Mechanical behaviour of Norway spruce fractions in single pellet pressing and consequences for using juvenile wood and branches

Abstract The rising demand for wood fuel pellets and increasing competition for conventional raw materials have intensified interest in alternative forest‑derived feedstocks. In this study, pellets were produced from sawdust originating from four debarked fractions of a single Norway spruce ( Picea abies ) tree: heartwood, sapwood, juvenile wood, and branches. Branches differ chemically and morphologically from stem wood, and their use may influence both pelletizing energy requirements and pellet quality. Pellets were produced using single pellet press systems at moisture contents between 6 and 12% (wb), and energy inputs were quantified as compression ( W comp ), friction ( W fric ), and total ( W tot ) . Pellet quality was evaluated through measurements of solid density, hardness, and mechanical durability. Overall, pellet quality was comparable among the stem‑derived fractions; however, pellets produced from branch material showed markedly inferior properties, e.g., durability and hardness, when processed under conditions optimized for softwood. The branch-derived feedstock also exhibited pronounced differences in cell morphology and chemical composition relative to the stem wood fractions. In several respects, pelletizing branch material appears more similar to pellet production from hardwood than from softwood. The implications of these findings for the utilization of juvenile wood and branches are discussed and recommendations for the industry is presented.