Characterization and Performance Evaluation of Geocomposite Materials Under Extreme Environmental Conditions

Waste containment infrastructure is essential to protect human health and the environment. This infrastructure should consist of robust barrier systems that can isolate municipal, industrial, medical and hazardous waste to avoid contaminant leakage and pollution under extreme environmental conditions. Thus, it is essential these barrier systems withstand high temperatures, pressures and strain deformations that can impact their long-term resilience. Recently, geocomposite materials that consist of geomembranes (GMX) and geosynthetic clay liners (GCL) have emerged as a promising barrier system due to their durability and low cost. GMX is usually made of High-Density Polyethylene or Low-Density Polyethylene while GCL consist of a layer of bentonite clay encapsulated between two polypropylene geotextiles. The promising combination of GCL and GMX gives rise to a durable, cost-effective barrier system under extreme environments.<br/><br/>This research focus on the degradation of GCL and GMX polymers in real-world applications. We simulated harsh, real-world conditions and studied oxidation, free radical formation, crystallinity and tensile properties to understand the material performance. Geocomposites were exposed to Cu (pH=2), Bauxite (pH=12) based mineral process solutions and DI water for 1, 6 and 10 months while applying a 20 kPa normal stress. Next, they were subjected to 2 GPa normal stress to mimic the strain these materials experience under high load in the field. This was followed by imaging, spectroscopy and mechanical characterization to analyze material stability.<br/><br/>SEM images show that GCL exists as bundles of fibers with an average diameter of 40 µm while GMX is a textured film with a thickness of 1.6 mm. Thermal studies via DSC revealed that GMX is composed of antioxidants while GCL does not contain antioxidants. We also quantified the heat of fusion and extracted polymer crystallinity. Both materials showed an increase in crystallinity (9.5% for GCL and 6% for GMX after 10-month immersion) following chemical and stress treatments. This increase in crystallinity was directly proportional to immersion time and solution strength. Higher crystallinity suggests higher degradation since free radicals formed during oxidation create crystalline regions/clusters that makes it more brittle.<br/><br/>FTIR results showed that Carbonyl Indices for both the Carbonyl compounds band (1650-1850 cm^-1) and Hydroperoxide/Alcohol band (3200-3550 cm^-1) increase for GMX and GCL with solution immersion and stress. This suggests that hydroperoxides, alcohol, and carboxyl groups form as a result of oxidation. XRD was performed to extract the crystallinity of the polymers. For GMX, we see a crystallinity increase of 10.5% and 5.5% in Cu and Bauxite solutions respectively, and for GCL it is 10.7% and 18.7%. We notice the impact is higher for GCL due to the lack of antioxidants. XPS confirmed the above results and revealed that C-C bonding has reduced in percentage after exposure, where alcohols (-OH), ketones (-C=O) and carboxyl groups (O-C=O) have increased in percentage, which is a clear indication of oxidation after treatment.<br/><br/>The mechanical properties were also consistent with spectroscopic and thermal results. Young’s modulus gradually increased for 1-, 6-, and 10-month samples. This is severe for 10-month samples: 23-27% for GMX and 37-41% for GCL. Yield strength and tensile strength also showed a similar trend. This proves that harsh chemicals and stress can deteriorate overall mechanical performance. Our research sheds light on micro-level chemical reactions and correlates that to macro-level catastrophic failure in barrier systems. We envision to extend our fundamental understanding and develop a universal model that can predict the life-time of geocomposites for harsh environmental conditions. The impact of this research is significant; it can reduce pollution and protect the environment from toxic, hazardous waste materials under extreme conditions.