Laura M. Sanchez; Pablo A. Ochoa Rodríguez; Daniel G. Actis; Verónica R. Elías; Griselda A. Eimer; Verónica Lassalle; Vera A. Alvarez
Abstract
In this work, iron oxide-based magnetic nanoparticles (MNPs) stabilized by polyacrylic acid (PAA) polymer were prepared and characterized as a continuation of a previous research already reported. MNPs composed by pure magnetite cores having good magnetic properties were developed, thus achieving an ...
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In this work, iron oxide-based magnetic nanoparticles (MNPs) stabilized by polyacrylic acid (PAA) polymer were prepared and characterized as a continuation of a previous research already reported. MNPs composed by pure magnetite cores having good magnetic properties were developed, thus achieving an improvement in the modified coprecipitation method used. The photocatalytic activity of the nanoparticles towards acid orange 7 (AO7), under both radiation types, UV-Vis and LED-Vis, was tested. Pollutant degradation percentages of 64 and 37 % were obtained by using UV-Vis and LED-Vis radiation, respectively.
Danila Merino; Vera A. Alvarez
Abstract
Novel starch-based films were previously proposed as agricultural mulches and their main properties were critically addressed. In this report, the effects of chemical modification by crosslinking (phosphorylation) and surface functionalization with chitosan on corn starch-films biodegradability were ...
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Novel starch-based films were previously proposed as agricultural mulches and their main properties were critically addressed. In this report, the effects of chemical modification by crosslinking (phosphorylation) and surface functionalization with chitosan on corn starch-films biodegradability were studied. The biodegradability assay was performed in soil using a professional substrate. The biodegradation and disintegration of samples were followed by measuring their weight loss (WL), water sorption (WS) and changes in appearance (by photographs). Additionally, changes in surface morphology at microscopic level were investigated by scanning electron microscopy (SEM), while structural and chemical changes were evaluated by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Results indicate that neither the chemical modification by phosphorylation, nor the chitosan-functionalization of the surface produced changes in films biodegradation time, which is a positive result. All materials degrade almost completely in three months following a three-step mechanism that involves plasticizer leaching, microbial development, bio-erosion of the surface and the starch molecular weight diminution. Copyright © VBRI Press.
Melina E. Bracone; Leandro N. Luduena; Vera A. Alvarez
Abstract
Cellulose nanofibrils can be obtained from microcrystalline cellulose by acid hydrolysis processes. Under optimum hydrolysis conditions is possible to obtain cellulose nanofibers with high surface/volume ratio, high aspect ratio (length to diameter), high crystallinity and improved thermal stability. ...
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Cellulose nanofibrils can be obtained from microcrystalline cellulose by acid hydrolysis processes. Under optimum hydrolysis conditions is possible to obtain cellulose nanofibers with high surface/volume ratio, high aspect ratio (length to diameter), high crystallinity and improved thermal stability. All these parameters then determine their effectiveness as reinforcement in a polymer matrix. In this work, cellulose nanofibrils were obtained from commercial microcellulose supplied by Aldrich. The acid hydrolysis synthesis was optimized studying the effect of reaction time and temperature and acid solution concentration. The optimized parameters were selected so as to obtain fibers with high crystallinity, high aspect ratio with diameter in nanoscale and high thermal stability. The morphology and size (length and diameter) of the fibers was analyzed by Field Emission Scanning Electron Microscopy (FESEM), the chemical structure by Fourier Transform Infrared Spectroscopy (FTIR), thermal stability by Thermogravimetric Analysis (TGA) and crystallinity by X-ray Diffraction (XRD). Copyright © VBRI Press.
M. Paula Guarás; Vera A. Alvarez; Leandro N. Ludueña
Abstract
A twin screw extrusion processing method was developed for the preparation of thermoplastic starch (TPS) for packaging applications. Different plasticizer combinations were used looking for the minimal temperature profile in the extruder in order to prevent the thermal degradation of TPS. The effect ...
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A twin screw extrusion processing method was developed for the preparation of thermoplastic starch (TPS) for packaging applications. Different plasticizer combinations were used looking for the minimal temperature profile in the extruder in order to prevent the thermal degradation of TPS. The effect of storage time at 25 °C and 50% of relative humidity on the properties of TPS was studied. Plasticized TPS samples observed by scanning electron microscopy showed homogeneous fracture surfaces without unstructured starch granules. X-ray diffractometry tests showed retro gradation of all TPS formulations with progressive Vh-type crystal structure formation. Temperature for maximum thermal degradation rate of raw materials was shifted to higher values after preparing the TPS, suggesting not only physical but also chemical interactions between plasticizers and starch molecules. Mechanical properties were significantly improved replacing 10 wt. % of glycerol by water as plasticizer, which was attributed to the increased gelatinization degree and the reduction of thermal degradation.
Romina P. Ollier; Matias R. Lanfranconi; Vera A. Alvarez; Leandro N. Ludue
Abstract
In this work, biodegradable nanocomposites based on polycaprolactone (PCL) reinforced with 2.5, 5.0 and 7.5 wt.% of two different clays, a commercial organo-clay (Cloisite 20A, C20A) and a laboratory modified bentonite with tributylhexadecyl phosphonium bromide (bTBHP), were prepared by melt intercalation ...
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In this work, biodegradable nanocomposites based on polycaprolactone (PCL) reinforced with 2.5, 5.0 and 7.5 wt.% of two different clays, a commercial organo-clay (Cloisite 20A, C20A) and a laboratory modified bentonite with tributylhexadecyl phosphonium bromide (bTBHP), were prepared by melt intercalation followed by compression molding. The study contemplates the analysis of chemical (Infrared Spectrometry, FTIR), morphological (X-Ray Diffractometry, XRD, Scanning Electron Microscopy, SEM, and Transmission Electron Microscopy, TEM), rheological, thermal (Differential Scanning Calorimetry, DSC, and Thermogravimetrical Analysis, TGA) and mechanical properties (tensile tests), which are important properties for packaging applications.In previous works, we concluded that higher clay dispersion degree inside the PCL matrix is expected when clays with large interlayer distance, strong hydrophobicity and strong processing stability are used. In the present work, the opposite result was obtained. Although the phosphonium treated clay (bTBHP) showed the largest interlayer distance (d001), strongest hydrophobicity and the best processing stability, the clay dispersion degree inside PCL was worse than in the case of the alkylammonium treated clay (C20A). PCL/bTBHP nanocomposites showed weaker mechanical properties in comparison with PCL/C20A ones, which is in accordance with the morphological analysis. On the other hand, the thermal properties of the matrix were not substantially affected by clay incorporation in both nanocomposites.
Jimena S. Gonzalez; Alejandra Ponce; Vera A. Alvarez
Abstract
During the last decade researchers have been working to find effective wound dressing materials. The materials have to be designed to hold moisture in the surface of the wound, providing the ideal environment for cleaning the wound, absorbing the exudates, eliminating the odour and promoting the healing ...
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During the last decade researchers have been working to find effective wound dressing materials. The materials have to be designed to hold moisture in the surface of the wound, providing the ideal environment for cleaning the wound, absorbing the exudates, eliminating the odour and promoting the healing process. In this scenario, hydrogels emerge as excellent options for that. However, due to poor mechanical and antimicrobial properties of many conventional hydrogels, composite hydrogels are now designed in order to improve mechanical stiffness and durability. For this purpose, nanocomposite based on poly(vinyl alcohol) (PVOH) and different concentration of bentonite (0-7 wt.%) were obtained by the freezing-thawing technique and characterized by means of morphological, physical, thermal, mechanical, barrier and antimicrobial properties. Herein it was developed a non-expensive, eco-friendly and a facile method to obtain nanocomposite hydrogels based on PVOH with reasonable mechanical properties (Young Modulus of 0.5-0.8 MPa), good microbial barrier properties, adequate water vapour transmission rates and excellent swelling behaviour (195-336%). Moreover, it was found that the porous sizes of the samples can be controlled by the addition of the clay. All obtained results indicate that the PVOH/ 3% bentonite hydrogels show potential to be used as wound healing.
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