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Fig. 8 NBSK pulp and paper properties as a function of LBG dosage and PFI refining level: a tensile index, b burst index, c tear index, d freeness, e scattering coefficient and f brightness. LBG adsorption was conducted at 25 C for 10 min
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the sheet matrix. At higher bonding levels, individual fibres will break and this requires less energy than removing fibres from the sheet matrix (Hannuksela et al. 2004; Leech 1954; Swanson 1950). Freeness is a measurement of pulp drainage (Smook and Kocurek 1982) and reflects fines content, flexibility and the degree of external fibrillation (Niskanen 1998). With increasing refining energy and LBG adsorption, freeness decreases (Niskanen 1998). With the application of 1 wt% LBG to NBSK pulp refined at 3000 rev a tensile strength of 108 N m g - 1 could be achieved at a freeness of 531 mL (Fig. 8d). To achieve a similar tensile
strength solely by refining, required 9000 rev and resulted in the lower freeness of 434 mL. Thus, LBG adsorption resulted in better drainage properties at equal tensile strength with less refining energy. Scattering coefficient decreased with refining level and LBG dosage (Fig. 8e), which suggests more bonding occurs after LBG adsorption and refining. The greatest change in scattering coefficient on LBG adsorption, a 14% decrease, occurs between unrefined pulp without LBG and unrefined pulp with 1wt% LBG. Increasing refining level diminished the impact of LBG dosage on scattering coefficient (Fig. 8e), indicating that refining is the dominant factor for
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