Exame de Qualificação de Doutorado do aluno Fernando Luiz Lavoie
Intitulado "Study on the durability of HDPE geomembranes applied in Geotechnics and the Environment through laboratory aged samples and in situ exhumed samples"
no dia 05/11/2020 às 14h00
no link: meet.google.com/ovc-jddn-vkx
ABSTRACT The polymer demand for geotechnical applications has been growing. The geomembrane is a geosynthetic, manufactured, polymeric product and is often specified in environmental projects. Geomembranes started to be used in the 1930s but became more widespread in the 1940s. In the 1970s, geomembranes began to be specified for landfills. Over the past forty years, millions of square meters of HDPE geomembrane have been used in different applications. One of the most important issues for HDPE geomembranes is durability, involving very long-term property requirements. A rupture in the liner that has a geomembrane may provide losses in terms of human lives, environmental impacts, and financial costs. The literature review of this work summarizes the mechanisms and concepts involved in the HDPE geomembrane aging and describes the important contributions of laboratory and field studies over the years around the world. This work is analyzing exhumed and aged HDPE geomembrane samples using physical and thermal analyses. The virgin samples were provided by many Brazilian manufacturers. The exhumed samples were collected in different Brazilian construction works in many geotechnical and environmental applications with different times of exposures. The preliminary results showed which the virgin sample 1L (1 mm-thick) presented a high density value and low stress cracking result, despite a good mechanical behavior noted. The CAM1 sample, which was exhumed from the slope liner of the shrimp farming pond after 8,25 years, obtained a very high melt flow index and did not obtain oxidation during the OIT test, that is the antioxidant content was completely depleted, differently of the CAM sample behavior, which was exhumed from the same pond but the bottom liner. The thermal analyses between the CLIQ sample (exhumed from an industrial water pond after 2,25 years) and a similar sample as a reference (1L sample) presented a different behavior in the TG curve for a heating rate of 5 ºC min-1 attributed to the reaction time. The TMA curves without purge gas showed the range of thermal stability between 30 and 65 ºC for the reference sample (1L), which is attributed to molecular relaxation. The exhumed sample did not have the same relaxation, probably because of the field exposition. The thermal analyses between the LCH (exhumed from a municipal landfill leachate pond after 5,17 years) and LTE (exhumed from a sewage treatment aeration pond after 2,75 years) samples showed significant changes in the LCH sample’s thermal decomposition probably caused by the interaction reactions between the polymer and the leachate. In the DMA analyses, the behavior of the LTE sample storage module shows which the LCH sample is less brittle, that is, more elastic. These results are following the physical results because the LTE sample presented low stress cracking resistance and low tensile elongation at break.