Cellulose (2021) 28:10183–10201
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temperature. At high LBG dosage levels, the amount of LBG adsorbed to fibre at 35 C is much higher than that at 25 C. The amount of LBG adsorbed to refined pulpat 25 C is comparable to the amount adsorbed to unrefined pulp at 35 C. When LBG concentration in solution increased ( [ 0.5wt%), the adsorption amount differentiates depending on temperature and surface condition of NBSK pulp. From Table 4 and Fig. 4, it was found that adsorption at 25 C is best described by the Langmuir model while adsorption at 35 C can be described by either the Langmuir model or Freundlich model. From the Langmuir model, the maximum adsorption capac- ity ( Q max ) of pulp fibres at 35 C was calculated to be 6.31 mg g - 1 ( ± 0.75 mg g - 1 , 95% confidence inter- val) o.d. pulp. This is greater than the Q max determined at 25 C, 2.34 mg g - 1 , suggesting that more surface sites are accessible at higher temperature. However, increasing temperature could hardly increase the total surface area of pulp fibres. Given the good fit of both models, neither can be definitively selected. Instead, we suggest that an alternate mechanism may be involved. There may be multi-layer adsorption at 35 C, and the adsorption occurs layer-by-layer (a pseudo-Langmuir mechanism). By this reasoning, the number of sites in each adsorption layer is constant and the increase in predicted Q max at 35 C reflects the presence of multiple layers.
number of data points used to prepare the model. The equilibrium constant for cationic starch adsorption to pulp fibre is much higher, for example Zakrajsˇek et al. (2009) reported K e = 40 L mg - 1 . This high equilib- rium constant could be due to the high concentration of adsorbed cationic starch resulting from the natural attraction between negatively charged pulp fibres and cationic starch. Unlike cationic starch, LBG is a natural carbohydrate polymer with a negative surface charge (de Jong and van de Velde 2007). The repulsive forces between LBG and NBSK pulp fibre will reduce adsorption capacity. Consequently, LBG adsorption to unrefined NBSK pulp is characterized by low adsorp- tion capacity and a relatively low equilibrium constant.
Factors influencing adsorption
Effect of temperature
The influence of temperature on LBG adsorption to NBSK pulp fibre at two temperatures, 25 C and 35 C on o.d. fibre, is reported in Fig. 5a. At low dosage levels ( \ 0.5wt%), LBG adsorption amount is comparable at both temperatures; the adsorption amount to refined pulp at 25 C is similar to the unrefined materials. At low dosage, it appears that LBG affinity to NBSK pulp fibre is not affected by
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25 o C unrefined 35 o C unrefined 25 o C refined
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LBG dosage of o.d. pulp (%)
LBG dosage of o.d. pulp (%)
Fig. 5 a Amount of LBG (mg g - 1 o.d. pulp) adsorbed to NBSK pulp after 10 min as a function of LBG concentration in aqueous solution (mg L - 1 ) at 25 C, 35 C for unrefined and refined NBSK pulp. b Fibre surface site coverage ( h ) calculated from Langmuir model at 25 C and 35 C for unrefined NBSK pulp
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