Polyisocyanurate

Polyisocyanurate, commonly abbreviated PIR, is a polymer produced by reacting polyisocyanates with polyols to form a highly crosslinked polyurethane network in which some of the urethane linkages have undergone trimerization to form isocyanurate rings. This chemical structure yields a rigid foam with high thermal stability, dimensional stability, and moisture resistance, and it is widely used for insulation.

Production and structure: PIR foams are typically produced by reacting di- or polyisocyanates, most commonly methylene diphenyl diisocyanate (MDI), with polyols in the presence of catalysts that promote isocyanurate ring formation. The result is a crosslinked network with increased crosslink density due to isocyanurate rings, giving higher thermal resistance than conventional polyurethane foams.

Properties: PIR foams have low thermal conductivity and high R-values per inch, largely closed-cell content, good dimensional stability, and enhanced fire performance relative to standard PUR foams. They resist moisture absorption and maintain insulating performance over time. Mechanical properties depend on formulation and processing; PIR is used as rigid boards and spray foams.

Applications: Used in building insulation: rigid boards for walls, roofs, and floors; sprayed insulation; cold-storage panels; refrigerator insulation; some automotive and appliance components.

Environmental and safety considerations: Manufacturing involves handling of isocyanates and blowing agents; appropriate safety measures are required. Blowing agents have evolved toward low global warming potential options. End-of-life disposal can be challenging; PIR insulation is long-lasting but cannot be easily recycled in many cases.