Enhanced Structural Behavior of Systems Polypropylene-Carbon Nanotubes in Acidic Medium
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Enhanced Structural Behavior of Systems Polypropylene-Carbon Nanotubes in Acidic Medium Felipe Avalos-Belmontes1, Miguel Flores-Godina1, RosaNarro-Cespedes1, Adali CastañedaFacio1, Martha Castañeda-Flores1, Maura Tellez-Rosas1, Luis Ramos-deValle2, and Roberto Zitzumbo-Guzman3 1
Universidad Autónoma de Coahuila, V. Carranza sn, 25000, Saltillo Coahuila, México Centro de Investigación en Química Aplicada, E Reyna sn, 25204, Saltillo Coahuila, México 3 Centro de Innovación Aplicada en Tecnologías Competitivas, México. 2
ABSTRACT The effect of carbon nanotubes (CNTs) on the thermal and chemical stability of polypropylene (PP) when subjected to oxidation in a fuming nitric was evaluated. The effect of CNTs on the crystalline morphology and melting and crystallization temperature of PP was studied. The results shown a thermal stability increased markedly; the decomposition temperature, increased from 293°C for pure PP to 320°C for PP with CNTs. The crystallization temperature increased perceptibly in presence of CNTs. The oxidative degradation with nitric acid produced a reduction in molecular weight; however, this negative effect was less pronounced in the PP compositions with carbon nanoparticles. The morphological changes evaluated with X-ray diffraction showed that the alpha type crystallinity remains, irrespective of the nucleating agent, and the intensity ratios between reflections peaks was taken as an indication of an increasing nucleating efficiency. INTRODUCTION With the addition of filler particles, and especially nanoparticles, the polypropylene can be tailored to cover many engineering applications. There are many studies that report on the use of different nanoparticles in polypropylene in order to impart or modify a given property. Inorganic and organic [1-4] nanoparticles have been used to enhance the mechanical, thermal, flame resistance and barrier properties of PP. In most cases, when added into PP, these nanoparticles act as nucleating agents, promoting thus the heterogeneous crystalline growth. In a recent work [4], the authors reported on the excellent nucleating ability of carbon nanoparticles (conc. 0.05%), as compared to commercial nucleating agents for PP. This excellent nucleating capacity of CNT and CNF has also been reported by other authors [5-6], though some authors have found that above 4 wt% this ability reaches a plateau and remains constant. On another hand, an important application of PP is in lead-acid car battery cases in which their outstanding properties make it the ideal option for long time performance. In these applications the PP is in contact with highly corrosive substances which can alter its composition and structure and significantly reduce its chemical and mechanical properties. The purpose of the present work is to study the relationship between the increase in the thermal and chemical resistance and the enhanced nucleation induced by carbon nanotubes. The
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reason for the use of very low nucleating agent concentrations (0.05 wt%) is to avoid the excess of nucleat
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