Natalia Herrera - Academia.edu (original) (raw)

Uploads

Papers by Natalia Herrera

Nanomaterials, 2021

The orientation of polymer composites is one way to increase the mechanical properties of the mat... more The orientation of polymer composites is one way to increase the mechanical properties of the material in a desired direction. In this study, the aim was to orient chitin nanocrystal (ChNC)-reinforced poly(lactic acid) (PLA) nanocomposites by combining two techniques: calendering and solid-state drawing. The effect of orientation on thermal properties, crystallinity, degree of orientation, mechanical properties and microstructure was studied. The orientation affected the thermal and structural behavior of the nanocomposites. The degree of crystallinity increased from 8% for the isotropic compression-molded films to 53% for the nanocomposites drawn with the highest draw ratio. The wide-angle X-ray scattering results confirmed an orientation factor of 0.9 for the solid-state drawn nanocomposites. The mechanical properties of the oriented nanocomposite films were significantly improved by the orientation, and the pre-orientation achieved by film calendering showed very positive effects...

The article focuses on the functional capabilities, technical characteristics and bench compositi... more The article focuses on the functional capabilities, technical characteristics and bench composition of the laboratory of ship auxiliary mechanisms, which was created at the Department of Operation of Water Transport at the Astrakhan State Technical University

Nursing Conference Committee is glad to announce "9th World Congress on Midwifery and Women's Hea... more Nursing Conference Committee is glad to announce "9th World Congress on Midwifery and Women's Health " during 12-13 February, 2020 at Sydney, Australia by focus on the theme: "Collaboration Era of Midwifery Ambassadors with Digital Nutrition : Redesigning the trend of Quality Care into a smart culture". Midwifery 2020 developments are maintaining their momentum. Nursing Conference program delves into strategic discussions. Midwifery Congress 2020 Young Scientist Awards: Nursing Conference Committee is intended to honour prestigious award for talented Young researchers, scientists, Young Investigators, PostGraduate students, Post-doctoral fellows, Trainees, Junior faculty in recognition of their outstanding contribution towards the conference theme. The Young Scientist Awards make every effort in providing a strong professional development opportunity for early career academicians by meeting experts to exchange and share their experiences on all aspects of Nursing.

Composites Part A: Applied Science and Manufacturing, 2018

Aligned nanocomposite tapes based on plasticized polylactic acid (PLA) and 1 wt.% cellulose nanof... more Aligned nanocomposite tapes based on plasticized polylactic acid (PLA) and 1 wt.% cellulose nanofibers (CNF) were prepared using uniaxial solid-state drawing, and the effects of drawing conditions including temperature, speed and draw ratio on the material were studied. Microscopy studies confirmed alignment and the formation of 'shish-kebab' morphology in the drawn tape. Mechanical properties demonstrate that the solid-state drawing is a very effective way to produce stronger and tougher PLA nanocomposites, and the toughness can be improved 60 times compared to the undrawn tape. Additionally, the thermal properties, i.e. storage modulus, glass transition temperature and degree of crystallinity were improved. These improvements are expected due to the synergistic effect of CNF in the nanocomposite and orientations induced by the solid-state drawing.

Polymers, 2017

The production of fully bio-based and biodegradable nanocomposites has gained attention during re... more The production of fully bio-based and biodegradable nanocomposites has gained attention during recent years due to environmental reasons; however, the production of these nanocomposites on the large-scale is challenging. Polylactic acid/chitin nanocrystal (PLA/ChNC) nanocomposites with triethyl citrate (TEC) at varied concentrations (2.5, 5.0, and 7.5 wt %) were prepared using liquid-assisted extrusion. The goal was to find the minimum amount of the TEC plasticizer needed to enhance the ChNC dispersion. The microscopy study showed that the dispersion and distribution of the ChNC into PLA improved with the increasing TEC content. Hence, the nanocomposite with the highest plasticizer content (7.5 wt %) showed the highest optical transparency and improved thermal and mechanical properties compared with its counterpart without the ChNC. Gel permeation chromatography confirmed that the water and ethanol used during the extrusion did not degrade PLA. Further, Fourier transform infrared spectroscopy showed improved interaction between PLA and ChNC through hydrogen bonding when TEC was added. All results confirmed that the plasticizer plays an important role as a dispersing aid in the processing of PLA/ChNC nanocomposites.

Manuscrito recibido el 16 de abril de 2010, aceptado el 22 de febrero de 2012) RESUMEN El objetiv... more Manuscrito recibido el 16 de abril de 2010, aceptado el 22 de febrero de 2012) RESUMEN El objetivo principal de este trabajo es identificar la época de inicio y fin de la estación lluviosa en la Argentina al norte de 30ºS mediante un índice adecuado y analizar su variabilidad interanual en regiones homogéneas respecto a la variabilidad temporal de la precipitación. Se utilizaron datos de precipitación diaria en 19 estaciones pluviométricas de la República Argentina provistos por el Servicio Meteorológico Nacional, para el período 1974-2004, y datos de viento zonal en el nivel de 850 hPa de los reanálisis del ECMWF (ERA-40) para el período 1979-1999. Se establecieron las fechas de inicio y fin de la estación lluviosa para cada estación pluviométrica mediante un criterio de acumulación de precipitación. Este criterio resulta ser adecuado para analizar regiones cuyo ciclo anual de precipitación es marcado. El análisis de la variabilidad interanual de las series de inicio y fin de la estación lluviosa muestra que ambas regiones poseen tendencias hacia una extensión en la longitud de la misma. Se encuentra que los cambios en la componente zonal del viento en niveles bajos, de valores positivos (de mediados de abril a principios de septiembre) a valores negativos (principios de septiembre a mediados de abril), representan el inicio y fin climatológico de la estación lluviosa.

Revista Cientifica Farem Esteli, Oct 22, 2012

Composites Part A: Applied Science and Manufacturing, 2016

Triacetate citrate plasticized poly lactic acid and its nanocomposites based on cellulose nanocry... more Triacetate citrate plasticized poly lactic acid and its nanocomposites based on cellulose nanocrystals (CNC) and chitin nanocrystals (ChNC) were prepared using a twin-screw extruder. The materials were compression molded to films using two different cooling rates. The cooling rates and the addition of nanocrystals (1 wt%) had an impact on the crystallinity as well as the optical, thermal and mechanical properties of the films. The fast cooling resulted in more amorphous materials, increased transparency and elongation to break, (approx. 300%) when compared with slow cooling. Chitin nanocomposites were more transparent than cellulose nanocomposites; however, microscopy study showed presence of agglomerations in both materials. The mechanical properties of the plasticized PLA were improved with the addition of a small amount of nanocrystals resulting in PLA nanocomposites, which will be further evaluated for film blowing and thus packaging applications.

El objetivo principal de este trabajo es identificar la época de inicio y fin de la estación lluv... more El objetivo principal de este trabajo es identificar la época de inicio y fin de la estación lluviosa en la Argentina al norte de 30ºS mediante un índice adecuado y analizar su variabilidad interanual en regiones homogéneas respecto a la variabilidad temporal de la precipitación. Se utilizaron datos de precipitación diaria en 19 estaciones pluviométricas de la República Argentina provistos por el Servicio Meteorológico Nacional, para el período 1974-2004, y datos de viento zonal en el nivel de 850 hPa de los reanálisis de ECMWF (ERA-40) para el período 1979-1999. Se establecieron las fechas de inicio y fin de la estación lluviosa para cada estación pluviométrica mediante un criterio de acumulación de precipitación. Este criterio resulta ser adecuado para analizar regiones cuyo ciclo anual de precipitación es marcado. El análisis de la variabilidad interanual de las series de inicio y fin de la estación lluviosa muestra que ambas regiones poseen tendencias hacia una extensión en la l...

Composites Science and Technology, 2015

ABSTRACT Plasticized polylactic acid (PLA) and its nanocomposite based on cellulose nanofibers (C... more ABSTRACT Plasticized polylactic acid (PLA) and its nanocomposite based on cellulose nanofibers (CNF) and glycerol triacetate (GTA) were prepared using a co-rotating twin-screw extruder. GTA was used as a plasticizer, a processing aid to facilitate nanofiber dispersion and as a liquid medium for their feeding. The optical, thermal and mechanical properties were characterized and the toughening mechanism was studied. The addition of GTA (20%) and CNF (1%) resulted in increased degree of crystallinity and decreased optical transparency. Furthermore, these additives showed a positive effect on the elongation at break and toughness, which increased from 2 to 31% and from 1 to 8 MJ/m3, respectively. The combination of slippage of the nanofiber-matrix interface and a massive crazing effect as a result of the presence of CNF is suggested for PLA toughening. CNF were expected to restrict the spherulite growth and therefore enhance the craze nucleation.

… : Educación física y …, 2003