Effect of bio-polyols with different chemical structures on foaming of polyurethane systems and foam properties

In the present work, we report on rigid polyurethane foams (PUR) prepared using three rapeseed oil-based polyols with different chemical structures. The first and the second polyols were made following the transesterification and transamidization methods, whereas the third one was prepared through epoxidation and a ring-opening reactions. The rapeseed oil-based PUR foams were next compared with reference foams obtained using polyether petrochemical polyols. The diversity of the chemical structures of the bio-polyols allowed an evaluation of the effect of the bio-component's structure on the properties of the foams obtained. It was noticed that the structures of the bio-polyols have a significant effect on the reactivity of the resultant polyurethane systems. The formulations modified with the bio-polyol containing amine groups were the most reactive and exhibited a faster decrease of the dielectric polarization than the formulations based on the bio-polyol obtained in the epoxidation and ring-opening reactions. The apparent densities of the rigid polyurethane foams were comparable −ca. 36-38 kg/m3. The PUR foams based on the bio-polyol obtained by the transesterification method were characterized by the lowest content of closed cells. A replacement of a petrochemical polyol with each of the rapeseed oil-based bio-polyols used increased the brittleness of the foams obtained. The values of the thermal conductivity coefficient increased vs the ageing time (24 h, 7 days, 30 days, 3 months and 3 years). The highest values of the thermal conductivity after different ageing times were noticed for the materials modified with the bio-polyol obtained in the transamidization reaction. The rigid polyurethane foams based on the bio-polyol obtained in the two-step methods were characterized by more beneficial mechanical properties. As far as the thermal stability and flammability are concerned, more favourable properties were noticed for the foams modified with the products of the rapeseed oil transamidization and transesterification reactions.