The solubilities of lignin monomeric model compounds and technical lignins (organosolv and kraft) in aqueous solutions of several deep eutectic solvents (DES) were here investigated. The effects of DES components, temperature and concentration, were evaluated. The results show aqueous solutions of DES to be a new class of powerful solvents where both the hydrogen bond donor and the hydrogen bond acceptor synergistically contribute to increase the solubility of the lignin model compounds, being the dispersive interactions with lignin the driving force behind the good performance of DES. The solubility of the model compounds is shown to be a good guide for the selection of the best DES for technical lignins solubility, leading to identifying an aqueous solution of DES allowing a solubility enhancement of 1181.7 ± 29.2 and 228.5 ± 9.7 times for kraft and organosolv lignin, respectively. The results indicate that the solubility of the technical lignins and their monomers in DES aqueous solutions is driven by a hydrotropic mechanism, here confirmed by dynamic light scattering that is here observed for the first time with DES as hydrotropes.

18In this work, cellulose nanofibrils (CNF) were produced from a Eucalyptus globulus bleached

A new approach for the chemical modification of the surface of paper based on the application of colloidal mixtures containing cationic starch and polyoxometalates on uncoated base paper is presented. Polyoxometalates with the Keggin-type structure and physical properties similar to those presented by coating pigments, namely H3PW12O40·23H2O, H4SiW12O40·24H2O, and K7PW11O39·9H2O, have been used in order to improve the quality of inkjet printing. The analysis of the different samples by FTIR-ATR spectroscopy showed the presence of the polyoxometalates (and the cationic starch) on the top surface of the paper. In addition, the determination of surface energy parameters, namely the polar component (σsp) and the dispersive component (σsd) of the surface energy, by contact angle measurements revealed that, for the new samples, the polar component level was much higher than that of the uncoated base paper. The quality of inkjet printing, evaluated by parameters such as the gamut area and the optical density, was considerably improved by these surface treatments.

Aggregation of particles is fundamental for improving the performance of many solid/liquid processes. Aggregation can be induced by different means, and one of the most common is based on the addition of polymeric additives, namely polyelectrolytes. In this work we have studied the flocculation of precipitated calcium carbonate (PCC), which is used as a filler in papermaking, and is induced by a range of cationic polyacrylamides with different structures, varying in molar mass and degree of branching. The flocculation process was monitored continuously using the LDS technique (laser diffraction scattering), which provides information about the size distribution and structure (fractal dimension) of the aggregates, for each sampling instant and, thus, about the kinetic curve for the flocculation process. This information has then been used to produce a model, based on an experimental design strategy, which allows us to relate flocculation efficiency with the PEL characteristics and concentration. The Partial Least Squares (PLS) regression method was selected to perform the regression, given the significant co linearity among the input variables. The results obtained lead us to conclude that the polymer intrinsic viscosity (related with the PEL molar mass and charge density, and supplying information about the volume of the polymer molecule in the solution) and the degree of branching are the parameters with a stronger influence on flocculation efficiency. The PLS models developed were also successfully validated using an independent data set, which provides confidence on their consistency and prediction accuracy.

Two industrial bleached Eucalyptus globulus kraft pulps (pulps A and B), cooked from the same wood stock with slightly different alkali charges and temperatures, showed different refinability in the laboratory beating of pulp using a PFI mill. The easy to refine pulp (A) and the difficult to refine pulp (B) did not reveal significant differences in their biometric data and general chemical composition, but pulp A showed ca. 5%–10% higher mechanical strength and twice as high refinability compared to pulp B. These differences were ascribed to slightly higher intrinsic viscosity and higher xylan content of pulp A compared to pulp B (1010 vs. 860 cm3 g−1 and 20.1 vs. 17.8%, respectively). The xylan structure and its location in fiber cells were also different, which affected the pulp’s refinability. The presence of high proportion of xylan in the bulk of fibers, rather than in their outer layers, seems to favor the pulp beating. An interpretation was also proposed, according to which the aggregation of cellulose fibrils during cooking, i.e. a partial coalescence of fibril crystallites, may also have a negative effect on pulp refinability.