Cellulose (2021) 28:10183–10201
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Adsorption experiments were conducted in capped 150 mL Erlenmeyer flasks. Control flasks containing only LBG or only fibre were run in parallel. The galactomannan detected in the supernatant of the fibre- only control was 0.14 mg g - 1 o.d. fibre (standard deviation of 0.05 mg g - 1 ). All conditions were tested as 2–4 replicates. After adsorption, all samples were centrifuged at 3500 r.p.m. for 15 min. The supernatant was preserved for compositional analysis. The experimental design for LBG adsorption kinetics and isotherm is summarized in Table 1. The kinetics study was conducted by adding 0.12–0.21 wt% LBG relative to o.d. pulp fibre (0.21wt% at 25 C, 0.14wt% at 35 C, and 0.12wt% at 45 C); the fibre consistency of the slurry was 0.5 wt%. Adsorp- tion was conducted at 25 C, 35 C, and 45 C in an incubator shaker with continuous agitation (150 r.p.m.) for 0.5 to 120 min for NBSK unrefined pulp. Adsorption isotherm experiments were conducted by varying LBG dosage from 0.1 to 2.1 wt% of o.d. pulp fibre. The PFI mill (Noram Quality Control & Research Equipment Limited) was used to refine the pulp to 3000 rev to compare with unrefined NBSK pulp. Adsorption was conducted at 25 C and 35 C with continuous agitation (150 r.p.m.) for 10 min in the incubator shaker for unrefined NBSK pulp. The isotherm experiments for refined NBSK pulp were conducted by varying LBG dosage from 0.2 to 0.6 wt% of o.d. pulp fibre at 25 C. Table 1 also summarizes the conditions tested to determine the effect of LBG concentration, tempera- ture, salt addition, and pH on adsorption. All trials were performed for 10 min with continuous agitation of 150 r.p.m. Sodium chloride was varied from 0–1 mol L - 1 and pH was varied from 2 to 13 in order to test the full range of conditions previously reported
in the literature. The buffer (0.1 M) was prepared with potassium chloride and hydrochloric acid (pH 2), sodium acetate and acetic acid (pH 5), sodium phosphate monobasic and dibasic (pH 7), sodium bicarbonate and sodium carbonate (pH 10), and potassium chloride and sodium hydroxide (pH 13).
LBG solution compositional analysis
The galactomannans were hydrolyzed from polysac- charides to monosaccharides with sulfuric acid in an autoclave at 121 C for 1 h according to National Renewable Energy Laboratory Analytical Procedures (Sluiter et al. 2008, 2006; Hames et al. 2008). The galactomannan monomer content in the supernatant was analyzed by Dionex AS50 HPLC (Thermo Scientific) coupled with an ion exchange PA1 column (Dionex), an ED50 electrochemical detector (pulsed amperometric detector) with a gold electrode, and an AS50 autosampler (Dionex). Deionized water was used as eluent with a flow rate of 1 mL min - 1 . The auxiliary pump added 0.2 M NaOH at 0.5 mL min - 1 . The samples were filtered through a 0.22 l m nylon syringe filter before injection. The injection volume was 10 l L. The fraction of LBG adsorbed to the pulp, f L , was determined by the difference of galactomannan con- tent in supernatant, relative to LBG control after adsorption: f L ¼ ð 1 Þ where C 0F is the galactomannan concentration (mg L - 1 ) detected in supernatant of fibre control flask, C 0L is initial LBG concentration (mg L - 1 ), C 0 F þ C 0 L C SL C 0 L 100 %
Table 1 LBG adsorption kinetics and isotherm experimental design for unrefined and refined NBSK pulp. Factors investigated for LBG adsorption: LBG dosage, temperature, NaCl addition, and pH. Note: standard deviation after ±
pH of sample suspension
Use
Refining (rev)
Dosage relative to o.d. pulp (wt%)
Adsorption temperature ( C)
Adsorption time (min)
NaCl addition (mol L - 1 )
Kinetics 0
0.12–0.21
25, 35, 45
0.5–120
0
5.33 ± 0.35
Isotherm 0
0.1–2.1
25, 35
10
0
5.43 ± 0.35
Isotherm 3000
0.2–0.6
25
10
0
5.04 ± 0.41
NaCl
0
0.2
25
10
0–1
5.08 ± 0.56
effect
pH
0
0.2
25
10
0
2–13
effect
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