Glass transition and thermal degradation of rigid polyurethane foams derived from castor oil–molasses polyols

Abstract

Rigid polyurethane (PU) foams having saccharide and castor oil structures in the molecular chain were prepared by reaction between reactive alcoholic hydroxyl group and isocyanate. The apparent density of PU foams was in a range from 0.05 to 0.15 g cm−3. Thermal properties of the above polyurethane foams were studied by differential scanning calorimetry, thermogravimetry and thermal conductivity measurement. Glass transitions were observed in two steps. The low-temperature side glass transition was observed at around 220 K, regardless of castor oil content. This transition is attributed to the molecular motion of alkyl chain groups of castor oil. The high-temperature side glass transition observed in the temperature range from 350 to 390 K depends on the amount of molasses polyol content. The high-temperature side glass transition is attributed to the molecular motion of saccharides, such as sucrose, glucose, fructose as well as isocyanate phenyl rings, which act as rigid components. Thermal decomposition was observed in two steps at 570 and 620–670 K. Thermal conductivity was observed at around 0.032 J sec−1 m−1 K−1. Compression strength and modulus of PU foams were obtained by mechanical test. It was confirmed that the thermal and mechanical properties of PU foams could be controlled by changing the mixing ratio of castor oil and molasses for suitable practical applications.