Biodiesel is an environmentally friendly alternative to petroleum diesel. It is biodegradable, nontoxic and has lower greenhouse gas emission profiles compared to petroleum diesel. Polyurethane (PU) products such as PU foams and PU coatings are widely used in many aspects of our life. Traditionally, the PU industry is heavily petroleum dependent because both the feedstocks - isocyanates and polyols - are petrochemical products. Bio-based PU products became a very promising research field due to concerns about the environment and the depletion of petroleum resources.
Waste cooking oil (WCO), which is abundantly available and about 2 or 3 times cheaper than virgin vegetable oil, is considered a good source for production of biodiesel. Also, post-consumer PET bottles contribute a large volume fraction in the solid waste stream and their non-biodegradability has caused concern. In this study, a sustainable process of value-added utilization of wastes, specifically WCO and post-consumer PET bottles for the production of biodiesel and PU foams, respectively, was developed. WCO collected from campus cafeteria was firstly converted into biodiesel, which can be used as vehicle fuel. Then crude glycerol (CG), a byproduct of the above biodiesel process, was incorporated into the glycolysis process of post-consumer PET bottles collected from campus to produce polyols. Thirdly, PU foams were synthesized through the reaction of the above produced polyols with isocyanate in the presence of catalysts and other additives. The characterization of the produced biodiesel demonstrated that its properties meet the specification of the biodiesel standard. The effect of CG loading on the properties of polyols and PU foams were investigated. With the increase of CG loading from 0% -15%, the hydroxyl value increased from 478 mg KOH/g to 592 mg KOH/g. This is most likely due to the high hydroxyl value of glycerol (1829 mg KOH/g). The PU foams produced showed density of 46.03-47.66 kg/m3 and compressive strength of 235.9 to 299.9 kPa, which are comparable to some petroleum-based analogs. A mass balance and a cost analysis for the conversion of WCO and waste PET into biodiesel and PU foams indicate potential economic viability of the developed process.
Soybean meal (SM) is the soy protein residue after the extraction of oil from soybeans. With its high protein content, SM has the potential to become one of the feedstocks for PU production. In this study, a novel way was developed to produce UV-curable PU acrylate coatings from SM. High oleic SM was hydrolyzed by dilute acid to amino acid oligomers, then a hydroxyl-terminated PU oligomer was synthesized through a non-isocyanate pathway: i) amination of the amino acid oligomers with ethylene diamine to produce amino-terminated compound; ii) amidation of the amino-terminated compound was reacted with ethylene carbonate. Functionalization of hydroxyl-terminated PU oligomers was achieved by esterification and acrylation reactions to produce PU acrylate oligomers. PU acrylate oligomers were then formulated with multifunctional monomer and photo initiator to form a PU coating under UV light. The PU oligomer after esterification showed a hydroxyl value of 223 mg KOH/g and viscosity around 6.1 Pa·s at 10.9 1/s shear rate. The UV-cured coating showed higher tensile strength (approximately 18.2 MPa) and modulus (approximately 450.1 MPa), and lower elongation at break (approximately 4.5%) compared to other PU acrylate coatings reported in literature, which might due to hydrogen bonding between amino acid and urethane bond and enhanced cross-linking density with the incorporation of oleic acid in esterification reaction.
In summary, the value-added conversion of WCO, post-consumer PET bottles and SM into Biodiesel and PU products (i.e. PU foams and coatings) have been successfully developed in this study. All the parameters of biodiesel produced from WCO meet the requirements in the ASTM D6751 standard. The PU foams showed good compressive strength and insulation properties and have potential application as construction materials. The PU coatings also showed promising mechanical properties and good thermal stability.