FUNCIO NES Y CO M PRO M ISO S

2.2.1   Preparation  of  model  compound  colloidal  suspension  

The model compounds used to represent individual components found in wood extractive are oleic acid (fatty acid, 90 % Aldrich), abietic acid (resin acid, 75 % Fluka Analytical), and triolein (triglyceride, 65 % Sigma). A range of concentrations of the individual colloidal suspensions (50 mg L-1 _{to 700 mg L}-1_)were

prepared in situ. A fixed mass of each compound was weighed out (to give the required concentration) and dissolved in 3.50 mL of acetone (AR grade, Chem-supply). For experiments with pulp fibre slurry, 54.0 mL of 1 mM KNO3 (aq) was added to a flask and stirred at 400 rpm, before 1.00 mL of model

compounds in acetone was added, with force, using an autopipette. For experiments with

microcrystalline cellulose slurry, 94.0 mL of 1 mM KNO3 (aq) was added to a flask and stirred at 400

rpm, before 1.00 mL of model compounds in acetone was added, with force, using an autopipette. In both cases, the colloidal suspensions were stirred for 15 min to allow for stabilisation before pulp fibre slurry or microcrystalline cellulose mixture was added to the flasks.

2.2.2   Preparation  of  wood  extractive  colloidal  suspension  

Thermomechanical pulp (TMP) from the Norske-Skog Boyer mill was freeze-dried then soxhlet extracted for 8 h with hexane. The hexane was removed by rotary evaporation and the resulting wood extractive product was stored at < 10°C until required. Wood extractive colloidal suspensions of a range of concentrations (50 mg L-1 _{to 400 mg L}-1_{) were used in deposition experiments. As stated under 2.2.1,}

dissolved in 3.00 mL of acetone (AR grade, Chem-supply). For experiments with pulp fibre slurry, 54.0 mL of 1 mM KNO3 (aq) was added into each flask and stirred at 400 rpm, before 1.00 mL of wood

extractives in acetone was added, with force, using an autopipette. For experiments with

microcrystalline cellulose mixture, 94.0 mL of 1 mM KNO3 (aq) was added into each flask and stirred at

400 rpm, before 1.00 mL of wood extractives in acetone was added, with force, using an autopipette. In both cases, the colloidal suspensions were stirred for 15 min to allow for stabilisation before the pulp fibre slurry or microcrystalline cellulose mixture was added to the flasks.

2.2.3   Preparation  of  TMP  pulp  fibre  slurry  

The TMP pulp, from which the wood extractives had been extracted, was used as an adsorbent

representing a cellulose surface and simulating the adsorption occurring in the papermaking process. A pulp slurry of 2.0 % consistency was made by stirring 4.0 g TMP pulp in 196 mL of 1 mM KNO3 (aq),

overnight. This was diluted to a final concentration of 0.5 % pulp consistency by mixing 25.0 g of prepared pulp slurry, 20.0 mL of 1mM KNO3 (aq) and 55.0 mL of the colloidal suspension before the

start of each experiment.

2.2.4   Preparation  of  microcrystalline  cellulose  mixture  

Microcrystalline cellulose mixture was employed as a further representation of the cellulose surface. In the current chapter this was in the form of an aqueous suspension while in the QCM experiments (Chapter 3) it was in the form of a solid coating. The aqueous suspension was made by mixing 3.5 g microcrystalline cellulose (Serva-Avicel PH 105, ca. 0.019 mm) with 35.0 mL of 1 mM KNO3 (aq) and

stirred overnight. 5.0 mL of microcrystalline cellulose slurry was then added to 95.0 mL colloidal suspension before the start of the experiment to ensure 0.5 % microcrystalline cellulose consistency in each flask.

2.2.5   Adsorption  experiment  methods  

A Radleys parallel 6-carousel reactor fitted with 250 mL wide neck round bottom flasks and 25 mm rare earth elliptical Teflon stirring bars, was used to prepare colloidal suspensions in situ and carry out

adsorption studies in triplicate. Experiments were conducted at a temperature of 50°C and pH of 5 - 5.5. For experiments with the pulp slurry and microcrystalline cellulose mixture, colloidal suspensions were prepared as described in 2.2.1 (for model compound suspensions) and 2.2.2 (for wood extractives suspensions). The suspensions were stirred for 15 min to allow for stabilisation before the pulp slurry or microcrystalline cellulose suspension was added to the flask.

For experiments with pH perturbations, after the addition of the pulp slurry or microcrystalline cellulose mixture, the suspension was stirred for about 5 - 10 min before pH perturbations were applied. The pH of the suspension was initially increased to 7 - 8 with KOH (aq). After stirring for about 5 min the pH was returned to 5 with HNO3 (aq) before the process of deposition commenced.

Sample ‘A’ was taken before the commencement of the 2 h deposition period at 50°C. Sample ‘B’ was taken straight from the reaction flask at the end of the 2 h deposition period. At the same time, a larger sample was transferred to a glass centrifuge tube. This sample was centrifuged at 1800 rpm for 10 min to sediment the pulp fibres/microcrystalline cellulose particles. Sample ‘C’ was then taken from the supernatant of the centrifuged sample. All sample volumes were measured using an auto-pipette and known to at least 3 significant figures.

2.2.6   Extraction  method  

Samples ‘A’, ‘B’ and ‘C’ were extracted with tertiary-butyl methyl ether (t-BME, HPLC grade, Scharlau) by the following method. An internal standard solution containing heptadecanoic acid (C17, >98 %, Sigma), pentadecanoic acid (C15, 99+ % Aldrich), cholesteryl stearate (CS, 99% Sigma) and glyceryl triheptadecanoate (GTH, ≥99 % Sigma) was prepared in toluene (99.9 % purity, Sigma-Aldrich), at concentrations of approximately 50 µg/ 100 µL each, known accurately. After adjustment of the sample pH with nitric acid to pH <4,100 µL of the internal standard solution was added to each sample,

followed by 2 mL of t-BME. The samples were shaken vigorously for 30 sec before being centrifuged at 1800 rpm for 10 min. After centrifugation, the t-BME layer of each sample was transferred, using Pasteur pipettes, into clearly labelled GC vials. The solvent in each GC vial was evaporated to dryness before 1.00 mL of toluene was added.

2.2.7   Analysis  by  gas  chromatography  

Each sample was analysed using a Varian CP-3380 gas chromatograph, fitted with a Varian 8100 auto- sampler and flame ionisation detector (FID). A 15 m Zebron capillary GC column, with internal diameter and film thickness of 0.53 mm and 0.15 µm, respectively, was used. An on-column method was employed, at a set pressure flow of 4 psi of a mixture of helium gas (carrier gas) and nitrogen gas (make-up gas) over a period of 50 min using a temperature ramping programme. The injector was set at 100°C for 1.5 min, ramped at 180°C/min to 325°C then held for 11 min. The column oven was set at 100°C for 2 min then ramped at 15°C/min to 320°C and held until the end of the run. The FID was set at 350°C for the entire run.

A spike solution, containing the internal standard solution along with oleic acid (GC standard, Fluka), dehydroabietic acid (99+ %, Helix Biotech) and triolein (65 %, Sigma) in toluene, at concentrations approximately 50 µg/100 µL each, known accurately, was used to determine the response factors for each set of results. All response factors were based on the C17 standard. The internal standards CS and GTH were used to correct the concentrations of fatty acids and triglycerides, and resin acids, respectively. Results were analysed using Varian Star version 6.20 software.