Prague, Czech Republic – The challenges involved in recycling thermoset polymers such as polyurethane foam have led to chemists looking to create alternatives designed for easier recycling. A team at the Czech Academy of Sciences’ Institute of Macromolecular Chemistry have been working on bio-based ultralow-density PU foams they hope should be easier to recycle at end of life.
The recyclability of the PU was enhanced by incorporating hydrolysable ester units into the polymer structure. Their starting point was succinic acid, a common diacid that can be produced via the fermentation of carbohydrates, and they made a series of biobased polyester polyols with different functionalities from succinic acid and tetraethylene glycol. These were then used to make ultralow-density, partly open-cell, semi-rigid PU foams.
Three different water-blown foam series were made, with pMDI as the isocyanate. One was based on the succinic acid polyols alone, while the other two combined it with polyols with higher functionality, either commercially available petrochemical derived, or biobased polyols derived from epoxidised tall oil fatty acids. Tall oil is a byproduct of the kraft process for making wood pulp.
Finally, they investigated whether the inclusion of hydrolysable ester groups did indeed make the foams more recyclable. This was achieved via microwave-accelerated solvolysis, without any catalyst being added.
They found that the 100% biopolyol based PU foams that included the tall-oil derived polyols gave foams with homogenous, fine cellular structures. They also had low density and good mechanical properties. The presence of the succinic acid based polyol component accelerated their solvolysis, and the team now plans to investigate their recycling in more detail, including their potential for biorecycling.
The work has been published in the journal ACS Sustainable Chem. Eng.