09. Sep 2026
Repeated recycling cuts TPU molecular weight by up to 80%
Researchers in the Czech Republic have found that repeated mechanical recycling can reduce the molecular weight of thermoplastic polyurethane by as much as 80%, potentially limiting the number of times the material can be reprocessed.
The team at the Centre of Polymer Systems at Tomas Bata University in Zlín studied TPU after one and two consecutive mechanical reprocessing cycles, examining changes in its molecular structure, rheology and emissions.
Gel permeation chromatography showed a pronounced reduction in molecular weight, accompanied by lower viscosity and a narrower molecular-weight distribution. The researchers said the results indicate extensive polymer-chain scission and declining processability as the TPU undergoes repeated recycling.
The study also examined volatile and low-molecular-weight compounds produced during reprocessing using techniques including pyrolysis gas chromatography-mass spectrometry and headspace solid-phase microextraction.
MDI, 1,4-butanediol and butylated hydroxytoluene were among the compounds identified. The researchers found that levels of 1-hexadecanol increased with each recycling cycle and suggested it could potentially be used as a molecular marker for repeatedly reprocessed TPU.
Migration tests using water found only limited release of low-molecular-weight compounds. However, 1,6-dioxacyclododecane-7,12-dione was detected in leachates from all the samples, which the researchers said may warrant consideration when assessing the environmental implications of recycled TPU.
Thermal analysis showed more moderate changes in melting temperature and crystallisation behaviour than in molecular weight.
The researchers said the findings highlight the need to consider degradation and emissions alongside the mechanical properties of recycled TPU when developing circular material systems.
The work, by Andrea Polachova, Martin Novak, Jaroslav Cisar, Milan Masar and Vladimir Sedlarik, is published in Polymer Degradation and Stability, volume 252, under the title Recyclability of thermoplastic polyurethane under repeated mechanical reprocessing: degradation mechanisms and volatile emissions.
Photo: an AI-generated image of a recycling facility