Distinct degradation behavior of crystalline and amorphous domains in cellulose under ionizing radiation

Cellulose typically undergoes hydrolytic degradation predominantly in amorphous regions, while crystalline domains are considered relatively stable. In contrast, ionizing radiation induces chain scission throughout the cellulose structure without inherent structural selectivity; however, because moisture is distributed differently between amorphous and crystalline domains, the resulting degradation behavior may differ between these structural regions. In this study, cellulose degradation under gamma-ray and X-ray irradiation was evaluated under dried, standard, and water-saturated conditions based on changes in degree of polymerization, carbonyl content, zero-span tensile strength, and leveling-off degree of polymerization (LODP). The results showed that radiation-induced degradation varied with moisture condition and differed from thermal aging behavior. Radiation-induced chain scission was more pronounced under dried conditions, whereas oxidative modification became more pronounced under wet conditions with increasing dose. These findings indicate that, although radiation-induced chain scission is intrinsically non-selective, the extent and distribution of chain scission differ between crystalline and amorphous regions, reflecting differences in moisture distribution between these domains. Compared with thermally aged papers at similar DP, irradiated papers retained higher mechanical strength, suggesting a structural pattern of degradation distinct from that of thermal aging. Overall, moisture associated with amorphous regions appears to influence the pathways of radiation-induced chain scission and oxidation.