In this paper, biobased carbons were used as fillers in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). The mechanical and electrical properties of these 100% biocomposites were analyzed. First, biocarbons were prepared from wood dust and cellulose fibers using carbonization temperatures ranging 900–2300 °C. XRD revealed significant improvements of the graphitic structure with increasing temperatures for both precursors, with slightly higher ordering in wood-dust-based carbons. An increase of the carbon content with continuous removal of other elements was observed with increasing temperature. The carbonized cellulose fiber showed an accumulation of Na and O on the fiber surface at a carbonization temperature of 1500 °C. Significant degradation of PHBV was observed when mixed with this specific filler, which can, most probably, be attributed to this exceptional surface chemistry. With any other fillers, the preparation of injection-molded PHBV composites was possible without any difficulties. Small improvements in the mechanical performance were observed, with carbonized fibers being slightly superior to the wood dust analogues. Improvements at higher filler content were observed. These effects were even more pronounced in the electrical conductivity. In the range of 15–20 vol.% carbonized fibers, the percolation threshold could be reached, resulting in an electrical conductivity of 0.7 S/cm. For comparison, polypropylene composites were prepared using cellulose fibers carbonized at 2000 °C. Due to longer fibers retained in the composites, percolation could be reached in the range of 5–10 vol.%. The electrical conductivity was even higher compared to that of composites using commercial carbon fibers, showing a great potential for carbonized cellulose fibers in electrical applications.

Every year, the pulp and wood-processing industry produces large side streams of bark, the valorisation of which is desirable for both economic and environmental reasons. We investigated organosolv extraction of antioxidants from Picea abies bark using various ratios of ethanol/water with the goal of obtaining high yields of these desirable compounds. The resulting extracts were analysed (I) for their total contents of phenols (TPC), flavonoids (TFC) and tannins (TTC), and (II) for their antioxidant activity using the DPPH radical scavenging method. The highest total yield of bark extract (14.78%) and the highest concentrations of dry extracts of TPC (324.80 mg g⁻¹), TFC (62.55 mg g⁻¹) and TTC (83.63 mg g⁻¹) were obtained under mild conditions (100 °C extraction temperature and an ethanol/water solvent ratio of 50%, v/v). DPPH antioxidant activity index (AAI) ranged from 0.68 (pure water extract) to 1.31. This antioxidant effect was increased to 1.59 by adding oligolignin from the organosolv process. In the extracts, gas chromatography–mass spectrometry (GC–MS) found nine aromatic carboxylic acids, including phenolic acids and the flavonoid compounds quercetin and (+)-catechin. Our environmentally friendly approach will form the basis for pilot plant and industrial applications.