(473j) Environmental Benefits of the Solvent-Targeted Recovery and Precipitation (STRAP) Process for Multilayer Plastic Films Recycling

Advances in the food packaging industry have brought diverse environmental and societal benefits; for instance, packaging is essential for enabling long shelf-lives, to mitigate food waste, and to increase food accessibility [1]. Food packaging often appears in the form of multilayer plastic films that leverage properties of different plastic materials to achieve different food protection goals (e.g., block temperature, light, and oxygen) [2,3]. Multilayer films help reduce packaging costs because, often, large amounts of single-layer materials are required to try to achieve the same properties [4]. Common plastics used in multilayer films include polyethylene (PE), ethylene vinyl alcohol (EVOH), and polyethylene terephthalate (PET). The films are commonly made of 2 to 17 layers of different polymers; however, some films can contain up to hundreds of distinct layers [5, 6].

Despite the many benefits of multilayer films, their production and use generate large amounts of non-biodegradable waste. In Europe, approximately 20% of food packaging is multilayer films; this proportion is expected to grow at an average of 9% per year due to current trends (e.g., convenience products, single-serve meals, and small packaging) [7]. Up to 40 % of the millions of tons of films produced end up as post-industrial waste due to inefficiencies and manufacturing errors. Traditional recycling methods (e.g., mechanical recycling) cannot recover each layer of the films due to their chemical incompatibility [8, 9]. Because of this, most film waste ends up in landfills, which is an environmental problem but, at the same time, a missed economic opportunity. Recently, a new technology called the STRAP process has been proposed as a promising alternative for recycling post-industrial film waste [10]. The process uses a series of solvent washes to separate the constituent polymers of different films. The first variation of this approach, STRAP-A, precipitates the polymers by adding antisolvents. A second process, STRAP-B, was proposed to reduce the use of antisolvents by leveraging the temperature-driven precipitation. Both approaches were able to deconstruct a post-industrial multilayer film composed mainly of PE, EVOH, and PET. A third process, STRAP-C, also leverages temperature-driven precipitation and was designed to treat a multilayer film of a different composition [11].

The environmental impacts and benefits of the STRAP processes over virgin resins production are highly relevant for implementing this technology commercially. Thus, this work evaluates the impacts on global warming potential, energy demand, water usage, and process toxicity using a life-cycle assessment methodology. The process is analyzed considering a product perspective [12]. From this perspective, the STRAP approach is seen as an alternative process to produce virgin-grade polymers (raw material of multilayer films). The functional unit considered is the production of 1 kg of multilayer film; therefore, we compare the environmental impacts of producing 1 kg of film from virgin resins with producing 1 kg of film from the recovered resins through the STRAP processes. We find that the STRAP-B and STRAP-C processes can help achieve the goals of a circular economy by reducing resource consumption and environmental impacts.

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