# Comparative Thermal and Fire Behavior of Rigid Polyurethane (PUR) and Polyisocyanurate (PIR) Foams Formulated with Recycled Poly(ethylene terephthalate) (PET) Polyols—Part 1

## TL;DR

PIR foams made with recycled PET polyols show better fire resistance and thermal stability than PUR foams, making them safer and more sustainable for insulation.

## Contribution

This study systematically compares the fire behavior of PIR and PUR foams using recycled PET polyols, revealing significant improvements in thermal and fire performance.

## Key findings

- PIR foams show a 50% reduction in peak heat release rate compared to PUR foams.
- Char yield increases from ~3 wt.% to >22 wt.% in PIR foams, indicating better fire resistance.
- PIR foams exhibit delayed thermal degradation and improved thermo-oxidative stability.

## Abstract

What are the main findings?
PIR foams with recycled PET-based polyester polyols show delayed thermal degradation and a char yield increase from ~3 wt.% to >22 wt.%.The PIR system exhibits a higher glass transition temperature and improved thermo-oxidative stability compared with PUR foam.Peak heat release rate is reduced by ~50% in PIR foams, indicating significantly lower fire intensity.

PIR foams with recycled PET-based polyester polyols show delayed thermal degradation and a char yield increase from ~3 wt.% to >22 wt.%.

The PIR system exhibits a higher glass transition temperature and improved thermo-oxidative stability compared with PUR foam.

Peak heat release rate is reduced by ~50% in PIR foams, indicating significantly lower fire intensity.

What are the implications of the main findings?
PIR foams demonstrate slower fire growth and enhanced condensed-phase stabilization during combustion.Halogen-free PIR formulations produce lower toxic gas emissions than conventional PUR systems.Recycled PET-derived polyols improve fire performance while supporting sustainable material design for advanced insulation applications.

PIR foams demonstrate slower fire growth and enhanced condensed-phase stabilization during combustion.

Halogen-free PIR formulations produce lower toxic gas emissions than conventional PUR systems.

Recycled PET-derived polyols improve fire performance while supporting sustainable material design for advanced insulation applications.

Rigid polyurethane (PUR) and polyisocyanurate (PIR) foams are widely used as thermal insulation materials due to their excellent thermal conductivity and low density. However, fire resistance remains a critical property determining their safe application in construction, transportation, and energy systems. This study provides a comparative overview of the fire behavior of PUR and PIR foams, focusing on structural aspects, decomposition mechanisms, flame retardancy, and performance of emission of toxic gases during the combustion process. Despite extensive studies on PUR and PIR foams, systematic comparative investigations addressing the combined influence of recycled PET-based polyester polyols, isocyanurate content, and fire-related properties—including thermal degradation, heat release, and toxic gas emissions—remain limited. PIR foams, characterized by higher isocyanate indices and the presence of isocyanurate rings, show superior thermal stability, reduced heat release rates, and enhanced char formation compared with PUR foams. Experimental analysis of thermal degradation (TGA/DTG) and heat release (cone calorimetry) confirms that PIR foams demonstrate higher resistance to ignition and slower fire propagation. The results emphasize the critical role of molecular architecture and crosslink density in shaping the fire performance of rigid foams, highlighting PIR systems as advanced insulation solutions for applications requiring stringent fire safety standards. The PIR foam was prepared using a polyester polyol derived from recycled PET, which could help in achieving better fire properties during the combustion process. Compared with PUR foams, PIR foams exhibited an approximately 50% reduction in peak heat release rate, an increase in char yield from about 3 wt.% to over 22 wt.%, and a shift of the main thermal degradation peak by approximately 55 °C toward higher temperatures, indicating substantially enhanced fire resistance.