Thermal behavior of cellulose acetate produced from homogeneous acetylation of bacterial cellulose

Cellulose acetate (CA) is one of the most important cellulose derivatives and its main applications are its use in membranes, films, fibers, plastics and filters. CAs are produced from cellulose sources such as: cotton, sugar cane bagasse, wood and others. One promissory source of cellulose is bacterial cellulose (BC). In this work, CA was produced from the homogeneous acetylation reaction of bacterial cellulose. Degree of substitution (DS) values can be controlled by the acetylation time. The characterization of CA samples showed the formation of a heterogeneous structure for CA samples submitted to a short acetylation time. A more homogeneous structure was produced for samples prepared with a long acetylation time. This fact changes the thermal behavior of the CA samples. Thermal characterization revealed that samples submitted to longer acetylation times display higher crystallinity and thermal stability than samples submitted to a short acetylation time. The observation of these characteristics is important for the production of cellulose acetate from this alternative source. (C) 2008 Elsevier B.V. All rights reserved.

Cellulose acetate membranes for osmosedimentation: Performance and morphological dependence on preparation conditions

Osmosedimentation is a new membrane-assisted separation technique, based on the rapid approach to sedimentation equilibrium when macromolecular solutions are contained within dialysis cells, in contact with solvent via a permselective membrane. Cellulose acetate membranes, cast from ternary solvent (acetone, acetic acid, water) solutions are suitable for osmosedimentation of proteins at low (2000 rpm) centrifugation speeds. Solute retention is improved when acetone-rich casting solutions are used. These membranes were examined by electron and optical microscopy, showing considerable morphological changes in the membrane support layer as the casting solution composition is changed. © 1986.

Preparação e caracterização de derivados celulósicos obtidos a partir da celulose bacteriana e obtenção de filmes para aplicações óticas

Pós-graduação em Química - IQ

Produção de polpa solúvel a partir de Eucalyptus urograndis

The wood of the gender Eucalyptus occupies a prominence place in relation to other cellulose sources, due to its chemical composition, its low cost, abundance and availability. The dissolving pulp obtaining occurs basically starting from three stages: prehydrolysis of the wood following by cooking and finally by the bleaching process. In the dissolving pulp production is necessary a pretreatment stage for the hemicelluloses removal. Among the chemical cooking processes, the Kraft process is the most used for cellulosic pulps production starting from eucalyptus, in the additive presence or not. The anthraquinone uses in the pulping process has as main purposes increasing the delignification rate as well as protecting the pulp regarding the degradation of the polysaccharide chains. The ECF bleaching process consists of the purification of the pulp through bleaching agents, being excepted the elementary chlorine. The dissolving pulp is a pulp of high a-cellulose content and purity destined to the cellulose derivatives production as carboxymethyl cellulose, nitrocellulose and microcrystalline cellulose. The production of a certain product, as well as its final application, is determined by the chemical properties of the pulp. The present work had as purpose producing cellulosic pulp with kappa number around 9 destined to the production of dissolving pulp in way to evaluate the use of the anthraquinone (AQ) in the Kraft process according to the chemical properties of the obtained pulps. It has been still intended developing an effective technology of bleaching for the high purity and quality dissolving pulp production. The prehydrolysis was accomplished in laboratory rotational autoclave for 30 minutes at 170ºC in the water:wood rate 3,5:1 (L:kg). The Kraft/AQ pulping were accomplished in laboratory rotational autoclave being initially modified the active alkali load (10, 13, 16 and 19%) at sulfidity of 25% ...

Thermal decomposition of microcrystalline cellulose and its pure and containing adsorbed cadmium cations derivatives.

We have studied the thermal decomposition of the microcrystalline cellulose and some of its derivative such as pure carboxymethylcellulose (CMCH), phosphate cellulose (FOSCEL) and oxycellulose (OXICEL) and also these same derivatives containing adsorbed cadmium cations. We have used the TG,DTG tecniques in order to determine the quantity of retained cadmium II cations on the surface of these adsorbents.

Development of a new analytical approach based on cellulose membrane and chelator for differentiation of labile and inert metal species in aquatic systems

A new procedure was developed in this study, based on a system equipped with a cellulose membrane and a tetraethylenepentamine hexaacetate chelator (MD-TEPHA) for in situ characterization of the lability of metal species in aquatic systems. To this end, the DM-TEPHA system was prepared by adding TEPHA chelator to cellulose bags pre-purified with 1.0 mol L-1 of HCl and NaOH solutions. After the MD-TEPHA system was sealed, it was examined in the laboratory to evaluate the influence of complexation time (0-24 h), pH (3.0, 4.0, 5.0, 6.0 and 7.0), metal ions (Cu, Cd, Fe, Mn and Ni) and concentration of organic matter (15, 30 and 60 mg L-1) on the relative lability of metal species by TEPHA chelator. The results showed that Fe and Cu metals were complexed more slowly by TEPHA chelator in the MD-TEPHA system than were Cd, Ni and Mn in all pH used. It was also found that the pH strongly influences the process of metal complexation by the MD-TEPHA system. At all the pH levels, Cd, Mn and Ni showed greater complexation with TEPHA chelator (recovery of about 95-75%) than did Cu and Fe metals. Time also affects the lability of metal species complexed by aquatic humic substances (AHS); while Cd, Ni and Mn showed a faster kinetics, reaching equilibrium after about 100 min, and Cu and Fe approached equilibrium after 400 min. Increasing the AHS concentration decreases the lability of metal species by shifting the equilibrium to AHS-metal complexes. Our results indicate that the system under study offers an interesting alternative that can be applied to in situ experiments for differentiation of labile and inert metal species in aquatic systems. (c) 2006 Elsevier B.V. All rights reserved.

Evaluation of the genotoxicity of cellulose nanofibers

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Evaluation of anti-inflammatory activity of derivatives from aerial parts of Baccharis uncinella

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Enhancement of thermal stability, strength and extensibility of lipid-based polyurethanes with cellulose-based nanofibers

Cellulose was extracted from lignocellulosic fibers and nanocrystalline cellulose (NC) prepared by alkali treatment of the fiber, steam explosion of the mercerized fiber, bleaching of the steam exploded fiber and finally acid treatment by 5% oxalic acid followed again by steam explosion. The average length and diameter of the NC were between 200-250 nm and 4-5 nm, respectively, in a monodisperse distribution. Different concentrations of the NC (0.1, 0.5, 1.0, 1.5, 2.0 and 2.5% by weight) were dispersed non-covalently into a completely bio-based thermoplastic polyurethane (TPU) derived entirely from oleic acid. The physical properties of the TPU nanocomposites were assessed by Fourier Transform Infra-Red spectroscopy (FTIR), Thermo-Gravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), X-Ray Diffraction (XRD), Dynamic Mechanical Analysis (DMA) and Mechanical Properties Analysis. The nanocomposites demonstrated enhanced stress and elongation at break and improved thermal stability compared to the neat TPU. The best results were obtained with 0.5% of NC in the TPU. The elongation at break of this sample was improved from 178% to 269% and its stress at break from 29.3 to 40.5 MPa. In this and all other samples the glass transition temperature, melting temperature and crystallization behavior were essentially unaffected. This finding suggests a potential method of increasing the strength and the elongation at break of typically brittle and weak lipid-based TPUs without alteration of the other physico-chemical properties of the polymer. (C) 2012 Elsevier Ltd. All rights reserved.

Cellulose nanocomposites with nanofibres isolated from pineapple leaf fibers for medical applications

Nanocellulose is the crystalline domains obtained from renewable cellulosic sources, used to increase mechanical properties and biodegrability in polymer composites. This work has been to study how high pressure defibrillation and chemical purification affect the PALF fibre morphology from micro to nanoscale. Microscopy techniques and X-ray diffraction were used to study the structure and properties of the prepared nanofibers and composites. Microscopy studies showed that the used individualization processes lead to a unique morphology of interconnected web-like structure of PALF fibers. The produced nanofibers were bundles of cellulose fibers of widths ranging between 5 and 15 nm and estimated lengths of several micrometers. Percentage yield and aspect ratio of the nanofiber obtained by this technique is found to be very high in comparison with other conventional methods. The nanocomposites were prepared by means of compression moulding, by stacking the nanocellulose fibre mats between polyurethane films. The results showed that the nanofibrils reinforced the polyurethane efficiently. The addition of 5 wt% of cellulose nanofibrils to PU increased the strength nearly 300% and the stiffness by 2600%. The developed composites were utilized to fabricate various versatile medical implants. (C) 2011 Elsevier Ltd. All rights reserved.

Use of Saponins as an Effective Surface Modifier in Cellulose Nanocomposites

The present paper deals with the extraction of saponins from the pericarp of Sapindus mukorossi to use as compatibilizer in nanocomposites. The nanofibrils extracted from banana fibres are utilized as reinforcement of nanocomposite. These nanofibers were treated with Saponin, GPS (3-Glycidoxypropyltrimethoxysilane) and APS (3-Aminopropyltriethoxysilane) to compare the effectiveness of surface treatment. The effectiveness of surface modification was reflected on the increase in mechanical (tensile test, flexural modulus, impact test) properties and decrease in the RMS (Roughness Measurement System) roughness investigation by SFM (Scanning force microscopy) analysis.

Cellulose-Based Bio- and Nanocomposites: A Review

Cellulose macro- and nanofibers have gained increasing attention due to the high strength and stiffness, biodegradability and renewability, and their production and application in development of composites. Application of cellulose nanofibers for the development of composites is a relatively new research area. Cellulose macro- and nanofibers can be used as reinforcement in composite materials because of enhanced mechanical, thermal, and biodegradation properties of composites. Cellulose fibers are hydrophilic in nature, so it becomes necessary to increase their surface roughness for the development of composites with enhanced properties. In the present paper, we have reviewed the surface modification of cellulose fibers by various methods. Processing methods, properties, and various applications of nanocellulose and cellulosic composites are also discussed in this paper.

Investigation of the two-photon absorption cross-section in perylene tetracarboxylic derivatives: Nonlinear spectra and molecular structure

We investigated the 2PA absorption spectrum of a family of perylene tetracarboxylic derivatives ( PTCDs): bis( benzimidazo) perylene ( AzoPTCD), bis( benzimidazo) thioperylene ( Monothio BZP), n-pentylimidobenzimidazoperylene ( PazoPTCD), and bis( n-butylimido) perylene ( BuPTCD). These compounds present extremely high two-photon absorption, which makes them attractive for applications in photonics devices. The two-photon absorption cross-section spectra of perylene derivatives obtained via Z-scan technique were fitted by means of a sum-over-states ( SOS) model, which described with accuracy the different regions of the 2PA cross-section spectra. Frontier molecular orbital calculations show that all molecules present similar features, indicating that nonlinear optical properties in PTCDs are mainly determined by the central portion of the molecule, with minimal effect from the lateral side groups. In general, our results pointed out that the differences in the 2PA cross-sections among the compounds are mainly due to the nonlinearity resonance enhancement.

Two-photon absorption in perylene derivatives

This work reports on the two-photon absorption (2PA) cross-section for bis (n-butylimido) perylene (BuPTCD), bis (benzimidazo) perylene (AzoPTCD), bis (benzimidazo) thioperylene (Monothio BZP), bis (phenethylimido) perylene (PhPTCD), bis (benzylimido) perylene (BePTCD) and n-pentylimido-benzimidazo perylene (PAzoPTCD) solutions measured using the Z-scan technique with femtosecond laser pulses at 775 nm. All perylene derivatives studied present large 2PA cross-sections, only comparable to the best ones reported in the literature. The experimental 2PA cross-sections obtained for each PTCD compound are in good agreement with a simplified sum-over-state calculation. The results of the present work indicates perylene derivatives as promising materials for two-photon applications. (C) 2003 Elsevier B.V. B.V. All rights reserved.

Perylene derivatives with large two-photon-absorption cross-sections for application in optical limiting and upconversion lasing

Perylene tetracarboxylic derivatives (PTCDs) display exceptionally high two-photon absorption (2PA) cross-sections (6, see Figure). In addition, the 2PA saturation behavior and strong two-photon-pumped fluorescence suggest that PTCD compounds may be attractive candidates for applications in optical limiting and two-photon-pumped upconversion lasing.