Susana Hernández-López

A comparative study of natural, formaldehyde-treated and copolymer-grafted orange peel for Pb(II) adsorption under batch and continuous mode

Natural, formaldehyde-treated and copolymer-grafted orange peels were evaluated as adsorbents to remove lead ions from aqueous solutions. The optimum pH for lead adsorption was found to be pH 5. The adsorption process was fast, reaching 99% of sorbent capacity in 10 min for the natural and treated biomasses and 20 min for the grafted material. The treated biomass showed the highest sorption rate and capacity in the batch experiments, with the results fitting well to a pseudo-first order rate equation. In the continuous test with the treated biomass, the capacity at complete exhaustion was 46.61 mg g(-1) for an initial concentration of 150 mg L(-1). Scanning electronic microscopy and energy dispersive X-ray spectroscopy indicated that the materials had a rough surface, and that the adsorption of the metal took place on the surface. Fourier transform infrared spectroscopy revealed that the functional groups responsible for metallic biosorption were the -OH, -COOH and -NH(2) groups on the surface. Finally, the thermogravimetric analysis indicates that a mass reduction of 80% can be achieved at 600 degrees C.

Synthesis and Thermal Cross-Linking Study of Partially-Aminated Epoxidized Linseed Oil

The reaction of diamines or triamines with epoxidized oils leads to different reactions of intra/intermolecular cross-linking and the disruption of the ester linkage. However, by controlling the reaction conditions of temperature, stoichiometry and catalyst, production of oxirane rings without cross-linking and/or disruption of ester group can be achieved. In this work, the synthesis of cross-linking aminated–epoxidized linseed oil resins in two stages is presented. The first one started with epoxidized linseed oil (55.4%) which was subjected to a partial aminolysis using three different amines (ethylenediamine, p-xylylenediamine and triethylenetetramine) and a ZnCl2 catalyst. Products were characterized by FT-IR, 1H-NMR and DSC. In the second stage, the thermal cross-linking reaction (thermal cure) for obtaining cross-linked polymers was studied by calorimetry using isothermal experiments. These results were extrapolated for producing sheet molding thermally cross-linked polymers.

Textural, structural and electrical properties of TiO2 nanoparticles using Brij 35 and P123 as surfactants

Abstract The effect of the use of the triblock copolymer Pluronic P123[(PEO)20(PPO)70(PEO)20, Aldrich] and the non-ionic polyoxyethylene-lauryl ether Brij 35 as surfactants on the textural, structural and electrical properties of nanosized TiO2 is analyzed in this work. The as-obtained samples were thermally treated at 400 °C to eliminate the surfactant, promote dehydroxylation and crystallize the sample. The TiO2 samples were characterized by thermal analysis, N2 physisorption, x-ray diffraction analysis, micro-Raman spectroscopy and scanning electron microscopy. To evaluate the TiO2 electrical features, I–V data were obtained. The x-ray diffraction results show that in the chemical synthesis using surfactants, the crystallite size is smaller than that of the commercial sample. The Raman spectroscopy results clearly indicate that, when P123 is used, the anatase phase of TiO2 is obtained, whereas when Brij 35 is used a mixture of the anatase and brookite phases is obtained. The specific surface area and crystallite size of the TiO2 prepared as indicated above are higher and smaller, respectively, than the corresponding properties found in commercial TiO2. The I–V plot showed a nonlinear behavior of the nanosized TiO2. The samples obtained with P123 showed the best electrical conductivity.

Cellulose-Based Polymer Composite with Carbon Black for Tetrahydrofuran Sensing

This work focused on studying the sensing efficiency of tetrahydrofuran (THF) by composite films made of thin layers of a cellulose-based polymer and carbon black. We analyze the reproducibility, durability, desorption time, and the sensitivity percent as a function of the amount of solvent. Two types of experiments were conducted, (1) progressive sensing test (PST) which consisted of progressively increasing the amount of solvent from 0.1 mL increments up to 1.0 mL and (2) multiple sensing test (MST) where the layers were subjected to consecutive pulses of the same amount of solvent, with a minimum of 0.1 mL and a maximum of 0.4 mL. The response and desorption times were a few seconds, and the sensitivity percent ranged from 1% to 170% and was dependent on the solvent quantity.

Biosynthesis of Silver Nanoparticles on Orthodontic Elastomeric Modules: Evaluation of Mechanical and Antibacterial Properties

In the present study, silver nanoparticles (AgNPs) were synthesized in situ on orthodontic elastomeric modules (OEM) using silver nitrate salts as metal-ion precursors and extract of the plant Hetheroteca inuloides (H. inuloides) as bioreductant via a simple and eco-friendly method. The synthesized AgNPs were characterized by UV-visible spectroscopy; scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS) and transmission electron microscopy (TEM). The surface plasmon resonance peak found at 472 nm confirmed the formation of AgNPs. SEM and TEM images reveal that the particles are quasi-spherical. The EDS analysis of the AgNPs confirmed the presence of elemental silver. The antibacterial properties of OEM with AgNPs were evaluated against the clinical isolates Streptococcus mutans, Lactobacillus casei, Staphylococcus aureus and Escherichia coli using agar diffusion tests. The physical properties were evaluated by a universal testing machine. OEM with AgNPs had shown inhibition halos for all microorganisms in comparison with OEM control. Physical properties increased with respect to the control group. The results suggest the potential of the material to combat dental biofilm and in turn decrease the incidence of demineralization in dental enamel, ensuring their performance in patients with orthodontic treatment.

Effect of thermal treatment on Zn nanodisks

Metallic Zn nanodisks with hexagonal morphology were obtained onto glass substrate under vacuum thermal evaporation. A thermal characterization of Zn nanodiks showed a lower oxidation temperature than source powder Zn. Different thermal treatment on Zn nanodisks played an important role on the morphology, crystal size and surface vibrational modes of ZnO. The growth of ZnO nanoneedles started at the edge of metallic zinc hexagonal structures according with SEM images, the higher temperature the longer needles were grown. XRD diffractogram confirmed the wurtzite structure of ZnO with metallic nuclei. A wide band between 530 and 580 cm−1 of Raman scattering corresponded at surface vibrational modes not observed at higher temperature.

Characterization of orientation in polyethylene by scratch testing

Abstract Microscratch experiments were performed to evaluate effects of uniaxial stretching by 200 % in low density polyethylene (LDPE) along parallel and perpendicular directions with respect to stretching. Penetration depth, healing depth and viscoelastic recovery have been determined. Clear orientation effects are seen. The direction parallel to the extension axis shows strong resistance to scratching and also the highest recovery (a memory effect). Unoriented material exhibits behavior intermediate between that of oriented samples in parallel and perpendicular directions. The sliding wear was determined by multiple scratching along the same groove and here also was found orientation dependence. Polarized micro-Raman experiments on the oriented LDPE samples were carried out. Since scratching and sliding wear results are strongly affected by polymer orientation, one can use both kinds of tests as a measure of orientation - and also to vary orientation to control tribological properties.

Thickness effect on electric resistivity on polystyrene and carbon black- based composites

Changes on electrical resistivity were experimentally studied for polystyrene and carbon black-based composites respect to the temperature. 22% w/w carbon black composite films at 30 μm, 2mm y 1cm thick were submitted to thermal heating-cooling cycles from room temperature to 100°C, slightly up to Tg of the composite. For each cycle changes on electrical resistivity constituent a hysteresis loop that depends on the sample thickness. The changes during the heating stage could be explained as a consequence of the thermal expansion and mobility of the polymer chains at Tg, producing a disconnecting of the electrical contacts among carbon black particles and an important increasing (200%) of the electrical resistivity. For each cycle, the hysteresis loop was observed in thicker samples, whereas for 30 ? m thickness sample the hysteresis loop was lost after four cycles.

Electric anisotropy in high density polyethylene + carbon black composites induced by mechanical deformation

High density polyethylene + carbon black composites with electrical anisotropy was studied. Electrical anisotropy was induced by uniaxial mechanical deformation and injection moulding. We show that anisotropy depends on the carbon black concentration and percentage deformation. Resistivity had the highest anisotropy resistivity around the percolation threshold. Perpendicular resistivity showed two magnitude orders higher than parallel resistivity for injected samples, whereas resistivity showed an inverse behaviour for 100% tensile samples. Both directions were set respect to the deformation axe. Anisotropy could be explained in terms of the molecular deformation (alignment) of the polymer chains as a response of the deformation process originating a redistribution of the carbon black particles in both directions. Alignment of the polymer chains was evidenced by polarized Raman spectroscopy.

Conductive polymeric composites based on multiwalled carbon nanotubes and linseed oil functionalized and cross-linked with diacetylenes from propargyl alcohol

Diacetylene-functionalized epoxidized linseed oil (DAELO) matrix was synthesized in order to improve the dispersion of multiwalled carbon nanotubes (MWCNTs) without the necessity of some chemical or physical modification of them. That fact was evidenced by the low critical concentration of DAELO-based composites in comparison (1.0 wt% MWCNTs) with the epoxidized linseed oil- (ELO-) based composites (5 wt% MWCNTs). For this, both series of composites were prepared by the ultrasonic dispersion method using the same conditions of solvent, dilution, and sonication time. It was shown that, tailoring the polymer matrix with groups rich in nonpolar electric density, as diacetylene, and capable of interacting by van der Waals forces, it is possible to improve the dispersion of carbon nanotubes (CNTs) without necessity of some modification knowing that those treatments usually affect lowering their electrical properties.