ポリメタクリル酸メチルおよびメタクリル酸メチルと アクリロニトリルとの共重合体のγ線による着色

第2報:退色における酸素の拡散機構

抄録

The optical absorption bands in visible region which are produced in γ-ray-irradiated PMMA and copolymers of MMA-AN are bleached with a sharp boundary line in oxygen atmosphere below the glass transition temperature.
By investigating the penetration rate of this boundary line, it is proved that this phenomenon is caused by oxygen molecules adsorbed on the plastic surface penetrated according to Fick's diffusion law and reacted with “chromophores”.
Adsorption of oxygen molecules on irradiated plastic surface needs the activation energy of about 9.38 Kcal/mole. Therefore, it takes an induction period before the appearance of the boundary line. This induction period is independent of the composition of plastics and dosage, but depends on the gas pressure of oxygen and temperature.
G-values for the production of chromophores are estimated by applying the diffusion law to the penetration rate of the boundary line. These values vary between 0.1 and 1.5 according to the composition of plastics. They coincide very well with the concentration of radical measured by the DPPH method and also with the G-values for the production of trapped radical measured by the use of ESR by many investigators.