EFFECT OF TIME OF ANNEALING ON GAS PERMEATION THROUGH COEXTRUDED LINEAR LOW-DENSITY POLYETHYLENE (LLDPE) FILMS

The effect of annealing on the permeation of oxygen, nitrogen, and car bon dioxide through coextruded linear low-density polyethylene (LLDPE) films is studied. The results indicate that the permeability coeffici ent P of nitrogen does not show a definite dependence on the time of a nnealing, t(a), whereas for the other gases this parameter increases w ith t(a). The analysis of the variation of the diffusion coefficient o f O-2 and N-2 with t(a) indicates that D undergoes a sharp decrease fr om t(a) = 0 to t(a) = 2 h, but for larger times of annealing the diffu sion parameter only undergoes a slight diminution; on the contrary, th e diffusion coefficient of CO2 gradually decreases with increasing t(a ). The fact that annealing increases the solubility of the gases in th e polymer films suggests that thermal treatments may favor the formati on of microcavities or molecular packing defects in the crystalline am orphous interface that can accommodate individual site molecules witho ut disturbing the natural dissolution process in the rubbery region of the polymer matrix. Finally, free volume theories are not sensitive e nough to interpret the effect of annealing on the permeation character istics of coextruded LLDPE films.