Sustainable Processes and Green Technologies for Biomass Valorisation and Preparation of New Biocomposites

This thesis investigates green and intensified processes for biomass valorisation, combining microwave-assisted hydrodistillation (MAHD), subcritical water extraction (SWE), extrusion and airlaying to obtain value-added extracts and hemp-based biocomposites with pilot-scale demonstrations. MAHD was applied to fresh, dried and pelletized hops to optimize essential-oil (EO) recovery and composition; milder microwave regimes improved preservation of volatile fractions, and scale-up to a pilot reactor (ETHOS XL) showed improved energy efficiency and matrix-dependent yield changes (fresh: yield decreased on scale-up; dried/pellets: yield increased up to ~4×), with sesquiterpenes favored by longer treatments. SWE of chestnut peels was optimized in a microwave-assisted pressurized reactor: the best conditions were 150 °C, 30 min and S/L 1:30, yielding up to 13.1 g GAE/100 g dry matrix (lab-scale) with tannins comprising ≈82.8% of total phenolics. Scale-up to a semi-industrial plant (60 kg batches) afforded comparable yields (≈12 g GAE/100 g DM) and preserved significant antioxidant (DPPH IC50 ≈2.9 μg/mL lab, 4.2 μg/mL pilot) and copper-chelating activities; extracts reduced ROS and inhibited triglyceride accumulation in high-glucose 3T3-L1 adipocytes in a dose-dependent manner, confirming biofunctional potential. Hemp hurds were incorporated into elastomer, PBAT and PBS matrices by melt-mixing/extrusion and compression molding (22–32 wt% hemp) and characterized by FESEM, XRD, rheology, DSC, contact-angle, flexural and impact tests. Polymer–hemp interactions were matrix-specific: PBS and PBAT showed stronger interfacial coating of fibers, while elastomeric blends displayed dispersed filler with embedded CaCO3 traces. Mechanical properties remained within the same order of magnitude as neat polymers; impact resistance decreased with higher hemp content while flexural modulus was marginally affected. Airlaying was used to produce high-biomass (≈80 wt%) insulation panels; thermal conductivity averaged λ = 0.068 ± 0.002 W·m⁻¹·K⁻¹ and acoustic absorption was comparable to conventional materials in relevant frequency ranges. Overall, the work demonstrates that combining dielectric heating, subcritical water, extrusion and airlaying enables sustainable recovery of bioactive compounds and manufacture of hemp-rich bioblends with retained functionality, and that careful process design permits pilot-scale translation with acceptable preservation of yield, activity and material performance, supporting circular-economy applications for agro-industrial residues.