Highly functional lactic acid ring-opened soybean polyols applied to rigid polyurethane foams

We synthesized polyols with high hydroxyl functionalities (F_OHs), between 9.0 and 12.6, and characterized them with differential scanning calorimetry, thermogravimetric analysis, and size exclusion chromatography after we parametrically studied the ring-opening reaction of epoxidized soybean oil with lactic acid (LA) as a function of the reaction temperature and lactic acid equivalent fraction (f_LA). An increase of only 20°C in the reaction temperature (from 80 to 100°C) caused changes in the hydroxyl number (+17.8%), F_OH (–25%), viscosity (–14.0%), and oligomeric content (–24.1%). f_LA mostly affected the ring-opening yield, and only for f_LA values above 0.4 was possible to achieve values higher than 80%. Rigid polyurethane foams (rPUFs) were synthesized and characterized with scanning electron microscopy, dynamic mechanical analysis (DMA), and compressive mechanical tests. rPUFs with a very high specific compressive strength (7.8 kPa kg^–1 m³) were synthesized solely with biobased soybean oil. DMA revealed a compromised relationship between the specific compressive strength and its temperature dependence. To increase the first one, the most relevant method was to increase F_OH. Instead, to increase the latter one, the OH number had to be maximized. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47959.