Kappa number
Encyclopedia
The Kappa number is an indication of the residual lignin
content or bleachability
of wood pulp
by a standarised analysis method.
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
s.
The Kappa number can be monitored by online Kappa analysers in a pulp mill
, but these have to be calibrated with the ISO 302:2004 method.
to obtain a pulp with a given degree of whiteness. Since the amount of bleach
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
K: Kappa number;
c: constant ≈ 6,57 (dependent on process and wood
);
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 are in the range 60-90.
Lignin
Lignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood...
content or bleachability
Bleaching of wood pulp
Bleaching of wood pulp is the chemical processing carried out on various types of wood pulp to decrease the color of the pulp, so that it becomes whiter. The main use of wood pulp is to make paper where whiteness is an important characteristic...
of wood pulp
Wood pulp
Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibres from wood, fibre crops or waste paper. Wood pulp is the most common raw material in papermaking.-History:...
by a standarised analysis method.
Measuring method
The Kappa number is determined by ISO 302:2004. ISO 302 is applicable to all kinds of chemical and semi-chemical pulps and gives a Kappa number in the range of 1-100. The Kappa number is a measurement of standard potassium permanganatePotassium permanganate
Potassium permanganate is an inorganic chemical compound with the formula KMnO4. It is a salt consisting of K+ and MnO4− ions. Formerly known as permanganate of potash or Condy's crystals, it is a strong oxidizing agent. It dissolves in water to give intensely purple solutions, the...
solution
Solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...
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
Hemicellulose
A hemicellulose is any of several heteropolymers , such as arabinoxylans, present along with cellulose in almost all plant cell walls. While cellulose is crystalline, strong, and resistant to hydrolysis, hemicellulose has a random, amorphous structure with little strength...
s.
The Kappa number can be monitored by online Kappa analysers in a pulp mill
Pulp mill
A pulp mill is a manufacturing facility that converts wood chips or other plant fibre source into a thick fibre board which can be shipped to a paper mill for further processing. Pulp can be manufactured using mechanical, semi-chemical or fully chemical methods...
, 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 wood pulpPulp (paper)
Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibres from wood, fibre crops or waste paper. Wood pulp is the most common raw material in papermaking.-History:...
to obtain a pulp with a given degree of whiteness. Since the amount of bleach
Bleach
Bleach refers to a number of chemicals that remove color, whiten, or disinfect, often via oxidation. Common chemical bleaches include household chlorine bleach , lye, oxygen bleach , and bleaching powder...
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
K: Kappa number;
c: constant ≈ 6,57 (dependent on process and wood
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...
);
l: lignin content in percent
The Kappa number for bleachable
Bleaching of wood pulp
Bleaching of wood pulp is the chemical processing carried out on various types of wood pulp to decrease the color of the pulp, so that it becomes whiter. The main use of wood pulp is to make paper where whiteness is an important characteristic...
pulps are in the range of 25-30, sack paper
Sack paper
Sack Kraft Paper, or just sack paper is a porous kraft paper with high elasticity and high tear resistance, designed for packaging products with high demands for strength and durability.-Manufacturing:...
pulps in the range 45-55 and pulps for corrugated fiberboard are in the range 60-90.