A practice‐based framework for defining functional units in comparative life cycle assessments of materials

Abstract

In comparative life cycle assessment (LCA) studies of materials, there is a mismatch between the current practice and existing guidelines regarding functional unit definition. The purpose of this study is to develop a practice-based framework for defining functional units in comparative LCAs of materials and provide guidance regarding in which situations different functional unit types are relevant. A literature review of comparative LCAs of materials identified three types of functional units: (i) the reference flow functional unit, (ii) the property functional unit, and (iii) the performance functional unit. These functional unit types, of which only the latter strictly complies with LCA guidelines, represent varying degrees of functional equivalence and technological maturity. The most relevant functional unit type depends on the goal of the study. We suggest that screening assessments of whether materials have comparable environmental impacts can apply reference flow functional units. Material comparisons for certain application areas with some important properties can apply property functional units. For comparisons of end products, performance functional units can be applied. However, even in such cases, complete functional equivalence can hardly be achieved due to more or less relevant product differences. The applicability of the framework is demonstrated for the case of comparing cemented carbide and polycrystalline diamond hard materials.

The meaning of life … cycles: lessons from and for safe by design studies

“…, representing the end-of-life treatment of the isolated material 1 or 2 independent from its application). Some cradle-to-gate LCAs 54 adopt this type of life cycle that excludes the application of materials in a final consumer product, the use of that product and also excludes the end-of-life treatment. When two materials could provide the same function for a product, the materials often need different auxiliary materials and different amounts.…”

“…• Trade-offs between different impact categories (e.g., global warming, resource use, acidification, human toxicity, ecotoxicity, …) of several materials fulfilling the same material function 54 LC of a chemical in one specific application Blue, green, red or orange only in Fig. 2 • Trade-offs due to shifting of emissions over different processes/stages of the 'chemical in one specific product' life cycle • Trade-offs between processes/stages of actual risks of a specific chemical in one specific product LC of a chemical including all its applications Blue in Fig.…”

Life Cycle Assessment of Synthetic Nanodiamond and Diamond Film Production

“…24 Although a mass-based functional unit does not reflect material properties or functions, it can still be relevant in studies with the aim to conduct approximate comparisons of materials' environmental impacts if these are used in similar applications, particularly for novel materials. 25 A mass-based functional unit of 1 g nanodiamonds (4−5 nm primary particles) was selected for detonation synthesis. The particle size and shape influence nanodiamond properties and are selected based on the intended application.…”

“…In cradle-to-gate studies, with the aim to assess the environmental impacts of a single product, the functional unit might be set equal to a physical output, such as mass . Although a mass-based functional unit does not reflect material properties or functions, it can still be relevant in studies with the aim to conduct approximate comparisons of materials’ environmental impacts if these are used in similar applications, particularly for novel materials . A mass-based functional unit of 1 g nanodiamonds (4–5 nm primary particles) was selected for detonation synthesis.…”

Environmental impact of the production process of washing, assorting and packaging fresh potatoes and measures to mitigate it

“…Likewise, it provides a quantitative basis for assessing potential improvements for the environment throughout its life cycle (Azapagic & Clift, 1999). This involves the energy and materials used (Furberg et al ., 2022), as well as the waste products resulting from the process itself. In other words, its impact on the environment is determined, thus assessing opportunities for improvement in its life cycle (Azapagic & Clift, 1999).…”