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

Abstract

We synthesized polyols with high hydroxyl functionalities (FOHs), 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 (fLA). An increase of only 20°C in the reaction temperature (from 80 to 100°C) caused changes in the hydroxyl number (+17.8%), FOH (–25%), viscosity (–14.0%), and oligomeric content (–24.1%). fLA mostly affected the ring‐opening yield, and only for fLA 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 FOH. Instead, to increase the latter one, the OH number had to be maximized.