Development of the mechanical pulp fibre surface as a function of refining energy

Thermomechanical pulps were produced by refining spruce wood (Picea abics) chips at various specific energy consumptions. The surface morphology and chemistry of isolated fibres were studied. Different types affines, i.e. flakes and fibrils, were characterized chemically to obtain information about their origin in the fibre wall. After the two mainline refining stages, 85% of the S2 fibre wall layer was revealed. The lignin coverage of mainline fibres was higher and the surface content of polysaccharides was lower than that of reject line fibres. Surface extractives were almost totally removed during screening. At a low energy consumption, fibrillar fines were formed from the outer fibre wall layers (P+S1), but the content of secondary wall material increased as a function of refining energy. During mainline refining, the flake-like fines originated from compound middle lamella (ML+P) while, in reject refining, they were also released from the outer secondary wall lover (S1).