Synthesis of Biobased Polyols from Soybean Meal for Application in Rigid Polyurethane Foams
2021
Bote, Sayli Devdas | Narayan, Ramani
Soybean meal or soymeal is an inexpensive protein–carbohydrate biomass and a coproduct of soybean processing. The composition of soymeal was determined before using it for the polyol synthesis. The soluble carbohydrates (SC) content of soymeal was determined by separating the carbohydrates from the other components using an ethanol–water solution. The protein content of soymeal was determined by the factor method. The moisture and ash content of soymeal was also determined. The entire soymeal without any purification was directly converted to a biobased polyol in a one-pot, two-step sequential process. The reaction of soymeal with ethanolamine yielded intermediate amine derivatives which were reacted with propylene carbonate to obtain the desired soymeal polyol. Both steps were conducted sequentially in the same reactor without any separation or purification. Different mass ratios (1:2, 1:3, 1:5) of soymeal to ethanolamine produced polyols with different hydroxyl values. The synthesized soymeal polyols had hydroxyl values of 550–650 mg of KOH/g and contained less than 2% insoluble matter. ¹³C NMR was used to determine the ratio of primary hydroxyl groups to secondary hydroxyl groups. The newly synthesized polyols contain urethane and amide backbone linkages which are less susceptible to degradation by UV-radiation and hydrolysis. The soymeal polyol was successfully used in the synthesis of biobased rigid polyurethane foams (PUF) containing 20% and 50% biobased polyol content. The compressive strength of a biobased PUF was higher than 200 kPa for a foam with a density of 40 kg/m³. Scanning electron microscopy was used to study the foam morphology.
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