Efeito das diferentes condições de resfriamento pós-extrusão na estrutura e comportamento mecânico do PVDF

Abstract

The polyvinylidene fluoride (PVDF) is a semi-crystalline fluorinated polymer frequently used as pressure sheath in flexible pipes (FP) in oil and gas exploitation. The FR safety and reliability is a subject of prime importance and their mechanical behaviour comprehension is not well understood, with the after extrusion cooling temperature effect remains an open question. In this work, the effect of different cooling temperatures after extrusion on the microstructure and mechanical properties in two PVDF grades was studied by naked eye observation, density, x-ray scattering (XRD), differential scanning calorimetry (DSC), Fourier transformed infrared spectroscopy (FTIR) and tensile tests. Also, the effect of stress relaxation in two different temperatures (23 and 130°C) on the same materials properties was studied. The PVDF microstructure showed to be sensitive to the different cooling temperatures after extrusion, in a way that there were density, crystallinity and mechanical resistance variations, varying almost independently by material grade. The stress relaxation effect act also distinctly by material grade; one of them showed the stress-whitening phenomena, which directly impacts the microstructure and tensile mechanical resistance, meanwhile on the other this phenomena was not observed with little impact in material properties.