Waste to Resource: Synthesis of Polyurethanes from Waste Cooking Oil

Waste cooking oil (WCO) is generated after frying or cooking food with vegetable oils. It can be obtained from domestic sources, fast-food places, and industries. The continuous reuse of WCO in foods poses serious health problems, and the improper disposal of WCO results in environmental pollution. Hence, scientists are searching for ways to convert WCO into a useful secondary raw material to produce energy or value-added products. Also, the large generation of WCO is an environmental hurdle, hence finding sustainable ways to reuse it can lead to an advantageous process. Under this perspective, our group collected and filtrated WCO from a domestic source after a one-time use in the deep frying of fish. The qualitative analysis based on iodine, acid value, Fourier transform infrared along with other tests showed that the WCO presented negligible differences when compared to the pure cooking oil. After that, the WCO was converted into a polyol through an epoxidation/ring-opening reaction. The synthesis yielded the WCO-polyol which presented a suitable hydroxyl number that enabled it to form rigid polyurethane foams (RPUFs) with competitive properties. In addition to that, our group introduced flame retardancy properties through the blending of dimethyl methylphosphonate (DMMP) or expandable graphite (EG) under increasing concentrations. Through that, several analyses were conducted to elucidate the properties of the WCO-based RPUF. Within this line, the majority of the RPUF presented a closed cell content greater than 90%. Also, a considerable improvement in flame retardancy was observed as the neat WCO-based RPUF had a burning time of 93 s and a weight loss of 46%. Yet, the addition of 10.73 wt % DMMP (DMMP-7) reduced to 8.5 s and 3%, respectively. Also, 16.69 wt % EG (EG-10) resulted in a decrease to 12.5 s and 5%, respectively. Overall, most of the properties of the foams were not compromised with the use of WCO-polyol. Hence, our research was successful in the production of biobased RPUFs. Additionally, further investigations can be performed to potentially improve the properties of the produced WCO foams which can be likely used on the commercial scale for consumer and income generation needs.

Automated summary

Waste cooking oil is a potential threat to health and the environment, but scientists are exploring ways to convert it into useful secondary raw materials. The research successfully transformed waste cooking oil into polyol and produced rigid polyurethane foams with competitive properties. The addition of flame retardants improved the flame retardancy performance of the product.