Stress cracking de blendas de policarbonato/polibutileno tereftalato em presença de etanol

Abstract

The aim of this work was to analyze the environmental stress cracking (ESC) resistance of a polycarbonate (PC) and polybutylene terephthalate (PBT) blend in contact with ethanol by means of two mechanical tests: (i) tensile test and (ii) constant tension (ii). For this, prior to being extruded, the PC/PBT (55/45) blend was previously analyzed by infrared spectroscopy (FTIR), it searching for presence of the transesterification reactions, and two thermal analyzes: differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), were carried out to classify this polymer blend. Subsequently, bar samples for tensile test were injected, the ethanol absorption behavior was evaluated and the mechanical tests, in the absence and presence of ethanol, were executed. For test (i), three deformation rates were applied, and for test (ii), three loads were evaluated. In (i), the ethanol was applied from a damp cotton, from the beginning of the test, and in (ii), when the equipment reached out the determined load until rupture, or for 20 min. After the mechanical analysis, visual inspections of the samples surfaces were performed, the cracks and fractures were characterized by scanning electron microscopy (SEM). The FTIR results suggested that there was no transesterification reaction, the DSC indicated that the blends exhibited relatively higher crystallinity than PBT, and associated with TG, suggested that the polymer blend was partially immiscible. The ethanol was continuously absorbed by the PC and the polymer blend for seven days and it acted as ESC agent, during the test (i), leading to the premature failure of PC and blend, in test (ii), the maximum applied load constantly affected mainly, the PC and the blend. The PBT showed superior ESC resistance to ethanol in both tests. On visual inspection, the PC was significantly affected, followed by the blend and the PBT. Finally, the micrographs indicated that the intensity of the crazes varied according to the material, with the formation of brittle fracture premature in the materials. It can be concluded that ethanol reduced the critical deformation energy of these materials, only under certain conditions. The location, density, and intensity of crazes were dependent on velocity, charge and material.