Estudo do fenômeno de stress cracking em poli (teretalato de etileno) (PET).

Abstract

The objective of this study is to evaluate the environmental stress cracking resistance (ESCR) of poly(ethylene terephthalate) (PET) in different active fluids: methanol, ethanol, i-propanol, n-butanol and sodium hydroxide (NaOH ) aqueous solutions in different concentrations. The ESCR was evaluated using both dynamic and static tensile testing, during which the samples were kept in contact with the active fluids. In the dynamic test two crosshead speeds were used (2 and 5mm/min) and in the static test several loads were applied (ranging from 700 to 1900N) and the stress relaxation was monitored as a function of time under constant strain. Absorption tests in sodium hydroxide aqueous solutions were also conducted. The surfaces of the exposed samples were analysed using optical microscopy and macrophotography. Measurements of intrinsic viscosity were conducted for molar mass determination. The results showed that the alcohols causes deterioration on the surface appearance, but without major consequences for the mechanical properties. On the other hand, NaOH aqueous solutions were highly aggressive to the PET, with large decrease in mechanical properties and molar mass. Thus the catastrophic failure in NaOH aqueous solutions may result from the simultaneous action of ESC and chemical attack.