Actual failure accidents of plastic bags often occur at the pin-hole and/or the crack, and also the edge that is just outside of the heat-sealed part becomes the failure initiation point. In this study, fracture mechanics tests and tear tests were performed to understand the resistance of heat-sealed parts and edge parts to introduced cracks. The fracture resistance and tear strength of the edge part was lower than that of the heat-sealed part, which was more obvious at higher heat sealing temperature. The optimum heat sealing temperature to obtain the balanced properties of heat-sealed polylactic acid (PLA) films was found to be 130°C.

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In this paper, the effects of intensity of electron beam, detergent and colorant on creep rupture of polypropylene resin (PP), which is widely used in medicine containers, were investigated and the evaluation method of the long-term forecast of creep rupture was examined. Concretely, first, PP resins including colorant or not were prepared and samples that variously changed intensity of the electron beam irradiation were made. Creep rupture test of those samples was carried in detergent having various consistencies. The effects of those factors on creep rupture were considered and long-term forecast was tried by using time-temperature superposition principle about creep deformation. The following results were obtained.
(1) Although creep rupture of PP resin receives the effects of the presence of colorant, intensity of electron beam irradiation and detergent, the time-temperature dependence of creep rupture of PP resin including those affecting factors can be estimated by using the time-temperature superposition principle for creep deformation of the original PP resin. Based on this equivalency, it is possible to predict the long-term forecast of creep rupture of PP resin.
(2) Creep rupture is affected by the presence of colorant, intensity of electron beam irradiation and detergent and it happens earlier when the intensity of electron beam irradiation and consistency of detergent are increased.

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