The dissolving pulp (DP) involving no lignin and the cold soda pulp involving much amounts of lignin were used in order to study the influence of gamma irradiation.
The experimentals were carried out in the presence of air (dryed state), in the water, methanol, acetic anhydride, acetic anhydride+methanol, dioxane, dimethyl sulfoxide and 1% NaOH solution as deaerated as possible from each solutions. The irradiation was for 100 hours at the temperature of 2021°C. Total irradiation dose was 1.47 × 10⁷ R.
The yields, lignin content, 1 % NaOH solubility, and then brightness were determined. In the case of acetic anhydride and the mixing solution of acetic anhydride and methanol the degree of acetylation also was determined.
The following results were obtained from the above-mentioned experiments.
1) Yield and analytical value
In the case of dimethyl sulfoxide which is a good solubilizer for pulp as well as especially in the case of 1% NaOH solution, the yield decreased by the irradiation.
It was found that this phenomenon was denoted remarkably for the cold soda pulp.
2) For the pulp immersed in the water the brightness of pulp was not pratically improved by the irradiation, but relatively remarkably improved for immersing in methanol. Thus phenomenon was observed in both DP and the cold soda pulp. The improvement of the degree of brightness is not the change in quality of lignin, but it may be considered reasonably to take place by the action of oxidizing bleach with a smaller amount of oxygen of air remaining in the material. And also by comparison with immersing in water, it is considered for immersing in methanol that the action of bleaching arises from the presence of an extremely small amount of oxygen. Additionally, 1% NaOH solubility gets a small value in the both systems. Therefore, it may be considered that the degree of brightness is improved by the oxidation reaction, but the degradation degree of pulp gives a small value.
3) From the scope of results obtained by the infrared analysis. it seems most reasonable to conclude that methanol does not react with lignin in the cold soda pulp even on irradiating.
4) In practice, it was found that the acetylation was accelerated by the gamma-rays irradiation.

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In kraf t pulping and neutral sulphite pulping of gamma-ray irradiated chips, the influence of irradiation on the defiberability of the yielded pulps were investigated.
The results were summerized as follow :
1) In kraft pulping, the defiberability becomes inferior by the irradiation of 5×10⁵R.
2) In neutral sulphite pulping, the defiberability seems to become somewhat better by the irradiation of 10⁶R. And kapper number does not change within the area of the high pulp yield but it becomes smaller according to the decrease of the total pulping yield by the irradiation of 10⁶R, in comparison with the case of no-irradiation.
Note : Defiberability is the degree of the easiness of defibering of the pulp which is only blown from the digester and not fiberized.

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Pre-irradiation of wood in alkaline aqueous ethanol increases kraft pulp yield by up to 1.2 %, as already reported. In order to clarify the mechanism of the pulp yield gain, the behaviors of lignin and carbohydrates during pre-irradiation and cooking were investigated.
The results are summarized as follows :
1) γ-Irradiation of guaiacylethane in alkaline agueous ethanol produced 5- (1-hydroxyethyl) -guaicylethane, which is formed by radical coupling between α-hydroxyethyl radical from ethanol and guaiacylethane radical having an unpaired electron at C-5. 5, 5'-Dehydrodiguaiacylethane, which may be a predominant product produced by γ-irradiation in the absence of ethanol, was also detected.
2) The yield of vanillin obtained by nitrobenzene oxidation of MWL decreased with an increase of γ-ray dosage. The presence of ethanol during γ-irradiation lessened the extent of this decrease and also the degradation of cellobiose.
3) Gel filtration of the products obtained by γ-irradiation of MWL and cellobiose in the presence of ¹⁴C-ethanol showed the possible combination between ethanol and MWL or cellobiose.
4) Molecular weight distributions of kraft lignin obtained from pre-irradiated beech chips were compared with those obtained from unirradiated chips. This result shows that γ-irradiation in the presence of ethanol decreases the ability of lignin to condense during kraft cooking.

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Studies have been made of kraft cooking of gamma irradiated wood. Beech (Fagus crenata Blume) wood meal suspended in aqueous alkaline alcohol was irradiated up to 1.5 KGy (0.15 Mrad) with gamma rays from a Co-60 source in the presence or absence of oxygen. The irradiated wood meals were washed thoroughly with fresh water, air dried and cooked under the ordinary cooking conditions.
The results are summarized as follows :
(1) Pre-irradiation in aqueous alkali have negligible effect on kraft cooking.
(2) In the case of ethanol addition (50 g/l), pre-irradiation in vacuo shows acceleration of delignification and stabilization of carbohydrates during kraft cooking. Cooked yield gain by pre-irradiation was about 1.2% in all over the range of delignification from 80 to 90%. Aqueous ethanol without alkali also shows positive but smaller effect than that with alkali.
(3) Propanol, iso-propanol and butanol show positive but smaller effects than ethanol. However, methanol does not show any positive effect.
(4) Irradiation in the presence of oxygen does not show any attractive effect on kraft cooking.

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