Cellulose (2021) 28:10183–10201
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(b)
(a)
(c)
(d)
Fig. 2 Linear fit of a pseudo-first-order kinetics and b pseudo-second-order kinetics of LBG adsorption to NBSK pulp at 25 C. c Linear fit of pseudo-second-order kinetics of LBG adsorption to NBSK pulp at 35 C and d at 45 C
mass of LBG is retained on the fibre up to a dosage of 0.5 wt%. Given the plateau in mass of LBG adsorbed for dosage between 0.5 and 2.1 wt%, it can be inferred that there is a finite number of adsorption sites on the fibre surface and that LBG adsorption is limited to the fibre surface. This inference is also supported by Wa˚gberg and Ha¨gglund (2001)’s conclusion that polymers with molar mass greater than 48 kDa can only adsorb on the external fibre surface; the weight- average molar mass of LBG was 1215 kDa ( ± 89 kDa standard deviation) in this work. Hannuksela et al. (2002) also observed that the fraction of guar gum adsorbed decreased with increasing concentration of guar gum; they attributed this to slow diffusion.
mass transfer limits are high the activation energy will be low reflecting the diffusion process. However, when agitation rate is sufficiently high, the activation energy will reflect the chemical interaction between LBG and cellulose.
Adsorption isotherms
LBG adsorption isotherms were investigated by varying initial dosage of LBG relative to the weight of o.d. pulp fibre. In Fig. 3a the fraction of LBG adsorbed is plotted as a function of dose while Fig. 3b plots the equilibrium concentration of LBG adsorbed as a function of dose. Increasing dosage causes the fraction of LBG adsorbed to decrease but a greater
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