic and relevant for human exposure, e.g., in occupational settings.