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Figure 1. The pulping scheme for different feed stocks and subsequent processing of fibers.
The carboxyl content in milliequivalents per 100 g of the pulp slurry was calculated as: ( ) = − × × V V N W Carboxyl content 100/ b a (1) Where, N is the normality of HCl (Equation (l)), V b and V a are the volumes of HCl in absence and presence of sample, and W is the weight of sample (g). Charge Determination : Charge estimation on the fibers was carried out using the colloidal titration method. [36] The fiber samples were disintegrated into pulp at a 0.075% consistency (mass of solids relative to total mass + water) in deionized water. The colloidal charge of 200 mL of the resulting pulp suspension was evaluated by titration using a CHEMTRAC ECA 2000 P streaming current analyzer. The charge neutralization points of fibers were determined by the addition of cationic polymers (poly(diallyldimethylammonium chloride) (polyDADMAC)) to the suspension. Hard-to-Remove Water Measurement : Hard to remove (HR) water was determined using TGA. [37] The sample was taken in platinum sample pans. The temperature was then raised to 110 ° C from 30 ° C at 10 ° C min − 1 . Drying experiments were run isothermally at 110 ° C for 15 min until no more drying occurred. The non-freezing bound water was calculated by sub- tracting the total freezable water from the moisture ratio in the
by using a high-resolution fiber quality analyzer: HiRes FQA, OpTest Equipment Inc, Hawkesbury, ON, Canada. Before testing, fiber quality analysis (FQA) was calibrated and used according to the manufacturers’ specifications. The whole pulp for each sample was taken and disintegrated before the meas- urement was done. Fourier Transform Infrared Spectroscopy (FTIR) : Fourier transform infrared (FTIR) spectra of the different fibers were recorded using a PerkinElmer Spectrum One FTIR spectrom- eter. For each sample, the diamond crystal of an attenuated total reflectance (ATR) accessory was brought into contact with the area to be analyzed. The contact area was a circle of about 1.5 mm in diameter. All spectra were recorded between 4000 and 500 cm − 1 with a resolution of 4 cm − 1 with 32 scans per sample. For comparison, spectra were adjusted to the same baseline. Brightness Measurement : The brightness of the fibers was measured by following the ISO 2470 standard method using the color spectrophotometer Color Touch X, Technidyne, Indiana, USA. This procedure was repeated for ten samples for each of the fibers, and the mean value was taken. Total Carboxyl Content Analysis : Acid-base titration was used to determine the total carboxyl content of the pulps. [34,35] 100 mg of pulp was dissolved in 20 mL 0.1 n NaOH and stirred with a magnetic stirrer for 2 h. An excess amount of 0.1 n NaOH was titrated with 0.1 n HCl using phenolphthalein as an indicator.
Table 2. Process condition.
Process
Feedstock
pH Water–solid ratio
Pulping chemicals
4% sodium carbonate based on Na 2 O a) 4% sodium carbonate based on Na 2 O
Carbonate hydrolysis
Hemp
11.2
8
Eucalyptus, bamboo, hardwood, softwood
11.3
4
12% active alkali 25% sulfidity (NaOH + Na 2 S) based on Na 2 O 12% active alkali 25% sulfidity (NaOH + Na 2 S) based on Na 2 O
Mild kraft
Hemp
12.8
8
Eucalyptus, bamboo, hardwood, softwood
13.3
4
a) Reporting on a Na
2 O basis indicates the actual chemical relationship between the pulping chemicals used. It is a standardized way of normalizing the concentration
strengths (based on Na 2 O).
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