Creep lifetime of ethylene vinyl acetate co-polymer film after pre-load relaxation

Abstract

Abstract The influence of the mechanical load and ultraviolet radiation on the lifetime of viscous and elastic ethylene vinyl acetate copolymer (EVA) films under the various loads are studied to establish its principles and to develop the basic concepts regarding their physical nature. The dumbbell samples of the cured (annealed at 135oC) EVA films (c-EVA) are pre-loaded and kept pre-strained till the complete load relaxation to reduce a viscous component prior to the creep under the load added to the relaxed value of the external force. The creep lifetime logarithm vs. added load dependencies measured at 21 oC with and without simultaneous ultraviolet irradiation with 365 nm wavelength light (from the EVA absorption tail) contain two linear segments each. The linear fragments are approximated with Zhurkov and Kauzmann-Eyring (KE) phenomenological models, which allows one to derive the quantitative parameters such as activation energy (found to be by several times lower than the dissociation energy of C – C bond); structural factor and force concentration factor as well as to estimate the density of the aligned polymer chains (per unit area) and the alignment level defined as the ratio of the polymer chain density to its maximal value (calculated to be 4 ∙ 1018 m-2). The specific surface energy of 0.01 J ∙m-2 calculated from the KE approximation is in a proper consent with Griffith’s criterion for the crack propagation.