Flame retardancy of polyurethane foams prepared from green polyols with flame retardants

Abstract

Polyurethane foams (PUFs) were synthesized using bis(2-hydroxyethylene terephthalate) (BHET), 1,4-cyclohexanedimethanol (CHDM), and polycaprolactone diol (PCLD), and their flame retardancies were investigated. BHET and CHDM are eco-friendly chemicals derived from waste polyethylene terephthalate, and PCLD is a precursor monomer used for synthesizing biodegradable polymers. Expandable graphite (EG) and tris(1-chloro-2-isopropyl) phosphate (TCPP) were used as flame retardants. For conventional PUFs prepared with an aliphatic polyol, thermal stability was significantly enhanced with EG and TCPP through thermogravimetric analysis (TGA) and micro-combustion calorimetry (MCC). PUFs prepared with BHET and CHDM exhibited higher thermal stability than conventional PUFs. This is attributed to the alicyclic and aromatic ring structures, which contribute to thermally stable char formation during pyrolysis. PCLD was introduced as an additional polyol, as well as a possible flame retardant, without the addition of EG and TCPP. PUFs were successfully prepared and exhibited improved resilience to burning up to 300°C due to the intrinsic thermal stability of PCLD. The limiting oxygen index (LOI) indicated that PUFs containing BHET moiety exhibited higher LOI values, whereas PUFs prepared with PCLD showed the lowest LOI value. PCLD can be used as a polyol; however, additional flame retardants are needed to obtain high flame retardancy for PUFs. © 2021 Wiley Periodicals LLC.