Preparation and physicochemical characterisation of polyurethane foams prepared using hydroxybutylated condensed tannins as a polyol source

Abstract

Renewable, bio-based and functional polyols are increasingly being sought as precursors for polyurethanes. A hydroxybutylated Pinus radiata bark tannin (HBBT) was prepared via a mild-base solvent-free synthesis and used as a polyol source in rigid polyurethane foams prepared in conjunction with commercial sorbitol or sucrose-based polyols. The resulting foams were physically and chemically characterised using FTIR spectroscopy, SEM, mechanical compression testing and thermogravimetric analysis. Addition of HBBT had minimal impact on the foam density, however the cellular structure became increasingly deformed at higher substitution levels. The specific modulus and strength increased with HBBT addition, by up to 50% at higher HBBT loadings. Thermal stability was improved through HBBT addition, increasing the degradation onset temperature, reducing mass loss at high temperature and providing higher char residuals. These findings indicate the potential to use HBBT in polyurethane foams for the building and construction industries, offering both improved mechanical properties and increased thermal resistance.