The Biopigment Eumelanin in the Sustainability Challenge: Interfaces With Metal Electrodes, UV-Absorption Enhancement of Plastics and its Biodegradability

The United Nations define sustainability as the ability to meet one generation's needs “without compromising the ability of future generations to meet their own needs”. The field of electronics features a dramatic increase of waste electrical and electronic equipment (WEEE) and the depletion of key elements necessary for EEE fabrication. The use of biodegradable organic (carbon-based) materials extracted from natural sources (bio-sourced) and processed with non-toxic solvents represents a valuable option to alleviate the environmental footprint of the electronic sector. Eumelanin, a dark-brown subcategory of melanins (a ubiquitous biopigment in flora and fauna), features broad ultraviolet-visible absorption, hydration-dependent electrical response as well as metal chelation, radical scavenging and redox activity. Eumelanin is a promising candidate in the field of green (sustainable) organic electronics. Organic (plastic) electronics is based on carbon-based conducting and semiconducting polymers and small molecules that feature conjugation (alternance of single and double carbon-carbon bonds) in their molecular structure. In addition of being mechanically flexible, devices based on organic electronic materials can be solution-processable and thus stand for their lower embodied energy (i.e. “energy spent in the production phase and stored in the inner constituents”) with respect to most inorganic ones, which are processed at high-temperature and under high-vacuum conditions. Sustainability is an issue also in the field of (non-conducting) plastics for packaging, where it concerns not only the packaging polymers but also the additives needed to enhance certain properties, such as thermal stability or ultraviolet (UV) radiation absorption. The core of this PhD thesis is devoted to the study of a number of functional properties of eumelanin in view of its use in sustainable organic electronic technologies as well as a greener additive for plastic packaging. Chapter 1 gives an overview on melanins, with a focus on the subcategory eumelanin and its properties. Chapter 2 provides a review of the state of the art of the potential applications of eumelanin demonstrated in the literature. Chapter 3 details the targets of the research: the investigation of eumelanin-metal interfaces under bias, the study of eumelanin as an additive for plastics and the assessment of eumelanin's biodegradability. Chapter 4 briefly explains the characterization techniques used.