Microwave liquefaction of precipitated Kraft lignin was carried out in polyethylene glycol (PEG) and glycerol (G) mixed with or without H₂SO₄ as catalyst. The influences of some independent variables on the yield and hydroxyl index were discussed. The viscosity, molecular distribution (GPC), and the types of volatiles measured by gas chromatography–Mass spectrometry (GC-MS) of all the liquefied products were determined. Response surface methodology (RSM) was used to optimize liquefaction conditions. Based on the results, lignin/solvents (wt%), catalyst/solvents (wt%), and reaction time were chosen as independent variables for a central composite design (CCD). The optimal liquefaction conditions were as: 20 wt% of lignin, 3 wt% of catalyst at 5 min with yield and hydroxyl number of 95.27% and 537.95 mg KOH.g⁻¹, respectively. Functional groups (measured by ATR-IR [attenuated total reflectance – infrared]) and the thermal degradation (TGA) of optimized bio-polyol and precipitated kraft lignin were determined.

Power plants have been using forestry biomasses to produce thermal and electrical energies. However, these industries lack of reliable parameters about their raw material in order to consolidate their position in this market. The present study aimed to characterize forestry wastes from pine (Pinus elliottii) plantations leftover of wood logs processing units. Wood, bark and a mixture of both of them were characterized by prompt (total moisture, hygroscopic moisture, ashes, volatile matter and fixed carbon contents), elementary (S, C, H, N and [O + Halogens] contents), and via wet (holocellulose, lignin and extractives contents) chemical analyses. Indeed, basic density and fuel properties (gross and net calorific values) were also determined. Compared to the wood, the bark presented higher extractives content, which affected the ashes content. Regarding the energetic properties, the bark showed the highest properties, but a detrimental character from an environmental standpoint. The wood-bark mixture presented intermediate properties between these two forestry wastes, but with more approximation to the wood.