Observation of the degradation due to irradiation of CR 39 polymer by long-term monitoring of mass loss

Abstract

We γ-irradiated CR 39 of three thicknesses with 51–3311 kGy. Mass loss during irradiation repeated the three-step pattern observed by Li et al. [Li, S.M., Garreau, H., Vert, M., 1990. Structure-property relationships in the case of the degradation of massive aliphatic poly(α-hydroxy acids) in aqueous media. J. Mater. Sci.: Mater. Med. 1, 123–139.] from thick PLA50. Mass loss following irradiation in thin CR 39 repeated the observations of Grizzi et al. [Grizzi, I., Garreau, H., Li, S., Vert, M., 1995. Hydrolytic degradation of devices based on poly( d, l-lactic acid) size-dependence. Biomaterials 16, 305–311.] in thin PLA50, whereas in thicker samples, it followed second-order kinetics. The graph of total mass loss per unit dose against dose absorbed displays the step-wise pattern from ESR spectroscopy [Nara, S., Shimada, S., Kashiwabara, H., Sohma, J., 1968. Relation of the decay of free radicals in irradiated polyethylene to the molecular motion of the polymer and the configuration of the free radicals. J. Polym. Sci., Polym. Phys. Ed. 6, 1435–1449.]. The implications for drug release from γ-irradiated microcapsules is discussed.