Comparison of Surface Properties of Sepiolite and Palygorskite: Surface Energy and Nanoroughness

The surface properties of two sepiolite samples and one palygorskite sample were compared using inverse gas chromatography (IGC). Samples were previously conditioned at appropriate temperatures for the removal of all zeolitic water. Dispersive (or Lifshitz–van der Waals) component of the surface energy (γsd), specific interactions (−ΔGas) with π electron donor bases (1-alkenes), and nanomorphology indices (IMχT) based on the injections of cycloalkanes and a branched alkane were measured. From IGC data, at 240 °C, it was found that the palygorskite was clearly distinguished from the sepiolites. The palygorskite possessed a lower γsd, larger −ΔGas with 1-alkenes, and remarkably higher IMχT. Slight differences could also be observed between the two sepiolite samples with the same origin. The results were rationalized in terms of the structural features of the two studied minerals. The larger channels of the sepiolite allow for a better insertion of the n-alkanes (longer retention times) while excluding the bulkier probes, such as cyclooctane or 2,2,4-trimethylpentane. Accordingly, the corresponding γsd values were larger and the IMχT values were lower (higher surface nanoroughness) for the sepiolites. Regarding Lewis acid–base properties, all the sample’s surfaces evidenced a very strong amphoteric character. The present results highlight the potential of the evaluated samples for, e.g., adsorption processes with volatile organic compounds or matrix–filler interactions regarding the production of composite structures with Lewis acid–base matrices.The present research was supported by the R&D project titled “FILCNF-New generation of composite films of cellulose nanofibrils with mineral particles as high strength materials with gas barrier properties” (PTDC/QUI-OUT/31884/2017, CENTRO 01-0145-FEDER-031884), funded by the Fundação para a Ciência e Tecnologia (FCT) and FEDER. Strategic Research Centre Project (UIDB/00102/2020) and Techn&Art Project (UID/05488/2018) funded by the FCT are also acknowledged.info:eu-repo/semantics/publishedVersio

Towards a natural classification : the taxonomy and evolution of Xanthorrhoea

The ability to increase the filler content of paper without significantly sacrificing its mechanical strength is of high interest for papermakers. In this work, three samples of ground calcium carbonate (GCC), differing in size and in brightness, modified with silica via the sol-gel method, were used as fillers in papermaking. Handsheets were produced using a eucalyptus kraft pulp furnish and with a filler amount near 20%. It was found that not only were the strength properties of the handsheets produced with the modified GCCs always significantly better than those obtained with the unmodified GCCs (e.g., the tensile index exhibited improvements of 16 to 20%), but bulk also was increased (by 7 to 13%). Some decreases in the light scattering and opacity values were noted when using the modified GCC, but the brightness was roughly the same. The enhanced fiber-to-filler bonding may be attributed to the hydrogen bonding between the cellulosic fibers and the hydroxyl groups of the silica coating the calcium carbonate particles

Improving Colloidal Stability of Sepiolite Suspensions: Effect of the Mechanical Disperser and Chemical Dispersant

To allow the use of fibrous-like clays, as sepiolite, in different applications, their disaggregation and the formation of stable suspensions are crucial steps to enhance their performance significantly, e.g., in cellulose nanofibrils/clay composite formulations, enabling an adequate mixture of the matrix and filler individual components. Three distinct physical treatments of dispersion (magnetic stirring, high-speed shearing, and ultrasonication) and four different chemical dispersants (polyacrylate, polyphosphate, carboxymethylcellulose, and alginate, all in the form of sodium salts) were tested to improve the dispersibility and the formation of stable suspensions of sepiolite. Two sepiolite samples from the same origin but with different pre-treatments were evaluated. The particle size and suspension stability were evaluated by dynamic light scattering, zeta potential measurements and optical microscopy. Additionally, the sepiolite samples were initially characterized for their mineralogical, chemical, and morphologic properties. Of the three physical dispersion treatments tested, the ultrasonicator typically produced more stable suspensions; on the other hand, the biopolymer carboxymethylcellulose showed a higher ability to produce stable suspensions, being, however, a smaller particle size obtained when polyphosphate was used. Remarkably, 47 out of 90 prepared suspensions of sepiolite stayed homogeneous for at least three months after their preparation. In sum, the combination of a high energy dispersing equipment with an appropriate dispersing agent led to stable suspensions with optimal properties to be used in different applications, like in the composite production.The authors acknowledge Luís Maria, Eirini Potsi, and Solange Magalhães for the help in the preparation of a few suspensions, particle size and zeta potential measurements.info:eu-repo/semantics/publishedVersio

Stabilization of Palygorskite Aqueous Suspensions Using Bio-Based and Synthetic Polyelectrolytes

Palygorskite is a natural fibrous clay mineral that can be used in several applications, for which colloidal stability in aqueous suspensions is a key point to improve its performance. In this study, methods of magnetic stirring, high-speed shearing, and ultrasonication, as well as different chemical dispersants, combined with these methods, namely carboxymethylcellulose, alginate, polyphosphate, and polyacrylate, were used to improve the dispersibility and the formation of stable suspensions of palygorskite in different conditions of pH. The stability and particle size of suspensions with a low concentration of palygorskite were evaluated by visual inspection, optical and electron microscopy, dynamic light scattering, and zeta potential measurements. Moreover, the palygorskite used in this work was initially characterized for its mineralogical, chemical, physical, and morphological properties. It was found that more stable suspensions were produced with ultrasonication compared to the other two physical treatments, with magnetic stirring being inefficient in all tested cases, and for higher pH values (pH of 12 and pH of 8, the natural pH of the clay) when compared to lower pH values (pH of 3). Remarkably, combined with ultrasonication, carboxymethylcellulose or in a lesser extent polyphosphate at near neutral pH allowed for the disaggregation of crystal bundles of palygorskite into individualized crystals. These results may be helpful to optimize the performance of palygorskite in several domains where it is applied.The present research was supported by the R&D project titled “FILCNF-New generation of composite films of cellulose nanofibrils with mineral particles as high strength materials with gas barrier properties” (PTDC/QUI-OUT/31884/2017, CENTRO 01-0145-FEDER-031884), Strategic Research Centre Project UIDB00102/2020, and Techn & Art (UID/05488/2018) funded by the Fundação para a Ciência e Tecnologia (FCT) and FEDER.info:eu-repo/semantics/publishedVersio

Impact of bacterial cellulose on the physical properties and printing quality of fine papers

Bacterial nanocellulose (BNC), due to its inherent nanometric scale and strength properties, can be considered as a good candidate to be used in papermaking. This work explored the possibility of using it in the production of fine paper as a wet-end component and for the paper coating. Filler-containing handsheet production was performed with and without the presence of common additives typically used in the furnish of office papers. It was found that, under optimized conditions, BNC mechanically treated by high-pressure homogenization could improve all the evaluated paper properties (mechanical, optical and structural) without impairing the filler retention. However, paper strength was improved only to a small extent (increase in the tensile index of 8% for a filler content of ca. 27.5%). On the other hand, when used at the paper surface, remarkable improvements in the gamut area of >25% in comparison to the base paper and of >40% in comparison to only-starch coated papers were achieved for a formulation having 50% BNC and 50% of carboxymethylcellulose. Overall, the present results highlight the possibility of using BNC as a paper component, particularly when applied at the paper substrate as a coating agent aiming at improving printing quality.Fundacão para a Ciência e a Tecnologia (FCT), Portugal is acknowledged by SFRH/BDE/108095/2015 grant and Strategic Research Centre Project (UIDB/00102/2020). This work was also carried out under the Project Inpactus - innovative products and technologies from eucalyptus, Project N.º 21874 funded by Portugal 2020 through European Regional Development Fund (ERDF) in the frame of COMPETE 2020 nº246/AXIS II/2017info:eu-repo/semantics/publishedVersio

On the morphology of cellulose nanofibrils obtained byTEMPO-mediated oxidation and mechanical treatment

The morphological properties of cellulose nanofibrils obtained from eucalyptus pulp fibres wereassessed. 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 duringhomogenization. It was shown that the nanofibrils production yield increases with the mechanicalenergy. The effect of mechanical treatment on the yield was confirmed by laser profilometry of air-driednanocellulose films. However, no significant differences were detected regarding the nanofibrils widthas measured by atomic force microscopy (AFM) of air-dried films. On the other hand, differences in sizewere found either by laser diffraction spectroscopy or by dynamic light scattering (DLS) of the cellulosenanofibrils 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 byAFM and the hydrodynamic diameter obtained by DLS. A length value of ca. 600 nm was estimated. TheDLS hydrodynamic diameter, as an equivalent spherical diameter, was used to estimate the nanofibrilslength assuming a cylinder with the same volume and with the diameter (width) assessed by AFM. Asimple method is thus proposed to evaluate the cellulose nanofibrils length combining microscopy andlight scattering methods

Polyoxometalate/laccase-mediated oxidative polymerization of catechol for textile dyeing

The synergistic effect between polyoxometalates (POMs), namely K5[SiW11VVO40]·11H2O and H5[PMo10 VV2O40]·13H2O and laccase from ascomycete Myceliophthora thermophila has been employed for the first time in oxidative polymerization of catechol. Such a laccase-mediator system allowed the formation of a relatively high molecular weight polycatechol as confirmed by size exclusion chromatography and electrospray ionization mass spectrometry (ESI-MS) (3990 Da when using K5[SiW11VVO40]·11H2O and 3600 Da with H5[PMo10VV 2O40]·13H2O). The synthesized polymers were applied as dyes for the dyeing of flax fabrics. The color intensity of flax fabrics colored with polymer solutions was evaluated by diffuse reflectance spectrophotometry via k/s measurements (+10% of fixation ratio). A new synthetic process allowed a dyeing polymer, provided upon flax coloration, better color fixation and color resistance when compared to that obtained by conventional synthesis with laccase solely or with addition of organic mediator (1-hydroxybenzotriazole)

Filmes de Celulose Nanofibrilada com Incorporação de Minerais como Substitutos de Plásticos em Embalagens Alimentares: Potencialidades e Dificuldades

Celuloses nanofibriladas (CNF) são nanomateriais com propriedades promissoras para produção de embalagens alimentares, sendo substitutos lógicos de polímeros de base petroquímica, especificamente plásticos. Contudo, estes materiais apresentam algumas limitações, como o seu elevado custo. A combinação de CNF com minerais argilosos representa uma excelente abordagem para a produção de materiais de elevado valor acrescentado com custos aceitáveis, possibilitando ainda a melhoria de algumas propriedades dos materiais, como por exemplo o efeito barreira a gases. Para a produção de filmes compósitos podem ser seguidas duas estratégias: evaporação de solvente ou filtração seguida de prensagem a quente. Os filmes obtidos por filtração apresentam propriedades mecânicas superiores às dos obtidos por evaporação de solvente e são preparados mais rapidamente. Assim, esta técnica apresentase como a mais apropriada e eficiente para a produção de filmes compósitos com boas propriedades mecânicasN/

Acacia wood fractionation using deep eutectic solvents: extraction, recovery, and characterization of the different fractions

The selective extraction and recovery of different lignocellulosic molecules of interest from forestry residues is increasing every day not only to satisfy the needs of driving a society toward more sustainable approaches and materials (rethinking waste as a valuable resource) but also because lignocellulosic molecules have several applications. For this purpose, the development of new sustainable and ecologically benign extraction approaches has grown significantly. Deep eutectic solvents (DESs) appear as a promising alternative for the processing and manipulation of biomass. In the present study, a DES formed using choline chloride and levulinic acid (ChCl:LA) was studied to fractionate lignocellulosic residues of acacia wood (Acacia dealbata Link), an invasive species in Portugal. Different parameters, such as temperature and extraction time, were optimized to enhance the yield and purity of recovered cellulose and lignin fractions. DESs containing LA were found to be promising solvent systems, as the hydrogen bond donor was considered relevant in relation to lignin extraction and cellulose concentration. On the other hand, the increase in temperature and extraction time increases the amount of extracted material from biomass but affects the purity of lignin. The most promising DES system, ChCELA in a ratio of 1:3, was found to not significantly depolymerize the extracted lignin, which presented a similar molecular weight to a la-aft lignin. Additionally, the P-31 NMR results revealed that the extracted lignin has a high content of phenolic OH groups, which favor its reactivity. A mixture of ChCl:LA may be considered a fully renewable solvent, and the formed DES presents good potential to fractionate wood residues.info:eu-repo/semantics/publishedVersio

Filmes de celulose nanofibrilada com incorporação de minerais: uma nova geração de materiais para embalagens alimentares e eletrónica impressa

O trabalho de investigação foi realizado no âmbito do projeto “FILCNF-New generation of composite films of cellulose nanofibrils with mineral particles as high strength materials with gas barrier properties” (PTDC/QUI-OUT/31884/2017, CENTRO 01-0145-FEDER-031884), financiado pelo Programa Operacional Regional do Centro na sua componente FEDER e pela Fundação para a Ciência e Tecnologia (FCT). Agradece-se ainda ao RAIZ pelo fornecimento da pasta branqueada de Eucalyptus globulus e pelo acesso ao homogeneizador de alta pressão, assim como ao centro de investigação CIEPQPF (UIDB00102/2020) pelas condições disponibilizadas.info:eu-repo/semantics/publishedVersio