LIGNINA: UN ADDITIVO FUNZIONALE PER LO SVILUPPO DI BIONANOCOMPOSITI ATTIVI DI POLI(BUTILENE SUCCINATO)

Lignocellulosic biomass, a promising renewable resource, is gaining attention in materials science, with lignin emerging as a valuable component due to its abundance, antioxidant, antimicrobial, and UV-shielding properties. However, lignin’s complex polyphenolic structure, further modified by delignification processes, poses challenges to its valorisation. This study, conducted in collaboration with Versalis S.p.A., focuses on a lignin-rich biomass (HSEL) derived from the Proesa® steam explosion process for bioethanol production. HSEL’s structural characteristics were compared to four technical lignins—softwood Kraft lignin (SKL), hardwood Kraft lignin (HKL), hardwood sulfite lignin (HLS), and hardwood organosolv lignin (HOSL)—and native milled wood lignin (MWL). HSEL demonstrated a structural resemblance to native lignin, lacking features of harsh delignification processes and exhibiting high phenolic OH content and good thermal stability, making it a promising candidate for polymeric applications. HSEL was incorporated into polybutylene succinate (PBS) as a filler with varying particle sizes—micro-sized L600, L250, and nanosized LNP—at 5, 10, and 15 wt%. LNP were produced using a green hydrotropic method, yielding nanoparticles of 155 nm with a 32.5% increase in phenolic OH content. Biocomposites with 5 wt% LNP exhibited superior mechanical and thermal properties, maintaining PBS’s elongation at break and inducing a nucleating effect, while composites with 15 wt% LNP achieved significant antioxidant and antimicrobial enhancements, surpassing other lignin-based fillers. Accelerated aging tests revealed that lignin accelerated PBS degradation in a particle size-dependent manner, with LNP inducing the most pronounced molecular weight reduction, suggesting a photocatalytic degradation mechanism. Mechanical testing under milder aging conditions confirmed the correlation between filler type and degradation extent. These findings establish steam explosion lignin, particularly in nanoparticulate form, as a sustainable and functional filler for PBS, enhancing its active properties and expanding its degradation spectrum. This research paves the way for innovative applications in active packaging and sustainable materials.