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Effect of Cooking Variables in Neutral Sulphite Anthraquinone Pulping of Jute.

Dr. A.F.M. Akhtaruzzaman,
Divisional Officer
Pulp and paper Division, Bangladesh Forest Research Institute, P. O. Box 273, Chittagong-4000, Bangladesh.

Mr. P. Das
Research Officer
Pulp and paper Division, Bangladesh Forest Research Institute, P. O. Box 273, Chittagong-4000, Bangladesh.

Dr. S.K. Bose.
Research Officer
Pulp and paper Division, Bangladesh Forest Research Institute, P. O. Box 273, Chittagong-4000, Bangladesh.

Abstract/ Executive Summary:

The effect of cooking variables, such as total alkali, cooking time, cooking temperature and liquor to fibre ratio, in neutral sulphite anthraquinone pulping of jute (Corchoru capsularis) has been studied. Regression equations relating these variables with the kappa number, total yield and physical strength properties have been worked out. The cooking variables were found to affect the degree of cooking, pulp yield and pulp strength properties. The cooking temperature and the extent of delignification were decisive factors on pulp’s yield and strength properties.

Keywords: Anthraquinone, Jute, Neutral sulphite pulping, Pulp yield, Physical strength properties.

Location: Bangladesh Forest Research Institute, Chittagong.

Start Date:

End Date:

Program Area: Postharvest and Agro-processing

Commodity: Jute

Objectives:

To optimize the cooking conditions of Neutral sulphite anthraquinone (NS-AQ) pulping of jute by studying the effects of alkali charge, cooking time, cooking temperature and liquor to material ratio.

Methodology:

Air dried jute cuttings (bast fibre) from white-B jute (Corchorus capsularis), were used as a fibrous raw material. The jute cuttings were chopped manually to 4-5 cm in length. They were mixed thoroughly to eliminate the variability in the raw material.

Pulping

Pulping was done in 2 litre stainless steel autoclaves, in a thermostatically controlled heated air bath. The amount of samples used in each cook was 250 g on oven dry basis. Analytical grades of AQ, Na₂SO₃ and Na₂CO₃ were used. The following cooking parameters were maintained:

Liquor to fibre ratio, varying (7:1 for optimization of alkali ratio)
Total alkali, varying
AQ dose, 0.1% on od jute
Alkali ratio, 0.83 ( 0.65 to 0.95 for optimization of alkali ratio)
Rise of temperature from room temperature 80° in 30 min. and 80 to cooking temperature in 90 min.
Cooking temperature, varying (170°C for optimization of alkali ratio
Cooking time, varying

AQ was mixed in the cooking liquor before adding it to the digester. At the end of the cook, the autoclaves were cooled as quickly as possible. The cooked material was washed overnight in running water, then disintegrated or mechanically refined. The defiberized pulp was screened on a flat vibratory screen with 0.38 mm slots.

Analyzes

The screened pulp was pressed to remove the excess water, weighed and sampled to determine the dry matter content. The pulp yield and kappa number were then determined. The pulp was refined in a PFI mill to different freeness values and hand sheets were made for determining the strength properties on conditioning the sheets at 23 ±1° and 50 ±2% RH. The pulp strength properties were determined according to SCAN Test Methods.

Source of Information: Cellulose Chemistry and Technology. 30:229-234,1996.

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The following conclusions are drawn from this study:

-Maximum delignification occurs with an alkali ratio in the 0.80 to 0.85 range.

-Fully chemically defiberized pulp can be obtained at a kappa number of about 27.

-Delignification is dependent on the total alkali charge, cooking temperature and liquor to fiber ratio. The delignification slows down toward the end of the cook.

-The alkali charge has a minor role on pulp yield. An elevated temperature reduces the yield. A more concentrated liquor is better to preserve the yield on extended delignification. The yield falls rapidly toward the end of the cook. Such a shift is dependent on the alkali charge, cooking temperature and liquor to fibre ratio.

-Pulp of exceptionally high physical strength properties can be obtained from jute by the NS-AQ process.

The alkali charge and liquor to fibre ratio show relatively relatively minor effect on the tearing strength of pulp; however, the cooking temperature contributes decisively to this property. Extended delignification improves tearing strength.

The tensile strength of the pulp is not dependent on the alkali charge. The property is improved when pulping is done at 173°C. A lower liquor to fibre ratio is more advantageous for tensile strength. An extended cook weakens this pulp property.

Knowledge Management: Journal