Addressing the complex challenge of understanding and quantifying substitutability for recycled plastics

Plastics are highly versatile materials, which can substantially vary in their properties, within a single polymer type, to cope with the range of different applications. Sorted bales of end-of-life plastics typically still contain a mixture of various plastic types and grades, which significantly affects the technical properties of the recycled material made from these bales. The evaluation of the technical recycling quality is crucial to determine which applications can be targeted with the produced recyclates, and if actual substitution of virgin plastics is possible. This is relevant from a technical perspective, but also for sustainability assessments such as life cycle assessment. The functionality of a plastic material is determined by a range of mechanical characteristics and by its ease of processing. These aspects cannot be generalized, as they are dependant on the intended application. This work, therefore, proposes a concept for calculating the effective technical substitutability, in which application specific functions generate a score for processability and mechanical recycling quality. To illustrate this concept, the substitutability of three commercially available recycled plastics is determined for four different application categories. The results show the strong application dependency of the changes in technical quality for a given recycled plastic stream. The approach is a step forward in the correct determination of the substitutability and consequently the proper assessment of the potential of end-of-life plastics as secondary resource.