For sustainability reasons, the use of recycled materials should be given preference in the development of plastic products [1]. This is generally a challenge in terms of both design and processing. Compared to virgin plastics, recyclates often have fluctuating quality properties with a comparatively lower performance level [2, 3], and the material can be multi-phase [3], especially in the case of so-called post-consumer recyclates (PCR), due to insufficient sorting depth, contamination or additives.
A plastic product requires an application-oriented product geometry and a suitable material for injection molding under energy-efficient conditions that, in combination with the selected product geometry, can safely withstand possible external loads. In the past, materials have often been selected based on economic considerations, using the cheapest material price per kilogram. According to the authors, this approach closes off many possibilities for design optimization and does not meet the general desire for a holistically developed, optimal product that takes into account technical, economic, and ecological constraints.
The goal of modern plastics product development must be to produce lightweight, sustainable, energy-efficient and high quality products. This means that the ratio of a potential material's "emissions" to its "performance for the technical requirements" must be considered and compared as the first indicator I_General. The "emissions" are the price (monetary output), the energy consumption during processing and the CO₂ footprint for the raw material production, while the "performance" refers to the price-related material volume and the material performance with regard to the possible product functionality.

$I_{General}=\frac{Price}{Volume}·\frac{Energy Consumption_{Process}·CO_2 Footprint}{Technical Performance}$

The authors present their approach and discuss the effectiveness of the developed KPI I_General using the example of a metal-plastic composite demonstrator.

References
[1] European Commission; A European Strategy for Plastics in a Circular Economy COM, 2018, 28 Final.
[2] G., Faraca; T., Astrup; Plastic waste from recycling centres: Characterisation and evaluation of plastic recyclability Waste Manag., 2019, 95, 388-398.
[3] M., Pracella; Blends and Alloys. In: Modification of Polymer Properties, 2017, 155-184.