Differential scanning calorimetry studies on high- and low-density annealed and irradiated polyethylenes: Influence of aging

Abstract

The effect of γ-radiation, followed by 10 years storage at ambient conditions, on the thermal behavior of different types of high- and low-density commercial polyethylenes was studied. First, samples were annealed to improve the crystalline content. Next, they were irradiated, after which fusion endotherms, melting temperatures, crystallinity indices, and lamellar thicknesses were obtained by differential scanning calorimetry (DSC). The change in the thermal parameters for the first and second meltings were related to the absorbed doses. Afterward, the samples were stored at ambient conditions for 10 years and then scanned again by DSC to assess the influence of aging on previously irradiated samples. The results showed that the changes on the morphological structure undergone by the samples with the storage time were highly dependent on the polyethylene type and the absorbed radiation dose. The high-density polyethylene was the most sensitive to radiation and storage, whereas the low-density polyethylene with the lowest molecular weight and the highest degree of branching was the least affected. In general, the changes observed during irradiation can be explained in terms of an increase of imperfections and chain scissions. The storage can be understood as a slow crystallization process at low radiation doses, and as a decrease of the crystalline structure at high doses. © 2003 Wiley Periodicals, Inc.