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 rigidity ...

content or bleachability of

wood pulp Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibers from wood, fiber crops, waste paper, or rags. Mixed with water and other chemical or plant-based additives, pulp is the major raw mate ...

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 form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., wi ...

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 Potassium permanganate is an inorganic compound with the chemical formula KMnO4. It is a purplish-black crystalline salt, that dissolves in water as K+ and , an intensely pink to purple solution. Potassium permanganate is widely used in the c ...

solution Solution may refer to: * Solution (chemistry), a mixture where one substance is dissolved in another * Solution (equation), in mathematics ** Numerical solution, in numerical analysis, approximate solutions within specified error bounds * Soluti ...

that the pulp will consume. The measurement is inflated by the presence of

hexenuronic acid Hexenuronic acid (HexA) is a bicyclic organic compound with the formula C13H20O10. It is an unsaturated sugar produced during the kraft process in the creation of wood pulp. Kraft process During the kraft process, which is the turning of wo ...

s 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 heteropolymer, heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all embryophyte, terrestrial plant cell walls.Scheller HV, Ulvskov H ...

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 ful ...

, 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 (whitening) from a fabric or fiber or to clean or to remove stains in a process called bleaching. It often refers specifically, to ...

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 Pulp is a Lignocellulosic biomass, lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibers from wood, fiber crops, Paper recycling, waste paper, or cotton paper, rags. Mixed with water and other chemica ...

process. It is approximately proportional to the residual lignin content of the pulp. K ≈ c*l K: Kappa number; c: constant ≈ 6,57 (dependent on process and

wood Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin th ...

); l: lignin content in percent The Kappa number for bleachable pulps are in the range of 25–30,

sack paper Kraft paper or kraft is paper or paperboard (cardboard) produced from chemical pulp produced in the kraft process. Sack kraft paper (or just sack paper) is a porous kraft paper with high Elasticity (physics), elasticity and high tear resistance ...

pulps in the range 45-55 and pulps for

corrugated fiberboard Corrugated fiberboard or corrugated cardboard 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 making corrugated ...

are in the range 60-110.

References

External links

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