TG-FTIR investigations of the pyrolysis of polyurethanes: Quantitative carbon dioxide tracing, decomposition mechanisms, products and mass balances for advanced recycling

Abstract

Polyurethanes (PUR) are versatile polymers used in a broad range of applications. Conventional mechanical recycling is thus difficult. Chemical recycling such as pyrolytic waste treatment presents new recycling options. Advanced recycling by pyrolysis may help to reduce environmental impacts from PUR wastes. The knowledge of mechanisms, products and yields is essential for the design of efficient pyrolysis processes. Rigid (RPUF) and flexible foams (FPUF), a cast elastomer (CE) and a thermoplastic Polyurethane (TPU) have been investigated by thermogravimetry (TG) and FTIR-spectroscopy. Two decomposition steps have been identified. CO₂ is mainly released in the first decomposition step between 250 °C and 400 °C. The second decomposition step at temperatures above 400 °C releases polyol fragments and marginal amounts of CO₂. Strong feedstock dependency is evident. Quantitative tracing for the CO₂ release was developed, validated and applied. This allows the resolution of specific decomposition phenomena, mass balancing and distinguishing potentially valuable volatiles from CO₂ and solid residues. CO₂ yields are 12.0 mass-% for RPUF, 4.0 mass-% for FPUF, 3.2 mass-% for CE and 5.3 mass-% for TPU. Considering solids and CO₂ as losses, recycling potentials were determined which are 74 mass-% for RPUF, 90 mass-% for FPUF, 95 mass% for CE and 93 mass-% for TPU. This facilitates further process development based on polymer-specific data.