ISSN ………… - International Network for Bamboo and Rattan

on wood chemistry (Browning 1952) 381 . Descriptions of wood and pulp analyses are found in different
publications (Sieber 1951 19a ; Merck 1957 53 ; Rydholm 1965) 70 and also in the charts brought out by the
professional associations of the Pulp Industry in various countries such as the USA (TAPPI Standards),
Sweden (CCA Standards), Germany (Merkblatt des Vereins der Zellstoff- und Papier-Chemiker und-
Ingenieure), Scandinavia (Scan- C Standards), and by the International Committee for Cellulose Analysis
(ICCA Standards).
3.3.1. Determination of residual lignin
3.3.1.1. Chlorine number and permanganate / kappa number
Determination of residual lignin in the pulp is the most important of all pulp analyses. It indicates the
degree of delignification obtained by the cook and forms the basis of comparison for many of the cooking
results, such as yield, screenings, pulp brightness, etc. It is based on measurement of a chemical reaction,
such as chlorination or permanganate oxidation. These methods are more rapid and suitable for adoption
in the mills, even though they have the drawback of giving only a relative figure for the lignin content and
not an absolute value.
Chlorine numbers are obtained by measuring the chlorine which reacts with lignin in substitution and
oxidation reactions. The Roe chlorine number indicates the grams of chlorine absorbed in 15 minutes at
20 0 C by 100 gram pulp containing 55 gram water. Its correlation with the lignin content of the pulp is
fairly straight-lined, with a factor of about 0.9 for sulphite and 0.8 for sulphate (kraft) pulps.
Permanganate numbers are based on the fact that lignin is rapidly oxidised by potassium permanganate.
At standardized conditions the excess permanganate can be determined after a certain reaction period. A
figure for the permanganate consumption can thus be obtained, which is a rapid and accurate measure of
the lignin content of the pulp. ICCA Standards redefined the permanganate number as Kappa number and
is related to the Klason lignin content by a factor of 0.13, and to the Roe chlorine number by a factor of
0.20 for sulphite and 0.16 for kraft pulp.
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