Ultrasound-assisted synthesis of lignin microcapsules for the controlled release of active compounds

Abstract

Lignin represents a highly valuable, yet very underutilized biobased material. Being the most abundant source of aromatics on the planet, it is produced in high quantities as by-product of pulp and paper industries and biorefineries. Due to the high degree of structural variability, which depends on the different plant origin and harsh conditions experienced during the processing, an exhaustive valorisation of lignin is all but straightforward. Among various possibilities, the synthesis of micro- and nano-structures from untreated technical lignins is one of the best solutions for the development of high added-value products exploiting the peculiar features of lignin, such as self-assembly capacity, antimicrobial and antioxidant activities. To this purpose, this Thesis work has been focused on the preparation of lignin microcapsules (LMCs) by a simple, green and easily scalable ultrasound-assisted method. By this strategy it is possible to encapsulate lipophilic substances like pesticides, food additives, flavours or water insoluble drugs in a shell of lignin, from which they can be released upon changing the environmental factors such as pH, salinity etc. To modulate the characteristics of the capsules, either ad hoc prepared green compatibilizers or an outer biopolymeric layer have been added to the formulation. The synthesized LMCs have been characterized from the dimensional and morphological point of view by dynamic light scattering and microscopy techniques. Furthermore, the encapsulation efficiency, their stability under different conditions and the kinetic of release of a model compound have been studied to demonstrate their potential as carriers of active molecules.