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Abstract
The deformation and fatigue behavior of ionomers have been studied by two different approaches: (1) investigation of the deformation mechanisms of thin films by TEM, (2) investigation of the fatigue properties of bulk specimens. The ionomers have also been characterized by their dynamic mechanical properties.
The major part of this study is concerned with Na ionomers (S-SSA-Na). Above a critical ion content of about 5 mol%, it appears that properties are strongly affected by an increasing volume fraction of ionic clusters. TEM micrographs show that shear deformation is involved in addition to crazing, and fatigue data show that the fatigue lifetime is enhanced compared to that of PS. The fracture surfaces of the fatigue specimens also show some evidence that shear deformation occurs during the fatigue crack propagation process.
We conclude that clusters play an important role in improving the fatigue properties. However, below the critical ion content, ionic crosslinks (multiplets) dominate, crazes appear to be less stable and the fatigue lifetime is reduced.
Ca ionomers have better fatigue properties than ionomers containing monovalent ions and shear deformation, as well as crazing, is observed in samples containing only 4.1 mol% ion content. These effects probably arise because the divalence nature of the counterion enhances the formation of clusters.
Other factors that can change the structure of aggregates are also studied, i.e., plasticizer (DMF) and excess neutralizing agent (NaOH). Results obtained support the conclusions drawn from the study of Na ionomers.
