THE EFFECT OF ANNEALING ON STRUCTURAL REA RRANGEMENTS AND MECHANICAL-PROPERTIES OF HARD-ELASTIC POLYETHYLENE

The effect of annealing on the structure and properties of hard elasti c samples of PE was studied by means of small-angle X-ray scattering, tensile testing, and cyclic loading. Three different regions in the st ress-strain curves were identified, and their parameters were determin ed. These regions were associated with the stage of elastic deformatio n, post-yield behavior, and the stage of strain recovery, which corres ponds to the unloading of polymer. Depending on the annealing temperat ure T-a, the yield stress was shown to be maximal for polymers anneale d at temperatures close to the melting temperature of the polymer (T-a = 129.4 degrees C). The same tendency was characteristic of the depen dence of long period, estimated from X-ray data, on the annealing temp erature T-a. Similar temperature dependences were obtained for the par ameters describing polymer behavior at the second and third stages of polymer deformation, but their maxima were associated with lower annea ling temperatures (125 and 115 degrees C). Permeation of liquids throu gh porous structure produced by tensile drawing of hard elastic PE fil ms was measured. The dependence of the permeability for liquid on T-a was found be similar to the corresponding curves for polymer yield poi nt and long period. The above behavior was rationalized within the fra mework of structural model.