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Laboratory Study of the Ultraviolet Radiation Effect on an HDPE Geomembrane

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Laboratory Study of the Ultraviolet Radiation Effect on an HDPE Geomembrane membranes Article Laboratory Study of the Ultraviolet Radiation Effect on an HDPE Geomembrane Fernando Luiz Lavoie 1,2,* , Marcelo Kobelnik 2, Clever Aparecido Valentin 2 , Érica Fernanda da Silva Tirelli 1, Maria de Lurdes Lopes 3 and Jefferson Lins da Silva 2 1 Department of Civil Engineering, Mauá Institute of Technology, São Caetano do Sul 09580-900, Brazil; [email protected] 2 São Carlos School of Engineering, University of São Paulo—USP, São Paulo 13566-590, Brazil; [email protected] (M.K.); [email protected] (C.A.V.); [email protected] (J.L.d.S.) 3 CONSTRUCT-GEO, Department of Civil Engineering, University of Porto, 4200-465 Porto, Portugal; [email protected] * Correspondence: [email protected]; Tel.: +55-119-8105-8718 Abstract: High-density polyethylene (HDPE) geomembranes are polymeric geosynthetic materials usually applied as a liner in environmental facilities due to their good mechanical properties, good welding conditions, and excellent chemical resistance. A geomembrane’s field performance is affected by different conditions and exposures, including ultraviolet radiation, thermal and oxidative exposure, and chemical contact. This article presents an experimental study with a 1.0 mm-thick HDPE virgin geomembrane exposed by the Xenon arc weatherometer for 2160 h and the ultraviolet fluorescent weatherometer for 8760 h to understand the geomembrane’s behavior under ultraviolet exposure. The evaluation was performed using the melt flow index (MFI) test, oxidative-induction time (OIT) tests, tensile test, differential scanning calorimetry (DSC) analysis, and Fourier transform infrared spectroscopy (FTIR) analysis. The sample exposed in the Xenon arc equipment showed Citation: Lavoie, F.L.; Kobelnik, M.; a tendency to increase the MFI values during the exposure time. This upward trend may indicate Valentin, C.A.; Tirelli, É.F.d.S.; Lopes, morphological changes in the polymer. The tensile behavior analysis showed a tendency of the M.d.L.; Silva, J.L.d. Laboratory Study sample to lose ductility, without showing brittle behavior. The samples’ OIT test results under both of the Ultraviolet Radiation Effect on an HDPE Geomembrane. Membranes device exposures showed faster antioxidant depletion for the standard OIT test than the high-pressure 2021, 11, 390. https://doi.org OIT test. The DSC and FTIR analyses did not demonstrate the polymer’s changes. /10.3390/membranes11060390 Keywords: high-density polyethylene; geomembrane; ultraviolet radiation; durability; thermal analysis Academic Editor: Isabel C. Escobar Received: 18 May 2021 Accepted: 23 May 2021 1. Introduction Published: 26 May 2021 Geomembranes are polymeric geosynthetic material used as a barrier in environ- mental facilities, such as landfills, mining facilities, and leachate ponds. This product is Publisher’s Note: MDPI stays neutral also utilized in waste liquid ponds, water ponds, farm ponds, adduction, and irrigation with regard to jurisdictional claims in canals [1–3]. High-density polyethylene (HDPE) geomembranes are usually used as liners published maps and institutional affil- in environmental construction work due to good mechanical properties, good welding iations. conditions, and excellent chemical resistance [4]. An HDPE geomembrane’s field performance is affected by different conditions and exposures, including ultraviolet radiation, thermal and oxidative exposure, and chemical contact. These exposures can change the polyethylene’s morphology, causing a reaction Copyright: © 2021 by the authors. between the polymer chain with the oxygen molecule. Accelerated laboratory tests and Licensee MDPI, Basel, Switzerland. exhumed sample evaluations indicate essential responses for the durability issue [5–7]. This article is an open access article The synergy between ultraviolet (UV) radiation and thermal exposure leads to the distributed under the terms and geomembrane’s lifetime [8,9]. The wavelength of solar radiation extends from the infrared conditions of the Creative Commons (higher than 700 nm), through the visible spectrum (400 to 700 nm), and into the ultraviolet Attribution (CC BY) license (https:// (lower than 400 nm). A series of free radical reactions control the polyolefin’s degradation. creativecommons.org/licenses/by/ 4.0/). Polymer chain scission and polymer property degradation can occur when UV radiation Membranes 2021, 11, 390. https://doi.org/10.3390/membranes11060390 https://www.mdpi.com/journal/membranes Membranes 2021, 11, 390 2 of 14 reaches the geomembrane surface [10]. To protect the polymer from UV radiation, carbon black is added to the resin during the manufacturing process, about 2 to 3% in mass, typically with a particle size of 22–25 nm [2,10]. There are different methods to study the ultraviolet radiation effects on HDPE ge- omembranes, as the outside natural radiation exposure demands long-term evaluation, and by the laboratory, using weatherometers [10]. The evaluation of ultraviolet radiation on HDPE geomembranes at the laboratory can be proceeded by different weatherometers: Xenon arc or an ultraviolet fluorescent tube device. Xenon arc weatherometer use in the geosynthetics field is remote due to the high cost involved [11]. Sahu et al. [12] evaluated the influence of ultraviolet light on the thermal properties of HDPE for different carbon black concentrations from 1 to 3%. The authors used an ultraviolet fluorescent weatherometer for a cycle of 192 h. The Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) were used to analyze the HDPE behavior before and after UV exposure. The analysis confirms that the carbon black was evenly dispersed without degradation in the HDPE matrix. Jiang et al. [13] investigated an HDPE resin after 800 h of exposure in a Xenon arc lamp device. Antioxidants and a UV absorber were added to understand their influences on ultraviolet resistance. The authors performed FTIR, DSC, and TG (thermogravimetric) analyses and the mechanical test. The results showed which UV absorbers presented better results than the antioxidants. The samples with UV absorbers added maintained their mechanical properties even after 600 h of exposure. The field study provided by Reis et al. [14] evaluated five 2.0 mm-thick high-density polyethylene geomembrane samples exposed in 8 different places in Portugal over 12 years. The samples presented slight variations in the tensile properties, increasing elongation properties, which was not explained by the authors. Locations with higher UV indexes suggest an impact on tensile properties and antioxidant depletion. The changes in the structural properties of high-density polyethylene film exposed to UV-B radiation were studied by Martínez-Romo et al. [15]. The crystalline phase fraction of high-density polyethylene film increased further after 30 days of exposure to UV-B radiation, affecting the physical properties such as stiffness, dissolution resistance, and dimensional stability. The results showed which sample had a high oxidation degree. Mendes et al. [16] analyzed HDPE samples with and without additives exposed to weathering in Rio de Janeiro, Brazil, up to 4000 h. The additives utilized were a phenol type antioxidant and two HALS-type light stabilizers. The authors used FTIR analysis, DSC analysis to determine the crystallinity, mechanical tests, and the variation of the sample’s molecular weight was evaluated by gel permeation chromatography. The results showed decreased elongation at break for the sample without additives, demonstrating the almost total loss in ductility. The increase in crystallinity and reduction of molecular weight for the sample without additives was still verified. The sample stabilized with the additives remained constant for the exposure time, demonstrating the additives’ effectiveness. Qureshi et al. [17] evaluated a linear low-density polyethylene (LLDPE) geomembrane with 3.0 mm of thickness without stabilizers under weather exposure in Saudi Arabia. After three months of exposure, the geomembrane presented losses higher than 50% in the tensile properties. A 16-year-old HDPE geomembrane exhumed from a mining facility in a freshwater pond in Argentina and a 6-year-old HDPE geomembrane exhumed from an environmental liner test site in Canada (both samples were 1.5 mm thick) were evaluated using the OIT test by Rowe and Ewais [18]. The exhumed sample, after 16 years of service, presented complete antioxidant depletion. The exhumed sample from the research site performed well, presenting a modest antioxidant depletion. The antioxidant depletion for the research site was faster for the slope location than the bottom location. Lavoie et al. [19] used thermal analysis to evaluate a 1.0 mm thick HDPE geomembrane exhumed sample from an industrial water pond after up to 2 years of service. Comparing the exhumed sample with a virgin reference sample, the heating rate of 5 ◦C min−1 at Membranes 2021, 11, 390 3 of 14 the TG analysis noted a different behavior for the exhumed sample, attributed to the reaction time. For the thermomechanical analysis (TMA), the molecular relaxation between 30–65 ◦C verified for the reference sample was not noted for the exhumed sample. Accord- ing to the authors, these differences can indicate changes in the polymer morphology. HDPE geomembranes are usually applied as a pond liner outdoors for the entire service life. This work evaluated a high-density polyethylene smooth geomembrane sample that was 1.0 mm thick, often used for geotechnical, environmental, and agricultural applications,
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