Pulp (CTMP) is produced with pressurized refining. Relatively low chemical

doses are applied, and the yield is typically above 90%. Chemimechanical pulp

(CMP) can be produced with refining at atmospheric pressure; the chemical treatment

Stage is more severe than in the CTMP process, and the yield is typically

below 90%. CMP is also the general name for all chemimechanically produced

Pulps. CTMP and CMP have been developed for the better use of hardwood and

The improvement of the bonding ability of the stiff long TMP-fibers, with the first

Pulping lines beginning operation during the 1950s and 1960s for hardwood applications.

The breakthrough in chemimechanical pulping occurred during the

S as result of the improved TMP technology. Because the key subprocess in

Chemimechanical pulping is refining, all developments of the TMP process could

Also be utilized for CMP production. This caused a rapid growth in the production

Of softwood CTMPs during the late 1970s and 1980s.

The difference between chemithermomechanical and chemimechanical pulping

Relates mainly to the process conditions utilized (see Tab. 4.2), and is apparent

Mainly in terms of the intensity of chemical treatment and pulp yield.

Mechanical Pulping Processes

Tab. 4.2 Possible defibration conditions for the production of chemithermomechanical

Pulp (CTMP) and chemimechanical pulp (CMP).

Wood type Predamping

[min]

Impregnation Preheating Cooking Yield

[%]

CTMP Softwood 10 1–5% Na2SO3 2–5 min

C

91–96

Hardwood 10 1–3% Na2SO3

NaOH

Min

C

88–95

CMP Softwood 10 12–20% Na2SO3 10–60 min

C

87–91

Hardwood 10 10–15% Na2SO3 10–60 min

C

80–88

Chemimechanical pulps can be produced, in principle, by a variety of combinations

Of chemical treatments and mechanical defibration. In practical operation,

Sodium sulfite is the dominating chemical in softwood pulping, while sodium hydroxide

and/or sodium sulfite are the common chemicals in hardwood pulping.

Sulfonation opens the wood structure and enables the access of water to the

fiber. Atack and Heitner [20] described this procedure (see Fig. 4.25), and assumed

That the softening of lignin could be led back to an exchange of the aliphatic hydroxyl

Groups or ether groups participating in hydrogen bonding between the lignin

Molecule chains, by solvated groups that cannot take over any bond between

The molecule chains.

HC

CH

CH2OH

R'O

OR

OH

OMe

HC

CH

CH2OH

R'O

SO3

OH

OMe

+ HSO3

ROH

Дата добавления: 2015-10-21