Has been extensively investigated and technologically developed by Fischer

et al. [88].

Alkali cellulose with a typical composition of 34% cellulose and 16% NaOH

(~1.9 mol NaOH mol–1 cellulose) is rather rapidly degraded at only a slightly elevated

temperature (30–50 °C), initiated by the uptake of oxygen. The reaction rate

Can be accelerated by the addition of transition metal ions, particularly Co or Mn

Salts. The course of the chain scissions, calculated from the weighted molecular

weight (determined by GPC measurement [68]) of alkali celluloses prepared from

Both hardwood sulfite and PHK dissolving pulps as a function of reaction time at

C, is illustrated graphically in Fig. 11.29.

0 2 4 6 8

HW-Sulfite HW-PHK

Chain Scissions [104/DP

W,t

-104/DP

W,0

]

Ageing time at 50 °C [h]

Fig. 11.29 Course of chains scissions (based on weighted

Molecular weight) of alkali celluloses prepared from hardwood

Sulfite and PHK dissolving pulps as a function of time

at 50 °C.

The ageing of alkali cellulose follows a pseudo zero-order reaction kinetics

Based on the number-average degree of polymerization DPn, according to the following

expression [56]:

DPn_t _

DPn_0 _ _ kA t _1_

Where kA is the reaction rate of the ageing process.

Pulp Properties and Applications

The deviation from linearity, which is particularly discernible for alkali cellulose

Made from a hardwood sulfite pulp, can be attributed to the change (decrease) in

polydispersity during degradation. Based on today’s knowledge of the reaction

Mechanism, chain scission is initiated by the reducing endgroups. In agreement

With these considerations, oxidative alkaline degradation of sulfite pulp proceeds

Faster as compared to the more narrowly distributed PHK dissolving pulp (see

Fig. 11.29).

The arguments in favor of electron beam treatment of dissolving pulp are a better

Control of viscosity degradation following a strict random scission mechanism,

Which results in better reactivity towards derivatization due to a better accessibility

In the crystalline regions.

Hardwood sulfite and PHK dissolving pulps were irradiated by means of a 10 MeV

Accelerator, applying dosages of between 0 and 30 kGy (Fig. 11.30).

0 10 20 30

HW-Sulfite: untreated after steeping

HW-PHK: untreated after steeping

Chain Scissions [104/DP

W,j

-104/DP

W,0

]

Radiation dose [kGy]

Fig. 11.30 Course of chain scissions (based on weighted

Molecular weight) of hardwood sulfite and PHK dissolving

Pulps, before and after steeping as a function of radiation

Dose.

After irradiation, the molecular weight was determined without any further

treatment and after alkalization with a caustic solution of 17.5% NaOH (steeping).

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