Study of the mechanical, thermal properties and flame retardancy of rigid polyurethane foams prepared from modified castor-oil-based polyols

Po1lyurethane foams (PUFs) were prepared using modified castor-oil-based polyols (MCOs). In the first stage, castor oil (CO) was converted into monoglycerides and diglycerides by alcoholysis with glycerol and pentaerythritol. Next, the polyester polyols were synthesised by condensation with the alcoholysis of CO and phthalic anhydride. The chemical and physical properties, foaming behaviour and miscibility with other components of the MCOs were studied by mechanical testing, Fourier transform infrared (FTIR) spectroscopy, gel permeation chromatography (GPC) and thermogravimetric analysis (TGA). The results showed that the components of the MCOs and the foaming behaviour of the foams prepared from the MCOs were similar to those of commercial polyester polyol PS-3152. The reaction activities esterification modified CO polyols were higher than those of alcoholysis modified CO polyols, due to the higher relative content of primary hydroxyl groups. The MCOs and CO had higher thermal stability and better miscibility with polyether polyol 4110 and the physical blowing agent cyclopentane than PS-3152. The properties and flame retardancy of PUFs prepared from MCOs were studied by mechanical testing, TGA and cone calorimetry. The results indicate that the PUFs prepared from castor-oil-based polyester polyols with a reasonable distribution of soft and hard segments had better mechanical properties and thermal conductivities than the PS-3152-based PUF5. Additionally, the MCO-modified PUFs exhibited much higher thermal stability during the pyrolysis process. The cone calorimetry results showed that adding flame retardant ammonium polyphosphate (APP) into PUFs can significantly decrease their heat release rate (HRR), total heat release (THR) and mass loss. These test results indicate that APP has a better synergistic effect with phthalic anhydride polyester polyols than long-chain fatty polyols. All of these unique properties of the MCO-modified rigid PUFs were correlated to the structures of these PUFs. This study may lead to the development of a new type of polyurethane foam using castor oil.