Estudo do envelhecimento de dutos de polietileno de alta densidade (PEAD)

Abstract

The use of polyethylene to produce pipes began in the 1950s, in North America, and since this time, it has been gaining market space, whether in the sanitation, oil and gas or mining industry. High-density polyethylene (HDPE) is the most used polyethylene grade for this application, because offers an excellent choice from both an economical and a technical point of view. However, despite its excellent properties, HDPE may have limited use time in many situations, depending on its area of application due to its low temperature resistance and contact with various fluids. The study of the ageing of this polymer in the different fluids becomes quite interesting, because the physical and chemical changes that can occur contribute to the reduction of the useful life of the parts in service. Knowing the different mechanisms that act on a polymeric material helps prevent and control the mode and time of failure. The objective of this work is the characterization of the High Density Polyethylene used in the production of pipelines, before and after aging, by the action of LUBRAX OB 440 oil, at room temperature and at 50 °C, during the time intervals of one, three, six and twelve weeks, respectively. The mechanical properties in tensile and impact mode were evaluated by using standard tests. The samples were also characterized by infrared spectroscopy (FTIR), melt flow index (MFI) determinations, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-ray diffraction (XRD), gravimetry and oil absorption determinations. The results showed that the temperature exerts a significant influence on the aging process of the polymer in the oil, since the mechanical properties of the HDPE aged at room temperature did not change during the immersion period. The samples submitted to aging at 50 ° C, however, showed an increase in the impact strength and a trend to decrease the modulus of elasticity. The results of the DSC tests of the aged samples showed that the samples submitted to the aging process in oil showed an increase in the crystallinity degree, regardless of the temperature used. This result was corroborated by the obtained XRD data. The thermogravimetric analysis, gravimetry and FTIR showed that the diffusion phenomenon of the oil in the sample is strongly influenced by temperature. The FTIR analyzis for samples aged at room temperature and at 50 ° C showed a peak at 1377 cm -1 corresponding to the diffusion of LUBRAX oil in the polymer matrix. Scanning electron microscopy of the samples showed that the most pronounced effect of aging ocurred at 50 ° C, with the presence of holes and regions with cracks in the micrographs.