The A. auriculiformis was collected from the Gazipur Forest Station, which is 10-year-old. Three trees were selected for this experiment. Sixty-cm-portions from the top and bottom and branches of these trees were discarded and remaining portion was debarked and chipped to 0.5 × 0.5 × 2 cm size. The chips were ground in a Wiley mill and 40-60 mesh size was used for chemical analysis. Physical, morphological and chemical properties The basic wood density of A. auriculiformis was determined according to PAPTAC Standard A. 8P. For the measurements of fiber length, the sample was macerated in a solution containing 1:1 HNO3 and KClO3. A drop of macerated sample was taken in a slide and fiber length was measured under a profile projector (Nikon V-12, Japan). The fiber diameter was measured in an image analyzer.
The extractive (T204 om88), 1% alkali solubility (T 212 om98), water solubility (T207 cm99), Klason lignin (T211 om83), and ash content (T211 os76) were determined in accordance with Tappi Test Methods. Holocellulose was determined by treating the extractive free wood meal with NaClO2 solution. The pH of the solution was maintained at 4 by adding CH3COOH- CH3COONa buffer and α-cellulose was determined by treating holocellulose with 17.5% NaOH.
Pulping
Pulping was carried out in a thermostatically controlled electrically heated digester. The capacity of the digester was 20 l. The normal charge was 1 kg oven dried (o.d.) A. auriculiformis. Pulping conditions of kraft, soda, and soda-anthraquinone (AQ) are as follows:
- Active alkali was 14%, 16%, 18%, and 20% on o.d. raw material as Na 2 O cooking time was 2, 2.5, and 3 h at maximum temperature (170°C). 90 min was required to reach the maximum temperature (170 °C) from room temperature.
- Liquor to material ratio was 4.
- AQ charge was 0.1% on o.d. raw material in soda- AQ process.
- Sulphidity was 25% for kraft process.
After digestion, the pulp was washed till it is free from residual chemicals, and it is screened by a flat vibratory screener (Yasuda, Japan). The screened pulp yield, total pulp yield, and screened reject were determined gravimetrically as percentage of o.d. raw material. The kappa number (T 236 om-99) of the resulting pulp was determined in accordance with Tappi Test Methods. Three replicates of all experiments were done and an average reading was taken. The standard deviations were analyzed using MS Excel.
Evaluation of pulps
Soda, soda-anthraquinone (AQ), and kraft pulps were beaten in a valley beater at different times to different freeness (°SR) and hand sheets of about 60 g m-2 were made in a Rapid Kothen Sheet Making Machine. The sheets were tested for tensile (T 494 om-96), burst (T 403 om-97), tear strength (T 414 om-98), folding endurance (T 511 om 96), and brightness (T525 om 92) according to TAPPI Standard Test Methods.
DEpD and DEpDEpD bleaching
The soda, soda-anthraquinone (AQ), and kraft pulps were bleached by DoEpD1 bleaching sequences (where D represents chlorine dioxide and Ep represents peroxide reinforced alkaline extraction). The kappa factor was 0.22-0.30 in the first stage of DoEpD1 bleaching sequences. The temperature was 70°C in Do stage for 60 min. Pulp consistency was 5%. The pH was adjusted to 2.5 by adding dilute H2SO4. In alkaline extraction stage, temperature was 70°C for 60 min in a water solution of 2% NaOH and 0.5% H2O2 (on o.d. pulp). Pulp consistency was 5%. In the final D1 stage, pH was adjusted to 4 by adding dilute H2SO4. The ClO2 charge in the D1 stage was half of the first stage. In case of 5-stage bleaching, the same amount of ClO2 was splitted to last 2-stage ClO2 charge. The brightness and viscosity (T 230 om-99) of the bleached pulp were determined in accordance with Tappi Test Methods. The physical properties of 5-stage bleached soda, soda-AQ, and kraft pulps were determined after 3000 revolution in PFI mill. The Standard deviation was analyzed using MS Excel.