Analía Vázquez

Mechanical properties and water absorption behavior of composites made from a biodegradable matrix and alkaline-treated sisal fibers

Biocomposites were produced using a biodegradable material as matrix, and sisal fibers as reinforcement. The biodegradable material is a commercial product called MaterBi-Y, which is based on a cellulose derivatives and starch system. The characterization of these biocomposites was not done before and it is necessary in order to select a material instead of nonbiodegradable matrices. An alkaline treatment was performed in order to improve the mechanical properties of the fiber. The effect of the treatment on fiber properties and on impact, flexural, and tensile properties of composites were determined. Fiber content enhances the tensile properties of the biodegradable matrix. Water sorption studies were performed. The experimentally observed tensile properties (modulus and tensile strength) of short sisal fiber-reinforced cellulose derivatives/starch composites with different fiber loading are compared with the calculated values obtained from the existing theories of reinforcement.

Effect of Water Sorption on the Flexural Properties of a Fully Biodegradable Composite

The water absorption process of the short-time process of a fully biodegradable composite is important in order to know the effect of water uptake on the mechanical properties before the polymer is hydrolysed. The matrix of the studied composites is a commercial blend based on starch and cellulose derivatives, named MaterBi-Y. The effect of the fibre content was also taken into account, because short sisal fibres’ content was changed from 5 to 15 wt%. Diffusion coefficients, the equilibrium water uptake and the flexural properties were determined during sorption experiments at different bath temperatures: 5, 25 and 60 C. Equations obtained from microscopic mass balances for diffusion in solids were used to model the water absorption of these composites as a function of immersion time.

Modeling of dynamic mechanical properties of epoxy and epoxy-phenolic reinforced with multi-wall carbon nanotubes

The viscoelastic properties of nanocomposites based on epoxy and epoxy-phenolic blend matrix reinforced with multi-wall carbon nanotubes were studied. The content of carbon nanotube (0.2 and 0.5u2009wt.%) and its surface state (pristine vs. oxidized) varied. The characterization of the nanocomposites was done by means of infrared spectroscopy and chemical methods. From the viscoelastic properties of nanocomposites, characteristic properties such as storage modulus (E0), tan δ and damping peak (tan δ) were obtained. The void content was also determined. Also, Weibull statistics are used to represent the failure of secondary bonds during the relaxation processes that lead to stiffness change over the full range of use temperatures. The incorporation of phenolic resin to an epoxy matrix leads to an increase of the relaxation modulus. The glass transition temperature of the epoxy-phenolic nanocomposites decrease when it is incorporated carbon nanotubes, independently of its state (pristine or oxidized).

Reactive oxygen species and nitric oxide are involved in polyamine-induced growth inhibition in wheat plants

AbstractPolyamines (PAs) produce H2O2 and nitric oxide (NO) during their normal catabolism and modulate plant growth and development. To explore the biochemical basis of PAs-induced growth inhibition in Triticum aestivum L seedlings, we examined the role of O2·-, H2O2 or NO in shoot and root development. Although all PA treatments resulted in a variable reduction of root and shoot elongation, spermine (Spm) caused the greater inhibition in a similar way to that observed with the NO donor, sodium nitroprusside (SNP). In both cases, O2·- production was completely blocked whereas H2O2 formation was high in the root apex under SNP or Spm treatments. Catalase recovered root and shoot growth in SNP but not in Spm-treated plants, revealing the involvement of H2O2 in SNP-root length reduction. The addition of the NO scavenger, cPTIO, restored root length in SNP- or Spm-treated plants, respectively, and partially recovered O2·- levels, compared to the plants exposed to PAs or SNP without cPTIO. A strong correlation was observed between root growth restoration and O2·- accumulation after treating roots with SNP + aminoguanidine, a diamine oxidase inhibitor, and with SNP + 1,8-diaminoctane, a polyamine oxidase inhibitor, confirming the essential role of O2·- formation for root growth and the importance of the origin and level of H2O2. The differential modulation of wheat growth by PAs through reactive oxygen species or NO is discussed.n Graphical abstractPolyamines, nitric oxide and ROS interaction in plants during plant growth

Influence of tribological test on the global conversion of natural composites

1Grupo de Nuevos Materiales, Universidad Pontificia Bolivariana – UFB, Medellín, Antioquia, Colombia 2Facultad de Ingeniería Agroindustrial, Universidad Pontificia Bolivariana – UFB, Medellín, Antioquia, Colombia 3Facultad de Ingeniería Textil, Universidad Pontificia Bolivariana – UFB, Medellín, Antioquia, Colombia 4Facultad de Ingeniería Mecánica, Universidad Pontificia Bolivariana – UFB, Medellín, Antioquia, Colombia 5Consejo Nacional de Investigaciones Científicas y Técnicas – CONICET, Instituto de Tecnología en Polímeros y Nanotecnología, Universidad de Buenos Aires – UBA, Buenos Aires, Capital Federal, Argentina 6Facultad de Ingeniería Química, Universidad Pontificia Bolivariana – UFB, Medellín, Antioquia, Colombia