Functionalization of casein and its use for preparing self-crosslinking protein-based materials

Abstract

Increasing the content of bio-derived raw materials in polymeric products is imperative to follow the agenda of environmental protection and circular economy in the chemical industry. Therefore, it is highly desirable to create new materials with improved biodegradability that retain the good performance of conventional synthetic polymers. From this perspective, the self-chemical crosslinking of proteins appears as an effective tool to improve the final properties of protein-containing materials, mainly their water resistance and mechanical properties. This letter presents a strategy for incorporating bio-based ketone pendant groups into casein which confers the self-crosslinking capability through the keto-hydrazide reaction. Casein is a low-cost protein of high industrial availability that has been successfully compatibilized with acrylic phases in hybrid latexes as shown in depth in several works. Here, ketone groups have been effectively incorporated into the protein's backbone through the reaction of pristine casein with the N-hydroxysuccinimide ester of bio-based levulinic acid, avoiding the use of acrylamide compounds. Then, the modified casein was used to synthesize hybrid acrylic/protein latexes. These results open an avenue for the development of self-crosslinkable room-temperature protein-based materials.