Cellulose nanofibers production using a set of recombinant enzymes.

Cellulose nanofibers (CNF) are renewable and biodegradable nanomaterials with attractive barrier, mechanical and surface properties. In this work, three different recombinant enzymes: an endoglucanase, a xylanase and a lytic polysaccharide monooxygenase, were combined to enhance cellulose fibrillation and to produce CNF from sugarcane bagasse (SCB). Prior to the enzymatic catalysis, SCB was chemically pretreated by sodium chlorite and KOH, while defibrillation was accomplished via sonication. We obtained much longer (µm scale length) and more thermostable (resisting up to 260 °C) CNFs as compared to the CNFs prepared by TEMPO-mediated oxidation. Our results showed that a cooperative action of the set of hydrolytic and oxidative enzymes can be used as a "green" treatment prior to the sonication step to produce nanofibrillated cellulose with advanced properties.

Thermoplastic blends of chitosan: A method for the preparation of high thermally stable blends with polyesters.

Chitosan is high potential material for new applications due to its properties, especially its antimicrobial activity, and because it is one of the most abundant natural polymers. However, chitosan can be processed only from solution limiting its applications. Methods for processing chitosan in molten have been a subject of recent interest. One method, involves thermoplastic its blends with poly(vinyl alcohol), however these blends undergo degradation due to acid residues from previous processing steps. Here we described a process to produce thermoplastic blends of poly(vinyl alcohol)-chitosan in a poly(lactic acid) matrix by avoiding degradation even at higher chitosan contents. The process involves the use of spray- and freeze-drying techniques to produce acid free blends of PVA/chitosan, then incorporated in PLA matrix by extrusion. These findings are expected to contribute to increasing and extending the applications of polysaccharides, such as chitosan, in new applications such as textiles, medical and food packing.

Furan-modified natural rubber: A substrate for its reversible crosslinking and for clicking it onto nanocellulose.

The conventional vulcanization process applied to elastomers is irreversible and hinders therefore their useful recycling. We demonstrate here that natural rubber can be reversibly crosslinked via the Diels-Alder coupling of furan and maleimide moieties. The furan-modified natural rubber used in this strategy was also exploited to bind it to maleimide-modified nanocellulose, thus generating a covalently crosslinked composite of these two renewable polymers.

Recycling tires? Reversible crosslinking of poly(butadiene).

Furan-modified poly(butadiene) prepared by the thiol-ene click reaction is crosslinked with bismaleimides through the Diels-Alder reaction, giving rise to a novel recyclable elastomer. This is possible because of the thermal reversibility of the adducts responsible for the formation of the network. The use of this strategy provides the possibility to produce recyclable tires.

Simple green approach to reinforce natural rubber with bacterial cellulose nanofibers.

Natural rubber (NR) is a renewable polymer with a wide range of applications, which is constantly tailored, further increasing its utilizations. The tensile strength is one of its most important properties susceptible of being enhanced by the simple incorporation of nanofibers. The preparation and characterization of natural-rubber based nanocomposites reinforced with bacterial cellulose (BC) and bacterial cellulose coated with polystyrene (BCPS), yielded high performance materials. The nanocomposites were prepared by a simple and green process, and characterized by tensile tests, dynamical mechanical analysis (DMA), scanning electron microscopy (SEM), and swelling experiments. The effect of the nanofiber content on morphology, static, and dynamic mechanical properties was also investigated. The results showed an increase in the mechanical properties, such as Young's modulus and tensile strength, even with modest nanofiber loadings.

Compatible ternary blends of chitosan/poly(vinyl alcohol)/poly(lactic acid) produced by oil-in-water emulsion processing.

Ternary compatible blends of chitosan, poly(vinyl alcohol), and poly(lactic acid) were prepared by an oil-in-water (O/W) emulsion process. Solutions of chitosan in aqueous acetic acid, poly(vinyl alcohol) (PVA) in water, and poly(lactic acid) (PLA) in chloroform were blended with a high-shear mixer. PVA was used as an emulsifier to stabilize the emulsion and to reduce the interfacial tension between the solid polymers in the blends produced. It proved to work very well because the emulsions were stable for periods of days or weeks and compatible blends were obtained when PVA was added. This effect was attributed to a synergistic effect of PVA and chitosan because the binary blends PVA/PLA and chitosan/PLA were completely incompatible. The blends were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), stress-strain tests, and Fourier transform infrared spectroscopy (FTIR). The results indicated that despite the fact that the system contained distinct phases some degree of molecular miscibility occurred when the three components were present in the blend.

Trapping of charge carriers in colloidal particles of self-assembled films from TiO(2) and poly(vinyl sulfonic acid).

Self-assembled electrodes consisting of TiO(2) nanoparticles and poly(vinyl sulfonic acid) (PVS) were prepared by the layer-by-layer (LbL) technique. The electrostatic interaction between the TiO(2) nanoparticles and PVS allowed the growth of visually uniform multilayers of the composite, with high control of the thickness and nanoarchitecture. The electrochemical and chromogenic properties of these TiO(2)/PVS films were examined in an electrolytic solution of 0.5 M LiClO(4)/propylene carbonate. The presence of two intercalation sites was noted during the positive potential scan, and they were attributed to different mobilities of charge carriers. Several charge/discharge cycles demonstrated the trapping of charge carriers in the TiO(2) sites. The absorbance change associated with the oxidation of the trapping sites was attributed to electronic transitions involving energy states in the gap band formed due to the strong distortion of the TiO(2) host. Using the quadratic logistic equation (QLE), it was possible to analyze the electronic intervalence transfer from Ti(3+) to Ti(4+). Using the parameters obtained from this fitting, the amount of trapping sites in the LbL film was also determined. Electrochemical impedance spectroscopy (EIS) data gave the time constant associated with diffusion and the trapping sites. The diffusion coefficient of lithium ions changed from ca. 4.5 x 10(-13) cm(2) s(-1) to 3.0 x 10(-14) cm(2) s(-1) for all the potential range applied, indicating that PVS did not hinder the ionic transport within the LbL film. Finally, on the basis of the spectroelectrochemical data and scanning electron micrographs, the trapping effects were attributed to the colloidal particles of Li(0.55)TiO(2).

Physicochemical properties and sensing ability of metallophthalocyanines/chitosan nanocomposites.

Electroactive nanostructured films of chitosan (Ch) and tetrasulfonated metallophthalocyanines containing nickel (NiTsPc), copper (CuTsPc), and iron (FeTsPc) were produced via the electrostatic layer-by-layer (LbL) technique. The multilayer formation was monitored with UV-vis spectroscopy by measuring the increase of the Q-band absorption from metallophthalocyanines. Results from transmission and reflection infrared spectroscopy suggested specific interactions between SO(3)(-) groups from metallophthalocyanines and NH(3)(+) from chitosan. The electroactive multilayered films assembled onto an ITO electrode were characterized by cyclic voltammetry, with Ch/NiTsPc films showing higher stability and well-defined voltammograms displaying reversible redox peaks at 0.80 and 0.75 V. These films could be used to detect dopamine (DA) in the concentration range from 5.0 x 10(-6) to 1.5 x 10(-4) mol L(-1). Also, ITO-(Ch/NiTsPc)(n)() electrodes showed higher electrocatalytic activity for DA oxidation when compared with a bare ITO electrode. On the other hand, only the Ch/FeTsPc and Ch/CuTsPc modified electrodes could distinguish between DA and ascorbic acid. These results demonstrate that versatile electrodes can be prepared by incorporation of different metallophthalocyanine molecules in LbL films, which may be used in bioanalytical applications.