Lignin, from biomass waste to sustainable materials for food packaging, antiviral coatings and agriculture

Our planet has been challenged for years by our reckless use of fossil fuels, which has led to the ongoing climate change and energy crisis. The transition to the use of renewable alternative sources has now became urgent and inevitable. The valorization of lignin can be a key component of this transition, and this Thesis aims to contribute promoting this process. Lignin is an aromatic polymer that constitutes approximately one third of the total lignocellulosic biomass and is isolated in huge quantities as a waste material of biofuel and paper production. About 98% of the 100 million tons of lignin produced each year is simply burned as low-value fuel, so this renewable polymer is widely available at very low cost. Lignin has valuable properties that make it a promising material for numerous applications. Despite the recent interest in lignin valorization from industry and researchers, this natural polymer is far from being fully exploited due to several limitations. The overall scope of this PhD Thesis is to address some of the challenges in lignin employment and to find new applications for this underutilized material. Chapter 1 defines the main lignin features and describes how this polymer can be utilized as filler for food packaging films, as antimicrobial agent and as fertilizer. This chapter also points out the main challenges and limitations for the lignin involvement in these three fields of application. In Chapter 2, lignin nanoparticles have been functionalized and efficiently incorporated into a film of poly(lactic acid), a biodegradable polymer already utilized in sustainable food packaging. The lignin nanoparticles addition provided the final film with outstanding mechanical properties, antioxidant and UV-barrier activities, improving its performance as food packaging material. Chapter 3 explores the use of lignin as an antiviral coating. Viruses can transmit through the contact with contaminated surfaces and the systematic disinfection of surfaces is labor and time consuming, hence the development of coatings able to directly inactivate viruses would be useful to minimize the contamination risk. All the antiviral coatings known so far are inappropriate for the application on a large scale, while lignin would be an abundant and cheap solution. This chapter investigates the activity of lignin coatings against herpes simplex virus type 2 and examines the mechanism of viral inactivation through reactive oxygen species generation on the lignin surfaces. Chapter 4 describes the preparation of lignin nanoparticles bearing nitrogen and phosphorous, which are designed for the application as controlled-release fertilizers. These particles were conceived to be degraded by an enzyme produced by the plant roots, so that they can release the nutrients mainly in the plant proximity. The final purpose of the research work outlined in this chapter is to develop nano-fertilizers with efficient delivery of the active principle only where it is neede