Rosestela Perera | Universidad Simón Bolívar (original) (raw)
Papers by Rosestela Perera
Rev. Fac. Ing. …, 2007
En este trabajo se estudió la compatibilidad en mezclas de Poliamida-6 (PA) y diferentes polietil... more En este trabajo se estudió la compatibilidad en mezclas de Poliamida-6 (PA) y diferentes polietilenos: polietileno de alta densidad (PEAD), polietileno de baja densidad (PEBD) y polietileno lineal de baja densidad (PELBD). Se utilizó un copolímero ...
In this work, the compatibility in blends of Polyamide 6 (PA) and three different Polyethylenes, ... more In this work, the compatibility in blends of Polyamide 6 (PA) and three different Polyethylenes, High-Density (HDPE), LowDensity (LDPE) and Linear Low-Density (LLDPE) polyethylenes, was studied. A copolymer of styrene/ethylene-butylene/ styrene functionalized with diethyl maleate (SEBS-g-DEM) was used as compatibilizing agent. The characterization of the blends was carried out using Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and through notched-Izod impact tests. Results from selective extraction tests displayed that interactions between PA and SEBS-g-DEM groups are likely present. Through DSC results, the fractionated crystallization phenomenon of the PA was unfolded, only in those blends where the PA was the dispersed phase. In general, an enhancement in the impact resistance of those reactive blends where LLDPE was used as the matrix was obtained. SEM analyses of the fractured surfaces of the blends ...
In the present work, the influence of the degradation during the processing of nanocomposites of ... more In the present work, the influence of the degradation during the processing of nanocomposites of poly (lactic acid) (PLA) with montmorillonite and its blends with low density polyethylene as dispersed phase on their morphology and tensile properties was studied. Polymers grafted with maleic anhydride were used as compatibilizer agents. The blends were prepared via melt blending in an internal mixer at 200°C and characterized in terms of solution viscometry of the PLA phase, infrared spectroscopy, and scanning and transmission electron microscopy. Results showed that the processing of PLA produced thermo-mechanical degradation in the polymer and a significant decrease in the viscosity molecular weight of the PLA phase in the different composites. The large sizes of the dispersed phases in the unfilled PLA blends and the low values of the tensile properties could be attributed to the thermo-mechanical degradation of the PLA matrix during its processing. The blends with PLA as matrix a...
Se prepararon compuestos de poli (acido lactico) con almidon de maiz en una extrusora doble torni... more Se prepararon compuestos de poli (acido lactico) con almidon de maiz en una extrusora doble tornillo. Se estudio la influencia de incorporar diferentes proporciones de carga en las propiedades y para ello se emplearon las tecnicas de viscosimetria en solucion, reometria dinamica en flujo oscilatorio, analisis termo-gravimetrico (TGA) y microscopia electronica de barrido. Tambien se determinaron las propiedades de traccion. Se establecio que la cinetica de degradacion termo-oxidativa del PLA y de las correspondientes fases de PLA en los compuestos con almidon de maiz bajo condiciones isotermicas en el reometro dinamico es por escision de cadenas al azar. Tambien se encontro que la degradacion termica e hidrolitica durante el procesado de la fase PLA en los compuestos se ajusto al modelo que considera el efecto catalitico de los grupos de acidos carboxilicos terminales en esta fase. Ademas, se utilizaron varios modelos para predecir las relaciones de viscosidad a frecuencia y temperat...
Latin American Applied Research, 1996
Grafting of Poltethylenes
En este trabajo se evaluo la estabilizacion del polipropileno (PP) cuando es esterilizado utiliza... more En este trabajo se evaluo la estabilizacion del polipropileno (PP) cuando es esterilizado utilizando radiacion Gamma a dosis de 25 y 50 kGy. El PP fue mezclado en fundido con diferentes compuestos, tales como aminas impedidas (Chimassorb 944), antioxidantes fenolicos (BHT), mezclas de estabilizante tipo fosfito con una amina impedida (Fiberstab L 112), copolimero de estireno-butadieno-estireno (SBS) y montmorillonita modificada organicamente con octadecilamina. De los resultados se infiere que la adicion de BHT+Chimassorb 944 otorga mayor estabilidad al PP, lo cual se refleja en una menor variacion de su indice de fluidez despues de la irradiacion. Esta variacion fue marcadamente inferior al compararla con la que experimento el PP puro y el PP con los otros aditivos anadidos por separado. El efecto de la variacion en el indice de fluidez fue mas notorio cuando se utilizo atmosfera de nitrogeno durante la irradiacion. Con respecto a las propiedades tensiles, se puede concluir que la ...
The Electron Paramagnetic Resonance (EPR) had its most important development at the end of World ... more The Electron Paramagnetic Resonance (EPR) had its most important development at the end of World War II. It is a non destructive technique of characterization and is the technique used for excellence to detect and characterize free radicals. It is well known that the presence of free radicals in polymeric materials is responsible for the appearance of a variety of effects in the polymer chains. There are, fundamentally, two ways for the generation of free radicals in a polymeric chain: chemical methods and irradiation with electromagnetic waves of medium and high energy. Gamma and x-rays produce ionization in all solids. In insulators and polymers chemical reactions may be promoted, some of which cannot be induced by other means. These last methods have the advantage that they do not leave polluting agents into the polymer. EPR has been used to interpret quantitatively and qualitatively the free radicals generated by the irradiation of polymeric materials. EPR results from different...
Preface Introduction Techniques Used to Prepare Grafted Polythylenes Secondary &/Or Degradation R... more Preface Introduction Techniques Used to Prepare Grafted Polythylenes Secondary &/Or Degradation Reactions in the Grafting Process Molecular Weight Distribution & Rheological Properties Thermal Properties & Thermogravimetric Analysis (TGA) Conclusion Index.
Polymer Degradation and Stability, 2012
The thermal properties and the kinetics of thermal degradation of nanocomposites of polypropylene... more The thermal properties and the kinetics of thermal degradation of nanocomposites of polypropylene (PP) and montmorillonite (OMMT) and an ethylene-co-vinyl acetate copolymer (EVA) as a minority phase, including a third elastomeric component represented by poly(ethylene-co-octene) (mPE) were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Two maleic anhydride modified PP (PP-g-AM), one of them commercial and the other one prepared in our laboratory, were used as compatibilizers. The expected nucleating effect of the organoclay in the nanocomposites and the increase on crystallization temperature was observed. The degradation kinetic parameters were obtained using the Coats e Redfern integral method to obtain the reaction order and the E 2 function methodology to calculate the activation energy. The PP/OMMT nanocomposites with mPE or EVA exhibited higher degradation temperatures and activation energies than the neat PP and also a higher decomposition temperature than the PP nanocomposites without the elastomeric minority phase. The employment of the commercial compatibilizer generated more exfoliated structures on the ternary nanocomposites that contributed to a better thermal stability. The degradation mechanisms involve crosslinking, chain branching and chain scission reactions for the ternary PP/OMMT/mPE nanocomposites and an additional accelerated deacetylation process for the ternary PP/OMMT/EVA nanocomposites.
Advanced Materials Research, 2008
Polypropylene/polyamide-6 and polypropylene/metallocene polyethylene blends containing 2.5 phr of... more Polypropylene/polyamide-6 and polypropylene/metallocene polyethylene blends containing 2.5 phr of organophilic modified montmorillonite were prepared in a twin-screw extruder followed by injection molding. In order to compare, blends without layered clay were also made. Styreneethylene- butylene-styrene copolymer and polypropylene grafted with anhydride maleic were used as compatibilizers in the ternary blends and in the PP nanocomposite preparation, respectively. The presence of tactoids, intercalated and exfoliated structures was observed by TEM in some of the samples containing layered clay and modified PP materials. Results showed that the compatibilized blends prepared without clay are tougher than those prepared with the nanocomposite of PP as the matrix phase and no significant changes in tensile moduli were observed between them. However, the binary blend with a nanocomposite of PP as matrix and metallocene polyethylene exhibited better tensile toughness and lower tensile mo...
Polymer Engineering & Science, 1996
... C . ROSALES, L. MARQUEZ, J. GONZALEZ, R. PERERA, and B. ROJAS ... in reactive processing some... more ... C . ROSALES, L. MARQUEZ, J. GONZALEZ, R. PERERA, and B. ROJAS ... in reactive processing some important characteristics, such as residence time distribution, mixing, and self-cleaning effects should be accurately controlled according to the poly-mer properties and usage. ...
Polymer Composites, 2006
ABSTRACT The preparation of polypropylene (PP) nanocomposites was studied using clay and three ty... more ABSTRACT The preparation of polypropylene (PP) nanocomposites was studied using clay and three types of modified PP (m-PP) as compatibilizers: diethyl maleate grafted PP (PP-g-DEM), maleic anhydride grafted PP (PP-g-MA), and PP grafted with carbamyl maleamic acid (PP-g-UMA). The clay was made organophylic by an acid treatment with octadecylamine. PP functionalization and blending were carried out in an internal mixer. Blends of PP containing 20 and 40 wt% each of the modified PP and 5 wt% of organophilic clay (IMt), in each case, were prepared. Samples were characterized by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), optical microscopy, and mechanical testing. The presence of tactoid, intercalated and exfoliated structures was observed by TEM in all the samples containing clay and modified PP, which also showed improved mechanical properties with tensile modulus as much as three times that of PP. Melting temperature did not vary significantly with the addition of clay. However, because of the clay's nucleating effect, an increase in the crystallization temperature was observed, accompanied by a slight decrease in the degree of crystallinity. The best results were obtained when PP-g-MA was used as the compatibilizer; intermediate results were obtained with the use of PP-g-UMA, followed by the results obtained when PP-g-DEM was used. Property enhancements were obtained when a higher percentage of modified PP was employed. POLYM. COMPOS., 27:451–460, 2006. © 2006 Society of Plastics Engineers
Rev. LatinAm. Met. …, 2006
This work is a brief compilation of our results from previous researches concerning the influence... more This work is a brief compilation of our results from previous researches concerning the influence of the rheological parameters on polyolefin blends, reactive blends, polymer grafting, polypropylene nanocomposites, polyamide nanocomposites (PA) and its blends. ...
Revista de Chimie, 2022
Nanocomposites of poly(lactic acid) with sepiolite needles (5 wt.%) were evaluated in terms of th... more Nanocomposites of poly(lactic acid) with sepiolite needles (5 wt.%) were evaluated in terms of the mechanical and biofilm formation properties. The nanocomposite exhibited higher values of the Young�s modulus and tensile strength at break compared to the PLA, without detriment in the percent elongation at break. These improvements were related to the high aspect ratio of the nanoclay, the polymer-clay interactions, and the degree of dispersion. The growth of Pseudomonas aeruginosa on the surface of the PLA and nPLA materials was promoted in different conditions. Medium with different concentration of nutrients were used and also were compared the effect of the medium physical state (solid or liquid medium). Biofilms were formed in all the conditions. However, the nanocomposite presented a higher area coverage of microorganisms on its surface, possibly due to the positive effects of the nanoclay on the bacterial adhesion.
Advanced Materials …, 2008
The need for solid-waste management has pushed the development of alternative systems for recycli... more The need for solid-waste management has pushed the development of alternative systems for recycling and revalue used plastic containers. Poly(ethylene terephthalate) (PET) is being widely used as raw material for beverage bottles. However, as has been widely reported, PET ...
Advanced Materials …, 2008
The need for solid-waste management has pushed the development of alternative systems for recycli... more The need for solid-waste management has pushed the development of alternative systems for recycling and revalue used plastic containers. Poly(ethylene terephthalate) (PET) is being widely used as raw material for beverage bottles. However, as has been widely reported, PET ...
Antec Conference Proceedings, 2004
Rev. Fac. Ing. …, 2007
En este trabajo se estudió la compatibilidad en mezclas de Poliamida-6 (PA) y diferentes polietil... more En este trabajo se estudió la compatibilidad en mezclas de Poliamida-6 (PA) y diferentes polietilenos: polietileno de alta densidad (PEAD), polietileno de baja densidad (PEBD) y polietileno lineal de baja densidad (PELBD). Se utilizó un copolímero ...
In this work, the compatibility in blends of Polyamide 6 (PA) and three different Polyethylenes, ... more In this work, the compatibility in blends of Polyamide 6 (PA) and three different Polyethylenes, High-Density (HDPE), LowDensity (LDPE) and Linear Low-Density (LLDPE) polyethylenes, was studied. A copolymer of styrene/ethylene-butylene/ styrene functionalized with diethyl maleate (SEBS-g-DEM) was used as compatibilizing agent. The characterization of the blends was carried out using Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and through notched-Izod impact tests. Results from selective extraction tests displayed that interactions between PA and SEBS-g-DEM groups are likely present. Through DSC results, the fractionated crystallization phenomenon of the PA was unfolded, only in those blends where the PA was the dispersed phase. In general, an enhancement in the impact resistance of those reactive blends where LLDPE was used as the matrix was obtained. SEM analyses of the fractured surfaces of the blends ...
In the present work, the influence of the degradation during the processing of nanocomposites of ... more In the present work, the influence of the degradation during the processing of nanocomposites of poly (lactic acid) (PLA) with montmorillonite and its blends with low density polyethylene as dispersed phase on their morphology and tensile properties was studied. Polymers grafted with maleic anhydride were used as compatibilizer agents. The blends were prepared via melt blending in an internal mixer at 200°C and characterized in terms of solution viscometry of the PLA phase, infrared spectroscopy, and scanning and transmission electron microscopy. Results showed that the processing of PLA produced thermo-mechanical degradation in the polymer and a significant decrease in the viscosity molecular weight of the PLA phase in the different composites. The large sizes of the dispersed phases in the unfilled PLA blends and the low values of the tensile properties could be attributed to the thermo-mechanical degradation of the PLA matrix during its processing. The blends with PLA as matrix a...
Se prepararon compuestos de poli (acido lactico) con almidon de maiz en una extrusora doble torni... more Se prepararon compuestos de poli (acido lactico) con almidon de maiz en una extrusora doble tornillo. Se estudio la influencia de incorporar diferentes proporciones de carga en las propiedades y para ello se emplearon las tecnicas de viscosimetria en solucion, reometria dinamica en flujo oscilatorio, analisis termo-gravimetrico (TGA) y microscopia electronica de barrido. Tambien se determinaron las propiedades de traccion. Se establecio que la cinetica de degradacion termo-oxidativa del PLA y de las correspondientes fases de PLA en los compuestos con almidon de maiz bajo condiciones isotermicas en el reometro dinamico es por escision de cadenas al azar. Tambien se encontro que la degradacion termica e hidrolitica durante el procesado de la fase PLA en los compuestos se ajusto al modelo que considera el efecto catalitico de los grupos de acidos carboxilicos terminales en esta fase. Ademas, se utilizaron varios modelos para predecir las relaciones de viscosidad a frecuencia y temperat...
Latin American Applied Research, 1996
Grafting of Poltethylenes
En este trabajo se evaluo la estabilizacion del polipropileno (PP) cuando es esterilizado utiliza... more En este trabajo se evaluo la estabilizacion del polipropileno (PP) cuando es esterilizado utilizando radiacion Gamma a dosis de 25 y 50 kGy. El PP fue mezclado en fundido con diferentes compuestos, tales como aminas impedidas (Chimassorb 944), antioxidantes fenolicos (BHT), mezclas de estabilizante tipo fosfito con una amina impedida (Fiberstab L 112), copolimero de estireno-butadieno-estireno (SBS) y montmorillonita modificada organicamente con octadecilamina. De los resultados se infiere que la adicion de BHT+Chimassorb 944 otorga mayor estabilidad al PP, lo cual se refleja en una menor variacion de su indice de fluidez despues de la irradiacion. Esta variacion fue marcadamente inferior al compararla con la que experimento el PP puro y el PP con los otros aditivos anadidos por separado. El efecto de la variacion en el indice de fluidez fue mas notorio cuando se utilizo atmosfera de nitrogeno durante la irradiacion. Con respecto a las propiedades tensiles, se puede concluir que la ...
The Electron Paramagnetic Resonance (EPR) had its most important development at the end of World ... more The Electron Paramagnetic Resonance (EPR) had its most important development at the end of World War II. It is a non destructive technique of characterization and is the technique used for excellence to detect and characterize free radicals. It is well known that the presence of free radicals in polymeric materials is responsible for the appearance of a variety of effects in the polymer chains. There are, fundamentally, two ways for the generation of free radicals in a polymeric chain: chemical methods and irradiation with electromagnetic waves of medium and high energy. Gamma and x-rays produce ionization in all solids. In insulators and polymers chemical reactions may be promoted, some of which cannot be induced by other means. These last methods have the advantage that they do not leave polluting agents into the polymer. EPR has been used to interpret quantitatively and qualitatively the free radicals generated by the irradiation of polymeric materials. EPR results from different...
Preface Introduction Techniques Used to Prepare Grafted Polythylenes Secondary &/Or Degradation R... more Preface Introduction Techniques Used to Prepare Grafted Polythylenes Secondary &/Or Degradation Reactions in the Grafting Process Molecular Weight Distribution & Rheological Properties Thermal Properties & Thermogravimetric Analysis (TGA) Conclusion Index.
Polymer Degradation and Stability, 2012
The thermal properties and the kinetics of thermal degradation of nanocomposites of polypropylene... more The thermal properties and the kinetics of thermal degradation of nanocomposites of polypropylene (PP) and montmorillonite (OMMT) and an ethylene-co-vinyl acetate copolymer (EVA) as a minority phase, including a third elastomeric component represented by poly(ethylene-co-octene) (mPE) were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Two maleic anhydride modified PP (PP-g-AM), one of them commercial and the other one prepared in our laboratory, were used as compatibilizers. The expected nucleating effect of the organoclay in the nanocomposites and the increase on crystallization temperature was observed. The degradation kinetic parameters were obtained using the Coats e Redfern integral method to obtain the reaction order and the E 2 function methodology to calculate the activation energy. The PP/OMMT nanocomposites with mPE or EVA exhibited higher degradation temperatures and activation energies than the neat PP and also a higher decomposition temperature than the PP nanocomposites without the elastomeric minority phase. The employment of the commercial compatibilizer generated more exfoliated structures on the ternary nanocomposites that contributed to a better thermal stability. The degradation mechanisms involve crosslinking, chain branching and chain scission reactions for the ternary PP/OMMT/mPE nanocomposites and an additional accelerated deacetylation process for the ternary PP/OMMT/EVA nanocomposites.
Advanced Materials Research, 2008
Polypropylene/polyamide-6 and polypropylene/metallocene polyethylene blends containing 2.5 phr of... more Polypropylene/polyamide-6 and polypropylene/metallocene polyethylene blends containing 2.5 phr of organophilic modified montmorillonite were prepared in a twin-screw extruder followed by injection molding. In order to compare, blends without layered clay were also made. Styreneethylene- butylene-styrene copolymer and polypropylene grafted with anhydride maleic were used as compatibilizers in the ternary blends and in the PP nanocomposite preparation, respectively. The presence of tactoids, intercalated and exfoliated structures was observed by TEM in some of the samples containing layered clay and modified PP materials. Results showed that the compatibilized blends prepared without clay are tougher than those prepared with the nanocomposite of PP as the matrix phase and no significant changes in tensile moduli were observed between them. However, the binary blend with a nanocomposite of PP as matrix and metallocene polyethylene exhibited better tensile toughness and lower tensile mo...
Polymer Engineering & Science, 1996
... C . ROSALES, L. MARQUEZ, J. GONZALEZ, R. PERERA, and B. ROJAS ... in reactive processing some... more ... C . ROSALES, L. MARQUEZ, J. GONZALEZ, R. PERERA, and B. ROJAS ... in reactive processing some important characteristics, such as residence time distribution, mixing, and self-cleaning effects should be accurately controlled according to the poly-mer properties and usage. ...
Polymer Composites, 2006
ABSTRACT The preparation of polypropylene (PP) nanocomposites was studied using clay and three ty... more ABSTRACT The preparation of polypropylene (PP) nanocomposites was studied using clay and three types of modified PP (m-PP) as compatibilizers: diethyl maleate grafted PP (PP-g-DEM), maleic anhydride grafted PP (PP-g-MA), and PP grafted with carbamyl maleamic acid (PP-g-UMA). The clay was made organophylic by an acid treatment with octadecylamine. PP functionalization and blending were carried out in an internal mixer. Blends of PP containing 20 and 40 wt% each of the modified PP and 5 wt% of organophilic clay (IMt), in each case, were prepared. Samples were characterized by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), optical microscopy, and mechanical testing. The presence of tactoid, intercalated and exfoliated structures was observed by TEM in all the samples containing clay and modified PP, which also showed improved mechanical properties with tensile modulus as much as three times that of PP. Melting temperature did not vary significantly with the addition of clay. However, because of the clay's nucleating effect, an increase in the crystallization temperature was observed, accompanied by a slight decrease in the degree of crystallinity. The best results were obtained when PP-g-MA was used as the compatibilizer; intermediate results were obtained with the use of PP-g-UMA, followed by the results obtained when PP-g-DEM was used. Property enhancements were obtained when a higher percentage of modified PP was employed. POLYM. COMPOS., 27:451–460, 2006. © 2006 Society of Plastics Engineers
Rev. LatinAm. Met. …, 2006
This work is a brief compilation of our results from previous researches concerning the influence... more This work is a brief compilation of our results from previous researches concerning the influence of the rheological parameters on polyolefin blends, reactive blends, polymer grafting, polypropylene nanocomposites, polyamide nanocomposites (PA) and its blends. ...
Revista de Chimie, 2022
Nanocomposites of poly(lactic acid) with sepiolite needles (5 wt.%) were evaluated in terms of th... more Nanocomposites of poly(lactic acid) with sepiolite needles (5 wt.%) were evaluated in terms of the mechanical and biofilm formation properties. The nanocomposite exhibited higher values of the Young�s modulus and tensile strength at break compared to the PLA, without detriment in the percent elongation at break. These improvements were related to the high aspect ratio of the nanoclay, the polymer-clay interactions, and the degree of dispersion. The growth of Pseudomonas aeruginosa on the surface of the PLA and nPLA materials was promoted in different conditions. Medium with different concentration of nutrients were used and also were compared the effect of the medium physical state (solid or liquid medium). Biofilms were formed in all the conditions. However, the nanocomposite presented a higher area coverage of microorganisms on its surface, possibly due to the positive effects of the nanoclay on the bacterial adhesion.
Advanced Materials …, 2008
The need for solid-waste management has pushed the development of alternative systems for recycli... more The need for solid-waste management has pushed the development of alternative systems for recycling and revalue used plastic containers. Poly(ethylene terephthalate) (PET) is being widely used as raw material for beverage bottles. However, as has been widely reported, PET ...
Advanced Materials …, 2008
The need for solid-waste management has pushed the development of alternative systems for recycli... more The need for solid-waste management has pushed the development of alternative systems for recycling and revalue used plastic containers. Poly(ethylene terephthalate) (PET) is being widely used as raw material for beverage bottles. However, as has been widely reported, PET ...
Antec Conference Proceedings, 2004