(131d) Cradle-to-Cradle Life Cycle Assessment of Multilayer Plastic Films Used in Sheet Molding Compound Process

Multilayer plastic films have a wide range of applications in many industries due to their unique carrier, barrier, and flexibility properties. Multilayer plastic film market is expected to surpass US$210 Bn. This has resulted in a significant generation of this type of plastic film waste, which unlike monolayer plastic films, cannot be treated or recycled using the conventional recycling techniques for monolayer plastic films. This is mainly due to heterogeneity, complexity of structure, and thermodynamic incompatibility of multiple layers of polymers with different chemical composition. Despite the recent efforts to overcome technical barriers for recycling or recovering this type of plastic film, to our knowledge, there is no study that identifies the environmental sustainability and tradeoffs between all possible end of life (EoL) alternatives for treating this type of waste. Therefore, the overarching goal of this study is to evaluate the life cycle environmental impact of multilayer plastic film supply chains, from the extraction of natural resources to waste handling and treatment (cradle-to-cradle). We consider six major scenarios based on the current typical, state-of-the-art and R&D technologies available as EoL treatment options, i.e., landfilling, incineration, pyrolysis, reuse, mechanical recycling (downcycling), and chemical recycling (downcycling). In this work, we are focused on high barrier/carrier plastic films, which are a specific type of multilayer plastic films that are used during the production process of Sheet Molding Compounds (SMC). SMCs are thermoset materials that are used for manufacturing products with high mechanical strength. High barrier/carrier films are used as a carrier that enables a continuous operation for SMC production and as a barrier that prevents the escape of styrene monomers from SMCs, which is crucial for the molding process. While we obtain life cycle inventory (LCI) data from our industry partners, technology vendors, LCI databases, and literature, we run experiments when there exists a gap in available LCI data. For the reuse scenario, we perform experiments for cleaning and thermally stitching the film to enable its reuse in the continuous SMC manufacturing process. In addition, for the mechanical recycling scenario, we perform experiments for pelletizing and molding the film to produce recycled or downcycled products. We use US Environmental Protection Agency (EPA) Tool for Reduction and Assessment of Chemicals and Other Environmental Impacts (TRACI) with Cumulative Exergy Demand (CExD) and economic circularity as complementary metrics to provide insights on environmental impacts, resource use, and circularity efficiency. Life cycle assessment (LCA) results for the landfilling (current typical) scenario indicates that the supply chain of virgin resins used to produce multilayer films contribute the most to the negative environmental impacts. This shows the great opportunity to mitigate these adverse environmental impacts by employing recycling and recovery strategies. Moreover, a preliminary comparative LCA is performed for landfilling, incineration, pyrolysis, and mechanical downcycling scenarios. For the incineration scenario, we assume that the energy generated through the incineration process is used to generate electricity. For the pyrolysis scenario, pyrolysis oil and char are considered as the final products of the pyrolysis process. For the mechanical downcycling scenario, we use the multilayer film waste to produce molded products with real-world applications. A substitution approach is used for the EoL products to evaluate the environmental impacts of each scenario. Comparative LCA results indicate that the mechanical downcycling scenario outperforms other scenarios in terms of the environmental sustainability performance. In this scenario, Global Warming Potential (GWP) and CExD are 50% and 80% less than those of the base case (landfilling) scenario, respectively. Also, economic circularity of the downcycling scenario is 25%, which is the highest among all scenarios. This indicates the advantage of mechanical downcycling over landfilling and energy recovery scenarios (i.e., incineration and pyrolysis) due to the substitution of virgin materials in producing molded products. Nevertheless, we will perform LCA on other possible alternatives for treating multilayer films such as reuse, closed loop mechanical and chemical recycling. By performing a comparative LCA on all EoL scenarios, we can identify the environmental bottlenecks in the supply chain, and identify the environmental tradeoffs between different scenarios, which is a step toward developing sustainable circular economy strategies for multilayer plastic films.