Chemical pulps, in relation to various yields.

Fig. 7.2 Characteristics of mechanical, semi-chemical, and chemical pulps.

With decreasing yield, an increased effluent load (biological oxygen demand;

BOD) and an increased strength potential is found, but this is to the disadvantage

Of light-scattering properties. In conventional chemical pulping, specific energy

Consumption is lower and the chemical consumption higher compared with the

Other processes. Freeness is measured with about 100 mL for (fines-containing)

Stone groundwood (SGW) and 800 mL (ca. 12 SR) for chemical pulp with a high

Long-fiber content. Light-scattering values are provided for the pulp before it

Undergoes additional mechanical treatment. The post-refining of a mechanical

Pulp increases the light-scattering coefficient, whereas the refining of a chemical

Pulp decreases this measure.

The grinding and refining processes separate the fibers in different ways. Figure

Shows the fractional composition according to the McNett principle versus

The yield of various pulps. The amount of long fibers in mechanical pulps (fraction

McNett R28) increases in the range SGW, RMP, TMP, CTMP more to the

Debit of the middle fraction than of the fines fraction.

The bonding ability of mechanical pulp fractions can vary widely, as shown in

Fig. 7.4 [41]. The high bonding ability of middle fractions is clear.

Latency and Properties of Mechanical Pulp

Fig. 7.3 Comparative fractional composition of various pulps

according to the McNett principle [40].

Fig. 7.4 Tensile index versus apparent density for the coarse

Fiber fraction, middle fraction and fines fraction of different

mechanical pulps (according to Mohlin [41]).

Mechanical pulps typically form bulky sheets with high light scattering

(Fig. 7.5). Thus, it is possible to produce paper with acceptable stiffness and opacity

At a considerably lower basis weight by using a mechanical pulp than a chemical

Pulp. When compared at the same freeness levels, TMP normally has the

Highest bulk and CTMP the lowest bulk of mechanical pulps. With regard to the

Mechanical pulps in Fig. 7.5, groundwood pulps usually exhibit the best optical

Properties (Fig. 7.5, below), whereas TMP and CTMP exhibit the best strength

Properties (Fig. 7.5, left and right). Because of their good strength properties,

These mechanical pulps require less reinforcement pulps when manufacturing,

Properties of Mechanical Pulp 1139

Fig. 7.5 Tensile index, tear index, and light-scattering

coefficient of different pulps depending on freeness [42].

For example, LWC paper. This compensates their lower light-scattering power and

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