Prague, Czech Republic – The thermoset nature of polyurethane foams makes them challenging to recycle, and their chemical structures mean they are usually difficult to break down via biodegradation. A team at the Czech Academy of Science’s Institute of Macromolecular Chemistry has been looking at whether it might be possible to modify the polymer structure to enhance its biodegradation potential.
The presence of ester linkages within the PU’s chemical structure, they said, is known to be important for the biodegradability of PU foams, but the impact of other hydrolysable groups, notably urethane, urea and amide linkages, has not been so widely explored. The effect of the PU network’s supramolecular structure and cellular morphology has not been well investigated, either.
They therefore prepared fully aliphatic PU foams, both with and without hydrolysable amide linkages. Six-month soil burial tests were then performed to look at their aerobic biodegradation, with the influence of supramolecular structure and cellular morphologies studied in addition to the effect of the foams’ chemical composition.
The release of CO2 was measured throughout the tests, along with the enzyme activities of proteases, esterases and ureases. Phospholipid fatty acid analysis was also carried out, and a genetic assessment of the microbe content was made.
They found a mineralisation rate of 30-50% for the foams, which indicated significant degradation, and also that the PU was being used by soil microorganisms as a source of nutrients and energy. The microbial biomass was unaffected, suggesting the degradation products were not causing toxicity issues to the microbes.
Another finding was that while the ester linkages were indeed readily cleaved by the enzymes produced by the soil microbes, amide linkages were not. Amide groups in the foam also led to a change in the supramolecular network because of the increased hard segment content, they said, which also reduces its biodegradability.
Overall, they concluded that it is important to consider both the polymer’s chemical composition and its macroscopic structure when designing novel PU materials with biodegradation in mind.
The work has been published in the journal Science of the Total Environment.