Alessandra de Souza Fonseca

Evaluation of reaction factors for deposition of silica (SiO2) nanoparticles on cellulose fibers

This study aimed to evaluate reaction conditions for deposition of SiO2 nanoparticles on the surface of cellulose fibers and their influence on moisture adsorption of the hybrid organic-inorganic material formed. SiO2 nanoparticle deposition was carried out with the sol-gel process testing four reaction times (2, 12, 18, and 24h) and three contents of the tetraethyl-orthosilicate (TEOS) precursor (1.9, 4.2 and 8.4g g(-1) of cellulose fiber). Modification time and TEOS content directly influence the amount of Si deposited on the fiber surface, nanoparticle diameter distribution, thermal stability, and resistance to moisture adsorption. There is a tendency of slight increase of nanoparticle size and the amount of Si deposited with increasing reaction time. SiO2 nanoparticles were bonded on the surface of the cellulose fibers and are able to improve thermal stability of the material, increasing onset degradation temperature. The moisture adsorption capacity of the modified cellulose fiber was reduced up to 50%.

How the chemical nature of Brazilian hardwoods affects nanofibrillation of cellulose fibers and film optical quality

A wide range of alternative cellulose fibers for the development of new green nanomaterials can be obtained from Brazil’s natural resources. The objective of the work is to evaluate the influence of the chemical composition of hardwoods on the nanofibrillation process and optical quality of nanofiber films. Wood wastes were selected from three native Amazonian species and from exotic planted Eucalyptus grandis species. Wood sawdust was submitted to chemical alkali and bleaching pretreatments. Nanofibers were produced from the bleached fibers after 10, 20, 30 and 40 passes through a Super Mass Colloider grinder, and films were produced by the casting method. Raw sawdust, alkali-treated fibers and bleached fibers were evaluated by the major chemical components, syringyl/guaiacyl ratio, Fourier transformed infrared spectroscopy, oxygen/carbon ratio and scanning electron microscopy. Morphological characteristics of nanofibers and films were analyzed by transmission and scanning electron microscopies. Optical parameters studied for the films were the opacity, total color difference and b value. The main challenge to delignification was attributed to the low syringyl/guaiacyl ratio. The different chemical natures of Amazonian and eucalyptus hardwoods greatly affected pretreatments and, consequently, the nanofibrillation and optical quality of the films. Consequences observed for highly purified cellulose starting fibers are: (1) lower diameters for individual nanofiber elements; (2) fewer opaque and colored films produced from nanofibers; (3) a tendency to stabilization of the nanofibrillation process after 20 passes through the grinder. For species whose chemical nature hindered cellulose purification, the increased number of passes through the grinder continuously decreased the opacity.

Properties of cellulose micro/nanofibers obtained from eucalyptus pulp fiber treated with anaerobic digestate and high shear mixing

High production costs remain the single greatest factor limiting wider use of cellulose micro/nanofibers by industry. The objective of the present study was to investigate the potential of using a low-cost bacteria-rich digestate (liquid anaerobic digestate—AD-supernatant) on milled eucalyptus fiber followed by high-shear mixing to obtain cellulose micro/nanofibers. The morphology, crystallinity, and thermal stability of micro/nanofibers obtained by this process were studied. The bacteria population in the AD-supernatant was comprised mostly of Bacteroides graminisolvens and Parabacteroides chartae. The digestate treatment partially removed amorphous components of the pulp fiber thereby decreasing micro/nanofiber diameters and enhancing the crystalline content. The treatment also increased the size of the crystalline cellulose. The morphology and crystallinity results demonstrate the effectiveness of digestate treatments coupled with high-shear mixing as a procedure for the production of micro/nanofibers.

Biocomposite of cassava starch reinforced with cellulose pulp fibers modified with deposition of silica (SiO 2 ) nanoparticles

Eucalyptus pulp cellulose fibers were modified by the sol-gel process for SiO2 superficial deposition and used as reinforcement of thermoplastic starch (TPS). Cassava starch, glycerol, and water were added at the proportion of 60/26/14, respectively. For composites, 5% and 10% (by weight) of modified and unmodified pulp fibers were added before extrusion. The matrix and composites were submitted to thermal stability, tensile strength, moisture adsorption, and SEM analysis. Micrographs of the modified fibers revealed the presence of SiO2 nanoparticles on fiber surface. The addition of modified fibers improved tensile strength in 183% in relation to matrix, while moisture adsorption decreased 8.3%. Such improvements were even more effective with unmodified fibers addition. This result was mainly attributed to poor interaction between modified fibers and TPS matrix detected by SEM analysis.

USO DE ESPÉCIES AMAZÔNICAS PARA ENVELHECIMENTO DE BEBIDAS DESTILADAS: ANÁLISES FÍSICA E QUÍMICA DA MADEIRA

The process of storing liquor in wooden barrels is a practice that aims to improve the sensory characteristics, such as color, aroma and flavor, of the beverage. The quality of the liquor stored in these barrels depends on wood characteristics such as density, permeability, chemical composition, anatomy, besides the wood heat treatment used to fabricate the barrels. Brazil has a great diversity of forests, mainly in the north, in the Amazon. This region is home to thousands of tree species, but is limited to the use of only a few native species to store liquors. The objective of this study was to determine some of the physical and chemical characteristics for four Amazon wood species. The results obtained in this study will be compared with others from woods that are traditionally used for liquor storage. The species studied were angelim-pedra (Hymenolobium petraeum Ducke) cumarurana (Dipteryx polyphylla (Huber) Ducke), jatoba (Hymenaea courbaril L.) and louro-vermelho (Nectandra rubra (Mez) CK Allen). The trees were collected from Precious Woods Amazon Company forest management area, in Silves, Amazonas. Analyzes such as: concentration of extractives, lignin amount, percentage of minerals (ash) and tannin content, density, elemental analysis (CHNS-O) and thermal analysis were done. It was observed that the chemical composition (lignin, holocellulose) and elemental analysis (percentage of C, H, N and O) of the woods have significant differences. The jatoba wood presented higher tannin content, and in the thermal analysis, was that which had the lowest mass loss.