Free Fatty Acid-Based Composites for Biomaterial Applications
Date: February 24, 2020
Principal Investigators: Rhett C. Smith and Andrew G. Tennyson, Clemson University
Keywords: Composites, free fatty acids (FFAs), cement
Summary:
This project set out to find value-added uses for low-value rendering products, which are often high in free fatty acids (FFAs). There is significant pressure on industries to produce more sustainable replacements for traditional petroleum and mineral-derived products, so this project specifically aimed to develop durable structural plastics and cement from FFA-content material.
The strategy proposed to turn high FFA-content feedstocks into plastics and cement was to react to these materials with elemental sulfur. Elemental sulfur is an affordable starting material because it is a waste product of fossil fuel refining, and oil companies are currently paying to store millions of tons of the sulfur. Although neither sulfur nor organic fats/oils are durable on their own, they can undergo a chemical reaction with one another to form new chemical bonds and in doing so create very durable solids.
At the beginning of the project, no one had reacted sulfur with fatty acids, so the first test under this grant was to test the reactivity of sulfur with pure fatty acid samples. Oleic acid is the most prevalent unsaturated fatty acid in rendering products, so it was tested first. A sulfur cement material was successfully prepared by the reaction of sulfur with oleic acid. During the course of this part of the study, we discovered that a compatibilizing agent was needed. We used zinc oxide for this purpose. Zinc oxide is often found in sunscreen, so it can be quite safe for skin contact in commercial goods. We evaluated the influence of the ratio of oleic acid to sulfur on the properties of the cement and established the optimum ratio for the desired strength profile.
We also showed that simply heating the surface of a scratched sample of the oleic acid-sulfur cement with a hairdryer or other heat source could restore the smooth surface. This thermal healing ability is not possible with usual cement products. We also demonstrated that oleic acid-sulfur cement blocks can be pulverized, remelted, poured into molds, and made into new blocks over many recycling trials. The blocks maintained 100% of their mechanical strength after these cycles, demonstrating another way that these cement outperform typical cement products. The influence of temperature on the stability and mechanical properties of the cement was also evaluated to establish the working temperature range for the cement.
After testing pure oleic acid, we tested linoleic acid for reaction with sulfur. We also recognized that rendering products are a complex mixture of many fatty acids and triglycerides, so we began testing technical grade mixtures of fatty acids that contained both saturated and unsaturated fatty acid molecules. Just as we did for oleic acid-sulfur cement, we also evaluated the proper fatty acid: sulfur ratio to optimize mechanical properties. Technical grade fatty acids produced very good cement that could be recycled by simply melting down the blocks and reshaping them, just as was observed for the oleic acid-sulfur cement. We fully characterized the chemical composition, the influence of temperature, and mechanical strength profiles of all the new cement made from linoleic acid and mixed-FFA.
The studies on fatty acid-sulfur cement established a good foundation for preparing cement from complex molecular mixtures from rendering. Brown grease was selected as the first product for testing. After our last progress report meeting, we obtained three samples from industrial partners from three different facilities. We developed methods to characterize the composition of the brown grease samples in a way relevant to predicting how they might react with sulfur in the cement-forming reaction. We then reacted brown grease with sulfur in several ratios and found that we could make brown grease-sulfur cement and plastics just as easily as the other FFA sulfur materials discussed above. These studies are in their beginning stages, but we have established that the brown grease-sulfur cement has similar temperature stability to those made from fatty acids and that for some ratios at least we obtain readily melt-processed and recyclable cement. Mechanical testing of the brown grease-sulfur samples is currently underway. We hope to have these data in time for the final report presentation at the end of March 2020.
To summarize, this project has been very successful in demonstrating the utility of high FFA feedstocks for making replacements for plastics and cement made from traditional petroleum and mineral sources. The technologies demonstrated in just the first 24 months of our work on this project have already led to three peer-reviewed journal articles and a full U.S. patent application for making cement and other durable goods from free fatty acids and even from complex chemical mixtures including brown grease.
Cement is the most-produced synthetic commodity of human civilization: more than 20 billion tons of cement are produced every year, making up a trillion-dollar industry. Given the enormity of the cement market and the wide range of applications where cement is used, technologies that leverage underappreciated rendering products like brown grease, trap grease, and dissolved air flotation wastewater sludge as valuable feedstocks for cement products even in niche markets has the potential for quite meaningful economic benefit to our rendering industrial partners.