Abstract
The behavior of radicals in polyethylene film in electron-beam-induced graft polymerization was studied. Four kinds of polyethylene film, namely, ultra-high molecular weight polyethylene （UHMWPE）, high-density polyethylene （HDPE）, low-density polyethylene （LDPE）, and LDPE-containing HDPE, were selected for the study. These polyethylene films were irradiated with an electron beam to quantify the radical concentrations in the polyethylene films. The radical concentrations in the polyethylene films were found to increase with increases in the electron beam irradiation dose. For a given irradiation dose, the radical concentration in the polyethylene films increased in the order of UHMWPE > HDPE > LDPE-containing HDPE > LDPE. This corresponded to the increase in the degree of crystallinity of the polyethylene films. The polyethylene films were irradiated with an electron beam to graft polymerization. The degree of grafting was found to increase with increases in the radical concentration in the polyethylene film. The relationship between the radical concentration in the polyethylene film and the degree of grafting exhibited the same tendency, irrespective of the degree of crystallinity of the polyethylene film. The degree of grafting could be controlled, therefore, according to the radical concentration in the polyethylene film. After being irradiated with an electron beam, the polyethylene films were stored at temperatures ranging from －80 to 20 ℃, in the atmosphere. As a result of being stored at 20 ℃ in the atmosphere, the radical concentration in the irradiated polyethylene films decreased over time. The residual ratio of radicals in the polyethylene film after being stored for 6 h decreased in the order of UHMWPE > HDPE ≥ LDPE-containing HDPE > LDPE. The rate of decline in the radical concentration in the polyethylene films decreased as their degree of crystallinity increased. When the irradiated polyethylene films were stored at －80 ℃ in the atmosphere, the radical concentration in the polyethylene film after being stored for 24 days was the same as that when the films were initially placed in storage. The radical concentration could be maintained indefinitely by storing the polyethylene films at －80 ℃.
