Corrugated fiberboards of AA-grade and their base papers-i. e., liner and medium sheets, were irradiated with dosages of 10, 25, 50, 100 kGy, and effect of gamma irradiation on the brightness and strength properties were investigated.
Changes in brightness values were within 0.5% for all irradiated sheets studied, and there was no visual change on the surface. Compressive strength and wet tensile strength of paperboards did not deteriorate up to the dosage of 100 kGy. Dry tensile strength of paperboards decreased with increasing dosages after the transient increase at 10 kGy, and reduction rate was kept within 15% even after 100 kGy irradiation. Burst-, tear- and punctute-strength also decreased with increasing dosages, but those reduction rate after 100 kGy were kept in the range of 30-40%. In our studies, only folding endurance markedly decreased with increasing dosages.
Burst strength reduction of corrugated fiberboard was within 10% at 25 kGy (usual sterilizing dosage), and reduction behavior was almost similar to that of base paperboard. However, puncture strength reduction of corrugated fiberboard was lower than that of paperboard. Reduction ratio of compressive strength and that of adhesive strength between liner and medium were within 10% even after 100 kGy irradiation.
In conclusion, there was no significant reduction in the mechanical properties of corrugated fiberboard and paperboards due to gamma irradiation except for folding endurance. Therefore, it is thought to be no problem for the practical use of corrugated fiberboard cases in sterilizing operations by gamma-rays.