Technical substitutability of recycled materials in life cycle Assessment: A comprehensive review and framework for quantification.

In evaluating environmental sustainability with methodologies like life cycle assessment (LCA), recycling is usually credited for avoiding impacts from virgin material production. Consequently, the LCA results are influenced by the manner in which the substitutability of virgin by recycled materials is estimated. This study reviews how the scientific community assesses the technical substitutability of recycled materials in LCA. Accordingly, 49 peer-reviewed papers were in-depth analysed, considering aspects such as materials studied, type of substitution, recycled material (rMaterial) application, and life cycle stages (LCSs) where substitution was evaluated. The results show that 49% of the papers investigated material substitutability through technical and economic aspects. 51% of the articles did not consider the final application of the rMaterial. Plastics were the most studied material, and mass was the most used property to quantify technical substitutability. Certain materials were more analysed in specific LCSs (e.g., metals in the natural resource extraction stage). As 51% of the papers developed a new approach for substitutability calculation, this shows that substitutability is still a concept in development. It was noticed in 33% of the papers that substitutability values were taken from external sources, and in some cases were used without considering whether they were representative for a specific case. Aspects such as harmonization, transparency, and consideration of the application of recycled materials, therefore, require more attention in substitutability evaluation. Based on the results, a step-wise framework to measure technical substitutability at different LCSs was developed to guide researchers in including substitutability in LCA studies.