Well-softened and the fiber requires minimal mechanical energy for its liberation

From the fiber compound. This mechanical pulp has an unsuitable quality for

Papermaking, however, as it is harsh and coarse. The softened lignin solidifies at

The fiber surface to a hard substance; the pulp has a high refining resistance. If

The defibration temperature is lower than the softening temperature of the lignin,

Then the mechanical pulp produced is coarse and has only a low level of strength

Properties. When the refining temperature is very close to the softening temperature,

A high percentage of the fibers can be defibrated without being destroyed.

The primary wall of these fibers can be damaged, and this allows fibrillation of the

secondary wall. According to Giertz [19], the shearing frequency in a refiner is be-

Refiner Processes

Tween 10 kHz and 1 MHz. Based on the fact that the softening temperature for

high polymers increases by 7° when the frequency increases by 1 tenth, it can be

assumed that the lignin of moist chips will be softened in the refiner at 120–

C.

The shearing frequency is estimated by rotational speed, disc diameter, and

plate pattern. Moreover, the type of refining – whether single disc, double disc or

conical disc – is also important. If the refining temperature is slightly above the

Softening temperature of the wood chips, then defibration occurs mainly in the

Zones with a high lignin concentration (i.e., in the middle lamella). In this way, a

High proportion of fibers is deliberated without being damaged. At the same time,

The middle lamella and primary wall are removed and milled down to fines, while

the outer secondary wall (S1) is fibrillated [19]. The mechanical and thermal processes

during refining can be divided into three phases:

Reduction of the chips sizes to units of matches.

2. Reduction of those “matches” to fibers.

_ Stress by pressure pulsation and shearing of the fiber –

Fatigue of the middle lamella

_ Thermal softening of lignin and hemicellulose

_ Rolling effect (= agglomeration of deliberated fibers)

_ Fiber cutting

Fibrillation of the deliberated fibers and fiber bundles.

Chemimechanical pulping involves a gentle chemical treatment stage combined

With mechanical defibration such as disc refining. The yields of these pulps are

generally in the range of 80–95%, and their properties are intermediate between

Those of high-yield chemical pulps and mechanical pulps. Chemithermomechanical

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