The Kappa number is an indication of the residual

lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidit ...

content or bleachability of

wood pulp Pulp is a fibrous Lignocellulosic biomass, lignocellulosic material prepared by chemically, semi-chemically, or mechanically isolating the cellulose fiber, cellulosic fibers of wood, fiber crops, Paper recycling, waste paper, or cotton paper, rag ...

by a standardized analysis method.

Measuring method

The Kappa number is determined by ISO 302:2004. ISO 302 is applicable to all kinds of

chemical A chemical substance is a unique form of matter with constant chemical composition and characteristic properties. Chemical substances may take the form of a single element or chemical compounds. If two or more chemical substances can be combin ...

and semi-chemical pulps and gives a Kappa number in the range of 1–100. The Kappa number is a measurement of standard potassium permanganate solution that the pulp will consume. The measurement is inflated by the presence of hexenuronic acids in the pulp. These compounds are formed during the chemical pulping process, from the

hemicellulose A hemicellulose (also known as polyose) is one of a number of heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all embryophyte, terrestrial plant cell walls. Cellulose is crystalline, strong, an ...

s. The Kappa number can be monitored by online Kappa analysers in a

pulp mill A pulp mill is a manufacturing facility that converts wood chips or other plant fiber sources into a thick fiber board which can be shipped to a paper mill for further processing. Pulp can be manufactured using mechanical, semi-chemical, or ...

, but these have to be calibrated with the ISO 302:2004 method.

Application

The Kappa number estimates the amount of chemicals required during bleaching of

to obtain a pulp with a given degree of whiteness. Since the amount of

bleach Bleach is the generic name for any chemical product that is used industrially or domestically to remove color from (i.e. to whiten) fabric or fiber (in a process called bleaching) or to disinfect after cleaning. It often refers specifically t ...

needed is related to the lignin content of the pulp, the Kappa number can be used to monitor the effectiveness of the lignin-extraction phase of the pulping process. It is approximately proportional to the residual lignin content of the pulp. : K ≈ c × L Where:
: K: Kappa number;
: c: constant ≈ 6,57 (dependent on process and

wood Wood is a structural tissue/material found as xylem in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulosic fibers that are strong in tension and embedded in a matrix of lignin t ...

);
: L: lignin content in percent. The Kappa number for bleachable pulps are in the range of 25–30, sack paper pulps in the range 45-55 and pulps for

corrugated fiberboard Corrugated fiberboard, corrugated cardboard, or corrugated is a type of packaging material consisting of a fluted corrugated sheet and one or two flat linerboards. It is made on "flute lamination machines" or "corrugators" and is used for maki ...

are in the range 60-110.

References

External links

Automated Kappa number analyzer

Kappa number (lignin) analyzer
{{DEFAULTSORT:Kappa Number Papermaking