Extraction of cellulose and preparation of nanocellulose from sisal fibers

In this work a study on the feasibility of extracting cellulose from sisal fiber, by means of two different procedures was carried out. These processes included usual chemical procedures such as acid hydrolysis, chlorination, alkaline extraction, and bleaching. The final products were characterized by means of Thermogravimetric Analysis (TGA), Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Differential Scanning Calorimetry (DSC) and Scanning Electronic Microscopy (SEM). The extraction procedures that were used led to purified cellulose. Advantages and disadvantages of both procedures were also analyzed. Finally, nanocellulose was produced by the acid hydrolysis of obtained cellulose and characterized by Atomic Force Microscopy (AFM).     

Elastic-pulse propagation in thin hollow cones

Elastic pulses were generated in a thin (3-mm) right circular conical shell with apex angle of 20 deg, by an axial impact of a drop weight. Radial-strain pulses of about 250-μs duration were measured at three locations along the cone by semiconductor strain gages. The relative amplitude decrease of the strain pulse was determined as a function of the distance traveled. An approximate analytical solution for this problem is presented. It is shown that, for cones made of material with Poisson's ratio ν=1/3, the approximation leads to the one-dimensional spherical-wave equation and the wave velocity is that of longitudinal waves in thin plates. The decay of amplitude predicted by the model depends on the distance traveled and on the wavelength and it agrees fairly well with the experimental results. The model also gives an upper bound on the amplitude decrease of the pulse.     

Thermodynamic behaviour of some glycol—water mixtures. Excess and partial volumes

Densities of water—glycol (mono- di-, tri- and tetraethyleneglycol) mixtures have been measured over the entire composition range at 298. 15 K. Mixtures involving monoethyleneglycol (MEG) have also been studied at different temperatures from 308.15 to 288.15 K. Deviations, V^E, from ideal volumes of mixing have been calculated: negative values are observed for all systems. They increase with the number of ether functions present in the organic molecule; a slight dependence of V^E towards temperature has been shown in the water—MEG mixtures. Partial molal volumes have also been calculated for both components of each system; they exhibit an extremum in the water-rich region.     

Brown HT

Journal of Thermal Analysis and Calorimetry - Thermal behavior of Brown HT food dye was studied in correlation with the physical and biological antioxidant properties. Brown HT’s structure...     

Poisson's ratio and the densification of glass under high pressure

Because of a relatively low atomic packing density, (Cg) glasses experience significant densification under high hydrostatic pressure. Poisson's ratio (nu) is correlated to Cg and typically varies from 0.15 for glasses with low Cg such as amorphous silica to 0.38 for close-packed atomic networks such as in bulk metallic glasses. Pressure experiments were conducted up to 25 GPa at 293 K on silica, soda-lime-silica, chalcogenide, and bulk metallic glasses. We show from these high-pressure data that there is a direct correlation between nu and the maximum post-decompression density change.     

Vapour permeation and sorption in fluoropolymer gel membrane based on ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide

The emissions of hydrocarbons from fossil fuels into atmosphere entail both an economic loss and an environmental pollution. Membrane separations can be used for vapour recovery and/or vapour removal from the permanent gas stream, given that the appropriate membrane is identified. A neat poly(vinylidene fluoride-co-hexafluoropropylene) membrane is impermeable to both the representatives of aliphatic hydrocarbons and branched hydrocarbons, namely hexane and isooctane, whereas the permeation flux is enhanced by the presence of 80 mass % of the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide in the membrane, as detailed in this work. The permeabilities of hydrocarbon vapours were determined from the binary mixture containing hydrocarbon and nitrogen to simulate the real input of an air stream containing a condensable hydrocarbon. The diffusion coefficient determined from sorption measurements was higher for hexane, as would be expected for a smaller molecule, whereas both the sorption isotherms and permeabilities of the hydrocarbons studied were found to be almost identical. It is possible that the sorption effect predominates in the transport mechanism for VOCs/N₂ separations.     

Tartrazine: physical,thermal and biophysical properties of the most widely employed synthetic yellow food-colouring azo dye

Journal of Thermal Analysis and Calorimetry - The food-colouring dye tartrazine is a significant additive and in the same time a biologically active material. Thermal behaviour of trisodium...     

A Comparison of Modeling Approaches for Dispersion Homopolymerization of MMA and Styrene in Supercritical CO2

A comparison of kinetic models for dispersion polymerization of MMA and styrene in supercritical CO₂ is presented. The limiting case of solution polymerization, as a simplified case, was also addressed. Calculation of the partition of components between the continuous and dispersed phases was emphasized. Experimental data for the solution and dispersion polymerizations of styrene and MMA, using different types of stabilizers, were used to guide the study. Although all the models analyzed can be considered as “adequate” in representing the behavior of the system, some of their strengths and drawbacks have been highlighted.

     

Structure-activity relationships of antibacterial acyl-lysine oligomers

We describe structure-activity relationships that emerged from biophysical data obtained with a library of antimicrobial peptide mimetics composed of 103 oligoacyllysines (OAKs) designed to pin down the importance of hydrophobicity (H) and charge (Q). Based on results obtained with OAKs displaying minimal inhibitory concentration < or = 3 microM, the data indicate that potent inhibitory activity of the gram-negative Escherichia coli and the gram-positive Staphylococcus aureus required a relatively narrow yet distinct window of HQ values where the acyl length played multiple and critical roles, both in molecular organization and in selective activity. Thus, incorporation of long-but not short-acyl chains within a peptide backbone is shown to lead to rigid supramolecular organization responsible for poor antibacterial activity and enhanced hemolytic activity. However, sequence manipulations, including introduction of a tandem lysine motif into the oligomer backbone, enabled disassembly of aggregated OAKs and subsequently revealed tiny, nonhemolytic, yet potent antibacterial derivatives.     

Efficient and convenient synthesis,characterization, and antimicrobial evaluation of some new tetracyclic 1,4-benzothiazines

In the present study, 20 new tetracyclic 1,4-benzothiazines (4a–4 t) were conveniently synthesized in good yields and characterized by different spectral and physical techniques. The in vitro antimicrobial evaluation of the synthesized benzothiazine derivatives was performed by serial dilution against two Gram-positive bacteria [Bacillus subtilis (MTCC 441) and Staphylococcus epidermidis (MTCC 6880)], two Gram-negative bacteria [Escherichia coli (MTCC 1652) and Pseudomonas aeruginosa (MTCC 424)], and two fungal strains [Candida albicans (MTCC 227) and Aspergillus niger (MTCC 8189)]. The derivatives 4 l and 4 t were found to be more potent than standard drug, i.e., fluconazole, against A. niger and C. albicans, respectively.