Cellulose nanocrystals/polyurethane nanocomposites. Study from the viewpoint of microphase separated structure.

Cellulose nanocrystals (CNC) successfully obtained from microcrystalline cellulose (MCC) were dispersed in a thermoplastic polyurethane as matrix. Nanocomposites containing 1.5, 5, 10 and 30 wt% CNC were prepared by solvent casting procedure and properties of the resulting films were evaluated from the viewpoint of polyurethane microphase separated structure, soft and hard domains. CNC were effectively dispersed in the segmented thermoplastic elastomeric polyurethane (STPUE) matrix due to the favorable matrix-nanocrystals interactions through hydrogen bonding. Cellulose nanocrystals interacted with both soft and hard segments, enhancing stiffness and stability versus temperature of the nanocomposites. Thermal and mechanical properties of STPUE/CNC nanocomposites have been associated to the generated morphologies investigated by AFM images.

Surface modification of multiwalled carbon nanotubes via esterification using a biodegradable polyol.

Multiwalled carbon nanotubes (MWCNT) were surface modified firstly oxidizing them with a H2SO4/HNO3 mixture to obtain more reactive carboxylic groups on their surface and then higher functionality. Secondly the oxidized nanotubes (MWCNT-COOH) were dispersed in tetrahydrofuran (THF) and made react via esterification with a poly(hexamethylene carbonate-co-caprolactone)diol, a potentially biodegradable polyol with hydroxyl groups at its ends. Modification process steps were characterized using Fourier transform infrared spectroscopy, FT-IR, ultraviolet spectroscopy, UV, solubility in different solvents, thermo-gravimetric analysis, TGA, as well as atomic force microscopy, AFM. Results suggest that surface carboxylic groups are reactive enough to graft polymer chains onto their surface.

Effects of amine molecular structure on carbon nanotubes functionalization.

Three amines with different molecular structure, triethylenetetramine (TETA) and two polyetheramines (Jeffamine D-230 and Jeffamine T-403) were employed to functionalize multi-walled carbon nanotubes (MWCNT) previously oxidized by acid treatment. The functionalized MWCNT were characterized by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, UV-vis spectroscopy and the surface modification was investigated by field emission scanning electron microscopy (FE-SEM). Thermogravimetric analysis (TGA) was employed to quantify the amount of amine groups anchored to MWCNTs. The results have shown that the efficiency of amine functionalization is in the order TETA > D-230 > T-403, thus showing that amine chemical structure and molecular weight are important parameters on functionalization of carbon nanotubes.

Purification and functionalization of carbon nanotubes by classical and advanced oxidation processes.

Advanced oxidation technologies (AOT) were applied for the production of accurately controlled oxidized multi-walled carbon nanotubes. Fenton process is effective to get carboxylic (-COO- or -COOH) and OH groups on the surface of carbon nanotubes while Photofenton and UV/H2O2 processes mostly produce OH groups on surface of multiwalled carbon nanotubes (MWCNT). All of them preserve the structure of MWCNT allowing to achieve accurately controlled oxidized MWCNT. Fourier transform infrared spectroscopy (FTIR) and thermogravimetical analysis (TGA) show that the acid treatment is the more efficient technique to generate COOH groups on MWCNT surface. However, this chemical technique generates strong damages on the MWCNT structure, as demonstrated by TGA, field emission scanning electron microscopy and transmission electron microscopy results.

The effect of thermal and vapor annealing treatments on the self-assembly of TiO2/PS-b-PMMA nanocomposites generated via the sol-gel process.

Polystyrene-block-poly(methyl methacrylate) (SMMA) block copolymer has been used as a structure-directing agent for generating TiO2 /SMMA nanocomposites via the sol-gel process using a hydrophobic surfactant. The aim of the work has been focused on the preparation of well-defined nanostructured composites based on the self-assembling capability of the block copolymer using two different annealing methods: thermal- and solvent-induced microphase separation. The addition of different amounts of nanoparticles caused strong variations in the self-assembled morphology of the TiO2 /SMMA nanocomposites with respect to the block copolymer, as observed by atomic force microscopy (AFM). To verify the confinement of the nanoparticles in the PMMA block 3D AFM images and corresponding AFM profiles have also been reported. UV light irradiation of the nanocomposite films provoked the removal of the organic matrix and consequently led to an array of TiO2 nanoparticles on the substrate surface.

Processing conditions analysis of Eucalyptus globulus plywood bonded with resol-tannin adhesives.

Phenol-formaldehyde resol containing mimosa tannin extract was employed to produce plywood panels with two plies from Eucalyptus globulus veneers. The effect of processing conditions and tannin content on the gelation time of the adhesive in the glue line was evaluated by dynamic-mechanical analysis (DMA). These results were related with shear strength and wood failure of glue line in the final panels. Hazardous petrochemical phenol could be partially substituted in resols in industrial applications by addition of mimosa tannin extracts.

Hybrid titanium dioxide/PS-b-PEO block copolymer nanocomposites based on sol-gel synthesis.

The poly(styrene)-b-poly(ethylene oxide) (SEO) amphiphilic block copolymer, with two different molecular weights, has been used as a structure directing agent for generating nanocomposites of TiO(2)/SEO via the sol-gel process. SEO amphiphilic block copolymers are designed with a hydrophilic PEO-block which can interact with inorganic molecules, as well as a hydrophobic PS-block which builds the matrix. The addition of different amounts of sol-gel provokes strong variations in the self-assembled morphology of TiO(2)/SEO nanocomposites with respect to the neat block copolymer. As confirmed by atomic force microscopy (AFM), TiO(2)/PEO-block micelles get closer, forming well-ordered spherical domains, in which TiO(2) nanoparticles constitute the core surrounded by a corona of PEO-blocks. Moreover, for 20 vol% sol-gel the generated morphology changes to a hexagonally ordered structure for both block copolymers. The cylindrical structure of these nanocomposites has been confirmed by the two-dimensional Fourier transform power spectrum of the corresponding AFM height images. Affinity between titanium dioxide precursor and PEO-block of SEO allows us to generate hybrid inorganic/organic nanocomposites, which retain the optical properties of TiO(2), as evaluated by UV-vis spectroscopy.

Liquid crystal alignment in electro-responsive nanostructured thermosetting materials based on block copolymer dispersed liquid crystal.

Novel well-defined nanostructured thermosetting systems were prepared by modification of a diglicydylether of bisphenol-A epoxy resin (DGEBA) with 10 or 15 wt% amphiphilic poly(styrene-b-ethylene oxide) block copolymer (PSEO) and 30 or 40 wt% low molecular weight liquid crystal 4'-(hexyl)-4-biphenyl-carbonitrile (HBC) using m-xylylenediamine (MXDA) as a curing agent. The competition between well-defined nanostructured materials and the ability for alignment of the liquid crystal phase in the materials obtained has been studied by atomic and electrostatic force microscopy, AFM and EFM, respectively. Based on our knowledge, this is the first time that addition of an adequate amount (10 wt%) of a block copolymer to 40 wt% HBC-(DGEBA/MXDA) leads to a well-organized nanostructured thermosetting system (between a hexagonal and worm-like ordered structure), which is also electro-responsive with high rate contrast. This behavior was confirmed using electrostatic force microscopy (EFM), by means of the response of the HBC liquid crystal phase to the voltage applied to the EFM tip. In contrast, though materials containing 15 wt% PSEO and 30 wt% HBC also form a well-defined nanostructured thermosetting system, they do not show such a high contrast between the uncharged and charged surface.

Physico-chemical characterization of lignins from different sources for use in phenol-formaldehyde resin synthesis.

During the last decades lignin has been investigated as a promising natural alternative to petrochemicals in phenol-formaldehyde (PF) resin production, due to their structural similarity. Physico-chemical characterization of three types of lignin, namely kraft pine lignin (L1), soda-anthraquinone flax lignin (L2), and ethanol-water wild tamarind lignin (L3) has been evaluated to determine which one is the most suitable chemical structure for above purpose. Characterization has been performed using Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectrometry ((1)H NMR) to analyse the chemical structure, gel permeation chromatography (GPC) for determining molecular weight (MW) and molecular weight distribution (MWD), differential scanning calorimetry (DSC) to measure the glass transition temperature and thermogravimetric analysis (TGA) to follow the thermal degradation. Both structural and thermal characteristics suggest that kraft pine lignin (L1) would be a better phenol (P) substitute in the synthesis of lignin-phenol-formaldehyde (LPF) resins, as it presents higher amounts of activated free ring positions, higher MW and higher thermal decomposition temperature.

Crystallization of poly(L-lactid acid) monitored by dielectric relaxation spectroscopy and atomic force microscopy.

An investigation was carried out on the crystallization process of poly(l-lactid acid) by dielectric relaxation spectroscopy and atomic force microscopy. Experimental results were generated by dielectric relaxation spectroscopy over a wide range of frequency and temperature in both the wholly amorphous state and during crystallization. The variation of the average relaxation time was studied during crystallization at 80 degrees C and the temperature dependence of this relaxation time for wholly amorphous and crystallized samples was analysed. This behaviour was modelled by Havriliak-Negami and Vogel-Fulcher equations. The sensitivity of the segmental dynamics to the degree of crystallinity was analysed, taking into account the relaxing segments and the thickness of the amorphous layer between lamellae. The morphologies obtained during crystallization processes at 80, 130 and 150 degrees C were monitored by atomic force microscopy at both the lamellar level and by analysing the multilayered superstructures formed. Hedrites, intermediate structures between single lamellar crystals and mature spherulites, were found to appear at the highest temperatures, whereas no evidence of hedrites was found at 80 degrees C, the spherulites seemed to be constructed from a framework of individual dominant lamellae that splay apart and branch. Complementary to the atomic force microscopy study, the evolution of the obtained morphologies was also followed by optical microscopy. Supporting evidence about the thermal behaviour of the polymers was obtained with differential scanning calorimetry.

Tracheal versus pulmonary deposition and clearance of inhaled Pasteurella haemolytica or Staphylococcus aureus in mice.

The aim of this investigation was to do a comparative study on the deposition and clearance of inhaled bacteria between the lungs and tracheae of mice exposed to aerosols of bacteria. Two hundred and eighty-eight mice were divided into four groups (n = 72) and exposed to aerosols of Pasteurella haemolytica or Staphylococcus aureus in four replicates. The numbers of bacteria were determined in the trachea and lungs of mice sacrificed 0, 2, 4, 8, 12, 24, 48 and 72 hours postexposure. Results indicated that bacterial deposition was greater in lungs than in tracheae. No significant (p greater than 0.05) difference was observed between P. haemolytica and S. aureus clearance rates. Although bacteria were rapidly eliminated from the whole respiratory tract, bacterial clearance was significantly (p less than 0.002) faster in tracheae than lungs. A significant (p less than 0.05) replicate effect was also observed.

Pulmonary recruitment of neutrophils and bacterial clearance in mice inoculated with aerosols of Pasteurella haemolytica or Staphylococcus aureus.

Pulmonary alveolar macrophages are considered to be the main phagocytic cell of the pulmonary defense mechanism. However recent studies indicate that neutrophils may also participate in the defense against inhaled bacteria. The aim of this investigation was to study in mice the correlation between numbers of phagocytic cells in the bronchoalveolar space and the pulmonary clearance of bacteria. White mice were exposed to aerosols of Pasteurella haemolytica (n = 129) or Staphylococcus aureus (n = 129) in three different experimental replicates. Another group of mice (n = 22) was sham exposed to an aerosol of sterile phosphate buffered solution in a single replicate. Animals were sacrificed at various times postaerosolization. The numbers of neutrophils and alveolar macrophages in lung lavages and the pulmonary bacterial clearance rates were determined and statistically analysed. No significant differences (p greater than 0.05) were observed in the rates of pulmonary clearance between the two genera of bacteria, but P. haemolytica had a significant (p less than 0.05) replicate effect. The number of alveolar macrophages was not significantly affected by either bacteria or phosphate buffered solution. Exposure to P. haemolytica resulted in dramatic, significant (p less than 0.01) but transient increases in neutrophils in the bronchoalveolar space as well as a significant (p less than 0.01) increase in the weights of lung. The correlation between neutrophils and clearance was positive for P. haemolytica but negative for S. aureus. These results indicate that both species of bacteria are rapidly eliminated from the lung despite a rather different cellular response.