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Cellulose (2021) 28:5807–5826
CTMP 0 min CTMP 30 min CTMP 60 min
to 10 g. The wires used during fractionation were 30, 100 and 200 of the ASTM series (nominal openings 595, 149 and 75 l m, respectively) and 400 mesh wire with a measured opening of 25 l m. The fractions were labelled to indicate residuals. For example R30 refers to fraction retained by 30 mesh wire. The scheme of experiments is shown in Fig. 2. A minimum of seven fractionations were carried out for each pulp. Five were done to collect fractions in separate vessels for further use, and two to weigh the fractions and measure their ash. To do so the fractions were collected on ashless filter paper (Macherey- Nagel MN 640 m) and dried in an oven at 105 Cprior the ash content determination. TAPPI standards T 211 om-02 and T 413 om-11 were used in conjunction to determine the ash content.
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Fiber length [μm]
Handsheet preparation
Fig. 1 Fiber length distributions of CTMP: 0 min refined (23 SR), 30 min refined (42 SR) and 60 min refiner (58 SR). The values given are weighted with respect to fiber length
Handsheets were prepared according to the SCAN C 26:99 standard with the exception of the drying (drum, surface temperature ca. 60 C) and the use of an auxiliary wire (90 gsm polyester satin, thread width approximately 300 l m). The auxiliary wire was placed on the sheet mould wire and removed after wet-pressing.
impellers. The impellers were placed 16 cm distance from each other. The batch size was 9.5 l and the fiber consistency 1.3 wt% before precipitation. For each batch, the depletion of Ca(OH) 2 was determined by the decrease in pH. At the beginning of the reaction, the temper- ature was ca. 20 C, but it was allowed to change freely during the exothermic precipitation process. TheCO 2 feed was 3 l/min and the target Ca(OH) 2 dose (before precipitation) was 1.0 wt%, corresponding to 50 wt%CaCO 3 filler (ash) content assuming 100 % conversion. TheCa(OH) 2 used was prepared from CaO. Slaking was carried out for 4 h. The CaO-to-H 2 O ratio used was 1:9. The initial temperature was 40 C, but the temperature was allowed to change freely.
Analytical procedures
Fiber analysis
The CTMPs, PCC-CTMPs and fractions were ana- lyzed using the L&W Fiber Tester (Lorentzen and Wettre, Kista, Sweden) using a dilution of approxi- mately 0.1 g fibers in 100 ml of water. Fiber length, fiber width, shape factor, the amount of fines and the kink index were determined and recorded as length- weighted averages. The ash and CaCO 3 contents of the samples were measured according to TAPPI standards T 211 om-02 and T 413 om-11 in conjunction.
Pulp fractionation
The pulps (CTMPs and PCC-CTMPs) were fraction- ated using a Bauer-McNett classifier according to the SCAN-M 6:96 standard, with the exception of the dosed fiber weight. In case of PCC-CTMP, 20 g of solids (CTMP and PCC combined, containing approx- imately 10 g of CTMP), were used in the fractiona- tion. In the case of the CTMP, the amount was equal to that used for the corresponding PCC-CTMP, i.e. close
Zeta potential
The zeta potentials of the pulps and fractions were measured using the streaming potential method (Mu¨tek SZP-06, BTG Instruments GmbH, Herrsching, German). The conductivity of the samples was increased to 0.30 ± 0.01 mS/cm with 0.1 M NaCl
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