Limited utilization options for secondary plastics may restrict their circularity.

Plastic recycling can provide environmental benefits by avoiding the detrimental impacts of alternative disposal pathways and enabling the substitution of primary materials. However, most studies aiming at increasing recycling rates have not investigated how the resulting secondary materials can be utilized in product manufacturing. This study assesses the future substitution potential of primary with secondary plastics, building on a material flow system of 11 plastic types in 54 product subsegments in Switzerland in 2017 with a recycling rate of 9%. In a prospective material flow analysis of a scenario for 2025, the collection rate of the plastic fractions collected in 2017 is increased to 80%. The secondary material flows are allocated to suitable uptaking product subsegments using a linear optimization. The maximum share of secondary materials utilizable in each product subsegment is estimated, whereby three sub-scenarios involving high, moderate and low allowed secondary material shares are modelled. Depending on plastic type and scenario, 21% to 100% of the secondary material gained can substitute for primary material, covering 11% to 17% of the total material demand. While the overall recycling rate could reach 23%, taking into account only the uptaken secondary materials a true recycling rate of only 17% results in the moderate applicability sub-scenario. Based on these results, the secondary material uptake can be said to constitute a limiting factor for increased future recycling. Therefore, thorough consideration of the possible secondary material application is a prerequisite for designing and assessing future recycling systems or for setting recycling rate targets.