Recycling and Disposal Methods for Polyurethane Wastes: A Review

Abstract

Polyurethanes (PU) are a general class of polymers prepared by the polyaddition of isocyanates and hydroxyl group containing compounds. PU foams are formed via the reaction of poly-isocyanate and multi-functional hydroxyl compounds resulting in urethane linkages. The foams are formed in wide range of densities and maybe flexible, semi-flexible or rigid in structure. To control the foam structure, blowing agents are employed. These agents are introduced during foam formation through volatilization of low-boiling liquids or through the formation of gas due to chemical reaction. Additionally, surfactants, catalysts, etc. are used during the manufacturing of foams. PU, including PU foams, is one of the most important groups of materials today and hence, their recycling has been of great interest. Many methods of recycling PU are available and many more are being studied further. However, no method has seen large scale commercialization or is brought into regular practice. The objective of this review is to bring to light the various technologies available and their current status of development as well as newer upcoming methods that may be available in the future.

Advances in Low-Density Flexible Polyurethane Foams by Optimized Incorporation of High Amount of Recycled Polyol

“…Among the chemical depolymerization methods, acidolysis may attract special interest. Gadhave et al reviewed various chemolysis processes for depolymerization of PU foams, including acidolysis, concluding that none of them was brought into industrial practice; however, acidolysis with HCl presents the advantage of carrying out the process in mild conditions (60 °C, atmospheric pressure) [ 9 ]. However, acidolysis using dicarboxylic organic acids instead of inorganic acids looks more promising.…”

Selectively Depolymerizable Polyurethanes from Unsaturated Polyols Cleavable by Olefin Metathesis

“…[ 1,2 ] Unfortunately, the majority of PU waste is disposed of in landfills or by incineration, with various estimates indicating that only ≈25–30% of PU waste is recycled. [ 3–5 ] Indeed, a recent popular news article illustrated the crux of the problem in highlighting the mounting volume of landfill waste from PU mattresses, driven by growth of online retailing and the ease with which mattresses can now be shipped. [ 6 ]…”

“…[ 2,7,8 ] For example, hydrolysis of PUs can be employed in certain cases to recover the original alcohol monomer (polyol), along with the amine analogue of the original isocyanate monomer. [ 9–13 ] Similarly, various amines, [ 14–20 ] alcohols, [ 14,15,17–19,21–25 ] and acids [ 5,26–32 ] have been used to displace the carbamate linkage and thereby depolymerize PUs. Generally speaking, however, these depolymerization strategies are energy intensive, requiring high temperature, high pressure, and/or long reaction times, and they are inefficient, requiring stoichiometric quantities of cleavage reagents to yield complex mixtures of monomers and oligomers (i.e., incomplete depolymerization) that must be further separated and purified.…”

Evaluation of biological degradation of polyurethanes

“…These polyols can then serve as building blocks for the synthesis of secondgeneration polymers. The major limits of chemical recycling are the processing temperature that leads to high energy consumption (in the example mentioned above, the glycolysis temperature is 190°C) and the side chemical reactions occurring on the urethane bond during the chemical reactions (Gadhave et al, 2019).…”