Synthesis of the bio-based polyurethanes having intrinsically flame retardant properties

Keywords: biopolymer, foam, silylation, polyurethane, reactive flame retardant. In this study, the epoxy ring opening of epoxidized soybean oil (ESBO) was carried out for the first time with chemical having two different functional groups and organo silane compounds to synthesize bio-based polyols and their polyurethanes, and then the flame retardant properties of these polyurethanes were investigated. Vinylphosphonic acid (VPA) with vinyl and phosphonic acid functionalities, (3-mercaptopropyl)trimethoxysilane (3-MPTMS) and 3-(aminopropyl)triethoxysilane (3-APTES) with mercapto and amino moities were used for the ring opening reactions. VPA based polyol (PolP), MPTMS based polyol (PSiTh) and APTES based polyol (PSiAm) were synthesized at the end of ring opening reactions. FTIR, 1H,13C and 31P spectroscopies confirmed that epoxy ring of ESBO was opened by phosphonic acid group of VPA and vinyl group was not involved for the ring opening. As for the silanol compounds, amidation and thio-etherification reactions occured over the mercapto and amino moities. The existence of alkoxy groups on the polyol chain and formation of hydroxyl groups were confirmed by NMR and FTIR spectroscopies. The flame retardant polyurethane foams of these polyols were prepared with one potmethod using (MDI)4,4'methylene-bis(phenylisocyanate) and labeled as PPPU, PUSiTh and PUSiAm respectively and FTIR spectroscopy was used for the characterization of these polyurethanes. Differantial scanning calorimetry (DSC), gel permeation chromotografy (GPC), viscosity measurements were performed for polyols, thermogravimetric analysis (TGA/DTA), X-ray diffractometer (XRD), scanning electron microscopy (SEM) were used to characterize polyurethanes. Permenant deformation testof polyurethanes was made and foam densities were measured. Chain extended polyurethanes of these polyurethanes were also prepared with prepolymer method using bisphenol-A bis (hydroxyphenylphosphate) (BABHPP) as a P-containing chain extender and labeled as PPPUCE, PUSiThCE, PUSiAmCE respectively. Lower oxygen index (LOI) value of polyurethanes were measured. The inclusion of phosphorus into the polymer chain of the PPPU increased the flame retardant behavior of the polyurethane with a LOI of 26.4% , while PUSiTh and PUSiAm had values LOI of 23.6-22.9% with silicone inclusion. Chain extended polyurethanes had 25 % higher LOI value than the corresponding non-chain extended polyurethanes as a result of synergic efect of phophorous.