High-resolution material flow analysis of the Swiss plastics system showed that even at a moderately increased recycling rate of 23%, product manufacturing can absorb secondary plastics covering only 11–17% of total plastic demand, so a supply surplus emerges and the 'true' recycling rate falls 10–42% below the apparent one (the low- to high-applicability sub-scenarios span 13–20%). Because these applicability limits were assigned empirically from currently observed uptake, the dominant causal barriers per product subsegment (technical, aesthetic, odor, legislative, economic) remain unidentified, and neither market responses to a surplus nor the dynamic co-evolution of supply and demand were modeled. The open problem is to determine the demand-side limit of plastics circularity in a property-explicit way: construct a property-based matching between secondary-material properties (varying by recycling pathway) and product requirements, embed it in a dynamic, demand-coupled assessment, quantify rebound effects from abundant low-cost secondary material, and establish the economic and policy conditions under which new applications or market adjustments could absorb projected surpluses. Comprehensive life-cycle assessment of chemical recycling routes is out of scope, as later work (Klotz et al. 2024; Krell et al. 2025) has substantially addressed it.

Background

Mechanical recycling converts post-consumer plastic waste into 'recyclates' — secondary plastics intended to substitute virgin (primary) polymer in new products — by re-melting and regranulating the collected polymer (as distinct from chemical recycling, which breaks the polymer down into monomers or chemical feedstocks). Whether recyclates actually displace virgin material is not guaranteed: recyclate properties deviate from virgin resin because different grades of the same polymer type, each tailored with specific chain-length distributions, side-chain configurations and additives, are mixed during collection, and because products contaminate and degrade during use. Manufacturers therefore restrict recyclate use to a subset of applications and to limited shares ('applicability'), for technical, aesthetic, odor, legislative and economic reasons.

Material flow analysis (MFA) tracks stocks and flows of a material through an economy. Klotz, Haupt and Hellweg (2022) combined a high-resolution MFA of the Swiss plastics system (11 plastic types, 54 product subsegments) with empirically derived applicability assignments to compute, alongside the conventional recycling rate (RR), a 'true recycling rate' (TRR) that counts only secondary material actually utilized in product manufacturing. In a 2025 scenario with increased collection, the RR was 23% but the TRR only 13–20%, and secondary material could cover at most 11–17% of total plastic demand; even at this modest recycling level, supply exceeded what manufacturing could absorb for several polymers (e.g., low-density polyethylene, LDPE, and polystyrene, PS). Because applicability was assigned empirically — from recycling pathways and uptake examples observed today — the dominant, subsegment-specific causal barriers remain unidentified, and the authors proposed a property-based matching of secondary-material characteristics to product requirements as the needed generalization. The assessment was also static (single target year with demand and recyclate quality held fixed), and it did not model two responses to a secondary-material surplus: consumption increases driven by cheap secondary material (circular economy rebound, Zink and Geyer 2017) and the development of new product applications or markets, whose viability under different economic or policy conditions is unknown.

Adjacent literatures frame the problem but do not close it. On the supply side, dynamic MFAs reconstruct polymer-level stocks and future waste arisings (Kawecki et al. 2021 for Europe; Abbasi et al. 2023 for Norway; Gao et al. 2025 for the Nordic countries, who estimate that enhanced mechanical recycling could supply about 27% of regional demand by 2050), but they treat demand coarsely and do not constrain uptake by recyclate properties. On the demand and quality side, Eriksen et al. (2019, 2020) estimated how material properties and product design limit closed-loop recycling of household plastics in Europe (covering polyethylene terephthalate, PET, PE and PP, the main packaging polymers); Kahlert and Bening (2022) compared projected recyclate production with pledged demand in Germany; Tonini et al. (2022) argued that 'quality of recycling' — whether a recyclate is adequate for a specific end application — lacks an operational definition; Mager et al. (2023) matched recyclate quality of the polyolefins (polyethylene, PE, and polypropylene, PP) against application-specific property windows for rigid packaging; and Golkaram et al. (2025) presented RecyQMeter, a first application–property matrix scoring recyclate quality per application. None of these integrates property-explicit applicability, market and rebound responses, and dynamic supply–demand co-evolution into one assessment of absorption capacity. Life-cycle assessment (LCA), which quantifies environmental impacts of product systems from raw-material extraction to end of life, supplies the evaluation frame: the environmental benefit of recycling depends on the virgin material actually substituted, so limited uptake partly annihilates achievable gains.

Problem Statement

Determine, in a property-explicit and dynamic way, the demand-side limit of plastics circularity: how much secondary plastic product manufacturing can actually absorb, under which conditions a supply surplus emerges, and with what net environmental consequence. This requires, as jointly supporting one objective: (1) constructing a property-based matching between measured secondary-material properties (varying by polymer type and recycling pathway) and the property requirements of product subsegments, thereby identifying the dominant causal barriers — technical, aesthetic, odor, legislative, economic — per subsegment and generalizing applicability beyond empirically observed uptake; (2) establishing whether and under what economic or policy conditions new product applications or market adjustments could be developed at scale to absorb projected secondary-material surpluses; (3) quantifying the magnitude, likelihood and net environmental consequences of rebound effects — consumption increases driven by abundant, low-cost secondary material — by coupling material flows with demand responses; and (4) modeling the multi-year co-evolution of secondary-material supply and product demand, for example as legacy in-use stocks of long-lived products age and their waste flows approach consumption levels. The objective comprises four jointly required parts: (1) an explicit per-subsegment statement of which of the barrier categories listed above dominate; (2) the economic or policy conditions under which new product applications or market adjustments absorb the projected surplus; (3) an explicit quantitative magnitude and likelihood for the rebound, with its net environmental consequences reported against a stated impact metric; and (4) a general model of the multi-year supply–demand co-evolution. Comprehensive life-cycle assessment of chemical recycling routes lies outside the scope of this objective, as later work (Klotz et al. 2024; Krell et al. 2025) has substantially addressed it.

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