Alejandro Benitez - Academia.edu (original) (raw)
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Papers by Alejandro Benitez
Congreso Internacional de Inteligencia Computacional, 2005
Polymer Degradation and Stability, 2013
The mechanical properties of two linear low density and low density polyethylenes containing a pr... more The mechanical properties of two linear low density and low density polyethylenes containing a prooxidant additive were monitored during accelerated aging (60 C in a convection oven) and weather exposure. Tearing tests (trouser) were performed for the first time in polyethylenes subjected to oxodegradation revealing a transition from an extensible to a non-extensible material, at exposure times when standard tensile tests were not able to detect any changes in the materials. The essential work of fracture (EWF) technique was also applied and the results were in agreement with those of trouser tests. The specific essential work of fracture first increased with exposure time until the sample experienced a transition to a less ductile state where EWF was no longer applicable. EWF and trouser tear tests were more sensitive detecting the onset of degradation probably because they employ notched specimens that impose more critical stress concentration conditions than conventional tensile tests.
Polymer Degradation and Stability, 2013
This article investigates the influence of a pro-oxidant additive on the accelerated and environm... more This article investigates the influence of a pro-oxidant additive on the accelerated and environmental degradation of linear low density polyethylene (LLDPE) and low density polyethylene (LDPE). Extruded cast films (100 mm) were prepared with various amounts of a pro-oxidant (a so-called "Oxo" additive) (0%, 1% and 2% w/w). The films were subjected to either environmental weathering or air oven aging (60 C) tests for 260 days. The chemical and physical changes induced by aging were monitored by: Gel Permeation Chromatography (GPC), Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Successive Self-nucleation and Annealing (SSA) thermal fractionation and tensile tests. Neat PE samples did not exhibit significant changes during the period evaluated. Crystallinity obtained from standard DSC tests during accelerated degradation exhibited variations due to a combination between annealing and recrystallization after chain scission. For both accelerated and environmental degradation a complete loss of mechanical properties was obtained although at different exposure times. SSA was shown to be the most sensitive technique applied since it evidenced early structural changes during degradation in LLDPE and LDPE that were undetected by GPC, tensile tests (i.e., strain at break) or FTIR at identical exposure times. SSA tests after accelerated degradation revealed that LLDPE linear sequences in between branching points are substantially more affected at longer exposure times than those in LDPE, a result that may imply differences in degradation mechanisms during the later stages of the degradation process.
Congreso Internacional de Inteligencia Computacional, 2005
Polymer Degradation and Stability, 2013
The mechanical properties of two linear low density and low density polyethylenes containing a pr... more The mechanical properties of two linear low density and low density polyethylenes containing a prooxidant additive were monitored during accelerated aging (60 C in a convection oven) and weather exposure. Tearing tests (trouser) were performed for the first time in polyethylenes subjected to oxodegradation revealing a transition from an extensible to a non-extensible material, at exposure times when standard tensile tests were not able to detect any changes in the materials. The essential work of fracture (EWF) technique was also applied and the results were in agreement with those of trouser tests. The specific essential work of fracture first increased with exposure time until the sample experienced a transition to a less ductile state where EWF was no longer applicable. EWF and trouser tear tests were more sensitive detecting the onset of degradation probably because they employ notched specimens that impose more critical stress concentration conditions than conventional tensile tests.
Polymer Degradation and Stability, 2013
This article investigates the influence of a pro-oxidant additive on the accelerated and environm... more This article investigates the influence of a pro-oxidant additive on the accelerated and environmental degradation of linear low density polyethylene (LLDPE) and low density polyethylene (LDPE). Extruded cast films (100 mm) were prepared with various amounts of a pro-oxidant (a so-called "Oxo" additive) (0%, 1% and 2% w/w). The films were subjected to either environmental weathering or air oven aging (60 C) tests for 260 days. The chemical and physical changes induced by aging were monitored by: Gel Permeation Chromatography (GPC), Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Successive Self-nucleation and Annealing (SSA) thermal fractionation and tensile tests. Neat PE samples did not exhibit significant changes during the period evaluated. Crystallinity obtained from standard DSC tests during accelerated degradation exhibited variations due to a combination between annealing and recrystallization after chain scission. For both accelerated and environmental degradation a complete loss of mechanical properties was obtained although at different exposure times. SSA was shown to be the most sensitive technique applied since it evidenced early structural changes during degradation in LLDPE and LDPE that were undetected by GPC, tensile tests (i.e., strain at break) or FTIR at identical exposure times. SSA tests after accelerated degradation revealed that LLDPE linear sequences in between branching points are substantially more affected at longer exposure times than those in LDPE, a result that may imply differences in degradation mechanisms during the later stages of the degradation process.