Iuliana Bejenari

The conversion of lignocellulosic waste ascends as a promising path to generate new materials with wide industrial and environmental uses. Pyrolytic biochar (PBc), hydrochar (Hc), and activated hydrochar (AcHc) produced from the waste of Picea Abies bark were considered bio-based sorbents for lead uptake from aqueous effluents. PBc was obtained through slow pyrolysis (550 °C), while Hc resulted under hydrothermal conversion (280 °C). In order to enhance the specific surface, Hc was subjected to a physical activation, resulting AcHc. All three carbonaceous materials were prepared through relatively simple processes from a readily locally available resource. The carbonaceous materials were characterized using infrared spectroscopy and scanning electron microscopy. The Pb (II) removal has been tested in batch mode on a synthetic monocomponent wastewater matrix, as well as on a real mine drainage effluent. A significant effect of pH was observed, while the equilibrium was achieved in a short time, about 60 min for PBc and Hc and 120 min for AcHc. Langmuir model predicted a maximum adsorption capacity of 15.94 mg/g for PBc, 9.99 mg/g for Hc, and 37.46 mg/g for AcHc. All materials studied had good uptake capacities for lead with no drastic effect of typical coexisting species.

In the context of sustainable use of resources, hydrothermal conversion of biomass has received increased consideration. As well, the hydrochar (the solid C-rich phase that occurs after the process) has caused great interest. In this work, spruce bark (Picea abies) wastes were considered as feedstock and the influence of hydrothermal process parameters (temperature, reaction time, and biomass to water ratio) on the conversion degree has been studied. Using the response surface methodology and MiniTab software, the process parameters were set up and showed that temperature was the significant factor influencing the conversion, while residence time and the solid-to-liquid ratio had a low influence. Furthermore, the chemical (proximate and ultimate analysis), structural (Fourier-transform infrared spectroscopy, scanning electron microscopy) and thermal properties (thermogravimetric analysis) of feedstock and hydrochar were analyzed. Hydrochar obtained at 280 °C, 1 h processing time, and 1/5 solid-to-liquid ratio presented a hydrophobic character, numerous functional groups, a lower O and H content, and an improved C matter, as well as a good thermal stability. Alongside the structural features, these characteristics endorsed this waste-based product for applications other than those already known as a heat source.

A bio-based polymeric matrix was developed by the copolymerization of a vegetable oil-based epoxy, epoxidized linseed oil (ELO), with dodecenyl succinic anhydride (DDSA). To obtain eco-friendly bio-composites, this matrix was combined with a natural filler: spruce bark powder (SB) with its hydrochar (HC) in various proportions ranged from 1 to 30 wt.%. The reactivities of these formulations were studied by DSC analysis that highlighted that both fillers have a high catalytic effect on the ELO–DDSA crosslinking reaction. The complementary studies by TGA, DMA, tensile tests, water absorption and Shore tests had shown that both HC and SB bring improvements to the mechanical properties of the composites, fulfilling multiple roles: (i) Both act as co-reactants in the copolymerization mechanism; (ii) HC acts as reinforcement, consolidating the network and providing stiffness and rigidity; and (iii) SB acts as plasticizer for reducing the brittle character of the epoxy resins.